JP2600646B2 - Optical head device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to an optical head device for writing or reading information on or from an optical information recording medium, which is a so-called three-beam method for detecting a track displacement for tracking an information track. The present invention relates to an improvement in detection characteristics of an optical system employing a method.

[Conventional technology]

FIG. 7 shows a conventional optical head device. In the figure,
1 is a semiconductor laser chip (LD chip) as a light source, 5 is
Light emitted from the LD chip 1, reference numeral 11 denotes a diffraction grating, reference numeral 12 denotes a beam splitter, reference numeral 13 denotes an objective lens, reference numeral 14 denotes an optical disk for optically writing / reading information constituting an optical information recording medium, reference numeral 15
Is a light detector that receives the light beam reflected from the disk 14,
Reference numeral 64 denotes an information track on the optical disk 14. The diffraction grating 11 and the objective lens constitute incident optical means. FIG. 8 is an enlarged view of an LD chip used in a conventional device and a mount for holding the LD chip. In the figure, 1 is, for example, Ga
The semiconductor laser chip is formed of a heterojunction such as As or GaAlAs, and the chip 1 is fixed on a mount 4 via a buffer layer 3 with the end faces 100, 200, and 300 parallel to each other. Next, the operation of the conventional device will be described with reference to FIG.
This will be described with reference to (b) and (c).

The light beam 5 emitted from the LD chip 1 passes through the diffraction grating 11 and is separated into three light beams as indicated by broken lines, and the three beam spots 60, 61, and Collected 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. Each of the spots 60, 61, and 62 is reflected from the disc 14 and re-transmits through the objective lens 13, and then is reflected by the beam splitter 12
Then, the traveling direction is bent at a right angle, and then the optical detector 15 moves toward the photodetector 15. As shown in FIG. 7B, the photodetector 15
Elements 15a, 15b, and 15c as light receiving sections. The central element 15a receives the reflected light of the zero-order light spot 60, and the elements 15b and 15c receive the reflected light of the primary light spots 61 and 62. Then, an electric signal corresponding to the light intensity is output. 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. Further, since the primary light spots 62 and 61 are arranged obliquely with respect to the track 64 as described above, when the disk is displaced in the R direction in the drawing, that is, in a direction perpendicular to the track 64, the spots 62 and 61 are displaced. Reflection occurs asymmetrically, and as a result, the output signals of the detector elements 15b and 15c change asymmetrically. As a result, spots 15
By taking the differential of the outputs of b and 15c, the track 64 and
An S-shaped track shift signal is obtained for the center shift of the center spot 60. The track shift signal is used to correct the position so that the spot 60 is correctly positioned on the center of the track 64 and the information is accurately read or written. To be used as a so-called tracking servo error signal. 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 when a current flows through a PN junction surface 2 formed therein. Such a current drive causes an increase in the temperature of the chip. It is known that when the chip temperature rises, it is necessary to supply a larger current than before the rise in order to keep the output light output constant. The life of the chip 1 decreases exponentially. Therefore, for the purpose of radiating the heat of the LD chip 1, a mount 4 made of a material having good thermal conductivity, such as silver or brass, and having an overwhelming volume compared to the LD chip is used for heat radiation. However, when the LD chip 1 is directly mounted on the mount 4, the thermal expansion coefficients of the two are greatly different, so that a slight stress change of the chip when driving the LD chip generates a large stress inside the chip. It is known that the life of No. 1 is deteriorated. Therefore, when mounting LD1 on mount 4,
Usually, the semiconductor chip is mounted with a buffer layer 3 made of a material such as Si having a thermal expansion coefficient similar to that of the LD chip 1 interposed therebetween.

The thicknesses a, b, and c of the LD chip 1, the buffer layer 3, and the mount 4 are typically about 50 to 90 μm, about 100 to 200 μm, and about 2000 μm, respectively.
The end faces indicated by 100 and 300 in the figure are arranged so as to be parallel to each other for reasons such as ease of assembly.

