Narimichi Maeda

High-performance compact optical WDM transceiver module for passive double star subscriber systems

High-performance transceiver-type optical WDM interface modules with a volume of only 36 cc have been developed for PDS subscriber systems. The new module comprises an optical WDM sub-module, hybrid-integrated transmitter and receiver circuits. In the WDM sub-module, a planar lightwave circuit chip was hermetically sealed together with laser and photodiode chips in order to minimize the size of the transceiver module. The lightwave circuit was formed on an optical-waveguide chip by adopting a high-silica based optical-waveguide technology. The circuit has a 3-dB directional coupler for bi-directional transmission with a 1.3-/spl mu/m wavelength through a single fiber and a wavelength division multiplexer between both 1.3-/spl mu/m and 1.55-/spl mu/m wavelengths. The overall characteristics of the fabricated WDM sub-module achieved were a responsitivity of 0.25/spl plusmn/0.05 A/W, an insertion loss approximately 3 dB at 1.55 /spl mu/m and an isolation of 35 dB between both wavelengths. Optical output power of the fabricated transceiver module was -3.8 dBm. Also, receiver sensitivity of less than -35 dBm with an overload of over -14 dBm were obtained by introducing high-speed automatic gain and threshold control techniques. Thus, an allowable span loss of over 30 dB and an optical dynamic range of over 20 dB were attained. The preamble bit length required to reach stable receiver operation was confirmed to be within three bits. >

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.

Inductorless variable equalizers using feedback and feedforward

Inductorless variable equalizers using networks with feedback and feedforward are investigated. They comprise two shaping networks, two adders, and a single variable gain element. They work over a full variation range and the variable element can share a common grounded terminal. The design of the variable characteristics is quite straightforward compared with conventional types. Equalization errors caused by component imperfection in this type of variable equalizer are analyzed and compensation methods for these errors are investigated. Some practical examples are given that prove the efficiency of the error compensation and the feasibility of this type of variable equalizer. Variable equalizers with high-input and low-output impedances using three or four transistors are illustrated. Owing to their simple structures and weak feedback and feedforward, they can be used in video or higher frequency bands. Experiments using transistors with an f_{\tau} of I GHz were performed over a ± 7-dB variation range and a bandwidth of 20 MHz.

A single-chip three-level regenerator IC for high-speed optical transmission systems applying duo-binary coding schemes

A three-level regenerator IC operating at 160 Mbit/s or more has been developed for high-speed optical transmission systems, such as local area network and computer links. It was a modified duo-binary class-II coding scheme and provides good performance for long-period pattern transients. Two decision circuits and a nonlinear timing extraction circuit consisting of 430 transistors and resistors are monolithically integrated on a single 2.5/spl times/2.5-mm/SUP 2/ chip using 3-/spl mu/m Si bipolar IC technology. The ICs are primarily designed for a 160-Mbit/s transmission bit rate, with a 1.2-1/24 mark ratio, a 5 V/spl plusmn/10% supply voltage, and 0-70/spl deg/C temperature range. The following characteristics are achieved: 5 mV decision sensitivity, +9.8/-7.8/spl deg/ static pattern jitter, /spl plusmn/7/spl deg/ timing phase shift, transition time of 0.95 ns, and power dissipation of less than 470 mW.

Master-slice monolithic integration design and characteristics of LD/LED transmitters for 100-400 mbit/s optical transmission systems

Monolithic integration of LD and LED transmitters operating at 100-400 Mbit/s is investigated using a 3-μm Si-bipolar process as a first step in the establishment of a master-slice IC technology for optical communication systems. An LD transmitter IC is developed as a master IC, which includes a differential current switch and an input buffer circuit for high-speed modulation and a current stabilizer and an APC circuit for the stabilization of the output optical power, An LED transmitter is fabricated by the minor change of wiring of the master IC. The former exhibits 0.5-ns rise and 0.7-ns fall times at the signal current of 40 mA. Also the latter exhibits 0.4-ns rise and 0.6-ns fall times at the signal current of 100 mA. Characteristics of LD and LED transmitters are estimated in order to prove the usefulness of the fabricated ICs. As a result, it is confirmed that both transmitters using the fabricated ICs operate at the modulation speed of 300-400 Mbit/s and output optical power fluctuations of less than ±0.5 dB over the ranges of 5V ±5 percent supply voltage and 0-50°C temperature. From these results, it is proven that the master-slice monolithic integration is feasible and will be very useful for reduction of the turn-around time in IC development.