JP3694943B2 - Optical apparatus and optical pickup - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention performs reproduction or recording and reproduction by irradiating various optical recording media including optical devices such as optical discs such as compact discs (CD), write-once compact discs (CD-R), and magneto-optical discs. The present invention relates to an optical device, for example, an optical pickup.
[0002]
[Prior art]
Conventional optical pickups that optically read a record on an optical recording medium include, for example, a semiconductor laser, a collimating lens, a beam splitter, a polarizing beam splitter, a quarter-wave plate, a focus lens, a focus lens driving device, a split-type photodetector, and the like. Discrete optical components individually configured are arranged in a predetermined positional relationship with high accuracy.
[0003]
FIG. 21 shows a configuration diagram of an example of a conventional optical pickup dedicated to reproduction of a compact disc (CD). The optical pickup 81 includes a semiconductor laser 82, a diffraction grating 83, a beam splitter plate 84, an objective lens 85, and a light receiving element 86 including a photodiode, and the laser light L from the semiconductor laser 82 is reflected by the beam splitter plate 84. Then, the light converged by the objective lens 85 and irradiated onto the optical disk 90, the return light reflected by the optical disk 90 passes through the beam splitter plate 84 and is received and detected by the light receiving element 86.
[0004]
However, such an optical pickup 81 not only has a large number of parts and is very large, but also requires high precision in its arrangement and has low productivity.
[0005]
In recent years, due to the demand for portable CD players, etc., research and development to reduce the size and reduce the number of parts of optical pickups has been actively conducted. Functional combination of optical elements, laser coupler (integrated light emitting / receiving unit), use of hologram elements Etc. are progressing. However, even in these developments, the arrangement of optical elements does not need to be adjusted sufficiently.
[0006]
[Problems to be solved by the invention]
As a method of reducing the size of the entire optical pickup, for example, instead of using a polarizing beam splitter in the middle of the optical path, an optical component such as a mirror plate having a reflective film formed on the back surface is installed to reflect light. Thus, a method has also been proposed in which a light receiving portion by a light receiving element or the like can be arranged on the same side as a light emitting portion made of a semiconductor laser or the like (Japanese Patent Laid-Open No. 2-162541).
[0007]
However, in this case, since the light emitting unit and the light receiving unit are arranged on the same side, the overall size of the apparatus is reduced. However, the light emitting unit and the light receiving unit are configured separately and arranged in a predetermined positional relationship with each other. Therefore, the number of parts does not decrease so much, and adjustment of the arrangement of the optical elements is required to the same extent as in the past.
[0008]
Further, as a solution to these problems, an optical pickup using a hologram element as shown in FIG. 22 has been proposed. An optical pickup 110 shown in FIG. 22 includes optical components such as a semiconductor laser 101, a photodetector 102, a hologram element 103, and an objective lens 104. In this case, the light emitted from the semiconductor laser 101 passes through the hologram element 103 and is converged by the objective lens 104 and irradiated to the disk 105 as the irradiated portion, and the return light reflected here is converged by the objective lens 104 again. Later, diffraction is performed in the hologram element 103, and a focus servo signal is detected using ± 1st order diffracted light of the return light.
[0009]
At this time, diffracted light is generated in the hologram element 103 even in outgoing light, but this diffracted light is almost discarded without being used. For this reason, the amount of return light is greatly reduced compared to the amount of emitted light. In order to compensate for this decrease in the amount of light, it is necessary to increase the output of the semiconductor laser LD, thereby increasing the power consumption.
[0010]
On the other hand, in an optical apparatus having a magneto-optical signal (MO signal) detection system utilizing the Kerr effect and capable of recording and reproducing, for example, as shown in FIG. 23 as an example of an optical pickup for a mini disk (MD), Further, the configuration is such that components for detecting polarization are added. The optical pickup 91 shown in FIG. 23 includes a semiconductor laser 92, an objective lens 96, a photodetector 99, a diffraction grating 93 used for detecting a tracking servo signal, a polarization beam splitter 94, a collimator lens 95, a Wollaston prism 97, and a focus servo. A multi-lens 98 for signal detection is provided.
In order to detect polarized light in this way, the number of parts is very large, the optical device is complicated, and since a large amount of power is required to perform recording, it is necessary to increase the laser output of the light source, After all, power consumption will increase.
[0011]
  The present invention has been made in consideration of such points, and in an optical apparatus such as an optical pickup, the number of optical components is reduced, alignment is simplified when optical arrangement is set, and the entire apparatus is simplified. It is designed to be compact and easy to manufacture. In addition, tracking servo signals, focus servo signals, and magneto-optical signals can be detected easily and reliably, and the light quantity is used effectively. Optical device with low powerAnd optical pickupThis is a proposal.
[0012]
[Means for Solving the Problems]
  The present invention includes a light emitting unit andA converging means for converging and irradiating the emitted light from the light emitting part to the irradiated part, a light receiving part arranged including the confocal vicinity of the return light from the irradiated part by the converging means, and an output from the light emitting part A first reflecting mirror for guiding the incident light to the converging means, a second reflecting mirror disposed near the confocal point,Reflective surface formed on the surfaceThe light emitting unit, the light receiving unit, the first reflecting mirror and the second reflecting mirror, and the wedge prism are formed on a common semiconductor substrate, and return light is formed on the semiconductor substrate. A non-reflective surface formed on the outer side of the optical diffraction limit region, and a focus servo signal is detected using the non-reflective surface using a knife edge method.An optical device is configured.
  In addition, the present invention provides a light emitting unit, a converging unit that converges and irradiates the emitted light from the light emitting unit to the irradiated unit, and a light receiving unit that is disposed including the confocal vicinity of the return light from the irradiated unit by the converging unit. A first reflecting mirror that guides the light emitted from the light emitting unit to the converging means, a second reflecting mirror disposed near the confocal point, and a wedge prism having a reflecting surface formed on the surface, The light emitting unit, the light receiving unit, the first reflecting mirror and the second reflecting mirror, and the wedge prism are formed on a common semiconductor substrate, and enclose an optical diffraction limit region of return light on the semiconductor substrate. And an optical pickup that detects a focus servo signal by using a knife edge method.
[0013]
Here, the vicinity of confocal by the converging means means an area within the focal depth of the converging means in the optical axis direction, and an area within the diffraction limit of light by the converging means in the direction orthogonal to the optical axis. And
On the other hand, the position away from the confocal point by the convergence means described later means an area other than these areas.
