JPH02121129A - Optical head - Google Patents

Abstract

PURPOSE:To ensure the stable quantity of light emitted from a semiconductor laser serving as a light source in a simple constitution by making use of the relation between the internal polarization dependent surface of an optical head and polarized surface of the light which made incident on the polarization dependent surface. CONSTITUTION:A semiconductor laser 108 is set so that the polarizing direction of the laser 108 is not coincident with the paper surface nor vertical to the paper surface. As a result, the incident light onto a polarized beam splitter 11 is separated into the transmitted light, i.e., the linearly polarized light which vibrates within the paper surface and the reflected light which vibrates within a surface vertical to the paper surface. This reflected light is received by a 2nd sensor 15. The output of the sensor 15 is given to a comparator 6 via an amplifier 5. The compression result of signals is sent to a laser control part 3. Based on this result, the part 3 controls a laser driver 4. Thus the quantity of light emitted from the laser 108 is stabilized.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical head used in an optical storage device that optically records and/or reproduces information, and particularly relates to an optical head that uses a semiconductor laser as a light source. In optical head,
The present invention relates to an optical head having means for controlling the amount of light emitted from a semiconductor laser to an appropriate value.

[Prior Art] Various media such as optical disks, optical cards, and optical tapes have been known as media for recording and reproducing information using light. Each of these has its own characteristics and is used depending on the purpose, application, etc. Among them, optical cards take advantage of characteristics 1 and ν such as ease of manufacture, good portability, and good accessibility, and in the future, they will be used for various purposes. It is thought that it will spread.

FIG. 11 is a schematic block diagram showing an example of an optical storage device configured for the above card-shaped recording medium.

In the figure, +01 is an optical card on which information is to be recorded, 1
03 is an optical head (the part surrounded by a dotted line in Figure 1+), +04 is a light beam, 105 is a shuttle on which the optical card +01 is placed, 108 is a cliff conductor laser light source, and +09 is a collimator lens. +10 is a polarizing beam splitter, +30 is an I/4 wavelength plate, and the combination of these two members allows light from the top of the figure towards 1 to pass through, but light from below towards 1- is bent in the right angle direction. Ill is an objective lens that functions to condense parallel light onto the optical card +01.

112 is a light sensor, 113 is a preamplifier, 114 is an autofocusing servo, 115 (or odotracking servo, 116 is a decoder, 117 is an interface, !!8 is a computer, 119 is an encoder, 1.2
0 is a laser driver, and 121 is a stepping motor, which functions to move the optical head 103 in a direction perpendicular to the paper surface.

122.123 is a pulley, and the pulley 122.123 is
A belt 124 is attached. On the belt 124 is a shuttle 105 on which the optical card +01 is placed and fixed.
is installed. The pulley 122 is attached to the shaft of a motor 126, and the rotation of the pulley 126 causes the optical card io+ to reciprocate in the direction of the arrow in the figure.

Next is the first one! The operation of the apparatus shown in the figure will be explained using the case of information reproduction as an example.

In FIG. 11, the light beam excavated from the semiconductor laser 108 is turned into parallel light by the collimator lens 109,
Polarizing beam splitter! The light passes through the 10 and 1/4 wavelength plates +30 and is further focused by the objective lens 11 to form a minute spot on the optical card +01. optical card +
The reflected light from 01 is modulated depending on whether or not there is an information bit in the area irradiated by the minute spot, and this modulated light becomes ascending light again by objective lens II+.
The light is incident on the optical sensor 112 by the polarizing beam splitter +10. The optical sensor 112 detects a photoelectric change in the modulated light, converts it into an electrical signal, and sends it to the preamplifier +13. A signal is sent from the preamplifier +13 to the autofocusing servo 114.

Auto focusing servo! By the signal from 14,
Objective lens 1 is controlled by an actuator (not shown).
! 1 in direction B, the light beam 104 is directed toward the optical card 1.
The distance between the objective lens II+ and the optical card 101 is controlled so as to focus on the optical card 101.

The signal from the preamplifier +13 is also sent to the auto-tracking servo 115, and the signal from the auto-tracking servo 115 causes an actuator (not shown) to move the objective lens In in the direction of the plane of the paper and the direction of the river, so that the light beam 104 is Control to focus on a predetermined position.

