JP2001060336A - Optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical head having high utilization efficiency of light in a structure equipped with a light source with plural wave lengths and a diffraction optical device capable of coping with information recording medium of a plurality of kinds. SOLUTION: Light emitted from a light source 1 selectively emitting light with a primary wave length and light with a secondary wave-length nearly two times as long are made parallel by a diffraction type collimeter lens 3, are raised by a raising mirror 15, and then are condensed on an information recording medium 11 by a diffraction type objective lens 4. These diffraction type lenses 3, 4 emit substantially secondary diffraction light to the light with the primary wave length, and emit substantially the primary diffraction light to the light with the secondary wave length.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head of an optical recording / reproducing apparatus, and more particularly, to a high light use efficiency having a plurality of wavelength light sources and a diffractive optical element capable of supporting a plurality of types of information recording media. Related to an optical head.

[0002]

2. Description of the Related Art An optical head is an important component for reading a signal from an optical recording medium such as an optical disk such as a compact disk (CD) or a DVD, or an optical card memory. The optical head uses not only a signal detection function but also a focus servo, to extract signals from the optical recording medium.
It is necessary to provide a control mechanism such as a tracking servo.

The optical head is generally composed of various optical components such as a light source, a photodetector, a condenser lens, a focus / track error signal detecting element, a rising mirror, a collimator lens, and the like. Laser light emitted from the light source is focused on the optical disk by the objective lens. The laser light collected on the optical disk is reflected and detected by the photodetector. Thereby, the reproduction signal is read. Further, the focus / track is controlled by the focus / track error signal detecting element, so that a signal can be stably read.

If a diffractive optical element is used as an optical element constituting the optical head in place of a currently used refractive optical element such as a lens or a prism, the size, thickness and weight of the optical head can be reduced. it can.

[0005] A diffractive optical element is an optical element that functions by effectively utilizing the diffraction phenomenon of light. This diffractive optical element has unevenness in the depth of a wavelength order or a refractive index distribution or an amplitude distribution. It has the feature that it is formed on the surface periodically or quasi-periodically. It is known that when the period of the diffractive optical element is sufficiently larger than the wavelength, the diffraction efficiency can be increased to almost 100% by forming the cross section into a sawtooth shape.

[0006]

However, when the period is sufficiently larger than the wavelength, the diffraction efficiency of the diffractive optical element becomes 10%.
0% is only for the design wavelength. FIG.
FIG. 2 shows the relationship between the normalized wavelength with the design wavelength set to 1 and the first-order diffraction efficiency of the diffractive optical element. As can be seen from FIG. 14, the diffraction efficiency gradually decreases as the wavelength deviates from the design value. Therefore, when a diffractive optical element is used in an optical head equipped with light sources of a plurality of wavelengths corresponding to a plurality of types of optical discs, in order to increase the light use efficiency, an optical path of that wavelength must be optimally designed. Only needed to be placed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the prior art, and has a light source having a plurality of wavelengths and a diffractive optical element capable of supporting a plurality of types of information recording media, and has a high light use efficiency. It is an object to provide an optical head.

[0008]

In order to achieve the above object, a first invention (corresponding to the invention described in claim 1) is:
One or more light sources that emit light of a first wavelength and light of a second wavelength having a wavelength approximately twice the first wavelength;
A light detector, and one or more diffractive optical elements provided in the optical path of the light of the first and second wavelengths, wherein the diffractive optical element substantially emits light of the first wavelength. An optical head which emits upper second-order diffracted light and emits substantially first-order diffracted light with respect to the light of the second wavelength.

Thus, for example, even if a diffractive optical element is arranged on the optical path of light of two wavelengths, a high diffraction efficiency can be obtained for both wavelengths, and an optical head having good optical characteristics can be realized. can do.

According to a second aspect of the present invention (corresponding to the second aspect of the present invention), the sectional shape of the diffractive optical element is substantially saw-toothed, and the first wavelength λ ₁ and the second wavelength λ ₂ In the case of a transmission type element, the depth of the sawtooth shape is substantially 2λ ₁ / (n−) with respect to the refractive index n of the material of the diffractive optical element.
1) to [lambda] ₂ / (n-1), and in the case of a reflective element entering from the substrate side, substantially from [lambda] ₁ / n to [lambda].
In the range of ₂ / 2n, in the case of a reflective element that enters from the air side is an optical head according to the first aspect of the present invention which is within the range of substantially lambda ₁ lambda _2/2.

Thus, for example, the diffraction efficiency of the diffractive optical element can be maximized for the light of the first wavelength and the light of the second wavelength.

A third aspect of the present invention (corresponding to the third aspect of the present invention) is the optical head according to the first aspect of the present invention, wherein the diffractive optical element is an objective lens for converging on an information recording medium. .

Thus, for example, the thickness and weight of the objective lens can be reduced.

According to a fourth aspect of the present invention (corresponding to the fourth aspect of the present invention), the diffractive optical element is a collimator lens for making the light emitted from the light source substantially parallel. An optical head.

Thus, for example, it is possible to reduce the thickness and weight of the collimator lens.

The fifth invention (corresponding to the fifth invention) is the optical head according to the first invention, wherein the diffractive optical element is a focus / track error signal detecting element.

Thus, for example, it is possible to reduce the thickness and weight of the focus / track error signal detecting element.

According to a sixth aspect of the present invention (corresponding to the sixth aspect of the present invention), the minimum period Λ _min of the diffractive optical element is equal to the first period Λ _min .
An optical head of the present invention the first to meet the relationship of lambda _min ≧ 10 [lambda] ₁ with respect to the wavelength lambda ₁ of the.

Thus, for example, a diffractive optical element having a high diffraction efficiency of 80% or more with respect to the light of the first wavelength can be realized.

According to a seventh aspect of the present invention (corresponding to the seventh aspect of the present invention), the minimum period Λ _min of the diffractive optical element is equal to the first period.
An optical head of the present invention the first satisfying the relation Λ _min ≧ 22λ ₁ with respect to the wavelength lambda ₁ of the.

Thus, for example, a diffractive optical element having a higher diffraction efficiency of 90% or more with respect to the light of the first wavelength can be realized.

According to an eighth aspect of the present invention (corresponding to the eighth aspect of the present invention), the optical axis of the light emitted from the light source obliquely enters the optical path of the light of the first and second wavelengths. A refractive optical means having an optical surface is provided, and a change in the diffraction angle of the diffracted light from the diffractive optical element due to the wavelength change of the emitted light, and a change in the refractive angle of the refracted light from the refractive optical means. And the optical head according to the first aspect of the present invention, which is generated in directions canceling each other.

Thus, for example, a thin optical head can be realized, and when a semiconductor laser beam is used as the light emitted from the light source, a wavelength band of about several nm is spread by a high-frequency module or self-excited oscillation. Even if the center wavelength of the emitted light changes due to a change in ambient temperature or environmental temperature, a good light-converged spot can be obtained on the optical disk surface.

A ninth invention (corresponding to the ninth invention) is the optical head according to the eighth invention, wherein the diffractive optical element is a grating having a uniform period.

This facilitates, for example, positioning and manufacturing of the diffractive optical element.

According to a tenth aspect of the present invention (corresponding to the tenth aspect of the present invention), the diffractive optical element is disposed in a convergent light path or a divergent light path having a numerical aperture of 0.39 or less. The optical head according to the eighth aspect of the present invention, wherein the period of the diffractive optical element is uniform.

This facilitates, for example, positioning and manufacturing of the diffractive optical element.

According to an eleventh aspect of the present invention (corresponding to the eleventh aspect of the present invention), the refractive optical means is a prism having three optical surfaces. Is the first surface, the surface on the light source side is the second surface, and the other surface is the third surface, light emitted from the light source passes through the second surface, and the first surface and the second surface The eighth aspect, wherein the third surface is reflected in order and the first surface is transmitted, and the lower part of the objective lens is lower than the highest position where the light emitted from the light source is incident on the second surface. 3 is an optical head of the present invention.

Thus, for example, the thickness of the optical head can be reduced.

The twelfth invention (corresponding to the twelfth invention) is the optical head according to the eleventh invention, wherein the Abbe number of the glass material of the prism is 64 or more.

As a result, for example, since the period of the diffractive optical element is increased, it is easy to manufacture and high diffraction efficiency can be obtained, the influence of wavelength fluctuation can be offset in a wide wavelength range, and good optical disc surface can be obtained. A focused spot can be obtained.

According to a thirteenth aspect of the present invention (corresponding to the thirteenth aspect), the SHG in which the light source emits light of two wavelengths is provided.
An optical head according to the first aspect of the present invention, which is a light source.

Thus, for example, it is possible to obtain a light source that emits light of the first wavelength and light of the second wavelength having a wavelength approximately twice the first wavelength.

According to a fourteenth aspect of the present invention (corresponding to the fourteenth aspect of the present invention), a transparent substrate in which light of first and second wavelengths propagates in a zigzag pattern is provided, and the diffractive optical element is provided on the transparent substrate. FIG. 2 is an optical head according to the first aspect of the present invention disposed above.

Thus, for example, it is possible to realize a thin and stable optical head.

The fifteenth aspect of the present invention (corresponding to the fifteenth aspect of the present invention) is characterized in that the first wavelength λ ₁ is 0.35 μm ≦
satisfies the relationship of λ ₁ ≦ 0.44 μm, or
Wavelength lambda ₂ is the said first optical head of the present invention satisfies the relationship 0.76μm ≦ λ ₂ ≦ 0.88μm.

As a result, for example, the focused spot can be narrowed down, and a high-density disk of, for example, 10 GB or more can be read, or a CD or CD can be read.
-R optical disk can be read.

The sixteenth invention (corresponding to the sixteenth invention) is characterized in that the first wavelength λ ₁ is substantially 0.35
The optical head according to the first aspect of the present invention, which satisfies the relationship of μm ≦ λ ₁ ≦ 0.44 μm, and wherein the diffractive optical element is a chromatic aberration correcting element for correcting chromatic aberration of the objective lens focused on the information recording medium.

Accordingly, for example, as the light emitted from the light source, 0.35 μm ≦ λ having a large chromatic dispersion of the glass material of the lens.
_When the semiconductor laser light in the range of ₁ ≦ 0.44 μm is used, even if the center wavelength of the emitted light changes due to the widening of the wavelength band of about several nm due to the high-frequency module or self-excited oscillation and the change in the environmental temperature, the objective lens Large chromatic aberration caused by the above can be corrected, and a good condensed spot can be obtained on the optical disk surface.

According to a seventeenth aspect of the present invention (corresponding to the seventeenth aspect of the present invention), the light of the first wavelength and the light of the second wavelength having a wavelength approximately twice the first wavelength are provided. One or more light sources for emitting light, a photodetector, an objective lens for converging light on an information recording medium, and a diffractive optical element provided in an optical path of light of the first and second wavelengths, A diffractive optical element is a chromatic aberration correction element having a stepped or substantially sawtooth-shaped step for correcting chromatic aberration of the objective lens,
The step is substantially 2λ _{1 with} respect to the first wavelength λ ₁ , the second wavelength λ ₂ , and the refractive index n of the material of the chromatic aberration correction element.
/ (N-1) to λ ₂ / (n-1).

Thus, for example, a chromatic aberration correction element having good light use efficiency for the light of the first wavelength and the light of the second wavelength can be obtained.

According to an eighteenth aspect of the present invention (corresponding to the eighteenth aspect of the present invention), the first wavelength λ ₁ is 0.35 μm ≦
satisfies the relationship of λ ₁ ≦ 0.44 μm, or
The optical head according to the seventeenth aspect, wherein the wavelength λ ₂ satisfies the relationship of 0.76 μm ≦ λ ₂ ≦ 0.88 μm.

The nineteenth invention (corresponding to the nineteenth invention) is the optical head according to the seventeenth invention, wherein the chromatic aberration correcting element is formed on an objective lens.

As a result, for example, the chromatic aberration correction element and the objective lens can be handled as one component, and the size and cost can be reduced.

A twentieth aspect of the present invention (corresponding to the twentieth aspect) is the optical head of the seventeenth aspect of the present invention, wherein the chromatic aberration correcting element and the objective lens are driven integrally by an actuator.

Thus, for example, since the optical axes of the chromatic aberration correction element and the objective lens do not shift, good optical characteristics can be obtained.

According to a twenty-first aspect of the present invention (corresponding to the twenty-first aspect of the present invention), the chromatic aberration correcting element is a convex diffractive lens and forms the convergent light with both the objective lens. 3 is an optical head of the present invention.

As a result, for example, the numerical aperture of the objective lens itself is reduced, thereby facilitating manufacture.

According to a twenty-second aspect of the present invention (corresponding to the twenty-second aspect of the present invention), a light of a first wavelength, a light of a second wavelength having a wavelength approximately twice the first wavelength, And one or more light sources that emit light of a third wavelength having a wavelength approximately 1.5 times the first wavelength, a photodetector, and light of the first, second, and third wavelengths One or more diffractive optical elements provided in the optical path of the, the diffractive optical element emits substantially fourth-order diffracted light with respect to the light of the first wavelength,
A second-order diffracted light is emitted substantially for the second wavelength light, and a third-order diffracted light is emitted substantially for the third wavelength light.

Thus, for example, even if the diffractive optical elements are arranged on the same optical path, a particularly high diffraction efficiency can be obtained for the first and second wavelengths among the three wavelengths, and the optical characteristics can be improved. A good optical head can be realized.

