JP2596627B2 - Optical diffraction grating element - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to an optical diffraction grating used for a video disk player, a compact disk (CD) player, and an optical pickup of a write-once and rewritable optical recording / reproducing apparatus. It relates to an element.

[Prior Art] Conventionally, as shown in FIG. 12, for example, in an optical pickup using an optical diffraction grating element 22, light emitted from a semiconductor laser 21 is transmitted through an optical diffraction grating element 22, a collimating lens 23 and an objective lens 24. Is focused on the record carrier 25 via the. The reflected light from the record carrier 25 is diffracted by the optical diffraction grating element 22 via the objective lens 24 and the collimating lens 23,
As shown in FIG. 13, for example, a point on the boundary between the light receiving units 26 a and 26 b in the light receiving element 26 divided into four parts, and light receiving units 26 c and 26 d
Is condensed as condensing spot S ₂₁ · S ₂₂ of the two points and the point on the borderline. Then, the light receiving units 26a to 2 in the light receiving element 26
From the output signals Sa to Sd of 6d, RES = (Sa−Sb) − (Sc + S
The objective lens 24 is driven so that the laser light emitted from the semiconductor laser 21 is focused on the information recording track of the record carrier 25 based on the radial error signal RES obtained by the operation formula d).

As shown in FIG. 14 (a), the optical diffraction grating element 22 has two regions 22a and 22b having different grating pitches. The grating pitch d ₂₁ and d ₂₂ of these regions 22a and 22b is Region 22a ・ 2
As described above, the reflected light from the record carrier 25 incident on the light receiving element 2b is formed as a lattice having a periodicity such that it is focused on two points on the boundary line in the light receiving element 26.

The cross-sectional shape of the optical diffraction grating element 22 includes a blaze angle θ
It is said that a sawtooth shape in which a peak and a valley are continuous has a high light diffraction efficiency and is effective, and is well known as a method of processing into such a shape. This is an ion etching method. In this method, for example, a material having a higher etching rate than a photoresist, such as GaAs or PMMA, is used as a substrate to be processed. Then, a photoresist is applied on the substrate, and a grating is manufactured by a holographic method, and the grating is used as a substrate etching mask. When etching the base material, as shown in FIG.
Then, an ion beam generated from, for example, an Ar gas, a CHF ₃ gas, or a CF ₄ gas is irradiated at a predetermined incident angle from obliquely above the direction in which the photoresists 27 are arranged. As a result, as shown in FIG. 2B, the photoresist 27 on the base material 28 functions as pinning, and the base material 28 is processed using the photoresist 27 as a vertex.

Here, when the ion beam is generated from Ar gas, the cross-sectional shape of the finally formed diffraction grating has a certain relationship with the incident angle of the ion beam as shown in FIG. Is formed into a slope having a blaze angle θ and a plane perpendicular to the slope. Further, when the ion beam is generated from CHF ₃ gas, the cross-sectional shape of the diffraction grating, as shown in FIG. The surface is machined so as to be recessed toward the peak, and the surface is curved and formed in a concave shape. Further, when the ion beam is generated from CF ₄ gas, the sectional shape of the diffraction grating is as shown in FIG.
The other surface forming a valley opposite to the slope for setting the blaze angle θ is formed substantially perpendicular to the surface of the base material 28,
The bottom of the valley formed by this surface and the slope for setting the blaze angle θ is processed so as to be a curved surface.

[Problems to be solved by the invention]

However, as described above, in the optical diffraction grating element 22 having the two regions 22a and 22b and having a different grating pitch between the regions 22a and 22b so as to diffract incident light in two different directions, ion etching is performed. When a diffraction grating is formed by the method, diffraction gratings having several kinds of grating pitches are often formed at the same time in view of easiness of production, mass productivity and cost. At this time, for example, in the regions 22a and 22b of the optical diffraction grating element 22 shown in FIG. 14 (a), as shown in FIGS. By changing the width L of the top and the width M of the top of the crest, or as shown in FIG.
As shown in (e), the lattice pitch is made different by changing the depth t of the valley to form a similar shape. As a result, between the optical diffraction grating element 22 of different regions 22a · 22b, different diffraction efficiency of the light, the light amount difference between the two focused spots S ₂₁ · S ₂₂ to be focused on the light receiving element 26 occurs . Therefore, even when the focus position of the objective lens 24 is at the information recording track position on the record carrier 25, the radial error signal RES does not become zero and an offset occurs.

[Means for solving the problem]

The optical diffraction grating element according to the first aspect of the present invention, in order to solve the above-described problems, has a peak portion and a valley portion that are alternately continuous,
A diffraction grating having a first region and a second region having mutually different grating pitches is formed by the shape having the slope for setting the blaze angle, and the first region and the second region diffract incident light in different directions. The following means are taken in the optical diffraction grating element.

