Quad photoreceivers, namely a 2 x 2 array of p-i-n photodiodes followed by a transimpedance amplifier (TIA) per diode,
are required as the front-end photonic sensors in several applications relying on free-space propagation with position and
direction sensing capability, such as long baseline interferometry, free-space optical communication, and biomedical
imaging. It is desirable to increase the active area of quad photoreceivers (and photodiodes) to enhance the link gain,
and therefore sensitivity, of the system. However, the resulting increase in the photodiode capacitance reduces the
photoreceiver's bandwidth and adds to the excess system noise. As a result, the noise performance of the front-end quad
photoreceiver has a direct impact on the sensitivity of the overall system. One such particularly challenging application
is the space-based detection of gravitational waves by measuring distance at 1064 nm wavelength with ~ 10 pm/√Hz
accuracy over a baseline of millions of kilometers.
We present a 1 mm diameter quad photoreceiver having an equivalent input current noise density of < 1.7 pA/√Hz per
quadrant in 2 MHz to 20 MHz frequency range. This performance is primarily enabled by a rad-hard-by-design dualdepletion
region InGaAs quad photodiode having 2.5 pF capacitance per quadrant. Moreover, the quad photoreceiver
demonstrates a crosstalk of < -45 dB between the neighboring quadrants, which ensures an uncorrected direction sensing
resolution of < 50 nrad. The sources of this primarily capacitive crosstalk are presented.