Extended range phase-sensitive swept source interferometer for real-time dimensional metrology

The measurement of center thicknesses and airgaps along its optical axis is crucial to a mounted optical system. Aiming to real-time dimensional metrology, an extended range phase-sensitive swept source interferometric system is developed. To yield high precision of measurement, reference interferometer sharing the same swept source with the measurement interferometer is introduced and a phase-sensitive approach based on phase-comparison between measurement signal and reference signal is exploited. The proposed phase-comparison method is theoretically developed and its merits over standard phase-sensitive approach are experimentally confirmed. In contrast to the standard phase-sensitive approach, the sensitivity under signal to noise ratio of 45 dB achieved by the phase-comparison method is improved from 222 nm to 25 nm and the processing time is shorten by 90%. Measurements of glass plates are performed to evaluate the performance of the developed system. Submicron precision about a range of 30 mm is realized by the developed system equipped by a commercial available swept source operating at a sweeping rate of 10 kHz. The developed system holds potential application in real-time contact-free on-axis metrology for the fabrication and testing of complex optical systems.