JP3484717B2 - Optical head and optical information recording / reproducing device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an optical head of an optical recording / reproducing apparatus.

[0002]

2. Description of the Related Art In a conventional optical head, as shown in FIG. 20, only the laser noise reducing means 5 is covered by a shield plate 7 alone, and a laser diode 12 is attached to the shield plate 7 in close contact with the shield plate 7.

[0003]

A structure in which a laser unit 12, a diffracting means 11 and an objective lens 10 are integrated as shown in FIG. 2 has been proposed. In such a conventional technique, when the above-mentioned structure is used, there arises a problem that the weight of the movable portion which is the focus position control mechanism increases. In order to avoid this, the laser unit 12 and the laser noise reduction means 5 are separated, and the laser unit 1 is separated by a conductor.
When 2 and the laser noise reduction means 5 are connected, there is a problem that high frequency noise leaks from the conductor.

[0004]

An optical head according to the present invention comprises a lens holder having a laser diode and an objective lens and a driving current for the laser diode superposed with a high frequency to reduce the coherence of the laser light. Laser noise reducing means, which is separate from the laser diode, that reduces laser noise, a driving coil attached to the lens holder, a support member that elastically supports the lens holder, and the periphery of the lens holder. A focus position control unit having a magnet for generating a magnetic field, and a conductive shield plate that covers the whole including the lens holder, the laser noise reduction unit, and the focus position control unit. To do.

Further, the optical information recording / reproducing apparatus of the present invention is characterized by using this optical head.

[0006]

Embodiment 1 Embodiment 1 of the present invention will be described below with reference to the drawings.
In the drawings, the same numbers are used for the same contents. The operation of the optical head of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory view showing the structure of an optical head in one embodiment of the present invention. The optical head includes a lens holder 1 having a laser unit, a diffracting means, an objective lens and a driving coil, a magnet 2 for generating a magnetic field around the lens holder 1, and a support spring 3 for elastically supporting the lens holder 1. A column 4, which is a fixed end of the support spring 3,
Laser noise reduction means 5 for superposing a high frequency on the laser diode drive current, feedthrough capacitor 6, line 33 connecting the laser noise reduction means 5 and the laser unit, line connecting the laser noise reduction means 5 and the feedthrough capacitor 6. 34, the shield case 7, and the emission hole 45.

FIG. 2 is an explanatory view showing details of the lens holder 1 in FIG. The lens holder 1 includes a focusing coil 8, a tracking coil 9, an objective lens 10, a diffractive means 11, and a laser unit 12.

FIG. 3 is an explanatory view showing details of the laser unit 12 in FIG. The laser unit 12 includes a laser chip 16 and the laser chip 16
18 for preventing overheating of the laser, a signal detecting photodiode 14 for reproducing recorded information and a position error signal from reflected light from a recording medium, and laser output detection for detecting the amount of light emitted from the laser chip 16. It comprises a wafer 19, a conducting wire 20, a bonding wire 21, a stem 22, a cap 23, and an emission window 24, which are formed on the same substrate by integrating the photo diode 15 and the preamplifier 13. The operation of the optical head of this embodiment will be described below with reference to FIGS. 1, 2 and 3.

Inside the lens holder 1, the laser light emitted from the laser chip 16 passes through the diffracting means 11 and then is focused on the recording medium by the objective lens 10. On the other hand, the reflected light from the recording medium enters from the objective lens and is condensed by the diffracting means 11 on the signal detecting photodiode 14 inside the laser unit 12 with astigmatism. In the signal detecting photodiode 14, light energy is converted into a current and input to the preamplifier 13. The preamplifier 13 converts the current into a voltage, amplifies the signal to a level sufficient for transmission, lowers the output impedance of the signal, and prevents noise from mixing in and the band from decreasing. Further, the preamplifier 13 may be provided with a function of processing the signal and generating the recording information and the position error signal. Further, in this embodiment, the preamplifier 13 is built in the laser unit 12, but it may be placed outside the laser unit 12. In that case, on the wafer 19,
Only the signal detecting photodiode 14 and the laser output detecting photodiode 15 are formed, and the preamplifier 13 is arranged on the substrate 39 of FIG. 1 together with the laser noise reducing means 5.

On the other hand, a part of the laser light emitted from the laser chip 16 also enters the laser output detecting photodiode 15. Since the output of the laser output detecting photodiode 15 is proportional to the light amount of the laser chip 16, the laser output detecting photodiode 15 can detect the output light output of the laser chip 16.

