We review our recent work on the generation of time- and wavelength-interleaved laser pulses and their applications in optical signal processing. Using phase and amplitude modulation on four continuous-wave lasers at ~1550 nm followed by chirp compensation, we have generated < 6 ps pulses switched sequentially among 4 center wavelengths with a repetition rate of 80 GHz. The pulses are nearly transform limited with a time-bandwidth product ~ 0.464. We applied time- and wavelength-interleaved pulses for new applications in nonlinear processing of communication signals. Fourwavelength DPSK multicasting with simultaneous NRZ-to-RZ pulse format conversion has been achieved with fourwave mixing. In addition, using optical parametric amplification with the interleaved pulses, we have demonstrated reconfigurable 40 Gb/s OTDM demultiplexing, as well as amplitude noise reduction in DPSK wavelength multicast.

Novel CWDM multilayer structure demultiplexer in silica is proposed and investigated. The refractive index of each layer in the structure follows fiber graded index profile with α-parameter less than one. The demultiplexer structure depends on the refractive index profile parameter, thickness, incidence angle, number of layers and channel's spacing. The effect of all of these parameters on the amount of spatial shift and the separation between adjacent channels is investigated.

Slow light is theoretically and experimentally demonstrated in a phase-shifted multichannel fiber Bragg grating (FBG) which has the ability not only to produce the slow-lights in multiple channels simultaneously but also to make the delay time tunable by changing the magnitude of the inserted phase shift. Phase shift is introduced into a phase-only sampled 51-channel FBG by utilization of a small piezoelectric transducer (PZT). On the other hand, the group delay of each channel can be further enhanced by incorporating stimulated Brillouin scattering (SBS).

High repetition rate pulsed fiber laser in 1μm is an attractive and novel source for optical transmission systems, since ytterbium-doped fiber (YDF) has the potential to provide broad gain spectrum and high optical conversion efficiency in this regime. Previous works in this area have explored the wavelength range above 1050 nm. In this paper, we focus more on the shorter wavelength band which is closer to the peak of the emission cross section of YDF at around 1030 nm. A 10-GHz harmonically mode-locked all-fiber laser is demonstrated. A pulse train with a pulsewidth of around 13 ps and wavelength tunable from 1023.5 nm to 1053.3 nm is achieved. The side-mode suppression ratio is more than 50 dB without any stabilization techniques.

A multimode interference (MMI) polarization splitter with easy fabrication process was demonstrated in Silicon-On-Insulator substrate. The minimum device size, 8 μm×1034 μm was designed by Quasistate imaging effect theory. Numerical simulations show that this optimized MMI polarization splitter has a good fabrication tolerance. The tolerance of width and length is ±0.04 μm and ± 10 μm for transverse electric (TE) mode and ±0.14 μm and ±35 μm for transverse magnetic (TM) mode. The bandwidths are 20 nm and 80 nm for TE and TM respectively. Experiment results exhibits a -15 dB polarization extinction ratio bandwidth of 20 nm for the through-path and much wider for the crosspath. The extinction ratio and crosstalk achieve (-27.3 dB, -22.6 dB) for TE and (-26.6 dB, -23.9 dB) for TM.

A vertical coupler composed of short range surface plasmon polariton waveguide and dielectric waveguide is studied theoretically and experimentally. The short range surface plasmon polariton mode is excited efficiently by the dielectric waveguide mode within tens of microns. Meanwhile, based on the hybrid coupler, a highly compact polarizer and a high performance sensor for ultra-thin layer sensing could be achieved.

A quantum dot (QD) doped fiber amplifier (QDFA) was theoretically modeled by using a two-level system. Combining with the finite difference-beam propagation method (FD-BPM), the proposed numerical method can calculate the signal gain efficiently. In this fiber amplifier, the PbS QD was as an active inner cladding. With the unique cladding structure of the doubly clad optical fiber, we can get good transmission stability, pump utilization and big mode field of the signal light. After a proper structure design of the PbS QD inner-cladding doped fiber, the 160nm bandwidth of the gain spectra can be achieved, which covers the S-C-L band of the optical communication band. And the noise figure of the amplifier presents a very flat characteristic. The optimization of the inner cladding doped model is also presented in the paper.

Starting from the structure of graphene, the electrical and optical properties of graphene is analyzed in this paper. Then, the transmission characteristics and the modulation for the optical pulses are discussed with the graphene waveguide model. Finally, the graphene based on the mode-locked fiber laser system is simulated, thereafter the role played by graphene will be found.

We propose an ultra-compact and broadband orthogonal coupler between a strip waveguide and a slot waveguide. Numerical simulations show that a 700-nm wide (full width at half maximum) coupling spectrum can be theoretically achieved and a coupling efficiency as high as 73% around 1500-nm wavelength can be obtained. The coupling length is only about 475 nm which makes the coupler very compact. This configuration does not include a tapering section and has a high tolerance to the waveguide height, alleviating the stringent fabrication requirements.

Coupling between long range surface plasmon polariton (LRSPP) waveguide mode and dielectric waveguide (DW) mode has been studied theoretically and experimentally. It is demonstrated that the fundamental and second-order TM-polarized mode of dielectric waveguide could couple with LRSPP mode efficiently, respectively.

Recent advances in the field of ultrafast laser inscription provide ample evidence underscoring the potential of this technique in fabricating novel and previously unthinkable 2D and 3D photonic and optofluidic platforms enabling current sensor, diagnostics, monitoring and biochemical research to scale new heights. In addition to meeting the demands for compact, active waveguide devices designed for diverse applications such as optical metrology, non-linear microscopy and astrophotonics, this technology facilitates the integration of microfluidics with integrated optics which creates a powerful technology for the manufacture of custom lab-on-chip devices with advanced functionality. This paper highlights the capabilities of ultrafast laser inscription in fabricating novel 3D microfluidic devices aimed for biomedical applications.

