JP2001290017A - Two-wavelength diffraction element and optical head device - Google Patents

Abstract

(57) Abstract: Provided is a high-performance optical head device capable of performing stable signal detection using a two-wavelength semiconductor laser. A diffraction grating 11B for diffracting incident light having a wavelength of lambda ₂ while passing through the A wavelength lambda ₁ of the incident light, the two least one polarization state of the transmitted light of wavelength in the wavelength lambda ₁ or wavelength lambda ₂ A two-wavelength diffraction element integrated with the phase plate 11C to be changed is manufactured and mounted on an optical head device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-wavelength diffractive element for an optical head device used in a recording device or a reproducing device for an optical recording medium such as an optical disk using light of at least two wavelengths as a light source, and its light. It relates to a head device.

[0002]

2. Description of the Related Art Information is recorded on an information recording surface of an optical recording medium such as an optical disk such as a CD or a DVD or a magneto-optical disk (hereinafter collectively referred to as an optical disk). Various optical head devices for reproducing recorded information have been used.

Normally, in this optical head device, information is optically recorded on an information recording surface by using a beam (light flux) such as a laser beam, and information recorded on the information recording surface is reproduced. However, in order to trace the beam on the track while following the rotation of the optical disk (with the beam focused on the track on the information recording surface),
Various tracking methods have been developed.

[0004] As a signal detecting method when reproducing the recorded information on the information recording surface using these tracking methods, there are the following methods.
For example, a three-beam method is known. In the three-beam method, one beam emitted from a semiconductor laser as a light source is diffracted by a diffraction grating, and three diffracted lights of the 0th order and ± 1st order among the diffracted lights are used as each beam. .
Of these, the zero-order light is used as a main beam for signal reproduction of pits recorded on the track, while the remaining ± first-order light is used as two tracking sub-beams. It is arranged so that it is irradiated before and after the pit by shifting by about 1/4 of the track pitch. As a result, the reflected lights of the three beams on the information recording surface are respectively incident on the light receiving elements arranged at appropriate positions, and are converted into electric signals corresponding to the intensity of the received light.

In such a three-beam method, a tracking error signal for track tracking servo is obtained by calculating the difference between the average values of the electric signals on the sub-beam side, and the main beam is used by utilizing the tracking error signal. Servo control is performed so as not to deviate from the track. That is, when the main beam is scanning the center of the track, the average level of both sub beams is the same level,
When the main beam deviates from the center of the track, a difference occurs in the average level of the sub-beams, which is detected as a tracking error signal.

As another signal detection method, a beam reflected on an information recording surface is parallel to a track.
There is also known a push-pull method in which a divided light receiving element receives a signal and a tracking error signal is detected from an output difference at this time. In this push-pull method, an offset occurs in the signal with only one beam, and the tracking accuracy deteriorates. Therefore, the differential push-pull method is used to cancel the offset.

That is, even in this differential push-pull method,
1 emitted from the semiconductor laser in the same manner as in the three-beam method described above.
Three beams of 0-order light and ± 1st-order light generated by diffracting this beam with a diffraction grating are used. The 0th-order light of the main beam is arranged on the track, and the ± 1st-order light is 2 beams. The sub-beams are arranged obliquely with respect to the track line direction, and are arranged so as to be shifted vertically by about 1/2 of the track pitch before and after the pit where the main beam is arranged. Then, the reflected light from the information recording surface is received by two divided light receiving elements arranged for each beam, and push-pull of the received light amount in the two light receiving units is performed. In the differential push-pull method, the offset is canceled by subtracting the push-pull value of the main beam and the push-pull value of the sub beam.

Recently, CD / DVD compatible optical head devices have been put into practical use, for example, in order to reproduce information recorded on both CDs and DVDs having different standards and configurations using the same optical head device. I have. In this compatible optical head device, in particular, when the reproduction of a CD-R or the like using a medium having a high wavelength dependency in the optical recording medium layer is assumed,
A semiconductor laser in the 790 nm wavelength band is used for reproducing a CD-based optical disk, and a semiconductor laser of 65 nm is used for reproducing a DVD-based optical disk.
A semiconductor laser having a wavelength band of 0 nm is used.

Here, a conventional optical head device in which a semiconductor laser in the 790 nm wavelength band and a semiconductor laser in the 650 nm wavelength band are arranged separately will be described with reference to the configuration example of FIG.

The optical head device has two semiconductor lasers 3A.
(650 nm wavelength band) and 3B (790 nm wavelength band)
, A wavelength synthesizing prism 9, a beam splitter 4, a collimator lens 5, an objective lens 6, and a photodetector 8. In this optical head device, a diffraction grating 10 for generating three beams is disposed between the semiconductor laser 3B and the wavelength synthesizing prism 9.

In this optical head device, the semiconductor laser 3
Light emitted from A and 3B is combined on the same optical axis α by a wavelength combining prism 9, passes through a beam splitter 4, is converted into parallel light by a collimator lens 5, and enters an objective lens 6. The beam transmitted through the objective lens 6 and condensed on the information recording surface of the optical disk 7 is reflected by the information recording surface (hereinafter referred to as signal light) along the same optical path as the original outward path. Going backwards. That is, this signal light is again converted into parallel light by the objective lens 6, collected by the collimator lens 5, and
The light reflected by the beam splitter 4 travels along the optical axis β deflected by 90 degrees with respect to the optical axis α of the original outward path, and is condensed on the light receiving surface of the photodetector 8. Incident. Then, the light is converted into an electric signal by the photodetector 8.

In the optical head device having such a configuration, the reflected light from the information recording surface becomes return light and becomes the semiconductor laser 3.
When the laser light enters the laser emission points A and 3B, the oscillation state of the laser fluctuates, and the output of the semiconductor lasers 3A and 3B fluctuates accordingly. Therefore, as a countermeasure, the semiconductor lasers 3A, 3B
The power supply is combined with a high-frequency superimposing circuit to reduce output fluctuations, or in the optical path between the semiconductor lasers 3A and 3B and the optical disk 7, a phase that becomes an almost quarter-wave plate with respect to the laser oscillation wavelength λ. A method of arranging the boards has been adopted. By using this phase plate, the phase in the return optical path changes by １ ／ wavelength with respect to the phase in the optical path in the outward path, and the polarization direction of the return light is orthogonal to the polarization direction of the laser oscillation light. And the output fluctuation of the semiconductor laser can be suppressed.

As a semiconductor laser that emits light of two wavelengths, for example, a monolithic two-wavelength semiconductor laser in which a semiconductor laser having a wavelength band of 790 nm and a semiconductor laser having a wavelength band of 650 nm are formed in one chip, A two-wavelength semiconductor laser comprising a plurality of chips in which laser chips in a band are arranged so that the distance between light emitting points is about 100 to 300 μm has also been proposed. When these semiconductor lasers are used, the number of parts is reduced, and the size and cost are reduced as compared with a conventional optical head device in which two semiconductor lasers as shown in FIG. it can.

[0014]

However, in the above-described optical head device, when a diffraction grating used for generating three beams by a three-beam method or a differential push-pull method is used in combination with a two-wavelength semiconductor laser, 7 for CD system playback
Even if light in the 90 nm wavelength band or the 650 nm wavelength band for DVD reproduction is incident on the diffraction grating, the diffracted light is formed, so that extra diffracted light may become stray light and enter the photodetector. This causes a problem that information cannot be recorded or the recorded information cannot be reproduced.

When the three-beam method or the differential push-pull method is used only for reproducing the CD system or only for reproducing the DVD system, the diffracted light generated by the diffraction grating emits the other wavelength light. Causes a light quantity loss, and causes a problem that signal light is reduced.

