This paper proposes Photonic Core Node based on a 2.56-Terabit/s opto-electronic switching fabric, which can economically handle the rapidly increasing multimedia traffics, such as Internet traffic. We have successfully developed the first prototype of Photonic Core Node. The prototype consists of a single-stage full-crossbar opto-electronic switching fabric, super-packet buffers for input queuing, and a desynchronized-round-robin scheduler. The switching fabric is upgradable up to 2.56 Tb/s, and employs wavelength-division-multiplexing techniques, which dramatically reduce the total number of optical switching elements down to one-eighth the number of those used in a conventional switching fabric. The super-packet buffer assembles 16 ATM cells routed to the same output port into a single fixed-length packet. The super-packet-switching scheme drastically reduces the overhead of optical switching from 32 to 2.9%, although it tends to decrease effective throughput. The desynchronized-round-robin scheduler maintains nearly 100% effective throughput for random traffic, recursively resolving the contention of connection requests in one scheduling routine while keeping fairness in a round robin manner. The proposed Photonic Core Node can accommodate not only ATM switching but also WDM optical path grooming/multiplexing, and IP routing by using IP input buffer interfaces, because optical switches are bit-rate/format-independent.

We report on the demonstration of a fast restorable all-optical WDM network. This network consisted of four 44 optical cross-connects (OXC's) and four in-line optical amplifiers. These OXC's monitored not only the status of various network elements and quality of optical signals but also the optical path of each channel continuously. Thus, this network could automatically identify the causes of most network failures. For the fast restoration, we implemented these OXC's by using thermo-optic polymer switches (switching time: < 1.5 ms) and used hardware interrupt when LOS was detected. In addition, we used a pre-planned routing table made by using a simple heuristic routing and wavelength assignment algorithm. The results show that this network could be restored from any single link failure within 6 ms even when the restoration path was 400 km.

This paper describes a new optical label switching technique; wavelength and pilot tone frequency are combined to form labels that are used to control transport network routing. This technique is very attractive for achieving simple nodes that offer extremely rapid forwarding. Experimental results on the discrimination of optical labels and all-optical label conversion are also presented.

Recent progress in ultrahigh bit rate optical transmission using time-division multiplexing and wavelength-division multiplexing is described. Latest over 1 Tbit/s transmission experiments are shown and the possibility of higher bit rate transmission is discussed.

The demonstrated capacity of 40-Gb/s WDM systems is now exceeding 3-Tb/s. We will discuss some of the enabling technologies for these high capacities and some of the technologies that may push the aggregate capacity of WDM systems towards 10-Tb/s.

We proposed and demonstrated a novel wavelength stabilization technique for dense wavelength division multiplexing (DWDM) systems using dithering-induced AM cancellation which improves both wavelength stability and data transmission performance. Our wavelength stabilization technique consists of an optical frequency discriminating function and a function for canceling AM components induced by frequency dithering of the light source. The frequency discrimination in this technique is based on an FM-AM conversion effect, obtained by interaction from frequency dithering of the light with the bandpass characteristic of an arrayed-waveguide grating (AWG) multiplexer. The AM cancellation function was added to suppress optical frequency discriminating errors occurring due to AM components induced by frequency dithering in this wavelength stabilization architecture. In this scheme, an electro-absorption (EA) modulator is employed not only for modulating high-speed data traffic but also for suppressing AM components induced by frequency dithering on the light signal. Since the EA modulator is usually used for modulating high-speed data traffic, dedicated optical devices are not required for suppressing the AM components. The wavelength stability of a light source can therefore be enhanced with simple architecture. In the demonstration, a reduction of fluctuations within 50 MHz versus changes in the modulation index, and long-term stability within 320 MHz after more than 60 hours was achieved in 10 Gbit/s NRZ transmission. We also confirmed that the proposed AM cancellation technique effectively reduces the transmission penalties due to frequency dithering in 10 Gbit/s NRZ data transmission performance.

Using the chirped grating with temperature control, we demonstrated the adaptive dispersion compensation at 40 Gbit/s RZ transmission. The simple monitoring of the 40 GHz frequency component enables us to automatic control of the adaptive dispersion compensator.

We demonstrate, through numerical simulations, the possibility of trans-oceanic single channel transmission at 160 Gbit/s with no active control. This was achieved using short period dispersion management, which supports short pulse propagation at practical map strengths. We demonstrate that through careful selection and optimisation of the system parameters the performance of this system can be extended. We also define the tolerable limits of the system to the residual dispersion slope and polarisation mode dispersion.

