JP2001249228A - Polarized light separating element and optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical head of high reliability with little variation by aging and temperature while realizing the simplification and non-adjustment of the assembly process, and to realize its miniaturization by a large functional combination. SOLUTION: Functions, such as an optical path length regulating function which makes optical path length of outward trip light flux differ from optical path length of return trip light flux, a polarized light separating function for detecting a magneto-optical signal, or a light flux reflecting function for guiding a part of light flux to a second photodetector for a light-emitting power detection, are assembled on an integral optical member. Thus, the optical member constitutes the cover of package of the optical head, and houses a photodetector and a light emitting element integrally.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head used for an optical disk device and the like, and more particularly to an optical member or a polarization splitting element which is a constituent member of the optical head.

[0002]

2. Description of the Related Art A conventional optical head of this type is disclosed in US Pat.
P-No. As disclosed in US Pat. No. 4,764,912, a bulk (square) type optical component obtained by shaving and polishing optical glass is frequently used. In particular, an optical head which also detects a magneto-optical signal requires a polarizing prism or the like. there were.

[0003]

However, in the above-mentioned optical head, the volume occupied by the bulk type optical component is large,
Since the processing itself is expensive and the location at the time of assembly is diversified, it has been difficult to reduce the size, cost and weight of the apparatus. Therefore, the performance in terms of access speed was sacrificed, which prevented its spread in the market. Also, the layout of the optical system, the light emitting element and the light receiving element are separated,
Exclusive optical components are used for the forward optical system starting from the light emitting element and the return optical system starting at the light receiving element as the end point, and this is extremely wasteful in terms of the number of components and space efficiency. Further, since the positional accuracy is accumulated, it is difficult to secure the positional accuracy of the optical system, and a complicated adjustment operation is required to remove the initial offset of the detection signal, particularly the focus error signal. The present invention has been made to solve such problems, and its main objects are to drastically reduce the number of optical components, reduce the size and weight, and simplify the adjustment process.

[0004]

The optical member and the method of manufacturing the same according to the present invention for solving the above-mentioned problems are: (1) an integral member through which a divergent or convergent forward light beam and a backward light beam are transmitted; (2) Regarding the above (1), the optical member is integrally formed and has a step on the surface, and (3) the above (1). The optical member is formed by bonding at least two separate parts, and a step is formed on the surface in a state where the separate parts are bonded. Is formed integrally with a transparent resin to form a step on the surface. (5) As a manufacturing method of the above (1), the optical member is integrally press-molded with glass to form a step on the surface. Features.

[0005] The configuration of another optical member of the present invention is as follows.
(6) Locally having at least a binary refractive index, the outward luminous flux and the return luminous flux are respectively transmitted through regions having different refractive indexes, and the optical path length of the outward luminous flux and the optical path length of the return luminous flux are different. (7) The forward light beam and the backward light beam are transmitted through the integrated member, and the refractive power of the region where the forward light beam is transmitted is different from the refractive power of the region where the backward light beam is transmitted. (8) In the above (7), a convex or concave curved surface is locally formed on the surface.

Also, an optical head according to the present invention comprises: (9) an optical member according to the above (1), (6) or (7), and a light-receiving element disposed substantially behind and behind the optical member; A light-emitting element disposed slightly higher or slightly lower than the light-receiving surface of the light-receiving element, wherein the outward light flux emitted from the light-emitting element and the return light flux reflected by the optical recording medium and traveling toward the light-receiving element are both optical members. (10) Regarding (9) above, detecting a change in the spot shape of the return light beam on the light receiving element and generating at least a focus error signal; (11) Regarding (9), the optical member is made of transparent resin, has a flange on the outer periphery, and a gate for injection molding is provided on the flange portion. (12) Regarding (9), the optical member is made of transparent resin. Formed of the optical member (13) Regarding (9) above, forming a diffraction grating or a hologram on the front or back surface of the optical member, 14) In regard to the above (13), the hologram is
The hologram is characterized in that the hologram is a blazed hologram blazed in a triangular shape in units of a diffraction groove pitch.

According to another aspect of the present invention, there is provided an optical head comprising: (15) the optical member according to (1), (6) or (7), and a light receiving element disposed substantially behind and behind the optical member. ,
Equipped with a light emitting element arranged slightly higher or slightly lower than the light receiving surface of the light receiving element, and a package holding the light receiving element and the light emitting element, in cooperation with the optical member and the package,
Sealing the light receiving element and the light emitting element.
Regarding item 5), the optical member and the package are fixed to each other via an adhesive, and the adhesive has a lower hardness after curing than the material of the optical member and the package.

Further, the present invention provides (17) a polarization splitting element and a method for manufacturing the same, comprising: a first optical member; and a second optical member bonded to the first optical member. Forming a depression including an inclined surface on the optical member, coating the inclined surface with a multilayer thin film of a dielectric material to have a polarization separating function, filling the depression with a transparent resin or liquid, and bonding the first and second optical members; (18) Regarding the above (17), the refractive indices of the first optical member, the second optical member, and the transparent resin or liquid filling the depression are substantially the same, (19) Regarding the above (17), the light beam incident on the inclined surface is a convergent light beam or a divergent light beam having an NA (numerical aperture) of 0.15 or less in the medium conversion.
Regarding 7), a plurality of slopes and depressions are formed in an integrated optical member, and a plurality of slopes are coated with a multilayer thin film of a common dielectric. (21) The method described in (17) above is described. (2) optical member, after the slope is coated with a dielectric multilayer thin film to have a polarization separating function, the depression is filled with a transparent resin, and the first and second optical members are bonded, and then an annealing process is performed. (23) As a method for manufacturing (22), a polarizing plate or a polarizing film is fixed or held on or in the surface of
After fixing or holding a polarizing plate or a polarizing film on the surface or inside of the optical member, an annealing process is performed.

Another structure of the optical head according to the present invention is as follows.
4) using the polarization beam splitting element described in (17) or (22) above, receiving a return light beam transmitted through the polarization beam splitting element with a light receiving element, and detecting a magneto-optical signal;
5) Using the polarization beam splitter described in (17), the forward beam and the backward beam are respectively transmitted through the first and second slopes having a polarization separation function, and the return beam transmitted through the second slope of the polarization beam splitter. (26) Regarding the above (25), the polarization plane of the forward luminous flux is made to coincide with the polarization transmission direction of the first slope, and the polarization of the return luminous flux is detected. The polarization separation direction of the second inclined surface is set to be rotated by approximately 45 degrees with respect to the surface, and (27) the optical member separated into a mirror-finished region and a diffuse reflection region having fine irregularities (2) a configuration in which a forward light beam and a backward light beam are transmitted through a mirror-finished region;
8) By using an optical member separated into a region where the anti-reflection coating is deposited and a non-coating region where the anti-reflection coating is not deposited, the central portion of the divergent light beam emitted from the light emitting element is transmitted through the anti-reflection coating region, Reflecting a part of the divergent light beam in the coating area, and having a second light-receiving element for light emission power detection for receiving the reflected light;
(29) With regard to the above (28), the second light emission power detection
And (30) that the first and second light receiving elements are formed on an integrated substrate, and that the first and second light receiving elements receive a return light beam that is reflected light from the optical recording medium. An optical member having a reflection surface formed in a region through which the forward light beam and the backward light beam do not pass is provided, and a second light receiving element for light emission power detection that reflects a part of the forward light beam on the reflective surface and receives the reflected light is provided. (31) In the above (30), the reflection surface is a slope or a curved surface, and the surface reflection light beam or the total reflection light beam of the slope or the curved surface is configured to be received by the second light receiving element. I do.

[0010]

According to the above construction of the present invention, (A) the optical components relating to the forward optical system and the return optical system can be shared, and the light emitting element and the light receiving element can be stored in a common package. (B) The optical path length in the forward path and the optical path length in the return path can be set to different values, and the spot can be accurately irradiated on the light receiving element, which is particularly effective for removing the initial offset of the focus error signal. (C) Adjustment for removing the initial offset of the focus error signal can be simplified. (D) Positioning of the optical component and the light receiving element is facilitated. (E) A polarization separation element for detecting a magneto-optical signal can be combined with and integrated with another optical component. (F) The output power of the light emitting element can be monitored without adding any special components. Numerous effects occur mainly on the basis of the above. As a whole, the adoption of an integrally formed optical member and a polarizing element can realize a great combination of functions, downsizing, and simplification of the adjustment process.

[0011]

(Embodiment 1) FIG. 1 is a side sectional view showing an optical head according to Embodiment 1 of the present invention, and FIG. 2 is a side sectional view of an optical pickup using the present optical head. In FIG. 1, reference numeral 10 denotes a light emitting element made of a semiconductor laser; 120, an optical member called a cover plate; 130, a hologram that is a curved diffraction groove for separating light beams; 170, a light receiving element that is a multi-division photodiode; Reference numeral 80 denotes a package that holds and stores the light emitting element 10 and the light receiving element 170. The package 80 is a frame having only one opening,
The opening surface is covered with the optical member 120 and adhered and sealed. An optical head 1 of this embodiment is formed by combining these elements. The optical head 1 has a light source and a detection optical system integrated with each other, and has a complex function as described later, and has a small cubic external shape of about 5 mm square as a whole.