Further, a focusing coil 8 for moving the lens holder 1 in the focus direction and a tracking coil 9 for moving the lens holder 1 in the track direction are attached to the side surface of the lens holder 1. The lens holder 1 is placed in a magnetic field, and the focusing coil 8 and the tracking coil 9 are placed.
By supplying a drive current from the focus position control means and the track position control means to the lens holder 1,
, The focus position control and track position control of the detection spot for detecting information from the recording medium can be performed. If a large position control in the track direction is required, the detection spot is moved by another track position control means that moves the entire optical head.
With the above mechanism, the optical head has a function of forming a spot of laser light on the recording medium and scanning the spot on the recording medium.

The laser noise reduction means 5 comprises a high frequency oscillator and a buffer amplifier, and its output is connected to the hot side of the laser chip. Due to the operation of the laser noise reduction means 5, the magnitude of the current flowing through the laser unit 12 fluctuates in a short cycle, and the wavelength of the laser light also fluctuates accordingly. This reduces the coherence of the laser light and reduces the laser noise due to the returning light. A high frequency current flows through the inside of the laser noise reduction means 5 and each line connected to the laser noise reduction means 5, and a part of the high frequency current is radiated into the air. Since the radiated high frequency adversely affects external circuits and peripheral devices as noise, it is necessary to prevent the high frequency from leaking by the shield case 7. The shield case 7 is connected to the ground of the optical head or the ground line side of the laser unit 12. The radiated high frequency generates a current on the surface of the shield case 7, is converted into heat energy there, is absorbed by the ground of the device, and is finally consumed as heat energy.

Further, the shield case 7 mechanically separates the lens holder 1 and the recording medium. When the shield case 7 is not attached, when the displacement amount of the lens holder 1 in the focus direction becomes extremely large, the lens holder 1 comes into contact with the rotating recording medium, and the lens holder 1 and the recording are performed. There is a risk of damaging both of the media. However, the shield case 7
If there is, the movable range of the lens holder 1 is limited,
Since the lens holder 1 acts as a stopper when the lens holder 1 approaches the recording medium, the above situation can be avoided. The shield case 7 only needs to be made of a conductive material, and may be made of metal, or may be made of resin and subjected to a conductive treatment.

FIG. 4 is a block diagram showing the circuit configuration of the optical head of FIG. In FIG. 4, the optical head is
It comprises a laser unit 12, a laser noise reduction means 5 and a feedthrough capacitor 6. In addition, the laser unit 1
Reference numeral 2 includes a signal detecting means 14, a laser output detecting means 15, a preamplifier 13 and a laser chip 16.
The signal detecting means 14 and the laser output detecting means 15
The output of is amplified by the preamplifier 13 and output. The laser noise reduction means 5 superimposes a high frequency on the laser diode drive current 17 to reduce laser noise. (Embodiment 2) FIG. 5 is an explanatory view showing the structure of an optical head according to another embodiment of the present invention. In the embodiment of FIG. 1, the feedthrough capacitor 6 is used in order to prevent the radiation noise from the laser noise reduction means 5 from leaking from each signal line to the outside, but as shown in FIG. At the same time as using the low-pass filter 26 by the LC network, the flexible cable 25 may lead out each signal line from the optical head. According to this configuration, since it is not necessary to use an expensive and large through-type capacitor, the optical head can be easily assembled, and cost reduction and space saving effects can be expected. FIG. 6 is an explanatory diagram showing an example of an equivalent circuit of the low pass filter 26 in FIG. The low pass filter 26 includes a coil 28 and a capacitor 3
It consists of zero. Connect the ground terminal 31 to the circuit ground,
When a signal is applied to the input terminal 27, it functions as a filter that passes only a signal having a frequency lower than the cutoff frequency determined by the values of the coil 28 and the capacitor 30. By setting the cutoff frequency sufficiently higher than the band of the signal passing through each signal line and sufficiently lower than the oscillation frequency of the laser noise reduction means 5 in FIG. 5, it is possible to prevent radiation noise from leaking from each signal line. You can (Embodiment 3) FIG. 7 is an explanatory diagram showing the structure of an optical head according to another embodiment of the present invention. By sealing the emission hole 45 in FIG. 1 with the transparent cover 43, the shield case 7 can be substantially sealed and a high dustproof function can be provided. Further, a conductive film may be formed on the surface of the transparent cover 43, in which case a higher electromagnetic shield effect can be obtained. That is, the shield case 7 is spatially
Although it is completely sealed electromagnetically, the laser beam can be freely entered and emitted through the transparent cover 43 as in the embodiment of FIG. 1, and the function as an optical head is as shown in FIG. Same as the example. With this configuration, it is possible to realize an optical head that is resistant to dust and has little radiation noise.

