The Erbium-doped fiber amplifiers (EDFA) are widely available in a today's commercial market, and are deployed in various optical transmission applications from terrestrial system to undersea system. Broad gain spectrum over 9 THz enabled huge growth of bandwidth usage in 1550nm region aimed at broadband Internet, and its broad gain characteristics triggered bandwidth competition on dense wavelength division multiplex (DWDM) network these ten years. At first, we briefly review the evolutional history of EDFA with previous achievements. And we will explain the primary and important key devices which compose EDFA. We will discuss design parameters, and recent trend and achievements of the devices, which cover Erbium-doped fibers (EDF), 980-nm laser diodes (LD), and gain flattening filters (GFFs). The chip structure of 980-nm LD is explained to achieve high power and to realize high reliability. These key devices enabled EDFA to prevail in commercial area. After the discussion of key components, we will introduce recent achievements of gain controlled EDFAs which are applied in conjunction with Re-configurable Optical Add/Drop Multiplexer (ROADM). We will report the transient gain dynamics of the cascaded EDFAs with a recirculating loop experiment.

We present model calculations of gain at 1550 nm for Er-Yb double clad amplifiers as a function of pump power, pump wavelength, signal input power, and fiber length. The absorption coefficient of Yb varies ( by a factor of ~ 5) with the pump wavelength in the range of 910 to 990 nm. However, semiconductor lasers may be available only at certain wavelengths. Thus it is important to calculate optical gain and amplified output power as a function of pump wavelength. The calculation shows that significant optical gain and amplified output power can be obtained even if the pump laser wavelength is not at the peak absorption wavelength. The gain decreases with increasing input signal. We show that a high power Er-Yb co-doped double-clad fiber amplifier also exhibits high gain for Yb transition near 1060 nm. This is not unexpected since the input pump causes population inversion in Yb. More than 100 W of amplified power can be obtained using 24m long fiber with 300 W of total pump power by using side-pumping method. Side pumping increases the efficiency over end pumping for high output power.

This study describes a novel fabrication technology of multimode polymer optical waveguide, which is named "Large-area Advanced Micro Molding"(LAMM). One of the features of the LAMM method is to replicate the core shape of a waveguide using a silicone rubber mold. The benefits of using the LAMM method are: a low fabrication cost, environment friendliness due to zero emission and organic solvent free fabrication, and possibility to fabricate core sizes (30-120 μm). The multimode waveguide fabricated by the LAMM method provided low optical power loss of 0.06 dB/cm at 850 nm due to a flat boundary between core and cladding. In addition, by using a sandwich structure with high-durability films, the waveguide showed a good stability of <0.1 dB (waveguide length 70 mm) when left at 85 °C / 85% RH for 2000 hours and 0.03 dB/cm for soldering process. Using this fabrication method, we applied waveguides to form Y-branch and create horizontal 90° reflection micromirrors. An optical module using this waveguide with opt-electric devices such as vertical cavity surface emitting laser diodes (VCSELs) and photodiodes (PDs) showed error-free data transmission at the rate of 3.125 Gbps.

We present a novel approach for packaging high-speed opto-electronic 12x-array devices in a compact, low-cost package for waveguide-based intra-system links. In order to avoid optical signal loss and crosstalk, the mutual alignment between PCB-embedded multimode waveguides and the opto-electronic components needs to be in the order of 5-10 micrometer, which is an order of magnitude tighter than standard PCB manufacturing tolerances. Our packaging concept uses a combination of passive alignment steps, tolerance stackup reduction and a misalignment-tolerant coupling scheme in order to bridge this gap in a cost competitive way. Using flip-chip technology, the opto-electronic components are placed onto a very thin substrate with holes for the light path. The top side of the 25 μm liquid crystal polymer (LCP) substrate not only provides fast and low-loss electrical connections, but also serves as alignment reference plane for the entire module, avoiding alignment tolerance accumulation over different assembly steps. Openings for the laser beams, passive lens alignment features, centering holes for mechanical alignment pins between module and board and optional MT-guide receptacles are all laser-cut within one single process step, with a precision better than 5 μm. A similar approach is used for the PCB-side optics, and a lens-pair coupling scheme provides for a sufficiently large misalignment tolerance between the package and the PCB. Mechanical rigidity of the package and thermal protection are provided by an epoxy filled aluminum frame. We will present our design considerations, the basic package concept, the actual experimental implementation and characterization results of our first prototype package.

