JPH0448231A - Parallel light measuring instrument - Google Patents

Abstract

PURPOSE:To measure and adjust the parallelism of a light beam effectively with simple constitution regardless of whether or not the light beam is coherent by detecting a light intensity distribution appearing on a photodetection surface and then measuring the parallelism of the light beam in luminous flux. CONSTITUTION:This invented parallel light measuring instrument consists of a light source unit LSU which emits parallel light, 1st and 2nd gratings GR1 and GR2 which have the same grating constant and are provided with transmis sion type diffraction gratings, and the photodetection surface SC which photodetects luminous flux transmitted through those gratings GR1 and GR2. When the luminous flux from the light source unit LSU is diverged or converged in a direction X, the light intensity distribution appearing on the photodetection surface SC is not uniform and fringes which are shown, for example, in a figure are formed. The intervals S of the fringes are determined by the grating con stant P of the 1st and 2nd gratings GR1 and GR2, the gap G between those gratings GR1 and GR2, the distance D between the 1st grating GR1 and photodetection surface SC, and the parallelism of the light beam, so the intervals S of the fringes are measured to measure the parallelism of the light beam.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a parallel light measuring device that can measure and adjust the parallelism of light rays used in optical sensors and the like.

(Conventional technology) Various lasers and L
Optical sensors using light sources such as ED are widely used. These sensors often use parallel light as part of their optical systems.

Parallel light is produced by combining it with a collimator lens for LEDs and laser diodes whose light emitting parts are close to a point, and by combining it with a beam expander for leNe lasers. The performance of the sensor itself is often influenced by the quality of parallel light 2, that is, the parallelism of the light rays in the parallel light beam, and the parallelism of the light rays is determined by the performance of each optical element as well as the relative position accuracy between each optical element. Therefore, the work of arranging each optical element requires a device that accurately measures the parallelism of light rays and a device that precisely displaces the relative position between each optical element.

Conventionally, the parallelism of a light beam is measured by measuring the distortion of the wavefront of the light beam using an interferometer for laser light, and for non-coherent lamp or LED light, the parallelism of the light beam is measured at a different location than near the light source. This is done by measuring the magnitude and light intensity distribution, and by tracing light rays using pinholes.

(Problems to be Solved by the Invention) The construction of the interferometer that measures the distortion of the wavefront of the light beam described above is difficult, and processing of the interference fringes that appear is not simple, and even if the laser light source has relatively poor coherence, The disadvantage was that the contrast of the interference fringes was poor and measurement was difficult. On the other hand, when measuring the size of the luminous flux or the light intensity distribution, there is a problem that it is difficult to accurately measure the outline or that it takes time to measure the contour, making it ineffective.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to effectively measure and adjust the parallelism of light rays with a simple configuration regardless of the presence or absence of coherence. An object of the present invention is to provide an optical measurement device.

(Means for Solving the Problems) The present invention relates to a parallel light measuring device capable of measuring the parallelism of light rays used in sensors applying optics, etc. a second diffraction grating that has the same lattice constant as the first diffraction grating and is arranged such that each grating line is parallel to the grating line of the first diffraction grating; This is achieved by measuring the parallelism of the light beams in the light beams by detecting the light intensity distribution appearing on the light receiving surface.

(Function) The parallel light measurement device of the present invention has two
The light flux that has passed through two diffraction gratings is received by the light receiving surface, and the parallelism of the light rays is determined from the light intensity distribution that appears on the light receiving surface and the change in the light intensity distribution that appears on the light receiving surface when one of the diffraction gratings is moved. It is something to be measured.

(Example) Fig. 'fS1 is a structural diagram showing an example of a parallel light measurement device of the present invention, and includes a light source unit LSD that emits parallel light and a 1r4 light source unit provided with a transmission type diffraction grating having a predetermined grating constant.
a second grating GR2 provided with a transmission type diffraction grating having the same grating constant as the child GRI and the first grating GRI;
It consists of a grating GRI and a light receiving surface SC that receives the light beam transmitted through the second grating GR2.

