JP2000113492A - Optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical head for an optical recording and reproducing device permitting a thinner type. SOLUTION: This optical head is provided with a diffracting optical element 5 and a diffracting optical means 9 having an optical surface on which the optical axis of the emitted light 2 from a light source 1 is diagonally made incident in an optical path from the light source 1 to an information recording medium 11. Here, variation in the diffraction angle of the diffracted light from the diffracting optical element 5 associated with variation in the wavelength of the emitted light 2 and variation in the diffraction angle of the diffracted light from the refracting optical means 9 are made to occur so as to offset each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for an optical recording / reproducing apparatus, and more particularly, to a thin optical head having good optical characteristics.

[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.

FIG. 19 shows a typical conventional optical head. As shown in FIG. 19, a laser beam 2 emitted from a semiconductor laser 1 as a light source is converted into a parallel beam by a collimator lens 3, and after passing through a focus / track error signal detecting optical element 8 constituted by a hologram element. The optical axis is bent by 90 ° by the rising mirror 20 and enters the objective lens 4. The laser light 2 condensed on the optical disk 11 by the objective lens 4 is reflected and travels back on the same optical path, becomes parallel light by the objective lens 4, is reflected by the rising mirror 20, and detects a focus / track error signal. Incident on the optical element 8 for use. The laser beam 2 incident on the focus / track error signal detecting optical element 8 is split there and condensed on a photodetector. Thus, the reproduction signal and the focus error signal and the track error signal, which are the servo signals, are read.

[0004]

As shown in FIG.
The height of the optical head is WD (working distance), the thickness of the objective lens 4, the space from the lower part of the objective lens 4 to the upper part of the rising mirror 20, the rising mirror 2
It is represented by the sum of heights of 0.

When an optical head is to be thinned, W
The minimum value of the sum of D, the lens thickness, and the space is almost determined by the type of the optical disk 11. For example, D
In the case of VD, WD, lens thickness and space are each set to 1.
Even if the minimum value is estimated to be 1 mm, the height of the rising mirror 20 needs to be larger than the beam diameter, for example, 3 mm. Therefore, in this case, the height of the optical head is 6.3 mm even when estimated to the minimum value, and it is difficult to further reduce the thickness.

The present invention has been made to solve the above-mentioned problems in the prior art, and has as its object to provide an optical head which can be made thinner and has good optical characteristics.

[0007]

In order to achieve the above object, a first aspect of the present invention (corresponding to the first aspect of the present invention) comprises a diffractive optical element provided in an optical path from a light source to an information recording medium. Refracting optical means provided in the optical path and having an optical surface on which an optical axis of light emitted from the light source obliquely enters, diffracted light from the diffractive optical element caused by a wavelength change of the emitted light. And the change in the refraction angle of the refracted light from the refraction optical means occurs in directions that cancel each other.

Thus, for example, a thin optical head can be formed, and when a semiconductor laser beam is used as the light emitted from the light source, the light is emitted due to the spread of a wavelength band of about 2 nm by the high-frequency module or a change in environmental temperature. Even if the center wavelength of the emitted light changes, a good condensed spot can be obtained on the optical disk surface.

A second aspect of the present invention (corresponding to the second aspect of the present invention) is the optical head according to the first aspect of the present invention, wherein a diffractive optical element is integrated with a refractive optical means.

As a result, for example, the structure is stabilized, and the alignment is facilitated.

The third invention (corresponding to the invention according to claim 3) is characterized in that the light emitted from the light source is made substantially parallel and the collimator means is provided with collimator means for making the light incident on the diffractive optical element. 1 is an optical head according to the present invention.

Thus, for example, the diffraction efficiency of light incident on the diffractive optical element and the amount of change in the diffraction angle can be made substantially equal over the entire surface.

According to a fourth aspect of the present invention (corresponding to the fourth aspect of the present invention), an optical element for detecting a focus / track error signal is provided between the light source and the refractive optical means. The optical head according to the first aspect of the present invention, wherein the diffractive optical element is integrated with the / track error signal detecting optical element.

As a result, for example, the structure is stabilized and the alignment becomes easy.

A fifth aspect of the present invention (corresponding to the fifth aspect of the present invention) is the optical head according to the first aspect of the present 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 sixth aspect of the present invention (corresponding to the sixth aspect of the present invention), the diffractive optical element is disposed in a convergent light path or a divergent light path, and is incident on the diffractive optical element. Depending on the degree of convergence or divergence of the light
The optical head according to the first aspect of the present invention, wherein a period of the diffractive optical element differs depending on a location.

Still further, according to a seventh aspect of the present invention (corresponding to the seventh aspect of the present invention), the period is adjusted so as to become larger as it goes from the substantially central portion to the outer peripheral portion of the diffractive optical element. An optical head according to the sixth aspect of the present invention.

Thus, for example, the amount of change in the diffraction angle of the diffracted light from the diffractive optical element can be accurately uniformed over the entire surface.

According to an eighth aspect of the present invention (corresponding to the eighth aspect of the present invention), the diffractive optical element is disposed in a converging light path having a numerical aperture of 0.39 or less or in a diverging light path. In the optical head according to the first aspect of the present invention, the period of the diffractive optical element is uniform.

This facilitates, for example, alignment and manufacture of a diffractive optical element.

A ninth aspect of the present invention (corresponding to the ninth aspect of the present invention) is the optical head according to the eighth aspect of the present invention, wherein the diffractive optical element is disposed in an optical path near the light source. .

Thus, for example, the area of the diffractive optical element can be reduced, and the cost can be reduced.

According to a tenth aspect of the present invention (corresponding to the tenth aspect of the present invention), the refracting optical means is an optical element having three incident or reflecting surfaces, and the diffractive optical element is provided with the refracting optical element. The optical head according to the first aspect of the present invention is formed on at least one of three surfaces of the optical means.

As a result, for example, the structure is stabilized and the alignment becomes easy.

Still further, according to an eleventh aspect of the present invention (corresponding to the eleventh aspect of the present invention), the diffractive optical element is of a reflective type, and the tenth aspect of the present invention is formed on a reflective surface of the refractive optical means. 2 is an optical head of the invention.

Thereby, for example, the diffraction efficiency of the diffractive optical element is improved.

According to a twelfth aspect of the present invention (corresponding to the twelfth aspect of the present invention), the refractive optical means is a prism formed of a low-dispersion glass material having three incident or reflected surfaces. 1 is an optical head according to a first aspect of the present invention.

A thirteenth invention (corresponding to the thirteenth invention) is the optical head according to the twelfth invention, wherein the Abbe number of the glass material is 50 or more.

As a result, for example, the period of the diffractive optical element becomes large, so that the production is easy and a high diffraction efficiency is obtained.
The effect of wavelength fluctuation can be offset in a wide wavelength range.

