Patent Application
20070274366
Other and further objects, features, and advantages of the invention will be more explicit from the following detailed description taken with reference to the drawings wherein:
Hereinafter, referring to the drawings, preferred embodiments of the invention will be described in detail.
Hereinafter, a plurality of embodiments of the invention will be described with reference to the accompanying drawings. In the following description, structures identical to those that are previously described in the preceding embodiments may be denoted by identical reference numbers and the overlapped description may not be repeated. When only a portion of a component is described, the other portions of the component are identical to those of the embodiments that have been previously described. It is possible to combine portions that are specifically described in each embodiment. In addition, it is possible to partially combine embodiments, as long as the combination causes no problem.
The optical pickup apparatus main body 31 is configured to include the LD 10, a laser diode driving circuit (hereinafter occasionally abbreviated as an LD driving circuit) 10A, a half wavelength plate (hereinafter occasionally referred to as a λ/2 plate) 11, a polarizing beam splitter 12, a collimating lens 22 as a spherical aberration correcting section, a quarter wavelength plate (hereinafter occasionally referred to as a λ/4 plate) 23, an objective lens 24, an APC light-receiving element 13, and a photodetector 27. In the embodiment, the LD 10 and the LD driving circuit 10A constitute a laser light source. In the first optical pickup apparatus 30 according to the embodiment, laser light is emitted, when the LD driving circuit 10A applies a LD driving current to the LD 10. The laser light emitted from the LD 10 is converted from P-polarized light to S-polarized light by the λ/2 plate 11, and then the polarized laser beam is transmitted through the polarizing beam splitter 12. The laser light that has been transmitted through the polarizing beam splitter 12 is transmitted through the collimating lens 22. At this time, to correct spherical aberration caused by a deference in a thickness of a light transmission layer of an optical recording medium 25 and change in temperature, as shown in
In the first embodiment of the invention, as shown in
When the output of the laser light emitted from the LD 10 is fixed, an increase in the divergence value of the light flux 26 that has been transmitted through the collimating lens 22 in accordance with movement of the collimating lens 22, as shown in
In the APC circuit 32, a mathematical calculation is conducted based on the output signal from the APC light-receiving element 13 to control a current supplied from the LD driving circuit 10A to the LD 10, so as to keep the objective output power fixed in response to a change in the divergence value.
Meanwhile, the laser light which enters the objective lens 24 within the effective diameter D1 is transmitted through the λ/4 plate 23, converted to circularly polarized light, and then the circularly polarized light enters the objective lens 24. The laser light is condensed on a recording surface of the optical recording medium 25 by the objective lens 24. The laser light reflected on the recording surface is once again transmitted through the objective lens 24, the λ/4 plate 23, and the collimating lens 22, and then reflected by a polarizing beam splitter 12. The reflected light enters the photodetector 27 and a signal according to the incident light is outputted from the photodetector 27. A focusing error signal, a tracking error signal, and a RF signal are obtained from the signal. These signals are outputted to the processing circuit 101.
It is possible to determine a relationship between the objective output power and the output signal, which is used for a mathematical calculating method that is conducted based on the output signal from the APC light-receiving element 13 at the APC circuit 32 as described below. First, the output signal from the APC light-receiving element 13 is taken as Z, when the output of the laser light emitted from the LD 10 is fixed. The objective output power at this time is taken as Y. The objective output power Y can be substantially expressed as a linear function of the output signal Z as follows:
Y=αZ+β (1)
where α and β are constant numbers.
The objective output powers Y1 and Y2 corresponding to the output signals Z1 and Z2 respectively, are achieved by changing the divergence value based on the equation (1) representing that the output signal Z times the constant number α plus the constant number β equals to the objective output power Y. Then, α and β are achieved by solving the following system of linear equations (2) and (3) for α and β.
Y1=αZ1 +β (2)
Y2=αZ2 +β (3)
Accordingly, a relational expression using the objective output power Y and the output signal Z can be obtained.
