JP4518009B2 - Three-wavelength diffraction element, three-wavelength diffraction element with phase plate, and optical head device - Google Patents

Description

  The present invention relates to a three-wavelength diffraction element, a three-wavelength diffraction element with a phase plate, and an optical head device.

  Reproduction and / or recording of information on optical recording media of different standards such as BD (next-generation DVD to be reproduced and / or recorded with a blue-violet semiconductor laser represented by Blu-ray or HD-DVD), DVD, CD, etc. In the compatible optical head device in which “reproduction and / or recording” is abbreviated as “reproduction / recording”), development of miniaturization and weight reduction of the device has been actively conducted.

  BD, DVD and CD with different standards have different wavelengths of laser light used for reproduction / recording. Laser light in the 405 nm wavelength band is used for BD, 660 nm wavelength band for DVD, and 780 nm wavelength band for CD. In order to reduce the size and weight of a compatible optical head device that uses these different types of optical recording media by exchanging them, a three-wavelength semiconductor laser that outputs laser light in the three wavelength bands described above has been developed.

  The use of a three-wavelength semiconductor laser is expected to reduce the number of components in the optical head device by sharing optical components such as lenses and diffraction elements. Usually, the diffraction element is formed of glass or plastic having a diffraction grating having a periodic uneven cross-sectional shape, and the diffraction efficiency is determined by the depth of the unevenness and the refractive index of the material. In other words, the diffraction efficiency cannot be freely controlled for the laser beams in the wavelength bands for BD, DVD, and CD. Furthermore, a plurality of diffraction gratings can be formed in order to obtain optimum diffraction directions for laser beams in respective wavelength bands for BD, DVD and CD, but as described above, the diffraction efficiency cannot be freely controlled. This makes it difficult to share diffraction elements.

  There is a demand for a diffractive element that has a high degree of freedom in design and can obtain optimum diffraction efficiency and diffraction direction with respect to laser light in three wavelength bands, that is, can use diffraction selectively in wavelength. For example, in a compatible optical head device using a two-wavelength semiconductor laser that outputs laser light in the 660 nm wavelength band and the 780 nm wavelength band, a diffraction element used for laser light in the DVD and CD wavelength bands has been proposed (Patent Document 1). In addition, there are few proposals of diffraction elements that can cope with laser light in the 405 nm wavelength band.

JP 2001-290017 A

  According to the present invention, in a compatible optical head device using a three-wavelength semiconductor laser, the conventional diffractive element does not have wavelength selectivity, so that the element cannot be shared, which is disadvantageous in reducing the size and weight of the compatible optical head device. Has been made to solve the problem.

  That is, for each of the laser beams in the three wavelength bands used in the compatible optical head device, a diffraction element capable of obtaining an appropriate diffraction efficiency and diffraction direction is obtained, and further, a phase that combines the phase change and the diffraction effect. The invention is made in order to obtain a diffraction element with a plate and reduce the size and weight of the compatible optical head device while having these functions by mounting these elements.

In the present invention, the first convex portion made of a resin exhibiting birefringence and the first concave portion made of a resin exhibiting optical isotropy are in contact with each other to form a concave-convex shape having a periodic cross section. A diffraction grating, a second convex portion made of a resin exhibiting birefringence, and a second concave portion made of a resin exhibiting optical isotropy are in contact with each other to form a second irregular portion having a periodic cross section. A diffraction grating and a third diffraction grating having a periodic concavo-convex portion or a third convex portion made of an inorganic material are overlapped, and incident light having three different wavelengths λ ₁ and λ ₂ is incident. and the light of wavelength _{λ 3 (λ 1 <λ 2} <λ 3), the first diffraction grating is configured to diffract the wavelength lambda ₁ of the light, the wavelength lambda ₂ of the light and the wavelength lambda ₃ of the light The refractive index and / or height of the first convex portion and the refractive index of the first concave portion are adjusted so as to transmit The second diffraction grating is configured to transmit the wavelength lambda ₁ of light and the wavelength lambda ₂ of light, so as to diffract the wavelength lambda ₃ of the light, the refractive index of the second protrusions and / or The height and the refractive index of the second recess are adjusted , and the third diffraction grating transmits the light having the wavelength λ ₁ and the light having the wavelength λ ₃ and diffracts the light having the wavelength λ _2. as such, the uneven portion or the third convex portion, the refractive index and / or height to provide an adjusted Tei Ru 3-wavelength diffraction element.

With this configuration, the three-wavelength diffractive element of the present invention is light having wavelength λ ₁ , light having wavelength λ ₂ , and light having wavelength λ ₃ incident on the element, and having light having wavelength λ ₁ and light having wavelength λ ₂ . When the polarization directions of light are orthogonal and the light of wavelength λ _{2 and} the light of wavelength λ ₃ are parallel, transmission and diffraction can be selectively controlled for each wavelength of light.

Also, a first diffraction grating having a concavo-convex shape in which a first convex portion made of a resin exhibiting birefringence and a first concave portion made of a resin exhibiting optical isotropy are in contact with each other to form a periodic cross section And a second convex part made of resin showing birefringence and a second concave part made of resin showing optical isotropy, and a second diffractive grating whose section has a periodic concavo-convex shape And a third diffraction pattern having two phase plates provided so as to sandwich the first diffraction grating and the second diffraction grating, and a periodic concavo-convex part or a third convex part made of an inorganic material. The first diffraction grating is composed of three different wavelengths λ ₁ , light having a wavelength λ ₂ , and light having a wavelength λ ₃ (λ ₁ <λ ₂ <λ ₃ ). Diffracting the light of wavelength λ ₁ and transmitting the light of wavelength λ _{2 and} the light of wavelength λ ₃ The refractive index and / or height of the first convex portion and the refractive index of the first concave portion are adjusted, and the second diffraction grating transmits the light of the wavelength λ _{1 and} the wavelength of the wavelength λ ₃ . to diffract light, refractive index and / or height of the second convex portion, and the refractive index adjustment of the second recess, the phase plate two is the wavelength lambda ₁ of the light have a phase difference of 2π for, have a phase difference of substantially π to the wavelength lambda ₂ of the light, and has a phase difference of substantially π to light of the wavelength [lambda] 3, the third The diffraction gratings of the concave and convex portions or the third convex portions transmit the light of the wavelength λ _{1 and} the light of the wavelength λ ₃ and diffract the light of the wavelength λ _2. or height to provide a phase fitted with three-wavelength diffraction element is adjusted.

With this configuration, the three-wavelength diffractive element with phase plate of the present invention has parallel polarization directions and is selected for light of wavelength λ ₁ , light of wavelength λ ₂ and light of wavelength λ ₃ incident on the element. Transmission and diffraction can be controlled.

