Low-noise large-area photoreceivers with low capacitance photodiodes

[0026]The present invention is directed to a quad photoreceiver based on low-capacitance quad photodiodes each followed by a transimpedance amplifier. In one embodiment of the present invention, there is provided a 1-mm-diameter InGaAs quad photodiode having 2.5-pF capacitance per quadrant. In conjunction with low-noise field effect transistor (FET)-input operational amplifiers, the associated low-capacitance quad photodiodes are each designed to provide a quad photoreceiver having an equivalent input current noise density of less than 3.2 pA / √Hz per quadrant up to a 3-dB bandwidth of ˜20 MHz. This constitutes up to ˜17-dB improvement in sensitivity over a quad photodiode having 20-pF capacitance per quadrant.

[0027]Referring to FIG. 1, a schematic block diagram of a quad photoreceiver 10 is shown for one embodiment of the present invention. The quad photoreceiver 10 includes four quadrants or sections 12, 14, 16, and 18 each having a photodiode 50 followed by a transimpedance amplifi