In the optical pickup apparatus 30, the objective output power emitted through the objective lens can be estimated based on the output signal Z sent from the APC light-receiving element 13 to the APC circuit 32, using the constant numbers α and β obtained according to the above-described method. Therefore, the LD driving current can be determined as needed so as to keep the objective output power fixed. The LD driving circuit 10A applies the LD driving current to the LD 10 to conduct an APC operation.
The optical pickup apparatus main body 31A includes the LD 10, the LD driving circuit 10A, the λ/2 plate 11, the polarizing beam splitter 12, the collimating lens 22 as the spherical aberration correcting section, the λ/4 plate 23, the objective lens 24, a first APC light-receiving element 41 as a light-receiving element, a second APC light-receiving element 40 as another light-receiving element, and the photodetector 27. In the embodiment, the LD10 and the LD driving circuit 10A constitute a laser light source. In the optical pickup apparatus 30A according to the embodiment, laser light is emitted, when the LD driving circuit 10A applies the LD driving current to the LD 10. The laser light emitted from the LD 10 is converted from the P-polarized light to the S-polarized light by the λ/2 plate 11, and then most of the polarized laser beam is transmitted through the polarizing beam splitter 12. The laser light that has been transmitted through the polarizing beam splitter 12 is transmitted through the collimating lens 22. At this time, to correct the spherical aberration caused by the difference in the thickness of the light transmission layer of the optical recording medium 25 and the change in temperature, as shown in
In the second embodiment of the invention, as shown in
The light flux that has been transmitted through the λ/2 plate 11 and then has entered the polarizing beam splitter 12 is partially reflected and enters the second APC light-receiving element 40. The second APC light-receiving element 40 is arranged so as to be entered by the laser light at a position closer to the laser light source than the collimating lens 22 along the optical path. The output signal in accordance with the amount of light received is sent from the second APC light-receiving element 40 to the APC circuit 32A. Therefore, a signal, which is not dependent on the movement and the divergence value of the collimating lens 22, but dependent on the output of the laser light emitted from the laser light source, is sent from the second APC light-receiving element 40 to the APC circuit 32A, to be used for the calculation conducted at the correcting circuit 33 in the APC circuit 32A.
The amount of light of the laser light received at the second APC light-receiving element 40 is not dependent on the divergence value, the objective output power, and the coupling efficiency. Therefore, when the output of the laser light emitted from the LD 10 is fixed, as shown in
When the output of the laser light emitted from the LD 10 is fixed, a change in the divergence value of the light flux 26 that has been transmitted through the collimating lens 22 in accordance with the movement of the collimating lens 22, as shown in
The APC circuit 32A includes the correcting circuit 33 for conducting the mathematical calculation based on the output signal from the first APC light-receiving. element 41 and the APC second light-receiving element 40. The APC circuit 32A controls a current supplied from the LD driving circuit 10A to the LD 10 so as to keep the objective output power fixed in response to a change in the divergence value, based on a corrected output signal X sent from the correcting circuit 33.
Meanwhile, the laser light which enters the objective lens 24 within the effective diameter D1 is transmitted through the λ/4 plate 23, and is converted to the circularly polarized light, and then the circularly polarized laser beam enters the objective lens 24 and condensed on the recording surface of the optical recording medium 25 by the objective lens 24. The resultant laser beam reflected by the recording surface of the optical recording medium 25 is once again transmitted through the objective lens 24, the λ/4 plate 23, and the collimating lens 22, and reflected by the polarizing beam splitter 12. The reflected light enters the photodetector 27 and a signal according to the incident light is outputted from the photodetector 27. The focusing error signal, the tracking error signal, and the RF signal are obtained from the signal. These signals are outputted to the processing-circuit 101.
It is possible to determine the relationship between the objective output power and the corrected output signal used for the mathematical calculating method that is conducted at the APC circuit 32A based on the output signal from the second APC light-receiving element 40 and the first APC light-receiving element 41, as described below. First, when the output of the laser light emitted from the LD 10 is fixed, a value calculated and outputted by the correcting circuit 33 using the output signals from the second APC light-receiving element 40 and the first APC light-receiving element 41, is defined as the corrected output signal X. In the second embodiment, the value X is expressed as:
X=(Output Signal from Second APC Light-receiving Element 40)−(Output Signal from First APC Light-receiving Element 41)
Y=αX+β (4)
where α and β are constant numbers.