[0014]
  Optical device according to the inventionAnd optical pickupUses the optical principle that light is always returned to the confocal position when the light emitted from the light emitting part is just focused on the irradiated part. Since the optical element in which the light receiving unit is arranged including the region near the confocal point by the means, that is, the region within the diffraction limit of the light by the converging unit is configured, the light emitted from the light emitting unit is irradiated as described above. In the focused state, the return light from the irradiated portion is surely transmitted to the light receiving portion arranged near the confocal position even if there is some problem in the positional accuracy of the optical component attached to the optical element. Incident light can be detected.
[0015]
Further, in the configuration of the present invention, by arranging a wedge prism having a reflecting surface formed on the surface, the reflected light is reflected from the irradiated portion by this reflecting surface, and is received at a position away from the confocal point. It is possible to detect the focus servo signal by detecting the received light in the unit.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The optical device of the present invention is constituted by a light emitting portion 14 constituted by a semiconductor laser LD and a first reflecting mirror 13, and a photodetector PD such as a photodiode, as shown in FIG. An optical element 17 formed on a semiconductor substrate 16 that is shared with the light receiving unit 15 is configured.
The optical element 17 emits light L emitted from the light emitting unit 14._FIs converged and irradiated to the irradiated portion 12 through the converging means 18, and the light receiving portion 15 is disposed including the confocal vicinity of the converging means 18, and the return light L reflected from the irradiated portion 12 by the light receiving portion 15._R, That is, a CLC (Confocal Laser Coupler) configuration.
[0017]
In addition, a second reflecting mirror 21 is disposed in the vicinity of the above-described confocal point separately from the light receiving unit 15, and the second reflecting mirror 21 returns light L as will be described later._RShall be reflected.
Further, the wedge prism 20 is disposed on the optical element 17. A reflecting surface (third reflecting mirror) 19 is formed on the surface of the wedge prism 20.
[0018]
The wedge prism 20, the reflection surface 19, and the second reflection mirror 21 return light L from the irradiated portion 12._RThe light is reflected at a portion other than the vicinity of the confocal point of the light receiving unit 15.
[0019]
The optical apparatus according to the present invention shown in FIG. 1 (hereinafter referred to as Example 1) is an example when applied to an optical pickup.
In FIG. 1, reference numeral 11 denotes an optical pickup as a whole, and reference numeral 12 denotes an optical recording medium as an irradiated portion, for example, an optical disc. The optical pickup 11 includes an optical element 17 in which a light emitting unit 14 by a semiconductor laser LD and a reflecting mirror 13, a light receiving unit 15 by a plurality of photodetectors PD, and a second reflecting mirror 21 are integrated on the same semiconductor substrate 16. Converging means 18 This example includes an objective lens and a wedge prism 20 having a reflecting surface 19 disposed on the surface thereof. The wedge prism 20 is disposed on the optical element 17 so as to cover the surface of the optical element 17 on the side where the light emitting unit 14 and the light receiving unit 15 are disposed.
[0020]
The wedge prism 20 emits light L_FAnd return light L from the irradiated part_RAnd an inclined surface 20a having a wedge angle θ, which will be described later, and an upper surface 20b parallel to the upper surface of the optical element 17 (see FIG. 3). A reflective film is formed on the upper surface 20b to form the reflective surface 19. The wedge prism 20 can be formed of, for example, glass or another transparent substrate.
[0021]
The light emitting unit 14 includes a semiconductor laser LD having a horizontal resonator structure and a first reflecting mirror 13. The first reflecting mirror 13 is selectively epitaxially grown by selecting the crystal plane of the semiconductor substrate constituting the optical element 17 and the crystal axis in the extending direction of the etching end face when forming the semiconductor laser LD. In addition, a specific crystal plane, for example, a {111} plane can be formed as a slope having a good morphology due to the atomic plane, or a plane having a certain angle of inclination with respect to the horizontal resonator plane. In this example, when this specific crystal plane is a {111} plane, the rising angle of the first reflecting mirror 13 is 54.7 ° as shown in the enlarged view of the light emitting portion 14 of the optical element 17 in FIG. It becomes.
[0022]
The light receiving unit 15 is composed of a plurality of photodetectors PD, and these photodetectors PD are in the diffraction limited region except for the portion where the light emitting unit 14 is arranged near the light emitting unit 14 on the surface of the optical element 17, that is, near the confocal position. And its peripheral part.
[0023]
Light emitted from the light emitting unit 14_FIs transmitted through the inclined surface 20 a of the wedge prism 20, converged on the irradiated portion 12 by the objective lens of the converging means 18, and reflected from the irradiated portion 12._RIs again transmitted through the wedge prism 20 through the inclined surface 20 a and focused on the surface of the optical element 17. A part of the light receiving unit 15 is located in the vicinity of the focal point, and the return light L_RIs detected. That is, this optical element has the aforementioned CLC configuration.
[0024]
This CLC configuration is the same as that described in Japanese Patent Application No. 5-21691 “Optical device”, which is an earlier application by the applicant of the present invention._RIs converged to the vicinity of the diffraction limit of the objective lens, and when the light receiving unit 15 is within the light diffraction limit, that is, the wavelength of the emitted light is λ and the numerical aperture on the optical element 17 side of the converging means 18 is NA, the optical axis of the emitted light Is arranged within a distance of 1.22λ / NA (within an Airy disk).
[0025]
Further, the return light L in which the second reflecting mirror 21 is formed outside the second reflecting mirror 21._RA knife edge surface 22 having an anti-reflection coating (AR coating) is formed surrounding the airy disk region. The knife edge surface 22 is formed so as to divide the region outside the second reflecting mirror 21 on the upper surface of the semiconductor laser LD of the light emitting unit 14 into two.
[0026]
As the light receiving unit 15 described above, as shown in a side view of the optical element 17 in FIG. 3A and a plan view of the optical element 17 in FIG. 3B, in the vicinity of the light emitting unit 14 on the surface of the optical element 17, that is, in the vicinity of the confocal point, A two-divided photodetector PD as part of the light receiving unit 15₁, PD₂2 split photo detector PD at a position away from the confocal point (outside the aforementioned Airy disc)_Three, PD_FourRespectively. The second reflecting mirror 21 is formed near the confocal surface on the surface of the optical element 17.
