KR100466668B1 - Optical member and optical device using the same - Google Patents

Abstract

(Problem) In the conventional diffraction grating, the wavelength fluctuation by a change of temperature is large, and the shift of the light receiving position in the light receiving part of the laser beam was large.

(Solution means) A convex portion 11a is formed on the transparent resin substrate as a first lattice portion, and a stepped portion 11b as a second lattice portion is formed on the inclined surface of the convex portion 11a. Each step of the stepped portion 11b determines h so that (n-1) h when the height dimension is h and the refractive index is n is an integer multiple of the wavelength, and the height h and the period p ) Determines the most appropriate singular. When the wavelength is 658 nm and 785 nm, the six stages are most suitable.

Description

Optical member and optical device using the same {OPTICAL MEMBER AND OPTICAL DEVICE USING THE SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical member to which two different wavelengths of laser light are incident, and more particularly, to an optical member for receiving laser beams of different optical axes from a light receiving unit and an optical device using the same.

The optical pickup mounted on the disk apparatus which can use both CD and DVD is equipped with a light emitting unit in which light sources of two different wavelengths of laser light are integrally mounted in order to simplify the structure. In the light emitting portion, since the light sources are arranged at small intervals, an optical path is formed in a state where the optical axis of the laser light is shifted. In the state where the optical axis is shifted, the position of light receiving at the light receiving portion is shifted, so it is necessary to match the light receiving position of both laser beams at the light receiving portion.

7 is a plan view showing a conventional optical member 30 formed to eliminate the misalignment. The optical member 30 has an uneven diffraction grating 30a formed on one side of the plate-shaped transparent member, and is formed at a position facing the light receiving portion 31.

The optical member 30 is mounted on a disc device for both CD and DVD. In this disc device, a laser light having a wavelength of 785 nm is used for a CD and a laser having a wavelength of 658 nm is used for a DVD. A light emitting portion for emitting light is formed. As shown in Fig. 7, the optical axis 30 of the return light reflected by the disk is shifted back to the optical member 30, and both laser beams are diffracted by the diffraction grating 30a of the optical member 30 to receive the light receiving portion 31. The light receiving positions coincide with each other at the position reaching. Further, the diffraction angle varies depending on the wavelength, and in the case shown in Fig. 7, the diffraction angle θ1 of λ1 becomes larger than the diffraction angle θ2 of λ2.

However, in the light emitting portion emitting the laser light, the wavelength is changed in accordance with the temperature change, so that the diffraction angle is changed in accordance with the temperature change in the conventional optical member 30, and as a result, in the light receiving portion of the laser light The light receiving positions do not coincide with each other, causing a problem of offset. For example, when the light-receiving position in the light-receiving portion is greatly shifted, diffracted light having a higher order than the first-order diffraction light leaks to the light-receiving portion, which may cause an offset.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems, and to provide an optical member and an optical device using the same, which can match optical axes of laser beams which are displaced with each other in the light-receiving section, and can reduce the influence of wavelength fluctuation due to temperature change. do.

Means to solve the problem

In the optical member to which the laser light of different wavelengths [lambda] 1 and [lambda] 2 is incident,

A diffraction grating is formed which diffracts the laser light of the first wavelength [lambda] 1 and transmits it without diffracting the laser light of the second wavelength [lambda] 2.

In this case, the diffraction grating has selectivity with respect to the first order diffracted light for the laser light of the first wavelength [lambda] 1, and selectivity with respect to zero order diffracted light for the laser light of the second wavelength [lambda] 2. Can be configured.

The diffraction grating has a first grating portion formed in an uneven shape and a second grating portion formed in a step shape on an inclined surface of the first grating portion, and the height h of one step of the second grating portion formed in the step shape is the second. (N-1) h = mλ2 with respect to the laser light of the wavelength lambda 2 (where n is a refractive index and m is a positive integer), and the laser light of the second wavelength lambda 2 is transmitted without diffraction, and It is preferable that the number of steps of the step shape of the second grating portion is set so that the laser light of the first wavelength λ1 can be diffracted by a predetermined angle.

Moreover, it is preferable that each end of the said 2nd grating part is formed in equal pitch in both the width direction and the height direction.

In the present invention, since the laser light of one wavelength is not diffracted, the diffraction angle of the other laser light can be reduced, the influence of wavelength fluctuation due to temperature change can be reduced, and the deviation of the light receiving position in the light receiving portion can be reduced. can do.

Further, when the first wavelength [lambda] 1 is 785 nm and the second wavelength [lambda] 2 is set to 658 nm, it can be applied to the optical pickup combining both CD and DVD.

