Optimum design of spectrometer in FD-OCT

Abstract

Fourier-domain optical coherence tomography (FDOCT) has attained popularity due to its static parts, high imaging speed[1], and high sensitivity[2]. FDOCT makes use of spectral interferometry and collects data in the spectral domain, either using a spectrometer with a detector array or by a single point detector with a wavelength-swept light source[3]. The axial resolution depends on the bandwidth of the spectrum. The spectral response of the spectrometer is always desired to be flat in order to have the best axial resolution corresponding to the light source spectrum. Unfortunately, the optics consisting of the spectrometer usually shape the spectrum. The optimum optics design and alignment will minimize the spectral shaping. The frequency response simulation by advanced optical design software displays a clear picture for our design and system alignment. The axial imaging range of FDOCT according to the Fourier transform relationship is ultimately limited by a fringe visibility degrading curve with increasing imaging depth due to the spectral sampling spacing called the fall-off [4]. This limitation is significant for applications of spectrometer-based FDOCT where a long imaging range is desirable (e.g the anterior segment of the eye), especially when imaging uses 1.3 mm light because large pixel-count arrays are not currently commercially available. Although resolving complex-conjugate ambiguity[5] and Sub-pixel shifting[6] have extended the image range, the imaging range of FDOCT is still limited by the fall-off, which is a primary concern in the design of a spectrometer-based FDOCT system. A mathematical model of spectrometer-based FDOCT can aid in understanding of signal formation, including fall-off [ref OL].