An overview of options and solutions related to broadband access by using optical fiber as a main transmission medium has been presented. The most promising approaches associated with next generation optical fiber-based access networks have been outlined.

The splice losses between PCF and SMF and between two PCFs with different structure are analyzed based on mode field radius of the fibres, respectively. And the effect of each structure parameter on the splice loss was discussed.

Based on the analysis of birefringence and leakage properties in rectangular lattice photonic crystal fibers(PCFs), we presented a technique of improving the properties of the fibers by the introduction of a doped-core. The influence of pure silica core, silica core with small air-hole, and a doped silica core on the mode profiles of the fiber are investigated and discussed. The influence of doping level on that of birefringence and leakage losses of the fibers is also explored, which is realized by applying the mutipole method. Our numerical simulation proves that, for PCFs with anisotropic claddings, it's possible to obtain an increased birefringence by doping, while maintaining or even reducing the leakage loss by increasing the hole pitch of the fiber. The technique eliminates the disadvantage of deforming mode field by the introduction of small air-hole core and the mode field of the fiber is also increased.

The principle, experimental implementation and verification, as well as preliminary device demonstrations of coherent acousto-optic mode coupling using a pair of acoustic gratings on dispersion compensating fibers (DCFs) are reviewed. The embodiment of polarization-dependent narrowband mode coupling and wavelength tuning features in a single strand of optical fiber offers interesting opportunities for functional integration in an all-fiber medium, and the generation of fiber optical vortex modes.

A novel micro-mechanical structure has been put forwarded. It is designed for high precision passive alignment and packaging of optical fibres in optoelectronics devices. The electroplated nickel micro clamp has been fabricated above the silicon V grooves. The clamps, work together with the V groove, fix the optical fibers with high precision for optical alignment when the fibers are inserted into the grooves. The fabrication of the micro clamp involves only one more photolithography and electroplating process. two single mode optical fibers have been fixed into the silicon V-groove by the nickel clamp; the measured insertion loss is lower than 0.1dB. The proposed nickel micro clamp is proved to be a low cost, high performance approach that could be widely applied in passive alignment and packaging of fiber in opto-electronics devices.

Since new modulation schemes have become a great center of interest, Mach-Zehnder fiber fused interferometers (MZI) became necessary to ensure the direct detection (DD) from phase modulated signals, like DPSK (Differential Phase Shift Keying) or DQPSK. As these modulation schemes are very interesting in optical transmissions due to their capabilities, MZIs cannot be overlooked in the future optical links. In this paper, we review the base principles for using MZI as DPSK demodulators, and the major characteristics associated to these devices. In order to evaluate the minimal characteristics required for efficient modulation format conversion, we propose some numerical simulation results. Based on these results, we depicted a new fabrication process for the realization of MZIs by adiabatic stretching of one of the interferometer's arm. This is carried out by a CO2 laser, and the fabrication major points that must be respected are discussed. After review the MZI thermal dependency mechanism, the last part presents the experimental results obtained for the quantification of MZI temperature control accuracy needed for its utilization as an 43 Gbit/s PSBT (Phase Shaped Binary Transmission) encoder.

The frequency selectivity of integrated optical ring resonators makes them key components for many devices, including filters, switches and sensors. The ion-exchange technique is an economical and simple method to fabricate good quality optical waveguides and useful devices. In this paper, with the mixed melt salt of AgNO₃ and KNO₃ used as the source of exchanging ions, a racetrack waveguide resonator was fabricated in K9 glass. The reflection and transmission spectra of the resonator were measured, and the coupling ratio and propagation loss were derived by an improved method. The phase shift of 2π was realized by using thermo-optical effect within 16 degree change of temperature. The resonator is a promising device for filtering, sensing and other applications.

On the basis of the optical thin film interference theory, a novel thin film multi-frequency filtering technology applied to CWDM filter, a comb-like filter, which is not applied to select single signal channel from the multi-channel, but to separate the multi-channel into two different sets of channels, is proposed in the article. According to the central wavelength and the width of pass-band of 8-channel CWDM system that were defined by the ITU-T, two kinds of thin-film filters for 8-channel CWDM system have been designed by the technology. A specific expression for these thin film structures has been described and the parameters of these structures have been analyzed and optimized. The transmission curves of the designed structures show that the design results are agreement with that of the theoretical calculation well. We can implement the function of the 8-channel CWDM using two above-mentioned thin-film filters, which make the CWDM system low-cost, simpleness and easy collimation. These thin film structures have the advantages of good stability, arbitrary wavelength spacing between the adjacent channels, perfect rectangular shape of the pass-band, less layers, low cost and easy encapsulation, which would make it more attractive to use in CWDM system and other fields.

Multi-stage discrete Raman amplifiers with midway isolators to suppress double Rayleigh backscattering (DRB) are fully investigated at constant nonlinearity. The results show that placing Raman pumps at the last stage only is sufficient. For most conditions, two isolators can achieve adequate performance improvement, while more isolators only lead to slightly OSNR increase. The optimum positions of the isolators are insensitive to varied Raman gains, nonlinear phase shifts and Rayleigh coefficients, but sensitive to different fiber lengths as well as Raman pumping schemes. Moreover, backward pumping scheme can derive better noise performance than bi-directional pumping when using midway isolators.

In this paper we describe advanced bi-directional Raman pumping schemes for extending the maximum reach achievable in long-span unrepeated WDM transmission systems operating at 10 Gb/s. We describe both first- and higher-order bi-directional Raman pumping schemes, pointing out that co-pumping, although critical in terms of noise transfer from pump to WDM signals, can be very effective in extending the maximum system reach. New co-propagating Raman pump lasers, characterized by high power levels and low relative intensity noise, are also proposed to further increase the maximum achievable span loss, avoiding transmission penalties induced by relative intensity noise transfer.

Raman Fiber Amplifier is the important component in the next generation optical network. High power Raman Fiber Laser is kinds of selection of the pumping source for Raman Amplifier. In the paper, we theoretically emulating the Fiber Raman Laser and optimizing the Raman Fiber Laser parameters for the output power, experimentally analyzes the device. The analyzing is based on the Raman Fiber Laser's model and doing the simulation with four-order Runge-Kutta arithmetic. The experiment set gave more than 500mw output Laser at 1428nm which is based on a Raman resonator using the high nonlinear efficient fiber, Fiber Bragg Gratings, and pumped by the 1342nm solid state Laser.

The polarization characteristics of electro-optical (EO) switches using fiber Sagnac interferometers (FSI) structures are theoretically investigated. Analytical solutions of output fields are presented when the twists and birefringence in a Sagnac loop is considered. Numerical calculations show that the twists of fiber, the orientation of the inserted phase retarder and the splitting ratio of the coupler will influence both the output intensity and the output polarization properties of the proposed switch. A polarization independent EO switch based on hybrid integration of a Sagnac interferometer and a PLZT retarder was experimentally implemented, which showed good coincidence with the analytical results. The experiment showed a switch with -22dB crosstalk and less than 31 ns switching time.

Spectrum steering is a new class of device architectures that use a MEMS mirror to steer a dispersed spectrum in two dimensions across a fixed spectral-plane spatial filter. Devices select among a set of pre-programmed filter shapes, inputs, or outputs and can tune the center wavelength of each filter. Spectrum-steering filters are not as generally flexible as devices with active spectral plane filters but are potentially more compact, lower cost, and simpler to control. We present two example spectrum-steering devices. The first is an optical channel monitor (OCM) with integrated input-selection switch in which a single large MEMS mirror tilts along one axis to measure the DWDM spectrum and tilts along the orthogonal axis to switch between two input ports. The powers of 100-GHz spaced channels are accurately measured with adjacent-channel power differences up to 10 dB without the use of deconvolution. The second is a spectral bandpass filter where the MEMS mirror tilts along one axis to tune the center wavelength over 38 nm, and tilts along the orthogonal axis to independently control the filter 3-dB passband width from 28 to 210 GHz. The resolution is sufficient to produce a flat-top demultiplexing filter for 50-GHz spaced channels with 30-dB adjacent-channel isolation. These filters could provide colorless and channel-plan-independent demultiplexing ports in broadcast-and-select architectures. The insertion loss is 4.6 dB and the PDL is 0.26 dB.

Novel compact design for 4-channel SOI-based reconfigurable optical add/drop multiplexer using microring resonators is presented and analyzed. Microring resonators have two important attributes as a key new technology for future optical communications, namely functionality and compactness. Functionality refers to the fact that a wide range of desirable filter characteristics can be synthesized by coupling multiple rings. Compactness refers the fact that ring resonators with radii about 30μm can lead to large scale integration of devices with densities on the order of 104 - 105 devices per square centimeter. A 4-channel reconfigurable optical add/drop multiplexer comprises a grid-like array of ridge waveguides which perpendicularly cross through each other. SOI-based resonators consisted of multiple rings at each of the cross-grid nodes serve as the wavelength selective switch, and they can switch an optical signal between two ports by means of tuning refractive index of one of the rings. The thermo-optic coeffcient of silicon is 1.86×10-4/K. Thus a temperature rise of 27K will increase the refractive index by 5×10-3, which is enough to cause the switching of our designed microring resonators. The thermo-optic effect is used to suppress the resonator power transfer, rather than to promote loss. Thus, the input signal only suffers small attenuation and simultaneously low crosstalk can be achieved by using multiple rings.

Low water peak single mode fiber (LWP-SMF) fabricated by PCVD based process has been described. Based on the whole process of PCVD fiber, the hydroxyl contamination and its sources are as follows: (1) raw material, such as SiCl₄, GeCl₄, O₂, C₂F₆, substrate tube and jacket tube; (2) leakage of the system including PCVD and collapsar; (3) surface contamination. The latter purification of deposited glass is extremely difficult, so the most effective solution is prevention. The hydroxyl contamination prevention and elimination measures, such as purity improvement of raw material, online purification during PCVD, surface absorption reduction and dilution effect with large preform, which are the key factors for LWP-SMF fabrication by PCVD based process, are revealed. Large scale production has revealed that LWP-SMF can be fabricated by PCVD based process combined with above mentioned process innovation. PCVD LWP-SMF complies with or exceeds the ITU recommendation G.652 (C and D) and IEC 6093-2-50 type B 1.3 optical fiber specification. With further development of high purity raw material, machine-airproof improvement and larger preform (above 150mm) combined with material composition and structure optimization in optical fiber or preform, high performance PCVD LWP-SMF with lower water peak or even zero-OH performance will be achieved. Besides, other type of optical fiber with low water peak, such as G.653, G.655 and G.656, can also be made with the advanced PCVD based process.

In this paper, a novel fiber manufacturing process based on PCVD is introduced. The fiber drawing length per preform can reach more than 5,000 km and the cost is lower. The fiber shows better optical and geometrical properties. Such large size preform combines the advantages of PCVD process for high quality and OVD process for low cost. This PCVD RIC process will be helpful for increasing the ability of inside vapor deposition process.