Further, in this case, by designing the number of steps of the stepped second grating portion to be six stages, it becomes possible to design in which the efficiency at the light receiving position is kept high with respect to both laser beams.

Further, it is preferable that a third grating portion having an uneven shape is formed on the surface of the second grating portion, and the unevenness is formed so that the period of the third grating portion formed at one end of the second grating portion is equal to or less than the wavelength of the laser beam. Do. Since the anti-reflection effect is exhibited by this unevenness, the loss due to light reflection can be reduced.

In addition, since the first grating portion and the second grating portion are integrally formed of resin, the manufacturing cost can be reduced.

In addition, the optical device of the present invention includes a light emitting portion in which a light emitting point for emitting a laser light of the first wavelength λ1 and a light emitting point for emitting a laser light of the second wavelength λ2 are shifted in a direction orthogonal to the optical axis; The optical member through which the light from the light emitting portion is transmitted is formed, and the optical axis of the laser light of the first wavelength λ1 and the optical axis of the laser light of the second wavelength λ2 coincide at a predetermined position.

In the present invention, since the light emitting portion in which the light source of the laser light of the two wavelengths is integrally formed and a single optical member capable of independently diffraction of the laser light of the two wavelengths are formed, the component score can be reduced to simplify the structure. Can be reduced.

1 is a schematic view showing an example of an optical apparatus on which the optical member of the present invention is mounted.

2 is a schematic diagram showing an optical member and its optical axis.

3 is a plan view showing a part of an optical member.

4 is a diagram showing the light efficiency with respect to the grating height when the number of stages is six stages.

Fig. 5 is a graph showing the light efficiency with respect to the grating height when the number of stages is five stages.

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

7 is a schematic diagram showing a conventional optical member and its optical axis.

* Description of symbols on the main parts of the drawings *

10: optical pickup 11: optical member

11a: convex portion (first lattice portion) 11b: stepped portion (second lattice portion)

11c: micro diffraction grating (third lattice portion) 12: light emitting portion

12a, 12b: light emitting element 13: collimator lens

14 beam splitter 15 objective lens

16: light receiver

Embodiment of the invention

1 is a schematic diagram showing an example of an optical device on which the 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 partially omitted plan view showing an optical member, and FIG. 5 is a diagram showing the light efficiency with respect to the grating height in the case of five stages.

The optical pickup 10 as the optical device shown in FIG. 1 includes a light emitting portion 12 having a semiconductor laser diode embedded therein, a collimator lens 13 having a laser beam emitted from the light emitting portion 12 as parallel light, A beam splitter 14, an objective lens 15, a light receiving portion 16, and a bone disposed between the light receiving portion 16 and the beam splitter 14 for reflecting laser light and transmitting light incident in the reflection direction. The optical member 11 of the invention is provided.

The light emitting portion 12 includes a light emitting element 12a for forming a light emitting point of a laser light having a wavelength of 785 nm (λ1) for CD and a light emitting element for forming a light emitting point of a laser light having a wavelength of 658 nm (λ2) for a DVD ( 12b) is arrange | positioned in the single case and spaced apart at the micro spacing S. As shown to FIG.

When the laser light of each wavelength λ1, λ2 emitted from the light emitting portion 12 is incident on the beam splitter 14, it is reflected from the beam splitter 14 in the direction of the disk D1, by the collimator lens 13 After becoming parallel light, it is incident on the objective lens 15. The laser light collected by the objective lens 15 forms a spot light on the disk D1, and the returned light reflected on the disk D1 has the objective lens 15 and the collimator lens ( 13, the optical member 11 is reached by passing through the beam splitter 14.

As shown in FIG. 2, the said optical member 11 is formed in plate shape from the transparent resin member, the glass member, or the composite material of resin and glass. In the optical member 11, the laser light of the wavelength λ2 for DVD is transmitted without diffraction and introduced into the light receiving portion 16, and the laser light of the wavelength λ1 for CD is diffracted and introduced into the light receiving portion 16. . 1, the concave lens 17 may be arrange | positioned between the optical member 11 and the light receiving part 16, and may enlarge the beam shape of the laser beam formed in the light receiving part 16. As shown in FIG.

The light receiving portion 16 is formed of a photodiode, and has a light receiving element in which four divisions of sensors A, B, C, and D are combined, and a side light receiving element consisting of sensors E and F formed on both sides of the light receiving element. . For example, the three-beam method and the phase difference method are applied as the tracking servo mechanisms of CD and DVD, respectively, and the astigmatism method is applied as the focusing servo mechanism. In the focusing servo mechanism of CD and DVD, the light receiving element is used as a common element.

