JP2560686B2 - Optical head device - Google Patents

Description

The present invention relates to a so-called three-beam method as a track displacement detection method for tracking an information track in an optical head device for writing or reading information on an optical information recording medium. The present invention relates to improvement of detection characteristics of an optical system adopting the method.

[Conventional technology]

A conventional optical head device is shown in FIGS. 7 (a), (b),
It is shown in (c). In each figure, 1 is a semiconductor laser chip (LD chip) which is a light source, 5 is light emitted from the LD chip 1, 11
Is a diffraction grating, 12 is a beam splitter as a separating means,
Reference numeral 13 is an objective lens, 14 is an optical disk for optically writing / reading information, which constitutes an optical information recording medium, and 15 is a disk.
A photodetector that receives the light flux reflected by 14 and 64 is an information track on the optical disc 14. The diffraction grating 11 and the objective lens constitute incident optical means. FIG. 8 shows an enlarged view of an LD chip used in a conventional device and a mount holding it. In the figure, 1 is, for example, GaAs or Ga.
This is a semiconductor laser chip made of a heterojunction such as AlAs, and the chip 1 is fixed on the mount 4 in a state where the respective end faces 100 and 300 are parallel to each other.

Next, regarding the operation of the conventional device, FIGS. 7 (a), (b),
This will be described with reference to (c).

The light beam 5 emitted from the LD chip 1 is separated into three light beams as shown by the broken line by passing through the diffraction grating 11, and the three beam spots 60, 61 on the optical disk 14 are passed through the beam splitter 12 and the objective lens 13. Focused as 62. Of these, the spot 60 is a zero-order diffracted light, and the spots 61 and 62 are first-order diffracted lights having the same intensity.
As shown in FIG. 7 (c), each beam spot is arranged such that a line 63 connecting the direction of the track 64 and the center of the spots 60, 61, 62 with respect to the zero-order beam spot 60 is slightly inclined. ing. The spots 60, 61, 62 are reflected by the disk 14, re-transmitted by the objective lens 13, bent by the beam splitter 12 at a right angle, and then travel toward the photodetector 15. As shown in FIG. 7 (b), the photodetector 15 is divided into three elements 15a, 15b and 15c as light receiving parts, and the central element 15a is arranged to reflect the reflected light of the 0th-order light spot 60 into elements. 15b and 15c receive the reflected light of the primary light spots 61 and 62 and output an electric signal according to the light intensity. As is well known, the zero-order light spot 60 is used to read or write information stored on the disk, and at the time of reading, the output of the central photodetector element 15a is used as a disk information signal. Also, the primary light spots 62 and 61 are, as described above,
Since the disk is displaced with respect to the track 64, when the disk is displaced in the R direction in the figure, that is, in the direction perpendicular to the track 64, the reflections of the spots 62 and 61 occur asymmetrically, resulting in the detector elements 15b and 15c. Output signal changes asymmetrically. As a result, as is well known, spots 15b, 15c
By activating the output of, an S-shaped track deviation signal is obtained with respect to the center deviation of the track 64 and the center spot 60. This track deviation signal positions the spot 60 correctly on the center of the track 64. It is used as a so-called tracking servo error signal for position correction in order to accurately read or write information. Since the details of the tracking servo have no relation to the essence of the present invention, the description is omitted here.

Next, FIG. 8 showing the structure of an LD used in a conventional optical head will be described. The LD chip 1 is an element that emits a laser beam 5 by passing a current through a PN junction surface 2 formed inside the LD chip 1. Such a current drive causes a temperature rise of the chip. It is known that in order to keep the output light output constant when the temperature of the chip rises in this way, it is necessary to supply a larger current than before the rise. Laser chip 1
Exponentially shortens the life of. Therefore, for the purpose of heat dissipation of the LD chip 1, for example, a mount 4 made of a material having good thermal conductivity such as silver or brass and having an overwhelmingly large volume compared to the LD chip is used for heat dissipation. The chip 1 is held on the mount 4 through a relatively soft material such as gold solder or indium solder, which does not generate internal stress in the LD chip 1. LD chip 1 and mount 4 thickness a, c
Are typically 50 to 90 μm and 2000 μm, respectively.
The respective end faces indicated by 100 and 300 are arranged to be parallel to each other for reasons such as ease of assembly 1.