In this paper, we describe a fabrication process of a long-length and low-loss polarization-maintaining fiber and present the measured optical properties of the polarization-maintaining fiber. The fabrication of the polarization-maintaining fiber is based on the pit-in jacket method, in which the core rod and stress application perform is fabricated by an updated PCVD process. Thus, polarization-maintaining fibers with the long-length not less than 15km can be obtained with a good longitudinal uniformity and a low-loss about 0.423dB/km@1310nm and 0.245dB/km@1550nm. The optical and geometrical properties of the polarization- maintaining fiber were measured. We also tested some special measurements. The results is well matched the specification of the present productions.

This paper describes the low attenuation at the 1400nm band of optical fiber, which depends on a deposited first cladding and core diameter ratio (D/d) of core rod on Vapor Phase axial Deposition (VAD) process and a dehydration method. By using the most suitable D/d for much more efficient productivity and the improved dehydration process, we developed Preform for Zero Water Peak Single Mode (ZWP-SM) fiber to produce over 1,300F.km.

In this paper, the ability of Bragg fiber array to guide optical mode is investigated theoretically. Simulation shows that Bragg fiber array can be looked as a good waveguide to guide inter-fiber modes, which are supported by the external reflection of the 1-D photonic crystal claddings of the Bragg fibers. The mechanism of leakage loss of the inter-fiber is analyzed, showing that the TM01-like mode has the lowest leakage loss and less than 1dB/m leakage loss can be achieve under the wavelength of 10.6μm. As an open waveguide or 2-D microcavity, the Bragg fiber array has wide potential applications including processes of interaction between light and atoms or molecules.

We study modulation instability (MI) in the fiber Bragg grating with nonlinearity management based on the coupled-mode theory. The role of both average Kerr nonlinearity and variance of Kerr nonlinearity between the layers of fiber grating in MI is identified. It is found that the variance of Kerr nonlinearity affect MI gain spectrum remarkably in both anomalous dispersion and normal dispersion regimes. In the anomalous dispersion regime, when the variance of Kerr nonlinearity is much smaller than the average Kerr nonlinearity, the MI gain spectrum is similar to that without the variance of Kerr nonlinearity, but the range of wave number for MI to occur is narrowed, and the amplitude of gain decreased. When the variance of Kerr nonlinearity is enhanced to be equivalent to the average Kerr nonlinearity, the role of variance of Kerr nonlinearity in MI becomes important: At low intensity, the range of wave number for MI to occur shrinks notably, and the gain gets only a single peak compared with the original one which has two symmetrical side-bands. At high intensity, there appear three MI ranges. In the normal dispersion regime, near the lower edge of photonic band gap, the amplitude of MI gain is slowed down due to the influence of variance of Kerr nonlinearity, and only two small symmetrical MI range appear, in sharp contrast to the original case without the influence of variance of Kerr nonlinearity, in which MI occurs for all wave numbers. Whereas in the case that far away from the edge of photonic band gap, we find that the range of wave number for MI to occur and the amplitude of MI gain increase as the value of variance of Kerr nonlinearity increases.

The effect of source wavelength instability on the performance of a system using chirped fiber Bragg gratings as dispersion compensators is numerically investigated, by which it's shown that source wavelength instability will surely induce an additional penalty for the system. And quantified relations of the EOP induced by group delay ripples and reflection ripples with the extent of wavelength instability is given.

The characteristics of uniform fiber Bragg gratings (FBGs) is analyzed. The reflected spectra in apodized uniformly periodic FBGs are calculated and the double exposure technique is used in suppressing the sidelobes of uniform gratings. After that, the corresponding FBGs filters used in DWDM networks and systems are imprinted. Based on the apodized FBGs, a cascaded FBGs filter module is proposed, in which two, or more, pieces of identical FBGs, with the same central wavelength, same bandwidth and same reflectivity, are spliced in series and each FBG is equipped with tuning device. By controlling the tuning device, the module can act either as a tunable single channel filter with its central wavelength and/or bandwidth being tunable, or as a double channel filter with its central wavelength being tunable. The tested results demonstrated that the module can dynamically tuned in the range of several nanometers.

We will discuss in this presentation a novel and simple erbium-doped fiber laser configuration for multi-wavelength oscillation at room temperature, in which a few-mode fiber Bragg grating was used as the wavelength-selective component. This multi-wavelength laser can be switched between dual- and triple-wavelength operations by properly adjusting polarization controller in the cavity. By using stain- or temperature-induced few-mode fiber grating, we also demonstrate a tunable multi-wavelength laser based on the proposed scheme. This multi-wavelength laser has the advantage of simple configuration, high stability, low cost and stable operation at room temperature.

Nonlinear fiber based devices and in particular multiple wavelength nonlinear fiber devices are reviewed. A number of important devices can be fabricated using various lengths of fiber in combination with the appropriate input signals and pumps of sufficient power. The low loss fiber provides a unique medium whereby these important nonlinear processes can occur. These processes include among others Brillouin scattering, Raman scattering, parametric amplification, wavelength conversation, self phase modulation, and four wave mixing. Possible applications for these processes include high bit rate dynamic dispersion compensation, 2R regeneration, the continuum generation and nonlinear polarization dynamics.

This paper analyzes the performance of DLOB and discusses the influence of SOA's linewidth enhancement factor and XGM on the performance of DLOB, gets the relation between linewidth enhancement factor and extinction ratio, transfer ratio. Then discusses the influence of state of polarization (SOP) on buffer's output power and finds their evolution regularity. Many useful conclusions are drawn.

A multi-port optical logic NOT gate based on multimode interference principle is proposed. To achieve different output states at the output ports of the device, plasma dispersion effect is applied to get phase difference between signal light and control light. Calculated result shows that the average extinction ratio and insertion loss of the device are 19.8 dB and 0.04 dB, respectively. The device is expected to contribute to future all-optical networks and computations.

We proposed and demonstrated a new concept of multi-wavelength-switchable single-longitudinal-mode fiber laser based on the linear cavity. In the cavity, a Sagnac loop filter with a long high-birefringence fiber is incorporated to enable the allowed oscillating wavelength compatible with ITU-T grid, a multi-section high-birefringence Sagnac loop filter is used to realize wavelength-switching operation, and a saturable absorber loop filter with unpumped Erbium-doped fiber is applied to achieve single-longitudinal-mode operation. The experiment has demonstrated 16-wavelength-switchable, 100GHz spacing, single-longitudinal-mode lasing operation with a large (>40dB) output signal to background noise ratio.

Magneto-optic switch has been widely researched due to its capabilities handling large beam cross sections, operating at low voltages, featured as low insertion loss and intrinsic non-reciprocity. However, the switching speed is rather slow: switching time of available magneto-optics switches are of hundreds microseconds. Previously, we developed a novel type high speed magneto-optic switch based on Faraday rotation effect of light in yttrium-iron-garnet (YIG). The switch shows its good performance and high reliabilities. However, it had some disadvantages: 1) Although it was polarization independently designed for the insertion loss, some dependence about 0.5dB was observed due to the components' misalignments since it has many components and adjustment points; 2) Faraday rotator assembly designed by using double YIG rods with diameter 3 mm require much higher switching current to rotate the light by 90°. And the heat generated when operating may also affect the YIG performance. 3) The narrow and sharp pulse width of nanosecond trigger impulse signal generated with short duration can't accumulate the high speed switching magnetic field large enough to drive the YIG reach saturation magnetic field within a trigger period. In this paper, we mainly devote to design an improved switch featured as compact optical route, much more effective Faraday rotator assembly and nanosecond trigger impulse signal with wider pulse width.

In order to overcome the defects of G.652 and G.655 optical fibers, new types of ITU recommendation G.656 optical fiber are introduced in the paper. Based on the theory of waveguide, the design principle was described. Several types of G.656 optical fiber are introduced here; these types optical fiber can be used for long haul transmission system and metro network. CWDM and DWDM can also be applied on S+C+L bands with these types fiber. These fibers are manufactured by PCVD process. The minimum dispersion value from 1460nm to 1625nm is greater than 2ps/nm km; the maximum value is less than 14ps/nm km. The effective area at 1550nm is around 52 to 66μm². The excellent polarization mode dispersion properties help the fiber to meet the requirement of high bit rate transmission. The PMD co efficiency of these fibers is less 0.05 ps/km^1/2. By use of improved PCVD process, excellent attenuation of these fibers was obtained, the water peak around 1385nm is almost removed; attenuation from 1310nm to 1650nm is less than 0.4 dB/km, attenuation at 1550nm is less than 0.22dB/km. Excellent attenuation performance will help the fiber to utilize the bandwidth effectively.

In this paper, dispersion compensating photonic crystal fiber with triple-cladding is put forward and the property of high negative dispersion is investigated. Plane-wave expansion (PWE) method is used to analyze. We discuss the variation of the dispersion in detail, with changing the geometry parameters. A triple-cladding dispersion compensating photonic crystal fiber with dispersion -4140 ps/nm/km and FWHM 10 nm is demonstrated at 1550 nm wavelength.

We have demonstrated the Photonic Crystal Fiber (PCF)-based Long Period Grating (LPG) by machanical stress, in which each groove of the microbending will induce a local index change in the fiber via the photoelastic effect and such gratings can be completely erased by removing the pressure from the fiber. A Mach-Zehnder interferometer (MZI) formed by cascading a pair of PCF-based LPGs has been investigated in details in this paper for the application as an all-PCF filter. Because of the microstructured air holes, the effective index shows strong wavelength dependence, which will result some different properties distinguished with conventional optical fiber and we can expect some novel characteristics of this grating device. However, in the previous work, sensitive interference spectrum was only observed when stripping off the acrylate coating, which make the fiber device very fragile. And the coupling characteristics have not been analyzed in details yet. Cascaded LPGs were demonstrated to form a MZI, where multiple resonances were eaisly obtained without stripping the acrylate fiber coating by applying a much larger stress. The cascaded PCF-based LPGs have performed anomalous grating characteristics. This grating device offers the unique advantages of being tunable, erasable, reconfigurable and good interfering efficiency makes it promising applications in WDM communication.

Fusion splicing erbium doped fiber (EDF) to other single mode fibers has become more critical as the required overall insertion loss for erbium doped fiber amplifiers (EDFA) has significantly decreased in the last few years. In this paper, we describe and discuss an approach to develop a low loss splice method for fusion splicing high numerical aperture (NA) 980/1600 wavelength-division-multiplexing (WDM) coupler fiber and EDF. The results indicate that the fiber end preparation before the fusion is especially critical for obtaining a low loss splice for the fiber pair.

Erbium doped fiber amplifiers have been widely deployed for signal amplification in optical transmission systems. High performance amplifiers require erbium doped fiber with high power conversion efficiency and consistent flat gain spectrum. In addition, all impairments associated with EDF must be under good control. This paper reviews the current status and recent progress on erbium doped fibers, illustrates C and L-band spectral characteristics resulting from different doping compositions, presents some approaches for efficient high power amplifiers, and discusses some EDF nonlinear effects with examples.