2 split photo detector PD_Three, PD_Four, Which detects a focus servo signal by the knife edge method as will be described later, is formed symmetrically with respect to the center of the reflected light irradiated by each photodetector.
[0027]
These photo detectors PD_Three, PD_FourBetween the surface of the optical element 17 forming the second reflecting mirror 21 and the light emitting point of the semiconductor laser LD, a semiconductor layer having a thickness of several μm, such as a cladding layer forming a pn junction, is formed. The vertical distance between them is only a few μm apart. For this reason, the surface on which the photodetector PD is formed is within the focal depth and may be considered as an in-focus position, that is, a confocal position surface.
Therefore, even when a lateral displacement of the lens occurs, there is no change in the spot position on the photodetector, which is convenient for detection of a tracking servo signal described later.
[0028]
The mirror surface of the second reflecting mirror 21 is formed by growing the optical element 17 along, for example, the {111} plane of the crystal, and is a flat surface with good crystallinity.
[0029]
Thus, since the mirror surface of the second reflecting mirror 21 is a crystal growth surface, the flatness is extremely good, and it becomes a mirror surface as it is. Since a part of the spot on the mirror surface is highly reflected, it is possible to detect a focus servo signal and a magneto-optical signal (MO signal) described later by using the reflected light from the mirror surface.
The second reflecting mirror 21 may be formed by vapor deposition of a metal having a good reflectance.
[0030]
The remaining portion of the upper surface of the semiconductor laser LD outside the second reflecting mirror 21 where the knife edge surface 22 is not formed is composed of a crystal growth surface, like the second reflecting mirror 21, and has a high reflectivity mirror surface 21. '.
[0031]
As described above, in this example, since the rising angle of the first reflecting mirror 13 is 54.7 °, the emitted light L from the light emitting unit 14 as shown in FIG._FIs emitted at an angle of 70.6 ° with respect to the horizontal direction.
Therefore, in this case, as shown in FIG. 3A, a wedge prism 20 having a wedge angle θ of 19.4 ° is arranged on the optical element 17, and the semiconductor laser LD of the light emitting unit 14 and the first reflecting mirror 13 are The gap between them is pasted so as to be filled with an adhesive having the same refractive index as that of the wedge prism 20, and the emitted light L from the wedge prism 20 is_FIs arranged so as to be perpendicular to the exit surface. Thereby, the outgoing light L from the prism surface_FSo-called coma does not occur.
[0032]
Next, the operation of the above-described optical device will be described.
The laser beam emitted from the semiconductor laser LD of the light emitting unit 14 is reflected by the first reflecting mirror 13 and is emitted obliquely upward with respect to the surface of the optical element 17._FProduce. This outgoing light L_FPasses through the inclined surface 20a of the wedge prism 20, is converged by the converging means 18 such as an objective lens, and is irradiated onto the irradiated portion 12 such as an optical disk.
[0033]
Then, the emitted light L is emitted by the irradiated portion 12._FIs reflected by the reflected light L_RProduce. Return light L_RIs again converged by the converging means 18 and enters the inclined surface 20a of the wedge prism 20 perpendicularly. Further return light L_RPasses through the inclined surface 20a and enters the vicinity of the confocal surface of the optical element 17. At this time, the return light L_RA two-divided photodetector PD arranged in the vicinity of the confocal as a part of the light receiving unit 15₁, PD₂The tracking servo signal is detected.
[0034]
Further return light L_RThe other part is near confocal, that is, the return light L_RAre reflected by the second reflecting mirror 21 arranged in the diffraction limit region, and the reflected light travels toward the upper surface 20 b of the wedge prism 20. Then, the reflected light is reflected again by the reflecting surface (that is, the third reflecting mirror) 19 formed on the upper surface 20 b of the wedge prism 20, and is separated from the confocal surface of the optical element 17 as a part of the light receiving unit 15. Two-segment photo detector PD formed at the position_Three, PD_FourAnd the focus servo signal is detected.
[0035]
Detection of various signals in the optical element 17 is performed as follows.
[0036]
Tracking servo signal detection is performed by a two-divided photodetector PD₁, PD₂Using the push-pull method. For example, the difference signal (PD₁-PD₂) Is used as a detection signal to detect a tracking servo signal.
[0037]
Detection of the focus servo signal is performed by the two-divided photo detector PD_Three, PD_FourUsing the knife edge method. At this time, as described above, the optical axis of the light reflected by the reflecting surface 19 is located at the center of the photodetector, and the two-divided photodetectors are arranged symmetrically with respect to the optical axis.
Furthermore, when the optical system is in focus, the signal intensity of the two photodetectors is equal, ie PD_Three= PD_FourThe position of the two-divided photodetector is set so that
[0038]
Here, detection of the focus servo signal by the knife edge method will be described.
First, as shown in FIG. 4, the detection of the focus servo signal by the knife edge method, which is normally performed, arranges the knife edge 50 at the focal position of the converging means 18, and this knife edge 50 causes the optical axis in the figure to be detected. Make sure the lower part is blocked.
[0039]
The emitted light L at the irradiated portion 12_FIs in focus, the return light L_RIs focused at the normal focal position where the knife edge 50 is arranged, and is not blocked by the knife edge 50, but the photodetector PD of the light receiving unit._A, PD_BThese photodetectors PD are evenly irradiated_A, PD_BThe signals at are equal.
[0040]
The irradiated portion 12 is shifted by δ to the position of the dotted line in the figure, and the emitted light L_FIs not focused on the irradiated portion 12, the return light L_RIs a dotted line (L_RAs shown by ′), the focal point is formed at the position ahead of the knife edge 50. However, since the light below the optical axis is blocked by the knife edge 50 at this time, the return light L_RIs a photo detector PD_BIrradiates the photo detector PD_AIs not irradiated.
[0041]
On the other hand, when the irradiated portion 12 is shifted in reverse to the dotted line position, the return light L_RIs focused at a position before the knife edge 50, and the portion below the optical axis is blocked by the knife edge 50, so that the photodetector PD_BThe photo detector PD is not irradiated_AOnly irradiated.
[0042]
Then, a signal (PD) is obtained using a differential amplifier 55 or the like connected to the photodetector._A-PD_B) Or (PD_A-PD_B) / (PD_A+ PD_B) As a detection signal, detection can be performed.
[0043]
The focus servo signal is detected by the optical apparatus of the present invention by applying this knife edge method.