Further, when the diffraction grating used for the three-beam method or the differential push-pull method and the phase plate provided for reducing the return light in order to suppress the fluctuation of the laser output are individually arranged, Since the wavefront aberration values of the optical elements are summed up, a problem arises that the total wavefront aberration value increases.

When a two-wavelength semiconductor laser is used, the distance between the light emitting points of the laser chips in each wavelength band is 100 to 3
Since they are separated by about 00 μm, there is a problem that a single photodetector having a small light receiving area as in the related art cannot be applied as a photodetector for receiving signals of a CD optical disk and a DVD optical disk.

An object of the present invention is to record / reproduce information on / from different types of optical recording media such as a CD optical disk and a DVD optical disk by using light of two wavelength bands using a semiconductor laser for two wavelengths as a light source. Another object of the present invention is to provide a two-wavelength diffraction element and an optical head device capable of performing stable signal detection.

[0019]

According to the present invention, there is provided a two-wavelength diffraction element to which light of at least one of the wavelengths λ ₁ or λ ₂ (λ ₁ ≠ λ ₂ ) is incident.
As well as transmitted through _the incident light, a diffraction grating for diffracting the other wavelength lambda ₂ of the incident light and changes the polarization state of the transmitted light of at least one wavelength of the two wavelengths lambda ₁ or wavelength lambda ₂ Provided is a two-wavelength diffraction element in which a phase plate is integrated.

Further, the diffraction grating has a periodic cross-sectional shape of a concavo-convex shape, and the phase difference between transmitted light between the concave portion and the convex portion is a wavelength λ.
Providing a diffraction element for two wavelengths is 2π for _one or either of the transmitted light through the wavelength lambda _2.

The diffraction grating transmits incident light in the first linear polarization direction without acting as a diffraction grating,
Provided is a two-wavelength diffraction element that is a polarizing diffraction element made of a birefringent material that acts as a diffraction grating for incident light in a second linear polarization direction orthogonal to the first linear polarization direction.

Further, the phase plate provides a two-wavelength diffraction element which is an organic thin film having a function of converting linearly polarized light having a wavelength λ having a relationship of λ ₁ ≦ λ ≦ λ ₂ into circularly polarized light.

The phase plate has a phase difference of 2π · (m ₁ −1/2) (m ₁ is a natural number) for one linearly polarized light and 2π · m for the other linearly polarized light. Provided is a two-wavelength diffraction element that is an organic thin film that generates a phase difference of ₂ (m ₂ is a natural number).

Further, a light source for emitting light having a wavelength lambda ₁ and wavelength lambda _2, comprising at least an objective lens that focuses the light of the wavelength lambda ₁ and wavelength lambda ₂ to the optical recording medium, the optical recording medium of the information An optical head device for performing recording / reproduction, wherein any one of the above two light sources is provided in an optical path between the light source and the objective lens.
An optical head device provided with a wavelength diffraction element is provided.

[0025]

Embodiments of the present invention will be described below in detail with reference to the drawings.

[First Embodiment] FIG. 1 is a schematic view showing a configuration of a two-wavelength diffraction element according to a first embodiment of the present invention. The two-wavelength diffraction element 1 has a configuration in which a diffraction grating and a phase plate are integrated. This two-wavelength diffraction element 1
Has a three-layer structure in which a first light-transmitting substrate 11A, a phase plate 11C, and a second light-transmitting substrate 11D are bonded to each other with an adhesive 11E.

The translucent substrate 11A in the present embodiment is
The phase plate 11 is made of a transparent material having a uniform refractive index.
Diffraction grating 1 having a uniform refractive index on the surface on the other surface opposite to the surface on which C is bonded (interfacing with air) on the other surface side
1B is formed. The grating depth (thickness) d ₁ of the concave-convex portion of the diffraction grating 11B and the refractive index n ₁ of the convex portion satisfy the following relational expression with respect to the incident light of the wavelength λ ₁ and the wavelength λ _2. Is formed. The phase difference formed by the refractive index difference between the incident light of wavelength λ ₁ and air is 2π · (n ₁ −1) · d ₁ / λ ₁ ≒ 2πN (1) Similarly, the incident light of wavelength λ ₂ The phase difference formed by the refractive index difference between light and air is 2π · (n ₁ −1) · d ₁ / λ ₂ ≠ 2πN (2) where n ₁ is the convex portion of the diffraction grating 11B. The refractive index, N, is a natural number.

The phase plate 11C is made of an organic thin film. For example, a polycarbonate film is stretched to form a birefringent film whose optical axes are aligned in the stretching direction to generate a phase difference function. In this case, when the incident light of the linearly polarized light having the wavelength λ ₁ passes through the organic thin film, the direction of the fast axis (birefringent axis) of the phase plate 11C and the straight line of the incident light are so set that a phase difference of substantially circular polarization is generated. The polarization direction is adjusted.

The diffraction grating 11B is may be processing the surface of the first light-transmitting substrate 11A having a refractive index n ₁ to irregularities, the film having a refractive index n ₁ on the first light-transmissive substrate 11A it may be deposited and processed to form a convex portion in the thickness d _1.

In the two-wavelength diffraction element 1 having the above structure,
When linearly polarized lights having the same polarization direction or orthogonal polarization directions are incident at different wavelengths of the wavelength λ ₁ and the wavelength λ ₂ , FIG.
As shown in FIG. ₁ , the linearly polarized incident light having _one wavelength λ ₁ is transmitted as circularly polarized light without being diffracted.
As shown in the above, a part of the other linearly polarized incident light having the wavelength λ ₂ is diffracted. This linearly polarized incident light of wavelength λ ₂ is
Generally, the light is emitted as elliptically polarized light. In other words, a two-wavelength diffractive element that functions as a diffraction grating for light of one wavelength but does not function as a diffraction grating for light of the other wavelength can be realized.

In this embodiment, the transparent substrate 11A and the transparent substrate 11A having the phase plate 11C and the diffraction grating 11B are formed.
D is bonded using the adhesive 11E, but a configuration in which only the light-transmitting substrate 11A and the phase plate 11C are bonded with the adhesive 11E without using the light-transmitting substrate 11D may be used.
This leads to a reduction in the number of parts and a reduction in weight.

[Second Embodiment] FIG. 2 is a schematic diagram showing a configuration of a two-wavelength diffraction element according to a second embodiment of the present invention. The second embodiment is a modification of the first embodiment.

In the two-wavelength diffraction element 1 of this embodiment, not only is the diffraction grating 11B formed only on the first light-transmitting substrate 11A, but also as shown in FIG. In 1, the diffraction grating 11G having a uniform refractive index is formed on the surface of the second light-transmitting substrate 11D. In this case, the grating depth (thickness) d ₂ of the concave-convex portion serving as the diffraction grating 11G and the refractive index n ₂ of the convex portion satisfy the following relational expression with respect to the incident light of the wavelength λ ₁ and the wavelength λ _2. It is formed so that. The phase difference formed by the refractive index difference between the incident light of wavelength λ ₁ and air is 2π · (n ₂ −1) · d ₂ / λ ₁ ≠ 2πN (3) Similarly, the incident light of wavelength λ ₂ The phase difference formed by the refractive index difference between light and air is 2π · (n ₂ −1) · d ₂ / λ ₂ ≒ 2πN (4) where n ₂ is the convex portion of the diffraction grating 11G. The refractive index, N, is a natural number.

Thus, it is possible to realize a wavelength-selective diffraction grating having a diffraction function for light of different wavelengths. That is, as shown in FIG. 2 (A), to the wavelength lambda ₁ of the incident light, the diffraction grating 11G exerts a diffraction effect can generate the 0-order light and ± 1-order diffracted light. On the other hand, as shown in FIG. 2 (B), to the wavelength lambda ₂ of the incident light, the diffraction grating 1
1B exerts a diffractive action, and can generate zero-order light and ± first-order diffracted light. Here, 11C and 11E in FIG. 2 mean the same elements as those in FIG.