Polymer optical waveguide devices are getting popular for next generation FTTH application. In order to accelerate the development of polymer optical devices, evaluation of waveguide characteristics should be speeded up. Polymer optical chip containing a combination of 45°-angled cut waveguide, Y-splitter and S-bend structures was designed and fabricated for simple evaluation of multimode waveguides. Input launching such as light source, mode scrambler was investigated for reliable measurement.

We have developed novel bismuth-based photonic crystal fiber which exhibits high nonlinearity γ ~ 780W^-1km^-1 and relatively low group-velocity-dispersion D ~ -25 ps/nm/km at 1560 nm. The new fabrication process was also developed for this novel photonic crystal fiber with 6-fold symmetric structure. The core diameter 2.7 μm of this fiber was designed to have modelately decreased normal dispersion and high nonlinearity. Spectral broadening induced by self-phase-modulation by 1550 nm fs-pulse propagation shows that the high nonlinearity and dispersion reduction is simultaneously achieved.

80Gb/s All-optical Boolean function XNOR has been demonstrated using a dual four wave mixing scheme in two identical highly nonlinear fibers. A numerical model based on nonlinear Schrodinger equation (NLS) in fiber has been employed to simulate the wave mixing process. The NLS equations have been solved using the split-step Fourier method. From the numerical model, system transmission rate is predicted to be as high as 250Gb/s.

The Wilson-Cowan mathematical model is popular for representing a neuron in the brain and may be viewed as two cross-coupled dynamical nonlinear neural networks, one excitatory and one inhibitory. This gives rise to two coupled first order equations. Varying an input parameter, the sum of input intensities from all other incoming neurons, causes the Wilson-Cowan neural oscillator to move through a supercritical Hopf bifurcation so as to switch its output from a stable-off when the input is below a firing threshold to a stable-oscillation (limit cycle) for signals above the threshold; the frequency of which depends on the level of input stimulation. The use of frequency to represent pulse rate makes the brain robust against electromagnetic interference and drift. We show that the laser diode rate equations for a single optically injected laser diode can also be modeled by two coupled first order equations that give rise to supercritical Hopf bifurcations. But the laser rate equations have a complex variable where that for the Wilson-Cowan model equations is real. By using the real part of the complex variable (a projection onto the real plane), the optically injected laser diode can exactly simulate the movement through supercritical Hopf bifurcation of the Wilson-Cowan equations by varying the amplitude and frequency of the optical injection.

Various advanced modulation formats, such as on-off-keying (OOK) with carving techniques, phase-shift-keying (PSK), frequency-shift-keying (FSK), etc, were investigated to obtain enhanced spectral efficiency or receiver sensitivity. Orthogonal modulation techniques with OOK and FSK or OOK and PSK are also useful for optical labeling in packet systems. Recently, we reported a versatile optical modulator consisting of a main Mach-Zehnder interferometer (MZI) which has two sub MZIs embedded in the two arms of the main MZI. The modulator can generate return-to-zero (RZ) OOK, binary phase-shift-keying (BPSK), quadrature phase-shift-keying (QPSK), wideband FSK, continuous-phase FSK, etc. By using this modulator, we demonstrated optical DQPSK modulation at 80Gbit/s. For QPSK modulation, two data signals are applied to the two sub MZ structures, to achieve control of in-phase and quadrature components. The versatile modulator can be also used for ultra high extinction ratio (ER) intensity modulation. The sub MZIs in the main MZI can compensate imbalance between the arms of the main MZI, where the imbalance is mainly due to fabrication error. The ER can be higher than 70dB. By using this technique, we can generate super stable two-tone lightwaves, where we can achieve large spurious suppression ration higher than 40dB.

We introduce an efficient Krylov-subspace based operator-exponential approach for solving the Maxwell equations. This solver exhibits excellent stability properties and high-order time-stepping capabilities. The usage of a non-uniform spatial grid facilitates the realization of a high-order spatial discretization in the presence of discontinuous material properties. This ideally complements the time-stepping capabilities of our solver so that many nonlinear wave propagation phenomena and/or coupled system dynamics in complex nano-photonic problems may be treated with high accuracy and efficiency.