[0044]
FIG. 5A is a diagram showing a schematic diagram of an optical path in the optical apparatus of the present invention.
As shown in FIG. 5A, the return light L from the irradiated portion 12_RIs focused by the surface of the optical element 17 which is converged by the converging means 18 and becomes the confocal position surface S, and since this surface is a reflecting surface, it is reflected here, and further the wedge prism surface The light detector PD is reflected by the reflective surface 19 of FIG._A, PD_BIs irradiated.
[0045]
On the surface of the optical element 17, a knife edge surface 22 that is non-reflective coated (AR coated) is formed in a portion below the optical axis in the figure._RAre not reflected and function in the same manner as the knife edge 50 of FIG.
[0046]
The emitted light L at the irradiated portion 12_FIs in focus, the return light L_RIs focused on the surface of the optical element 17 that is the normal focal position, that is, the confocal position surface S, and the return light L is applied to the knife edge surface 22._RIs not irradiated, the return light L on the confocal position plane S_RIs reflected as it is, and the photodetector PD of the light receiving part_A, PD_BThese photodetectors PD are evenly irradiated_A, PD_BThe signals at are equal.
[0047]
The irradiated portion 12 is shifted by δ to the position of the dotted line in the figure, and the emitted light L_FIs not focused on the irradiated portion 12, the return light L_RAs shown by the dotted line in the figure, the focal point is formed at a position ahead of the surface of the optical element 17 that is the confocal position surface S. However, since the light below the optical axis is not reflected by the knife edge surface 22 at this time, the return light L_RIs a photo detector PD like a dotted line_AIrradiates the photo detector PD_BIs not irradiated.
[0048]
On the other hand, when the irradiated portion 12 is shifted in reverse to the dotted line position, the return light L_RIs focused at a position before the surface of the optical element 17 at the confocal position, and the light at the portion below the optical axis is not reflected by the knife edge surface 22, so that the photodetector PD_AThe photo detector PD is not irradiated_BOnly irradiated.
[0049]
Then, using a differential amplifier 55 or the like connected to the photodetector, a signal (PD_A-PD_B) Or (PD_A-PD_B) / (PD_A+ PD_B) As a detection signal, for example, a detection signal as shown in FIG. 5B can be obtained and a focus servo signal can be detected.
[0050]
Therefore, in the optical apparatus of the first embodiment shown in FIGS. 1 and 3, for example, the difference signal (PD_Three-PD_Four) Or (PD_Three-PD_Four) / (PD_Three+ PD_Four) As a detection signal, the focus servo signal can be detected.
[0051]
The light reflected by the second reflecting mirror 21 is emitted light L in the wedge prism 20 as shown in FIG. 3A._FIt propagates in the wedge prism 20 through an optical path different from the optical axis. Therefore, the outgoing light L_FIt propagates in the wedge prism 20 without multiple interference.
[0052]
According to the optical device of the present invention, the wedge prism 20 goes directly to the converging means and the irradiated part, so that the emitted light is diffracted by the hologram element as in an optical pickup using a conventional hologram element, and ± 1 There is no generation of the next diffracted light and the loss of the amount of light accompanying this.
Therefore, the output of the laser LD of the light source can be set lower than the conventional one, and thereby the amount of heat generated in the light emitting part can be suppressed.
[0053]
Further, when the first-order diffracted light is generated from the normal emitted light, it is necessary to design the diffracted light to propagate out of the pupil plane of the objective lens so that the diffracted light does not enter the objective lens and cause interference.
According to the optical apparatus of the present invention, this design restriction is eliminated, and problems such as suppression of heat generated with the output of the semiconductor laser LD and miniaturization of the optical system can be handled preferentially.
[0054]
In the above example, the knife edge surface 22 is the return light L on the upper surface of the semiconductor laser LD._RThe pattern formed on exactly half of the portion outside the optical diffraction limit is the pattern of the knife edge surface 22 where the irradiated portion 12 emits light L_FWhen the light beam is out of focus, that is, defocused by the convergence means 13, the return light L_RThe spot irradiated on the surface of the optical element 17 may be applied to the knife edge surface 22 so that the reflected light is attenuated. Accordingly, in addition to the above-described example, some examples of pattern formation of the knife edge surface 22 are conceivable. An example of pattern formation on the knife edge surface 22 will be described below.
[0055]
6A and 6B show examples of pattern formation of the knife edge surface 22 formed on the surface of the optical element 17 in the optical apparatus of the first embodiment shown in FIGS. 1 and 3, respectively.
The pattern (pattern 1) shown in FIG. 6A is the same pattern as that shown in FIG. 3B.
[0056]
The knife edge surface 22 can be produced with a mask and alignment accuracy and by batch processing using a method generally widely used in the manufacture of semiconductors.
Further, if it is difficult to produce the knife edge surface 22 as shown in FIG. 6A in the manufacturing process, a simplified pattern (pattern 2) with a boundary line as a straight line is formed as shown in FIG. 6B. To do.
[0057]
In addition to the method of forming the knife edge surface 22 by applying a non-reflective coating on the mirror-grown crystal growth surface as described above, a film having a low reflectance such as an insulating film is formed on the upper surface of the semiconductor laser LD. There is also a method of forming a highly reflective film such as a metal film on a portion other than the knife edge surface 22 later. In any method, the optical element 17 can be easily incorporated as one step in the manufacturing process of the optical element 17 and can be formed simply and at low cost.
At this time, the outgoing light L emitted through the first reflecting mirror 13_FThe pattern is formed so that there is no influence on the pattern.
[0058]
Return light L_RSince the spot diameter at the confocal position surface depends on the magnification of the optical system, the light intensity and the amount of light used for the detection of the focus servo signal and the magneto-optical signal also depend on the magnification of the optical system.
[0059]
FIG. 7 shows the relationship between the numerical aperture on the optical element 17 side of the converging means 18 in the optical apparatus of Example 1 and the light intensity used for the detection of the focus servo signal and the magneto-optical signal. FIG. 7 shows the numerical aperture NA on the irradiated portion 12 side of the converging means 18._DIs 0.45, and the numerical aperture NA on the optical element 17 side of the converging means 18_CIs changed, the return light L to the confocal position_RThe change of the ratio of the light quantity used for the above-mentioned signal detection with respect to is shown.