That is, the blaze shape of the first region and the second region is such that the depth of each valley, the width of the valley, and the blaze angle are set to be the same between the two regions, and the cross-sectional shape of the valley is The other surface that forms the valley opposite the slope that sets the angle is curved toward the peak and has a concave shape.

The optical diffraction grating element according to the second aspect of the present invention, in order to solve the above-described problem, has a peak portion and a valley portion that are alternately continuous,
A diffraction grating having a first region and a second region having mutually different grating pitches is formed by the shape having the slope for setting the blaze angle, and the first region and the second region diffract incident light in different directions. The following means are taken in the optical diffraction grating element.

That is, the blaze shape of the first region and the second region is such that the depth of each valley, the width of the valley, and the blaze angle are set to be the same between the two regions, and the cross-sectional shape of the valley is The other surface forming the valley opposite to the slope for setting the angle is formed at a right angle to the substrate surface of the diffraction grating, and a portion connecting this surface and the slope for setting the blaze angle forms a curved surface. No.

[Operation] According to the configuration of claim 1, the first of the optical diffraction grating elements is provided.
The light quantity of both condensed spots formed on the light receiving element of the optical recording / reproducing apparatus is equalized by the second area and the optical recording / reproducing apparatus can perform high-accuracy tracking servo.

Further, the maximum range of the optical phase difference between the first region and the second region for obtaining a predetermined round-trip diffraction efficiency can be widened.

According to the configuration of the second aspect, the first of the optical diffraction grating elements is provided.
The light quantity of both condensed spots formed on the light receiving element of the optical recording / reproducing apparatus is equalized by the second region and the second area, so that the optical recording / reproducing apparatus can perform high-accuracy tracking servo.

Further, the allowable range of the optical phase difference for obtaining a predetermined round-trip diffraction efficiency can be widened.

Embodiment 1 First, the invention on which the present invention is based will be described below with reference to FIGS. 1 to 5.

As shown in FIG. 2, the optical pickup includes a semiconductor laser 1 that emits laser light, a collimating lens 3 that converts the laser light emitted by the semiconductor laser 1 into parallel light, and a light that enters through the collimating lens 3. An objective lens 4 for condensing on a record carrier 5; and an optical diffraction grating element 2 for diffracting reflected light from the record carrier 5 incident via the objective lens 4 and the collimating lens 3 and condensing it on a light receiving element 6.
And a light receiving element 6 for converting incident light into an electric signal.

As shown in FIG. 3, the light receiving element 6 has four light receiving portions 6a, 6b, 6c, 6d with a cross-shaped boundary line interposed therebetween. Output signals of these light receiving sections 6a, 6b, 6c, 6d are respectively
Assuming that Sa, Sb, Sc, Sd, the radial error signal RES is RES
= (Sa + Sb)-(Sc + Sd), and the objective lens 4 is driven such that the laser beam emitted by the semiconductor laser 1 is focused on the information recording track of the record carrier 5 based on the same signal. Configuration.

As shown in FIG. 1 (a), the optical diffraction grating element 2 has a region 2a as a first region having a mutually different grating pitch.
And a region 2b as a second region. These areas
The grating pitches d ₁ and d ₂ of 2a and 2b are obtained by reflecting the reflected light from the record carrier 5 incident on the areas 2a and 2b with the point on the boundary between the light receiving portions 6a and 6b of the light receiving element 6 and the light receiving portion 6c, respectively. -It is formed so that it is diffracted and condensed at two points, a point on the boundary line of 6d.

The sectional shapes of the regions 2a and 2b in the optical diffraction grating element 2 are as follows.
For example, it is etched by an ion beam generated from Ar gas, and has a sawtooth shape having a high light diffraction efficiency as shown in FIGS. The sawtooth shape of these regions 2a and 2b is composed of an asymmetrical V-shaped valley having a right angle at the bottom and a flat top at the peak, and the lattice pitch d ₁ and d ₂ is equal to the two regions 2a and 2b. For the purpose of equalizing the 0th-order diffraction efficiencies and the 1st-order diffraction efficiencies between them, they are set by making the occupation ratios of the valleys and the peaks different. That is, in the region 2a and region 2b is set to the same depth t Oyo blaze angle θ of the valley, the amount corresponding to the difference between the grating pitch d ₂ of the grating pitch d ₁ and region 2b of the regions 2a, The width M of the top of the peak of the region 2b is wide.

In the optical diffraction grating element 2, the blaze angle θ and the depth of the valley are set so as to appropriately converge the condensed beam on the record carrier 5 and to improve the S / N in the output signal of the optical pickup. The optical phase difference set by t is set as follows.