Further, a light source that emits light of _three different wavelengths λ ₁ , light of wavelength λ ₂ , and light of wavelength λ ₃ (λ ₁ <λ ₂ <λ ₃ ) , and light of each wavelength is collected on the optical recording medium. an objective lens for, is condensed and a photodetector for detecting light reflected by the optical recording medium, an optical head device for reproducing and / or recording information of the optical recording medium, the light source wherein the optical path between the objective lens, the above-mentioned three-wavelength diffraction element or to provide an optical head apparatus above phase fitted with 3-wavelength diffraction element is that is installed with. Furthermore, the wavelength λ ₁ is a 405 nm wavelength band for BD, the wavelength λ ₂ is a 660 nm wavelength band for DVD, and the wavelength λ ₃ is a 780 nm wavelength band for CD. Providing equipment.

  With this configuration, the optical head device of the present invention can selectively diffract light of three different wavelengths while being a single element, so the number of components of the optical head device can be reduced, The optical head device can be reduced in size and weight.

  The diffraction element for three wavelengths of the present invention can selectively control the diffraction efficiency and the diffraction direction according to the wavelength of the laser light incident on the element, that is, has a wavelength selective diffraction effect.

  The three-wavelength diffractive element with a phase plate of the present invention is a small diffractive element having a phase control effect in addition to the above-described wavelength selective diffraction effect.

  Further, since the optical head device of the present invention is equipped with the above-described three-wavelength diffraction element or the three-wavelength diffraction element with a phase plate, the device can be reduced in size and weight while having these effects. .

“First Embodiment”
FIG. 1 is a cross-sectional view showing the configuration of the three-wavelength diffraction element according to the first embodiment of the present invention. The three-wavelength diffraction element has two diffraction gratings, and each diffraction grating has two diffraction gratings. Different resins are in contact with each other, and the cross-sectional shape is a periodic concavo-convex shape. The concavo-convex convex portion is made of a resin exhibiting birefringence, and at least the concavo-convex convex portion is filled with the filled optical It has a configuration made of an isotropic resin. In this configuration, the first, second, and third transparent substrates are provided, and two different resins are in contact with each other between the first and second transparent substrates and between the second and third transparent substrates. The cross-sectional shape has periodic irregularities, and a filling adhesive or the like is used as an optically isotropic resin.

  Note that at least the space between the convex portions (concave portions) is filled means that the spaces between the convex portions are filled, or the spaces between the convex portions are filled and the convex portions are further completely filled.

  As the first transparent substrate 1, the second transparent substrate 2, and the third transparent substrate 3, transparent material substrates such as glass, quartz glass, and plastic can be used. Further, by forming an antireflection film on the air-side surface of the first transparent substrate 1 and the third transparent substrate 3, unnecessary reflection of the laser light transmitted through the diffraction element can be prevented. preferable.

  As the birefringent resin that is the material of the first convex portion 4 and the second convex portion 5, a polymer liquid crystal or the like can be used. As a method for forming the convex portion, for example, a liquid crystal monomer such as nematic liquid crystal is uniformly applied on the first transparent substrate 1 and the second transparent substrate 2 and polymerized by irradiating with UV light. What is necessary is just to process so that a cross section may become uneven | corrugated using techniques, such as lithography and an etching.

The first convex portion 4 and the filling adhesive 6 are constituent elements of the first diffraction grating, and the second convex portion 5 and the filling adhesive 7 are constituent elements of the second diffraction grating. Two diffraction gratings are stacked with the transparent substrate 2 interposed therebetween to form a three-wavelength diffraction element. In this three-wavelength diffraction element, light of three different wavelengths λ ₁ , λ _2, and λ ₃ is incident and used. The first diffraction grating diffracts incident light of wavelength λ ₁ , and wavelength λ transmitted through the ₂ and wavelength lambda ₃ of the incident light, the second diffraction grating with which transmits incident light having a wavelength of lambda _1, has a configuration that diffracts incident light having a wavelength lambda _3. Hereinafter, description will be made assuming that the convex portion is made of polymer liquid crystal.

As the filling adhesive 6 constituting the first diffraction grating, the refractive index is substantially the same as the ordinary refractive index of the polymer liquid crystal that is the material of the first convex portion 4 with respect to the wavelength λ ₃ that transmits the diffraction grating, for example. Choose the same thing. On the other hand, as the filling adhesive 7 constituting the second diffraction grating, the refractive index thereof is, for example, the ordinary refractive index of the polymer liquid crystal that is the material of the second convex portion 5 with respect to the wavelength λ ₁ that transmits the diffraction grating. Select approximately the same.

  Further, the first convex portion 4 made of the polymer liquid crystal is orthogonal to the extraordinary refractive index axis direction of the first convex portion 4 and the second convex portion 5 made of polymer liquid crystal is perpendicular to the axial direction of the extraordinary light refractive index. And the second diffraction grating are stacked.

At this time, in the axial direction of the first extraordinary refractive index of the convex portion 4, when the laser beam of wavelength lambda ₁ is linearly polarized light having a polarization direction, wavelength lambda ₁ of the laser beam, three-wavelength diffraction element Can be diffracted by the first diffraction grating and transmitted without being diffracted by the second diffraction grating. On the other hand, when the polarization direction of the laser beam polarization direction and wavelength lambda ₃ of the wavelength lambda ₁ of the laser beam is orthogonal, laser light having a wavelength lambda ₃ is, when passing through the diffractive element for the three wavelengths, the first diffraction grating Is diffracted by the second diffraction grating.

  As described above, according to the diffraction element of the first embodiment, diffraction can be controlled in a wavelength selective manner by utilizing the polarization dependence of the two diffraction gratings.

  In addition, the height of the first convex portion 4 and the second convex portion 5 is appropriately determined in consideration of the extraordinary light refractive index of the polymer liquid crystal that is the material of the convex portion and the refractive index of the filling adhesive. Thus, desired diffraction efficiencies can be obtained for the wavelengths of the laser beams that pass through the diffraction element for three wavelengths.

The diffractive element for three wavelengths of the first embodiment is a compatible optical head device for reproducing / recording BD, DVD, and CD having different standards, and a 405 nm wavelength band for BD as a laser beam of wavelength λ ₁ , wavelength λ _For tracking of BD and CD in a compatible optical head device equipped with a three-wavelength semiconductor laser that outputs laser light in the 660 nm wavelength band for DVD as the laser light ₂ and laser light in the 780 nm wavelength band for CD as the laser light of wavelength λ ₃ It can be used as a diffraction element for obtaining the three beams. On the other hand, in the DVD, when reproduction / recording of the RAM standard is not performed, since tracking can be performed without using three beams, a laser beam that diffracts by the two diffraction gratings of the three-wavelength diffraction element is not required, and is transmitted straight ahead. It is sufficient to use only light.

