JPH10122839A - Three-dimensional shape measuring device by optically synchronous detection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a highly sensitive three-dimensional shape measurement even under an environment where a disturbance light is mixed by individually performing the phase modulation of output light from a laser light source that is branched into a plurality of systems by a branch means so that they are related constantly one another. SOLUTION: When a reflection signal light 14 and a reference light 13 enter a optically synchronous detection means 6 with a constant phase difference, interference fringes are formed and a phase grating G with a refractive index distribution corresponding to the interference fringes is formed at the detection means 6 after a constant response time which is determined by the material of the incidence detection means 6. By adjusting the phase modulation using a phase modulation means 3, the position and the grating interval of the grating G formed by the detection means 6 can be adjusted properly. After an effective grating G has been formed in the detection means 6, only the signal light 14 with a constant phase difference to the reference light 13 is diffracted by the formed grating G out of input light 16 where a disturbance light 15 has been mixed in the signal light 14 that enters the detection means 6, and is outputted as a synchronous detection light 17 by the interference with the reference light 13. As the result, only the signal light 14 is converted into an electrical signal 18 by a light receiving means 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the application of photorefractive effects to optical information processing.
The present invention relates to a three-dimensional shape measuring apparatus using optical synchronous detection using a photorefractive material.

[0002]

2. Description of the Related Art In recent years, electrical image processing technology has become mainstream due to the dramatic progress of computer image processing technology and semiconductor technology. However, rate limiting by parallel / serial conversion and LSI (Large Scale Integrated Circuit) Due to bandwidth limitations due to wiring delays, etc., the limit to speeding up with only electrical image processing technology is beginning to appear, and new optical information processing that actively takes advantage of new nonlinear optical phenomena, taking advantage of the massive parallelism inherent in light Research on is active. Above all, a significant suggestion has been made regarding the possibility of optically synchronous detection of an optical signal using generation of a phase conjugate wave by two-wave mixing and four-wave mixing, which is an interference phenomenon of light waves caused by the photorefractive effect. For the operation principle of optical synchronization detection, for example,
"Optical Lock-in Detection Using Anisotropic Self-Diffraction in BSO Single Crystal" (Optics Vol. 24, No. 7, 1995)
July) or “Photorefractive
optical lock-in detecto
r "(Optics Letters / Vol.16,
No. 18 / Sep. 15, 1991).

On the other hand, regarding the three-dimensional shape measurement of an object,
Measurement of a three-dimensional shape from a stereo pair image, measurement of a three-dimensional shape from a moire fringe image, and the like have been put to practical use using the above-described computer image processing technology. The moire fringe is
A stripe pattern different from the original pattern that can be observed when two or more regular patterns are overlapped or a regular pattern is regularly sampled. For example, when a shadow of a straight grid is projected on a target object, the shadow of the grid line is deformed according to the shape of the object. When the shadow of the deformed grid line (the deformed grid image) is superimposed on the original straight grid, a slight shift in the pitch or direction of the grid of the deformed grid image is observed as moire fringes.

[0004]

In the above-described conventional three-dimensional shape measurement, measurement can be performed using incoherent general light such as natural light as a light source, but disturbance light such as sunlight is superimposed on observation light. In such a case, there is a problem that the SN ratio of an information signal such as a deformed grating image in the observation light is extremely reduced, and three-dimensional shape measurement based on image information such as the deformed grating image cannot be performed. Further, by using monochromatic light or simply using laser light having coherent polarization characteristics as a light source, it was not possible to sufficiently remove noise components from high-luminance disturbance light. An object of the present invention is to apply the photorefractive effect and remove optical signal noise by high-speed optical synchronization detection utilizing the superparallelism inherent in light, thereby solving the above-mentioned problems of the conventional three-dimensional shape measurement. It is another object of the present invention to provide a three-dimensional shape measuring apparatus capable of performing highly sensitive three-dimensional shape measurement even in an environment where disturbance light is mixed.