In this work, we report a sensing configuration of the fiber taper intrinsic Fabry-Perot interferometer directly inscribed in single-mode optical fiber tapers with different waist diameters from 14 to 80 μm using a femtosecond laser micromachining system. By controlling the inscribing depth and intensity of the fs laser pulse, the fringe visibility can exceed 9.0 dB when the fiber taper waist diameter is around 15 μm, which is sufficient for most sensing applications. The sensor sensitivity depends on the fiber taper waist diameter, while a smaller diameter corresponds to a large sensitivity. Different free spectral ranges can be achieved for various cavity lengths. Such a structure can combine the high sensitivity properties of fiber taper sensors with the high resolution features of Fabry-Perot interferometer sensors. Meanwhile, this structure can have a number of outstanding advantages, such as its small size, unique geometry, easy fabrication, low cost and capability for mass production. These fiber taper intrinsic Fabry-Perot interferometer sensors have high potential in fast detection and high precision measurement while maintaining superior reliability for chemical and biological sensing.

Fiber directional couplers made of highly asymmetric twin-cores (ATC), one of which is doped with erbium, are designed to achieve an inherently gain flattened erbium doped fiber amplifier (EDFA). The refractive index profiles of the fibers as well as the spacing between the two cores were carefully designed to achieve a targeted gain with low gain excursions across the C-band. One of the designs yielded a theoretical median gain ~ 38 dB with an excursion within ±1 dB. In order to suite fabrication of such an inherently gain flattened EDFA by the MCVD fiber preform fabrication process, the design had to be modified and a more modest target of about 20 dB was set with excursion below ± 1.5 dB for metro-centric applications. It involved preparation of two independent preforms, which required selective polishing of the cladding from one side by a certain amount to meet the required nominal separation between the two cores set at the design stage of the fiber. Several intricate operations were required to implement the fiber drawing step from the two assembled preforms. Preliminary characterization of the fabricated fiber shows filtering of ASE peak through selective wavelength coupling from Er-doped core to un-doped core.

We have fabricated new type of erbium doped fibre having core glass compositions of zirconia-yttria-alumino-phosphosilicate. With the proper combination of zirconia and aluminium with other codopants, high concentration of 4000 ppm erbium-ions was doped in the fibre core-glass by conventional MCVD and solution doping process without any phaseseparation. The fabricated fibre exhibited wide gain band-width covering both C and L bands. The optical gain and noise characteristics were studied for both single-channel and multi-channel amplification at C-band regime for different input signal levels. This novel zirconia-erbium-doped fibre (Zr-EDF) has produced intrinsically flat gain of maximum gaindifference of 2dB with average optical gain 22.5dB and noise figure of 4.5 dB for simultaneous four-channel amplification at input signal level of -30dBm/channel in the optimized condition. The performances of Zr-EDF in terms of gain-flattening and noise characteristics were found to be promising for small-signal multi-channel amplification which would be applicable in dense-wavelength division multiplexing (DWDM) system.

A compact short-cavity fiber laser configured with Er³⁺/Yb³⁺ highly co-doped phosphate glass fiber which has linear polarization and single frequency output is fabricated experimentally. The threshold power of the laser is about 30mW, and larger than 100mW output power is achieved with slope efficiency of 20% at 1549nm. At the meantime, sine modulation, positive pulse and chaos state in the output power at different experimental condition are observed. And a new theoretical model is proposed to describe the mechanism of the observed intensity instability behavior in the fiber laser and the numerical results proved its feasibility. It is confirmed that the self-pulsing behavior is mainly caused by different small external feedback. So there is an efficient way to overcome self-pulsing behavior in the compact single polarized fiber laser by minimizing the external feedback.

In this paper, a novel soliton compressor based on dispersion decreasing fiber (DDF) assistant by Raman gain is studied. The influence of Raman gain on compression quality is analyzed. The compressor is optimized by choosing proper gain. An optimization of the linear decreasing DDF compression method is made through distributed optical fiber Raman amplification with gain coefficient of 4.5dB/km. The pulse with width of 10ps is compressed down to 878.7fs, and the compression factor is 11.38. Our research results show that distributed Raman amplification in DDF not only increases the compression factor, but also improves the quality of compressed pulse.

A stable dual-wavelength with a tunable wavelength spacing fiber laser based on a chirped two phase-shifted grating filter is demonstrated. In the ring cavity, a chirped grating with two π-phase shifts servers as an ultra-narrow dualwavelength transmission band filter. The grating is attached in a triangular cantilever for chirp rate tuning. A semiconductor optical amplifier biased in low-gain regime is induced to reduce the gain competition of the two wavelengths caused by erbium-doped fiber. And a feedback fiber loop working as a mode filter guarantees the laser in a single-longitudinal-mode operation. Two lasing lines with different wavelength spacing from approximately 0.15 to 0.37 nm are experimentally demonstrated.

The availability of high quality optical fibers with transmission window, larger than that of silica fiber, extends the use of optical fibers and open new application fields. There is increasing demand of optical fiber with transmission over 2 microns, where silica is opaque, for applications as diverse as sensing, fiber lasers and amplifiers, defense (IRCM), spectroscopy... No materials can fulfill all applications needs. Engineers have to make some compromise when choosing the right materials for the right application. Heavy metal fluoride glass is one of these materials. The glass, under bulk form, has a wide transmission window from 0.3 up to 8 microns, without any absorption peaks. Heavy metal fluoride glass fibers are drawn using the preform technique, the same technique used for silica fiber. This technique has proven to allow good control of fiber dimensions and geometry. Fluoride glass fibers with different exotics shapes have already been obtained, such as D-shaped, square, of centered fiber, multi cladding fibers and microstructured fibers.... As far as active fibers are concerned, heavy metal fluoride glasses have low phonon energy and can contain high concentration of active ions, rare-earth elements. Therefore, new laser lines have been already demonstrated using fluoride glass fibers. Fiber lasers with output power exceeding 10 w have been obtained by different groups. This paper will present the latest development of fluoride glass fiber technology, including fibers optical and mechanical properties, fiber lasers and power handling.