In the three-wavelength diffractive element of the first embodiment, the second diffraction grating does not generate diffracted light as unnecessary light with respect to the BD laser light having the wavelength λ ₁ , while it is for CD having the wavelength λ ₃ . For the laser beam, the first diffraction grating does not generate diffracted light as unnecessary light. That is, in the compatible optical head device, unnecessary diffracted light that becomes noise is not generated, so that favorable reproduction / recording characteristics can be obtained.

  Further, the three-wavelength diffraction element of the first embodiment can design the diffraction efficiency and the diffraction direction with a high degree of freedom for each of the laser beams having the wavelengths for BD and CD. Since the wavelength selective use is possible, it is possible to realize a compatible optical head device equipped with a three-wavelength semiconductor laser that is required to be small and light.

  Here, as a compatible optical head device, a two-wavelength semiconductor laser that outputs laser light in a 660 nm wavelength band for DVD and a 780 nm wavelength band for CD, and a semiconductor laser that outputs laser light in a 405 nm wavelength band for BD Even in a compatible optical head device that performs two BD, DVD, and CD reproduction / recording, the three-wavelength diffractive element according to a third embodiment to be described later may be mounted. The same function as described above can be exhibited by installing the diffraction element for three wavelengths at a position through which the laser beams pass in common.

“Second Embodiment”
FIG. 3 is a cross-sectional view showing the configuration of the three-wavelength diffractive element according to the second embodiment of the present invention, and a periodic projection made of an inorganic material on one surface of the three-wavelength diffractive element in the first embodiment. third diffraction grating is further formed with a part, and has a three-wavelength diffraction element second diffraction grating transmits incident light of wavelength lambda ₂ of the three-wavelength diffraction element of the first embodiment . Here, in the third diffraction grating, the inorganic material may be a periodic convex portion, but the inorganic material may be continuously connected at a periodic uneven portion, that is, a valley bottom. The description of the configuration of the three-wavelength diffraction element according to the first embodiment is omitted.

  In the same manner as in the first embodiment, the convex portions are made of polymer liquid crystal, and the material filling the space between the convex portions is assumed to be a filling adhesive that is an optically isotropic resin.

  This configuration also has three transparent substrates 13, 14 and 15, and the first transparent substrate 13, the second transparent substrate 14, and the third transparent substrate 15 are made of glass, quartz glass, plastic, or the like. it can. Further, by forming an antireflection film on the surface of the first transparent substrate 13, unnecessary reflection of the laser light transmitted through the three-wavelength diffraction element can be prevented. A third convex portion 18 made of an inorganic material is formed on the surface of the third transparent substrate 15, and a laser that transmits the three-wavelength diffraction element by forming an antireflection film on the surface. Unnecessary reflection of light can be prevented.

Here, the height of the second convex portion 17 is the difference between the extraordinary light refractive index of the polymer liquid crystal and the refractive index of the filling adhesive 20 with respect to the laser light having the wavelength λ ₂ that passes through the diffraction element for three wavelengths. the product of the height of the convex portion 17 is an integral multiple of the wavelength lambda _2, is selected for example to be 1-fold. A diffraction grating including the second convex portion 17 and the filling adhesive 20 as constituent elements is referred to as a second diffraction grating.

On the other hand, the height of the first convex portion 16 is such that the three wavelengths in the diffraction grating (which is referred to as the first diffraction grating) including the first convex portion 16 and the first filling adhesive 19 as constituent elements. The laser beam is selected so as to obtain a desired diffraction efficiency with respect to the laser beam having the wavelength λ ₁ that is transmitted through the diffraction element.

It is desirable to select SiO ₂ (quartz) as the inorganic material that is the material of the third convex portion 18 because it is easy to process by film formation or etching. In particular, when quartz glass is selected as the third transparent substrate 15, it is preferable that no SiO ₂ film be formed. However, depending on the application, Ta ₂ O ₅ , SiON, or the like that is substantially colorless and transparent at least between a wavelength of 380 nm and a wavelength of 820 nm may be used. Here, the height of the third convex portion 18 is the difference between the refractive index of the convex portion 18 and the refractive index of air with respect to the laser beam having the wavelength λ ₁ that passes through the three-wavelength diffraction element, and the height thereof. product represents an integer multiple of the wavelength lambda _1, is selected for example to be doubled.

The filling adhesive 19 is selected so that its refractive index is substantially the same as the ordinary refractive index of the polymer liquid crystal that is the material of the first convex portion 16 with respect to the wavelength λ ₃ that passes through the diffraction element for three wavelengths. To do. On the other hand, as the filling adhesive 20, a material whose refractive index is substantially the same as the ordinary light refractive index of the polymer liquid crystal that is the material of the second convex portion 17 with respect to the wavelength λ ₁ that passes through the diffraction element for three wavelengths is selected. To do.

  Further, the axial direction of the extraordinary light refractive index of the first convex portion 16 made of the polymer liquid crystal is orthogonal to the axial direction of the extraordinary light refractive index of the second convex portion 17 made of the polymer liquid crystal. And the second diffraction grating are stacked.

At this time, the first axis direction of the extraordinary light refractive index of the convex portion 16, when a laser beam having a wavelength lambda ₁ is linearly polarized light having a polarization direction, the laser beam of wavelength lambda ₁ is diffracted for the three wavelengths When transmitting through the element, it is diffracted by the first diffraction grating, transmitted without being diffracted by the second diffraction grating, and not diffracted by the third diffraction grating by the third convex portion 18 and air.

On the other hand, if the polarization direction of the polarization direction and wavelength lambda ₂ of the laser beam having a wavelength lambda ₁ of the laser beam is orthogonal, laser light having a wavelength lambda ₂ is, when passing through the three-wavelength diffraction element, a first diffraction grating Then, the second diffraction grating does not diffract, but the third diffraction grating diffracts.

On the other hand, if the polarization direction of the laser beam in the polarization direction and wavelength lambda ₃ of the wavelength lambda ₁ of the laser beam is orthogonal, laser light having a wavelength lambda ₃ is, when passing through the diffractive element for the three wavelengths, the first diffraction The second diffraction grating can diffract without diffraction by the grating. In the third diffraction grating, when the wavelength lambda ₃ is approximately twice the wavelength lambda _1, wavelength lambda ₃ because the wavelength lambda ₁ is not diffracted hardly diffraction.

The diffractive element for three wavelengths of the second embodiment is a compatible optical head device for reproducing / recording BD, DVD and CD having different standards, and a 405 nm wavelength band for BD as a laser beam of wavelength λ ₁ and for DVD In a compatible optical head device equipped with a three-wavelength semiconductor laser that outputs a laser beam in the 780 nm wavelength band for CD as a laser beam in the 660 nm wavelength band and wavelength λ ₂ , three beams for tracking BD, DVD, and CD are obtained. Can be used as a diffractive element.

