Phase Measurement Method Based on Digital Dual Frequency Comb for High-Precision High-Speed Heterodyne Interferometry

A Picometre-Level Resolution Test Method without Nonlinearity for Heterodyne Interferometer Measurement Electronics

“…where AC i is the AC photocurrent signal; shot i and dark i are the shot noise current and dark current, respectively; k is the Boltzmann constant; T denotes the absolute temperature; and RL is the load resistance. When the amplitudes of the signal decrease, SNR deteriorates as well, which will increase the phase measurement error [18].…”

“…where i AC is the AC photocurrent signal; i shot and i dark are the shot noise current and dark current, respectively; k is the Boltzmann constant; T denotes the absolute temperature; and R L is the load resistance. When the amplitudes of the signal decrease, SNR deteriorates as well, which will increase the phase measurement error [18]. Furthermore, the center frequency of measurement electronics depends on the frequency difference of the dual-frequency laser, which is distributed in the range of 0.5 MHz to 20 MHz [8,12].…”

“…The measurement electronics under examination is composed of two 450 MHz high-bandwidth, low-noise photodetectors (Thorlabs, model: APD430A2), a high-precision self-developed phasemeter, and a host computer. It is worth mentioning that the phasemeter possesses a phase resolution of 0.77 mrad in the 2.5 MHz-37 MHz bandwidth, which is equivalent to the displacement resolution of 19 pm in the double-pass heterodyne interferometer [18].…”

“…Secondly, different phase calculation principles will also result in differences in resolution. At present, many different phase unwrapping methods [17][18][19], such as pulse filling and phase-locked amplification, have been proposed to improve resolution. Finally, there is a form of accommodation between the above two factors; that is, the signal-to-noise ratio of the electrical signal from the photodetector should be sufficient to achieve the highest resolution of the phase meter.…”

“…The currently used test methods can be divided into three categories, namely, electrical methods, methods based on the PZT stage, and equivalent methods. Within electrical methods, a signal generator is used to offer electrical signals as ideal interference signals [8,9,12,[17][18][19] to directly test the resolution of the phase meter. However, it is evident that this method ignores the influence of noise on the resolution during the photoelectric conversion process.…”