JPH08249704A - Optical head device - Google Patents

Abstract

(57) Abstract: The present invention relates to an optical head device for recording / reproducing / erasing information stored on light such as an optical disk. An inexpensive optical head device is provided. SOLUTION: By arranging a blazed hologram 1 in which the diffraction efficiency of unnecessary-order diffracted light is suppressed in the vicinity of an objective lens 4, the effective diameter of the hologram 1 is increased,
Increase the assembly tolerance. Further, by integrating the hologram 1 and the objective lens 4, the servo signal does not deteriorate even if the objective lens 4 moves due to tracking tracking.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device for recording / reproducing or erasing information stored on an optical medium or a magneto-optical medium such as an optical disk or an optical card.

[0002]

2. Description of the Related Art Optical memory technology using an optical disk having a pit pattern as a high-density and large-capacity storage medium includes digital audio disk, video disk,
It has been put to practical use while expanding its use with document file discs and even data files. The mechanism by which information is recorded / reproduced on / from an optical disk via a finely focused light beam with high reliability can be attributed solely to the optical system.

The basic function of the optical head device, which is the main part of the optical system, is large in the light-collecting property for forming a minute spot of diffraction limit, the focus control and tracking control of the optical system, and the detection of the pit signal. Be separated. These are expressed by a combination of various optical systems and photoelectric conversion detection methods, depending on the purpose and application. In particular, in recent years, in order to reduce the size and thickness of the optical pickup head device, an optical signal using a hologram is used. A pickup head device is disclosed.

As a first conventional example, FIG. 20 shows "Kurata,
Miyake, Sakai, Kubo, Ishikawa: “High efficiency hologram element by ion beam etching”, Proc. 1039-10
40 "is a block diagram of the optical head shown in FIG.

In FIG. 20, reference numeral 2 is a radiation light source such as a semiconductor laser. Light beam 3 emitted from this radiation source 2
The (laser light) passes through the hologram 101, enters the objective lens 4, and is condensed on the information medium 5. Information medium 5
The light beam reflected by is traced back to the original optical path and enters the hologram 101. The forward + 1st order diffracted light 6 generated from the hologram 101 enters the photodetector 7. By calculating the output of the photodetector 7, a servo signal and an information signal can be obtained.

Here, the amount of light (zero-order diffracted light amount) transmitted through the hologram 101 in the outward path from the radiation light source 2 to the information medium 5 and the hologram diffracted in the return path +
The hologram 101 is blazed in order to maximize the light utilization efficiency represented by the product of the amount of first-order diffracted light.

Further, the outward -1st order diffracted light 8 shown in FIG.
As described above, the diffracted light generated from the hologram 101 on the outward path is designed not to enter the objective lens 4 by increasing the diffraction angle of the −1st order diffracted light 8. Also,
In order to miniaturize the optical head device, the radiation light source 2 and the photodetector 7 are placed close to each other.

As described above, since the diffraction angle is increased and the radiation light source 2 and the photodetector 7 are arranged close to each other, the hologram 101 is necessarily arranged close to the radiation light source 2.

Next, as a second conventional example, JP-A-64-6
FIG. 21 shows a configuration diagram of the optical head shown in Japanese Patent No. 2838. As shown in the figure, the hologram is characterized by being integrated with the objective lens. If the objective lens 4 is movable independently of the hologram 101, the configuration shown in FIG.
As shown in, when the objective lens 4 moves due to track following or the like, the light beam 31 on the hologram 101 also moves. Therefore, the image of the + 1st-order diffracted light on the return path on the photodetector 7 also moves, which adversely affects the servo signal.

On the other hand, in the conventional example shown in FIG. 21, since the hologram 101 and the objective lens 4 are integrally provided by holding means 13 while holding a certain relative position, a driving device for tracking control. Even if the objective lens 4 moves with respect to 100, the light beam reflected from the information medium 5 hardly moves on the hologram 101.
Therefore, despite the movement of the objective lens 4, the signal obtained from the photodetector 7 does not deteriorate.

Further, the one disclosed in Japanese Patent Laid-Open No. 62-145545 has a blaze characteristic in the diffraction direction of the diffraction grating to suppress crosstalk, and particularly, the forward path emitted from the light source. For the purpose of preventing the occurrence of crosstalk due to the −1st-order diffracted light being irradiated onto the record carrier, reflected on the record carrier and incident on the photodetector by passing the light of (1) through the diffraction grating. There is.

[0012]

In the first conventional example, as is apparent from FIG. 20, the diffraction angle is increased and the radiation source 2 and the photodetector 7 are arranged close to each other. ,
Inevitably, the hologram 101 will be arranged close to the radiation source 2. Therefore, the projection of the aperture of the objective lens 4 on the hologram 101, that is, the effective diameter R is also very small. Therefore, in assembling the optical head, the tolerance of the relative position between the hologram 101 and the radiation light source 2 becomes small, and there is a problem that the assembling cost increases.

Further, according to the optical system configuration of the second conventional example, since the hologram 101 is not blazed, the utilization efficiency of light is low and the S / N ratio of the servo signal and the information signal is low. .