According to a fourteenth aspect of the present invention (corresponding to the fourteenth aspect of the present invention), the refractive optical means is a prism formed of a glass material having a refractive index of n, and one of the base angles of the prism is And the other of the base angles θ is s
The optical head according to the first aspect of the present invention, which has an angle θ that substantially satisfies inθ = n · sin (3θ−90 °).

Thus, for example, the optical axis of the light incident on the refractive optical means and the optical axis of the light emitted from the refractive optical means can be made substantially orthogonal.

According to a fifteenth aspect of the present invention (corresponding to the fifteenth aspect of the present invention), the refractive optical means is a prism formed of a glass material having a refractive index n, and one of the base angles θ of the prism is one. , Sin (2θ−45 °) = 1 / n · sin θ, and the other base angle θ ₁ is θ + 85 ° ≦ θ ₁
An optical head according to the first aspect of the present invention, which satisfies ≦ θ + 95 °.

Thus, for example, the beam diameters of the light incident on the refracting optical means and the light emitted from the refracting optical means can be made substantially the same, and their optical axes can be made substantially orthogonal.

According to a sixteenth aspect of the present invention (corresponding to the sixteenth aspect of the present invention), there is provided an optical head according to the first aspect of the present invention, wherein the light source has a plurality of light source sections for emitting mutually different wavelengths. is there.

Thus, for example, a plurality of types of information recording media can be handled.

Still further, according to a seventeenth aspect of the present invention (corresponding to the seventeenth aspect of the present invention), the diffractive optical element is provided near the light source that emits light of the smallest wavelength among the plurality of light sources. An optical head according to the sixteenth aspect of the present invention, which is disposed only in the optical path.

Thus, for example, it is possible to realize the cost reduction and to optimize the optical characteristic of the short wavelength which is most susceptible to the influence of the wavelength fluctuation.

Still further, according to an eighteenth aspect of the present invention (corresponding to the eighteenth aspect of the present invention), the diffractive optical element has a sawtooth cross-sectional shape, and the minimum value among the different wavelengths is λ ₁ ,
When the maximum value is λ ₂ and the refractive index of the diffractive optical element is n, the groove depth L of the diffractive optical element is λ ₁ / (n−
1) The sixteenth above which satisfies the relationship of ≦ L ≦ λ ₂ / (n−1)
Is an optical head according to the present invention.

Thus, for example, the diffraction efficiency of the diffractive optical element can be increased for a plurality of wavelengths.

Still further, according to a nineteenth aspect of the present invention (corresponding to the nineteenth aspect), the groove depth L of the diffractive optical element is
The first, which is substantially (λ ₁ + λ ₂ ) / [2 (n−1)].
8 is an optical head according to the invention.

Thus, for example, the diffraction efficiency of the diffractive optical element can be increased in a most balanced manner for a plurality of wavelengths.

Still further, according to a twentieth aspect of the present invention (corresponding to the twentieth aspect of the present invention), the diffractive optical element has a stepped shape having a cross section of p steps, and the minimum value among the different wavelengths is λ. ₁ , when the maximum value is λ ₂ and the refractive index of the diffractive optical element is n, the groove depth L of the diffractive optical element is
(P−1) · λ ₁ / [p · (n−1)] ≦ L ≦ (p−1) · λ
An optical head according to the sixteenth aspect, wherein the optical head satisfies the relationship of ₂ / [p · (n−1)].

Thus, for example, the diffraction efficiency of the diffractive optical element can be increased for a plurality of wavelengths.

Still further, according to the twenty-first aspect of the present invention (corresponding to the twenty-first aspect), the groove depth L of the diffractive optical element is
The optical head according to the twentieth aspect of the present invention, which is substantially (p−1) · (λ ₁ + λ ₂ ) / [2p (n−1)].

Thus, for example, the diffraction efficiency of the diffractive optical element can be increased in a most balanced manner for a plurality of wavelengths.

According to a twenty-second aspect of the present invention (corresponding to the twenty-second aspect of the present invention), the refractive optical means is a prism formed of a glass material having a refractive index of n, and the bottom surface of the refractive optical means is set at an installation reference. Assuming that the installation angle of the surface is θ _b and the angle at which the optical axis from the light source to the refracting optical means is the installation reference surface is θ _p , one of the base angles θ of the prism is sin ( θ−θ _b ) = n · sin (4θ−2θ _b)
−θ _p −90 ° −θ ′) and n · sin θ ′ = sin (θ−θ
_b ) is substantially satisfied, and the other angle θ ₁ of the base angle is θ
Satisfying substantially the _{1 = θ + 90 ° -2θ b} -θ p is the first optical head of the present invention.

[0048] Furthermore, the 23 present invention (corresponding to the invention of claim 23, wherein) is above the 22 optical head of the present invention for the theta _b is substantially satisfies 2 ° ≦ θ _b ≦ 10 ° is there.

Thus, for example, the optical head can be made thinner.

According to a twenty-fourth aspect of the present invention (corresponding to the twenty-fourth aspect of the present invention), the refractive optical means is a prism having three optical surfaces, and the information recording medium among the three optical surfaces. When the side is the first surface, the light source side is the second surface, and the other side is the third surface, light emitted from the light source passes through the second surface, and the first surface and the third surface Reflected in order,
An optical head according to the first aspect of the present invention, which transmits through the first surface.

Thus, for example, the optical head can be made thinner by zigzag propagation in the optical path in the prism.

Further, a twenty-fifth aspect of the present invention (corresponding to the twenty-fifth aspect of the present invention) comprises a refractive optical means having a prism having three optical surfaces in an optical path from a light source to an information recording medium. When the information recording medium side is the first surface, the light source side is the second surface, and the other is the third surface, the light emitted from the light source passes through the second surface, An optical head that reflects the first surface and the third surface in this order and transmits the first surface.

Thus, for example, the optical head can be made thin.

According to a twenty-sixth aspect of the present invention (corresponding to the twenty-sixth aspect of the present invention), the wavelength λ of the emitted light is 0.35
The optical head according to the first aspect of the present invention substantially satisfies μm ≦ λ ≦ 0.5 μm.

In a twenty-seventh aspect of the present invention (corresponding to the twenty-seventh aspect of the present invention), the third surface is parallel to the reference plane of the refractive optical means. Head.

According to a twenty-eighth aspect of the present invention (corresponding to the twenty-eighth aspect of the present invention), an objective lens is provided in an optical path between the information recording medium and the refractive optical means, and the second surface is provided. In the twenty-fourth aspect, the height of the uppermost portion of the transmitted outgoing light with respect to the setting reference plane of the refractive optical means is higher than the height of the lowermost part of the objective lens with reference to the setting reference plane. Alternatively, the optical head according to the twenty-fifth aspect of the present invention.

[0057]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) An optical head according to a first embodiment of the present invention will be described with reference to FIGS. 1 (a) and 2 (b).
The coordinate axes are as shown in the figure and will be described in detail.