We report an eight-channel reconfigurable optical add-drop multiplexers (ROADMs) based on cascaded microring resonators with low power-consumption and compact footprint. Microheaters are fabricated on top of the microring resonators, which can be modulated through the thermo-optic effect to achieve the reconfigurability of the device. We demonstrate the reconfigurable add-drop multiplexing functionality with the channel spacings of 100GHz and 50GHz, with the channel centre wavelengths aligned to the International Telecommunication Unit (ITU) grid. The crosstalks for the two channel spacings are less than -22.5dB and -15.5dB, respectively. The tuning efficiency is about 4.854 mw/nm and the tuning speed is about 12.4 kHz.

We propose a compact water depth sensor with a long period fiber grating (LPFG) using a heat-shrinkable tube. The pressure property of the LPFG is investigated experimentally to confirm the feasibility of the water depth sensor. Moreover, the water depth in the 2m long water-filled pipe is successfully estimated by the proposed water sensors.

Graded index HCS(GI-HCS) optical fibers are designed with unique features for computer networks in automation and process control, such as Ethernet, in an industrial environment. We demonstrated for the first time 1Gb/s transmission over 700m of a GI-HCS optical fiber with a 62.5 μm core and 200 μm clad. The transceiver used is an off-the-self Gigabit Ethernet VCSEL transceivers for multimode optical fiber. The field- terminated crimp and cleave connectors were found to have no detrimental effect.

A method to correctly measure the dispersion of an optical fiber as a function of wavelength is proposed and demonstrated by utilizing the partially degenerate four wave mixing process. This is done for a highly nonlinear fiber for which the dispersion values are very small and there is no prior knowledge about the zero dispersion wavelength. Powers in the idler frequencies are measured for different values of wavelength separation between the pump wavelengths to extract the dispersion map of the highly nonlinear fiber.

We introduce parametric tunable dispersion compensation scheme that has strong advantages in operating bandwidth and tuning response. The parametric tunable dispersion compensator (P-TDC) using highly-nonlinear fiber with a low dispersion slope achieves wide grid-less operating bandwidth of more than 1 THz and fast tuning responses of a few tens of microseconds. We also develop the setup of the P-TDC for practical usage, utilizing polarization diversity scheme. Field transmission using the polarization-insensitive P-TDC is also successfully demonstrated.

Radiation resistance property of a series of optical preforms/fibers of different compositions including those available commercially has been investigated to find out a suitable fiber in the UV-Visible wavelength range. The fibers drawn from commercial preforms exhibit feeble transmission in the UV zone prior to the radiation exposure and considerable darkening even with very low dose of radiation; although the preforms contain high OH in the core and it is claimed that higher OH content provides better transmission and radiation tolerance in the UV region. Radiation Induced Attenuation (RIA) dynamics for the wavelength range of 200 to 850 nm has been characterized 'real-time' under γ radiation. Dependence of RIA on the OH concentration in the core has been analyzed for wavelength band of 400-500 nm and at 630 nm. The generation of E' and NBOH color centers is responsible for the absorption at the above two wavelength bands respectively and is strongly influenced by the fiber composition. The effect of dose rate up to the accumulated dose of 1MRad has been studied. This systematic study led to the fabrication of a fiber with better radiation resistance characteristics in the wavelength range of 400-700 nm with out any radiation induced absorption peak at 630 nm.

We propose a new structure of optical fiber temperature sensor with cascaded long-period fiber gratings (LPFGs) and investigate the temperature dependent loss of cascaded LFPGs. Each of the cascaded LPFGs has the same resonance wavelength with the same temperature change, because the cascaded LPFGs are made of a heat-shrinkable tube and a screw. The total resonance loss of proposed cascaded LPFGs shows higher temperature sensitivity than that of a single LPFG. The thermal coefficient of 4-cascaded LPFG also shows more than 4 times larger than that of a single one.

The dispersion characteristics of Arsenic Trisulfide As₂S₃ chalcogenide glass were analyzed and a kind of As₂S₃ microstructured optical fiber was designed to shift the zero dispersion wavelength from longer than 4 μm to around 2 μm. The supercontinuum generation in the designed fiber with selected pump wavelengths and pulse durations were simulated through numerically solving the Generalized Nonlinear Schrödinger Equation. The results reveal that the broadest supercontinuum covering 1.1 μm to 5.5 μm can be obtained with pump laser with duration 150 fs centered at 2.0 μm which is slightly longer than the first zero dispersion wavelength. When the pump wavelength is around the zero dispersion wavelength apparent dispersive waves which are significant for spectral broadening can be observed.

Two liquid level sensors based on different long-period fiber gratings are proposed and compared. The long-period gratings have the same characteristics (length, grating period) but are fabricated in different optical fibers (photosensitive B-Ge codoped optical fibers with different dopants concentrations). The principle of this type of sensor is based on the refractive index sensitivity of long-period fiber gratings. By monitoring the resonant wavelength shifts of a given attenuation band, one can measure the immersed lengths of long-period fiber gratings and then the liquid level. The levels of two different solutions are measured. The maximum shift (7.69 nm) of the investigated resonance wavelength was observed in LPG1 (fabricated in Fibercore PS1250/1500). By controlling the fiber dopants concentrations one can improve the readouts of a fiber-optic liquid level sensor based on long-period fiber gratings.