In FIG. 2, reference numeral 2 denotes an optical pickup case, in which the above-described optical head 1 is housed. The mirror 40 and the objective lens 50 are also housed, and are driven integrally (focusing servo, tracking servo) as a whole. The objective lens 50 is the only lens, and forms a finite compact optical system. Specifically, the distance between the object point and the image point (total track) of the objective lens 50 is as short as about 15 mm, so that the case 2 is small and lightweight, and the entire optical pickup is about 2 g in this embodiment.
r and lighter. Reference numeral 60 denotes an optical recording medium, that is, an optical disk, on which a track groove (not shown) having a minute pitch is formed on a recording surface.

In FIG. 1, an optical member 120 called a cover plate has a step L formed on a surface near the light emitting element 10 and is divided into a plane portion 121 and a step portion 122. The optical member 120 is made of PMMA (polymethyl methacrylate), PC (polycarbonate), or A
Injection molding of an optical resin such as PO (amorphous polyolefin) can be performed by a simple method, and low-melting glass can be molded by a hot press. Here, it is practically impossible to mount the light emitting element 10 on the same plane as the light receiving surface of the light receiving element 170, that is, the surface. This is because the light receiving element 170 is manufactured by a semiconductor manufacturing process, and a semiconductor wafer is diced into small pieces to form an outer shape. Therefore, a through hole cannot be formed at the center. It is also conceivable to mount the light emitting element 10 on the light receiving element 170.
4 (see FIG. 4) and the opposite surface 12 are interfaces for internal reflection of the laser chip, so they must not contact the light receiving element 170 or the like, and must be fixed using the bottom surface 14 as shown in FIG. There is. In the present embodiment, in order to minimize the number of components, a depression 171 and a slope 172 are formed at substantially the center of the light receiving element 170 as shown in FIGS. 3 and 4, and the light emitting element 10 is horizontally fixed to the depression 172. Then, the light beam 100 emitted from the emission surface 11 is reflected by the inclined surface 172 and emitted as a divergent light beam 101a in a direction perpendicular to the plane of the light receiving element 170. The inclined surface 172 is inclined at approximately 45 °, and can be relatively easily formed on the light receiving element 170 made of a silicon substrate together with the depression 171 by anisotropic etching. When a thin gold film is deposited on the slope 172, a reflection surface having excellent reflection efficiency can be obtained.

Here, it should be noted that when the light emitting element 10, that is, the laser chip is mounted as described above,
As shown in FIG. 4, a virtual light emitting point 1 obtained by mirror-moving the light emitting point 14 of the light emitting element 10 on the slope 172 of the light receiving element 170 as a boundary.
5 is necessarily lower than the light receiving surface of the light receiving element 170 (FIG. 4).
Shift to the left). At the present time, the technology of the surface emitting type semiconductor laser has not been established, the light receiving element and the light emitting element cannot be integrally manufactured in a continuous process in a completely monolithic type. Is mounted on the light receiving element 170, and the slope 17
The best method is to emit the light beam 101f in the vertical direction using the light emitting device 2. Therefore, the virtual light emitting point 15 is located at a position lower than the light receiving element 170, and specifically lowers by about 0.08 mm in this embodiment.

[0015] If you decide to increase the number of parts,
For example, a stem (rectangular metal block, not shown) is fixed to the surface of the light receiving element 170, and the light emitting element 10
May be mounted in parallel (that is, perpendicular to the light receiving element 170). In this case, the light emitting point of the light receiving element 10 is shifted upward from the light receiving element (not shown). In any case, the light emitting point must be slightly shifted upward or downward with respect to the light receiving surface of the light receiving element 170 for mounting.

Next, returning to FIGS. 1 and 2, the optical behavior of the optical head of this embodiment will be described. The forward light beam 101f, which is a divergent light beam emitted from the light emitting element 10, is the optical member 1
The hologram 13 formed on the surface of the optical member 120 is incident on and transmitted through the substantially central portion of the optical member 120, that is, the flat portion 121.
0 is emitted, and the 0th-order light 102f (light flux not diffracted by the hologram 130) enters the mirror 40 and the objective lens 50. Light flux 10 condensed by objective lens 50
3f forms an image of the spot 104 on the recording surface of the optical recording medium 60. The light beam 103r reflected by the optical recording medium 60 follows the reverse optical path, becomes the light beam 102r, and becomes the hologram 130r.
Return beam 10 which is +/- 1 order light diffracted into
1r passes through the inside of the optical member 120, exits from the step 122, and enters the light receiving surface of the light receiving element 170, that is, the surface.

As shown in FIGS. 5 and 6, the hologram 1
Numeral 30 is divided into two in the radial direction of the optical recording medium 60, that is, in the direction perpendicular to the track grooves, or in other words, in the push-pull modulation direction. Two types of hologram patterns 1
The patterns 30a and 130b are designed so as to diffract and separate into two +/- 1 order light beams, that is, a total of four return light beams 101r, and at the same time, to generate remarkable astigmatism. As shown in FIG. 7, the light-receiving element 170 has a strip-shaped light-receiving pattern 173 which is divided into four parts independently by a semiconductor process.
The light beam 101r is condensed individually into the light receiving spots 10
5 is formed. The shape of the light receiving spot 105 changes according to the focus error due to the astigmatism described above.
The light quantity taken into 73 changes. In this embodiment, the change in light amount is photoelectrically converted (so-called astigmatism method) as a focus error signal, and the light amount difference between light beams transmitted through the two-partitioned patterns 130a and 130b of the hologram 130 is photoelectrically converted as a track error signal (so-called astigmatic method). Push-pull method).

In FIG. 6, in the reference state where the amount of the focus error is zero, the return light beam 101r irradiated onto the light receiving element 170 is located at the center of the astigmatic difference (focal line interval) D, that is, the minimum confusion circle 103. Must be set to position. As a result, astigmatism D is evenly distributed before and after the position of the circle of least confusion 103 as shown in FIG. 6, so that when the focus error is in the reference state, as shown in FIG. 7 or FIG. The light receiving spot 105 having the shape of the circle of least confusion is formed, and the light amount taken into each of the channels 173a to 173d of the light receiving pattern 173 becomes uniform. Here, of each channel, (173a-173c) + (173d-173b) =
The focus error signal 106 generated by the addition / subtraction operation of (173a + 173d)-(173b + 173c) becomes zero. Next, when the distance between the optical recording medium 60 and the objective lens 50 changes and the amount of focus error increases, the convergence degree of the return light beam 101r changes according to the principle of geometrical optics, and the focal line 1
The position 04 shifts in the optical axis direction. Then, FIG. 8 (a)
Alternatively, as shown in FIG. 8C, the shape of the light receiving spot 105 changes to an ellipse, the amount of light taken into each channel of the light receiving pattern 173 changes, and the level of the focus error signal 106 changes. The astigmatism is set to D, and the objective lens 50
Let R be the magnification (lateral magnification: image side / object point side), and let d be the value indicating the focus error of the area where the focus error signal monotonically changes by distance: d = D * (R * R ) / 2, and the focus error signal 106 changes with a curve as shown in FIG. In the case of the present embodiment, the magnification of the objective lens 50 is about 1 / depending on the processing difficulty and the distance between the object point and the image point.
Since it is set to four times, there is actually a relation of d = D / 32. The focus error signal 106 and the track error signal described above are used as error signals for focusing servo and tracking servo, respectively, and are controlled so that the spot 104 is accurately formed on the optical recording medium 60. In the present invention, the details of this servo system are not important, so detailed description is omitted.However, in order to accurately control the focusing servo, the focus error signal 106 is set to zero in the reference state, that is, a state where there is no initial offset. It is indispensable to set to.

As described above, in this embodiment, a finite optical system is formed, and as shown in FIGS.
The focal point of the objective lens 50 (the position of the spot 104) is in an optically conjugate relationship. In addition, the focal point of the return light beam 101r, in this case, the circle of least confusion 103, and the focal point of the objective lens 50 have a conjugate relationship. Accordingly, an optical conjugate relationship is established between the virtual light emitting point 15 and the circle of least confusion 103. Here, if the virtual light emitting point 15 and the minimum confusion circle 103 are located on the same plane in the optical axis direction, the light receiving spot shape on the light receiving element 170 becomes the minimum confusion circle 103 in the reference state, and the focus error signal 106 No offset occurs.

