JP3817438B2 - Optical member and optical device using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical member on which laser beams having two different wavelengths are incident, and more particularly to an optical member that receives laser beams whose optical axes are shifted from each other with a light receiving unit and an optical apparatus using the optical member.
[0002]
[Prior art]
In order to simplify the structure, an optical pickup mounted on a disk device that can use both CD and DVD has a light emitting unit on which two light sources of laser beams having different wavelengths are integrally provided. Yes. In the light emitting unit, since the light sources are arranged at a minute interval, an optical path is formed with the optical axis of the laser beam shifted. In a state where the optical axis is deviated, the light receiving position at the light receiving unit is shifted, so it is necessary to match the light receiving positions of both laser beams at the light receiving unit.
[0003]
FIG. 7 is a plan view showing a conventional optical member 30 provided to eliminate the deviation. The optical member 30 is provided with a concave and convex diffraction grating 30 a on one surface side of a plate-like transparent member, and at a position facing the light receiving portion 31.
[0004]
The optical member 30 is mounted on a disc device for both CD and DVD. The disc device emits a laser beam having a wavelength of 785 nm (λ1) for CD and a laser beam having a wavelength of 658 nm (λ2) for DVD. A light emitting unit is provided. As shown in FIG. 7, the optical axis of the return light reflected by the disk returns to the optical member 30 with the optical axis shifted, and both laser beams are diffracted by the diffraction grating 30 a of the optical member 30 to be received by the light receiving unit 31. The light receiving positions coincide with each other at the arrival position. The diffraction angle varies depending on the length of the wavelength. In the case shown in FIG. 7, the diffraction angle (θ1) of λ1 is larger than the diffraction angle (θ2) of λ2.
[0005]
[Problems to be solved by the invention]
However, since the light emitting section that emits the laser light has a characteristic that the wavelength varies depending on the temperature change, in the conventional optical member 30, the diffraction angle varies due to the temperature change, and as a result, the light receiving section receives the laser light. The positions do not coincide with each other, causing an offset problem. For example, when the light receiving position at the light receiving unit is greatly shifted, diffracted light of higher order than the first order diffracted light may leak into the light receiving unit, resulting in an offset.
[0006]
SUMMARY OF THE INVENTION The present invention solves the above-described problems, and an optical member that can match the optical axes of laser beams that are shifted from each other at a light receiving unit, and that can reduce the influence of wavelength fluctuation due to a temperature change, and an optical device using the same. The purpose is to provide.
[0007]
[Means for Solving the Problems]
The present invention is an optical member provided with a diffraction grating that diffracts laser light having a first wavelength λ1 and transmits laser light having a second wavelength λ2 without being diffracted.
The diffraction grating includes a first grating part formed in an uneven shape, a second grating part formed as a stepped step having a predetermined number of steps on the inclined surface of the first grating part, And a third lattice portion formed of minute irregularities formed on the surface of the second lattice portion,
The second grating portion has selectivity with respect to the first-order diffracted light with respect to the laser light with the first wavelength λ1 and selection with respect to the zero-order diffracted light with respect to the laser light with the second wavelength λ2. And a depth dimension (h) per step of the second grating portion is (n−1) with respect to the laser light having the second wavelength λ2. ) H = mλ2 (where n is a refractive index and m is a positive integer), and the period of the third grating portion is less than or equal to the wavelength of the laser light (λ1 and λ2). It is what.
[0010]
Moreover, it is preferable that each step part of the said 2nd grating | lattice part is formed in the width direction and the depth direction at equal pitch.
[0011]
In the present invention, since the laser beam of one wavelength is not diffracted, the diffraction angle of the other laser beam can be reduced, the influence of wavelength fluctuation due to temperature change can be reduced, and the shift of the light receiving position in the light receiving unit can be reduced. Can be small.
[0012]
Further, by setting the first wavelength λ1 to 785 nm and the second wavelength λ2 to 658 nm, the present invention can be applied to an optical pickup that uses both CD and DVD.
[0013]
Further, in the above case, by designing the number of stepped steps of the second grating part to be 6, it is possible to design while maintaining high efficiency at the light receiving position for both laser beams. Become.
[0015]
In addition, since the first lattice part and the second lattice part are integrally formed of resin, the manufacturing cost can be reduced.