In the conventional device having the configuration described above,
In the case of detecting the deviation between the track and the zero-order light spot 60 based on the difference in the amount of light of one primary light reaching the photodetector, when the disk 14 has caused an angular deviation in the track in the direction (FIG. 7A) (J direction), there is a drawback that the detection characteristics fluctuate, and there is a problem in error signal detection for tracking a correct 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 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. In this case, typically, spots 50, 51 and 50, 52
Is designed to be about 110 to 200 μm at the interval of, so that the beam spot 51 returning above the LD chip is
However, the central spot 50 is reflected again from the emission point of the original LD chip, and the lower primary spot 52 is reflected again from the front surface of the buffer layer 3 toward the disk. 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, respectively, and the light returning to the LD side is the point A, D
Is reflected again. The figure shows a case where the LD end face 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.
It can be seen from the figure that there is a difference in distance of Δ2. Now,
The original primary light takes the optical path of AGC or AGE in the figure, but the light that has been reflected from the disk and returned to points A and D on the LD again as described above has been re-reflected at the LD end. Facing the disk 14. The path of the light beam that enters the point C after experiencing such re-reflection can be considered as AGBGAGC, AGBGDGC, AGCGDGC, if attention is paid only to the case where the demultiplexing into the primary light is performed only once. On the other hand, the path of light that undergoes LD end 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 the state in which the disk 14 or the LD chip 1 and the buffer layer 3 as a whole are inclined in the J direction in the drawing, the coherence length of the LD is generally the direct coherence length between the AGC and the above, and AGE. Although the light beam is not long enough to cause interference between the light beams, the light beam re-entering the point C causes an interference phenomenon. That is, according to the symbol in FIG. 9, the optical path difference between the original 2Δ1 and the optical path difference between 2Δ2 and 2Δ1 + 2Δ2 is 2Δ1 + 2Δ2. Therefore, Δ2 changes according to the minute rotation of the disk 14 in the J direction, and LD Δ1 changes according to the minute rotation in the J direction, the above three optical path differences change, and a relative phase difference occurs between the light fluxes and the intensity of the spot C with the rotation of the disk 14 or LD. Changes due to interference. 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 intensities of the spots 61 and 62 demultiplexed by the diffraction grating are equal to each other. In the absence of such an interference phenomenon, in FIG. 7, when the center of the center beam 60 and the center of the track 64 are correctly matched. Each of the beam spots 61 and 62 will be equally displaced to the left and right of the track 64, and the intensity of the reflected light from these spots will be equal. As a result, the output difference between the photodetector elements 15b and 15c will be Equilibrate to zero. Further, when a left and right track shift occurs from this state, the output difference between the elements 15b and 15c changes between positive and negative, and the tracks 64 are periodically arranged. As shown in FIG. Is defined as one cycle, a 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. 3B, the track deviation becomes a track shift detection output in which the combined track point rises from the zero level by b, and the detection characteristics deteriorate. Also, the same phenomenon occurs with respect to the inclination of the 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. 9A, it is calculated that the combined track point floating amount b / a (a and b are defined in FIG. 10B) deteriorates at a cycle of about 1 ° with respect to the disk inclination θD. Revealed. FIG. 11 (b) shows a state in which the slope of 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 respect to the slope of LD. . With respect to the inclination of the LD, the lift of the combined track point changes at a cycle of about 0.2 °. In FIG. 9, the reflectance of the disk 14 is 80%, L
The end face reflectivity of the D chip 1 is 30% (GaAs reflectivity) and the front face reflectivity of the buffer layer 3 is 30% (Si reflectivity). 5: 1 beam splitter
Calculating the transmittance of 12 as 50%, it was found that the floating amount of the combined track reached a maximum of about 26%, and this fact was confirmed experimentally. Such a special change means that the combined track detection characteristics change significantly due to the disc angle deviation that occurs when using an optical head and the LD angle deviation that can occur over time in an actual optical disk system. This is a serious obstacle to correct information recording / reproduction by the head.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-described problems, and a light detection point for detecting two primary lights with respect to a tilt of a recording medium and a tilt of a light source. It is an object of the present invention to provide an optical system of an optical head device capable of correctly detecting a track deviation amount without floating from a zero level of an operation output of a device.

[Means for solving the problem]

In the optical head device according to the present invention, of the light flux reflected from the information recording medium and focused again on the light source side, attention is paid to the primary light component incident on the front surface of the buffer layer and reflected. A light beam processing unit is provided on the front surface of the buffer layer to eliminate the reflection of light or to prevent the light from being collected again on the information recording medium after being reflected.

