JPS63106933A - Optical information reproducing device - Google Patents

Abstract

PURPOSE:To form the titled device to a thin shape by constituting it so that a separating action of an incident light and a reflected light, an action of an astigmatism optical grating lens, and an action of a reflecting mirror for curving an optical path can be executed by one piece of a reflection type diffraction grating lens. CONSTITUTION:Among light beams which are made incident on a reflection type diffraction grating lens 16, a 0-th order diffracted light which is not diffracted by a reflection type diffraction grating carved on the surface of this lens 16 is made incident on an objective lens 18. The objective lens 18 is provided so that a light emitting point of a semiconductor laser 1 is an object point, and a point on the surface of a disk is an image point, therefore, the 0-th order diffracted light 17 which is made incident on the objective lens 18 is condensed as a condensing spot 19 of a diffraction limit onto an information recording surface 10 on the disk 9 from the objective lens 18. A primary diffracted light or a -1st order diffracted light of the reflection type diffraction grating lens 16 is divided into two by the first reflection type diffraction grating lens 16a and the second reflection type diffraction grating lens 16b, and thereafter, converted to a first luminous flux 23 and a second luminous flux 24, which are condensed to a 4-split light detector 20.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is for reproducing information on an optical information recording medium (hereinafter referred to as a disk) in an optical disk device such as an optical disk memory or a digital audio disk. The present invention relates to an optical information reproducing device.

[Prior Art] FIG. 13 is a diagram showing an example of the configuration of a conventional optical information reproducing apparatus disclosed in Japanese Patent Application Laid-Open No. 60-28044. In the figure, (1) is a semiconductor laser, (2) is an emitted light, and (3) is a semiconductor laser.
) is the first glass substrate, (4) is the ophaxis gelating lens for collimation, (5) is the parallel light beam, (6)
is the second glass substrate, (7) is the focusing ophaxis gelating lens, (8) is the first-order diffracted light, (9) is the disk, (10) is the information recording surface, (11) is the optical axis, (12)
) is the zero-order transmitted light, (13) is a grating lens for astigmatism, and (14) is a four-split photodetector.

Next, the operation will be explained. The emitted light (2) from the semiconductor laser (1) is collected by a collimating ophaxis gelating lens (4) formed on a part of the glass substrate (3) of ff1l, and is focused on the first glass substrate (3). ) A parallel beam of light that makes an angle of several tens @ with respect to the normal to the surface (5)
The light then enters a converging ophthalmic gelating lens (7) formed on a part of the second glass substrate (6).

The first-order diffracted light (8) by this converging ophaxis gelating lens (7) is focused on the information recording surface (10) of the disk (9). In this case, the first-order diffracted light (8)
The ophaxis gelating lens (7) is formed such that its optical axis is perpendicular to the information recording surface (10).

The reflected light of the 1st-order diffracted light (8) containing the bit information placed at the focal point goes again to the converging ophaxis gelating lens (7), but the 0th-order transmitted light (1
2) simply travels backward as transmitted light, and has an optical axis (11) that is different from the optical axis of the parallel light beam (5), which is the incident light on the converging ophaxis gelating lens (7).

Therefore, it is possible to separate the emitted light (2) or parallel light beam (5) from the semiconductor laser (1) from the zero-order transmitted light (12) containing bit information from the information recording surface (10).

From the reflected light consisting of the 0th-order transmitted light (12) obtained in this way, a grating lens for astigmatism optics (3) formed on a part of the first glass substrate (3) is used for four-split light detection. A recording information signal, a focus error signal, and a tracking error signal are detected by a light-receiving optical system consisting of a detector (14).

[Problems to be Solved by the Invention] Since the conventional optical information reproducing device is configured as described above, it has the following problems.

■Since two transmissive opaxis gelating lenses and a transmissive inline grating lens are used, the light utilization efficiency is extremely low. For example, the diffraction efficiency of the first-order diffracted light of the collimating ophaxis gelating lens (4) is determined when the numerical aperture is 0.
．． It is relatively high since it is about 1, but it is still at most 3
0%, and in the case of the converging ophaxis gelating lens (7), the reference (15December 1985/
Vo 1, 24, k24/ APPLIED 0
As shown in PTIC 8, pages 4307 to 4311), the diffraction efficiency of the first-order diffracted light is only 21%. Furthermore, the diffraction efficiency of the first-order diffracted light of the grating lens for astigmatic optics (13) is only 30% as shown in the above-mentioned document. Therefore, even if the diffraction efficiency of the 0th-order diffracted light of the converging off-axis gelating lens is 50% and the reflectance of the disk is 100%, the collimating off-axis gelating lens (3
) to the grating lens for astigmatism optics (13), the efficiency is only 0.95%.

