Optical Doppler coherence tomography based on a field-programmable gate array

Abstract

We report the design of and results obtained by using a Field Programmable Gate Array (FPGA) to digitally process Optical Doppler Tomography signals. The processor fits into the analog signal path in an existing OCT setup. We demonstrate both Doppler frequency and envelope extraction using the Hilbert transform, all in a single FPGA. An FPGA implementation has certain advantages over a general purpose Digital Signal Processor (DSP) due to the fact that the processing elements operate in parallel as opposed to the DSP, which is primarily a sequential processor. In this paper, we demonstrate that the use of a FPGA enables sampling rates exceeding DSP-based solutions. In addition, this implementation has the important feature that calculation of the phase in addition to the amplitude of the interference fringe pattern only requires few additional resources. The proposed implementation of Doppler frequency extraction in a single FPGA is feasible for real-time Doppler OCT applications requiring high signal sampling rates.