FIG. 1A is a plan view showing the basic structure of the optical head and the state of light propagation according to the first embodiment of the present invention, and FIG. 1B is a plan view showing the present invention. FIG. 2 is a side view illustrating a basic configuration of the optical head and a state of light propagation according to the first embodiment. FIG. 2A is a diagram illustrating a state in which diffracted light is generated when light of different wavelengths is incident on the diffractive optical element in the optical head according to the embodiment, and FIG. FIG. 6 is a diagram illustrating a state in which refracted light is generated when light of different wavelengths is incident on a refracting optical element in the optical head according to the embodiment, and is a diagram for describing an operation principle of chromatic aberration correction.

As shown in FIGS. 1 (a) and 1 (b), in the optical head according to the present embodiment, diffraction occurs in an optical path from a light source 1 to an optical disk 11 such as a DVD or CD as a recording medium. A refractive optical unit 9 having an optical surface 21 (corresponding to the first surface of the refractive optical unit of the present invention) on which the optical axis of the optical element 5 and the light 2 emitted from the light source 1 are obliquely incident is arranged. The light source 1 and the photodetectors 13a and 13b are integrated in a light source / photodetector unit 17.

A laser beam 2 having a wavelength of, for example, λ = 0.658 μm emitted from a semiconductor laser as a light source 1 in the y-axis direction is, for example, substantially collimated with a beam diameter of 3.25 mm in the z-axis direction by a collimating lens 3. It becomes light and focus /
The light passes through the track error signal detecting optical element 8 (using the 0th-order diffracted light) and is incident on the diffractive optical element 5 which is a parallel grating having a uniform period of Λ = 60.7 μm, for example. This diffractive optical element 5 has, for example, a side surface 15 of a refractive optical element having three incident or reflective surfaces, one of which has a base angle of θ = 38 ° and the other is a substantially right-angle prism (the refraction of the present invention). (Corresponding to the second surface of the optical means) as shown in FIGS. 1 (a) and 1 (b). The light 2 is diffracted by the grating 5 by, for example, an angle of q = 0.4 ° from the y-axis to the z-axis, and is totally reflected by the inclined surface 21 of the prism 9. Thereafter, the light is further reflected by the bottom surface 14 (corresponding to the third surface of the refractive optical means of the present invention) on which the reflective layer 16 is formed, and is, for example, 24.4 ° from the normal of the inclined surface 21.
The light is obliquely incident on the slope 21 and is refracted. For example, the beam diameter in the y-axis direction is 2.8 mm, the light is emitted in the vertical direction (z-axis direction), and is focused on the optical disk 11 by the objective lens 4. .

The laser beam 2 reflected by the optical disk 11 is turned in the opposite direction, passes through the objective lens 4, the prism 9, and the grating 5 in that order, and is split by the focus / track error signal detecting optical element 8 (1). The signal light 19a, 19b) using the next-order diffracted light is detected by the photodetectors 13a, 13b.

In the present embodiment, the refractive optical means 9
For example, a triangular prism whose glass material (meaning a transparent substance such as glass or resin) is BK7 glass, having a height of 3.7 mm, a depth of 4 mm, and a width of 4.7 mm was used. Then, the light is applied to the inclined surface 21 and the bottom surface 14 in the prism 9.
And the light is emitted from the inclined surface 21 whose optical axis is inclined.
The height of the uppermost portion of the (refractive optical means) with reference to the installation reference surface 101 (indicated by reference numeral 102 in the figure) is the height of the lowermost portion of the objective lens 4 with respect to the installation reference surface 101 Since the height of the optical head is higher than 103, the height of the optical head itself can be made extremely thin (for example, 5.3 mm) while serving as a rising mirror of the conventional optical head.

In particular, when the refractive index of the glass material is n, the present inventors consider that when one of the base angles is substantially a right angle, the other base angle θ
Is an angle θ that substantially satisfies sin θ = n · sin (3θ−90 °)
At this time, it was discovered that the optical axes of the light incident on the prism 9 and the light emitted from the prism 9 were substantially orthogonal. With such a configuration, there is an effect that the arrangement of the optical components is easy and the alignment is simple. Also, the vertical surface 1 of the prism 9
The structure in which the grating 5 is integrated with the grating 5 stabilizes the structure, and furthermore, since these can be handled as one part, the alignment is further facilitated.

As the diffractive optical element 5, FIGS.
A grating having a sawtooth cross section as shown in FIG. 2B or a staircase-shaped uniform period formed on a substrate 7 such as glass as shown in FIG. 2A is used.
L = 1.29 μm (sawtooth shape) and L = 1.13 μm (eight-step shape) were set to maximize the first-order diffraction efficiency.
By using a grating with a uniform period, the manufacture of the element is easy and the alignment in the optical system can be simplified.

The focus / track error signal detecting optical element 8 is, for example, a hologram element formed on a resin substrate, a glass substrate, a LiNbO ₃ crystal or the like. In particular, in the case where a LiNbO ₃ crystal is used, the light use efficiency can be increased by using a quarter-wave plate between the focus / track error signal detecting optical element 8 and the optical path of the optical disk 11 because of the polarization property. There is.

Further, the collimator lens 3 is provided, and the substantially parallel light is made incident on the diffractive optical element 5, whereby
The diffraction efficiency of light incident on the diffractive optical element 5 and the amount of change in the diffraction angle can be made substantially equal over the entire light incident area.

Next, the principle of the behavior of a light wave when a wavelength fluctuation occurs will be described with reference to FIGS. 2 (a) and 2 (b).

As shown in FIG. 2A, the diffractive optical element 5
Then, when the light 6 having the wavelength λ ₁ enters, the first-order diffracted light 10a is generated at the diffraction angle θ _da . Wavelength fluctuation occurs, for example,
When the wavelength decreases to λ ₂ , the smaller diffraction angle θ
_The diffracted light 10b is generated by _db . As a result, a phenomenon occurs in which the direction of the emitted light is different due to the wavelength fluctuation. This phenomenon is called dispersion.

On the other hand, as shown in FIG. 2B, when the light 6 'having the wavelength λ ₁ is incident on the prism 9 of the refractive optical element from an oblique direction at an incident angle θ _i , the refracted light has a refractive angle θ _ra. 12a
Occurs. When the wavelength fluctuates, for example, when the wavelength decreases to λ ₂ , the refracted light 12b with a larger diffraction angle θ _rb
Occurs. This is because the refractive index of the glass material forming the prism fluctuates due to the wavelength fluctuation. As a result, a dispersion phenomenon that the directions of the emitted light are different occurs.

Therefore, when a diffractive optical element and a refractive optical element having an optical surface on which light is obliquely incident are combined,
In both elements, the directions in which the emitted light fluctuates with respect to the wavelength fluctuation are opposite to each other.
It has been found that there is a condition that the direction of the emitted light can be kept constant regardless of the wavelength fluctuation.