[0005]

The first characteristic configuration of the three-dimensional shape measuring apparatus by optical synchronization detection according to the present invention for achieving this object is described in claim 1.
As described in the above, a laser light source, a branching means for branching the output light from the laser light source into two systems, and separately phase-modulating the output light branched by the branching means so as to have a constant relationship to each other. Two phase modulators, one outputting a signal light and the other outputting a reference light, a spatial modulator for spatially modulating the signal light, and a spatially modulated signal light modulated by the spatial modulator. Input the reference light and the input light mixed with disturbance light to the reflected signal light obtained by irradiating the object to be measured, the reflected signal light having a certain relationship with the reference light from the input light Optical synchronization detecting means having a photorefractive effect for selectively detecting synchronization and outputting as synchronization detection light, light receiving means for receiving the synchronization detection light and converting it to an electric signal, and converting the electric signal converted by the light receiving means into an electric signal. Place based on Measurement processing means for executing the object measurement process of the object, and the measured object is measured based on the spatial modulation information of the reflected signal light and the spatial modulation information of the spatially modulated signal light, which are synchronously detected and converted into the electric signal. The point is that the three-dimensional shape of the object is measured.

According to a second feature of the present invention, as described in claim 2 of the claims, in addition to the above-mentioned first feature, the compound semiconductor in which the optical synchronization detecting means has a quantum well structure is provided. It is in the point that is.

The operation will be described below. According to the first characteristic configuration, the output light from the laser light source branched into two systems by the branching unit is separately subjected to phase modulation so as to have a fixed relationship to each other, so that the signal light and the reference light are referred to. A constant phase difference occurs between the light beams, and further, the same phase difference occurs between the reflected signal light and the reference light obtained by irradiating the object to be measured after modulating the signal light with the spatial modulation means. Then, when the reference light and the reflected signal light are incident on the optical synchronization detecting means so that interference fringes are generated, the optical synchronization detecting means having a photorefractive effect after a predetermined response time elapses is applied to the interference fringes. A phase grating having a corresponding refractive index distribution is formed therein. By appropriately adjusting the phase modulation by the phase modulation means, the position and the interval of the phase grating formed in the optical synchronization detection means can be appropriately adjusted. Once an effective phase grating is formed in the optical synchronization detecting means as described above, the reference light and the input light in which disturbance light is mixed into the reflected signal light incident on the optical synchronization detecting means. Only the reflected signal light having a certain phase difference is diffracted by the formed phase grating, emphasized by interference with the reference light, and output as synchronous detection light. As a result, other disturbance light is removed by the optical synchronization detecting means, so that only the desired reflected signal light is converted into an electric signal by the light receiving means at the next stage and the predetermined Is performed.

Further, the spatially modulated signal light and the reference light that irradiate the object to be measured are, for example, before and after the branching means.
The large-diameter beam whose beam diameter is expanded or a single beam is converted into a two-dimensionally expanded beam bundle into a plurality of beam bundles. The spatial modulation is performed so as to form a dimensional regular lattice pattern. As another spatial modulation method, when a single beam is irradiated while scanning over the surface of the object to be measured without being converted into a large-diameter beam or a beam bundle as described above, it is determined according to the scanning direction. It is also possible to perform spatial modulation by applying intensity modulation to project a regular lattice pattern on the measured object. In this way, when the regular lattice pattern spatially modulated by the spatial modulation means is projected on the object to be measured and observed from another direction, the regular lattice pattern is in accordance with the surface shape of the object to be measured. A deformed lattice pattern is formed.

As a result, since the deformed lattice pattern can be extracted with high sensitivity by the optical synchronization detecting means, the measurement processing means analyzes the deformation state of the lattice pattern, and thereby the object to be measured is analyzed. It is possible to measure the three-dimensional shape with high accuracy.