Also, in the optical path (outward path) from the radiation light source 2 to the information medium 5, diffracted light is generated from the hologram 101, so that this diffracted light is also reflected by the information medium 5 and the photodetector 7 by the objective lens 4. Focused on top.

+1 generated on an optical path (hereinafter referred to as a return path) which is reflected from the information medium 5, condensed by the objective lens 4, diffracted by the hologram 101 and reaches the photodetector 7.
If the second-order diffracted light is used for signal detection, the −1st-order diffracted light generated on the outward path is incident on the photodetector 7 at the same position as the + 1st-order diffracted light on the return path.

This state is shown in FIG. The + 1st-order diffracted light 8 in the backward path and the 0th-order diffracted light 81 in the backward path and the 0th-order diffracted light 61 in the forward path are incident on the hologram 101 and diffracted, and the + 1st-order diffracted light 6 in the backward path is on the information medium 5. Since they are reflected at different positions, they naturally have different information. Therefore, the optical system having the configuration in which the lens and the hologram are integrated has a problem that the −1st-order light 8 on the outward path causes noise to be mixed in the servo signal and the information signal, resulting in a decrease in S / N.

Further, the one disclosed in Japanese Patent Laid-Open No. 145545/1987 has a structure in which the diffraction grating is blazed in a sawtooth shape, the inclination of the slope is α, and the optical axis of the + 1st order diffracted light with respect to the normal to the slope. Where β is the angle of refraction and n is the refractive index of the diffraction grating substrate, then n × sin α = sin β d × sin β = λ is satisfied, and the −1st-order diffracted light has no calculated intensity, but the 0th-order diffracted light also has the calculated intensity. The light for reading the signal on the disc is not strong because there is no light. That is,
Only the configuration in which the signal cannot be reproduced is shown.

[0018]

In order to solve the above problems, the present invention provides a radiation light source, a condensing optical system for converging a light beam from the radiation light source into a minute spot on an information medium, and the information. A photodetector comprising a plurality of photodetectors for receiving a light beam reflected and diffracted by a medium and outputting a photocurrent, and a light beam reflected by the information medium and diffracted as + 1st order diffracted light to the photodetector. In a diffracted light other than the zero-order light among the diffracted light generated in the forward optical path from the radiation light source to the information medium by blazing the cross-sectional shape of the hologram. The amount of light incident on the photodetector is suppressed, and the hologram is located near the condensing optical system and away from the radiation light source, thereby diffracting diffracted light of an unnecessary order. Constituting the optical head device using a blazed hologram suppressing rates.

Further, a radiation light source, a condensing optical system for receiving a light beam emitted from the radiation light source and converging it on an information medium, and a blazed hologram integrally supported by a support of the condensing optical system, The light beam reflected on the information medium receives the + 1st order diffracted light generated when the light beam is incident on the condensing optical system integrated with the hologram, and is obtained by dividing each diffracted light or each diffracted light into a plurality of pieces. And an optical detector configured to generate a photocurrent according to the amount of light.

Further, a radiation light source, a condensing optical system for receiving the light beam from the radiation light source and converging it into a minute spot on the information medium, and a light beam reflected and diffracted by the information medium, outputs a photocurrent. An optical head device comprising: a photodetector including a plurality of photodetectors; and a hologram for diffracting the light beam reflected by the information medium as + 1st-order diffracted light to guide the light beam to the photodetector. An optical head device is constructed in which the cross-sectional shape of the hologram is blazed and the + 1st-order diffracted light generated from the hologram includes two spherical waves having focal points on the front side and the rear side of the photodetector surface.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram according to the first embodiment of the present invention. In the figure, 1 is a blazed hologram, and 2 is a radiation light source such as a semiconductor laser. The feature of this embodiment is that the blazed hologram 1 is installed close to the objective lens 4. The operation will be described below.

The light beam 3 (laser light) emitted from the radiation light source 2 passes through the blazed hologram 1 and enters the objective lens 4, and is condensed on the information medium 5. Information medium 5
The light beam reflected by is traced back to the original optical path and enters the blazed hologram 1. The returning + 1st order diffracted light 6 generated from the blazed hologram 1 is detected by the photodetector 7
Incident on. By calculating the output of the photodetector 7, a servo signal and an information signal can be obtained.

In the conventional example, as shown in FIG. 20, in the blazed hologram, the −1st order diffracted light on the outward path is the objective lens 4
It is installed close to the radiation source 2 so as not to be incident on.

On the other hand, in this embodiment, the blazed hologram 1 is arranged so as to suppress the diffraction efficiency of unnecessary orders.
Is blaze. Therefore, although the blazed hologram 1 is arranged near the objective lens 4 and the photodetector 7 and the radiation light source 2 are arranged close to each other, the blazed hologram 1 causes noise with respect to the servo signal and the information signal. The feature is that the amount of unnecessary light incident on the photodetector 7 is significantly reduced.

Here, the effect that the diffraction efficiency of the -1st-order diffracted light becomes smaller than that of the + 1st-order diffracted light by the blazing is that "Fujita, Nishihara, Koyama:" Electron beam drawing fabrication Blazing of Micro Fresnel Lens ”IEICE Technical Report, Vol.82,
No. 47, PAGE. 49-55 (OQE82-2
5) 1982 ”and the like.

