Yoshitaka Takasaki

Optical Pulse Formats for Fiber Optic Digital Communications

Some new optical pulse formats are investigated for solving practical problems in fiber optic communication systems. These pulse formats provide many advantageous features such as error monitoring capability, abundant timing information, uniform optical power utilization, stable detection of optical input, and so forth. It is shown that a modification of Personicks receiver design theory can be used for comparison of various optical pulse formats. The comparison suggests that for state-of-the-art fiber systems with moderate fiber loss and moderate repeater spacing, where no pulse equalization is required, some new classes of 1 binary digit converted to 2 binary digits (1B2B) or 2B3B formats will permit the realization of very simple and reliable repeaters for fiber optic digital transmission. A future low-loss fiber system may permit a very long repeater spacing with the help of equalization. In this case, application of the correlative signal-processing technique is shown to be very promising. Experimental 6.3 Mbit/s and 100 Mbit/s transmissions demonstrate some advantageous features of these optical pulse formats.

Timing Extraction in Baseband Pulse Transmission

Timing extraction through nonlinearity in the presence of pulse overlaps is studied for baseband PCM or PAM systems. It is shown that the systematic jitter can be reduced by proper choices of nonlinearity, coding scheme, and pulse waveform. Discussions on choice of nonlinearity indicate that square-law rectification is desirable for elimination of jitter sources. This nonlinearity derives a frequency-domain expression for amplitude and phase of the timing wave that separates the effects of pulse pattern and pulse shapes and provides insight to their contributions to timing jitter. Proper choices of coding scheme and pulse waveform reduce amplitude and phase variation in the timing wave. For example, an optimum prefiltering (or correlative coding) reduces amplitude variation to one eighth for bipolar sequence. In the case of symmetrical reshaping by a Bessel (flat delay) filter, the maximum jitter exceeds 20 degrees if the order of a filter is less than ten. An asymmetrical reshaping makes the maximum jitter less than four degrees for the same order of filter. Some features of nonlinearities that approximate square-law rectification are discussed.

Multipled block codes for all-optical transports

Multipled block codes (MBCs) for all-optical transport are investigated. Each block of the MBC comprises N subblocks, each n bits in length. A feature of the MBC family is that the clock component can be recovered through logical processing. First, coding efficiency is studied to show that choosing n=2N results in the maximum efficiency. Next, the jitter problem due to deviations in processing delays is investigated. Recovery of the clock component by the combined use of delay-and-multiply and delay-and-add logical processing is investigated. Numerical and simulation results show that the former causes no jitter when the pulse duty is chosen adequately, and only minor jitter is generated due to the latter. Applications of this type of line code to various systems such as trunk lines, cross connects, interconnects and local area networks (LANs) are discussed. Transmission frame processing suitable for photonic implementation is investigated. It is also shown that the applications of this type of line code to superbroadband cross connects, interconnects, and LANs are promising owing to simple clock recovery and frame processing capabilities. >

Upgrading strategies for B-ISDN subscriber loops

Upgrading strategies for broadband-ISDN subscriber loops are investigated. A five-step process for optimizing phase-by-phase system upgrading from existing narrowband ISDN to future superbroadband ISDN is developed. The process is designed to be as simple as possible and to include as many environmental conditions, such as network models, subscriber capacities and associated penetrations, and cost trends for system components, as possible. A typical example is given to show the efficacy of the optimization process. It is shown that more general aspects of system upgrading can be extrapolated from the representative examples given. >

A variable transimpedance preamplifier for use in wide dynamic range optical receivers

A preamplifier with an automatic gain control (AGC) function based on a new circuit configuration suitable for monolithic integration is proposed as an approach for realizing optical receivers with wide dynamic ranges. This new preamplifier, intended for transmission systems operating above 100 Mb/s, is designed for fabrication using 3-/spl mu/m Si-bipolar IC technology. The fabricated IC exhibits a bandwidth of more than 220 MHz and an equivalent input noise current of about 3 pA//spl radic/Hz at a maximum transimpedance of 18 k/spl Omega/. To examine the AGC capability of the new preamplifier IC, a 140-Mb/s transmission experiment was carried out using a laser diode (LD) transmitter and a p-i-n receiver with its gain controlled by the new preamplifier. An optical dynamic range of 21.5 dB was achieved and thus it should be possible to realize optical receivers with wide dynamic ranges using this preamplifier.

