Using light-beam scanning technology based on a potassium tantalate niobate (KTa_1-xNb_xO₃, KTN) single crystal, we constructed a wavelength-swept light source for industrial applications. The KTN crystal is placed in an external cavity as an electro-optic deflector for wavelength scanning without any mechanical operation. Cavity arrangement and mechanism elements are specially designed for long-term stability and environmental robustness. In addition, we updated the handling of the KTN crystal. We used a pair of thermistors for accurate temperature monitoring, and weakly irradiated the crystal with a 405-nm light during operation to achieve drift suppression. We selected a moderate repetition rate of 20 kHz to suit the practical application. The output of the light source was 6.2 mW in average power, 1314.5 nm in central wavelength, and 83.3 nm in bandwidth. The interference fringes of the light enable us to specify the thickness of a wafer sample by the peak positions of the point spread functions. We measured the thickness of a silicon wafer as 3651 μm in the optical path length using a reference quartz plate. The distribution of the obtained values is about 0.1 μm (standard deviation). We experimentally confirmed that this property persists continuously at least over 153 days. Our light source has a remarkable feature: extremely low timing jitter of the sweep. Thus, we can easily reduce the noise level by averaging several fringes, if necessary.

Date Published: 20 February 2017
PDF: 12 pages
Proc. SPIE 10110, Photonic Instrumentation Engineering IV, 101100Q (20 February 2017); doi: 10.1117/12.2250229

Published in SPIE Proceedings Vol. 10110:
Photonic Instrumentation Engineering IV
Yakov G. Soskind; Craig Olson, Editor(s)