In this document, blazing is used to improve the condensing characteristics of the Fresnel lens, but in this embodiment, in order to suppress the light quantity of the −1st order diffracted light in the forward path generated from the hologram. Use blaze.

FIG. 2 shows an example in which the blazed hologram 102 is realized as a relief type transmission hologram having a sawtooth cross-sectional shape. In FIG. 2, the height difference between the peak and the valley of the relief is d, the refractive index of the transparent substrate forming the hologram 102 is n, and the refractive index around the hologram 102 is n.
₀ and the wavelength of the radiation light source 2 is λ, the phase modulation amount φ is φ = 2π × d (n−n ₀ ) / λ ...

FIG. 3 is a graph showing the relationship in which the horizontal axis represents the phase modulation amount φ and the vertical axis represents the diffraction efficiency. As shown in the above document, φ = 2π may be set for the purpose of maximizing the diffraction efficiency of the + 1st order diffracted light.

On the other hand, in this embodiment, the 0th-order diffracted light 61 in the forward path in FIG. 1 is reflected on the information medium 5 and diffracted by the blazed hologram 1 and the + first-order diffracted light 6 in the backward path.
Is used for signal detection, the diffractive efficiency (transmittance) of the 0th-order diffracted light 61 on the outward path must be high. Furthermore, the diffraction efficiency of the −1st order diffracted light on the outward path, which is unnecessary for light detection
It must be smaller than the diffraction efficiency of the + 1st order diffracted light.

Therefore, for example, when sawtooth blazing is performed as shown in FIG. 2, as is apparent from FIG.
It is possible to suppress the light amount of the −1st-order diffracted light on the outward path by setting it within the range of up to 2π.

By constructing an optical head device using such a blazed hologram 102, the blazed hologram 1 is arranged near the objective lens 4 as well.
Moreover, even though the photodetector 7 and the radiation light source 2 are arranged close to each other, the amount of unnecessary light that enters the photodetector 7 and becomes noise with respect to the servo signal and the information signal is extremely small. There is an effect that.

4 and 5 show an example of a method for producing a blazed hologram. In FIG. 4, a hologram 10 is formed with a photoresist 10 on a transparent substrate 9 such as glass, and as shown in FIG. 4A, an ion beam 11 is obliquely irradiated (reactive ion beam etching). ) Etch. In this way, a relief type blazed hologram 102 as shown in FIG.

By repeating the etching several times as shown in FIGS. 5A, 5B and 5C, a stepwise cross-sectional shape can be obtained. Reference numerals 200 and 201 denote etching portions.

It has already been reported that the blazing effect can be sufficiently obtained by the method shown in FIG. 5 (eg,
J. Logue and M.M. L. chishoru
m: "General approaches to
mask design for binary opt
ics, "Proceedings of SPIE
Vol. 1052, pp. 19-24 (J. Rogue and M. El Sisholum "General Approaches Two Mask Design for Binary Optics" Proceedings of SP IP Volume 1052 Page 1
9-24)).

Further, when a stepwise cross-sectional shape is created by etching twice as shown in FIG. 5, the degree of freedom in controlling the diffraction efficiency can be made higher than that of the sawtooth-shaped cross-sectional shape shown in FIG. it can. That is, the first etching depth and the second etching depth can be controlled independently to reduce the diffraction efficiency of unnecessary diffracted light and at the same time increase the efficiency of reciprocal light utilization.

Below, an example of the design of diffraction efficiency in the case of producing a blazed hologram using the production method shown in FIG. 5 is shown. Further, the configuration of an optical head device using the hologram produced based on the design and its effect will be described.

It is assumed that the _first etching amount shown in FIG. 6A is d ₁ and the second etching amount shown in FIG. 6B is d ₂ . d ₁ is the sum of the step d ₁₂ of the first and second steps and the step d ₂₃ of the second and third steps from the top. When a light beam is made incident on the relief hologram 102, the phase modulation amounts φ ₁ and φ ₂ received by the light beam are φ ₁ = 2π · d ₁ (n−n ₀ ) / λ. ··· Equation 2 φ ₂ = 2π · d ₂ (n−n ₀ ) / λ is given by Equation 3.

At this time, if the phase modulation amounts of the light beam due to d ₁₂ and d ₂₃ are φ ₁₂ and φ ₂₃ , respectively, φ ₁
Is equal to the sum of φ ₁₂ and φ ₂₃ .

The diffraction efficiency η can be calculated by the Fourier transform of the phase modulation amount as follows: η ₋₁ = 2 / π ² × (1−SIN (φ ₂ )) × (1−COS (φ ₁ )) ... ₀ = 1/4 × (1 + COS (φ ₂ )) × (1 + COS (φ ₁ )) ... Equation 5 η ₊₁ = 2 / π ² × (1 + SIN (φ ₂ )) × (1-COS (φ ₁ )) Equation 6 η ₊₂ = 1 / π ² × (1-COS (φ ₂ )) × (1 + COS (φ ₁ )) Equation 7 (where η _{-1 to} η ₊₂ are respectively (Diffraction efficiency from −1st order to + 2nd order).