Comparing to core-modes of optical fibers, some cladding-modes are more sensitive to the surroundings which are very valuable to sensing application; recently, a novel type of FBG sensor with core-offset structure attracts more and more interests. Normally, the forward core-mode is not only reflected and coupled to the backward core mode by the Fiber Bragg Grating in the step-type photosensitive single mode fiber, but also coupled to the backward cladding-modes and the radiation modes, eventually they will leak or be absorbed by the high refraction index coating layer. These backward cladding-modes can also be used for sensing analysis. In this paper, we propose and develop a core-offset structure to obtain the backward core-mode and backward cladding-modes by using the wavelength shift of the backward core-mode and the power of the backward cladding-modes in Fiber Bragg Grating sensor, and the power of the backward cladding-modes are independent from temperature variation. We develop a mode coupling sensor model between the forward core-mode and the backward cladding-modes, and demonstrate two coupling methods in the core-offset structure experimentally. The sensor is fabricated and demonstrated for refractive index monitoring. Some specific works are under investigation now, more analysis and fabrication will be done to improve this cladding-mode based sensor design for applicable sensing technology.

A review of passive devices and sensors manufactured from optical fiber microwires at the Optoelectronics Research Centre (University of Southampton) is presented.

By modifying the resonant condition of microfiber resonator sensors while taking the coupling effect into account, we theoretically investigate coupling influence on the resonant wavelength and sensitivity. Numerical calculation shows significant difference in resonant wavelength and sensitivity with different coupling strength. Tuning the coupling can shift the resonant position as far as several nanometers and change the sensitivity as large as 30 nm/RIU in an all-coupling microfiber coil resonator.

In this paper we investigate the temperature characteristic of an optical microfiber coil resonator (OMCR) which is wrapped on Teflon coated PMMA rob and embedded in low index polymer Teflon. The micro fiber used to fabricated the OMCR was 4 ~ 5μm in diameter and 14 mm in waist region length. The PMMA rob has a diameter of 2 mm. Our sample shows high temperature sensitivity as much as 80 pm/°C. The test result suggests OMCR could be of good value in application of temperature sensing.

Optical responses in Bi-layer metallic nanowire grating are investigated. There are two kinds of Surface Plasmon resonances: lateral propagating Surface Plasmon waveguide modes excited by the diffraction of the grating which lead to dips in transmission; Surface Plasmon resonance between the slits of the grating, which leads to high extinction ration of TM to TE transmission. With simultaneous resonances, a compacted device of integrated color filter and polarizer can be achieved. In order to improve the transmission of TM light, an undercut structure is proposed. The mechanism of the enhancement is analyzed. Bi-layer metallic nanowire gratings are fabricated by laser interference lithography and subsequent E-beam deposition. The measured transmission and reflection spectra confirmed the theoretical and numerical simulations. The results will have wide potential applications in Displays, Optical communication, and integrated Optics.

The transmission property of a subwavelength metallic slit with perpendicular groove is investigated by using finite element method. The lengths for the slits at both sides of the groove are set as the length of a metallic slit without groove at the surface plasmon fundamental mode resonance. In the grooved subwavelength metallic slit, enhanced transmission is found to be attributed to two kinds of resonance including surface plasmon waveguide resonance along the propagating direction and the transversely constructive interferential resonance. For the former resonance, integer antinodes of surface plasmon are formed in the groove. For the later resonance, there is a tradeoff between the maximum amplitude and the full width at half maximum of the transmitted peaks with the change of the groove width. And, the transmission enhancement of the grooved subwavelength metallic slit is related to the number of groove and the incident wavelength. Furthermore, the above resonances also exist in the structure whose lengths of metallic slits are set as the length of a slit without groove at the surface plasmon high-order mode resonance. By optimizing the geometric parameters, the transmission enhancement of the grooved subwavelength metallic slit as high as about 15367% is achieved.

Adding functionality to structured optical fibres promises to enhance their application range. This functionality critically depends on the evanescent field and both accessing and controlling it. We have explored a key approach based on depositing layers inside optical fibres. Of these, self-assembly of nanoparticles has proven to be surprisingly versatile, enabling us to demonstrate improved methods for optical field localisation. This work is reviewed here.

Optical sensors based on nanoparticles induced Localized Surface Plasmon Resonance are more sensitive to real-time chemical and biological sensing, which have attracted intensive attentions in many fields. In this paper, we establish a simulation model based on nanoparticles imprinted polymer to increase sensitivity of the LSPR sensor by detecting the changes of Surface Plasmon Resonance signals. Theoretical analysis and numerical simulation of parameters effects to absorption peak and light field distribution are highlighted. Two-dimensional simulated color maps show that LSPR lead to centralization of the light energy around the gold nanoparticles, Transverse Magnetic wave and total reflection become the important factors to enhance the light field in our simulated structure. Fast Fourier Transfer analysis shows that the absorption peak of the surface plasmon resonance signal resulted from gold nanoparticles is sharper while its wavelength is bigger by comparing with silver nanoparticles; a double chain structure make the amplitude of the signals smaller, and make absorption wavelength longer; the absorption peak of enhancement resulted from nanopore arrays has smaller wavelength and weaker amplitude in contrast with nanoparticles. These simulation results of the Localized Surface Plasmon Resonance can be used as an enhanced transduction mechanism for enhancement of sensitivity in recognition and sensing of target analytes in accordance with different requirements.

In this paper, the power confinement and the power density in the slot region of a vertical and horizontal slot waveguide are optimized; full-vectorial H and E-field profiles along with Poynting vector are also shown for both of these silicon waveguides. Bending loss of such slot waveguides is also presented.

To provide integrated and high quality broadband services, higher carrier frequencies are required in wireless communications. Currently, there is a great deal of interests in wireless communications at sub-terahertz or terahertz frequencies, i.e., the millimeter-wave (MMW) or sub-millimeter-wave (sub-MMW). In this work, we will discuss our recent advances in millimeter-wave photonic wireless links for high data rate (10 - 20 Gb/s) communications. The concept of fiber-to-the-antenna (FTTA) system using radio-over-fiber (ROF) technologies will be given in the introduction. Then a design and the structure of the high speed MMW photonic transmitter, namely near-ballistic unitraveling- carrier photodiode (NBUTC-PD), will be discussed in section 2. In section 3, the operation principle of photonic mm-wave waveform generator (PMWG), which is used to produce the optical pulse train for the photonic transmitter at the antenna-site will be illustrated. We then demonstrate the use of the NBUTC-PD and the PMWG for the downstream and upstream high data rate communications in the W-band.