The objective output powers Y1 and Y2 corresponding to the output signals X1 and X2 respectively, are achieved by changing the divergence value based on the equation (4) representing that the corrected output signal X times the constant number α plus the constant number β equals to the objective output power Y. Then, α and β are achieved by solving the following system of linear equations (5) and (6) for α and β.
Y1=αX1+β (5)
Y2=αX2+β (6)
Accordingly, the corrected output signal X—the objective output power Y relational expression can be obtained.
In the optical pickup apparatus, the objective output power emitted through the objective lens can be estimated by using the constant numbers α and β obtained according to the above-described method. This calculation is conducted in the APC circuit including the correcting circuit 33. Accordingly, the LD driving current can be determined as needed so as to keep the objective output power fixed. The LD driving circuit 10A applies the LD driving current to the LD 10 to conduct the APC operation.
The optical pickup apparatus main body 31B is configured to include the LD 10, the LD driving circuit 10A, the λ/2 plate 11, the polarizing beam splitter 12, the collimating lens 22 as the spherical aberration correcting section, the first APC light-receiving element 41 as a light-receiving element, the second APC light-receiving element 40 as another light-receiving element, the beam attenuating section for attenuating the laser light emitted from the LD 10, and the photodetector 27. In the embodiment, the LD 10 and the LD driving circuit 10A constitute a laser light source. In the optical pickup apparatus 30B according to the embodiment, laser light is emitted, when the laser diode (LD) driving circuit 10A applies the LD driving current to the LD 10. The laser light emitted from the LD 10 is converted from the P-polarized light to the S-polarized light by the λ/2 plate 11, and then most of the polarized laser beam is transmitted through the polarizing beam splitter 12. The laser light that has been transmitted through the polarizing beam splitter 12 is transmitted through a beam attenuating plate 16 of an attenuator unit 15 or a light-transmitting glass plate 17. The beam attenuating plate 16 is a beam attenuating section arranged on an optical path of laser light emitted from a laser light source, for attenuating the laser light, in the third embodiment. The beam attenuating plate 16 and the light-transmitting glass plate 17 are mounted on a sliding portion 18. The sliding portion 18 is adapted to be operated by a motor or the like. That is, the sliding portion and the motor are devices for driving the beam attenuating section. The attenuator unit 15 includes the beam attenuating plate 16, the light-transmitting glass plate 17, the sliding portion 18, and the device for driving these components such as a motor.
When it is necessary to use output light emitted from the objective lens weaker than that used for CDs or DVDs to support blue-ray disks or the like, the sliding portion 18 is operated so as to place the beam attenuating plate 16 on the optical path of the laser light. When the laser light has no need to be attenuated, the sliding portion 18 is operated so as to place the light-transmitting glass plate 17 on the optical path of the laser light. The laser light that has been transmitted through the attenuator unit 15 is transmitted through the collimating lens 22 as the spherical aberration correcting section, and the laser light which enters the objective lens 24 within the effective diameter D1 is transmitted through the λ/4 plate 23, and is converted to the circularly polarized light, and then the circularly polarized laser light enters the objective lens 24 and condensed on the recording surface of the optical recording medium 25 by the objective lens 24. The resultant laser beam reflected on the recording surface is once again transmitted through the objective lens 24, the λ/4 plate 23, the collimating lens 22, and the attenuator unit 15, and reflected by the polarizing beam splitter 12. The reflected light enters the photodetector 27 and a signal according to the incident light is outputted from the photodetector 27. The focusing error signal, the tracking error signal, and the RF signal are obtained from the signal. These signals are outputted to the processing circuit 101.
The collimating lens 22 is moved in the direction of the optical axis, as shown in
The light flux that has been transmitted through the λ/2 plate 11 and then has entered the polarizing beam splitter 12 is partially reflected and enters the second APC light-receiving element 40. The second APC light-receiving element 40 is arranged so as to be entered by the laser light at a position closer to the laser light source than the attenuator unit 15 along the optical path. The output signal from the second APC light-receiving element 40 is sent to the APC circuit 32B, and the determining circuit 34 as described later.
