High-speed KTN optical beam deflector for swept-source optical coherence tomography

We have developed an electro-optic (EO) optical beam deflector using KTa_1-xNb_xO₃ (KTN) crystal. The combination of the huge second order EO (Kerr) effect of KTN crystal and control of the electron injection into the crystal makes the deflection angle appreciable. We describe the operation principle for this fast and large angle deflection. We also describe the packaging of the KTN deflector and beam shaping lenses at the high-frequency deflection. We built swept light sources equipped with a KTN deflector for optical coherence tomography (OCT). With OCT, an imaging technique using laser interferometry, it is possible to obtain depth-resolved information about biological tissue with micrometer-scale spatial resolution. A 200-kHz scan rate was obtained with a 20-mW average output power at a scan range exceeding 100 nm. The coherence length measured by using the relative signal decay from a different path delay is 7 mm. We obtained OCT images of biological tissue using our swept light source OCT system.