Since other functions are the same as those of the embodiment shown in FIG. 1, detailed description thereof will be omitted. (Embodiment 4) FIG. 8 is an explanatory view showing the structure of an optical head according to another embodiment of the present invention. In the embodiment shown in FIG. 1, as shown in FIG. 3, the laser unit 12 has the preamplifier 13 built therein. However, as shown in FIG.
3 may not be built in the laser unit 12, but may be formed on another substrate and placed outside. In this case, one substrate 3
9, the laser noise reduction means 5 and the preamplifier 13
Both of them may be configured, or the preamplifier 13 may be separated as a separate substrate together with the laser noise reduction means 5 as shown in FIG. In the case of using a separate substrate, the preamplifier 13 can be kept away from the laser noise reduction means 5 that emits a large amount of noise, and a low noise signal output is possible.

In any case, the preamplifier 13 is shielded from the external electromagnetic field by the shield case 7. This makes it possible to construct an optical head that is resistant to external noise.

Since other functions are the same as those of the embodiment shown in FIG. 1, detailed description thereof will be omitted. (Fifth Embodiment) FIG. 9 is an explanatory view showing the structure of an optical head according to another embodiment of the present invention. If the preamplifier 13 is separated from the laser noise reduction means 5 as a separate substrate as in the embodiment of FIG. 8, the preamplifier 13 should be kept away from the laser noise reduction means 5 that generates a large amount of noise. It is possible to output a signal with low noise. In order to further enhance this effect, as shown in FIG. 9, a conductive shield plate 47 may be provided between the substrates of both the laser noise reduction means 5 and the preamplifier 13. The shielding plate 47 may be a metal plate, or may be a resin partition wall integrally molded with other components inside the optical head and subjected to a conductive treatment. The shielding plate 47 reduces interference between the laser noise reduction means 5 and the preamplifier 13, and prevents high frequency noise generated from the laser noise reduction means 5 from being mixed into the preamplifier 13. It enables low noise signal detection.
Further, it is possible to prevent the high frequency from radiating from the output line of the preamplifier 13 due to the mixing.

Since other functions are the same as those of the embodiment shown in FIG. 1, detailed description thereof will be omitted. (Sixth Embodiment) FIG. 10 is an explanatory diagram showing the structure of an optical head according to another embodiment of the present invention. In the embodiment shown in FIG. 9, the conductive shield plate 47 is provided between the substrates of both the laser noise reduction means 5 and the preamplifier 13. However, as shown in FIG. You may substitute the support | pillar 4. Here, the pillar 4 may be made of metal, or may be made of resin and subjected to a conductive treatment. By arranging the preamplifier 13 on the surface of the support column 4, the support column 4 acts as a shield plate, and the interference between the laser noise reduction means 5 and the preamplifier 13 can be reduced. Further, since the lens holder 1 and the preamplifier 13 can be connected to each other over a short distance, it is possible to detect a signal with a lower noise.

Since the other functions are the same as those of the embodiment shown in FIG. 1, detailed description thereof will be omitted. (Embodiment 7) FIG. 11 is an explanatory diagram showing the structure of an optical head according to another embodiment of the present invention. In the embodiment shown in FIG. 8, a thin conductor is used for the wiring inside the shield case 7, but a flexible cable may be used as shown in FIG. In this case, a substrate area is provided on the flexible cable,
The laser noise reduction means 5 and / or the preamplifier 13 or both may be integrated with the flexible cable. In the embodiment of FIG. 11, only the laser noise reduction means 5 is constructed on the flexible cable. With this configuration, the wiring process is greatly simplified, so that cost reduction and productivity improvement can be expected. In addition, the space for connection and the thickness of the substrate are reduced, which is effective for downsizing the optical head.

On the other hand, in the structure shown in FIG. 11, the line 33 connecting the laser noise reducing means and the laser unit and the line 35 connecting the preamplifier and the signal detecting means are spatially separated by the lens holder 1 and the magnet 2. Has become. Due to the effect of these metal partition walls, from the line 33 connecting the laser unit and the laser unit, which is the output line of the high level high frequency signal,
The line 35 connecting the preamplifier, which is a minute information signal input line, and the signal detecting means is provided without a special shield plate.
It can be electromagnetically separated.

