JPH0536111A - Optical information read-out device - Google Patents

Abstract

PURPOSE:To eliminate a stray light to a detector with simple constitution without using a hologram to an optical information read-out device. CONSTITUTION:This device is constituted so that a photodetector 10 is jointed to a prism face forming an obtuse angle with an incident plane to the prism 3, a polarizing film 4 reflecting one part of a laser light beam and transmitting one part of a luminous flux reflected by the optical disk 6 is formed on the surface of a prism slope, after only a reflected luminous flux is reflected in the prism 3, is made incident on the detector 10. By such simple constitution, an excellent focusing error and a tracking error signals are attained without being influenced by the stray light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information reader for optically reading information on a recording medium such as an optical disk.

[0002]

2. Description of the Related Art Various optical information readers have been proposed which irradiate a recording medium with a light beam and receive the reflected light from the recording medium by a light detecting means to reproduce recorded information. For example, Japanese Unexamined Patent Publication No. 63-136334 (conventional example 1) discloses a device as shown in FIG. 16 (perspective view) and FIG. 17 (front view). The light emitted from the semiconductor laser 50 is converted into parallel light by the collimator lens 51, reflected by the polarizing film 53 of the beam splitter 52, and reaches the optical disc 55 through the objective lens 54. The light beam reflected by the optical disk 55 passes through the objective lens 54 again and the polarizing film of the beam splitter 52.
Reach 53. The light transmitted through the polarizing film 53 has a focus error, a tracking error signal detection function and a light collection function,
A hologram 56 having a polarization function is incident on a parallel plate 57 having a reflecting surface. The incident light is reflected by the hologram 56, further internally reflected in the parallel plate 57, and incident on the detector 58.

Further, Japanese Unexamined Patent Publication No. 64-13239 (Prior Art 2) discloses a device as shown in FIG. 18 (perspective view) and FIG. 19 (plan view). The light emitted from the semiconductor laser 59 is partially reflected by the inclined surface 61a of the prism 61 formed on the semiconductor substrate 60, and reaches the optical disc through an objective lens (not shown). The light beam reflected by the optical disk reaches the inclined surface 61a of the prism 61 through the objective lens again. A polarizing film is applied to the inclined surface 61a. The light transmitted through the polarizing film is received by the signal light detecting photodetector 62 formed on the surface of the semiconductor substrate 60. The light reflected by the signal light detecting photodetector 62 is internally reflected by the upper surface of the prism 61, and then enters the signal light detecting photodetector 63. The photodetector 64 is a rear monitor and is used for APC that keeps the amount of light emitted from the objective object constant.

[0004]

However, the apparatus disclosed in the prior art example 1 uses the hologram 56, but the hologram 56 generally has a large wavelength dependency, and the semiconductor laser 50 is exposed to the outside air. When the wavelength fluctuates due to the temperature, the condensed state of the reflected light flux and the polarization angle fluctuate, and the spot on the detector 58 changes, so that the focus error and the tracking error signal are likely to be offset. Further, in order to apply the conventional optical system to a magneto-optical disk, it is necessary to add a polarization function to the hologram 56 in addition to the above-mentioned function, and it is technically difficult to form such a hologram 56. . In addition, when an element other than the hologram has a polarization function, a separate member (for example,
It is necessary to add a polarization beam splitter, a wave plate, etc.), which leads to a problem that the pickup becomes large in size and high in cost.

Next, in the device disclosed in the above-mentioned conventional example 2, stray light is incident on the photodetectors 62, 63 for signal detection by causing the emitted light flux of the semiconductor laser 59 to be obliquely incident on the prism 61 when viewed from above. It is configured so that it does not enter. This is because when the semiconductor laser and the prism are arranged in a straight line when viewed from above the semiconductor substrate, the emitted light from the semiconductor laser is partially reflected by the polarizing film on the prism inclined surface toward the optical disc, but the rest is inside the prism. This is because the light then enters the photodetector for signal detection and becomes stray light, which adversely affects the detection of focus error and tracking error signals. However, when such a method is used, the pickup tends to be large in plan view, and it is difficult to align the positions and angles of the semiconductor laser 59, the prism 61, and the photodetectors 62 and 63 for signal detection.

The present invention has been proposed to solve the above-mentioned problems, and does not use a hologram, has a simple structure, a small number of parts, is low in cost, is compact, and has little stray light. The purpose is to provide a device.

