Analysis of Laser Diodes as Transmitter and Preamplifiers in Time Compression Multiplexing Systems

We propose that a laser diode used as a transmitter in the transmission mode is used as a low bias current preamplifier in the receiving mode for time compression multiplexing (TCM) transmission. By adopting the low bias current approach, the preamplifier is wavelength and polarization independent. The maximum bias current is determined to be about 0.5 It h (Jth = threshold current) by experiments. A transmission experiment at 3.5 Mb/s reveals that about 4 dB of improvement in receiver sensitivity can be obtained by using a laser preamplifier at I = 0.54/th when compared to an unbiased laser. Receiver sensitivity of the proposed configuration (laser preamplifier at low bias current and photodiode) is estimated by considering the laser preamplifier noise and circuit noise. The laser preamplifier noise is calculated by treating the laser as a traveling wave amplifier with highly reflecting facets.