JP2002311221A - Optical member and optical device which uses the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid the problem that a conventional diffraction grating is much influenced by the changes in the wavelength. SOLUTION: A first diffraction grating 11A is formed in the incidence face side of an optical member 11, and a second diffraction grating 11B is formed in the emitting face side. The first diffraction grating 11A is formed by superposing steps 11b on the inclined faces of projections 11a formed into recesses and projections. The second diffraction grating 11B is also formed by superposing steps 11d on the inclined faces of projections 11c. The first diffraction grating 11A and the second diffraction grating 11B are arranged in the opposite directions to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical member through which laser beams of two different wavelengths pass, and more particularly, to an optical member for correcting an optical axis shift of each laser beam and an optical device using the same.

[0002]

2. Description of the Related Art An optical pickup mounted on a disk device capable of using both a CD and a DVD is provided with two light emitting elements for laser light having two different wavelengths in order to simplify the structure. A light emitting unit is mounted. In the light emitting section, since the light emitting elements are arranged at minute intervals, an optical path is formed in a state where the optical axis of the laser light is shifted.

FIG. 8 is a schematic diagram of a conventional optical pickup 40. The light emitting unit 12 of the optical pickup 40 includes
The light emitting elements 12a that emit laser beams of different wavelengths from each other,
12b is built in. The optical pickup 40 includes a collimator lens 13 that converts laser light emitted from the light emitting unit 12 into parallel light, a beam splitter 14 that reflects incident laser light and transmits light incident from the reflection direction, Objective lens 15 and light receiving section 1
6 is provided.

In the optical pickup 40, if one light emitting element 12a of one wavelength λ1 is designed to pass through the center of the optical system, the optical axis of the wavelength λ1 forms an optical path shown by a dashed line in FIG. The optical axis of the light emitting element 12b having the other wavelength λ2 forms an optical path indicated by a broken line. As shown in FIG. 8, the optical axis of the wavelength λ2 is formed obliquely, and the returning light reflected and returned to the disk D1 is also received by the light receiving unit 16 with the optical axis shifted. The detection accuracy in is reduced.

Therefore, by disposing the optical member 41 shown in FIG. 9 in front of the light receiving surface of the light receiving section 16 in order to eliminate the deviation, the positional deviation of the optical axis can be corrected. The optical member 41 shown in FIG. 9 has a sawtooth-shaped diffraction grating 41a formed on the laser light emission surface side. They are matched on the light receiving surface. At this time, the diffraction angle of the wavelength λ1 (785 nm) is set to θ1, and the wavelength λ2
When the diffraction angle of (658 nm) is θ2, θ1> θ2
Is established.

[0006]

However, in the above-mentioned conventional optical member, positioning must be performed so that both optical axes coincide with each other at the light-receiving portion, so that high positioning accuracy is required and the manufacturing process becomes complicated. . In addition, since the wavelength of the light emitting element fluctuates due to a change in temperature, when the wavelength of the laser beam fluctuates due to heat, the light receiving position shifts, and the optical axes of the light receiving sections do not coincide. As a result, the detection accuracy at the light receiving unit decreases.

[0007] The present invention is to solve the above-mentioned problems,
It is an object of the present invention to provide an optical member in which optical axes shifted from each other can be made coincident with each other without positioning the light receiving unit with high precision, and the influence of wavelength fluctuation can be reduced.

Another object of the present invention is to provide an optical device capable of reducing the cost by simplifying the structure.

[0009]

According to the present invention, there is provided a first diffraction grating provided on an incident surface side of a laser beam emitted from a light emitting element having a different wavelength with an optical axis shifted, and a second diffraction grating provided on an emission surface side. 2 diffraction gratings, wherein the first diffraction grating and the second
Each of the diffraction gratings has a first grating portion formed in an uneven shape, and a step-shaped second grating portion formed so as to overlap an inclined surface of the first grating portion, When the overall depth from the lower stage to the upper stage of the second grating portion is d, the depth per stage is h, and the refractive index in the diffraction grating is n, (n-1) h Is set to an integral multiple of the wavelength λ, and the depth h per one step is set. Based on the depth h of each step, the optimum depth d and the width of each step are optimized. By determining the value, when the laser light is incident on the first diffraction grating, the laser light of one wavelength is diffracted, and when the laser light is emitted from the second diffraction grating, the one of the wavelengths is emitted. The optical axis of the laser light having the wavelength is diffracted so as to coincide with the optical axis of the laser light having the other wavelength.

