The interference device for measuring the phase shift of light waves

 

(57) Abstract:

Usage: in the field of measurement technology, namely in laser interferometry to measure the linear movement of various objects with high accuracy. The inventive device is an acousto-optic interferometer with an electronic measuring circuit implemented on the system phase-locked loop, which has a measuring and a reference input paths, each of which uses a delay line. 2 Il.

The invention relates to the field of measuring equipment, namely, laser interferometry and can be used for measuring linear displacements of various objects (elements of machine tools, coordinate measuring machines, measuring robots and others) with high accuracy.

To date for measuring linear displacement of already developed quite a large number of designs laser acousto-optic interferometers. In particular, a device for measuring phase shifts of light waves laser acousto-optic interferometer (analog) [1]. This device consists of an optically coupled laser, mnogoopytnogo acoustooptics, deflecting wedge, similar elements of the interferometer base channel, a turning prism, biprism, the afocal optical focusing systems measuring, reference and basic channels, reflecting mirrors, three optical diaphragms, three focusing lenses, three photodetectors and electronic measuring systems,

For designs of laser interferometers, there is the concept of spatial period lPPthat means a moving object, resulting in phase shift 2 . In the above construction of the laser interferometer is the spatial period is not regulated and is a multiple of IPP=n/2, where is the wavelength of the laser radiation, n is the number of double strokes of the beam in the optical interferometer scheme.

The essential advantage of the device described above is automatic compensation of errors introduced by the acoustooptic modulator and changes of the refractive index of air, through the creation of an additional reference channel.

However, in this device there are two major shortcomings. The first is to limit the measurement accuracy, typical for phase measurement methods phase cdotu regulation of the spatial period lPPand, as a consequence, the need for additional conversion value of phase shift in the metric system when determining the actual movement of the object.

The need to improve the accuracy of the measurements leads to the fact that the phase is a measure of transition to the frequency display of the phase shift. A known design of a laser interferometer with frequency indication of the phase shift [2] (similar), which is a way of measuring the phase shift of light waves, which contains optically coupled laser Michelson interferometer comprising a beam splitter, the measuring and the reference corner cube reflectors, dual optical valve, located in the reference channel of the interferometer modulator (e.g., acousto-optic cell), slit chart and PV, the emitter of ultrasonic waves, connected in series resonance amplifier and switch the oscillator.

The disadvantages of this device include functionality associated with the inability of smooth adjustment of the spatial period lPPgenerated by the interferometer, as well as the insufficient accuracy of measurements, OGG common features is a device for implementing the method of measuring the phase shift of light waves [3] (prototype), which contains optically United monochromatic light source, an acousto-optic modulator (AOM) with one electrical input and spatially separated keywords. output optical flows, the collimator, the elements of the optical system of the interferometer reflecting the triple-prism, the photodetector is electrically connected to the first input of the phase detector of extreme values (PDAS), the first output of which is connected to the input of the pulse counter, and the output of the latter is the output of the entire device, and the second output is electrically connected to the generator input, managed code, and its output is connected as the second input PDAS, and with the electrical input of the AOM.

This solution allows you to create a laser measuring system with a triangular function measuring conversion and managed spatial period.

The disadvantage of this technical solution is the limit of measurement accuracy due to errors introduced by the acoustooptic modulator and instability axis of the directivity diagram of the radiation source.

The present invention is aimed at achieving technical achiev="ptx2">

The invention is directed to the achievement of the technical result, which is to improve the measurement accuracy when extending functionality.

This result is achieved in that the proposed interference device for measuring the phase shift of light waves, containing optically United monochromatic light source, an acousto-optical modulator with one electrical input and three spatially separated keywords. optical flows, the collimator, the measuring path, consisting of series-connected optical and electrical channels, and the optical channel is implemented with a moving triple-prism scheme Mach-Zehnder interferometers in the first and one of the second keywords. optical flow, and the electrical channel consists of a generator, managed code, pulse meter, a photo detector, phase detector, the first output of which is connected to the input pulses, the output of the latter is the output of the device, and the second output of the phase detector is connected to the generator input, managed code, and its output is connected to the electrical input of the acousto-optical modulator is elektricheskogo channels, moreover, the optical channel is implemented by the circuit of the Mach-Zehnder interferometers, in which the spatial combined third and another part of the second keywords. optical flow, and electrical channel consists of serially connected photodetector and the first delay line, the output of which is connected to a second input of the phase detector, and measuring the tract entered the second delay line between the output of the photodetector and the first input of the phase detector.

The proposed set of features was not previously known, and this result can only be achieved in this device.

The construction and operation of the device, you receive the graphic material.

In Fig. 1 shows a structural diagram of the interference device for measuring the phase shift of light waves; Fig. 2 is a graphic explanation of the process of formation of the functions of measuring conversion for different values of the spatial period lPP.

