Phase-conjugate distance-measurement interferometer with frequency modulation of a laser-diode

Laser-diode phase-conjugate interferometer with two self-pumped (cat) phase-conjugate mirrors instead of two ordinary mirrors is constructed for distance measurement over extended ranges. The measurement is based on frequency-modulated continuous-wave techniques. A wide-tunable laser diode (LD),with an external cavity is used to generate the chirping signal. The interferometer is immune to spatially nonuniform phase distortion, but can only detect the spatially uniform phase change introduced by the displacement of one cat mirror. The distance can be measured by detecting the beat frequency with an rf spectrum analyzer. The linear regression of the beat frequency as a function of the distance has been ascertained. The system has been characterized over a measurement range from 0.09 mm to 15.75 mm within 2.49 nm of 0.08 nm in wavelength diversities.