In this paper, we propose a wavelength locker free, simple and cost effective wavelength setting and monitoring method that estimates wavelength on a software basis. This method uses preliminarily measured wavelengths at selected sets of drive current and device temperature, which are stored in the memory of the transceiver module. We then determine the relationship among the wavelength, the drive current, and the device temperature as a linear function. This function enables us to estimate the wavelength by setting and monitoring the drive current and device temperature. The same procedure is done for output power estimation. We measured the wavelength estimation accuracy using two practical DFB-LDs and confirmed that the discrepancy between the estimated wavelength and the measured wavelength was less than ±1 GHz.

An all-optical logic NOR gate operating at 40 Gb/s has been demonstrated using an SOA-based Mach-Zehnder interferometer (MZI). An optical loop mirror is used as a delayed interferometer to reshape the return-to-zero (RZ) NOR sequence from the MZI output port. The performance of the NOR operation is numerically analyzed by solving the rate equation of an SOA. An increase in signal output power enhances the Q factor and extinction ratio. Faster SOAs such as quantum-dot SOAs can achieve higher Q value. The demonstrated technique has potential for optical logic operation at ultrahigh speed

Multi-wavelength (a.k.a. broadband) photodetector having a detection capability ranging from near ultra-violet to infrared can be useful as a common detector for various applications such as optical communication and optical interconnects etc. The capability of using single detector in receiver system for optical communication covering both data and transport systems, not only makes the total system cost lower, but it also makes easier the system vendors to reduce the inventory. We proposed detector having the detection capability ranging from 350 nm to 2000 nm, wavelengths that covers all optical communication wavelengths application. This invited paper has two-fold objectives: (a) provide a comprehensive overview of conventional photo detectors and their types, being used in today's optical communication and (b) introduce a development of broadband photodetector which authors pioneered. The features of proposed broadband detector are simple structure, low-cost, high quantum efficiency, high sensitivity, and high speed. Performance results so far attained will be presented along with its possible applications.

Laser oscillation with polysilane waveguide tunable external resonator was observed at 1537nm. The resonator consists of the polysilane single-mode waveguide and the Bragg grating on the core. 5.6 mW laser power was obtained with 70% Bragg reflection. The wavelength shift due to resonator temperature was measured as 0.096 nm/°C in the range of 30-70°C.

1.278μm laser emission has been observed in a SOI structure which has been nanopatterned to contain an array of nanopores. The optical transition is identified to be associated with phononless recombination mediated by the bistable, carbon-related G center. The present work is focused on increasing the luminescence intensity from nanopatterned Si by increasing the number of G centers present in the material. The G center density is increased by increasing the concentration of substitutional atoms in the lattice prior to nanopatterning. To this end, solid-phase epitaxial regrowth of carbon-rich silicon is utilized in order to take advantage of the increased solid solubility of carbon in silicon at the interface between crystalline and amorphous solid silicon.

Si/β-FeSi₂/Si (SFS) structures with β-FeSi₂ particles on Si(001), and SFS structures with β-FeSi₂ continuous films were epitaxially grown on both Si(001) and Si(111) substrates by molecular-beam epitaxy (MBE). All the samples exhibited the same photoluminescence (PL) peak wavelength of approximately 1.54 μm at low temperatures. However, the PL decay times for the 1.54 μm emission were different, showing that the luminescence originated from different sources. The decay curves of the SFS structures with β-FeSi₂ continuous films were fitted assuming a two-component model, with a short decay time (~10 ns) and a long decay time (~100 ns), regardless of substrate surface orientation. The short decay time was comparable to that obtained in the SFS structure with β-FeSi₂ particles. The short decay time was due to carrier recombination in β-FeSi₂, whereas the long decay time was probably due to a defect-related D1 line in Si. We obtained 1.6 μm electroluminescence (EL) at a low current density of 2 A/cm² up to around room temperature. The temperature dependence of the EL peak energy of the SFS diodes with β-FeSi₂ particles can be fitted well by the semi-empirical Varshni's law. However, EL peak positions of the SFS diodes with the β-FeSi₂ films showed anomalous temperature dependence; they shifted to a higher energy with increasing temperature, and then decreased. These results indicate that the EL emission originated from several transitions.