Note that during the initial operation of the device, the interface +17
A servo pull-in command is sent from the autofocusing servo 114 to the autotracking servo 115.

Several specific methods have been proposed for the autofocusing servo 114 and the autotracking servo 115, but for example, the light beam 104 is divided into a plurality of parts using a grating or the like, and the optical card 10! A track for autofocusing or autotracking is preformatted in advance, information is reproduced using at least one of the plurality of light beams, and signals for autofocusing and autotracking are extracted using the other beams. Examples are suggested. Further, the signal from the preamplifier +13 is sent to the decoder +16, where it undergoes necessary electrical processing, and then sent to the interface 117. Information signals are sent from interface 117 to computer 118 . Also from the interface 117.

The signal is sent to the encoder +19, modulated as necessary, and then sent to the semiconductor laser 1 via the laser driver 120.
Controls the oscillation of 08.

Furthermore, the stepping motor 121 and motor servo from the interface) 17! 27, and the rotation of the position control motor 126 in the direction perpendicular to the plane of the paper of the optical head 103 is controlled.

[Problems to be Solved by the Invention] In the optical head 103 described using FIG. 11, stabilization of the output of the semiconductor laser 108 is an important technical issue in order to prevent erroneous recording or erroneous reproduction of information. One example is technology. Various proposals have been made to address this technical problem, for example, Japanese Patent Publication No. 54-10481.
An example of this is disclosed in the publication No. In this publication, a photoelectric conversion element collects laser light emitted from the side opposite to the reproducing laser beam of a semiconductor laser, compares the output voltage from the photoelectric conversion element with a reference voltage, and calculates the comparison result. A technique for controlling the output of a semiconductor laser based on this has been disclosed. However, when this technique is applied to the optical head shown in FIG. 11, it may have the following drawbacks.

FIG. 12 shows a schematic diagram of the optical card +01. optical card +
01 is constructed by adhering a transparent protective layer +31 and a support base 132, and information recording 6133 is provided on the adhesion surface. Light enters from the transparent protective layer +31 side. In order to take advantage of the features of the optical card 101 such as portability and flexibility, the transparent protective layer I3] and the support base 132 are often made of polymer resin, and in particular, polycarbonate is used due to its manufacturing convenience. Widely used. However, polycarbonate is known to have the drawback of causing birefringence during vsJ manufacturing, transportation, and storage.

For optical card lots with such birefringence, the first
When recording/reproducing information with the optical head 103 shown in the + figure, the polarizing beam splitter 110 cannot completely direct the opposite light beam from the optical card +01 to the optical sensor 112, and a portion of the light beam is directed to the optical sensor 112. It returns to the laser 108. At this time, as mentioned above, if the optical head uses the technique described in Japanese Patent Publication No. 54-10481 to stabilize the output of the semiconductor laser for 10 days, the returned light will be transmitted to the photoelectric conversion element inside the semiconductor laser lO8. As a result, the control circuit operates to reduce the output of the semiconductor laser 108.

For this reason, for example, during recording, a sufficient amount of light does not reach the optical card 101, making it impossible to perform good recording.

A further conventional example of stabilizing the output of the semiconductor laser 108 is the technique described in Japanese Patent Publication No. 18354/1983. According to an embodiment in the same publication, a prism for reflecting a reflected light beam from a recording medium to a photodetector for information reproduction is provided in the optical path from the semiconductor laser to the recording medium, and the prism allows A part of the luminous flux heading towards the recording medium is reflected and guided to one side of the two-split sensor.
The amount of light emitted by the semiconductor laser is controlled based on the difference No. 43 between the output of that sensor and the output of the other sensor.

According to this method, the photodetector for controlling the amount of light emitted by the semiconductor laser is located outside the semiconductor laser, so the problem of light returning from the optical card to the semiconductor laser is solved. Ru.

However, the technique described in Japanese Patent Publication No. 63-18354 has the following drawbacks.5 Namely, the reflected light beam from the recording medium is necessarily returned to the semiconductor laser by the prism, and the light beam is detected for information reproduction. The light beam is separated into the light beam that travels to the vessel.

