Optical Delay Line Scanning

The purpose of an optical delay line in OCT is to create a variable distance path for the light in the arm to travel. This allows for light from each coherence-gated region within the sample to be measured independently from the contribution of light from surrounding depths. These systems use optical delas to vary the delay of split ultrashort pulses relative to each other so that their nonlinear response could be measured. By looking at the nonlinearities induced with respect to the pulse delays, one can deduce the length of the original pulse.

OCT delay lines can be characterized by three major criteria-repetition rate, modulation frequencey, and scan depth. In addition, duty cycle, bandwidth support (for Fourier-domain implmentations), and linearity are all major considerations that will affect the difficulty and quality of implementation for the overall system. Two basic techniques, length (time)domain and Fourier (frequency) domain, have been used in implementing optical delay lines.

Grating-based Fourier-domain optical delay.