In this paper we introduce some methods to improve performance of cladding pumped L-band EDFA. C-band seeds, ASE end-reflectors, and hybrid configurations use the cladding pumped fiber and convential EDF have been studied.

A novel temperature-independent FBG-type torsion sensor has been proposed and analyzed. Two FBGs with different Bragg wavelengths are symmetrically bonded to the surface of the torsion beam with an identical angle. This sensor is able to achieve torsional angle measurement over the range from -40° to +40° without suffering from the influence of temperature within the range between -15°C and 75°C.

A novel unsymmetrical intrinsic Fabry-Perot fiber optic strain sensor has been developed to improve the measurement of strain for different structures. Sensing principle, structure and sensing characteristics are studied. Some kinds of the unsymmetrical intrinsic Fabry-Perot interferometric (UIFPI) strain sensor are designed and fabricated. Temperature and strain characteristic of these sensors have been tested. The experiments indicate that these UIFPI sensors possessing favorable linear static and dynamic strain characteristic. The temperature characteristics of the UIFPI strain sensors with different carrier materials are distinct and the naked fiber-optic structure sensor is not sensitive to temperature. The experimental results reveal that the sensitivity is also depended on the cavity length of the UIFPI sensor.

A new distributed interferometic sensor for strain and vibrations measurement is proposed in this paper. It measures the first simultaneous information by using Mach-Zehnder Interferometer. We illustrate important points in regard to the proposed distributed signals measurement, and present the preliminary results on the application of optical fiber interferometic sensor (OFIS) for the measurements of distributed signals in long-distance region, and discuss the principles of distributed OFIS based on long-length Mach-Zehnder interferometic technique. We also adopt a new technique by using optical delay effect to improve the spatial resolution of distributed interferometic sensor. It is completely different from the spatial-resolution technique of optical time-domain reflectometry (OTDR). This type of OFIS has better sensitivity and resolution than the others. In addition, this paper describes a form of passive phase demodulation for recovering a signal of interest from a Mach-Zender optical fiber interferometric sensor. It achieves a 100Hz-2KHz frequency of vibrations resolution, with 100-m practical spatial resolution, over a sensing length of 6.8 km. At the time of writing, the system is only partially completed; therefore the content of this paper will focus on the principle of distributed sensor. The results mainly are presented in laboratory.

A novel configuration for the transducer of magnetostrictive fiber-optic sensors was proposed and implemented. It is composed of a rectangle and two half-circles. The transducer with the novel configuration has not only higher sensitivity than that of traditional configurations, but good directivity. The magnetostriction was analyzed compared with that of cylindrical transducers. It is shown that the system sensitivity can be improved by increasing the long-side of rectangle and shortening the perimeters of the two half-circles. Two transducers with cylindrical and racetrack configurations were fabricated. Moreover, an experimental setup to measure the low-intensity magnetic field detection responses was built up. Experimental results verified the analysis. For its good directivity, three of them can be compounded as a vector magnetometer to measure three orthogonal components of magnetic field.

We report a miniature optical fiber chemical sensor that consists of a fused-biconical single-mode optic fiber coupler. The absorption of the evanescent wave changes when the waist cladding refractive index n₂ is slightly modified. Consequently, the coupling visibility also changes. By putting the device in the water polluted, the trace amounts of chromium and nitrite in water can be detected. The coupler fabrication and design of the chemical sensor are described. The performance and characteristic of this system clearly establish the usefulness of the technique for detecting very low concentrations of the dissolved contaminants. And the sensor has shown preferable sensitivity and time response.

Recent evolution of silica-based nonlinear fibers and their applications are reviewed. Important design issues of the fiber in order to enhance the nonlinearity and tailor the dispersion performance are discussed. In addition, recent demonstration results such as ultra-broadband wavelength conversion and supercontinuum generation experiments are also introduced in this paper.

Recently, smaller diameter fibers have been investigated for flexible wiring and compact packaging. This paper summarizes the attributes of smaller diameter fibers. Applications of these fibers are also introduced in this report.

The influences of the Ge doped core to the properties of holey fibers are investigated in this paper. Numerical simulation shows that for holy fibers with conventional triangular transverse structure, proper-doped core can enhance the nonlinear coefficient and shift the near zero flattened dispersion region to long wavelength. By introducing a Ge doped core, a high nonlinearity holey fiber design for 1.55μm is proposed, with a nonlinear coefficient of 22 W^-1km ^-1 and a wavelength region of 165nm in which the dispersion value is within ±1 ps/km/nm.

A new feature of relationship between macro-bending losses and bending length of mono-mode fibers is found experimentally: when bending radius is 4mm nearly no loss is detected on the condition that bending angle is less than 20 degrees. The similar phenomena happen when bending radius is 3mm or 2mm. The turning bending degree that bending losses will increase rapidly is called critical angle by us. The result will give us some new clues that how the bending losses change with bending length on earth. And some theoretical work should be done to explain the phenomenon.

We describe our work on the micro/nano-scale design and integration of polymer optical waveguide wires and miniaturized optical devices for applications in an optical module system that we call "optical printed circuit board" (O-PCBs) and VLSI photonic integrated circuits. We fabricate the O-PCBs using planar arrays of polymer waveguides to perform the functions of transporting, switching, routing and distributing optical signals on flat modular boards. The VLSI photonic integrated circuits are designned to perform similar functions on a chip scale. We fabricate the polymer waveguides using thermal or ultra-violet (UV) embossing and imprinting technique. The optical boards which have 2-dimensional array of waveguides are attached to the electrical printed circuit board (E-PCBs) which carry the transmitter circuits and the receiver circuits of 2.5 Gbps or 10Gbps. In order to increase the efficiency of lightwave coupling between the lasers and the waveguide, we perform the alignment experiment between the laser and the waveguide via microlens and between the waveguide and the detector via microlens. The microlenses are fabricated by placing droppings of resins. Also, the 45-degree mirror to couple the light between the laser and the waveguide and the waveguide and the detector are fabricated by embossing technique to reduce the processing steps and for low-cost production purpose. For VLSI nano-scale photonic integration, we use photonic band-gap crystals and plasmonic waveguide structures. We discuss scientific issues and technological issues concerning the integration of micro- and nano-photonic devices and circuits.

Recent results on the nonlinear optical properties of silicon-on-insulator waveguides are reviewed. Interest on two photon absorption (TPA) in silicon has been raised by its potential applications for square law detection in autocorrelators for measuring pulsewidths and cross correlators for high speed all-optical clock recovery, high speed optical switches and optical wavelength conversion. The results reported by different groups on two photon absorption, optical Kerr effect, and Raman gain are compared and the range of possible values for the nonlinear figure of merit are calculated. The nonlinear figure of merit obtained from the average values of the various published experimental values suggests that silicon is suitable for all-optical nonlinear refractive switches which need only pi phase change but is not suitable for switches which need several pi of nonlinear phase change. The recent developments on obtaining optical gain using stimulated Raman scattering in silicon are also discussed.

The optical waveguide design of quantum well EA traveling-wave modulator is investigated by the evaluation criteria, which contain material parameters, couple loss, microwave properties. The result shows that the material design is very important for good performance, and the thickness of core layer is larger than absorption layer is better and the thickness of active layer should be optimized.

In this paper, we propose a novel compound high order microring resonator all-pass filter by employing an assistant microring between two cascaded microrings. It improves the dispersion compensation ability and provides a wide bandwidth. The extension of group delay range is shown in its group delay response, which allows flexible choice of the microring size for technical convenience and bend loss improvement. The careful design of coupling coefficients is able to optimize the group delay response.

We present a theoretical investigation of the ultrafast all optical switching based on pulse trapping in photonic crystal fibers. We numerically solve the coupled nonlinear Schrodinger equations for two independent ultrashort pulses propagation in photonic crystal fiber using a standard split-step Fourier algorithm to analyze the phenomenon of pulse trapping across the zero-dispersion wavelength. It is shown that one pulse (for example the second one) of the signal pulse train propagating in the normal dispersion region can be trapped by an ultrashort soliton pulse propagating in the anomalous dispersion region. The soliton and trapped pulse co-propagate along the fiber. The soliton pulse is red-shifted due to soliton self-frequency shift and the trapped pulse is blue-shifted to satisfy the group velocity matching. Only the second pulse among the signal pulse train is trapped by the soliton pulse and the optical spectrum of the trapped pulse is distinctly blue-shift through the cross phase modulation and is separated from the untrapped ones, thus it can be picked out easily by use of a wavelength filter such as a fiber Bragg grating. The ultrafast all optical switching with a 1THz repetition frequency is confirmed directly. As the input peak power of the pump pulse increases, the red-shift of the soliton is considerably enhanced with the simultaneous further blue-shift of the trapped pulse to satisfy the condition of group velocity matching.

In this paper, a novel scheme for adiabatic pulse compression using silica-based functional fibers with enhanced nonlinearity is proposed and investigated in detail. The numerical results show that the pulse compression in this kind of fiber satisfies the adiabatic condition by selecting the reasonable systematic parameters. Although the higher order nonlinear effects, especially the Raman self-frequency-shift, are obvious due to the increased gradually nonlinearity, high quality compressed pulse can also be obtained except generating an extra-time-delay according to retarded frame.

An all-fiber passively Q-switched erbium fiber ring laser with nonlinear polarization rotation is experimentally demonstrated. By incorporating a length of single mode fiber and polarization dependent isolator into the erbium fiber ring laser, intensity dependent transmission can be implemented due to nonlinear polarization rotation, which can act as an artificial saturable absorber for switching. Such a passively Q-switched erbium fiber ring laser has the simple and all-fiber configuration. In addition, passive harmonic mode-locking and chaotic pulses are also generated from the erbium fiber ring laser.

Characteristics of the output pulse shape of stimulated Brillouin scattering optical limiting process induced by the seed field is numerically simulated. Rules of limiting pulse shape controlled by the seed field are obtained as follows: When seed pulse duration is chosen to be five times as that of the pump pulse duration, and delay time is just the same as that of pump pulse duration, the best limited temporal profile can be obtained. At the same time, it is affected by the pump power: as the pump power increases, it falls endlessly before it becomes zero. Study indicates that controlling of SBS optical limiting pulse shape can be achieved by using a seed pulse.

We experimentally investigate the generation of a low-noise ultra short pulse train from 40GHz to160GHz by using Comb-like profiled fiber (CPF) for adiabatic soliton conversion and compression. Highly nonlinear fibers allow us to reduce total length of CPF as well as to utilize Kerr effect in the fiber effectively. We demonstrate generations of 160GHz soliton train of 750fs, the compression to 500fs of 40GHz externally-modulated pulse with wideband tunability over 30nm. Then we apply the CPF pulse compression technique to achieve the programmable repetition tunability from 5 to 500 MHz in low pedestral 300fs pulse train generation.