First, let us consider the influence of the diffracted light generated in the outward path on the servo signal. Astigmatism is a method that is often used as a focus servo signal detection method. This is a method that utilizes the fact that the shape of the light spot on the disc changes as shown in FIG. In FIG. 7, (b) shows just focus, (a) and (c)
Represents the defocused state. The focus servo signal FE is given by the calculation of FE = (S1 + S4)-(S2 + S3) ... Equation 8 with the outputs from the four-division photodetector as S1 to S4.

If, for example, the astigmatism method is adopted when the optical head device is constructed by using the hologram, the −1st-order diffracted light generated in the outward path also has astigmatism. Therefore, the light is reflected on the disk and is incident on the photodetector, and the shape of the diffracted light on the photodetector changes as shown in FIG. 7 due to defocus.

However, since the −1st-order diffracted light on the outward path is a conjugate wave of the + 1st-order diffracted light, the direction of the shape change on the photodetector with respect to the defocus is opposite to that of the + 1st-order diffracted light. For example, when the + 1st order diffracted light on the return path has the shape shown in FIG. 7A on the photodetector, the −1st order diffracted light on the forward path has the shape shown in FIG. 7C on the photodetector. Further, when the + first-order diffracted light on the return path has the shape of FIG. 7C on the photodetector, the −1st-order diffracted light on the forward path has the shape of FIG. 7A on the photodetector.

Therefore, the -1st order diffracted light on the outward path is shown in FIG.
A false servo signal as shown in (b) is generated. As described above, the direction of the shape on the photodetector with respect to the defocus of the −1st-order diffracted light on the outward path is the reverse of the + 1st-order diffracted light, and thus this false focus servo signal is originally shown in (a) of FIG. It works in the opposite phase of the focus servo signal of and cancels the original focus servo signal.

Therefore, it is necessary to reduce the ratio E ₁ of the amount of the −1st-order diffracted light on the forward path entering the photodetector to the + _1st-order diffracted light generated on the return path. Here, E ₁ = (η ₋₁ × η ₀ ) / (η ₀ × η ₊₁ ) = η ₋₁ / η _{+1 (} Equation 9)

Therefore, from Equations 4 and 6, E ₁ = (1−COSφ ₂ ) / (1 + COSφ ₂ ) ...

Therefore, when the hologram 102 is formed by the method shown in FIG. 6, if the design is made so that φ ₂ is about π / 2, E ₁ becomes small, and the focus is achieved without increasing the diffraction angle. The deterioration of the servo signal can be suppressed.

If the optical head device is constructed by using this hologram 102 as the blazed hologram 1 of FIG. 1, the blazed hologram of FIG. 1 can be obtained even if the radiation light source 2 and the photodetector 7 are arranged close to each other. 1 can be arranged near the objective lens 4 and the effective diameter R1 of the blazed hologram 1 shown in FIG. 1 can be increased, so that the tolerance of the position of the blazed hologram 1 when assembling the optical head device can be relaxed.

Next, consider the influence of the diffracted light in the forward path on the information signal. For example, -1 generated from the hologram on the outward path
As shown in FIG. 23, the diffracted light of the second order is reflected by the information medium 5 and enters the hologram, and the diffracted light of the 0th order (return path) enters the photodetector. Similarly, as shown in FIG. 9, the N-th order diffracted light 62 on the outward path is reflected by the information medium 5 and the hologram 1
The (N + 1) th-order diffracted light on the return path, which is generated when the light enters the light source 03, also enters the photodetector.

Of the light incident on these photodetectors, the one having the highest light intensity is the + first-order diffracted light on the return path generated when the forward-order 0th-order diffracted light 61 enters the hologram 103 (this is designated as L1). ). The next strongest light is light that includes 0th order or + 1st order diffraction in either the forward path or the backward path.

That is, the 0th-order diffracted light in the returning path (which is defined as L2) generated when the −1st-order diffracted light in the forward path is incident on the hologram and the + 2th time in the backward path generated when the + 1st-order diffracted light in the outward path enters the hologram Origami (this is L3).

Therefore, by designing the light quantities of these two lights to be sufficiently smaller than the light quantity of L1, it is possible to suppress the influence of unnecessary diffracted light on the information signal, that is, noise.

Considering not only the amount of light but also the size of the spot on the information medium 5, the higher the diffracted light, the greater the amount of aberration and defocus, so that the information medium 5 is not so much.
There is no change in the amount of light reflecting the information of the upper pit, and no noise is generated even when the light enters the photodetector 7. Therefore,
The light quantity of the first-order diffracted light and the forward + 1st-order diffracted light incident on the photodetector, that is, the light quantities of L2 and L3 may be reduced.

Therefore, if the ratio of the amount of unnecessary light (L2 and L3) to the amount of L1 is E ₂ , then E ₂ = (η _-1 × η ₀ + η ₊₁ × η ₊₂ ) / (η ₀ x η ₊₁ ) = η _-1 / η ₊₁ + η _{+ 2} / η ₀ Equation 11 is obtained. Substituting the diffraction efficiency obtained from the expressions shown in Expressions 4 to 7 into the expression shown in Expression 11, E ₂ = (1-SIN (φ ₂ )) / (1 + SIN (φ ₂ )) + 4 / π ² × (1-COS (φ ₂ ) / (1 + COS (φ ₂ )) ... Equation 12 From this Equation 12, the ratio E ₂ of unnecessary diffracted light is φ
_It can be seen that it depends only on ₂ and not on φ ₁ . Therefore, a graph showing the relationship between the ratio E ₂ of unnecessary diffracted light and φ ₂ is shown in FIG. As can be seen from this graph, E ₂ becomes 0.03 or less when φ ₂ is 0.2π to 0.45π. At this time, E ₁ is equal to the first term of E ₂ , so E 1
_{When 2} is small, E ₁ is also small and the focus servo signal is less deteriorated.

