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The article presents a joint-transform phase correlator with a sharp correlation peaks produced by the numerical Fourier transformation of a phase in a joint-power spectrum. The phase can be measured by six-step phase-shifting interferomety with a tunable laser-diode (LD). The algorithm in six steps is not sensitive to the LD power alterations. A best discrimination performance can be obtained from the phase correlator. Calculation results were also presented.

Laser diodes (LDs) have been applied to a phase-measuring interferometer through the wavelength tunability of LDs by controlling their currents. Laser-diode interferometers based on a heterodyne technique are reviewed. A two-wavelength laser-diode interferometer is demonstrated with current control of dual LDs in opposite directions. A synthetic wavelength makes it possible to extend the range of interferometric measurements. The wavelength is controlled by the laser injection current and is stepwise or rampwise changed to introduce a time-varying phase difference between the two beams of an interferometer with unbalanced optical path lengths. The optical output is demodulated with a phase-extraction algorithm. Systematic phase errors caused by the LD-power variation and by the difference between the beat frequency and ramp frequency are analyzed. A feedback interferometer with electronics is used to eliminate the phase error by locking the interferometer on a preset phase. Typical experimental results are shown. [ABSTRACT FROM AUTHOR]

Frequency doubling of a Ti:sapphire laser with a KNbO crystal has been used to generate wavelength tunable amplitude-squeezed lights in the second harmonic mode. The crystal is placed in an enhancement cavity designed to resonate only the fundamental mode, and the phase matching condition is achieved by changing the crystal temperature. Noise reduction of 1.8-2.0 dB below the shot noise level is observed between 427.28 and 433.76 nm. [ABSTRACT FROM AUTHOR]