Adrian DOBROIU^*, Manabu SATO and Naohiro TANNO^†

Graduate Program of Human Sensing and Functional Sensor Engineering, Graduate School of Science and Engineering, Yamagata University, 4-3-16 Johnan, Yonezawa 992-8510, Japan

(Received May 2, 2003; Accepted June 16, 2003)

We propose a new technique for processing the heterodyne beat signals obtained in interferometry by sinusoidal modulation of the optical path difference. This technique achieves a high degree of signal stabilization with respect to phase drifts, while removing earlier restrictions imposed on the modulation index. Four Fourier harmonics of the interference signal allow the determination of the current modulation index, and then the coherent component of the intensity can be calculated. The method was tested both numerically and experimentally, and compared to a previous technique that uses the same input data. The effects of phase drifts are canceled on a wide range of the modulation index values, while the reference method achieves the same performance only for particular isolated values. A simplified version of the method is proposed for cases when the signal-to-noise ratio is low.

Key words: optical phase modulation, phase drift suppression, heterodyne beat signals, optical coherence tomography

^*On leave from the National Institute for Laser, Plasma, and Radiation Physics, PO Box MG-36, Bucharest, Romania. Present address: Kawase Initiative Research Unit, RIKEN, 2-1 Hirosawa, Wako 351-0198 Japan. E-mail address: dobroiu@riken.jp
^†Also with the Japan Science and Technology Corporation, Regional Joint Research Project of Yamagata Prefecture, 2-2-1 Matsuei, Yamagata 990-2473 Japan.