Even if there are correlation algorithms to eliminate the correlation errors (phase modulation depth error, 13 etc.), the algorithms are complex, and the real-time performance is not good. ![]() 12 However, this method has certain requirements on the sampling frequency of the board, and the solving accuracy is not high. And there are electro-optic modulators instead of polarization elements in the structure of the interferometer, so its structure is simpler. Compared with quadrant phase measurement method, in the PGC, only one measurement signal is needed for signal processing. 4, 5 The phase-solving method of PGC is similar to that of heterodyne interference signal in principle. 3 External modulation uses an electro-optical modulator (or other components) to modulate the phase of one light arm. Internal modulation mainly controls the temperature or current of the laser, thereby modulating the wavelength of the laser. ![]() 9 – 11 The former can be divided into internal modulation and external modulation based on wavelength modulation and phase modulation. There are two main displacement calculation methods of the homodyne interferometers at present: one is phase generated carrier (PGC) method 3 – 5 (more classical work on PGC like 6 – 8), and the other is the quadrant phase measurement method. 1, 2 The displacement calculation methods determine the design and measurement precision of the interferometers. Homodyne interferometers are widely used in high-precision displacement measurement for their ultrameasurement accuracy.
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