In three-wavelength diffraction element of the second embodiment, the laser light for BD wavelength lambda _1, a second diffraction grating, the third diffraction grating, does not generate diffracted light as unnecessary light, On the other hand, the laser light for DVD of wavelength lambda _2, the first diffraction grating, the second diffraction grating, does not generate diffracted light as unnecessary light. On the other hand, the laser light for CD of wavelength lambda _3, not diffracted in the first diffraction grating, in the third diffraction grating, approximately twice the wavelength lambda ₃ is the wavelength lambda ₁ for BD for CD Therefore, almost no diffracted light is generated as unnecessary light.

  In other words, the compatible optical head device does not generate unnecessary diffracted light that causes noise, so that excellent reproduction / recording characteristics can be obtained, and the diffraction effect can be selectively used while being a single element. Therefore, a compatible optical head device equipped with a three-wavelength semiconductor laser that is required to be small and light can be realized.

  Moreover, the diffraction element for three wavelengths of 2nd Embodiment can design a diffraction efficiency and a diffraction direction with a high freedom degree with respect to each of the laser beam of the wavelength for BD, DVD, and CD.

  Further, compared to the three-wavelength diffractive element of the first embodiment, the degree of freedom in designing the diffraction efficiency for BD, DVD, and CD laser light is reduced, but it corresponds to reproduction / recording of the DVD-RAM standard. be able to.

“Third Embodiment”
FIG. 5 is a cross-sectional view showing the structure of the diffraction element according to the third embodiment of the present invention, with a phase plate in which two phase plates are laminated so as to sandwich the three-wavelength diffraction element of the first embodiment. A diffraction element for three wavelengths. The description of the configuration of the three-wavelength diffraction element according to the first embodiment is omitted.

  In the present embodiment, four transparent substrates 31, 32, 33, and 34 are used. In the same manner as in the first embodiment, the convex portions are made of polymer liquid crystal, and the material filling the space between the convex portions is assumed to be a filling adhesive that is an optically isotropic resin. Further, the two phase plates are made of, for example, a birefringent resin.

  As the first transparent substrate 31, the second transparent substrate 32, the third transparent substrate 33, and the fourth transparent substrate 34, glass, quartz glass, plastic, or the like can be used. Further, an antireflection film is formed on the air-side surfaces of the first transparent substrate 31 and the fourth transparent substrate 34, so that unnecessary reflection of the laser light transmitted through the three-wavelength diffraction element with a phase plate can be prevented. Can be prevented.

The filling adhesive 39 is selected so that its refractive index is substantially the same as the ordinary refractive index of the polymer liquid crystal that is the material of the first convex portion 37 for the wavelength λ ₃ that passes through the three-wavelength diffraction element with a phase plate To do. On the other hand, as the filling adhesive 40, its refractive index is substantially the same as the ordinary refractive index of the polymer liquid crystal that is the material of the second convex portion 38 with respect to the wavelength λ ₁ that transmits the three-wavelength diffraction element with a phase plate. Select. The heights of the first and second convex portions 37 and 38 are appropriately determined in consideration of the extraordinary light refractive index of the polymer liquid crystal that is the material of the convex portion and the refractive index of the filling adhesive. Thus, a desired diffraction efficiency can be obtained with respect to the wavelength of the laser beam transmitted through the three-wavelength diffraction element with a phase plate.

The phase plate 35 consisting of the first birefringent resin, the laser beam having a wavelength lambda _1, is a retardation value equal to the wavelength lambda _1, and the wavelength lambda ₂ or wavelength lambda _3, approximately 1 wavelength The birefringent material and thickness are determined so as to be / 2. Similarly, the phase plate 36 made of the second birefringent resin is similarly doubled so that the retardation value is equal to the wavelength λ ₁ and approximately half the wavelength with respect to the wavelength λ ₂ or λ _3. Determine refractive material and thickness.

  When the first to fourth transparent substrates are laminated to form a three-wavelength diffraction element, the angle formed by the fast axis of the first phase plate 35 and the axial direction of the extraordinary refractive index of the first convex portion 37 is For example, the angle formed by the axis direction of the extraordinary light refractive index of the first convex portion 37 and the axial direction of the extraordinary light refractive index of the second convex portion 38 is 45 ° (may be 135 °, 225 °, 315 °, etc.). For example, the angle formed by 90 ° (may be 270 °, etc.) and the fast axis of the first phase plate 35 and the fast axis of the second phase plate 36 is, for example, 90 ° (may be 270 °, etc.). Laminate to.

In the three-wavelength diffractive element with phase plate of the third embodiment formed in this way, the laser light of wavelength λ ₁ is linearly polarized light having a polarization direction in the axial direction of the extraordinary light refractive index of the first convex portion 37. To do. When the laser light having the wavelength λ ₁ is transmitted through the diffraction element for three wavelengths with a phase plate, the laser light is transmitted through the first phase plate 35 without changing its polarization state, and the first convex portion 37 and the first filling adhesion are transmitted. A diffraction grating (referred to as a first diffraction grating) that is diffracted by a diffraction grating including an agent 39 and that includes a second convex portion 38 and a second filling adhesive 40 (this is referred to as a second diffraction grating). Without being diffracted, the light passes straight and passes through the second phase plate 36 without changing its polarization state.

On the other hand, assuming that the polarization direction of the laser light having the wavelength λ _{1 and} the laser light having the wavelength λ ₂ for the three wavelengths with the phase plate have the same polarization direction, when the laser light having the wavelength λ ₂ passes through the diffraction element, The first phase plate 35 transmits the light with its polarization direction rotated by approximately 90 °, passes straight through the first diffraction grating without being diffracted, diffracts at the second diffraction grating, and passes through the second phase plate 36. Further, the polarization direction is rotated by approximately 90 °, and the light is transmitted back to the polarization direction before entering the three-wavelength diffraction element with a phase plate.

Similarly, assuming that the polarization direction of the laser beam having the wavelength λ _{1 and} the laser beam having the wavelength λ ₃ have the same polarization direction, the laser beam having the wavelength λ ₃ passes through the diffractive element for three wavelengths with the phase plate. at first phase plate 35, the polarization direction transmitted by rotating approximately 90 °, and straightly transmitted without diffracting the first diffraction grating, diffracted at the second diffraction grating, a second phase plate 36 Further, the polarization direction is rotated by approximately 90 °, and the light is transmitted back to the polarization direction before entering the three-wavelength diffraction element with a phase plate.

  As described above, according to the three-wavelength diffraction element with a phase plate of the third embodiment, the diffraction effect is selectively obtained by utilizing the wavelength dependency of the two phase plates and the polarization dependency of the two diffraction gratings. Can be controlled.