[Third Embodiment] FIG. 3 is a schematic diagram showing a configuration of a two-wavelength diffraction element according to a third embodiment of the present invention. As in the first embodiment, the two-wavelength diffraction element 2 according to the third embodiment is formed by integrating a diffraction grating and a phase plate, and includes a first light-transmitting substrate 21A and a phase plate 21C.
And a second light-transmitting substrate 21D are bonded to each other with a filler 21F and an adhesive 21E.

The first light-transmitting substrate 21A is formed of a translucent material such as a glass substrate, on one surface of the interface is not in contact with the outside (air), an extraordinary refractive with the ordinary refractive index n _o diffraction grating 21B of the transmissive birefringence linear grating is the rate n _e are periodically formed is provided. This diffraction grating 2
1B is made of a birefringent material forming the uneven portion, is in the recess are allowed to fill the filling material 21F of substantially equal refractive index n _s and ordinary refractive index n _o of the birefringent material. Thus, a polarizing diffraction grating is formed that does not diffract incident light of ordinary polarization but diffracts incident light of extraordinary polarization.

Assuming that the grating depth of the concavo-convex portion of the polarizing diffraction grating 21 B is d ₁ , for ordinary polarized incident light,
Since there is no difference in refractive index between the uneven portion and the filler 21F, there is no phase difference, and the light is transmitted straight without being diffracted.
On the other hand, for extraordinary polarized light, the wavelength is set to, for example, λ ₂
When, to generate a phase difference given by _{2π · (n e -n s)} · d 1 / λ 2 ...... (5), it acts as a diffraction grating.

Further, the phase plate 21C is the first embodiment is provided with the same as the phase plate 11C at the two-wavelength diffraction element 1 in the form, the wavelength lambda ₁ of the linear polarization of the incident light organics previously described The direction of the fast axis (birefringence axis) of the phase plate 21C and the direction of the linear polarization of the input light are adjusted so as to generate a phase difference that becomes substantially circularly polarized light when transmitted through the thin film.

The two-wavelength diffractive element 2 having such a configuration has:
The polarization planes of the wavelengths λ ₁ and λ ₂ having different wavelengths are orthogonal to each other, and one of the wavelengths λ ₁
Become light in ordinary polarization, the linearly polarized light and the other wavelength lambda ₂ of the light becomes extraordinarily polarized light is incident from the diffraction grating 21B side, the circularly polarized light without incident light ordinarily polarized light of wavelength lambda ₁ is diffracted The incident light of the extraordinary polarized light of wavelength λ ₂ is partially diffracted. The incident light having the wavelength λ ₂ is generally emitted as elliptically polarized light.

[0040] Incidentally, when the incident light polarization of the wavelength lambda ₁ and wavelength lambda ₂ are parallel, as a phase plate 21C, for example, 2 [pi · (m ₁ -1/2) is with respect to the wavelength lambda ₁ of the linearly polarized light (m ₁ 2 [pi · is a phase difference between natural number), relative to the linearly polarized light of wavelength lambda ₂
An organic thin film having a function of generating a phase difference of m ₂ (m ₂ is a natural number) is used, and a phase plate 21C is arranged on the light incident side and a diffraction grating 21B is arranged on the light emitting side in the two-wavelength diffraction element 2. The preferred configuration is as follows.

In this case, when the wavelengths λ ₁ and λ ₂ whose polarization planes are parallel pass through the phase plate 21C, the polarization plane of the wavelength λ ₁ is rotated by 90 °, but the polarization plane of the wavelength λ ₂ is not rotated. , And enters the diffraction grating 21B as orthogonally polarized light. As a result, a two-wavelength diffractive element that diffracts one incident light but transmits the other incident light without diffracting the incident light having the wavelengths λ ₁ and λ ₂ is obtained.

[Fourth Embodiment] FIG. 4 is a schematic diagram showing a configuration of a two-wavelength diffraction element according to a fourth embodiment of the present invention. The fourth embodiment is a modification of the above-described third embodiment.

In the two-wavelength diffractive element 2 of this embodiment, only the first light-transmitting substrate 21A is provided with a polarizing diffraction grating 21B (grating depth d ₁ ) formed of a birefringent material. In addition, as shown in FIG.
A polarizing diffraction grating 21G made of a birefringent material is provided. This diffraction grating 21G includes a diffraction grating 21B.
Using a birefringent material having the same ordinary refractive index n _o and extraordinary refractive index n _e and but ordinary refractive index direction in the birefringent material is a birefringent material forming the diffraction grating 21B It is formed so as to be orthogonal to the ordinary light refractive index direction. Here, 21D is a translucent substrate.

Accordingly, assuming that the grating depth of the polarizing diffraction grating 21G is d ₂ , for incident polarized light of wavelength λ ₂ ,
Since there is no difference in refractive index between the uneven portion and the filler 21F, there is no phase difference, and the light is transmitted straight without being diffracted.
On the other hand, with respect to the incident polarized light of wavelength lambda _1, to generate a phase difference given by _{2π · (n e -n s)} · d 2 / λ 1 ...... (6), it acts as a diffraction grating.

Thus, it is possible to realize a wavelength-selective diffraction grating having a diffraction function for light of different wavelengths.
That is, as shown in FIG. 4A, only the diffraction grating 21G exerts a diffractive action on the incident light having the wavelength λ ₁ .
On the other hand, as shown in FIG. 4B, only the diffraction grating 21B exerts a diffractive action on the incident light having the wavelength λ ₂ , and can generate the 0th-order light and ± 1st-order diffracted light, respectively.

Although FIG. 4 shows a configuration in which the phase plate 21C and the polarizing diffraction grating 21G are in contact with each other, a separate glass substrate is provided, and the polarizing diffraction grating 21G is formed on one surface thereof. After being integrated with the glass substrate 21A on which the polarizing diffraction grating 21B is formed, the phase plate 21C may be bonded to the light incident side.

[0047] As in the third embodiment, a wavelength lambda ₁ in the case of parallel incident light polarization of the wavelength lambda _2, as a phase plate 21C, for example to the wavelength lambda ₁ of the linearly polarized light 2 [pi · (m ₁
An organic thin film having a function of generating a phase difference of -1/2) (m ₁ is a natural number) and a phase difference of 2π · m ₂ (m ₂ is a natural number) for linearly polarized light of wavelength λ ₂ is used. In the two-wavelength diffraction element 2, the phase plate 21C may be arranged on the light incident side, and the diffraction grating 21B may be arranged on the light emission side. In this case, when the incident light of the wavelengths λ ₁ and λ ₂ having parallel polarization planes is transmitted through the phase plate 21C, the polarization plane of the wavelength λ ₁ is rotated by 90 °, but the polarization plane of the wavelength λ ₂ is not rotated. , And enters the diffraction gratings 21B and 21G as orthogonally polarized light. As a result, a two-wavelength diffraction element is obtained, in which the wavelength λ ₁ is diffracted by the diffraction grating 21G and the wavelength λ ₂ is diffracted independently by the diffraction grating 21B. Here, a phase plate (not shown) is provided on the light emission side of the two-wavelength diffraction element, which further generates a phase difference of substantially circular polarization when incident light of wavelength λ ₁ or λ ₂ is transmitted. Is also good.

[Fifth Embodiment] FIG. 5 is a schematic diagram showing a configuration of a two-wavelength diffraction element according to a fifth embodiment of the present invention. The two-wavelength diffraction element 2A of the fifth embodiment is the same as the two-wavelength diffraction element 1 or 2 of the first to fourth embodiments.
In this embodiment, a deflecting function layer for deflecting only _one of the wavelengths λ ₁ and λ ₂ is added.