In the present embodiment, for example, since θ _i = 24.4 ° in the prism, the wavelength is λ = 0.65.
When it is reduced from 8 μm, for example, by 2 nm, the refractive index of the prism is n = 1.51426455, and 1.
514327214, the refraction angle is 0.00
It becomes larger by 1888 °. On the other hand, the period Λ = 60.7μ
When the light is incident on the diffractive optical element of m, the diffraction angle decreases by 0.001888 ° when the wavelength is reduced by 2 nm. Therefore, it has been found that combining them cancels out the influence of the wavelength fluctuation. Accordingly, the optical axis of the light emitted to the objective lens 4 is constant irrespective of the wavelength fluctuation, and there is an effect of forming a good spot without chromatic aberration on the optical disc 11.

Also, as explained above, when the wavelength is λ =
In this case, the light source 1 is reduced by about 2 nm from 0.658 μm. In general, the light source 1 has a weight of about ± 1 nm with respect to the center wavelength (wavelength width of 2 n
m) Spread. Even with this degree of wavelength spread,
As described above, the prism 9 and the grating 5
It was possible to cancel chromatic dispersion by combining.

However, at this time, for example, at the center wavelength (design wavelength) of λ = 0.658 μm,
It was also found that even if chromatic dispersion could be completely canceled, chromatic dispersion gradually occurred when wavelength variation further occurred (shifted from the center wavelength) due to temperature change.

The present inventors have found that when the glass material forming the prism 9 has a lower dispersion, the rate of occurrence of chromatic dispersion becomes smaller due to the above-mentioned temperature change. At the same time, it was also found that the period of the diffractive optical element 5 for correcting the chromatic aberration can be increased when the glass material forming the prism 9 has a low dispersion, so that the diffractive optical element 5 can be easily manufactured and high diffraction efficiency can be obtained. Had the effect.

When examined in detail, the wavelength variation due to the temperature change was actually within the range of ± 20 nm, and within this range, the lateral spread due to the chromatic aberration of the spot condensed by the objective lens was due to the Abbe number of the glass material. Is greater than or equal to 50, the wavefront aberration is less than or equal to 70 mλ, so that it is practically suppressed to a problem-free level, and it has been found that the signal reproduction of the optical disk 11 can be favorably performed. Therefore, as glass materials, BK7 (abbe number is 64.2), FC5, FK5,
FCD1, FCD10, FCD100, VC79 (abbe number is 57), P-BK40 (abbe number is 64) and the like are preferable.

(Second Embodiment) An optical head according to a second embodiment of the present invention will be described with reference to FIG.
The following description focuses on the differences from this embodiment.

FIG. 3 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.

As shown in FIG. 3, in the present embodiment, in the optical path from the collimating lens 3 to the refracting optical means 9, it is integrated with the focus / track error signal detecting optical element 8 to form a diffractive optical element. 5 are provided. The integration of the focus / track error signal detecting optical element 8 and the diffractive optical element 5 stabilizes the structure, allows them to be handled as one part, and facilitates alignment.

As shown in FIG. 3, the diffractive optical element 5 may be arranged on the front side of the focus / track error signal detecting optical element 8 or on the back side. The substrate on which the diffractive optical element 5 is formed may be integrated with the focus / track error signal detecting optical element 8.
Further, a focus / track error signal detecting optical element 8
May be processed to form the diffractive optical element 5.

(Third Embodiment) An optical head according to a third embodiment of the present invention will be described with reference to FIG.
The following description focuses on the differences from this embodiment.

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

As shown in FIG. 4, in the present embodiment, a diffractive optical element 5a is provided in the optical path of substantially parallel light from the refractive optical means 9 to the objective lens 4. With such an arrangement, the distance between the diffractive optical element 5a and the light source / photodetector unit 17 provided with the photodetector is increased, and other diffracted light (other than the first-order diffracted light generated by the diffractive optical element 5a) Unnecessary light) can be arranged so as not to enter the photodetector, and the S / N of the detection light is improved.

The concave and convex shape of the diffractive optical element 5a may be formed toward the objective lens 4 as shown in FIG.
The reverse is also acceptable.

(Fourth Embodiment) An optical head according to a fourth embodiment of the present invention will be described with reference to FIG.
The following description focuses on the differences from this embodiment.

FIG. 5 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.

As shown in FIG. 5, in the present embodiment, in the optical path of substantially parallel light from the refractive optical means 9 to the objective lens 4, the diffractive optical element 5 b is provided with a right-angle prism as the refractive optical means 9. It is provided integrally on the slope. With such an arrangement, the distance between the diffractive optical element 5b and the light source / photodetector unit 17 provided with the photodetector increases, and other diffracted light (other than the first-order diffracted light generated by the diffractive optical element 5b) Unnecessary light) can be arranged so as not to enter the photodetector, and the S / N of the detection light is improved. Further, the integration makes the structure stable and can be handled as one part, thereby simplifying the alignment.

(Fifth Embodiment) An optical head according to a fifth embodiment of the present invention will be described with reference to FIG.
The following description focuses on the differences from this embodiment.

FIG. 6 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.

In the optical systems of the optical heads according to the first to fourth embodiments, for example, only the beam diameter in the z-axis direction is reduced to 0.86 times for the light that has been made substantially parallel by the collimator lens 3. Thus, the optical system (the same magnification in the x-axis direction) was incident on the objective lens 4.

In the optical system according to the present embodiment, the light that has been made substantially parallel by the collimator lens 3 enters the objective lens 4 with almost the same beam diameter (same magnification) in the z-axis direction and the x-axis direction. It is an optical system.

In FIG. 6, the refractive optical means 9a is, for example, a prism made of BK7, the base angle between the bottom surface 14 'and the inclined surface 21' is, for example, θ = 33 °, and the bottom surface 1 '
The base angle between 4 ′ and side surface 15 ′ is, for example, θ ₁ = 12
1.6 °. The diffractive optical element 5c is formed on, for example, the glass substrate 7, and is integrated with the side surface 15 'of the prism 9a. With the integrated structure, the structure is stable and can be handled as one part, so that the alignment is simplified.

The present inventors have found that when a prism made of a glass material having a refractive index n is used as a refractive optical means, the bottom surface 14 'and the side surface 1'
One base angle of 5 ′ is sin (2θ−45 °) = 1 /
The angle θ substantially satisfies the equation of n · sin θ, and the bottom surface 14 ′
And the other base angle formed by the side surface 15 ′ is θ + 85 ° ≦ θ ₁ ≦
When the angle theta ₁ which satisfies the equation θ + 95 °, while (no beam shaping) were approximately the same beam diameter of the emitted light from the incident light and the prisms 9a of the prism 9a, found that the optical axis can be substantially orthogonal did. With such a configuration,
There is an effect that the arrangement of the optical components is easy and the alignment can be simplified.