This paper presents our recent progress in the development of a Si wire waveguiding system for microphotonics devices. We have developed function devices that integrate several fundamental components and confirmed that they exhibited excellent characteristics due to the accuracy of the Si microfabrication. The propagation loss of the waveguide is less than 1.2dB/cm, and branching devices and basic filters show good characteristics. Using the fundamental microfabrication technique, we have developed other passive and dynamic functional devices. As an example of our recent advances using passive devices, we present a polarization diversity system consisting of a separator and a rotator. As a component of a dynamic functional device, we show a low-loss rib-type silicon wire waveguide with low-impedance p-i-n structure and its optical attenuation characteristics.

We present a 1.54 μm, 77 K, pulsed GaSb quantum well (QW) laser diode grown monolithically on a Si(100)-5° substrate. The III-Sb device is grown on an AlSb nucleation layer on Si with the 13% mismatch accommodated by a self-assembled 2D array of pure 90° dislocations. We demonstrate the simultaneous formation of this interfacial misfit dislocation (IMF) array along with antiphase domain suppression in the growth of AlSb on 5° miscut Si (001) substrate. The lomer dislocation spacing in the IMF (~ 3.46 nm) corresponds to the 13% mismatch between AlSb and Si and is also well matched to the step length of the 5° miscut Si (001) substrate. The resulting bulk material has both very low defect density (~7 × 105/cm²) and very low APD density (~ 103/cm²) confirmed by transmission electron and atomic force microscope images. The GaSb QW based laser diodes are grown on this high quality AlSb layer and the resulting devices operate at 77 K under pulsed conditions (2 μsec pulse-width and a 0.1% duty cycle) with an emission wavelength of 1.54 μm and a threshold current density of 2 kA/cm² for a 100 μm x 2mm device. The maximum peak power from the device is ~ 20 mWatts.

We have tried to monolithically merge light emitting devices into Si large-scale integrated circuits in a single chip for realization of optoelectronic integrated circuits (OEICs). OEICs could be realized for parallel information processing, optical interconnection and other applications. Structural defect-free GaPN and InGaPN layers were grown on a Si (100) substrate by using migration enhanced epitaxy and molecular beam epitaxy. A dislocation-free Si/GaPN/Si structure, which is a basic structure for OEICs, was successfully grown as well. In addition, control of electron and hole concentrations in GaPN was achieved by S(or Te)- and Mg-doping, respectively. Subsequently, a lattice-matched InGaPN/GaPN double-heterostructure (DH) light emitting diode (LED) was realized on a Si substrate. Moreover, fabrication process flow for OEIC was developed and applied to a Si/InGaPN/GaPN DH LED/Si layers. As a result, LEDs and metal-oxide-semiconductor field effect transistors were monolithically integrated in a single chip for the first time. When the luminescence efficiency is improved and micro-size LEDs based on GaPN are developed, novel OEICs would be realized.

As the scaling of single-crystalline silicon (c-Si) size comes into the region below 4 nm corresponding to the Bohr radius of exciton in c-Si, the original optical, electrical, thermal, and chemical properties of c-Si are substantially modified due to the occurrence of quantum confinement effect. As a consequence, some useful functions are induced in various manners. Nanoporous silicon (PS), composed of highly packed quantum-sized nanosilicon dots, is regarded as a typical quantum silicon material. This paper summarizes various physical effects induced in PS: bannd gap widening, complete carrier depletion, surface activity, and so on. To indicate their technological potential, the present status of application studies is addressed in terms of visible electroluminescent device, components for photonic integration, field-induced ballistic electron emitter, thermally induced ultrasonic emitter, and biocompatible scaffold. Further technological potential is discussed from viewpoints of exploring functional integration.

Silicon photonics technology is expected to be key to high-performance, low-power photonic networks. It is also expected that using Si photonics technology will make it possible to integrate photonic key components, such as optical waveguides, optical switches, polarization rotators, light emitters, and optical gain on Si chip C-MOS devices. We propose approaches to fabricating these key components on Si wafers. That is, we introduce some key technologies; (a) all-optical switching in a Si nanowire waveguide, (b) a Si waveguide polarization rotator, (c) material synthesis and waveguide formation of rare earth-doped SiOx thin-films for Si-based light emitters, and (d) a technique for fabricating nano-structured III-V semiconductors, such as Sb-based quantum dot structures, on Si wafers. We also propose a concept for applying Si photonics, i.e., a way to use Si photonics in information and communications technology (ICT).

