JP4591602B2 - Wavelength selective diffraction element and optical head device - Google Patents

Description

  The present invention relates to a wavelength-selective diffractive element and an optical head device, and more particularly to a wavelength-selective diffractive element on which light of two different wavelengths is incident and an optical head device equipped with the wavelength-selective diffractive element.

  Information is recorded on or reproduced from an information recording surface of an optical recording medium such as an optical disc such as a CD or DVD, or an optical recording medium such as a magneto-optical disc (hereinafter collectively referred to as “optical disc”). Various optical head devices are used. In these optical head devices, diffractive elements are used in various applications.

In the optical head device, since the optical disk is rotated while condensing the laser beam on the track formed on the information recording surface of the optical disk, it is necessary to prevent the focused laser beam from coming off the track. For this reason, various tracking methods have been developed. Among these tracking methods, the three-beam method used when reproducing information is well known. Also, a push-pull method used for recording information, that is, a method of receiving reflected light from an optical disk using a light receiving element divided in two parallel to a track and taking a difference between the two divided reflected lights, particularly canceling an offset of a signal. The differential push-pull method for this is well known.
The three-beam method and the differential push-pull method are common in that a diffractive element is used and a main beam that is 0th-order diffracted light and a sub-beam that is ± 1st-order diffracted light are generated.

  2. Description of the Related Art In recent years, CD and DVD compatible optical head devices (hereinafter referred to as compatible optical head devices) have attracted attention for recording or reproducing information on both CD and DVD optical discs having different standards and configurations. In this compatible optical head device, a 790 nm wavelength semiconductor laser is used for reproduction in the case of an optical disc that is premised on information reproduction in a CD system such as a CD-R. In the case of a DVD optical disk, a semiconductor laser having a wavelength of 650 nm is used for reproduction.

  A first conventional optical head device in which two semiconductor lasers are separately disposed will be described with reference to the configuration example of FIG. Light emitted from the semiconductor lasers 3A and 3B is synthesized on the same optical axis by the wavelength synthesis prism 9, and after passing through the beam splitter 4, is converted into parallel light by the collimator lens 5, and after passing through the objective lens 6, the optical disc 7 Is condensed on the information recording surface. The condensed light is reflected by the information recording surface, and the reflected light travels backward along the same optical path as the forward path.

That is, the reflected light becomes parallel light again by the objective lens 6, is condensed by the collimator lens 5, and then enters the beam splitter 4. The light reflected by the beam splitter 4 travels along an optical axis that forms an angle of 90 ° with the optical axis of the forward path, and is collected on the light receiving surface of the photodetector 8. The signal light is converted into an electric signal by the photodetector 8. In FIG. 9, a three-beam generating diffraction grating 10 is used for light in the wavelength band of 790 nm (hereinafter also referred to as λ ₂ ).

In such an optical head device, a semiconductor laser for emitting light of two wavelengths, for example 790 nm (hereinafter also referred to as lambda ₁₎ semiconductor laser and 650nm wavelength band monolithic a semiconductor laser having a wavelength band formed in one chip Two-wavelength semiconductor lasers have been proposed. Further, a two-wavelength semiconductor laser composed of a plurality of chips in which laser chips of each wavelength band are arranged so that the distance between the light emitting points is about 100 to 300 μm has been recently proposed. If these semiconductor lasers are used, the number of parts can be reduced as compared with the conventional optical head device in which the two semiconductor lasers shown in FIG. 9 are separately configured, and the size and cost of the device can be reduced. Therefore, a three-beam generating diffraction grating corresponding to a two-wavelength semiconductor laser is strongly desired.

  The optical head apparatus of the 2nd prior art example in which the diffraction element is used is shown. In an optical head device that records information on an optical disk, light emitted from a semiconductor laser is reflected by the optical disk to become return light, and this light is guided to a light receiving element that is a photodetector using a beam splitter. As this beam splitter, a hologram diffraction element (hologram beam splitter) is used.

Figure 11 shows a schematic of a conventional compatible optical head device using a hologram beam splitter ((if for emitting light of a) lambda ₁ wavelength band, to emit light (b) lambda ₂ wavelength band). Light emitted from the semiconductor laser 3 that emits light in the 650 nm wavelength band and light in the 790 nm wavelength band is converted into parallel light by the collimator lens 5 and is condensed on the surface of the optical disk 7 by the objective lens 6. The reflected light from the optical disc 7 passes again through the objective lens 6 and the collimating lens 5, and is then passed through the photodetector 8A (FIG. 11B) or 8B (FIG. 11A) by the hologram beam splitter 11. It reaches the constituent light receiving element. The light receiving element converts the received reflected light into an electric signal, the electric signal is amplified by an amplifier, and further gain is applied by an automatic gain correction circuit to adjust the signal level within a certain range. However, the amplifier and the automatic gain correction circuit are not shown in FIG.

On the other hand, as a diffraction element compatible with CD and DVD, Patent Document 1 discloses that an optical path difference for one incident light is an integral multiple of the wavelength and an optical path difference for the other incident light is a non-integer of the wavelength. A doubled wavelength selective diffractive element is described. This will be described below. In general, the diffraction efficiency of a two-level (rectangular) diffraction grating in which peaks and valleys appear alternately is approximated by the following equation, where λ is the wavelength and R is the optical path difference. Here, η ₀ represents the zero-order diffraction efficiency, η _m represents the m-order diffraction efficiency, and m is an integer other than zero.

Here, when the optical path difference for one incident light is an integral multiple of the wavelength, η ₀ = 1 and η _m = 0 from the above equation. Furthermore, if the optical path difference with respect to the other incident light is a non-integer multiple of the wavelength, a wavelength-selective diffraction element that satisfies 0 <η ₀ <1 and 0 <η _m <1 can be obtained.

  Although the case of a two-level diffraction element has been described here, the optical path difference of one level (step) is an integral multiple of the wavelength for one incident light and a non-integer of the wavelength for the other incident light. As long as the condition of double is satisfied, a wavelength-selective diffraction element can be obtained even in a multi-level grating shape, particularly a pseudo-blazed grating shape.

Hereinafter, an example of a conventional optical head device using this wavelength selective diffraction element will be described.
FIG. 13 shows a third conventional optical head device in which the wavelength selective diffraction element is used as an aperture limiting element. The aperture limiting element 18 is made of a glass substrate such as synthetic quartz glass, and FIG. 12 shows an example of the configuration of a conventional wavelength selective diffraction element used as the aperture limiting element. As shown in FIG. 12, only in the periphery of the aperture limiting element 18 is a diffraction grating whose optical path difference is twice the wavelength λ ₁ of the DVD system. At that time, since the optical path difference is approximately 1.6 times the wavelength λ ₂ of the CD system, light having a wavelength of λ ₁ can be transmitted and 70% or more of light having a wavelength of λ ₂ can be diffracted. In FIG. 12, the grating surface of the diffraction grating is divided into two parts because the light diffracted in both the forward path and the return path travels along the same optical path as the non-diffracted transmitted light and is condensed on the photodetector. This is to prevent it.

As shown in FIG. 13, the emitted light from the semiconductor lasers 3A and 3B is synthesized on the same optical axis by the wavelength synthesis prism 9, and after passing through the beam splitter 4, becomes collimated light by the collimator lens 5 and becomes an aperture limiting element. 18 is incident. The light of λ ₁ is transmitted without being diffracted at the peripheral part (shaded part in FIG. 12B) and the central part (inside the circle in FIG. 12B) of the aperture limiting element 18, and the DVD system is transmitted by the objective lens 6. The optical disc 7 is focused on the information recording surface (FIG. 13A).

Further, the light of λ ₂ is diffracted at the peripheral portion of the aperture limiting element 18 and only the light transmitted through the central portion is condensed on the information recording surface of the optical disc 7 with a small numerical aperture (FIG. 13B). The reflected light from the optical disk passes through the objective lens 6, the aperture limiting element 18, and the collimating lens 5 again and then enters the beam splitter 4. The light reflected by the beam splitter 4 travels along an optical axis that forms an angle of 90 ° with the optical axis of the forward path, and is collected on the light receiving surface of the photodetector 8. The signal light is converted into an electric signal by the photodetector 8. Although omitted in FIG. 13B, the light of λ ₂ diffracted by the aperture limiting element 18 is also collected on the information recording surface of the optical disc 7 and reflected, and then the same optical path as the signal light. The light is focused on a portion of the photodetector 8 that is different from the light receiving surface.

FIG. 15 shows a fourth conventional optical head device in which a wavelength-selective diffraction element is used as a wavelength-selective deflecting element. The wavelength selective deflection element is made of a glass substrate such as synthetic quartz glass, and as shown in FIG. 14 which is another example of the configuration of the conventional wavelength selective diffraction element, the optical path difference R of one level (step). is but equal to the wavelength lambda ₁ of DVD system, shown lattice of 5-7 multilevel pseudo blazed diffraction grating 19 level (4-6 steps) are formed (FIG. 14 6 level (5-stage) But not limited to this number of levels).

At this time, light having a wavelength of λ ₁ is transmitted without being diffracted, and light having a wavelength of λ ₂ can be diffracted by one diffraction order by 60% or more and deflected.
As shown in FIG. 15, the emitted light of wavelength λ ₁ (FIG. 15A) emitted from one light emitting point of the two-wavelength semiconductor laser 3 and the wavelength λ ₂ emitted from a different light emitting point. The outgoing light (FIG. 15B) passes through the beam splitter 4, becomes parallel light by the collimating lens 5, and is condensed on the information recording surface of the optical disk 7 by the objective lens 6.

The reflected light from the optical disk 7 passes through the objective lens 6 and the collimating lens 5 again and then enters the beam splitter 4. The light reflected by the beam splitter 4 has an angle of 90 ° with the optical axis of the forward path. The light travels along the optical axis and enters the wavelength selective deflecting element 19. The light of wavelength λ ₁ incident on the wavelength selective deflecting element 19 is transmitted without being deflected by the wavelength selective deflecting element 19 and then condensed on the light receiving surface of the photodetector 8 (FIG. 15A). ). On the other hand, the light of wavelength λ ₂ incident on the wavelength selective deflection element 19 is deflected by the wavelength selective deflection element 19 and then collected on the light receiving surface of the same photodetector as the light detector 8 of wavelength λ _1. It is illuminated (FIG. 15 (b)).

  However, in the case of the optical head device of the first conventional example, that is, when the diffraction element for generating three beams used in the three-beam method or the differential push-pull method is used in combination with the two-wavelength semiconductor laser, the following problems occur. appear. That is, the diffractive element generates a diffracted light with a diffractive effect with respect to any incident light in the 790 nm wavelength band for CD optical disks and the 650 nm wavelength band for DVD optical disks. As a result, unwanted unwanted diffracted light becomes stray light and enters the photodetector, making it impossible to record or reproduce information. In addition, the diffraction grating provided for generating three beams of incident light for one optical disk diffracts the incident light for the other optical disk to generate unnecessary diffracted light, resulting in loss of light quantity and reducing signal light. Will occur.

