Fig. 3.

Finding an optimal displacement range for minimizing speckle while preserving target resolution. (a), OCT enface projection of a 1951 USAF resolution test target. The red dashed line indicates the location of OCT B-scans for panels (b) and (c)). (b), OCT B-scan obtained by averaging 100-frames when the DM was set to ‘flat’ mode (red dashed rectangle: region used for speckle contrast quantification; inset: enface projection). (c), APM-OCT B-scan obtained by averaging 100-frames when the facets of the DM were randomly modulated with a uniform distribution having a displacement range of 0.3 μm (0 ± 0.15 μm) (inset: enface projection). Note that the second layer of the target became visible (red arrows, right inset shows side view cross section obtained with a fiber microscope). (d), Speckle contrast as a function of the number of B-scans averaged for different random mirror displacement ranges; the color bar specifies the displacement range. (e), Speckle contrast as function of mirror displacement range replotted from (d) N = 20 and N = 100 (the black and cyan arrows in (d) identify the curves from the points were extracted). Note that NSC declines rapidly towards its asymptote over the same displacement range for N = 20 and N = 100. The target resolution (red curve) was obtained from N = 20 for efficiency, since each of the points on the curve required acquisition and processing of an ensemble of N OCT volumes.