[0007]

In order to achieve the above object, the present invention provides an optical system using at least a semiconductor laser, an objective lens, a prism, and a photodetecting means for receiving reflected light from an optical disk. In the information reading device, the light detecting means is joined to the prism surface forming an obtuse angle with the incident surface to the prism, and the inclined surface of the prism reflects a part of the emitted light from the semiconductor laser and reflects it on the optical disk. Is provided with a polarizing film that transmits the generated light flux, and after the transmitted light reflected by the optical disc and transmitted through the polarizing film is internally reflected at least once in the prism,
The optical information reading device is configured to enter the light detecting means. Also, it is reflected by the optical disc,
An optical information reading device is provided, in which a condenser lens having a total reflection coating on the transmitted light emission side surface is provided on a prism surface extending in the traveling direction of transmitted light transmitted through a polarizing film on a prismatic surface. . Further, the optical information reading device is provided with a semiconductor laser so that the radiated light is incident on the prism inclined surface from a direction substantially orthogonal to the prism surface provided with the light detecting means.

[0008]

Since the hologram is not used as described above, the spot on the detector does not change, and the focus error and tracking error signals are less likely to be offset. Further, since a detector is provided on the prism surface that forms an obtuse angle with the entrance surface to the prism, and unnecessary light is emitted from the other prism end surface, stray light can be reduced. Further, since the semiconductor laser is arranged in a direction orthogonal to the prism surface on which the light detecting means is provided, it is not necessary to provide a condenser lens or a collipator lens.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment of the present invention in which light emitted from a semiconductor laser 1 is collimated by a collimator lens 2 into a parallel light beam and is polarized by a polarizing film 4 formed on a slope 3a of a prism 3. Part of the light is reflected and reaches the optical disk 6 through the objective lens 5. The light transmitted through the inclined surface of the prism 3 (shown by a broken line) is partially reflected by the bottom surface of the prism 3 after being totally reflected, and the rest is directly incident on the prism end surface 3b.
Incident on. Since the antireflection coating 7 is applied to the prism end face 3b, all the light incident on the prism end face 3b goes out of the prism 3 and does not become stray light. The light flux reflected by the optical disc 6 reaches the polarizing film 4 again through the objective lens 5. The light transmitted through the polarizing film 4 is reflected by the prism 3
The light enters the condenser lens 8 joined to the bottom surface of the prism 3. The condenser lens 8 has a total reflection coating 9 on its emission surface. Therefore, the parallel light flux incident on the condenser lens 8 becomes a condensed light at the exit end face thereof and is totally reflected.

The totally reflected condensed light is incident on the upper surface of the prism 3 before forming an image. Photodetector on top of prism 3
Photodetector through cover glass 10a to protect 10 1
0 is joined. The photodetector 10 may be bonded to the upper surface of the prism 3 without providing the cover glass 10a. A part of the light incident on the upper surface of the prism 3 is transmitted and is received by the detector 11 of the photodetector 10. The light reflected by the remaining photodetector 10 is internally reflected by the bottom surface of the prism 3 and, after image formation, becomes divergent light and is received by the detector 12 of the photodetector 10. Then, the signals recorded on the optical disk 6 can be detected from the detected light amounts of the detector 11 and the detector 12 of the photodetector 10. Here, the three-divided regions 11a, 11b, and 11c of the detector 11 are set to A,
Let B and C be the three-divided regions 12a, 12b and 12c of the detector 12 be D, E and F, respectively. Focus error signal (FE)
Are the areas 11a and 11c of the detector 11 and the area of the detector 12.
The difference signal of the sum signals of the region 11b of the detector 11 and the regions 12a and 12c of the detector 12 is detected from the sum signal of 12b. That is, FE = A + C + E- (B + D + F). Also,
The tracking error signal (TE) is due to the difference signal between the areas 11a and 11c of the detector 11 or the area 11 of the detector 11.
a from the sum signal of the area 12c of the detector 12 to the detector 11
Is detected by the difference signal of the sum signal of the region 11c of the detector 12 and the region 12a of the detector 12. That is, TE = A-C or (A +
F)-(C + D). Further, the information signal (RF) is supplied to all areas 11a to 11c of the detector 11 and all areas 12a of the detector 12.
It is detected by the sum signal of ~ 12c. That is, RF = A + B
+ C + D + E + F.

FIG. 2 shows the principle of detecting the focus error signal. Of these, FIG. 2A shows a spot image of the photodetector 10 at the time of focusing. The spot images are before and after the image forming point x (see FIG. 1), are equidistant from the image forming point x, and the spot images on the detectors 11 and 12 are equal (lower part of FIG. 2-A). Therefore, the focus error signal (FE) based on the above equation becomes zero. FIG. 2B shows the disk 6
And the objective lens 5 is approaching. In this case, the light flux reflected by the disk 6 and transmitted through the objective lens 5 becomes divergent light. Therefore, the image formation point x is on the rear side (a position farther from the focal point position on the optical axis) than that at the time of focusing, and the spot image on the detector 11 is larger than the spot image on 12 (lower part of FIG. 2B). . Therefore, FE> 0. FIG. 2C shows a state in which the disc 6 and the objective lens 5 are away from each other. The light flux reflected by the disk 6 and transmitted through the objective lens 5 becomes focused light. Therefore, the image formation point is on the front side (a position closer to the focus position on the optical axis) than that at the time of focusing, and the spot image on the detector 11 is smaller than the spot image on the detector 12.
(Figure 2C, lower row). Therefore, FE <0. The focus error signal is detected as described above. The tracking error signal is obtained by detecting the push-pull signal by the AC of the detector 11 of the photodetector 10 or the (A + F)-(C + D) of the detectors 11 and 12.

