Tomoyuki Ohtsuka

Smart optical receiver with automatic decision threshold setting and retiming phase alignment

The requirements for a smart optical receiver are discussed, and a design architecture suitable for introducing ICs based on automatic decision threshold setting and retiming phase alignment using digital/analog signal processing feedback is proposed. With the proposed architecture, the decision threshold level and the retiming clock phase of received data in the decision circuit are automatically adjusted to the optimum position. This obviates the need for decision threshold level and retiming clock phase adjustments in production testing, and it reduces the power penalty (receiver sensitivity degradation) on the received optical waveform variation. The power penalty caused by temperature and supply-voltage variations and aging in installation is also reduced. The performance of the proposed architecture is estimated; the power penalty as compared with the manual optimum adjustment is less than 0.4 dB, and the robustness to avalanche photodiode multiplication factor variations and crosstalk are improved. >

Digital optical CATV system using hubbed distribution architecture

A hubbed distribution architecture based on a bus-star configuration, three-level single single-mode fiber transmission using M-TPC line code, and high-speed IC technology is proposed. The architecture is cost-effective and compact. It is well suited to metropolitan area CATV systems and would allow a gradual transition to a broadband ISDN (integrated-services digital network) subscriber loop in the future. The proposed architecture is applied to a digital optical CATV system prototype. The equipment making up this system consists of a transmitter, hubs including video selectors, and subscriber unit. Two video channels are selected for each subscriber from eight video channels at hub stations. The transmission speed is 900 Mb/s, three-level for the trunk line and 200 Mb/s, three-level for each subscriber loop. Very compact and low-cost equipment is realized by using recently developed high-speed ICs. Experimental results show that the system satisfies requirements and that its commercial application is feasible. >

3-Gbit/s, 16-channel GaAs multiplexer and demultiplexer LSIs

A 16-channel multiplexer and demultiplexer LSI chip set has been designed, fabricated, and tested. A maximum operating speed of 3 Gb/s and a low power consumption of 2.0 W were realized. Using these ICs, the required mounting space was reduced by 1/70 and power consumption to 1/5 that of conventional discrete medium-scale integrated circuits. A high transconductance was obtained by using 1- mu m-long tungsten-silicide gate MESFETs. The transconductance was 270 mS/mm for a threshold voltage of -0.20 V at a gate bias of 0.6 V, and 230 mS/mm for a threshold voltage of -0.70 V at a gate bias of 0 V. A 5-20- mu m logic gate width was adopted to obtain wideband operation and lower power consumption. These optimizations were performed by computer simulation using the modified SPICE model.<<ETX>>

Gigabit transmitter/receiver GaAs IC chip set for optical communications

The authors discuss gigabit transmitter/receiver GaAs ICs for optical communications, focusing on their circuit design architecture and performance. The key technologies for the gigabit transmitter/receiver ICs are discussed and a design architecture for them based on these key technologies is proposed. This architecture is applied to fabricate transmitter/receiver ICs (high-sensitivity preamplifier IC and high-power laser diode driver IC) using a high-transconductance MESFET process. These GaAs ICs have been successfully applied to a 2.4-Gb/s transmitter receiver, which has demonstrated good performance with a minimum average received optical power -31.8 dBm.<<ETX>>

32-channel digital optical CATV distribution system

The authors discuss a digital optical CATV system with increased channels, focusing on its network configuration, WDM and TDM (wavelength and time division multiplexing) schemes, and its application to a 32-channel CATV distribution system. The key technologies for low-cost increased-channel CATV are discussed, and the economical number of TDM channels and the required interchannel isolation in the WDM demultiplexer are clarified. Bit-synchronized compensation for the propagation delay differences in WDM is proposed, as is a new multiplexing scheme suitable for low-power, compact TDM equipment. A compact 32-channel TDM and WDM video distribution system was designed based on a bus-star configuration and newly developed high-speed LSI technology. The transmission characteristics of the transmitter/receiver equipment developed for feeder loops were found to be good, and experimental results show that the proposed design with its versatile hardware will be a powerful tool for a low-cost multichannel digital optical CATV system.<<ETX>>