JP4138095B2 - Optical head - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical head having a structure that suppresses generation of noise by superimposing a high-frequency current on a semiconductor laser that is a light source.
[0002]
[Prior art]
In recent years, in the field of consumer optical discs, recording / reproducing devices such as mini-discs have become popular in addition to read-only discs such as compact discs. In addition, these devices are being miniaturized so as to follow the trend of light, thin and small eras.
[0003]
Hereinafter, an optical head using a conventional high-frequency superposition circuit used in these devices will be described.
[0004]
FIG. 8 is a cross-sectional view of an integrated unit in which the light source and the photodetector are housed in one unit. In FIG. 8, 1 is an integrated unit, 1a is a package, 1b is a semiconductor laser as a light source, 1c is a light detection substrate, 1e is a terminal, 1f is a bonding wire for connecting the semiconductor laser 1b, the light detection substrate 1c and the terminal, 2 Is a hologram made of resin or glass, 2a is a diffraction region formed on the hologram 2, 3 is an objective lens, 4 is a recording medium, 5a is a light beam, and 5b is a light beam diffracted by the diffraction region 2a of the hologram.
[0005]
FIG. 9 is a perspective view showing a state where the integrated unit of FIG. 8 and the high-frequency superimposed circuit board are mounted on a flexible substrate. In FIG. 9, 6 is a flexible substrate, 6a is an integrated unit mounting surface, 6b is a land portion, 6c and 6e are bridge portions, 6d is a signal extraction portion, 6f is a high frequency superposition circuit mounting surface, and 16 is high frequency superposition. It is a circuit board.
[0006]
FIG. 10 is an exploded perspective view showing a state in which the flexible substrate 6 shown in FIG. 9 is bent and mounted on the optical base. In FIG. 10, 7 is a holder for fixing the integrated unit 1, 7a is an opening for passing light emitted from the integrated unit 1, and 8 is a shield case made of an electromagnetic shielding material such as metal.
[0007]
As shown in FIG. 9, the flexible substrate 6 on which components are mounted is bent at the bridge portion 6e so that the back surface of the integrated unit 1 is on the inside. Next, the integrated unit 1 is positioned and fixed to the holder 7, and the shield case 8 is attached to the holder 7 by bonding or the like by inserting a 90 ° bent shield case 8 from the high frequency superimposed circuit board side to the holder 7 side at the bridge portion 6c. Fix it.
[0008]
FIG. 11 is a perspective view showing the operation of the optical head using the integrated unit mounted as shown in FIG. In FIG. 11, 9 is an optical base, 10 is a rising mirror for allowing a light beam emitted from the integrated unit 1 to enter the objective lens 3, 3 is an objective lens, 4 is a recording medium, and 5a is a light beam emitted from the integrated unit. , 11 is the main shaft, 12 is the subshaft, and H is the height of the shield case 8.
[0009]
The operation of the conventional example configured as described above will be described.
[0010]
A light beam 5 a emitted from the semiconductor laser 1 b in the integrated unit 1 passes through the hologram 2, enters the objective lens 3, and is condensed on the recording medium 4. The light beam reflected by the recording medium 4 again enters the hologram 2 through the objective lens 3. The light beam is diffracted by the diffraction region 2a formed on the hologram 2 and condensed on a photodetector configured on the light detection substrate 1c to obtain a focus error signal, a tracking error signal, and an information signal of the recording medium.
[0011]
Next, the high frequency superimposing circuit will be described. As a semiconductor laser used in the recording / reproducing optical head, a single mode type having high coherence is used in order to obtain a high optical output during recording. While the optical head is recording / reproducing, part of the reflected light beam from the recording medium returns to the semiconductor laser, causing interference in the semiconductor laser chip and generating noise. This noise is mixed into the information signal and the servo signal and causes signal deterioration. As a countermeasure, noise suppression is performed using a high frequency superposition circuit. In general, a high-frequency superimposing circuit employs a technique in which a current of several hundred MHz is superimposed on a semiconductor laser to emit light in a longitudinal multimode, thereby reducing the coherence and suppressing the generation of noise.
