Swept source line or full field oct system with dithered laser injection current to reduce speckle noise and coherence repeats

Abstract

A swept‑source line‑field Optical Coherence Tomography (OCT) system that reduces speckle noise and coherence repeats by dithering the injection current of a semiconductor gain chip in an external‑cavity tunable laser. The laser incorporates a tunable interference filter whose passband admits a small number of longitudinal modes. High‑frequency current modulation perturbs the refractive index and feedback phase of the gain chip, producing rapid optical‑phase fluctuations and fast selection or hopping among modes admitted by the passband during each line‑field exposure. When the dither frequency is on the order of or higher than the line‑field sensor rate, the detector time‑averages multiple speckle realizations within a single exposure, thereby lowering speckle contrast and reducing coherence‑repeat artifacts. The approach enhances image quality in medical diagnostics and industrial non‑destructive testing without post‑processing.

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