The twenty-third aspect of the present invention (claim 23)
The sectional shape of the diffractive optical element is substantially sawtooth.
A first wavelength λ₁, The second wavelength λ_Two, Third
Wavelength λ_ThreeFor the refractive index n of the material of the diffractive optical element
In the case where the depth of the sawtooth shape is a transmission type element,
Quality 4λ₁/ (N-1) and 2λ_Two/ (N-1) and 3λ _Three
/ (N-1) within the range of the minimum value and the maximum value,
In the case of a reflective element that enters from the substrate side, it is substantially 2λ.
₁/ N and λ_Two/ N and 3λ_Three/ 2n minimum and maximum
Field of a reflective element that falls within the range of values and enters from the air side.
In effect, 2λ₁And λ_TwoAnd 3λ_ThreeMinimum of / 2
The twenty-second aspect of the present invention, wherein the value and the maximum value are within the range.
An optical head.

Thus, for example, a diffractive optical element having the highest diffraction efficiency can be obtained for the light of the first and second wavelengths among the light of the first to third wavelengths.

In the twenty-fourth aspect of the present invention (corresponding to the twenty-fourth aspect), the minimum period Λ _min of the diffractive optical element is
Satisfy a relationship of Λ _min ≧ 22λ ₁ with respect to the first wavelength lambda ₁ is an optical head of the present invention of the first 22.

Thus, it is possible to realize a diffractive optical element having a high diffraction efficiency of, for example, 80% or more with respect to the light of the first wavelength.

In the twenty-fifth aspect of the present invention (corresponding to the twenty-fifth aspect), the first wavelength λ ₁ is 0.35 μm ≦
satisfies the relationship of λ ₁ ≦ 0.44 μm, or
Wavelength lambda ₂ is, meets the relationship of 0.76μm ≦ λ ₂ ≦ 0.88μm, or the third wavelength lambda _3, 0.57
The optical head according to the twenty-second aspect of the present invention satisfies the relationship of μm ≦ λ ₃ ≦ 0.68 μm.

As a result, for example, since the focused spot can be narrowed down, for example, it is possible to read a high-density optical disk of, for example, 10 GB or more, or a CD or CD-R optical disk. Alternatively, a DVD or DVD-R optical disk having a two-layer structure can be read.

According to a twenty-sixth aspect of the present invention (corresponding to the twenty-sixth aspect), the first wavelength λ ₁ is substantially 0.35
The optical head according to the twenty-second aspect of the present invention, wherein the diffractive optical element satisfies the relationship of μm ≦ λ ₁ ≦ 0.44 μm, and the diffractive optical element is a chromatic aberration correcting element for correcting chromatic aberration of the objective lens focused on the information recording medium.

Also, the twenty-seventh aspect of the present invention (corresponding to the twenty-seventh aspect of the present invention) provides a light having a first wavelength, a light having a second wavelength substantially twice as long as the first wavelength, And one or more light sources that emit light of a third wavelength having a wavelength that is approximately 1.5 times the first wavelength, a photodetector, an objective lens that focuses light on an information recording medium, One or more diffractive optical elements provided in an optical path of light of the first, second and third wavelengths, wherein the diffractive optical element has a stepped or substantially sawtooth shape for correcting chromatic aberration of the objective lens. A chromatic aberration correcting element having a step of 4λ, wherein the step is 4λ with respect to the first wavelength λ ₁ , the second wavelength λ ₂ , the third wavelength λ ₃ , and the refractive index n of the material of the diffractive optical element. within the range of minimum and maximum value of ₁ / (n-1) and 2λ ₂ / (n-1) and 3λ ₃ / (n-1) An optical head according to claim Rukoto.

Thus, for example, it is possible to obtain a chromatic aberration correction element having particularly good light use efficiency for the light of the first and second wavelengths among the light of the first to third wavelengths.

According to a twenty-eighth aspect of the present invention (corresponding to the twenty-eighth aspect of the present invention), the first wavelength λ ₁ is 0.35 μm ≦
satisfies the relationship of λ ₁ ≦ 0.44 μm, or
Wavelength lambda ₂ is, meets the relationship of 0.76μm ≦ λ ₂ ≦ 0.88μm, or the third wavelength lambda _3, 0.57
The optical head according to the twenty-seventh aspect, wherein the optical head satisfies the relationship of μm ≦ λ ₃ ≦ 0.68 μm.

A twenty-ninth aspect of the present invention (corresponding to the twenty-ninth aspect of the present invention) is the optical head of the twenty-seventh aspect of the present invention, wherein the chromatic aberration correcting element is formed on an objective lens.

A thirtieth invention (corresponding to the thirty-first invention) is the optical head according to the twenty-seventh invention, wherein the chromatic aberration correcting element and the objective lens are driven integrally by an actuator.

According to a thirty-first aspect of the present invention (corresponding to the thirty-first aspect), the chromatic aberration correcting element is a convex diffractive lens, and forms the convergent light with both the objective lens and the objective lens. Is an optical head according to the present invention.

The thirty-second aspect of the present invention (corresponding to the thirty-second aspect of the present invention) provides a light having a first wavelength and a second wavelength having a wavelength substantially 1.5 times the first wavelength. One or more light sources for emitting light, a photodetector, and the first and second light sources.
A single or a plurality of diffractive optical elements provided in the optical path of light having a wavelength of, the diffractive optical element emits substantially third-order diffracted light with respect to the light having the first wavelength, An optical head which emits substantially second-order diffracted light with respect to light of a second wavelength.

Thus, for example, even if the diffractive optical elements are arranged in the same optical path, a high diffraction efficiency can be obtained for light of any wavelength, and an optical head having good optical characteristics can be realized. it can.

The thirty-third aspect of the present invention (claim 33)
The sectional shape of the diffractive optical element is substantially sawtooth.
A first wavelength λ₁, The second wavelength λ_TwoAnd said
For the refractive index n of the material of the diffractive optical element, the sawtooth shape
Is substantially 3λ in the case of a transmissive element.₁/ (N
-1) to 2λ_Two/ (N-1), on the substrate side
In the case of a reflective element that enters from₁/ 2
n to λ_Two/ N in the range of
In the case of a projection type element, it is substantially 3λ.₁/ 2 to λ _TwoRange
The optical head according to the thirty-second aspect of the present invention, wherein

Thus, for example, a diffractive optical element having the highest diffraction efficiency with respect to the light of the first and second wavelengths can be obtained.

According to a thirty-fourth aspect of the present invention (corresponding to the thirty-fourth aspect), the minimum period Λ _min of the diffractive optical element is
Satisfy Λ _min ≧ 16λ ₁ relationship to the first wavelength lambda ₁ is an optical head of the present invention of the first 32.

Thus, a diffractive optical element having a high diffraction efficiency of, for example, 80% or more with respect to the first wavelength can be realized.

The thirty-fifth invention (corresponding to the thirty-fifth invention) is characterized in that the first wavelength λ ₁ is 0.35 μm ≦
satisfies the relationship of λ ₁ ≦ 0.44 μm, or
32. The optical head according to claim 32, wherein the wavelength λ ₂ satisfies the relationship of 0.57 μm ≦ λ ₂ ≦ 0.68 μm.

The thirty-sixth aspect of the present invention (corresponding to the thirty-sixth aspect) is characterized in that the first wavelength λ ₁ is substantially 0.35
The optical head according to the thirty-second aspect of the present invention, wherein the diffractive optical element satisfies the relationship of μm ≦ λ ₁ ≦ 0.44 μm, and the diffractive optical element is a chromatic aberration correcting element for correcting chromatic aberration of the objective lens focused on the information recording medium.

The thirty-seventh aspect of the present invention (corresponding to the thirty-seventh aspect of the present invention) provides a light having a first wavelength and a second wavelength having a wavelength approximately 1.5 times the first wavelength. A light source or a plurality of light sources that emit light, an optical detector, an objective lens that condenses light on an information recording medium, and a diffractive optical element provided in an optical path of the light of the first and second wavelengths. Wherein the diffractive optical element is a chromatic aberration correcting element having a stepped or substantially sawtooth-shaped step for correcting chromatic aberration of the objective lens, wherein a first wavelength λ ₁ , a second wavelength λ ₂ , the chromatic aberration correction The optical head is characterized in that the step is substantially in the range of 3λ ₁ / (n−1) to 2λ ₂ / (n−1) with respect to the refractive index n of the material of the element.

As a result, for example, it is possible to obtain a chromatic aberration correction element having good light use efficiency with respect to the light of the first and second wavelengths.

In the thirty-eighth aspect of the present invention (corresponding to the thirty-eighth aspect), the first wavelength λ ₁ is 0.35 μm ≦
satisfies the relationship of λ ₁ ≦ 0.44 μm, or
37. The optical head according to claim 37, wherein the wavelength λ ₂ satisfies the relationship of 0.57 μm ≦ λ ₂ ≦ 0.68 μm.

As a result, for example, the focused spot can be narrowed down, and a high-density optical disk of, for example, 10 GB or more can be read, or a DVD or DVD-R optical disk having a two-layer structure can be read. Can be.

A thirty-ninth aspect of the present invention (corresponding to the thirty-ninth aspect) is the optical head of the thirty-seventh aspect of the present invention, wherein the chromatic aberration correcting element is formed on an objective lens.

A fortieth aspect of the present invention (corresponding to the forty-third aspect of the present invention) is the optical head of the thirty-seventh aspect of the present invention, wherein the chromatic aberration correcting element and the objective lens are driven integrally by an actuator.

Also, in the forty-first aspect of the present invention (corresponding to the forty-first aspect of the present invention), the chromatic aberration correcting element is a convex diffractive lens, and the thirty-seventh aspect forms a convergent light with both the objective lens. Is an optical head according to the present invention.

The forty-second aspect of the present invention (corresponding to the forty-second aspect of the present invention) comprises a light having a first wavelength, a light having a second wavelength having a wavelength substantially twice as large as the first wavelength, And one or more light sources that emit light of a third wavelength having a wavelength approximately 1.5 times the first wavelength, a photodetector, and light of the first, second, and third wavelengths And one or more diffractive optical elements provided in the optical path of the, the diffractive optical element emits substantially sixth-order diffracted light with respect to the light of the first wavelength,
An optical head that emits substantially third-order diffracted light with respect to the second wavelength light and emits substantially fourth-order diffracted light with respect to the third wavelength light. .

Thus, for example, even if the diffractive optical elements are arranged in the same optical path, a high diffraction efficiency can be obtained for three wavelengths, and an optical head having good optical characteristics can be realized.

Also, in the forty-third aspect of the present invention (claim 43)
The sectional shape of the diffractive optical element is substantially sawtooth.
A first wavelength λ₁, The second wavelength λ_Two, Third
Wavelength λ_ThreeFor the refractive index n of the material of the diffractive optical element
In the case where the depth of the sawtooth shape is a transmission type element,
Quality 6λ₁/ (N-1) and 3λ_Two/ (N-1) and 4λ _Three
/ (N-1) within the range of the minimum value and the maximum value,
In the case of a reflective element entering from the substrate side, substantially 3λ
₁/ N and 3λ_Two/ 2n and 2λ_Three/ N minimum and maximum
It is within the range of the large value and the reflection type element that enters from the air side
In that case, substantially 3λ₁And 3λ_Two/ 2 and 2λ_ThreeThe most of
43. The optical system according to the above item 42, which is in the range between the small value and the maximum value.
Is

Thus, for example, a diffractive optical element having the highest diffraction efficiency with respect to the light of the first to third wavelengths can be obtained.

The forty-fourth aspect of the present invention (corresponding to the forty-fourth aspect of the present invention) comprises a light having a first wavelength, a light having a second wavelength having a wavelength approximately twice as large as the first wavelength, And one or more light sources that emit light of a third wavelength having a wavelength that is approximately 1.5 times the first wavelength, a photodetector, an objective lens that focuses light on an information recording medium, One or more diffractive optical elements provided in an optical path of light of the first, second and third wavelengths, wherein the diffractive optical element has a stepped or substantially sawtooth shape for correcting chromatic aberration of the objective lens. Is a chromatic aberration correcting element having a step of, wherein the step is substantially equal to the first wavelength λ ₁ , the second wavelength λ ₂ , the third wavelength λ ₃ , and the refractive index n of the material of the diffractive optical element. Upper 6λ ₁ / (n−
(1) An optical head characterized by being within a range of a minimum value and a maximum value among 3λ ₂ / (n−1) and 4λ ₃ / (n−1).

As a result, for example, a chromatic aberration correction element having good optical characteristics with respect to light of the first to third wavelengths can be obtained.

The forty-fifth aspect of the present invention (corresponding to the forty-fifth aspect of the present invention) is the optical head of the forty-fourth aspect of the present invention, wherein the chromatic aberration correcting element is formed on an objective lens.

The forty-sixth aspect of the present invention (corresponding to the forty-sixth aspect) is the optical head of the forty-fourth aspect of the present invention, wherein the chromatic aberration correcting element and the objective lens are driven integrally by an actuator.

Further, in the forty-seventh aspect of the present invention (corresponding to the forty-seventh aspect), the chromatic aberration correcting element is a convex diffractive lens, and forms the convergent light with both the objective lens. Is an optical head according to the present invention.

Further, the forty-eighth aspect of the present invention (corresponding to the forty-eighth aspect of the present invention) is substantially the same as the following.
a light source that emits light having a wavelength λ that satisfies the relationship of μm, a photodetector, and one or more diffractive optical elements provided in an optical path of light emitted from the light source. An optical head is a chromatic aberration correction element for correcting chromatic aberration of an objective lens condensed on an information recording medium.

