Over roughly the past decade, the lightwave-research community has converged upon a broad architectural vision of the emerging national-scale core network. The vision has been that of a transparent, reconfigurable, wavelength-routed network, in which signals propagate from source to destination through a sequence of intervening nodes without optoelectronic conversion. Broad benefits have been envisioned. Despite the spare elegance of this vision, it is steadily becoming clear that due to the performance, cost, management, and multivendor-interoperability obstacles attending transparency, the needs of civilian communications will not drive the core network to transparency on anything like a national scale. Instead, they will drive it to 'opaque' form, with critical reliance on optoelectronic conversion via transponders. Transponder-based network architectures in fact not only offer broad transmission and manageability benefits. They also make networking at the optical layer possible by offering to the nodes managed and performance-engineered standard-interface signals that can then be reconfigured for provisioning and restoration purposes by optical-layer elements. Because of this, the more pressing challenges in lightwave networking are steadily shifting towards the mechanisms that will be used for provisioning and restoration. Among these are mechanisms based on free-space micromachined optical crossconnects. We describe recent progress on these new devices and the architectures into which they fit, and summarize the reasons why they appear to be particularly well-matched to the task of provisioning and restoring opaque multiwavelength core long-haul networks.

This paper discusses global area optical transport ring networks using wavelength division multiplexing (WDM) technologies and proposes a novel optical add/drop multiplexer (OADM) architecture suitable for such an application field. Study on the requirements of a global area ring application elucidates the appropriate ring/protection architecture as the path switched bi-directional ring. The proposed OADM architecture has flexibility in terms of path provisioning and scalability. We conclude that the proposed OADM can effectively configure the large-scale path switched bi-directional rings.

A wavelength division multiplexing (WDM) optical path-based Internet protocol (IP) backbone network is proposed as a cost-effective way of realizing robust IP-over-photonic systems. The WDM optical path is based on WDM transmission and wavelength routing. Between end-to-end IP backbone routers, the WDM optical path, a fat and robust optical pipe, is defined across photonic transport systems (PTS's). Tera-bit class PTS's will be required for the future IP backbone network and this level of performance is achievable. Optical layer routing is done at intermediate nodes, so the electrical packet-by-packet routing required by existing systems is eliminated. An optical signal format that permits cost-effective IP packet transmission is presented. WDM optical paths directly accommodate the IP packets via layer-2 frames. The cost-effectiveness of the proposed system, especially for heavy traffic, is demonstrated from the viewpoint of the overall network traffic transport capability and network node cost. The proposed system is as robust as existing systems; e. g. fault/degradation localization mechanism and optical layer network protection one are implemented. Thus the proposed IP-over-photonic system will create cost-effective and robust IP backbone networks.

A novel 10-Gb/s fast acquisition bit-synchronization circuit for use in a Tb/s throughput optical packet switch has been developed. The circuit is a best-sampled-data-select type based on multiple phase-clocks, and it processes the asynchronous input packets into a synchronous data stream in a serial manner, which is advantageous in terms of circuit scale and consumption power compared with the parallel processing type. The circuit was developed using Si-bipolar ultrahigh-speed gate arrays and it was used to develop a 10-Gb/s optical asynchronous packet receiver module. The core logic of this circuit module required about 100 gates, consume 6 W, and the size of the module was reduced to only 170 mm (W)130 mm (D) 10 mm (H). Using the receiver module, a fast acquisition time of 9 bits and receiver sensitivity penalty of less than 1.5 dB due to re-synchronization were measured.

WDM transmission experiments over cascaded sections of optical links including wavelength converting 2R-transponders have been carried out in a loop testbed. Using dispersion compensated links and simple direct modulated transponder lasers, up to 11 cascaded crossconnects and 1750 km trunk lines have been bridged with 2.5 Gbit/s NRZ signals. The limitations are given mainly due to the accumulated jitter as it is shown by numerical simulations. The results indicate, that 2R-transponders are a useful approach to a flexible WDM network design using bitrate-transparent wavelength conversion.