Therefore, when the hologram 102 is produced by the method shown in FIG. 6, φ ₂ is 0.2π to 0.4.
If the design is made to be 5π, E ₂ becomes small, and deterioration of the information signal and the focus servo signal can be suppressed without increasing the diffraction angle.

If the optical head device is constructed by using this hologram 102 as the blazed hologram 1 of FIG. 1, the blazed hologram of FIG. 1 can be obtained even if the radiation light source 2 and the photodetector 7 are arranged close to each other. 1 can be arranged near the objective lens 4, and therefore, the effective diameter R1 of the blazed hologram 1 of FIG. 1 can be increased, so that the tolerance of the position of the blazed hologram 1 at the time of assembling the optical head device can be relaxed. .

Next, the improvement of the light use efficiency will be described.
In order to obtain a servo signal or an information signal, the 0th-order diffracted light in the forward path is reflected by the disk, and then the + 1st-order diffracted light generated upon incidence on the hologram is received by the photodetector, and the output from the photodetector is electrically converted. Calculate in the circuit.

Therefore, in order to improve the S / N ratio of the signal,
Is the product of the 0th order diffracted light on the outward path and the + 1st order diffracted light on the return path.
It is necessary to increase the utilization efficiency η of the obtained light. What
The light utilization efficiency η is calculated from the equations 5 and 6 as follows: η = 1 / 2π²× SIN²(Φ₁) × (1 + SIN (φ₂)) × (1 + COS (φ ₂ )) ... Equation 13 is obtained. As is clear from Equation 13, φ₁ = Π / 2
In addition, the round trip light utilization efficiency η is maximum (0.14).
It

FIG. 11 shows the relationship between φ ₁ and diffraction efficiency. However, φ ₂ is a constant value that minimizes E ₂ (φ ₂ = 0.32
π). As can be seen from this graph, φ ₁ is 0.
When 31π to 0.69π, the light use efficiency η becomes 0.1 or more.

Therefore, when the relief type blazed hologram 102 is manufactured by the method shown in FIG.
_{If 1} is designed to be 0.31π to 0.69π,
The light utilization efficiency η can be set to 0.1 or more.

This relief type blazed hologram 10
2 is used as the blazed hologram 1 in FIG. 1 to configure the optical head device, the 0th-order diffracted light in the forward path and the +1 in the backward path
Since the light utilization efficiency η given by the product of the second-order diffracted lights can be increased, the S / N ratio of the servo signal and the information signal can be improved.

The second embodiment of the present invention is shown in FIG. In this embodiment, the hologram 102 and the objective lens 4 are provided, for example, by holding a fixed relative position by the holding means 13. Therefore, even if the objective lens 4 moves for tracking control, the hologram 102 moves integrally and the light beam reflected from the information medium 5 hardly moves on the hologram 102. Therefore, the objective lens 4
, The signal obtained from the photodetector 7 does not deteriorate. Moreover, since the hologram is blazed, the light utilization efficiency η is large and the S / N ratio of the servo signal and the information signal is high.

If the hologram 102 is manufactured by the method shown in FIG. 6 and designed so that φ ₂ is about π / 2, the proportion E 1 of unnecessary diffracted light is reduced and the diffraction angle is increased. Without it, the deterioration of the focus servo signal can be remarkably suppressed.

If the optical head device is constructed by using this hologram 102 as the blazed hologram 102 of FIG. 12, the blazed hologram 102 of FIG. 12 can be obtained even if the radiation source 2 and the photodetector 7 are arranged close to each other. Can be arranged near the objective lens 4, and therefore the effective diameter R1 of the blazed hologram 102 in FIG. 12 can be increased, so that the blazed hologram 102 at the time of assembling the optical head device can be made.
The tolerance of the position of can be relaxed.

Here, as shown in FIG. 22, only the objective lens 4 and the transmission type blazed hologram 101 are integrated by the holding means 3 and moved independently of the radiation light source 2. There is an effect that the movable body can be made thinner and lighter when driving for focus control and tracking control, and accurate and high-speed servo tracking can be realized.

[0065] Furthermore, when creating a hologram 102 by the method shown in FIG. 6, phi ₂ is 0.2π~
If the design is made to be 0.45π, the proportion E ₂ of the unnecessary diffracted light becomes small, so that the deterioration of the information signal and the focus servo signal can be suppressed without increasing the diffraction angle.

If the optical head device is constructed by using this hologram 102 as the blazed hologram 102 shown in FIG. 12, the effective diameter R1 of the blazed hologram 102 shown in FIG. 12 can be increased. The tolerance of the position of the digitized hologram 102 can be relaxed.

