In addition to a conventional phase α the interference signal of a sinusoidal-wavelength-scanning interferometer has a phase-modulation amplitude <i>Z<sub>b</sub></i> that is proportional to the optical path difference <i>L</i> and amplitude <i>b</i> of the wavelength scan. <i>L</i> and <i>b</i> are controlled by a double feedback system so that the phase α and the amplitude <i>Z<sub>b</sub></i> are kept at 3π/2 and π, respectively. The voltage applied to a device that displaces a reference mirror to change the optical path difference becomes a ruler with scales smaller than a wavelength. Voltage applied to a device that determines the amplitude of the wavelength scan becomes a ruler marking every wavelength. These two rulers enable one to measure an absolute distance longer than a wavelength in real time.
© 2002 Optical Society of America
(120.3180) Instrumentation, measurement, and metrology : Interferometry
(120.5050) Instrumentation, measurement, and metrology : Phase measurement
(120.5060) Instrumentation, measurement, and metrology : Phase modulation
Osami Sasaki, Kazuhiro Akiyama, and Takamasa Suzuki, "Sinusoidal-Wavelength-Scanning Interferometer with Double Feedback Control for Real-Time Distance Measurement," Appl. Opt. 41, 3906-3910 (2002)