Pie-Yau Chien

Distance- and velocity-detection interferometer by using a frequency triangular-modulated laser diode

A scheme for distance and velocity signal detection is implemented. This technique is based on a laser diode with its frequency modulated by a triangular waveform and followed by time gating.

DISTANCE AND VELOCITY MEASUREMENTS BY THE USE OF AN ORTHOGONAL MICHELSON INTERFEROMETER

A novel signal processing scheme for detecting distance and velocity signals simultaneously is demonstrated. In this method, a frequency-modulated diode laser is used to illuminate a dual-channel Michelson interferometer with two orthogonal output signals. The distance and the velocity signals then exist on the beat frequencies of the output interferometric signal. Two interferometric output signals with a quadrature phase shift are used to adjust the gating time period of frequency counters for beat-frequency measurement. The distance and velocity signals can thus be obtained from the counting number within the gated-in time period.

Vibration Suppression in a Flexible Structure Based on Fiber Optics Michelson Interferometric Sensor

A two-wavelength fiber optics Michelson interferometric sensor has been employed to detect the vibration signal in a flexible beam. The synthetic wavelength and synthetic heterodyne detection schemes have been adopted for signal processing on optical phase detection. The active control technique was also developed and implemented to suppress the vibration signal that was generated from the piezoelectric transducer. A 38 dB suppression has been obtained.

Electrically nulled interferometric sensor based on triangular phase modulation

Abstract We describe a technique for nulling the optical phase change induced by a fiber interferometric sensor. This scheme utilizes a triangular waveform to modulate an integrated optic phase modulator. The output signal of the interferometer is then mixed with a switching pulse train with proper pulse width and space. The switching pulse trains are generated from a triangular waveform and three comparators with different polarity. The operating principle is demonstrated by using a fiber optic gyroscope (FOG). A sensor system with wide dynamic range and linear scale factor has been successfully implemented by using this technique.

Measurement of absolute displacement by a double-modulation technique based on a Michelson interferometer.

A novel method is presented for of measuring absolute displacement with a synthesized wavelength interferometer. The optical phase of the interferometer is simultaneously modulated with a frequency-modulated laser diode and optical path-length difference. The error signal originating from the intensity modulation of the source is eliminated by a signal processing circuit. In addition, a lock-in technique is used to demodulate the envelope of the interferometric signal. The displacement signal is derived by the self-mixing technique.

Displacement measurement by synthesized light source based on fiber Bragg gratings

This work presents a novel two-wavelength interferometer based on fiber Bragg gratings. Two light sources with different wavelengths are generated from separate fiber Bragg gratings. The high wavelength accuracy of fiber Bragg gratings allows us to enhance the measured accuracy of the interferometer. In addition, a Michelson interferometer is used to reliably measure the path-length difference signal, thereby demonstrating the proposed interferometers effectiveness.

Distance and velocity detection based on a deep sinusoidal phase-modulated interferometer

A deep phase-modulation signal with a sinusoidal waveform is employed on a Michelson interferometer for detecting distance and velocity signals simultaneously. This approach is simple to implement and has a wide-dynamic-range capability with a linear scale factor.

Optical interferometric signal generator based on electrical phase-locked loop technique

To simulate a phase-modulated interferometer, a novel electrical signal generator has been demonstrated. There are two phase-locked loop (PLL) circuits used in our system to process the phase signal. The first PLL is adopted as a voltage-controlled phase shifter, and the second PLL is used to amplify the phase signal to get a phase shift with a dynamic range over ±16π rad. This system can be further modulated with sinusoidal, sawtooth, and triangular wave forms for interferometric signal detection.

Absolute displacement measurement by using the synthesized modulation index of a frequency-modulated interferometer

A novel absolute displacement measurement by using a heterodyne interferometer, with a frequency-modulated laser diode has been successfully implemented. In this signal processing scheme, the synthesized modulation index of a phase-modulated interferometer is used for measuring the displacement, which is independent of the variation of the modulation frequency. The error induced from the intensity modulation in the laser diode can be eliminated.

Frequency multiplier using cascade integrated-optic phase modulators based on Sagnac interferometer

Abstract This work presents a frequency multiplier generated by a fiber optic Sagnac interferometer based on cascade integrated-optic phase modulators. The effective V π of this interferometer can be reduced to V π /2 N , where N is the number of phase modulators. The generated frequencies depend on the applied modulation amplitude and the number of integrated-optic phase modulators. The output frequency can be multiplied by simultaneously using two integrated-optic phase modulators employed with π rad out of phase of each other. Experimental results indicate that a stable frequency of 1.008 GHz, i.e., 24 times higher than the modulation frequency, can be easily achieved by applying a low modulation frequency to the optical interferometric system.