JPS632087B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical system adjustment device that can detect and adjust the parallelism of a beam and the inclination of an optical axis of a parallel optical system with high precision.

Generally, when a lens is used to focus incident light, if the incident light is a parallel beam parallel to the optical axis of the lens, the incident light will enter the focal point F' of the lens, as shown in Figure 1A. However, when the incident light is a convergent light or a diverging light emitted from a light source on the optical axis of the lens, the incident light is focused forward or toward the focal point F', respectively, as shown in FIG. 1B or C. When the lens is focused on the optical axis at the rear and the incident light is a parallel beam that is not parallel to the optical axis of the lens, Fig. 1D
As shown in , the light is focused at a position away from the optical axis within the focal plane including focal point F'. Utilizing this, the convergence position of the incident light is detected, and by measuring the amount of deviation Z of the convergence position from the focal point F' in the optical axis direction, the parallelism of the incident light can be determined by measuring the distance of the convergence position from the optical axis. Conventionally, a method has been used in which the inclination of the optical axis is detected by measuring h, and two quantities Z and h are set to zero, thereby obtaining a parallel beam parallel to the optical axis. However, this method has drawbacks such as it is quite difficult to adjust the optical lens and the accuracy of beam measurement and adjustment is low (measuring accuracy of approximately ±2' for parallelism and ±20'' for tilt). In particular, practical problems have arisen in the case of optical systems belonging to ultra-precision fields such as optical disk pickups that use semiconductor lasers.

In view of the above points, it is an object of the present invention to provide a lens system adjustment device that can detect and adjust the parallelism of a beam of a parallel optical system and the inclination of an optical axis with high precision.

First, the principle of the present invention will be explained with reference to FIG. In Figure 2, 1 is a prism with surfaces 1a and 1b.
The angle formed by the prism is set to be the critical angle with respect to the air of the glass constituting the prism, and the surface 1b is formed into a reflective mirror by applying a reflective film. 2 and 3 are light receiving elements that detect light transmitted through the surface 1a of the prism 1. First, consider a ray a that enters the prism 1, is reflected by the surface 1a, and then enters the rear surface 1b perpendicularly. The angle at which this ray a enters the prism 1 and the rear surface 1a, that is, the surface 1a of the ray _a0
Since the angle of incidence on the surface is θ _c , the ray a ₀ is totally reflected at the surface 1a. Ray a ₁ totally reflected by surface 1a is surface 1
Light ray _a2 , which is incident perpendicularly to b and reflected by surface 1b, takes the same path as ray _a1 , enters surface 1a again at an incident angle _θc , is totally reflected, and is totally reflected by surface 1a. The ray _a3 takes the same path as the ray _a0 , exits the prism 1, and returns to the light source. Therefore, in this case,
Since both the light ray a ₀ and the light ray a ₂ are totally reflected by the surface 1a and are not transmitted at all, no light enters the light receiving elements 2 and 3, and the detected value thereof is zero. Next, considering ray b,
Since the angle at which this ray b enters the rear surface 1a of the prism 1, that is, the angle of incidence of the ray b ₀ on the surface 1a is greater than θ _c , the ray b ₀ is totally reflected on the surface 1a. The light ray b ₁ totally reflected by the surface 1a is incident on the surface 1b almost perpendicularly, and the light ray b ₂ reflected by the surface 1b
enters the surface 1a again, but at this time the angle of incidence of the ray b ₂ on the surface 1a is smaller than θ _c , so the ray
A part of b ₂ is transmitted and enters the light receiving element 3 as a light beam b ₃ ', and the light beam b ₃ reflected by the surface 1a exits the prism 1. Therefore, in this case, only the light receiving element 3 performs detection. In addition, in the case of ray c, since the angle at which this ray c enters the prism 1 and enters the rear surface 1a, that is, the angle of incidence of the ray c ₀ on the surface 1a is smaller than θ _c , a part of the ray c ₀ is a ray The light ray c 1 is transmitted as c ₁ ′, enters the light receiving element 2, and is reflected by the surface 1a _.
is reflected by surface 1b and enters surface 1a again as ray _c2 , but since the incident angle of ray _c2 to surface 1a at this time is greater than θ _c , it is totally reflected, and the ray c that is totally reflected by surface 1a ₃ goes out of prism 1. Therefore, in this case, only the light receiving element 2 performs detection. Furthermore, in either case, the angle of incidence on surface 1a is the critical angle θ _c
If the angle of incidence is smaller, the smaller the incident angle, the greater the transmittance at the surface 1a, so the detection values of the light receiving elements 2 and 3 are large. Thus, only when the detection values of the light receiving elements 2 and 3 are both zero, the incident light is a parallel beam parallel to the optical axis.