In the present embodiment, the optical surface on which the optical axis of light is obliquely incident on the refractive optical element 9a is the inclined surface 21 '.
And the side surface 15 ', the overall dispersion due to the refraction effect was larger than in the first to fifth embodiments. Therefore, in the present embodiment, the diffractive optical element 5c for correcting chromatic dispersion of refraction is, for example, a uniform periodic grating having a period of 39.7 μm. As described above, by making the period in the present embodiment smaller than the period 60.7 μm of the diffractive optical element described in each of the above embodiments, the dispersion of diffraction can be increased. The dispersion due to the action could be canceled.

(Sixth Embodiment) An optical head according to a sixth embodiment of the present invention will be described with reference to FIGS. 7 and 8, focusing on differences from the fifth embodiment. .

FIG. 7 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. 8 is an optical head according to a sixth embodiment of the present invention. And the first-order diffraction efficiency (solid line) of the diffractive optical element (transmission grating) of the optical head according to the fifth embodiment.

As shown in FIG. 7, in the present embodiment, a reflection type grating 5d having a structure in which a reflection layer 16 is provided on the bottom surface of the refractive optical means 9a as a prism is provided.
Is provided. By forming an integrated structure, the structure is stable. In particular, since the reflective layer is provided on the surface of the uneven shape, there is an effect that the reflective layer can also serve as a protective layer.

The reflection type grating 5d has, for example, a sawtooth shape or a step shape with a groove depth of 0.22 μm, and has an optimum groove depth of 1 as compared with a transmission type diffractive optical element.
Since the thickness was reduced to about / 6, the etching time at the time of manufacturing was shortened, and the amount of sagging of the cross section was reduced, thereby facilitating the manufacturing. In addition, as shown in FIG. 8, the value of the first-order diffraction efficiency was able to be improved as compared with the transmission grating.

(Seventh Embodiment) An optical head according to a seventh embodiment of the present invention will be described with reference to FIGS.
(B), FIG. 10 (a) and FIG. 10 (b) will be described focusing on points different from the fifth embodiment.

FIG. 9A is a side view showing a basic structure of an optical head and a state of light propagation in a seventh embodiment of the present invention, and FIG. 9B is a seventh 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. FIG. 10A is a graph showing a relationship between diffraction efficiency and groove depth when a blazed grating having a sawtooth cross section is used as the diffractive optical element of the optical head according to the seventh embodiment of the present invention; FIG. 10B shows an eight-level grating (FIG. 2) having an eight-step cross section as a diffractive optical element of the optical head according to the seventh embodiment of the present invention.
(B) is a graph showing the relationship between the diffraction efficiency and the groove depth when () is used.

The optical head of this embodiment has a two-wavelength configuration. That is, for example, for the DVD 11a,
A semiconductor laser light source 1a having a wavelength λ ₁ = 0.658 μm;
For example, the wavelength λ ₂ = 0.
In the configuration provided with the semiconductor laser light source 1b of 80 μm, both wavelengths are multiplexed and demultiplexed by the beam splitter 18. The beam splitter 18 is not limited to this as long as it is an element capable of multiplexing / demultiplexing, such as a wedge prism. Light source 1a, 1b
Are light source / photodetector modules 17a, 17
b.

On the side of the refracting optical means 9a, which is a prism,
The integrated diffractive optical element 5c has λ ₁And λ_TwoOf the two wavelengths
Configuration.

As the diffractive optical element 5c, a blazed gray
If the wavelength is λ ₁Fig. 10
As shown by the solid line in (a), the depth of the groove is L = λ.₁/
In the case of (n-1), the first-order diffraction efficiency takes the maximum value. Ma
The wavelength is λ_TwoIn this case, it is indicated by a broken line in FIG.
Thus, the depth of the groove is L = λ_Two1st order diffraction at / (n-1)
The efficiency takes the maximum value. We have found that the depth of the groove is λ₁
/ (N-1) ≦ L ≦ λ_Two/ (N-1) for both wavelengths
A high diffraction efficiency of 80% or more
I did. In particular, L is approximately (λ₁+ Λ_Two) / [2 (n-1)] and
Values are almost the same for both wavelengths.
It was also found that efficiency could be balanced.

Further, as shown in FIG. 10B, when the cross-sectional shape is a step-like shape having p steps, the groove depth is (p−
1) · λ ₁ / [p · (n−1)] ≦ L ≦ (p−1) · λ ₂ /
In the case of [p · (n−1)], high diffraction efficiency can be realized for both wavelengths, and in particular, L is approximately (p−1) · (λ ₁ + λ ₂ ) /
In the case of [2p (n-1)], it was also found that the best balance was obtained for both wavelengths.

FIG. 10B is a diagram showing the relationship between the diffraction efficiency and the groove depth when a grating having eight steps in cross section is used as the diffractive optical element 5c. In the figure, when the wavelength is lambda _1, as indicated by the solid line, the depth L of the groove is 1-order diffraction efficiency when _{L = 7λ 1/8 (n} -1) is a maximum value. Further, when the wavelength is lambda _2, the maximum as indicated by the broken line, the depth L of the groove is 1-order diffraction efficiency when _{L = 7λ 2/8 (n} -1) is shown in FIG. 10 (b) Take a value.

In this embodiment, the case of two wavelengths has been described. However, the present invention is not limited to the two wavelengths, and a configuration corresponding to a plurality of wavelengths is possible. For example, 0.35 μm to 0.50 μm
The above result can be applied to the case of a plurality of wavelengths equal to or more than three wavelengths including the blue / green wavelengths. That is, among the plurality of wavelengths, considering the minimum value as λ ₁ and the maximum value as λ ₂ and applying the above equation, the first-order diffraction efficiency of the diffractive optical element can be increased with respect to the plurality of wavelengths. For example, a high-density optical disk of 10 GB or more, DVD, DVD-R, CD, C
It is possible to configure an optical head capable of reading out many optical discs such as DRs.

(Eighth Embodiment) An optical head according to an eighth embodiment of the present invention will be described with reference to FIGS. 11 and 12, focusing on differences from the above-described fifth embodiment.

FIG. 11 is a side view showing a basic structure of an optical head and a state of light propagation according to an eighth embodiment of the present invention. FIG. 12 is a diffractive optic of the optical head according to the eighth embodiment of the present invention. This is a relationship between the diffraction angle difference of the first-order diffracted light and the incident angle when two wavelengths differing by 2 nm are incident on the element 5d (grating having a period Λ = 39.7 μm) at the same incident angle.

As shown in FIG. 11, in the optical head of the present embodiment, θ = 33 °
A prism 9b with θ ₁ = 123 ° was used, and as the diffractive optical element 5d, for example, a grating 5d having a uniform period of 39.7 μm was used. Grating 5d
Is a focus / track error signal detecting optical element 8a
And a diverging light path near the light source 1, that is, a sealing window of the light source / photodetector unit 17c. As shown, the grating 5d has a configuration in which the groove shape is arranged so as to face the light source 1 to prevent the groove from being damaged. However, the reverse operation is also possible. As the optical element 8a for detecting a focus / track error signal, for example, a polarizing hologram element such as a UV-cured liquid crystal was used, and a λ / 4 plate was integrated on the surface. By integrating the grating 5d and the focus / track error signal detecting optical element 8a, the structure is stabilized, and they can be handled as one part, which facilitates alignment.
Further, by arranging the grating 5d in the optical path near the light source 1, the area of the diffractive optical element 5d can be significantly reduced, and the cost can be reduced.

