JPH0810494B2 - Optical pickup - Google Patents

Description

The present invention relates to an optical pickup provided with a light receiving means for monitoring a light beam emitted to the recording medium side of a laser diode.

[Related Art] In recent years, a light beam is condensed and irradiated on a recording medium, and the reflected or transmitted light is received to record information at a high density on the recording medium or to transfer information recorded on the recording medium at a high speed. Attention has been paid to an optical information recording / reproducing apparatus which can reproduce the information on a disc.

An optical pickup is used for converging and irradiating the recording medium with the above-mentioned light beam, and for receiving return light. The optical pickup includes an optical system such as an objective lens, a light source, and a light receiving element. Further, this optical pickup can be moved by a linear motor or the like so that any track on the recording medium can be randomly accessed. Therefore, it is desirable that the optical pickup is small and lightweight, and a laser diode is widely used as a light source.

By the way, the laser diode, because its light emission output changes depending on the temperature, etc., the laser light emitted from the laser diode is received by the monitoring light receiving means of the pin diode, etc., and the output current from this light receiving means Automatic output control (APC), which controls the current supplied to a laser diode to automatically control the output of emitted laser light to an appropriate level, is widely used.

The light receiving element in the case of APC control described above is, for example, JP-A-58
As in the conventional example disclosed in Japanese Patent Laid-Open No. 161156, the light emitted from both ends of the laser diode is received by the monitor light emitted to the opposite side to the light emitted to the recording medium side. If the monitor light emits abnormally, both ends of the laser diode are short-circuited and protected.

[Problems to be Solved by the Invention] In the above conventional example, since the light emitted to the recording medium side is not directly received, the reliability is not sufficient. For example, the emitted light to the recording medium side may emit more than the above even if the monitor light causes no abnormality. In this case, the information already recorded on the recording medium may be destroyed, which is a big drawback. Even if abnormal light emission does not occur, if the characteristics of the emitted light amount on the monitor light side and the recording medium emission side change over time and the relationship between the two emitted light amounts changes, recording at an appropriate level may occur. This makes it impossible to perform reproduction, and the rate of occurrence of signal reading errors increases, and recording is performed so that reading errors easily occur. Therefore, the reliability of the recording or reproducing device is reduced.

The present invention has been made in view of the above points, and an object thereof is to provide an optical pickup capable of performing recording and reproduction at an appropriate level without causing a reading error or the like.

[Means and Actions for Solving Problems] In the present invention, a collimator lens that collimates divergent light from a light source, an objective lens that condenses and irradiates the collimated light onto a recording medium, the collimator lens, and the A beam splitter arranged in an optical path between the objective lens and the optical path of light reflected from the recording medium and an optical path of light emitted from the light source; and a beam splitter that receives the light branched by the beam splitter. In an optical pickup including an information photodetector and a control photodetector, which optically records or reproduces information on the recording medium, in the optical path between the light source and the beam splitter, A light-receiving surface is disposed on the light-source side so as to face the central side of the light from the light-source, and a monitor light-receiving means is provided. By performing APC control by force, the amount of light irradiated on the recording medium can be maintained at an appropriate level. Further, the light receiving means also plays a role of blocking the center of the light flux from the light source, and makes the light flux used for converging and irradiating the recording medium into an annular light flux so as to reduce a focus error such as defocus.

EXAMPLES The present invention will be specifically described below with reference to the drawings.

1 to 4 relate to the first embodiment of the present invention, FIG. 1 shows the optical pickup of the first embodiment, and FIG. 2 shows the recording medium side illuminated by a light receiving element arranged for monitoring. FIG. 3 shows the entire optical pickup, and FIG. 4 shows the APC circuit.

As shown in FIG. 3, the optical pickup 1 of the first embodiment is arranged so as to face a disk-shaped recording medium (hereinafter referred to as a disc) 3 which is rotationally driven by a spindle motor 2, and a linear motor (not shown). Etc. in the radial direction of the disk 3 (left-right direction in FIG. 3, vertical direction in FIG. 1) R
You can move to.