  As a method for solving this problem, as described above, in Patent Document 1, the optical path difference is set to an integral multiple of the wavelength of one incident light, and the optical path difference of the other incident light is set to the wavelength. It describes that a wavelength-selective diffraction element having a non-integer multiple is formed. However, the condition that the optical path difference is an integral multiple of the wavelength of incident light in one wavelength band is satisfactory because it reduces the degree of design freedom for the other wavelength and the degree of freedom in selecting diffraction efficiency. It was not a thing.

  In the case of the optical head device of the second conventional example, that is, when the hologram beam splitter is used in combination with a monolithic two-wavelength semiconductor laser, the following problem occurs. That is, when light having a wavelength λ is incident on a hologram beam splitter composed of a diffraction element having a grating pitch P, sin θ is proportional to λ / P, where θ is the diffraction angle of the light. For this reason, the 650 nm wavelength band and the 790 nm wavelength band have different wavelengths, so the diffraction angles are different, and it is necessary to enlarge the light receiving area when receiving the diffracted light with the same photodetector.

  When the size is increased, there is a problem that high-frequency characteristics are deteriorated and the optical disk cannot be reproduced at high speed. In addition, when each light receiving surface of the photodetector is formed for light in the 650 nm wavelength band and the 790 nm wavelength band, the number of light receiving elements increases twice, and this increases the complexity of the signal processing circuit. .

As a method for solving this problem, Patent Document 2 discloses that a diffraction grating having an optical path difference equal to the wavelength λ _{1 of the} DVD system and a surface different from the substrate surface on which the diffraction grating is formed have an optical path difference of the CD system. Is formed to form a diffraction grating having the same wavelength λ ₂ and detect a signal with the same small photodetector.

However, the above-described diffraction efficiency formula is an approximation formula that is established only when the pitch of the diffraction grating is considered to be very large compared to the optical path difference of the diffraction grating, and the optical path difference of the grating becomes large, or As the pitch becomes smaller, the approximate expression no longer holds. Even if the optical path difference is set to n times the wavelength (n is a natural number), that is, in the above equation, η ₀ = 1 and η _m = 0, the actual condition does not satisfy η ₀ = 1, or η _m = It may not be zero. The fact that the above approximate expression does not hold is called a resonance phenomenon of the diffraction grating, and as the grating pitch becomes smaller or the optical path difference becomes larger, the approximate expression becomes more inconspicuous.

  Usually, the grating pitch of the hologram beam splitter is as small as 5 μm or less, and the grating pitch is small compared to the optical path difference. Therefore, there is a problem that the transmittance of the wavelength to be transmitted is lowered due to the resonance phenomenon described above.

Further, in the case of the optical head device of the third conventional example, in order to prevent unnecessary light of wavelength λ ₂ diffracted by the aperture limiting element from entering the signal detecting light receiving element. It is necessary to reduce the pitch of the diffraction grating and increase the diffraction angle of the diffracted light. However, as described above, when the pitch of the diffraction grating is reduced, the transmittance of light having a wavelength of λ _{1 to be} transmitted is reduced, and the characteristics as an aperture limiting element are deteriorated.

Further, in the case of the fourth conventional example of an optical head apparatus, transmits light of the wavelength lambda _1, in order to diffract the light of the wavelength lambda ₂ it is necessary to increase the number of levels of the pseudo blazed diffraction grating and 5-7 was there. If the number is increased, the total optical path difference becomes as long as 4 to 6 times the wavelength λ ₁ , so that the transmittance of light having the wavelength of λ _{1 to be} transmitted is lowered and the characteristics as a wavelength selective deflecting element are deteriorated. Had.

Japanese Patent Laid-Open No. 4-129040 JP 2000-76689 A

  The object of the present invention is to solve the above-mentioned problems and to have a high degree of design freedom, that is, the diffraction efficiency can be set arbitrarily, and no optical path difference occurs with respect to light having a wavelength to be transmitted, and the grating pitch. It is an object to provide a wavelength selective diffraction element in which the transmittance of a wavelength to be transmitted does not decrease even when the wavelength is small. Another object of the present invention is to provide an optical head device capable of stably recording and reproducing information provided with this wavelength selective diffraction element and a two-wavelength semiconductor laser.

The present invention uses by the incidence of two optical wavelengths lambda ₁ and wavelength _{λ 2 (λ 1 <λ 2} ), a periodic concavo-convex shaped grating and a transparent substrate formed on the surface, the concavo-convex portion of the grating and a filling member filled, comprise a material in which any of the uneven member or the filling member to form the uneven portion has an absorption edge of light in a wavelength range shorter than the wavelength lambda _1, the wavelength lambda high refractive index than the refractive index of the wavelength lambda ₂ of light on the _first light, and the a uneven member and the filling member, either one wavelength of the wavelength lambda ₁ of the light or the wavelength lambda ₂ of light It has the same refractive index for light and transmits light of one wavelength without being diffracted, and has a different refractive index for light of the other wavelength and diffracts light of this other wavelength. A wavelength selective diffractive element is provided.

Further, to detect a light source for emitting two light wavelengths lambda ₁ and wavelength lambda _2, an objective lens for focusing the two light to the optical recording medium, the reflected light from the optical recording medium of the two optical An optical head device comprising: a photodetector ; wherein the wavelength selective diffraction element is disposed in an optical path between the light source and the objective lens.

  By using the wavelength selective diffraction element of the present invention, an optical element that functions as a diffraction grating or a hologram beam splitter that generates three beams for a specific wavelength is realized. By mounting such a wavelength-selective diffractive element in the optical head device, the diffraction efficiency and angle can be set independently for CD and DVD light. Can be detected.

  Furthermore, in the optical head device using the wavelength selective diffraction element of the present invention, in addition to the reduction in the number of semiconductor lasers by mounting the semiconductor laser for two wavelengths, it is possible to further reduce the number of parts and the size of the device, In recording and reproduction of information on CD optical discs and DVD optical discs, stable recording and reproduction performance with high light utilization efficiency can be realized.

It is a figure which shows the 1st aspect of the wavelength selective diffraction element of this invention, (a) The side view which shows a mode when the light of wavelength (lambda) ₁ injects, (b) When the light of wavelength (lambda) ₂ injects The side view which shows a mode. It is a figure which shows the 2nd aspect of the wavelength selective diffraction element of this invention, (a) The side view which shows a mode when the light of wavelength (lambda) ₁ injects, (b) When the light of wavelength (lambda) ₂ injects The side view which shows a mode. It is a figure which shows the 3rd aspect of the wavelength selective diffraction element of this invention, and is a wavelength selective diffraction element which laminated | stacked the wavelength selective diffraction element of FIG. 1 and FIG. 2, (a) Light of wavelength (lambda) ₁ injects The side view which shows a mode when it does, (b) The side view which shows a mode when the light of wavelength (lambda) ₂ injects. It is a figure which shows the 4th aspect of the wavelength selective diffraction element of this invention, and is a wavelength selective diffraction element which laminated | stacked the wavelength selective diffraction element of FIG . 1 and FIG. 2, (a) Light of wavelength (lambda) ₁ injects The side view which shows a mode when it does, (b) The side view which shows a mode when the light of wavelength (lambda) ₂ injects. FIG. 6 is a diagram showing a fifth embodiment of the wavelength selective diffraction element of the present invention, which is a wavelength selective diffraction element in which a phase plate is combined with the wavelength selective diffraction element of FIG. 3, and (a) light having a wavelength λ ₁ is incident The side view which shows a mode when it does, (b) The side view which shows a mode when the light of wavelength (lambda) ₂ injects. It is a figure which shows the 6th aspect of the wavelength selective diffraction element of this invention, and is a wavelength selective diffraction element which combined the phase plate with the wavelength selective diffraction element of FIG. 4, (a) Light of wavelength (lambda) ₁ injects The side view which shows a mode when it does, (b) The side view which shows a mode when the light of wavelength (lambda) ₂ injects. It is a figure which shows the 7th aspect of the wavelength selective diffraction element of this invention, and is a wavelength selective diffraction element which combined the phase plate with the wavelength selective diffraction element of FIG. 3, (a) Light of wavelength (lambda) ₁ injects The side view which shows a mode when it does, (b) The side view which shows a mode when the light of wavelength (lambda) ₂ injects. 1 is a schematic side view showing a first aspect of an optical head device of the present invention. FIG. 10 is a schematic side view showing an example of a conventional optical head device. FIG. 5 is a schematic side view showing a second aspect of the optical head device of the present invention. It is a figure which shows the other example of the conventional optical head apparatus, (a) Schematic side view which shows a mode that the light of wavelength (lambda) ₁ is diffracted, (b) The outline which shows a mode that the light of wavelength (lambda) ₂ is diffracted Side view. It is a figure which shows one example of the conventional wavelength selective diffraction element, (a), (b) Sectional drawing. It is a figure which shows another example of the conventional optical head apparatus, (a) Schematic side view which shows a mode that recording and reproduction | regeneration are performed with the light of wavelength (lambda) 1, (b) Recording and reproduction | regeneration with the light of wavelength (lambda) ₂ The schematic side view which shows a mode that is performed. It is a figure which shows the other example of the conventional wavelength selective diffraction element, (a), (b) Sectional drawing. In view showing still another example of a conventional optical head device, (a) the wavelength lambda recorded in _a light, play a schematic side view showing a state that has been performed, recorded in (b) the wavelength lambda ₂ of light The schematic side view which shows a mode that reproduction | regeneration is performed. It is a figure which shows the 8th aspect of the wavelength selective diffraction element of this invention, (a) The side view which shows a mode when the light of wavelength (lambda) ₁ injects, (b) The light of wavelength (lambda) ₂ is permeate | transmitted and diffracted FIG. A diagram showing a third embodiment of the optical head device of the present invention, (a) the wavelength lambda recorded in _a light, reproduction schematic side view showing a state in which have been made, in the light of (b) the wavelength lambda ₂ The schematic side view which shows a mode that recording and reproduction | regeneration are performed. It is a figure which shows the 9th aspect of the wavelength selective diffraction element of this invention, (a) A side view which shows a mode when the light of wavelength (lambda) ₁ injects, (b) A mode that the light of wavelength (lambda) ₂ is diffracted FIG. It is a figure which shows the 4th aspect of the optical head apparatus of this invention, (a) The schematic side view which shows a mode that recording and reproduction | regeneration is performed with the light of wavelength (lambda) ₁ , (b) With the light of wavelength (lambda) ₂ The schematic side view which shows a mode that recording and reproduction | regeneration are performed.

