Avalanche photodiode based optical coherence tomography

Optical Coherence Tomography (OCT) is used to perform in vivo high-resolution imaging of biological tissue microstructures. In the present study, we evaluate the optimum conditions to use Avalanche photodiodes (APDs) in OCT to achieve maximum signal-to-noise (S/N) ratios. The optical sources employed in OCT have a large bandwidth. Due to beating within the source line-width, excess photon noise (EPN) is generated in addition to shot noise (SN). Usually, high speed OCT requires large optical power, which makes the EPN to dominate over the SN. Therefore, balanced detection is used to reduce the EPN. We analyse the optimisation of the OCT configuration with respect to the APD noise performance. When using APDs, another parameter has to be considered in the S/N analysis: that of the voltage across the APDs, which determines, both, the gain and the noise.