Distributed balanced photodetectors for broad-band noise suppression

A novel velocity-matched distributed balanced photodetector with a 50-Ohm coplanar waveguide output transmission line has been experimentally demonstrated in the InP/InGaAs material system. Distributed absorption and velocity matching are employed to increase the saturation photocurrent. A common-mode rejection ratio greater than 27 dB has been achieved. The radio-frequency (RF) link experiment conducted at 4.16 GHz shows that the relative intensity noise of the laser has been suppressed by more than 24 dB and shot-noise limited performance has been achieved. Significant improvement of signal-to-noise ratio has been observed over a wide range of frequencies and phase mismatch of input RF signals.