According to a second characteristic configuration, after the reference light and the reflected signal light form interference fringes on the optical synchronization detecting means, the optical synchronization detecting means sets a refractive index corresponding to the interference fringes. The response time required to form a phase grating having a distribution therein can be greatly reduced. When the spatial modulation by the spatial modulation unit is performed by irradiating a single beam while scanning the surface of the object to be measured, the scanning speed is low because the phase grating formed on the optical synchronization detection unit differs depending on the scanning position. In the case of high speed, there is a possibility that the generation of the phase grating is delayed and the optical synchronization of the reflected signal light cannot be accurately detected, or the object to be measured is rotated or moved by control from the measurement processing means, The problem is that the sampling speed for extracting information by rotating or moving the object to be measured is limited by the response time, for example, when trying to measure a more advanced three-dimensional shape by increasing the amount of information extraction from the deformed lattice pattern. However, there is a possibility that this will become apparent as the processing speed increases. According to this characteristic configuration, the minimum response time currently obtained with a paraelectric or compound semiconductor material having a photorefractive effect is the BSO of the paraelectric.
In contrast to the millisecond order of (Bi ₁₂ SiO ₂₀ ) and the order of 10 microseconds for a GaAs compound semiconductor, there is a possibility that the speed can be reduced to the order of microseconds or less by employing a quantum well structure in the compound semiconductor. By realizing a response time on the order of microseconds, it is possible to measure an ultra-high-speed, high-sensitivity, high-accuracy three-dimensional shape suitable for real-time processing.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a three-dimensional shape measuring apparatus using optical synchronization detection according to an embodiment of the present invention. As shown in FIG. 1, the three-dimensional shape measuring apparatus converts a laser light source 1 and an output light 10 from the laser light source 1 into two.
The branching means 2 for branching into a system and the output lights 10a and 10b branched by the branching means 2 are respectively subjected to phase modulation so as to have a fixed relationship with each other. Two phase modulating means 3 and 4 for outputting a reference light 13, a spatial modulating means 9 for spatially modulating the signal light 11, and a spatially modulated signal light 12 modulated by the spatial modulating means 9 to an object to be measured. 5, the input light 16 in which disturbance light 15 is mixed with the reflected signal light 14 obtained by irradiating the reference light 1
3 to input the reference light 13 from the input light 16.
A synchronous detection means 6 having a photorefractive effect for selectively detecting the reflected signal light 14 having a fixed relationship with the reflected signal light 14 and outputting the same as a synchronized detection light 17; Light receiving means 7 for conversion
And measurement processing means 8 for executing predetermined object measurement processing based on the electric signal 18 converted by the light receiving means 7.

The oscillation wavelength of the laser light source 1 is determined according to the sensitivity range of the optical synchronization detecting means 6. The oscillation wavelength range is from 400 nm to 700 nm when the optical synchronization detecting means 6 is configured using BSO,
In the case of As, it is 900 nm to 1500 nm.
In the present embodiment, as the optical synchronization detecting means 6, BS
O, GaAs, or AlGaAs / GaAs quantum well structure compound semiconductor is used.

The branching means 2 is a beam splitter generally used in laser optics. The phase modulating means 3 and 4 are EOM (optical modulator utilizing electro-optic effect)
Alternatively, the phase modulators 3 and 4 are composed of AOMs (optical modulators utilizing an acousto-optic effect), and the phase modulators 3 and 4 respectively have different modulation indices μ ₁ and μ ₂ and modulation signals 19 with different modulation angular frequencies ω ₁ and ω ₂ , 20 is input.

The spatial modulation means 9 is an optical glass flat plate having a regular two-dimensional lattice pattern A formed on its surface and capable of transmitting the reference light 13 according to the lattice pattern. Also, a liquid crystal display panel comprising a conductive thin film made of tin-doped indium oxide or the like sandwiched between transparent electrodes formed on the surface of an optical glass flat plate from both sides so that the lattice pattern A can be freely changed. But it doesn't matter.