“First Embodiment of Wavelength Selective Diffraction Element”
(Λ ₁ <λ ₂ ) light having a wavelength λ ₁ and a wavelength λ ₂ is incident on the wavelength selective diffraction element 1A of the present embodiment shown in FIG. 1 (FIG. 1 (a) the light having the wavelength λ ₁ is incident. FIG. 1B shows a state where light having a wavelength λ ₂ is incident). The wavelength-selective diffractive element 1A is a diffractive element including a transparent substrate 11A having a diffraction grating 12A (consisting of a concavo-convex member), which is a concavo-convex portion of the grating, on the surface, and a filling member 13A filled therebetween. The filling member 13A is protected by the transparent substrate 14A. Wavelength lambda equal refractive index of the diffraction grating 12A filling member 13A with respect to the _first light, the refractive index of the diffraction grating 12A and the filler member 13A is different with respect to the wavelength lambda ₂ of light.

Here, one of the diffraction grating 12A or the filling member 13A, includes organic pigments having a absorption edge of light (wavelength) in a wavelength range shorter than the wavelength lambda _1. The meaning of containing here is a case where the concavo-convex member or the filling member actually contains (includes) an organic pigment and a case where the organic pigment itself constitutes one of the two members. However, since organic pigments are often included, the following description will be made assuming that organic pigments are actually included.

For example, assuming that contains organic pigment in the diffraction grating 12A, the diffraction grating 12A by anomalous dispersion effect, the difference in the refractive index in the refractive index and the wavelength lambda ₂ at a wavelength lambda _1, the difference in the refractive index of the filling member 13A Can be bigger. Accordingly, if the material of the diffraction grating 12A containing the organic pigment and the filling member 13A are appropriately selected (and the organic pigment is also appropriately selected), the difference in refractive index at the wavelength λ ₁ of these materials is set to zero. The difference in refractive index at λ ₂ can be increased.

Therefore, when the wavelength lambda ₁ of the light passes through the diffraction grating 12A because the same refractive index, the function of the diffraction grating is straightly transmitted without generating. On the other hand, when the light of wavelength λ ₂ is transmitted, it functions as a diffraction grating because the refractive index is different, and the diffraction efficiency can be changed by the height d ₁ of the diffraction grating 12A and the grating shape, and the grating of the diffraction grating 12A. The diffraction angle can be changed by changing the pitch.

  Here, the difference in refractive index due to the anomalous dispersion effect is utilized not in the anomalous dispersion region in the dispersion curve but in a region where the refractive index has greatly changed due to the anomalous dispersion effect. In addition, this effect can also be used because the refractive index is shifted to the higher overall in the entire wavelength region of the normal dispersion region. The same applies hereinafter.

In the above description, the organic pigment is included in the diffraction grating 12A. However, the same applies to the case where the filling member 13A includes an organic pigment.
Organic pigments are excellent in that the wavelength dispersion (the wavelength dependence of the refractive index) can be easily changed by changing the molecular skeleton or substituent. Furthermore, unlike pigments, organic pigments have excellent heat resistance and radiation resistance and are durable.

The larger the difference in refractive index between the concavo-convex member and the filling member at the wavelength λ _2, the smaller the depth of the grating, which is preferable because the dependency of diffraction efficiency on the incident angle can be reduced. However, in consideration of the relationship between the refractive index dispersion at the wavelength λ ₂ and the absorption amount of the optical material that actually exists, the difference in refractive index can take a value from 0.02 to 0.10.

“Second Embodiment of Wavelength Selective Diffraction Element”
A wavelength-selective diffraction element 1B according to this embodiment shown in FIG. 2 is a diffraction element including a transparent substrate on the surface of which a diffraction grating 12B made of a concavo-convex member is formed, and a filling member 13B filled therebetween. For the wavelength lambda ₁ of light different from the refractive index of the diffraction grating 12B and the filling member 13B (FIG. 2 (a)), equal to the refractive index of the diffraction grating 12B and the filling member 13B with respect to the wavelength lambda ₂ of light (FIG. 2 (b)). Although 11A and 14A such as 11B and 14B have different alphabets, the same numerals indicate the same components as in FIG. 1 and are transparent substrates.

Also in this embodiment, an organic pigment having a light absorption edge in a wavelength region shorter than the wavelength λ ₁ is included in either the diffraction grating 12B or the filling member 13B. For example, assuming that contains organic pigment in the diffraction grating 12B, the diffraction grating 12B with anomalous dispersion effect, the difference in the refractive index in the refractive index and the wavelength lambda ₂ at a wavelength lambda _1, the difference in the refractive index of the filling member 13B Can be bigger. Therefore, if the material of the diffraction grating 12B containing the organic pigment and the filling member 13B are appropriately selected (and the organic pigment is also appropriately selected), the difference in refractive index at the wavelength λ ₁ of these materials is increased and the wavelength is increased. The difference in refractive index at λ ₂ can be zero.

At this time, when the light of wavelength λ ₁ is transmitted through the diffraction grating 12B, the wavelength selective diffraction element 1B functions as a diffraction grating and is diffracted at a specific angle according to the size of the grating pitch. The diffraction efficiency of the transmission efficiency and the diffraction light of the rectilinear light can vary by changing the height d ₂ and lattice shape of the diffraction grating 12B. On the other hand, when light of wavelength λ ₂ is transmitted, it is transmitted straight without being diffracted.

“Third Embodiment of Wavelength Selective Diffraction Element”
A wavelength selective diffraction element 1C of this embodiment shown in FIG. 3 is a combination of the wavelength selective diffraction elements of the first and second embodiments. The wavelength-selective diffractive element 1C includes a transparent substrate 11C having a diffraction grating 12C formed on the surface and a transparent substrate 16C having a diffraction grating 15C formed on the surface, and the transparent substrate 17C is formed by the filling members 13C and 14C. Has a laminated structure in which Here, with respect to the wavelength lambda ₁ of the light equal to the refractive index of the diffraction grating 12C and the filling member 13C, the refractive index of the diffraction grating 12C filling member 13C with respect to the wavelength lambda ₂ of light is different.

Also, different refractive index of the diffraction grating 15C and the filling member 14C with respect to the wavelength lambda ₁ of the light, equal to the refractive index of the diffraction grating 15C and the filling member 14C with respect to the wavelength lambda ₂ of light. Accordingly, as shown in FIG. 2A for the upper portion of the wavelength selective diffraction element 1C shown in FIG. 3A and for the lower portion of FIG. 1A, the light of wavelength λ ₁ is a diffraction grating. It is diffracted at 15C, passes through the diffraction grating 12C, and only 15C acts as a diffraction grating.

On the other hand, and FIG. 3 (b) the upper portion of the wavelength-selective diffraction element 1C shown is FIG. 2 (b), as shown FIG. 1 the lower part (b), respectively, light of the wavelength lambda ₂ is diffracted grating The light passes through 15C and is diffracted by the diffraction grating 12C, and only 12C acts as the diffraction grating. Therefore, each composite element functions as a diffraction element independently for two types of wavelengths.

“Fourth Embodiment of Wavelength Selective Diffraction Element”
Further, the transparent substrate 17C in the wavelength selective diffraction element 1C shown in FIG. 3 is not used, and the diffraction grating 12D formed on the transparent substrate 11D as in the wavelength selective diffraction element 1D of this embodiment shown in FIG. A structure in which the diffraction grating 14D formed on the transparent substrate 15D is stacked via the filling member 13D may be employed. The relationship between the refractive index values of the filling member and the diffraction grating with respect to the wavelengths λ ₁ and λ ₂ is the same as that in the third embodiment.

In the fourth embodiment, the organic pigment is included in the diffraction gratings 12D and 14D or included in the filling member 13D. Figure 4 when a wavelength-selective diffraction element 1D shown in (a), light of the wavelength lambda ₁ is diffracted by the diffraction grating 14D, transmission to without diffraction grating 12D, 14D only acts as a diffraction grating. On the other hand, in the case of the wavelength selective diffraction element 1D shown in FIG. 4B, the light with the wavelength λ ₂ is transmitted through the diffraction grating 14D and diffracted by the diffraction grating 12D, and only 1 2 D acts as the diffraction grating.
Therefore, also in this embodiment, each compounded element functions as a diffraction element independently for two types of wavelengths.

“Fifth Embodiment of Wavelength Selective Diffraction Element”
The wavelength-selective diffraction element 1E of this embodiment shown in FIG. 5 is the same as the wavelength-selective diffraction element 1C described in the third embodiment, except that a phase plate 12E is provided on the outer side (lower side in the figure) of the transparent substrate 11C. The transparent substrate 11E is arranged thereon. Examples of the phase plate 12E include a half-wave plate and a quarter-wave plate. By integrating the phase plate 12E with the wavelength selective diffraction element, it is preferable that the diffraction effect and the effect of changing the polarization state can be combined with the incident light while being small.

Here, FIG. 5A shows a state in which the light of wavelength λ ₁ is diffracted by the diffraction grating 15C, and the 0th-order diffracted light and the ± 1st-order diffracted light pass through the phase plate 12E, and FIG. 5B shows the wavelength λ _2. This shows that the 0th-order diffracted light and the ± 1st-order diffracted light are diffracted by the optical diffraction grating 12C and transmitted through the phase plate 12E.

“Sixth Embodiment of Wavelength Selective Diffraction Element”
A wavelength-selective diffraction element 1F of this embodiment shown in FIG. 6 is the same as the wavelength-selective diffraction element described in the fourth embodiment, except that a phase plate 12F is provided outside the transparent substrate 11D, and the transparent substrate 11F is provided thereon. It is the composition which arranged. FIG. 6A shows a state in which the wavelength λ ₁ is incident, and FIG. 6B shows a state in which the wavelength λ ₂ is incident. By integrating the phase plate 12F with the wavelength selective diffraction element, the diffraction effect and the polarization state can be changed with respect to incident light while being smaller than the wavelength selective diffraction element 1E of the fifth embodiment. It can be combined and is preferable. Further, the wavelength selective diffraction element 1F is preferable because the number of manufacturing steps is reduced because the number of transparent substrates is one less than that of the wavelength selective diffraction element 1E.

“Seventh Embodiment of Wavelength Selective Diffraction Element”
The wavelength-selective diffraction element 1G of this embodiment shown in FIG. 7 is arranged between the filling members 13C and 14C using the phase plate introduced in the fifth embodiment as the phase plate 11G. In this case, the organic pigment may be included in both of the diffraction gratings 15C and 12C, may be included in the filling members 14C and 13C, or may be included in one diffraction grating 15C and the other filling member 13C. Or may be included in one filling member 14C and the other diffraction grating 12C. Examples of the phase plate 11G include a half-wave plate and a quarter-wave plate.

As shown in FIG. 7A, the incident light of wavelength λ ₁ is separated into ± 1st order diffracted light by the diffraction grating 15C, or 0th order diffracted light is transmitted, and both proceed to the phase plate 11G, and ± 1st order diffracted light. The polarization state of the 0th-order diffracted light changes. These lights further proceed to the next diffraction grating 12C, but are transmitted without being diffracted because the refractive indexes of 13C and 12C are equal.