The correction of the spherical aberration caused by the movement of the collimating lens 22, the detection of the divergence value by using the first APC light-receiving element 41, and the detection of the output of the laser light emitted from the laser light source by using the second APC light-receiving element 40 as another light-receiving element in the third embodiment, are identical to those in the second embodiment of the invention.
However, in the third embodiment of the invention as shown in
A mechanism for stabilizing the objective output power, that is, for keeping the objective output power fixed, by using the second APC light-receiving element 40 and the first APC light-receiving element 41 in the third embodiment of the invention, is identical that in the second embodiment of the invention. The objective output power significantly depends on whether the beam attenuating plate 16 is placed on the optical path in the attenuator unit 15 or not. Therefore, it is necessary to securely detect whether the beam attenuating plate 16 is placed on the optical path or not, that is, whether an attenuator mechanism is ON or OFF, in order to control the objective output power. It is essential to detect ON/OFF for the attenuator mechanism, since operation troubles or the like with the motor or the sliding portion 18 can occur. To achieve this, in the third embodiment of the invention, the output signals from the second APC light-receiving element 40 and the first APC light-receiving element 41 are compared with each other at the determining circuit 34 to detect ON/OFF for the attenuator mechanism.
For example, when a rate of the output signal from the second APC light-receiving element 40 to the output signal from the first APC light-receiving element 41 is defined as a calculated result W at the determining circuit 34, it will be described that the calculated result W is obtained using the expression as follows:
W=(First Output Signal from APC Light-receiving Element 41)/(Second Output Signal from APC Light-receiving Element 40)
When the attenuator mechanism was changed from ON to OFF with the output of the laser light emitted from the LD 10 fixed, provided that a transmission rate of the beam attenuating plate 16 to the laser light is 50%, and the transmission rate of the light-transmitting glass plate 17 to the laser light is 100%, the output signal from the first APC light-receiving element 41 is doubled and the calculated result W is thereby doubled.
Here, a comparison between the output signal from the second APC light-receiving element 40 and the output signal from the first APC light-receiving element 41 is taken as the calculated result W obtained by calculating the rate of both signals. However, as long as a change in the calculated result W in association with ON/OFF of the attenuator mechanism is larger than a change in the calculated result W in association with the correction of the spherical aberration, or a change in the calculated result W in association with a change in the output of the laser light, any calculation may be acceptable to compare the output signal from the second APC light-receiving element 40 with the output signal from the first APC light-receiving element 41.
As described above, the comparison between the output signal from the second APC light-receiving element 40 and the output signal from the first APC light-receiving element 41 is conducted at the determining circuit 34 to detect ON/OFF of the attenuator mechanism. The determining circuit 34 determines not based on the output signal from the device for driving the beam attenuating section, but based on a signal from a light-receiving element for receiving the light flux that has been transmitted through the beam attenuating plate on the optical path, as well as a signal from another light-receiving element for receiving the light flux to be transmitted therethrough on the optical path. Therefore, it is possible to directly determine whether the beam attenuating section is placed on the optical path or not.
The calculation conducted by the correcting circuit 33 in the APC circuit 32B, the APC circuit 32B, and the APC operation by these components in the third embodiment are identical to those in the second embodiment of the invention. In the third embodiment of the invention, in particular, the constant numbers α and β are prepared for a case where the attenuator mechanism is ON and a case where the attenuator mechanism is OFF respectively. The constant numbers α and β are then used by switching the constant numbers α and β between both cases, based on a result determined by the determining circuit 34 about whether the attenuating mechanism is ON or OFF. Accordingly, the objective output power can be fixed, regardless of whether the attenuating mechanism is ON or OFF.
As a result, even though the divergence value is changed by correcting the spherical aberration, caused by the difference in the thickness of the light transmission layer of the optical recording medium 25, it is possible to keep the objective output power fixed, thus allowing the optical pickup apparatus to enhance the versatility for the variety of optical recording media and to improve the signal read quality level, compared with the optical pickup apparatus according to the related art.
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and the range of equivalency of the claims are therefore intended to be embraced therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-145988 | May 2006 | JP | national |