That is, when the wavelength of the incident light is lambda, the average of the grating pitch d ₁ of the region 2a shown in FIG. 1 (a) is at (2.2 ± 0.2) λ,
In the optical diffraction grating element 2 average grating pitch d ₂ is (2.8 ± 0.2) λ in the region 2b, the blaze angle θ and valleys depth t, the blaze angle θ is of 30 to 45 DEG And the valley depth t is within the range of depths at which an optical phase difference of 0.7π to 0.9π is generated, the 0th-order diffraction efficiencies of the regions 2a and 2b and the 1st-order diffraction efficiencies are The combinations are set to be almost equal. At this time, a range in which one of the zero-order diffraction efficiencies deviates from the other zero-order diffraction efficiency and a range in which the other one of the first-order diffraction efficiencies deviates from one of the first-order diffraction efficiencies may be allowed up to 5%. it can.
With the above setting, 12% in the optical diffraction grating element 2
High reciprocating diffraction efficiency as described above is obtained. The reciprocating diffraction efficiency, and d ₁ 0-order d ₂ primary reciprocating diffraction efficiency is the product of the first-order diffraction efficiency in the 0 order diffraction efficiency of the grating pitch d ₂ of the region 2b in the region 2a of the grating pitch d _1, area It illustrates a d ₂ 0-order d ₁ primary reciprocating diffraction efficiency is the product of the first-order diffraction efficiency of the zero-order diffraction efficiency of the region 2a of 2b. From these d ₁ 0-order d ₂ 1 order reciprocating diffraction efficiency and d ₂ 0-order d ₁ 1 primary reciprocating diffraction efficiency is to fundamentally influence the quantity of light incident on the light receiving element 6. Note that the conditions of the lattice pitches d ₁ and d ₂ are 2.2λ, respectively, as described above.
And 2.8λ have a tolerance of ± 0.2λ,
Within these ranges, each round-trip diffraction efficiency of 12% or more can be obtained under the above conditions. In the following examples, λ is the case where the oscillation wavelength λ of a semiconductor laser generally used as a light source of an optical pickup is 780 nm.

The numerical value of 12% or more in the double reciprocating diffraction efficiency is a desirable efficiency as the optical diffraction grating element 2 for obtaining a good video signal when the optical diffraction grating element 2 is used for an image pickup, for example. That is, in an optical pickup that handles video signals, an S / N of 45 dB or more is required for an output signal in order to obtain a good video signal. % Is desired.

When setting the blaze angle θ and the optical phase difference, first, the depth t of the valley at each blaze angle θ, that is, the optical phase difference, the zero-order diffraction efficiency of the regions 2a and 2b, the region 2a ・
2b of first-order diffraction efficiency, d ₁ 0-order d ₂ primary reciprocating diffraction efficiency and d ₂
The relationship with the 0th order d1 _1st order round-trip diffraction efficiency was investigated. Some of the results are shown below.

For example, when the blaze angle θ is 35 °, the dependence of the diffraction efficiency on the depth t of the valley is such that when the optical diffraction grating element 2 is formed of, for example, quartz glass and its refractive index is 1.454, FIG. As shown in the graph of (a), when the depth t of the valley where the optical phase difference is about 0.79π is around 0.68 μm, the 0th-order diffraction efficiencies of the regions 2a and 2b and the 1st-order diffraction efficiencies are Are almost uniform, and both the d ₁ 0 order d ₂ 1 order reciprocal diffraction efficiency and the d ₂ 0 order d ₁ 1 order reciprocal diffraction efficiency in both regions 2a and 2b are 13.1%.
About.

When the blaze angle θ is 30 °, which is the smallest value in the range of 30 to 45 °, the 0th-order diffraction efficiencies and the 1st-order diffraction efficiencies in the regions 2a and 2b are almost equal, and d ₁ in the regions 2a and 2b 0th order d ₂
Primary reciprocating diffraction efficiency and d ₂ 0-order d ₁ primary reciprocating diffraction efficiency and 12%
This is because the valley depth t is set to 0.61 μm and the optical phase difference is set to 0.71 μm, as shown in the graph of FIG.
This is the case when it becomes π.

When the blaze angle θ is 45 °, which is the largest value in the range of 30 to 45 °, the 0th-order diffraction efficiencies and the 1st-order diffraction efficiencies in the regions 2a and 2b are almost the same, and the double reciprocating diffraction efficiencies in the regions 2a and 2b Is 12% or more when the depth t of the valley is set to 0.76 μm and the optical phase difference is 0.88π, as shown in the graph of FIG.

On the other hand, when the blaze angle θ is 25 °, which is a value smaller than the range of 30 to 45 °, the 0th-order diffraction efficiencies and the 1st-order diffraction efficiencies of the regions 2a and 2b are almost the same, as shown in FIG. As shown in the graph, this is the case where the depth t of the valley is set to 0.50 μm and the optical phase difference is 0.58π. Becomes about 10% and d ₁ 0-order d ₂ 1 order reciprocating diffraction efficiency and d ₂ 0-order d ₁ 1 primary reciprocating diffraction efficiency in the region 2a · 2b at this time, it becomes 12% or less.