In the conventional device having the above-described configuration, 2
When detecting the deviation between the track and the 0th-order light spot 60 due to the difference in the amount of light of the one primary light reaching the photodetector, when the disk 14 causes an angular deviation in that direction (see J in FIG. 7A). There is a drawback that the detection characteristics fluctuate in the direction), and there is a problem in detecting the error signal for the correct tracking of the track. In addition, when the LD similarly shifts in the J direction, there is a problem that the same characteristic fluctuation occurs.

This phenomenon will be described in detail below with reference to FIGS. 7 and 9.

7 (a), (b) and (c), the disk 14
The three spots 60, 61, and 62 condensed on the mirror are reflected by the beam splitter 12, and then travel to the photodetector 15. Returning to the side, re-imaging is performed at points 50, 51, and 52 conjugate with the three spots 60, 61, and 62 on the disk by the objective lens 13, respectively. At this time, typically spots 50, 51, and 50, 52
The beam spot 51 returning above the LD chip is not re-reflected by the LD because it is designed to have an interval of 110 to 200 μm, but the central spot 50 is emitted from the original DL chip. From the point, the lower primary spot 52 is reflected again from the end face of the mount 4 and faces the disc side. The phenomenon that occurs at this time will be described with reference to FIG. 9, which extracts only necessary parts from FIG. 60 and 5 in the figure
0,62 and 52 are conjugate points, and the light returned to the LD side is points A and D.
Is reflected again. The figure shows the case where the LD end surface 100 and the disk 14 are parallel to each other. Strictly speaking, the spot 52 and the reflection surface by the LD end have Δ1, the spot 62 and the condensing point C on the disk.
From the figure, it can be seen that there is a difference of Δ2 in distance. Now,
Original primary light takes the optical path of AGC or AGE in the figure, but as described above, the light reflected from the disk and returning to the A and D points of the LD again is re-reflected at the LD end and then re-disced. Turn to side 14. There are three possible paths of the luminous flux entering the point C after undergoing such re-reflection, if only the demultiplexing into the primary light is carried out once: AGBGAGC AGBGDGC AGCGDGC. On the other hand, the path of light that undergoes LD-side re-reflection to point E on the disk is only AGBGAGE because there is no reflection on the F side in the figure. Now, considering that the disk 14 or the LD chip 1 and the mount 4 as a whole are tilted in the J direction in the figure, the coherence length of the LD is generally between the AGC and the above, and , Is not long enough to cause interference, but an interference phenomenon occurs between the light beams re-incident at point C. That is, according to the symbols in FIG. 9, the optical path difference between and is 2Δ1, the optical path difference is 2Δ2, and the optical path difference is 2Δ1 + 2Δ2. Since Δ2 changes in accordance with the rotation and Δ1 changes in accordance with the minute rotation of the LD in the J direction, the above-mentioned three optical path differences change, and a relative phase difference occurs between the light fluxes ,. The intensity of the spot C changes due to interference as the LD rotates. On the other hand, E
Since there is only the above-mentioned re-reflected light to the side, the interference phenomenon unlike the side C does not occur. Originally, the intensity of the spots 61 and 62 demultiplexed by the diffraction grating are equal to each other, so if there is no such interference phenomenon, the center of the center beam 60 and the center of the track 64 in FIG. In addition, the beam spots 61 and 62 are arranged on the left and right sides of the track 64 so as to be offset from each other, and the intensities of the reflected light from these spots are equal to each other. Becomes zero in balance. Further, when a left / right track deviation occurs from this state, the output difference between the elements 15b and 15c changes to positive and negative, and the tracks 64 are periodically arranged. Therefore, as shown in FIG. Is set as one cycle, and the correct track deviation detection output in which the combined track point crosses the zero level can be obtained. However,
The interference phenomenon described above occurs due to the tilt of the disk.For example, the light intensity incident on the detector element 15b is
If the intensity is higher than the intensity of light incident on 5c, the 10th
As shown in FIG. 7B, the combined track point becomes the track deviation detection output in which the combined track point floats from the zero level, and the detection characteristics deteriorate. Also, the same phenomenon occurs with respect to the inclination of LD.