The forty-ninth aspect of the present invention (corresponding to the forty-ninth aspect of the present invention) is the optical head of the forty-eighth aspect of the present invention, wherein the chromatic aberration correcting element is formed on an objective lens.

The fiftieth invention (corresponding to the fiftyth invention) is the optical head according to the forty-eighth invention, wherein the chromatic aberration correcting element and the objective lens are driven integrally by an actuator.

The fifty-first aspect of the present invention (corresponding to the fifty-first aspect of the present invention) is directed to the forty-eighth aspect, wherein the chromatic aberration correcting element is a convex diffractive lens and forms convergent light with both the objective lens. Is an optical head according to the present invention.

[0092]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described more specifically with reference to embodiments.

<First Embodiment> First, the first embodiment of the present invention will be described.
The optical head according to the embodiment will be described in detail with reference to FIGS.

FIG. 1 is a side view showing a basic structure of an optical head and a state of light propagation according to a first embodiment of the present invention.
FIG. 2 is a graph showing the relationship between the normalized wavelength of the diffractive optical element and the diffraction efficiency when the period is sufficiently larger than the wavelength in the optical head of the embodiment, and FIG. 5 is a graph showing a relationship between a normalized grating period of a diffractive optical element and first-order and second-order diffraction efficiencies.

As shown in FIG. 1, in the optical head according to the present embodiment, a light source 1 controls a recording medium such as DVD or C
A diffractive collimator lens 3, a diffractive objective lens 4, and a diffractive focus / track error signal detecting element 8 as diffractive optical elements are arranged in an optical path to an optical disk 11 such as D. By using the diffractive optical element in this manner, it is possible to reduce the thickness, weight, and cost of the optical head.

The light source 1 is a light source capable of selectively emitting a laser beam having a first wavelength and a laser beam having a second wavelength substantially twice as long as the first wavelength. A light source / photodetector unit 17 together with a detector (not shown)
Is integrated within. In the present embodiment, an SHG light source is used as the light source 1 so that the above two wavelengths can be obtained. However, two semiconductor lasers of each wavelength may be used.

The laser light 2 emitted in the y-axis direction from the semiconductor laser as the light source 1 passes through the diffraction type focus / track error signal detecting element 8 (using the 0th-order diffraction light), and is integrated with the diffraction type. For example, the collimator lens 3 turns the light into substantially parallel light 6 having a beam diameter of 3.25 mm. The light path is bent in the z-axis direction by the rising mirror 15. And the laser beam 6 bent in the z-axis direction is
The light is focused (converged light 7) on the optical disk 11 by the diffraction objective lens 4.

The laser beam 7 reflected by the optical disk 11 is turned in the opposite direction, passes through the diffraction type objective lens 4, the rising mirror 15, and the diffraction type collimator lens 3 in order, and directs the optical path in the -y axis direction. The light is divided by the diffraction type focus / track error signal detection element 8 (using first-order or second-order diffracted light) and detected by a photodetector.

In the optical head of this embodiment, the wavelength λ ₁ of the _first wavelength laser light 2 emitted from the light source 1 satisfies, for example, 0.35 μm ≦ λ ₁ ≦ 0.44 μm. By mounting the light source 1 of one wavelength, the focused spot can be narrowed down, and as a result, for example, a high-density disk of 10 Gbytes or more can be read. The wavelength λ ₂ of the _second wavelength laser light 2 emitted from the light source 1 is, for example, 0.76 μm ≦ λ ₂ ≦ 0.
By mounting the light source 1 of the second wavelength, which satisfies the relationship of 88 μm, it is possible to read, for example, an optical disc of CD or CD-R. As described above, in the present embodiment, the wavelength of the emitted light is determined according to the type of the optical disk to be read, and the laser light 2 having that wavelength is selectively emitted.

The diffractive optical element generally shows a high diffraction efficiency at a design wavelength, but the diffraction efficiency gradually decreases as it deviates from the design wavelength. Therefore, if a diffractive optical element is arranged in an optical path through which both the light of the design wavelength and the light of the other wavelengths pass, the diffraction efficiency will decrease for either wavelength.

However, when the period of the diffractive optical element is sufficiently larger than the wavelength, as shown in FIG. 2, when the wavelength becomes a half of the design wavelength (normalized wavelength = 1), the first-order diffraction efficiency hardly increases. 0, but the second-order diffraction efficiency is almost 100%
It turned out to be very high. The present inventors have proposed a two-wavelength optical head capable of supporting both a high-density optical disc and a CD or CD-R optical disc.
The relationship of the magnitude of the wavelength between the wavelengths is set to about twice (in the actual case, about 1.8 times to about 2.1 times) to correspond to a high-density optical disk (light of the first wavelength is emitted). ), The second-order diffracted light is used substantially for the diffractive optical element, and the diffractive optical element corresponds to the CD or CD-R optical disc (the second order).
), The first-order diffracted light is used substantially for the diffractive optical element, so that even if the diffractive optical element is arranged in the same optical path, the diffraction efficiency is high for both wavelengths. Was obtained, and it was found that an optical head having good optical characteristics could be realized.

Normally, the diffraction angle in a diffractive optical element is determined by the wavelength, the period, and the diffraction order. However, the present inventors use substantially the second-order diffracted light at the first wavelength, and use the second-order diffracted light substantially twice the wavelength. By using the first-order diffracted light substantially at the second wavelength, it has been found that the diffraction angles can be equalized even at different wavelengths. When this is applied to a lens, the focal lengths of the diffractive objective lens 4 and the diffractive collimator lens 3 in the present embodiment can be made almost the same at the first and second wavelengths, respectively. Therefore, the distance from the light source 1 to the collimator lens 3 can be made substantially constant regardless of the wavelength.
Similarly, the focal length of the objective lens 4 can be made constant. Further, since the diffraction angles are equal, the focus /
Since the optical path for splitting the light from the track error signal detecting element 8 to the photodetector is exactly the same, the photodetector can be shared for both wavelengths.

The cross-sectional shape of a diffractive optical element, such as the diffractive collimator lens 3 and the diffractive objective lens 4 of the present embodiment, which can obtain high diffraction efficiency and practically uses only a single diffraction order, is substantially It has an upper saw tooth shape. Here, with respect to the first wavelength λ ₁ , the second wavelength λ ₂ , and the refractive index n of the material of the diffractive optical element, the depth L of the sawtooth shape is determined by the diffractive collimator lens 3 and the diffractive objective lens. In the case of a transmissive element such as _No. 4, it is substantially in the range of L ₁ = 2λ ₁ / (n−1) to L ₂ = λ ₂ / (n−1), and is shown in the present embodiment. However, in the case of a reflective element which is incident from the substrate side as described in other embodiments, it is substantially in the range of L ₁ = λ ₁ / n to L ₂ = λ ₂ / 2n. Further, in the case of a reflective element, such as entering from the air side, as from substantially L ₁ = λ ₁ within the range of L ₂ = λ _2/2, diffraction for both wavelengths Efficiency was increased.

For example, λ₁= 0.40 μm, λ_Two= 0.
In the case of 80 μm and n = 1.5, L₁= L_TwoIs
From the above, L = 1.6 μm for the transmissive element and L for the reflective element
= 0.27 μm (incident from the substrate side), 0.4 μm (air
Incident from the side). Also, λ₁ = 0.425 μm, λ
_Two= 0.80 μm, n = 1.5, transmission type element
L = 1.6 μm to 1.7 μm, and L =
0.27 μm to 0.28 μm (incident from the substrate side), L =
0.4 μm to 0.425 μm (incident from the air side)
You. Completely 2λ like the latter₁= Λ_TwoIf not
Has L₁≠ L_TwoAnd the preferred groove depth is L₁From
L_TwoBut the groove depth is L₁When the first
Wavelength λ₁And the groove depth is L_Twoage
The second wavelength λ_TwoFocus on efficiency for
The average size (0.5 (L ₁+ L_Two)) And
In this case, a balanced state is obtained for both wavelengths. wave
The shorter the length, the more importance is placed on light use efficiency.
The groove depth of the element is L₁Is more desirable to be set to
I can say.

As shown in FIG. 2, for example, when the diffraction efficiency is 8
The wavelength range of 0% or more is 0.36 μm to 0.47 μm.
m, 0.65 μm to 1.1 μm (in the present embodiment, the normalized wavelength 1.0 corresponds to the second wavelength λ ₂ ). Therefore, the diffractive optical element of the present embodiment can secure a diffraction efficiency of 80% or more at both wavelengths when the period Λ is sufficiently larger than the wavelength λ. It is also possible to use a multi-level diffractive optical element whose cross-sectional shape is approximated by a step-like shape, and the optimal groove depth at that time is, when the number of levels is p, the transmission type element. Is substantially L ₁ = 2 (p−1) λ ₁ /
From [p (n-1)], L ₂ = (p-1) λ ₂ / [p (n
-1)], and in the case of a reflective element that enters from the substrate side, substantially L ₁ = (p−1) λ ₁ / p
There the n in the range of _{L 2 = (p-1)} λ 2 / 2pn,
Further, in the case of a reflective element that enters from the air side, L ₁ = (p−1) λ ₁ / p to L ₂ = (p−
1) It is desirable to be within the range of λ ₂ / 2p.

The cross-sectional shape of a transmission-type diffractive optical element such as the focus / track error signal detecting element 8 of the present embodiment, which uses the 0th-order diffracted light on the outward path and the 1st or 2nd-order diffracted light on the return path, is substantially saw-toothed. Shape. Here, for the first wavelength λ ₁ , the second wavelength λ ₂ , and the refractive index n of the material of the diffractive optical element, the sawtooth-shaped depth L of the transmission element is used.
Is substantially from L ₁ = λ ₁ / (n−1) to L ₂ = λ ₂ /
[2 (n-1)], and in the case of a reflective element that is incident from the substrate side as described in another embodiment, L ₁ = λ _1. / 2n to L ₂
= In the range of λ ₂ / 4n, in the case of a reflective element, such as entering from the air side, L from substantially L ₁ = λ _1/2
2 = as is λ in the range of _2/4, and as the round-trip light utilization efficiency is increased. It is also possible to use a multi-level diffractive optical element whose cross-sectional shape is approximated by a step-like shape, and the optimal groove depth at that time is, when the number of levels is p, the transmission type element. Is substantially L
₁ = (p−1) λ ₁ / [p (n−1)] and L ₂ = (p
-1) In the case of a reflective element which is within the range of λ ₂ / [2p (n−1)] and is incident from the substrate side, substantially L
₁ = (p-1) λ ₁ / 2pn to L ₂ = (p-1) λ ₂
/ 4 pn, and in the case of a reflective element that enters from the air side, substantially L ₁ = (p−1) λ
It is preferably in a range of ₁ / 2p of _{L 2 = (p-1)} λ 2 / 4p.

In FIG. 2, it is assumed that the period of the diffractive optical element is sufficiently larger than the wavelength, and the reflection loss on the surface of the diffractive optical element is ignored. Next, the relationship between the normalized grating period 規格 / λ normalized by the wavelength λ of the diffractive optical element and the diffraction efficiency was examined in detail, including the reflection loss on the surface. The result is shown in FIG. In FIG. 3, the solid line indicates the first-order diffraction efficiency, and the broken line indicates the second-order diffraction efficiency. The cross-sectional shape of the diffractive optical element was substantially a sawtooth shape, and the groove depth was set to an optimum value as described above.
In this case, by applying a non-reflective coating to the surface of the diffractive optical element, the diffraction efficiency is improved by the reflection loss.

As can be seen from FIG. 3, the first-order diffraction efficiency is generally better, but both diffraction efficiencies tend to decrease as Λ / λ decreases. Both diffraction efficiencies are 80
% Or more is 10 or more, so that the minimum period Λ _min of the diffractive optical element is Λ _min ≧ ₁ for the first wavelength λ ₁ .
By satisfying the relationship of 10λ _1, the diffraction efficiency can be made 80% or more for both wavelengths. Further, the minimum period Λ _min of the diffractive optical element is equal to the first wavelength λ ₁
By satisfying the relationship of Λ _min ≧ 22λ ₁ , the diffraction efficiency can be made 90% or more for both wavelengths.

The diffractive lenses 3, 4 are formed of, for example, concentric gratings, and have a structure in which the period gradually decreases toward the outer periphery. In this embodiment, the numerical aperture NA of the diffraction type collimator lens 3 is, for example, 0.15, for a minimum period of the outermost peripheral portion is 13Ramuda _1, over the lens throughout the diffraction efficiency for both wavelengths It can be 80% or more. However, the NA of the diffractive objective lens is, for example, 0.6 and 0.45 for the first and second wavelengths, respectively, and the minimum period of the outermost periphery is 3.3λ ₁ , Since it is 2.2λ ₂ , the diffraction efficiency decreases in the periphery.

In the present embodiment, substantially second-order diffracted light is emitted with respect to the first wavelength and the second-order diffracted light is emitted with respect to the second wavelength so that the diffraction efficiency is increased with respect to both wavelengths. Although the first order diffracted light is emitted substantially, the fourth order diffracted light is emitted substantially for the first wavelength, and the second order diffracted light is emitted substantially for the second wavelength. However, the operation is possible (in this case, for example, the groove depth is 4λ ₁ /
(N−1) to 2λ ₂ / (n−1)). However, since the depth of the groove becomes larger with respect to the wavelength as the light becomes higher, the diffraction efficiency tends to decrease as can be seen from FIG. 13 described later.