Therefore, even if a recording medium does not have birefringence as introduced in the section on conventional examples, especially when a recording medium with low reflectance is used, the S/N of the output of the photodetector for information reproduction is
This is not preferable because the ratio decreases.

In order to prevent this, it is possible to increase the output of the semiconductor laser, but this is not preferable as it increases the cost.

A further conventional example is the technique described in Japanese Patent Publication No. 8495/1983. According to the example in the publication, a detector captures the light beam at a position that is not focused by the objective lens among the divergent light beams from the semiconductor laser, and the output of the semiconductor laser is stabilized by the output of this detector. Therefore, the problems of the above two conventional examples are solved. However, with the above means, the amount of light hl reaching the detector is small, and the S/N ratio of the output of the detector is reduced, which poses a problem in accurately stabilizing the semiconductor laser. In order to receive a sufficient amount of light by the detector, it is necessary to increase the output of the semiconductor laser, which is not preferable.

[Means for Solving the Problems] An object of the present invention is to provide an optical head that eliminates the drawbacks of the conventional device described above and stabilizes the amount of light emitted from a semiconductor laser, which is a light source, with a simple configuration. be.

The above-mentioned object of the present invention is to provide a semiconductor laser light source that emits linearly polarized light with a plane defined by transmitted light and anti-Q-1 light on a polarization-dependent plane provided in an optical path that depends on the polarization direction. 1, and a plane containing the transmitted light or reflected light and perpendicular to the first plane is the second plane, and the polarization direction of the incident light, which is direct #9 polarization, is the second plane. By configuring the device so that they do not coincide on either side of the hand, both the transmitted light and the reflected light are simultaneously extracted from the polarization-dependent surface, the amount of light of either one is received by the sensor, and the output from the sensor is This is achieved by controlling the amount of light emitted from the semiconductor laser light source by υj.

According to one embodiment of the present invention, in an optical head using a semiconductor laser that emits linearly polarized light, the light splitting function by the polarization dependent surface of a commonly used optical element is actively utilized.
The above object can be easily achieved using the components of a normal optical head.

[Examples] Hereinafter, the optical head according to the present invention will be described in detail based on specific examples.

The configuration of a first embodiment of the optical head according to the present invention is shown as a schematic block diagram in FIG.

In the figure, 108 is a semiconductor laser that emits linearly polarized light, 109 is a collimator lens that converts the light from the semiconductor laser 108 into a parallel beam, lO is a beam shaping prism for converting the beam shape, 11 is a beam splitter, and lO is a beam shaping prism for converting the beam shape.
la is the dividing surface, 12 is a quarter wavelength plate, III is an objective lens that focuses the light on the recording medium, io+ is the recording medium, 1
3 is a sensor lens system consisting of a spherical lens and a cylindrical lens;
+4 is the first signal that detects the information reproduction signal and the AP and AT times the signal.
sensor, 16 is a condensing system (for example, a condensing lens), 15
is a second sensor as a sensor for controlling the amount of light emitted. 5
is an amplifier that amplifies the output of the second sensor 15, and 6 is a CP
A comparator for comparing the basic signal from U7 with the output from amplifier 5 is an interface, 2 is an encoder, and 3 is a laser control section for controlling laser driver 4 using the signal from comparator 6.

Interface! The signal that should be recorded more is encoder 2.
Based on the result, the laser driver 4 drives the semiconductor laser 108.6 The divergent light beam from the semiconductor laser 108 is sent to the collimator lens 1.
09, the beam is refracted by the beam shaping prism IO, and the beam shape is converted. After that, the beam is transmitted through the polarizing beam splitter 11 and the quarter-wave plate 12, and is transmitted through the objective lens I11 to the optical card 103. The light is focused and records information. The light beam reflected by the optical card 10+ travels the optical path backwards, is reflected by the polarizing beam splitter 11, and is sent to the sensor lens system 13 consisting of a spherical lens and a cylindrical lens.
After passing through, No. sensor! Reach 4. The output from the first sensor I4 is used for auto-tracking servo and auto-focusing servo, and is further used as an information reproduction signal.

