4-bit multiplexer/demultiplexer chip set for 40-Gbit/s optical communication systems

We have designed and fabricated a low-power 4:1 multiplexer (MUX), a 1:4 demultiplexer (DEMUX), and a 1:4 DEMUX with a clock and data recovery (CDR) circuit using undoped-emitter InP/InGaAs heterojunction bipolar transistors (HBTs). Our HBTs exhibit an f_T of about 150 GHz and an f_max of about 200 GHz at a collector current density of 50 kA/μm² and a collector-to-emitter voltage of 1.2 V. Error-free operations at bit rates of up to 50 Gbit/s have been confirmed for the 4:1 MUX and 1:4 DEMUX, which dissipate 2.5 W and 2.6 W, respectively. In addition, 40-Gbit/s error-free operation for the full clock rate 1:4 DEMUX with the CDR has been achieved for the first time.