Here, the first grating [iRl and the second grating GR2 are adjusted so that their respective surfaces are parallel to each other and their respective grating lines are parallel to each other.

If the light beam from the light source unit LSLI is perfectly parallel light, the light intensity distribution appearing on the light receiving surface SC will be the same as that of the light source unit LS
If the light intensity distribution has the same shape as the light intensity distribution when it exits I+, and the light intensity distribution when it exits the light source unit LSD is uniform, then the light receiving surface SU has uniform brightness within the range where the light beam hits. A distribution with a certain degree of strength can be created. However, when the light beam from the light source unit LS[I is a light beam that spreads or narrows in the X direction, the light intensity distribution appearing on the light receiving surface SC becomes uneven, and, for example, stripes shown in 341 occur.

The interval S between the stripes is determined by the lattice constant P of the two gratings GRI and GR2, the gap G between the two gratings GRI and GR2, the distance 1i11D between the first grating GRI and the light receiving surface SC, and the parallelism of the light rays. Therefore, by measuring the distance S between the stripes, the parallelism of the light beam can be measured.

Next, the principle of the present invention described above will be briefly explained using FIG. FIG. 2 is a schematic representation of FIG. 1 viewed from the Y direction. In general, parallel light can be thought of as a beam of light from a point light source at an infinite distance, and non-parallel light can be thought of as a beam of light from a point light source at a finite distance, or a beam of light that is converging to a point at a finite distance. . Here, the first
Consider a light beam that is almost spreading from a virtual point light source LS whose distance from the grating GRI is F.

The light beam LB from the virtual point light source LS passes through the first grating GRI placed at a distance of 111iF11, and then passes through the first grating GRI placed at a distance of 111iF11.
The light passes through the second grating GR2, which is spaced apart by a distance, and hits the light-receiving surface SC located at a distance 11D from the first grating GRI.However, the lattice constants of the two gratings GRI and GR2 are equal to P. As shown in the figure, the relative positional relationship between the first grating GRI and the second grating GR2 determines whether the first! A part of the group of light rays that have passed through the g-ray GRI passes through the transparent part of the second grating GR2 and reaches the light receiving surface SC, and the rest is blocked by the non-transparent part of the second grating GR2. Therefore, repeating bright and dark areas, ie, stripes, are formed on the light-receiving surface SC. Here, let S be the interval between the dark parts. Then, focusing on the directions of the two rays heading toward the two dark areas, if the interval between the rays on the first grating GRI is L, then the interval on the second grating GRZ is (L + P). These relationships are expressed by the following equation (1).

L/F -(L+P)/(F1G)・S/(F◆D
)...(1) Therefore, the position F of the virtual point light source LS,
In other words, the parallelism of the light rays is determined by the following formula (2
).

F - (S/P)・G-D (2) Also, when the above formula (2) is expressed for S, 5- (P/G
)・(F10), and it can be seen that the measurement magnification of this measurement system can be arbitrarily changed by G. In other words, even if the density of the silk formed on the light-receiving surface SC changes greatly depending on the level of parallelism of the light rays, if the MG between the two gratings GRI and GR2 is adjusted so that the stripe spacing can be easily measured, the grating GR
1. Parallelism of light rays can be measured without replacing GR2 itself. Furthermore, between the two grids GRI and GR2 [G
By gradually widening the beam from a narrow state, it is possible to adjust the beam to accurate parallelism.

FIG. 3 is a structural diagram showing another example of the parallel light measuring device of the present invention, corresponding to FIG. 1, and has the same configuration.

The same reference numerals are given to the parts and the explanation is omitted. 1st lattice GRI
an X stage X-5T that moves the second grating GR2 in the X direction, a Z stage 2-57 that moves the second grating GR2 in the Z direction, and an image sensor Is that receives the light flux that has passed through the first tether GRI and the second grating GR2. It is equipped with

The light source unit LSD is a laser diode LD.
, a collimator lens CL, and a mechanism (not shown) for displacing the relative positions of the laser diode LD and the collimator lens CL.