As shown in FIG. 1, the optical pickup 1 has a laser diode 4 as a light source mounted in its housing, and a laser beam emitted from a recording medium side emission end face 4A (not on the monitor side) of the laser diode 4. Is collimated by the collimator lens 5 and is then incident on the shaping prism 6, so that the luminous flux having an elliptical cross section is shaped into a circle. On the emission surface side of the shaping prism 6, as shown in FIG. 2, the center of the light beam is located at the center axis,
Further, for example, a disc-shaped monitor light-receiving element 7 is attached so that the light-receiving surface faces the direction in which the incident laser light is received. The photoelectric conversion output corresponding to the amount of light received by the light receiving element 7 is input to the APC circuit 8, and this output controls the optical output of the laser diode 4.

By the way, the light beam having a circular cross section on the peripheral side, the central portion of which is shielded by the light receiving element 7, is incident on a polarizing prism (polarizing beam splitter) 9 and, for example, of P-polarized light incident on the polarizing prism 9. Almost 10 light beams
It is transmitted by 0%, and further transmitted by 11 through the λ / plate to be circularly polarized light. Then, the circularly polarized light beam is condensed by the objective lens 12 and applied to the disk 3.

This disc 3 is provided with a recording film 3B portion in which pit rows corresponding to information are formed on the inner surface of each base 3A on both sides, and in this case, the recording film 3B on the lower side is focused in a spot shape. Is irradiated. Then, this disk 3
The return light reflected by is condensed by the objective lens 12 and further converted into S-polarized light having a polarization direction different by 90 ° from the forward path by the λ / 4 plate 11 and returned to the polarizing prism 9 side. After being almost 100% reflected by the polarizing prism 9, it is split into transmitted light and reflected light by a half mirror (beam splitter) 13. The transmitted light of the half mirror 13 is condensed by the condenser lens 14 and received by the information photodetector 15. The light reflected by the half mirror 13 passes through the critical angle prism 16 and is received by the control photodetector 17.

The signal photoelectrically converted by the information photodetector 15 is signal-processed by a waveform shaping circuit or the like so that the information recorded in the pit train or the like on the disc 3 can be reproduced.

Further, the control photodetector 17 is formed of, for example, a light receiving element divided into four, and each one is divided into two in directions orthogonal to each other.
Signals for focus control and tracking control are obtained from the pair of operation outputs. That is, in FIG. 1, a focus control signal by the critical angle method is obtained by the differential output of a pair of elements divided into upper and lower parts (addition is made for elements adjacent to each other in the vertical direction on the paper surface above and below). 2 vertically
A tracking control signal by the push-pull method is obtained by the divided differential output of the pair of elements. Then, the focus control signal and the tracking control signal are respectively applied to the focus coil 18 and the tracking coil 19 which form the lens actuator through the transfer compensation circuit and the drive circuit, and the focus control and the tracking control are performed.

By the way, in the optical pickup 1 of the first embodiment,
As shown in FIGS. 1 and 2, the monitor light receiving element 7 is
On the optical path on the side of emission to the disc 3, the optical axis is the light receiving element 7
It is set to be the center of. Then, the photoelectric conversion output of the light receiving element 7 is input to the APC circuit 8, and the light emission output of the laser diode 4 is automatically controlled.

The APC circuit 8 has a structure as shown in FIG. 4, for example. The anode potential of the light receiving element 7 such as a pin photodiode is input to the differential amplifiers 21 and 22 for APC control. The differential amplifiers 21 and 22 compare with the reference potentials V1 and V2 applied to the other input ends, respectively, and the current that flows in the laser diode 4 by the differential output on the side where the switch 23 is turned on is read mode or write mode. Is applied to the control end of the constant current circuit 24 which maintains an appropriate level.

In the read mode, the switch 23 is
The signal level applied to the switching control terminal of is always kept at high level, and the differential amplifier for read mode level setting 21
The constant current of the constant current circuit 24 is held at a value suitable for the light emission output in the read mode.