Also, when the blaze angle θ is 50 °, which is a value larger than the range of 30 to 45 °, the zero-order diffraction efficiencies and the first-order diffraction efficiencies of the regions 2a and 2b are almost the same, as shown in FIG. As shown in the graph, the valley depth t is set to 0.76 μm, and the optical phase difference is 0.88π. It becomes about 11% and d ₁ 0-order d ₂ 1 order reciprocating diffraction efficiency and d ₂ 0-order d ₁ 1 primary reciprocating diffraction efficiency in the region 2a · 2b at this time, thus likewise, a 12% or less.

Next, the above results were arranged and the relationship between the reciprocation diffraction efficiency, the blaze angle, and the optical phase difference was examined. The results shown in the graph of FIG. 5 were obtained. According to the figure, the blaze angle θ is in the range of 30 to 45 ° and the optical phase difference is 0.7π to
It can be seen that a reciprocating diffraction efficiency of 12% or more can be obtained in the range of 0.9π. The allowable range for obtaining a round-trip diffraction efficiency of 12% or more is as described above. However, a desirable range for obtaining a higher diffraction efficiency is when the blaze angle θ is
34 to 40 °, and the optical phase difference is in the range of 0.77π to 0.85π.

In the above configuration, the laser beam emitted from the semiconductor laser 1 is incident on the optical diffraction grating element 2, and the 0th-order diffracted light by the regions 2 a and 2 b of the optical diffraction grating element 2 is converted into parallel light by the collimating lens 3. The light is focused on the information recording track of the record carrier 5 by the objective lens 4. At this time, the above two areas
Since the zero-order diffraction efficiencies in 2a and 2b are the same, the condensed beam on the record carrier 5 becomes a good beam condensed appropriately on the recording track. The reflected light from the record carrier 5 enters the optical diffraction grating element 2 via the objective lens 4 and the collimating lens 3, and the first-order diffracted light from the areas 2a and 2b is collected on the light receiving element 6. At this time, of the laser light emitted from the semiconductor laser 1, the laser light incident on one area of the optical diffraction grating element 2, for example, the area 2 a, is reflected by the record carrier 5, and then reflected on the other side of the optical diffraction grating element 2. The light enters a region, for example, a region 2b. The light incident to the region 2b is converged as converged spot S ₁ on the boundary of the light receiving portion 6a · 6b of the light receiving element 6, the light incident to the region 2a is condensing on the boundary line of the light receiving portion 6c · 6d and it is focused as a spot S _2.

Here, in the optical diffraction grating element 2, as described above, d ₁₀
Since the d ₂ 1 order reciprocal diffraction efficiency and the d ₂ 0 order d ₁ order reciprocal diffraction efficiency are set to be equal, the light amount of the condensed spots S ₁ and S ₂ formed on the light receiving element 6 is reduced. When the focal position of the objective lens 4 is on the information recording track of the record carrier 5, the radial error signal RES obtained by the equation of RES = (Sa + Sb)-(Sc + Sd) becomes zero. Therefore, when the above-described focal position is shifted from the information recording track, the radial error signal RES corresponds to the shift amount, and the track shift is accurately corrected. Thereby, highly accurate tracking servo can be performed.

Furthermore, since a 12% or more, and d ₁ 0-order d ₂ 1 order reciprocating diffraction efficiency and d ₂ 0-order d ₁ 1 primary reciprocating diffraction efficiency, the use of the optical diffraction grating element 2 to the image pickup, A high S / N of 45 dB or more can be easily realized, and a good video signal can be obtained. Also, when used for a CD pickup, the burden on other components is reduced, and a high-quality reproduced signal can be obtained.

As described above, the configuration of the present invention has two regions with different grating pitches, and in a light diffraction grating element having a sawtooth cross-sectional shape, the amount of light diffracted in each region is equal. It is effective when you want to design like this.

Next, an embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 6 (a), an optical diffraction grating element 8 according to the present embodiment, similar to the optical diffraction grating element 2 above, are first and second regions of different grating pitch d ₁ · d ₂ Two areas 8a
8b. These regions 8a and 8b are etched with an ion beam generated from, for example, CHF ₃ gas, thereby forming a slope for setting a blaze angle θ as shown in FIGS. 6 (b) and (c), respectively. The lower part of the other surface that forms the valley opposite to the valley is curved toward the hill to form a concave shape, and goes from the lowermost part of the valley to the hill toward the hill by a width d ′ and a height t ′. The undercut portion 9 is generated.
This undercut portion 9 has a width d ′ of each lattice pitch d _1.
10-20% of about d _2, 40 to 60% of height t 'of valley depth t
About. In the optical diffraction grating element 8, similarly to the optical diffraction grating element 2, the valley depth t and the blaze angle θ of the two regions 8 a and 8 b are set to be the same, and the grating pitch d _{1 of the} region 8 a and the region by the amount corresponding to the difference between the grating pitch d ₂ of 8b, the width M of the top of the mountain portion of the region 8b is wider.

Furthermore, in the optical diffraction grating element 8 having the undercut portion 9 described above, in order to appropriately condense the condensed beam on the record carrier 5 and to obtain a round-trip diffraction efficiency of 12% or more in the regions 8a and 8b, The blaze angle θ and the optical phase difference are set as follows.