For example, a first diffraction grating on the incident surface side and a second diffraction grating on the emission surface side are provided so as to face each other, and the inclination direction of the grating portion of the first diffraction grating and the second diffraction grating are opposite to each other. Are formed in a direction in which the inclination direction of the grating portion of the diffraction grating coincides.

According to the present invention, the optical axes of the laser beams emitted with the optical axes shifted can be matched. Moreover, since the directions of the optical axes of the laser beams of the respective wavelengths can be matched, even if the light receiving surfaces of the light receiving units are displaced in the optical axis direction, the light receiving positions of the optical axes may not match each other. Absent. Further, since only the laser light of one wavelength is diffracted, the influence of wavelength fluctuation can be reduced.

Further, a cavity may be formed between the first diffraction grating and the second diffraction grating through which the laser light passes. When formed in this way,
Since the laser light is refracted in the cavity, the diffraction angles of the first diffraction grating and the second diffraction grating can be reduced, and the influence of wavelength fluctuation can be further reduced.

The wavelength of the one laser beam is 785.
By setting the wavelength of the other laser beam to 658 nm in nm, it can be mounted on an optical pickup compatible with both CD and DVD. Further, in this case, by designing the number of steps in the second grating portion to be six, it is possible to design the laser beam with high efficiency.

[0014] Further, the first grid portion and the second grid portion may be integrally formed of resin. As a result, the cost of the mold can be reduced and the manufacturing process can be simplified, so that the cost can be reduced.

[0015] Further, an irregular third grating portion may be formed on the surface of the second grating portion, and the third grating portion may be formed with a period equal to or less than the wavelength of the laser beam. Good. As a result, the antireflection function can be exhibited, so that it is not necessary to provide an expensive antireflection film, and the cost can be reduced.

Further, the optical device according to the present invention is characterized in that the light emitting points of the laser beams having different wavelengths are shifted from each other in a direction perpendicular to the optical axis, and the optical element through which the light from the light emitting section passes. A member and a light receiving unit for receiving the laser light, wherein an optical axis of the laser light of one wavelength and an optical axis of the laser light of the other wavelength are matched at a predetermined position. It is.

According to the present invention, since the number of parts can be reduced and the structure can be simplified, the manufacturing cost can be reduced.

For example, since the optical member can be disposed in the optical path from the light emitting section to the recording medium or in the optical path from the recording medium to the light receiving section, the installation position of the optical member is not limited. .

[0019]

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 partial plan view showing a first embodiment of the optical member and its optical axis. FIG. 3 is a partially enlarged plan view of the optical member of FIG. 2, and FIGS. 4 and 5 are diagrams showing light efficiency with respect to the grating depth when the number of steps is six or five.

An optical pickup 10 as an optical device shown in FIG. 1 has a light emitting section 12 having a built-in semiconductor laser diode, a collimator lens 13 for converting laser light emitted from the light emitting section 12 into parallel light, and incident thereon. A beam splitter that reflects laser light and transmits light incident from the reflection direction; an objective lens 15; a light receiving unit 16; and an optical device of the present invention disposed between the light emitting unit 12 and the beam splitter 14. A member 11 is provided.

In the light emitting section 12, a light emitting element 12a for forming a light emitting point of a laser beam having a wavelength of 785 nm (λ1) for CD and a wavelength of 658 nm (λ) for DVD.
The light emitting element 12b that forms the light emitting point of the laser light of 2) is disposed with a small space (S). For this reason, since the light emitting points are shifted, the optical axes of the laser lights emitted from the light emitting unit 12 are shifted from each other.

The wavelengths .lambda.1, .lambda.
When the laser light of No. 2 enters the beam splitter 14,
Reflected by the beam splitter 14 in the direction of the disk D1,
After being collimated by the collimator lens 13, the light enters the objective lens 15. The laser light condensed by the objective lens 15 forms a spot light on the disk D1. The return light reflected by the disk D1 passes through the objective lens 15 and the collimator lens 13 with the optical axes deviated from each other, passes through the beam splitter 14, and reaches the optical member 11.