When a two-wavelength semiconductor laser is used as a light source, the distance between the light emitting points of the laser chips in each wavelength band is 100 to 100.
Because apart about 300 [mu] m, when align the optical axis of the incident light to the two-wavelength diffraction element, for example, in the light emitting point of the wavelength lambda _1,
The incident light having the wavelength λ ₂ is obliquely incident light off the optical axis. In Figure 5, it is deflected on the same optical axis the wavelength lambda ₁ of the incident light by the diffraction grating 21H to the incident light of wavelength lambda ₂ to be obliquely incident light to form a deflecting function layer, the wavelength lambda ₁ and wavelength lambda ₂ are both the same The light is emitted from the two-wavelength diffraction element as light on the optical axis.

As a specific configuration of the diffraction grating 21H forming the deflecting function layer, a type A having no polarization dependence in the deflecting function is used.
And type B having polarization dependence.

[0051] Type A, the translucent surface of the substrate of uniform refractive index n ₁ at stepwise shape processed diffraction grating for wavelength lambda ₁ and wavelength lambda ₂ of the incident light, staircase one step of the diffraction grating The contact depth d ₁ is formed so as to satisfy the above-mentioned relational expressions (1) and (2). The number of steps is four to eight. Such diffraction grating of the wavelength lambda ₁ light is transmitted without being diffracted and is incident, 5 with respect to the incident wavelength lambda ₂
0% or more is diffracted as a first-order diffracted light in a diffraction angle direction defined by a grating pitch.

Such a type A diffraction grating is formed by the surface of the second light-transmitting substrate 11D in the two-wavelength diffraction element 1 of FIG. 1 or the two-wavelength diffraction element 2 of FIG. 3 or FIG.
Is formed on the surface of the first light-transmitting substrate 21A or the second light-transmitting substrate 21D.

[0053] Type B, the birefringent material of the extraordinary refractive index n _e is formed on a transparent substrate as a periodic grating with sawtooth or stepped at the ordinary refractive index n _o, birefringent material has a sandwich structure by a separate light-transmitting substrate substantially equal to the refractive index n _s and ordinary refractive index n _o of the filler filling the concavo-convex portion of the diffraction grating.

Here, with respect to the ordinary polarized incident light, since there is no difference in refractive index between the birefringent material and the filler, there is no phase difference, and the incident light is transmitted straight without being diffracted. on the other hand,
For extraordinarily polarized incident light, and the wavelength for example, lambda _2,
The grating depth of the stepped diffraction grating is d, and the number of steps is N (N ≧
3) If, by configuring as _{2π · (n e -n s)} · d = {(N-1) / N} · λ grating depth d which is defined by ₂ ... (7), first order A diffraction grating having a phase difference at which the efficiency of folding light becomes 60% or more, that is, a deflection function layer is obtained. The case of a sawtooth blaze grating corresponds to the case where N is infinite.

The diffraction grating made of the type B birefringent material is formed on the phase plate 11C side of the second light-transmitting substrate 11D in the two-wavelength diffraction element 1 shown in FIG. 1 or FIG. Alternatively, in the two-wavelength diffraction element 2 of FIG. 3 or FIG. 4, after being formed on the surface of the first light-transmitting substrate 21A, it is bonded to another light-transmitting substrate using a filler.

In addition, both type A and type B
The diffraction grating, which is shaped like a staircase or blaze, is a so-called hologram pattern in which the grating pitch is spatially distributed or the grating pattern on the translucent substrate surface is not a straight line but a spatial curve. By doing so, the aberration of the optical system may be corrected, or a configuration may be adopted in which a lens function such as light collecting property or diverging property is added.

[0057] As in the third embodiment, FIG. 3 or the incident light polarization of the wavelength lambda ₁ and wavelength lambda ₂ in Fig. 4 are parallel, as a phase plate 21C, with respect to a wavelength lambda ₁ of the linearly polarized light 2 [pi · is Te (m ₁ -1/2) (m ₁ is a natural number) the phase difference of, for the wavelength lambda ₂ of the linearly polarized light 2π · m ₂ (m ₂
With the use of organic thin film having a function of generating a phase difference of a natural number), the phase plate 21C arranged on the light incident side in the diffractive element for two wavelengths, orthogonalization incident light polarization of the wavelength lambda ₁ and wavelength lambda ₂ I do. Thereafter, a configuration in which a diffraction grating made of a type B birefringent material and a deflecting function layer are stacked may be used. In FIG. 5, the type B diffraction grating 21H
2 shows a configuration example in the case where is used.

[Sixth Embodiment] Next, as a sixth embodiment, an optical head device equipped with the two-wavelength diffraction element of the first to fifth embodiments will be described. FIG. 6 is a schematic configuration diagram showing an optical head device according to the sixth embodiment.

An optical head device is used for a DVD-type optical disc.
Wavelength λ₁Laser and CD-based light that generate laser light
Wavelength λ for disk_TwoSemiconductor laser that generates laser light
And two semiconductor lasers integrated with each other.
Wavelength semiconductor laser 3 and two-wavelength diffraction element 1 or 2
, A beam splitter 4, a collimator lens 5, and a pair
It is configured to include an object lens 6 and a photodetector 8, and
Recording of information by irradiating the disk 7 with a laser beam
-It is for regenerating. Here, for example, DVD-based light
Wavelength λ for disk₁To λ₁= 650 nm, CD optical disc
Wavelength λ for disk _TwoTo λ_Two= 790 nm.

In the optical head device thus configured, the light of wavelength λ ₁ emitted from the two-wavelength semiconductor laser 3 travels straight on the optical axis α without being diffracted by the two-wavelength diffraction element 1 or 2. The light passes through the beam splitter 4 and is made into parallel light by the collimator lens 5. Thereafter, the parallel light is transmitted to the optical disk 7 by the objective lens 6.
The light is focused on the information recording track on the (DVD) information recording surface. Then, the light reflected by the information recording surface again passes through the objective lens 6 and the collimator lens 5, is reflected by the beam splitter 4, and travels along the optical axis β deflected by 90 degrees with respect to the optical axis α on the outward path. Are collected on the light receiving surface of the photodetector 8.

On the other hand, with respect to the light of wavelength λ ₂ emitted from the two-wavelength semiconductor laser 3, a part (for example, 10% to 40%) of the incident light is converted into ± first-order diffracted light by the two-wavelength diffraction element 1 or 2. The light is diffracted, further passes through the beam splitter 4, and is made parallel by the collimator lens 5. Thereafter, the parallel light is transmitted to the optical disk 7 (CD system) by the objective lens 6.
0th-order light and ±
The first-order diffracted light is collected as three beams. Then, the light reflected on the information recording surface again passes through the objective lens 6 and the collimator lens 5, is reflected by the beam splitter 4, and is collected on the light receiving surface of the photodetector 8.

As described above, in the case of the optical head device equipped with the two-wavelength diffraction element 1 or 2 of the present embodiment, the wavelength λ ₁
Is transmitted straight without being diffracted by the two-wavelength diffractive element 1 or 2, so that there is no reduction in efficiency and no stray light is generated. Therefore, as an optical detection method for a DVD-based optical disk, a tracking error signal is detected by a heterodyne detection method or a phase difference method, and an optical disk information is detected by an astigmatism method using a general photodetector composed of four divided light receiving surfaces. Detection of a focus signal on a recording surface and detection of a pit signal as recording information can be stably performed.

On the other hand, in the case of a CD optical disk, detection of a focus signal and detection of a pit signal on an optical disk information recording surface by an astigmatism method are performed using the same photodetector having a four-division light receiving surface as in the DVD system. Further, by detecting the ± 1st-order diffracted light on the other two light receiving surfaces of the photodetector, the tracking error signal is detected by the three-beam method.