In this embodiment, three diffractive optical elements are used. However, it is not necessary to use all the diffractive optical elements, and only one of them has an effect. Further, the direction of the diffractive optical element may be opposite to that of the present embodiment. In particular, if the grooved surface of the objective lens 4 is placed on the opposite side to the optical disk 11, the influence of dust and dust from the optical disk 11 can be avoided, and the surface can be wiped. Further, the positions of the collimator lens 3 and the focus / track error signal detecting element 8 may be reversed.

<Second Embodiment> Next, a second embodiment of the present invention will be described.
The optical head according to the second embodiment will be described with reference to FIG. 4, focusing on the differences from the first embodiment.

FIG. 4 is a side view showing a basic configuration of an optical head and a state of light propagation according to a second embodiment of the present invention.

The optical head according to the present embodiment has, for example, 1
This is an ultra-thin optical head that is compatible with high-density disks of 0 Gbytes or more and CD and CD-R optical disks.

As shown in FIG. 4, the diffraction focus /
The track error signal detecting element 8a is arranged on the window side of the light source / photodetector unit 17. Further, instead of the rising mirror, refracting optical means 9 which is a prism having three optical surfaces is used. An aspheric lens is used as the objective lens 4a.

The refracting optical means 9 has a first surface (slope) 10 on the information recording medium side and a second surface (side) 1 on the light source side.
2. When the other surface is a third surface (bottom surface) 14, for example, a first wavelength λ ₁ satisfying a relationship of 0.35 ≦ λ ₁ ≦ 0.44 μm and a size approximately twice as large as the first wavelength λ ₁ For example,
The laser beam 2 emitted from the light source 1 that selectively emits the second wavelength λ ₂ that satisfies the relationship of 0.76 ≦ λ ₂ ≦ 0.88 μm is substantially collimated by the diffractive collimator lens 3.
Becomes The substantially parallel light 6 passes through the second surface 12 of the refracting optical means 9 and is totally reflected by the first surface 10.
The light is reflected on the third surface 14 on which the reflective film 16 such as 1 or a multilayer film is formed. The substantially parallel light 6 reflected on the third surface 14 of the refracting optical means 9 passes through the first surface 10 and has an optical axis with respect to the substantially parallel light 6 between the diffractive collimator lens 3 and the refracting optical means 9. The state is substantially 90 ° bent. By adopting such a configuration that the light propagates in the refraction optical means 9 in a zigzag manner, the highest position (optical position) of the incident beam on the second surface 12 of the refraction optical means 9 which has been converted into the substantially parallel light 6 by the collimator lens 3 is obtained. Since the lower part of the objective lens 4a can be made lower than the head lower part or the height from the optical base (not shown) in the z-axis direction, the height (size in the z-axis direction) of the optical head can be significantly reduced. Thus, it is possible to achieve ultra-thinness.

The specifications of the refracting optical means 9 are as follows. That is, the installation angle θb of the bottom surface of the refractive optical means 9 is, for example, 5.0 °, and one of the base angles θ of the refractive optical means 9 is θ.
Is, for example, 29.3 °, the other angle θ ₁ of the base angle of the refractive optical means 9 is, for example, 114.3 °, and the length of the third surface (bottom surface) 14 is 4.4 mm. BK7 is used as a glass material of the refraction optical means (prism) 9. In this case, the diameter of the beam entering the refracting optical unit 9 is set to be equal to the diameter of the beam exiting from the refracting optical unit 9 (configuration without beam shaping). Further, when the refractive index of the glass material of the refractive optical unit 9 has n, the installation angle of the bottom surface of the refractive optical means 9 and theta _b, one of the angle theta of the base angle of the refractive optical unit 9, sin (θ-θ _b ) = N · sin (4θ−2θ)
_b− 90 ° −θ ′), n · sin θ ′ = sin (θ−θ
The relationship of _b ) is substantially satisfied, and the other angle θ ₁ of the base angle of the refractive optical means 9 substantially satisfies the relationship of θ ₁ = θ + 90 ° −2θ _b . In the present embodiment, the setting angle of the refractive optical means 9 is, for example, θ _b = 5 °. However, if it is substantially in the range of 2 ° to 10 °, the left end of the objective lens 4a and the refractive optical means 9 There is enough room for the distance between
It turned out to be favorable.

Also in the present embodiment, the diffractive optical elements 3 and 8a emit substantially the second-order diffracted light with respect to the light of the first wavelength, as in the case of the first embodiment. By emitting substantially first-order diffracted light for the light of the second wavelength, high diffraction efficiency can be realized for both wavelengths.

Note that the focus / track error signal detecting element 8a is similar to that of the first embodiment.
It may be integrated with the diffractive collimator lens 3. Also,
The objective lens 4 may be a diffractive lens.

<Third Embodiment> Next, the third embodiment of the present invention will be described.
The optical head according to the second embodiment will be described with reference to FIG. 5, focusing on the differences from the second embodiment.

FIG. 5 is a side view showing a basic configuration of an optical head and a state of light propagation according to a third embodiment of the present invention.

As shown in FIG. 5, in this embodiment, the diffractive optical element 5 which is integrated with the focus / track error signal detecting element 8a and has, for example, a grating having a period of 10 μm and having a uniform period in the x-axis direction. Is arranged. Further, an aspheric lens is used as the collimator lens 3a.

The light source 1 has, for example, 0.35 ≦ λ ₁ ≦ 0.
A semiconductor laser that emits the laser light 2 of the first wavelength λ ₁ that satisfies the relationship of 44 μm, and a second laser that satisfies the relationship of, for example, 0.76 ≦ λ ₂ ≦ 0.88 μm, which is approximately twice the wavelength. The semiconductor laser that emits the laser light 2 having the wavelength λ ₂ is arranged close to the semiconductor laser, and can emit light selectively. The diffractive optical element 5 emits substantially second-order diffracted light at a diffraction angle of, for example, 4.7 ° with respect to the laser light 2 having the first wavelength, and emits second-order diffracted light with respect to the laser light 2 having the second wavelength. Emits substantially first-order diffracted light at the same diffraction angle of, for example, 4.7 °. Therefore, since the diffraction angle of the diffractive optical element 5 can be made substantially the same with respect to the laser light 2 of the first and second wavelengths, the optical axis of the laser light 2 emitted from the diffractive optical element 5 is almost the same. Can be the same.

In this embodiment, since a semiconductor laser is used as the light source 1, a wavelength spread of about 1 nm typically occurs due to a high-frequency module or self-sustained pulsation. A phenomenon occurs in which the center wavelength changes.

In the present embodiment, the refractive optical means 9
Since the optical axis of the laser beam 2 is obliquely incident on the side surface 12 and the slope 10 of the laser beam, if the wavelength band is wide, chromatic dispersion such as a different refraction angle occurs. If the diffractive optical element 5 is arranged in the optical path such that the change in the diffraction angle of the diffracted light cancels out the change in the refraction angle in the refraction optical means 9, the chromatic dispersion is canceled out and the optical disc 11 can be favorably condensed. In particular, from 0.35 μm
In the wavelength band of 0.44 μm (first wavelength), since the chromatic dispersion of the glass (refractive optical means 9 as a prism) is very large, canceling it by the diffractive optical element 5 is good on the optical disk 11. It is very effective in forming a focused light spot.

The present inventors have found that when the glass material constituting the refractive optical means 9 as a prism has a low dispersion, chromatic aberration can be offset to a degree that causes almost no problem in a wide wavelength range, and at the same time, It has also been found that since the period of the diffractive optical element 5 for correcting chromatic aberration can be increased, the element can be easily manufactured and high diffraction efficiency can be obtained. In practice, the wavelength variation is almost within the range of ± 10 nm at the first wavelength. In this case, if the Abbe number of the glass material is 64 or more, the optical disc 1
It has also been found that a light spot less affected by chromatic aberration can be formed on the light-emitting device 1. Therefore, as a glass material, B
K7, FC5, FK5, FCD1, FCD10, FCD
100 or the like is desirable.

In the optical head according to the present embodiment, the diffractive optical element 5, which is a grating having a uniform period, is disposed in a converging light path or a diverging light path from the light source 1 to the collimator lens 3a. When the diffractive optical element 5 which is a grating for correcting chromatic aberration is arranged in such a convergent light path or a divergent light path, the present inventors have different correction effects depending on the incident angle (the light is incident obliquely). The chromatic aberration correction effect increases as the case increases). Therefore, strictly, it is necessary to change the periodic distribution of the diffractive optical element 5 in the z-axis direction according to the convergence angle of the emitted light 2. However, when the diffractive optical element 5, which is a grating for correcting chromatic aberration, is arranged in the convergent light path or the divergent light path having a numerical aperture of 0.39 or less, the spot on the optical disk 11 by the objective lens 4a is used. Was found not to be a problem with chromatic aberration. For this reason, it becomes possible to use the diffractive optical element 5 which is a grating having a uniform period, so that alignment and manufacturing are facilitated.

<Fourth Embodiment> Next, a fourth embodiment of the present invention will be described.
The optical head according to the third embodiment will be described with reference to FIG. 6, focusing on differences from the third embodiment.

FIG. 6A is a side view showing a basic structure of an optical head and a state of light propagation according to a fourth embodiment of the present invention, and FIG. 6B is a fourth embodiment of the present invention. FIG. 3 is a plan view showing a basic configuration of an optical head and a state of light propagation in FIG.

As shown in FIG. 6, in the present embodiment, the light source 1a for the light of the first wavelength λ _{1 and} the light source 1b for the light of the second wavelength λ ₂ , which is almost twice the wavelength, Are arranged in separate light source / photodetector units 17a and 17b together with the photodetector 13 provided for each wavelength, and both wavelengths are multiplexed / demultiplexed by the beam splitter 18. The beam splitter 18 may be a wedge prism or the like, and is not limited to this as long as it is an element capable of multiplexing / demultiplexing.

A diffractive optical element 5a, which is a grating for correcting chromatic aberration of the refractive optical element 9a, is provided integrally on a side surface of the refractive optical means 9a as a prism. The diffractive optical element 5a emits substantially second-order diffracted light for the first wavelength light and substantially 1st-order diffracted light for the second wavelength light, as in the case of the third embodiment. By emitting the next diffracted light, high efficiency can be realized for both wavelengths. Further, by arranging the diffractive optical element 5a, which is a grating for correcting chromatic aberration, in the optical path of the substantially parallel light 6, the diffraction efficiency and the chromatic aberration correction effect can be made substantially equal over the entire surface of the element. In addition, since the diffractive optical element 5a is integrated with the refracting optical means 9a, the structure is stable and can be handled as one part, so that the alignment becomes easy.

In the present embodiment, the installation angle of the bottom surface 14 of the refracting optical means 9a, which is a prism, is 0, and the bottom surface 14 can be directly placed on an optical base (not shown) on which it is mounted. Therefore, alignment becomes easy. The diffraction optical element 5a, which is a grating,
Are the other surfaces 10, 1 of the refractive optical means 9a, which are prisms.
4 may be arranged.

<Fifth Embodiment> Next, a fifth embodiment of the present invention will be described.
The optical head according to the second embodiment will be described with reference to FIG. 7, focusing on differences from the first embodiment.

FIG. 7 is a side view showing a basic structure of an optical head and a state of light propagation according to a fifth embodiment of the present invention.

As shown in FIG. 7, in the optical head of the present embodiment, the rising mirror 15 and the objective lens 4a
A chromatic aberration correction element 19 that corrects chromatic aberration of the objective lens 4a is disposed in the optical path between. Here, the objective lens 4a and the collimator lens 3 are aspherical lenses.

The present inventors have found that 0.35 μm to 0.44 μm
In the wavelength band of m (first wavelength), the chromatic dispersion of glass is very large. For example, when the glass material of the objective lens 4a is VC
79 (Abbe number 57.7) and the wavelength is, for example, λ ₁ =
In the case of design with a specification of 0.4 μm and a numerical aperture of NA = 0.6, even if the incident wavelength changes by ± 1 nm, the focused spot position is larger than the depth of focus (± 0.56 μm). Change (for example, 0.8 μm), and a problem that a good spot cannot be obtained (defocusing) occurs. For example, this problem occurs when the wavelength band is widened (wavelength spread about ± 1 nm) by a high-frequency module or self-excited oscillation.

In the present embodiment, the objective lens 4a
By arranging the chromatic aberration correcting element 19 for correcting the chromatic aberration, an optical head that can solve such a problem is realized.

Furthermore, when writing and reading to and from a rewritable optical disk are performed at high speed, the focal point position is liable to fluctuate markedly with the light of the first wavelength, and the effect of the present invention is great.

The chromatic aberration correcting element 19 is a convex diffractive lens, and has a pattern shape such that the period of the concentric grating gradually decreases as it goes to the outer peripheral portion. A second-order diffracted light is generated substantially for the light of the first wavelength, and a substantially first-order diffracted light is generated for the light of the second wavelength, which is substantially twice the wavelength of the first wavelength. The cross section has a substantially saw-tooth shape having a step (groove depth) L that causes the following.

Here, with respect to the first wavelength λ ₁ , the second wavelength λ ₂ , and the refractive index n of the material of the chromatic aberration correcting element 19,
The step L is substantially equal to L ₁ , as in the first embodiment.
= 2λ ₁ / (n−1) to L ₂ = λ ₂ / (n−1), and the diffraction efficiency increases for both wavelengths.

In this embodiment, the chromatic aberration correcting element 1
9 has, for example, an F number of 10.0 (numerical aperture NA = 0.0
5) is a convex diffractive lens, and as shown in FIG.
The substantially parallel light 6 becomes gentle convergent light by the chromatic aberration correcting element 19, and finally becomes convergent light 7 having, for example, a numerical aperture NA = 0.66 by the objective lens 4a. Therefore, the numerical aperture of the objective lens 4a itself can be substantially reduced to, for example, about 0.6, and chromatic aberration can be corrected, and manufacturing becomes easy.