As shown in FIG. 2, the optical member 11 is
The optical member 11 has a plate-like shape formed by molding a transparent resin using a mold. The first diffraction grating 11A is formed on the laser light incident surface side of the optical member 11, and the second diffraction grating 11A is formed on the emission surface side. A diffraction grating 11B is formed.

The first diffraction grating 11A has a first grating portion in which a plurality of projections 11a are formed in a continuous saw blade shape. Each convex portion 11a is formed in a right-angled triangular shape with a vertical surface and an inclined surface.
b (second lattice portion) is formed.

The second diffraction grating 11B has a first grating portion formed by continuously forming a plurality of convex portions 11c having the same shape as the first diffraction grating 11A. A step portion 11d as a second lattice portion is formed on each inclined surface of the portion so as to overlap with each other. However, the inclination direction of each step 11d is formed in a direction opposite to the direction of inclination of each step 11b of the first diffraction grating 11A (direction in which the inclined surfaces are parallel to each other).

In the optical member 11 shown in FIG. 2, each flat surface of the step 11b of the first diffraction grating 11A and each flat surface of the step 11d of the second diffraction grating 11B face each other. The stepped portion 11b is formed such that the lowermost flat surface of the stepped portion 11b and the uppermost flat surface of the stepped portion 11d face each other. However, they do not necessarily have to match.

As shown in FIG. 3, the step portion 11b (1
1d) is a shape in which the heights of the flat surfaces S1 to S6 are gradually changed so that the number of steps is six, and the width dimension w and y in the x direction of each step are provided.
Are formed at equal pitches (h = d
/ 5, w = p / 6). Here, p is a period, and this period is equal to the width dimension of the convex portion 11a (11c).

In the optical member 11 shown in FIG. 3, the lattice depth dimension, which is the distance from the lowermost flat surface S1 to the uppermost flat surface S6, is d, the depth dimension per stage is h, and the refraction of the resin. Assuming that the rate is n and the wavelength of the laser beam is λ, (n−1)
The relational expression of h = mλ holds. Here, m is a positive integer. From the above equation, by setting the depth dimension h such that (n-1) h is a positive integer multiple of the wavelength, the wavelength λ
When the laser light passes through the optical member 11, the laser light is not diffracted.

From the above equation, in the optical member 11,
By setting h such that (n−1) h is a positive integer multiple of λ2 with respect to the laser light of λ2 (658 nm), the laser light is emitted when the laser light of λ2 enters the optical member 11. The light can be transmitted in the state of the zero-order diffracted light without being diffracted. By setting h in this way, when the laser light of λ2 passes through the optical member 11, it is not diffracted on either the entrance surface or the exit surface, and
The laser light of No. 2 can travel straight in the optical member 11 while keeping the zero-order diffracted light.

On the other hand, in the present embodiment, since the laser beam of λ2 is designed not to be diffracted, it is necessary to align the optical axis of the laser beam of λ1 (785 nm) with the optical axis of the laser beam of λ2. Therefore, the first diffraction grating 11A of the optical member 11 diffracts the first-order diffracted light of the λ1 laser light toward the optical axis side of the λ2 laser light by forming the shape shown in FIGS. The laser beam of λ1 can be diffracted in a direction opposite to the above by the second diffraction grating 11B provided in the opposite direction to the first diffraction grating, and the optical axis of the laser beam of λ1 and the laser beam of λ2 Of the optical axes can be matched.

The lattice depth dimension d (= 5) is greater than the depth dimension h.
h) is determined, and the period p is set in advance in the range of, for example, 30 to 50 nm. Therefore, the shape of the optical member 11 is determined by determining the number of remaining steps. Therefore, when the number of stages was changed one by one, it was confirmed that an optimum value was obtained when the number of stages was six as shown in FIG. The reason will be described with reference to the diagram shown in FIG.