At this time, the wedge prism 20 is made of BK7 or the like, the thickness on the optical axis of the confocal optical system is 1 mm, the refractive index is 1.52, and the position of the light emitting unit 14 and the standing of the first reflecting mirror 13 are set. The raising angle is set as shown in FIG. The light intensity distribution is calculated assuming a Gaussian beam distribution.
[0060]
For example, the magnification of an optical pickup used for a compact disc is usually about 3.5 to 6 times. Considering these, the numerical aperture NA on the optical element 17 side of the convergence means_CIs about 0.075 to 0.128, and about 6 to 19% of the return light can be used for the focus servo signal, which indicates that a sufficient amount of light for signal detection can be obtained.
[0061]
Further, the focus servo signals are calculated when the magnification of the convergence means is 3.5 times and 5 times, and the curves are shown in FIGS. 8A and 8B, respectively. In the drawing, the solid line is the focus servo signal when the pattern of the knife edge surface 22 shown in FIG. 6A (pattern 1) and the dotted line is the pattern of the knife edge surface 22 shown in FIG. 6B (pattern 2).
In either case, signal detection can be performed without any problem.
[0062]
On the other hand, the pattern of the knife edge surface 22 is basically the pattern of FIG. 6A (pattern 1), but increases the amount of light used to detect the focus servo signal and maintains the quality of the S-shaped curve of the signal. Is a photodetector PD that detects the tracking servo signal for the first reflecting mirror 13 as in the pattern formation example (pattern 3) shown in FIG. 9A.₁, PD₂It is preferable to form the knife edge surface 22 on the same side. In this case, PD₁And PD₂It is necessary to form a reflective film or the like on the photodetector so as to have a certain degree of reflectance.
[0063]
Further, a photodetector PD that detects a tracking servo signal with respect to the first reflecting mirror 13.₁, PD₂Even if the knife edge surface 22 is not formed on the same side as the photo detector PD₁And PD₂Is provided with a constant reflectivity so that the reflected light from the reflecting surface on the semiconductor laser LD and the reflected light from the photodetector are the same in the photodetector PD._Three, PD_FourBy detecting the received light, the signal level is raised and a signal advantageous for S / N, C / N, etc. can be obtained.
[0064]
According to the same viewpoint as that of the pattern 3 shown in FIG. 9A, as shown in FIG. 9B, a simplified pattern (pattern 4) of the knife edge surface 22 in which the boundary line is a straight line circumscribing the Airy disk. It can also be taken.
[0065]
Further, in order to increase the sensitivity of the detection signal of the focus servo as compared with the pattern 4 with the same ease of pattern formation as the pattern 4 shown in FIG. 9B, as shown in FIG. 10C and FIG. A pattern (pattern 5 and pattern 6) of the knife edge surface 22 may be formed as a straight line so as to surround the Airy disk.
[0066]
Next, an example of a method for manufacturing the optical device according to the first embodiment will be described with reference to the drawings.
First, as one method, a method using a wafer batch process is shown in FIGS. 13A to 13E.
[0067]
As shown in FIG. 13A, a semiconductor wafer 31 on which a large number of CLC devices (that is, optical elements 17) each having a light emitting element and a light receiving element are formed in advance, and a glass wafer 30 serving as a wedge prism are prepared. In the figure, 31a indicates one device.
[0068]
Next, as shown in FIG. 13B, the glass wafer 30 and the semiconductor wafer 31 are bonded with, for example, a UV resin (ultraviolet curable resin) to form a laminated body 32. When UV resin is used, it is irradiated and solidified by irradiating ultraviolet rays later. The glass wafer 30 may be the one already formed in the shape of the wedge prism 20, or the sloped prism 20 a may be formed on the glass wafer 30 after forming the laminated body 32 to form the wedge prism 20. .
After this bonding, a reflective film, a non-reflective film, or the like is formed on the surface of the glass wafer 30 (upper surface in the drawing).
[0069]
Next, the back surface of the semiconductor wafer 31 is lapped, and although not shown, contact holes 34, electrode pads, wirings, and the like are formed in the semiconductor wafer 31.
Thereafter, as shown in FIG. 13C, the stacked body 32 is cut vertically and horizontally to obtain an element 32a. The element 32a in this example is cut into the size of two devices as shown in FIG. 13E.
[0070]
Next, as shown in FIG. 13D, the element 32a is mounted on a wiring board 33 that also serves as a heat sink.
At this time, as shown in the enlarged view of FIG. 13E, the element 32a is mounted on the wiring board 33.
[0071]
Although not shown, this is further cut for each unit device to obtain an optical device in which the wedge prism 20 and the optical element 17 are fixed.
[0072]
Regarding the bonding method at this time, FIGS. 14A and 14B are side views showing a state in which a wafer corresponding to FIG. 13B is bonded. In FIG. 13B, the inclined surface of the surface of the glass wafer 30 is not expressed, but in FIG. 14A and FIG. 14B, this inclined surface, that is, an inclined surface that becomes a surface having the wedge angle θ of the wedge prism 20 later is expressed.
[0073]
As shown in FIG. 14A, the gap between the glass wafer 30 and the semiconductor wafer 31 is filled with an adhesive 36 having a refractive index equivalent to that of the glass wafer 30. If it is not filled in this manner, coma aberration occurs, and a problem occurs when reproducing an optical disk. Here, since the filling portion of the adhesive 36 is close to the light emitting position of the semiconductor laser LD, the temperature rises locally to about 200 ° C., assuming that the output power during reproduction is about several mW, for example. There is. Therefore, it is preferable to use, for example, a silicon-based or epoxy-based adhesive having heat resistance as the adhesive 36.
[0074]
Further, instead of filling the gap with an adhesive, as shown in FIG. 14B, after filling the gap with SOG (spin-on glass) 37, the SOG 37 and the glass wafer 30 can be bonded with the adhesive 36.
[0075]
As shown in FIGS. 14A and 14B, the glass wafer on which the inclined surface is formed is hereinafter referred to as a wedge prism array. The manufacturing method of the wedge prism array can be roughly divided into two types of manufacturing processes. One is a manufacturing process using a glass press technique, and the other is a manufacturing process using a glass grinding technique. Each manufacturing process is shown in FIG.FIG.17A to 17E.
[0076]
The manufacturing process by the glass press technique is performed according to the following process.
First, as shown in FIG. 15A, a trapezoidal column-shaped mold 40 made of super steel, for example, is prepared.
Next, as shown in FIG. 15B, several trapezoidal columnar molds 40 are aligned and fixed by a U-shaped mold 41.