That is, the average of the grating pitch d ₁ is at (2.2 ± 0.2) λ, the optical diffraction grating element 8 is the average of the grating pitch d ₂ is (2.8 ± 0.2) λ, the blaze angle θ and the depth of the valley t Means that the blaze angle θ is in the range of 34 to 42 ° and the depth t of the valley is
Is set so that the 0th-order diffraction efficiencies of the regions 8a and 8b and the 1st-order diffraction efficiencies of the regions 8a and 8b are substantially equal within the range of the depth at which an optical phase difference of 0.7π to 1.1π is generated. Have been. At this time, a range in which one of the zero-order diffraction efficiencies deviates from the other zero-order diffraction efficiency and a range in which the other one of the first-order diffraction efficiencies deviates from one of the first-order diffraction efficiencies may be allowed up to 5%. it can. In addition, in the present optical diffraction grating element 8, by having the undercut portion 9, the minimum and maximum blaze angles θ are smaller and the blaze angle θ is in a narrower range than the optical diffraction grating element 2,
The depth t of the valley is deep, that is, the maximum range of the optical phase difference is wide.

In order to set the above-mentioned blaze angle θ and the optical phase difference, the optical phase difference at each blaze angle θ and the region 8a
0 order diffraction efficiency of 8b, 1-order diffraction efficiency of the region 8a · 8b, d ₁ 0-order
The relationship between the d ₂ first order reciprocal diffraction efficiency and the d ₂₀ order d ₁ 1 order reciprocal diffraction efficiency was examined, and the results were as follows.

For example, when the blaze angle θ is 38 °, when the refractive index of the optical diffraction grating element 8 is 1.454, the graph shown in FIG. 7A is obtained, and the optical phase difference is about 0.91π. When the depth t of the valley becomes about 0.78 μm, the 0th-order diffraction efficiencies of the regions 8a and 8b and the 1st-order diffraction efficiencies are almost equal, and the two regions 8a
· 8b d ₁ 0-order d ₂ 1 order reciprocating diffraction efficiency and d ₂ 0-order d ₁ 1 primary reciprocating diffraction efficiency Both in, is about 12.7%.

When the blaze angle θ is 34 °, which is the smallest value in the range of 34 to 42 °, the 0th-order diffraction efficiencies and the 1st-order diffraction efficiencies in the regions 8a and 8b are almost the same, and both reciprocations in the regions 8a and 8b The diffraction efficiency becomes 12% or more when the valley depth t is set to 0.66 μm and the optical phase difference becomes 0.77π, as shown in the graph of FIG.

D ₁ 0-order in the largest value of 42 °, substantially aligned and the 0 order diffraction efficiency between the first-order diffraction efficiency between the region 8a · 8b, and a region 8a · 8b blaze angle θ is 34-42 DEG 's and d ₂ 1 order reciprocating diffraction efficiency and d ₂ 0-order d ₁ 1 primary reciprocating diffraction efficiency is 12% or more, as shown in the graph of FIG. (c), valley depth t is 0.90μm And the optical phase difference is 1.05π.

On the other hand, when the blaze angle θ is 30 ° which is a value smaller than the range of 34 to 42 °, the zero-order diffraction efficiencies and the first-order diffraction efficiencies of the regions 8a and 8b are almost equal to each other. As shown in the graph, the valley depth t is set to 0.54 μm and the optical phase difference is 0.63π. Becomes about 10.5% and d ₁ 0-order d ₂ 1 order reciprocating diffraction efficiency and d ₂ 0-order d ₁ 1 primary reciprocating diffraction efficiency in the region 8a · 8b in this case, it becomes 12% or less.

When the blaze angle θ is 45 °, which is a value larger than the range of 34 to 42 °, the zero-order diffraction efficiencies and the first-order diffraction efficiencies of the regions 8a and 8b are almost the same, as shown in FIG. As shown in the graph, the depth t of the valley is set to 1.00 μm, and the optical phase difference is 1.16π. Becomes about 10.5% and d ₁ 0-order d ₂ 1 order reciprocating diffraction efficiency and d ₂ 0-order d ₁ 1 primary reciprocating diffraction efficiency in the region 8a · 8b in this case, would likewise, a 12% or less.

Next, the above results were arranged and the relationship between the reciprocating diffraction efficiency, the blaze angle, and the optical phase difference was examined. The results shown in the graph of FIG. 8 were obtained. According to the figure, the blaze angle θ is in the range of 34 to 42 ° and the optical phase difference is 0.7π to
It can be seen that a reciprocating diffraction efficiency of 12% or more can be obtained in the range of 1.1π. A desirable range in which higher diffraction efficiency can be obtained is a range in which the blaze angle θ is 36 to 40 ° and the optical phase difference is 0.81π to 0.95π.