FIG. 4 is a diagram showing the relationship between the grating depth (μm) and the efficiency for each of the diffracted lights of wavelengths λ1 and λ2. However, the period (p) of the diffraction gratings 11A and 11B at this time is
Are each 20 μm, and each has a refractive index of 1.54. The efficiency on the vertical axis in FIG. 4 refers to the 0th-order diffracted light (0T) and the 1st-order diffracted light (1T) of the laser light after passing when the light amount of the laser light before passing through the diffraction grating 11A is assumed to be 1.
T) and the ratio of the amount of light of the second-order diffracted light (2T). It should be noted that the second diffraction grating 11B has the same waveform as that of FIG. 4 except that the direction in which the laser light passes is reversed and the diffraction direction is reversed.

As shown in FIG. 4A, by setting the grating depth d of the diffraction grating to around 6 μm, 658 n
m 0th-order diffracted light and 785 nm first-order diffracted light can be output with high efficiency.

Incidentally, in the lattice depth dimensions shown in FIGS. 4B and 4C, the 0th-order diffracted light of 658 nm and the 1st diffraction light of 785 nm are used.
It is not preferable because it is impossible to obtain the next-order diffracted light with high efficiency. In addition, it is not preferable to increase the lattice depth d because the fluctuation with respect to the wavelength variation increases.
In addition, although the second-order diffracted light of 785 nm can be obtained with the lattice depth dimension shown in (b), the efficiency of the second-order diffracted light deteriorates, which is not preferable.

Therefore, the lattice depth d is set to 6.1 μm.
The optical member 11 with high efficiency can be obtained by forming the width and depth of each step of the steps 11b and 11d at the same pitch in the vicinity.

FIG. 5 shows a step 11b (1) shown in FIG.
It is formed by changing the number of steps 1d) to five. In the configuration shown in FIG. 5, by setting the grating depth dimension d of the diffraction gratings 11A and 11B to around 5.8 μm (e), 65
Both the 1st-order diffracted light of 8 nm and the 0th-order diffracted light of 785 nm can be obtained with relatively high efficiency.

In the above-mentioned optical member 11, it is preferable that the steps 11b and 11d of the diffraction gratings 11A and 11B have six or five steps.
Preferably, it is a step. The wavelengths are 658 nm and 78
In combinations other than the combination of 5 nm, the lattice depth dimension d and the number of steps are different.

The six-stage optical member 11 formed as described above transmits a 658 nm laser beam without diffracting it, and diffracts a 785 nm laser beam, thereby obtaining a laser beam of 785 nm.
The optical axis of the first-order diffracted light of 85 nm and the optical axis of the zero-order diffracted light of 658 nm can be matched on the light receiving surface of the light receiving unit 16. Also, in the case of five stages, by transmitting the 785 nm laser light without diffracting it and diffracting the 658 nm laser light, the optical axis of the 658 nm −1st-order diffracted light can be adjusted.
The optical axis of the 0-order diffracted light of 5 nm can be matched with the light receiving surface of the light receiving unit 16.

FIG. 6 is a partial plan view showing a second embodiment of the optical member of the present invention. Optical member 21 shown in FIG.
The optical member 11 has a cavity 5 formed between a first diffraction grating 11A and a second diffraction grating 11B. The wavelength λ1 (λ) incident from the first diffraction grating 11A
The laser light of 2) passes through the cavity 5 and is emitted from the second diffraction grating 11B. The cavity 5 is preferably an air layer, but may be a layer filled with a liquid.

By forming the cavity 5 as described above, the laser beam can be largely bent by the refraction action, so that the amount of diffraction of the laser beam by the first diffraction grating 11A and the second diffraction grating 11B is reduced. it can.

The optical member 31 shown in FIG. 7 is a partial plan view showing a modified example of the optical members 11 and 21. The optical member 31 is formed by further forming a jagged minute diffraction grating (third grating portion) 11e on the flat surface of each step of the step portions 11b and 11d formed on the optical members 11 and 21. . At this time, when one protrusion (or recess) of the minute diffraction grating 11e has a width of one cycle,
Preferably, the period is equal to or less than the wavelength of the laser light. As a result, the anti-reflection function can be exhibited, so that it is not necessary to form an expensive anti-reflection film, and the cost can be reduced.

In the optical members 11, 21 and 31,
Since the convex portions 11a and 11c and the step portions 11b and 11d are both made of resin and are integrally molded using a mold, the manufacturing cost can be reduced.