A new cascaded microwave photonic filter consisting of two or more infinite impulse response (IIR) filters based on active loops. is presented. Owing to wavelength conversion, the interference between the modulated optical signals of different taps from different active loops can be avoided and the stable transmission characteristic of the cascaded filter can then be achieved. The cascaded filter can increase the free spectral range (FSR) and the Q value significently by designing the FSR differences of the IIR filters. The cascaded filter with two IIR filters is demonstrated, and the measured results of a high Q of 3338 and rejection ratio of about 40 dB are obtained. The tunability can also be realized.

We report on a functional, highly reproducible and cost effective sensing platform based on photonic crystal fibers (PCFs). The platform consists of a centimeter-length segment of an index-guiding PCF fusion spliced to standard single mode fibers (SMFs). The voids of the PCF are intentionally sealed over an adequate length in the PCF-SMF interfaces. A microscopic collapsed region in the PCF induces a mode field mismatch which combined with the axial symmetry of the structure allow the efficient excitation and recombination or overlapping of azimuthal symmetric modes in the PCF. The transmission or reflection spectrum of the devices exhibits a high-visibility interference pattern or a single, profound and narrow notch. The interference pattern or the notch position shifts when the length of the PCF experiences microelongations or when liquids or coatings are present on the PCF surface. Thus, the platform here proposed can be useful for sensing diverse parameters such as strain, vibration, pressure, humidity, refractive index, gases, etc. Unlike other PCF-based sensing platforms the multiplexing of the devices here proposed is simple for which it is possible to implement PCF-based sensor arrays or networks.

We report a highly tunable liquid-filled photonic bandgap fiber (LF-PBGF) based on both bend and temperature change. By bending the LF-PBGF and changing its temperature, the blue shift of the red edge of the bandgap resulting from bend loss and temperature increasing is speeded up, and higher bandwidth tunability is achieved. Numerical and experimental results are presented, and 177-nm bandwidth tunability is achieved by tuning the temperature of the LF-PBGF with bend radius of 5 mm from 40°C to 60°C, and the average compression rate is 8.85 nm/°C.

We fabricate a miniature tapered photonic crystal fiber (PCF) interferometer with enhanced sensitivity by a new acid microdroplets etching method. This method, without elongating the PCF, moving and re-fixing the device during etching and measuring refractive index sensitivity, is very simple, cost-efficient and highly stable over time. We investigate the refractive index sensing properties with different PCF diameters both theoretically and experimentally. The size decreases and the sensitivity increases an order of magnitude after etching the PCF. If we can optimize the etching process, we can fabricate more uniformly and thinly tapered PCF interferometer with higher sensitivity (~ 100 times) theoretically in the future.

We propose a novel photonic crystal fiber (PCF) design for single-polarization single-mode (SPSM) operation. The proposed SPSM-PCF characteristics are investigated by using a full-vector finite element method (FEM) with perfect matched layer (PML) boundary conditions. The proposed SPSM-PCF performs SPSM operation for a wide range of wavelength. The results show that this is a good design methodology to realize broadband SPSM operation.

A novel all-fiber flat-top comb filter is proposed based on Sagnac loop interferometer of photonic crystal fiber (PCF). The transmission function of the proposed Sagnac loop filter is expressed theoretically by Jones transmit-matrix. The influences of birefringence of PCF, the lengths of two sections of PCFs and the rotatable angle of polarization controllers on its output spectra are numerically studied. On the basis of theoretical analysis, a wavelength switchable comb filter with flat-top spectral response is realized. This kind of filter can be expected to be used widely in DWDM systems in the future.

A dual-core photonic crystal fiber (DC-PCF) is proposed for pressure/temperature sensing based on the mode coupling of the two fiber cores. The two solid fiber cores separated by an air hole in the cross-section lead to two independent waveguides inside the DC-PCF which accompany with mode coupling. Pressure/temperature sensor based on the DCPCF is achieved when one fiber core on the input side is connected to a broadband light source and the other fiber core on the output side is connected to an optical spectrum analyzer. A pressure/temperature sensor based on the DC-PCF is designed with a transmission spectrum which is essentially sensitive to the pressure/temperature applied on the DC-PCF. As an example we design a pressure sensor based on a 10-cm DC-PCF for the sensing pressure range from 0 to 1000 MPa with a sensitivity of -3.47 pm/MPa, and a temperature sensor based on a 4-cm DC-PCF for the sensing temperature range from 0 to 1000 °C with a sensitivity of 20.7 pm/ °C. The fiber bending analysis of the DC-PCF is also presented.

We put forward an improved structure with three cascaded birefringent plates. This interleaver consists of four parts which are input spectral displacer, wavelength filter, birefringence crystal combination and spectral coupler. We carry on the preliminary design of structures of the four parts and the simulation of three-level crystal filter. Analyze the relationship between the filtering performance and the parameters of crystal plates. From the result of simulation, this kind of interleaver can meet the requirement of de-multiplexing of 25GHz grid and the isolation is significantly improved by increasing the crystal cascade grades, as well as 0.5-dB bandwidth. Finally we can get a relatively flattopped spectra. Besides the isolation can reach to 40-dB and the 0.5-dB bandwidth is 17GHz.