According to the above configuration, both regions 8a of the optical diffraction grating element 8
Since the 0th-order diffraction efficiency in 8b is the same, the record carrier 5
The upper condensed beam is a good one which is properly condensed on the recording track. Also, in the optical diffraction grating element 8, the d ₁₀ order
Since the d ₂ 1 order reciprocating diffraction efficiency and d ₂ 0-order d ₁ 1 primary reciprocating diffraction efficiency is set to be equal, equal quantity of the light receiving element collecting light are formed in 6 spots S ₁ · S ₂ is That is, in the optical recording / reproducing apparatus using the optical diffraction grating element 8, it is possible to perform high-accuracy tracking servo. Further, since the d ₁ 0-order d ₂ 1 order reciprocating diffraction efficiency and d ₂ 0-order d ₁ 1 primary reciprocating diffraction efficiency is 12% or more, the use of the optical diffraction grating element 2 to the image pickup, Higher than 45dB
S / N can be easily realized, and a good video signal can be obtained. Also, when used for a CD pickup, the burden on other components is reduced, and a high-quality reproduced signal can be obtained.

Embodiment 2 Another embodiment of the present invention will be described below with reference to FIGS. 9 to 11.

As shown in FIG. 9 (a), an optical diffraction grating element 10 according to the present embodiment, similar to the optical diffraction grating element 2 above, are first and second regions of different grating pitch d ₁ · d ₂ Two areas 10a
・ It has 10b. These regions 10a and 10b are, for example, CF ₄
9 (b) and 9 (c), respectively, by being etched with an ion beam generated from the gas.
As shown in FIG. 5, the other surface forming the valley opposite to the slope for setting the blaze angle θ is formed substantially at right angles to the substrate surface, and the surface and the slope for setting the blaze angle θ The connecting portion is a curved surface 11. Curved surface 11 in FIG. (B) (c), the width d "10 to 20% of the grating pitch d ₁ · d _2, the height t" of the valley depth t 20
It will be about 40%. Further, the optical diffraction grating element 10, like the optical diffraction grating element 2 of the depth t and blaze angle θ of the valley of the two regions 10a · 10b are set to the same, the grating pitch d ₁ and the region of the region 10a by the amount corresponding to the difference between the grating pitch d ₂ of the 10b, the width M of the top of the mountain portion of the region 10b is wider.

Further, in the optical diffraction grating element 10 having the above-mentioned curved surface 11, in order to appropriately condense the condensed beam on the record carrier 5, and to obtain a reciprocating diffraction efficiency of 12% or more in the regions 10a and 10b, The brace angle θ and the optical phase difference are set as follows.

That is, the average of the grating pitch d ₁ is at (2.2 ± 0.2) λ, the optical diffraction grating element 10 is the average of the grating pitch d ₂ is (2.8 ± 0.2) λ, the blaze angle θ and the depth of the valley t Means that the blaze angle θ is in the range of 32 to 43 ° and the depth t of the valley is
Within the range of the depth at which an optical phase difference of 0.65π to 1π occurs, the 0th-order diffraction efficiencies of the region 10a and the region 10b are 1
The combinations are set such that the diffraction efficiencies are substantially equal to each other. At this time, a range in which one of the zero-order diffraction efficiencies is shifted from the other zero-order diffraction efficiency, and a range in which the other one of the first-order diffraction efficiencies is shifted from one of the first-order diffraction efficiencies can be allowed up to 5%. . Incidentally, in the present optical diffraction grating element 10, the minimum and maximum blaze angles θ are smaller and the blaze angle θ is in a narrower range than the optical diffraction grating element 2 due to the above-mentioned shape, while the optical phase difference is smaller. The tolerance of is widened.

In order to set the above-mentioned blaze angle θ and the optical phase difference, the optical phase difference at each blaze angle θ and the region 10a
0th-order diffraction efficiency of 10b, 1st-order diffraction efficiency of regions 10a and 10b, d
₁ 0 was examined a relationship between the primary d ₂ 1 order reciprocating diffraction efficiency and d ₂ 0-order d ₁ 1 primary reciprocating diffraction efficiency, were as follows.

For example, when the blaze angle θ is 35 ° and the refractive index of the optical diffraction grating element 10 is 1.454, the optical phase difference is about 0.72π as shown in the graph of FIG. When the depth t of the valley is around 0.62 μm, the 0th-order diffraction efficiencies and the 1st-order diffraction efficiencies of the regions 10a and 10b are almost the same, and both regions 10a
・ The d ₁ 0 order d ₂ 1 order reciprocal diffraction efficiency and d ₂ 0 order d ₁ 1 at 10b
The next round-trip diffraction efficiency is about 13.0%.

When the blaze angle θ is 32 °, which is the smallest value in the range of 32 to 43 °, the 0th-order diffraction efficiencies and the 1st-order diffraction efficiencies in the regions 10a and 10b are almost the same, and both reciprocations in the regions 10a and 10b The diffraction efficiency becomes 12% or more when the depth t of the valley is set to 0.56 μm and the optical phase difference becomes 0.65π, as shown in the graph of FIG.