[0077]
In this manner, a wedge prism array mold 42 including 40 trapezoidal columnar molds and a U-shaped mold 41 as shown in FIG. 15C is manufactured.
[0078]
Next, a pressing process is performed using the wedge prism array mold 42. As shown in FIG. 16D, a glass material 44 is poured into a wedge prism array mold 42, pressed on by a pressing metal 43, and pressed from above to perform pressing.
[0079]
In this way, a wedge prism array 45 having a side view in FIG. 16E and a plan view in FIG. 16F is formed.
[0080]
Further, as shown in FIG. 16G, a necessary number (four in FIG. 16G) of the semiconductor wafer 31 made of, for example, GaAs on which the optical element of the CLC structure is formed and the wedge prism array 45 are bonded.
[0081]
Thereafter, the device is cut into individual devices to obtain an optical device in which the target optical element 17 and the wedge prism 20 are bonded.
[0082]
On the other hand, the manufacturing process by the glass grinding technique is performed according to the following process.
First, as shown in FIG. 17A, a semiconductor wafer 31 made of, for example, GaAs, on which an optical element having a CLC structure is formed, and a glass wafer 30 are bonded together.
As described above, the bonding may be performed by bonding with an adhesive as described above, or after forming SOG (spin-on glass) on the surface of the semiconductor wafer 31 and then lapping the surface of the SOG.
In this way, as shown in FIG. 17B, a laminated body 32 composed of the glass wafer 30 and the semiconductor wafer 31 is formed.
[0083]
Next, as shown in a perspective view in FIG. 17C and a side view in FIG. 17D, the surface of the glass wafer 30 is obliquely ground with a donut-shaped diamond grindstone 46 to form an inclined surface. The diamond grindstone 46 used at this time sets conditions such as the roughness of the grindstone and the grinding speed so that an optical grade grinding surface can be obtained.
[0084]
Thus, a wedge prism array 45 is formed on the semiconductor wafer 31 as shown in FIG. 17E.
[0085]
Since the wedge prism 20 is manufactured by the glass press technique, the glass grinding technique, the glass mold technique or the like as described above, the shape thereof has a relatively large degree of freedom.
[0086]
Further, the size of the wedge prism 20 can be reduced as follows.
FIG. 11 shows a side view of another example (hereinafter referred to as Example 2) of the optical apparatus of the present invention. The optical device according to the second embodiment has an output light L_FAnd return light L_RWhile the position where the light passes through is set to the same position as in the first embodiment, the surface on which the reflection surface 19 is formed is formed thinner. By reducing the thickness of the portion where the reflecting surface 19 is formed, the horizontal movement distance of the reflected light is reduced, and the left and right sizes of the optical element 17 and the wedge prism 20 in the figure can be reduced.
[0087]
Since other configurations are the same as those of the optical device of the first embodiment, portions corresponding to those of the first embodiment are denoted by the same reference numerals, and redundant description is omitted.
Various signals can be detected in the same manner as in the first embodiment.
[0088]
Next, FIG. 12A shows a side view of another example (Example 3) of the optical apparatus of the present invention.
In the optical device of FIG. 12A, the upper surface of the wedge prism 201 is a downward wedge surface as shown in FIG. 12B or an upward wedge surface as shown in FIG. 12C with respect to the optical device of Example 1 described above. It is a configuration.
[0089]
The reflected light is divided on the left and right sides of the wedge surface, and two two-divided photodetectors PD_Three, PD_FourAnd PD_Five, PD₆And receive the focus servo signal. In this case, it is not necessary to form the knife edge surface 22 on the semiconductor laser LD.
Since other configurations are the same as those of the optical device of the first embodiment, portions corresponding to those of the first embodiment are denoted by the same reference numerals, and redundant description is omitted.
[0090]
The focus servo signal is detected in the optical apparatus of the third embodiment as follows.
Two two-divided photodetector PD_Three, PD_FourAnd PD_Five, PD₆When the in-focus state, the received light amount of the two-divided photodetector is equal, that is, PD_Three= PD_Four, PD_Five= PD₆Arrange so that In this case, in FIG. 12B and FIG. 12C, the light reflected by the wedge prism surface is irradiated to the two-divided photodetector as indicated by solid lines in the figure.
[0091]
Here, when the irradiated portion 12, for example, the disc is displaced, the light reflected at the center of the upper surface of the wedge prism 201 is the same as that at the time of focusing, and the light beam irradiated on the upper surface of the wedge prism 201 is shown in FIGS. As shown by the dotted line in the figure, the spot irradiated with the light reflected by the detector spreads outward in FIG. 12B and inward in FIG. 12C. Therefore, the amount of received light is greater in the outer photo detector in FIG. 12B and in the inner photo detector in FIG. 12C.
[0092]
When the irradiated portion 12 is displaced in the opposite direction, the amount of received light is increased in the same way in the case of FIG. 12B but on the outer side in the case of FIG. 12C.
[0093]
Thus, for example, {(PD_Three-PD_Four+ (PD₆-PD_Five)} As a detection signal, the difference signal becomes 0 in the case of focusing, and when the irradiated portion 12 is displaced, a signal having a different sign is obtained according to the direction, and detection of the focus servo signal is performed. It can be performed.
[0094]
The detection of various signals such as tracking servo signals and RF signals can be performed in the same manner as in the first embodiment.
[0095]
In the optical apparatus according to the present invention, when a magneto-optical signal is further detected, a polarization detection system such as an analyzer (polarizer) is basically arranged in front of a photodetector for detecting a focus servo signal, or a tracking servo is used. A magneto-optical signal can be detected by adding an analyzer (polarizer) on a photodetector near the confocal that detects the signal, or by adopting any arrangement.
An example of an optical apparatus that detects a magneto-optical signal to which the present invention is applied will be described below.
[0096]
FIG. 18 shows a perspective view of an example of an optical apparatus (hereinafter referred to as Example 4) that detects a magneto-optical signal to which the present invention is applied. The optical device of the fourth embodiment shown in FIG. 18 is configured by arranging two analyzers 23a and 23b on the upper surface 20b of the wedge prism 20 with respect to the optical device of the first embodiment. The portion where the analyzers 23a and 23b are formed functions as a reflecting surface.