■In order to read the bit information recorded on the information recording surface (10) of the disk (9) in the converging ophaxis gelating lens (7), the numerical aperture on the exit side must be NA-0.45 to 0. .5 is necessary. Moreover, since the parallel light beam (5), which is the incident light, is inclined by about 30° with respect to the exit side optical axis (11) of the convergent ophaxis gelating lens (7), the maximum equivalent diffraction angle is The value reaches as much as 57@, the minimum grating spacing for semiconductor laser light with a wavelength of λ-780 μm is about 0.82 μm, and the grating width when using a rectangular diffraction grating is 0.4
There was a problem in that the diameter was about 1 μm, and processing accuracy of a submicron was required. Furthermore, in order to increase the diffraction efficiency, the grating shape must be blazed, but there is also the problem that it is not easy to make the grating shape triangular with a grating spacing of 0.82 μm.

■Semiconductor laser (1), first glass substrate (3), second
The glass substrate (6) and the 4-split photodetector (14) are built into one housing (15), but the configuration shown in Figure 13 has larger dimensions and requires automatic focusing and auto-tracking. In order to achieve this, the above casing (
15) The entire actuator must be driven integrally, and although it is not shown in FIG. 13, there is a problem in that the driving weight of the actuator increases.

■In order to obtain a diffraction-limited focusing spot for reading out the bit information on the information recording surface (10), the first-order diffracted light of the above-mentioned focusing ophaxis gelating lens (7) is used. As mentioned above, the numerical aperture of the rating lens is NA-0.45 to 0.5, and the minimum grating interval is about 0.82 μm. Such a high numerical aperture focusing off-axis gelating lens is sensitive to changes in the wavelength of the semiconductor laser (1) that is the light source, and the focal length and diffraction angle of the focusing off-axis gelating lens are large. There was a problem in that the aberrations increased as the aberrations changed.

■There were many components, and there was a problem in assembling that the relative positions of each other had to be precisely aligned.

This invention was made to solve the above-mentioned problems. It has a simple structure with a reduced number of parts and can be made thinner. Furthermore, it is easy to manufacture and adjust, and is inexpensive and suitable for mass production. The object of the present invention is to obtain an optical information reproducing device with good characteristics.

[Means for Solving the Problems] The optical information reproducing device according to the present invention provides a single objective lens with the functions of a collimating off-axis gelating lens and a converging off-axis gelating lens. A single reflective diffraction grating lens has the functions of a facsimile gelating lens for separating incident light and reflected light, a grating lens for astigmatic optics, and a reflecting mirror for bending an optical path.

[Function] The optical information reproducing device of the present invention uses one single objective lens to perform the function of focusing the light emitted from the semiconductor laser onto the information recording surface, so that the light incident on the information recording surface and the By using a single reflective diffraction grating lens to separate the reflected light from the information recording surface and to bend the optical path, it has a simple structure with a small number of parts, and can be made smaller and thinner. can be achieved.

Moreover, the minimum grating spacing of the reflective diffraction grating lens used here is approximately 2 μm, which can be easily obtained through a process that applies microfabrication technology used in the manufacture of ordinary LSIs, etc., and can be manufactured in large quantities with high precision. Moreover, it can be manufactured at low cost and is suitable for mass production. Further, by using an aspherical lens made of plastic or the like as the objective lens, it can be made into a single lens, and mass production by injection molding or the like is possible.

[Example] Hereinafter, one example of the present invention will be described with reference to the drawings. 1st
The figures are a perspective view showing one embodiment of the invention, FIG. 2(a) is a first side view, and FIG. 2(b) is a plan view of FIG. 1.

