Phase-modulating Laser Diode Interferometer Research Articles

Sinusoidal phase-modulating laser diode interferometer for wide range displacement measurement.

A sinusoidal phase-modulating laser diode interferometer for wide range displacement measurement is proposed. To realize wide range displacement measurement, a signal processing method utilizing a look-up table to estimate the dynamic value of the effective sinusoidal phase-modulating depth is detailed, and the error caused by the residual amplitude modulation and the effective sinusoidal phase-modulating depth in wide range displacement measurement can be eliminated. It is discussed that the extended measurement range depends on the monotone intervals of several specific functions. The simulation and experimental results prove that the sinusoidal phase-modulating laser diode interferometer with the proposed method could realize centimeter level displacement measurement range.

Large-range displacement measurement using sinusoidal phase-modulating laser diode interferometer

A signal processing method of realizing a large-range displacement measurement in a sinusoidal phase-modulating laser diode interferometer is proposed. The method of obtaining the dynamic value of the effective sinusoidal phase-modulating depth is detailed, and the residual amplitude modulation is also taken into account. Numerical simulations and experiments are carried out to compare this method with the traditional one. We prove that, with this method, the sinusoidal phase-modulating laser diode interferometer can realize a centimeter-level displacement measurement range with high precision, which is much better than the traditional method.

Sinusoidal phase-modulating laser diode interferometer insensitive to intensity modulation for real-time displacement measurement with feedback control system

In sinusoidal phase modulating laser diode (LD) interferometer, the injection current of the LD is sinusoidally modulated to realize the modulation of the wavelength. However, the light intensity of LD is also modulated, which affects the measurement accuracy. An all-fiber sinusoidal phase modulating LD interferometer for real-time displacement measurement is proposed where the influence of the intensity modulation is eliminated with a new algorithm. It is made clear that an optimal depth of the sinusoidal phase modulation (SPM) exists in the algorithm. Moreover, the SPM depth is locked at the optimal value by controlling the injection current with a feedback control system. The feasibility of the proposed interferometer for displacement measurement is verified by experiments.

Two-wavelength sinusoidal phase-modulating interferometer for nanometer accuracy measurement

A two-wavelength sinusoidal phase-modulating (SPM) laser diode (LD) interferometer for nanometer accuracy measurement is proposed. To eliminate the error caused by the intensity modulation, the SPM depth of the interference signal is chosen appropriately by varying the amplitude of the modulation current periodically. Then, the refine theory is induced to the measurement, and the two-wavelength interferometer (TWI) is combined with the single-wavelength LD interferometric technique to realize static displacement measurement with nanometer accuracy. Experimental results indicate that a static displacement measurement accuracy of 5 nm can be achieved over a range of 200 \mu m.

Sinusoidal phase-modulating laser diode interferometer insensitive to the intensity modulation of the light source

In a conventional sinusoidal phase-modulating laser-diode (SPM-LD) interferometer, the wavelength of the LD is sinusoidally modulated by varying its injection current. However, the intensity modulation is associated with the wavelength modulation, which affects the measurement accuracy. We propose an SPM-LD interferometer insensitive to the intensity modulation of the light source, in which the influence of the intensity modulation is eliminated by choosing the appropriate sinusoidal phase modulation depth. Computer simulations and experiments are performed for real-time displacement measurement with the proposed SPM-LD interferometer. The measurement accuracy has been improved and the measurement repeatability is less than 1 nm. No additional components are required in our proposed method that leads to a simple system compared with the other previously proposed methods.

Sinusoidal phase modulating laser diode interferometer for on-machine surface profile measurement

A disturbance-free sinusoidal phase modulating laser diode interferometer using an accelerated integrating-buckets processing system is described. Several techniques make it suitable for use in on-machine measurements: the charge-coupled device (CCD)-based additive operation on integrating buckets shares the burden of data processing imposed on the computer to shorten the measurement time; the use of high-speed shutter function of the CCD camera enables each bucket to be collected without disturbance, while the interference signal's stability is enhanced with the feedback control during the entire data-collecting time; by using a dedicated waveform generator, the phase modulating system is more compact and the modulating signal matches the CCD camera's exposure time easily and exactly. A surface profile measurement on a diamond-turned aluminum disk is demonstrated to evaluate the performance of this system.