As shown in FIG. 7B, the incident light of wavelength λ ₂ is not diffracted by the diffraction grating 15C, passes through to the phase plate 11G, changes its polarization state, and proceeds to the diffraction grating 12C. The incident light is separated into ± 1st order diffracted light and 0th order diffracted light by the diffraction grating 12C.

  As shown in FIG. 7, the phase plate 11G is disposed between the diffraction gratings 15C and 12C, so that the wavelength selective diffraction element 1F according to the sixth embodiment in which the phase plates are integrated is compared with the wavelength. The selective diffraction element 1G is preferable because the number of transparent substrates can be reduced by one, the number of manufacturing steps can be reduced, and the element thickness can be reduced.

  The wavelength selective diffraction element has been described in the first to seventh embodiments. In the case of one wavelength-selective diffraction element, the case where two wavelength-selective diffraction elements are laminated, and the case where two wavelength-selective diffraction elements and a phase plate are laminated are described. An element and a phase plate can be laminated and used.

In the wavelength selective diffractive element, the diffraction efficiency can be changed by changing the grating height d ₁ , d ₂ or the grating shape, so that a suitable efficiency can be obtained as a three-beam generating element or a hologram beam splitter. The lattice height may be used. Further, the diffraction efficiency of a specific order may be increased by using a stepped multi-step or a blazed diffraction grating as the concavo-convex portion of the wavelength selective diffraction element. The diffraction angle may also be set to a grating pitch that achieves a desired diffraction angle, and these methods can be used for wavelength selective diffraction elements as they are, as they are for conventional three-beam generating elements and hologram beam splitters. .

In the above description, the combination of the two wavelength-selective diffraction elements has been described with respect to the case where it functions as a diffraction grating with respect to light having both wavelengths λ _{1 and} λ ₂ . However, to function as a three-beam generating diffraction grating and the hologram beam splitter with respect to the wavelength lambda ₁ of the light may be a combination that does not function as a diffraction grating for the wavelength lambda ₂ of the light, and in the opposite case There may be. The wavelength to be selectively diffracted and the function of the diffraction grating can be used in combination depending on the purpose.
In the above description, it has been described that the grating heights d ₁ and d ₂ contribute to the diffraction efficiency and the grating pitch contributes to the diffraction direction. However, the lower the grating height, the less the sagging at the edge of the grating shape, and the fine pitch. It is preferable because of its excellent shape controllability such as easy production. Further, the lower the lattice height, the shorter the device manufacturing time, which is preferable in terms of the process.

As described above, an organic pigment having an absorption edge in a wavelength region shorter than the shorter wavelength λ _{1 of the} two wavelengths λ ₁ and λ ₂ (λ ₁ <λ ₂ ) is included in the concavo-convex member or the filling member. Increases the refractive index due to the anomalous dispersion effect.

For example, assuming that the filling member 13A shown in FIG. 1 contains an organic pigment, the refractive indexes of the diffraction grating 12A (made of a concavo-convex member) and the filling member 13A with respect to light of wavelength λ ₁ are expressed as n _12A (λ ₁ ), N _13A (λ ₁ ), and the refractive index for the light of λ ₂ are n _12A (λ ₂ ) and n _13A (λ ₂ ), respectively. For wavelength λ ₁ (FIG. 1A), n _12A (λ ₁ ) = n _13A (λ ₁ ), and for wavelength λ ₂ (FIG. 1B), n _12A (λ ₂ ) > N _13A (λ ₂ ), and n _12A (λ ₂ ) −n _13A (λ ₂ ) can be increased.

If an organic pigment is included in the diffraction grating 12A, n _12A (λ ₁ ) = n _13A (λ ₁ ) for the wavelength λ ₁ (FIG. 1 (a)), and for the wavelength λ ₂ (FIG. 1B), n _13A (λ ₂ )> n _12A (λ ₂ ), and n _13A (λ ₂ ) −n _12A (λ ₂ ) can be increased. That is, the wavelength-selective diffraction element for light of a wavelength lambda ₁ has no diffraction effect, an effect of diffraction to light having a wavelength lambda _2.

Further, for example, assuming that an organic pigment is contained in the filling member 13B shown in FIG. 2, the refractive indices of the diffraction grating 12B and the filling member 13B with respect to light of wavelength λ ₁ are n _12B (λ ₁ ) and n _13B (λ ₁ ) and the refractive indices for light of wavelength λ ₂ are n _12B (λ ₂ ) and n _13B (λ ₂ ), respectively. N _13B (λ ₁ )> n _12B (λ ₁ ) with respect to wavelength λ ₁ (FIG. 2A), and n _13B (λ ₁ ) −n _12B (λ ₁ ) can be increased. For the wavelength λ ₂ (FIG. 2B), n _12B (λ ₂ ) = n _13B (λ ₂ ). If an organic pigment is contained in the diffraction grating 12B, n _12B (λ ₁ )> n _13B (λ ₁ ) and n _12B (λ ₁ ) with respect to the wavelength λ ₁ (FIG. 2A). −n _13B (λ ₁ ) can be increased, and for the wavelength λ ₂ (FIG. 2B), n _12B (λ ₂ ) = n _13B (λ ₂ ).
That no, has the effect of a wavelength-selective diffraction element is a diffraction with respect to the wavelength lambda ₁ of the light, the effect of diffraction with respect to the wavelength lambda ₂ of light.
As described above, when an organic pigment is used for the concavo-convex member or the filling member, with respect to light of _one wavelength (for example, λ ₁ ), the refractive index between these two materials is made equal while the other wavelength ( For example, the difference in refractive index can be increased with respect to light of λ ₂ ).

  The organic pigment may be formed by a vapor deposition method or the like, or the organic pigment is mixed with a resin binder, a polymerizable monomer, a polymerization initiator, a sensitizer, a solvent, a surfactant, etc., and an appropriately adjusted composition is used. You may form into a film. In the case of using the composition, after applying the composition on a transparent substrate, the solvent is preferably removed by heating and further polymerized and cured. Moreover, you may heat-process after polymerization hardening as needed.

  In the above composition, when the organic pigment is contained in a resist that can be etched, the remaining polymerized and cured portion selectively cured can be etched to easily produce a desired lattice shape. Furthermore, when the resist is a photoresist, a lattice can be directly formed by photolithography, which is particularly preferable.

In the case where the wavelength λ ₁ and the wavelength λ ₂ are the 650 nm wavelength band and the 790 nm wavelength band, respectively, a red organic pigment is preferably used.
The red organic pigment has no significant absorption in any of the above wavelength bands and can achieve high transmittance. On the other hand, absorption appears at a wavelength shorter than 650 nm, and then the absorption rapidly increases as the wavelength decreases and has an absorption maximum in the vicinity of 550 nm. Therefore, due to the anomalous dispersion effect, the refractive index is increased in the 790 nm wavelength band and the 650 nm wavelength band. A large value can be realized.

  The yellow organic pigment has an absorption edge near 500 nm in the short wavelength region as compared with the red organic pigment. For this reason, there is no absorption in the CD-type 790 nm wavelength band and the DVD-type 650 nm wavelength band, and thus the transmittance is a good material. However, on the other hand, the region where the wavelength dispersion is large is shorter than the red organic pigment. The difference between the refractive indexes of the 650 nm wavelength band and the 790 nm wavelength band is small.

  As the red pigment, organic pigments classified into diketopyrrolopyrrole, anthraquinone, quinacridone, condensed azo, perylene and the like can be used. These organic pigments may be used alone or in combination of two or more. Especially, the diketopyrrolopyrrole type represented by Pigment Red 254 and the anthraquinone type represented by Pigment Red 177 are excellent in durability, and are preferably used as the red organic pigment of this element.

  Photoresists containing red organic pigments are used in the production of color filters for liquid crystal displays, and some commercially available color filter resists can be used as they are. Moreover, you may adjust the density | concentrations and compounds, such as a red organic pigment, a resin binder, a polymeric monomer polymerization initiator, a sensitizer, a solvent, and surfactant, as needed.

In any case, it is preferable that the light absorption characteristics after formation (film formation) be adjusted as follows for the concave-convex member or the filling member of the lattice formed using the red organic pigment. The wavelength at the absorption edge is preferably in the range from 580 nm to 620 nm, and the wavelength at the absorption edge is complex refractive index n ^* (λ) = n (λ) + i · k (λ) (the real part n (λ) is usually Of the imaginary part i · k (λ), k (λ) is the absorption coefficient, and λ is the wavelength). When the wavelength is decreased, k (λ) becomes 0.01 for the first time at a wavelength of 650 nm or less. The exceeding wavelength λ is defined as the absorption edge.

  The reason why k (λ) is set to 0.01 is that when k (λ) is increased from 0, the value is close to 0 and larger than the measurement error, and the increase tendency can be clearly grasped. When the wavelength of the absorption edge is larger than 620 nm, absorption loss (decrease in transmittance) becomes a problem. When the wavelength is smaller than 580 nm, a large chromatic dispersion is obtained between the 650 nm wavelength band and the 790 nm wavelength band. Is difficult.

  From the viewpoint of obtaining large chromatic dispersion, it is necessary that the absorption coefficient increases rapidly as the wavelength decreases. Since the red organic pigment has an absorption maximum in the vicinity of a wavelength of 550 nm, the absorption coefficient is preferably a large value at this wavelength. Table 1 shows the absorption coefficient k at 550 nm and the difference in refractive index (Δn) between 650 nm and 790 nm of the organic pigments used in Examples 1, 3, 4, 10, and 11 of the present invention.

  In the optical glass catalog of SCHOTT, flint glass is described as an optical glass having a large wavelength dispersion. Δn of flint glass such as trade names SF6 and SF58 is 0.012 and 0.015, respectively. Compared with these values, it is difficult to say that Δn is large due to the anomalous dispersion effect when k (550 nm) is 0.05 or less in Table 1 using the red organic pigment. Therefore, the absorption coefficient k at a wavelength of 550 nm is preferably larger than 0.05.

  In addition to the above method of etching a resist containing an organic pigment before curing to form a lattice, a cured member (film or vapor deposition film) may be formed by photolithography and etching treatment, In addition, a resist containing an organic pigment may be filled as a filling member in the uneven portions of the lattice formed on the substrate surface. Examples of other filling members include a photocurable resin and a thermosetting resin.

  The larger the Δn of the composition containing the red organic pigment described above, the smaller the film thickness of the red organic pigment composition, which is preferable. The larger the Δn, the higher the refractive index at a wavelength of 650 nm. For this reason, as a photocurable resin and a thermosetting resin, those having a high refractive index at a wavelength of 650 nm are preferable, and those having a refractive index of 1.6 or more are preferably used.

  As such a photocurable resin and a thermosetting resin, a composition containing a compound represented by the following formula 1 as described in JP-A No. 2000-309958 has a high refractive index and a refractive index. Can be preferably used in this application. However, it is not limited to this compound.