Further, FIG. 13 shows a third embodiment of the present invention. In FIG. 13, 2 is a radiation light source, 4 is an objective lens, and 5 is an information medium. In this embodiment, the spot size detection method (SSD method) is used as the focus servo signal detection method.

As disclosed in Japanese Patent Application Laid-Open No. 2-185722, the SSD method can remarkably reduce the assembly tolerance of the optical head device, and can obtain a servo signal stably with respect to wavelength fluctuation. This is a possible detection method.

In order to realize the SSD method, the + 1st-order diffracted light on the backward path of the hologram is designed to be two types of spherical waves having different curvatures. Each spherical wave is designed so as to have a focus on the front side e and the rear side f of the photodetector surface.
As shown in FIG.
The split photodetector 71 receives the light. However, the same figure (b)
Shows the just focus state, and (a) and (c) show the defocus state. Therefore, the focus error signal FE is obtained by the following equation: FE = (S10 + S30-S20)-(S40 + S60-S50).

Even when the SSD method is used, the S / N ratio can be improved by further blazing the hologram 104 to improve the light utilization efficiency. In particular, using a method such as that shown in FIGS. 4, 5 and 6,
FIG. 1 shows an example of realizing a blazed hologram for the SSD method.
5 shows.

In FIG. 15, the A area 151 generates a spherical wave 141 (FIG. 13) having a focus on the front side of the photodetector, and the B area 152 generates a spherical wave 142 having a focus on the rear side of the photodetector (FIG. 13). 13) is generated.

The far-field pattern of the wavefront diffracted from the hologram pattern as shown in FIG. 15 is partially cut off as shown in FIG. 17 reflecting the fact that the hologram pattern is divided, but the focus servo signal is affected. There is no. However, FIG. 17B shows the just focus state, and FIGS. 17A and 17C show the defocus state. Therefore, the focus error signal FE is also obtained by the calculation shown in Expression 14.

By dividing the areas in this way to blaze each of the divided areas and suppress the unnecessary ratios E ₁ and E ₂ of the diffracted light as described above, a more stable information signal can be obtained. Since an information signal having a high S / N ratio can be obtained and the effective aperture of the hologram can be increased, an optical head having a large assembly tolerance can be configured.

Furthermore, by integrating the blazed hologram and the objective lens in this way, the diffracted light generated from the hologram does not move on the photodetector regardless of the movement of the objective lens due to tracking tracking. Therefore, it is possible to configure an optical head device that can obtain a stable focus error signal in parallel with tracking tracking.

The light reflected on the information medium 5 has a diffraction pattern by being diffracted by the track grooves on the information medium 5. Therefore, a change in the relative position between the focused spot on the information medium 5 and the track groove causes a change in the light amount distribution on the hologram. For example, with the X direction in FIG. 15 as the direction parallel to the track groove of the information medium, the + Y direction becomes brighter and the −Y direction becomes darker, or the opposite light amount change occurs.

Therefore, it is desirable that the area division of FIG. 15 is made into several to several tens as shown here. This is because by dividing the hologram area into multiple sections in this way, the relative symmetry in the + Y direction and the −Y direction is reduced, and on the hologram due to the relative position change of the focused spot on the information medium 5 and the track groove. This is because it is possible to prevent an offset from occurring in the focus servo signal due to the influence of the change in the light intensity distribution. Therefore, if the hologram area is divided into multiple areas, stable focus servo characteristics can be obtained.

A fifth embodiment is shown in FIG. 16 in order to extract the change in the light amount distribution on the hologram due to the change in the relative position between the focused spot on the information medium 5 and the track groove as a tracking error signal TE. Thus, further diffraction areas 153 and 154 may be provided on the hologram. The tracking error signal detection diffracted light 163 from the diffraction areas 153 and 154 is received by the tracking error signal detection photodetector 72 (FIG. 18), and TE = S70-S80 ... The error signal TE can be obtained.

Although the embodiment using the transmission hologram has been described above, the optical head can be similarly constructed by using the reflection blazed hologram. This is shown in FIG. 19 as a sixth embodiment. FIG. 19 shows an optical head device using a reflective blazed hologram. In the figure, 11
Reference numeral 0 indicates a driving means such as an actuator.

By constructing the optical head device using the reflection-type blazed hologram 105 as shown in the figure, the same effect as when the above-mentioned transmission hologram is used can be obtained.

Furthermore, the reflection-type blazed hologram 105
Can also serve as the folding mirror of the optical axis, so that the thin optical head device as shown in FIG. 19 can be configured with a small number of parts.

In addition, all the optical components such as the radiation light source 2, the photodetector 7, the reflection type blazed hologram 105, and the objective lens 4 are integrated by the all optical system holding means 14 such as an aluminum casing. When integrally driven, there is an effect that the relative position with respect to the radiation light source 2 does not change even if the objective lens 4 moves following a track, and off-axis aberration does not occur.

Furthermore, since off-axis aberration does not occur, the objective lens 4 can be made smaller and thinner, and an even smaller and thinner optical head device can be constructed.

[0083]

As is clear from the above description,
According to the present invention, the following effects can be obtained.

(1) Since the hologram is blazed, the diffraction efficiency of the 0th-order diffracted light in the forward path and the + 1st-order diffracted light in the backward path is increased, so that the light utilization efficiency is improved and the S / N ratio of the servo signal or the information signal is increased. The ratio is improved.