We present a novel scheme for simultaneous measurement of the external RI and temperature by using the sandwiched long-period gratings (SLPGs). An LPG pair coupling between the guided mode and the low-order cladding mode acts a temperature reference element, and another LPG in-between coupling with the higher-order cladding mode performances an RI sensor. The period and length of the paired LPG (with a center to center distance 47.5mm) are 643 μm and 22.5mm, respectively, and those of LPG in-between are chosen to be 428 μm and 23mm, respectively. The experimental results show that the RI sensitivities of a paired LPG coupling with the third order cladding mode is -6.71 nm/R.I.U (refractive index unit), and the sensitivity of the LPG in between coupling with the ninth order cladding mode is -27.77 nm/R.I.U. The temperature sensitivities of these LPGs are -0.315nm/°C; and -0.337nm/°C;, respectively.

Simultaneous measurement of temperature and force using a single fiber Bragg grating based on broadened reflection spectrum is proposed and demonstrated. The wavelength peak shift and the bandwidth broadening with the change of temperature and force allow discrimination between the temperature and force effects. Standard deviation errors of 1.8°C and 0.16N have been obtained with temperature and force ranges of up to 20~100°C and 0~8N, respectively.

In this paper, a novel temperature stabilization technique for Fiber Bragg Grating is presented, named dual-arm adverse expanding technique. Experiment demonstrates, the Bragg wavelength shift of FBG treated with this technique is only 0.03nm in range from 12°C to 62°C. It is equivalent to 0.07 nm/100°C. Temperature stability of FBG treated is 14 times higher than that of bare one. The Bragg wavelength shift of FBG induced by temperature is eliminated mostly.

Proposed and demonstrated in this letter is a scheme of fiber Bragg grating (FBG) interrogation system based on thermistance and matching-FBG of temperature sensitivity enhancement. According to the relationship between the period of the matching-FBG and the resistance value of the thermistance, the scheme interrogates the wavelength-shift by adjusting the matching-FBG's temperature and detecting the resistance value of the thermistance. In measured experiments, the results show that the precision of the proposed system is 0.048nm in a range of 5.9nm.

Design and construction of temperature-insensitive fiber Bragg grating (FBG) liquid level sensor based on bending cantilever beam (BCB) is proposed and demonstrated. The BCB induces spatially gradient strain on the unique sensing FBG, resulting in a Bragg bandwidth modulation. The broadening of FBG spectrum bandwidth and the reflected optical power are corresponded to liquid level changes, insensitive to spatially uniform temperature variations. In the liquid-level range of 500 mm and temperature change from 20^oC to 80^oC, the liquid level measurement fluctuates less than 2% without any temperature compensation. By a pin-photodiode (PD) optical power detecting, the liquid-level sensor avoids expensive and complex demodulation techniques and potentially costs low.

An innovative algorithm based on the evolutionary programming (EP) method is developed for recovering distributions of axial strain along a fiber grating from its reflection spectral response. The proposed method exhibits a number of attractive features that prove to be effective for solving the inverse problems. The basics of EP are reviewed and the detailed programming procedures of the proposed algorithm are presented. By combining EP and the matrix method for calculating the reflection spectrum of a FBG, we obtain a new method for the distributed sensing. The numerical simulations show good agreements between the original and the reconstructed strain profiles.

Transmission systems employing Raman amplifier technology have to put up with much higher level of design complexities, when compared to conventional transmission lines with doped fiber optical amplifier. Even for the construction of a fundamental, basic building block - a unit of a fiber Raman amplifier (FRA), the designer have to struggle with the problems associated with the interactions between pump / signal waves mediated by Raman process, have to wander within the vast degrees of freedom given the choice of pumping directions / ratios, and have to contemplate with the wavelength dependent fiber loss / noise figure profiles. The problem further evolves into steps-higher, demanding and time-consuming one when extended to that of a system design employing Raman amplifiers. Optimizing OSNR and designing ultra-long haul links with best Q performances, while adjusting variables in the span length, Rayleigh penalty, pump noise, nonlinear penalty, dispersion and gain distribution is a problem which can be easily stated, but in reality is not a process which can be easily achieved. We present efficient, optimal design methods for Raman amplified WDM transmission links: 1. for the multi-channel gain flatness, 2. transient control under signal reconfigurations, and 3. for the estimation of optimum system Q value and corresponding link design parameters.

The amplification effect on forward and backward stimulated Brillouin scattering lines in the forward pumped S band discrete DCF fiber Raman amplifier (FRA) has been studied. The pumped threshold power of the forward first order Stokes SBS (FSB₁^- ), second order Stokes SBS (FSB₂^-) and third order SBS (FSB₃^-) in the forward pumped FRA are 1.5 mW, 1.4 mW and 1.7 mW respectively. The Stokes SBS lines are amplified by FRA and fiber Brillouin amplifier (FBA) at the same time. The gain of amplification is given as G_A=G_R multiplied by G_B where G_R is Raman gain and G_B is Brillouin gain. In the experiments, the saturation gain of FSB₁^-, FSB₂^- and FSB₃^- are about 52dB, 65dB and 65dB respectively. The saturation Raman gain of 10km DCF forward FRA is about 14dB, so the Brillouin gain of FSB₁^- , FSB₂^- and FSB₃^- are about 38dB, 51dB and 51dBrespectively. There are pumped threshold power of the first order, second order and third order Stokes backward SBS (B-SBS) line BSB₁^-, BSB₂^- and BSB₃^- in the forward pumped discrete DCF FRA, and they are about 4.7mW, 17.1mW and 67mW respectively. The saturation gain of the first order, second and third Stokes backward SBS line BSB₁^-, BSB₂^-and BSB₃^- are about 60dB and the saturation gain of 10km DCF forward pumped FRA is about 27dB, so the gain of FBA is about 33dB. The forward and backward cascaded SBS lines have been observed.

C-band and S-band fiber Raman gain spectrum pumped by single wavelength high power fiber Raman laser were tested and the proper chirped Bragg fiber grating as gain flattening filter was designed to flatten actually tested gain spectrum. Besides, FWDM (filter wavelength division multiplexer) and 1427nm/1505nm CWDM (coarse wavelength division multiplexer) are used as C-band and S-band fiber Raman amplifier pump-signal couplers respectively. The gain media are 50 km G652 fiber and 5km DCF (dispersion compensation fiber). C-band fiber dispersion compensation Raman amplifier with bandwidth from 1519nm to 1574nm (55nm) and average gain 15.2dB and ripple ±0.8dB was successfully obtained. S-band fiber dispersion compensation Raman amplifier with bandwidth from 1488nm to 1541nm (53nm) and average gain 10.1dB and ripple ±0.9dB was successfully obtained. During the test of C-band fiber Raman amplifiers, broadband ASE light source and WDM-emulator were used to simulate the DWDM (dense wavelength division multiplexing) signal source that can make the whole test more accurate. It is very significant for extending range of communication band of fiber and increasing the capacity of fiber communication especially for ultra-long haul and ultra-high capacity communication system. At last, the result of experiment using these setup and influence caused by gain flattening filter and different type fibers location arrangements (G652 fiber and DCF) and corresponding solutions were also discussed.

In this paper, we report novel long-period fiber gratings (LPFGs) fabricated by using a new writing technique that is mainly based on the thermal shock effect of focused high-frequency CO₂ laser pulses at several kHz. Based on these novel LPFGs, an amplified spontaneous emission (ASE) noise filter and a gain equalizer have been demonstrated for the noise reduction and the gain spectrum flattening of Er-doped fiber amplifiers (EDFAs), respectively. By use of the unique bending, twisting and loading features of the LPFG, three tunable gain equalizers have been demonstrated for dynamic gain flattening of EDFAs. In addition, a number of novel fiber-optic sensors, including a bend-insensitive LPFG sensor that could solve the problem of cross-sensitivity between bend and other measurands, a torsion sensor that can realize absolute measurement of twist rate, and a load sensor that can achieve simultaneous measurement of transverse load and temperature using a single LPFG element are proposed and demonstrated. The unique features of these LPFGs are mainly due to the asymmetrical distribution of the refractive index on the cross-section of the LPFG induced by high-frequency CO₂ laser pulses.

We design a new double-layer grating template, which has the advantages of period uniformity, period number adjustability and continuous period regulation. Under the new template, we research the relationship between the spectrum and the grating templates: the resonant wavelength is mainly determined by the grating period; the intensity of transmission peak loss lies in the external pressures; the bandwidth of transmission spectrum can be controlled by the period number. Therefore, various applications can be realized by optimizing the transmission spectrum by reasonably selecting the matched parameters.

The detection of the change of concentration of cupric ions (Cu²⁺) by long-period grating (LPG) sensors was presented in this paper. A polymeric affinity coating was chemically attached to the surface of the LPG sensor with reaction times of 4 hours, 8 hours, and 12 hours, which is characterized of its surface appearance by scanning electronic microscope (SEM). By comparing the surface appearance of the polymeric affinity coating, a proper reaction time was chosen as the final experimental condition. The optimal experimental condition was applied to the LPG sensor, which was first dipped into cupric sulfate (CuSO₄) solutions of different concentrations and then ethylene diamine tetraacetic acid (EDTA) solution. The intensity changes of typical transmission spectrum with Cu²⁺ concentrations were studied. Results showed that the intensity-based method of LPG sensor can reflect the change of the output light power and can be used to indicate the concentration of Cu²⁺.

We study the performance of all-optical switching in long period fiber grating based on the coupled nonlinear Schrodinger equations. The switching rate of long period fiber grating in the on-resonance and off-resonance case is obtained, respectively. It is found that in both cases, the on-off ratio of all-optical switching in long period fiber grating can be improved remarkably, and the phenomenon of pulse breakup can be avoided effectively, by using the higher order super-Gaussian pulses.

We present the design and fabrication of a broadband all-fiber wavelength-division multiplexing (WDM) filter based on the long-period grating (LPG) technology. By utilizing the improved LPGs, i.e. the LPG with step-changed index modulation, an LPG with a 3-dB flat-bottom stop-band was designed with transfer matrix method. The fabrications of the designed LPG and the broadband WDM filter are also realized by using the point-by-point grating writing technique in the experiments.

A high power Ytterbium-doped fiber laser (YDFL) with China-made double clad fiber (DCF) is introduced in this paper. The Geometric parameter and laser characteristics of the newly designed fiber have been studied. When both ends of the fiber were pumped by two high-power laser diode with the total lunched power about 600W , we got the laser output of 330W, with an optical-to-optical efficiency of 55%.

Based on beam characteristic of semiconductor lasers, The paper details a pumping system, which couples single LD to multimode with hyperboloid micro-lens at first, and then combines sixteen LD fiber coupled modules which with 2W output power to parallel pump fiber lasers which with fiber Bragg grating on each end by using a multimode coupler at each end. The total conversion efficiency of optical to optical is 40% and output power from fiber is 13W. Because this pumping system has merit of small volume, compact structure, replaced easy, long lifetime and high pumping efficiency, it more fits to end and side pumping for fiber lasers.