As described above, according to the present embodiment, among the luminous fluxes emitted from the semiconductor laser 1, the luminous flux transmitted through the polarizing film 4 is emitted from the prism end face 3b after the bottom surface reflection of the prism 3 or directly from the prism end face 3b. Since it is emitted, unnecessary light does not enter the detectors 11 and 12 of the photodetector 10, and the reflected light from the disk 6 enters the prism 3 and then is collected and reflected by the condenser lens 8. , A photodetector 10 bonded to the prism 3 after being internally reflected multiple times in the prism 3.
Since the detectors 11 and 12 are designed to receive light,
Good focus error and tracking error signals can be obtained.

FIG. 3 shows a second embodiment of the present invention, in which parts corresponding to those of the first embodiment are designated by the same reference numerals (the same applies to the following embodiments). A part of the light emitted from the semiconductor laser 1 is reflected by the polarizing film 4 provided on the inclined surface 3a of the prism 3, and reaches the optical disc 6 through the objective lens 5 not shown. The light (shown by the broken line) transmitted through the inclined surface of the prism 3 is partially incident on the prism end surface 3b after total reflection on the bottom surface of the prism 3, and the rest is directly incident on the prism end surface 3b. Since the antireflection coating 7 is applied to the prism end face 3b, all the light incident on the prism end face 3b goes out of the prism 3 and does not become stray light.

The light flux reflected by the optical disk 6 is again
It reaches the polarizing film 4 through the objective lens 5. The light transmitted through the polarizing film 4 enters the prism 3 and is totally reflected by the bottom surface of the prism 3. The totally reflected light is incident on the upper surface of the prism 3 before forming an image. A cover glass 10a is provided on the upper surface of the prism 3.
The photodetector 10 is joined via the. The photodetector 10 may be bonded to the upper surface of the prism 3 without providing the cover glass 10. A part of the light incident on the upper surface of the prism 3 is transmitted to the detector 11 of the photodetector 10.
Is received by. The light reflected by the remaining photodetector 10 is
The light is internally reflected by the bottom surface of the prism 3 and, after image formation, becomes divergent light and is received by the detector 12 of the photodetector 10. Then, the signals recorded on the optical disk 6 can be detected from the detected light amounts of the detector 11 and the detector 12 of the photodetector 10. The focus error and tracking error signal detection principles are the same as in the first embodiment.

As described above, according to the present embodiment, among the luminous flux emitted from the semiconductor laser 1, the luminous flux transmitted through the polarizing film 4 is reflected by the bottom surface of the prism 3 and then emitted from the prism end surface 3b or directly on the prism end surface. Since the light is emitted from 3b, unnecessary light does not enter the detectors 11 and 12 of the photodetector 10, and good focus error and tracking error signals can be obtained. Further, since it is a finite optical system, a collimator lens and a condenser lens are not required, which contributes to cost reduction and downsizing.

FIG. 4 (partial view) and FIG. 5 (overall view) show a third embodiment of the present invention. The light emitted from the semiconductor laser 1 is reflected by the reflecting surface 14 provided on the semiconductor substrate 14.
The prism 3 which is totally reflected by a and is provided on the semiconductor substrate 14
A part of the light is reflected by the polarizing film 4 provided on the inclined surface 3a, and reaches the optical disk 6 through the total reflection mirror 13 and the objective lens 5. The light transmitted through the slope of the prism 3 (shown by the broken line) is
After entering the prism end face 3b, all the light goes out of the prism 3 and does not become stray light. The light emitted from the side opposite to the emission direction of the semiconductor laser 1 is the semiconductor substrate 14
The light is received by the detector 15 provided above, and the output of the detector 15 controls the objective emission light to be constant.