FIG. 12 shows the lens holder 1 in FIG.
It is an explanatory view showing the details of. The lens holder 1 includes a focusing coil 8, a tracking coil 9, an objective lens 10, a diffractive means 11, and a laser unit 12. The lens holder 1 shown in the present embodiment is thinner than the lens holder 1 of FIG. 2 in the laser beam emitting direction, and the space saving effect by using the flexible cable in the configuration of FIG. 11 is further enhanced. You can make the most of it. The operation of the lens holder 1 shown in FIG. 12 is the same as that shown in FIG.

FIG. 13 is an explanatory view showing the details of the laser unit 12 in FIG. The laser unit 12 includes a laser chip 16, a signal detecting photodiode 14, and a laser output detecting photodiode 15 which are integrated on a single substrate, and a wafer 19 and a reflecting surface 4.
0, terminal 20. Laser light emitted from the laser chip 16 in a direction parallel to the surface of the wafer 19 is changed in traveling direction by 90 ° at the reflecting surface 40 and is emitted in the normal direction of the wafer 19. Although not shown in the drawing, the preamplifier 13 of FIG. 11 may be integrally formed on the wafer 19. Other operations are the same as those in FIG. 3, and thus detailed description will be omitted. (Embodiment 8) FIG. 14 is an explanatory diagram showing the structure of an optical head according to another embodiment of the present invention. In the embodiment of FIG. 11, only the laser noise reduction means 5 is constructed on the flexible cable, but in the embodiment of FIG. 14, both the laser noise reduction means 5 and the preamplifier 13 are connected to the flexible cable. Make up above. As a result, this configuration has the effects of further reducing costs and improving productivity, as compared with the configuration of FIG. (Embodiment 9) FIG. 15 is an explanatory diagram showing the structure of an optical head according to another embodiment of the present invention. In this embodiment, both the laser noise reduction means 5 and the preamplifier 13 are formed on a flexible cable and, at the same time, are arranged on the side surfaces of different magnets 2 which are opposed to each other. As a result, the laser noise reduction means 5 that generates a high-level high-frequency signal and the preamplifier 13 that handles a minute signal are electromagnetically isolated by the lens holder 1 and the magnet 2 to reduce interference between them. can do. Further, since the empty space around the magnet 2 is used, the structure is advantageous for downsizing the optical head. (Embodiment 10) FIG. 16 is an explanatory diagram showing the structure of an optical head according to another embodiment of the present invention. In this embodiment, both the laser noise reduction means 5 and the preamplifier 13 are constructed on a flexible cable as in the embodiment of FIG. 15, but the preamplifier 13 is shielded by the shield case 7. In the
It is located near the lens holder 1 on the side surface without the column 4. With this configuration, the lens holder 1 and the preamplifier 13 can be connected to each other at a short distance.
It is possible to detect signals with even lower noise.

The other functions are the same as in FIG. 1, so detailed description will be omitted. (Embodiment 11) FIG. 17 is an explanatory diagram showing the structure of an optical head according to another embodiment of the present invention. In the present embodiment, both the laser noise reduction means 5 and the preamplifier 13 are formed on a flexible cable, and further located on the bottom surface of the shield case 7 near the lens holder 1. With this configuration, the lens holder 1 and the preamplifier 13 can be connected to each other in a short distance, and an empty space around the lens holder 1 is used, which is advantageous in reducing noise and downsizing the optical head. It becomes a structure.

The other functions are the same as those in FIG. 1, so detailed description will be omitted. (Embodiment 12) FIG. 18 is an explanatory view showing the structure of an optical head according to another embodiment of the present invention. In this embodiment, both the laser noise reduction means 5 and the preamplifier 13 are constructed on a flexible cable, and the preamplifier 13 is located on the surface of the shield case 7 in the laser light emitting direction. According to this configuration, the preamplifier 13 can be mounted even when many mechanical parts are present on the bottom surface of the optical head, and when the preamplifier 13 has an adjustment point, laser light emission of the optical head is performed. Adjustment from the side surface becomes easy.

The other functions are the same as those in FIG. 1, so detailed description will be omitted. (Embodiment 13) FIG. 19 is an explanatory diagram showing the structure of an optical head according to another embodiment of the present invention. As shown in the figure, the laser noise reduction means 5 and / or the preamplifier 13 or both may be constructed on a flexible cable and at the same time integrated with the bottom of the lens holder 1. In this configuration, the laser noise reduction means 5 and the preamplifier 13 can be connected to the lens holder 1 at the shortest distance. Therefore, it is possible to detect a signal with lower noise, and the output line of the laser noise reduction means 5 for transmitting a high-level high-frequency signal can be shortened, so that high-frequency noise radiated from the output line can be reduced. On the other hand, similarly to the embodiment of FIG. 15, since the empty space at the bottom of the lens holder 1 is used, the structure is advantageous for downsizing the optical head.