The reflected signal light 1 is supplied to the optical synchronization detecting means 6.
When the light 4 and the reference light 13 enter with a certain phase difference, interference fringes are formed. After the incidence, after a certain response time determined by the material of the light synchronization detecting means 6, a refractive index distribution corresponding to the interference fringes is formed. A phase grating G is formed on the optical synchronization detecting means 6. By appropriately adjusting the phase modulation by the phase modulating means 3, the position and the grating interval of the phase grating G formed in the optical synchronization detecting means 6 can be appropriately adjusted. After the effective phase grating G is once formed in the optical synchronization detecting means 6 as described above, the input light 16 in which disturbance light 15 is mixed with the reflected signal light 14 incident on the optical synchronization detecting means 6 is used. Among them, only the reflected signal light 14 having a certain phase difference from the reference light 13 is diffracted by the formed phase grating G, is enhanced by interference with the reference light 13, and is output as the synchronization detection light 17. As a result, since the other disturbance light 15 is removed by the optical synchronization detecting means 6, the desired reflected signal light 14 can be obtained regardless of the mixing of the disturbance light 15.
Is converted into an electric signal 18 by the light receiving means 7 at the next stage, and a predetermined process is performed.

The light receiving means 7 comprises a two-dimensional light receiving element such as a CCD. The measurement processing means 8 is constituted by a computer suitable for high-speed digital signal processing.

Between the deformed lattice pattern B, which is the spatial modulation information of the reflected signal light 14 which has been synchronously detected and converted into the electric signal 18, and the lattice pattern A, which is the spatial modulation information of the spatially modulated signal light 12. The measurement processing means 8 executes an image processing program to measure the three-dimensional shape of the measured object 5 based on the correlation.

Hereinafter, another embodiment will be described. The object to be measured 5 is installed on an optical movable table that can rotate, move vertically and horizontally, and the measurement processing unit 8 changes the attitude and position of the object to be measured 5 and the spatial modulation unit 9 and spatial modulation. Is also a preferred embodiment. Accordingly, an effect similar to that of irradiating the spatially modulated signal light 12 while substantially scanning the surface of the measured object 5 can be obtained.

[0020]

As described above, according to the present invention,
By applying the photorefractive effect and removing optical signal noise by high-speed optical synchronization detection taking advantage of the superparallelism inherent in light, high-sensitivity and high-speed three-dimensional shape measurement even in an environment where disturbance light is mixed Is now possible.

In the claims, reference numerals are provided for convenience of comparison with the drawings, but the present invention is not limited to the configuration shown in the attached drawings.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a three-dimensional shape measuring apparatus based on optical synchronization detection according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser light source 2 Branching means 3, 4 Phase modulation means 5 Object to be measured 6 Optical synchronization detection means 7 Light receiving means 8 Measurement processing means 9 Spatial modulation means 10, 10a, 10b Output light 11 Signal light 12 Spatial modulation signal light 13 Reference light 14 reflected signal light 15 disturbance light 16 input light 17 synchronization detection light 18 electric signal

Claims (2)

[Claims] 1. A laser light source (1), branching means (2) for branching output light (10) from the laser light source (1) into two systems, and the output light branched by the branching means (2) (10a) and (10b) are separately subjected to phase modulation so as to have a fixed relationship with each other, and one outputs a signal light (11) and the other outputs a reference light (13). 3) (4), a spatial modulating means (9) for spatially modulating the signal light (11), and a spatially modulated signal light (12) modulated by the spatial modulating means (9) are converted into an object to be measured ( 5)
The reflected signal light (14) obtained by irradiating the
5) The input light (16) mixed with the reference light (13) is input, and the reference light (1) is extracted from the input light (16).
Optical synchronization detecting means (6) having a photorefractive effect for selectively detecting synchronously the reflected signal light (14) having a fixed relationship with 3) and outputting the same as synchronous detection light (17).
And receiving the synchronization detection light (17) and receiving an electric signal (1).
8) a light receiving means (7) for converting the light into the light;
And a measurement processing means (8) for performing a predetermined object measurement process based on the electric signal (18) converted in (1). The reflected signal light (8) is synchronously detected and converted into the electric signal (18). The three-dimensional shape of the object to be measured (5) is measured based on the spatial modulation information of (14) and the spatial modulation information of the spatially modulated signal light (12). Measuring device. 2. A three-dimensional shape measuring apparatus according to claim 1, wherein said optical synchronization detecting means is a compound semiconductor having a quantum well structure.