In Figures 1 and 2, (16) is a semiconductor laser (1
) and a reflective diffraction grating lens placed in the middle of the optical path leading to the objective lens (18), (2o) is a semiconductor laser (1)
This is a 4-split photodetector installed at a different position from the installation position of .

Next, the operation will be explained. The divergent emitted light (2) from the semiconductor laser (1) is directly transmitted to the reflective grating lens (1).
6). As shown in FIG. 1, this reflective diffraction grating lens (16)
□, the first reflective grating lens (16a) and the second reflective grating lens (16a) are divided into two parts.
6b). And the dividing line above! ■
are arranged parallel to the track (21) of the disk (9).

Of the light incident on the reflective diffraction grating lens (16), the O-th order that is not diffracted by the reflective diffraction grating carved on the surface of the reflective diffraction grating lens (16) is transmitted to the objective lens (18). incident.

The objective lens (18) is designed so that the light emitting point of the semiconductor laser (1) is the object point and the point on the disk surface is the image point. The second-order diffracted light (17) is focused by the objective lens (18) onto the information recording surface (10) of the disk (9) as a diffraction-limited focused spot (19).

Figure 3 shows pits (22) on the information recording surface (10).
This figure shows the relationship between and the focused spot (19).

The reflected light of the focused spot (19) containing pit information from the information recording surface (10) is reflected again by the objective lens (1).
8), and is converted by the objective lens (18) into convergent light having the light emitting point of the semiconductor laser (1) as a condensing point, and enters the reflective diffraction grating lens (16).

Of the convergent light incident on the reflective diffraction grating lens (16), the O-th order generated by the reflective diffraction grating lens (16) has its optical path bent and then reverses the divergent output light (2). The first-order diffracted light or the first-order diffracted light of the reflective grating lens (16) is focused on the semiconductor laser (1) in a progressive manner, but the first-order diffracted light or first-order diffracted light of the reflective grating lens (16) is focused on the first reflective grating lens (16a). Second reflective grating lens (1
6b), and then converted into a first light beam (23) and a second light beam (24), which are respectively focused on the four-split photodetector (20).

As shown in FIG. 2(b), the first light beam (23) and the light beam (24) of 31i2 do not overlap with the optical path of the divergent emitted light (2), and from the semiconductor laser (1) to the Since they form non-zero angles θ1 and θ2 with the optical axis (25) leading to the reflective diffraction grating lens (16), only the reflected light having the pit information of the information recording surface (10) is divided into the four divided beams. can be led to a detector (20).

FIG. 4 shows the pattern shape of the 4-split photodetector (20) and the first convergence of the IJI light beam (23) and the second light beam (24) on the 4-split photodetector (20). Spot (2
8) and the second focused spot (29).

The photodetecting section (PDl) of the 4-split photodetector (20), (
By calculating the photocurrents from PD2), (PD3), and (PD4), an information signal, a focus error signal, and a tracking error signal can be obtained.

In other words, the information signal is (PD1+PD2+PD3+PD4
), the focus error signal is calculated using the modified Foucault method (PD1+PD3)-(P
By the calculation of (PD2+PD4), the tracking error signal is calculated by (PD1+PD4)-(PD2+PD) using the Pushinible method.
It can be obtained by the calculation of 3).

The grating pattern engraved on the first reflective grating lens (16a) and the second reflective grating lens (16b) includes the semiconductor laser (1), the split photodetector (20) and the first reflective grating lens. The arrangement positional relationship of the reflective diffraction grating lens (16a) and the second reflective diffraction grating lens (113b), the wavelength of the emitted light of the semiconductor laser (1), and the first luminous flux (23
) and the aberration added to the second light beam (24), and more precisely, it is expressed as an equiphase curve in which the phase difference defined by equation (1) is an even or odd multiple of π.

ΔΦ−Φ −Φ +Σ , C, xiyjLD
PD 1J 1 (0≦11 j≦1σ) (1) In the first equation, ΦLD is the value on the surface of the reflective diffraction grating lens (16) when the semiconductor laser (1) is the wave source. The phase, Φ, and D are the centers of the photodetecting sections (PD2) and (PD3) of the 4-split photodetector (20) or the photodetecting section (
The phase and coordinates (x, y) on the reflective diffraction grating lens (16) surface with the wave source at the center of PDI) and (PD4) are as shown in FIG. These are the coordinates taken.