The three-wavelength diffractive element with phase plate of the third embodiment can be used as a diffractive element for obtaining three beams for tracking BD and CD. That is, a compatible optical head device for reproducing / recording BD, DVD and CD having different standards based on the configuration shown in FIG. 7 and having a wavelength of 405 nm as a laser beam of wavelength λ ₁ and a wavelength of λ ₂ In a compatible optical head device equipped with a three-wavelength semiconductor laser 53 that outputs a laser beam in a 660 nm wavelength band for DVD as a laser beam and a 780 nm wavelength band for a CD as a laser beam having a wavelength λ ₃ , for tracking BD and CD It can be used as a diffraction element for obtaining three beams. On the other hand, in the DVD, when the reproduction / recording of the RAM standard is not performed, since tracking can be performed without using three beams, only the laser beam that directly transmits two diffraction grating lights of the three-wavelength diffraction element with a phase plate is used.

  In the compatible optical head device of FIG. 7, the three-wavelength diffractive element with phase plate of the third embodiment is installed as the diffractive element 52, and the laser light emitted from the three-wavelength semiconductor laser 53 is polarized after passing through the diffractive element 52. The light is reflected by the beam splitter 54, passes through the collimating lens 55, the quarter wavelength plate 56, and the objective lens 57, and is condensed on the optical recording medium 58. The laser light reflected from the optical recording medium 58 passes through the objective lens 57, the quarter-wave plate 56, the collimator lens 55, and the polarization beam splitter 54 and is collected on the photodetector 59. As the polarization beam splitter 54, it is desirable to select a polarization beam splitter having the same polarization dependency with respect to reflection / transmission with respect to the laser light of the three wavelength bands. The quarter-wave plate 56 can also generate a quarter-phase difference with respect to the laser light in the three wavelength bands, and can convert linearly polarized light into circularly polarized light or circularly polarized light into linearly polarized light. It is desirable to select.

In the compatible optical head device of FIG. 7, the three-wavelength diffraction element with a phase plate of the third embodiment emits diffracted light, which is unnecessary light in the second diffraction grating, with respect to the BD laser light having the wavelength λ _1. On the other hand, almost no diffracted light, which is unnecessary light, is generated in the first diffraction grating even for the laser beam for CD having the wavelength λ ₃ . In other words, in the compatible optical head device, unnecessary diffracted light that becomes noise is hardly generated, and thus excellent reproduction / recording characteristics can be obtained.

  Further, the three-wavelength diffraction element with phase plate of the third embodiment can design the diffraction efficiency and the diffraction direction with a high degree of freedom for each of the laser beams having the wavelengths for BD and CD. Since the effect can be used in a wavelength selective manner, a compatible optical head device equipped with a three-wavelength semiconductor laser that is required to be small and light can be realized. In particular, it can be used when the polarization direction of laser light output as linearly polarized light from a three-wavelength semiconductor laser is substantially the same in three wavelength bands, and a phase plate that controls the polarization direction is laminated. The number of parts mounted on the optical head device can be reduced.

“Fourth Embodiment”
FIG. 6 is a cross-sectional view showing the configuration of the diffraction element according to the fourth embodiment of the present invention, in which two phase plates are laminated so as to sandwich the three-wavelength diffraction element of the first embodiment. One of the phase plates has a periodic concavo-convex portion or a convex portion made of an inorganic material that transmits incident light of wavelength λ ₁ and wavelength λ ₃ and diffracts incident light of wavelength λ ₂ . 3 diffraction gratings are further formed. Here, in the third diffraction grating, the inorganic material may be a periodic convex portion, but the inorganic material may be continuously connected at a periodic uneven portion, that is, a valley bottom. The description of the configuration of the three-wavelength diffraction element according to the first embodiment is omitted. In the present embodiment, four transparent substrates 41, 42, 43 and 44 are used. In the same manner as in the first embodiment, the convex portions are made of polymer liquid crystal, and the material filling the space between the convex portions is assumed to be a filling adhesive that is an optically isotropic resin. The two phase plates are assumed to be made of birefringent resin.

  As the first transparent substrate 41, the second transparent substrate 42, the third transparent substrate 43, and the fourth transparent substrate 44, glass, quartz glass, plastic, or the like can be used. Further, by forming an antireflection film on the air-side surface of the first transparent substrate 41, unnecessary reflection of the laser light transmitted through the diffraction element can be prevented. By forming an antireflection film on the surface of the third diffraction grating, unnecessary reflection of the laser light transmitted through the three-wavelength diffraction element with a phase plate can be prevented.

The filling adhesive 50 is selected so that its refractive index is substantially the same as the ordinary light refractive index of the polymer liquid crystal that is the material of the first convex portion 45 for the wavelength λ ₃ that transmits the three-wavelength diffraction element with a phase plate To do. On the other hand, as the filling adhesive 51, the refractive index is substantially the same as the ordinary light refractive index of the polymer liquid crystal that is the material of the second convex portion 46 with respect to the wavelength λ ₁ that transmits the three-wavelength diffraction element with a phase plate. Select. Here, the height of the second protrusion 46 is such that the extraordinary light refraction of the polymer liquid crystal that is the material of the second protrusion 46 with respect to the laser light having the wavelength λ ₂ that passes through the three-wavelength diffraction element with a phase plate. the difference between the rate and the refractive index of the filler adhesive 51 is an integral multiple of the wavelength lambda _2, is selected for example to be 1-fold.

On the other hand, the height of the first convex portion 45 is such that the diffraction grating for a three-wavelength with a phase plate is provided in a diffraction grating (referred to as a first diffraction grating) including the first convex portion 45 and the first filling adhesive 50. The laser beam is selected so that a desired diffraction efficiency can be obtained with respect to the laser beam having the wavelength λ _{1 that} is transmitted.

It is desirable to select SiO ₂ (quartz) as the inorganic material that is the material of the third convex portion 47 because it is easy to process by film formation or etching. In particular, when quartz glass is selected as the fourth transparent substrate 44, it is desirable not to form a SiO ₂ film. However, depending on the application, Ta ₂ O ₅ , SiON, or the like that is substantially colorless and transparent at least between a wavelength of 380 nm and a wavelength of 820 nm may be used. Here, the height of the third convex portion 47 is the difference between the height of the refractive index of the convex portion 47 and the refractive index of air with respect to the laser beam having the wavelength λ ₁ transmitted through the three-wavelength diffraction element with a phase plate. product is an integral multiple of the wavelength lambda _1, is selected for example to be doubled.

As the first phase plate 48, the laser beam of wavelength lambda _1, the retardation value, determine the birefringent material and thickness to be equal to the wavelength lambda _1. Similarly, the phase plate 49 made of the second birefringent resin similarly has a retardation value equal to the wavelength λ ₁ and approximately half the wavelength with respect to the wavelength λ ₂ or the wavelength λ _3. Determine birefringent material and thickness.