In the present embodiment, the chromatic aberration correction element 19 and the objective lens 4a are driven integrally by an actuator. With such a configuration, the optical axes of the two elements can always be kept coincident, so that good optical characteristics can be obtained.

<Sixth Embodiment> Next, the sixth embodiment of the present invention will be described.
The optical head according to the fifth embodiment will be described with reference to FIGS. 8 and 9, focusing on differences from the fifth embodiment.

FIG. 8 is a side view showing a basic structure of an optical head and a state of light propagation according to a sixth embodiment of the present invention.
FIG. 9A is a sectional view showing an objective lens on which a chromatic aberration correcting element of an optical head according to a sixth embodiment of the present invention is formed, and FIG. 9B is a plan view thereof.

In the present embodiment, as shown in FIGS. 8 and 9, the chromatic aberration correcting element 19a having a concentric pattern shape and a substantially saw-tooth shape (step s) cross section on the objective lens 4c. Are formed. By thus integrating the chromatic aberration correction element 19a and the objective lens 4c,
It is possible to reduce the size of the optical head and facilitate alignment.

The first wavelength λ₁, Approximately twice the wavelength of the first wavelength
The second wavelength λ which is long_TwoOf the chromatic aberration correcting element 19a
Is s with respect to the refractive index n of₁= 2λ₁/ (N-
1) to s_Two= Λ_Two/ (N-1)
Is set and the design wavelength λ ₁Or λ_TwoLight is incident
The phase difference is λ₁, Λ_TwoAgainst
And substantially 4π, 2π (substantially for both wavelengths)
No phase jump). For this reason, the same as when there is no step
(Same as when there is no chromatic aberration correcting element 19a), both wavelengths
Almost no light loss, and the objective lens 4c
The light is condensed well. However, the wavelength of the incident light is
From the depth of the groove of the chromatic aberration correction element 19a.
Phase difference from 4π and 2π respectively
Therefore, the chromatic aberration correction element 19a is provided with the wavelength of the objective lens 4a.
Wavefront conversion is performed to cancel the focus fluctuation due to the shift.
U. That is, the wavelength of the substantially parallel light (incident light) 6 becomes longer.
And the refractive index of the glass material of the objective lens 4c becomes small.
In addition, the focal length of the objective lens 4c becomes longer. But the color
The phase difference at the step of the aberration correction element 19a is the first and the second.
Smaller than 4π, 2π for wavelength
Therefore, light emitted from the chromatic aberration correction element 19a becomes convergent light.
So as to substantially shorten the focal length of the objective lens 4c.
It works and there is no fluctuation of the focal length in total.

In the present embodiment, the phase difference at the step of the chromatic aberration correcting element 19a is substantially 4π and 2π with respect to the first and second wavelengths, respectively. The step s is set to s ₁ = 2λ ₁ / (n−1) so that the phase jump at the step of the element 19 a does not substantially occur.
To s ₂ = λ ₂ / (n−1), but the phase difference at the step of the chromatic aberration correcting element 19a is substantially 8π, with respect to the first and second wavelengths, respectively. The step s is changed from s ₁ = 4λ ₁ / (n−1) to s ₂ so as to be 4π.
= 2λ ₂ / (n−1), the function still works. However, in this case, since the step is large, the light loss is larger than the former.

<Seventh Embodiment> Next, a seventh embodiment of the present invention will be described.
The optical head according to the embodiment is described with reference to FIG.
The following description focuses on the differences from the first embodiment.

FIG. 10 is a side view showing a basic structure of an optical head and a state of light propagation according to a seventh embodiment of the present invention.

In the present embodiment, the objective lens 4 is provided in the optical path between the rising mirror 15 and the objective lens 4a.
A chromatic aberration correction element 19b for correcting the chromatic aberration of a is arranged.

The chromatic aberration correcting element 19b has a pattern shape of a typical diffractive lens in which the period gradually decreases toward the periphery. The cross section of the chromatic aberration correction element 19b has a stepped shape as shown in FIG.
₁ , a second wavelength λ ₂ , which is approximately twice the first wavelength,
With respect to the refractive index n of the material of the chromatic aberration correction element 19b, the minimum step s of the step shape is substantially s ₁ = 2λ ₁ / (n
−1) to s ₂ = λ ₂ / (n−1). In this case, the light use efficiency becomes good for both wavelengths. Since the phase difference is substantially 4π and 2π with respect to each wavelength, the step s of the staircase shape is equivalent to having no element at each design wavelength. The substantially parallel light 6 having the wavelength passes through as it is. However, when the wavelength is changed from the design wavelength, the phase difference is shifted. Therefore, as in the case of the sixth embodiment, the parallel light becomes divergent light or convergent light, and plays a role of canceling the focus fluctuation generated in the objective lens 4a. Fulfill.

<Eighth Embodiment> Next, an eighth embodiment of the present invention will be described.
The optical head according to the embodiment is described with reference to FIG.
The following description focuses on the differences from the first embodiment.

FIG. 11A is a side view showing the basic structure of an optical head and the state of light propagation in an eighth embodiment of the present invention, and FIG. 11B is an eighth embodiment of the present invention. FIG. 3 is a plan view showing a basic configuration of an optical head and a state of light propagation in FIG.

The optical head according to the present embodiment includes a transparent substrate 20 through which light of the first and second wavelengths propagates in a zigzag manner, and a plurality of diffractive optical elements 4b and 8 are provided on the transparent substrate 20.
d, 3b and 22 are arranged.

The off-axis type diffraction objective lens 4b,
As in the case of the first embodiment, the reflective diffractive collimator lens 3b emits substantially second-order diffracted light for the light of the first wavelength, and the second diffracted light is approximately twice as large. With respect to the light having the wavelength of?, Substantially the first-order diffracted light is emitted. Since the diffraction type objective lens 4b is a transmission element having a substantially sawtooth cross-sectional shape, the depth of the sawtooth shape with respect to the first wavelength λ ₁ , the second wavelength λ ₂ , and the refractive index n of the material. L is substantially L ₁
= 2λ ₁ / (n−1) to L ₂ = λ ₂ / (n−1), and the diffractive collimator lens 3 b has a substantially sawtooth-shaped reflective element (substrate side). , And the sawtooth-shaped depth L is substantially L ₁ = λ ₁ /
If n is set to be in the range of L ₂ = λ ₂ / 2n, high diffraction efficiency can be obtained for both wavelengths.

For example, on the back surface of a transparent substrate 20 such as glass having a thickness of 3 mm, for example, 0.35 μm ≦ λ ₁ ≦ 0.4
Light having a _first wavelength λ ₁ satisfying the relationship of 4 μm, for example,
The second satisfying the relationship of 0.76 μm ≦ λ ₂ ≦ 0.88 μm
The light source 1 that selectively emits the light having the wavelength λ ₂ is disposed. The light source 1 is mounted on a slope of an inverted pyramid-shaped hole of a silicon substrate 21 formed by anisotropic etching, and light 2 from the light source 1 enters the transparent substrate 20 from an oblique direction. The light 2 incident on the transparent substrate 20 becomes propagation light and enters the diffraction-type wavelength stabilizing element 22. Here, for example, a part of the first-order or second-order diffracted light having a selected wavelength of about several% to 10% is returned to the light source 1 for wavelength stabilization. The remaining zero-order diffracted light propagates in the transparent substrate 20 in a zigzag manner. Diffractive optical elements 22, 3b, 8d and transparent substrate 2
For example, Ag, Al,
Reflective film 16 made of a metal layer such as Au or a dielectric multilayer film
a is formed. The light 2 propagating in the transparent substrate 20 in a zigzag manner is converted into substantially parallel light 6 by the diffractive collimator lens 3b, and the off-axis transmission type objective lens 4 is formed.
b converges on the optical disk 11 (convergent light 7). The light 7 reflected by the optical disk 11 is turned in the opposite direction, and is transmitted again from the transmission type objective lens 4b to the transparent substrate 2 again.
The light enters the inside of the optical element 0 and becomes the propagating light 6, and enters the reflective twin lens 8d which is a focus / track error signal detecting element. The reflective twin lens 8d has a structure in which two reflective lenses having the same specifications are arranged in an array. The propagating light is split into two by the reflection twin lens 8d, propagates in the transparent substrate 20 in a zigzag manner, and is focused on the photodetector 13 formed on the silicon substrate 21.

The reflective collimator lens 3 of the present embodiment
b, each grating of one reflective lens constituting the reflective twin lens 8d has an elliptical shape having the same eccentricity, each having a major axis in the y-axis direction which is the optical axis direction of the propagating light, The period becomes smaller toward the outer periphery. The center position of the elliptical pattern is gradually shifted toward the outer periphery from the entrance side and the exit side with respect to the lens, whichever is closer to the square light (the y direction for the lens 3b and the -y direction for the lens 8d). . By forming the reflective collimator lens 3b in such a shape, coma aberration and astigmatism that normally occur under the influence of oblique incidence can be eliminated, and good collimation can be achieved.

The off-axis transmissive diffractive optical lens used as the transmissive objective lens 4b of the present embodiment has a curvature and a center position such that the period gradually decreases in the light traveling direction (y direction). Is composed of a curved grating that is part of an ellipse that is gradually shifted.

In the present embodiment, the configuration in which each optical component is arranged on the transparent substrate 20 is adopted, so that an optical head that can be easily aligned and can be reduced in size and weight can be realized. Also, the four diffractive optical elements 22, 3
For b, 8d and 4b, the depth of the groove is set to the wavelength order, and therefore, it is possible to collectively produce the grooves by, for example, injection molding or 2P method, and to accurately determine the relative position. It can be set and cost can be reduced.

<Ninth Embodiment> Next, a ninth embodiment of the present invention will be described.
The optical head according to the embodiment is described with reference to FIG.
The following description focuses on the differences from the first embodiment.

FIG. 12 is a graph showing the relationship between the normalized grating period Λ / λ normalized by the wavelength λ of the diffractive optical element of the optical head according to the ninth embodiment of the present invention and the diffraction efficiency.

The optical head of this embodiment differs from the optical head of the first embodiment in the wavelength of the light source and the depth of the groove of the diffractive optical element. The optical head according to the present embodiment includes one or more light sources that emit light of a first wavelength and light of a second wavelength having a wavelength approximately 1.5 times the light of the first wavelength. , One or more diffractive optical elements provided in the optical path of the light of the first and second wavelengths. The diffractive optical element emits substantially third-order diffracted light with respect to the first wavelength light, and emits substantially second-order diffracted light with respect to the second wavelength light.

In the optical head of this embodiment, the light source
Is the first wavelength λ₁Is substantially equal to 0.
35 μm ≦ λ₁≦ 0.44 μm
1 wavelength λ₁By installing a light source for
The pot can be squeezed small, so that, for example, 1
Can read high-density discs of 0 GB or more
You. Also, the second wavelength λ emitted from the light source_TwoThe light is like
0.57 μm ≦ λ _TwoSatisfies the relationship of ≤0.68 μm
And the second wavelength λ_TwoBy mounting a light source for
For example, optical data of DVDs and DVD-Rs having a two-layer structure
The disk can be read.

The present inventors have developed a high-density optical disk and a DV
In a two-wavelength optical head capable of supporting both D and DVD-R optical discs, the relationship between the wavelengths of the two wavelengths is set to about 1.5 times (in practice, about 1.4 times to 1 time). .About.7), and when a high-density optical disk is to be used (when light of the first wavelength is emitted), the diffractive optical element uses substantially the third-order diffracted light to produce a DVD or DVD-R.
When the optical disc is used (when the light of the second wavelength is emitted), by using the second-order diffracted light substantially for the diffractive optical element, even if the diffractive optical element is arranged in the same optical path, It has been found that high diffraction efficiency can be obtained even for light having a wavelength of, and an optical head having good optical characteristics can be realized.

Usually, the diffraction angle in the diffractive optical element is determined by the wavelength, the period, and the diffraction order. However, the present inventors have used substantially the third order diffracted light at the first wavelength and have a diffraction angle of about 1.5.
It has been found that, by using the second-order diffracted light at the second wavelength which is twice the wavelength, the diffraction angle can be made substantially equal even if the wavelength is different.

The cross-sectional shape of the diffractive optical element is substantially a sawtooth shape. Here, the first wavelength λ ₁ , the second wavelength λ ₂ ,
For the refractive index n of the material of the diffractive optical element, the depth L of the sawtooth shape is substantially L ₁ =
In the case of a reflection type element which is in the range of 3λ ₁ / (n−1) to L ₂ = 2λ ₂ / (n−1) and is incident from the substrate side, L ₁ = 3λ ₁ / 2n From L ₂ = λ ₂ / n
In the range of, also, in the case of a reflective element, such as entering from the air side, L ₂ from substantially L ₁ = 3λ _1/2 =
as in the range of lambda _2, for both wavelengths as the diffraction efficiency is maximized. For example, λ ₁ =
When 0.40 μm, λ ₂ = 0.65 μm, and n = 1.5, L = 2.4 μm to 2.6 μm for the transmissive element and L = 0.40 μm to 0.43 μm for the reflective element ( L = 0.60 μm to 0.65 μm (incident from the air side).

