Photodiode working in zero-mode: detecting light power change with DC rejection and AC amplification

We propose a new mode of operation when using a photodiode to extract a variable optical signal from a constant (ambient) background. The basic idea of this 'zero-mode' of operation is to force the photodiode to operate at either zero current or zero voltage. We present possible implementations of this novel approach and provide the corresponding equivalent circuits while also demonstrating experimentally its performance. The gain and bandwidth of the zero-mode photodetector are measured and simulated, and they show highly agreement. The gain compression effect because of the nonlinearity of the forward bias region is also explored. Comparing to the conventional photoconductive photodetector, the zero-mode photodetector is able to obtain higher AC gain and lower noise. With the same component used in the circuit, the measured input referred root mean square noise of zero-mode photodetector is 4.4mV whereas that of the photoconductive mode photodetector is 96.9mV respectively, showing the feasibility of the zero-mode of operation for measuring the small variable light signal under a high power constant background light.