[OPTICAL REVIEW Vol. 6, No. 1 (1999) 62-67]
Sinusoidal Phase-Modulating Superluminescent Diode Interferometer with Fabry-Perot Etalone for Step-Profile Measurement
Kenichiro TSUJI,1 Osami SASAKI2,* and Takamasa SUZUKI2
1Graduate School of Science and Technology,2 Faculty of Engineering, Niigata University, 8050, Ikarashi 2, Niigata, 950-2102 Japan
(Received July 14, 1998; Accepted October 8, 1998)
In this paper we use a superluminescent diode (SLD) as the light source of an interferometer and extract a narrow spectrum from a wide spectrum of the SLD with a Fabry-Perot Etalone (FPE). By varying sinusoidally the distance between the two mirrors of FPE, the central wavelength of the narrow spectrum is scanned sinusoidally. The distance between the mirrors is exactly set by a feedback control system, and sinusoidal phase-modulated SLD light that has a large scanning width of about 10 nm can be obtained with high stability and spatial uniformity. The phase of the interference signal has two different components. One is amplitude Zb of sinusoidal phase modulation, which is proportional to the optical path difference (OPD) and the scanning width. The other is conventional phase α, which provides a fractional value of the OPD in the range of the wavelength. By combining the two values of the OPD obtained from Zb and α, an exact OPD larger than the wavelength can be measured with high accuracy in α. Characteristics of the interferometer are made clear through step-profile measurements.
Key words : superluminescent diode, Fabry-Perot Etalone, feedback control system, interferometer, sinusoidal phase-modulation, step-profile measurement