In the light receiving portion 16, the wavelength is changed in accordance with the temperature change, so that the spot of the laser light is shifted in the direction orthogonal to the direction of the EF leading to the sensor E and the sensor F. As a result, higher order diffracted light leaks to the light receiving element. Problems will arise. Therefore, the optical member 11 which improved the said shift | shift is shown next.

On the exit surface side of the laser beam 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 is formed on the inclined surface of each convex portion 11a. Lattice portion) is formed. The diffraction grating 11A is comprised by the said convex part 11a and the step part 11b.

The first grating portion is formed in a substantially sawtooth shape, and each of the convex portions 11a is a right triangle formed in a vertical plane and an inclined plane in the same shape. The stepped portion 11b is formed so that the flat surfaces S1 to S6 gradually change in height to have six stages, and the width dimension w in the x direction and the height dimension h in the y direction of each stage. ) Are all formed at the same pitch (h = d / 5, w = p / 6). However, p is a period and this period is the width dimension of the convex part 11a.

In the diffraction grating 11A formed in the optical member 11 shown in Fig. 3, when the height dimension of each stage is h, the refractive index of the resin is n, and the wavelength of the laser light is λ, (n-1) h = mλ Relation is established. However, m is a positive integer. By defining h such that (n-1) h is an integer multiple of the wavelength in the above relation, it is possible to transmit the laser light of the wavelength λ without diffraction.

By setting h so that (n-1) h becomes a positive integer multiple of λ2 with respect to the laser light of λ2 (658 nm) in the above formula, the zeroth order is not diffracted when the laser light of λ2 is incident on the diffraction grating 11A. It can transmit in a diffracted light state.

Since the lattice height dimension d (= 5h) of the convex part 11a is determined by the above, and the period p is also preset in the range of 30-50 micrometers, for example, the optical member ( 11) shape is determined. Therefore, as a result of changing the stages by one stage, it was confirmed that the shape having the six stages shown in FIG. 3 was most suitable. The reason will be described with reference to FIG. 4.

4 is a graph showing the relationship between grating height and efficiency for each diffracted light of wavelengths? 1 and? 2. However, the period p was 20 µm and the refractive index was 1.54. In addition, the efficiency of the vertical axis of FIG. 4 shows that the 0th order diffraction light (0T) and the ± 1st order diffraction light after the passage when the light quantity of the laser beam before the passage when the laser beam passes the diffraction grating 11A are 1 ( ± 1T) and the light amount ratio of the ± 2nd order diffracted light (± 2T).

As shown in Fig. 4A, by setting the grating height dimension (d) of the diffraction grating to around 6 µm, the 0th-order diffracted light at 658 nm (λ2) and the first-order diffracted light at 785 nm (λ1) are obtained. It can be obtained with high efficiency.

By forming the optical member 11 as described above, it has the selectivity to select the first order diffracted light for the laser light of λ1, and the selectivity to select the 0th order diffracted light for the laser light of λ2. Further, both the first diffracted light of λ1 and the zero-order diffracted light of λ2 can be obtained with high efficiency.

Further, in the grating height dimensions shown in Figs. 4B and 4C, the first order diffracted light of 785 nm (λ1) and the zeroth order diffracted light of 658 nm (λ2) cannot be obtained with high efficiency. In addition, it is not preferable to increase the height dimension d because the variation with respect to the variation in wavelength becomes large. Further, at the height of (b), second-order diffracted light of 785 nm can be obtained, but the efficiency becomes worse, which is not preferable.

Therefore, the grating height dimension d is set to around 6 µm (more precisely around 6.1 µm), and the diffraction grating maintaining high efficiency by forming the width dimension and the height dimension of each step of the stepped portion 11b at equal pitches, respectively. 11A can be obtained.

5 is a diagram in which the number of stages of the diffraction grating 11A shown in FIG. 3 is changed from six stages to five stages. However, also in this case, as mentioned above, the width dimension and the height dimension of each stage are formed in equal pitch.

In Fig. 5, by setting the grating height dimension (d) of the diffraction grating to be about 5.8 mu m (e), both the 658 nm -1st diffraction light and the 785 nm 0th order diffracted light can be efficiently obtained. In this case, since λ1 and λ2 are reversed, 658 nm may be λ1 and 785 nm may be λ2.

As described above, the grating height dimension (d) of the diffraction grating is a shape determined by Fig. 4A or Fig. 5E, which transmits only the 0th order diffracted light of the laser light of 658 nm and also the laser of 785 nm. Only the first diffracted light of light can be diffracted, or only the 658 nm -first diffracted light can be diffracted and only the 785 nm zero-order diffracted light can be transmitted, thereby receiving an optical axis of 785 nm and an optical axis of 658 nm. Can match at.