A method based on the quantum-behaved particle swarm optimization algorithm is presented to design a bandpass filter of the fibre Bragg gratings. In contrast to the other optimization algorithms such as the genetic algorithm and particle swarm optimization algorithm, this method is simpler and easier to implement. To demonstrate the effectiveness of the QPSO algorithm, we consider a bandpass filter. With the parameters the half the bandwidth of the filter 0.05 nm, the Bragg wavelength 1550 nm, the grating length with 2cm is divided into 40 uniform sections and its index modulation is what should be optimized and whole feasible solution space is searched for the index modulation. After the index modulation profile is known for all the sections, the transfer matrix method is used to verify the final optimal index modulation by calculating the refection spectrum. The results show the group delay is less than 12ps in band and the calculated dispersion is relatively flat inside the passband. It is further found that the reflective spectrum has sidelobes around -30dB and the worst in-band dispersion value is less than 200ps/nm . In addition, for this design, it takes approximately several minutes to find the acceptable index modulation values with a notebook computer.

In the nonlinear polarization rotation (NPR) mode locking fiber laser, the electric fields of different intensity of pluses will have different nonlinear phase shifts because of self phase modulation (SPM) and cross-phase modulation (XPM) effects. In this paper we analysis the SPM and XPM effect on the characteristics of pulses in fiber which were influenced when we adjustment the wave plates in the NPR fiber lasers. At the same time, we discussed the pulses waveform's influence caused by the strength of the SPM and XPM in fibers.

The coupling characteristics of fluid-filled dual-core photonic crystal fibers are numerically investigated. The transmission spectrum is obtained in different temperatures. With the help of a vector finite element method we acquire the properties of the minimum coupling length. Finally, the coupling characteristic is experimental studied by the way of temperature tuning.

Bright-dark soliton pairs and bright or dark solitons have all been observed by adjusting the triggering level of a digital oscilloscope in a self-mode locking erbium-doped fiber ring laser.

A novel ring fiber laser based on Er-doped photonic crystal fiber (EDPCF) is demonstrated. EDPCF is used as gain medium to implement stable CW operation. The laser output wavelength can be continuously tuned over the range from 1529 to 1535 nm by adjusting the polarization state of the light inside the cavity. Stable dual-wavelength CW operation is also observed with proper settings of the intracavity polarization controllers. The laser stability in terms of the output power and the operation wavelength is characterized, and less than ±0.05 dB power fluctuation as well as 18 pm wavelength perturbation are obtained.

The experiment of tunable DBR fiber laser based on temperature and PZT is described and studied. A DBR laser has also been introduced in this paper. A DBR laser cavity is applied as a turning part of the optical fiber cavity. The central frequency of spectrum output from DBR laser is changed by temperature and stress. Experimental results show that the tunable DBR fiber laser based on closed-loop PZT modulation is linear and the tuning range can achieve to about 0.8nm.

Long period fiber gratings (LPFGs) with different periods in the standard single mode fiber were fabricated, using laser direct writing method, by femtosecond laser pulses with pulse width of 200 fs and the repetition rate of 250 kHz at a center wavelength of 800 nm in air. Comparative with bare LPFG in temperature sensor, LPFG had been encapsulated using large coefficient of thermal expansion of epoxy polymer and Aluminum to enhance the temperature sensitivity. The results showed that the temperature sensitivity of encapsulated LPFG was 2 times than that of bare LPFG. In addition, we also researched the relationship between resonant wavelength and surrounding refractive index (SRI) when LPFG immersed in refractive index of solution of different index at 20 degree Celsius.

We demonstrate a method to characterize the gain spectrum of Stimulated Brillouin scattering in an optical fiber by using two tunable CW laser sources. Brillouin amplifier configuration is used, in which one laser is used to create SBS in the fiber and frequency modulated light from a second laser is launched from the other end of the fiber in order to extract the SBS gain spectrum. Experimental results are presented to demonstrate the gain bandwidth and the Brillouin frequency shift. Experiments at larger pump powers indicate the invocation of second-order Brillouin scattering in the forward direction. This method discussed to extract the gain spectrum of the fiber does not warrant the use of high-speed modulator or detectors, and does not use heterodyne measurements.

In this paper, a degree of polarization (DOP) tunable single-mode fiber ring depolarizer is proposed and demonstrated. The fiber ring is made of a 2×2 coupler and a piece of single-mode fiber delay line, which is wound into a coil performing as a half-wave plate. For a random input state of polarization, the full depolarization can be realized by rotating the whole set of fiber ring through a proper angle, and for a linearly-polarized input light, the output DOP can change from one to zero. In our experiment for a fiber ring with a delay line of 10 meters, a Fabry-Perot (FP) laser with 8-meter coherent length is depolarized with a DOP less than 1%.

We demonstrate an ultra-long cavity all-fiber Erbium-doped fiber laser that is passively mode-locked by nonlinear polarization rotation. The length of the resonant cavity amounts to 4.046 km, which is achieved by incorporating a 4 km single mode fiber. The laser generates stable mode-locked pulses with a 50.90 kHz fundamental repetition rate. The maximum average power of output pulses is 2.73 mW, which corresponds to per-pulse energy of 53.63 nJ.

We come up with a model of subwavelength-diameter fiber taper-based Bragg gratings (SWDFT-BGs) and numerically investigated the chirp characteristics of Bragg gratings written in local single-mode fiber tapers based on coupled-mode theory and transfer matrix method. The effective modal refractive index varies along adiabatic subwavelength-diameter fiber tapers (SWDFTs), which results in an effective chirp in grating period. Additionally, SWDFT-BGs with full width at half maximum (FWHM) up to 4.9 nm and time-delay slope over 25 ps/nm were achieved in simulations. This offers an idea for fabricating single-mode chirped fiber Bragg gratings using uniform phase-mask and paves ways for waveguide dispersion engineering and wide-bandwidth optical filters.