Next, an embodiment of the present invention using the above-described principle will be described. In FIGS. 3 and 4, 10 is a prism, and a surface 10a is coated with an anti-reflection coating for light rays having an incident angle near the critical angle of the glass constituting the prism.
and a surface 10b which forms a reflecting mirror by applying a reflective film, and the angle formed by the surfaces 10a and 10b is set to be the critical angle θ _c of the glass constituting the prism 10 with respect to air. 11 and 1
2 is a light receiving element that detects the transmitted light from 10a,
It is fixedly arranged with respect to the prism 10.
Reference numeral 13 denotes an optical system to be tested, which has a lens 14 . 1
Reference numeral 5 denotes a mounting part for mounting the test optical system 13 in a predetermined direction using the reference plane 13a of the test optical system 13, and 16 indicates a mounting part for mounting the test optical system 13 in a predetermined direction using the reference plane 13a.
It is a fixed member that is rotatably held around the optical axis O, and is equipped with a scale for reading the rotational direction, and is integrally mounted with the optical system 13 and the mounting part 15 to be tilted up and down in the plane of the paper in Fig. 4 with respect to the optical axis O. Furthermore, it has a scale for reading the elevation angle. 17 is a light source disposed on the optical axis O so as to be movable in the optical axis direction. In addition, the optical axis O is emitted from the light source 17.
Each member is arranged so that, in the absence of the optical system 13 to be tested, the light traveling along the prism 10 enters the prism 10, enters the surface 10a at a critical angle of incidence θ _c , is totally reflected, and enters the surface 10b perpendicularly. It is located. Reference numeral 18 makes the sensitivity of the light receiving element 11 and the light receiving element 12 the same level, that is, the light from the light source is transmitted to each light receiving element 11, 1.
This is a correction circuit for correcting the difference in reflectance up to 2, and outputs a signal corresponding to the value obtained by multiplying the input by the reflectance at the surface 10b. 19 is a subtraction circuit, 20 is an absolute value circuit, 21 is a peak detector, 2
2 is a motor drive circuit; 23 is a motor that rotates the mounting portion 15 around the optical axis O via a transmission mechanism;
24 is a minimum value detection circuit, 25 is an elevation angle control device,
26 is an adder circuit, 27 is a minimum value detection circuit, 28 is a motor drive circuit, and 29 is a motor that moves the light source 17 along the optical axis O.

Since the embodiment of the present invention is configured as described above, when the optical system 13 to be tested is attached to the mounting part 15 and the light source 17 is turned on, the motor 23 is started and the lens 14 of the optical system 13 to be tested is turned on. The light from the light source 17 is rotated around the optical axis O, and at this time the light from the light source 17 is directed to the lens 1.
4, and when the optical axis of the lens 14 of the optical system to be tested 13 is tilted with respect to the optical axis O or the light source 17 is not at the focal position of the lens 14, the light that enters the prism 10 If the light is not parallel to the optical axis O, the light is incident on the light receiving elements 11 and/or 12 based on the above-mentioned principle of the present invention, and thus a signal is output from the light receiving elements 11 and 12.
The output _I1 from the light receiving element 11 corrected by the correction circuit 18 and the output I2 from the light receiving element ₁₂ are calculated by the subtraction circuit 1.
9, and further in the absolute value circuit 20 |I ₁ −I ₂
| is calculated. At the peak detector 21 |I ₁ −I ₂ |
When the maximum value of is detected, a signal is output to the motor drive circuit 22 to stop the motor 23.
Thus, when the beam incident on the prism 10 is tilted, the angle of incidence on the surface 10a is maximum or minimum when the direction of the beam tilt is within the plane of the paper in FIG. That is, since |I ₁ −I ₂ | takes the maximum value, the inclination direction of the beam is adjusted within the plane of the paper in FIG. Next, while the elevation angle control device 25 is actuated to tilt the fixed member 16 and elevate the lens 14 with respect to the optical axis O, the minimum value detection circuit 24 to which the signal from the absolute value circuit 20 is input is activated to |I ₁ −I ₂ ｜
At this time, the elevation angle control device 25 detects the minimum value of
to stop. Thus, in FIG.
Regarding rays b and c, which are inclined by the same angle in opposite directions to ray a, which is incident perpendicular to b, the angle of incidence of ray b ₂ on surface 1a is equal to the angle of incidence of ray c ₀ on surface 1a. Therefore, since the difference between the outputs of the light receiving elements 2 and 3 becomes 0, the optical axis of the lens 14 of the optical system 13 to be tested is adjusted to coincide with the optical axis O. Furthermore, the motor 29 is operated, and the correction circuit 18
The output I ₁ of the light receiving element 11 corrected by and the light receiving element 1
2 output I ₂ is input to the adder circuit 26 (I ₁ + I ₂ )
The minimum value detection circuit 27 calculates (I ₁ +
I ₂ ) is detected and a signal is output to the motor drive circuit 28 to stop the motor 29. The light source 17 is thus positioned at the focal point of the lens 14, and the light emitted from the light source 17 is converted into parallel light parallel to the optical axis O by the lens 14 and enters the prism 10.