In the embodiment shown in FIG.
For +1a in 1, a lens whose transmittance and reflectance depend on the polarization direction of incident light is used. That is, in the figure, the component vibrating in the direction parallel to the plane of the paper is transmitted through the polarization dependent surface 11a,
Components that vibrate in the direction perpendicular to the plane of the paper are reflected. Here, the semiconductor laser 108 that emits linearly polarized light is arranged so that its polarization direction does not match the plane of the paper and is not perpendicular to the plane of the paper. In other words, the joint portion of the laser chip in the semiconductor laser 108 is rotated about the optical axis of the collimator lens +09 at zero relative to the plane of the paper.
Rotate and arrange within a range of 90 degrees. This makes it a polarizing beam splitter! 1 is separated into transmitted light, which is a linearly polarized light that vibrates within the plane of the paper, and inverse q·1 light that vibrates within a plane perpendicular to the plane of the paper. The second sensor 15 receives the reflected light. By arranging the condensing system 16 and concentrating the light on the light receiving section of the second sensor 15, it is possible to reduce the area of the light receiving section, so the S/N of the output from the second sensor 15 can be reduced. Suitable for improvement and improvement.

The output from the second sensor 15 enters the comparator 6 via the amplifier 5. On the other hand, in response to a signal from the interface 1, the CPU 7 sends to the comparator 6 a base wall signal indicating a suitable amount of light emission corresponding to each state of recording and reproduction. The comparator 6 compares the two signals and sends the result to the laser controller 3, and based on this signal, the laser controller 3 controls the laser driver 4 to stabilize the amount of light emitted by the semiconductor laser 108. .

In order to help understand the features of the present invention explained in FIG. 1, FIG. , a schematic diagram of the end face 20 of the laser chip in the semiconductor laser 108 viewed from the collimator lens +09 side, where the Z-axis represents an axis orthogonal to the y-axis. The joint portion 21 of the laser chip is inclined at an angle θ with respect to the Y axis.

The origin of light emission is the intersection of the end surface 20 and the X-axis, and the diverging light flux is represented by an elliptical cross section as shown by the isointensity line 22. The zero-divergence light flux is linearly polarized light vibrating in the AA' direction in the figure. . It is particularly preferable that the angle θ satisfies the following conditions: 5° x 1θ1 x 45°. ” - If the lower limit of the conditional expression is exceeded, the amount of light reaching the second sensor 15 becomes small, leading to a decrease in the sensor output. On the other hand, when the upper limit is exceeded, the effect becomes small, especially in an optical head that uses the beam shaping prism 10 to change the beam shape, and it becomes difficult to obtain a substantially circular spot with the optical card 101-1.

FIG. 3 shows a second embodiment of the invention. In FIG. 3, the surface reflection component from the entrance surface 10a of the beam shaping prism 10 is used. Conventionally, the parallel light beam from the collimator lens 109 is made incident on the incident surface IOa at the Brewster angle, and the semiconductor laser 1
By making the polarization direction of the diverging light beam 08 coincide with the plane of FIG. 3, loss of light quantity at the incident surface 10a is prevented. However, in this embodiment, the polarization direction of the diverging light beam of the semiconductor laser 108 is arranged to be oblique to the plane of the drawing. Therefore, the S-polarized component of the incident light beam is reflected by the incident surface 10a and is received by the second sensor 15. The handling of the output from the second sensor 15 is the same as that already explained using FIG. 1, so a description thereof will be omitted. The features of the configuration of this embodiment are as follows. That is, in order to prevent the loss of light t, 1 in the conventional example, the direction of the optical axis of the collimator lens 109 is limited so as to satisfy the Brewster angle with respect to the incident surface 10a, and the polarization direction of the semiconductor laser 108 is also limited. However, in this embodiment, the semiconductor laser 10
A part of the luminous flux is actively divided in order to control the amount of light emitted by the person Q-1, and for that purpose, it is sufficient to set the polarization direction of the luminous flux of the person Q-1 to the above-mentioned arrangement 6, and 11; 1. Restrictions on the shooting angle, that is, Brewster's angle, become unnecessary. Therefore, it provides flexibility in the configuration and arrangement of the entire optical head.

A third embodiment of the present invention will be described using FIG. 4.