  When laminating the first to fourth transparent substrates as diffraction elements, the angle formed between the fast axis of the first phase plate 41 and the axial direction of the extraordinary light transmittance of the first convex portion 45 is, for example, 45 °, The angle formed by the axial direction of the abnormal light transmittance of the first convex portion 45 and the axial direction of the abnormal light transmittance of the second convex portion 46 is, for example, 90 °, and the fast axis of the first phase plate 48 and the first axis The two phase plates 49 are laminated so that the angle formed by the fast axis is 90 °, for example.

In the three-wavelength diffraction element with a phase plate of the fourth embodiment formed in this way, the laser light having the wavelength λ ₁ is linearly polarized light having a polarization direction in the axial direction of the extraordinary light transmittance of the first convex portion 45. Then, when the laser light having the wavelength λ ₁ is transmitted through the three-wavelength diffraction element with a phase plate, the laser beam is transmitted through the first phase plate 48 without changing its polarization state. A diffraction grating (this is referred to as a second diffraction grating) that is diffracted by a diffraction grating including a filling adhesive 50 (referred to as a first diffraction grating) and includes a second convex portion 46 and a second filling adhesive 51. ) Through the second phase plate 49 without changing its polarization state, and through the third diffraction grating without diffracting.

On the other hand, the laser light of wavelength lambda ₂ having the same polarization direction as the polarization direction of the laser beam having the wavelength lambda ₁ is, when passing through the diffractive element for the phase Backed three wavelengths at the first phase plate 48, the polarization direction thereof Is transmitted through the first diffraction grating without being diffracted, and is transmitted through the second diffraction grating without being diffracted. The light is transmitted with the polarization direction rotated by approximately 90 °, and is diffracted by the third diffraction grating.

Similarly, assuming that the polarization direction of the laser beam having the wavelength λ _{1 and} the laser beam having the wavelength λ ₃ have the same polarization direction, the laser beam having the wavelength λ ₃ passes through the diffractive element for three wavelengths with the phase plate. The first phase plate 48 transmits the light with its polarization direction rotated by approximately 90 °, passes straight through the first diffraction grating without being diffracted, diffracts at the second diffraction grating, and the second phase plate 49. Further, the polarization direction is rotated by approximately 90 ° and transmitted. In the third diffraction grating, when the wavelength lambda ₃ is approximately twice the wavelength lambda _1, the wavelength lambda ₁ as described above is straightly transmitted without being diffracted, a wavelength lambda ₃ is hardly diffracted.

  As described above, according to the three-wavelength diffraction element with a phase plate of the fourth embodiment, the wavelength dependency of the two phase plates, the polarization dependency of the two diffraction gratings, and the wavelength dependency of the diffraction grating made of an inorganic material are obtained. By utilizing this, the diffraction effect can be controlled in a wavelength selective manner.

The three-wavelength diffractive element with phase plate of the fourth embodiment is a compatible optical head device for reproducing / recording BD, DVD and CD having different standards, and a 405 nm wavelength band for BD as a laser beam having a wavelength λ ₁ . Three beams for tracking BD, DVD and CD in a compatible optical head device equipped with a three-wavelength semiconductor laser that outputs laser light in the 780 nm wavelength band for CD as laser light in the 660 nm wavelength band and wavelength λ ₂ for DVD It can be used as a diffraction element for obtaining

The three-wavelength diffraction element with a phase plate of the fourth embodiment does not generate diffracted light, which is unnecessary light in the second diffraction grating and the third diffraction grating, with respect to the BD laser light having the wavelength λ ₁ whereas, for the DVD laser light of wavelength lambda _2, the first diffraction grating, it does not generate diffracted light is unnecessary light in the second diffraction grating.

On the other hand, with respect to laser light for CD of wavelength lambda _3, not diffracted in the first diffraction grating, in the third diffraction grating, approximately twice the wavelength lambda ₃ is the wavelength lambda ₁ for BD for CD Therefore, diffracted light that is unnecessary light is hardly generated.

  In other words, the compatible optical head device does not generate unnecessary diffracted light that causes noise, so that excellent reproduction / recording characteristics can be obtained, and the diffraction effect can be selectively used while being a single element. Therefore, a compatible optical head device equipped with a three-wavelength semiconductor laser that is required to be small and light can be realized. In particular, it can be used when the polarization direction of laser light output as linearly polarized light from a three-wavelength semiconductor laser is substantially the same in three wavelength bands, and a phase plate that controls the polarization direction is laminated. The number of parts mounted on the optical head device can be reduced.

  Further, the three-wavelength diffractive element with phase plate of the fourth embodiment can design the diffraction efficiency and the diffraction direction with a high degree of freedom for each of the laser beams having the wavelengths for BD, DVD and CD. In addition, the degree of freedom in designing the diffraction efficiency for BD, DVD, and CD laser light is reduced compared to the three-wavelength diffraction element with phase plate of the third embodiment. Can respond.

"Example 1"
This example is a specific example of the first embodiment shown in FIG. 1, it referred to work made methods below. First, the glass of the first air-side surface of the transparent substrate 1, forming an anti-reflection film by vacuum deposition. Next, the first transparent substrate 1 made of glass, a liquid crystal monomer having birefringence is uniformly applied, by polymerization by irradiation with UV light, a polymer liquid crystal film. At this time, the coating conditions are determined so that the alignment direction of the liquid crystal molecules is selected to be perpendicular to the paper surface and the thickness is 1.8 μm. This polymer liquid crystal film has an ordinary light refractive index of 1.542 and an extraordinary light refractive index of 1.588 with respect to a wavelength of 405 nm. The ordinary light refractive index with respect to the wavelength of 660 nm is 1.517, and the extraordinary light refractive index is 1.556. The ordinary light refractive index with respect to the wavelength of 780 nm is 1.514, and the extraordinary light refractive index is 1.552. The polymer liquid crystal film is processed so as to have a concavo-convex cross section using photolithography and etching techniques.

  Similarly, a polymer liquid crystal film is formed on the second transparent substrate 2 made of glass using the liquid crystal monomer. At this time, the liquid crystal molecules are selected so that the alignment direction of the liquid crystal molecules is parallel to the paper surface, and the film is formed to have a thickness of 3.3 μm. Further, processing is performed using a photolithography and etching technique so that the cross section becomes uneven. At this time, the period and direction of the convex part 5 to be formed are different from the period and direction of the convex part 4 made of the polymer liquid crystal of the first transparent substrate 1. That is, the pitch is several μm to several tens of μm, and the lattice angle is different by about 1 °.