A novel 1470-nm-band (S+ band) wavelength-division multiplexing (WDM) transmission system is described. The first advantage of S+-band transmission is suppression of degradation caused by four-wave mixing (FWM), which has been the dominant impairment factor in WDM transmission systems on dispersion-shifted fibers (DSFs). FWM suppression by using the S+ band instead of the conventional 1550-nm-band (M band) is successfully demonstrated. The second advantage is expansion of the usable bandwidth by using the S+ band together with other wavelength bands. A triple-wavelength-band WDM repeaterless transmission experiment using the S+ band, the M band and the L band (1580-nm-band) is conducted over DSF, and it is shown that degradation due to inter-wavelength-band nonlinear interactions is negligible in the transmission. Moreover, the transmission performance of an S+-band linear repeating system is estimated by computer simulation, and compared with that of other wavelength-band systems. In the experiments, thulium-doped fiber amplifiers (TDFAs) are used for amplification of signals in the S+ band.

We analyze the dispersion-managed optical transmission system for the non-return-to-zero (NRZ) pulse format. First, we investigate the physical image of dispersion management by computing small-signal-based transfer functions, and summarize the dependence of transmission performance on system parameters. Next, the Q-map is computed numerically to design long-distance large-capacity dispersion-managed transmission systems for a single channel in a more detailed manner. It is shown that the third-order dispersion of fibers negatively influences transmission performance, and third-order dispersion compensation is proved to be an effective method for extending the transmission distance of high bit-rate systems. Utilizing these results, guidelines can be derived for the optimal design of long-distance large-capacity NRZ transmission systems.

We have proposed and demonstrated a novel optical regenerator architecture employing electroabsorption modulators as wavelength converters. The employment of EA modulators is advantageous for high-speed operation and flexibility in the bit-rate for the pulse regeneration. In addition, the EA modulator-wavelength-converter acts also as a photo diode for clock extraction. Compensation of the optical SNR and Q-factor has been demonstrated, even in cascaded noise load. Furthermore, against dispersion loading, we have confirmed that waveform recovery and Q-factor improvement is obtained by midway insertion of the optical regenerator. The proposed architecture will offer a wide-band-electronics-free optical regenerator in multi-tens of gigabit per second WDM networks.

The statistical behavior of the amplitude probability distribution of intermodulation distortion interference in multichannel optical-cable TV systems was experimentally investigated. In multichannel transmission, the non-linearity of a laser diode (LD) or an electrical amplifier can cause intermodulation distortion (composite-second-order beat; CSO, composite-triple-beat; CTB, etc. ). Even though it has been discussed as laser-clipping distortion, intermodulation distortion is usually distortion from AM-VSB carriers. The statistical analysis and evaluation of the distortion in transmitted channel is in controversial. We evaluated the distortion in 20 frequency-division-multiplexed 16-QAM channels, with each carrier carrying 80 Mbps for an optical cable TV system. We first enumerated the distortion components causing interference in each transmission channel so as to identify the intermodulation products. Then, in selected channels, we precisely measured the power of each kind of distortion and the amplitude distributions of the intermodulation distortion from sinusoidal and digital-modulated carriers on cable TV as a function of optical modulation depth (OMD) of LD. And we clarified how the probability distribution function (PDF) changed as the OMD increased. Also, the BER performance of a 16-QAM signal was measured and compare to the intermodulation behavior of the different distortion sources. We found evidence that the amplitude distribution of intermodulation distortion from digital carriers differs from that of thermal noise. Experimental results showed that the PDF of the intermodulation distortion changed when the ratio of intermodulation distortion among all undesired signals varied with the OMD. The BER performance varied with intermodulation of both analogue and digital carriers even when the carrier to interference noise power ratio (CIR) is the same.