On the other hand, in the write mode, a low-level pulse is applied to the switching control terminal of the switch 23 only when the light is emitted, and when the low-level pulse is applied, the output of the differential amplifier 22 for setting the light level is applied. The light emission output of the laser diode 4 is controlled. In this case, the light emission output of the laser diode 4 is at a higher level than in the read mode, and pits can be formed on the disc 3.

On the other hand, in addition to the APC control described above, a comparator 25
Is provided. If the amount of light received by the light emitting element 7 is equal to or higher than the allowable level V ₃ , the switch 26 such as a relay switch or an analog switch connected in parallel to both ends of the laser diode 4 is closed to connect both ends of the laser diode 4 to each other. A protection means is provided that can prevent short-circuiting, stop emission of light by the laser diode 4, and write undesired data to the disk 3. In the first embodiment, since a part of the light beam focused and irradiated on the disk 3 is directly received to control the light emission output of the laser diode 4, for example, the laser beam is not only destroyed due to abnormal light emission, but is also deteriorated by aging. Even if the light emission output of the diode 4 changes, the influence of the change can be almost eliminated.

Further, as shown in FIG. 2, the light receiving element 7 shields the central portion of the circular light beam portion incident on the objective lens 12 used for converging and irradiating the disk 3 and the light in the objective lens 12 is blocked. The light is collected at the annular portion on the outer peripheral side of the light receiving element 7. Therefore, as described in Japanese Patent Application Laid-Open No. 56-16004, aberrations such as defocus can be substantially reduced by condensing light only at this annular portion. Therefore,
The spot diameter of the spot light focused and irradiated on the disc 3 can be reduced. Therefore, the recording density can be increased.

Further, since this spot system can be made small to increase the light condensing density, when the peripheral speeds on the inner and outer peripheral sides of the disk are different, the energy density for forming pits on the outer peripheral side becomes insufficient. It can be done without incident. It is also possible to prevent the formation of pits from becoming impossible even in a slightly defocused state from the focused state. In other words, since the recordable tolerance range can be widened, the variation range allowed for the optical system can be widened, and if it is set to the optimum value, the margin before malfunction can be increased and stable operation can be performed. Alternatively, the reliability can be increased.

FIG. 5 shows an optical pickup 31 according to the second embodiment of the present invention.
Indicates.

This pickup 31 uses laser diodes 32 and 33 of two different wavelengths λ1 and λ2, for example, reproduction and recording are performed by the laser diode 32 of wavelength λ1, and the other (of wavelength λ1)
It can be erased by a laser diode 33, and is used for a phase change type erasable disk 34, for example.

The laser light flux of the erasing laser diode 33 is made into a parallel light flux by the collimator lens 34, and then is incident on the polarizing prism 35 as S-polarized light. Then, after being reflected by the polarizing prism 35, it is circularly polarized by the λ / 4 plate 36 and further reflected by the wavelength separation filter 37 formed by a dichroic mirror or the like. This reflected light is converted into P-polarized light by passing through the λ / 4 plate 36 again, and is transmitted through the polarization prism 35. The light transmitted through the polarization prism 35 is further transmitted through the λ / 4 plate 38 to be circularly polarized light, and then is condensed and irradiated onto the disk 34 by the objective lens 39. The recorded information on the disk 34 is erased by the spot light that is focused and irradiated. The light reflected by the disk 34 is converted into S-polarized light by the λ / 4 plate 38, and thus is reflected by the polarizing prism 35.

On the other hand, the light flux of the recording / reproducing laser diode 32 is made into a parallel light flux by the collimator lens 41, and then the shaping prism 42
Is incident on and the elliptical light flux is shaped into a circular light flux. After that, the S-polarized light enters the polarizing prism 35, is reflected, and then becomes circularly polarized by the λ / 4 plate 38. Then, the objective lens 39 focuses and irradiates the disc 34 in a spot shape.

