Real-time digital design for an optical coherence tomography acquisition and processing system

We present a real-time, multi-dimensional, digital, optical coherence tomography (OCT) acquisition and imaging system. The system consists of conventional OCT optics, a rapid scanning optical delay (RSOD) line to support fast data acquisition rates, and a high-speed A/D converter for sampling the interference waveforms. A 1M-gate Virtex-II field programmable gate array (FPGA) is designed to perform digital down conversion. This is analogous to demodulating and low-pass filtering the continuous time signal. The system creates in-phase and quadrature-phase components using a tunable quadrature mixer. Multistage polyphase finite impulse response (FIR) filtering and down sampling is used to remove unneeded high frequencies. A floating-point digital signal processor (DSP) computes the magnitude and phase shifts. The data is read by a host machine and displayed on screen at real-time rates commensurate with the data acquisition rate. This system offers flexible acquisition and processing parameters for a wide range of multi-dimensional optical microscopy techniques.