A low-cost customized analog circuit design for optical coherence microscopy

Optical Coherence Microscopy (OCM) enables the acquisition of high resolution, en face images. Most current OCM systems are based on slow analog or high speed digital demodulation schemes. In this paper we demonstrate a low-cost, high speed analog fringe generation and demodulation method. A high power operational amplifier drives a mirrored piezoelectric stack mounted in the reference arm of the interferometer. The drive signal is synchronized with the demodulation frequency of two analog lock-in amplifiers, which extract the first and second harmonic power of the coherence fringes. Tenth order Bessel low-pass filters (LPFs) allow fast system response and reduce carrier frequency noise. Four outputs (X and Y components of first and second harmonic) are acquired with a low-cost data acquisition board and combined to eliminate the slow phase drift in the interferometer. C# software processes and displays the image, and performs automatic interferometer pathlength matching and adjustment. We present images of Arabidopsis leaf in situ, sections of carrot, and ex vivo rat ovary. Excellent image quality is achieved at acquisition speeds up to 40,000 samples/second.