JPS60253805A - Optical displacement detection apparatus - Google Patents

Abstract

PURPOSE:To enhance the resistance of the titled apparatus against a change with, time, by simplifying a mechanism so that the beam from an object to be detected converged by the hologram of a recording medium and the ratio of the converged beam and transmitted beam is changed on the basis of the change in the incident angle to the hologram due to the change in an optical axis direction to detect displacement. CONSTITUTION:The coherent beam 2 of a semiconductive laser 1 is converged to an optical disc 5 by a lens 4 through a beam splitter 3 and the reflected beam thereof is reflected by the splitter 3 through the lens 4 to be incident to a beam detector 7 through a recording medium on which a hologram was recorded. In this case, the hologram of the recording medium 6 is recorded by the interference of beams 8a, 8b and the beam 8a is allowed to be incident to the medium 6 at an incident angle theta from the converging point F1 on the recording surface of the disc 5 through a beam splitter 9 while the beam 8b is converged at a converging point F2 in this side of the medium 6 through a lens 10 and the splitter 9. Then, the detector 7 is arranged in the vicinity of the point F2 and, at the max. position of the output thereof, the position free from displacement on the recording surface of the disc 5 is determined.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical displacement detection device for optically detecting displacement of an object to be detected in the optical axis direction.

BACKGROUND TECHNOLOGY AND PROBLEMS For example, in an optical disc player, a focus servo is required to maintain a predetermined distance between the optical disc and the optical system. It is necessary to detect displacement from a predetermined position in the axial direction.

Various methods such as the astigmatism method and the knife edge method are conventionally known as methods for detecting focus errors. However, conventional methods detect focus errors by preparing multiple photodetectors, changing the angle of incidence on these photodetectors, and calculating the difference between the outputs of each photodetector. are doing.

However, if a plurality of photodetectors are used in this way and the difference in their outputs is to be determined, the mechanism becomes complicated.

In addition, in order to detect the change in the angle of incidence with a photodetector,
Since these photodetectors need to be placed accurately, they are not easy to assemble and are susceptible to misalignment due to aging.

OBJECTS OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide an optical displacement detection device that has a simple mechanism, is easy to assemble, and is resistant to deterioration over time.

Summary of the Invention The present invention includes a recording medium on which a hologram forming a predetermined angle with respect to the surface is recorded, and a photodetector that detects light from an object to be detected that is focused by the hologram, An optical system that changes the ratio of convergent light and transmitted light from the hologram by changing the angle of incidence on the porogram due to the displacement of the object to be detected in the optical axis direction, and detects the displacement based on the change in this ratio. This relates to a type displacement detection device.

EXAMPLE Hereinafter, an example of the present invention applied to an optical tisf player will be described with reference to FIGS. 1 to 6.

FIG. 1 shows the configuration of this embodiment. Coherent light 2 emitted from a semiconductor laser 1 such as a laser diode passes through a beam splitter 3 and is focused onto a recording surface of an optical disk 5 by a lens 4 .

The light 2 reflected by the recording surface of the optical disc 5 enters the lens 4 again. The light 2 converged by this lens 4 and reflected by the beam splitter 3 enters a recording medium 6 such as a photographic plate on which a hologram is recorded, and via this recording medium 6, it is transmitted to a single photodetector 7. incident. The shape and area of the photodetector 7 can be changed in various ways depending on the arrangement position, and may be in the shape of a disk, for example.

The hologram on the recording medium 6 is illuminated by light 8 as shown in FIG.
This was recorded by interference between a and 8b. light 8
a is an angle corresponding to the incident angle of the light 2 reflected by the recording surface of the optical disk 5 located at the convergence point F1 (distance X from the lens 4) shown in FIG. 1 and incident on the recording medium 6; At θ, the light 8b, which is likely to be incident on the surface of the recording medium 6 in FIG. The light converges at a convergence point F2 in front of the recording medium 6.

Holograms are classified into several types depending on their recording method, and in this embodiment, a phase hologram J1 is used.

The phase hologram is a phase liquid aJ! The reproducing light is diffracted by J, and in this embodiment, the light is converged by this diffraction. In the phase hologram, the utilization rate of the reproduction light is increased to 10 by selecting the intensity and exposure time of the lights 8a, 8b, which are the recording lights for the recording medium 6.
It is also possible to set it to 0%.

As described above, a photographic plate or the like is normally used as the recording medium 6, but in the case of a phase hologram, the material of the medium is appropriately selected depending on the above-mentioned utilization rate. Gelatin is used as a medium in order to obtain a higher utilization rate than silver salts used in ordinary photographic plates.