Further, the linearly polarized light having the wavelength λ ₁ transmitted through the two-wavelength diffraction element 1 or 2 is converted into a phase plate 11C as shown in FIG. 1 or 3 made of an organic thin film having a phase difference generating function.
Or, it becomes circularly polarized light by 21C. Therefore, the return light reflected by the information recording surface and transmitted through the unpolarized beam splitter 4 passes through the two-wavelength diffractive element 1 or 2 again, so that the return light has a linear polarization direction orthogonal to the linear polarization direction of the laser oscillation light. And enter the light emitting point of the semiconductor laser. Therefore, the return light from the optical disk does not interfere with the laser oscillation light, and the oscillation output does not fluctuate, so that information can be stably recorded and reproduced on the optical disk. Similarly, for the light of wavelength λ ₂ , the polarization state of the return light to the two-wavelength semiconductor laser 3 is different from the polarization state of the laser oscillation light. Recording / reproduction of information on an optical disc that has been performed.

Here, when the two-wavelength diffraction element 1 of the first and second embodiments is used as the two-wavelength diffraction element, a diffraction grating independent of the direction of the linearly polarized light of the incident light is formed. There is no restriction on the arrangement of diffraction elements for two wavelengths.
There is a degree of freedom in the configuration that the phase plate 11C may be on the semiconductor laser side with respect to the diffraction grating 11B or vice versa. On the other hand, when the two-wavelength diffraction element 2 of the third and fourth embodiments is used, if the polarization direction of the incident light of the wavelength λ ₁ is orthogonal to the polarization direction of the incident light of the wavelength λ ₂ , only one wavelength is used. Since it becomes a polarizing diffraction grating that acts on, by changing the grating depth of the birefringent material forming it,
There is a degree of freedom to adjust the efficiency ratio between the zero-order transmitted light and the ± first-order diffracted light according to the purpose. In particular, the transmittance of the zero-order light is set to 70
% Is effective for an optical head device for recording, which is preferably set to not less than%.

The grating pitch of the two-wavelength diffraction elements 1 and 2 is appropriately determined according to the optical system of the optical head device on which the diffraction elements are mounted and the tracking method of the optical recording medium. In addition, by using a birefringent material such as polycarbonate having an optical axis aligned in a plane as an organic thin film having a phase difference generating function as a phase plate, the incident angle of incident light can be reduced as compared with a conventional quartz phase plate. Since the phase difference fluctuation due to the difference is small, a constant and uniform phase difference can be generated even in a configuration in which the divergent light is arranged near the semiconductor laser such that it enters the two-wavelength diffraction element. In particular, by bonding two types of phase plates made of organic thin film with aligned optical axes in the plane so that the directions of the two optical axes are at an angle in the plane, the incident light of linearly polarized light in a wide wavelength band can be obtained. even, it is possible to generate a phase difference becomes substantially circularly polarized light, to the wavelength lambda ₁ and wavelength lambda ₂ of the incident light, to reduce the fluctuation of laser oscillation output more effectively, recorded and stable information of the optical disc Can be played.

In FIGS. 1 and 3, the phase plate has a structure in which a polycarbonate birefringent film is fixed to a glass substrate using an adhesive, but an organic thin film having a phase difference generating function is made of glass. The film may be formed directly on the substrate. For example, specifically, by applying a film for an alignment film on a glass substrate, and performing a desired alignment treatment to form an alignment film, and applying a mixed liquid of a liquid crystal and a monomer that is a birefringent material, The optical axis direction of the liquid crystal molecules is aligned with the alignment direction of the alignment film. Further, a photopolymerization curing agent is previously contained in the liquid mixture of the liquid crystal and the monomer, and the monomer is polymerized by irradiating a light source for photopolymerization to form a polymer liquid crystal layer. Without forming a phase plate.

In the above-described embodiment, the configuration in which the two-wavelength diffraction element is applied to the generation of the beam of the three-beam method for the light of the wavelength λ ₂ used in the CD-type optical disk has been described. with respect to the wavelength lambda ₁ of the light used in the differential push-pull method or a DVD family optical disc, it is also effective as a structure which acts as a diffraction grating.

Further, the two-wavelength diffraction element of the second embodiment
1. The surface of the light-transmitting substrate 11A as the light incident surface and the light emitting surface
Waves on both sides of the surface of the transparent substrate 11D.
Long λ ₁Light and wavelength λ_TwoFunction as diffraction grating for only light
The optical data of CD and DVD
We will generate three beams with different specifications according to the disk
You may do it.

Similarly, in the two-wavelength diffractive element 2 of the fourth embodiment, the two-wavelength diffractive element 2 is also provided on the surface of the phase plate 21C opposed to the birefringent material diffraction grating 21B formed on the surface of the translucent substrate 21A. diffraction grating of the refractive material is formed, each provided with a polarizing diffraction grating which functions as a polarization and polarization only the diffraction grating of the wavelength lambda ₂ wavelength lambda _1, in association with the CD system and DVD family optical disc specifications Different three beams may be generated.

In the example of the optical head device shown in FIG. 6, the beam splitter 4 is used, and the unit of the two-wavelength semiconductor laser 3 and the photodetector 8 are separated. Instead of using a hologram beam splitter, the light reflected on the information recording surface is diffracted and separated, and focused on a photodetector located near the semiconductor laser in the two-wavelength semiconductor laser unit. You may comprise. In this case, since the semiconductor laser and the photodetector are arranged in the same unit, the size of the optical head device can be reduced.

In the two-wavelength diffraction element of the fifth embodiment, since a deflection function layer is added, the two-wavelength diffraction element can be used in combination with a two-wavelength semiconductor laser in which the light emitting points in each wavelength band are separated. Even if there is, the emitted light can be handled as a light source emitted from the same light emitting point position. Therefore, when mounted on an optical head device, adjustment of the light source position is simplified and mounting accuracy is improved. Since the two-wavelength diffraction element is a light source device in which the two-wavelength semiconductor laser is fixed at the light emission window position of the package in which the two-wavelength semiconductor laser is disposed, it can be handled in the same manner as a conventional single-wavelength light source. The assembly adjustment of the head device is greatly simplified.

[0073]

EXAMPLES In the following examples, specific examples of the configuration of the above-described embodiment will be described.

Example 1 Example 1 is a specific example of the first embodiment shown in FIG. The first light-transmitting substrate 11A has a refractive index n ₁
Is made of a material having a uniform refractive index of n ₁ = 1.5, and is processed into an uneven shape to form a diffraction grating 11B which forms an interface with air.
Then, the lattice depth d ₁ of the uneven portion is calculated as (n ₁ -1) ·
Let d ₁ be λ ₁ , that is, d ₁ = 1.3 μm. With such a configuration, the incident light having a wavelength of λ ₁ = 650 nm used for a DVD-based optical disc has a phase difference of 2π, while the incident light having a wavelength of λ ₂ = 790 nm used for a CD-based optical disc has The resulting phase difference does not become 2π. Thereby, as shown in FIG. 1 (B), it acts as a diffraction grating for light of wavelength λ ₂ , and as shown in FIG. 1 (A), as a diffraction grating for light of wavelength λ ₁ A wavelength-selective diffraction grating that does not work is obtained.

In this case, the wavelength λ acting as a diffraction grating
The transmittance of the zero-order light is almost 70% for only the incident light of _2.
And the diffraction efficiency of ± 1st-order diffracted light is almost 10%.
A wavelength diffraction element can be configured. Note that the wavelength λ ₁ and the wavelength λ ₁ are provided on the surface of the first light-transmitting substrate 11A on which the diffraction grating 11B forming the interface with air and the surface of the second light-transmitting substrate 11D forming the interface with air are provided. An anti-reflection film is formed to suppress the occurrence of Fresnel reflection to incident light of λ ₂ to 1% or less.