The position where the recording / reproducing light beam is condensed and irradiated onto the disk 34 is located on the downstream side where the erasing light beam is irradiated. After that, in FIG. 5, when a track on the paper surface is being scanned (for example, the rotation of the disk 34 causes the disk 34 to rotate).
When the track No. moves in the direction indicated by the arrow A, after the erasing light beam is irradiated, the recording / reproducing light beam on the downstream side of this light beam can be focused and irradiated later on the same track. Later data can be recorded.
For this reason, the optical axis of the erasing light beam and the optical axis of the recording / reproducing light beam are slightly displaced.

The light beam (for recording / reproducing) reflected by the disk 34 passes through the objective lens 39 and is converted into P-polarized light by the λ / 4 plate 38.
This P-polarized light is transmitted through the polarizing prism 35, and further the λ / 4 plate 36
Is converted into circularly polarized light by and passes through the wavelength separation filter 37. The light transmitted through the filter 37 is split by the half mirror 43 into transmitted light and reflected light. Then, the transmitted light is received by the information photodetector 45 which is condensed by the condenser lens 44.

On the other hand, the light reflected by the half mirror 43 is incident on the critical angle prism 46, and the light reflected by the critical angle prism 47 is received by the four-division photodetector 47 to obtain a control signal. There is.

By the way, for example, the monitor light receiving element 51 is arranged such that the light receiving surface of the polarizing prism 35 faces the erasing laser diode 33 and the center of the light receiving surface is located on the optical axis of the collimator lens 34. Then, this light receiving element
The output of 51 is input to the APC circuit 52, and the laser diode 33
Control the light emission output of. The APC circuit 52 may have the structure shown in FIG. 4 or may have another structure.

Further, the light receiving surface of the shaping prism 42 faces the recording / reproducing laser diode 32 side, and the monitor light receiving element 53 is arranged so that the center of the light receiving surface is located at the center of the circle formed into a circular light beam by the shaping prism 42. It is set up. The photoelectric conversion output of the light receiving element 53 is input to the APC circuit 54 and the laser diode 3
The emission output of 2 is controlled.

Also in the second embodiment, the light condensed and emitted to the disk 34 side is directly received to control the light emission output, so that the same effect as the first embodiment is obtained.

FIG. 6 shows a third embodiment of the present invention.

The third embodiment is a magneto-optical type optical pickup 71.
Indicates.

In this pickup 71, the light from the laser diode 72 is collimated by the collimator lens 73 and shaped by the shaping prism 74, and then the light shielding plate provided with the monitor light receiving element 75 is provided.
It is incident on the half mirror 77 to which 76 is attached. The light transmitted through the half mirror 77 is condensed by the objective lens 78 and condensed and irradiated on the magneto-optical disk 79. The light focused and irradiated on the magneto-optical disk 79 is, for example, an arrow P in FIG.
It is polarized as shown by and passes through the base 79A and the magnetic recording film 7
The spot is focused on 9B. The light reflected by the memory film 79B has its polarization direction rotated by a minute angle in accordance with the magnetization direction of the irradiated portion. This reflected light is half mirror 77
Almost 50% is reflected at. The reflected light is further split by the half mirror 81 into transmitted light and reflected light. Then, the transmitted light passes through the analyzer 82 and then is received by the information photodetector 84 by the condenser lens 83. On the other hand, the reflected light passes through the critical angle prism 85 and is received by the quadrant photodetector 86 to obtain a control signal.

The output of the monitor-like light receiving element 75 is input to the APC circuit 87, and the light emission output of the laser diode 72 is automatically controlled by the output of the APC circuit 87.

By the way, the shielded light attached to the half mirror 77
As shown in FIG. 7, reference numeral 76 is a cross shape, and the cross is set at an angle of 45 ° with the polarization direction P. The light receiving element 75 is attached to the central portion of the cross light shielding plate 76. Installed.