The light source 1 has a wavelength width typically expanded by about 2 nm due to high-frequency superposition. We have shown in FIG.
As shown in FIG. 2, as the angle of incidence of light (always having a wavelength spread of 2 nm) incident on the grating 5d deviates from 0 ° (perpendicular incidence) (oblique incidence), the diffraction angle difference of the first-order diffracted light increases. Was found. That is, when the parallel light is incident on the uniform periodic grating, the chromatic aberration correction effect is the same over the entire beam, but when the divergent light or the convergent light is incident on the uniform periodic grating, the dispersion becomes stronger as the light beam is inclined. That is, when the optical axis is perpendicularly incident, the chromatic aberration correction effect is stronger at the periphery than at the center of the beam.

When examined in detail, the diffraction angle difference is 0.00
The occurrence of 1 ° means that the focal length of the objective lens is 2.
When 14 mm is used, it corresponds to a distance of 37 nm in the y-axis direction on the optical disk 11 (chromatic aberration). The distance in the y-axis direction that is not a problem due to chromatic aberration is 10n
m, the diffraction angle difference is 0.27 m
deg, and thus it was found that the incident angle needed to be within 22.9 °. This is a value corresponding to a numerical aperture NA of 0.39.

In the present embodiment, since the NA of the diverging light 2 (the NA of the collimator lens 3) is, for example, 0.3,
A good spot was obtained without any problem of chromatic aberration.

(Ninth Embodiment) An optical head according to a ninth embodiment of the present invention will be described with reference to FIGS.
With reference to (b), a description will be given mainly of points different from the eighth embodiment.

FIG. 13A is a side view showing a basic configuration of an optical head and a state of light propagation in a ninth embodiment of the present invention, and FIG. 13B is a ninth 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 has a two-wavelength configuration. That is, for example, for a DVD, the wavelength λ
₁ = 0.658 μm semiconductor laser light source 1a and CD-R
For example, a semiconductor laser light source 1b having a wavelength λ ₂ = 0.80 μm is provided for a CD or a CD. Light source 1a, 1b
Are light source / photodetector modules 17c and 17c, respectively.
d.

The present inventors have found that the shorter the wavelength of the light source, the smaller the pit size on the optical disk 11, and the more easily the light source is affected by the chromatic aberration of the focused spot.
In this embodiment, the diffractive optical element 5d is disposed only in the optical path in the vicinity of the wavelength is small lambda ₁ of the light source 1a, in this wavelength to obtain a converged light spot having no aberration. For the lambda ₂ wavelength is large, a configuration not provided a grating for chromatic aberration correction, also work well in the generation of little chromatic aberration with respect to this wavelength, such an arrangement was effective to reduce the cost .

The optical path near the long wavelength light source 1b includes:
The focus / track error signal detecting optical element 8b is
It was arranged in the sealing window of the light source / photodetector unit 17d.

Next, another example of the present embodiment using a light source 1a having a blue wavelength will be described with reference to FIG.

FIG. 14 is a graph showing the wavelength dependence of the refractive index of the glass material (BK7).

As shown in the figure, the wavelength is about 0.5 μm
Below this, the chromatic dispersion, which is the amount of change in the refractive index of the glass material of the refractive optical means 9a (the differential value of the refractive index curve in FIG. 14), sharply increases. For example, at a wavelength λ = 0.4 μm, λ =
It can be seen that the chromatic dispersion is four times as large as the chromatic dispersion at 0.658 μm.
The period of d is λ = 0.658 μm when λ = 0.4 μm.
Is 1/4 of the period, that is, about 10 μm.

At a wavelength of 0.5 μm or less,
As described above, since the chromatic dispersion is large, the change in the refraction angle of the refracted light emitted from the refraction optical means 9a becomes very large even with a slight wavelength fluctuation, and the optical characteristics are greatly reduced.
Therefore, the effect of the present invention of canceling out by the diffracted light emitted from the diffractive optical element 5d is large.

The above description is not limited to two wavelengths.
As long as the light source includes a light source of λ = 0.5 μm or less, even one wavelength is effective (for example, see FIG. 18). However, as the wavelength becomes shorter, the light absorption of the glass material increases. Therefore, the wavelength range is desirably 0.35 μm ≦ λ ≦ 0.5 μm.

(Tenth Embodiment) An optical head according to a tenth embodiment of the present invention will be described with reference to FIGS. 15 and 16, focusing on differences from the first embodiment.

FIG. 15 is a side view showing a basic structure of an optical head and a state of light propagation according to a tenth embodiment of the present invention. FIG. 16 is a graph (normal incidence, wavelength width Δλ = 2 nm) showing the relationship between the period of the diffractive optical element (grating) of the optical head and the diffraction angle difference of the first-order diffracted light in the tenth embodiment of the present invention. .

In the optical head of this embodiment, the diffractive optical element 5c is arranged in the divergent light path from the light source 1 to the collimator lens 3 (in other words, in the convergent light path from the collimator lens 3 to the photodetector). Then, the periodic distribution in the z-axis direction was changed according to the degree of convergence or divergence of the incident light. In the present embodiment, since the optical axis of the outgoing light 2 is perpendicular to the diffractive optical element 5c, the period is set to be smaller at the center and larger at the outer periphery. When the optical axis is inclined, the period may be changed according to the inclination of the light beam entering each area.

From FIG. 16, the inventor of the present invention has found that the smaller the grating period, the larger the diffraction angle difference, that is, the larger the chromatic aberration correction effect, and the more the light enters obliquely, the larger the chromatic aberration correction effect. Figure 12
From these results, it was found from these results that if the period becomes larger as the light is inclined, the amount of change in the diffraction angle of the diffracted light from the diffractive optical element can be accurately uniformed over the entire surface.

(Eleventh Embodiment) An optical head according to an eleventh embodiment of the present invention will be described with reference to FIG. 17 focusing on differences from the first embodiment.

FIG. 17 is a side view showing a basic structure of an optical head and a state of light propagation in an eleventh embodiment of the present invention.

The optical head according to the present embodiment has a configuration in which the diffractive optical element is removed from the first embodiment. That is, in the optical path from the light source 1 to the optical disk 11, there is provided a refractive optical unit 9 comprising a prism having three optical surfaces, wherein the optical disk side has a first surface, the light source 1 side has a second surface, and a bottom surface. When the side is the third surface, the light emitted from the light source 1 is transmitted through the second surface, is reflected in the order of the first surface and the third surface, and is transmitted and emitted through the first surface. Thus, the height of the optical head itself is made extremely thin (for example, 5.3 mm) while acting as a rising mirror of the conventional optical head.
We were able to.