The light beam reflected by the optical disk 6 reaches the polarizing film 4 again through the objective lens 5 and the total reflection mirror 13. The light transmitted through the polarizing film 4 enters the prism 3 and is totally reflected by the prism end face 3b. The totally reflected light is incident on the bottom surface of the prism 3 before forming an image. The bottom surface of the prism 3 is joined to a semiconductor substrate 14, and the semiconductor substrate 14 is provided with detectors 11 and 12. A part of the totally reflected light enters the detector 11 and is received. The light reflected by the detector 11 is reflected by the prism end face 3b, becomes an divergent light after being imaged, and is received by the detector 12. And the detector 11
The signal recorded on the optical disk 6 can be detected from the amount of light detected by the detector 12. The focus error and tracking error signal detection principles are the same as in the first embodiment. As shown in FIG. 5, the semiconductor substrate 14, the total reflection mirror 13, and the objective lens 5 are housed in a case 16 so that they can be integrally driven in the track direction and the focus direction. In this embodiment, the light emitted from the semiconductor laser 1 is reflected by the reflecting surface 14a provided on the semiconductor substrate 14, but the light emitted from the semiconductor laser 1 provided on the planar semiconductor substrate 14 is emitted. The light is reflected by the surface of the prism 3,
The structure may be such that it passes through the opening formed in the semiconductor substrate 14 and is guided to the objective lens and the optical disk.

As described above, according to the present embodiment, among the light fluxes emitted from the semiconductor laser 1, the light flux transmitted through the polarizing film 4 is directly emitted from the prism end face 3b, so that unnecessary light is incident on the detectors 11 and 12. And good focus error and tracking error signals can be obtained. Further, on the same semiconductor substrate 14, the semiconductor laser 1 and the detectors 11, 1 are provided.
2. The prism 3 can be arranged, which contributes to cost reduction and compactness.

FIG. 6 (partial view) and FIG. 7 (overall view) show a fourth embodiment of the present invention. Basically the same as in the third embodiment, except that the reflecting surface 14a (see FIG.
The third embodiment is different from the third embodiment in that the semiconductor laser 1 is arranged on a surface perpendicular to the surface on which the photodetectors 11 and 12 are formed instead of providing the reference laser. As shown in FIG. 7, the semiconductor substrate 14, the total reflection mirror 13, and the objective lens 5 are contained in a case 16,
It is designed to be integrally driven in the track direction and the focus direction. The effects of this embodiment are as follows. Since the process of forming the reflecting surface on the semiconductor substrate can be omitted, the manufacturing is facilitated, which contributes to cost reduction.
Further, since the number of reflecting surfaces between the semiconductor laser and the disk is reduced by one, the deterioration of aberration due to the reflecting surfaces is reduced.

FIG. 8 shows a fifth embodiment of the present invention and shows an optical system for a magneto-optical disk. The light emitted from the semiconductor laser 1 is collimator lens 2
As a result, a parallel light beam is formed and enters a λ / 2 plate 17 joined to the slope 3a of the prism 3. The surface of the λ / 2 plate 17 is provided with a polarizing film 4 whose phase difference does not change with respect to transmitted light. A part of the light flux is reflected by the polarizing film 4, passes through the objective lens 5, and reaches the magneto-optical disk 6a. The light transmitted through the polarizing film 4 and the λ / 2 plate 17 (shown by a broken line) is partially reflected by the bottom surface of the prism 3 and then is incident on the prism end surface 3b, and the rest is directly incident on the prism end surface 3b. Since the antireflection coating 7 is applied to the prism end face 3b, all the light incident on the prism end face 3b goes out of the prism 3 and does not become stray light.

The light beam reflected by the magneto-optical disk 6a passes through the objective lens 5 again, and is applied to the λ / 2 plate 17 by the polarizing film 4
Reach The light transmitted through the polarizing film 4 passes through the λ / 2 plate 17, enters the prism 3, and enters the condenser lens 8 joined to the bottom surface of the prism 3. The condenser lens 8 has a total reflection coating 9 on its emission surface. Therefore, the parallel light flux incident on the condenser lens 8 becomes a condensed light at the exit end face thereof and is totally reflected. The totally reflected condensed light is incident on the upper surface of the prism 3 before forming an image. A polarizing film 18 is applied to a part of the upper surface of the prism 3. In addition, the cover glass 10 via the polarizing film 18
A photodetector 10 having a is joined. The photodetector 10 may be bonded to the upper surface of the prism 3 without providing the cover glass 10a. A part of the light reaching the polarizing film 18 is transmitted and is received by the detector 11 of the photodetector 10. The polarizing film 18 is coated at least in the area corresponding to the detector 11. The light reflected by the remaining polarizing film 18 is internally reflected by the bottom surface of the prism 3, becomes an divergent light after being imaged, and is received by the detector 12 of the photodetector 10. Then, the detector 11 and the detector 12 of the photodetector 10 are
The differential detection of the signal recorded on the magneto-optical disk 6a can be performed based on the detected light amount. The focus error signal and tracking error signal detection principles are the same as those in the first embodiment, and a description thereof will be omitted.

