Proposed photonic integrated circuits, as introduced above, can benefit in many instances from the inclusion of an optical amplifier to compensate for coupling, splitting, and absorption losses. Efforts at NTT, Hitachi, Oki, and NEC aim to develop viable amplifier elements, presumably for use in PICs, such as integrated receivers and switches. Some of the recent efforts have focused on techniques to provide reasonable gains with polarization independence (Magari et al. 1994; Kitamura, Komatsu, and Kitamura 1994). In theory, use of integrated semiconductor preamps as receiver front ends can provide receiver sensitivities close to the quantum limit. The use of optical amplifiers in semiconductor switches promises to provide low loss (or even gain) and very good on/off ratios. Such switches are particularly attractive, since most semiconductor switches incorporate a significant amount of loss and have marginal on/off or crosstalk levels. Lossless switches may be scaleable to larger sizes. Recent work at Hitachi has demonstrated lossless switching in a 4 x 4 crossbar configuration (Kirihara et al. 1994).
Although there is work at AT&T and Bellcore in the United States, it appears that the Japanese efforts are somewhat more serious and clearly more widespread. Thus, the JTEC panel estimates that the Japanese are slightly ahead of the United States in these areas.