Submicrosecond speed optical coherence tomography system design and analysis using acousto-optics

Abstract

We introduce a novel high speed no moving parts optical coherence tomography (OCT) system that acquires sample data at less than a microsecond/data point sampling rate. The basic principle of the proposed OCT system relies on using an acousto-optic deflector (AOD). This OCT system has the attractive features of an acousto-optic scanning heterodyne interferometer coupled with an acousto-optic variable optical delay line (ODL) operating in a reflective mode. Fundamentally, OCT systems use a broadband light source for high axial resolution inside the sample or living tissue under examination. Inherently, acousto-optic (AO) devices are Bragg-mode wavelength sensitive elements. In this paper, we identify that Bragg cell generated two beams naturally have an unbalanced and orthogonal spectrum with respect to each other. This mismatch in spectrums in turn violates the ideal auto-correlation condition for a high signal-to-noise ratio broadband interferometric sensor such as OCT. We solve this fundamental limitation of Bragg cell use for OCT by deploying a new interferometric architecture where the two interfering beams have the same power spectral profile over the bandwidth of the broadband source. With the proposed acousto-optic based system, high (e.g., MHz) intermediate frequency can be generated for low 1/f noise heterodyne detection. System issues such as resolution, number of axial scans, and delay-path selection time are addressed. Experiments described demonstrate our high speed acousto-optically tuned OCT system where optical delay lines can be selected at sub-microsecond speeds.