Invited paper Two-level AMI line coding family for optical fibre systems

Abstract Conditions that must be satisfied in the design of line coding have been considered. It is shown that a two-level AMI family is promising for satisfying these conditions. Details regarding the two-level AMI family were investigated and an attempt was made to demonstrate how the members of the family could be applied efficiently under loss-limited, as well as band-limited, conditions. A zero substitution scheme is presented that has been developed to overcome timing extraction problems in a correlative two-level AMI system devised for use under band-limited circumstances. Finally, the potential of optical fibre systems will be discussed, establishing a new communications concept for the coming fibre optic age. An example of line coding that can adapt an arbitrary signal clock rate to a given line rate is demonstrated to illustrate the promising features of such a new concept.

Optimizing Optical Transmitters and Receivers for Transmitting Multichannel Video Signals Using Laser Diodes

Analog transmission using laser diodes is quite attractive for transmitting multiplexed video signals, owing to the wide modulation bandwidth of laser diodes. Optimizations for transmitting color-TV signals (7 channel frequency division multiplexed) in the VHF band using buried heterostructure laser diodes are investigated. The major transmission objectives are a carrier to noise ratio of larger than 48 dB and intermodulation products of less than -55 dB. Design curves for minimizing distortion at the transmitter are demonstrated. A modulation index of 70 percent is shown to be capable of attaining the objective. Both the avalanche photodiode (APD) and the pinphotodiode (PD) are considered for use in the receiving amplifier. Minimum receiving power of -11 dBm obtained with the PD receiver is in good agreement with theoretical values. Deterioration of signal to noise ratio due to fiber guided transmissions is also reviewed in comparison with aerial transmissions.

Optimizing Pulse Shaping for Baseband Digital Transmission with Self-Bit Synchronization

An effort is made to devise pulse shaping methods for self-bit-synchronizing systems that minimize both intersymbol interference and pattern-dependent jitter. Attention is confined to minimum-phase shaping which is considered from the standpoint of baseband applications. A short review of jitter analyses is also provided. It lays stress on discerning jitter components that accumulate along repeater chains from those that do not. Pulse shaping functions for the signal path, i.e., Nyquists problem under minimum-phase constraint, are investigated first and found to result in Bessel filtering as well as its steepest descent modifications. It is observed that reducing intersymbol interference leads to increased pattern-dependent jitter. Next, pulse shaping functions for the timing path are developed. A broad sense symmetrical waveform concept produces a method of synthesizing shaping networks that can drastically reduce waveform dependent jitter, at the sacrifice of increased intersymbol interference. Finally, simultaneous minimizations of intersymbol interference and timing jitter are attempted. A minimal oscillatory tail shaping method incorporating a predistortion technique is shown to be quite efficient for this purpose and thus attractive for simple implementations.

New Fiber Optic Analog Baseband Transmission Plan for Color TV Signals

A new fiber optic baseband analog transmission plan is proposed. It arranges the original signal into a pulse train for driving the laser diode to generate baseband components at the transmitter. The receiver can be just the same as those used in conventional direct linear intensity modulation systems using light emitting diodes (LED). Advantages of this new plan are (i) potentially cheap fibers can be used, since the plan requires neither an extra wide bandwidth nor special light acceptance conditions, (ii) long repeater spacings can be attained, since abundant light can be coupled into fibers using laser diodes and also the simple structures required for fibers are suitable for realizing low transmission losses, and (iii) the transmitter and receiver can be quite simple. Some candidate pulse arranging plans for generating baseband components are investigated. A pulse frequency arranging plan and pulse width arranging plan seem to be promising for efficient picture transmissions. An experiment using pulse frequency arrangement proves the theory developed here to attain a color TV transmission using a 10 km long step index low-loss fiber for a signal to noise ratio of 44 dB. Future improvements are expected by redesigning the transmitter and receiver and also by improving the mode stability of laser diodes.

Upgrading strategies for B-ISDN architectures and services

Upgrading strategies for new broadband services that take advantage of B-ISDN architectures are investigated for the time frame of ATM applications. A new concept of super-multimedia services is introduced, which makes efficient use of super-multichannel and super-high-definition features of future broadband services keeping compatibilities with existing services. After defining super-multimedia services, upgradable B-ISDN architectures are discussed for accommodating such new broadband services. Then three phase upgrading of super-multimedia services that is suitable for B-ISDN architectures is investigated. Finally, an example of upgrading strategy that incorporate multi-window type terminals is shown to exhibit good compatibility with existing broadband services and also to adapt the recent trend of service personalization. The possibility of providing super-multimedia services at almost the same cost as existing standard TV services is also discussed.<<ETX>>