However, as described above with reference to FIG. 4, the virtual light emitting point 15 is approximately 0.08 m from the light receiving surface of the light receiving element 170.
m behind. Also shown in FIG.
The image plane 107 (which may be considered as a plane including the circle of least confusion 103) of the +/− 1 order light formed by the
Due to the geometrical optical aberration caused by 0 and the hologram 130, the hologram 130 is curved toward the front side (closer to the optical member 120), so that the displacement of the virtual light emitting point 15 can be automatically corrected to some extent. However, it is difficult to design such that the amount of curvature of field (indicated by W in FIG. 10) and the above-mentioned deviation amount of the virtual light emitting point 15 are matched under actual various constraint conditions. 0.08 also in the case of
mm, the amount of curvature of field W is as large as 0.13, which is excessive correction. Eventually, a displacement of 0.05 mm remains, which is about 1.6 μm when converted into the focus error signal 106.
m offset.

Therefore, if this state is left as it is, an initial offset will occur in the focus error signal 106. In this embodiment, in order to eliminate this, a step is provided on the surface of the optical member 120 called a cover plate as described above. The optical path length is adjusted. This is a very simple method and is a characteristic item of the present invention. Assuming that the step between the surfaces 121 and 122 is L, the refractive index of the optical member 120 is n (= 1.
5), and the optical path length to be corrected is Δs (= 0.13 mm−
0.08 mm = 0.05 mm), L = nΔs / (n−1) = 1.5 * 0.05 / (1.5
-1) Accordingly, when L = 0.15 mm is set, the positional difference between the virtual light emitting point 15 and the light receiving element 170 in the optical axis direction is corrected, and the initial offset of the focus error signal 106 is canceled.

Here, as a feature of this embodiment, a great advantage is that the step of adjusting the initial offset of the focus error signal can be eliminated. Since the accuracy of the step L is directly transferred to the mold accuracy, the step L has sufficient ability to fall within a dimensional tolerance of +/− 10 μm. When this tolerance is replaced with the change in the image plane position of the return light beam 101r based on the virtual light emitting point 15, Δs = L * (n-1) / n = 10 μm * (1.5-1)
/1.5 gives Δs = 3.3 μm. Further, when this Δs is converted into the amount of the focus error, that is, the initial offset, 3.3
/32=0.1 μm, which is a sufficient error with respect to a general offset allowable value (about 1 μm or less), so that the adjustment can be performed without any problem.

In the present embodiment, the surface 122 is higher than the surface 121 by the step L, that is, the direction of extending the optical path length on the return path with respect to the optical path length on the outward path. However, the luminous flux 101 on the return path
When the curvature of field of r is small (such as when the diffraction angle due to the hologram is small), the optical path length may be adjusted in a direction to shorten the optical path length of the return light flux 101r in reverse. A step may be formed so as to be concave with respect to 121.

In addition, in this embodiment, a so-called astigmatism method is used as a method for detecting the focus error signal 106. However, the present invention is not limited to this, and a focus error detection method such as a spot size method may be used. A similar problem may occur, and this can be said to be a unique problem in an optical head in which the light emitting element 10 and the light receiving element 170 are housed in the same package 80. Therefore, the present invention and this embodiment are widely applicable to this type of optical head. Also, the optical member 120 may be integrated by bonding a separate optical component instead of integral molding to form a step L on the surface, but the dimensional accuracy is slightly sacrificed.

Further, the optical member 120 in the present embodiment has a main purpose of being able to set the optical path length of the forward light beam 101f and the optical path length of the backward light beam 101r to different lengths, but conceptually. A member through which a plurality of light beams are transmitted, for setting the optical path lengths of the respective members freely. Therefore, other than the optical head, it is a device including an optical system,
Even when there are a plurality of convergent light beams and divergent light beams passing close to each other, the applicable range of the present invention can be expanded. (Embodiment 2) FIG. 11 is a side sectional view showing an optical head of Embodiment 2. In this embodiment, the basic specifications of the optical system are similar to those of the above-described embodiment, but the hologram 230 formed on one surface of the optical member 220 has a small triangular groove having a saw-tooth shape in the sectional direction of the diffraction groove. Is different from the blazed hologram composed of the optical member 220 in that a simple diffraction grating having a straight groove, that is, a grating 240 is formed on the other surface of the optical member 220.

Since the hologram 230 is blazed, the return light flux 201r, which is the primary light of diffraction, is known as is known.
Is diffracted to only one side. Therefore, the focus error signal cannot be detected by the operation detection using astigmatism as in the first embodiment. Instead, a focus error signal called a known double knife edge method (or Foucault method) is used instead. (Details omitted). Also, as is well known, the track error signal is obtained by using the +/− 1 order light 201 b generated by the grating 240.
It can be detected by the beam method. In the present embodiment, as described above, the number of diffracted light beams generated by the hologram 230 is half of that in the first embodiment, and thus the light receiving pattern (not shown) on the light receiving element 270 is shifted to one side.
0 and the package 80 can be made smaller. In addition, since the grating 240 can be formed integrally with the optical member 220, the function is being compounded. Therefore, a very small optical head can be provided as a functionally simple optical head that performs only reproduction of a CD (compact disk). In addition, the step portion 222 provided on the optical member 220 in FIG. 11 has a forward light beam (first-order diffracted light) 2 similar to the first embodiment.
It is provided to adjust the optical path length of 01r to cancel the initial offset of the focus error signal. (Embodiment 3) In Embodiment 1 described above, the optical member 120 having the step L is used in order to correct the positional deviation between the minimum confusion circle 103 of the return light beam 101r and the virtual light emitting point 15 in the optical axis direction. However, there are other means for correcting the optical path length.

Embodiment 3 shown in FIG. 12 is characterized in that the optical path length is changed by locally changing the refractive index. That is, the material B (3) having a different refractive index from the surrounding material A (321) in the optical member 320 partially.
22) is included. Specifically, a so-called two-color molding method using two-stage injection molding is used. For example, the material B (322) is injection-molded using a small mold, a part of the mold is replaced, and the periphery thereof is injection-molded with the material A (321). Specific materials are selected as: Material A: PMMA (refractive index: about 1.5) Material B: PC (refractive index: about 1.6) In this case, unlike the first embodiment, since an extreme difference in refractive index between resin and air is not used, it is necessary to maintain the difference in refractive index over a relatively long distance in the optical axis direction. Assuming that the refractive index of the material A is nA, the refractive index of the material B is nB, the optical path length to be corrected is ΔS, and the distance where the refractive index difference exists is L, L = nB * Δs / (nB−nA) = 1.6 * 0.05 / (1.6-15) Therefore, L may be set to 0.75 mm. Since the refractive index is a value unique to the material and can be managed very accurately, there is an effect that the optical path length can be adjusted more accurately than in the case of the first and second embodiments.

Instead of molding the material B (322) with the same end face as shown in FIG. 12, the material B (322) may be completely enclosed in the material A. Further, instead of the two-color molding method described above, a method of fitting a separate component having a different refractive index may be used, but the dimensional accuracy is slightly disadvantageous. Furthermore,
If the material is not limited to resin, there is a possibility that the refractive index may be locally changed by a method such as ion doping like a refractive index distribution lens (a so-called GRIN lens). (Embodiment 4) As Embodiment 4, another method for correcting the optical path length will be described. In FIG. 13, a lens surface 422 is locally formed on a plane 421 of the optical member 420. In this case, instead of using the refractive index difference as described above, the refraction by the lens is positively used to shift the focal length, that is, the focal position. A concave lens surface may be formed for a light beam whose optical path length is to be extended, and a convex lens surface may be formed for a light beam whose optical path length is to be shortened. However, in order to apply to the optical head described in the first embodiment, it is necessary to prevent unnecessary aberration from being applied to the light beam, and the lens surface 422 is desirably an aspherical shape. (Embodiment 5) FIGS. 14 and 15 show another embodiment of an optical head using a cover plate, that is, an optical member 520, as Embodiment 5. FIG. In this embodiment, the principle of the optical system is the same as that of the first embodiment, except that the shape of the optical member 520 is different and that the hologram element 530 is provided separately. Back surface 521 and hologram element 530
Of the alignment marks 52 on the surface 531 of the light-receiving element 570 at the same planar position.
2, 532, 572 are formed (FIG. 15). These alignment marks are used for positioning at the time of assembling, are crosshairs having a line width of about 10 μm, and are formed by etching, die engraving, or the like. In this type of optical head, the position accuracy of the light receiving spot 505 in the planar direction with respect to each channel of the light receiving pattern 573 of the light receiving element 570 is determined by the light receiving spot 50 in order to ensure the quality of the detection signal.
About 10% of the diameter of 5 (in other words, the circle of least confusion)
It must be: In this embodiment, the light receiving spot 50 is used.
5 has a diameter of about 150 μm, so that an alignment accuracy of +/− 15 μm is required. However, since the alignment marks (522, 532, 572) can be formed by etching using a photomask, each component can be marked with a positional tolerance of approximately +/− 5 μm. Therefore, when assembling and positioning each alignment mark so as to be seen through from the optical axis direction,
At the level of −10 μm, the light receiving pattern 573 and the light receiving spot 505 can be aligned. Next, a method of assembling the optical head according to the present embodiment will be described. In FIG. 14, the light receiving element 570
The light emitting element 10, which is a laser chip mounted on the depression 571 on the light receiving element 570, is fixed inside the frame of the package 80. This fixing method is usually based on a silver paste brazing method. The planar outer shape of the package 80 has an outer shape along the optical member 520,
The opening surface has good flatness. Next, a small amount of adhesive 85 is applied to the opening surface of this package,
20 is placed on the XY-θ table to precisely adjust the alignment mark 522 so that the alignment mark 522 matches the alignment mark 572, and the adhesive 85 is cured.

