JP3658092B2 - Optical pickup head device, optical information processing device, and optical pickup head device assembly adjustment method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical pickup head device that records optical information on an optical recording medium such as an optical disk or an optical card, and reproduces or erases the recorded optical information, an optical information processing device using the optical pickup head device, and The present invention relates to an assembly adjustment method for an optical pickup head device.
[0002]
[Prior art]
In recent years, with the diversification of optical disk systems that record information on optical recording media, there is a demand for optical pickup head devices that accurately read and write information on optical recording media. FIG. 13 shows a configuration of an example of a conventional optical pickup head device. In FIG. 13, the linearly polarized divergent beam 70 emitted from the semiconductor laser light source 10 is converted into parallel light by the collimator lens 20 and then enters the polarization beam splitter 30. All the beams 70 incident on the polarization beam splitter 30 pass through the polarization beam splitter 30 and then enter the quarter-wave plate 31. The quarter wave plate 31 is converted into a circularly polarized beam. The beam converted into circularly polarized light is condensed on the optical recording medium 40 by the objective lens 21.
[0003]
A track is formed on the optical recording medium 40. The beam 70 reflected and diffracted by the optical recording medium 40 passes through the objective lens 21 again and then reenters the quarter-wave plate 31. The quarter wave plate 3 converts the re-incident reflected light into a linearly polarized beam having a direction different from that of the light emitted from the light source 10 by 90 degrees. The beam 70 transmitted through the quarter-wave plate 31 is totally reflected by the polarization beam splitter 30 and then converted into a convergent beam by the condenser lens 22. The convergent beam 70 converted by the condenser lens 22 passes through the parallel plate 32 and then enters the photodetector 50. As the beam 70 passes through the parallel plate 32, astigmatism is given to detect a focus error signal. The photodetector 50 outputs an electrical signal corresponding to the amount of incident beam. The electrical signal output from the photodetector 50 is input to the signal processing unit 80.
[0004]
The configuration of the signal processing unit 80 is shown in FIG. The photodetector 50 includes four light receiving portions 50A, 50B, 50C, and 50D. Signals output from the light receiving unit 50A and the light receiving unit 50C are added by the adding unit 892, signals output from the light receiving unit 50B and the light receiving unit 50D are added by the adding unit 891, and signals output from the light receiving units 50A and 50D are added. Signals output from the light receiving unit 50B and the light receiving unit 50C by the unit 894 are added by the adding unit 893, respectively. The signals output from the adders 891 and 892 are differentially calculated by the arithmetic unit 871, and the signals output from the adders 893 and 894 are differentially calculated by the arithmetic unit 872. A signal output from the calculation unit 871 is output from the terminal 401, and a signal output from the calculation unit 872 is output from the terminal 402. A signal output from the terminal 401 is a focus error signal, and a signal output from the terminal 402 is a tracking error signal. The detection method of the focus error signal is well known as the astigmatism method, and the detection method of the tracking error signal is well known as the push-pull method. The focus error signal and the tracking error signal are respectively input to the focus control actuator 90 and the tracking control actuator 91 so that the beam 70 emitted from the light source 10 is focused on a desired position on the optical recording medium 40. The position of the objective lens 21 is controlled.
[0005]
In FIG. 13, the X axis is a direction orthogonal to the track on the optical recording medium 40, the Y axis is a direction parallel to the track on the optical recording medium 40, and the Z axis is a direction orthogonal to the optical recording medium 40. FIG. 15 shows the relationship between the relative displacement in the Z-axis direction between the objective lens 21 and the optical recording medium 40 and the focus error signal. S1 represents a state in which the beam 70 focused on the optical recording medium 40 is in focus. The amplitude of the focus error signal is FEp-p, and the range in which the change in the focus error signal exhibits linearity is Zs. Usually, Zs is designed to be 5 to 20 μm.
[0006]
FIG. 16 shows the relationship between the position of the beam 70 in the X-axis direction, the focus error signal, and the tracking error signal when the beam 70 is at the position S1 in the Z direction. The period of the track on the optical recording medium 40 is 0.74 μm. The tracking error signal varies depending on the position of the beam 70 in the X-axis direction, but the focus error signal is insensitive to the position of the beam 70 in the X-axis direction.
[0007]
[Problems to be solved by the invention]
FIG. 16 shows a case where the wavefront aberration of the beam 70 condensed on the optical recording medium 40 is zero. When the wavefront aberration of the beam 70 condensed on the optical recording medium 40 is not zero, FIG. The situation is different. For example, in FIG. 17, the wavelength of the beam 70 emitted from the light source 10 is λ, and the beam 70 condensed on the optical recording medium 40 is 40 mλ rms in the direction of 45 degrees with respect to both the X axis and the Y axis. The figure shows the relationship between the position of the beam 70 in the X-axis direction, the focus error signal, and the tracking error signal when there is astigmatism. Also in this case, the beam 70 is at the position S1 in the Z-axis direction. The tracking error signal changes in the same manner as in FIG. 16, but the focus signal shows a behavior different from that in FIG. That is, the focus error signal also changes according to the position of the beam 70 in the X-axis direction. The change of the focus error signal with respect to the position of the beam 70 in the X-axis direction is defined as groove crossing noise, and the amplitude thereof is FEerr.
[0008]
FIG. 18 shows the relationship between the wavefront aberration WFE of the beam 70 and the groove crossing noise FEerr. Here, the groove crossing noise FEerr is normalized by the amplitude FEp-p of the focus error signal. The groove crossing noise FEerr causes defocusing. The defocus amount DFO is given by DFO = FEerr / FEp-p * Zs, and its unit is μm. When the linear range Zs of the focus error signal is 10 μm, for example, if FEerr / FEp-p is 0.1, defocusing of 1 μm occurs. According to FIG. 18, when FEerr / FEp-p is 0.1, the wavefront aberration WFE of the beam 70 is 8 mλ. This amount is an amount that can be easily generated when the optical element is manufactured and when the optical pickup head device is assembled.
