Downconversion master slave optical coherence tomography for simultaneous en-face imaging at two depths

We report the production of two en-face optical coherence tomography (OCT) images from two different depths in real time, using three interferometers in a configuration of double downconversion master slave OCT. Two active mixers are used to produce the analog product of two photodetection signals. A low-cost digitizer with a sampling rate just at the level of twice the inverse of the tuning interval is used, with a much lower sampling rate than that required by the conventional A-scan-based OCT imaging at the same tuning rate. Not employing a fast digitizer for the photodetected signal, as conventional OCT imaging does, the selection of temporal windows from the photodetected signals is achieved by low-cost RF switches. Optimum conditions for the active mixers and switches employed are evaluated to optimize the downconversion operation.