[Action]

The light beam refocused on the front surface of the buffer layer is not reflected by the light beam processing unit, 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 the invention)

A first embodiment of the present invention will be described with reference to FIG. In the drawing, the same components as those of the conventional embodiment are denoted by the same reference numerals, and the description is omitted. In this embodiment, an anti-reflection layer 400 is newly added as a light beam processing unit on the front surface 200 of the buffer layer 3 in addition to the conventional structure. Because of this layer 400,
Even if the primary return light 82 is incident on the front surface 200 of the buffer layer 3, the ratio of the reflected light is 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 front surface of the buffer layer in this way, the light re-incident to the primary light on the disk can be effectively made only one, and the light between the plurality of re-incident lights can be reduced as in the related art. The buffer effect due to the phase shift caused by the disc tilt and the end face tilt on the LD side can be prevented, so that the differential from the photodetector elements 15b and 15c eliminates the floating from the zero level at the time of tracking when detecting the track shift. can do. 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 ": page54", the refractive index on a medium having a refractive index of ns Thickness of the medium The reflectance by just attaching It can be. (Where N = 0, 1, 2... Λ is the wavelength of light) As an example, antireflection when Si is used as the buffer layer will be described. The refractive index of Si is ms ≒ 3.4, and the reflectance without an anti-reflection coating is In contrast, a thickness of CeF3 of n = 1.60 as an anti-reflection film If only the reflection is applied, the reflectance is R ≒ 0.02, and the floating of the combined track point from the zero level due to the interference is smaller than that of the past.
It can be reduced to 1/15. However, λ was set to 0.8 μm.

Another simple method of using the anti-reflection layer 400 is to apply black ink used for calligraphy on the front surface 200 of the buffer layer. According to the experiment, the reflectance of the Si surface is 3
%. Therefore, the floating of the combined track detection output can be improved to about 1/10 of the conventional one. Needless to say, in addition to the application of black as described above, the phenomenon can be improved by applying a substance having a reflectance lower than that of the original mount.

FIG. 2 shows a second embodiment of the present invention. In the present embodiment, the front surface 200 of the buffer layer 3 is machined so as to be shifted from the optical axis of the optical head condensing optical system shown by a dashed line by 90 ° from the conventional embodiment by θ. As a result,
The primary light 82 reflected from the disk to the LD side is buffer layer 3
After being reflected by the front surface 200, the light beam 82 travels in a direction different from the original light beam 82 by 2θ as a light beam 92. As shown in the figure, if u is a half angle of the light beam emitted from the LD and condensed, if θ> u, the incident light beam 82 and the reflected light beam 92 do not overlap at all. Therefore, the interference phenomenon can be prevented without being condensed. Of course, even if θ is slightly smaller than u, the amount of light reflected and returned to the primary light on the disk again can be reduced, so that it is still effective in improving the interference phenomenon.

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

In the present embodiment, the portion where the primary light 82 incident on the LD side is incident on the front surface of the buffer layer 3 is chamfered at an angle θ, so that the reflected light 92 is deviated from the incident light 82 as in the second embodiment. It is configured as follows. By doing so, the interference phenomenon can be reduced as in the second embodiment, and the interference phenomenon can be eliminated when θ> u.

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

In this embodiment, the front surface 200 of the buffer layer 3 is arranged so as to be shifted from 90 ° by θ in the plane with respect to the optical axis of the light condensing system shown by a dashed line. When θ> u with respect to the half angle u provided for condensing the LD, the light incident on the buffer layer 3 and the reflected light can be separated similarly to the second embodiment, so that the interference phenomenon can be prevented. Further, even when θ <u, the interference phenomenon can be reduced. That is, in the second, third, and fourth embodiments, at least the refocused portion on the front surface of the buffer layer constitutes a light beam processing unit with an inclined surface. Is not incident.

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

In this embodiment, as shown in the figure, the front surface 200 of the buffer layer 3 is processed as a saw-toothed surface having an angle θ to constitute a light beam processing unit. As in the second embodiment, the light incident on the front surface 200 is reflected by changing the direction by 2θ, and the interference phenomenon can be prevented and reduced.

FIG. 6 shows a sixth embodiment of the present invention. In the present embodiment, a hole indicated by 110 is formed in a portion where the primary light 82 of the reflected light from the LD is incident on the front surface 200 of the buffer layer 3 to constitute a light beam processing unit. Since the light is reflected at the defocus point by this hole, the light re-condensed by the objective lens due to the end face reflection causes a defocus, and the interference phenomenon can be reduced.