(2) Due to the optimum design of the cross-sectional shape of the blazed hologram, among the diffracted light generated in the outward optical path from the radiation light source to the information medium, the diffracted light other than the outward zero-order light is transmitted to the photodetector. By suppressing the amount of incident light, the diffraction angle can be increased, and deterioration of the information signal and the focus servo signal can be suppressed without preventing unnecessary diffracted light from entering the photodetector.

Therefore, if the optical head device is constructed by using this blazed hologram, it is possible to simultaneously arrange the photodetector and the radiation light source and increase the effective diameter R1 of the blazed hologram 1. Therefore, it is possible to reduce the positional tolerance during assembly.

(3) By using the structure in which the blazed hologram is integrated with the objective lens, the diffracted light in the outward path generated from the hologram does not move on the photodetector regardless of the movement of the objective lens due to tracking tracking.

Therefore, a stable focus error signal can be obtained in parallel with the tracking following.

Further, since the hologram is blazed, the diffraction efficiency of unnecessary diffracted light such as −1st order diffracted light on the outward path is smaller than the diffraction efficiency of + 1st order diffracted light on the backward path and 0th order diffracted light on the outward path. Therefore, the deterioration of the servo signal and the information signal due to the unnecessary diffracted light such as the −1st order diffracted light on the outward path is significantly reduced. Therefore, very stable servo and information reading can be realized.

(4) By using the SSD method as the focus servo signal detection method, it is possible to construct an optical head device having a larger assembly tolerance.

Further, the hologram pattern is divided into 2
With the configuration in which spherical waves having different curvatures are generated as the + 1st order diffracted light in the return path from the seed region, it is possible to easily realize the blazed hologram and the SSD method at the same time.

Therefore, it is possible to remarkably reduce the assembly tolerance of the optical head device and at the same time construct an optical head device which can obtain a signal with a very good S / N ratio.

(5) Since the optical head device is constructed by using the reflection type blazed hologram, it can also serve as the folding mirror of the optical axis, so that the thin optical head device can be constructed with a small number of parts. .

In addition, when all the optical components such as the radiation light source, the photodetector, the reflection type blazed hologram, and the objective lens are integrally driven by the all optical system holding means, the objective lens moves by following the track. Even so, the relative position with respect to the radiation source does not change, and there is an effect that off-axis aberration does not occur.

Furthermore, since no off-axis aberration is generated, the objective lens can be made smaller and thinner, and an even smaller and thinner optical head device can be constructed.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an optical head device according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a blazed hologram which is a requirement of the first embodiment of the present invention.

FIG. 3 is a graph showing the relationship between the phase modulation amount φ of a blazed hologram and the diffraction efficiency, which is a requirement of the first embodiment of the present invention.

FIG. 4 is a schematic explanatory view of an example of manufacturing a blazed hologram which is a requirement of the first embodiment of the present invention, in which (a) is a cross-sectional view of a reactive ion beam etching process and (b) is first Sectional view of hologram of Example

FIG. 5 is a schematic explanatory view of another example of manufacturing a blazed hologram that is a requirement of the embodiment of the present invention, in which (a) is a cross-sectional view of the first reactive ion beam etching step and (b) is 2 is a cross-sectional view of the reactive ion beam etching step in (c) is a cross-sectional view of the hologram.

FIG. 6 is a schematic explanatory view of another example of manufacturing a blazed hologram which is a requirement of the embodiment of the present invention, in which (a) is a cross-sectional view of the first reactive ion beam etching step and (b) is 2 is a cross-sectional view of the reactive ion beam etching step in (c) is a cross-sectional view of the hologram.

FIG. 7 is a plan view showing a state of diffracted light on a photodetector in an embodiment of the present invention, (a) is a plan view showing a defocused state, and (b) is a plan view showing a just focus state. ) Is a plan view showing the defocused state

FIG. 8 is a diagram for explaining the influence of the diffracted light in the forward path on the focus servo signal, where (a) is a waveform diagram of an original servo signal and (b) is a waveform diagram of a false servo signal.

FIG. 9 is a schematic cross-sectional view for explaining how outgoing diffracted light enters a photodetector.

FIG. 10 is a diagram showing the relationship between the amount of phase modulation of a blazed hologram that is a requirement of the present invention and unnecessary diffracted light.

FIG. 11 is a diagram showing the relationship between the phase modulation amount of a blazed hologram and the light utilization efficiency light, which is a requirement of the present invention.

FIG. 12 is a schematic sectional view of an optical head device according to a second embodiment of the present invention.

FIG. 13 is a schematic perspective view of an optical head device according to a third embodiment of the present invention.

FIG. 14 is a plan view showing a state of diffracted light on a photodetector in a third embodiment of the present invention, (a) is a plan view showing a defocused state, and (b) is a plan view showing a just focused state. Figure (c) is a plan view showing a defocused state.

FIG. 15 is a plan view showing a hologram pattern according to a fourth embodiment of the present invention.

FIG. 16 is a plan view showing a hologram pattern according to a fifth embodiment of the present invention.