Sinusoidal phase-modulating laser diode interferometer for measuring angular displacement

We propose a sinusoidal phase-modulating laser diode interferometer for measuring small angular displacement. The interferometer is based on a Fabry-Perot plate. It has a simple structure and is insensitive to external disturbance. Sinusoidal phase-modulating interferometry is used for improving the measurement accuracy. A charge-coupled device (CCD) image sensor is used for measuring the distance between the reflected beams from two faces of the Fabry-Perot plate. From the distance, the initial angle of incidence is calculated. Compared with Michelson interferometers and autocollimators, this interferometer has the advantage of compact size and simple structure. The numerical calculation and experimental results verify the usefulness of this novel interferometer.

Sinusoidal phase-modulating laser diode interferometer capable of accelerated operations on four integrating buckets

We propose a sinusoidal phase-modulating laser diode interferometer that uses a charge-coupled device (CCD)-based additive operation on four integrating buckets. By shifting the injection-current bias of a laser diode to introduce additional phase shifts, a portion of the subtractive operations on the integrating buckets become additive operations, which are achieved in the CCD. This approach serves to reduce both data processing and measurement time.

Double sinusoidal phase-modulating distributed-Bragg-reflector laser-diode interferometer for distance measurement.

A previously proposed double sinusoidal phase-modulating (DSPM) laser-diode interferometer measures distances larger than a half-wavelength by detecting modulation depth. Although it requires a vibrating mirror to provide the second modulation to the interference signal, such vibrations naturally affect measurement accuracy. We propose a static-type DSPM laser-diode interferometer that uses no mechanical modulation. Our experimental results indicate a measurement error of +/- 1.6 microm.

Photothermal Phase-Modulating Laser Diode Interferometer with High-Speed Feedback Control

We propose a photothermal phase-modulating laser diode interferometer equipped with a high-speed feedback control system. The CCD camera’s shutter-function raises the modulating frequency, which in turn elicits a higher feedback response, thus enabling us to eliminate nearly all external disturbance. With the recent application of a system purpose-built for discriminating between numerous fringe sequences, we have also reduced processing time.

Laser diode interferometer used for measuring displacements in large range with a nanometer accuracy

In this paper, the displacement of an object is measured with a photothermal phase-modulating laser diode interferometer. A feedback control system is designed to reduce the measurement errors caused by the fluctuations in the optical wavelength of the laser diode and the vibrations of the optical components in the interferometer. A new method is proposed to enlarge the measuring range of displacement. Using this method, the measuring range is enlarged from half wavelength to nearly 125 μm and the measurement accuracy is about 1 nm . The simulation and experimental results have shown the usefulness of the method and the feedback control system.

Real-time displacement measurement with a two-wavelength sinusoidal phase-modulating laser diode interferometer

A two-wavelength interferometer that uses two separate modulating currents with different phases but the same frequencies to detect a greater degree of object displacement in real time is proposed and demonstrated. The measurement error was 57 nm, roughly 1/80 of the synthetic wavelength. We have confirmed that this modulating technique enables us to equip our prototype interferometer with a simple feedback-control system that eliminates external disturbance.

Real-time two-dimensional surface profile measurement in a sinusoidal phase-modulating laser diode interferometer

A real-time 2-D surface profile measurement system is described. In this system, a laser diode and a 2-D charge-coupled device image sensor are used as a light source and a photodetector, respectively. The phase is detected from the sinusoidal phase-modulating interference signal using the high-speed electrical circuit. The time required for phase detection is 20 ms for 50 x 40 measuring points. Because the phases can be obtained for even and odd fields of the image sensor, the original spatial resolution of the image sensor is not reduced in this system. Repeatability of the measurement is -14 nm, rms.

Sinusoidal phase modulating laser diode interferometer with feedback control system to eliminate external disturbance

We propose a sinusoidal phase modulating laser diode interferometer that is insensitive to vibrations of the optical components and fluctuations in the optical wavelength of the laser diode. These external disturbances cause fluctuations in the phase of the interference signal. After we analyze the sinusoidal phase modulation in a laser diode interferometer, we describe the method of the feedback control of the injection current of the laser diode to eliminate the phase fluctuations of the interference signal. We construct two sinusoidal phase modulating interferometers for movement measurements and surface profile measurements, respectively. The experimental results make it clear that the interferometers work well in mechanically noisy circumstances.