Semiconductor laser 1, prism 3, and λ / 2
The plate 17 is configured to satisfy the following conditions. The polarization direction of the incident light from the semiconductor laser 1 to the polarization film 4 provided on the λ / 2 plate 17 is configured to match the P polarization direction or the S polarization direction. Further, the azimuths of the fast axis or the slow axis of the λ / 2 plate 17 are from the semiconductor laser 1 to the polarizing film 4.
It is arranged so as to form an angle of approximately 22.5 ° with respect to the polarization direction of the incident light. Therefore, when the light flux reflected by the magneto-optical disk 6a and transmitted through the polarization film 4 is transmitted through the λ / 2 plate 17, the polarization direction thereof is rotated by 45 °, and the polarization direction of the incident light on the polarization film 18 is the P polarization direction or , The angle of about 45 ° with respect to the S polarization direction. Further, the polarization direction of the reflected light beam from the polarizing film 4 is arranged so as to be parallel or perpendicular to the groove of the magneto-optical disk 6a.

FIG. 9 is an explanatory view showing the polarization state of incident light from the semiconductor laser 1 to the detectors 11 and 12 of the photodetector 10. The emitted light from the semiconductor laser 1 is linearly polarized light, which is polarized in the in-plane direction of the paper and is incident on the polarizing film 4 (FIG. 9A). The polarization direction of the incident light matches the P polarization direction on the polarizing film 4 as described above. λ / 2 plate 17
The polarizing film 4 applied to the polarizing film 4 has a reflectance of 50% with respect to the P polarization direction and a transmittance of 100% with respect to the S polarization direction.
Therefore, there is no phase difference with respect to the transmitted light. Therefore, FIG. 9B
As shown in, the light reflected by the polarizing film 4 is linearly polarized light and has an intensity of 1 /
It becomes a luminous flux of 2. This light flux enters the magneto-optical disk 6a via the objective lens 5.

The reflected light is rotated in the directions of θ _K and −θ _K depending on the direction of magnetization on the magneto-optical disk 6a under the influence of the reflectivity of the magneto-optical disk 6a and the Kerr effect, and the polarization state as shown in FIG. 9C is obtained. Becomes The reflected light flux of the magneto-optical disk 6a passes through the objective lens 5 again and enters the polarizing film 4. Since the polarizing film 4 has the characteristics as described above, the transmitted light does not lose the signal intensity of the S-polarized component, which is the information signal component, and the intensity of only the P-polarized component becomes 1/2 and the transmitted light becomes On the other hand, since it has no phase, it becomes linearly polarized light (FIG. 9D). Transmitted light flux is λ / 2 plate 17
When transmitted through, the polarization direction is rotated by 45 °, reflected and condensed by a condenser lens, and the incident light polarization direction to the polarization film 18 becomes an angle of about 45 ° with respect to the P-polarized or S-polarized direction, It is incident on the polarizing film 18.

The polarizing film 18 has a P-polarization reflectance of 0% and an S-polarization reflectance of 100%. As described above, the azimuth of the polarization direction of the incident light beam is P polarization direction and S polarization direction on the polarization film 18, Almost
Since it becomes 45 °, the incident light (reflected light at the polarizing film 18 and transmitted light) to the detectors 11 and 12 on the photodetector 10 is in a state as shown in FIG. 9E. The information signal (RF) is detected by the detector 11
11a to 11c sum signal and detector 12 total area 12
It is detected by the difference signal of the sum signal of all regions a to 12c.
That is, RF = A + B + C- (D + E + F). By doing so, the in-phase noise component is canceled. In the present embodiment, the incident polarization direction to the polarizing film 4 is set to the in-plane direction of the paper surface. However, when the polarization direction is perpendicular to the paper surface, the description contents of the S-polarized component and the P-polarized component other than the polarization film 18 are The same explanation can be obtained by simply changing the positions.

As described above, according to this embodiment, of the luminous flux emitted from the semiconductor laser 1, the luminous flux transmitted through the polarizing film 4 is
After being reflected by the bottom surface of the prism 3, it is emitted from the prism end surface 3b or directly emitted from the prism end surface 3b, so that unnecessary light does not enter the detectors 11 and 12.
Good focus error and tracking error signals can be obtained. In addition, it is possible to read information from the magneto-optical disk. Further, since the hologram is not used, the semiconductor laser 1
However, even when the wavelength changes due to the outside air temperature, the condensed state of the reflected light flux and the polarization angle rarely change, so that the focus error and the tracking error signal are less likely to be offset. Further, since the beam splitter, focus error signal detection, tracking error signal detection, and magneto-optical signal detection element are integrated in spite of being an optical system for the magneto-optical disk 6a, it is compact and low cost can be realized.

Next, a sixth embodiment of the present invention will be described. For convenience, description will be given with reference to FIG. The difference from the fifth embodiment is that λ
The λ / 4 plate 17 is used in place of the / 2 plate, and the azimuth of the fast axis or the slow axis of the λ / 4 plate 17 is about 45 with respect to the polarization direction of the incident light from the semiconductor laser 1 to the polarizing film 4. And the polarizing film 4 provided on the surface of the λ / 4 plate 17
Have different characteristics. That is, the polarizing film 4 has characteristics that the polarization direction of the incident light is 50% with respect to the P polarization direction and 100% with respect to the S polarization direction, and the phase difference with respect to the transmitted light is 90 ° or −90 °. .