We have developed a low-latency, error-correcting-code-(ECC-)adaptable skew-compensation technique, which is needed for high-speed and long-distance parallel optical interconnections. A new frame-coding technique called shuffled mB1C encoding, which requires no clock-rate conversion circuit and no data buffering, and a new skew-measurement method which is suitable for ECC adaptation have been developed for the compensation. Full-digital skew-compensation circuits using these new techniques were able to compensate for a two-clock-cycle skew, even when one transmission channel was removed. The maximum latency for skew compensation was only five clock cycles.

In the present paper, a new coding scheme for infrared ASK communication systems--Pulse Sequence Modulation (PSM)--will be proposed, which uses a combination of pulse sequences so that it canattain zero-spectrum points at specific frequencies within the main-lobe region. The interference to the other IR systems was a problem of the conventional infrared ASK communication systems. The proposed PSM coding scheme reduces the interference by decreasing the emission at specific frequencies, and helps multiple IR communication systems co-exist without deteriorating coding efficiency.

Recent technologies for increasing memory density in random access memory optical disks including magnetic super resolution method, super resolution method in phase change disk, blue laser diode, near field optics, and photo chromic memory are reviewed.

We have developed an InP-based monolithic optical frequency discriminator consisting of a temperature-insensitive optical filter and dual photodiodes. This integrated device detects the optical frequency deviation of the input light as differential photocurrent from the dual photodiodes, and the photocurrent is fedback to the light source for frequency stabilization through a differential amplifier. The FSR and extinction ratio of the filter are 50 GHz and 20 dB. The total opto-electronic conversion efficiency is 40%. In a frequency stabilization experiment using the developed discriminator, the frequency fluctuation of a DFB laser was reduced to less than 10 MHz.

We developed an optical transceiver diode (TRAD) module for bi-directional time-compression-multiplexing (TCM) transmission systems. A wavelength-insensitive structure as a receiver and a low-capacitance configuration in the module provide a high sensitivity. Stable switching of 156 Mbit/s NRZ burst signals between the transmitter and receiver modes is achieved. In addition, it is shown that optical module cost can be further reduced by using passive alignment on a Si bench.

This paper describes design techniques for suppressing crosstalk in an optical transceiver module using PLC-hybrid-integration technologies and for achieving burst-mode operation with high sensitivity and wide dynamic range using CMOS-IC technologies. An arrangement that reduces the electrical crosstalk to less than -100 dB was designed using three-dimensional electromagnetic field analysis. The configurations of a newly developed instantaneous-response CMOS LD driver circuit is also described and instantaneous-response CMOS receiver circuit techniques are reviewed. With these techniques, we have succeeded in building optical transceiver modules for ATM-PON systems using PLC-hybrid-integration and inexpensive standard CMOS-IC fabrication processes. Under full-duplex operation at 156 Mb/s, fabricated transceiver modules showed receiver sensitivity of better than -34 dBm and dynamic range of over 28 dB, which satisfy both the class-B and class-C specifications recommended by ITU-T (International Telecommunication Union-Telecommunication standardization sector) G983.1 for the optical transceiver module for an ONU (optical network unit).

After a short introduction to the different requirements to and techniques for wavelength conversion, focus is on cross-gain and cross-phase modulation in SOA based converters. Aspects like jitter accumulation, regeneration and conversion to the same wavelength is discussed. It is predicted that jitter accumulation can be minimised while also assuring a high extinction ratio by using a 9-10 dB ratio between the signal and CW power. Using this guideline simulations show that 20 cross-gain modulation converters can be cascaded at 10 Gbit/s with only 20 ps of accumulated jitter and an extinction ratio of 10 dB. The regenerative capabilities of the cross-phase converters are described and verified experimentally at 20 Gbit/s. By controlling the input power to an EDFA, the noise redistribution and improvement of the signal-to-noise ratio is demonstrated. In a similar experiment at 2.5 Gbit/s, the regeneration causes a reduction of the required input power to an in-line EDFA of 6 dB for a power penalty of 1 dB at a bit error rate of 10^-9. If two converters are concatenated the power requirement is reduced 8 dB. Obviously, the power reduction allows for longer spans between in-line EDFAs. A simple scheme for regeneration without wavelength conversion is assessed at 2.5 Gbit/s resulting in 4.5 dB lower required EDFA input power. The scheme is characterised by a quasi-digital transfer function that is ideal for regeneration. A combination of cross-gain and cross-phase conversion is used to perform conversion to the same wavelength at 20 Gbit/s. The insertion penalty for this dual-stage converter is below 2 dB and is mainly caused by extinction ratio degradation from the cross-gain converter. Finally, a new device for all-optical wavelength conversion has been proposed and 2.5 Gbit/s operation has been simulated with good results.