The proposed device (Fig. 1) consists of the following elements: a monochromatic light source (laser) 1, acousto-optic modulator (AOM) 2, the collimator 3, reflecting the triple prism 4, the measuring path, consisting of about the CLASS="ptx2">

Optical channel 5 measurement circuit includes mirrors 9, 11 and beam splitter cube 10.

Electrical channel 6 measurement circuit includes a photodetector 12, the delay line 13, the phase detector 14, the pulse counter 15, the controlled oscillator code (GUK) 16.

Optical channel 7 of the reference path includes a beam-splitting cubes 17, 18 and mirror 19, 20.

Electrical channel 8 control path includes a photodetector 21, the delay line 22.

The proposed device operates as follows.

The laser beam 1 is directed to AOM 2, after which it is distributed on the first E (+1), zero (E (0) and minus first E (-1) diffraction order output spectrum. The collimator 3 output order is sent to the measuring circuit in the form of parallel rays.

The first order modulation E (+1) extends to triple-prism 4, is returned into the optical channel 4, beam splitter cube 10 combined spatial and interferes with the zero order diffraction E (0) at the output of the photodetector 12.

Optical channel 7 anchor tract collected under the scheme of the interferometer of Mach-Zehnder interferometers based on two beam-splitting cubesat and interfere at the input of the photodetector 21.

Optical heterodyning in the plane of the important aspect of keywords. optical flow leads to the outputs of the photodetectors 12 and 21 of the measuring and reference frequency signals. These signals pass through the delay lines 13 and 22 receive the time delays t1, t2and act accordingly on the first (test) and second (reference) inputs of phase detector 14.

When moving triple-prism 4 to the first input of phase detector 14 is formed by the sequence information of the logical pulse, which is fed to the input of the pulse counter 15. At the output of the pulse counter 15 produces a digital code corresponding total phase signal.

On the second output of the phase detector 14 is formed of the digital code input to the input unit GUK 16. The output frequency signal of the latter is fed to the electrical input of the AOM 2.

In this device, the function measuring the conversion of the phase detector is a ramp with a negative slope (symmetric triangular function). This kind of function measuring conversion is quite common, allowing you to exclude from the conversion process neulasta.

As one of the variants of the algorithms of the phase detector may be next. The phase difference between the input frequency signal is converted into a digital code N. If the output of the digital combination of N corresponds to two extreme values (N= 0 when =0 or N=Nmaxwhen =2 ), then the first output information is formed logical pulse.

The essence of the operation of the device is as follows.

1. Studies show that the value of the spatial period lPPfor the measuring circuit bases of the reference channel is defined by the formula:

IPP=(1+2k), (1) ,

where

K- gross ratio control loop measuring circuits;

the time delay of propagation of ultrasonic waves in the acousto-optic modulator;

the wavelength of the radiation source.

The introduction of the reference channel leads to the fact that the value in the formula (1) is determined by the difference of the delays in the measuring and reference channels =t=t2-t1. . By adjusting the value of t due to a change in t1and/or t2you, ultimately, to control the spatial period.

Using modern electronic database you can change t with a little of the VA signal delay can be different, on the basis of ultrasonic, electromagnetic delay lines, based on the RC-elements, on the basis of electronic devices (timers).

2. The errors inherent in the laser acousto-optical measuring systems, include the following:

the error caused by the presence of the reflected acoustic wave in the modulator and slow fluctuations of the velocity of propagation of acoustic waves in AOM due to temperature changes svetoslava;

the uncertainty due to instability of the axis of the directivity diagram of the radiation source.

The use of diagrams with two paths inteferometry (test and reference) allows the parasitic phase raids that occur in both channels, to compensate for each other. As a result, these errors can be completely excluded from the conversion process measurement data, which increases the measurement accuracy.

Schematically, generator, managed code can be built on the basis of the well-studied diagrams of the frequency synthesizer or a two stage scheme: d / a Converter + a voltage controlled oscillator, = controlled oscillator code.

Thus, the proposed device is. is using delay lines in the measuring circuit provides the additional ability to control the spatial period.

The interference device for measuring the phase shift of light waves, containing optically United monochromatic light source, an acousto-optical modulator with one electrical input and three spatially separated keywords. optical flows, the collimator, the measuring path, consisting of series-connected optical and electrical channels, and the optical channel is implemented with a moving triple-prism scheme Mach-Zehnder interferometers in the first and one of the second keywords. optical flow, and the electrical channel consists of a generator, managed code, pulse meter, a photo detector, phase detector, a first output of which is connected to the input of the pulse counter, the yield of the latter is an output device, and the second output of the phase detector is connected to the generator input, managed code, and its output is connected to the electrical input of the acousto-optic modulator, characterized in that the device additionally introduced the reference tract, consisting of EME Mach-Zehnder interferometers, in which spatial combined third and another part of the second keywords. optical flow, and electrical channel consists of serially connected photodetector and the first delay line, the output of which is connected to a second input of the phase detector, and measuring the tract entered the second delay line between the output of the photodetector and the first input of the phase detector.

 

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