Differential board/backplane optical interconnects for high-speed digital systems. II. Simulation results

For pt.I see ibid., vol.11, no.7, p.1234-49 (1993). The performance of a DC-coupled fully-differential interconnect is analyzed in terms of the deterministic vertical and horizontal eye closure at Gb/s for different optical power levels and extinction ratios in the two complementary arms. Two types of transmitters are investigated, one based on an ideal optical modulator switch (IOMS) and the other based on conventional modulation of two separate lasers. In general, it is found that the timing jitter increases when the imbalance between the power levels in the two arms increases, when the difference between the laser turn-on delay in the two arms increases, and when the receiver and transmitter bandwidth is reduced. To achieve low latency and to accept a maximum power imbalance of 4-5 dB at the receiver, the IOMS and the lasers should be modulated to produce an extinction ratio of at least 10 dB, and the lasers should be biased above threshold. If low latency is not the main concern, an improvement in the maximum tolerable imbalance can be obtained with regular laser modulation by biasing the lasers below threshold. The fitter can be reduced and the maximum tolerable imbalance be increased if faster receivers and transmitters are employed