In this embodiment, an acrylic UV (ultraviolet) curable resin having excellent workability is used as the adhesive 85, and the adhesive hardness after the curing is smaller than that of the optical member 570 or the package 80. Very soft ones are selected. Since the package 80 requires a metal wiring mold, generally, a material such as epoxy resin or ceramics is used, while the optical member 520 uses an optical resin such as PMMA as described in the first embodiment. The coefficient of thermal expansion between the two differs by at least one digit. If these two materials are joined firmly, a stress is generated in the optical member 520 in response to a temperature change, and the optical characteristics such as transmitted wavefront aberration and birefringence are deteriorated. Therefore, the adhesive 85 for joining these members must be a very soft material that absorbs the difference in the coefficient of thermal expansion. It has been experimentally confirmed that if the hardness is about 60 on the Shore A scale after curing, the optical member 520 hardly suffers optical distortion. This hardness is positioned considerably softer than the hardness after curing of a general adhesive.
The hardness is about one digit lower than the hardness of the 20 materials (PMMA and PC). FIG. 16 shows a single body of the optical member 520. The optical member 520 has a plane shape of about 5 mm square, and a flange 524 is formed on an outer peripheral portion thereof. In the present embodiment, it is assumed that the optical member 520 is manufactured by injection molding using a metal mold.
4 employs a side gate system provided on the outer peripheral side surface.

The utility of the flange portion 524 is to firstly improve the overall rigidity and secondly to make the pressure of the resin flowing from the side gate type gate 525 uniform during molding. In the optical head of this embodiment, the optical member 520
Among them, the effective area in which the optical characteristics are to be ensured is a central area having a diameter of about 2 mm. When optical distortion due to stress is generated in the central portion 526, optical characteristics such as transmitted wavefront aberration and birefringence are deteriorated, and the reliability of information recording and reproduction of the optical head is significantly deteriorated. If the flange portion 524 is formed on the outer peripheral portion as in the present embodiment, the rigidity against external force and thermal deformation is greatly improved, and the stress generated at the central portion 526 is greatly reduced. Further, at the time of injection molding, the flow pressure of the resin is uniformly alleviated by the flange portion 524, and the residual stress after molding can be reduced to almost zero in the central portion 526, which also contributes to improvement of optical characteristics. . (Embodiment 6) Embodiment 6 is an embodiment relating to the polarization beam splitter of this embodiment. The polarization separation element described here is an optical element for use in an optical head or the like of a magneto-optical disk device that requires reproduction of a magneto-optical signal (MO signal). The gist of this example is that a significant shift from the conventional manufacturing method
An object of the present invention is to manufacture a polarization separation element for detecting a magneto-optical signal by a simple method. Hereinafter, this embodiment will be described with reference to FIGS.

In FIG. 17, the first optical member 620 has a depression 621 and an approximately 45-degree slope 622 at the center. The first optical member 620 is integrally injection-molded with an optical resin such as PMMA (polymethyl methacrylate), and can be manufactured in large quantities at low cost. On the other hand, the second optical member 6
Numeral 30 denotes a parallel flat plate, which is formed by ordinary optical glass cutting because it does not include a curved surface or a slope, and can be supplied in large quantities at low cost.

FIG. 18 shows a state in which the first optical member 620 and the second optical member 630 are combined to form the polarization splitting element 601. The depression 621 of the first optical member 620 is
It is filled with a resin 640 and covered with a second optical member 630.
The chemical composition of the resin 640 is adjusted so that the refractive index after curing is about 1.5, which is the same as that of the first and second optical members. The resin 640 filled in the depression 621 in a state where the first and second optical members are united functions as a triangular prism. In this embodiment, the resin 640 is U
Although a V (ultraviolet) curable resin is used and is cured by UV irradiation after merging, the present invention is not limited to this, and a thermosetting resin or the like may be used.

A multi-layered dielectric thin film is coated (deposited) on the slope 622 or on one side of the first optical member 620 as shown in FIG. 19, and a dielectric A (625) and a dielectric B (6) are coated.
26) are alternately stacked. This is a vapor deposition technique usually called a multi-coat, but in the present embodiment, it is considered that the first optical member 620 serving as the base material is a resin. That is, since the heat resistance temperature (glass transition point; TG) of the resin (PMMA is assumed in this embodiment) is extremely low at about 80 ° C. as compared with glass, the evaporation is performed at about 70 ° C. or less. ing. Further, since the coefficient of thermal expansion of the resin is large, the deposition material is selected in consideration of the occurrence of cracks due to stress strain with the deposition material. Specifically, dielectric A: MgF2 (magnesium boride), refractive index = 1.3 Dielectric B: ZrO2 (zirconium oxide), refractive index = 2.2: 0.3 to 0.4λ (λ is used (Wavelength: about 780 nm) and alternately laminated at a film thickness of P-polarized light or S-polarized light at their interface.
The difference in transmittance due to polarized light is accumulated so that desired polarized light transmission characteristics can be obtained.

Here, the portion filled with the resin 640 and the first optical member 620 in FIG.
626), it functions as a so-called polarization beam splitter. As a result of the experiment, finally, the number of layers of the deposited thin film has an optimum value in the range of 10 to 20 layers including the dielectrics A and B, and the S-polarized light transmittance with respect to the P-polarized light transmittance (transmittance of the P wave 651). (Transmittance of S wave 652), that is, a polarization transmission characteristic with an extinction ratio of about 100: 1 was obtained.

The combination of the vapor deposition materials described above is only one example. However, no change in characteristics or generation of cracks due to temperature change is recognized, and a sufficiently usable polarization separation element 601 can be supplied. However, in order to secure the extinction ratio,
It is premised that birefringence due to residual stress does not occur inside the resin 640 after assembly. Therefore, in the present embodiment, an annealing process is performed at the end of the manufacturing process to remove the residual stress inside the resin 640. As annealing conditions,
One hour at 70 ° C. is sufficient.

By the way, the angle of incidence θ (central value of 45) of the light beam to be incident on the polarization separation element 601 thus constructed
It should be noted that the above extinction ratio varies depending on the degree). That is, when the incident angle θ changes, the effective film thickness of the dielectrics A and B changes, so that the reflection and transmission characteristics of light rays change. The incident angle θ at which the extinction ratio (about 50: 1 or more) necessary for detecting the magneto-optical signal can be ensured even when the film thickness is controlled optimally is about +/− 9 in terms of the incident angle inside the polarizing element 601. It has been confirmed by optical simulations and experiments that the degree is limited. This corresponds to the convergence (or divergent light flux) of NA 0.15 in terms of NA (numerical aperture) in the medium.

In addition, in addition to the advantage that the manufacturing method is simple, the polarization separation element 601 shown in the present embodiment has the shape accuracy of the optical member 620, particularly the surface accuracy of the inclined surface 622, which is lower than that of the conventional glass shaving. There is a remarkable advantage that it is greatly reduced as compared with the case of the polarization beam splitter according to the first embodiment. The reason for this is that even if the surface accuracy of the slope 622 is poor, the resin 640 fills in the resin.
The refractive index of 40 is 0.0 with respect to the refractive index of the optical member 620.
Even if the difference is about three, if the slope 622 has a surface accuracy (undulation) of about 20 μ or less, it can be used without any problem in optical characteristics. This is the required value of the slope accuracy of the triangular prism that composes the conventional polarization beam splitter.
It means that it is relaxed about 20 times. Also, since parts can be manufactured by injection molding, very small external shapes can be manufactured. When applied to an optical head for magneto-optical detection, a very small detection optical system can be realized.

In this embodiment, the concave slope 622 is molded with the resin 640. However, if the peripheral sealing property is good, the same function can be exerted even if a liquid such as silicon oil is filled. In this case, there is an advantage that the problem of birefringence, which has to be considered in the resin 640, can be easily avoided. (Embodiment 7) FIG. 20 shows another embodiment of a polarization beam splitter as a seventh embodiment. In this embodiment, the function of the polarizing beam splitter described in the sixth embodiment is replaced by a polarizing film or a polarizing plate. In FIG. 20, an optical member 720 is formed of an optical resin, and a polarizing plate 740 is fitted and fixed in a depressed portion. The polarizing plate is made by mixing fine silver particles in a glass plate and stretching by heating to give a polarizing function.
Although the performance, that is, the extinction ratio is excellent, a polarizing film made by stretching a film containing iodine may be used. However, such a polarizing film generally has poor heat resistance, and has a drawback that a film stretched in a high-temperature environment is contracted by residual stress to deteriorate polarizing characteristics.