When gelatin is used as the medium, the recording lights 8a and 8b and the reproduction light 2 usually have different wavelengths, depending on the material of the photosensitive moon. for example,
While the wavelength of light 2 is in the band around 0.8 μm,
The wavelengths of the lights 8a and 8b are in shorter wavelength bands than the respective bands.

When light with different wavelengths is incident on a hologram,
Even if the incident angle is the same, the outgoing angle is different, so in order to obtain the same convergence point, it is necessary to make the incident angle different for light having different wavelengths.

, take orthogonal coordinates with the center of the recording medium 6 as the origin and the direction perpendicular to the recording medium 6 as the two axes, and the coordinates of the convergence point F2 in FIG. 2 as (xl yl, z,) ,
Let the coordinates of the light source of the light 8a be (1'+,, Ql, r+), the coordinates of the point where the light 2 in FIG. The coordinates of the point that simply passes through and converges due to the action of the lens 4 are (pz, Q2, rz), and the wavelength of the recording lights 8a and 8b is λ5, and the wavelength of the reproduction light 2 is λ2. In this case, if the enlargement magnification of the hologram after recording is m, the hologram imaging formula is expressed as follows.

If the hologram on the recording medium 6 is an on-axis bologram as shown in FIGS. 1 and 2, then the position of the convergence point F2 in FIG. 2, that is, the recording medium of the photodetector 7 in FIG. In contrast to 6, the positional relationship can be determined from only 2.

A bologram, which is a diffraction grating, is recorded on the recording medium 6 by the light beams 8a and 8b as described above, but the intensity of the diffracted light changes depending on the previous angle of incidence on the diffraction grating, and it depends on the Bragg angle condition. The highest diffraction efficiency is achieved when

That is, when the recording surface of the optical disc 5 is located at the convergence point F1 as shown in FIG. 1, the light 2 reflected by the optical disc 5 is incident on the bologram on the recording medium 6 at an angle θ. From now on, light 8a passes through the hologram to jii.
The light traveling in the opposite direction and being converged by the hologram become light 8b.
When the incident angle is θ, the ratio of convergent light is highest.

Therefore, if the photodetector 7 is placed near the convergence point I72 shown in 2H, when the recording surface of the optical disc 5 is located at the convergence point f-''1, the photodetector 7 (The output of 7 is the largest.

On the other hand, when the recording surface of the optical disk 5 is displaced from the position of the convergence point F1, the angle of incidence of the light 2 entering the recording medium 6'' also changes, as is clear from the 1-mens imaging formula. Then, the ratio of light converged by the bologram decreases, and the output of the photodetector 7 also decreases.

As a result, the output of the photodetector 7 has a substantially symmetrical distribution having a maximum value when the recording surface of the optical disc 5 is located at the convergence point F1, as shown in FIG. Therefore, when the output of the photodetector 7 is maximum, this is the position where there is no focus error, that is, no displacement of the recording surface of the optical disc 5.

In this embodiment as described above, the displacement of the recording surface of the optical disc 5 from the convergence point F1 can be detected by the four photodetectors 7, and there is no need to calculate the difference between the outputs of the plurality of photodetectors. Since there is no such thing, Wl and IQ are easy.

In addition, in this embodiment, the change in the incident angle of the light 2 is detected by the photodetector 7.
Since the photodetector 7 detects the intensity of the convergent light itself from the hologram on the recording medium 6 instead of directly detecting it, the photodetector 7 does not need to be placed so precisely. , easy to assemble, and resistant to misalignment due to aging.

In addition, the astigmatism method uses a cylindrical lens in the shape of a bullet hole, which is expensive as it requires polishing, but holograms can be easily mass-produced using photographic technology, making them extremely useful. It's cheap.

FIG. 4 shows an example of application of the embodiment shown in FIG.
It has a mechanism for adjusting waste.

In this application example, a plate-shaped birefringent medium 11 is attached to the beam 1 and the splitter 3, and this birefringent medium 11
An annular reflecting medium 12 that reflects one of the lights 2 separated by the lens 4 is attached to the lens 4. Further, an annular photodetector 13 that detects the light 2 reflected by the reflection medium 12 and the beam splinter 3 and transmitted through the hologram on the recording medium 6 is arranged so as to be in contact with the outer periphery of the photodetector 7. There is.

The incident angle of the light 2 that is reflected by the anti-fouling medium 12 and the beam splitter 3 and enters the hologram on the recording medium 6 is much larger than the incident angle of the light 2 that is reflected by the optical disk 5 and the beam splitter 3. different. For this reason, most of the light 2 reflected by the reflective medium 12 simply passes through the hologram of the recording medium 6''.