When the centers of the photodetectors (PD2) and (PD3) are the wave sources, the grating pattern of the first reflective diffraction grating lens (16a) makes the centers of the photodetectors (PDI) and (PD4) the wave sources. In this case, the second reflective grating lens (1
A grid pattern of 6b) is obtained. In both cases, (1)
In the equation, the value of the coefficient C1j of the third term and the order 1. j
By selecting , various aberrations can be generated.

When all the coefficients are taken as an example, a lattice pattern as shown in FIG. 5 is obtained. In FIG. 5, for convenience of illustration,
The grid pattern is drawn only every 66 lines. When light enters the reflective diffraction grating lens (16) having the grating pattern as shown in FIG. 5 in the configuration shown in FIG. 16a) and a second reflective grating lens (16b)
The first reflective grating lens (16
The part incident on a) becomes the first beam (23) and the second
The portion incident on the reflective diffraction grating lens (16b) becomes a second beam (24).

In FIG. 1, by installing the 4-split photodetector (20) at the condensing position of the first light beam (23) and the second light beam (24), the modified Foucault method can be used as described below. A focus error signal can be obtained by

FIG. 6 shows the first-order diffracted light or the eleventh-order diffracted light diffracted by the first reflective grating lens 16a) when the distance between the objective lens (18) and the disk (9) changes. 1 shows changes in the light flux (23) of the photodetector (20) and changes in the focused spot on the photodetector (PDI) and (PD4) of the 4-split photodetector (20).

Similar to FIG. 6, FIG. 7 shows the first-order diffracted light or Changes in the second light beam (24), which is the 1st-order diffracted light, and the photodetector (PD2) of the 4-split photodetector (20)
, (PD3) shows changes in the condensed spot.

In Fig. 6, when there is no focus shift, the same figure (
As shown in b), a photodetector (PDI).

The focused spots (28) on (PD4) are symmetrical and have equal outputs.

Next, when the disk (9) approaches the objective lens (18), the first light beam (2
3) is the above-mentioned photodetector (PDI).

Although the light beam is condensed after the installation position of (PD4), the optical axis (26) does not change its position or direction, so as shown in Figure (a), the light/detection unit ( P
The power incident on DI) increases.

On the other hand, when the disk (9) moves away from the objective lens (18), the first light beam (23) reaches the installation position of the photodetector (PDI) and (PD4) as shown in FIG. 6(C). Since the light beam is condensed closer to the front, in this case, the power incident on the photodetector (PD4) is greater than the power incident on the photodetector (PDI).

Therefore, by calculating the difference between the photocurrent output from the photodetector (PDI) and the photocurrent output from the photodetector (PD4), a focus error signal corresponding to the amount of movement of the disk (9) can be obtained. Obtainable.

In the case of FIG. 7, if the difference between the photocurrent output from the photodetector (PD2) and the photocurrent output from the photodetector (PD3) is calculated, the focus can be similarly adjusted according to the amount of disk movement. Since an error signal can be obtained, the sum of the focus error signal and the focus error signal obtained with the first light beam (23) can be used as the focus error signal of the optical information reproducing apparatus according to the present invention.

FIG. 8 is a wiring diagram showing the circuit configuration for obtaining a focus error signal. In FIG. 30b) is a summing amplifier that adds the outputs of the photodetectors (PD2) and (PD4), and (31) is a summing amplifier (3).
This is a differential amplifier whose inputs are the outputs of 0a) and 30b. With the circuit configuration shown in FIG. 8, the focus error signal can be obtained as the output of the differential amplifier (31) by calculating (PD1+PD3)-(PD2+PD4), and the disk movement amount and focus error shown in FIG. Signal relationships are obtained.

Next, a tracking error signal can be obtained by a method similar to the push-pull method. In FIG. 1, the dividing line 11 of the reflective diffraction grating lens (16) is defined by the disc (
Since the first reflective diffraction grating lens (16) is arranged substantially parallel to the track (21) of the first reflective grating lens (9), the diffracted and reflected light by the pit (22) of the condensing spot (19) is
The power on the surface a) and the power on the surface of the second reflective grating lens (16b) are equal when there is no track deviation, but become different values when there is track deviation.