[0012]
In the above, the recording / reproducing optical head has been described. However, even in a reproduction-only optical head, if a semiconductor laser oscillating close to a single mode is used, generation of noise is suppressed by using a high-frequency superimposing circuit. Yes.
[0013]
[Problems to be solved by the invention]
In such an optical head, the integrated unit 1 that is a light source and the high-frequency superposed circuit board 16 are stacked, and a space must be provided for electrical insulation between the shield case 8 and the high-frequency superposed circuit board 16. There was a drawback that the dimension H of 11 was increased.
[0014]
Further, in the configuration of the conventional example, the distance between the high-frequency superimposed circuit board 16 and the semiconductor laser 1b becomes long, so that loss occurs in the high-frequency band. For this reason, in order to increase the superposition effect, the oscillation output of the high frequency superposition circuit must be increased. As a result, there are drawbacks that electromagnetic radiation noise and power consumption increase, and the cost increases.
[0015]
It is an object of the present invention to provide a small-sized optical head that can reduce the cost of such an optical head and has low electromagnetic radiation noise and low power consumption.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, the present invention has the following configuration.
[0017]
That is, the optical science head of the present invention, light source, a high frequency superimposing means for superimposing a high-frequency current to the light source, a focusing means for focussing on the recording medium the light beam emitted from said light source, said recording medium Diffracting means for diffracting light reflected from the light incident through the condensing means into a plurality of light beams, light detecting means for entering the light beams diffracted by the diffracting means, and light detecting means are formed. And the light source is disposed on the light detection substrate so as to be sandwiched between positions where the plurality of light beams are incident on the light detection means. A focus error signal, a tracking error signal, and an information signal of the recording medium are calculated from the light disposed on the superimposing means and received by the light detecting means .
[0021]
The present invention, by the above configuration, at a low cost, less electromagnetic radiation noise and power consumption, compact optical head is obtained.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to FIGS.
[0023]
(Embodiment 1)
FIG. 1 is a cross-sectional view of an integrated unit used in an optical head according to a first embodiment of the present invention.
[0024]
In FIG. 1, 1 is an integrated unit, 1a is a package, 1b is a semiconductor laser, 1c is a light detection substrate on which a photodetector is formed, 1d is a high-frequency superimposed circuit substrate on which a high-frequency superimposed circuit is formed, and 1e is a terminal 1f is a bonding wire, 2 is a hologram made of resin or glass, 2a is a diffraction region formed on the hologram surface, 3 is an objective lens for converging the light beam 5a emitted from the light source on the recording medium 4, Reference numeral 5b denotes a light beam obtained by diffracting the light beam reflected by the recording medium 4 in the diffraction region 2a.
[0025]
FIG. 2 is a perspective view showing a flexible substrate on which the integrated unit of FIG. 1 is mounted. In FIG. 2, 6 is a flexible substrate, 6a is an integrated unit mounting surface, 6b is a land portion, 6c is a bridge portion, and 6d is a signal extraction portion.
[0026]
FIG. 3 is an exploded perspective view showing a state in which the flexible substrate 6 shown in FIG. 2 is bent at the bridge portion 6c and mounted on the optical base. In FIG. 3, 7 is a holder for fixing the integrated unit 1, 7a is an opening for passing light emitted from the integrated unit 1, and 8 is a shield case made of an electromagnetic shielding material such as metal.
[0027]
FIG. 4 is a perspective view showing the operation of the optical head using the integrated unit 1 mounted as shown in FIG. In FIG. 4, 9 is an optical base, 10 is a rising mirror for causing the light beam emitted from the integrated unit 1 to enter the objective lens, 3 is an objective lens, 4 is a recording medium, 5a is a light beam emitted from the integrated unit, 11 is the main shaft, 12 is the sub shaft, and H is the height of the shield case 8.