[0043]

As described above, according to the present invention, optical axes shifted from each other can be matched at a predetermined position. In addition, even if the light receiving portions are positioned so as to be shifted in the optical axis direction, the light receiving positions do not shift from each other, so that the positioning accuracy can be reduced. Further, since only the laser light of one wavelength is diffracted, the influence of wavelength fluctuation due to temperature change can be reduced.

Further, by providing a cavity between the first diffraction grating and the second diffraction grating, laser light can be refracted in the cavity, and as a result, the first diffraction grating and the second diffraction grating can be refracted.
Can reduce the amount of diffraction of the laser light of one wavelength by the diffraction grating, so that the influence of wavelength fluctuation due to temperature change can be reduced.

Further, the optical device of the present invention can reduce the number of parts and simplify the structure, so that the 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 partial plan view showing a first embodiment of the optical member of the present invention;

FIG. 3 is a partially enlarged plan view of the optical member of FIG. 2;

FIG. 4 is a diagram showing a relationship between grating depth and efficiency when the number of optical members is six;

FIG. 5 is a diagram showing the relationship between the grating depth and the efficiency when the number of optical members is five;

FIG. 6 is a plan view showing a second embodiment of the optical member of the present invention.

FIG. 7 is a plan view showing a part of a modification of the optical member of the present invention.

FIG. 8 is a schematic diagram showing an optical path in a conventional optical device;

FIG. 9 is a schematic diagram showing a conventional optical member and its optical axis;

[Explanation of symbols]

 Reference Signs List 5 cavity portion 10 optical pickup 11, 21, 31 optical member 11A first diffraction grating 11B second diffraction grating 11a, 11c convex portion 11b, 11d step portion 11e micro diffraction grating 12 light emitting portion 12a, 12b light emitting element 13 collimator lens 14 Beam splitter 15 Objective lens 16 Receiver

Claims (9)

[Claims] 1. A first diffraction grating provided on an incident surface side and a second diffraction grating provided on an emission surface side of laser light emitted from a light emitting element having a different wavelength and having an optical axis shifted. Each of the first diffraction grating and the second diffraction grating has a first grating portion formed in an uneven shape and a step-like shape formed so as to overlap an inclined surface of the first grating portion. A second grating portion, wherein the overall depth from the lower stage to the upper stage of the second grating portion is d, the depth per stage is h, and the refractive index in the diffraction grating is n. Then, the depth dimension h per step is set so that (n−1) · h is an integral multiple of the wavelength λ, and the total depth is determined based on the depth dimension h of each step. Dimension d
And determining the optimum value of the width dimension of each step, the laser light is diffracted at one wavelength when the laser light is incident on the first diffraction grating, and the laser light is diffracted by the second diffraction grating. An optical member characterized in that when emitted from a grating, the optical axis of the laser light of one wavelength is diffracted so as to coincide with the optical axis of the laser light of the other wavelength. 2. A first diffraction grating on the incident surface side and a second diffraction grating on the emission surface side are provided to face each other, and
The optical member according to claim 1, wherein the inclination direction of the grating portion of the diffraction grating and the inclination direction of the grating portion of the second diffraction grating coincide with each other. 3. The optical member according to claim 1, wherein a cavity is formed between the first diffraction grating and the second diffraction grating through which the laser light passes. 4. The wavelength of the one laser beam is 785 nm.
4. The optical member according to claim 1, wherein the wavelength of the other laser beam is 658 nm. 5. The optical member according to claim 4, wherein the number of steps in the second grating portion is six. 6. The optical member according to claim 1, wherein the first grating portion and the second grating portion are both integrally formed of resin. 7. The unevenness of the third grating portion is further formed on the surface of the second grating portion, and the third grating portion is formed with a period equal to or less than the wavelength of the laser beam. Item 1
7. The optical member according to any one of items 6 to 6. 8. A light emitting unit in which light emitting points of laser light of different wavelengths are shifted from each other in a direction orthogonal to an optical axis;
The optical member according to any one of claims 1 to 6, through which light from the light emitting unit passes, and a light receiving unit that receives the laser light, and an optical axis of the laser light of one wavelength and the other. An optical device wherein an optical axis of a laser beam having a wavelength is matched at a predetermined position. 9. The optical device according to claim 8, wherein the optical member is disposed in an optical path from the light emitting unit to a recording medium or in an optical path from the recording medium to a light receiving unit.