[0167] Further, the cross-sectional shape is approximated by a step shape.
It is also possible to use a multilevel diffractive optical element.
The optimum groove depth at that time is expressed by p as the number of levels.
Sometimes, in the case of a transmissive element, substantially L₁= 3 (p-
1) λ₁/ [P (n-1)] to L_Two= 2 (p-1) λ
_Two/ [P (n-1)] and incident from the substrate side
In the case of a reflective element such that₁= 3 (p
-1) λ₁/ 2pn to L _Two= (P-1) λ_Two/ Pn
Reflective type within the range and incident from the air side
In the case of an element, substantially L₁= 3 (p-1) λ₁/ 2p
To L_Two= (P-1) λ_Two/ P
Good.

As in the present embodiment, 1.5λ ₁
= Λ ₂ , L ₁ ≠ L ₂ , and the preferred groove depth is in the range of L ₁ to L ₂ , but when the groove depth is L ₁ , the first wavelength λ becomes efficiency-oriented with respect to _1, the groove depth is taken as L ₂ becomes efficiency-oriented with respect to the second wavelength lambda _2, just the size of the average (0.5
In the case of (L ₁ + L ₂ )), the two wavelengths are balanced. Since the light utilization efficiency as the wavelength is shorter is important, the depth of the grooves of the diffraction optical element can be said to that set in L ₁ more desirable.

As can be seen from FIG. 12, the second-order diffraction efficiency is generally better than the third-order diffraction efficiency. However, both diffraction efficiencies tend to decrease as Λ / λ decreases. Since 回 折 / λ at which both diffraction efficiencies become 80% or more is 16 or more, the minimum period Λ _min of the diffractive optical element is set to satisfy the relationship Λ _min ≧ 16λ _{1 with} respect to the first wavelength λ ₁ . Thereby, the diffraction efficiency can be made 80% or more for both wavelengths.

<Tenth Embodiment> Next, an optical head according to a tenth embodiment of the present invention will be described with reference to FIG. 13, focusing on differences from the first embodiment.

FIG. 13 is a graph showing the relationship between the normalized grating period Λ / λ normalized by the wavelength λ of the diffractive optical element of the optical head and the diffraction efficiency according to the tenth embodiment of the present invention.

The optical head of this embodiment differs from the optical head of the first embodiment in the wavelength of the light source and the depth of the groove of the diffractive optical element. The optical head of the present embodiment is substantially equivalent to the light of the first wavelength, the light of the second wavelength having a wavelength approximately twice that of the light of the first wavelength, and the light of the first wavelength. One or more light sources that emit light of a third wavelength having 1.5 times the wavelength, a photodetector, and one or more light sources provided in the optical paths of the light of the first, second, and third wavelengths A plurality of diffractive optical elements. The diffractive optical element has a first
A fourth-order diffracted light for the light having the wavelength
Emits substantially second-order diffracted light with respect to light having a wavelength of
Substantially the third order diffracted light with respect to the light having the wavelength of

In the optical head of the present embodiment, the light of the first wavelength λ ₁ emitted from the light source is, for example, substantially 0.1 mm.
By satisfying the relationship of 35 μm ≦ λ ₁ ≦ 0.44 μm and mounting the light source of the first wavelength λ ₁ , the focused spot can be narrowed down, and as a result, for example, 10G
High-density discs of bytes or more can be read.
The light of the second wavelength λ ₂ emitted from the light source is, for example,
By substantially satisfying the relationship of 0.57 μm ≦ λ ₂ ≦ 0.68 μm and mounting the light source of the light of the second wavelength λ ₂ , for example, it is possible to read an optical disk of CD or CD-R. The light of the third wavelength λ ₃ emitted from the light source is substantially, for example, 0.76 μm ≦ λ ₃ ≦ 0.88 μm
And the light source of the third wavelength λ ₃ is mounted, for example, a DVD including a two-layer structure, a DV
The optical disk of DR can be read.

The present inventors have developed a high-density optical disk and a DV
In a three-wavelength optical head capable of supporting various optical disks such as D, DVD-R, CD, and CD-R, the ratio of the magnitudes of the wavelengths among the three wavelengths is set to about 1: 2: 1.5 ( In practice, 1: 1.8-2.1: 1.4-1.
7) When a high-density optical disk is used (when light of the first wavelength is emitted), a fourth-order diffracted light is used substantially for the diffractive optical element, and when a CD or CD-R optical disk is used. (When emitting light of the second wavelength), a DVD, D
When corresponding to a VD-R optical disk (when emitting light of the third wavelength), the diffractive optical element is substantially 3
By using the next-order diffracted light, even if the diffractive optical elements are arranged on the same optical path, it is possible to obtain a particularly high diffraction efficiency for the light of the first and second wavelengths among the light of the three wavelengths,
It has been found that an optical head having good optical characteristics can be realized. Note that the first wavelength is used for the light of the third wavelength.
And only about 5% worse than the light of the second wavelength.

Normally, the diffraction angle in the diffractive optical element is determined by the wavelength, the period, and the diffraction order. However, the present inventors use substantially the fourth order diffracted light at the first wavelength, and substantially use the fourth order diffracted light at the second wavelength. By using the second-order diffracted light and using substantially the third-order diffracted light at the third wavelength, it has been found that the diffraction angles can be made substantially equal even if the wavelength is different.

The sectional shape of the diffractive optical element is substantially a sawtooth shape. Here, the first wavelength λ ₁ , the second wavelength λ ₂ ,
For the third wavelength λ ₃ and the refractive index n of the material of the diffractive optical element, the depth L of the sawtooth shape is substantially L ₁ = 4λ ₁ / (n−1) in the case of the transmission type element. ) And L ₂ = 2λ ₂ /
Yes (n-1) and in the minimum and maximum value range of _{L 3 = 3λ 3 / (n} -1), in the case of a reflective element, such as incident from the substrate side, substantially L ₁ = 2λ ₁ / n and L ₂ =
λ ₂ / n and L ₃ = 3λ ₃ / 2n are within the range of the minimum value and the maximum value, and in the case of a reflective element that enters from the air side, L ₁ = 2λ ₁ and in the L ₂ = lambda ₂ and L ₃ = 3 [lambda] ₃ / minimum of 2 and be within the scope of the maximum value, for any of the three wavelengths as the diffraction efficiency is maximized. For example, λ ₁ = 0.40 μ
m, λ ₂ = 0.80 μm, λ ₃ = 0.65 μm, n =
In the case of 1.5, L = 3.2 μm-
3.9 μm, L = 0.53 μm to 0.
65 μm (incident from the substrate side), L = 0.8 μm to 0.9
8 μm (incident from the air side).

[0177] Further, a multi-section in which the cross-sectional shape is approximated by a step shape is used.
It is also possible to use a multilevel diffractive optical element.
The optimum groove depth at that time is expressed by p as the number of levels.
Sometimes, in the case of a transmissive element, substantially L₁= 4 (p-
1) λ₁/ [P (n-1)] and L _Two= 2 (p-1) λ_Two
/ [P (n-1)] and L_Three= 3 (p-1) λ_Three/ [P
(N-1)] within the range of the minimum value and the maximum value,
In the case of a reflective element that enters from the substrate side,
Upper L₁= 2 (p-1) λ₁/ Pn and L_Two= (P-1) λ
_Two/ Pn and L_Three= 3 (p-1) λ_Three/ 2pn
It is within the range of the small value and the maximum value, and is incident from the air side.
In the case of a reflective element such as₁= 2 (p−
1) λ₁/ P and L_Two= (P-1) λ_Two/ P and L_Three= 3
(P-1) λ_Three/ 2p within the range of the minimum and maximum values
It is in.

As can be seen from FIG. 13, the second-order diffraction efficiency
Is generally better than the third and fourth order diffraction efficiencies,
Both orders of diffraction efficiency decrease as Λ / λ decreases.
Tend to be less. Each of the three orders of diffraction efficiency
Since Λ / λ which is 80% or more is 22 or more, diffracted light
Minimum period of element_minIs the first wavelength λ₁Against
_min≧ 22λ₁By satisfying the relationship
Making the diffraction efficiency over 80% for three wavelengths
it can.

<Eleventh Embodiment> Next, an optical head according to an eleventh embodiment of the present invention will be described, focusing on differences from the tenth embodiment.

The optical head of this embodiment is different from the optical head of the tenth embodiment in the depth of the groove of the diffractive optical element and the diffraction order used. The optical head according to the present embodiment has light of the first wavelength, light of the second wavelength having a wavelength approximately twice the first wavelength, and approximately 1.5 times the light of the first wavelength. One or more light sources that emit light of a third wavelength having a wavelength of?, A photodetector, first, second, and third light sources.
And one or more diffractive optical elements provided in the optical path of light of the wavelength The diffractive optical element emits substantially sixth-order diffracted light with respect to the first wavelength light, emits substantially third-order diffracted light with respect to the second wavelength light, and emits third-order diffracted light. A fourth-order diffracted light is substantially emitted with respect to this light.

In the optical head of this embodiment, the wavelength of the light having the first wavelength λ ₁ emitted from the light source substantially satisfies the relationship of 0.35 μm ≦ λ ₁ ≦ 0.44 μm, for example.
By mounting the light source of the first wavelength λ ₁ ,
The focused spot can be narrowed down, and as a result, for example, a high-density disk of 10 GB or more can be read. The wavelength of the light of the second wavelength λ ₂ emitted from the light source is, for example, substantially 0.57 μm ≦ λ ₂ ≦ 0.68
By satisfying the relationship of μm and mounting the light source of the light of the second wavelength λ ₂ , for example, an optical disk such as a CD or a CD-R can be read. The wavelength of the light of the third wavelength λ ₃ emitted from the light source is, for example, substantially 0.76 μm.
By satisfying the relationship of m ≦ λ ₃ ≦ 0.88 μm and mounting the light source of the light of the third wavelength λ ₃ , it is possible to read, for example, DVDs and DVD-R optical disks having a two-layer structure.

The present inventors have developed a high-density optical disk and a DV
In a three-wavelength optical head capable of supporting various optical disks such as D, DVD-R, CD, and CD-R, the ratio of the magnitudes of the wavelengths among the three wavelengths is set to about 1: 2: 1.5 ( In practice, 1: 1.8-2.1: 1.4-1.
7) When corresponding to a high-density optical disk (when emitting light of the first wavelength), a sixth-order diffracted light is used substantially for the diffractive optical element, and when corresponding to a CD or CD-R optical disk. (When emitting light of the second wavelength), the third order diffracted light is used substantially for the diffractive optical element, and DVD, D
When supporting a VD-R optical disk (when emitting light of the third wavelength), the diffractive optical element is substantially 4
By using the next-order diffracted light, even if the diffractive optical elements are arranged on the same optical path, high diffraction efficiency can be obtained for any of the three wavelengths.

The diffractive optical element according to the present embodiment uses a larger diffraction order than the diffractive optical element according to the tenth embodiment. In particular, when the period of the diffractive optical element is large, the diffractive optical element according to the present embodiment is used. The diffractive optical element of this embodiment has a higher diffraction efficiency for the third wavelength.

The sectional shape of the diffractive optical element is substantially a sawtooth shape. Here, the first wavelength λ ₁ , the second wavelength λ ₂ ,
For the third wavelength λ ₃ and the refractive index n of the material of the diffractive optical element, the depth L of the sawtooth shape is substantially L ₁ = 6λ ₁ / (n−1) in the case of a transmission type element. ) And L ₂ = 3λ ₂ /
(N−1) and L ₃ = 4λ ₃ / (n−1) are within the range of the minimum value and the maximum value, and in the case of a reflective element that enters from the substrate side, substantially L ₁ = 3λ ₁ / n and L ₂ =
In the case of a reflective element that falls within the range between the minimum value and the maximum value of 3λ ₂ / 2n and L ₃ = 2λ ₃ / n, and that enters from the air side, L ₁ = 3λ ₁ And L ₂ = 3λ
_The diffraction efficiency was maximized at any of the three wavelengths by being within the range of the minimum value and the maximum value of 2/2 and L ₃ = 2λ ₃ . For example, λ ₁ = 0.40
μm, λ ₂ = 0.80 μm, λ ₃ = 0.65 μm, n =
In the case of 1.5, L = 4.8 μm to
5.2 μm, L = 0.80 μm to 0.
87 μm (incident from substrate side), L = 1.2 μm to 1.3
μm (incident from the air side).

[0185] Further, a multi-section whose cross-sectional shape is approximated by a staircase shape is used.
It is also possible to use a multilevel diffractive optical element.
The optimum groove depth at that time is expressed by p as the number of levels.
Sometimes, in the case of a transmissive element, substantially L₁= 6 (p-
1) λ₁/ [P (n-1)] and L _Two= 3 (p-1) λ_Two
/ [P (n-1)] and L_Three= 2 (p-1) λ_Three/ [P
(N-1)] within the range of the minimum value and the maximum value,
In the case of a reflective element that enters from the substrate side,
Upper L₁= 3 (p-1) λ₁/ Pn and L_Two= 3 (p-1)
λ_Two/ 2pn and L_Three= (P-1) λ_Three/ Pn
It is within the range of the small value and the maximum value, and is incident from the air side.
In the case of a reflective element such as₁= 3 (p-
1) λ₁/ P and L_Two= 3 (p-1) λ_Two/ 2p and L_Three=
(P-1) λ_ThreeWithin the minimum and maximum values of / p
This is desirable in the sense that light utilization efficiency is good.

<Twelfth Embodiment> Next, an optical head according to a twelfth embodiment of the present invention will be described, focusing on differences from the above-described fifth or sixth embodiment.

The optical head of this embodiment is different from the optical head of the fifth or sixth embodiment in the wavelength of the light source and the step of the chromatic aberration correcting element.

