KR20030040093A - Diffraction grating member and method manufacturing therefor - Google Patents

Abstract

PURPOSE: To provide a diffraction grating member capable of obtaining prescribed diffracted light even when the edge angle or fitting angle of an injection metal mold cutting tool is not accurately adjusted. CONSTITUTION: In the diffraction grating member having a rectangular wave-like diffraction grating part provided with a recessed plane and projecting plane, at least one of the recessed plane and the projecting plane is constituted of a plurality of inclined face having the same inclination angle in the same direction so that an inclined step part having a difference in level is formed between both the inclined faces.

Description

Diffraction grating member and its manufacturing method {DIFFRACTION GRATING MEMBER AND METHOD MANUFACTURING THEREFOR}

The present invention relates to a diffraction grating member and a method of manufacturing the same, and more particularly, to a diffraction grating member having a rectangular wave-shaped diffraction grating having a concave portion plane and a convex portion plane.

Conventionally, some diffraction grating members are shown in FIG. The diffraction grating member 100 has a rectangular wave-shaped diffraction grating portion 103 having a concave portion plane 101 and a convex portion plane 102.

The diffraction grating member 100 irradiates the optical disk with light for DVD recording and reproduction and the CD reproducing light generated from a laser diode as a light emitting element, or induces the reflected light from the optical disk to the photodiode so as to induce the optical disk. It is used for optical pickup for signal recording, reproduction, and tracking.

In the optical pickup of the above-mentioned DVD and CD, as the tracking detection, it is common to adopt a phase difference method in which DVD is sufficient as one beam and a three beam method for CD. Conventionally, in the optical pickup, two LDs having different wavelengths are used to arrange a diffraction grating for generating three beams only on the CD side LD (780 nm band). Recently, however, two-wavelength LDs in which two LD chips are housed in one package have been proposed. In the case of using these two-wavelength LDs, the three-beam method is used only for CD playback and the phase difference method is used for DVD recording and playback. A wavelength selective diffraction grating member which emits three beams only on the CD side and one beam on the DVD side is used.

The diffraction grating member which makes such diffraction is realized by making the optical phase difference ((refractive index n-1) x depth) of the uneven part of a grating | lattice about DVD wavelength. However, it is apparent from the calculation that the depth of the concave plane of the diffraction grating member is about five times that of the diffraction grating for one wavelength that has been conventionally used.

Usually, such a diffraction grating member 100 has a method of directly etching the diffraction groove to the base material by etching, but as shown in Fig. 5, the concave portion 111 (the convex of the diffraction grating member 100 is formed by cutting). A mold 110 is formed by forming a rectangular wave-shaped surface 113 comprising a sub-plane 102 and a convex-plane 112 (forming the recess plane 101 of the diffraction grating member 100). In addition, a method of making the resin by injection molding the mold 110 is suitable for mass production.

In either case, however, since the grating depth d (shown in FIG. 5) is deeper than that of a general diffraction grating, the convex plane 102 and the concave plane 101 of the diffraction grating member 100 tend to be inclined. there is a problem.

That is, in the manufacturing method by etching, when the diffraction grating member having a large area is made, the variation in etching amount due to the location of the diffraction grating is likely to occur, so that the above inclination occurs. In forming the diffraction grating with the mold 110, when cutting the mold 110, as shown in FIG. 6, the edge of the cutting surface 121 of the die cutting bite 120 is inclined. Inclination occurs in the concave plane 111 and the convex plane 112 of the mold 110 due to variations in the holding accuracy of the bite of the machine tool or the moving precision of the bite.

In this way, in the three-beam diffraction grating member 100, when the uneven corner portions 101 and 102 are inclined, an intensity difference occurs between the +1 order light and the -1 order light, which are the sub beams of the 3 beams, and thus the track error signal of the pickup There is an offset, which causes a problem that stable track servo control cannot be performed.

That is, as shown in FIG. 7, when the uneven surface portions 101 and 102 are inclined and a difference in depth DELTA d = d2-d1 (nm) occurs at both ends of the grating, as shown in FIG. 8, +1 There is a difference approximately proportional to [Delta] d between shading and -1 shading.

In order to perform the tracking servo control as in the present example, it is required that the difference of the ± first-order diffraction light is 3% or less, and to realize this, it is necessary to make? D from FIG. 8 smaller than 1 Onm.