The advantage of this embodiment is that the polarizing plate or the polarizing film is lined with an optical member 720 which is much stronger than the polarizing plate or the polarizing film. It is difficult. Therefore, the polarization separation element 701 having excellent environmental resistance can be obtained.
However, if there is a slight shear shift in the adhesive layer that fixes the optical member 720 and the polarizing plate or the polarizing film 740, the polarizing plate or the polarizing film 740 may be slightly shrunk, and a long-term change may occur. In this embodiment, as a preventive measure, an annealing process is performed after the assembling process to reduce the residual stress in advance to prevent a change with time. Annealing conditions may be about 70 ° C. for about 1 hour. (Embodiment 8) Embodiment 8 is one in which the polarization separation element shown in Embodiment 6 is applied to an optical head for detecting a magneto-optical signal, and will be described below with reference to FIGS. 21, 22, and 23. FIG.

In FIG. 21, an optical member 820 is similar to the optical member 620 shown in the sixth embodiment, and the concave slopes are three types of slopes 828a, 828b, 828 having different slope directions.
c.

In the present embodiment, a hologram element 830 is used in place of the second optical member 630 of the sixth embodiment, and a polarization splitting element 801 is formed by these elements and functions are combined. Optical members 820 are provided on the concave slopes 828a to 828a to 828c.
Is filled in three places with a resin having a refractive index of about 1.5, which is equivalent to the refractive index of FIG. 22 shows the assembled optical head. The optical member 820 has the polarization separation function described in the sixth embodiment and also has the optical path length adjustment function of the return light beam described in the first embodiment. Is characteristic.

FIG. 23 is a plan view of the optical head viewed from the optical axis direction, and shows each component shown in FIG. In the figure, arrows 829 indicate the directions of the three slopes formed on the optical member 820, that is, the polarization transmission directions, and the slope 828c at the center is along the bonding surface of the light emitting element 10, that is, the direction of the polarization plane. On the other hand, slopes 828a and 828b on both sides
The slope is oriented in a direction rotated by approximately 45 degrees with respect to the direction of the slope 828c. In this embodiment, a magneto-optical disk is assumed as an optical recording medium (not shown), and the specification of the optical head is to detect the Kerr rotation angle in the return light beam 801r generated when reflected by the optical recording medium as a modulation component. The format is The light beam incident on the optical recording medium is linearly polarized light, and is P-polarized light with respect to the inclined surface 828c in this embodiment. Therefore, the outward light beam (801f in FIG. 22) passes through the slope 828c with almost no loss. The return light beam 801r (four light beams in total) is a pair of two light beams and tries to transmit through the slopes 828a and 828b. However, as described above, the slopes 828a and 828b are separated from each other by approximately 45 degrees in different directions. Due to the rotation, the Kerr rotation angle, which is the magneto-optical signal modulation component included in the return light beam 801r, can be differentially detected and detected after being polarized in the orthogonal 45-degree direction.

By the way, the 3 formed on the optical member 820
There is no functional problem even if the central slope 828c is omitted from the recessed slopes. However, in the present embodiment, the slope is intentionally formed from the viewpoint of the component manufacturing method, and the dielectric multilayer thin film as described in the sixth embodiment is coated here. The reason is that assuming that there is no inclined surface 828c and the surface is flat, when the dielectric thin film is deposited,
In order for the incident angle of f to become 0 degree and reflect a considerable portion without transmitting the forward light beam 801f, and conversely, in order not to coat this minute portion, a delicate and precise masking process is required. It is necessary. That is, it can be said that the slope 828c exists as a dummy. However, there is a secondary effect that the extinction ratio of the laser beam emitted from the light emitting element 10 is improved by using the polarization separation function, that is, the filter effect, by the inclined surface 828c, and the quality of the magneto-optical signal is slightly improved. . (Embodiment 9) Embodiment 9 is one in which the polarization separation element shown in Embodiment 7 is applied to an optical head for detecting a magneto-optical signal, and is shown in FIGS.

In this embodiment, the polarization separation function by the concave slopes 828a and 828b described in the eighth embodiment is replaced by polarizing plates 940a and 940b. Therefore, the polarization transmission directions of the polarizing plates 940a and 940b shown in FIG.
8b.

In this embodiment, as shown in FIG. 24, the polarizing plates 940a. With the 940b fitted and fixed to the optical member 920, the polarizing plate protrudes by a step L from the plane of the optical member 920. This is equivalent to the step L described in the first embodiment, and is provided to adjust the optical path length of the return light beam to cancel the initial offset of the focus error signal. (Embodiment 10) In Embodiment 10, functions other than those described so far are added to the optical member 1020, and are shown in FIG.

On the surface of the optical member 1020 on the light emitting element 10 side, a mirror-finished flat portion 1021 and a step portion 1022 are provided.
In addition, a diffuse reflection surface 1023 made of minute irregularities is integrally formed. The minute unevenness present on the irregular reflection surface 1023 is a roughened surface having an unevenness height and pitch of several λ to several tens λ (where λ is a used wavelength), and partially embossed or sandblasted on an injection molding die. The process is performed by transferring the rough mold surface during molding.
On the other hand, the flat portion 1021 and the step portion 1022 need to efficiently transmit the forward light fluxes 1001f and 1001r of the optical system, respectively. It is possible to do. In this type of optical head, since the light emitting element 10 and the light receiving element 1070 are close to each other, the divergent light beam emitted from the light emitting element 10 is used by being incident on the entrance pupil of an objective lens (not shown) and used. Other than the light flux of the part, there is a risk of being reflected inside the optical head and returning to the light receiving element 1070. This is called stray light, which is added as DC noise to the detection signal and causes deterioration in signal quality. Therefore, it is desirable to eliminate the light as much as possible. In this embodiment, from this viewpoint,
As a measure for absorbing unnecessary stray light generated in the optical head, the above-mentioned irregular reflection surface 1023 is provided. The diffuse reflection surface 1023 absorbs stray light and diffuses stray light that has not been completely absorbed in any direction, and reflects the stray light in all directions.
The same effect as described above) is obtained, and the noise is not added to various detection signals that are differentially detected as a result.

In order to further enhance the stray light absorption effect of the irregular reflection surface 1023, it is more effective to apply a black paint or the like (so-called black coating) to this surface, which is in line with the gist of this embodiment. . (Embodiment 11) Embodiment 10 is for removing stray light. In this embodiment, of the luminous flux emitted from the light emitting element, unnecessary luminous flux at the peripheral portion is actively utilized. .

In FIG. 27, a divergent light beam emitted from the light emitting element 10 is reflected by a 45-degree slope 1172 formed on the light receiving element 1170 by etching. Of this light beam, the light beam at the center enters the optical member 1120 as a forward light beam 1101f. In the present embodiment, the forward light flux 11
A non-reflective coating is vapor-deposited only on the region 1121 through which 01f passes. If this antireflection coating is subjected to multi-layer deposition (multicoat), a surface having an extremely low reflectance of 0.5% or less can be obtained. On the other hand, the uncoated area surface 1122 without the anti-reflection coating
Has a reflectivity of about 5% based on the Fresnel equation.

On the upper surface of the light receiving element 1170, the light emitting element 1
0, the second light receiving element 1 having a relatively large area
175 are integrally formed. As shown in FIG. 27, the peripheral light beam 1101b reflected by the non-coating area 1122 is received by the second light receiving element 1175. The peripheral light beam 1101b is proportional to the light amount of the outward light beam 1101f, which is the central light beam, and is also proportional to the light emission power of the light emitting element 10. Therefore, a signal that is received by the second light receiving element 1175 and photoelectrically converted (power monitor signal 1176)
Is checked, the emission power, that is, the output power of the objective lens can be monitored. The power monitor signal 117
By feeding back 6 to a drive current control circuit (not shown) of the light emitting element 10, an APC (auto power control) control system can be configured, and the light emission power of the light emitting element 10 can be accurately controlled to achieve a stable operation. Information recording / reproduction becomes possible. (Twelfth Embodiment) A twelfth embodiment is an embodiment in which unnecessary peripheral light flux described in the eleventh embodiment is more positively taken into the second light receiving element.

In FIG. 28, the outward light beam 1201f enters the antireflection coating area 1221 of the optical member 1220. On the other hand, the light flux 1201b in the peripheral portion is
The light is reflected / condensed on the curved surface 1223 formed integrally with the light receiving element 220, and can be efficiently incident on the second light receiving element 1275. Therefore, the signal level of the power monitor signal 1276 is improved, and more accurate APC control can be performed.

In FIG. 28, although 1223 is formed as a curved surface, the effect can be expected even if it is a slope. Also, curved surface 1
Instead of using the surface reflection of the H.223, a form of performing total reflection using another shape may be used. Further, even if the curved surface or the inclined surface is formed by a separate member and is combined with the optical member 1220, the functions are the same, and thus belong to the gist of the present invention.