The optical head according to the present embodiment includes one or more light sources that emit light of the first wavelength and light of the second wavelength having a wavelength approximately 1.5 times that of the light of the first wavelength. , A light detector, an objective lens for converging light on an information recording medium, and a diffractive optical element provided in an optical path of light of the first and second wavelengths. The diffractive optical element is a chromatic aberration correction element having a stepped or substantially sawtooth step for correcting the chromatic aberration of the objective lens, and includes a first wavelength λ ₁ , a second wavelength λ ₂ , and a chromatic aberration correction element. For the refractive index n of the material, the step is substantially in the range of 3λ ₁ / (n−1) to 2λ ₂ / (n−1).

According to the configuration of the present embodiment, a chromatic aberration correction element having good light use efficiency for the light of the first and second wavelengths can be obtained.

In the optical head of this embodiment, the wavelength of the light of the first wavelength λ ₁ emitted from the light source substantially satisfies the relationship of 0.35 μm ≦ λ ₁ ≦ 0.44 μm, for example.
By mounting the light source of the first wavelength λ ₁ ,
The focused spot can be narrowed down, and as a result, for example, a high-density disk of 10 GB or more can be read. The wavelength of the light of the second wavelength λ ₂ emitted from the light source is, for example, substantially 0.57 μm ≦ λ ₂ ≦ 0.68
μm, and by mounting the light source of the light of the second wavelength λ ₂ , for example, a DVD including a two-layer structure,
A DVD-R optical disk can be read.

<Thirteenth Embodiment> Next, an optical head according to a thirteenth embodiment of the present invention will be described, focusing on differences from the above-described fifth or sixth embodiment.

The optical head of this embodiment is different from the optical head of the fifth, sixth or seventh embodiment in the wavelength of the light source and the step of the chromatic aberration correcting element.

The optical head according to the present embodiment has the first wavelength
Light having a wavelength approximately twice that of the light of the first wavelength.
About 1.5 times the light of the second wavelength and the light of the first wavelength
Singular or plural that emit light of a third wavelength having a wavelength of
Light source, photodetector, and objective
In the optical path of light of the first, second, and third wavelengths.
And one or more diffractive optical elements. Up
The diffractive optical element corrects chromatic aberration of the objective lens.
Chromatic aberration compensator with stepped or substantially sawtooth steps
A positive element and a first wavelength λ₁, The second wavelength λ_Two, Third
Wavelength λ_ThreeFor the refractive index n of the material of the diffractive optical element
And the step is 4λ₁/ (N-1) and 2λ _Two/ (N-1)
And 3λ_ThreeWithin the range of the minimum value and the maximum value of / (n-1)
It is in.

According to the structure of the present embodiment, the first to third
Of the light of the first wavelength and the light of the first and second wavelengths,
In particular, it is possible to obtain a chromatic aberration correction element having optical characteristics with good light use efficiency.

In the optical head of this embodiment, the wavelength of the light of the first wavelength λ ₁ emitted from the light source substantially satisfies the relationship of 0.35 μm ≦ λ ₁ ≦ 0.44 μm, for example.
By mounting the light source of the first wavelength λ ₁ ,
The focused spot can be narrowed down, and as a result, for example, a high-density disk of 10 GB or more can be read. The wavelength of the light of the second wavelength λ ₂ emitted from the light source is, for example, substantially 0.57 μm ≦ λ ₂ ≦ 0.68
By satisfying the relationship of μm and mounting the light source of the light of the second wavelength λ ₂ , for example, an optical disk such as a CD or CD-R can be read. The wavelength of the light of the third wavelength λ ₃ emitted from the light source is, for example, substantially 0.76 μm.
By satisfying the relationship of m ≦ λ ₃ ≦ 0.88 μm and mounting the light source of the light of the third wavelength λ ₃ , it is possible to read, for example, DVDs and DVD-R optical disks having a two-layer structure.

<Fourteenth Embodiment> Next, an optical head according to a fourteenth embodiment of the present invention will be described, focusing on differences from the thirteenth embodiment.

The optical head of this embodiment is different from the optical head of the thirteenth embodiment in the level difference of the chromatic aberration correction element.

The optical head according to the present embodiment has the first wavelength
Light having a wavelength approximately twice that of the light of the first wavelength.
About 1.5 times the light of the second wavelength and the light of the first wavelength
Singular or plural that emit light of a third wavelength having a wavelength of
Light source, photodetector, and objective
In the optical path of light of the first, second, and third wavelengths.
And one or more diffractive optical elements. Up
The diffractive optical element corrects chromatic aberration of the objective lens.
Chromatic aberration compensator with stepped or substantially sawtooth steps
A positive element and a first wavelength λ₁, The second wavelength λ_Two, Third
Wavelength λ_ThreeFor the refractive index n of the material of the diffractive optical element
And the step is 6λ₁/ (N-1) and 3λ _Two/ (N-1)
And 4λ_ThreeWithin the range of the minimum value and the maximum value of / (n-1)
It is in.

The chromatic aberration correcting element according to the present embodiment is the first type.
When the cycle of the chromatic aberration correcting element is sufficiently large compared to the wavelength, although the level difference is larger than that of the chromatic aberration correcting element of the third embodiment, the first to third wavelengths It is possible to obtain a chromatic aberration corrector having optical characteristics with good light use efficiency with respect to light.

In the optical head of this embodiment, the wavelength of the light of the first wavelength λ ₁ emitted from the light source substantially satisfies the relationship of 0.35 μm ≦ λ ₁ ≦ 0.44 μm, for example.
By mounting the light source of the first wavelength λ ₁ ,
The focused spot can be narrowed down, and as a result, for example, a high-density disk of 10 GB or more can be read. The wavelength of the light of the second wavelength λ ₂ emitted from the light source is, for example, substantially 0.57 μm ≦ λ ₂ ≦ 0.68
By satisfying the relationship of μm and mounting the light source of the light of the second wavelength λ ₂ , for example, an optical disk such as a CD or a CD-R can be read. The wavelength of the light of the third wavelength λ ₃ emitted from the light source is, for example, substantially 0.76 μm.
By satisfying the relationship of m ≦ λ ₃ ≦ 0.88 μm and mounting the light source of the light of the third wavelength λ ₃ , it is possible to read, for example, DVDs and DVD-R optical disks having a two-layer structure.

The optical heads according to the first to fourteenth embodiments have been described above. However, the present invention is not limited to these embodiments, and the configuration of the optical head according to each embodiment is described. The combined optical head is also included in the present invention, and can achieve the same effect.

The objective lens and the collimator lens used in the above embodiment are named for convenience, and are the same as generally used lenses.

Although the above embodiment has been described with reference to an optical disk as an example, it is designed so that a similar information recording / reproducing apparatus can reproduce a plurality of media having different specifications such as thickness and recording density. Card or drum,
Application to a tape-shaped product is also included in the scope of the present invention.

Further, in the above embodiment, light of a plurality of wavelengths is handled, but substantially 0.35 μm ≦ λ
The optical head may include only one light source that emits light having a wavelength λ that satisfies the relationship of ≦ 0.44 μm (when one light source is used in FIGS. 7 to 10). In this case, the photodetector further includes one or more diffractive optical elements provided in an optical path of light emitted from the light source,
If the diffractive optical element is a chromatic aberration correcting element that corrects chromatic aberration of the objective lens focused on the information recording medium, the chromatic dispersion of the glass material of the lens is large as the light emitted from the light source.
When the semiconductor laser light in the range of 5 μm ≦ λ ≦ 0.44 μm is used, even if the center wavelength of the emitted light changes due to a widening of a wavelength band of about several nm due to a high-frequency module or self-excited oscillation or a change in environmental temperature, By correcting large chromatic aberration caused by the objective lens, it is possible to obtain a good condensed spot on the optical disk surface. Further, in this case, if the chromatic aberration correction element is formed on the objective lens, the chromatic aberration correction element and the objective lens can be handled as one component, and the size and cost can be reduced. Further, if the chromatic aberration correcting element and the objective lens are driven integrally by the actuator, the optical axes of the chromatic aberration correcting element and the objective lens do not deviate, so that good optical characteristics can be obtained. Further, if the chromatic aberration correcting element is a convex diffractive lens and the convergent light is formed by both the objective lens and the objective lens, the numerical aperture of the objective lens itself is reduced, thereby facilitating the manufacture.

[0205]

As described above, according to the present invention,
With a configuration including a plurality of wavelength light sources and a diffractive optical element capable of supporting a plurality of types of information recording media, an optical head with high light use efficiency can be realized.

[Brief description of the drawings]

FIG. 1 is a side view showing a basic configuration of an optical head and a state of light propagation according to a first embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the normalized wavelength of the diffractive optical element and the diffraction efficiency in the optical head according to the first embodiment of the present invention.

FIG. 3 is a graph showing the relationship between the normalized grating period of the diffractive optical element and the first-order diffraction efficiency and the second-order diffraction efficiency in the optical head according to the first embodiment of the present invention.

FIG. 4 is a side view showing a basic configuration of an optical head and a state of light propagation according to a second embodiment of the present invention.

FIG. 5 is a side view showing a basic configuration of an optical head and a state of light propagation according to a third embodiment of the present invention.

FIG. 6A is a side view showing a basic configuration of an optical head and a state of light propagation according to a fourth embodiment of the present invention;
(B) is a plan view showing a basic configuration of an optical head and a state of light propagation according to a fourth embodiment of the present invention.

FIG. 7 is a side view showing a basic configuration of an optical head and a state of light propagation according to a fifth embodiment of the present invention.

FIG. 8 is a side view showing a basic configuration of an optical head and a state of light propagation according to a sixth embodiment of the present invention.

FIG. 9A is a sectional view showing an objective lens on which a chromatic aberration correcting element of an optical head according to a sixth embodiment of the present invention is formed, and FIG. 9B is an optical head according to a sixth embodiment of the present invention. Plan view showing an objective lens formed with a chromatic aberration correcting element of FIG.

FIG. 10 is a side view showing a basic configuration of an optical head and a state of light propagation according to a seventh embodiment of the present invention.

FIG. 11A is a side view showing a basic configuration of an optical head and a state of light propagation according to an eighth embodiment of the present invention;
(B) is a plan view showing a basic configuration of an optical head and a state of light propagation according to an eighth embodiment of the present invention.

FIG. 12 is a graph showing the relationship between the normalized grating period and the diffraction efficiency of the diffractive optical element of the optical head according to the ninth embodiment of the present invention.

FIG. 13 shows a normalized grating period Λ / λ of the diffractive optical element of the optical head according to the tenth embodiment of the present invention.
Graph showing the relationship between diffraction and diffraction efficiency

FIG. 14 is a graph showing the relationship between the normalized wavelength of the diffractive optical element of the conventional optical head and the first-order diffraction efficiency.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source 2 Emitted light 3 Collimator lens 4 Objective lens 5 Grating 6 Parallel light 7 Convergent light 8 Focus / track error signal detection element 9 Refractive optical means 10 Slope (first surface) of refractive optical means 11 Information recording medium 12 Refractive optical means Side surface (second surface) 13 photodetector 14 bottom surface of refractive optical means (third surface) 15 rising mirror 16 reflective film 17 light source / photodetector unit 18 beam splitter 19 chromatic aberration correction element 20 transparent substrate 21 silicon substrate 22 Wavelength stabilizing element

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuo Hosomi 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture F-term in Matsushita Electric Industrial Co., Ltd. 5D119 AA41 AA43 BA01 EA01 EC03 EC47 FA05 JA03 JA07 JA09 JA29 JA46 JB02 JB04 JB10

Claims (51)