In such a configuration, the operation will be described by taking as an example a case where the focal lengths of the laser diode LD and the collimator lens CL are adjusted. In the initial state, the light beam from the unadjusted light source unit LSIJ passes through the two gratings GRI and GR2 and enters the image sensor Is. Between the grating GRI and the second grating GR2 [G7! Assume that l< has been adjusted. The light source unit LS is determined by the distance between the stripes on the image sensor IS and the equations (1) and (2) described above.
The virtual focus position of I, ie the parallelism of the rays, is calculated. However, it is not possible to tell whether the light rays are spreading too far or being caught between them just by looking at the spacing between the stripes. Therefore, X stage
When 5T is slightly displaced, the stripes scan in the X-axis direction.

The direction of this scanning is opposite when the light beam is expanding and when it is narrowing. Therefore, by measuring the interval between stripes and the scanning direction, the state of the light beam can be determined, and the previous error is corrected using a mechanism that displaces the relative position of the laser diode LD and the collimator lens cL.
5T to move the second grating GR2 toward the image sensor IS, widen the grating interval G to increase the measurement magnification, and perform the same measurement and adjustment as described above. By repeating this operation, the parallelism of the light beam is adjusted to N density. can be adjusted to

Additionally, since this device measures the X-direction component of the parallelism of light rays, by providing a mechanism that rotates the light source unit LSII around its tip axis, it is possible to measure error components of the parallelism of light rays in all directions. , can be adjusted.

In addition, a mechanism that processes signals from the image sensor Is to displace the relative positions of the X stage X-5T, Z stage 1-5T, laser diode LD and collimator lens CL, and the light source unit LSD about its optical axis. A controller may be added to control the rotating mechanism.

In the embodiments described above, measurement and adjustment of the focal length have been described, but if the distortion and inclination of the stripes are detected, the distortion and inclination of the light beam can also be measured and adjusted at the same time.

In addition, the accuracy of the lattice constant of the diffraction grating, which affects the accuracy of the measurement according to the present invention, can be measured using waste paper. Even if there is, there is no problem with adjustment.

In the embodiments described above, a device using two transmission type diffraction gratings has been described, but the same effect can be obtained by using a reflection type diffraction grating as the second grating and using the light beam reflected to the light source unit side.

(Effects of the Invention) As described above, according to the parallel light measuring device of the present invention, the parallelism of light rays can be precisely measured with a simple configuration and adjusted in a simple process, reducing device costs and parallelism of light rays. It is possible to significantly reduce the number of man-hours required for measurement and adjustment of degrees.

[Brief explanation of the drawing]

FIG. 1 is a structural diagram showing an example of a parallel light measuring device of the present invention,
FIG. 2 is a diagram for explaining the present invention in detail, and FIG. 3 is a structural diagram showing another example of the parallel light measuring device of the present invention. GRI...first lattice, GR2...'iE2 lattice, S
C... Light reception. Surface, LStl...Light source unit, LB...Light flux, L
S...-virtual point light source, X-5T...X stage, Z-
5T...2 stage, Is...image sensor, L
D...Laser diode, CL...Collimator lens.

Claims (1)

[Claims] 1. The first diffraction grating has the same lattice constant as the first diffraction grating, and each grating line is parallel to the grating line of the first diffraction grating. and a light-receiving surface that receives the light beams transmitted through each of the diffraction gratings, and by detecting the light intensity distribution appearing on the light-receiving surface, the parallelism of the light rays in the light beams is determined. A parallel light measuring device characterized in that it measures degrees. 2. The parallel light measuring device according to claim 1, wherein the light receiving surface is an image sensor. 3. The parallel light measuring device according to claim 1, further comprising means for arbitrarily changing the gap distance between the first diffraction grating and the second diffraction grating. 4. The parallel light measuring device according to claim 1, further comprising means for moving at least one of the first and second diffraction gratings in a direction perpendicular to grating lines within the plane of the diffraction grating. 5. The parallel light measuring device according to claim 1, further comprising means for displacing the relative position of an optical element in the light source unit that emits the luminous flux. 6. The parallel light measuring device according to claim 1, further comprising means for rotating the light source unit around its optical axis.