The phase plate 11C is made of polycarbonate.
By stretching the film, the optical axes are aligned in the stretching direction
The phase difference function is generated by forming a birefringent film. This
Here, by adjusting the stretching conditions, specifically,
The fast axis of the phase plate 11C is set to the wavelength λ. ₁For the linear polarization direction of
With the arrangement inclined at 45 °, the wavelength λ₁4 minutes
As a one-wavelength plate. Therefore, this
In the phase plate 11C, for example, the wavelength λ₁Linearly polarized incident light
When transmitted through the phase plate 11C, the light is emitted as circularly polarized light.
You.

Incidentally, the polycarbonate film itself constituting the phase plate 11C is a thin film having a thickness of about 20 μm to 80 μm, and the film thickness distribution cannot be said to be uniform. There is a possibility that the transmitted wavefront aberration of the laser light transmitted through the optical disk varies greatly. Therefore, in this example 1, the polycarbonate phase plate 11C is bonded to the transparent substrate 11A, 11D which is excellent in thickness accuracy and surface accuracy and has little deformation by using an adhesive having substantially the same average refractive index. The transmitted wavefront aberration as the two-wavelength diffraction element 1 can be suppressed to a stable and small value. Specifically, the root-mean-square wavefront aberration value of the light having the wavelengths λ ₁ and λ ₂ was 0.015λ (where λ = λ ₁ or λ ₂ ) or less.

Therefore, the wavelength λ ₁ and the wavelength λ _{2 in} which the linear polarization direction is inclined by + 45 ° or −45 ° with respect to the optical axis of the phase plate 11C are added to the two-wavelength diffraction element 1 having such a configuration.
When the linearly polarized light of different wavelengths are incident, one wavelength lambda ₁
The linearly polarized incident light is straightly transmitted becomes circularly polarized light without being diffracted, but some other linear polarized incident light of wavelength lambda ₂ is is diffracted, becomes elliptically polarized diffracted light efficiency described above Generated and transmitted. That is, it acts as a diffraction grating for light of one wavelength, but does not act as a diffraction grating for light of the other wavelength.

By mounting the two-wavelength diffractive element having such a structure on the optical head device, the structure of the device is simplified, so that the number of components can be reduced and the size can be reduced. For each of the optical discs, a stable recording / reproducing signal having high light use efficiency can be detected.

"Example 2" Example 2 is a specific example of the second embodiment shown in FIG. In addition to the first light-transmitting substrate 11A on which the diffraction grating 11B is formed, the second light-transmitting substrate 11D is made of a uniform refractive index material having a refractive index n ₂ of n ₂ = 1.5. To form a diffraction grating 11G which forms an interface with air. Then, the lattice depth d ₂ of this uneven portion is calculated as (n ₂ −
1) · d ₂ becomes λ ₂ , that is, d ₂ = 1.58 μ
m. With this configuration, the transmittance of the zero-order light for only the incident light having the wavelength λ ₁ = 650 nm is approximately 60%,
A wavelength-selective diffraction grating having a diffraction efficiency of ± 1st-order diffracted light of about 10% is obtained. That is, it is possible to realize a wavelength-selective two-wavelength diffraction element having a diffraction function for light of different wavelengths λ ₁ and λ ₂ .

In this case, as shown in FIG. 2A, the diffraction grating 11G exerts a diffractive action on the incident light having the wavelength λ ₁ , and generates the 0th-order light and ± 1st-order diffracted light. On the other hand, as shown in FIG. 2B, the diffraction grating 11B exerts a diffractive action on the incident light having the wavelength λ ₂ , and generates 0th-order light and ± 1st-order diffracted light. Therefore, by mounting the two-wavelength diffraction element having such a configuration in the optical head device, three beams for signal detection can be generated independently for each of the CD and DVD optical discs. Highly stable recording / reproducing signals can be detected.

Example 3 Example 3 is a specific example of the third embodiment shown in FIG. On one surface of the first light-transmitting substrate 21A, the ordinary refractive index n _o = 1.5, processing the birefringent material of the extraordinary refractive index n _e = 1.65 to irregularities formed comprising polarizing diffraction A grating 21B is provided. Then, the concave portion is filled with a filler 21F substantially equal uniform refractive index n _s and ordinary refractive index n _o of the birefringent material, not diffracted for ordinarily polarized incident light, the extraordinarily polarized incident light On the other hand, a polarizing diffraction grating that diffracts light is formed.

In this configuration, for example, the incident light having a wavelength λ ₁ = 650 nm used for a DVD-based optical disk is made to be ordinary light and the wavelength λ ₂ = 790 nm used for a CD-based optical disk to the polarizing diffraction grating 21B. By making the polarization directions of the wavelength λ ₁ and the wavelength λ ₂ orthogonal to each other so that the incident light of the wavelength corresponds to the extraordinary light, the wavelength λ ₁ does not act as a diffraction grating for the wavelength λ ₁ , but the wavelength λ 1 _For the incident light of No. ₂ , a wavelength-selective diffraction grating acting as a diffraction grating is obtained. Specifically, let the lattice depth d ₁ be d ₁ = 0.92 μ
m, the transmittance of the zero-order light with respect to only the incident light of wavelength λ ₂ = 790 nm is approximately 70%, and ±
A wavelength-selective two-wavelength diffraction element in which the diffraction efficiency of the first-order diffracted light is approximately 10% can be realized.

For example, when the two-wavelength diffraction element 2 having the structure of the third embodiment is used in an optical head device, a two-wavelength semiconductor laser comprising two laser chips for emitting a wavelength λ ₁ and a wavelength λ ₂ respectively. In general, since the emitted light from the semiconductor laser is linearly polarized light, each laser chip may be mounted on the base such that the polarization directions of the wavelengths λ ₁ and λ ₂ are orthogonal to each other.

In the case where a two-wavelength semiconductor laser that emits light with the polarization directions of the wavelengths λ ₁ and λ ₂ aligned in the same direction is used, the two-wavelength semiconductor laser and the two-wavelength diffraction element 2 are used.
A phase plate or a rotator that rotates the polarization plane of light of _one of the wavelengths λ ₁ and λ ₂ by 90 ° and does not rotate the polarization plane of the light of the other wavelength is disposed between them. Good.
For example, for light of wavelength λ ₁ = 650 nm, 5 /
If a phase plate serving as a two-wave plate is used, the wavelength λ ₂ = 790 n
For light with a wavelength of m, it becomes almost a 4/2 wavelength plate,
The polarization direction of the outgoing light of wavelength λ ₁ transmitted through the phase plate is 90 °
Rotates, but the polarization direction of the emitted light having a wavelength lambda ₂ does not rotate. Therefore, the emitted lights of wavelengths λ ₁ and λ _{2 have} polarization directions orthogonal to each other.

Further, instead of the above-mentioned phase plate, a polarization direction switching element capable of switching the rotation direction between 0 ° and 90 ° by applying a voltage may be used. As a configuration in this case, for example, a transparent electrode and an orthogonal alignment film are formed on each side of a pair of glass substrates, and after forming a cell, a nematic liquid crystal is injected to form a twisted nematic liquid crystal element. Then, when the voltage application between the transparent electrodes of the liquid crystal element is turned on / off, a polarization direction switching element for rotating the linear polarization direction of the incident light by 90 ° can be formed. If such an element is arranged between the semiconductor laser and the two-wavelength diffractive element 2, for example, the voltage is turned off for light incident at a wavelength of λ ₁ and the polarization direction is not changed. _With respect to the light of the _second wavelength, the polarization direction can be switched by turning on the voltage to change the polarization direction.