[0097]
The analyzers 23a and 23b have an angle of 90 ° between the detection directions of the analyzers and return light L_RAre formed so that the angle formed by the directions of the analyzers 23a and 23b is 45 °. That is, for example, the return light L_RAre arranged so that the direction of the analyzer 23a is 45 ° clockwise and the direction of the analyzer 23b is 45 ° counterclockwise.
Since other configurations are the same as those of the optical apparatus of the first embodiment, the same reference numerals as those of the optical apparatus of the first embodiment are used, and redundant description is omitted.
[0098]
In this optical apparatus, the tracking servo signal and the focus servo signal are detected in the same manner as in the optical apparatus of the first embodiment.₁, PD₂The tracking servo signal is detected with, and the two-divided photodetector PD_Three, PD_FourThe focus servo signal can be detected at.
[0099]
The magneto-optical signal is detected by dividing the light that has passed through the analyzers 23a and 23b into two-divided photodetectors PD._Three, PD_FourDetects the received light respectively. At this time, the direction of polarization of the received light is rotated with respect to the direction of polarization of the outgoing light, so that two photodetectors PD_ThreeAnd PD_FourThe amount of light received at the is large or small.
[0100]
Thus, for example, the difference signal (PD_Three-PD_Four) As a detection signal, the sign of the detection signal changes in accordance with the direction in which the polarization direction is rotated, so that the magneto-optical signal can be detected.
[0101]
FIG. 19 is a perspective view of still another example (hereinafter referred to as Example 5) of an optical apparatus that detects a magneto-optical signal to which the present invention is applied. The optical device of Example 5 shown in FIG. 19 is a two-divided photodetector PD formed near the confocal position with respect to the optical device of Example 1.₁, PD₂Two analyzers 23 a and 23 b are arranged and formed on each of them, and a reflecting surface 19 is arranged and formed on the upper surface 20 b of the wedge prism 20.
[0102]
The analyzers 23a and 23b have an angle of 90 ° with respect to the detection direction, and return light L_RAre formed so that the angle formed by the detection directions of the analyzers 23a and 23b is 45 °. That is, for example, return light L_RAre arranged so that the direction of the analyzer 23a is 45 ° clockwise and the direction of the analyzer 23b is 45 ° counterclockwise.
Since other configurations are the same as those of the optical device of the first embodiment and the optical device of the fourth embodiment, the same reference numerals as those of these optical devices are used and redundant description is omitted.
[0103]
The magneto-optical signal is detected by dividing the light passing through the analyzers 23a and 23b and reflected by the reflecting surface 19 into a two-divided photodetector PD._Three, PD_FourDetects the received light respectively. At this time, the direction of polarization of the received light is rotated with respect to the direction of polarization of the outgoing light, so that two photodetectors PD_ThreeAnd PD_FourThe amount of light received at the is large or small.
[0104]
Thus, for example, the difference signal (PD_Three-PD_Four) As a detection signal, the sign of the detection signal changes in accordance with the direction in which the polarization direction is rotated, so that the magneto-optical signal can be detected.
[0105]
The detection of various signals such as tracking servo signals and RF signals can be performed in the same manner as in the first embodiment.
[0106]
FIG. 20 is a perspective view of still another example (hereinafter referred to as Example 6) of an optical apparatus that detects a magneto-optical signal to which the present invention is applied. The optical device of Example 6 shown in FIG. 20 is formed by arranging two polarization hologram elements 25a and 25b on the surface of the wedge prism 20 with respect to the optical device of Example 1. The portion where the polarization hologram elements 25a and 25b are formed has a function as a reflecting surface.
[0107]
The polarization hologram elements 25a and 25b have an angle of 90 ° with respect to the detection direction, and the emitted light L_FThe pattern is formed such that the angle formed by the directions of the polarization hologram elements 25a and 25b with respect to the main polarization direction is 45 °. That is, for example, the direction of the polarization hologram element 25a is 45 ° clockwise and the direction of the polarization hologram element 25b is 45 ° counterclockwise with respect to the polarization direction of the emitted light.
[0108]
The photodetector PD of the light receiving unit 15_Three, PD_FourAre formed apart from each other in order to receive the reflected light that has been split and diffracted by the polarization hologram elements 25a and 25b.
The other configurations are the same as those of the optical device of the first embodiment and the optical devices of the fourth and fifth embodiments, and therefore, the same reference numerals as those of the optical devices are used and redundant description is omitted.
[0109]
In this optical apparatus, the return light L from the irradiated portion 12_RIs reflected by the second reflecting mirror 21 and applied to the polarization hologram elements 25a and 25b, and then diffracted by the polarization hologram elements 25a and 25b. The diffracted light obtained at this time travels in a predetermined direction by the diffraction patterns of the polarization hologram elements 25a and 25b, and the photodetector PD._ThreeAnd PD_FourIs incident on.
[0110]
Note that detection of various signals such as a focus servo signal, a tracking servo signal, and an RF signal can be performed in the same manner as in the first embodiment.
[0111]
The magneto-optical signal is detected by the two-divided photodetector PD used for detecting the focus servo signal._Three, PD_FourTo do. The magneto-optical signal is the output light L_FSince the polarization direction is rotated in either direction according to the signal content with respect to the polarization direction, the polarization direction is diffracted by the polarization hologram elements 25a and 25b and received and detected by the two-divided photodetector. For example, the difference signal (PD_Three-PD_Four) Is a detection signal, the sign of the detection signal changes in accordance with the direction in which the polarization direction is rotated, so that the magneto-optical signal can be detected.
[0112]
As described above, in the optical device of each embodiment, an optical device such as an optical pickup that is compact as a whole, has a simple diffraction grating pattern, and does not require precise adjustment can be manufactured.
[0113]
In addition, since the optical disk can be efficiently irradiated with the semiconductor laser light, it can be used as an optical pickup for a super-resolution reproduction dedicated disk or a recording / reproduction disk. In particular, since an extremely small and light weight can be achieved, an optical pickup that is optimal for a data disk that requires a high random access speed can be configured.
[0114]
Further, the irradiated portion 12 changes not only the optical disc with the concavo-convex recording pit like a normal CD, the magneto-optical disc or the micro disc for recording with the light and magnetic field applying means, but also the optical characteristics such as the reflectance by the phase change The present invention can also be applied to an optical pickup of a phase change disk according to the recording mode.
That is, the recording is the outgoing light L_FAnd reproduction is performed for each return light L._RBy adopting a configuration in which a photodetector PD receives and detects a reproduction signal, these disks can be applied as the irradiated portion 12.