[0009]
In recent years, in order to increase the recording capacity, attempts have been made to shorten the wavelength λ of the light source and raise the numerical aperture NA of the objective lens to about 0.6. However, the depth of focus is λ / (NA)² Therefore, shortening the wavelength of the light source and increasing the numerical aperture of the objective lens both result in a shallow depth of focus. For this reason, there has been a problem that defocusing caused by the groove crossing noise FEerr becomes unacceptable.
[0010]
The present invention has been made to solve the above-described problems of the conventional example, and an optical pickup head device capable of reducing the groove crossing noise FEerr, an optical information processing device using the optical pickup head device, and An object of the present invention is to provide an assembly adjustment method for an optical pickup head device.
[0011]
[Means for Solving the Problems]
  In order to achieve the above object, a first optical pickup head device of the present invention includes a light source, a condensing optical system for converging a beam emitted from the light source as a minute spot on the optical recording medium, and the optical recording medium. A first beam branching element for branching the beam reflected and diffracted by the optical element, an optical element for giving astigmatism to the beam branched by the first beam branching element, and astigmatism by the optical element. A first photodetector that receives the applied beam and outputs a photocurrent corresponding to the amount of light; and an optical path from the optical recording medium to the first photodetector, and is provided by the optical recording medium. A second beam branching element that branches the reflected beam; a second photodetector that receives the beam branched by the second beam branching element and outputs a photocurrent according to the amount of light; and With optical optics A drive unit for controlling focus and tracking to perform relative positioning with the optical recording medium, and a surface including the light receiving unit of the first photodetector and light reception by the first photodetector. Relative positional relationship between the surface of the second photodetector and the focal point of the beam received by the second photodetector. DifferentThus, the first photodetector and the second photodetector are integrated..
[0012]
The said structure WHEREIN: It is preferable that the said 2nd beam branching element is integrated with the said condensing optical system.
In addition, it is preferable that the second beam branch element is disposed in an optical path from the first beam branch element to the first photodetector.
[0013]
  Further, the second optical pickup head device of the present invention includes a light source, a condensing optical system for converging a beam emitted from the light source as a minute spot on the optical recording medium, and a reflection and diffraction by the optical recording medium. A first beam branching element for branching the beam, an optical element for giving astigmatism to the beam branched by the first beam branching element, and a beam given astigmatism by the optical element A first photodetector that receives light and outputs a photocurrent corresponding to the amount of light; and a beam that is provided in an optical path from the optical recording medium to the first photodetector and reflected by the optical recording medium. A second beam detector integrated with the converging optical system to be branched, and a second light detector that receives the beam branched by the second beam splitter and outputs a photocurrent according to the amount of light. And the vessel A third beam branching element formed at the periphery of the beam branching element, and a drive unit for controlling focus and tracking for relative positioning of the condensing optical system and the optical recording medium. Each of the first photodetector and the second photodetector has a light receiving portion divided into four regions, and the surface including the light receiving portion of the first photodetector and the first light detector The relative positional relationship between the focal point of the beam received by the photodetector is relative to the focal plane of the beam received by the second photodetector and the surface including the light receiving portion of the second photodetector. Different from general positional relationshipThe first photodetector has four light receiving portions, and the four light receiving portions of the second photodetector are provided in the periphery thereof..
[0014]
In the above configuration, it is preferable that the third beam branching element is a diffraction element.
Further, it is preferable that the third beam branching element has a lens action.
[0015]
Further, the second beam branching element and the third beam branching element are diffractive elements, and the diffracted light rates of the first-order diffracted light of the second beam branching element and the third beam branching element are equal. preferable.
[0016]
In the first and second optical pickup head devices, when the beam received by the second photodetector has astigmatism, the beam emitted from the light source focuses on the optical recording medium. At this time, it is preferable that the beam received by the second photodetector is received by the second photodetector in a state of being further defocused than the focal line.
[0017]
  The second beam branching element is preferably a diffraction element.
  Furthermore, it is preferable that the second beam branching element has a lens action..
[0018]
Furthermore, it is preferable that the first photodetector and the second photodetector are formed on the same semiconductor substrate.
[0019]
  In the first optical pickup head device, it is preferable that each of the first photodetector and the second photodetector has four light receiving portions..
[0020]
On the other hand, the first optical information processing apparatus of the present invention includes a light source, a condensing optical system for converging the beam emitted from the light source as a minute spot on the optical recording medium, and the diffraction reflected by the optical recording medium. First and second beam branching elements for branching the split beam, an optical element for giving astigmatism to the beam branched by the first beam branching element, and astigmatism being given by the optical element A first photodetector that receives the beam and outputs a photocurrent according to the amount of light; and a second beam that receives the beam branched by the second beam branching element and outputs a photocurrent according to the amount of light. A photodetector, a signal processing unit that generates a focus error signal and a tracking error signal from signals output from the first and second photodetectors, and a focus error signal and a traffic generated by the signal processing unit. A drive unit for controlling focus and tracking to perform relative positioning between the condensing optical system and the optical recording medium using a King error signal, and the signal processing unit includes the first optical detection A first computing unit that computes a signal output from the detector, a second computing unit that computes a signal output from the second photodetector, the first computing unit, and the second computation A third calculation unit that calculates a signal output from the unit, and a focus error signal is generated from the signal output from the third calculation unit.