We have proposed and demonstrated a novel multiwavelength Brillouin-erbium fiber laser (BEFL) with a linear cavity, in which, the Brillouin pump is self-excited within the cavity, doesn't require the injection from the external cavity or direct generation within the intracavity. In this scheme, more than 115 Stokes lines with relatively uniform amplitudes have been generated. The experiment also demonstrates that such a self-seeded BEFL performs good repetition and stability for both the operating wavelengths and the output power of each Stokes line. Meanwhile, the effect of the 980nm pump on the performance of the laser is investigated.

By means of the coupling mode theory and the method of the extension of coupling coefficient, the corresponding coupling model is corrected for PBS. Considering the angle of the two Y-branch waveguides in PBS, the coupling length of 1430 is figured out, which is different from that of 2186μm without considering of the coupling in the Y branches in the previous design. And the simulation of the device performances are carried out by beam propagation method (BPM), the extinction ratio of the TE and TM mode is -26dB and -23dB, respectively.

This paper presents a new parallel finite-difference time-domain (FDTD) numerical method in a low-cost network environment to stimulate optical waveguide characteristics. The PC motherboard based cluster is used, as it is relatively low-cost, reliable and has high computing performance. Four clusters are networked by fast Ethernet technology. Due to the simplicity nature of FDTD algorithm, a native Ethernet packet communication mechanism is used to reduce the overhead of the communication between the adjacent clusters. To validate the method, a microcavity ring resonator based on semiconductor waveguides is chosen as an instance of FDTD parallel computation. Speed-up rate under different division density is calculated. From the result we can conclude that when the decomposing size reaches a certain point, a good parallel computing speed up will be maintained. This simulation shows that through the overlapping of computation and communication method and controlling the decomposing size, the overhead of the communication of the shared data will be conquered. The result indicates that the implementation can achieve significant speed up for the FDTD algorithm. This will enable us to tackle the larger real electromagnetic problem by the low-cost PC clusters.

A full-vector finite element method has been used to investigate the high-index-core Bragg fibers including mode field distribution and mode effective index. The influence on the high-index-core Bragg fiber dispersion properties of the low-index-layer filling ratio variations of different rings has been identified. Near-zero flattened dispersion over wide wavelength range was demonstrated in the one-dimensional high-index-core microstructured optical fibers with non-uniform low-index-layer filling ratio in different rings. Both flattened dispersion and low confinement loss can be achieved with finite number of low-index-layer rings.

In this article, two application examples of signal processing for optical interleaver design are presented. The optical interleaver has become an important building block of the dense wavelength division multiplexing (DWDM) system. Numerous design diagrams have been proposed for the optical interleaver, and, among these diagrams, the Mach-Zehnder interferometer type interleaver and the Michelson interferometer type interleaver might be the most popular ones. The Mach-Zehnder interferometer is a special case of the finite impulse response (FIR) filter, and the Michelson interferometer belongs to the category of the infinite impulse response (IIR) filter. In this article, we demonstrate how signal processing techniques could be applied to design the Mach-Zehnder interferometer type interleaver and the Michelson interferometer type interleaver. Detailed Z-domain transfer functions of these two types of interferometers are presented. The two case studies presented in this article demonstrate how signal processing has become a great enabling technology for optical device design.

This paper studies PMD compensation problems in the optical communication. In an adaptive compensation process of a practical PMD compensator, three main parts are included: an equalizer, a detection part and an algorithm. In order to achieve faster and simpler, particle swarm optimization (PSO) algorithm was introduced to this process. Although the original PSO algorithm is easy to trap into sub-optima, we proposed a new modified PSO to avoid sub-optima but keep the simplicity at the same time. This is the first time to introduce the conception of collision into PSO arithmetic, so it is called collision PSO. Through the numerical simulation, this proposed method showed the better result than the original PSO methods.

We have studied the statistics of the output pulse width and effective broadening of the pulses which are affected by Polarization Mode Dispersion (PMD) of optical fiber. In this work, first we simulated numerically the optical fiber PMD. After the model examination according to the known characteristics and criterion for PMD, we have computed and shown the effect of the optical fiber PMD on the pulse shape. We have used the Monte Carlo method to investigate the dependence of the average output pulse width and effective broadening on the average Differential Group Delay (DGD) for Gaussian and super-Gaussian pulses (which are representative of RZ and NRZ data formats, respectively). It is shown that the previous analytical result for RZ data format is valid for NRZ data format. Also, we have shown that the dependence of the average effective broadening on the bit format and input pulse width is faded as the average DGD diminishes.

Fiber spinning has been widely used in reducing polarization mode dispersion of optical transmission fibers in the past decade. It also affects the polarization evolution in fibers, which has measurable effects. This paper reviews and reports the progress in understanding the properties of polarization evolution in spun fibers in both of the cases with and without the influence of external factors. Theoretical formalism is constructed and various properties of the polarization evolution are revealed through numerical modeling. Some aspects of the features have been experimentally explored.

Bragg fibres have many special characteristics. Therefore this kind of fibre attracts more and more attention. In this paper, genetic algorithm is applied to design Bragg fibres to realise desired dipersion and attenuation characteristics.

The photosensitivity and thermal decay of DCF Bragg grating written in Yb³⁺-doped and Er³⁺/Yb³⁺-co-doped DCF are experimentally investigated, respectively. Variation of amplitude of reflective-index modulation and effective reflective index with the UV exposure time are observed. Depend on the photosensitivity relations of hydrogen-loaded rare-earth-doped DCF, we fabricate diversiform reflectivity of DCF Bragg gratings with phase mask method, and the best reflectivity of the grating is 99.9%. The thermal decay characteristics according to the different anneal thermal, 100°C, 150°C, 200°C and 250°C are got. These results are very significant to estimate the properties of grating, such as thermal, wavelength and anneal time.

The successful fabrication of multi-wavelength FBG by using the high precision exposure clamp of scanning stage that made by ourselves are introduced. Only a single phase mask is used, and the wavelengths of FBGs fit the wavelength standard of the ITU-T. FBGs with four different wavelengths are fabricated by using one phase mask, and they have been used in a 4×10Gb/s, 1000 km conventional single mode optical fiber(G.652) transmission system. In each channel, 6 FBGs are used for the dispersion compensation and the power penalty in each channel is less than 1.8dB.

The necessity of packaging and the basic principle of temperature compensation package for fiber gratings are expatiated. A method of packaging fiber gratings with the negative temperature coefficient material is introduced, and the temperature characteristic and long-term stability of packaged fiber gratings are measured. This packaging keeps the compact structure and doesn't influence the intrinsic characteristic of fiber gratings. In addition, its temperature coefficient is reduced to 0.0005nm/°C, and this result reaches applicable request. The more important is this packaging can keep good long-term stability. After half a year, the characteristic, reflecting wavelength and temperature coefficient of the packaged fiber gratings have little changed, and this result realizes the high stability packaging for fiber gratings.

We report on a 40 Gbit/s NRZ (non-return-to-zero) code transmission experiments including an dynamic Polarization mode dispersion (PMD) compensation. The dynamic PMD compensator is made up of two-stage four degrees. The first stage adopts polarization controller and fixed time-delayed line. The second stage is variable Differential Group Delay (DGD) element. The PMD monitoring technique is based on degree of polarization (DOP) as error signal. A novel practical adaptive optimization algorithm was introduced in dynamic adaptive PMD compensation. The experimental results show that the performance of the PMD compensator is excellent for 40Gbits/s NRZ transmission systems with the large the DGD. With this compensator, a significant improvement of system performance can be achieved in the eye pattern of a received signal.

A new formalism is used to calculate the combined effect of PMD and PDL. By means of a Monte Carlo simulation, a probability distribution for the largest pulse spreading in a fiber with PMD and PDL is simulated, which can be approximated by a generalized lambda distribution.

We review and discuss various aspects of polarization mode dispersion (PMD) both with respect to impairments on optical transmission systems, as well as mitigation methods. Some novel statistical properties of the outage probability in transmission lines with finite number of birefringent elements is also presented.

With the thermal diffusion method, the Tl⁺ -ion diffusion process in Tl⁺-Na⁺ ion-exchanged glass is in details described by the electroneutrality field and the stress, which are generated by the huge dimension difference for Tl⁺ and Na⁺ ions and the large difference in diffusion coefficients between Tl⁺ and Na⁺ ions. The results of the theoretical analysis and the experiment data by X-ray energy dispersive spectra indicate that the Tl⁺ diffusion process is found to be a new diffusion law.

Si-nanowire waveguides are attractive structures for constructing various optical devices that are extremely small, and that can be flexibly connected as devices on a silicon (Si) wafer. The waveguides can be bent with extremely small curvatures of less than a few micrometers of bending radius because the large difference of refractive indices between the Si-core (n = 3.5) and the silica cladding material (n = 1.5) strongly confines the optical power in the waveguide core. Therefore, these waveguides are promising for flexible optical interconnections on Si chips as well as for constructing many extremely small optical devices. We used Si-nanowire waveguides to fabricate optical directional couplers and demonstrated their fundamental characteristics. Their coupling-length was extremely short, several micrometers, because of strong optical coupling between the waveguide cores. Therefore, we could construct ultra compact power combiners/dividers. We have also demonstrated wavelength demultiplexing functions for these devices with a long coupled waveguide. Optical outputs from a device with a 100-μm long coupled waveguide changed reciprocally with 20-nm wavelength spacing between the parallel and cross ports. Ultra small optical add-drop multiplexers (OADMs) with Bragg grating reflectors made of the Si-nanowire waveguides have been also demonstrated. The dropping wavelength bandwidth of the OADMs was less than 0.7 nm, and these dropping wavelengths could be precisely designed by adjusting the grating period, and this indicated the possibility of applying these devices in dense WDM systems. Using the Si-nanowire waveguide, we have also demonstrated nonlinear-optic effects such as the spectral broadening of optical short pulses due to self-phase modulation and nonlinear transmittance based on two-photon absorption. At a 12 W input power level, we observed a 1.5-π nonlinear phase shift as well as strong saturation of optical output power from a 4-mm Si-nanowire waveguide sample, and that indicates the possibility of constructing integrated nonlinear-optic wavelength conversion devices or optical limiters with Si-nanowire waveguides.

Parametric devices based on four-wave mixing in fibers provide many functions that are required by optical communication systems. When operated in the linear regime, parametric devices provide amplification, frequency conversion and phase conjugation, all with high gain levels and broad bandwidths. They can also be used to monitor and switch signals. When operated in the nonlinear regime, parametric devices regenerate optical signals. In this paper the current status of research on parametric devices is reviewed briefly, and some promising directions for future research are indicated.

