Electro-Optic Deflector Based on KTN Crystal for Phase-Stable Swept Light Source for OCT

We have developed a wavelength-swept laser source with ultrahigh phase stability. A potassium tantalate niobate (KTa(1-x)NbxO(3), KTN) single crystal was employed as an electro-optic deflector for a high-speed wavelength sweep in the laser cavity. The device structure and performance of a KTN deflector is described. The device includes the beam-shaping optics, which can enhance the resolution of a KTN deflector. A 200-kHz sweep rate was obtained with an average output power of 20 mW and a coherence length of 8 mm for a wavelength range exceeding 100 nm. We demonstrated a swept source with ultrahigh phase stability in the 1.3 mu m wavelength range as a result of the low-jitter operation of the deflector. The standard deviation of timing jitters measured between adjacent A-lines was confirmed to be less than 78 ps, which corresponds to a phase difference of 0.017 radians at a Michelson interferometer path difference of 1.5 mm. In addition to realizing the phase stability of neighboring A-lines, a long-term stable sweep was demonstrated by eliminating the refresh operation that was previously needed to prevent output power decay.