[0021]
The second optical information processing apparatus of the present invention includes a light source, a condensing optical system for converging the beam emitted from the light source as a minute spot on the optical recording medium, and the diffraction reflected by the optical recording medium. First and second beam branching elements for branching the split beam, an optical element for giving astigmatism to the beam branched by the first beam branching element, and astigmatism being given by the optical element A first photodetector that receives the beam and outputs a photocurrent according to the amount of light; and a second beam that receives the beam branched by the second beam branching element and outputs a photocurrent according to the amount of light. A photodetector, a signal processing unit that generates a focus error signal and a tracking error signal from signals output from the first and second photodetectors, and a focus error signal and a traffic generated by the signal processing unit. A drive unit for controlling focus and tracking to perform relative positioning between the condensing optical system and the optical recording medium using a King error signal, and the signal processing unit includes the first optical detection A first calculation unit that calculates a signal output from the detector, a detection unit that detects a signal output from the second photodetector, and a second that calculates a signal output from the detection unit A calculation unit; a third calculation unit that calculates signals output from the first calculation unit and the second calculation unit; and a focus error signal is generated from a signal output from the third calculation unit. Generated.
[0022]
In the first and second optical information processing apparatuses, it is preferable that the first calculation unit has at least functions of the second calculation unit and the third calculation unit.
[0023]
Also, the assembly adjustment method of the optical pickup head device of the present invention is reflected by the light source, a condensing optical system for converging the beam emitted from the light source as a fine spot on the optical recording medium, and the optical recording medium, First and second beam branching elements that branch the diffracted beam, an optical element that gives astigmatism to the beam branched by the first beam branching element, and astigmatism is given by the optical element A first photodetector that receives the beam and outputs a photocurrent according to the amount of light; and a beam branched by the second beam branch element; and outputs a photocurrent according to the amount of light. Two photodetectors, arithmetic means for generating a focus error signal and a tracking error signal from signals output from the first photodetector and the second photodetector, and the focus error signal And a method for assembling and adjusting an optical pickup head device comprising a drive unit for controlling focusing and tracking for performing relative positioning between the condensing optical system and the optical recording medium using a tracking error signal. , Receiving a signal output from the second photodetector, detecting a change in the signal, and using the output signal as a first evaluation function, the first photodetector or the second photodetector The jitter of the mark train recorded on the optical recording medium is detected from the signal output from the optical recording medium, the output jitter signal is used as the second evaluation function, and the first evaluation function and the second evaluation function are weighted. The relative positional relationship between the condensing optical system of the optical pickup head device and the optical recording medium is adjusted using the result of the pasting.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of an optical pickup head device according to the present invention, an optical information processing device using the optical pickup head device, and an assembly adjustment method for the optical pickup head device will be described in detail with reference to the drawings. In addition, the same number is attached | subjected when the component similar to the conventional optical pick-up head apparatus can be used.
[0025]
(First embodiment)
A first embodiment relating to an optical pickup head device of the present invention and an optical information processing device using the same will be described with reference to FIGS. FIG. 1 is a diagram illustrating a configuration example of an optical pickup head device according to the first embodiment.
[0026]
The linearly polarized divergent beam 70 emitted from the semiconductor laser light source 10 is converted into parallel light by the collimating lens 20. The collimated beam 70 is incident on the polarization beam splitter 30 as the first beam branching element. All the beams 70 incident on the polarization beam splitter 30 pass through the polarization beam splitter 30 and enter the quarter-wave plate 31. When passing through the quarter-wave plate 31, the beam 70 is converted into a circularly polarized beam. The beam 70 converted into circularly polarized light is condensed on the optical recording medium 40 by the objective lens 21 as a condensing optical system.
[0027]
A track is formed on the optical recording medium 40. The beam 70 reflected and diffracted by the optical recording medium 40 passes through the objective lens 21 again and then reenters the quarter-wave plate 31. When the light passes through the quarter-wave plate 31 again, the beam 70 is converted into a linearly polarized beam having a direction different from that of the light emitted from the light source 10 by 90 degrees. The beam 70 transmitted through the quarter wavelength plate 31 is totally reflected by the polarization beam splitter 30 and converted into a convergent beam by the condenser lens 22. The convergent beam 70 converted by the condenser lens 22 is branched into two by an optical element providing astigmatism and a half mirror 33 as a second beam branching element. The beam 70A transmitted through the half mirror 33 is incident on the photodetector 50 as the first photodetector. On the other hand, the beam 70B reflected by the half mirror 33 is incident on the photodetector 51 as the second photodetector.
[0028]
Astigmatism is given to the beam 70A in order to detect a focus error signal when the beam 70A passes through the half mirror 33. On the other hand, since the beam 70B is reflected by the half mirror 33 and does not pass through the half mirror 33, astigmatism is not given to the beam 70B. Accordingly, the relative positional relationship between the surface including the light receiving portion of the photodetector 50 and the focal point of the beam 70 </ b> A received by the photodetector 50 is the same between the surface including the light receiving portion of the photodetector 51 and the photodetector 51. The relative positional relationship with the focal point of the received beam 70B is different. The beams 70A and 70B are received by the photodetectors 50 and 51, respectively, and converted into electrical signals corresponding to the respective light amounts. The electrical signals output from the photodetectors 50 and 51 are input to the signal processing unit 81 shown in FIG.
[0029]
FIG. 2 shows a configuration of the photodetectors 50 and 51 and the signal processing unit 81 in the optical information processing apparatus. The photodetectors 50 and 51 include four light receiving units 50A to 50D and 51A to 51D, respectively. Signals output from the light receiving unit 50A and the light receiving unit 50C of the photodetector 50 are added by an adding unit 892. Similarly, signals output from the light receiving unit 50B and the light receiving unit 50D are added by the adding unit 891. Signals output from the light receiving unit 50A and the light receiving unit 50D are added by the adding unit 894. Signals output from the light receiving unit 50B and the light receiving unit 50C are added by the adding unit 893.