Finally, each of the embodiments described above can be applied not only alone, but also by combining the contents of the inventions of the embodiments as appropriate to achieve a more complex function.

[0053]

As described above, according to the present invention, optical components relating to the forward optical system and the return optical system can be shared, and the light emitting element and the light receiving element can be housed in a common package. Since the spot can be accurately illuminated on the light receiving element by setting the optical path length of the forward path and the optical path length of the return path to different values, it is particularly effective for removing the offset of the focus error signal. In addition, since the adjustment process for removing the offset can be eliminated and the positioning of the optical component and the light receiving element can be easily performed, the assembling process can be simplified, and at the same time, there is little change over time and temperature characteristics. An optical head can be provided.

Further, a polarization splitting element for detecting a magneto-optical signal can be combined with and integrated with other optical components, thereby enabling stable signal detection with little change with time.

Further, the output power of the light emitting element can be monitored without adding any special parts. And so on.

Through the whole, the use of integrally molded optical members and polarization separation elements, and the integration of the hologram element can realize a great combination of functions, miniaturization, and simplification of the adjustment process. The impact on the equipment market is great.

[Brief description of the drawings]

FIG. 1 is a side sectional view of an optical head including an optical member according to a first embodiment.

FIG. 2 is a side sectional view of an optical pickup including the optical head according to the first embodiment.

FIG. 3 is a perspective view showing a light emitting element and a light receiving element of the optical head according to the first embodiment.

FIG. 4 is a front sectional view showing a light emitting element and a light receiving element of the optical head according to the first embodiment.

FIG. 5 is a plan view showing a hologram of the optical head according to the first embodiment.

FIG. 6 is a perspective view showing a hologram function of the optical head according to the first embodiment.

FIG. 7 is a plan view showing a light emitting element and a light receiving element of the optical head according to the first embodiment.

FIGS. 8A, 8B, and 8C are explanatory diagrams showing changes in a light receiving spot of the optical head according to the first embodiment.

FIG. 9 is a graph showing a focus error signal of the optical head according to the first embodiment.

FIG. 10 is an explanatory diagram illustrating the field curvature of the optical head according to the first embodiment.

FIG. 11 is a side sectional view showing an optical head according to a second embodiment.

FIG. 12 is a side sectional view showing an optical member according to a third embodiment.

FIG. 13 is a side sectional view showing an optical member according to a fourth embodiment.

FIG. 14 is a side sectional view showing an optical head according to a fifth embodiment.

FIG. 15 is a plan view showing an optical head according to a fifth embodiment.

FIG. 16 is a perspective view showing an optical member of the optical head according to the fifth embodiment.

FIG. 17 is a perspective view showing a polarization beam splitter of a sixth embodiment.

FIG. 18 is a cross-sectional view illustrating a polarization beam splitter according to a sixth embodiment.

FIG. 19 is a cross-sectional view showing a multilayer thin film of the polarization beam splitter of Example 6.

FIG. 20 is a perspective view illustrating a polarization separation element according to a seventh embodiment.

FIG. 21 is a perspective view showing a polarization separation element of the optical head according to the eighth embodiment.

FIG. 22 is a side sectional view showing an optical head according to an eighth embodiment.

FIG. 23 is a plan view showing an optical head according to an eighth embodiment.

FIG. 24 is a side sectional view showing an optical head according to a ninth embodiment.

FIG. 25 is a plan view showing an optical head according to a ninth embodiment.

FIG. 26 is a side sectional view showing an optical head according to a tenth embodiment.

FIG. 27 is a side sectional view showing an optical head according to a tenth embodiment.

FIG. 28 is a side sectional view showing an optical head according to a tenth embodiment.

[Explanation of symbols]

Reference Signs List 1 optical head 2 case 10 light emitting element 15 virtual light emitting point 40 mirror 50 objective lens 60 optical recording medium 80 package 120, 220, 320, 420, 520, 620, 7
20,820,920,1020,1120,1220
Optical member 130, 230, 1030 Hologram 530, 830, 930 Hologram element 622, 822a, 822b, 822c Slope 740, 940a, 940b Polarizer 170, 270, 570, 870, 970, 1070
1170, 1270 light receiving elements 1175, 1275 second light receiving elements 101f, 201f, 302f, 401f, 501f,
801f, 901f, 1001f, 1101f, 120
1f Forward light fluxes 101r, 201r, 302r, 401r, 501r,
801r, 901r, 1001r Return light flux

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] February 13, 2001 (2001.2.1)
3)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction contents]

[Document Name] Statement

Patent application title: Polarization splitting element and optical head

[Claims]

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing beam splitter and an optical head used in an optical disk device or the like.

[0002]

2. Description of the Related Art A conventional optical head of this type is disclosed in US Pat.
P-No. As disclosed in US Pat. No. 4,764,912, a bulk (square) type optical component obtained by shaving and polishing optical glass is frequently used. In particular, an optical head which also detects a magneto-optical signal requires a polarizing prism or the like. there were.

[0003]

However, in the above-mentioned optical head, the volume occupied by the bulk type optical component is large,
Since the processing itself is expensive and the location at the time of assembly is diversified, it has been difficult to reduce the size, cost and weight of the apparatus. Therefore, the performance in terms of access speed was sacrificed, which prevented its spread in the market. Also, the layout of the optical system, the light emitting element and the light receiving element are separated,
Exclusive optical components are used for the forward optical system starting from the light emitting element and the return optical system starting at the light receiving element as the end point, and this is extremely wasteful in terms of the number of components and space efficiency. Further, since the positional accuracy is accumulated, it is difficult to secure the positional accuracy of the optical system, and a complicated adjustment operation is required to remove the initial offset of the detection signal, particularly the focus error signal. The present invention has been made to solve such problems, and its main objects are to drastically reduce the number of optical components, reduce the size and weight, and simplify the adjustment process.

[0004]

According to the present invention, there is provided a polarization beam splitting element and a method of manufacturing the same, comprising: (1) a first optical member and a second optical member bonded to the first optical member; Forming a depression including a slope on the first or second optical member, coating the slope with a dielectric multilayer thin film to have a polarization separation function, filling the depression with a transparent resin or a liquid,
(2) Regarding the above (1), the first optical member, the second optical member,
The refractive index of the transparent resin or the liquid that fills the depression is substantially the same. (3) Regarding the above (1), the luminous flux incident on the slope is 0.15 in terms of NA (numerical aperture) in the medium.
(4) Regarding the above (1), the slopes and depressions are formed at a plurality of places in an integrated optical member, and the plurality of slopes are coated with a common dielectric multilayer thin film. (5) As the manufacturing method of the above (1), the slope described above is coated with a dielectric multilayer thin film to have a polarization separating function, the depression is filled with a transparent resin, and the first and second optical members are formed. After bonding, an annealing process is performed, (6) a polarizing plate or a polarizing film is fixed or held on the surface or inside of the optical member, and (7) the manufacturing method of the above (6) is as follows. After fixing or holding a polarizing plate or a polarizing film on the surface or inside of the optical member, an annealing process is performed.

The optical head according to the present invention further comprises: (8) using the polarization beam splitter described in (1) or (6) above, receiving the return light beam transmitted through the polarization beam splitter by the light receiving element, (9) using the polarization beam splitter described in (1) above, transmitting the forward light beam and the backward light beam through the first and second slopes each having a polarization beam splitting function; (10) With respect to the above (9), the return light beam transmitted through the second slope is received by the light receiving element to detect a magneto-optical signal. The polarization direction of the second inclined plane is set to be rotated by approximately 45 degrees with respect to the polarization plane of the returning light beam so as to coincide with the transmission direction.

[0006]

According to the above construction of the present invention, (A) the optical components relating to the forward optical system and the return optical system can be shared, and the light emitting element and the light receiving element can be stored in a common package. (B) A polarization separating element for detecting a magneto-optical signal can be combined with and integrated with another optical component. As a result, by adopting the polarization splitting element of the present invention, it is possible to realize a great combination of functions and downsizing.

[0007]

(Embodiment 1) Embodiment 1 is an embodiment relating to the polarization beam splitter of this embodiment. The polarization separation element described here is an optical element for use in an optical head or the like of a magneto-optical disk device that requires reproduction of a magneto-optical signal (MO signal). The gist of the present embodiment is to manufacture a polarization splitting element for detecting a magneto-optical signal by a simple method by largely changing the conventional manufacturing method. Hereinafter, this embodiment will be described with reference to FIGS.

In FIG. 1, the first optical member 620 has a depression 621 and an approximately 45-degree slope 622 at the center. The first optical member 620 is integrally injection-molded with an optical resin such as PMMA (polymethyl methacrylate), and can be manufactured in large quantities at low cost. On the other hand, the second optical member 6
Numeral 30 denotes a parallel flat plate, which is formed by ordinary optical glass cutting because it does not include a curved surface or a slope, and can be supplied in large quantities at low cost.