As an example, when the spot interval on the disk is 22 μm and the spot interval of the light flux returning to the LD end is 110 μm,
As shown in Fig. (A), it is calculated that the total track lift amount b / a (a and b are defined in Fig. 10 (b)) changes with a cycle of about 1 ° with respect to the disk inclination θD. Revealed by. Further, FIG. 11 (b) shows a state in which the inclination of the LD is changed by only 0.02 ° from the state of (a), and it can be seen that the value of b / a also changes with the inclination of the LD. . The lift of the combined track point changes in a cycle of about 0.2 ° with respect to the inclination of the LD. Also, in FIG. 9, the reflectance of the disk 14 is 80%, L
The end face reflectance of the D chip 1 is 30% (the reflectivity of GaAs), the end face reflectance of the mount 4 is 30%, the splitting ratio of the 0th order light and the 1st order light by the diffraction grating is 5: 1, and the beam splitter 12 The transmittance of
When calculated to be 50%, it was found that the maximum lifting amount of the combined truck was about 26%, and this fact was confirmed experimentally. Such a characteristic change means that in the actual optical disc system, the combined track detection characteristic largely changes due to the disc angle deviation that occurs when using the optical head and the LD angle deviation that may occur over time. It has been a serious obstacle to correct recording / reproducing of information by the head.

The present invention has been made in order to solve the problems as described in detail above, and is a photodetector for detecting two primary lights whose combined track points detect the inclination of the recording medium and the inclination of the light source. The present invention provides an optical system of an optical head device capable of correctly detecting the amount of track deviation without floating from the zero level of the operation output of.

[Means for solving problems]

In the optical head device according to the present invention, among the light beams reflected from the information recording medium and condensed again on the light source side, focusing on the primary light component that is incident on the mount front surface and reflected,
A light flux processing section is provided on the front surface of the mount to eliminate the reflection of the primary light or prevent the primary light from being condensed again on the information recording medium after being reflected.

[Action]

The light flux that is re-focused on the front surface of the mount is not reflected by the light flux processing section or is not reflected toward the incident optical means of the information recording medium and is not focused on the information recording medium.

Example of Invention

A first embodiment of the present invention will be described with reference to FIG. In the figure, the same parts as those in the conventional embodiment are designated by the same reference numerals, and the description thereof will be omitted. In this embodiment, in addition to the conventional structure, an antireflection layer 400 is newly added as a light flux processing unit on the front surface 300 of the mount 4. Due to this layer 400, even if the primary return light 82 is incident on the front surface of the mount 4,
The reflection rate is configured to be extremely small.

By adding the anti-reflection layer 400 in this manner, the light that is re-reflected from the LD side to the point C in FIG. 9 substantially takes the path of the AGBGAGC, that is, is described in the section of the problem of the prior art. It is only the light shown. By lowering the reflectivity of the mounting surface in this way, it is possible to effectively re-inject only one light beam into the primary light beam on the disc, and, as in the conventional case, between the re-incident light beams, It is possible to prevent the interference effect due to the phase shift caused by the tilt and the end surface tilt on the LD side, and thus eliminate the floating from the zero level at the time of the combined track when detecting the track shift by the differential between the photodetector elements 15b and 15c. You can Next, an example of forming an antireflection layer will be described. One is a method using an antireflection film using an optical thin film. For example, as is well known in “Tsujiuchi:“ Introduction to Optics II ”: page 54”, etc. Thickness of the medium The reflectance by just attaching Can be (However, N = 0,1,2 ... λ is the wavelength of light.) As an example, the antireflection when using Si as a mount will be described. The refractive index of Si is Ms ≈ 3.4, and the reflectance without the anti-reflection coating is In contrast, a thickness of CeF3 of n = 1.60 as an anti-reflection film When only attached, the reflectance becomes R ≈ 0.02, and the floating from the zero level of the combined track point due to interference is
It can be reduced to 1/15. However, λ was set to 0.8 μm.

