Balanced homodyne detection circuit design analysis for high gain and low noise performance

The study, generation, and application of squeezed states of light has been a widely researched area in quantum optics. Vacuum fluctuations or photon shot noise quantified in terms of quadrature operators, impose a quantum limit on the sensitivity of quantum sensing and quantum communication systems. Thus, squeezing the quadratures reduces the quantum uncertainty in a particular quadrature. The amount of squeezing is, however, highly limited by the optics in the experiments and the performance of the balanced homodyne detection (BHD) systems employed for the detection of the squeezed states of light. In this paper, we have analytically studied the steady state, transient and noise responses of the balanced homodyne detection (BHD) circuitry by comparing two configurations i.e., a variable gain circuit with a differential amplifier and a current subtracting circuit with differential fine-tuning circuit (DFTC) and an adjustable bias (ABV). The current subtracting circuit design with DFTC and ABV has been adopted from Xiaoli et al. [1] in order to compensate for any differences in the photodiode performance characteristics in the two arms. A variable gain configuration is used to compensate for the unequal beam splitter ratio and uneven optical powers in the two arms. In order to further improve the noise performance of the system, a differential amplifier is used in the output of the variable gain configuration. A high transimpedance gain (~>70 dB) and a low noise (~<500nV/ √ Hz) performance can be achieved using these circuits as per our analysis.