In formula, R < ¹ > -R < ⁶ > represents a C1-C10 hydrocarbon group or hydrogen, respectively. X represents S or O, and the number of S is 50% or more with respect to the total of S and O constituting the three-membered ring. Y represents O, S, Se or Te, p is 0-6, q is an integer in the range of 0-4.

In order to form a lattice on the substrate surface, the substrate itself may be etched or molded, or another optical material may be coated on the substrate, and then this optical material is etched or molded. A lattice may be produced. In addition, organic pigments formed by the above evaporation are also included.
Hereinafter, a case where the wavelength selective diffraction element is mounted on the optical head device will be described.

“First Embodiment of Optical Head Device”
FIG. 8 shows a first embodiment of the optical head device of the present invention, which is an optical head device using a wavelength selective diffraction element 1A (FIG. 1) that generates three CD beams as a wavelength selective diffraction element. . In the optical head device configured as described above, a two-wavelength semiconductor laser 3 (a semiconductor laser emitting a laser beam having a wavelength λ ₁ for a DVD optical disk and a semiconductor emitting a laser beam having a wavelength λ ₂ for a CD optical disk) The light having the wavelength λ ₁ emitted from the laser (integrated with the laser) passes straight through without being diffracted by the wavelength selective diffraction element 1 A, further passes through the beam splitter 4, and is collimated by the collimator lens 5. Become.

  Thereafter, the parallel light is condensed on the information recording track of the optical disc 7 (DVD system) by the objective lens 6. Then, the light reflected by the optical disk 7 passes through the objective lens 6 and the collimating lens 5 again, is reflected by the beam splitter 4, and is collected on the light receiving surface of the photodetector 8.

On the other hand, a part of the emitted light (for example, 5% to 40%) of the light of wavelength λ ₂ emitted from the two-wavelength semiconductor laser 3 is diffracted as ± first-order diffracted light by the wavelength selective diffraction element 1A. This light including the ± first-order diffracted light further passes through the beam splitter 4 and is collimated by the collimating lens 5. Thereafter, the parallel light is condensed by the objective lens 6 onto the information recording track of the optical disk 7 (CD system) as three beams of 0th order diffracted light and ± 1st order diffracted light. Then, the light reflected by the optical disk 7 passes through the objective lens 6 and the collimating lens 5 again and is reflected by the beam splitter 4, and the 0th-order diffracted light and the ± 1st-order diffracted light are collected on the light receiving surface of the photodetector 8. Lighted.

As described above, when the optical head device provided with the wavelength-selective diffraction element 1A of the present invention, in order to straightly transmitted without light of wavelength lambda ₁ is diffracted by the wavelength-selective diffraction element, without causing decrease in efficiency No stray light is generated. Therefore, in a DVD-type optical disk, a tracking error signal is detected by a phase difference method using one beam using a DVD-type photodetector (four-divided light receiving surface), and further, a focusing error on the optical disk surface by an astigmatism method is detected. Signal detection and pit signal detection as recording information can be performed stably.

  On the other hand, in a CD-type optical disc, focusing error signal detection and pit signal detection on the optical disc information recording surface are performed by the astigmatism method using the same photodetector 8 with a four-divided light receiving surface as in the DVD type. Further, the tracking error signal is detected by the three-beam method by receiving ± first-order diffracted light at the other two light receiving surfaces of the photodetector.

In the above description, the example in which the wavelength-selective diffraction element is applied to the three-beam method with respect to the light having the wavelength λ ₂ of the CD system has been described, but may be applied to the differential push-pull method used for information recording. Further, even if the wavelength selective diffraction element 1B that generates three beams with respect to the light of wavelength λ ₁ of the DVD system is applied, it is effective for more accurate tracking error detection than the method using one beam. Even if the wavelength-selective diffractive element 1C or 1D that independently generates three beams is applied to the light of wavelength λ ₁ of the DVD system and the light of wavelength λ ₂ of the CD system, each of the optical disks of the CD system and the DVD system can be applied. The optimum diffraction grating can be designed. In addition, the light for one optical disk is diffracted by the diffraction grating for the other optical disk, which is effective without causing loss of light quantity.

Also, in an optical head device that records information on CD and DVD optical disks, the value of the ratio of the 0th-order diffraction efficiency to the 1st-order diffraction efficiency in the diffraction grating for generating three beams is often 15 or more. In this case, the diffraction efficiency can be set arbitrarily, which is particularly useful.
Note that the grating pitch of the wavelength selective diffraction element is appropriately determined according to the optical system of the optical head device in which the element is used and the tracking error signal detection method of the optical disk.

“Second Embodiment of Optical Head Device”
FIG. 10 shows a second embodiment of the optical head apparatus of the present invention, which is an optical head apparatus using the wavelength selective diffraction element 1C as a hologram beam splitter. In such an optical head device thus constructed, light having a wavelength lambda ₁ emitted from the wavelength lambda ₁ and wavelength lambda semiconductor laser 3 for two wavelengths for emitting _second light, about 70% of the incident light by the hologram beam splitter After being transmitted, the collimated lens 5 converts the light into parallel light. Thereafter, the parallel light is condensed on the information recording track of the optical disk 7 (DVD system) by the objective lens 6. Then, the light reflected by the optical disk 7 passes through the objective lens 6 and the collimating lens 5 again, and about 10% of the light diffracted by the wavelength selective hologram beam splitter is condensed on the light receiving surface of the photodetector 8. Is done.

On the other hand, the light of wavelength λ ₂ emitted from the two-wavelength semiconductor laser 3 is also converted into parallel light by the collimator lens 5 after approximately 70% of the emitted light is transmitted through the hologram beam splitter. Thereafter, the parallel light is condensed on the information recording track of the optical disc 7 (CD system) by the objective lens 6. The light reflected by the optical disc 7 is transmitted through the objective lens 6 and the collimator lens 5 again, identical to about 10% of light diffracted by the hologram beam splitter, it was used for detection of the wavelength lambda ₁ of the light The light is collected on the light receiving surface of the photodetector 8.

  Thus, in the case of an optical head device equipped with the wavelength-selective diffraction element 1C of the present invention, information can be recorded and reproduced on optical disks having different operating wavelengths using the same photodetector. The head device can be reduced in size and performance. Note that the grating pitch of the wavelength selective diffraction element is appropriately determined according to the optical system of the optical head device in which it is used. Usually, since the grating pitch of this wavelength selective diffraction element is 5 μm or less, the transmittance of light having a wavelength to be transmitted does not decrease even when the grating pitch is 5 μm or less. It is highly efficient and useful. Further, a DVD-type optical disc may be configured such that a wavelength-selective polarization hologram beam splitter is integrally driven with an objective lens.

  In the example of the optical head device shown in FIG. 8, the beam splitter 4 is used and the two-wavelength semiconductor laser 3 (light source unit) and the photodetector 8 are separated. However, a wavelength-selective hologram beam splitter is used instead of the beam splitter 4, and the light reflected by the optical disk is condensed on a photodetector arranged in the vicinity of the semiconductor laser in the two-wavelength semiconductor laser (light source unit). It may be diffracted as if. In this case, since the semiconductor laser and the photodetector are arranged in the same light source unit, the optical head device can be miniaturized.

“Eighth Embodiment of Wavelength Selective Diffraction Element”
The wavelength-selective diffraction element 1H of this embodiment shown in FIG. 16 is the same as the wavelength-selective diffraction element of the first embodiment, except that a diffraction grating exists only at the periphery. The wavelength-selective diffractive element 1H is a diffractive element including a transparent substrate 11H having a diffraction grating 12H (consisting of a concavo-convex member), which is a concavo-convex part of the grating, on the surface, and a filling member 13H filled therebetween. The filling member 13H is protected by the transparent substrate 14H. For the wavelength lambda ₁ of the light equal to the refractive index of the filling member 13H and the diffraction grating 12H, the refractive index of the filling member 13H and the diffraction grating 12H is different with respect to the wavelength lambda ₂ of light.

Therefore, when the wavelength lambda ₁ of the light passes through the diffraction grating 12H, since the same refractive index, the function of the diffraction grating is straightly transmitted without generating. On the other hand, when light of wavelength λ ₂ is transmitted, it functions as a diffraction grating because the refractive index is different, and most of light of wavelength λ ₂ can be diffracted by adjusting the height of the grating.

“Third Embodiment of Optical Head Device”
FIG. 17 shows a third embodiment of the optical head device of the present invention, in which the wavelength-selective diffraction element 1H of the present invention is arranged between the collimating lens and the objective lens as an aperture limiting element. . Light emitted from the semiconductor lasers 3A and 3B is synthesized on the same optical axis by the wavelength synthesizing prism 9, and after passing through the beam splitter 4, becomes collimated light by the collimator lens 5 and becomes a wavelength selective diffraction element which is an aperture limiting element. Incident at 1H.

The light of λ ₁ is transmitted without being diffracted at the periphery and center of the aperture limiting element, and is focused on the information recording surface of the DVD optical disk 7 by the objective lens 6 (FIG. 17A). Further, the light of λ ₂ is diffracted at the periphery of the aperture limiting element, and only the light transmitted through the center is condensed on the information recording surface of the optical disc 7 with a small numerical aperture (FIG. 17B). The reflected light from the optical disk again passes through the objective lens 6, the aperture limiting element (wavelength selective diffraction element 1 </ b> H), and the collimating lens 5 and then enters the beam splitter 4. The light reflected by the beam splitter 4 travels along an optical axis that forms an angle of 90 ° with the optical axis of the forward path, and is collected on the light receiving surface of the photodetector 8. The signal light is converted into an electric signal by the photodetector 8.

Although not shown in FIG. 17B, the light of λ ₂ diffracted by the aperture limiting element is also condensed on the information recording surface of the optical disc 7 and reflected, and then travels in the same optical path as the signal light. The light travels and is collected at a portion off the light receiving surface of the photodetector 8. Since the wavelength-selective diffraction element of the present invention is used, functions as an aperture stop only for the wavelength lambda ₂ of light, also the wavelength lambda ₁ of the transmittance does not drop even by reducing the pitch of the diffraction grating Therefore, the grating pitch can be reduced and the diffraction angle of the light of λ ₂ can be increased, separation from the signal light is facilitated, and it does not reach the light receiving element for signal detection as stray light. Compared to the above, it is possible to record and reproduce information stably.

“Ninth Embodiment of Wavelength Selective Diffraction Element”
The wavelength-selective diffraction element 1J of this embodiment shown in FIG. 18 is the same as the wavelength-selective diffraction element of the first embodiment, but the shape of the concavo-convex portion is a blazed shape or a pseudo-blazed shape. The wavelength-selective diffraction element 1J (which is a four-level pseudo-blazed shape in FIG. 18) is a transparent substrate on which a diffraction grating 12J (consisting of a concavo-convex member), which is a concavo-convex part of the grating, is formed on the surface. 11J and a filling member 13J filled therebetween, and the filling member 13J is protected by the transparent substrate 14J. To the wavelength lambda ₁ of the light equal to the refractive index of the filling member 13J and the diffraction grating 12J, the refractive index of the filling member 13J and the diffraction grating 12J is different with respect to the wavelength lambda ₂ of light.