[0016]
In the optical device of the present invention, the light emitting point that emits the laser light having the first wavelength λ1 and the light emitting point that emits the laser light having the second wavelength λ2 are shifted in a direction perpendicular to the optical axis. And an optical member according to any one of claims 1 to 5 through which light from the light emitting unit is transmitted, an optical axis of the laser light having the first wavelength λ1, and a second wavelength λ2 The optical axis intersects at a position where the light receiving unit is provided .
[0017]
In the present invention, since the light emitting unit integrally provided with the light source of the two-wavelength laser light and the single optical member capable of independently diffracting the two-wavelength laser light are provided, the number of parts is reduced. The structure can be simplified by reducing the cost, and the cost can be reduced.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
1 is a schematic view showing an example of an optical device on which the optical member of the present invention is mounted, FIG. 2 is a schematic view showing an optical member and its optical axis, FIG. 3 is a partially omitted plan view showing the optical member, and FIG. Is a diagram showing the efficiency of light with respect to the grating depth in 6 steps, and FIG. 5 is a diagram showing the efficiency of light with respect to the grating depth in 5 steps.
[0019]
An optical pickup 10 as an optical device shown in FIG. 1 includes a light emitting unit 12 incorporating a semiconductor laser diode, a collimator lens 13 that collimates laser light emitted from the light emitting unit 12, and incident laser light. A beam splitter 14 that reflects and transmits light incident from the reflection direction, an objective lens 15, a light receiving unit 16, and the optical member 11 of the present invention disposed between the light receiving unit 16 and the beam splitter 14 are provided. I have.
[0020]
The light emitting unit 12 includes a light emitting element 12a that forms a light emitting point of a laser beam having a wavelength of 785 nm (λ1) for a CD and a light emitting element 12b that forms a light emitting point of a laser beam having a wavelength of 658 nm (λ2) for a DVD. They are arranged in a single casing with a minute spacing (S).
[0021]
When the laser beams having the wavelengths λ 1 and λ 2 emitted from the light emitting unit 12 enter the beam splitter 14, the laser beams are reflected in the direction of the disk D 1 by the beam splitter 14 and converted into parallel light by the collimator lens 13 and then incident on the objective lens 15. To do. The laser light condensed by the objective lens 15 forms a spot light on the disk D1, and the return light reflected by the disk D1 passes through the objective lens 15 and the collimator lens 13 with the optical axes being shifted from each other, and passes through the beam splitter 14. Is transmitted to the optical member 11.
[0022]
As shown in FIG. 2, the optical member 11 is formed in a plate shape with a light transmissive resin member, a glass member, or a composite material of resin and glass. In this optical member 11, the laser beam of wavelength λ 2 for DVD is transmitted without being diffracted and guided to the light receiving unit 16, and the laser beam of wavelength λ 1 for CD is diffracted and guided to the light receiving unit 16. As shown in FIG. 1, a concave lens 17 may be disposed between the optical member 11 and the light receiving unit 16 so as to expand the beam shape of the laser light formed on the light receiving unit 16.
[0023]
The light receiving portion 16 is formed of a photodiode, and includes a light receiving element in which four divided sensors A, B, C, and D are combined, and a side portion including sensors E and F provided on both sides of the light receiving element. It has a light receiving element. For example, a three-beam method and a phase difference method are applied as tracking servo mechanisms for CD and DVD, respectively, and an astigmatism method is applied as a focusing servo mechanism. In the CD and DVD focusing servo mechanism, the light receiving element is used as a common element.
[0024]
In the light receiving unit 16, as the wavelength changes due to the temperature change, the spot of the laser beam is shifted in the direction orthogonal to the EF direction connected by the sensor E and the sensor F. As a result, higher-order diffracted light enters the light receiving element. Leakage will cause an offset problem. Therefore, the optical member 11 in which the deviation is improved is shown below.
[0025]
On the laser beam emission surface side of the optical member 11, a first lattice portion in which a plurality of convex portions 11a are continuously formed is formed, and a stepped step portion 11b (on the inclined surface of each convex portion 11a). (Second lattice portion) is formed. The convex portion 11a and the step portion 11b constitute a diffraction grating 11A.
[0026]
The first lattice portion is formed in a substantially saw blade shape, and each of the convex portions 11a has the same shape, and is a right triangle formed by a vertical surface and an inclined surface. Further, the step portion 11b is formed so that the flat surfaces S1 to S6 gradually change in height and the number of steps becomes six, and the width dimension w in the x direction and the depth in the y direction of each step. Each dimension h is formed at an equal pitch (h = d / 5, w = p / 6). However, p is a period and this period is the width dimension of the convex part 11a.