As another convenient method of forming the antireflection layer 400, it is possible to apply black ink used for calligraphy on the front surface 300 of the mount. According to experiments, the reflectance of the Si surface could be suppressed to about 3% by applying black ink. Therefore, the floating of the combined track detection output can be improved to about 1/10 of the conventional one. Needless to say, the development can be improved by applying a substance having a reflectance lower than the reflectance of the original mount, in addition to applying the black ink as described above.

FIG. 2 shows a second embodiment of the present invention. In this embodiment, the front surface 300 of the mount 4 is processed so as to be tilted so as to deviate from the optical axis of the optical head condensing optical system shown by the alternate long and short dash line by 90 from the conventional embodiment. As a result, the primary light 82 reflected from the disc to the LD side is the front surface.
After being reflected by 300, it will travel as a light beam 92 in a direction different from the original light beam 82 by 2θ. As shown in the figure, if the half angle of the light beam emitted from the LD and condensed is u> θ, then the incident light beam 82 and the reflected light beam 92 do not overlap at all, so the objective lens 13 again places them on the disc. It is possible to prevent the interference phenomenon without being condensed on the. Of course, even if .theta. Is slightly smaller than u, the amount of light reflected and returned to the primary light on the disk can be reduced, and therefore it is still effective in improving the interference phenomenon.

 FIG. 3 shows a third embodiment of the present invention.

In the present embodiment, the reflected light 92 deviates from the incident light 82 by chamfering the portion of the front surface of the mount 4 where the primary light 82 incident on the LD side is incident at an angle θ. It is configured as follows. By doing so, the interference phenomenon can be reduced as in the second embodiment. Θ> u
In the case of, the interference phenomenon can be eliminated.

 FIG. 4 shows a fourth embodiment of the present invention.

In this embodiment, the front surface 300 of the mount 4 is arranged so as to deviate by 90 from 90 ° with respect to the optical axis of the focusing system shown by the alternate long and short dash line in the plane. When θ> u with respect to the half-angle u used for condensing the LD, the incident light to the mount 4 and the reflected light can be separated as in the second embodiment, so that the interference phenomenon can be prevented. Further, even if θ <u, it is possible to reduce the interference phenomenon. That is, in the second, third and fourth embodiments, at least the re-focusing portion of the front surface of the mount is used as the inclined surface to configure the light flux processing section.
It is not incident in 14 directions.

 FIG. 5 shows a fifth embodiment of the present invention.

In this embodiment, the front surface 300 of the mount 4 is as shown in the figure.
Is processed as a sawtooth surface having an angle θ to form a light flux processing unit. As in the second embodiment, the light incident on the front surface 300 is reflected by changing the direction by 2θ, and the interference phenomenon can be prevented or reduced.

FIG. 6 shows a sixth embodiment of the present invention. In this embodiment, on the front surface 300 of the mount 4, the primary light 82 of the reflected light from the LD
A hole indicated by 110 is formed in a portion where is incident, and the light beam processing unit is configured. Since the light is reflected at the defocus point by this hole, the light re-focused by the objective lens is defocused due to the end face reflection, and the interference phenomenon can be reduced.