Recently, AlGaInAs-silicon evanescent lasers have been demonstrated as a method of integrating active photonic devices on a silicon based platform. This hybrid waveguide architecture consists of III-V quantum wells bonded to silicon waveguides. The self aligned optical mode leads to a bonding process that is manufacturable in high volumes. Here give an overview of a racetrack resonator laser integrated with two photo-detectors on the hybrid AlGaInAs-silicon evanescent device platform. Unlike previous demonstrations of hybrid AlGaInAs-silicon evanescent lasers, we demonstrate an on-chip racetrack resonator laser that does not rely on facet polishing and dicing in order to define the laser cavity. The laser runs continuous-wave (c.w.) at 1590 nm with a threshold of 175 mA, has a maximum total output power of 29 mW and a maximum operating temperature of 60 C. The output of this laser light is directly coupled into a pair of on chip hybrid AlGaInAs-silicon evanescent photodetectors used to measure the laser output.

Although silicon photonics is now attracting much attention and some devices are manufactured already, development of light sources based on Si related materials is still a big issue. In this talk, promising candidates of light sources with Ge quantum dots are introduced and their characteristics are discussed. We fabricated three kinds of structures embedding Ge dots as light sources, that is, micro-cavities with Si/SiGe distributed Bragg reflector (DBR), photonic crystals and micro-disks formed on SOI substrates.

This paper introduces a high-capacity storage device based on the holographic optical disc storage system and applied field. It details a novel configuration of a single beam holographic storage system. Through coding the object light and reference light in same optical beam with a spatial light modulator (SLM), we achieve the aim of interference storage. The experimental results indicated this configuration can be used commercially. This system has the advantages of huge memory capacity and high access speed, thus offering a very useful storage alternative in the internet areas of communications and multimedia systems.

Solution of the light propagation model and applied implementation at optical mobile fibreless networks for indoors requires knowledge of the light behaviour at reflection. Except knowledge of the static directional characteristics of the reflected lights the knowledge of the dynamic behaviour is significant as well. Wall surfaces in precincts are furnished with paints containing colouring substances. Their metastable levels implicate time delay at reflections. By reason that typical life time in metastable states is about 10-3-10-6s it happens at bit rates above 1Mbit.s-1 to SNR influencing. Functional effect is the growth of bit error rate. The principal problem of the dynamic reflectance is that due to time delay on the pigments metastable levels the reflected light will influence far from bit interval that is a source of light for reflectance but within some of the resulting bit periods. Each surface with paints has a typical directional light distribution and in paper Fourier spectra for mostly used walls are presented.

The Self phase modulation effect is one of the main fiber non-linearity which is reduced by selecting dispersion compensated fiber (DCF). Further, this fiber is used in transmission of eight channels at 40 Gb/s up to the transmission distance of 280 km. The channel spacing is 200 GHz and EDFA used as booster amplifier has saturable gain of 25 dB, output saturation power 7 dBm and noise figure 4.5 dB.

Spectroscopic analyses have been performed on Tb³⁺ and Yb³⁺ co-doped in borosilicate glass, to assess their potential as green laser and amplifier gain media. The energy transfer efficiencies between Tb³⁺ and Yb³⁺ are clarified based on experimental observations and numerical analyses on the emission decay dynamics.

In this paper, we proposed a FDTD joined signal processing method which was based on superposition theorem and convolution theorem, to analyze the performances of Microring Resonator Filters in time domain and frequency domain. We present the transmission characteristics under high and low transfer rates in different speeds of signal at 10Gbit/s, 40Gbit/s, 80Gbit/s and 100Gbit/s. Transmission characteristics were analyzed in time domain which is agreed well with the result calculated by FDTD directly. Furthermore, the time required by our method reduced significantly compared with FDTD method.

In this study, we investigated the performance of slow light generation via SBS or SRS in tellurite glass based on characterization of Raman and Brillouin gain coefficients and an evaluation method of slow light generation we developed. The effects of different heavy metal oxides additions on slow light generation via SRS in tellurite glass are also discussed. Our results show that designed tellurite glass is a promising candidate for slow light generation via SBS or SRS due to its high Raman and Brillouin gain coefficients.