This paper proposes a nonlinear distortion suppression scheme for optical direct FM Radio-on-Fiber system. This scheme uses the interaction between the nonlinearities of DFM-LD and OFD to suppress a 3rd order intermodulation distortion. We theoretically analyze the carrier to noise-plus-distortion ratio (CNDR) and show a controlling method in the MZI type OFD to realize the proposed suppression scheme.

We investigated the characteristics of optical duobinary signals in achieving high fiber input power transmission focusing on the idea of optimum residual dispersion equalization. We confirm through calculations and experiments that setting the total link dispersion at a non-zero value allows high fiber launched power (+18 dBm) and large dispersion tolerance (350 ps/nm) at 10 Gbit/s. We demonstrate repeaterless 250-km single mode fiber (SMF) transmission with a 10-Gbit/s optical duobinary signal. We also demonstrate high-speed complete optical duobinary coding and transmit synchronous digital hierarchy (SDH) frames over optical duobinary signals for the first time.

The effectiveness and possible applications of all-optical signal processing using highly-nonlinear dispersion-shifted fibers (HNL-DSFs) are described. Transparent and simultaneous processings of multi-channels WDM signal are key features of optical fiber processors. Simultaneous wavelength conversion of 3210 Gb/s WDM signal by four-wave mixing, all-optical 3R regeneration of 220 Gb/s WDM signal using nonlinear loop mirrors, and simultaneous recovery of 2020 GHz WDM optical clocks by supercontinuum were successfully demonstrated using HNL-DSFs, and possible applications of ultra-fast and multi-channel processing in future photonic networks are discussed.

This paper describes a simple polarization-independent wavelength conversion method using degenerated four-wave mixing (FWM) in single-mode fibers pumped with cross-polarized high frequency, saw-tooth pulses from a single pump source. Successful polarization-independent wavelength conversion is experimentally confirmed with less than 12% and 5.6% variation using a gain-switched LD pumping and a mode-locked fiber laser pumping, respectively. We clarify that the interference effect between two orthogonal pump pulses must be taken into account to achieve a good polarization-insensitive operation, since even the small pulse edges bring about the large polarization fluctuations when they are interfered. Furthermore, it is reveal that the shorter pump pulse broadens its own spectrum due to the self-phase modulation in fibers, resulting in poor FWM efficiency. Finally, possibility of high-speed operation is discussed taking into account the pump pulse conditions.

We fabricated a 1.55-µm polarization insensitive Michelson interferometric wavelength converter (MI-WC). The MI-WC consists of a two-channel spot-size converter integrated semiconductor optical amplifier (SS-SOA) on a planar lightwave circuit (PLC) platform. Clear eye opening and no power penalty in the back-to-back condition were obtained at 10 Gb/s modulation. We also confirmed the polarization insensitive operation on the input signal. Moreover, for an application of the MI-WC to DWDM networks, we demonstrated the selective wavelength conversion of 2.5 G/s optical packets from Fabry-Perot laser diode (FP-LD) light to four ITU-T grid wavelengths. We confirmed the good feasibility of this technique for use in DWDM networks. The wavelength conversion we describe here is indispensable for future all-optical networks, in which optical signal sources without wavelength control will be used at user-end terminals.

We propose a novel optical add/drop multiplexer (OADM) utilizing free spectral range (FSR) periodicity of an arrayed-waveguide multiplexer (AWG). In this OADM, wavelength-division multiplex (WDM) signal is multiplexed and/or de-multiplexed in two steps. Power penalty due to coherent crosstalk is drastically reduced compared with that of conventional OADM where AWG multiplexers are opposite to each other. The calculated power penalty due to the coherent crosstalk is about 0.7 dB after the 16 OADMs in the case of 128 wavelengths. It was confirmed through a computer simulation that more than one hundred channels at 10 Gbps data rate could be accommodated in an OADM network with 16 nodes. These results show that the OADM network with over 1 Tbps capacity and 16 nodes could be constructed.

A photonic crystal fibre has an array of microscopic air holes running along its length. The periodicity of the array is broken by a deliberate "defect" that acts as a waveguide core. Light is confined to this core by the holes. Although some designs of photonic crystal fibre guide light by total internal reflection and so can be considered analogues of conventional optical fibres, their properties can be strikingly different. Other designs guide light by photonic bandgap confinement and represent a totally new type of fibre.