Specifically, as shown in FIG. 7, when the grating pitch of the diffraction grating member 100 is 30 μm, the inclination angles of the surfaces 101 and 102 are required to be 0.019 degrees or less.

Usually, it becomes difficult to finish the tip 121 of the cutting bite 120 which cut-forms the groove | channel of a metal mold | die with this precision. In order to realize such a high precision machining, it is necessary to perform a test machining to mechanically correct the incidence of the inclination and the mounting angle of the bite. However, such a correction is theoretically possible, but in the case of minute processing with a pitch of 30 µm, it is very difficult to accurately measure the inclination of about 10 nm of the cutting bite 120, and even if it is possible, the time is as long as the test processing. I get caught.

Accordingly, an object of the present invention is to provide a diffraction grating member capable of obtaining a predetermined diffracted light without precisely adjusting the cutting edge angle or installation angle of a cutting bite for producing an injection molding die.

BRIEF DESCRIPTION OF THE DRAWINGS Sectional drawing which shows the structure of a metal mold | die and a diffraction grating in the manufacturing method of the diffraction grating member concerning embodiment of this invention.

2 is a perspective view showing a state of cutting of a mold in the method for manufacturing a diffraction grating member according to the embodiment of the present invention;

3 is a graph showing the inclination of the grating plane and the imbalance of diffracted light of the diffraction grating member according to the embodiment of the present invention;

4 is a cross-sectional view showing another example of a diffraction grating member according to the present invention;

5 is a sectional view showing a diffraction grating member according to a conventional example;

6 is a cross-sectional view showing a method for manufacturing a diffraction grating member injection molding fixture according to a conventional example;

7 is a diagram showing the inclination of the diffraction surface of the diffraction grating member according to the prior art;

8 is a graph showing the inclination of the grating plane and the imbalance of diffracted light of the diffraction grating member according to the prior art.

※ Explanation of code in main part of drawing

10 diffraction grating member 11 inclined surface

12: inclined surface 13: recessed plane

14 convex part plane 15 diffraction grating part

16: inclined end 20: molding mold

21: inclined plane 22: inclined plane

23 convex part flat 24 concave part flat

25: diffraction grating forming unit 30: byte

40: base material 50: molding mold

51: inclined plane 52: inclined plane

53: convex part plane 54: concave part plane

60: diffraction grating member 70: bite

In this invention, in order to solve the said subject, the diffraction grating member and the manufacturing method were comprised as follows.

The diffraction grating member of the present invention has a rectangular wave-shaped diffraction grating portion having a concave portion plane and a convex portion plane, wherein at least one of the concave portion plane and the convex portion plane has a plurality of inclined surfaces having the same inclination angle in the same direction. And an inclined end portion having a step between both inclined surfaces.

According to the present invention, the difference in depth due to the inclination of the grating can be reduced, and the imbalance of the ± first-order diffracted light can be eliminated.

In the diffraction grating member of the present invention, the inclined end portion is formed in the concave portion plane.

According to the diffraction grating member according to the present invention, it is easy to cut an end in the convex portion of the molding die corresponding to the concave plane of the diffraction grating member, so that the mold can be manufactured with high precision.

In the diffraction grating member according to the present invention, the concave portion plane has an inclined end portion formed with two inclined surfaces, the end edge of the concave portion which is the shallowest position of one of the two inclined surfaces, and the deepest of the other inclined surfaces. The end edge part of the recess which is a position is arrange | positioned in the same depth position.

According to the present invention, the maximum and minimum depths of the two inclined planes generated at the time of preparing the diffraction grating member are not largely different from the design theory value of the concave portion of the diffraction grating member, thereby obtaining a value close to the designed optical performance value.

In the method for manufacturing a diffraction grating according to the present invention, in cutting the convex part plane of a molding die for forming the diffraction grating part of the diffraction grating member having a rectangular wave diffraction grating part having a concave part plane and a convex part plane, The cutting surface is divided into the first and second circuits in the parallel direction of the lattice and is cut in the same feed conditions with the same bite.In each cutting, the cutting point of the bite is changed in the lattice parallel direction with respect to the cutting position of the cutting bite. The grating mold is composed of a plurality of inclined surfaces having the same inclination angle in the same direction, and forms an inclined end portion having a step between both inclined surfaces, and is manufactured by injection molding the diffraction grating forming material with the mold.