Therefore, the output of the photodetector 13 changes approximately linearly as shown in FIG. The area and shape of the photodetector 13 are set so that when the recording surface of the optical disc 5 is located at the convergence point Fl, the position of the lens 4 corresponds to the part where the position of the lens 4 changes linearly. There is.

To adjust the focus in the following application example,
The reference position of the lens 4 is set as an initial process before the optical disc 5 is operated so that the moving direction of the lens 4 can be determined when a nail error is detected.

FIG. 6 shows the procedure of this initial processing.

First, the memories lVl+ &OMz (not shown) for recording the sampling outputs of the photodetectors 13 and 7 are cleared by cello-clearing, and these memories lVl+
, set the address counter n of M2 to 1, and then set the lens 4
Set the driving voltage (■) to O to drive the lens in the optical axis direction.

Next, set the terminal to be used in the program 11014 to 13, and turn on the switch circuit 15 to the L P F 16 side according to the command from the terminal A. And L P F
16, switch circuit 15, A I) converter] 7 and terminal B, the ()-sampling output of photodetector 13 is stored in address n of memory M.

Next, a command B from the terminal of the program l1014 turns on the switch circuit 15 to the L P F 18 side. Then, the sampling output of the photodetector 7 is stored in address n-1 of the memory M2 via the switch circuit 15, the AD converter 17, and the terminal B.

The data in memory MZ (n) is transferred to memory 1vjz (n
4) If the data in M2(n) is smaller than the data in M2(n) and the data in M2(n) is 0, this initial processing is terminated. If none of the above applies, the terminal to be used in the program 11014 is set to C, the driving voltage (■) is increased by a unit amount, and this driving voltage (■) is output from the terminal C.

The drive voltage (2) output from the terminal C is supplied to the drive circuit 22 via the DA converter 21, and the lens 4 is driven in the optical axis direction. Thereafter, the address counter n is incremented by 1 and sampling of the output of the photodetector 13.7 is repeated.

Note that the outputs of the photodetectors 3 and 7 are sampled at a frequency twice as high as the servo band (several kHz to 10-odd kHz) by the drive circuit 22. Also, the LPF 16° 18 is used to remove various noises. There are 0 to 10 kll
Extract the signal in the z band.

Through the above initial processing, the sampling outputs of the photodetectors 13 and 7 shown in FIGS. 5 and 3 are recorded in the memories M1 and M2, respectively.

And note 1. The value of the stored data in the memory M1 that is the same as the address in the memory M2 where the value of the a data is the maximum, that is, the value at a predetermined position in the linearly changing part in FIG. 4 as the reference position.

Therefore, in order to perform the flux adjustment (during the operation of the optical disk 5), it is first determined whether the output of the photodetector 7 is at the maximum value, and if it is not the maximum value, the output of the photodetector 13 is lower than the reference value. Lens 4 depending on whether it is also large or small.
Determine the direction of movement.

In the following, an embodiment in which the present invention is applied to an optical disc player has been described, but it goes without saying that the present invention can be applied to other devices besides optical disc players.

Effects of the Invention - As described in L, according to the optical displacement detection device according to the present invention, the displacement of the object to be detected in the optical axis direction can be detected by changing the angle of incidence on the hologram even with one photodetector. Moreover, since there is no need for a circuit to calculate the difference between the outputs of a plurality of photodetectors, the mechanism is simple.

In addition, the photodetector does not directly detect the displacement of the incident angle, but the photodetector detects the convergent light p from the hologram.
Since it detects strong and weak abutments, there is no need to place the photodetector very accurately, and it is easy to assemble and is resistant to changes over time.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view showing one embodiment of the present invention, FIG.
The figure is a schematic side view showing the hologram recording method used in the embodiment shown in Fig. 1, and Fig. 3 is a graph showing the output of the photodetector in the embodiment shown in Fig. 1. FIG. 4 is a schematic side view showing an example of application of the embodiment shown in FIG.
FIG. 5 is a graph showing the output of another photodetector in the applied example shown in FIG. 4, and FIG. 6 is a flowchart showing the procedure of initial processing in the applied example shown in FIG. In the symbols used in the drawings, 2--
−−−−−−−−−−−−−−Recording medium 7−−−−−
-1---It is a photodetector. Agent Saturn Yoshio Katsunekan Figure 1 Figure 3 Figure 5 Figure 4 Figure 6

Claims (1)

[Claims] The recording medium has a recording medium on which a hologram forming a predetermined angle with respect to the surface is recorded, and a photodetector that detects the light from the object to be detected that is focused by the hologram, and An optical displacement detection device that changes the ratio of convergent light and transmitted light from the hologram by changing the angle of incidence on the hologram due to the displacement of the object to be detected, and detects the displacement based on the change in this ratio.