Taking into account pump depletion, numerical simulations have been undertaken to investigate the amplification of strong optical signal pulses in fiber optical parametric amplifiers (FOPAs). It is shown that a strong signal pulse experiences not only amplitude amplifying and temporal width broadening but also pulse splitting processes, which never be addressed in the FOPA studies. The pulse splitting phenomenon that the underlying mechanism is attributed to four-wave mixing, is explained intuitively by employing concept of signal gain saturation and optimum fiber length. Further calculations indicate that this phenomenon appears repeatedly as fiber length increased. Another interesting result is that a sub-pulse formed in the pulse splitting process is compressed by a factor of 9 and amplified by 19 times after evolution in FOPA for 2000m, compared with the incident Gaussian pulse. It indicates that there are potential applications of pulse splitting phenomenon in pulse compression, signal sampling and time-division multiplex system.

On amplifying of picosecond pulses in fiber optical parametric amplifiers, group-velocity dispersion (GVD) and third-order dispersion (TOD) effects are numerically investigated. It comes to two very interesting results. One is that GVD of the signal (idler) induces obviously the idler (signal) pulse broadening even though GVD of the idler (signal) is zeroed. The other is: on condition that signs of TOD coefficients for signal and idler are quite the contrary, TOD would lead to two oscillatory structures respectively near the trailing edge and the leading edge, rather than conventional one oscillatory structure. In conclusion, any dispersion-induced modifying of the signal (idler) pulse shape will be coupled to the idler (signal) and result in corresponding modifying of the idler (signal) pulse shape. It is extremely helpful for further experimental study.

In this paper, a four-channel waveguide amplifier array based on Er-Yb co-doped phosphate glass is proposed and theoretically designed, the performance of multi-wavelength amplification of the proposed Er-Yb co-doped phosphate glass waveguide array is investigated by numerical calculation. As example, the amplification characteristics of the proposed array for four wavelengths, 1539.4nm, 1540.2nm,1542.0nm and 1541,8nm, is discussed.

Non-uniform designs for Erbium doped waveguide amplifiers (EDWA) and Yb: Er co-doped waveguide amplifiers (YEDWA) were presented based on the standard rate equations including six Er energy levels and two Yb energy levels. Numerical results were shown that the design of the non-uniform EDWA operated by gain value get a gain improvement of 110.3% than uniform one, and designs of non-uniform EDWA and YEDWA operated by pump efficiency get gain improvements of 21.03% and 10.17% than uniform ones, even get gain improvements of 2.25% and 7.26% than the absolute gain maximum of uniform EDWA and YEDWA, respectively. The optimization of population inversion in ⁴I_11/2 could be demonstrated by the photoluminescence (PL) enhancement observed in cascaded Er doped glass measurement at room temperature.

A detailed theoretical and experimental study of the buried waveguide contour, which depends on exchange time and window width by Tl⁺-Na⁺ exchange techniques, is reported. Modeling, which includes the effect of ion-exchange time and window width, agrees well with our experiments showing that a buried waveguide contour depends on the relation of τ = square root of D_efft and W/2. The same index profile is formed a curve in the interference fringes, and the refractive index profile is a semicircular or semielliptical in waveguide. These results may be used in the proper design of integrated optical circuits and self-focus microlens that need the semicircular or semielliptical waveguides at different sections, such as optical power splitters, diffractive waveguide gratings, and so on.

This paper addresses the fabrication of thermal ion-exchange waveguides and error analysis in m-lines technology. Planar waveguides are fabricated on home-made Er-Yb co-doped phosphate glass substrate by thermal ion-exchange method, the effect of exchange temperature, anneal time, exchange time, and molten salt composition on the refractive index profile is investigated using m-line technology and uncertainty of measurement is also given.

Hole-assisted lightguide fiber (HALF) is a microstructured fiber composed of a high index core, a low index cladding and a small number of air holes surrounding the core. The characteristics of HALF are studied by using the full-vector finite element method. The contour lines of power flow intensity and transverse electric distributions are plotted for the fundamental mode and the first four higher order modes. The effect of the structural parameters, such as hole-to-core spacing and relative size of air holes to the cutoff wavelengths of fundamental mode and higher order mode, core power confinement factor, and mode field diameter is analyzed. Due to these holes, there are variations between HALF and conventional step-index fiber. It's found that when the distance between the air holes and core is shorter or the relative size of air holes becomes larger, the effect of air hole on the HALF turns greater: core power confinement factor becomes larger; mode diameter becomes smaller; the cutoff wavelengths of fundamental mode and higher order mode move to shorter wavelength. In terms of waveguide design, the structural parameters of erbium-doped HALF are optimized to obtain high-efficiency operation of a fiber laser or amplifier.

The rhodamine B-doped polymer optical planar waveguide with low propagation loss of 0.44 dB/cm has been fabricated and measured by using scanning near-field optical microscopy and m-line method. The mode structure, near-field topography and near-field fluorescence are obtained, respectively. This may have potential applications in the study of polymer waveguide laser and amplifier.

Optoelectronic packaging has become a most important factor that influences the final performance and cost of the module. In this paper, low microwave loss coplanar waveguide(CPW) on high resistivity silicon(HRS) and precise V groove in silicon substrate were successfully fabricated. The microwave attenuation of the CPW made on HRS with the simple process is lower than 2 dB/cm in the frequency range of 0~26GHz, and V groove has the accuracy in micro level and smooth surface.These two techniques built a good foundation for high frequency packaging and passive coupling of the optoelectronic devices. Based on these two techniques, a simple high resistivity silicon substrate that integrated V groove and CPW for flip-chip packaging of lasers was completed. It set a good example for more complicate optoelectronic packaging.

In this paper, we present a novel cross section shape DCF. Truncated from a circular DCF, the inner cladding of this DCF is bounded by two equal angular spiral curves. By using the concept of mean transverse path between successive encounters of the core, we developed a new method to calculate the absorption efficiency per unit fiber length. For a spiral shape DCF with the largest radius R=100μm , radius of doped core r₀=4μm , and the angle parameter of spiral curve θ=0.04 , we calculated the mean transverse path between successive encounters of the core l_r=2903μm . The corresponding l_c with other truncated shape cross section having the same cross sectional area is l_c=3454μm . Final results show that the absorption efficiency η increases 16% for our spiral shape DCF.

We present theoretical analysis of tunable bandgap guidance in virtue of bandgap theory. By means of plane-wave method a novel tunable photonic bandgap microstructure fiber (MF) was investigated by tuning the refractive index of nematic liquid crystal crystal (NLC) filled in the holes of MFs. Moreover, by using a full-vector finite-element method (FEM) with anisotropic perfectly matched layers (PMLs), the dispersion curves of NLC filled MFs have been computed with different value of the refractive index of NLC. Moreover, the leakage loss of the fundamental modes of the NLC filled MFs has been analyzed.

Using a full-vector finite element method, the phase modal birefringence and group modal birefringence to lateral pressure alone slow axis and fast axis versus wavelength in birefringence microstructure fiber was analyzed. In the wave band of our research, 600nm-1700nm, when different direction pressure is applied, the phase modal birefringence (B) and group modal birefringence (G) have different change to wavelength in microstructure fiber. Moreover, the results reveal that the pressure sensitivity of B and G have different change to wavelength when applying different direction lateral pressure. Our research has great signification in designing microstructure fiber and using microstructure fiber in sensing field et.al., especially using in multidimensional sensor.

We present for the first time, to the best of our knowledge, active waveguide device and array in Er³⁺-Yb³⁺ codoped lithium silicate glass directly written by near-IR femtosecond laser pulses. We show that in Er³⁺-Yb³⁺ codoped lithium silicate cylinder waveguide of diameter 4um is produced by use of a microscope objective with a numerical aperture of NA=0.1 and laser pulse of 400fs duration with a energy of 3μJ generated by a Ti:sapphire amplifier. The sample could be translated parallel to the laser beam axis by a computer-controlled three-dimensional translation stage. We analyze its guided wave characterization. This one-step process provides a simple and flexible method for the fabrication of integrated optics components.

Nonlinear optical (NLO) processes in pi-electron organic and polymer systems have attracted considerable interest because their understanding has led onto many compelling technological promise as well as the discovery of new phenomena, new theoretical insights, and new materials and devices. In recent years, as the field has progressed toward technological applications, the main issues have focused on high-performance materials that comply with device manufacturing and end-use conditions. New challenges in materials synthesis are being presented. In has now been demonstrated on pilot plant scales that high-performance electro-optic polymer thin films can be routinely used in optoelectronic integrated circuit fabrication in existing microelectronic device manufacturing facilities. The key steps are standard, including spin coating, photolithography, etching, metallization, and multilayer assembly. Nanocrystal quantum dots (QDs) have been incorporated into various NLO polymers and the optical properties of the nanocomposite films have been studied by femtosecond laser Z-scan instrumentation. Nanodevices have been fabricated by UV-assisted imprinting fabrication techniques. Photonic devices based on nanomaterials and ring resonators e.g., optical switches and dispersion compensators, are discussed.

A new method of tuning fiber Bragg grating by electromagnetic force is proposed. The wavelength shift of the fiber Bragg grating is 1.16nm in the range of the current intensity from 0 to 85.5mA. The researches indicate that the system has advantages of simple configuration and high sensitivity.

In this paper,we introduce a novel tunable external-cavity semiconductor laser that simultaneously achieves rapid tuning rate and tuning precision by mechanical control. A stepping motor is applied in the tuning system. By control of the angular displacement of stepping motor, we can modify the centre wavelength of FBG.

In this letter, long period gratings fabricated in single-mode microstructure fibers (index-guiding MF and PBG MF) were achieved by putting periodic pressure on the cladding along the fiber length, furthermore, the characteristics of the LPGs were discussed.

After an analysis of the spectral characteristics of the long-period grating (LPG) with decreasing the fiber cladding diameter, we experimentally investigated the spectra of etched LPG pairs (LPGPs) with ~3 dB transmissivity (as in-fiber M-Z interferometers). The evolutions of the transmission spectra were characterized as the cladding diameters were decreased by HF etching process. A shift of the stop-band of LPG and interference pattern of LPGP to longer wavelength was observed with the reduction of cladding diameter, in which that of higher order cladding mode induced a larger shift. The responses of the LPGs and LPGPs with different etching degrees to the change of the surrounding refractive-index were measured, and an increased sensitivity is observed in the experiment.

The reflection characteristics of Multi-mode fiber Bragg grating (MM-FBG) with non-uniform profile of index change were numerically studied in this work. The reflection spectrum of MM-FBG was obtained by solving the coupled mode equations (CMEs) using shooting method. For a standard multimode fiber with 342 guided modes, the initial problem within the shooting method frame is very slow when it was solved using numerical methods. We obtained the analytical solution of the initial problem of the CMEs by diagonalization so that the numerical simulation is fast enough to be finished within several hours using personal computer. The reflection was obtained for a standard multimode fiber with diameter of 62.5 micron. There are 35 reflection peaks in the spectrum where 18 of them are corresponding to forward-propagation mode coupled to same order backward mode and the other 17 peaks are corresponding to forward mode coupled to backward mode with neighboring order.