FIG. 17 is a plan view showing a state of diffracted light on the photodetector in the fourth embodiment of the present invention, (a) is a plan view showing a defocused state, and (b) is a plan view showing a just focused state. Figure (c) is a plan view showing a defocused state.

FIG. 18 is a schematic perspective view of a main part of an optical head device according to a fifth embodiment of the present invention.

FIG. 19 is a schematic sectional view of an optical head device according to a sixth embodiment of the present invention.

FIG. 20 is a schematic sectional view of a conventional optical head device.

FIG. 21 is a schematic sectional view of another conventional optical head device.

FIG. 22 is an explanatory diagram of a problem of the conventional optical head.

FIG. 23 is an explanatory diagram of a problem of another conventional optical head.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Blazed hologram 2 Radiation light source 3 Light beam 4 Objective lens 5 Information medium 6 Return path + 1st order diffracted light 7 Photodetector 8 Outgoing path −1st order diffracted light 9 Transparent substrate 10 Photoresist 11 Ion beam 13 Holding means 14 All optical system Holding means 31 Light beam on hologram 61 Forward 0th order diffracted light 62 Forward Nth order diffracted light 63 Return N + 1st order diffracted light 71 6-division photodetector 72 Tracking error signal detection photodetector 102 Blazed hologram 103 hologram 104 hologram 105 reflective blazed hologram 110 driving means 141 spherical wave (+ 1st-order diffracted light) 142 spherical wave (+ 1st-order diffracted light) 151 hologram divided region (focus error signal detection diffracted light generation region) 152 hologram divided region (focus For error signal detection Diffraction light generation area) 153 Hologram division area (tracking error signal detection diffraction light generation area) 154 Hologram division area (tracking error signal detection diffraction light generation area) 162 Focus error error signal detection diffraction light 163 Tracking error signal Diffracted light for detection 200 Etching part 201 Etching part

Front page continuation (72) Inventor Yoshikazu Hori 1006, Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor, Seiji Nishino, 1006, Kadoma, Kadoma, Osaka

Claims (6)

[Claims] 1. A radiation light source, a hologram, an objective lens for transmitting or reflecting a light beam emitted from the radiation light source by the hologram, and converging 0th-order diffracted light of the hologram onto a small spot on an information medium, An optical head device comprising a photodetector comprising a plurality of photodetectors for receiving a + 1st-order diffracted light diffracted by the hologram receiving and diffracting a light beam reflected and diffracted by an information medium,
The cross-sectional shape of the hologram is blazed to a height h, and the amplitude φ of the phase modulation amount of the light beam of the light beam determined by the height h of the blazing is larger than π radians and is larger than 2π radians. In the forward optical path from the radiation light source to the information medium, diffracted light other than the 0th-order light among the diffracted light generated from the hologram is incident on the photodetector. An optical head device, characterized in that the amount of light emitted is suppressed. 2. An objective lens and a blazed hologram are integrated, and a portion where the objective lens and the blazed hologram are integrated is movable independently of a radiation light source. Optical head device. 3. A radiation source, a photodetector, a blazed hologram, and an objective lens are provided inside a housing, and the blazed hologram is a reflection hologram, and reflects a light beam emitted from the radiation source. Bending the central axis of the light beam in the same direction as the optical axis of the objective lens to focus the light beam on the information medium by the objective lens,
2. The optical head according to claim 1, wherein the reflection-type blazed hologram receives the light beam reflected by the information medium, generates + 1st-order diffracted light, and receives the + 1st-order diffracted light by the photodetector. apparatus. 4. The hologram surface is divided into a plurality of divided areas, and the + 1st order diffracted light generated from some of the plurality of divided areas forms a focal point or a focal line on the front side of the photodetector surface. Of the plurality of divided areas, the + 1st-order diffracted light generated from the other part of the part of the plurality of areas extends in the same direction as the focal point or the focal line behind the photodetector surface. The optical head device according to claim 1, wherein the optical head device has a focal line. 5. A hologram surface is divided into a plurality of divided areas, and areas H1 and H2 are provided in the divided areas,
An output E1 obtained by providing a photodetector region P1 and a photodetector region P2 on the photodetector surface and receiving the diffracted light diffracted from the hologram region H1 by the photodetector region P1;
An arithmetic circuit for arithmetically operating an output E2 obtained by receiving the diffracted light diffracted from the hologram area H2 by the photodetector area P2 and tracking the results of arithmetic operations of the output E1 and the output E2 by the arithmetic circuit. The optical head device according to any one of claims 1 to 4, wherein the optical head device outputs an error signal. 6. A radiant light source, an objective lens that receives a light beam emitted from the radiant light source and converges it into a minute spot on an information medium, and a light beam reflected and diffracted by the information medium, and diffracts as + 1st-order diffracted light. An optical head device comprising a hologram for guiding a light beam to the photodetector and a photodetector comprising a plurality of photodetectors for receiving the + 1st-order diffracted light and outputting a photocurrent, wherein The light source, the photodetector, the hologram and the objective lens are fixed, the hologram is a reflection type blazed hologram, and the reflection type blazed hologram reflects the light beam emitted from the radiation source, An optical head device, characterized in that the central axis of a light beam is bent in the same direction as the optical axis of the objective lens to guide the light beam to the objective lens.