Low-Noise, Large-Area Quad Photoreceivers Based on Low-Capacitance Quad Photodiodes

The Laser Interferometry Space Antenna’s (LISAs) scientific mission to detect gravity waves demands stringent noise limits on the system components, especially the large-area quad photoreceiver front end, for ultra-high-precision (≈10 pm/Hz1/2) distance measurements. The optical LO (local oscillator) power on LISA is limited to 100 μW to keep power dissipation and thermal fluctuation low on the optical bench. Consequently, a large-area quad photoreceiver having an equivalent input current noise of the order of 1 pm/Hz1/2 is needed. Additionally, the quad photoreceiver must demonstrate low crosstalk between individual quadrants to allow accurate direction sensing of the incoming optical beam. This performance must be achieved over a bandwidth of 2 to 20 MHz to meet LISA’s requirements. Commercially available quad photodetectors do not have the combination of large area, low capacitance (and therefore low noise), and low crosstalk, which is critical for LISA’s scientific objectives.