The third embodiment is effective when the substrate 79A forming the disk 79 uses a member or the like that exhibits birefringence in the thickness direction with respect to a light beam obliquely incident. In other words, when using a substrate that exhibits birefringence in the thickness direction,
When transmitted through this substrate, due to the effect of birefringence, the ratio of the ellipticity to the incident light having the P-polarized light component and the S-polarized light component, that is, the incident light incident along the cross direction of the light shielding plate 76 is large. Become. Therefore, the light focused and irradiated on the recording film 79B has a component other than the linearly polarized light component,
The C / N ratio deteriorates, and the return light reflected by the recording film 79B also lowers the C / N in the same manner. It can prevent the deterioration. Although FIG. 6 shows the case of the magneto-optical disk 79, it can also be applied to the case of an optical disk or the like.

The position where the monitor light-receiving means is provided is not limited to the above-mentioned one, and it is arranged on the optical path between the end face from which the light source such as a laser diode is emitted and the periphery of the objective lens that focuses and irradiates the disc. Just do it. Further, the center of the light receiving surface is arranged on the optical axis so that not only the central part of the circular light beam is shielded but also the peripheral part may be shielded, or the central part and the peripheral part are arranged so as to be shielded. May be.

Although the present invention receives the reflected light from the disk, it can also be used in the case of the method of receiving the transmitted light. Further, the present invention can be applied not only to a disc but also to a card-shaped recording medium.

[Effects of the Invention] As described above, according to the present invention, a collimator lens that collimates divergent light from a light source, an objective lens that condenses and irradiates the collimated light onto a recording medium, the collimator lens, and the A beam splitter arranged in an optical path between the objective lens and the optical path of light reflected from the recording medium and an optical path of light emitted from the light source; and a beam splitter that receives the light branched by the beam splitter. In an optical pickup including an information photodetector and a control photodetector, which optically records or reproduces information on the recording medium, in the optical path between the light source and the beam splitter, The light receiving surface for monitoring is arranged on the light source side so that the light receiving surfaces face each other, and the monitor light receiving means for blocking the central side of the light from the light source is provided. Can be reliably detected, and an appropriate amount of emitted light can be controlled.
Therefore, it is possible to reliably prevent destruction of valuable recording data due to abnormal light emission, etc., and by shielding the central side of the light beam focused and irradiated on the recording medium through the objective lens, it is possible to reduce the influence of aberration, etc. It is possible to reduce the diameter of the light spot that is focused and irradiated on the recording medium, which enables high-density recording.

[Brief description of drawings]

1 to 4 relate to a first embodiment of the present invention.
FIG. 1 is a block diagram showing the optical pickup of the first embodiment, FIG. 2 is an enlarged view showing the periphery of a portion provided with a monitor light receiving element, and FIG. 3 is an illustration showing the outer shape of the first embodiment. 4 and 5 are circuit diagrams showing the configuration of an automatic output control circuit, FIG. 5 is a configuration diagram of a second embodiment of the present invention, and FIG. 6 is a configuration diagram of a third embodiment of the present invention. The drawing is an enlarged view of line BB 'in the third embodiment of the present invention. 1 ... Optical pickup 3 ... Disc, 4 ... Laser diode 5 ... Collimator lens 6 ... Shaping prism, 7 ... Monitor light receiving element 12 ... Objective lens, 15 ... Information photodetector 17 ... ... Control photodetector

Claims (1)

[Claims] 1. A collimator lens for collimating divergent light from a light source into parallel light, an objective lens for converging and irradiating the parallel light onto a recording medium, and an optical path disposed between the collimator lens and the objective lens. A beam splitter that splits an optical path of light reflected from the recording medium with an optical path of light emitted from the light source; an information photodetector and a control photodetector that receive the light split by the beam splitter. And an optical pickup that optically records or reproduces information on or from the recording medium, in the optical path between the light source and the beam splitter,
An optical pickup characterized in that a monitor light receiving means is provided on the light source side so that a light receiving surface is opposed to the light source, and the central side of light from the light source is shielded.