According to the present invention, in preparing a mold for injection molding a diffraction grating, when cutting the convex surface portion of the mold, cutting is performed twice with one bite. For this reason, it is possible to easily obtain a diffraction grating having less mismatch of ± first-order diffraction light without the need for preparing a special cutting bite or making special adjustments to the bite.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of the diffraction grating member which concerns on this invention is described based on drawing. 1 to 3 show an embodiment of the diffraction grating member 10 according to the present invention.

The diffraction grating member 10 according to the present embodiment has a rectangular wave-shaped diffraction grating portion 15 having a concave portion plane 13 and a convex portion plane 14. The structure of such a basic diffraction grating member is the same as that of the diffraction grating member 100 shown as a prior art example.

The diffraction grating member 10 according to the present example is used for a combined optical pickup of a DVD and a CD having the same purpose as the conventional example.

In addition, in this example, as shown in FIG. 1, the concave part plane 13 and the convex part plane 14 are provided in the diffraction grating member 10, and the concave part plane 13 and the concave part plane 13 are provided. An inclination comprising two rows of inclined surfaces 11 and 12 that form the same inclination angle θ (FIG. 1) along the parallel direction of the convex portion plane 14, and a stepped step between the inclined surfaces 11 and 12. An end 16 is formed. Inherently, the value of θ is preferably 0, but in actual processing, it takes time to set θ to 0, and when a diffraction grating member is produced as a product, it becomes very expensive.

Therefore, in the diffraction grating member 10 according to the present example, the inclined plane 13 is formed with the inclined end portions 16 by two inclined surfaces 11 and 12, and one of the two inclined surfaces 11 and 12. The shallowest position 12a of the inclined surface 12 and the deepest position 1la of the other inclined surface 11 are formed at the same depth position h.

According to the diffraction grating member 10, the average depth of the concave plane 13 of the diffraction grating member 10 is approximately equal to the designed value, and the phase difference of the light from each surface is canceled out. Therefore, a value close to the designed optical performance value is obtained.

That is, as shown in FIG. 3, the imbalance between + 1st light beam and -1th light beam due to the inclination of the bite 30 when creating the uneven surface portions 23 and 24 of the molding die 20 is shown. Can be reduced to about 1/4 compared to the case where the same inclination bite is used in the conventional example.

Next, the manufacturing method of the diffraction grating member concerning this invention is demonstrated. In this example, the diffraction grating member 10 is formed by injection molding optical resin into a molding die 20 in which irregularities of a predetermined rectangular diffraction grating are formed.

That is, in this example, the molding die 20 has a concave portion 24 (corresponding to the convex portion 14 of the injection-molded diffraction grating member 10) and a convex portion 23 (the same concave portion plane) 13), a rectangular wave-shaped diffraction grating forming portion 25 is cut and installed.

As shown in FIGS. 1 and 2, the diffraction grating forming portion 25 of the molding die 20 cuts the base material 40 formed of metal into the bite 30 to form the convex portion 23 and the concave portion plane. To form (24).

In this example, as shown in FIG. 2, in forming the convex part 23 of the shaping | molding die 20, the same conveyance is divided | segmented into the same byte 30 by dividing 1st and 2nd in a parallel direction of a grating | lattice. The cutting is carried out under conditions, and the cutting is performed by changing the cutting positions of the bite 30 to the entire 30a and the rear part 30b in the lattice parallel direction with respect to the cutting position of the cutting bite 30. Subsequent to the two cutting operations, the concave portion plane 24 is cut.

As a result, two rows of inclined surfaces 21 and 22 having the same inclination angle are formed on the convex portion 23 of the molding die 20, and the concave portion 24 is formed. By these processes, the convex part plane 23 and the concave part plane 24 which consist of both inclined surfaces 21 and 22 are formed, and the diffraction grating formation part 25 is formed.

The cutting of the convex part plane 23 of the shaping | molding die 20 is demonstrated in detail. In this example, as shown in FIGS. 1 and 2, by moving one bite 30, the convex portion 23 of the molding die 20 is inclined to the first inclined surface 21 and the second inclined surface 22. Divided and cut.

This cutting does not need to be completed once for one surface, but the necessary recovery can be performed to form a final plane.