In the figure, the light source is a semiconductor laser array 21 having a plurality of light emitting points. The luminous flux from each light emitting point is optical card +0
1 has functions such as recording, reproduction, verification, erasure, servo, scratch, and dust detection. In this embodiment, the polarization direction of each light beam from the semiconductor laser array 21 is oblique to the plane of the drawing. Therefore, as in the embodiment shown in FIG. 1, a portion of each light beam is reflected to the second sensor 15 by the surface +1a of the polarizing beam splitter 11. In this embodiment, each luminous flux is separated by the second sensor 15 so that each luminous flux can be independently received by a number of light receiving sections corresponding to the number of light emitting points provided on the second sensor. , a configuration in which the imaging system 16 is disposed between the polarizing beam splitter 11 and the second sensor 15 is particularly preferable. This is because at the location of the sensor 15 each light beam is spatially separated and thus treated independently, thus amplifying the sensor output 58.5□.

This is because it is possible to amplify each of the signals M and 5 and send information regarding good light emission M without mutual crosstalk to the comparator 6.

FIG. 5 shows the configuration of a semiconductor laser array suitable for this example.
It is schematically shown in FIG. In the configuration shown in FIG. 5, independent light emitting points 301.30s, 30 in the same semiconductor layer 31
s is provided. The polarization direction of the luminous flux from each light emitting point is AA
', which is oblique to the y and z axes in FIG. In the configuration shown in FIG. 6, independent light emitting points 30. ．． 3
0□30, respectively, are different L conductor layers 31. ．． 3
+,,31. It's inside. The polarization direction of the light beam from each light emitting point is the AA' direction, which is also oblique to the y and z axes.

The configuration shown in FIG. 5 performs auto-tracking using the light beam from the light emitting point 3030 when the y-axis direction coincides with the information recording direction of the optical card +01 (that is, the direction of arrow A in FIG. 11). This method is suitable for the three-beam method.

The configuration shown in FIG. 6 is effective for scratch/dust detection, recording/reproduction, confirmation, and erasing operations on the same recording track when the y-axis coincides with the direction of the arrow in FIG. 1i.

The difference between Moe's polarization-dependent plane and the first plane can be seen in the drawings of the embodiment.

becomes.

The present invention is not limited to the above-mentioned embodiments, and various modifications and applications are possible.

In the embodiments not shown in FIGS. 2, 5, and 6, the polarization direction of linearly polarized incident light is inclined at an angle θ with respect to the Y axis. The case where the joint surface is tilted is shown. As a result, the light flux incident on the polarization-dependent (? plane +1a or IOa) in the embodiments shown in FIGS. There are 61 pieces, which are cylindrical!1
1, and since no special parts are required, it is also effective in reducing costs.

As a further embodiment, a beam shaping prism is used to align the junction surface of two semiconductor lasers with the Y axis without tilting it, as shown in Fig. 11! 0 and the beam splitter I+,
It is also possible to insert a wavelength plate 4I represented by a % wavelength plate or a local wavelength plate. By setting the optical axis of the wavelength-saving plate at a desired angle with respect to the direction of linearly polarized light of incident light, the wavelength-saving plate can produce transmitted light that is elliptically polarized light with a preferable ellipticity. Therefore, the beam splitter 11 plays the role of an analyzer for the elliptically polarized light, thereby achieving the object of the present invention. Furthermore, by setting the optical axis of the local wavelength plate at a desired angle, the transmitted light can be made into linearly polarized light that oscillates in a direction oblique to the Y-axis. Therefore, similar effects can be obtained. As mentioned above, in an apparatus in which a wavelength plate is set in the optical path and its optical axis can be set to a desired value, it is possible to make the optical fit ratio of the three beams separated by the polarization dependent plane variable. This is an advantage over the method of tilting the junction of the semiconductor laser with respect to the Y axis as described in Fi1.

As an example, FIG. 12 shows an embodiment in which the 111j wavelength handler 41 is arranged between the collimator lens 109 and the beam shaping prism IO, and a wavelength plate 41 is arranged in the same position as in FIG. 11, or a D array is arranged. An example of a light source is shown in FIG.

Also, as a matter of course, FIG. 1 shows a case where the transmitted light of the polarizing beam splitter 11 is used as the bidirectional light for recording on the recording medium Ml, and the reflected light is used as the light for controlling the laser light amount. However, the opposite configuration (transmitted light is the amount of laser light;
It is also possible to adopt a configuration in which the tlI+ light is used as the official light and the anti-Q=j light is used as the recording light on the recording medium and the playback light.