A 1.55-µm hybrid integrated wavelength-converter module was fabricated using a two-channel spot-size converter integrated semiconductor optical amplifier (SS-SOA) on a planar-lightwave-circuit (PLC) platform. Clear eye opening and penalty-free wavelength conversion were obtained at 2.5-Gb/s modulation with a wide wavelength difference of 46 nm. The module showed good characteristics including low insertion loss (0.1 dB), and high conversion efficiency (-0.2 dB). It also showed stable wavelength conversion for as wide as a 13 temperature range.

A clock recovery circuit is a key component in optical communication systems. In this paper, an optoelectronic clock recovery circuit is reported that monolithically integrates a resonant tunneling diode (RTD) and a uni-traveling-carrier photodiode (UTC-PD). The circuit is an injection-locked-type RTD oscillator that uses the photo-current generated by the UTC-PD. Fundamental and sub-harmonic clock extraction is confirmed for the first time with good clock recovery circuit characteristics. The IC extracts an electrical 11.55-GHz clock signal from 11.55-Gbit/s RZ optical data streams with the wide locking range of 450 MHz and low power dissipation of 1.3 mW. Furthermore, the extraction of a sub-harmonic clock from 23.1-Gbit/s and 46.2-Gbit/s input data streams is also confirmed in the wider locking range of 600 MHz. The RMS jitter as determined from a single sideband phase noise measurement is extremely low at less than 200 fs in both cases of clock and sub-harmonic clock extraction. To our knowledge, the product of the output power and operating frequency of the circuit is the highest ever reported for injection-locked-type RTD oscillators. These characteristics indicate the feasibility of the optoelectronic clock recovery circuit for use in future ultra-high-speed fully monolithic receivers.

Waveguide photodiodes (WGPDs) are key devices for high-speed optical receivers in trunk lines because of their potential ability to provide both high efficiency and a high-speed response. We have designed a waveguide photodiode for 40-Gb/s-range optical receivers. The optical coupling characteristics were simulated in detail to optimize the waveguide structure, and the electrodes of the photodiode were designed to form a coplanar transmission line to match the system impedance, which minimized frequency-response degradation. A highly beryllium-doped, low-temperature-grown InGaAs contact layer grown by gas source molecular beam epitaxy was used to reduce the series resistance, and approximately 40% reduction of series resistance was achieved. The fabricated device exhibited both a very high external quantum efficiency of 81% for 1.55-µm light and a sufficient bandwidth of more than 40 GHz. Though we used a simple conventional fabrication process, excellent characteristics were achieved due to the optimized optical design and well suppressed parasitic parameters.

A GaAs/AlGaAs directional-coupler-type device that use polariton propagation was fabricated and its switching operation was demonstrated. The length of the switching region is as small as 300 µm. The output signal modulation under an electric field shows typical characteristics of directional-coupler type switching. The measured operation voltage is 2 V for an operation wavelength of 805 nm at 10 K. The corresponding signal extinction ratio is 8 dB. These experimental results confirm the efficient operation of the polariton devices, which can be applied to especially small optical -switching devices with low-voltage operation.