FIG. 5 shows a second embodiment of the present invention, in which the same components as those in the embodiment shown in FIG.
is a prism, and the angle formed by the surfaces 30a and 30b does not need to be a critical angle for the air of the glass constituting the prism 10, and may be a right-angled prism, for example. Reference numeral 31 denotes a reflecting mirror, through which light from a light source enters the surface 30a at an incident angle approximately equal to the critical angle of air for the glass constituting the prism 30.
The light beam is arranged so as to be adjustable so that it is totally reflected by a and then enters the reflecting mirror 31 perpendicularly. Reference numeral 32 denotes an optical isolator consisting of a combination of a polarizing beam splitter and a 1/4 wavelength plate, which serves to block light returning to the light source and to reduce noise when the light source is a semiconductor laser, for example.

According to this second embodiment, its operation is similar to that of the embodiment shown in FIG. The same effect can be obtained by

As described above, according to the present invention, the parallelism of the beam of the parallel optical system and the inclination of the optical axis can be detected and adjusted extremely easily and with high precision by using the critical angle of the prism. effective. Furthermore, in the case of the second embodiment, the returned light is prevented from returning to the light source 17 by the optical isolator 32, which is extremely effective in cases where the returned light affects the output, such as in semiconductor lasers. . Here, total reflection surfaces (surfaces 1a, 10a, 30
a) does not need to be one surface of the prism, and may simply be a transparent plate such as a glass plate.

In the above explanation, the adjustment operations are performed using a motor, but each adjustment operation may also be performed manually while observing the output of the light receiving element, especially when vibrations are likely to cause adverse effects. Manual adjustment is preferred. Further, the light receiving element may be divided into one for use, and other photoelectric conversion devices may also be used. Further, in the second embodiment, the surface 30a is not coated with an antireflection film, but this is sufficient for practical use if particularly high precision is not required.

Furthermore, after aligning the optical axes using the device of the present invention, if the optical axis of another device to which the optical system to be tested is to be attached is aligned with the optical axis O in advance, then the optical system to be tested is attached to the device. , it becomes possible to incorporate the optical system to be tested with the optical axis aligned with very high precision.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the parallelism of incident light and the image formation state by the lens, Fig. 2 is an explanatory diagram showing the principle of the invention, and Figs. 3 and 4 are illustrations of the first embodiment according to the invention. The schematic diagram shown in FIG. 5 is a diagram showing a second embodiment according to the present invention. 1, 10, 30...prism, 2, 3, 11,
12... Light receiving element, 13... Test optical system, 14...
... Lens, 15 ... Mounting part, 16 ... Fixing member,
17... Light source, 18... Correction device, 19... Subtraction circuit, 20... Absolute value circuit, 21... Peak detector, 22, 28... Motor drive circuit, 23, 29
... Motor, 24, 27 ... Minimum value detection circuit, 2
5... Elevation angle control device, 26... Addition circuit, 31
... Reflector, 32... Optical isolator.

Claims (1)

[Claims] 1. A light source disposed on the optical axis, and a catadioptric device disposed obliquely to the optical axis so that the light emitted from the light source along the optical axis is incident at a critical angle. a reflective surface disposed so that the light along the optical axis that is totally reflected by the catadioptric surface is incident perpendicularly, and the light that is directly transmitted through the catadioptric surface and the light that is totally reflected by the catadioptric surface is Furthermore, a photoelectric conversion device disposed behind the catadioptric surface so as to individually detect the light transmitted through the catadioptric surface after being reflected by the reflective surface; An optical system adjustment device, comprising: a holding mechanism that holds a test optical system therebetween. 2. A light source arranged on the optical axis, a catadioptric surface arranged obliquely with respect to the optical axis so that the light emitted from the light source along the optical axis is incident at a critical angle, and the catadioptric surface A reflective surface arranged so that the light along the optical axis that is totally reflected by the surface is incident perpendicularly, and the light that is directly transmitted through the catadioptric surface and the light that is totally reflected by the catadioptric surface and further reflected by the reflective surface. a photoelectric conversion device disposed behind the catadioptric surface so as to be able to individually detect the light transmitted through the catadioptric surface after the light has been transmitted, and a test optical system between the light source and the catadioptric surface. a holding mechanism that holds the photoelectric conversion device so as to be adjustable around the optical axis and in a vertical direction with respect to the optical axis; a device that detects the maximum difference in output of the photoelectric conversion device for two incident lights; 1. An optical system adjustment device, comprising: a device for detecting a minimum value of the sum of outputs, and capable of detecting a deviation of an optical axis of an optical system to be tested. 3. It is characterized by being equipped with a device for detecting the minimum value of the difference in output between two incident lights of the photoelectric conversion device, and capable of detecting the deviation of the optical axis and the focal position of the optical system to be tested. An optical system adjustment device according to claim 2.