[0115]
Each of the above-described examples is an example of the present invention, and various other configurations are possible without departing from the gist of the present invention.
[0116]
【The invention's effect】
  According to the present inventionSince the number of components can be reduced and a simple optical device can be configured, it is possible to simplify processes such as an assembly process and a position adjustment process such as an optical axis, and the optical apparatus can be easily manufactured at low cost.
[0117]
In addition to reducing the size and weight of the optical device, the operation of the device, that is, the response speed is improved.
[0118]
Since the emitted light can be used effectively, it can be reproduced and recorded with a lower output of the semiconductor laser LD than the similar system using the conventional hologram element, thereby reducing power consumption and being thermally stable. Turn into.
[0119]
As the power consumption decreases, the linear velocity in recording and reproduction can be increased with the same power consumption as before.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an example of an optical device of the present invention.
FIG. 2 is an enlarged view of a side surface of a light emitting unit of the optical element in FIG.
FIG. 3A is a side view of the optical element of FIG.
B is a plan view of the optical element of FIG.
FIG. 4 is a configuration diagram of an optical system for explaining focus servo signal detection by a normal knife edge method.
FIG. 5A is a schematic configuration diagram of an optical system for focus servo signal detection by a knife edge method in the optical apparatus of the present invention.
B is a curve of the focus servo detection signal.
FIG. 6 is an example of a knife edge surface formation pattern.
A A pattern example identical to the pattern shown in FIG. 3B.
B is an example of a pattern different from FIG. 6A.
FIG. 7 is a diagram showing the relationship between the numerical aperture on the optical element side of the irradiated portion and the amount of light used for detection of the focus servo signal.
FIG. 8 is a diagram illustrating a relationship between a defocus amount and a detection signal of a focus servo signal.
A This is the case when the magnification of the optical system is 5 times.
B: The case where the magnification of the optical system is 3.5 times.
FIGS. 9A and 9B show another example of the formation pattern of the knife edge surface.
FIGS. 10A and 10B are other examples of a knife edge surface formation pattern. FIGS.
FIG. 11 is a side view of an optical element of another example of the optical apparatus of the present invention.
FIG. 12 is a side view of an optical element of still another example of the optical apparatus of the present invention.
A is a side view seen from a plane perpendicular to the first reflecting mirror.
B, C It is the side view seen from the surface parallel to the 1st reflective mirror.
13A to 13E are manufacturing process diagrams of an example of a method for manufacturing an optical device according to the present invention.
14A and 14B are manufacturing process diagrams of an example (another example) of the manufacturing method of the optical device according to the present invention.
FIGS. 15A to 15C are manufacturing process diagrams of still another example of the method for manufacturing an optical device according to the present invention. FIGS.
FIG. 16DG  It is one manufacturing process figure of the further another example of the manufacturing method of the optical apparatus of this invention.
17A to 17E are manufacturing process diagrams of still another example of the method of manufacturing an optical device according to the present invention.
FIG. 18 is a perspective view of an example of an optical apparatus that detects a magneto-optical signal to which the present invention is applied.
FIG. 19 is a perspective view of another example of an optical apparatus for detecting a magneto-optical signal to which the present invention is applied.
FIG. 20 is a perspective view of still another example of an optical apparatus that detects a magneto-optical signal to which the present invention is applied.
FIG. 21 is a configuration diagram of a conventional optical pickup.
FIG. 22 is a configuration diagram of a conventional optical pickup using a hologram element.
FIG. 23 is a configuration diagram of a conventional optical pickup for a mini disc (MD).
[Explanation of symbols]
11 Optical pickup
12 Irradiated part (optical disc)
13 First reflector
14 Light emitting part
15 Receiver
16 Semiconductor substrate
17 Optical elements
18 Convergence means
19 Reflecting surface (third reflecting mirror)
20, 201 Wedge prism
θ Wedge angle
21 Second reflector
21 'Mirror surface
22 Knife edge surface
23, 23a, 23b Analyzer
25, 25a, 25b Polarization hologram element
30 Glass wafer
31 Semiconductor wafer
32 Laminate
32a element
33 Wiring board
34 Contact hole
36 Adhesive
37 SOG
40 Trapezoidal column mold
41 U-shaped mold
42 Mold for wedge prism array
43 Press fitting
44 Glass material
45 wedge prism array
46 Diamond wheel
50 Knife edge
55 Differential Amplifier
S Confocal position plane
LD semiconductor laser
PD [PD₁, PD₂, PD_Three, PD_Four, PD_Five, PD₆] Photo detector
PD_A, PD_B  Photo detector
L_F    Outgoing light
L_R    Return light

Claims (3)

A light emitting unit;
Converging means for convergently irradiating the irradiated portion with the emitted light from the light emitting unit,
A light receiving portion arranged by including the confocal vicinity of the return light from the irradiated portion by the convergence means;
A first reflecting mirror for guiding the emitted light from the light emitting unit to the converging means;
A second reflecting mirror disposed in the vicinity of the confocal point;
A wedge prism having a reflective surface formed on the surface ;
The light emitting unit, the light receiving unit, the first reflecting mirror and the second reflecting mirror, and the wedge prism are formed on a common semiconductor substrate, and the return light is formed on the semiconductor substrate. An optical device comprising a non-reflective surface formed on the outer side surrounding an optical diffraction limit region, wherein a focus servo signal is detected by using the knife-edge method with the non-reflective surface .   The optical apparatus according to claim 1, wherein the light receiving unit disposed in the vicinity of the confocal includes a plurality of light receiving elements, and a tracking servo signal is extracted by the light receiving elements. A light emitting unit;
Converging means for convergently irradiating the irradiated portion with the emitted light from the light emitting unit,
A light receiving portion arranged by including the confocal vicinity of the return light from the irradiated portion by the convergence means;
A first reflecting mirror for guiding the emitted light from the light emitting unit to the converging means;
A second reflecting mirror disposed in the vicinity of the confocal point;
A wedge prism having a reflective surface formed on the surface;
The light emitting unit, the light receiving unit, the first reflecting mirror and the second reflecting mirror, and the wedge prism are formed on a common semiconductor substrate, and the return light is formed on the semiconductor substrate. It has a non-reflective surface formed on the outside surrounding the optical diffraction limit region, and the focus servo signal is detected by using the knife-edge method with the non-reflective surface.
An optical pickup characterized by that.

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