Furthermore, a semiconductor laser array, which is a hybrid configuration of multiple semiconductor lasers, is used as a light source.

In particular, when controlling the amount of light emitted from only a certain semiconductor laser among the plurality of semiconductor lasers, it is possible for the purpose of the present application to tilt only that semiconductor laser. That is, as shown in FIG. 1O, a plurality of semiconductor lasers 30.
．． 30 □, 3 required to control the amount of 303
Only 0□ is inclined with respect to the y-axis. By using such a light source in the apparatus shown in FIG. 4, the semiconductor lasers 30, . 30. The light flux from can be used conveniently without dropping the light +H.

[Effects of the Invention] As described in detail below, according to the optical head of the present invention, in order to control the light emitting end of a semiconductor laser that emits linearly polarized light, the polarization dependent plane inside the optical head and the polarized light Target 1 can be achieved with a simple configuration by utilizing the relationship between the polarization plane and the polarization plane incident on the dependent plane. The present invention makes it possible to individually control the amount of light emitted from a plurality of light emitting points, especially in the case of a conductor laser array, and has a practical effect on lx, 'Al, and so on. be.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram for explaining a first embodiment of the optical head of the present invention. FIG. 2 is a diagram showing the arrangement of laser light sources in the first embodiment. FIGS. 3 and 4 respectively show the second embodiment of the present invention. It is a block diagram which shows 3rd Example. FIGS. 5 and 6 are diagrams each showing the arrangement of light emitting points in an embodiment of the present invention using a light source having a plurality of light emitting points. 7 to 10 are diagrams showing further embodiments of the present invention. FIG. 11 and FIG. 12 are diagrams for explaining a conventional optical card reproducing device and an optical card, respectively. 108...! Conductor laser, +09... Collimator Rem shaping prism,! DESCRIPTION OF SYMBOLS 1... Polarization 12... Quarter wavelength plate, +01... Optical card, 14... First sensor, 16... Imaging system. IO...Vibeam splitter, 111...Objective lens, 13...Sensor lens system, 15...Second sensor.

Claims (5)

[Claims] (1) An optical head used in an optical storage device that optically records and/or reproduces information. It is a semiconductor laser light source that emits linearly polarized light, and has a transmittance and/or reflectance for the incident light. a polarization-dependent surface that depends on the polarization direction; an objective lens that images either transmitted light or reflected light from the polarization-dependent surface onto an optical record carrier; and a first lens that receives the reflected light beam from the record carrier. an optical head having at least a sensor, the first plane being a plane defined by the transmitted light and the reflected light on the polarization dependent surface, and a plane containing the transmitted light or the reflected light and perpendicular to the first plane; means for adjusting the polarization direction of the incident light so that the polarization direction of the incident light, which is linearly polarized light, does not coincide with either the first plane or the second plane when further provided with a second sensor that receives light that does not travel to the objective lens among the transmitted light or reflected light from the polarization dependent surface, and uses the output from the second light receiving section to detect the semiconductor An optical head characterized by controlling the amount of light emitted from a laser light source. (2) The means for adjusting the polarization direction of the incident light so that it does not coincide with either the first plane or the second plane is characterized by tilting the bonding surface of the semiconductor laser light source. An optical head according to claim 1. (3) In the optical head according to claim (1), the semiconductor laser light source is a semiconductor laser array light source having a plurality of light emitting points, and further between the polarization dependent surface and the second sensor. and an imaging system, the second sensor having a plurality of light receiving sections corresponding to the number of the plurality of light emitting points, and using outputs from the plurality of light receiving sections to detect the semiconductor laser array light source. An optical head characterized in that the amount of light emitted from each light emitting point within the head is controlled. (4) The optical head according to claim 1, wherein the polarization dependent surface is an entrance surface of a beam shaping prism provided between a semiconductor laser light source and an objective lens. (5) The optical head according to claim 1, wherein the polarization dependent surface is a splitting surface of a polarizing beam splitter provided between a semiconductor laser light source and an objective lens.