FIG. 3 shows a state in which the first optical member 620 and the second optical member 630 are combined to form the polarization splitting element 601. The depression 621 of the first optical member 620 is filled with the resin 640 and covered with the second optical member 630. The chemical composition of the resin 640 is adjusted so that the refractive index after curing is about 1.5, which is the same as that of the first and second optical members. The resin 640 filled in the depression 621 in a state where the first and second optical members are united functions as a triangular prism. In this embodiment, UV is used as the resin 640.
Although a (ultraviolet) curable resin is used and UV irradiation is performed after the coalescing for curing, a thermosetting resin or the like may be used.

[0010] As shown in FIG. 3, a dielectric thin film is coated (deposited) on the inclined surface 622 or on one entire surface of the first optical member 620, and a dielectric A (625) and a dielectric B (62).
6) are alternately stacked. This is a vapor deposition technique usually called a multi-coat, but in the present embodiment, it is considered that the first optical member 620 serving as the base material is a resin. That is, since the heat resistance temperature (glass transition point; TG) of the resin (PMMA is assumed in this embodiment) is extremely low at about 80 ° C. as compared with glass, the evaporation is performed at about 70 ° C. or less. ing. Further, since the coefficient of thermal expansion of the resin is large, the deposition material is selected in consideration of the occurrence of cracks due to stress strain with the deposition material. Specifically, dielectric A: MgF2 (magnesium boride), refractive index = 1.3 Dielectric B: ZrO2 (zirconium oxide), refractive index = 2.2: 0.3 to 0.4λ (λ is used (Wavelength: about 780 nm) and alternately laminated at a film thickness of P-polarized light or S-polarized light at their interface.
The difference in transmittance due to polarized light is accumulated so that desired polarized light transmission characteristics can be obtained.

Here, the portion filled with the resin 640 and the first optical member 620 in FIG.
26), it functions as a so-called polarization beam splitter. As a result of the experiment, finally, the number of layers of the deposited thin film has an optimum value in the range of 10 to 20 layers including the dielectrics A and B, and the S-polarized light transmittance with respect to the P-polarized light transmittance (transmittance of the P wave 651). (Transmittance of S wave 652), that is, a polarization transmission characteristic with an extinction ratio of about 100: 1 was obtained.

The combination of the vapor deposition materials described above is only one example. However, no change in characteristics or cracks is observed due to temperature change, and a sufficiently usable polarization separation element 601 can be supplied. However, in order to secure the extinction ratio,
It is premised that birefringence due to residual stress does not occur inside the resin 640 after assembly. Therefore, in the present embodiment, an annealing process is performed at the end of the manufacturing process to remove the residual stress inside the resin 640. As annealing conditions,
About one hour at 70 ° C. is sufficient.

By the way, the angle of incidence θ (central value of 45) of the light beam to be incident on the polarization separation element 601 thus constructed
It should be noted that the above extinction ratio varies depending on the degree). That is, when the incident angle θ changes, the effective film thickness of the dielectrics A and B changes, so that the reflection and transmission characteristics of light rays change. The incident angle θ at which the extinction ratio (about 50: 1 or more) necessary for detecting the magneto-optical signal can be ensured even when the film thickness is controlled optimally is about +/− 9 in terms of the incident angle inside the polarizing element 601. It has been confirmed by optical simulations and experiments that the degree is limited. This corresponds to the convergence (or divergent light flux) of NA 0.15 in terms of NA (numerical aperture) in the medium.

In addition, in addition to the advantage that the manufacturing method is simple, the polarization separation element 601 shown in the present embodiment has the shape accuracy of the optical member 620, particularly the surface accuracy of the inclined surface 622, which is lower than that of the conventional glass shaping method. There is a remarkable advantage that it is greatly reduced as compared with the case of the polarization beam splitter according to the first embodiment. The reason for this is that even if the surface accuracy of the slope 622 is poor, the resin 640 fills in the resin.
The refractive index of 40 is 0.0 with respect to the refractive index of the optical member 620.
Even if the difference is about three, if the slope 622 has a surface accuracy (undulation) of about 20 μ or less, it can be used without any problem in optical characteristics. This is the required value of the slope accuracy of the triangular prism that composes the conventional polarization beam splitter.
It means that it is relaxed about 20 times. Also, since parts can be manufactured by injection molding, very small external shapes can be manufactured. When applied to an optical head for magneto-optical detection, a very small detection optical system can be realized.

In this embodiment, the concave slope 622 is molded with the resin 640. However, if the peripheral sealing property is good, the same function can be exerted even if a liquid such as silicon oil is filled. In this case, there is an advantage that the problem of birefringence, which has to be considered in the resin 640, can be easily avoided. (Embodiment 2) FIG. 4 shows another embodiment of a polarization beam splitting element. In this embodiment, the function of the polarizing beam splitter described in the first embodiment is replaced by a polarizing film or a polarizing plate. In FIG. 4, the optical member 720 is formed of an optical resin, and a polarizing plate 740 is fixed to the recessed portion. A polarizing plate is a glass plate mixed with fine silver particles and heated and stretched to give a polarizing function, but the performance, that is, the extinction ratio is excellent, but it is not limited to this. It may be a polarizing film made in advance. However, such a polarizing film generally has poor heat resistance, and has a drawback that a film stretched in a high-temperature environment is contracted by residual stress to deteriorate polarizing characteristics.

The advantage of this embodiment is that the polarizing plate or the polarizing film is lined with an optical member 720 which is much stronger than the polarizing plate or the polarizing film. It is difficult. Therefore, the polarization separation element 701 having excellent environmental resistance can be obtained.
However, if there is a slight shear shift in the adhesive layer that fixes the optical member 720 and the polarizing plate or the polarizing film 740, the polarizing plate or the polarizing film 740 may be slightly shrunk, and a long-term change may occur. In this embodiment, as a preventive measure, an annealing process is performed after the assembling process to reduce the residual stress in advance to prevent a change with time. Annealing conditions may be about 70 ° C. for about 1 hour. (Embodiment 3) Embodiment 3 is an application of the polarization separation element shown in Embodiment 1 to an optical head for detecting a magneto-optical signal, which will be described below with reference to FIGS. 5, 6, and 7. FIG.

In FIG. 5, the optical member 820 is similar to the optical member 620 shown in the first embodiment, and the concave slopes are three types of slopes 828a, 828b, 828c having different slope directions.
Consists of

In the present embodiment, a hologram element 830 is used instead of the second optical member 630 of the first embodiment, and the polarization splitting element 801 is constituted by these elements and functions are combined. Optical members 820 are provided on the concave slopes 828a to 828a to 828c.
Is filled in three places with a resin having a refractive index of about 1.5, which is equivalent to the refractive index of FIG. 6 shows the assembled optical head. The optical member 820 has the polarization splitting function described in the first embodiment and also has the optical path length adjusting function of the return light beam described in the first embodiment. Is characteristic.

FIG. 7 is a plan view of the optical head viewed from the optical axis direction, and shows each component shown in FIG. 6 in a see-through manner. In the figure, arrows 829 indicate the directions of the three slopes formed on the optical member 820, that is, the polarization transmission directions, and the slope 828c at the center is along the bonding surface of the light emitting element 10, ie, the direction of the polarization plane. On the other hand, the slopes 828a and 828b on both sides are oriented in a direction rotated by approximately 45 degrees with respect to the direction of the slope 828c. In this embodiment, an optical recording medium (not shown)
The specification of the optical head is such that the Kerr rotation angle in the return light beam 801r generated when reflected by the optical recording medium is detected as a modulation component. The light beam incident on the optical recording medium is linearly polarized light, and is P-polarized light with respect to the inclined surface 828c in this embodiment. Accordingly, the forward light beam (801f in FIG. 6) passes through the slope 828c with almost no loss. Also, the return light beam 801
r (a total of four light beams) is a pair of two light beams,
8a and 828b, but as described above, the slope 828a and the slope 828b are substantially
Since the rotation is performed by 5 degrees, the Kerr rotation angle, which is a magneto-optical signal modulation component included in the return light beam 801r, can be differentially detected after being polarized and transmitted in the orthogonal 45-degree direction.

By the way, the 3 formed on the optical member 820
There is no functional problem even if the central slope 828c is omitted from the recessed slopes. However, in the present embodiment, the slope is intentionally formed from the viewpoint of the component manufacturing method, and the dielectric multilayer thin film as described in the first embodiment is coated here. The reason is that assuming that there is no inclined surface 828c and the surface is flat, when the dielectric thin film is deposited,
In order for the incident angle of f to become 0 degree and reflect a considerable portion without transmitting the forward light beam 801f, and conversely, in order not to coat this minute portion, a delicate and precise masking process is required. It is necessary. That is, it can be said that the slope 828c exists as a dummy. However, there is a secondary effect that the extinction ratio of the laser beam emitted from the light emitting element 10 is improved by using the polarization separation function, that is, the filter effect, by the inclined surface 828c, and the quality of the magneto-optical signal is slightly improved. . (Embodiment 4) Embodiment 4 is one in which the polarization separation element shown in Embodiment 2 is applied to an optical head for detecting a magneto-optical signal, and is shown in FIGS.