As described in detail above, according to the present invention, the light flux processing unit is provided on the front surface of the mount that holds the light source, and the proportion of the primary light reflected from the recording medium that is re-reflected decreases. Or
Alternatively, since it is configured so as to deviate from the incident optical means, it is possible to eliminate or reduce the interference phenomenon that has deteriorated the conventional combined track deviation detection characteristic, and read or write the optical head device with the medium tilt, and the aging of the optical edge at right angles. Even if there is a slight change, it can be performed stably.

[Brief description of drawings]

FIG. 1 is a diagram showing the structure of an LD used in the first embodiment of the present invention, and FIG. 2 is a diagram showing the LD used in the second embodiment of the present invention.
FIG. 3 is a diagram showing a structure of an LD used in a third embodiment of the present invention, FIG. 4 is a diagram showing a structure of an LD used in a fourth embodiment of the present invention, FIG. 5 is a diagram showing the structure of an LD used in the fifth embodiment of the present invention, FIG. 6 is a diagram showing the structure of the LD used in the sixth embodiment of the present invention, and FIG. FIG. 8 is a schematic diagram of the configuration of an optical head device, FIG. 8 is a diagram showing the structure of an LD used in a conventional optical head device, and FIG. 9 is a diagram for explaining the interference phenomenon of primary light on a disk to be solved by the present invention. A model diagram, FIG. 10 is a diagram comparing the matching track deviation detection output with respect to the track deviation amount in the conventional apparatus with and without the disk tilt, and FIG. 11 is a change in the matching track deviation detection output with respect to the disk tilt in the conventional apparatus. It is a figure which shows a mode that occurs. 1 ... LD chip, 4 ... Mount, 11 ... Diffraction grating, 12
…… Beam splitter, 13 …… Objective lens, 14 …… Disk, 15 …… Photodetector, 300 …… Front of mount. In the drawings, the same reference numerals indicate the same or corresponding parts.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kazuo Iwata, Kazuo Iwata 800 Iwamatsu, Oshima-cho, Nitta-gun, Gunma Mitsubishi Electric Corp. Gunma Manufacturing Co., Ltd. (56) References Sho 61-195529 (JP, U)

Claims (3)

(57) [Claims] 1. A light source placed on the upper surface of a mount formed on a horizontal plane and on the front surface of the mount so that a light emitting surface is substantially aligned with the light source, and light emitted from this light source is branched into a plurality of light sources. Incident optical means for narrowing light as a spot on the information recording medium, and interposed in the incident optical means,
In an optical head device provided with a separating means for separating light from the light source side and a reflected light flux from the information recording medium, and a light detecting means comprising a plurality of light receiving portions for receiving the light flux separated by the separating means, An optical head device, wherein substantially the entire front surface of the mount is formed as an inclined surface that is inclined in the vertical direction of the mount. 2. A mount formed by forming a front surface perpendicular to the upper surface formed on a horizontal plane, a light source mounted on the upper surface of the mount and having a light emitting surface perpendicular to the upper surface, Incident optical means for branching the light emitted from the light source into a plurality of pieces and narrowing each light as a spot on the information recording medium, and light incident from the incident optical means and reflected from the light source side and the information recording medium. An optical head device comprising a separating means for separating a light flux and a light detecting means comprising a plurality of light receiving portions for receiving the light flux separated by the separating means, wherein the mount is mounted on a light emitting surface of the light source. An optical head device, wherein the mount is tilted in the left-right rotation direction so that the front surfaces of the mounts are not parallel to each other. 3. A light source mounted on the upper surface of the mount formed on a horizontal plane and on the front surface of the mount so that the light emitting surface is substantially aligned, and the light emitted from this light source is branched into a plurality of light sources. Incident optical means for narrowing light as a spot on the information recording medium, and interposed in the incident optical means,
In an optical head device provided with a separating means for separating light from the light source side and a reflected light flux from the information recording medium, and a light detecting means comprising a plurality of light receiving portions for receiving the light flux separated by the separating means, An optical head device characterized by being formed in a sawtooth shape over substantially the entire front surface of the mount.