[Claims] A light source that emits light of a first wavelength and light of a second wavelength having a wavelength that is approximately twice the first wavelength; a photodetector; One or more diffractive optical elements provided in an optical path of light of a second wavelength, wherein the diffractive optical element emits substantially second-order diffracted light with respect to the light of the first wavelength. An optical head that emits substantially first-order diffracted light with respect to the second wavelength light. 2. The diffractive optical element has a substantially sawtooth cross-sectional shape.
The first wavelength λ₁, The second wavelength λ_TwoThe diffraction
For the refractive index n of the material of the optical element, the depth of the sawtooth shape
Is substantially 2λ in the case of a transmissive element.₁/ (N-
1) to λ_Two/ (N-1), from the substrate side
In the case of an incident reflective element, substantially λ ₁/ N to λ
_Two/ 2n, a reflective element that enters from the air side
In the case of a child, substantially λ₁To λ_TwoWithin the range of / 2
The optical head according to claim 1. 3. The optical head according to claim 1, wherein the diffractive optical element is an objective lens that converges on an information recording medium. 4. The optical head according to claim 1, wherein the diffractive optical element is a collimator lens that makes light emitted from the light source substantially parallel. 5. The optical head according to claim 1, wherein the diffractive optical element is a focus / track error signal detecting element. 6. The minimum period Λ of the diffractive optical element._minBut the first
Wavelength λ₁Against _min≧ 10λ₁Satisfies the relationship
The optical head according to claim 1. 7. The minimum period of the diffractive optical element Λ_minBut the first
Wavelength λ₁Against _min≧ 22λ₁Satisfies the relationship
The optical head according to claim 1. 8. A refracting optical means having an optical surface on which an optical axis of light emitted from a light source is obliquely incident is provided in an optical path of light having the first and second wavelengths, and a wavelength of the light having the wavelength of the emitted light is provided. 2. The optical head according to claim 1, wherein the change in the diffraction angle of the diffracted light from the diffractive optical element and the change in the refraction angle of the refracted light from the refraction optical unit occur in directions that cancel each other. 9. The optical head according to claim 8, wherein the diffractive optical element is a grating having a uniform period. 10. The optical head according to claim 8, wherein the diffractive optical element is arranged in a convergent light path or a divergent light path having a numerical aperture of 0.39 or less, and the period of the diffractive optical element is uniform. 11. The refracting optical means is a prism having three optical surfaces, of the three optical surfaces, the first surface on the information recording medium side, the second surface on the light source side, and the other. When the third surface is the third surface, the light emitted from the light source
Transmitting through a surface, reflecting in the order of the first surface and the third surface,
9. The optical head according to claim 8, wherein the lower part of the objective lens is lower than the highest position where the light emitted from the light source is incident on the second surface, wherein the light is transmitted through the first surface. 10. 12. The optical head according to claim 11, wherein the Abbe number of the glass material of the prism is 64 or more. 13. The optical head according to claim 1, wherein the light source is an SHG light source that emits light of two wavelengths. 14. The optical head according to claim 1, further comprising a transparent substrate through which light of the first and second wavelengths propagates in a zigzag manner, and wherein the diffractive optical element is disposed on the transparent substrate. 15. The first wavelength λ ₁ is 0.35 μm ≦ λ.
_2. The optical head according to claim 1, wherein a relationship of ₁ ≦ 0.44 μm is satisfied, or the second wavelength λ ₂ satisfies a relationship of 0.76 μm ≦ λ ₂ ≦ 0.88 μm. 16. The first wavelength λ ₁ is substantially 0.35 μm.
2. The optical head according to claim 1, wherein a relationship of m ≦ λ ₁ ≦ 0.44 μm is satisfied, and the diffractive optical element is a chromatic aberration correction element that corrects chromatic aberration of the objective lens focused on the information recording medium. 17. A light source and a light source for emitting light of a first wavelength and light of a second wavelength having a wavelength approximately twice the first wavelength, a photodetector, and an information recording medium. An objective lens for condensing light, and a diffractive optical element provided in an optical path of the light having the first and second wavelengths, wherein the diffractive optical element has a stepwise or substantially stepwise shape for correcting chromatic aberration of the objective lens. A chromatic aberration correction element having a sawtooth-shaped step,
The step is substantially 2λ _{1 with} respect to the first wavelength λ ₁ , the second wavelength λ ₂ , and the refractive index n of the material of the chromatic aberration correction element.
/ Optical head, characterized in that (n-1) from within the range of lambda ₂ / (n-1). 18. The first wavelength λ ₁ is 0.35 μm ≦ λ.
18. The optical head according to claim 17, wherein the relationship of ₁ ≦ 0.44 μm is satisfied, or the second wavelength λ ₂ satisfies the relationship of 0.76 μm ≦ λ ₂ ≦ 0.88 μm. 19. The optical head according to claim 17, wherein the chromatic aberration correction element is formed on an objective lens. 20. The optical head according to claim 17, wherein the chromatic aberration correction element and the objective lens are driven integrally by an actuator. 21. The optical head according to claim 17, wherein the chromatic aberration correction element is a convex diffractive lens, and forms convergent light with both the objective lens. 22. A light having a first wavelength, a light having a second wavelength having a wavelength approximately twice the first wavelength, and a light having a wavelength approximately 1.5 times the first wavelength. One or more light sources that emit light of different wavelengths, a photodetector, and the first and second light sources.
And one or more diffractive optical elements provided in the optical path of light of the third wavelength, wherein the diffractive optical element emits substantially fourth-order diffracted light with respect to the light of the first wavelength. An optical head for emitting substantially second-order diffracted light with respect to the second wavelength light and emitting substantially third-order diffracted light with respect to the third wavelength light; . 23. A cross-sectional shape of the diffractive optical element is substantially saw-toothed.
The first wavelength λ₁, The second wavelength λ_TwoThe third
Wavelength λ_ThreeFor the refractive index n of the material of the diffractive optical element
In the case where the depth of the sawtooth shape is a transmission type element,
Quality 4λ₁/ (N-1) and 2λ_Two/ (N-1) and 3λ_Three
/ (N-1) within the range of the minimum value and the maximum value,
In the case of a reflective element that enters from the substrate side, it is substantially 2λ.
₁/ N and λ _Two/ N and 3λ_Three/ 2n minimum and maximum
Field of a reflective element that falls within the range of values and enters from the air side.
In effect, 2λ₁And λ_TwoAnd 3λ_ThreeMinimum of / 2
23. The optical head according to claim 22, which is within a range of the maximum value and the maximum value.
De. 24. The optical head according to claim 22, wherein the minimum period Λ _min of the diffractive optical element satisfies the relationship Λ _min ≧ 22λ _{1 with} respect to the first wavelength λ ₁ . 25. The first wavelength λ ₁ is 0.35 μm ≦ λ.
₁ ≦ 0.44 μm is satisfied, or the second wavelength λ ₂ satisfies the relationship of 0.76 μm ≦ λ ₂ ≦ 0.88 μm, or the third wavelength λ ₃ is 0.57 μm.
23. The optical head according to claim 22, wherein a relationship m ≦ λ ₃ ≦ 0.68 μm is satisfied. 26. The first wavelength λ ₁ is substantially 0.35 μm.
23. The optical head according to claim 22, wherein a relationship of m ≦ λ ₁ ≦ 0.44 μm is satisfied, and the diffractive optical element is a chromatic aberration correction element that corrects chromatic aberration of the objective lens focused on the information recording medium. 27. A light having a first wavelength, a light having a second wavelength having a wavelength approximately twice the first wavelength, and a light having a wavelength approximately 1.5 times the first wavelength. A light source or a plurality of light sources that emit light of different wavelengths, a photodetector, an objective lens for condensing light on an information recording medium, and provided in an optical path of the light of the first, second, and third wavelengths. A single or a plurality of diffractive optical elements, wherein the diffractive optical element is a chromatic aberration correction element having a stepped or substantially sawtooth-shaped step for correcting chromatic aberration of the objective lens, and has a first wavelength λ ₁ , For the wavelength λ ₂ , the third wavelength λ ₃ , and the refractive index n of the material of the diffractive optical element, the step is 4λ ₁ / (n−1) and 2
An optical head characterized by being within the range of the minimum value and the maximum value of λ ₂ / (n−1) and 3λ ₃ / (n−1). 28. The first wavelength λ ₁ is 0.35 μm ≦ λ.
₁ ≦ 0.44 μm is satisfied, or the second wavelength λ ₂ satisfies the relationship of 0.76 μm ≦ λ ₂ ≦ 0.88 μm, or the third wavelength λ ₃ is 0.57 μm.
The optical head according to claim 27, wherein a relationship of m ≦ λ ₃ ≦ 0.68 μm is satisfied. 29. The optical head according to claim 27, wherein the chromatic aberration correction element is formed on an objective lens. 30. The optical head according to claim 27, wherein the chromatic aberration correction element and the objective lens are driven integrally by an actuator. 31. The optical head according to claim 27, wherein the chromatic aberration correcting element is a convex diffractive lens, and forms convergent light with both the objective lens. 32. One or more light sources for emitting light of a first wavelength and light of a second wavelength having a wavelength approximately 1.5 times the first wavelength; a photodetector; One or more diffractive optical elements provided in the optical path of the light of the first and second wavelengths, wherein the diffractive optical element converts substantially third-order diffracted light with respect to the light of the first wavelength. An optical head that emits light and emits substantially second-order diffracted light with respect to the light of the second wavelength. 33. The cross-sectional shape of the diffractive optical element is substantially saw-toothed, and the saw-toothed shape is defined by a first wavelength λ ₁ , a second wavelength λ ₂ , and a refractive index n of a material of the diffractive optical element. Is substantially 3λ ₁ / (n−
1) to 2λ ₂ / (n−1), and in the case of a reflective element incident from the substrate side, substantially 3λ ₁ / 2n
In the range of lambda ₂ / n from the optical head according to claim 32 in the case of a reflective element, which is within the range of substantially 3 [lambda] _1/2 of lambda ₂ incident from the air side. 34. The optical head according to claim 32, wherein the minimum period Λ _min of the diffractive optical element satisfies the relationship of Λ _min ≧ 16λ _{1 with} respect to the first wavelength λ ₁ . 35. The first wavelength λ ₁ is 0.35 μm ≦ λ.
33. The optical head according to claim 32, wherein the relationship of ₁ ≦ 0.44 μm is satisfied, or the second wavelength λ ₂ satisfies the relationship of 0.57 μm ≦ λ ₂ ≦ 0.68 μm. 36. The first wavelength λ ₁ is substantially 0.35 μm.
33. The optical head according to claim 32, wherein a relationship of m ≦ λ ₁ ≦ 0.44 μm is satisfied, and the diffractive optical element is a chromatic aberration correction element that corrects chromatic aberration of the objective lens focused on the information recording medium. 37. One or more light sources for emitting light of a first wavelength and light of a second wavelength having a wavelength approximately 1.5 times the first wavelength, a light detector, and information An objective lens for converging light on a recording medium, and a diffractive optical element provided in an optical path of the light having the first and second wavelengths, wherein the diffractive optical element corrects a chromatic aberration of the objective lens. Alternatively, it is a chromatic aberration correcting element having a substantially sawtooth-shaped step, and the step is substantially 3 with respect to the first wavelength λ ₁ , the second wavelength λ ₂ , and the refractive index n of the material of the chromatic aberration correcting element.
An optical head characterized by being in the range of λ ₁ / (n−1) to 2λ ₂ / (n−1). 38. The first wavelength λ ₁ is 0.35 μm ≦ λ.
38. The optical head according to claim 37, wherein the relationship of ₁ ≦ 0.44 μm is satisfied, or the second wavelength λ ₂ satisfies the relationship of 0.57 μm ≦ λ ₂ ≦ 0.68 μm. 39. The optical head according to claim 37, wherein the chromatic aberration correction element is formed on an objective lens. 40. The optical head according to claim 37, wherein the chromatic aberration correction element and the objective lens are driven integrally by an actuator. 41. The optical head according to claim 37, wherein the chromatic aberration correction element is a convex diffractive lens, and forms convergent light with both the objective lens. 42. A light having a first wavelength, a light having a second wavelength having a wavelength approximately twice as large as the first wavelength, and a third light having a wavelength approximately 1.5 times as large as the first wavelength. One or more light sources that emit light of different wavelengths, a photodetector, and the first and second light sources.
And one or more diffractive optical elements provided in an optical path of light of a third wavelength, wherein the diffractive optical element emits substantially sixth-order diffracted light with respect to the light of the first wavelength. An optical head for emitting substantially third-order diffracted light with respect to the second wavelength light and emitting substantially fourth-order diffracted light with respect to the third wavelength light; . 43. A cross-sectional shape of the diffractive optical element is substantially saw-toothed, and has a first wavelength λ ₁ , a second wavelength λ ₂ , a third wavelength λ ₃ , and a refractive index n of a material of the diffractive optical element. On the other hand, when the depth of the sawtooth shape is a transmission element, the depth is substantially 6λ ₁ / (n−1), 3λ ₂ / (n−1) and 4λ _3.
/ (N-1) within the range of the minimum value and the maximum value,
In the case of a reflective element entering from the substrate side, substantially 3λ
In the range of minimum and maximum value of ₁ / n and 3 [lambda] ₂ / 2n and 2 [lambda] ₃ / n, in the case of a reflective element that enters from the air side, the substantially 3 [lambda] ₁ and 3 [lambda] _2/2 the optical head according to claim 42 which is within the range of minimum and maximum value of 2 [lambda] _3. 44. A light having a first wavelength, a light having a second wavelength having a wavelength approximately twice as large as the first wavelength, and a light having a wavelength approximately 1.5 times as large as the first wavelength. A light source or a plurality of light sources that emit light of different wavelengths, a photodetector, an objective lens for condensing light on an information recording medium, and provided in an optical path of the light of the first, second, and third wavelengths. A single or a plurality of diffractive optical elements, wherein the diffractive optical element is a chromatic aberration correction element having a stepped or substantially sawtooth-shaped step for correcting chromatic aberration of the objective lens, and has a first wavelength λ ₁ , The step is substantially 6λ ₁ / (n−2) with respect to the wavelength λ ₂ , the third wavelength λ ₃ , and the refractive index n of the material of the diffractive optical element.
1) An optical head characterized by being within a range of a minimum value and a maximum value among 3λ ₂ / (n−1) and 4λ ₃ / (n−1). 45. The optical head according to claim 44, wherein the chromatic aberration correction element is formed on the objective lens. 46. The optical head according to claim 44, wherein the chromatic aberration correction element and the objective lens are driven integrally by an actuator. 47. The optical head according to claim 44, wherein the chromatic aberration correction element is a convex diffractive lens, and forms convergent light with both the objective lens. 48. Substantially 0.35 μm ≦ λ ≦ 0.44 μ
a light source that emits light having a wavelength λ that satisfies the relationship of m, a photodetector, and one or more diffractive optical elements provided in an optical path of light emitted from the light source. An optical head comprising a chromatic aberration correction element for correcting chromatic aberration of an objective lens condensed on an information recording medium. 49. The optical head according to claim 48, wherein the chromatic aberration correction element is formed on the objective lens. 50. The optical head according to claim 48, wherein the chromatic aberration correction element and the objective lens are driven integrally by an actuator. 51. The optical head according to claim 48, wherein the chromatic aberration correction element is a convex diffractive lens, and forms convergent light with both the objective lens.