[0027]
In the diffraction grating 11A formed on the optical member 11 shown in FIG. 3, assuming that the depth dimension of each step is h, the refractive index of the resin is n, and the wavelength of the laser light is λ, (n−1) h = The relational expression mλ holds. Here, m is a positive integer. By determining h so that (n−1) h is a positive integer multiple of the wavelength, the laser beam having the wavelength λ can be transmitted without being diffracted.
[0028]
From the above formula, when λ2 (658 nm) laser light is incident on the diffraction grating 11A by setting h so that (n−1) h is a positive integer multiple of λ2. Without being diffracted to 0, it can be transmitted as the 0th-order diffracted light.
[0029]
As described above, the grating depth dimension d (= 5h) of the convex portion 11a is determined, and the period p is also set in advance within a range of, for example, 30 to 50 μm. Therefore, the optical member 11 is determined by determining the number of remaining steps. The shape will be determined. Therefore, when the number of steps was changed step by step, it was confirmed that the shape having six steps as shown in FIG. 3 was optimal. The reason will be described with reference to FIG.
[0030]
FIG. 4 is a diagram showing the relationship between the grating depth and the efficiency for each diffracted light of wavelength λ1 and wavelength λ2. However, the period (p) is 20 μm and the refractive index is 1.54. Also, the efficiency of the vertical axis in FIG. 4 is the zero-order diffracted light (0T) and ± 1st-order diffracted light (0) after passing when the amount of laser light before passing through the diffraction grating 11A is 1. The ratio of the amount of light of ± 1T) and ± 2nd order diffracted light (± 2T) is shown.
[0031]
As shown in FIG. 4A, the grating depth dimension d of the diffraction grating is set to around 6 μm, so that 658 nm (λ2) zero-order diffracted light and 785 nm (λ1) first-order diffracted light are obtained with high efficiency. be able to.
[0032]
By forming the optical member 11 as described above, it has the selectivity to select the first-order diffracted light for the λ1 laser light, and the selectivity to select the 0th-order diffracted light for the λ2 laser light. To have. In addition, both the first-order diffracted light of λ1 and the 0th-order diffracted light of λ2 can be obtained with high efficiency.
[0033]
4B and 4C, the first-order diffracted light of 785 nm (λ1) and the zero-order diffracted light of 658 nm (λ2) cannot be obtained with high efficiency. Also, it is not preferable to increase the depth dimension d because the variation with respect to wavelength variation increases. In addition, although the 785 nm secondary diffracted light is obtained at the depth of (b), it is not preferable because the efficiency is deteriorated.
[0034]
Accordingly, the lattice depth dimension d is set to around 6 μm (more precisely, around 6.1 μm), and the width dimension and the depth dimension of each step of the stepped portion 11b are both formed at an equal pitch, thereby increasing efficiency. The maintained diffraction grating 11A can be obtained.
[0035]
The diagram shown in FIG. 5 is obtained by changing the number of steps of the diffraction grating 11A shown in FIG. 3 from six to five. However, also in this case, as described above, the width dimension and the depth dimension of each step are formed at the same pitch.
[0036]
In the case shown in FIG. 5, by setting the grating depth dimension d of the diffraction grating in the vicinity of 5.8 μm (e), it is possible to efficiently obtain both the 658 nm minus 1st order diffracted light and the 785 nm zeroth order diffracted light. In this case, λ1 and λ2 are reversed, and 658 nm may be λ1 and 785 nm may be λ2.
[0037]
As described above, by setting the grating depth d of the diffraction grating to the shape determined by (a) of FIG. 4 or (e) of FIG. 5, only the 0th-order diffracted light of the 658 nm laser light is transmitted and Only the first-order diffracted light of the 785 nm laser beam is diffracted, or only the 658-nm first-order diffracted light is diffracted, and only the 785-nm zero-order diffracted light can be transmitted, and the optical axis of 785 nm and the optical axis of 658 nm Can be matched by the light receiving unit 16.
[0038]
Therefore, since one laser beam is not diffracted, the laser beam is not affected by the wavelength variation, and although the other laser beam is diffracted, the diffraction angle is smaller than that of the conventional one, so that the influence of the wavelength variation as a whole can be reduced. In the optical member 11 described above, it is more preferable in terms of light efficiency that the number of steps is 6 steps and 5 steps, so that the shape is 6 steps.
