Abstract

The protocol transparency provided by WDM and WDMA systems has the advantage of allowing network interfaces (use different protocols at different bit rates) attached to the same network. For optimized performance, the receiver has to be able to adjust to the bit rates dictated by the transmitter. A 20-channel WDM system with quasi-protocol-transparency has been commercialized recently,¹ as each line card of the system is prescribed for a specific protocol at a fixed bit rate. A receiver that is optimized for a specific bit rate can only achieve suboptimal sensitivity at lower bit rates due to excessive thermal noise allowed by the bandwidth of the receiver. Therefore, a receiver optimized for a range of bit rates is desirable for full protocol transparent operations. In order for a receiver to be optimally configured for a range of bit rates, the transimpedance of the preamplifier needs to be tunable. We propose in Ref. 2 to achieve the variable bit-rate capability by tuning the gate voltage of a microFET used as an active feedback resistor in the transimpedance amplifier. Transimpedance amplifiers using active feedback resistor have been described previously, for example, in Ref. 3. Because of their small parasitic capacitance, active feedback resistors can achieve wideband nonintegrating response and stability against ringing and oscillation. Here, we report the characteristics of a receiver whose performance can be optimized for bit rates ranging from 300 to 1,500 Mbps. The receiver is part of an eight-chamel receiver array. The other seven receivers use passive feedback resistors in the transimpedance amplifiers.

© 1996 Optical Society of America