In this embodiment, since there is no chromatic aberration correction grating, chromatic aberration becomes a problem for an optical disk having a small pit, such as a DVD, but a low dispersion glass having a large Abbe number is used for the glass material of the prism 9. And was considerably reduced. Also, there is no problem of chromatic aberration for an optical disk having a large pit, such as a CD or a CD-R, and a thin optical head has been made possible.

The optical heads of the first to eleventh embodiments of the present invention have been described above. In addition to the optical heads of these embodiments, optical heads obtained by combining the configurations of the respective optical heads are also provided. Of course, it is possible and has the same effect. Note that the objective lens and the collimator lens used in the description of the embodiments are named for convenience, and are the same as generally used lenses.

In the above embodiment, the case where the angle between the bottom surface of the refractive optical means and the y-axis is 0 ° has been described. However, the present invention is not limited to this. For example, as shown in FIG. 9c may be inclined by an angle θ _{b with} respect to the installation reference plane 1701. In this case, the refractive optical means
A prism formed of a glass material having a refractive index of n.
Assuming that the angle formed by 1 is θ _p and the installation angle of the bottom surface of the refractive optical means 9c is θ _b , one of the bottom angles of the prism θ is sin (θ−θ _b ) = n · sin (4θ− 2θ _b −θ _p −
90 ° −θ ′) and n · sin θ ′ = sin (θ−θ _b ), and the other angle θ ₁ of the base angle is θ ₁ = θ + 90 °
It is assumed that the relationship substantially satisfies −2θ _b −θ _p .
The configuration shown in FIG. 18 is an example in which the diffractive optical element is arranged only in the divergent light path from the light source 1 to the collimator lens 3.

As a result, the distance between the left end of the objective lens 4 and the prism 9c in the drawing has a margin, so that the distance between the objective lens 4 and the prism 9c can be further reduced as a whole. .

In FIG. 18, the specifications of the prism 9c are, for example, θ _b = 5.0 °, θ = 34.8 °, θ ₁ = 1.
At 13.8 °, the length of the base was 4.4 mm, and BK7 was used as a glass material. Further, as the diffractive optical element 5e, for example, a grating 5e having a uniform period of 42.8 μm is formed and used on a glass substrate, and a focus / track error signal detecting optical element 8a is formed on the back surface of the glass substrate. (Ie, the grating 5e is integrated with the focus / track error signal detecting optical element 8a), and the light source / photodetector unit 17c is a divergent light path near the light source 1. Was placed in the sealing window. Although the grating 5e is arranged with the groove shape facing the collimator lens 3 as shown in the figure, the operation is also possible with the reverse. Grating 5e
By integrating the optical element 8a for focus / track error signal detection, the structure is stabilized, and they can be handled as one part, which facilitates alignment. Further, by arranging the grating 5e in the optical path near the light source 1, the area of the diffractive optical element 5e can be significantly reduced, and the cost can be reduced.

Further, the light emitted from the light source 1 is diffracted by, for example, 0.88 ° in the z-axis direction by the grating 5e. Therefore, θ _q = 1.88, which is the sum of this angle and θ _p.
The mounting angle of the light source 1 is inclined by an angle of °. At the same time, the collimator lens 3, the grating 5e, and the focus / track error signal detecting optical element 8a provide θ _p = 1.
Tilt by 0 °.

The installation angle of the prism 9c is, for example,
Although it was set to 5 °, it was found that if the angle was substantially in the range of 2 ° to 10 °, a sufficient margin was created between the left end of the objective lens 4 and the prism 9c, which was preferable.

It should be noted that even in the configuration of FIG. 18 without the chromatic aberration correction grating 5e, the first configuration shown in FIG.
As in the case of the optical head according to the first embodiment, an ultra-thin optical head can be configured when chromatic aberration is not so problematic. In that case, θ _q = θ _p .

[0137]

As described above, according to the present invention,
A thin optical head having good optical characteristics can be realized.

[Brief description of the drawings]

FIG. 1A is a plan view showing a basic configuration of an optical head according to a first embodiment of the present invention and a state of light propagation. FIG. 1B is a plan view showing an optical head according to the first embodiment of the present invention. Side view showing the basic configuration of a light source and how light propagates

FIGS. 2A and 2B are diagrams showing a state in which diffracted light is generated when light having different wavelengths is incident on a diffractive optical element in the optical head according to the first embodiment of the present invention; FIGS. FIG. 4 is a diagram illustrating a state in which refracted light is generated when light of different wavelengths enters a refracting optical element in the optical head according to the first embodiment.

FIG. 3 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. 4 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. 5 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.

FIG. 6 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. 7 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. 8 shows the first-order diffraction efficiency of the diffractive optical element (reflection type grating) of the optical head according to the sixth embodiment of the present invention, and the diffractive optical element (transmission type grating) of the optical head according to the fifth embodiment. Showing the first-order diffraction efficiency of

9A 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. 9B is a side view showing an optical head according to a seventh embodiment of the present invention. Plan view showing basic configuration and light propagation

FIG. 10A is a graph showing the relationship between the diffraction efficiency and the groove depth when a blazed grating having a sawtooth cross section is used as the diffractive optical element of the optical head according to the seventh embodiment of the present invention. (B): The relationship between the diffraction efficiency and the groove depth when an 8-level grating having an 8-stage cross section is used as the diffractive optical element of the optical head according to the seventh embodiment of the present invention. Diagram showing the graph shown

FIG. 11 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.

FIG. 12 shows the diffraction angle difference and the incident angle of the first-order diffracted light when two wavelengths having different wavelengths by 2 nm are incident on the diffractive optical element of the optical head according to the eighth embodiment of the present invention at the same incident angle. Diagram showing the relationship

13A is a side view showing a basic configuration of an optical head and a state of light propagation according to a ninth embodiment of the present invention. FIG. 13B is a side view showing an optical head according to a ninth embodiment of the present invention. Plan view showing basic configuration and light propagation

FIG. 14 is a diagram showing the wavelength dependence of the refractive index of a glass material (BK7).

FIG. 15 is a side view showing a basic configuration of an optical head and a state of light propagation according to a tenth embodiment of the present invention.

FIG. 16 is a graph (normal incidence, wavelength width Δλ = 2 nm) showing the relationship between the period of the diffractive optical element (grating) of the optical head and the diffraction angle difference of the first-order diffracted light in the tenth embodiment of the present invention. Figure

FIG. 17 is a side view showing a basic configuration of an optical head and a state of light propagation according to an eleventh embodiment of the present invention.

FIG. 18 is a side view showing a basic configuration of an optical head and a state of light propagation according to an embodiment of the present invention.

FIG. 19 is a side view showing the configuration of a conventional optical head.