That is, as shown in FIG. 10, if there is a track deviation, the photodetector (PDI), (PD4) on the 4-split photodetector (2o) and the photodetector (PD2), ( P
Since the powers of the first condensing spot C28) and the second condensing spot (29) on D3) are different, the light detection unit (PD
I), (PD4) and (PD2), (PD3) are connected to the summing amplifier (32a) and the summing amplifier (32), respectively.
After addition in step b), the difference between the outputs of the summing amplifier (32a) and the summing amplifier (32b) is added to the differential amplifier (33).
If you calculate with , a positive or negative signal will be output. When there is no track deviation, the output of the differential amplifier (33) is zero. That is, a tracking error signal corresponding to the track deviation can be obtained.

Next, the optical information reproducing device according to the present invention has the advantage that even when the oscillation wavelength of the semiconductor laser (1), which is the light source, changes due to temperature change, no offset occurs in the focus error signal and the tracking error signal. Explain something.

(The oscillation wavelength of an aAs semiconductor laser depends on the temperature.
Since it changes by about 0.20 nm/'C, for example, if the ambient temperature changes by 50°C, the oscillation wavelength will change by lOnm. This amount of wavelength change is a non-negligible amount when a diffractive optical element is used.

FIG. 11 shows how the diffraction angle of the incident light changes in the reflective diffraction grating lens (16) when the oscillation wavelength of the semiconductor laser (1) changes, and the four-split photodetector (
20) shows how the condensed spot changes on the top.

Regarding the chief ray incident on the reflective grating lens (16), the difference between the oscillation wavelength λ of the semiconductor laser (1) and the grating period and diffraction angle θ of the reflective grating lens (16) with respect to the chief ray d s1nθ−λ ...(2
) holds true.

Here, if the wavelength changes from λ to λ+Δλ, the increase in the diffraction angle Δθ can be calculated by differentiating equation (2) as follows: d cosθΔθ−Δλ (3)
can be obtained from equation (3). That is, the following relationship holds: Δλ Δθ−tanθ □ (4) λ.

In FIG. 11(a), the reflective grating lens (
16) and the four-split photodetector (20) is R, and the movement of the principal ray on the four-split photodetector (20) when the oscillation wavelength of the semiconductor laser (1) changes by Δλ. occurs almost parallel to the X axis shown in FIG. 11, and when the oscillation wavelength becomes long, the first light beam (23)
The principal ray of moves from point F to point F1+, the principal ray of the second beam (24) moves from point F to point F2+,
When they become shorter, they move from points F and - to point F2-, respectively.

That is, since it moves along the dividing line 1□ of the 4-split photodetector (20) shown in FIG. 11(b), the photocurrent output of the photodetector (PDl) and the photodetector ( PD4
) is equal to the photocurrent output, and even if the focused spot moves from point F1 to point F1+ or point F1'''', the difference signal between the photocurrent outputs of the photodetector (PDI) and the photodetector (PD4) is the same. There is no offset in the focus error signal.

Similarly, the photodetector (PDI) and (PD2).

Calculation of photocurrent output of (PD3) and (PD4) (PD1+
It is clear from FIG. 11 that no offset occurs in the tracking error signal obtained by PD4)-(PDZ+PD3).

If the amount of movement of the chief ray on the four-split photodetector (20) is ΔX, then Equation (5) is obtained.

λ In other words, it can be seen that the amount of movement ΔX is proportional to the amount of wavelength change Δλ. This wavelength change amount Δλ and the 4-split photodetector (20
) FIG. 12 shows an example of the relationship between the amount of change in position of the chief ray and the amount of change ΔX of the principal ray.

As is clear from the above description, the semiconductor laser (1
) even if the oscillation wavelength of the 4-split photodetector (20
) will move along the dividing line 12, and neither the focus error signal nor the tracking error signal will be offset or degraded in sensitivity.

