Proceedings of the
9th International Conference of Asian Society for Precision Engineering and Nanotechnology (ASPEN2022)
15 – 18 November 2022, Singapore

High Precision Distance Measurement based on External Cavity with Dual Periodic Grating

Shuhei Goda1, Shuzo Masui3, Shotaro Kadoya2, Masaki Michihata1,a and Satoru Takahashi2

1Department of Precision Engineering, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan

2Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1, Komaba, Meguro-ku, Tokyo, 153-8904, Japan

3Institute of Innovative Research, Tokyo Institute of Technology, 4259, Midori-ku, yokohama kanagawa, 226-8853, Japan


A very high-resolution measurement technique is the one based on the resonance phenomenon. In resonance measurements, the cavity length can be estimated using the resonance wavelength and mode number. The optical resonance phenomenon using an external cavity mechanism laser provides high Q-values and is suitable for high-precision distance measurement systems. For measurements using resonance, the advantages are ease of traceability and lack of influence from phase jumping. For dimensional measurement, the longitudinal mode number is also necessary for the cavity length measurement of the external cavity mechanism. We propose a method to accurately number longitudinal modes of external cavity wavelength-scanning diode lasers (ECDLs) for more accurate distance measurement. A method to find the longitudinal mode number of ECDL much accurately, which uses dual periodic gratings is proposed. Dual periodic gratings can resonate in multiple wavelength bands simultaneously. In this paper, a method to increase the longitudinal mode number difference k by using a dual periodic grating instead of a conventional grating so that the resonance occurs in two distant wavelength bands is proposed. The proposed method is validated by experimentally comparing the estimation dispersion of the longitudinal mode number between the single periodic grating and the dual period grating. Experimental verification shows that the dispersion of the longitudinal mode number estimation is decreased by about 150 times. The estimation dispersion of the longitudinal mode number was achieved to 1. (229 words)

Keywords: External Cavity Diode Laser, Dual periodic grating, Longitudinal mode number, Optical resonance, Dimensional measurement

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