D ₁ 0-order in the largest value of 43 °, substantially aligned and the 0 order diffraction efficiency between the first-order diffraction efficiency between the regions 10a · 10b, and the region 10a · 10b of the blaze angle θ is 32 to 43 DEG d ₂ 1
The the next reciprocating diffraction efficiency and d ₂ 0-order d ₁ 1 primary reciprocating diffraction efficiency is 12% or more, as shown in the graph of FIG. (C), valley depth t is set to 0.86μm , Optical phase difference is 1.00π
This is the case.

On the other hand, when the blaze angle θ is 27 °, which is a value smaller than the range of 32 ° to 43 °, the zero-order diffraction efficiencies and the first-order diffraction efficiencies of the regions 10a and 10b are almost equal to each other. As shown in the graph, the depth t of the valley is set to 0.46 μm, and the optical phase difference is 0.54π. Area 10a ・ 1 at this time
It becomes about 10.0% and d ₁ 0-order d ₂ 1 order reciprocating diffraction efficiency and d ₂ 0-order d ₁ 1 primary reciprocating diffraction efficiency in 0b, becomes 12% or less.

When the blaze angle θ is 47 °, which is a value larger than the range of 32 to 43 °, the zero-order diffraction efficiencies and the first-order diffraction efficiencies of the regions 10a and 10b are almost the same, as shown in FIG. As shown in the graph, the depth t of the valley is set to 0.98 μm, and the optical phase difference is 1.14π. Area 10a ・ 1 at this time
Becomes about 10.0% and d ₁ 0-order d ₂ 1 order reciprocating diffraction efficiency and d ₂ 0-order d ₁ 1 primary reciprocating diffraction efficiency in 0b, thus Similarly, a 12% or less.

Next, the above results were arranged and the relationship between the reciprocating diffraction efficiency, the blaze angle, and the optical phase difference was examined. The results shown in the graph of FIG. 11 were obtained. As shown in the figure, the blaze angle θ is in the range of 3-43 ° and the optical phase difference is 0.65π-
It is understood that a reciprocating diffraction efficiency of 12% or more can be obtained in the range of 1π. A desirable range in which higher diffraction efficiency can be obtained is a range in which the blaze angle θ is 36 to 40 ° and the optical phase difference is 0.77π to 0.91π.

According to the above configuration, similar to the configuration shown in the first embodiment,
The condensed beam on the record carrier 5 becomes a good beam condensed appropriately on the recording track, and the present optical diffraction grating element 10
In an optical recording / reproducing apparatus using the above, it is possible to perform highly accurate tracking servo. Further, when the present optical diffraction grating element 2 is used for a video pickup, a high S / N of 45 dB or more can be easily realized, and a good video signal can be obtained. Also, when used for CD pickup,
The burden on other components is reduced, and a high-quality reproduced signal can be obtained.

〔The invention's effect〕

In the optical diffraction grating device according to the first aspect of the present invention, as described above, the first region and the second region have the same valley depth, valley width, and blaze angle between the two regions. The cross-sectional shape of the valley is set so that the other surface forming the valley facing the slope for setting the blaze angle is curved toward the hill to form a concave shape.

This makes it possible to equalize the light amounts of the two condensed spots formed on the light receiving element and perform highly accurate tracking servo.

Further, there is an effect that the maximum range of the optical phase difference for obtaining a predetermined round-trip diffraction efficiency can be widened.

In the optical diffraction grating device according to the second aspect of the present invention, as described above, the first region and the second region have the same valley depth, valley width, and blaze angle between the two regions. The cross-sectional shape of the valley is set such that the other surface forming the valley opposite to the slope for setting the blaze angle is formed at right angles to the substrate surface of the diffraction grating, and In this configuration, a portion connected to a slope for setting a corner forms a curved surface.

Thus, as in the case of the first aspect, it is possible to perform high-accuracy tracking servo by equalizing the light amounts of both condensed spots formed on the light receiving element.

Further, there is an effect that an allowable range of an optical phase difference for obtaining a predetermined reciprocating diffraction efficiency can be widened.

[Brief description of the drawings]