Example 4 Example 4 is a specific example of the fourth embodiment shown in FIG. In addition to the diffraction grating 21B provided on the first translucent substrate 21A, the phase plate 21C is provided with a polarizing diffraction grating 21G formed of a birefringent material. In this case, uses a birefringent material having a diffraction grating 21B and the same ordinary refractive index n _o = 1.5 and an extraordinary refractive index n _e = 1.65, the ordinary refractive index direction in the birefringent material Are formed so as to be orthogonal to the ordinary light refractive index direction of the birefringent material forming the diffraction grating 21B. That is, with respect to the incident polarized light having a wavelength lambda ₁ used in the DVD-based optical disc, a diffraction grating 2
It is a 1B In the ordinary refractive index n _o, a diffraction grating 21G In extraordinary refractive index n _e. On the other hand, with respect to the incident polarized light having a wavelength lambda ₂ used in the CD system optical disk, the polarization diffraction grating 21
In B, the extraordinary light refractive index _ne is used.
In 1G the ordinary refractive index n _o.

Therefore, for incident polarized light of wavelength λ ₂ , there is no difference in refractive index between the uneven portion of the diffraction grating 21 G and the filler 21 F, so that there is no phase difference and the light does not act as a diffraction grating and goes straight. To Penetrate. On the other hand, with respect to the incident polarized light of wavelength lambda _1, and generates a phase difference represented by the equation (6), it acts as a diffraction grating. Specifically, by setting the grating depth d ₂ of the polarizing diffraction grating 21G to d ₂ = 0.78 μm, the transmittance of the zero-order light is substantially reduced for only the incident light having the wavelength λ ₁ = 650 nm. 70%, and a wavelength-selective diffraction grating having a diffraction efficiency of ± 1st-order diffracted light of about 10% is obtained. That is, it is possible to realize a wavelength-selective two-wavelength diffraction element having a diffraction function for light of different wavelengths λ ₁ and λ ₂ .

In this case, as shown in FIG. 4 (A), only the diffraction grating 21G exerts a diffractive action on the incident light having the wavelength λ ₁ , while the wavelength as shown in FIG. λ ₂
Only the diffraction grating 21B exerts a diffractive action on the incident light of, and 0th-order light and ± 1st-order diffracted light are generated, respectively. Therefore, by mounting the two-wavelength diffraction element having such a configuration on the optical head device, the CD system and the DV
Since three beams for signal detection can be generated independently for each optical disk of the D system, a stable recording / reproducing signal with high light use efficiency can be detected.

[0090] In this Example 4, as compared to the two-wavelength diffraction element 1 of Example 2 described above (see FIG. 2), used in the wavelength lambda ₁ of the incident light and the CD-type optical disk used in the DVD family optical disc Since the transmission efficiency of the 0th-order light and the diffraction efficiency of the ± 1st-order diffracted light of the incident light having the wavelength λ ₂ can be set independently and to arbitrary values, it can be easily applied to various optical system configurations of the optical head device. Applicable.

Example 5 Example 5 is a modified example in which the configuration of the phase plate is changed in the two-wavelength diffraction elements 1 and 2 of Examples 1 to 4 described above.

In the two-wavelength diffraction elements 1 and 2, two types of organic thin films having a phase difference generating function used as the phase plate 11C or 21C are laminated to obtain a wavelength λ.
_A phase plate, which is a quarter-wave plate for both ₁ = 650 nm and λ ₂ = 790 nm, is formed (not shown).

More specifically, for example, a polycarbonate film phase plate X having a retardation value of 180 nm and a polycarbonate film phase plate Y having a retardation value of 360 nm form an angle of approximately 60 ° in the fast axis direction. As described above, an integrated laminated phase plate is attached by bonding with an adhesive. That is, when forming the laminated phase plate, the fast axis is set to a direction intermediate between the fast axis directions of the phase plate X and the phase plate Y, and the incident polarization directions of the wavelength λ ₁ and the wavelength λ ₂ are set. The laminated phase plate is fixed to a transparent substrate such as a glass substrate with an adhesive so that the fast axis forms an angle of 45 °.

By mounting the two-wavelength diffractive element having the phase plate having such a structure on the optical head device, the wavelength λ ₁ and the wavelength λ ₂ which are reflected on the information recording surface of the optical disk and enter the semiconductor laser are returned. The light does not affect the laser oscillation state because the polarization direction of each light is orthogonal to the polarization direction of the laser emission light. Thus, also be suppressed variation of lasing intensity for any of the laser beam having a wavelength lambda ₁ and wavelength lambda _2, it is stable recording and playback.

Example 6 Example 6 is a specific example of the fifth embodiment shown in FIG. On one surface of the first light-transmitting substrate 21A, the ordinary refractive index n _o = 1.5, extraordinary refractive index n _e = 1.65 of the birefringent material is processed and formed into 8-step staircase shape formed by polarization Diffraction grating 21H is provided. Further, the second light-transmitting substrate 2
1D is provided with a polarizing diffraction grating 21G formed by processing the same birefringent material into a concave and convex rectangular shape. Here, the diffraction grating 21H acts as the ordinary refractive index n _o with respect to ordinary light polarized incident light, the diffraction grating 21G is orientation axis direction of the birefringent material to act as extraordinary refractive index n _e is perpendicular It has a configuration. Next, the first light-transmitting substrate 21A and the second
Of the birefringent material with the ordinary light refractive index n _o = 1.5
The concave portion of the diffraction grating is filled with a filler 21F having a uniform refractive index n _s substantially equal to.

Further, an organic thin film having a phase difference generating function is used as the phase plate 21C, and the phase plate 21C is fixed to one surface of the first light-transmitting substrate 21A with an adhesive 21E.
Here, the phase plate 21 </ b> C forms a birefringent film by stretching a polycarbonate film in the same manner as in Example 1 to generate a phase difference function. The phase plate 21C has a wavelength λ ₁ = 650 n
The birefringence is such that the phase difference for incident light of m is 5π, and the phase difference for incident light of wavelength λ ₂ = 790 nm is approximately 4π.
It has become. Further, a polarizing diffraction grating 21B formed by processing the same birefringent material into an uneven rectangular shape is provided on the third translucent substrate 21K. Here, the diffraction grating 21B is set to the orientation axis direction of the birefringent material that acts as the ordinary refractive index n _o with respect to ordinary light polarized incident light. The polarizing diffraction grating 21B and the diffraction grating 21G have the same configuration and operation as described in Example 4. The concave diffraction grating 21B is filled with a filler 21I substantially equal uniform refractive index n _s and ordinary refractive index n _o of the birefringent material.

When the extraordinary light having the wavelength λ ₁ is incident on the two-wavelength diffraction element 2A having such a configuration, the polarization plane is rotated by 90 ° after passing through the phase plate 21C to become ordinary light polarization, and the diffraction grating 21H and the diffraction grating 21B. Are diffracted only by the diffraction grating 21G to generate 0th-order light and ± 1st-order diffracted light. On the other hand, when extraordinary light polarized light of wavelength λ ₂ is incident, since the plane of polarization does not rotate after transmission through the phase plate 21C, it is diffracted by the diffraction grating 21H and the diffraction grating 21G with the extraordinary light polarized, and is not diffracted by the diffraction grating 21B.