[Effects of the Invention] As described above, according to the present invention, a reflective diffraction grating lens is disposed between a semiconductor laser and an objective lens, and this reflective diffraction grating lens has the effect of separating and concentrating input and output light. The structure is designed to simultaneously function as a sensor optical system to generate a signal to constantly irradiate a light spot onto the information recording surface, and to bend the optical path necessary to make the device thinner, reducing the number of parts. In addition, a highly accurate error signal can be obtained with less deterioration of the focus error signal and tracking error signal due to changes in the oscillation wavelength of the semiconductor laser. In addition, the reflective diffraction grating lens can be mass-produced with high precision by injection molding, metal film deposition, etc., and has the effect of providing an inexpensive optical information reproducing device.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an optical information reproducing device according to an embodiment of the present invention, FIGS. 2(a) and (b) are a side view and a plan view of the device, and FIG. 3 is a pit on a disk surface. FIG. 4 is a diagram showing the relationship between the pattern of the 4-split photodetector and the focal spot, FIG. 5 is a diagram showing an example of a grating pattern, FIG. 6(a), (b) and (c) and Fig. 7 (a), (b), and (c) are diagrams showing changes in the luminous flux of diffracted light when the disk moves, and Fig. 8 (a), (b), and (c) is a wiring diagram showing the circuit configuration for obtaining the focus error signal, FIG. 9 is a diagram showing the relationship between the disk movement amount and the focus error signal, and FIGS. 10 (a), (b), and (
c) is a wiring diagram showing the circuit configuration for obtaining a tracking error signal, ffllll diagrams (a) and (b) are diagrams for explaining changes in the diffraction angle due to changes in wavelength, and Fig. 12 shows the position of the chief ray. FIG. 13, which is a diagram showing the relationship between the change and the amount of wavelength change, is a front view of a conventional optical information reproducing device. In the figure, (1) is a semiconductor laser, (2) is an emitted light,
(9) is an optical information recording medium (disk), (16) is a reflective diffraction grating lens, (1
6a) is the first reflective grating lens, (16b) is the second reflective grating lens, (17) is the 0th order credit, (
18) is the objective lens, (2o) is the 4-split photodetector, (2
1) is a truck. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Agent Patent attorney Masuo Oiwa (and 2 others) Figure 1 160: 11'l Fake Fuse<otrr Mashiko Lens
20: 4 minutes zusu tip tora kouki Fig. 2 (.) Fig. 2 (b) Fig. 3 Fig. 4 and 9 Fig. 5-O-1, 5-1-, 50, 511, 52X ( rnm) Fig. 6 (0) Fig. 6 (b) Fig. 6 (C) Fig. 7 (0) Fig. 7 (b) Fig. 7 (C) Fig. 8 (a) Fig. 9 Fig. 1Q (G) Figure 11 (a) Figure 12 Figure 13 Procedural amendment (voluntary) Showa Year, Month, Day 2, Name of the invention Optical information reproducing device 3, Relationship with the person making the amendment Patent applicant address 2-2-3 Marunouchi, Chiyoda-ku, Tokyo. Name (601) Mitsubishi Electric Corporation Representative Moriya Shiki 4, Agent Address 2-2-3-5 Marunouchi, Chiyoda-ku, Tokyo
, Detailed description of the invention in the specification to be amended. 6. Contents of the amendment”2

Claims (3)

[Claims] (1) An objective lens for condensing the emitted light from the semiconductor laser onto an optical information recording medium, and an objective lens for condensing the emitted light from the semiconductor laser onto the objective lens in the optical path from the semiconductor laser to the objective lens. a first reflective diffraction grating lens and a second reflective grating lens for guiding the reflected light containing information from the optical information recording medium to a position different from the installation position of the semiconductor laser and dividing the reflected light into two; reflective diffraction grating lenses on the same plane, and a dividing line separating the first reflective diffraction grating lens and the second reflective diffraction grating lens is parallel to the track of the optical information recording medium. What is claimed is: 1. An optical information reproducing device comprising: a reflective diffraction grating lens disposed so as to provide a reflection diffraction grating lens; and a 4-split photodetector for detecting the reflected light separated by the reflective diffraction grating lens. (2) The optical information reproducing device according to claim (1), wherein the light focused onto the optical information recording medium is 0th order diffracted light in a reflective diffraction grating lens. (3) The light reflected on the optical information recording medium, diffracted by the reflective diffraction grating lens, and incident on the 4-split photodetector is:
The optical information reproducing apparatus according to claim 1, wherein the first-order diffracted light or the -first-order diffracted light in the reflective diffraction grating lens.