To develop high nonlinear optical fibers for all-optical switching applications, 7.5 wt% AgNO₃ was incorporated into tellurite glasses with composition of 75TeO₂-20ZnO-5Na₂CO₃ (TZN75) under precisely-controlled experimental conditions to form 7.5Ag-TZN75 glass. Surface Plasmon resonance absorption peak of Ag nanocrystals embedded in 7.5Ag-TZN75 glass was found to center at 552 nm. By degenerated four-wave mixing method, the non-resonant nonlinear refractive index, n2, of 7.5Ag-TZN75 glass was measured to be 7.54×10^-19 m²•W^-1 at 1500 nm, about 3 times of the reference TZN75 glass without any dopant and 27 times of the silicate glasses and fibers, and the response time is about 1 picosecond.

A terahertz (THz) polarization filter based on liquid crystal cavities is designed. The P and S polarized light are both transmitted and the minimum transmittance of P and S polarized light at pass-band is higher than 99.5%.The P polarized light and S polarized light can be both separated distinctly at a small angle. We discuss the influence of each structural parameter on spectral performance, such as rectangle degree, duty cycle, spectral period etc systematically. The results show that the refractive index of the thin-film layers mainly influences the rectangle degrees and duty cycle. The liquid crystal cavities are inversely proportional to the spectral period. The center-frequency tunable characteristics can be realized by changing the incident angle with small angle.

A centrosymmetric structure containing anisotropic medium is proposed. The polarization filtering property of the structure is studied systematically by the transfer matrix method. The results demonstrate that transmittance, isolation and FWHM of transmission spectra are influenced by period N. FWHM is also influenced by incident angle. In addition, center frequency and frequency spacing are determined by incident angle and thickness of medium cavity. On this basis, a detailed design example is given. Isolations of transmission spectra of TM-polarized light and TE-polarized light respectively are 40.46dB and 42.37dB.Transmittances of them respectively are higher than 99.209% and 97.594%. Their center frequencies of transmittance windows accord with the ITU standard. The structure is very simple and transmission spectra of TM and TE polarized lights are completely separated. It is easy to be accomplished and will have worthiness in practical application.

Broadband optical antennas are of interest as they can transmit more information like traditional microwave UWB antennas. This paper presents a design of broadband optical antennas with a concentric disk structure. An equivalent circuit for the optical antenna with a disk structure is introduced. The broadband radiation at optical frequencies was demonstrated via the computer simulation.

With 4th-order Runge-kutta method and relaxation method, we obtain the power distribution of pump light and signal light along fiber by solving the steady-state rate equations in ytterbium-doped double-cladding fiber amplifier. The relationships between the output power and the fiber length are discussed with different pump power and different doped concentrations of the fiber. The change of the output power versus the pump power is calculated. The power distribution along fiber and the relationship between output power and input power are analyzed when the signal is injected from z=L and z=0 respectively.

We have proposed and demonstrated a passively harmonic mode-locked fiber laser based on a single-walled carbon nanotube saturable absorber (SWCNT-SA) that has a controllable repetition rate. With the pump power fixed, we have experimentally observed harmonically mode-locked optical pulses with repetition rates that can be controlled over the range from the fundamental to the seventh-order mode through careful adjustment of the polarization controller only. From the experimental results, we deduce that the likely origin of the self-stabilization is the result of global and local soliton interactions induced by the continuous wave (CW) components.

A compact polarization beam splitter (PBS) based on a silicon-based negative refractive photonic crystal slab is proposed and numerically demonstrated. The PBS has good performance that the crosstalk and extinction ratio are above 20dB over 80nm wavelength band.

The design and simulation results of temperature-insensitive arrayed waveguide gratings based on silicon nanowires are presented. The temperature dependent wavelength shift is minimized by using negative thermo-optic coefficient material SU-8 as the upper-cladding. Simulation results show that by using an appropriate thickness and width of the waveguide, quasi-athermal operation can be achieved. For temperature varying from 0°C to 80°C, the TD-CWS can be controlled down to 0.036nm with little polarization dependence for 272nm×253nm waveguide.

We demonstrate a fiber laser sensing technique based on fiber Bragg grating Fabry-Perot (FBG-FP) cavity interrogated by pulsed laser, where short pulses generated from active mode-locked erbium-doped fiber ring laser and current modulated DFB laser are adopted. The modulated laser pulses launched into the FBG-FP cavity produce a group of reflected pulses. The optical loss in the cavity can be determined from the power ratio of the first two pulses reflected from the cavity. This technique does not require high reflectivity FBGs and is immune to the power fluctuation of the light source. Two short pulse laser sources were compared experimentally with each other on pulse width, pulse stability, pulse chirp and sensing efficiency.

We demonstrate the packaging of CO₂ laser written long-period fiber gratings (LPFGs) using different polymer materials. We use three different silicone rubber polymers to package the LPFGs by simply coating it outside the grating. After the polymer coating, the resonance wavelength of LPFG was found to shift towards shorter wavelength by about 6 nm, and the temperature sensitivity of the packaged gratings was studied experimentally. Experiments showed that the gratings packaged by different polymers have different temperature characteristics and all of them have good thermal stability.

Many methods have been proposed to analyze the characteristics of FBG-based cavity, as a novel method for analyzing reflection spectra of FBG-based Fabry-Perot (F-P) cavity, V-I transmission matrix combines the exactitude of traditional effective index method and the speed of coupled-mode method. In this paper, we demonstrate the analysis of F-P cavity based on non-matching fiber Bragg gratings using the V-I matrices method. The evolution of F-P cavity spectra were numerical analyzed with different grating length and reflectivity. Simulation results show that difference between length and reflectivity of two gratings should not be too large, and if the length and reflectivity of two gratings are both different, it would be better to make the longer grating's reflectivity larger.

We demonstrated experimentally the fabrication of tilted long-period fiber gratings (LPFGs) with different tilt angles by CO₂ laser. The experiment results reveal that the LPFGs written with different tilt angles have quite different transmission spectra, the polarization sensitive LPFGs can be written with large tilt angles by the CO₂ laser.