[0030]
The signals output from the adders 891 and 892 are differentially calculated by a calculation unit 871 serving as a first calculation unit. The signals output from the adders 893 and 894 are differentially calculated by the calculator 872. A signal output from the calculation unit 872 is output from the terminal 402 and becomes a tracking error signal.
[0031]
On the other hand, signals output from the light receiving unit 51A and the light receiving unit 51C in the photodetector 51 are added by an adding unit 896. The signals output from the light receiving unit 51B and the light receiving unit 51D are added by the adding unit 895. The signals output from the adding units 895 and 896 are differentially calculated by a calculation unit 873 serving as a second differential calculation unit. The signal output from the calculation unit 873 is input to a calculation unit 874 as a third calculation unit after the signal intensity is adjusted by the variable gain amplification unit 831. The calculation unit 874 receives the signals output from the calculation unit 871 and the variable gain amplification unit 831 and performs a differential calculation. A signal output from the calculation unit 874 is output from the terminal 401 and becomes a focus error signal.
[0032]
The focus error signal and the tracking error signal output from the terminals 401 and 402 are respectively input to an actuator 90 as a focus control drive unit and an actuator 91 as a tracking control drive unit. The actuators 90 and 91 respectively control the position of the objective lens 21 so that the beam 70 emitted from the light source 10 focuses on a desired position on the optical recording medium 40.
[0033]
In the first embodiment, the beam 70B received by the photodetector 51 is reflected by the half mirror 33 and is not given astigmatism. Therefore, even if the relative positions of the optical recording medium 40 and the objective lens 21 in the Z-axis direction shown in FIG. 1 change, only the size of the beam 70B received on the photodetector 51 changes. The similar shape of the cross section is maintained. That is, even if the relative positions of the optical recording medium 40 and the objective lens 21 in the Z-axis direction change, the signal output from the calculation unit 873 does not change, and thus a signal that adversely affects the focus error signal is not output. This is because the optical detector 51 is arranged at a position sufficiently away from the focal point of the beam 70B, so that adjustment of the optical axis direction with the beam 70B of the optical detector 51 when assembling the optical pickup head device is unnecessary. It means that there is. In other words, even if the relationship between the photodetector 51 and the focal position of the beam 70B is slightly shifted, the focus error signal is not affected at all. Compared to the conventional example shown in FIG. 13, the increase in the number of steps for assembling the optical pickup head device due to the provision of the photodetector 51 is small, and the stability of the focus error signal is not impaired.
[0034]
On the other hand, the signal output from the calculation unit 873 includes groove crossing noise. However, by performing the differential calculation in the calculation unit 874, the groove crossing noise included in the focus error signal is reduced. The gain of the variable gain amplifying unit 831 is selected so that the groove crossing noise included in the focus error signal is minimized.
[0035]
FIG. 3 shows the position of the beam 70 in the X-axis direction when the beam 70 focused on the optical recording medium 40 has astigmatism of 30 mλ and the beam 70 is at the position S1 in the Z-axis direction. The relationship between the signal obtained from the terminal 411 and the tracking error signal obtained from the terminal 402 is shown. The period of the track on the optical recording medium 40 is 0.74 μm. The signal obtained from the terminal 411 corresponds to a focus error signal obtained by a conventional optical pickup head device, and includes groove crossing noise.
[0036]
FIG. 4 shows the relationship between the position of the beam 70 in the X-axis direction, the focus error signal obtained from the terminal 401, and the tracking error signal obtained from the terminal 402 under the same conditions as in FIG. As is clear from FIG. 4, the focus error signal obtained from the terminal 401 has extremely reduced groove crossing noise. That is, the focus error signal obtained from the optical pickup head device and the optical information processing device of the present invention contains almost no groove crossing noise. As a result, even if the wavelength of the light source is shortened, the numerical aperture of the objective lens is increased. However, there is almost no defocus due to groove crossing noise. Therefore, when the optical pickup head device and the optical information processing device of the present invention are used, it is possible to stably read or record information on an optical recording medium on which information is recorded at high density.
[0037]
In the description of the first embodiment, reading information from the optical recording medium is not described because it is different from the object of the present invention, but is output from each light receiving unit of the photodetector 50 or 51. It is obtained by adding the signals.
[0038]
(Second Embodiment)
A second embodiment relating to the optical information processing apparatus of the present invention will be described with reference to FIG. FIG. 5 shows the configuration of the signal processing unit 82 of the optical information processing apparatus according to the second embodiment. The optical pickup head device used in the optical information processing apparatus in the second embodiment is the same as that in the first embodiment shown in FIG.
[0039]
The difference between the signal processing unit 81 of the first embodiment and the signal processing unit 82 of the second embodiment is the configuration of the calculation unit that calculates the signals output from the addition units 891, 892, 895, and 896. As shown in FIG. 5, the signals output from the adders 891 and 892 are set to levels at which the noise across the grooves included in the focus error signal output from the terminal 401 is minimized by the variable gain amplifiers 832 and 833, respectively. Amplified. The arithmetic unit 875 receives signals output from the adding units 895 and 896 and the variable gain amplifying units 832 and 833 and performs arithmetic operations. A signal output from the calculation unit 875 is output from the terminal 401 and becomes a focus error signal.
[0040]
The calculation unit 875 functions as the calculation units 871, 873, and 874 in the signal processing unit 81 of the first embodiment. Therefore, even in the optical information processing apparatus using the signal processing unit 82 of the second embodiment, the groove crossing noise included in the focus error signal output from the terminal 401 is small. In addition, although the structure of the calculating part was described here, it cannot be overemphasized that various structures are applicable also about an adding part similarly to a calculating part.
