Time division multiplexing for multipoint measurement of dynamic displacement using interferometer with phase-modulated reference light

Abstract

For the purpose of multipoint dynamic displacement measurement, we investigate application of time division multiplexing (TDM) technique to a fiber optic interferometer, in which the phase of the reference light is modulated and the channels of the probe light are switched in synchronization with the modulation frequency. In the proposed TDM method, measurements at multiple points are synchronized without any complicated control. By changing the duty ratio of the switching time, bandwidth allocated for each channel of measurement is changed arbitrarily. Simulation and proofof-concept experiment confirm the principle and the effectiveness of the proposed method.

Real-time laser shape measurement using intensity correlation with phase modulation signal

“…The interferometric measurement is effective in many cases especially for measuring a displacement of less than the optical wavelength. In our research team, we have been studying a dynamic displacement measurement using a phase-modulated interferometer [5][6][7][8][9][10][11][12][13] , which can measure an unsteady movement of several tens of nanometers with a frequency up to 100 MHz 7 . On the other hand, incoherent methods including time-of-flight and modulation methods are useful for large displacement measurement ranging from millimeters to meters.…”

Sensitivity improvement of submicron dynamic displacement measurement system composed of phase-modulated fiber optic interferometer

“…The methods include low coherence interferometry, [1][2][3][4][5] laser Doppler vibrometry, 6,7) confocal method, [8][9][10] and laser interferometry. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] To monitor submicron dynamic displacement with high frequencies, these optical systems generally use a single photoreceiver having a short response time. Since highfrequency vibration generally takes place in relatively small and thin objects, single-point measurement is effective enough in some cases.…”

“…In order to achieve both high precision and a simple optical system for measuring high-frequency dynamic displacement with submicron scale amplitude, we have proposed and investigated a fiber optic interferometer with a high-frequency phase-modulated light as a reference light. [15][16][17][18][19][20][21][22] The system configuration is similar to the one proposed by Sasaki et al, [23][24][25][26][27][28] but the signal processing procedure is completely different in that the temporal waveform is analyzed to derive the displacement. So far, we have successfully performed precision measurements of dynamic displacements on the order of several tens of nanometers.…”

“…We also have developed a method that enables stable measurement even in the presence of disturbances 18) and confirmed the principle of multi-point measurement. 20) On the other hand, when the reflected optical power from an object was less than −30 dBm, it was difficult to measure the displacement due to the degradation of S/N of the received signal. Especially when measuring biomedical tissues with low reflectivity, further sensitivity improvement is desirable.…”

Laser displacement measurement using intensity modulation with a phase-modulated radio-frequency signal

“…The coherent-based distance or displacement measurement systems using interferometry can provide very accurate measurements within the range of laser coherence. [1][2][3][4][5][6][7][8][9][10][11] The highest performance of interferometric measurement is represented by the application to gravitational wave detection. 11) The incoherent-based measurement systems based on triangulation, [12][13][14] confocal detection, 15) time-of-flight, [16][17][18] or signal phase shift [19][20][21] can also provide high accuracy.…”