〔The invention's effect〕

As described in detail above, according to the present invention, the light beam processing unit is provided on the front surface of the buffer layer holding the light source, so that the ratio of the primary light of the reflected light from the recording medium re-reflected is reduced or It is configured to deviate from the optical means, and it is possible to remove or reduce the interference phenomenon that has degraded the conventional track shift detection characteristic, and to perform reading or writing of the optical head device with the medium tilt, the aging of the angle of the LD end face. Even if there is a slight change, it can be performed stably.

[Brief description of the 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 a structure of an LD used in a fifth embodiment of the present invention, FIG. 6 is a diagram showing a structure of an LD used in a sixth embodiment of the present invention, and FIG. 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 an interference phenomenon of primary light on a disk to be solved by the present invention. FIG. 10 is a model diagram, and FIG. 10 is a diagram comparing the track deviation detection output with respect to the track deviation amount with and without the disk inclination in the conventional apparatus. FIG. 11 is a graph showing the change in the combined track deviation detection output with respect to the disk inclination in the conventional apparatus. It is a figure showing a situation that occurs. 1 ... LD chip, 3 ... Buffer layer, 4 ... Mount, 11 ...
... Diffraction grating, 12 ... Beam splitter, 13 ... Objective lens, 14 ... Disc, 15 ... Photodetector, 200 ... Front of buffer layer. In the drawings, the same reference numerals indicate the same or corresponding parts.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kazuo Iwata 800 Iwamatsu, Ojima-cho, Nitta-gun, Nitta-gun, Gunma Mitsubishi Electric Corporation Gunma Works (56) References JP-A-58-207689 (JP, A) 61-250845 (JP, A)

Claims (3)

(57) [Claims] 1. A semiconductor laser chip for emitting a laser beam, a mount for radiating the semiconductor laser chip, and a semiconductor laser chip disposed between the semiconductor laser chip and the mount, wherein the semiconductor laser chip is mounted on the mount. A buffer that fixes and acts as a moderator for stress generated by a temperature rise during laser light emission of the semiconductor laser chip, and a light beam emitted from the semiconductor laser chip is split into a plurality of light beams, Focusing means for narrowing each of the light fluxes as a plurality of light spots on the information recording medium, light emitted from the semiconductor laser chip, reflected light from the information recording medium, An optical head device comprising: a separating unit that separates the light beam; and a photodetector that receives the light flux separated by the separating unit. An optical head device, wherein the optical head device is formed as an inclined surface which is inclined by 90 from the 90 ° with respect to the optical axis of the light collecting means in the vertical direction of the buffer. (However, θ is approximately θ ≧ u with respect to the light collection half angle u of the light beam emitted from the semiconductor laser chip and incident on the light collection means.)
Is an angle that satisfies. ) 2. A semiconductor laser chip for emitting a laser beam, a mount for radiating the semiconductor laser chip, and a semiconductor laser chip disposed between the semiconductor laser chip and the mount, wherein the semiconductor laser chip is mounted on the mount. A buffer that fixes and acts as a moderator for stress generated by a temperature rise during laser light emission of the semiconductor laser chip, and a light beam emitted from the semiconductor laser chip is split into a plurality of light beams, Focusing means for narrowing each of the light fluxes as a plurality of light spots on the information recording medium, light emitted from the semiconductor laser chip, reflected light from the information recording medium, An optical head device comprising: a separating unit for separating the light; and a photodetector for receiving the light beam separated by the separating unit. An optical head device characterized in that the optical head device is tilted and arranged to rotate by θ with respect to a light emission surface from a body laser chip. (However, θ is approximately θ ≧ u with respect to the light collection half angle u of the light beam emitted from the semiconductor laser chip and incident on the light collection means.)
Is an angle that satisfies. ) 3. A semiconductor laser chip for emitting a laser beam, a mount for radiating the semiconductor laser chip, and a semiconductor laser chip disposed between the semiconductor laser chip and the mount, wherein the semiconductor laser chip is mounted on the mount. A buffer that fixes and acts as a moderator for stress generated by a temperature rise during laser light emission of the semiconductor laser chip, and a light beam emitted from the semiconductor laser chip is split into a plurality of light beams, Focusing means for narrowing each of the light fluxes as a plurality of light spots on the information recording medium, light emitted from the semiconductor laser chip, reflected light from the information recording medium, An optical head device provided with a separating means for separating light and a light detector for receiving the light beam separated by the separating means, wherein substantially the entire front surface of the buffer is sawed. An optical head device formed as a toothed surface.