We have developed the design procedure of multi-wavelength pumped Raman amplifiers, introducing superposition rule and account for pump-to-pump energy transfer. It is summarized with respect to the pumping wavelength and power allocation. The comparisons between simulated and experimental results are presented. Section 2 reviews the fundamentals of Raman amplifier. In this section, Raman gain spectra measured for different fibers are presented and the difference among the spectra is discussed. Section 3 describes the way to determine the pumping wavelength allocation by introducing superposition method. By means of this design method, some optimized design examples are presented, where the peak levels of Raman gain are fixed to 10 dB for the wavelength range from 1525 nm to 1615 nm (C- plus L-band) in all cases. From these results, it is confirmed that better gain flatness can be obtained by using the larger number of pumps. Section 4 explains how the pump-to-pump energy transfer changes the gain profile by experimental and simulated results. In this section, simulation modeling to perform precise numerical simulation is also presented. From the above discussion, the design procedure can be simplified: (1) one determines pump wavelengths with which a desired composite Raman gain can be obtained by adding in logarithmic scale individual Raman gain spectra shifted by the respective wavelength differences with adequate weight factors. And (2), one predicts how much power should be launched in order to realize the weight factors through precise numerical simulations. Section 5 verifies the superposition rule and the effect of pump-to-pump energy transfer by comparing a measured Raman gain with a superposed one. The agreement of two gain profiles shows that the multi-wavelength pumped Raman gain profile contains only the individual gain profiles created by the respective pump wavelengths. Section 6 concludes this paper.

In order to realize automatic-level-controlled (ALC) erbium doped fiber amplifiers (EDFAs) with both wide dynamic range and good noise performance, we propose EDFAs employing the automatic power control (APC) scheme and a variable attenuation slope compensator (VASC). The VASC consists of two asymmetrical Mach-Zehnder interferometers (MZIs) concatenated in series and thermo optic (TO) heaters are attached to the arms of each MZIs. By adjusting the electric power supplied to the TO heaters, an almost linear attenuation slope can be varied by plus minus 5 dB or more over the operational wavelength band of 30 nm. The EDFA employing the APC scheme and the VASC has exhibited a dynamic range as large as 20 dB with the output power variation as small as 0.7 dB, which is as good as that of the EDFA employing the APC scheme and a variable optical attenuator (VOA). The noise figure (NF) of the EDFA employing the VASC was degraded about 4.1 dB with increasing the input power by 20 dB, while it was degraded about 7.3 dB with increasing the input power by only 15 dB in the EDFA employing the VOA. The EDFA employing the VASC can realize the ALC operation over a wider dynamic range with reduced noise figure degradation. In the EDFA employing the VASC, the power excursion was suppressed to less than 1.1 dB, when the input signal level was changed between -23 dBm/ch and -18 dBm/ch with the rise/fall time of 8 ms.

In erbium doped optical fiber amplifiers (EDFAs) used in modern high-capacity wavelength division multiplexing (WDM) systems, the gain flatness of EDFA is very important in wide-band long-haul systems. In the EDFAs using the passive gain equalizers, the gain flatness deteriorates due to gain-tilt when the operating condition of the EDFA changes, while the EDFAs should maintain the gain flatness even if the operating condition has changed. To solve this problem, we have developed an active gain-slope compensation technique of an EDFA using a thulium-doped optical fiber (TDF) as a saturable absorber. The actively gain-slope compensated EDFA with the TDF compensator keeps the gain profile constant for the wide gain dynamic range more than 8 dB with the low noise figure less than 6 dB in the wavelength range of 1539-1564 nm.

We will present the theoretical analysis of and experimental measurements on the transmission characteristics of multi-channel long period fiber gratings in terms of the physical parameters like the separation distance, grating length and number of gratings. These parameters can be used to control the spectral channel spacing, number of channels, loss peak depth, and channel bandwidth of multi-channel long period fiber gratings.

In an ideal fiber grating having a uniform refractive index modulation, the reflection or the transmission spectrum is symmetric with equal amount of side lobes on both sides of the resonant wavelength of the fiber grating. It is observed that a long-period fiber grating made by a non-uniform UV laser beam through a uniform amplitude mask has an asymmetric transmission spectrum. The asymmetric characteristic is explained with Mach-Zehnder effect in the long-period fiber grating. The non-uniform UV laser beam makes also a non-uniform index modulation along the fiber core. Therefore, a beam coupled to a cladding mode at a section of the grating can be re-coupled to the core mode after passing a certain distance. The re-coupled beam makes Mach-Zehnder-like interference with the un-coupled core mode. However, it is presented that the asymmetric phenomenon can be overcome by scanning the UV laser beam along the fiber over the mask. The beam scanning method is able to suffer the same fluence of the UV laser beam on the fiber. Finally, a linearly chirped long-period fiber grating was made using the non-uniform UV laser beam. Due to the asymmetricity the chirping effect was not clearly observed. It is also presented that the beam scanning method could remove the asymmetric problem and recover the typical spectrum of the linearly chirped fiber grating.