In this embodiment, the polarization separating function by the concave slopes 828a and 828b described in the third embodiment is replaced by polarizing plates 940a and 940b. Therefore, the polarization transmission directions of the polarizing plates 940a and 940b shown in FIG.
It corresponds to the direction of b.

In this embodiment, as shown in FIG.
40a. With the 940b fitted and fixed to the optical member 920, the polarizing plate protrudes by a step L from the plane of the optical member 920. Since the optical path length of the return light beam is adjusted by the step L to cancel the initial offset of the focus error signal, the step of adjusting the focus error signal detection optical system can be omitted.

[0023]

As described above, according to the present invention, optical components relating to the forward optical system and the return optical system can be shared, and the light emitting element and the light receiving element can be housed in a common package.

Further, a polarization splitting element for detecting a magneto-optical signal can be combined with and integrated with other optical parts, and stable signal detection with little change over time can be realized.

Throughout the whole, the use of integrally molded optical members and polarization separation elements, and the integration of hologram elements can greatly realize complex functions, miniaturization, and simplification of the adjustment process. The impact on the equipment market is great.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a polarization separation element according to a first embodiment.

FIG. 2 is a cross-sectional view illustrating a polarization beam splitter of Example 1.

FIG. 3 is a cross-sectional view showing a multilayer thin film of the polarization beam splitter of Example 1.

FIG. 4 is a perspective view illustrating a polarization beam splitter according to a second embodiment.

FIG. 5 is a perspective view illustrating a polarization separation element of the optical head according to the third embodiment.

FIG. 6 is a side sectional view showing an optical head according to a third embodiment.

FIG. 7 is a plan view showing an optical head according to a third embodiment.

FIG. 8 is a side sectional view showing an optical head according to a fourth embodiment.

FIG. 9 is a plan view showing an optical head according to a fourth embodiment.

[Description of Signs] 10 Light-emitting element 15 Virtual light-emitting point 80 Package 830, 930 Hologram element 622, 822a, 822b, 822c Slope 740, 940a, 940b Polarizer 1175 Second light-receiving element 801f, 901f Outgoing light flux 801r, 901r Return light flux

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──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02B 7/00 G02B 7/00 F G11B 7/135 A G11B 7/135 11/105 551M 11/105 551 G02B 1/10 A (72) Inventor Takashi Takeda 3-3-5 Yamato, Suwa City, Nagano Prefecture Inside Seiko Epson Corporation (72) Inventor Toshio Arimura 3-5-5 Yamato Suwa City, Nagano Prefecture Seiko Epson Corporation Inside

Claims (31)

[Claims] 1. An integral member through which a divergent or convergent forward light beam and a backward light beam are transmitted, wherein the optical path length of the forward light beam and the light path length of the backward light beam are different from each other. Optical member. 2. The optical member according to claim 1, wherein the optical member is integrally formed and has a step on its surface. 3. The optical device according to claim 1, wherein the optical member is formed by bonding at least two separate components, and a step is formed on the surface in a state where the separate components are bonded. Element. 4. A method for manufacturing an optical member according to claim 1, wherein the optical member according to claim 1 is injection-molded integrally with a transparent resin to form a step on the surface. 5. A method for manufacturing an optical member, comprising: pressing the optical member according to claim 1 integrally with glass to form a step on the surface. 6. A local light beam having at least a binary refractive index, wherein a forward light beam and a backward light beam pass through regions having different refractive indices, respectively, and an optical path length of the forward light beam and an optical path length of the backward light beam are different from each other. An optical member characterized by being configured differently. 7. A refracting power in a region where the forward light beam and the backward light beam are transmitted through the integrated member, and the forward light beam is transmitted,
An optical member characterized in that the refraction power of a region through which the return light beam is transmitted is different from that of the optical member. 8. The optical member according to claim 7, wherein a convex or concave curved surface is locally formed on the surface. 9. The optical member according to claim 1, 6 or 7, a light receiving element disposed substantially behind and behind the optical member, and slightly higher or slightly higher than a light receiving surface of the light receiving element. A forward light beam emitted from the light emitting device and a backward light beam reflected by the optical recording medium toward the light receiving element are both transmitted through the optical member. An optical head characterized in that: 10. The optical head according to claim 9, wherein a change in the spot shape of the return light beam on the light receiving element is detected to generate at least a focus error signal. 11. The optical head according to claim 9, wherein said optical member is formed of a transparent resin, has a flange on the outer periphery, and a gate for injection molding is provided on said flange portion. 12. The optical member is formed of a transparent resin,
10. The optical head according to claim 9, wherein alignment marks for positioning are formed or printed on the front or back surface of the optical member and the front surface of the light receiving element. 13. The optical head according to claim 9, wherein a diffraction grating or a hologram is formed on a front surface or a back surface of the optical member. 14. The optical head according to claim 13, wherein the hologram is a blazed hologram blazed in a triangular shape in units of a diffraction groove pitch. 15. The optical member according to claim 1, 6 or 7, a light receiving element disposed substantially behind and behind the optical member, and slightly higher or slightly higher than a light receiving surface of the light receiving element. A light-emitting element disposed low, a light-receiving element and a package for holding the light-emitting element, wherein the optical element and the package cooperate to seal the light-receiving element and the light-emitting element. Light head. 16. The optical member and the package,
16. The optical head according to claim 15, wherein the optical head is fixed to each other via an adhesive, and the adhesive has a lower hardness after curing than the materials of the optical member and the package. 17. A method according to claim 17, further comprising a first optical member, a second optical member adhered to the first optical member, a depression including a slope formed in the first or second optical member, Polarized light is formed by coating a slanted surface with a dielectric thin film to have a polarization separating function, filling the depression with a transparent resin or liquid, and bonding the first and second optical members. Isolation element. 18. The liquid crystal display device according to claim 17, wherein said first optical member, said second optical member, and a transparent resin or a liquid filling said depression have substantially the same refractive index.
The polarized light separating element according to any one of the preceding claims. 19. The polarization beam splitter according to claim 17, wherein the light beam incident on the inclined surface is a convergent light beam or a divergent light beam having a numerical aperture (NA) of 0.15 or less in a medium. 20. The polarization separation device according to claim 17, wherein the slope and the depression are formed at a plurality of positions in an integrated optical member, and a plurality of the slopes are coated with a common dielectric multilayer thin film. element. 21. The inclined surface according to claim 17, which is coated with a dielectric thin film to have a polarization separating function, fills the depression with a transparent resin, and attaches the first and second optical members. A method for manufacturing a polarization splitting element, which comprises performing an annealing process later. 22. A polarization splitting element formed by fixing or holding a polarizing plate or a polarizing film on the surface or inside of an optical member. 23. A method for manufacturing a polarization beam splitting element, wherein an annealing process is performed after fixing or holding the polarizing plate or the polarizing film on the surface or inside of the optical member according to claim 22. 24. A polarization beam splitter according to claim 17 or 22, wherein a return light beam transmitted through said polarization beam splitter is received by a light receiving element to detect a magneto-optical signal. Light head. 25. The polarization separation element according to claim 17, wherein the forward light beam and the return light beam are respectively transmitted through first and second slopes having a polarization separation function, and transmitted through a second slope of the polarization separation element. The received return light beam is received by the light receiving element,
An optical head characterized in that it is configured to detect a magneto-optical signal. 26. The polarization plane of the forward light beam is made to coincide with the polarization transmission direction of the first inclined surface, and the polarization separation direction of the second inclined surface is rotated by about 45 degrees with respect to the polarization surface of the return light beam. 26. The optical head according to claim 25, wherein: 27. An optical member which is separated into a mirror-finished region and an irregular reflection region having fine irregularities, and wherein the forward light beam and the backward light beam are transmitted through the mirror-finished region. Light head. 28. An optical member separated into an area where an anti-reflection coating is deposited and an uncoated area where an anti-reflection coating is not deposited, and a central portion of a divergent light beam emitted from the light emitting element is placed in the anti-reflection coating area. An optical head, comprising: a second light-receiving element for detecting light emission power, which transmits the light, reflects a part of the divergent light beam in the uncoated region, and receives the reflected light. 29. A light-receiving element comprising: a second light-receiving element for detecting light emission power; and a first light-receiving element for receiving a return light beam which is reflected light from an optical recording medium, wherein the first and second light-receiving elements are provided. The optical head according to claim 28, wherein is formed on an integrated substrate. 30. A light emitting power detecting device that uses an optical member having a reflection surface formed in a region through which the forward light beam and the backward light beam do not transmit, reflects a part of the forward light beam on the reflective surface, and receives the reflected light. An optical head comprising a second light receiving element. 31. The reflection surface is a slope or a curved surface,
31. The optical head according to claim 30, wherein a light beam reflected on the surface of the inclined surface or the curved surface or a light beam totally reflected is received by the second light receiving element.