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.

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.

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.

In the literature [9], the optimum discrete interpolation of one-dimensional signals is presented which minimizes various measures of approximation error simultaneously. In the discussion, the ratio λ of the weighted norm of the approximation error and that of the corresponding input signal plays an essential role to determine the structure of the set of signals. However, only the upper bound of λ is provided in [9]. In this paper, we will present more exact and systematic discussion of the optimum discrete interpolation of one-dimensional signals which minimizes various measures of approximation error at the same time. In this discussion, we will prove that the exact value of λ is identical with the upper limit, for ω (|ω| π), of the largest eigen value of a matrix including the weighting function W(ω) and the Fourier transforms of the optimum interpolation functions. Further, we will give a sufficient condition for W(ω) under which the ratio λ is equal to one, where the approximation error, if it is interpolated by sinc, is included in the set of band-limited signals defined by W(ω). Finally, as application of the presented approximation, we will propose a direction to interactive signal processing on Internet and a transmultiplexer system included in it. The transmultiplexer system included in this discussion can realize flexible arrangement of sub-bands which is inevitable in realizing the above proposal on interactive signal processing.

This paper proposes a fast encoding algorithm for iterated function system (IFS) coding of gray-level homogeneous fractal images. In order to realize IFS coding of high order fractal images, it is necessary to solve a set of simultaneous equations with many unknowns. Solving the simultaneous equations using a multi-dimensional, numerical root-finding method is however very time consuming. As preprocessing of numerical computation, the proposed algorithm employs univariate polynomial manipulation, which requires less computation time than multivariate polynomial manipulation. Moreover, the symmetry of the simultaneous equations with respect to the displacement coefficients enables us to derive an equation with a single unknown from the simultaneous equations using univariate polynomial manipulation. An experimental result is presented to illustrate that the encoding time of the proposed algorithm is about 5 seconds on a personal computer with a 400 MHz Pentium II processor.

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.

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).

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.

We propose a new bit timing recovery (BTR) scheme, called perturbed sampling BTR (PSBTR), that can operate near the symbol rate in high-bit-rate wireless systems. A peculiar sample clock, the duty factor of which is not 50%, is used in the PSBTR scheme. We call this type of clock a perturbed sample clock and use it for clock recovery. In PSBTR, there is no cycle slip of the sample clock, and the PSBTR circuit is mostly digital. We examine the performance of the PSBTR scheme under additive white Gaussian noise (AWGN) by computer simulation and experiment, and from these results, clarify the relationship between the performance and circuit parameters of the PSBTR circuit. The overall results indicate that the PSBTR scheme performs well and can be employed as a BTR scheme for high-bit-rate wireless systems.

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.

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.

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 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.

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.

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.

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.

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.

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.

On the reverse (mobile-to-base) link of direct sequence code division multiple access (DS-CDMA) mobile radio, closed-loop fast transmit power control (TPC) must be sufficiently fast to track fast multipath fading. However, in urban areas, the line-of-sight (LOS) path may appear abruptly when a mobile station appears from behind a building and later suddenly the LOS may disappear, resulting in an abrupt path-loss change in the order of 30 to 40 dB. This "on-off" path loss change can be considered as a special case of shadowing. This "on-off" shadowing causes two problems at the base station: generation of severe multiple access interference (MAI) to other users when the LOS path appears and degradation of the quality of its own signal when the LOS path disappears. This paper proposes a new closed-loop fast TPC based on Markov-state transitions (called Markov fast TPC). State transition is determined by the past history of the received binary TPC commands sent from the base station. The TPC step size is associated with each state. By changing the step size between as small as 0.8 dB and as large as 4 dB, the Markov fast TPC can better track "on-off" shadowing as well as multipath fading compared to conventional one-state closed-loop fast TPC. A new SIR estimation method used in TPC command generation is also proposed. The TPC error is evaluated by computer simulation to demonstrate the adaptability of the proposed Markov fast TPC in a Rayleigh fading channel superimposed by "on-off" shadowing.

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.