The analytic expression for the transmission spectrum of cascaded long-period fiber gratings is presented in a closed form. When several identical gratings are cascaded in-series with a regular distance, the transmission spectrum is revealed to have a series of regularly spaced peaks, suitable for multi-channel filters. The analytic solution is obtained by diagonalizing the transfer matrix of each grating unit that is composed of a single grating and a grating-free region between adjacent gratings. The spectrum of the device is simply described with the number of cascaded gratings and a single parameter that has the information of the phase difference between the modes. With the derived equation, the spectral behaviors of the proposed device are investigated. The intensity of each peak can be controlled by adjusting the strength of a single grating. The separation between adjacent gratings determines the spacing between the peaks. The finesse of the peaks can be increased by cascading more gratings. The derived analytic results are compared with the known results of paired gratings and phase-shifted gratings.

The present paper discusses several promising application areas for optical data links based on high-performance vertical-cavity surface-emitting laser diodes (VCSELs). Both 850 and 980 nm emission wavelength devices realized in the GaAs-AlGaAs or InGaAs-AlGaAs material systems are considered. We show data transmission results of 10 Gb/s signals at 830 nm wavelength over a new high-bandwidth multimode silica fiber of up to 1.6 km length. The same fiber type is employed to demonstrate the first 40 Gb/s transport over 300 m distance by means of a 4-channel coarse wavelength-division multiplexing approach. A first 1 10 linear VCSEL array capable of 10 Gb/s per channel operation is presented for use in next generation parallel optical modules. To improve the singlemode emission characteristics for output power in the 5 mW range we introduce a new device concept incorporating a long monolithic cavity. For low-cost short-distance data links we investigate graded-index polymer optical fibers and report on up to 9 Gb/s transmission over a length of 100 m. Polymer waveguides are also used in an optical layer of a hybrid electrical-optical printed circuit board. Transmitted 10 Gb/s optical data over a prototype board show the potential of this new technology. Finally we present two-dimensional VCSEL arrays for highly parallel data transport on a CMOS chip level. Both 980 and 850 nm bottom emitting devices with modulation capabilities up to 12.5 Gb/s are discussed.

Highly reliable and high power weakly index guided buried-stripe type 980 nm pump laser diodes developed for undersea applications are reviewed. The 10,000-hour large scale reliability tests of the first generation LD chips shows that 16.7 FIT for the random failure was confirmed at 10C with 60% confidence level at 120 mW output power. We also fabricated a FBG locked co-axial type module using a can-sealed LD with a two-lens system, which showed a stable FBG locked mode oscillation at 980 nm under the temperature range from 5C to 45C. The 5,000-hour heat cycle test of the modules reveals that the cumulative failure rate after 27 years at 10C is expected to be 0.023%. These first generation LD modules were employed in the transoceanic commercial systems such as Pacific Crossing-1 and the Japan-US cable system projects. We have also succeeded in developing the 980 nm LD for higher output operation with optimizing waveguide design. The 1000 µm long LD showed CW kink-free operation up to 545 mW optical output and a maximum output power of over 650 mW, which was limited by thermal rollover. In addition, a preliminary aging test at 350 mW optical output power at 50C has shown stable operation up to 2,300 h. We also confirmed 300 mW kink-free fiber output power with a co-axial type module with the improved coupling efficiency of approximately 78%. These figures are the highest reported operation levels for 980-nm co-axial type modules.

We have measured the temperature dependence of the gain characteristics in 1.3-µm AlGaInAs/InP strained multiple-quantum-well (MQW) semiconductor lasers using Hakki-Paoli method. By measuring the temperature dependences of the peak gain value and the gain peak wavelength, we evaluated the temperature dependences of the threshold current and the oscillation wavelength, respectively. The small temperature dependence of the threshold current in AlGaInAs/InP lasers is caused by the small temperature dependence of the transparency current density, which is represented by the characteristic temperature T_Jtr of 116 K. In AlGaInAs/InP high T₀ lasers, the temperature dependence of the oscillation wavelength is slightly larger than that in GaInAsP/InP lasers because of the larger temperature dependence of bandgap wavelength 0.55 nm/K.

The effect of wavelength detuning on the device performance of identical-epitaxial-layer (IEL) electroabsorption (EA) modulator integrated distributed feedback (DFB) lasers is studied in detail. Based on the lasing behavior of integrated devices with different amount of wavelength detuning and the photocurrent spectra under different reverse biases, the optimal wavelength detuning is experimentally determined to be around 30-40 nm for our IEL integrated devices. By adopting gain-coupled DFB laser section, integrated devices with optimal wavelength detuning have demonstrated excellent single mode performances. The extinction ratio is measured to be greater than 15 dB at -3 V, and the modulation bandwidth is around 8 GHz.