[0041]
(Third embodiment)
A third embodiment relating to the optical information processing apparatus of the present invention will be described with reference to FIG. FIG. 6 shows the configuration of the signal processing unit 83 of the optical information processing apparatus according to the third embodiment. The optical pickup head device used in the optical information processing apparatus in the third embodiment is the same as that in the first embodiment shown in FIG.
[0042]
The difference between the signal processing unit 81 of the first embodiment and the signal processing unit 83 of the third embodiment is that the detection units 811 and 812 and the low-pass filtering units 821 and 822 are provided on the input side of the calculation unit 873. It is. The detection units 811 and 812 and the low-pass filtering units 821 and 822 play the role of envelope detection. The optical information processing apparatus using the signal processing unit 83 of the third embodiment is particularly effective when information is recorded as a pit string on the optical recording medium 40.
[0043]
When information is recorded in the optical recording medium 40 as a pit string, when the signals output from the adders 895 and 896 are input to the detectors 811 and 812, respectively, the DC component is removed from the low-pass filter units 821 and 822. Thus, only a signal corresponding to the groove crossing noise is output. Therefore, for example, even if non-uniform stray light is incident on the light receiving portions 51A to 51D of the photodetector 51 and the signals output from the light receiving portions 51A to 51D include electrical direct current offsets having different levels, the direct current Since the component is removed, the focus error signal is not affected, and a stable optical information processing apparatus is obtained. Note that the form of signal detection using the detection unit has already been disclosed in, for example, Japanese Patent Application Laid-Open No. 56-41538, and a detailed description thereof will be omitted.
[0044]
(Fourth embodiment)
A fourth embodiment relating to an optical pickup head device of the present invention and an optical information processing device using the same will be described with reference to FIGS. FIG. 7 is a diagram illustrating a configuration example of the optical pickup head device according to the fourth embodiment. The optical pickup head device of the fourth embodiment shown in FIG. 7 is the same as the optical pickup head device of the first embodiment shown in FIG. 1 in the configuration of the optical system that receives the beam 70 condensed by the condenser lens 22. Different.
[0045]
As shown in FIG. 7, the convergent beam 70 converted by the condenser lens 22 passes through the parallel plate 32 and then enters the hologram element 60 as the second beam branching element. Astigmatism is given to the beam 70 in order to detect a focus error signal when passing through the parallel plate 32. In the hologram element 60, a Fresnel zone plate is recorded as a pattern. The hologram element 60 receives the beam 70 and generates 0th-order diffracted light 70C and 1st-order diffracted light 70D. The zero-order diffracted light 70 </ b> C and the first-order diffracted light 70 </ b> D generated by the hologram element 60 are incident on the photodetector 52.
[0046]
The relationship between the beams 70C and 70D and the light receiving portion of the photodetector 52 is shown in FIG. The photodetector 52 has eight light receiving parts 52A to 52H formed on a silicon substrate. The beam 70C is received by the light receiving parts 52A to 52D, and most of the beam 70D is received by the light receiving parts 52E to 52H formed around the light receiving parts 52A to 52D. The beam 70D is the first-order diffracted light of the hologram element 60, and has a focal point at a position different from the beam 70C by a Fresnel zone plate having a lens action. Both the beams 70C and 70D are provided with astigmatism by transmitting through the parallel plate 32. Here, when the beam 70C has a minimum circle of confusion on the photodetector 52, the beam 70D is detected by the photodetector 52. It is designed to receive light in a state of being sufficiently defocused above the focal line. Therefore, the beam 70D becomes a substantially circular beam on the photodetector 52, and the change in the size of the beam 70 does not affect the focus error signal. The beams 70C and 70D received by the photodetector 52 are converted into electrical signals corresponding to the light amounts. The electrical signal output from the photodetector 52 can be configured, for example, by inputting it into the signal processing unit 81 of the first embodiment shown in FIG.
[0047]
In FIG. 2, the photodetectors 50 and 51 are disconnected, the signal output from the light receiving unit 52A of the photodetector 52 is output to the terminal 406, the signal output from the light receiving unit 52B is output to the terminal 403, and output from the light receiving unit 52C. The signal output from the light receiving unit 52D to the terminal 404, the signal output from the light receiving unit 52E to the terminal 410, the signal output from the light receiving unit 52F to the terminal 407, and the light receiving unit 52G If the output signal is input to the terminal 409 and the signal output from the light receiving portion 52H is input to the terminal 408, the groove crossing noise included in the focus error signal obtained from the terminal 401 is reduced.
[0048]
In the optical pickup head device shown in the fourth embodiment, the light receiving portions 52A to 52D as the first photodetector and the light receiving portions 52E to 52H as the second photodetector are configured as one photodetector 52. Therefore, the optical pickup head device is small and inexpensive.
[0049]
Further, the hologram element 60 and the parallel plate 32 constitute an optical pickup head device as separate parts. For example, a Fresnel zone plate is formed on the parallel plate 32, and the role of the hologram element 60 and the parallel plate 32 is one. It may be realized with parts.
[0050]
(Fifth embodiment)
A fifth embodiment relating to an optical pickup head device of the present invention and an optical information processing device using the same will be described with reference to FIGS. FIG. 9 is a diagram illustrating a configuration example of the optical pickup head device according to the fifth embodiment. The optical pickup head device of the fifth embodiment shown in FIG. 9 differs from the optical pickup head device of the fourth embodiment shown in FIG. 7 in that the second beam branching element is formed on the objective lens 23. Different.