FIG. 10 is an explanatory view showing the polarization state of incident light from the semiconductor laser 1 to the detectors 11 and 12 of the detector 10. Light emitted from the semiconductor laser 1 is linearly polarized light, which is polarized in the in-plane direction of the paper and is incident on the polarizing film 4 (FIG. 10A). The polarization direction of the incident light matches the P polarization direction on the polarizing film 4 as described above. λ / 4
The polarizing film 4 provided on the plate 17 has a polarization direction P of incident light.
50% reflectance in the polarization direction, 10 transmittance in the S polarization direction
At 0%, a phase difference of 90 ° occurs with respect to the transmitted light. Therefore,
As shown in FIG. 10B, the light reflected by the polarizing film 4 is a linearly polarized light beam having an intensity of 1/2. This light flux enters the magneto-optical disk 6a through the objective lens 5.

The reflected light is rotated in the directions of θ _K and −θ _K depending on the direction of magnetization on the magneto-optical disk 6a under the influence of the reflectivity of the magneto-optical disk 6a and the Kerr effect, and has a polarization state as shown in FIG. 10C. Become. The reflected light flux of the magneto-optical disk 6a passes through the objective lens 5 again and enters the polarizing film 4. Since the polarizing film 4 has the above-mentioned characteristics, the transmitted light becomes a right-handed or left-handed elliptically polarized light depending on its optical rotation direction (θ _k , −θ _K ) (FIG. 10D). Further, the signal intensity of the S-polarized component, which is an information signal component, is not lost, and the intensity of only the P-polarized component is halved. Further, when the transmitted light flux passes through the λ / 4 plate 17, it is shown in FIG.
As shown in, the elliptically polarized light is different in the major axis direction of the ellipse depending on whether the elliptically polarized light is the clockwise elliptically polarized light or the counterclockwise elliptically polarized light.

The elliptically polarized light is reflected by the condenser lens 8, condensed, and then enters the polarizing film 18. At this time, the directions of the major axes of the elliptically polarized light are substantially aligned with the P polarization direction or the S polarization direction on the polarization film 18. The polarizing film 18 has a P-polarization reflectance of 0
%, S-polarized light reflectance is 100%, and as described above, the azimuth of the polarization direction of the incident light beam is substantially the same as the P-polarized light direction and the S-polarized light direction on the polarizing film 18, so that Incident light to the detectors 11 and 12 (reflected by the polarizing film 18 and transmitted light)
Is in the state shown in FIG. 10E. Information signal (RF)
Is detected by the difference signal between the sum signal of all areas 11a to 11c of the detector 11 and the sum signal of all areas 12a to 12c of the detector 12. That is, RF = A + B + C- (D + E + F). By doing so, the in-phase noise component is canceled.
In the present embodiment, the incident polarization direction to the polarizing film 4 is set to the in-plane direction of the paper surface. However, when the polarization direction is perpendicular to the paper surface, the description contents of the S-polarized component and the P-polarized component other than the polarization film 18 are The same explanation can be obtained by simply changing the positions. Since this embodiment is constructed as described above, in addition to the effect of the fifth embodiment, as described in JP-A-2-276045, the azimuth of the fast axis or the slow axis of the wave plate with respect to the incident light. The alignment accuracy of is less than 1/2 as compared with the case of the fifth embodiment.

FIG. 11 shows a seventh embodiment of the present invention. The fifth embodiment differs from the fifth and sixth embodiments in that a total reflection prism 19 is provided near the objective lens 5 and the optical path is bent. FIG. 11B shows a state in which the light beam reflected by the polarizing film 4 is bent by the total reflection prism 19 in the optical path in a direction orthogonal to the incident direction, passes through the objective lens 5, and reaches the magneto-optical disk 6a. There is.

With this structure, in addition to the effects of the fifth and sixth embodiments as the effects of this embodiment, it is possible to contribute to the realization of a pickup suitable for thinning. Further, it can be applied to a separation optical system in which only the total reflection prism 19 and the objective lens 5 are separated from other optical systems and only the former is a movable part.

FIG. 12 shows an eighth embodiment of the present invention. This embodiment is different from the above embodiments in that the light emitted from the semiconductor laser 1 becomes a parallel light flux by the collimator lens 2 and one of the light flux transmitted through the parallel film 4 on the inclined surface of the prism 3 without being reflected. A detector 20 for receiving the light is provided, and the output of the detector 20 controls the objective emission light to be constant. With this configuration, in addition to the effects of the above-described embodiment, the effect of the present embodiment is that the amount of light emitted from the objective lens is not affected by the influence of the return light from the disc. In addition, in this embodiment, the detector 20 is added to the configuration of the fifth embodiment, but the first, second, sixth, and seventh
The same applies to the examples.