[0028]
The operation of the optical head configured as described above will be described below.
[0029]
In the present embodiment, in the integrated unit 1, the semiconductor laser 1b is disposed on the light detection substrate 1c, and the high-frequency superimposed circuit substrate 1d is disposed below the light detection substrate 1c. The light detection signal of the light detection substrate 1c is connected to the terminal 1e through the bonding wire 1f so as to extract the signal to the outside. The anode side of the semiconductor laser 1b passes through the light detection substrate 1c or is directly connected to the high-frequency superimposed circuit substrate 1d by a bonding wire 1f. With this configuration, it is possible to superimpose a high-frequency oscillation current generated by the high-frequency superposition circuit board 1d on the DC drive current of the semiconductor laser 1b supplied from the outside of the integrated unit.
[0030]
The integrated unit 1 configured as described above is mounted on a flexible substrate 6 as shown in FIG. 2, and then the integrated unit 1 is positioned and fixed to a holder 7 as shown in FIG. Next, a 90 ° bent shield case 8 is inserted into the holder 7 side at the bridge portion 6c from the back side of the integrated unit 1, and the shield case 8 is fixed to the holder 7 by adhesion or the like.
[0031]
As shown in FIG. 4, the integrated unit assembled in this way is fixed to an optical base on which optical components are mounted with a fastening member such as an adhesive or a screw.
[0032]
Note that the process of detecting the light emitted from the semiconductor laser is the same as that in the conventional example, and therefore will be omitted.
[0033]
As described above, according to the present embodiment, the semiconductor laser 1b and the high-frequency superimposed circuit board 1d can be connected at a short distance, so that the loss between the semiconductor laser and the high-frequency superimposed circuit board can be eliminated. Therefore, it is only necessary to superimpose with a lower oscillation output than in the prior art, so low power and low electromagnetic radiation noise can be realized.
[0034]
In addition, since the high-frequency superimposed circuit board that has been conventionally arranged on the rear surface of the integrated unit 1 does not exist in the present embodiment, the dimension H can be made smaller than that of the conventional example, and the main shaft 11 of the optical head The distance between the axes of the sub-shafts 12 can be shortened, and the size can be reduced.
[0035]
Further, since only the integrated unit 1 in which the high-frequency superposed circuit board, the light detection board, and the semiconductor laser are sealed in the same package is mounted on the flexible board, the required area can be reduced and the cost of the flexible board can be reduced. Can be measured.
[0036]
In this embodiment, the package 1a and the hologram 2 are integrated, but it goes without saying that they may be used separately.
[0037]
Further, in order to obtain the superposition effect, it is sufficient to connect the semiconductor laser 1b and the high-frequency superposition circuit board 1d at a short distance. Therefore, it is sufficient that the semiconductor laser 1b is installed on the high-frequency superposition circuit board 1d. May be arranged separately from these. At this time, the light detection substrate may be a separate package.
[0038]
(Embodiment 2)
FIG. 5 is a sectional view of an integrated unit used in the optical head according to the second embodiment of the present invention.
[0039]
In FIG. 5, 13 is a beam splitter for branching a light beam, 13a is a reflecting surface of the beam splitter, 14 is a photodetector, and 5c is a light beam reflected by the reflecting surface 13a. Since other than these are the same as those in FIG. 1, the same reference numerals as those in FIG.
[0040]
The operation of the optical head configured as described above will be described below.
[0041]
The semiconductor laser 1b, the light detection substrate 1c, and the high-frequency superimposed circuit substrate 1d are disposed in the integrated unit 1 in the same manner as in the first embodiment.