Then, so as to fill the protrusions 5 formed of the second transparent substrate 2 liquid crystal polymer, bonding the third transparent substrate 3 with the filler adhesive 7. Note that the surface not bonded to the third transparent substrate 3, the anti-reflection film is formed. At this time, as the filling adhesive 7, an adhesive having a refractive index of 1.542 for a wavelength of 405 nm, a refractive index of 1.515 for a wavelength of 660 nm, and a refractive index of 1.512 for a wavelength of 780 nm is selected. Here, let the diffraction grating which has the convex part 5 and the filling adhesive 7 be a 2nd diffraction grating.

Then, so as to fill the protrusions 4 formed of a first transparent substrate 1 polymer liquid crystal, by using a filling adhesive 6, to adhere the adhesive to non surface of the second transparent substrate 2. At this time, as the filling adhesive 6, an adhesive having a refractive index of 1.544 for a wavelength of 405 nm, a refractive index of 1.518 for a wavelength of 660 nm, and a refractive index of 1.514 for a wavelength of 780 nm is selected. Here, the diffraction grating having the convex portions 4 and the filling adhesive 6 is defined as a first diffraction grating.

  In the thus produced three-wavelength diffraction element of this example, when laser light having a wavelength of 405 nm and linearly polarized light whose polarization direction is perpendicular to the plane of the paper is transmitted through this element, the first diffraction grating Diffraction occurs from the relationship between the extraordinary light refractive index and the refractive index of the filled adhesive and the grating height (1.8 μm). At this time, the 0th-order transmittance is about 67% and the first-order diffraction efficiency is about 13.5%. On the other hand, in the second diffraction grating, the ordinary light refractive index of the polymer liquid crystal and the refractive index of the filling adhesive 7 are the same, so that the light passes straight without being diffracted.

  When laser light having a wavelength of 780 nm and linearly polarized light whose polarization direction is parallel to the paper surface is transmitted through this element, in the first diffraction grating, the ordinary refractive index of the polymer liquid crystal and the refractive index of the filling adhesive 6 are equal. The second diffraction grating diffracts from the relationship between the difference between the extraordinary light refractive index of the polymer liquid crystal and the refractive index of the filling adhesive 7 and the grating height (3.3 μm). At this time, the 0th order transmittance is about 74%, and the first order diffraction efficiency is about 10%.

  On the other hand, when laser light having a wavelength of 660 nm and linearly polarized light whose polarization direction is parallel to the paper surface is transmitted through this element, the first diffraction grating has the ordinary refractive index of the polymer liquid crystal and the refractive index of the filling adhesive 6. Since it is almost equal, it passes straight through without almost diffracting, and the second diffraction grating is diffracted from the relationship between the extraordinary refractive index of the polymer liquid crystal and the refractive index of the filling adhesive 7 and the grating height (3.3 μm). To do. At this time, the 0th order transmittance is about 64%, and the first order diffraction efficiency is about 14.6%.

  The three-wavelength diffractive element of this example is a compatible optical head device for reproducing / recording BD, DVD and CD with different standards, and has a 405 nm wavelength band for BD, a 660 nm wavelength band for DVD, and 780 nm for CD. In a compatible optical head device equipped with a three-wavelength semiconductor laser that outputs a laser beam in the wavelength band, it can be used as a diffractive element for obtaining three beams for tracking BD and CD.

"Example 2"
This example is a three-wavelength diffraction element having the structure shown in FIG. The convex portion 10 made of polymer liquid crystal formed on the first transparent substrate 8 and the convex portion 11 made of polymer liquid crystal formed on the second transparent substrate 9 are bonded with a filling adhesive 12 so as to face each other. ing. Further, an antireflection film is formed on the surface of the first transparent substrate and the second transparent substrate that are not bonded. Here, the diffraction grating having the convex portion 10 and the filling adhesive 12 is a first diffraction grating, and the diffraction grating having the convex portion 11 and the filling adhesive 12 is a second diffraction grating.

  The convex part 10 of the 1st transparent substrate 8 and the convex part 11 of the 2nd transparent substrate 9 are produced similarly using the same material as the diffraction element for 3 wavelengths of Example 1. FIG. As the filling adhesive 12, an adhesive having a refractive index of 1.542 for a wavelength of 405 nm, a refractive index of 1.517 for a wavelength of 660 nm, and a refractive index of 1.512 for a wavelength of 780 nm is selected.

  The diffractive element for three wavelengths of this example is the same as the diffractive element for three wavelengths of Example 1, in a compatible optical head device equipped with a three-wavelength semiconductor laser for reproducing / recording BD, DVD and CD having different standards. It can be used as a diffractive element for obtaining three beams for tracking CDs, and the same effect can be obtained.

  Furthermore, since the number of transparent substrates constituting the element can be reduced, the diffractive element itself can be reduced in size and weight.

"Example 3"
This example is a specific example of the second embodiment shown in FIG. 3, it referred to work made methods below.

First, the glass of the air-side surface of the first transparent substrate 13, forming the antireflection film by vacuum deposition. Next, the first transparent substrate 13 made of glass, the same as the convex portions 4 comprising a polymer liquid crystal of Example 1 (FIG. 1), to form the convex portion 16. Similarly, the second transparent substrate 14 made of glass, forming a polymer liquid crystal film using the same liquid crystal monomer. At this time, the liquid crystal alignment direction is selected so as to be parallel to the paper surface, and the film is formed so as to have a thickness of 16.1 μm. Further, processing is performed using a photolithography and etching technique so that the cross section becomes uneven. At this time, the period and direction of the convex part 17 to be formed are different from the period and direction of the convex part 16 made of the polymer liquid crystal of the first transparent substrate 13.

Then, so as to fill the protrusions 17 made of a polymer liquid crystal of the second transparent substrate 14, bonding the third transparent substrate 15 using a packed adhesive 20. As the filling adhesive 20, the same one as the filling adhesive 4 of Example 1 (FIG. 1) is used. Here, the diffraction grating having the convex portion 17 and the filling adhesive 20 is the second diffraction grating.

In addition, the convex part 18 which consists of inorganic materials is formed in the surface which the 3rd transparent substrate 15 has not adhere | attached. The convex portion 18 made of an inorganic material is formed before bonding to the second transparent substrate 14, and an antireflection film is formed on the surface thereof. Work made method after forming the quartz by sputtering in the third transparent substrate 15, using a photolithography and etching technique, it is processed so that the cross section is convex. At this time, the period and direction of the protrusions 18 to be formed are the period and direction of the protrusions 16 made of the polymer liquid crystal of the first transparent substrate 13 and the protrusions made of the polymer liquid crystal of the second transparent substrate 14. 17 different periods and directions. At this time, the refractive index for the wavelength of 405 nm of the quartz film to be formed is 1.470, the refractive index for the wavelength of 660 nm is 1.456, and the refractive index for the wavelength of 780 nm is 1.454. Moreover, the depth of the convex part to be etched is 1.72 μm. Here, the diffraction grating having the convex portion 18 is the third diffraction grating.