[0039]
In the present embodiment, the combination of wavelengths 658 nm and 785 nm has been described, but other combinations of wavelengths may be used. The optimal number of steps and the depth dimension of the stepped portion differ depending on the combination of wavelengths.
[0040]
Moreover, the manufacturing cost can be reduced because the convex portion 11a constituting the first lattice portion and the step portion 11b constituting the second lattice portion are integrally formed of resin.
[0041]
A diffraction grating 11B shown in FIG. 6 is a plan view showing a part of a modification of the diffraction grating 11A.
[0042]
The diffraction grating 11B is formed by overlapping a minute diffraction grating (third grating part) 11c made of jagged irregularities on the flat surfaces S1 to S6 of the step part 11b of the diffraction grating 11A. In the minute diffraction grating 11c, it is preferable that one period is shorter than the wavelengths λ1 and λ2 of the laser beam, where one period is from the convex part to the adjacent convex part. Thereby, the same antireflection effect as when an expensive antireflection film is formed can be exhibited.
[0043]
【The invention's effect】
As described above, the present invention can match the shifted optical axes at a predetermined position, diffract only the laser beam of one wavelength, and can make the diffraction angle of the other laser beam smaller than the conventional one. The influence of wavelength fluctuation due to temperature change can be reduced as compared with the case where both laser beams are diffracted.
[0044]
In addition, the optical device of the present invention is composed of a light emitting unit that emits laser light of two wavelengths and a single optical member that matches the optical axes of the laser beams, so the number of parts is reduced and the structure is simplified. Cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of an optical device on which an optical member of the present invention is mounted;
FIG. 2 is a schematic diagram showing an optical member and its optical axis;
FIG. 3 is a plan view showing a part of an optical member;
FIG. 4 is a diagram showing the light efficiency with respect to the grating depth when the number of steps is six;
FIG. 5 is a diagram showing the light efficiency with respect to the grating depth when the number of steps is 5;
FIG. 6 is a plan view showing a part of a modification of the optical member of the present invention,
FIG. 7 is a schematic diagram showing a conventional optical member and its optical axis;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Optical pick-up 11 Optical member 11a Convex part (1st grating | lattice part)
11b Step part (second lattice part)
11c Micro diffraction grating (third grating part)
Reference Signs List 12 light emitting parts 12a, 12b light emitting element 13 collimator lens 14 beam splitter 15 objective lens 16 light receiving part

Claims (6)

An optical member provided with a diffraction grating that diffracts laser light having a first wavelength λ1 and transmits laser light having a second wavelength λ2 without diffracting the laser light,
The diffraction grating includes a first grating part formed in an uneven shape, a second grating part formed as a stepped step having a predetermined number of steps on the inclined surface of the first grating part, And a third lattice portion formed of minute irregularities formed on the surface of the second lattice portion,
The second grating portion has selectivity with respect to the first-order diffracted light with respect to the laser light with the first wavelength λ1 and selection with respect to the zero-order diffracted light with respect to the laser light with the second wavelength λ2. And a depth dimension (h) per step of the second grating portion is (n−1) with respect to the laser light having the second wavelength λ2. ) H = mλ2 (where n is a refractive index and m is a positive integer), and the period of the third grating portion is less than or equal to the wavelength of the laser light (λ1 and λ2). An optical member. The second of each stage of the grating portion, the optical member according to claim 1, characterized in that formed at an equal pitch both the width direction and depth direction. The optical member according to claim 1 or 2 , wherein the first wavelength λ1 is 785 nm and the second wavelength λ2 is 658 nm. The optical member according to any one of claims 1 to 3, wherein the number of stepped steps of the second lattice portion is six. The optical member according to any one of claims 1 to 4, wherein both the first lattice portion and the second lattice portion are integrally formed of resin. A light emitting point that emits a laser beam having a first wavelength λ1 and a light emitting point that emits a laser beam having a second wavelength λ2 are shifted in a direction perpendicular to the optical axis; An optical member according to any one of claims 1 to 5 through which light is transmitted is provided, and an optical axis of the laser beam with the first wavelength λ1 and an optical axis with the second wavelength λ2 are provided with a light receiving unit. An optical device characterized by intersecting at a predetermined position .

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