[0051]
The configuration of the objective lens 23 is shown in FIG. The objective lens 23 has regions 23A and 23B, and the region 23B is the same as a normal lens. In the region 23A, a concentric blazed Fresnel zone plate as a second beam branching element is formed. The diffraction efficiency of the zero-order diffracted light in the region 23A is 80%, and the diffraction efficiency of the first-order diffracted light is 10%.
[0052]
When the thickness t of the substrate of the optical recording medium 40 is 0.6 mm, information recorded on the optical recording medium 40 is read using a beam that passes through the region 23B of the objective lens 23 and the 0th-order diffracted light of the region 23A. On the other hand, when the thickness t of the substrate of the optical recording medium 40 is 1.2 mm, the information recorded on the optical recording medium 40 is read using the first-order diffracted light in the region 23A of the objective lens 23. Regarding the method of reading this information and the configuration of the Fresnel zone plate formed on the objective lens, see, for example, Y.C. Koma, et al. "Dual focus optical head for 0.6 mm and 1.2 mm disks", Optical Data Storage '94 SPIE Vol. 2338, p282 (1994). The detailed description is omitted.
[0053]
The beam 70 reflected by the optical recording medium 40 is incident on the objective lens 23 again, and zero-order diffracted light 70E and first-order diffracted light 70F are generated by the region 23A. The two beams 70E and 70F enter the photodetector 52 through the quarter-wave plate 31, the polarization beam splitter 30, the condenser lens 22, and the parallel plate 32. The relationship between the beams 70E and 70F is substantially the same as the relationship between the beams 70C and 70D of the fourth embodiment shown in FIG. As the signal processing unit, the same one as in the case of the fourth embodiment can be used.
[0054]
Similarly to the case of the fourth embodiment, the pickup head device of the fifth embodiment also includes the light receiving parts 52A to 52D as the first photodetector and the light receiving parts 52E to 52H as the second photodetector. A single optical detector 52 is formed, and the optical pickup head device is small and inexpensive. Furthermore, by forming the second beam branching element on the objective lens 23, an optical pickup head device capable of reading information recorded on optical recording media having different substrate thicknesses is obtained.
[0055]
(Sixth embodiment)
A sixth embodiment relating to an optical pickup head device of the present invention and an optical information processing device using the same will be described with reference to FIG. 11A shows the configuration of the objective lens 24 used in the optical pickup head device according to the sixth embodiment, and FIG. 11B shows the relationship between the beams 70E to 70G and the light receiving unit of the photodetector 52. The optical pickup head device of the sixth embodiment uses an objective lens 24 shown in FIG. 11A in place of the objective lens 23 in the optical pickup head device of the fifth embodiment shown in FIG.
[0056]
In the objective lens 24 shown in FIG. 11A, a Fresnel zone plate as a second beam branching element is formed in the region 24A, and the pattern of the Fresnel zone plate is the same as the pattern formed in the region 23A of the objective lens 23. Are the same. In the region 24B of the objective lens 24, a Fresnel zone plate that generates a beam having a focal point at a position different from the region 24A is formed as a third beam branching element. In both the regions 24A and 24B, the diffraction efficiency of the 0th-order diffracted light is 80%, and the diffraction efficiency of the 1st-order diffracted light is 10%.
[0057]
When the thickness t of the substrate of the optical recording medium 40 is 0.6 mm, the information recorded on the optical recording medium 40 is read using the 0th-order diffracted light from the regions 24A and 24B of the objective lens 24. On the other hand, when the thickness t of the substrate of the optical recording medium 40 is 1.2 mm, the information recorded on the optical recording medium 40 is read using the first-order diffracted light from the region 24A of the objective lens 24.
[0058]
The beam reflected by the optical recording medium 40 enters the objective lens 24 again, and the 0th-order diffracted light 70E and the 1st-order diffracted light 70F are generated by the region 24A, and the 0th-order diffracted light 70E and the 1st-order diffracted light 70G are generated by the region 24B. The The three beams 70E, 70F, and 70G enter the photodetector 52 through the quarter-wave plate 31, the polarization beam splitter 30, the condenser lens 22, and the parallel plate 32. The relationship between the beams 70E to 70G and the photodetector 52 is shown in FIG. The beam 70G is received by the light receiving units 52E to 52H in the same manner as the beam 70F.
[0059]
In the objective lens 24 of the sixth embodiment, by making the diffraction efficiencies of the regions 24A and 24B equal, the intensity distribution of the 0th-order diffracted light transmitted through the objective lens 24 becomes close to a Gaussian distribution and is collected on the optical recording medium 40. The side rope of the emitted beam can be kept low, and the effects of crosstalk and intersymbol interference from adjacent tracks can be reduced. Further, the intensity distribution of the beam 70E received by the light receiving parts 52A to 52D of the photodetector 52 and the intensity distribution of the beams 70G and 70H received by the light receiving parts 52E to 52H are substantially equal.
[0060]
(Seventh embodiment)
A seventh embodiment relating to the assembly adjustment method of the optical pickup head device of the present invention will be described with reference to ZY12. FIG. 12 shows the configuration of the signal processing unit 84 used in the assembly adjustment method of the optical pickup head device of the seventh embodiment. The assembled optical pickup head device is, for example, the optical pickup head device of the first embodiment shown in FIG. As the optical recording medium 40, an optical recording medium in which information is recorded in a mark row is used.
[0061]
In FIG. 12, the signal output from the photodetector 50 is input to the adders 891 to 894, and then the focus error signal and the tracking error signal are output from the terminals 401 and 402, respectively. The signal output from the differential operation unit 871 is also input to the detection unit 813. The signal input to the detection unit 813 is detected by the detection unit 813 and then input to the low-pass filtering unit 823. From the low-pass filtering unit 823, the envelope of the signal detected by the detection unit 813 is output as the signal S2. The low-pass filtering unit 823 and the detecting unit 813 are signal processing units that detect an envelope of information recorded on the optical recording medium 40.