An optical add-drop multiplexer with a grating-loaded directional coupler in silica waveguides is demonstrated. The device for this configuration has a large fabrication tolerance and is small in size. A new scheme, in which the coupling length of the directional coupler is twice the complete coupling length, enables low cross-talk for both add and drop operations. This device is polarization-independent due to its relatively low-temperature process.

This paper reports on time-space conversion-based differential processing of optical signals using a high-resolution arrayed-waveguide grating (AWG) and a spatial filter at a wavelength of 1.55 µm. We clarify the advantages of the AWG device and show where it is applicable. In order to reduce loss at the spatial filter, we propose a new phase-only filter that functions as a differential filter. The difference between the exact differential filter and the proposed phase-only filter is calculated theoretically. We confirm experimentally that the optical pulse can be differentiated by the proposed filter. For application of differential processing, we also proposed a phase modulation to amplitude modulation (PM-AM) conversion and demonstrated the PM-AM conversion at 10 Gbit/s signals using a PSK-non-return-to-zero (NRZ) format.

Precise plastic V-grooved alignment parts for connecting single-mode optical fiber arrays to multi-port optical devices were successfully molded with a thermosetting resin by using a highly productive injection molding technique. The molded parts are two types of V-grooved blocks that are compatible with the size of optical devices having eight or twelve optical ports. Their dimensional accuracy must be better than 1 µm over the whole length of the V-grooves for efficient optical coupling. This strict requirement was satisfied using precisely processed molding tools with a specially chosen resin under optimum molding conditions. The feasibility of the optical alignment parts was assured by an evaluation of their loss characteristics and reliability in coupling single-mode fibers to 18 power splitters, where the average optical loss was 0.2 dB and the change in loss was less than 0.2 dB under a temperature cycling test and also under a damp heat test. These results show that plastic molded parts can be used for precise coupling of single-mode optical devices, and will lead to a breakthrough in innovation in the field of optical packaging.

Aiming at wideband and flat supercontinuum generation (SC) from optical fibers in the 1.55-µm wavelength region, we study both experimentally and theoretically how SC spectra are influenced by group-velocity dispersion (GVD) of fibers. In the anomalous GVD region, since the peak power of pump pulses is kept high during propagation through the fiber by the higher-order soliton effect, the Raman effect has an adverse effect to flat and wideband SC generation. In the zero GVD region, the interplay of the third-order dispersion (TOD) and the self-phase modulation splits the SC spectrum into two main components. On the other hand, in the normal GVD region, nevertheless the SC spectrum broadens wider and smoother than those in anomalous and zero GVD regions, it is still asymmetric when TOD of the fiber can not be ignored. From these results, we find that a dispersion-flattened fiber with normal GVD is the most suitable for flat and wideband SC generation. A 280-nm wide SC spectrum with the spectral-density fluctuation less than 10 dB is actually generated from such a fiber.

Coaxial-core erbium-doped fiber amplifiers (EDFA's) having a property of self-regulated gain spectrum are developed. The operation of a coaxial-core EDFA is based on the partial separation of the light paths for different wavelength channels in the directionally-coupled waveguides of a coaxial-core geometry. The degree of channel equalization depends on the geometrical and optical parameters of the coaxial-core EDFA and on relative channel power levels. A numerical analysis based on the coupled-mode theory and on the rate equation shows that, under fully optimized conditions, a coaxial-core EDFA provides equalization rates in excess of -0.4 dB per dB of input-power imbalance in the case with two WDM channels. A cascade experiment demonstrates the effect of coaxial-core EDFA's toward channel-power equalization in fiber links with a small number of WDM channels.

The dependence of a linear electro-optic (LEO) coefficient induced into boron-codoped germanosilicate fibre on thermal poling conditions (poling voltage, poling temperature and poling time) has been systematically carried out using a Mach-Zehnder interferometer. The LEO coefficient increases as a 2.7 power law with the poling voltage; it can be maximally induced into the silica fibre within a temperature range from 250 to 300; it exponentially increases with poling time until saturation but after that it then decreases. Possible mechanisms of thermal poling are discussed in the light of the experimental results.