Photonic crystals have seen major advances in the past few years in the optical range. The association of in-plane waveguiding and two-dimensional photonic crystals (PCs) in thin-slab or waveguide structures leads to good 3D confinement with easy fabrication. Such structures, much easier to fabricate than 3D PCs open many exciting opportunities in optoelectronic devices and integrated optics. We present experiments on a variety of structures and devices, as well as modelling tools, which show that 2D PCs etched through waveguides supported by substrates are a viable route to high-performance PC-based photonic integrated circuits (PICs). In particular, they exhibit low out-of-plane diffraction losses. Low-loss waveguides, high finesse microcavities, and their mutual coupling are demonstrated. PACS: 42.70 QS, 42.55 Sa, 42.82 m, 42.50-p.

A wavelength demultiplexer made of 2-D photonic crystal capable of simultaneously separating many channels from WDM light is analyzed in order to study the properties and clarify the design parameters. Numerical analyses are carried out for the optical filter structure and the demultiplexer structure which consists of several filters and waveguides carved in the crystal. The results of this paper show the considerations regarding the frequency tuning, the device size, the bandwidth and integration of filters. Further more, for a photonic crystal filter, a method for realizing a flat-top pass-band generally required from the dense-WDM systems is presented and its property is shown. The calculation method is the scattering matrix method which is proper to the analysis of the frequency domain in a 2-D photonic crystal with finite size and with some defects.

A novel temperature insensitive wavelength filter consisting of GaAlAs/GaAs distributed Bragg reflectors (DBRs) has been demonstrated. This micromachined DBR is mechanically tuned by differential thermal expansion. The strain-induced displacement of one mirror can generate wavelength tuning and trimming functions with an adjustable temperature dependence. We succeeded in the control of temperature dependence in this micromachined semiconductor filter by properly designing a vertical cavity structure. The achieved temperature dependence was as small as +0.01 nm/K, which is one-tenth of that of conventional semiconductor based optical filters. Also, a wavelength trimming of over 20 nm was demonstrated after completing the device fabrication. In addition, we demonstrated a 4 4 multiple wavelength micromachined vertical cavity filter array. The multi-wavelength filter array with a wavelength span of 45 nm was fabricated by partially etching off a GaAs wavelength control layer loaded on the top surface of device.

We have developed a new planar lightwave circuit (PLC) platform eliminating Si terraces for hybrid integrated optical modules. This PLC platform has the advantage of a lower fabrication cost than the conventional PLC platform with an Si terrace, because it does not require fabrication processes such as Si terrace forming and mechanical polishing. Using our new PLC platform structure, we fabricated a transceiver for optical access networks and an 8-channel multi-channel photoreceiver for wavelength division multiplexing (WDM) interconnection systems.

A fully integrated Low Dropout (LDO), low quiescent current regulator has been fabricated in a 0.6 µm CMOS technology. It is stable with low and high effective series resistance (ESR) capacitors. A dynamic feedback (DNFB) bias technique is used to bias the error amplifier in the LDO such that good current efficiency is achieved while maintaining a good transient response. In order to compare the performance of the LDO regulators with and without dynamic feedback, the error amplifiers are configured to have a large bias current (LC), a small bias current (SC) and a bias with dynamic feedback current using switches. The measurement results show that DNFB's line and load regulations are 0.145%/V and 11 ppm/mA, respectively. Besides, there is about 33% reduction in settling time and voltage drop compared with SC LDO when load current is switching from 0 mA to 50 mA. In order to reduce the dropout voltage, a dropout reduction circuitry based on DNFB is also designed to reduce the threshold voltage of LDO's output PMOS. The measured dropout reduction is 8.1 mV which can be further reduced by a larger feedback ratio in DNFB. The quiescent current of this LDO is measured to be 59.4 µ A and this LDO can provide a maximum output current of 250 mA at an input voltage of 3.6 V. The active area of this LDO is 760 µ m 714 µ m.

An experimental report was presented on a high temperature performance of a ZrN barrier in the model system of W/ZrN/poly-Si as a poly-metal gate electrode configuration. The absence of interdiffusion, reaction and/or mixing of the ZrN barrier with adjoining W and poly-Si layers resulted in a successful demonstration of the thermally stable poly-metal gate electrode configuration which tolerated annealing at 850 for 1 h.