1 to 5 show the invention on which the present invention is based. FIG. 1A is a schematic front view showing an optical diffraction grating element. FIG. 1B is a cross-sectional view taken along the line AA in FIG. FIG. 1 (c) is a sectional view taken along the line BB in FIG. 1 (a). FIG. 2 is a schematic explanatory view showing the configuration of the optical pickup. FIG. 3 is an explanatory view showing a condensed spot on the light receiving element. 4 (a) has a blaze angle of 35 °, FIG. 4 (b) has a blaze angle of 30 °, FIG. 4 (c) has a blaze angle of 45 °, and FIG. 4 (d) has a blaze angle of 25 °. Figure (e) shows the blaze angle
10 is a graph showing the relationship between the optical phase difference in the optical diffraction grating element in each case of 50 ° and the zero-order diffraction efficiency of each region, the first-order diffraction efficiency of each region, and the round-trip diffraction efficiency of each region. FIG. 5 is a graph showing the relationship between the reciprocating diffraction efficiency, the blaze angle, and the optical phase difference in the optical diffraction grating device. 6 to 8 show one embodiment of the present invention. FIG. 6 (a) is a schematic front view showing an optical diffraction grating element. FIG. 6 (b) is a sectional view taken along the line CC in FIG. 6 (a). FIG. 6 (c) is a sectional view taken along the line DD in FIG. 6 (a). 7 (a) has a blaze angle of 38 °, FIG. 7 (b) has a blaze angle of 34 °, FIG. 7 (c) has a blaze angle of 42 °, and FIG. 7 (d) has a blaze angle of 30 °. Figure (e) shows the blaze angle
It is a graph which shows the relationship between the optical phase difference in the optical diffraction grating element in each case of 45 degree | times, and the 0th-order diffraction efficiency of each area | region, the 1st-order diffraction efficiency of each area | region, and the round trip diffraction efficiency of each area | region. FIG. 8 is a graph showing the relationship between the reciprocal diffraction efficiency, the blaze angle, and the optical phase difference in the optical diffraction grating device. 9 to 11 show another embodiment of the present invention. FIG. 9 (a) is a schematic front view showing an optical diffraction grating element. FIG. 9 (b) is a sectional view taken along the line EE in FIG. 9 (a). FIG. 9 (c) is a sectional view taken along the line FF in FIG. 9 (a). 10 (a) has a blaze angle of 35 °, FIG. 10 (b) has a blaze angle of 32 °, FIG. 10 (c) has a blaze angle of 43 °, and FIG. 10 (d) has a blaze angle of 27 °. Figure (e) shows the blaze angle
It is a graph which shows the relationship between the optical phase difference in the optical diffraction grating element in each case of 47 degree | times, the 0th-order diffraction efficiency of each area | region, the 1st-order diffraction efficiency of each area | region, and the round trip diffraction efficiency of each area | region. FIG. 11 is a graph showing the relationship between the round-trip diffraction efficiency, the blaze angle, and the optical phase difference in the optical diffraction grating element. 12 to 15 show a conventional example. FIG. 12 is a schematic explanatory view showing the configuration of the optical pickup. FIG. 13 is an explanatory diagram showing a condensed spot on the light receiving element. FIG. 14 (a) is a schematic front view showing an optical diffraction grating element. FIG. 14 (b) is a sectional view taken along the line GG in FIG. 14 (a). FIG. 14 (c) is a cross-sectional view taken along the line HH in FIG. 14 (a). FIG. 14 (d) is a cross-sectional view of another optical diffraction grating element taken along line GG in FIG. 14 (a). FIG. 14 (e) is a cross-sectional view of another optical diffraction grating element taken along the line HH in FIG. 14 (a). 15 (a) to 15 (c) are explanatory longitudinal sectional views showing a process of manufacturing a diffraction grating by etching with an ion beam generated from Ar gas. FIG. 15 (d) is an explanatory longitudinal sectional view showing a diffraction grating produced by etching with an ion beam generated from CHF ₃ gas. FIG. 15 (e) is an explanatory longitudinal sectional view showing a diffraction grating produced by etching with an ion beam generated from CF ₄ gas. 1 is a semiconductor laser, 2 ・ 8 ・ 10 is an optical diffraction grating element, 2a ・
8a and 10a are areas (first areas), 2b, 8b and 10b are areas (second areas)
Area), 5 is a record carrier, 6 is a light receiving element, 9 is an undercut portion, 11 is a curved portion, θ is a blaze angle, and d ₁ and d ₂ are lattice pitches.

Claims (2)

(57) [Claims] 1. A diffraction grating having a first region and a second region having mutually different grating pitches is formed by a shape in which peaks and valleys are alternately continuous and have a slope for setting a blaze angle. In the optical diffraction grating device for diffracting incident light in different directions by the first region and the second region, the first region and the second region have a depth of each valley, a width of the valley, and a blaze angle which are both different. The same shape is set between the regions, and the cross-sectional shape of the valley is such that the other surface forming the valley facing the slope for setting the blaze angle is curved toward the hill and has a concave shape. Characteristic optical diffraction grating element. 2. A diffraction grating having a first region and a second region having mutually different grating pitches is formed by a shape in which peaks and valleys are alternately continuous and have a slope for setting a blaze angle. In the optical diffraction grating device for diffracting incident light in different directions by the first region and the second region, the first region and the second region have a depth of each valley, a width of the valley, and a blaze angle which are both different. The cross-sectional shape of the valley is set to be the same between the regions, and the other surface forming the valley opposite to the slope for setting the blaze angle is formed at right angles to the substrate surface of the diffraction grating. An optical diffraction grating element characterized in that a portion where this surface and a slope for setting a blaze angle are connected forms a curved surface.