The feasibility of a tunable optical fiber grating with a quasi-active and low cost actuator device fabricated by shape memory alloy is investigated. The driving force and displacement of the shape memory alloy actuator are measured. It is found that the SMA actuator with 0.3 mm diameter and 2 mm length driven by 7 V voltage after 5 sec can change the length of the fiber about 60μm, here the strain is about 3%. For the optical communication in the wavelength 1550nm regime, the tunable spectrum width is about 50nm. Therefore, the actuator can use to drive optical fiber grating, it will lead to change the fiber Bragg grating resonance wavelength. This device perhaps plays the key role of tunable optical filter or OADM.

In this paper, the experiment on all-optical switching based on microstructured optical fiber (MOF) is reported. In experiment, a 25-meter-long MOF(γ=36W^-1km^-1@1550nm) is used as nonlinear medium of nonlinear optical loop mirror and the input signal is generated by a 10GHz tunable picosecond laser source (u²t TMLL1550), with a full-width at half-maximum (FWHM) pulse width of 2 ps centered at 1550 nm. With the increase of input power, a π nonlinear phase shift is obtained by 40/60 coupler in experiment, but the same thing not be found by 48/52 coupler. Strong confinement of electromagnetic radiation in the fiber core allow that microstructured optical fiber can have a much higher nonlinearity per unit length than conventional fibers, and consequently devices based on such fibers can be much shorter in length than their conventional counterparts. Additionally, the switching can also be used as reshaping devices.

A compact integrated 1310/1550nm Y-branch waveguide wavelength demultiplexing coupler based on multimode interference is demonstrated. Theoretical analysis and simulation results for the demultiplexer configuration are presented. The structure performance can be optimized with an appropriate choice of some structural parameters such as input and output waveguide widths, refractive index profiles and coupler length. The contrasts achieve 9.8 and 9.4dB for a graded-index Y-branch wavelength demultiplexer at 1310 and 1550nm, and the corresponding insertion losses are 0.60 and 0.73dB at 1310 and 1550nm, respectively. For a step-index Y-branch wavelength demultiplexer, contrasts are 7.6 and 7.5dB, and insertion losses are 0.75 and 0.83dB at 1310 and 1550nm, respectively.

For 2 x 2 fused coupler, all power launched into first fiber is able to couple its whole power to second fiber after fusion. When fabricating monolithic fused coupler, degree of coupling (i.e. total power transfer from one fiber to another fiber) depends on all fibers put together in closed contact. For 3 x 3 coupler, the arrangements of fibers are normally equilateral triangle and linear array, each of which has its own advantages and applications. There are also other factors that determine the spectral characteristics of 3 x 3 fused coupler besides the arrangements of fibers. One of the factors is twist, specifically known as intertwined twist used in this work. In an equilateral triangle arrangement of fibers placed on a conventional Coupler Workstation, there is never total power transfer from the launched fiber to the non-launched fibers. The intertwined twist also modifies the equilateral triangle arrangement at fusion region and this causes more power to couple to one non-launched fiber then the other non-launched fiber. However, it is possible to get as close as 33 ± 3% splitting ratio among the three output ports by manipulating intertwined twist in the newly triangular arrangement of fibers.

In coherent optical systems or sensors, polarization matching between the two superposed waves must be achieved by some means. One of the methods used in practice is the feedback control of the input polarization. In this paper, a new theoretical analysis of the feedback control principle of the input polarization is given, by which polarization matching between the superposed waves can be obtained. Numerical simulation indicates it agrees with the experimental results.

Multiplexer/demultiplexer for WDM system based on off-axis holographic Fresnel lens was fabricated. The principle and fabricating technology of the demultiplexer with the central working wavelength of 1310 nm and the channel spacing of 25 nm were described. The reduction of third-order aberrations was the main consideration. The theoretical analysis indicates that third-order aberration can be effectively reduced if the condition tanα_C/tanα_R=-λ_C/λ_O is applied in geometry design and long object distance is selected. The experiment method and results were presented in this paper, and results verified the theoretical analysis.

In this paper, we introduced a novel method to fabricate 40Gbit/s optical time division multiplexer by using PZT to modify the length of fiber, and investigated its polarization sensitivity. Optical fiber couplers were sensitive to polarization. Their coupling ratio changed with the fluctuation of polarization state, so the output power of multiplexer fluctuated. Polarization scrambler was adopted to reduce the polarization sensitivity of OTDM system for the first time and its validity was testified by the experiment.

In this paper, we present the design and fabrication of a novel compact broad-band isolator with high isolation performance. With properly adding waveplates into the scheme, the fabricated device is demonstrated to achieve an isolation value of more than 40dB covering a broad-band wavelength range of 300nm in simulation. Its temperature insensitive and super low PMD character also has been demonstrated. Theoretical analysis and experimental results show each set of parameters concerning the isolator with high performance, which indicates the proposed technique is promising in the application of optical networks.

Thin Film Filters (TFFs) are minimum phase filters, and the Hilbert Transform law is related to the relationship between a TFF's amplitude and phase response. It should be possible to obtain the phase response from the amplitude response by this law, but the Cauchy Integral is too complex to calculate the phase response directly. In this paper, a method to reconstruct the phase response from the amplitude response was proposed, and then the group velocity delay and the chromatic dispersion of a TFF could also be obtained just by simple calculations. An experimental setup based on the RF modulation was designed. The test results were in good agreement with the theoretical value within passband, as determined by contrast analysis, and the validity of the method was proven. In addition, the dispersion characteristic of TFFs was also analyzed.

The microstrip patch antenna is a low-profile robust planar structure. A wide range of radiation patterns can be achieved with this type of antenna and, due to the ease of manufacture, is inexpensive compared with other types of antennas. However, patch-antenna designs have some limitations such as restricted bandwidth of operation, low gain, and a potential decrease in radiation efficiency due to surface-wave losses. The PBG patch antenna shows significantly reduced levels of surface modes compared to conventional patch antennas, thus improving the gain and far-field radiation pattern. A general procedure is presented to determine the fields scattered by a periodic structure due to a complex excitation in terms of the structure's plane-wave response. Specifically, the scattered field from an electric line source over a semiinfinite metallo-dielectric photonic bandgap (PBG) material is described. An effective description for the artificial crystal's plane-wave response is used, consisting of angularly parameterized response functions. A methodology for analyzing the electromagnetic response of such a material to a nonplane-wave excitation is provided, whereby a general complex excitation is spectrally decomposed into an integral over a continuous spectrum of homogeneous and inhomogeneous plane waves. An analytic solution for the scattering of each plane wave by the PBG material halfspace is then utilized. The complete scattered field is given in a closed integral form, which is computed both numerically and in the asymptotic limit. The effect of the PBG crystal half-space on the scattered field due to an electric line source is presented for frequencies that correspond, for a normally incident plane wave, to a transmission bandgap, a transmission band edge, and an antireflecting plateau. The focusing effects and electric- and magnetic-wall behavior of the PBG crystal are demonstrated. The presented approach promotes both the physical understanding of PBG material systems and the efficiency of the numerically modeling of these systems at frequencies beyond the quasi-static limit of the traditional effective medium theories.

A wavelength 0.85μm-based optical power splitter designed with Multi Mode Interference (MMI) by ion exchange on K9 glass was introduced. The waveguide material is K9 glass made in China and formed by K⁺-Na⁺ pure melt salt ion exchange method. The grade index profile of planar ion-exchanged waveguide on K9 was studied and accorded with erfc function through compare of experimental and theoretic index profiles. The fabrication process of planar ionexchanged waveguide device was described. The basic theory of 1×8 MMI optical power splitter was illuminated by using guided-model propagation analysis. The working wavelength is 0.85μm, and the structure parameters of 1×8 MMI splitter were designed. The core pitch on this chip is chosen as 250μm to take the fiber connections into account, and the typical cladding diameter of optical fibers as 125μm. The critical parameters in the fabrication of the MMI power splitter are the multimode section width and length. In general the key performance specifications of the optical power splitter are insertion loss and uniformity. The output performances and the refractive index change's influence of the device were simulated by Bear Propagation Method (BPM). The uniformity was 0.93×10^-2dB, the average insertion loss was 9.12dB, and the maximal insertion loss was 9.14dB. The result shows that the advantages of the method include low loss, ease of fabrication, and low material cost.

The characteristics of localized fields of doped photonic crystal fibers (PCFs) are studied by numerical simulation method in the paper. An interesting phenomenon is produced with the enhancement of stimulated radiation, which is the transmittivity being greater than one. And the numerical results show clearly the relation between the characteristics of localized fields, the abnormal group velocity in photonic band gaps and the negative imaginary component of the complex effective index of refraction of doped medium. Based on the relations the amplification of stimulated emission can be realized by introducing active impurities into the defect media of PCFs. Furthermore, the narrow transmission bands can be obtained by introducing line defects into the doped PCFs, which are used as channels in wavelength-division multiplexed (WDM) communication systems. And the doped PCFs can also be used to make optical amplifiers employed in dense WDM communication systems.

A novel design method about photonic crystal fiber (PCF) with large area model field (LAMF) is demonstrated. Different from ordinarily design that the core of PCF formed by missing one air holes in the center of section, many air holes distributed in heartland all together come into being the core region. Air holes are arranged regularly in core region and outer cladding regions according to different periodical character, respectively. The effective refractive index (n _eff ) of core region should be higher than cladding region because of total internal reflection (TIR) requirement. In this paper, two kinds of typical scheme are offered to realize LAMF-PCF. First, Λ, the spacing of neighboring air holes in whole section is fixed, once the radius of air holes in the core region r_c is smaller than the cladding air holes r_cla, LAMF-PCF will be formed. The modal area only lessens a little as r_c is reduced. Especially, optimal size of r_c can nearly make MFA insensitive to wavelength. On the contrary, dispersion parameter of PCF will take place visible change along with r_c reduced, and ultra-flattened dispersion character can be realized when r_c is optimized. Another method of designing LAMF-PCF is keeping all air holes uniform in the whole section of PCF, but the space of neighboring air holes in the core region Λ_c is longer than the cladding region Λ_cla, so n_eff of core region is higher than the cladding region and TIR can take place.

In this paper, we have proposed a novel compact electro-optical switch based on silicon/montmorillonite (MMT) photonic crystals and investigate its optically controlled on-off switch properties numerically by using the finite-difference time-domain method. The numerical simulation results show an excellent electro-optic switch at a wavelength of 1300nm was achieved with applied voltage as low as 0.5V, an extinction ratio of 20dB and a length of only 15μm.