Therefore, since one side of the laser light is not diffracted and is not affected by the wavelength fluctuation, while the other side of the laser light is diffracted, the diffraction angle is smaller than that of the related art, and thus the influence of the wavelength fluctuation can be reduced as a whole. In the case where the number of stages in the optical member 11 is 6 stages and 5 stages, it is more preferable to set the shape to 6 stages in view of light efficiency.

In this embodiment, a combination of wavelengths of 658 nm and 785 nm has been described, but other wavelength combinations may be used. By varying the wavelength combination, the number of stages or height dimensions that are most suitable for the stepped portions are changed.

Moreover, since the convex part 11a which comprises the said 1st grating part and the step part 11b which comprises a 2nd grating part are formed integrally with resin, manufacturing cost can be made low.

The diffraction grating 11B shown in FIG. 6 is a plan view showing a part of a modification of the diffraction grating 11A.

The diffraction grating 11B is formed by superposing a fine diffraction grating (third grating portion 11c) made of jagged irregularities on the flat surfaces S1 to S6 of the stepped portion 11b of the diffraction grating 11A. It is. In this micro diffraction grating 11c, when one period is made from the convex part to the adjacent convex part, it is preferable that this one period is formed shorter than the wavelength (lambda) 1 or (lambda) 2 of the said laser beam. Thereby, the antireflection effect equivalent to the case of forming an expensive antireflection film can be exhibited.

As described above, according to the present invention, the misaligned optical axis can be matched at a predetermined position, and only the laser light of one wavelength can be diffracted and the diffraction angle of the other laser light can be made smaller than before. The influence of the wavelength fluctuation due to the temperature change can be reduced.

In addition, since the optical device of the present invention is composed of a light emitting portion emitting two wavelengths of laser light and a single optical member that coincides the optical axis of each laser light, the number of parts can be reduced, the structure can be simplified, and the cost can be reduced. Will be.

Claims (9)

In an optical member in which laser light of different wavelengths λ1 and λ2 is incident in a state in which optical axes are shifted from light emitting elements having different wavelengths, The optical member is provided with a diffraction grating which diffracts the laser light of the first wavelength [lambda] 1 and transmits the laser light of the second wavelength [lambda] 2 without diffraction, And an optical axis of the laser beam of the first wavelength [lambda] 1 and an optical axis of the laser beam of the second wavelength [lambda] 2 coincide at a predetermined position of the light receiving portion. 2. The diffraction grating of claim 1, wherein the diffraction grating has selectivity with respect to the first order diffracted light with respect to the laser light of the first wavelength [lambda] 1, and with respect to the zeroth order diffracted light with respect to the laser light of the second wavelength [lambda] 2. Optical member, characterized in that it has a selectivity. 3. The height of the second grating portion according to claim 2, wherein the diffraction grating has a first grating portion formed in an uneven shape and a second grating portion formed in a step shape on an inclined surface of the first grating portion, h) is (n-1) h = mλ2 with respect to the laser light of the second wavelength λ2 (where n is a refractive index and m is a positive integer), and the laser light of the second wavelength λ2 is diffracted And the number of steps of the step shape of the second grating portion is set so that the laser beam of the first wavelength [lambda] 1 can be diffracted by a predetermined angle. 4. The optical member according to claim 3, wherein each end of the second grating portion is formed at equal pitches in both the width direction and the height direction. The optical member according to claim 3, wherein the first wavelength (λ1) is 785 nm and the second wavelength (λ2) is 658 nm. 6. The optical member according to claim 5, wherein the number of steps of the step shape of the second grating portion is six stages. The uneven | corrugated 3rd grating part is formed in the surface of the said 2nd grating part, and the unevenness | corrugation is made so that the period of the 3rd grating part formed in the 1st stage of the said 2nd grating part may be below the wavelength of the said laser beam. An optical member, characterized in that formed. 8. The optical member according to claim 7, wherein both of the first grating portion and the second grating portion are integrally formed of resin. A light emitting portion in which the light emitting point emitting the laser light of the first wavelength λ1 and the light emitting point emitting the laser light of the second wavelength λ2 are shifted in a direction orthogonal to the optical axis, and the light from the light emitting portion is transmitted An optical member according to any one of claims 1 to 8, wherein the optical axis of the laser beam of the first wavelength lambda 1 and the optical axis of the laser beam of the second wavelength lambda 2 coincide at a predetermined position. Optics made with.