[0098] Here, when the average grating pitch of the diffraction grating 21H polarizing and 28 .mu.m, the wavelength for nearly 80% of the wavelength lambda ₂ of the extraordinarily polarized light incident to tilt theta = 1.6 ° optical axis direction lambda _It functions as a deflecting function layer that deflects by first-order diffraction in the same optical axis direction as 1. That is, the wavelength λ arranged at a distance of 100 μm from the laser emission point of the wavelength λ _{1 on} a surface approximately 3.6 mm away from the surface on which the diffraction grating 21H is formed.
_The light emitted from the laser emission point _{No. 2} is deflected to the same axis as the light emitted from the laser emission point having the wavelength λ1.

When a linear diffraction grating having a spatially uniform grating pitch is used, since the first-order diffracted light has an aberration such as coma, the phase distribution of the first-order diffracted light is reduced so that no aberration occurs. A hologram grating pattern in which the in-plane grating pattern shape is spatially distributed so as to add a pattern is used. Furthermore, it may be a hologram grating pattern for correcting the chromatic aberration of the optical system due to difference in wavelengths of lambda ₁ and wavelength lambda ₂ when necessary. In addition, as in the case of Example 4, each of the CD- and DVD-based disks is independently used for signal detection by the polarizing diffraction grating 21B and the diffraction grating 21G.
Generate a beam. In FIG. 5, a polarizing diffraction grating 21H,
Although the configuration example in which the diffraction grating 21B, the diffraction grating 21G, and the phase plate 21C are integrated has been described, the individual diffraction elements may be individually manufactured and then used in combination.

In the sixth embodiment, compared to the two-wavelength diffractive element 2 of the fourth embodiment (see FIG. 4), the CD system and the DVD are used.
Even when a laser chip for each wavelength band of the system uses a two-wavelength semiconductor laser in which the light emitting points are spaced apart from each other, most of light of one wavelength is deflected by the deflection function layer, and consequently the same. The light source device emits light of two wavelengths from the light emitting point. As a result, signals from a CD optical disk and a DVD optical disk can be received by a single photodetector having a small light receiving area as in the related art, so that downsizing and high-speed response of the optical head device can be realized.

As described above, according to the two-wavelength diffraction element of this embodiment, the diffraction grating function of generating three or more beams for a specific wavelength without deteriorating the wavefront aberration, and the incidence of linearly polarized light An optical element having both a phase plate function of converting light into circularly polarized outgoing light can be realized by a single element, and downsizing by reducing the number of components can be achieved.

Also, by mounting the two-wavelength diffraction element of this embodiment on an optical head device, it is possible to use a two-wavelength semiconductor laser as a light source, and to simplify the configuration of the optical system and the light source. The number of parts can be reduced and the size can be reduced. In addition, when recording / reproducing a signal to / from a plurality of types of optical disks such as a CD optical disk and a DVD optical disk, for example, the light use efficiency is high,
Moreover, stable signal detection can be performed, and high recording / reproducing performance can be realized.

[0103]

As described above, according to the present invention, 2
When recording / reproducing information on / from different types of optical recording media such as CD-based optical discs and DVD-based optical discs using light in two wavelength bands using a semiconductor laser for wavelength as a light source, two wavelengths that can perform stable signal detection. Diffraction element and an optical head device using the same can be realized.

[Brief description of the drawings]

FIG. 1 shows a configuration of a two-wavelength diffraction element according to a first embodiment of the present invention, where (A) is a schematic diagram showing an optical path of incident light of one wavelength, and (B) is another wavelength. FIG. 3 is a schematic diagram showing an optical path of incident light of FIG.

FIG. 2 shows a configuration of a two-wavelength diffraction element according to a second embodiment of the present invention, where (A) is a schematic diagram showing an optical path of incident light of one wavelength, and (B) is another wavelength. FIG. 3 is a schematic diagram showing an optical path of incident light of FIG.

FIGS. 3A and 3B show a configuration of a two-wavelength diffraction element according to a third embodiment of the present invention, wherein FIG. 3A is a schematic diagram showing an optical path of incident light of one wavelength, and FIG. FIG. 3 is a schematic diagram showing an optical path of incident light of FIG.

FIGS. 4A and 4B show a configuration of a two-wavelength diffraction element according to a fourth embodiment of the present invention, in which FIG. 4A is a schematic diagram showing an optical path of incident light of one wavelength, and FIG. FIG. 3 is a schematic diagram showing an optical path of incident light of FIG.

5A and 5B show a configuration of a two-wavelength diffraction element according to a fifth embodiment of the present invention, wherein FIG. 5A is a schematic diagram showing an optical path of incident light of one wavelength, and FIG. FIG. 3 is a schematic diagram showing an optical path of incident light of FIG.

FIG. 6 is a schematic configuration diagram illustrating an optical head device according to a sixth embodiment of the present invention.

FIG. 7 is a schematic configuration diagram showing a configuration example of a conventional optical head device.

[Explanation of symbols]

1, 2, 2A 2-wavelength diffraction element 3 2-wavelength semiconductor laser 4 beam splitter 5 collimator lens 6 objective lens 7 optical disk (optical recording medium) 8 photodetector 11A, 21A, 11D, 21D, 21K translucent substrate ( Glass substrate) 11B, 11G Diffraction grating 11C, 21C Phase plate 11E, 21E Adhesive 21B, 21G, 21H Polarizing diffraction grating 21F, 21I Filler

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masahiro Murakawa 1-8 Machiikedai, Koriyama-shi, Fukushima Prefecture Second industrial park in Koriyama Asahi Glass Koriyama Electric Materials Co., Ltd. F-term (reference) 2H049 AA03 AA13 AA45 AA57 AA64 AA66 BA03 BA07 BA42 BB05 BB42 BB62 BC03 BC21 5D119 AA20 AA41 AA43 BA01 CA16 EC41 EC45 EC47 EC48 FA05 FA08 JA22 JA27 JA32

Claims (6)

[Claims] 1. A two-wavelength diffraction element to which light of at least one of the wavelengths λ ₁ or λ ₂ (λ ₁ ≠ λ ₂ ) is incident, wherein the incident light of the _one wavelength λ ₁ is transmitted. a diffraction grating for diffracting the other wavelength lambda ₂ of the incident light, that the two phase plates, changing at least one of the polarization state of the transmitted light of wavelength in the wavelength lambda ₁ or wavelength lambda ₂ are integrated A diffraction element for two wavelengths, characterized in that: 2. The diffraction grating according to claim 1, wherein a cross-sectional shape of the diffraction grating is a periodic uneven shape, and a phase difference between transmitted light of the concave and convex portions is 2π with respect to transmitted light of either the wavelength λ ₁ or the wavelength λ _2. The two-wavelength diffraction element according to claim 1, wherein 3. The diffraction grating transmits the incident light in the first linear polarization direction without acting as a diffraction grating, and transmits the incident light in a second linear polarization direction orthogonal to the first linear polarization direction. 2. The two-wavelength diffraction element according to claim 1, wherein the diffraction element is a polarizing diffraction element made of a birefringent material acting as a diffraction grating. 4. The method according to claim 1, wherein the phase plate is an organic thin film having a function of converting linearly polarized light having a wavelength λ having a relationship of λ ₁ ≦ λ ≦ λ ₂ into circularly polarized light. Diffraction element for wavelength. 5. The phase plate has a phase difference of 2π · (m ₁ −1/2) (m ₁ is a natural number) for one linearly polarized light and 2π · m for the other linearly polarized light. 4. An organic thin film which generates a phase difference of ₂ (m ₂ is a natural number).
The diffraction element for two wavelengths according to 1. A light source 6. A for emitting light having a wavelength lambda ₁ and wavelength lambda _2, comprising at least an objective lens that focuses the light of the wavelength lambda ₁ and wavelength lambda ₂ to the optical recording medium, the optical recording medium of the information An optical head device for performing recording / reproduction, wherein the two-wavelength diffraction element according to any one of claims 1 to 5 is provided in an optical path between the light source and the objective lens. Optical head device.