Therefore, when the wavelength lambda ₁ of the light passes through the diffraction grating 12J, because the same refractive index, the function of the diffraction grating is straightly transmitted without generating. On the other hand, when the light of wavelength λ2 is transmitted, it functions as a diffraction grating because the refractive index is different, and the uneven shape is a blazed shape or a pseudo-blazed shape, so that the wavelength can be adjusted by adjusting the height d of the grating. Most of the light of λ2 can be diffracted to a specific diffraction order.

“Fourth Embodiment of Optical Head Device”
FIG. 19 shows a fourth embodiment of the optical head device of the present invention, in which the wavelength selective diffraction element 1J of the present invention is disposed between the beam splitter 4 and the photodetector 8 as a wavelength selective deflection element. It has a configuration. Emission light of wavelength λ ₁ emitted from one emission point of the semiconductor laser 3 for two wavelengths (FIG. 19A) and emission light of wavelength λ ₂ emitted from a different emission point (FIG. 19B) ) Passes through the beam splitter 4, becomes parallel light by the collimator lens 5, and is condensed on the information recording surface of the optical disk 7 by the objective lens 6.

The reflected light from the optical disk 7 passes through the objective lens 6 and the collimating lens 5 again and then enters the beam splitter 4. The light reflected by the beam splitter 4 has an angle of 90 ° with the optical axis of the forward path. The light travels along the optical axis formed and enters the wavelength selective diffraction element 1J which is a wavelength selective deflection element. The light having the wavelength λ ₁ incident on the wavelength selective deflection element is transmitted without being deflected by the wavelength selective deflection element, and then condensed on the light receiving surface of the photodetector 8 (FIG. 19A).

On the other hand, the light having the wavelength λ ₂ incident on the wavelength selective deflecting element is deflected by the wavelength selective diffractive element 1J which is the wavelength selective deflecting element, and then the same light detection as that of the light detector 8 having the wavelength λ ₁ is performed. The light is collected on the light receiving surface of the container (FIG. 19B). Since the wavelength-selective diffractive element of the present invention is used, the light of wavelength λ ₁ can be transmitted with high transmittance, and the light of wavelength λ ₂ can be diffracted, that is, deflected. Information can be recorded and reproduced more stably than when a deflection element is used.

"Example 1"
A red resist CFRP-RH1019 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) containing an organic pigment (red pigment) was used as an uneven member. This red resist was uniformly coated on a glass substrate to a thickness of 6.0 μm by a spin coating method, and held at 100 ° C. for 5 minutes. Next, a photomask was placed on the red resist side of the glass substrate and exposed to ultraviolet light. Thereafter, alkali development was performed, and the mixture was held at 220 ° C. for 60 minutes.

  In this way, a diffraction grating 12A as shown in FIG. 1 was formed with a grating pitch of 60 μm and a grating height of 6.0 μm. The concavo-convex member had an absorption edge at a wavelength of 590 nm, and the absorption coefficient k at a wavelength of 550 nm was 0.21. The refractive index was 1.654 at a wavelength of 650 nm and 1.626 at a wavelength of 790 nm, and the difference in refractive index between the two wavelengths was 0.028.

  Next, the refractive index after polymerization is 1.656 at a wavelength of 650 nm, 1.646 at a wavelength of 790 nm, and a photopolymer having a refractive index difference of 0.010 is filled as a filling member into a concavo-convex portion of a lattice in a monomer state. Then, another glass substrate was laminated, and the diffraction grating and the photopolymer were sandwiched. Thereafter, the monomer was irradiated with ultraviolet rays and polymerized to produce a wavelength selective diffraction element.

  When semiconductor laser light having a wavelength of 790 nm was incident on the device thus fabricated, the transmittance of the 0th-order diffracted light was 74%, and the diffraction efficiencies of the + 1st-order diffracted light and the −1st-order diffracted light were each 10%. When a semiconductor laser beam having a wavelength of 650 nm is incident, the transmittance of the 0th-order diffracted light is 92%, and the diffraction efficiencies of the + 1st-order diffracted light, the −1st-order diffracted light, and the high-order diffracted light are all 0.5% or less. In addition, this device exhibited a diffraction function having wavelength selectivity with the light of the two wavelengths.

"Example 2"
Using the same red resist as that used in Example 1 as a concavo-convex member, a glass substrate is uniformly coated by spin coating, and a red resist film having a thickness of 6.0 μm is formed under the same conditions as in Example 1, such as temperature and time. Produced. A SiO ₂ film having a thickness of 60 nm was formed by sputtering on the film thus prepared, and a photoresist was applied on the SiO ₂ film by spin coating.

Next, a photomask was placed on the SiO ₂ film side of the glass substrate and exposed to ultraviolet light, and then dry etching was performed. In this way, a diffraction grating 12A as shown in FIG. 1 was produced with a grating pitch of 4 μm and a grating height of 6.0 μm. Next, the photopolymer used in Example 1 was filled in the concave and convex portions of the grating as a filling member in a monomer state, and the diffraction grating and the photopolymer were laminated with another glass substrate and sandwiched. Thereafter, the entire surface of the glass substrate was irradiated with ultraviolet rays to polymerize the monomer to produce a wavelength selective diffraction element.

  When a semiconductor laser beam having a wavelength of 790 nm is incident on the wavelength selective diffraction element thus fabricated, the transmittance of the 0th-order diffracted light is 74%, and the diffraction efficiencies of the + 1st-order diffracted light and the −1st-order diffracted light are both 10%. there were. When a semiconductor laser beam having a wavelength of 650 nm is incident, the transmittance of the 0th-order diffracted light is 92%, and the diffraction efficiencies of the + 1st-order diffracted light, the −1st-order diffracted light, and the high-order diffracted light are all 0.5% or less. In addition, this element exhibited a diffraction function having wavelength selectivity with respect to the light of the two wavelengths.

"Example 3"
Red resist A-0011 (Dainippon Ink & Chemicals, Inc.) containing an organic pigment (red pigment) was used. Using this red resist as an uneven member, the glass substrate was uniformly coated by spin coating. Thereafter, in the same manner as in Example 1, the film was held at 100 ° C. for 5 minutes, the entire surface of the glass substrate was irradiated with ultraviolet light, and held at 220 ° C. for 60 minutes to produce a film having a thickness of 7.0 μm. A SiO ₂ film was formed on the thus prepared film by sputtering in the same manner as in Example 2, and the photoresist coated on the SiO ₂ film was subjected to dry etching after UV exposure. In this way, a diffraction grating 12A as shown in FIG. 1 was produced with a grating pitch of 4 μm and a grating height of 7.0 μm.

  The concavo-convex member had an absorption edge at a wavelength of 580 nm, and the absorption coefficient k at a wavelength of 550 nm was 0.19. The refractive index was 1.631 at a wavelength of 650 nm and 1.607 at a wavelength of 790 nm, and the difference in refractive index between the two wavelengths of light was 0.024.

  Next, the refractive index after polymerization is 1.632 at a wavelength of 650 nm, 1.624 at a wavelength of 790 nm, and the difference in refractive index at both wavelengths is 0.008. The concavo-convex portion was filled, and a diffraction grating and a photopolymer were laminated on another glass substrate and sandwiched. Thereafter, the entire surface of the glass substrate was irradiated with ultraviolet rays to polymerize the monomer to produce a wavelength selective diffraction element.

  When semiconductor laser light having a wavelength of 790 nm was incident on the device thus fabricated, the transmittance of the 0th-order diffracted light was 74%, and the diffraction efficiencies of the + 1st-order diffracted light and the −1st-order diffracted light were 10%. When a semiconductor laser beam having a wavelength of 650 nm is incident, the transmittance of the 0th-order diffracted light is 92%, and the diffraction efficiencies of the + 1st-order diffracted light, the −1st-order diffracted light, and the high-order diffracted light are all 0.5% or less. In addition, this element exhibited a diffraction function having wavelength selectivity with respect to the light of the two wavelengths.

"Example 4"
As a red organic pigment, Pigment Red 177 containing 14.8% (based on mass, the same shall apply hereinafter) is a pigment-containing liquid containing 70% of CF Red AGR-01 manufactured by Gokoku Color Co., Ltd., pentaerythritol tetraacrylate (manufactured by Nippon Kayaku Co., Ltd.) A mixture was prepared by mixing 22% KAYARAD-DPHA) and 5% propylene glycol-1-monomethyl ether-2-acetate. Further, Irgacure 907 (manufactured by Ciba Specialty Chemicals) was mixed as a photopolymerization initiator so as to be 0.7% with respect to the above mixture to prepare a composition.

This composition was coated uniformly on a glass substrate as a concavo-convex member by a spin coating method, and held at 100 ° C. for 3 minutes. Next, the entire surface of the composition was irradiated with ultraviolet rays, and then kept at 200 ° C. for 60 minutes to produce a film having a thickness of 5.5 μm. A SiO ₂ film having a thickness of 60 nm was formed by sputtering on the film thus prepared, and a photoresist was applied on the SiO ₂ film by spin coating. Next, a photomask was placed on the SiO ₂ film side of the glass substrate and exposed to ultraviolet light, and then dry etching was performed. In this way, a diffraction grating 12A as shown in FIG. 1 was produced with a grating pitch of 4 μm and a grating height of 5.5 μm.

The wavelength of the absorption edge of the concavo-convex member was 600 nm, and the absorption coefficient k at 550 nm was 0.10. The refractive index was 1.636 at a wavelength of 650 nm and 1.601 at a wavelength of 790 nm, and the difference in refractive index between the two wavelengths was 0.035.
Next, the refractive index after polymerization is 1.638 at a wavelength of 650 nm, 1.624 at a wavelength of 790 nm, and a photopolymer having a difference in refractive index at two wavelengths of 0.014 is used as a filling member in a monomer state to form irregularities in the lattice. Then, another glass substrate was laminated, and the diffraction grating and the photopolymer were sandwiched. Thereafter, the monomer was irradiated with ultraviolet rays and polymerized to produce a wavelength selective diffraction element.

  When semiconductor laser light having a wavelength of 790 nm was incident on the device thus fabricated, the transmittance of the 0th-order diffracted light was 74%, and the diffraction efficiencies of the + 1st-order diffracted light and the −1st-order diffracted light were each 10%. When a semiconductor laser beam having a wavelength of 650 nm is incident, the transmittance of the 0th-order diffracted light is 92%, and the diffraction efficiencies of the + 1st-order diffracted light, the −1st-order diffracted light, and the high-order diffracted light are all 0.5% or less. In addition, this element exhibited a diffraction function with wavelength selectivity at the above two wavelengths.