[0027]

As described above, according to the present invention, the laser diode is mounted on the lens holder, the focus position control means controls the focus position of the lens holder, and at the same time the laser noise reducing means is separated from the laser diode. In the optical head to be arranged as a whole, the lens holder, the laser noise reduction means, and the focus position control means are entirely covered with a shield case, so that the high frequency radiated from the laser noise reduction means and each connection line is generated by the optical head. It can be prevented from leaking to the outside.

Therefore, since the optical information recording / reproducing apparatus using this optical head does not generate a high frequency, the level of electromagnetic radiation noise can be suppressed sufficiently low.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the structure of an embodiment of an optical head of the present invention.

FIG. 2 is an explanatory diagram showing details of the structure of the optical head of FIG.

FIG. 3 is an explanatory diagram showing details of the structure of the optical head of FIG.

FIG. 4 is a block diagram showing an example of a circuit configuration of the optical head of FIG.

FIG. 5 is an explanatory view showing the structure of another embodiment of the optical head of the present invention.

6 is an explanatory diagram showing details of the structure of the optical head of FIG.

FIG. 7 is an explanatory view showing the structure of another embodiment of the optical head of the present invention.

FIG. 8 is an explanatory view showing the structure of another embodiment of the optical head of the present invention.

FIG. 9 is an explanatory view showing the structure of another embodiment of the optical head of the present invention.

FIG. 10 is an explanatory view showing the structure of another embodiment of the optical head of the present invention.

FIG. 11 is an explanatory view showing the structure of another embodiment of the optical head of the present invention.

12 is an explanatory view showing details of the structure of the optical head of FIG.

13 is an explanatory diagram showing details of the structure of the optical head of FIG.

FIG. 14 is an explanatory view showing the structure of another embodiment of the optical head of the present invention.

FIG. 15 is an explanatory view showing the structure of another embodiment of the optical head of the present invention.

FIG. 16 is an explanatory view showing the structure of another embodiment of the optical head of the present invention.

FIG. 17 is an explanatory view showing the structure of another embodiment of the optical head of the present invention.

FIG. 18 is an explanatory view showing the structure of another embodiment of the optical head of the present invention.

FIG. 19 is an explanatory view showing the structure of another embodiment of the optical head of the present invention.

FIG. 20 is an explanatory diagram showing an example of a structure of a conventional optical head.

[Explanation of symbols]

1 lens holder 2 magnets 3 Support spring 4 props 5 Laser noise reduction means 6 feedthrough capacitors 7 Shield case 8 Focusing coil 9 Tracking coil 10 Objective lens 11 Diffraction means 12 Laser unit 13 Preamplifier 14 Signal detection means 15 Laser output detection means 16 laser chips 17 Laser diode drive current 18 radiator 19 wafers 20 conductors 21 Bonding wire 22 Stem 23 Cap 24 exit window 25 flexible cable 26 Low pass filter 27 input terminals 28 coils 29 output terminals 30 capacitors 31 Ground terminal 32 prism 33 Line connecting laser noise reduction means and laser unit 34 Line connecting laser noise reduction means and feedthrough capacitor 35 Line connecting preamplifier and signal detection means 36 Line connecting preamplifier and external circuit 37 slits 38 Reflector 39 substrate 40 reflective surface 41 Collimating lens 43 transparent cover 45 exit hole 47 Shield

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-4445 (JP, A) JP-A-63-62934 (JP, A) JP-A-62-9545 (JP, A) Sankaihei 2- 26128 (JP, U) Actual development Sho 63-62929 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) G11B ^7/ 09-7/22 G11B 33/14

Claims (2)

(57) [Claims] 1. A lens holder having a laser diode and an objective lens; separate from the laser diode for reducing laser noise by superimposing a high frequency on a drive current of the laser diode to reduce coherence of laser light. A focus of the body, which includes a laser noise reducing unit, a driving coil attached to the lens holder, a support member that elastically supports the lens holder, and a magnet that generates a magnetic field around the lens holder. An optical head comprising: a position control unit; and a conductive shield plate that covers the entire lens holder, the laser noise reduction unit, and the focus position control unit. 2. An optical information recording / reproducing apparatus comprising the optical head according to claim 1.