Twenty-Gbit/s signal transmission using a simple high-sensitivity optical receiver

High-speed optical transmission technologies have rapidly matured at −10 Gbit/s, and now experiments at the several ten gigabit/s level are being carried out using intensity modulation/direct detection schemes. Optical multiplexing is so effective that 100-Gbit/s multiplexing has already been reported by Takada.1 On the other hand, there are many difficulties involved in receiving and demultiplexing such high speed signals. In conventional receivers, high-gain broadband electrical amplifiers which produce no ripples in frequency response are required as shown in Fig. 1 (a). The PIN-photodiode in these receivers is broadband but has poor sensitivity. This problem was overcome by using an optical preamplifier, as shown in Fig. 1(b)1, but broadband amplifiers are still required.