"Example 5"
The same red resist as used in Example 1 was uniformly coated on the glass substrate by spin coating, and a red resist film having a thickness of 6.0 μm was produced under the same conditions as in Example 1, such as temperature and time. A SiO ₂ film is formed on the film thus produced by sputtering and dry-etched in the same manner as in Example 2 to obtain a diffraction grating 12A as shown in FIG. 1 having a grating pitch of 4 μm and a grating height. The thickness was 4.0 μm.

  Next, the refractive index after polymerization is 1.632 at a wavelength of 650 nm, 1.624 at a wavelength of 790 nm, and the difference in refractive index between the two wavelengths is 0.008. In this state, the concavo-convex portion of the grating was filled as a filling member, and the diffraction grating and the photopolymer were laminated on another glass substrate and sandwiched. Thereafter, the entire surface of the glass substrate was irradiated with ultraviolet rays to polymerize the monomer to produce a wavelength selective diffraction element.

  When a semiconductor laser beam having a wavelength of 650 nm was incident on the device thus fabricated, the transmittance of the 0th-order diffracted light was 72%, and the diffraction efficiencies of the + 1st-order diffracted light and the −1st-order diffracted light were 10%. Further, when a semiconductor laser beam having a wavelength of 790 nm is incident, the transmittance of the 0th-order diffracted light is 95%, and the diffraction efficiencies of the + 1st-order diffracted light, the −1st-order diffracted light, and the higher-order diffracted light are all 0.5% or less. In addition, this device exhibited a diffraction function having wavelength selectivity with respect to the above-mentioned two wavelengths of light, and also exhibited a wavelength selectivity different from that of the device of Example 2.

"Example 6"
The same red resist as used in Example 1 was uniformly coated on the glass substrate by spin coating, and a red resist film having a thickness of 6.0 μm was produced under the same conditions as in Example 1, such as temperature and time. A SiO ₂ film is formed on the film thus produced by sputtering and dry-etched in the same manner as in Example 2 to obtain a diffraction grating 12A as shown in FIG. 1 having a grating pitch of 4 μm and a grating height. The thickness was 4.0 μm.

  Next, a photopolymer having a refractive index after polymerization of 1.632 at a wavelength of 650 nm and 1.624 at a wavelength of 790 nm and a difference in refractive index between two wavelengths of 0.008 is used as a filling member in a monomer state. The element produced in Example 2 was laminated, and the entire surface of the glass substrate was irradiated with ultraviolet rays to polymerize the monomer, thereby producing a wavelength selective diffraction element.

  When a semiconductor laser beam having a wavelength of 650 nm was incident on the device thus fabricated, the transmittance of the 0th-order diffracted light was 70%, and the diffraction efficiencies of the + 1st-order diffracted light and the −1st-order diffracted light were 10%. When a semiconductor laser having a wavelength of 790 nm was incident, the transmittance of 0th-order diffracted light was 72%, and the diffraction efficiencies of + 1st-order diffracted light and -1st-order diffracted light were 10%. Moreover, the diffraction efficiency of second-order or higher-order diffracted light was 0.5% or less for light of any wavelength.

"Example 7"
In the optical head device for two wavelengths of this example, the wavelength selective diffractive element manufactured in Example 1 is composed of a two-wavelength semiconductor laser 3 and a beam splitter 4 like the wavelength selective diffractive element 1A shown in FIG. It has a configuration arranged between them. Since the wavelength selective diffractive element of the present invention is used, three beams for tracking error detection can be generated with respect to the light of wavelength λ ₂ without diffracting the light of wavelength λ ₁ and few. It was possible to record and reproduce stable information with a good S / N in terms of the number of parts.

"Example 8"
In the optical head device for two wavelengths of this example, the wavelength selective diffractive element produced in Example 6 is composed of a two-wavelength semiconductor laser 3 and a collimating lens 5 like the wavelength selective diffractive element 1C shown in FIG. It has a configuration arranged between them. Since the wavelength-selective diffraction element of the present invention is used, independently with respect to the wavelength lambda ₁ of light and the wavelength lambda ₂ of the light can be designed hologram beam splitter, any wavelength lambda ₁ and wavelength lambda ₂ Was also efficiently collected on the light receiving surface of the same photodetector 8, and stable information recording and reproduction with a good S / N could be performed with a small number of parts.

"Example 9 (comparative example)"
A yellow resist CY-S673A (manufactured by Fuji Film Olin Co., Ltd.) containing an organic pigment (yellow pigment) was used as the uneven member. This organic pigment was uniformly coated on a glass substrate by a spin coating method, and then held at 100 ° C. for 5 minutes. Next, after irradiating the entire surface of the glass substrate with ultraviolet rays, the glass substrate was held at 220 ° C. for 60 minutes to form a film having a thickness of 6.0 μm. This film had an absorption edge at a wavelength of 480 nm. The refractive index was 1.590 at a wavelength of 650 nm and 1.576 at a wavelength of 790 nm. The difference in refractive index between the two wavelengths was 0.014.

  On the other hand, the difference in refractive index at the two wavelengths in the case of a film formed in the same manner using a red resist CFRP-RH1019 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) containing a red pigment having an absorption edge at a wavelength of 590 nm is 0. 028, twice the value of the yellow resist.

  Using the above yellow resist, a wavelength-selective diffractive element similar to that in Example 1 was produced, and when a semiconductor laser beam having a wavelength of 790 nm was incident, the transmittance of the 0th-order diffracted light was 90, and the + 1st-order diffracted light and −1 The diffraction efficiency of the next diffracted light was 3% each. The diffraction efficiency was 1/3 that of the red resist CFRP-RH1019.

"Example 10 (comparative example)"
A red resist CFRP-RP103 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) was used as a concavo-convex member, and this resist was uniformly coated on a glass substrate by a spin coating method and held at 90 ° C. for 2 minutes. Next, the whole surface was irradiated with ultraviolet light, and then kept at 190 ° C. for 30 minutes to produce a film having a thickness of 6.0 μm. The wavelength of the absorption edge in this concavo-convex member was 580 nm, and the absorption coefficient k at a wavelength of 550 nm was 0.05. The refractive index was 1.548 at a wavelength of 650 nm and 1.534 at a wavelength of 790 nm, and the refractive index difference at the two wavelengths was 0.014.

  On the other hand, the difference in refractive index at the two wavelengths in the case of a film formed in the same manner using a red resist CFRP-RH1019 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) containing a red pigment having an absorption edge at a wavelength of 590 nm is 0. 028, twice that of the red resist CFRP-RP103.

  Using the above-described red resist CFRP-RP103, a wavelength-selective diffraction element similar to that in Example 1 was manufactured, and when a semiconductor laser beam having a wavelength of 790 nm was incident, the transmittance of the 0th-order diffracted light was 90%. The diffraction efficiencies of the folded light and the −1st order diffracted light were 3%, respectively. The diffraction efficiency was 1/3 that of the red resist CFRP-RH1019.

"Example 11 (comparative example)"
As a red organic pigment, pigment red liquid containing 14.7% of pigment red 209 is a pigment-containing liquid, 73% of CF Red AGR-02 manufactured by Gokoku Color Co., Ltd., 22% of pentaerythritol tetraacrylate (KAYARAD-DPHA manufactured by Nippon Kayaku Co., Ltd.), propylene A mixture was prepared by mixing 5% of glycol-1-monomethyl ether-2-acetate. Further, Irgacure 907 (manufactured by Ciba Specialty Chemicals) was mixed as a photopolymerization initiator so as to be 0.7% with respect to the above mixture to prepare a composition.

  This composition was coated uniformly on a glass substrate as a concavo-convex member by a spin coating method, and held at 100 ° C. for 3 minutes. Next, the entire surface of the composition was irradiated with ultraviolet rays, and then kept at 200 ° C. for 60 minutes to produce a film having a thickness of 6.0 μm. The wavelength of the absorption edge in this concavo-convex member was 570 nm, and the absorption coefficient k at a wavelength of 550 nm was 0.05. The refractive index was 1.605 at a wavelength of 650 nm and 1.590 at a wavelength of 790 nm, and the difference in refractive index between the two wavelengths was 0.015.

  On the other hand, the difference in refractive index at the two wavelengths in the case of a film formed in the same manner using a red resist CFRP-RH1019 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) containing a red pigment having an absorption edge at a wavelength of 590 nm is 0. 028, which was approximately twice the value of the composition in this example.

  Using the composition in this example, a wavelength selective diffractive element similar to that in Example 1 was produced, and when a semiconductor laser beam having a wavelength of 790 nm was incident, the transmittance of the 0th order diffracted light was 90%, and the + 1st order diffracted light and The diffraction efficiency of -1st order diffracted light was 3% each. The diffraction efficiency was 1/3 that of the red resist CFRP-RH1019.

"Example 12"
85% CF red EX-2739 manufactured by Gokoku Dye Co., Ltd., which is a pigment-containing liquid containing 14.7% pigment red 254 as a red organic pigment, 12% pentaerythritol tetraacrylate (KAYARAD-DPHA manufactured by Nippon Kayaku Co., Ltd.), propylene A mixture was prepared by mixing 3% of glycol-1-monomethyl ether-2-acetate. Further, Irgacure 907 (manufactured by Ciba Specialty Chemicals) was mixed as a photopolymerization initiator so as to be 0.2% with respect to the above mixture to prepare a composition.

This composition was coated uniformly on a glass substrate as a concavo-convex member by a spin coating method, and held at 100 ° C. for 3 minutes. Next, the entire surface of the composition was irradiated with ultraviolet rays, and then kept at 200 ° C. for 60 minutes to produce a 4.9 μm thick film. A SiO ₂ film having a thickness of 60 nm was formed by sputtering on the film thus prepared, and a photoresist was applied on the SiO ₂ film by spin coating. Next, a photomask was placed on the SiO ₂ film side of the glass substrate and exposed to ultraviolet light, and then dry etching was performed. In this way, a diffraction grating 12A as shown in FIG. 1 was manufactured with a grating pitch of 4 μm and a grating height of 4.9 μm.

  The wavelength of the absorption edge of the concavo-convex member was 590 nm, and the absorption coefficient k at 550 nm was 0.28. The refractive index was 1.703 at a wavelength of 650 nm and 1.656 at a wavelength of 790 nm, and the difference in refractive index between the two wavelengths was 0.047.

  Next, 0.1% of tetrabutylammonium bromide was added to the compound represented by Formula 2, bis (β-epithiopropyl) sulfide, and stirred for 5 minutes, and then the concave and convex portions of the lattice as a filling member in a monomer state. Then, another glass substrate was laminated, and the diffraction grating and the filling member were sandwiched. Thereafter, the filling member was cured by heating at 100 ° C. for 4 hours. The refractive index of the filling member after curing was 1.704 at a wavelength of 650 nm and 1.697 at 790 nm.