[0042]
The light beam 5a emitted from the semiconductor laser 1b in the integrated unit 1 passes through the hologram 2 and the beam splitter 13, enters the objective lens (not shown) as in the first embodiment, and is a recording medium (not shown). Focused on top. The light beam reflected by the recording medium again enters the beam splitter 13 through the objective lens. The light beam 5c reflected by the reflecting surface 13a of the beam splitter is incident on the photodetector 14 and an information signal of the recording medium is obtained. On the other hand, the light beam that has passed through the reflecting surface 13a is diffracted by the diffraction region 2a formed on the hologram 2 and condensed on the photodetector configured on the light detection substrate 1c to obtain a focus error signal and a tracking error signal. It is done.
[0043]
As described above, according to the present embodiment, it is possible to further reduce the size by disposing the prism in the integrated unit of the first embodiment.
[0044]
(Embodiment 3)
FIG. 6 is a cross-sectional view of an integrated unit used in an optical head according to the third embodiment of the present invention.
[0045]
In FIG. 6, 1a is a package made of a ceramic multilayer substrate in which capacitors, coils, and resistors are formed, 1b is a semiconductor laser, 1h is a photodetector substrate on which a photodetector and a transistor for a high-frequency superposition circuit are formed, 1e Is a terminal, 1f is a bonding wire, and 1g is a land portion formed on the ceramic substrate. Since other than these are the same as those in FIG. 1, the same reference numerals as those in FIG.
[0046]
The operation of the optical head configured as described above will be described below.
[0047]
In the integrated unit 1, the semiconductor laser 1b is disposed on the light detection substrate 1h, and these two points are disposed on a package 1a formed of a ceramic multilayer substrate. Capacitors, coils, and resistors used in the high frequency superposition circuit are formed on the ceramic multilayer substrate, and transistors used in the high frequency superposition circuit are formed on the light detection substrate 1h, and the ceramic multilayer substrate, the light detection substrate 1h, and the semiconductor laser 1b. Are connected by a bonding wire 1f. With this configuration, a high-frequency oscillation current generated by the ceramic multilayer substrate 1a and the light detection substrate 1h can be superimposed on the DC drive current of the semiconductor laser 1b supplied from the outside of the integrated unit.
[0048]
As described above, according to the present embodiment, the number of components can be reduced by making the package a part of the high-frequency superposition circuit.
[0049]
In this embodiment, the package 1a is a ceramic multilayer substrate. However, it goes without saying that the package may be a resin package, and capacitors, coils, and resistors may be formed on another ceramic multilayer substrate and configured inside the package. .
[0050]
In this embodiment, the transistor used in the high-frequency superposition circuit is formed on the light detection substrate 1h, but may be formed on a semiconductor substrate provided separately from the light detection substrate.
[0051]
(Embodiment 4)
FIG. 7 is a cross-sectional view of an integrated unit used in an optical head according to the fourth embodiment of the present invention.
[0052]
In FIG. 7, reference numeral 1i denotes a light detection / high frequency superimposed circuit board on which a photodetector, a capacitor, a coil, a resistor, and a transistor are formed. Since other than this is the same as FIG. 1, the same reference numerals as those in FIG.
[0053]
The operation of the optical head configured as described above will be described below.
[0054]
In the integrated unit 1, the semiconductor laser 1 b is disposed on the light detection / high-frequency superimposed circuit board 1 i. Capacitors, coils, resistors, and transistors used in the high frequency superposition circuit are formed on the photodetection / high frequency superposition circuit substrate 1i, and the photodetection / high frequency superposition circuit substrate 1i and the semiconductor laser 1b are connected by a bonding wire. With this configuration, it is possible to superimpose a high-frequency oscillation current generated by the photodetection / high-frequency superposition circuit board 1i on the DC drive current of the semiconductor laser 1b supplied from the outside of the integrated unit.
[0055]
As described above, according to the present embodiment, since the high-frequency superimposing circuit and the semiconductor laser can be connected in the shortest time, the loss between the semiconductor laser and the high-frequency superimposing circuit board can be eliminated, and it is only necessary to superimpose with a low oscillation output. Low power and low electromagnetic radiation noise can be realized.