In this example, the width W of the bite 30 is set to be substantially the same as the width w of the concave portion 24, and the concave portion 24 of the molding die 20 is cut to form a convex portion. In cutting-making the plane 23, as shown in FIG. 1 and FIG. 2, one bite 30 is conveyed to the dimension corresponding to W / 2, and the convex part 23 is made to separate the first half and the second half separately. I am cutting.

In this example, in the method of manufacturing such a diffraction grating, the bite 30 uses a normal die cutting bite provided with a diode single crystal cutting chip.

By such cutting, in this example, the highest position 22a of one of the inclined surfaces 22 of the two inclined surfaces 21, 22 of the convex part plane 23 of the mold and the most of the other inclined surfaces 11 The lower position 21a becomes the same depth position.

In this example, the above-described configuration of the diffraction grating is obtained by injection molding the optical resin using the mold thus prepared. As the injection molding method, a conventionally known method is used.

According to the present example, a diffraction grating having a small difference of ± 1st order diffracted light can be easily produced without using a die cutting bite having a special shape or making special adjustments to the bite.

Further, in the above example, the case where the concave plane (the convex plane of the molding die) of the diffraction grating member is formed with two inclined planes is described. However, in the present invention, the convex plane may be formed of a plurality of inclined planes in addition to the concave plane. Can be. Moreover, only the convex part plane of a diffraction grating member can be comprised by several inclined surface.

In the above case, as shown in FIG. 4, when cutting the shaping mold 50, approximately half of the width dimension w of the uneven part planes 53 and 56 of the diffraction grating member 60 to be prepared is formed. The shaping | molding die 50 can be shape | molded by cutting with the bite 70 provided with the width dimension W1.

At this time, by simply moving the bite 70 in parallel, as shown in FIG. 4, the two inclined surfaces 51 and 52 of the convex part plane 53 of the shaping | molding die 50, and the concave part plane 56 are shown. The highest part and the lowest part of the two inclined surfaces 54 and 55 of () become mutually the same position, and the effect falls compared with the above-mentioned embodiment example.

As described above, according to the diffraction grating member and the manufacturing method according to the present invention, the following excellent effects can be exhibited.

According to the present invention, the difference in depth due to the inclination of the grating can be reduced, and the imbalance of the ± first-order diffracted light can be eliminated.

In addition, according to the diffraction grating member having the inclined end portion formed in the concave section plane according to the present invention, it is easy to cut the end of the forming mold convex part corresponding to the concave plane of the diffraction grating member, thereby making the mold accurate. It can be manufactured well.

According to the diffraction grating member according to the present invention, the maximum and minimum depths of the two inclined surfaces generated during the creation of the diffraction grating member are not largely different from the design theory of the concave portion of the diffraction grating member, so that an excellent value close to the designed optical performance value is obtained. Obtained.

According to the method for manufacturing a diffraction grating member according to the present invention, when preparing a mold for injection molding the diffraction grating, cutting is made twice with one bite when cutting the convex surface portion of the mold. For this reason, it is possible to easily obtain a diffraction grating having less mismatch of ± first-order diffraction light without the need for preparing a special cutting bite or making special adjustments to the bite.

Claims (4)

A diffraction grating member having a rectangular wave-shaped diffraction grating portion having a concave portion plane and a convex portion plane, At least one of the concave portion plane and the convex portion plane is composed of a plurality of inclined surfaces that form the same inclination angle in the same direction, the diffraction grating member, characterized in that the inclined end portion having a step between the two inclined surfaces are formed. The method of claim 1, An inclined end portion is formed in the concave portion plane. The method of claim 2, The concave plane has an inclined end portion formed at two inclined surfaces, the end edge of the concave portion being the shallowest position of one of the two inclined surfaces, and the end edge portion of the concave portion which is the deepest position of the other inclined surface. A diffraction grating member, characterized in that disposed on. In cutting the convex part plane of the shaping | molding die which forms the diffraction grating part of the diffraction grating member which has a rectangular wave-shaped diffraction grating part provided with the concave part plane and the convex part plane, The cutting surface is divided into the first and second circuits in the parallel direction of the lattice and is cut in the same feed conditions with the same bite.In each cutting, the cutting point of the bite is changed in the lattice parallel direction with respect to the cutting position of the cutting bite. A method of manufacturing a diffraction grating member comprising a plurality of inclined surfaces having the same inclination angle in the same direction in a lattice mold, and forming inclined ends having a step between both inclined surfaces and injection molding the diffraction grating forming material with the mold. .