  When semiconductor laser light having a wavelength of 790 nm was incident on the device thus fabricated, the transmittance of 0th-order diffracted light was 73%, and the diffraction efficiencies of + 1st-order diffracted light and -1st-order diffracted light were 9% each. When a semiconductor laser beam having a wavelength of 650 nm is incident, the transmittance of the 0th-order diffracted light is 95%, and the diffraction efficiencies of the + 1st-order diffracted light, the −1st-order diffracted light, and the higher-order diffracted light are all 0.5% or less. In addition, this element exhibited a diffraction function with wavelength selectivity at the above two wavelengths.

"Example 13"
As a red organic pigment, Pigment Red 254 is a pigment-containing solution containing 14.7% of Pigment Red CF-EX-2739 made by Gokoku Color Co., Ltd. 91% pentaerythritol tetraacrylate (Nippon Kayaku KAYARAD-DPHA), 7% propylene A mixture was prepared by mixing 2% of glycol-1-monomethyl ether-2-acetate. Further, Irgacure 907 (manufactured by Ciba Specialty Chemicals) was mixed as a photopolymerization initiator so as to be 0.2% with respect to the above mixture to prepare a composition.

This composition was coated uniformly on a glass substrate as a concavo-convex member by a spin coating method, and held at 100 ° C. for 3 minutes. Next, the entire surface of the composition was irradiated with ultraviolet rays, and then kept at 200 ° C. for 60 minutes to produce a film having a thickness of 2.7 μm. A SiO ₂ film having a thickness of 60 nm was formed by sputtering on the film thus prepared, and a photoresist was applied on the SiO ₂ film by spin coating. Next, a photomask was placed on the SiO ₂ film side of the glass substrate and exposed to ultraviolet light, and then dry etching was performed. In this way, a diffraction grating 12B as shown in FIG. 2 was produced with a grating pitch of 4 μm and a grating height of 2.7 μm.

  The wavelength of the absorption edge of the concavo-convex member was 590 nm, and the absorption coefficient k at 550 nm was 0.29. The refractive index was 1.756 at a wavelength of 650 nm and 1.695 at a wavelength of 790 nm, and the difference in refractive index between the two wavelengths was 0.061.

  Next, the filling member used in Example 12 was used to fill the uneven portions of the grating in the same manner, and another glass substrate was laminated to sandwich the diffraction grating and the filling member. Thereafter, the filling member was cured by heating at 100 ° C. for 4 hours. The refractive index of the filling member after curing was 1.704 at a wavelength of 650 nm and 1.697 at 790 nm.

  When a semiconductor laser beam having a wavelength of 790 nm is incident on the device thus fabricated, the transmittance of the 0th-order diffracted light is 97%, and the diffraction efficiencies of the + 1st-order diffracted light and the −1st-order diffracted light are each 0.5% or less. there were. When a semiconductor laser beam having a wavelength of 650 nm is incident, the transmittance of the 0th-order diffracted light is 70%, and the diffraction efficiencies of the + 1st-order diffracted light, the −1st-order diffracted light, and the higher-order diffracted light are all 10%. The element exhibited a diffraction function having wavelength selectivity with the light of the two wavelengths.

"Example 14"
A composition containing the same red organic pigment as used in Example 12 was used as a concavo-convex member, which was uniformly coated on a glass substrate by a spin coating method and held at 100 ° C. for 3 minutes. Next, the entire surface of the composition was irradiated with ultraviolet rays, and then kept at 200 ° C. for 60 minutes to produce a film having a thickness of 10.0 μm. A SiO ₂ film having a thickness of 60 nm was formed by sputtering on the film thus prepared, and a photoresist was applied on the SiO ₂ film by spin coating. Next, a photomask was placed on the SiO ₂ film side of the glass substrate and exposed to ultraviolet light, and then dry etching was performed. In this way, a wavelength selective diffraction element 12H as shown in FIG. 16 was fabricated with a grating pitch of 10 μm and a grating height of 10.0 μm. This diffractive element has a diffraction grating only in the peripheral part (see FIG. 12B).

  Next, the filling member used in Example 12 was used to fill the concave and convex portions of the grating in the same manner, and another glass substrate was laminated to sandwich the diffraction grating and the filling member. Thereafter, the filling member was cured by heating at 100 ° C. for 4 hours. When a semiconductor laser beam having a wavelength of 650 nm is incident on the device thus fabricated, the transmittance of the 0th-order diffracted light is 95%, and the diffraction efficiencies of the + 1st-order diffracted light and the −1st-order diffracted light are each 0.5% or less. there were. Further, when a semiconductor laser beam having a wavelength of 790 nm was incident, the transmittance of 0th-order diffracted light was 10%, and this element exhibited a diffraction function having wavelength selectivity with the above-mentioned two wavelengths of light.

"Example 15"
A composition containing the same red organic pigment as used in Example 12 was used as a concavo-convex member, which was uniformly coated on a glass substrate by a spin coating method and held at 100 ° C. for 3 minutes. Next, the entire surface of the composition was irradiated with ultraviolet rays, and then kept at 200 ° C. for 60 minutes to produce a film having a thickness of 15.0 μm. A SiO ₂ film having a thickness of 60 nm was formed by sputtering on the film thus prepared, and a photoresist was applied on the SiO ₂ film by spin coating. Next, a photomask was placed on the SiO ₂ film side of the glass substrate and exposed to ultraviolet light, and then dry etching was performed. Thereafter, by repeating the steps from SiO ₂ film formation to dry etching, a wavelength selective diffraction element 12J as shown in FIG. 18 has a grating pitch of 30 μm, a height of each step of 5.0 μm, and a total height of 15. The thickness was 0 μm.

  Next, the filling member used in Example 12 was used to fill the concave and convex portions of the grating in the same manner, and another glass substrate was laminated to sandwich the diffraction grating and the filling member. Thereafter, the filling member was cured by heating at 100 ° C. for 4 hours. When a semiconductor laser beam having a wavelength of 650 nm is incident on the device thus fabricated, the transmittance of the 0th-order diffracted light is 90%, and the diffraction efficiencies of the + 1st-order diffracted light and the −1st-order diffracted light are each 0.5% or less. there were. When a semiconductor laser beam having a wavelength of 790 nm is incident, the transmittance of the + 1st order diffracted light is 75%, and the diffraction efficiencies of the 0th order diffracted light and the −1st order diffracted light are both 0.5% or less. The diffraction function with wavelength selectivity at the above two wavelengths was shown.

"Example 16"
In the two-wavelength optical head device of this example, the wavelength-selective diffraction element produced in Example 14 is arranged between the collimating lens 5 and the objective lens 6 like the wavelength-selective diffraction element 1H shown in FIG. It has been configured. Since the wavelength-selective diffraction element of the present invention is used, without changing the numerical aperture of the wavelength lambda ₁ of the light, it is possible to reduce the numerical aperture of the wavelength lambda ₂ of light, also the grating pitch of the diffraction element smaller However, since the transmittance of light of wavelength λ ₁ does not decrease, the grating pitch can be reduced, the diffraction angle of light of wavelength λ ₂ can be increased, there is little stray light, and stable information recording and reproduction with good S / N. Was able to do.

"Example 17"
In the two-wavelength optical head device of this example, the wavelength-selective diffractive element manufactured in Example 15 is arranged between the beam splitter 4 and the photodetector 8 like the wavelength-selective diffractive element 1J shown in FIG. It is an arranged configuration. Since the wavelength-selective diffraction element of the present invention is used, it is possible to diffract the light of the wavelength lambda ₂ at a high diffraction efficiency, and to reflect light having a wavelength lambda ₁ at a high transmittance, the wavelength lambda ₁ and wavelength lambda Any of the _two lights was efficiently condensed on the light receiving surface of the same photodetector 8, and stable information recording and reproduction with a good S / N could be performed with a small number of parts.

  As described above, when the wavelength selective diffraction element of the present invention is used, an optical element that functions as a diffraction grating or a hologram beam splitter that generates three beams for a specific wavelength is realized. By mounting such a wavelength-selective diffractive element in the optical head device, the diffraction efficiency and angle can be set independently for CD and DVD light. Can be detected.

  Furthermore, in the optical head device using the wavelength selective diffraction element of the present invention, in addition to the reduction in the number of semiconductor lasers by mounting the semiconductor laser for two wavelengths, it is possible to further reduce the number of parts and the size of the device, In recording and reproduction of information on CD optical discs and DVD optical discs, stable recording and reproduction performance with high light utilization efficiency can be realized.

1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H, 1J: Wavelength selective diffraction element 3: Semiconductor laser 3A for two wavelengths, 3B: Semiconductor laser 4: Beam splitter 5: Collimator lens 6: Objective lens 7: Optical disc 8, 8A, 8B: Photo detector 9: Wavelength synthesis prism 10: Diffraction grating 11 for generating three beams 11: Hologram beam splitters 11A, 14A, 11B, 14B, 11C, 16C, 17C, 11D, 15D, 11E, 11F: Transparent substrates 12A, 12B, 12C, 15C, 12D, 14D: Diffraction gratings 13A, 13B, 13C, 14C, 13D: Filling members 12E, 12F, 11G: Phase plates

Claims (4)

Two light beams having a wavelength λ ₁ and a wavelength λ ₂ (λ ₁ <λ ₂ ) are incident and used .
Comprising a transparent substrate provided with the periodic uneven grating surface, and a filling member filled in the concave-convex portion of the grating,
Include a material either uneven member or the filling member to form the uneven portion has an absorption edge of light in a wavelength range shorter than the wavelength lambda _1, the refractive index with respect to the wavelength lambda ₁ of the light the wavelength lambda Higher than the refractive index of the light of ₂ ,
And wherein the concave-convex member and the filling member, the diffraction light of a wavelength of the one having the same refractive index for one of the wavelengths of the wavelength lambda ₁ of the light or the wavelength lambda ₂ of light A wavelength-selective diffractive element characterized by having a different refractive index with respect to light of the other wavelength and diffracting the light of the other wavelength. A wavelength-selective diffraction element according to claim 1, wherein the light of said wavelength lambda ₁ is for diffracting the transmitted the wavelength lambda ₂ of light not diffracted, light of the wavelength lambda ₂ passes through without diffraction of the wavelength lambda ₁ A wavelength selective diffraction element comprising: the wavelength selective diffraction element according to claim 1 diffracting light; and the wavelength selective diffraction element being laminated. Either the uneven part or the filling member contains an organic pigment,
The wavelength-selective diffraction element according to claim 1, wherein a red organic pigment is used as the organic pigment. A light source for emitting two light wavelengths lambda ₁ and wavelength lambda _2, an objective lens for focusing the two light to the optical recording medium, light detector for detecting light reflected from the optical recording medium of the two optical comprising a vessel, a,
An optical head and wherein in the optical path, the wavelength-selective diffraction element according to claim 1, wherein is provided between the light source and the objective lens.

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