[0056]
【The invention's effect】
As described above, according to the present invention, since the semiconductor laser and the high-frequency superposition circuit board can be connected at a short distance, the loss between the semiconductor laser and the high-frequency superposition circuit board can be eliminated, and the superposition can be performed with a low oscillation output. Therefore, low power and low electromagnetic radiation noise can be realized.
[0057]
In addition, since the components disposed on the rear surface of the conventional integrated unit do not exist in the present invention, the distance between the main shaft and the sub shaft of the optical head can be shortened, and the size can be reduced.
[0058]
Further, since only the integrated unit needs to be mounted on the flexible substrate, the required area can be reduced, and the cost of the flexible substrate can be reduced.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a schematic configuration of an integrated unit used in an optical head according to a first embodiment of the present invention. FIG. 2 is mounted with the integrated unit according to the first embodiment of the present invention. FIG. 3 is a perspective view showing a flexible substrate. FIG. 3 is an exploded perspective view showing a state in which the flexible substrate is mounted on the optical base according to the first embodiment of the present invention. FIG. 5 is a perspective view showing an operation of an optical head using such an integrated unit. FIG. 5 is a cross-sectional view showing a schematic configuration of an integrated unit used in an optical head according to a second embodiment of the invention. Sectional drawing which showed schematic structure of the integrated unit used for the optical head concerning the 3rd Embodiment of this invention. FIG. 7: Schematic structure of the integrated unit used for the optical head concerning the 4th Embodiment of this invention. Sectional view shown [Fig. 8] Conventional light source and light FIG. 9 is a perspective view showing a state in which a conventional integrated unit and a high-frequency superposition circuit board are mounted on a flexible substrate. FIG. 11 is an exploded perspective view showing a state in which a flexible substrate is bent and mounted on an optical base. FIG. 11 is a perspective view showing an operation of an optical head using a conventional integrated unit.
DESCRIPTION OF SYMBOLS 1 ... Integrated unit 1a ... Package 1b ... Semiconductor laser 1c ... Photodetection board 1d ... High frequency superposition circuit board 1e ... Terminal 1f ... Bonding wire 1g ... Land part 1h ... Substrate 1i ... Photodetection / high frequency superposition circuit board 2 ... Hologram 2a ... Diffraction area 3 ... Objective lens 4 ... Recording medium 5a, 5b, 5c ... Light beam 6 ... Flexible substrate 6a ... Integrated unit mounting surface 6b ... Land part 6c, 6e ... Bridge part 6d ... Signal extraction part 6f ... High frequency superposition circuit mounting Surface 7 ... Holder 8 ... Shield case 9 ... Optical base 10 ... Rising mirror 11 ... Main shaft 12 ... Subshaft 13 ... Beam splitter 14 ... Photodetector

Claims (4)

A light source;
High frequency superimposing means for superimposing a high frequency current on the light source;
Condensing means for focusing the light beam emitted from the light source on a recording medium;
Diffracting means for diffracting light that is reflected from the recording medium and incident through the light collecting means into a plurality of light fluxes;
A light detection means on which the light beam diffracted by the diffraction means enters;
A light detection substrate on which light detection means is formed,
The light source is disposed on the light detection substrate so as to be sandwiched between positions where the plurality of light beams enter the light detection means,
The light detection substrate is disposed on the high-frequency superimposing means;
An optical head in which a focus error signal, a tracking error signal, and an information signal of the recording medium are calculated from light received by the light detection means.     The optical head according to claim 1, wherein the high-frequency superimposing unit, the light detection substrate, and the light source are sealed in the same package. The optical head according to claim 2 , wherein a hologram having the diffraction means formed on a surface thereof is fixed to the package.   The optical head according to claim 1, wherein the high-frequency superimposing means is formed of a semiconductor substrate.

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