[0062]
On the other hand, signals output from the adders 891 and 892 are further added by an adder 897. The signal added by the adder 897 is input to the jitter detector 817, and jitter is detected. A signal indicating jitter is represented by S1. The signals S1 and S2 are added after performing desired weighting in the evaluation unit 818, and then output from the terminal 512.
[0063]
When assembling the optical pickup head device, the relative tilt between the objective lens 21 and the optical recording medium 40 is adjusted by applying focus and tracking servo. At this time, adjustment is made so that the signal output from the terminal 412 is minimized. The wavefront aberration remaining in the optical system with respect to the direction parallel to the X axis and the Y axis is caused by the change of the signal S1, and the wavefront aberration remaining in the optical system with respect to the direction of 45 degrees along the X axis and the Y axis is Each is detected by a change in S2. Therefore, when the assembly adjustment method of the optical pickup head device of the seventh embodiment is used, the wavefront aberration remaining in the optical system can be made smaller than when the assembly adjustment method of the conventional optical pickup head device is used. it can. As shown in FIG. 18, as the wavefront aberration remaining in the optical system is smaller, the groove crossing noise included in the focus error signal is also reduced. At this time, an allowable range for an error factor such as defocus due to disturbance is widened, and information from the optical recording medium can be read more stably than in the case of using the conventional assembly adjustment method of the optical pickup head device. Further, as the noise across the groove is reduced, the sound generated from the drive unit when the seek operation is performed is reduced, so that it is possible to provide an optical information processing apparatus with low operation sound.
[0064]
【The invention's effect】
As described above, the first optical pickup head device of the present invention is reflected by the light source, the condensing optical system for converging the beam emitted from the light source as a fine spot on the optical recording medium, and the optical recording medium, A first beam branching element that branches the diffracted beam; an optical element that imparts astigmatism to the beam branched by the first beam branching element; and a beam that is provided with astigmatism by the optical element A first photodetector that outputs a photocurrent according to the amount of light, and a second detector that is provided in an optical path from the optical recording medium to the first photodetector and branches the beam reflected by the optical recording medium. Relative to the light beam branching element, the second photodetector for receiving the beam branched by the second beam branching element, and outputting a photocurrent according to the amount of light, and the focusing optical system and the optical recording medium. For accurate positioning ; And a driving unit that performs the scan and tracking control,
The relative positional relationship between the surface including the light receiving portion of the first photodetector and the focal point of the beam received by the first photodetector is the second relative to the surface including the light receiving portion of the second photodetector. This is different from the relative positional relationship with the focal point of the beam received by the photodetector.
[0065]
That is, since the astigmatism is not given to the beam branched by the second beam branching element, even if the relative positions of the optical recording medium and the condensing optical system in the optical axis direction change, the second light Similarity is maintained only by changing the cross-sectional size of the beam received on the detector. Therefore, by processing the output of the second photodetector, it is possible to cancel out components that adversely affect the focus error signal. Further, it is not necessary to adjust the position of the second photodetector in the optical axis direction by sufficiently separating the light receiving surface of the second photodetector from the focal point of the beam branched by the second beam branching element. Can do.
[0066]
According to the second optical pickup head device of the present invention, in addition to the configuration of the first optical pickup head device, the second beam branching element is integrated with the condensing optical system. A third beam branching element is formed in the periphery of the first light detector, and the first and second photodetectors each have a light receiving portion divided into four parts. That is, for example, the beam is branched (diffracted) by a third optical branching element such as a hologram element in which the Fresnel zone plate is recorded, and thus branched (diffracted) beams (for example, 0th order diffracted light and 1st order diffracted light). Can be used to record and reproduce a plurality of types of optical recording media having different substrate thicknesses.
[0067]
Further, a first optical information processing apparatus of the present invention uses the optical pickup head device, and generates a focus error signal and a tracking error signal from signals output from the first and second photodetectors. And a drive unit that performs focus and tracking control in order to perform relative positioning between the condensing optical system and the optical recording medium using the focus error signal and the tracking error signal generated by the signal processing unit, The signal processing unit includes a first calculation unit that calculates a signal output from the first photodetector, a second calculation unit that calculates a signal output from the second photodetector, and a first calculation. And a third calculation unit that calculates a signal output from the second calculation unit, and a focus error signal is generated from the signal output from the third calculation unit.
[0068]
That is, as described above, by using the optical pickup head device of the present invention, no astigmatism is given to the beam branched by the second beam branching element. Even if the relative position in the axial direction changes, the similar shape is maintained only by changing the size of the cross section of the beam received on the second photodetector. In particular, by performing a differential operation on the output from the first photodetector and the output from the second photodetector by the second computing unit, it is possible to reduce the groove crossing noise included in the focus signal. As a result, even if the wavelength of the light source was shortened or the numerical aperture of the objective lens of the condensing optical system was increased, almost no defocusing due to groove crossing noise occurred, and information was recorded at high density. Information can be stably read from the optical recording medium, or information can be recorded on the optical recording medium with high density.
[0069]
According to a second optical information processing apparatus of the present invention, in addition to the configuration of the first optical information processing apparatus, the second optical information processing apparatus includes a detection unit that detects a signal output from the second photodetector. The second calculation unit calculates a signal output from the detection unit. That is, the second optical information processing apparatus is effective particularly when information is recorded as a pit string on the optical recording medium, and a direct current component is removed from the output of the detection unit. Therefore, even if non-uniform stray light is incident, the electrical DC offset component is removed, and a stable optical information processing apparatus is obtained without affecting the focus error signal.