Recent status of the polymer optical fiber (POF) for high speed data communication and telecommunication is reviewed. The GI POF was proposed for the first time 20 years ago at Keio University, and several methodologies to fabricate GI POF have been currently proposed worldwide. In this paper, we both theoretically and experimentally verify that the most transparent GI POF can be obtained by the polymer-dopant system. The relation between the refractive index profile and the dispersion characteristics of the GI POF was quantitatively clarified. The refractive index profile of the GI POF obtained by the interfacial-gel polymerization process was controlled to enable to transmit the order of gigabit per second bit rate. Furthermore, the accurate approximation of the refractive index profile and consideration of mode dependent attenuation enabled to precisely predict the dispersion characteristics of the GI POF.

In this work, a CMOS on-chip current reference circuit for memory, operational amplifiers, comparators, and data converters is proposed. The reference current is nearly insensitive to temperature and supply-voltage variations. In the proposed circuit, the current component with a positive temperature coefficient cancels that with a negative temperature coefficient each other. While conventional current reference circuits are based on bipolar transistors in BiCMOS, bipolar, or CMOS processes, the proposed circuit can be integrated on a single chip with other digital and analog circuits using a standard CMOS process and extra masks are not required. Measured results are demonstrated for two different prototypes. The first is fabricated employing a 1.0 µm p-well double-poly double-metal CMOS process and operates at 5 V nominally. The second, based on a 0.6 µm n-well process, is optimized for 3 V to 5 V operation. The latter prototype achieves the temperature coefficient of 98 ppm/ over a temperature range from -25 to 75 and the output variation of 1.5% with the supply-voltage changes from 2.5 V to 5.5 V. A simple calibration technique for reducing output current variations improves circuit yield.

A microprocessor integrated with DRAM on the same die has the potential to improve system performance by reducing memory latency and improving memory bandwidth. In this paper we evaluate the performance of a single chip multiprocessor integrated with DRAM when the DRAM is organized as on-chip main memory and as on-chip cache. We compare the performance of this architecture with that of a more conventional chip which only has SRAM-based on-chip cache. The DRAM-based architecture with four processors outperforms the SRAM-based architecture on floating point applications which are effectively parallelized and have large working sets. This performance difference is significantly better than that possible in a uniprocessor DRAM-based architecture, which performs only slightly faster than an SRAM-based architecture on the same applications. In addition, on multiprogrammed workloads, in which independent processes are assigned to every processor in a single chip multiprocessor, the large bandwidth of on-chip DRAM can handle the inter-access contention better. These results demonstrate that a multiprocessor takes better advantage of the large bandwidth provided by the on-chip DRAM than a uniprocessor.

We successfully fabricated plastic ferrules and split alignment sleeves for single-mode fiber-optic connectors by the injection molding process. Liquid crystalline polymer (LCP) was used as the molding material for the ferrule. We introduced an eccentricity control mechanism into the ferrule mold and realized an eccentricity of less than 1 µm. As the molding material for the sleeve, thermosetting epoxy resin was used. Suitable mechanical properties were realized by employing appropriate dimensional design and the molding process. The optical characteristics of a system combining these plastic components are compatible with single-mode SC-type connectors and are also stable under hot and humid conditions.

The problem of transient scattering caused by abrupt extinction of a terminative conducting screen in a waveguide is considered. First, a boundary-value problem is formulated to describe the transient phenomena, the problem in which the boundary condition depends on time. Then, application of the Fourier transformation with respect to time derives a Wiener-Hopf-type equation, which is solved by a commonly known decomposition procedure. The transient fields are obtained through the deformation of the integration path for the inverse transformation and the results are represented in terms of the incomplete Lipschitz-Hankel integrals. Numerical examples showing typical transient phenomena are attached.