[Explanation of symbols]

 Reference Signs List 1 light source 2 emitted light 3 collimator means 4 objective lens 5 diffractive optical element 6 incident light 7 substrate 8 focus / track error signal detecting optical element 9 refractive optical means 10 diffracted light 11 information recording medium 12 refracted light 13 photodetector 14 refraction Bottom surface of optical means (third surface) 15 Side surface of refractive optical means (second surface) 16 Reflective film 17 Light source / photodetector unit 18 Beam splitter 19 Signal light 20 Start-up mirror 21 Slope of refractive optical means (First surface) )

Claims (28)

[Claims] 1. A diffractive optical element provided in an optical path from a light source to an information recording medium, and a refraction having an optical surface provided in the optical path, on which an optical axis of light emitted from the light source obliquely enters. Optical means, wherein the change in the diffraction angle of the diffracted light from the diffractive optical element due to the wavelength change of the emitted light and the change in the refraction angle of the refracted light from the refraction optical means occur in directions that cancel each other. An optical head, characterized in that: 2. The optical head according to claim 1, wherein said diffractive optical element is integrated with said refractive optical means. 3. The optical head according to claim 1, further comprising: a collimator for making the light emitted from the light source substantially parallel light to be incident on the diffractive optical element. 4. An optical element for detecting a focus / track error signal is provided between the light source and the refractive optical means, and the diffractive optical element is integrated with the optical element for detecting a focus / track error signal. The optical head according to claim 1, wherein: 5. The optical head according to claim 1, wherein the diffractive optical element is a grating having a uniform period. 6. The diffractive optical element, wherein the diffractive optical element is disposed in a convergent light path or a divergent light path, and according to a degree of convergence or a degree of divergence of light incident on the diffractive optical element. 2. The optical head according to claim 1, wherein the period of the optical head differs depending on the location. 7. The optical head according to claim 6, wherein the period is adjusted so as to become larger as it goes from a substantially central portion to an outer peripheral portion of the diffractive optical element. 8. The diffractive optical element has a numerical aperture of 0.39.
The optical head according to claim 1, wherein the optical head is arranged in the following convergent light path or divergent light path, and the period of the diffractive optical element is uniform. 9. The optical head according to claim 8, wherein the diffractive optical element is disposed in an optical path near the light source. 10. The refracting optical means is an optical element having three incident or reflecting surfaces, and the diffractive optical element is formed on at least one of the three surfaces of the refracting optical means. Item 2. The optical head according to item 1. 11. The optical head according to claim 10, wherein said diffractive optical element is of a reflection type, and is formed on a reflection surface of said refractive optical means. 12. The optical head according to claim 1, wherein the refractive optical means is a prism formed of a low-dispersion glass material having three incident or reflected surfaces. 13. The optical head according to claim 12, wherein the Abbe number of the glass material is 50 or more. 14. The refracting optical means is a prism formed of a glass material having a refractive index of n, wherein one of the base angles of the prism is substantially a right angle, and the other of the base angles θ is sin θ = n 2. The optical head according to claim 1, wherein the optical head has an angle θ that substantially satisfies sin (3θ−90 °). 15. The refracting optical means is a prism formed of a glass material having a refractive index n, and one of the base angles θ of the prism is sin (2θ−45 °).
= 1 / n · sin θ, the other of the base angles θ
_2. The optical head according to claim 1, wherein 1 satisfies θ + 85 ° ≦ θ ₁ ≦ θ + 95 °. 16. The optical head according to claim 1, wherein the light source has a plurality of light source units that emit different wavelengths. 17. The device according to claim 16, wherein the diffractive optical element is disposed only in an optical path near a light source unit that emits light of the smallest wavelength among the plurality of light source units.
An optical head according to item 1. 18. The diffractive optical element has a sawtooth cross-sectional shape, and of the different wavelengths, a minimum value is λ ₁ , and a maximum value is λ ₂ ,
When the refractive index of the diffractive optical element is n, the groove depth L of the diffractive optical element is λ ₁ / (n−1) ≦ L ≦ λ ₂ / (n
The optical head according to claim 16, wherein the relationship of -1) is satisfied. 19. The optical head according to claim 18, wherein a groove depth L of the diffractive optical element is substantially (λ ₁ + λ ₂ ) / [2 (n−1)]. 20. The diffractive optical element has a cross-sectional shape having a step shape of p steps, and among the different wavelengths, a minimum value is λ ₁ , and a maximum value is λ ₂ ,
Assuming that the refractive index of the diffractive optical element is n, the groove depth L of the diffractive optical element is (p−1) · λ ₁ / [p · (n−1)].
≦ L ≦ (p-1) · λ 2 / [p · (n-1)] The optical head according to claim 16, characterized in that to satisfy the relationship. 21. The groove depth L of the diffractive optical element is substantially
Above, (p-1) · (λ ₁+ Λ_Two) / [2p (n-1)]
21. The optical head according to claim 20, wherein: 22. The refracting optical means is a prism formed of a glass material having a refractive index n, wherein an installation angle between the bottom surface of the refracting optical means and an installation reference plane is θ _b , If the angle at which the optical axis incident on the prism becomes the installation reference plane is θ _p , one of the base angles θ of the prism is sin (θ−θ _b ) = n
・ Sin (4θ−2θ _b −θ _p −90 ° −θ ′) and n · sin
Claim θ '= sin (θ-θ b) and was substantially satisfied, other angle theta ₁ of the base angles, characterized by satisfying substantially the _{θ 1 = θ + 90 ° -2θ} b -θ p 2. The optical head according to 1. 23. The optical head according to claim 22, characterized in that said theta _b is substantially satisfies _{2 ° ≦ θ b ≦ 10 °} . 24. The refracting optical means is a prism having three optical surfaces, of which the information recording medium side is a first surface,
When the light source side is the second surface and the other is the third surface, the emitted light from the light source is transmitted through the second surface, is reflected in the first surface, the third surface in order, and The optical head according to claim 1, wherein the optical head transmits light through the first surface. 25. A refracting optical unit having a prism having three optical surfaces in an optical path from a light source to an information recording medium, wherein the information recording medium side of the three optical surfaces is a first surface,
When the light source side is the second surface and the other is the third surface, the emitted light from the light source passes through the second surface and the first surface
An optical head which reflects light in the order of a surface and a third surface and transmits the light through the first surface. 26. The wavelength λ of the outgoing light is 0.35 μm
The optical head according to claim 1, wherein ≤? ≤ 0.5 m is substantially satisfied. 27. The optical head according to claim 25, wherein the third surface is parallel to an installation reference surface of the refractive optical unit. 28. An objective lens in an optical path between the information recording medium and the refractive optical means, wherein the outgoing light transmitted through the second surface is most likely to be located with respect to a reference plane for setting the refractive optical means. 26. The optical head according to claim 24, wherein a height of an upper portion is higher than a height of a lowermost portion of the objective lens with respect to the installation reference plane.