[0070]
The method of adjusting and assembling the optical pickup head device according to the present invention is suitable for assembling the optical pickup head device, detects a change in the signal by receiving a signal output from the second photodetector, Using the output signal as the first evaluation function, the jitter of the mark row recorded on the optical recording medium is detected from the signal output from the first photodetector or the second photodetector and output. Using the jitter signal as the second evaluation function and weighting the first evaluation function and the second evaluation function, the relative positions of the condensing optical system of the optical pickup head device and the optical recording medium are used. Adjust the relationship.
[0071]
When assembling the optical pickup head device, focus and tracking servo are applied to adjust the relative inclination between the objective lens of the condensing optical system and the optical recording medium. At this time, the first evaluation function and the second evaluation function It adjusts so that the signal showing the result of performing the weighting to be minimized. The wavefront aberration remaining in the optical system with respect to the direction parallel to the X axis and the Y axis is the wavefront aberration remaining in the optical system with respect to the direction of 45 degrees along the X axis and the Y axis due to the change in the first evaluation function. Are respectively detected by a change in the second evaluation function. Therefore, when the assembly adjustment method for the optical pickup head device of the present invention is used, the wavefront aberration remaining in the optical system can be made smaller than when the assembly adjustment method for the conventional optical pickup head device is used.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration example of an optical pickup head device according to a first embodiment of the invention.
FIG. 2 is a diagram illustrating a configuration of a photodetector and a signal processing unit of the optical information processing apparatus according to the first embodiment.
FIG. 3 is a diagram illustrating a relationship between an output signal from a terminal 411 of the signal processing unit and a tracking error signal in the first embodiment.
FIG. 4 is a diagram showing a relationship between a focus error signal and a tracking error signal in the first embodiment.
FIG. 5 is a diagram illustrating a configuration of a signal processing unit of an optical information processing apparatus according to a second embodiment of the present invention.
FIG. 6 is a diagram showing a configuration of a signal processing unit of an optical information processing apparatus according to a third embodiment of the present invention.
FIG. 7 is a diagram illustrating a configuration example of an optical pickup head device according to a fourth embodiment of the present invention.
FIG. 8 is a diagram showing a relationship between a beam and a light receiving unit of a photodetector in the fourth embodiment.
FIG. 9 is a diagram showing a configuration example of an optical pickup head device according to a fifth embodiment of the present invention.
FIG. 10 is a diagram showing a configuration of an objective lens according to a sixth embodiment of the present invention.
11A is a diagram illustrating a configuration of an objective lens according to a sixth embodiment of the present invention, and FIG. 11B is a diagram illustrating a relationship between a beam and a light receiving unit of a photodetector according to the sixth embodiment.
FIG. 12 is a diagram showing a configuration of a signal processing unit used in an assembly adjustment method for an optical pickup head device according to a seventh embodiment of the present invention.
FIG. 13 is a diagram showing a configuration of a conventional optical pickup head device.
FIG. 14 is a diagram showing a configuration of a signal processing unit in a conventional optical pickup head device.
FIG. 15 is a view showing a waveform of a focus error signal obtained from a conventional optical pickup head device.
FIG. 16 is a diagram showing a relationship between a focus error signal and a tracking error signal when there is no wavefront aberration of an optical system obtained from a conventional optical pickup head device.
FIG. 17 is a diagram showing a relationship between a focus error signal and a tracking error signal when there is wavefront aberration of an optical system obtained from a conventional optical pickup head device.
FIG. 18 is a diagram showing the relationship between wavefront aberration and groove crossing noise of an optical system obtained from a conventional optical pickup head device.
[Explanation of symbols]
10: Semiconductor laser light source
20: Collimating lens
21: Objective lens
22: Condensing lens
23: Objective lens
23A-23B: Area
24: Objective lens
24A-24B: Area
30: Polarizing beam splitter
31: 1/4 wavelength plate
32: Parallel plate
33: Half mirror
40: Optical recording medium
50-52: Photodetector
50A to 50D: light receiving part
51A-51D: Light-receiving part
52A to 52H: Light receiving portion
60: Hologram element
70: Beam
70A to 70G: Beam
80 to 84: Signal processing unit
90 to 91: Drive unit
401 to 412: Terminals
811 to 813: detection unit
817: Jitter detector
818: Evaluation section
821-823: Low-pass filtering part
831 to 833: Variable gain amplifier
871-875: Calculation unit
891-897: Adder

Claims (1)

  A light source, a condensing optical system for converging the beam emitted from the light source as a minute spot on the optical recording medium, a first beam branching element for branching the diffracted beam reflected by the optical recording medium, An optical element that imparts astigmatism to the beam branched by the first beam branching element, a first beam that receives astigmatism from the optical element, and outputs a photocurrent corresponding to the amount of light. And a second optical system integrated with the condensing optical system provided in the optical path from the optical recording medium to the first optical detector for branching the beam reflected by the optical recording medium. A beam branching element, a second photodetector for receiving a beam branched by the second beam branching element and outputting a photocurrent according to the amount of light, and a peripheral part of the second beam branching element Formed third bee A branch unit; and a drive unit that controls focus and tracking to perform relative positioning between the condensing optical system and the optical recording medium, and the first photodetector and the second light. Each of the detectors has a light receiving portion divided into four regions, and a relative relationship between the surface including the light receiving portion of the first photodetector and the focal point of the beam received by the first photodetector. The positional relationship is different from the relative positional relationship between the surface including the light receiving portion of the second photodetector and the focal point of the beam received by the second photodetector, and the first photodetector is An optical pickup head device having four light receiving portions and provided with four light receiving portions of the second photodetector in the periphery thereof.

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