Customized analog circuit design for fiber-based optical coherence microscopy

Optical coherence microscopy (OCM) is an interferometric method for acquiring high-resolution, depth-resolved, en face images. In this article we demonstrate a fiber-based OCM system with analog fringe generation and signal demodulation. A high power operational amplifier drives a mirrored piezoelectric stack mounted in the reference arm of the interferometer causing a displacement equal to 0.42 times the light source center wavelength. The drive signal is synchronized with the demodulation frequency of two analog lock-in amplifiers which extract the first and second harmonics of the interferometric component of the signal. Four outputs (X and Y components of first and second harmonics) are acquired with a data-acquisition board and combined to eliminate the slow phase drift in the interferometer. A sample image of carrot tap root is presented. High dynamic range images are obtained at acquisition speeds up to 40 000 pixelss.