Advantage of low NEP balanced receivers in swept source OCT

Low NEP balanced receivers generally do not result in better sensitivity in a shot-noise-limited swept source OCT system. However, there is an advantage if RIN is significant. A lower NEP, even in the shot-noise-limited case, does allow for lower reference arm powers. This, in turn, reduces fixed pattern artifact signals caused by stray optical component reflections inside a swept source laser cavity. An NEP reduction of √10 allows the reference power to be reduced 10 dB while maintaining SNR. This reduces the pattern to noise ratio by 10 dB because pattern noise is directly detected (20 dB scaling per decade reference power), whereas the image signal is heterodyne detected (10 dB scaling per decade of reference power). We present sensitivity and fixed pattern measurements taken with six commercial balanced receivers, including an APD receiver. We also present an NEP survey of 23 commercial receivers over a wide range of bandwidths and transimpedances.