FIG. 13 (cross-sectional view) and FIG. 14 (view taken along arrow A) show a ninth embodiment of the present invention, which has substantially the same structure as the fourth embodiment and enables magneto-optical signal detection. Is. The configuration of the fourth embodiment is that the incident surface of the semiconductor laser radiation on the reflecting surface 3a is 45 ° with respect to the polarization direction of the semiconductor laser, and the reflecting surface 3a has both P-polarized reflectance and S-polarized reflectance.
At 50%, the phase difference for reflected and transmitted light is 0 or 180d
eg a polarizing film is provided, a reflecting surface 3b is provided with a polarizing film having a phase difference of 0 or 180 deg with respect to the reflected light, and on the photodetector 11 of the reflecting surface 3c (see FIG. 14). The hatched area (shown in the figure) is provided with a polarizing film having a P-polarized reflectance of 0% and an S-polarized reflectance of 100%. The total reflection mirror 13 has a phase difference of 0 or 180 ° with respect to the reflected light. The difference is that a polarizing film is applied.

Referring to FIG. 7, the semiconductor laser 1 will be described.
Half of the radiated light from is reflected by the reflecting surface 3a,
Similar to the embodiment, the light is reflected by the mirror 13 and reaches the magneto-optical disk 6 through the objective lens 3. Further, all the light transmitted through the reflecting surface 3a goes out of the prism 3 from the end surface 3b of the prism 3 as in the fourth embodiment and does not become stray light (not shown). The light beam reflected by the optical disk 6 passes through the objective lens 5 and the total reflection mirror 13 again and reaches the polarizing film on the reflecting surface 3a (FIG. 13). The light transmitted through the polarizing film enters the prism 3 and is totally reflected by the end surface 3a of the prism 3. The totally reflected light enters the bottom surface 3c of the prism 3 before forming an image at one point. The photodetector 1 bonded to the semiconductor substrate 14 is provided on the end face 3c.
1, 12 are provided (Fig. 14).

A part of the totally reflected light enters the photodetector 11 and is received. The remaining reflected light is reflected by the end surface 3b of the prism 3, forms an image at one point, becomes divergent light, and is received by the photodetector 12. The signals recorded on the magneto-optical disk 6 can be detected based on the differential detection light amounts of the photodetector 11 and the photodetector 12. The focus error and tracking error signal detection methods are the same as in the first embodiment. The semiconductor substrate 14, the total reflection mirror 13, and the objective lens are the case 16 as in the above embodiment.
And is driven integrally in the track direction and the focus direction described in the fourth embodiment (see FIG. 7).

Next, the polarization states of the incident light from the semiconductor laser 1 to the photodetectors 11 and 12 will be described step by step in FIGS. 15A, 15B, 15C, 15D and 15E. The light emitted from the semiconductor laser 1 is linearly polarized light, which is polarized in the direction perpendicular to the paper surface of FIG.
Incident on the polarizing film of (see Figure 15A). The polarizing film has a reflectance of 50% for the P direction and a transmittance for the S direction for the polarization direction of the incident light.
At 50%, no phase difference occurs in transmitted light. The polarization direction of the incident light is 45 ° with respect to the P and S directions on the polarizing film.
As shown in 15B, the reflected light is linearly polarized light with an intensity of 1/2.
Becomes This light flux enters the magneto-optical disk 6 through the objective lens 5 (see FIG. 7). The reflected light is rotated in the directions of θ _k and −θ _k depending on the reflectance of the magneto-optical disc 6 and the direction of magnetization on the magneto-optical disc 6 due to the Kerr effect.
The polarization state becomes as shown in C.

The reflected light beam from the magneto-optical disk 6 passes through the objective lens 5 again and enters the polarizing film on the reflecting surface 3a. The polarizing film has the characteristics as described above, and as shown in FIG. 15D, the transmitted light has a half intensity and is non-phase with respect to the transmitted light, so that it becomes linearly polarized light. The transmission constraint is that total reflection is performed on the end face 3b, and the reflection phase difference on the end face 3b is 0 deg.
Incident on. However, the polarization direction of the incident light on the end face 3C is approximately 45 °. The polarization film on the end face 3c has a P-polarization reflectance of 0% and an S-polarization reflectance of 100%. As described above, the polarization direction of the incident light beam is approximately 45 ° with respect to the P and S directions, so it becomes 19e. As shown, the incident lights of the photodetectors 11 and 12 have almost the same intensity. In this embodiment configured as described above, in addition to the effects of the above-described embodiment, since the magneto-optical signal can be detected with a simple configuration without using a member such as a condenser lens and a collimator lens, cost reduction, Can be made compact.