A highly nonlinear photonic crystal fiber (PCF) is proposed to construct a nonlinear optical loop mirror (NOLM) for pulse compression and shaping. The proposed highly nonlinear PCF is a large air-filling fraction holey fiber with a small fiber core. The characteristics of the fiber have been studied. The NOLM made up of this PCF and an asymmetrical coupler for pulse compression and pedestal suppression is theoretically investigated. The results show that when compared with a soliton-effect compression in which only a piece of PCF is used, a NOLM based on a highly nonlinear PCF significantly suppresses pulse pedestals with a relatively short loop length. For a given input pulse, there exists an optimal loop length at which the high quality compressed pulse can be obtained. The proposed scheme can be used to compress long pulses by use of appropriate fiber lengths and works well for a broad range of input soliton orders.

Photonic crystal fiber (PCF) has aroused growing interest over the past few years becauce PCFs exhibit many unusual properties, especially an endlessly single mode and highly tunable dispersion. Polyethylene have distinguish advantages such as the real part of dielectric constant keep constant in the frequency range from 0.1THz to 2THz that the material dispersion contribute little to total dispersion, and the imaginary part of the dielectric constant is close to zero in THz frequencies that the material loss is low. This offer a new possibility of constituting polyethylene PCF for low loss and low dispersion THz waveguide. In this paper, propagation properties of polyethylene PCF in THz frequencies are analyzed by full-vector model. Numerical results demonstrate that effective index of fundamental mode decreases with frequency decreasing and near zero-dispersion can be obtained over a wide frequency region.

A novel photonic crystal fiber with ultra-flattened dispersion and large mode area is demonstrated. All air holes are arranged in the section according to triangular regulation and with identical spacing. The thirteen air holes, which in the middle of the section arrayed in the shape of snowflake, are smaller than the other air holes in the outer cladding region, form the large core region of PCF. Because the effective refractive index of the core region is higher than the cladding region, total internal reflective (TIR) can occur in the interface between the core and cladding, and optical field can be located mainly within the region of snowflake form. Obviously, this kind of PCF has large mode area because the thirteen holes holding together increase the core area of PCF visibly. On the other hand, not only ultra-flattened dispersion character can be realized in a broadband wavelength range, but also the flattened dispersion curve can easily be shifted in parallel from negative to zero, even to positive when the air holes of the core region is changed while the air holes size of cladding and spacing in the whole section remain fixed. Desired dispersion character and modal area can be realized in our designed PCFs with special section structure by optimizing the match of the spacing and air hole size in core and cladding regions.

A method to predict the Raman gain and Raman gain coefficient of some fibre types is developed by analyzing the relationship between stimulated Raman scattering and the doping constituents. The calculated results were compared with measurement results on dispersion-shift fibre(DSF)and dispersion compensating fibre(DCF). Agreement between the calculated and measured data on DCF is quiet well.

In order to achieve higher output powers, double-clad fibers (DCF's) are widely used by optical fiber lasers and amplifiers. In this paper, we present a comprehensive mathematical model for the novel multi-mode (MM) double-clad (DC) Er: Yb co-doped hexagonal fiber, Based on the rate and propagation equations, the pump light and forward and backward-amplified spontaneous emissions (ASE±) light transmission in the fiber are analyzed numerically and measured. The simulative and experimental results show that pump power was absorbed almost completely when the length of the fiber is about 3.5~4 m, the suitable length of the fiber in optical fiber lasers is 2~2.5 m. and the 2 m long fiber emits at 1535 and 1543 nm simultaneously, and the peak-value wavelength of ASE+ changes to the long wavelength with the increase of the pump power. The results investigated are useful for the design of optical fiber lasers.

In this paper, we present a comprehensive mathematical model for the novel double cladding fiber, based on the rate and propagation equations, the output signal power and noise characteristics of double-cladding erbium-ytterbium co-doped fiber amplifiers with a reflector are analyzed numerically. Due to the contributions of the reflector to reflect the un-absorbed pump power, pump light transmitted in the active fiber is increased and the output performances are improved, it is shown that the amplifiers with the reflector have about the same high-power output signal as those without it, only using half-lengths of fiber. The pumping scheme and numerical results could be useful for the real optimized design of DCF amplifier in the near future.

We simulated beam combination of Yb-Doped Double-Clad-Fiber(DCF) lasers theoretically by using a new external cavity and this system suits both of 1D array and 2D array. The numerical simulation result of 1D linear array shows that light energy from fiber lasers can be coupled into fiber cores through a single round trip. In comparison with several 2D arrays, we find that both the radius of the central spot shroten with the number of fibers increasing, on the contrary, the optical feedback through a single round trip coupled into cores increase gradually.

In this paper, a practical two-stage scheme is suggested for generating a C+L-band erbium-doped fiber amplified spontaneous emission (ASE) broadband light source. A considerable power increase of the L-band ASE spectrum is achieved by injecting the C-band ASE into the long section erbium-doped fiber. The C+L-band ASE source is obtained by combining the enhanced L-band ASE with the C-band ASE from two stages respectively. A spectrum flat ASE source with nearly 80nm bandwidth and about 15.9dBm output power is obtained with a total pump power of 180mW. Namely, the pump conversion efficiency is about 21.6%. Such a broadband incoherent light source is desirable for various applications in some areas like sliced wavelength- division multiplexed local-access networks, characteristic measurement for dense wavelength-division multiplexed components, and fiber-optic sensor systems etc.

We proposed and demonstrated a new configuration of the low noise figure C+L- band erbium- doped fiber amplifier. In the configuration, a preamplifier is used to reduce the noise figure, and an improved double-pass configuration with a fiber Bragg grating was employed to enhance the L-band gain and while to reduce the noise figure. The experiment demonstrated that the noise figure in the new broad-band amplifier was improved by ~2 dB, and the gain was enhanced up to above 25dB over the region from 1525 to 1605nm.

In this paper, a novel scheme for band selection in an amplified spontaneous emission source (ASE) based on erbium-doped fiber is demonstrated. C-band operation is obtained without backward ASE feedback whereas L-band operation is obtained with backward ASE feedback with the used of a 1X2 optical switch. A selective ASE source with an output power of 27.6mW for the C-band and 11.8mW for the L-band is obtained experimentally with a total pump power of 100mW of 1480nm laser diode. This band selective ASE source convenience the users select the necessary band when needed without any form of upgrading or additional module attachment therefore has the potential use for the dual-band DWDM device characterization and metro networks.

In this paper, we investigate the 1480nm pumped L-band erbium doped fiber amplified spontaneous emission source of three major configurations: one-stage double-pass forward pump configuration, two-stage with C-band ASE injection configuration, one-stage double- pass bi-directional pump configuration. The characteristics are compared in terms of the output power, pumping conversion efficiency, bandwidth, and mean wavelength stability. It is shown that the one- stage double-pass bi-directional pump configuration has a better performance than the other two configurations.

The optical fiber acousto-optic sensor (OFS) coated with piezoelectric ZnO has previously been investigated both theoretically and practically. While fabricating OFS, the performance of it will be affected by many parameters. Based on the equivalent circuit's model of cylindrical resonator of acoustic optic devices, an optimization method has been presented in this paper. By considering the effects towards the performance of optical fiber sensor due to some parameters, including electrode's thickness, Piezoelectric ZnO film thickness, the fiber's radius, resonator length, series impedance, and so on, the partial optimization of target functions including reflectance and coupling efficiency is programmed to produce optimized values. Also, combined with the effects of reflectance and coupling efficiency, the optimized values have been made based on the theory of multi-targets optimization.

In this paper, the feasibility of a new vehicle axle detector for roadways based on fiber optic Mach-Zehnder interferometer was evaluated. This new vehicle axle detector used in this study has a relatively simple sensing principle. Thus the system can be composed of inexpensive and reliable components for the application to transportation system compared with the traditional vehicle axle detectors. The configuration and performance of the new vehicle axle detector was described. The process of conversion of the detected interferometer sensor signal into the weight of a vehicle axle was proposed. Simulating results show that the sensing response of the embedded fiber optic vehicle axle detector based on Mach-Zehnder interferometer can meet the requirements of a vehicle axle detector. In addition, a high-speed signal processing system was designed for the interferometer. The new vehicle axle detector has good potential as a basic sensor unit which can be widely used in ITS to detect the vehicle axle weight and identify the type of a vessel which passes over the detector.

In recent years, Fiber Bragg grating (FBG) sensors become a focus in civil structure health monitoring because they have many advantages and show superior potential for health monitoring to ensure their structural integrity, durability and reliability. In this paper, fiber Bragg grating (FBG) sensors are used to monitoring the strain of steel structure. A designed novel titanium alloy slice is introduced to package the used FBG. A shallow rectangular groove is notched on the titanium alloy slice. Coated with a thin layer of epoxy, the FBG is fixed and protected on the groove. In order to eliminate to the temperature vibration effect on the wavelength shift of FBG sensors, a FBG temperature sensor is used for compensation. The traditional resistance strain gauges are also used to measure the strain for the comparison with the FBG sensors to validate the effectiveness. The strain of the flat steel at the elastic and yield stage of the steel are measured by monitoring the shift of center wavelength of FBG sensors and the change of the resistance strain gauges. The experimental results show that FBG sensors packaged by titanium alloy slice possess good stain sensing property and the strain sensitivity coefficients are 1.25pm/με. The shifts of center wavelengths of FBG are in good linear relationship with the tensile force and the strain measured by the resistance strain gauge. The linear correlation coefficients both reach 0.999.

The thickness of metallic foil is measured by differential low-coherence interferometry. Two tandem Michelson Interferometers (MI), of which reflective surfaces measured are the corresponding surfaces of metallic foil, are used as basic interferometric system to obtain interference fringes on a spectrometer. Therefore, the interference fringes only depend on the path differences due to the thickness of metallic foil. The interference fringes are analyzed with a modified extremum method based on the least root mean square (RMS) deviation. The experimental results on thickness measurement are presented.

A improved train real-time tracing system based on distributed Fiber Bragg Grating sensors is introduced in this paper. Without delicate sensing head, the system can realize the real-time detection of the railway condition and trains' running behavior such as the position, velocity, acceleration, load on axle, number of the axles and so on. To some extent, the system can also implement warning of the train accidents. The system will be significant to the railroad transport.

Quartz optical fiber or preform is composed of core and cladding with different refractive index (RI). Their compositions are different from the core to cladding in order to acquire desired RI profile. The physical properties from core to cladding are different, such as thermal expansion coefficients, thermal capacity and glass transition temperatures, which have much effect on the properties of optical fiber. The material composition and structure in PCVD single mode (SM) fiber was introduced in this paper. The composition of PCVD SM fiber was SiO₂-GeO₂-F-(Cl). F acted as a water-getter to reduce water peak besides lowering the RI of quartz glass and GeO₂-F co-deposition was adopted in PCVD fiber. The functional graded material (FGM) design in PCVD SM fiber, which can reduce the attenuation, PMD, splicing loss and improve microbending resistance, was analyzed and discussed.