Development of a compact DFB laser interferometer for high-speed inline displacement measurement

A compact fiber laser interferometer, capable of precise displacement measurements, was
devised using a 1550 nm DFB laser for frequency modulation up to 300 kHz. The system
comprises a fiber laser, a fiber-optic interferometer, and a wavelength modulation system. The presented method offers nanometer-scale precision and incorporates a hydrogen cyanide (HCN) gas cell for monitoring the laser's central wavelength. A technique to compensate for modulation depth has been developed to maintain a consistent modulation depth over extensive measurement ranges. Preliminary trials reveal a measurement bias of less than 40 nm achieved over a 300 mm range at a speed of 100 mm/s compared to a calibrated interferometer. This approach proves beneficial for high-precision measurements for inline semiconductor manufacturing processes.