[0039]

As described above, according to the present invention, since the hologram element is not used, the spot movement on the detector due to the wavelength variation is small and the focus and the track offset can be reduced. In addition, a detector is provided on the prism surface that forms an obtuse angle with the incident surface to the prism, and unnecessary light is emitted from the other prism end surface, so good focus error and tracking error signals are not affected by stray light. Is obtained. Further, it is possible to provide an optical information reading device which does not cause a complicated structure, an increase in size, and an increase in cost in order to obtain the above effects.

[Brief description of drawings]

FIG. 1 is a sectional view of an optical system according to a first example of the present invention.

FIG. 2 is an explanatory diagram of a principle of detecting a focusler signal.

FIG. 3 is a sectional view of an optical system according to a second example of the present invention.

FIG. 4 is a partial view of an optical system according to a third embodiment of the present invention.

FIG. 5 is an overall schematic diagram of an optical system according to a third example.

FIG. 6 is a partial view of an optical system according to a fourth example of the present invention.

FIG. 7 is an overall schematic diagram of an optical system according to a fourth example.

FIG. 8 is a sectional view of an optical system according to a fifth example of the present invention.

FIG. 9 is an explanatory diagram showing a polarization state of incident light from a semiconductor laser according to a fifth example to a detector.

FIG. 10 is an explanatory diagram showing a polarization state of incident light from the semiconductor laser according to the sixth example on the detector.

FIG. 11 is a sectional view of an optical system according to a seventh example of the present invention.

FIG. 12 is a sectional view of an optical system according to an eighth example of the present invention.

FIG. 13 is a sectional view according to a ninth embodiment of the present invention.

14 is a view on arrow A in FIG.

FIG. 15 is an explanatory diagram showing a polarization state of incident light from the semiconductor laser according to the ninth example to the detector.

16 is a perspective view of an optical system according to Conventional Example 1. FIG.

FIG. 17 is a front view of an optical system according to Conventional Example 1.

FIG. 18 is a perspective view of an optical system according to Conventional Example 2.

FIG. 19 is a plan view of an optical system according to Conventional Example 2.

[Explanation of symbols]

1 Semiconductor laser 2 Collimator lens 3 prism 4 Polarizing film 5 Objective lens 6 optical disks 7 Anti-reflection coat 8 Condensing lens 9 Total reflection coat 10 photo detector 11 Detector 12 Detector

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[Procedure amendment]

[Submission date] February 12, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction content]

[0008]

Since the hologram is not used as described above, the spot on the detector does not change, and the focus error and tracking error signals are less likely to be offset. Further, since a detector is provided on the prism surface that forms an obtuse angle with the entrance surface to the prism, and unnecessary light is emitted from the other prism end surface, stray light can be reduced.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0038

[Correction method] Change

[Correction content]

The reflected light beam from the magneto-optical disk 6 passes through the objective lens 5 again and enters the polarizing film on the reflecting surface 3a. The polarizing film has the characteristics as described above, and as shown in FIG. 15D, the transmitted light has a half intensity and is non-phase with respect to the transmitted light, so that it becomes linearly polarized light. The transmitted light beam is totally reflected by the end face 3b and the reflection phase difference at the end face 3b is 0 deg.
Incident on. However, the polarization direction of the incident light on the end face 3C is approximately 45 °. The polarization film on the end face 3c has a P-polarization reflectance of 0% and an S-polarization reflectance of 100%. As described above, the polarization direction of the incident light beam is approximately 45 ° with respect to the P and S directions, so it becomes 19e. As shown, the incident lights of the photodetectors 11 and 12 have almost the same intensity. In this embodiment configured as described above, in addition to the effects of the above-described embodiment, since the magneto-optical signal can be detected with a simple configuration without using a member such as a condenser lens and a collimator lens, cost reduction, Can be made compact.

Claims (3)

[Claims] 1. An optical information reading apparatus using an optical system having at least a semiconductor laser, an objective lens, a prism, and a light detecting means for receiving reflected light from an optical disk, wherein the light detecting means is a prism slope. A polarizing film, which is joined to a prism surface forming an obtuse angle and which reflects a part of light emitted from the semiconductor laser and transmits the light flux reflected by the optical disk, is formed on the surface of the prism slant surface. An optical information reading device, characterized in that the transmitted light that has passed through the polarized film is internally reflected at least once in the prism and then enters the light detecting means. 2. A condenser lens having a total reflection coating on the side surface of the transmitted light is provided on the prism surface on the extension of the traveling direction of the transmitted light reflected by the optical disk and transmitted through the polarizing film on the prism inclined surface. The optical information reading device according to claim 1, wherein 3. The optical device according to claim 1, wherein a semiconductor laser is arranged so that the radiated light is incident on the prism inclined surface from a direction substantially orthogonal to the prism surface on which the light detecting means is provided. Expression information reader.