Seeded second harmonic generation is investigated by including an in-phase second-harmonic pulse. Soliton compression from a broader input pulse with low threshold pump intensity is numerically demonstrated in collinear quasi-phase-matching grating. Through changing the group-velocity mismatch and pump intensity, frequency shift of another input signal pulse can be obtained with pulse duration of few cycles, which show potential tool in ultrafast pulse application and is useful for generation of shorter pulses with clean temporal profiles.

A novel dispersion compensating fiber with multiple windows is firstly proposed. The proposed DCF is based on hybrid photonic crystal fiber. This type of DCF gets a multiple negative dispersion windows by the coupling between the hybrid guiding mode in the edge of each band-gap and the index guiding mode in the cladding deficit area. This is very different from the ordinary dual-core mechanism. This proposed DCF can be widely used in dispersion compensating system, the photonic generation of UWB signals, the pulse forming system and the compressing of optical soliton.

Defect centers play a major role in the radiation-induced transmission loss for silica optical fibers. We have investigated characteristics of the best known defect centers E' in silica optical fiber material irradiated with γ ray at room temperature, and measured by using electron spin resonance (ESR) and spectrophotometer. The results show that the defect concentrations increase linearly with radiation doses from 1kGy to 50kGy. We have established the mechanism models of radiation induced defect centers' formation. We have also studied the influences of thermal annealing on defect centers. The radiation induced defect centers can be efficiently decreased by thermal annealing. Particularly, the defect concentration is less than the initial one when the temperature of thermal annealing is over 500°C for our silica samples. These phenomena can also be explained by the optical absorption spectra we have obtained.

The attenuated total reflectance (ATR) hollow waveguides capable of transmitting CO₂ laser have attracted wide research interest due to its advantages of simple structure, no end reflection, small beam divergence and good transmission modes. In this work, GeO₂ ATR hollow waveguides for delivery of CO₂ laser radiations were fabricated via an acid-induced liquid phase deposition (LPD) process. GeO₂ hollow waveguide samples were deposited from acidic aqueous germanate ion solutions with different GeO₂ concentrations. The morphology, compactness and surface roughness of the LPD-derived GeO₂ ceramic film were examined by SEM. The crystalline structure of the film sample was determined using XRD. The low-loss window of the GeO₂ waveguide tube was observed by a FTIR spectrometer. We measured the transmission loss of the sample for delivery of a 10.6 μm TEM₀₀ CO₂ laser beam. The results show that the variations in loss are consistent with the quality change of the GeO₂ ceramic films grown in solutions at different concentrations.

Reducing the radiation-induced transmission loss in low water peak single mode fiber (LWP SMF) has been investigated by using photo-bleaching method with 980nm pump light source and using thermal-bleaching method with temperature control system. The results show that the radiation-induced loss of pre-irradiation optical fiber can be reduced effectively with the help of photo-bleaching or thermal-bleaching. Although the effort of photo-bleaching is not as significant as thermal-bleaching, by using photo-bleaching method, the loss of fiber caused by radiation-induced defects can be reduced best up to 49% at 1310nm and 28% at 1550nm in low pre-irradiation condition, the coating of the fiber are not destroyed, and the rehabilitating time is just several hours, while self-annealing usually costs months' time. What's more, the typical high power LASER for photo-bleaching can be 980nm pump Laser Diode, which is very accessible.

We propose and experimentally demonstrate a simple method to generate ultra-wideband (UWB) pulses with different pulse shape, based on incoherent optical arbitrary waveform generation. Pulses with opposite polarity are obtained using the phase-modulator-based dual-input intensity modulator. Monocycle, doublet and high-order UWB pulses meeting the FCC regulation are generated. Both temporal waveform and power spectral of the signal generated are evaluated.

A kind of fiber drawing machine based on gas furnace is introduced in this paper. Furnace vents were designed with a special eccentric angle and elevation angle to form a specific size focus ring. The high temperature area of the furnace is focused on gas ring. Different heating furnace structure for different preform dimension can be obtained by changing the eccentric angle and elevation angle. Gas heating source was selected through analysis and comparison of hydrocarbons and acetylene gas temperature characteristics. In the experiments, we draw out a hollow fiber at about 1280°C and got a minimum optical fiber drawing speed of 1m / min. The furnace temperature can also be set below this temperature by gas selection and flow control to draw out various low temperature optical fiber.

A strongly guided InP/InGaAsP multimode interference power splitter is designed and simulated by using 3D FD-BPM method. A 1-by-4 multimode interference power splitter is fabricated in terms of the simulation result. The device has 40nm available bandwidth and 2.6dB pass band flatness around 1550nm. Furthermore, the insertion loss is no higher than 10dB at the designed wavelength 1550nm.

We generate a flat, polarized and single mode Supercontinuum (SC) spanning at least from 600nm to 1700nm in a 20m length of highly refringent photonic crystal fibers (PCFs) pumped by a 1064 nm nanosecond microchip laser. The spectrum and polarization properties of the SC are investigated experimentally. The experimental results and the analysis provide useful information that helps to optimize and tune the properties of the polarized SC sources.

Three asymmetric multi-core fibers namely 3-linear-core-array fiber, 5-linear-core-array fiber and 5-circular-core-array fiber were designed. The supermode characteristics were investigated using a finite element method (FEM) with perfect matched layer (PML) boundaries. The profiles of supermodes supported by these multi-core fibers were presented. The dispersion characteristics of these multi-core fibers had been analyzed. The numerical results show that the peak value group velocity dispersion of the 5-circular-core-array fiber can reach -2.4×105ps/nm•km, and the GVD bandwidth is up to 25nm(1535-1560nm), covering almost the whole C-wavelength band. It can compensate for more than 13000 times its own length that of the ordinary SMF.

A dual-parallel-core fiber is proposed for dispersion compensation of single mode fibers (SMFs) by using coupled-mode theory. From the numerical results, the two-parallel-core structure exhibits very high negative chromatic dispersion [-9.7794 × 10⁵ps/km/nm], and full width at half maximum dispersion (FWHM) of ~6nm.