  Next, the unadhered surface of the second transparent substrate 14 is bonded using a filling adhesive 19 so as to fill the convex portions 16 made of polymer liquid crystal on the first transparent substrate 13. As the filling adhesive 19, the same one as the filling adhesive 6 used in Example 1 (FIG. 1) is used. Here, the diffraction grating having the convex portion 16 and the filling adhesive 19 is the first diffraction grating.

  In the thus produced three-wavelength diffraction element of this example, when laser light having a wavelength of 405 nm and a linearly polarized light whose polarization direction is perpendicular to the paper surface is transmitted through the element, the first diffraction grating has Diffraction occurs from the relationship between the difference between the extraordinary light refractive index and the refractive index of the filling adhesive 19 and the grating height (1.8 μm). At this time, the 0th-order transmittance is about 67% and the first-order diffraction efficiency is about 13.5%. In the second diffraction grating, since the ordinary light refractive index of the polymer liquid crystal and the refractive index of the filling adhesive are equal, they pass straight without being diffracted. Further, in the third diffraction grating, the difference between the optical path length of the concave portion and the optical path length of the convex portion is 810 nm, which is twice the wavelength, so that the light passes straight without being diffracted.

  When laser light having a wavelength of 660 nm and linearly polarized light whose polarization direction is parallel to the paper surface is transmitted through the element, the ordinary refractive index of the polymer liquid crystal and the refractive index of the filling adhesive 19 are substantially equal in the first diffraction grating. Therefore, in the second diffraction grating, the difference between the optical path length of the concave portion and the optical path length of the convex portion is 660 nm, which is one wavelength, so that it passes straight through without being diffracted. . The third diffraction grating diffracts from the relationship between the refractive index difference between the convex quartz and the concave air and the grating height (1.72 μm). At this time, the 0th-order transmittance is 69%, and the first-order diffraction efficiency is 12.6%.

  When laser light having a wavelength of 780 nm and linearly polarized light whose polarization direction is parallel to the paper surface is transmitted through this element, in the first diffraction grating, the ordinary refractive index of the polymer liquid crystal and the refractive index of the filling adhesive 19 are equal. The second diffraction grating diffracts from the relationship between the extraordinary light refractive index of the polymer liquid crystal and the refractive index of the filling adhesive 20 and the grating height (16.1 μm). At this time, the 0th order transmittance is about 73% and the first order diffraction efficiency is about 11%. In the third diffraction grating, the difference between the optical path length of the concave portion and the optical path length of the convex portion is 780 nm, which is one time the wavelength, so that the light passes straight without being diffracted.

  The three-wavelength diffractive element of this example is a compatible optical head device for reproducing / recording BD, DVD and CD with different standards, and has a 405 nm wavelength band for BD, a 660 nm wavelength band for DVD, and 780 nm for CD. In a compatible optical head device equipped with a three-wavelength semiconductor laser that outputs laser light in the wavelength band, it can be used as a diffractive element for obtaining three BD, DVD, and CD tracking beams.

"Example 4"
This example is a diffractive element having the structure shown in FIG. The convex portion 23 made of polymer liquid crystal formed on the first transparent substrate 21 and the convex portion 24 made of polymer liquid crystal formed on the second transparent substrate 22 are bonded with a filling adhesive 26 so as to face each other. ing. An antireflection film is formed on the surface of the first transparent substrate 21 that is not bonded. Here, the diffraction grating having the convex portion 23 and the filling adhesive 26 is a first diffraction grating, and the diffraction grating having the convex portion 24 and the filling adhesive 26 is a second diffraction grating.

On the other hand, a convex portion 25 made of an inorganic material is formed on the surface of the second transparent substrate 22 that is not bonded. The convex portion 25 made of an inorganic material is formed before the convex portion 24 made of a polymer liquid crystal formed on the other surface of the second transparent substrate 22 is formed. Work made method is similar to the convex portion 18 made of an inorganic material for forming the third transparent substrate 15 of Example 3 (Figure 3). Further, an antireflection film is formed on the surface. Here, the diffraction grating having the convex portions 25 is the third diffraction grating.

  The convex part 24 of the transparent substrate 22 is produced in the same manner using the same material as the three-wavelength diffraction element of Example 3. As the filling adhesive 26, the filling adhesive 12 used in the diffraction element of Example 2 (FIG. 2) is used.

  The diffractive element for three wavelengths of this example is the same as the diffractive element of Example 3, in a compatible optical head device equipped with a three-wavelength semiconductor laser for reproducing / recording BD, DVD and CD having different standards. It can be used as a diffraction element for obtaining three beams for CD tracking, and the same effect can be obtained.

  Furthermore, since the number of transparent substrates constituting the element can be reduced, the diffractive element itself can be reduced in size and weight.

"Example 5"
This embodiment is a specific example of the third embodiment shown in FIG. 5, referred to work made methods below.

  First, an antireflection film is formed on the air-side surface of the first transparent substrate 31 made of glass using a vacuum deposition method. Next, the liquid crystal monomer having the birefringence used in Example 1 is uniformly applied to the first transparent substrate 31 made of glass, and polymerized by UV irradiation to obtain a polymer liquid crystal film. At this time, the application conditions are determined so that the alignment direction of the liquid crystal molecules is selected to be 45 degrees to the right of the paper depth and the thickness is 8.8 μm.

  Similarly, an antireflection film is formed on the air-side surface of the fourth transparent substrate 34 made of glass using a vacuum vapor deposition method. Next, the above-mentioned liquid crystal monomer having birefringence is uniformly applied to the fourth transparent substrate 34 made of glass, and polymerized by irradiation with UV to obtain a polymer liquid crystal film. At this time, the liquid crystal alignment direction is selected so as to be a 45 degree left depth direction, and the coating conditions are determined so that the thickness is 8.8 μm.

  The same convex part 37 as the convex part 4 which consists of a polymer liquid crystal of Example 1 (FIG. 1) is formed in the 2nd transparent substrate 32 made from glass. Similarly, the same convex part 38 as the convex part 5 which consists of a polymer liquid crystal of Example 1 (FIG. 1) is formed in the 3rd transparent substrate 33 made from glass.

  Next, the polymer liquid crystal film 35 of the first transparent substrate 31 is bonded face-to-face using a filling adhesive 39 so as to fill the convex portions 37 made of the polymer liquid crystal of the second transparent substrate 32. As the filling adhesive 39, the same adhesive as the filling adhesive 6 of Example 1 (FIG. 1) is used. Here, the diffraction grating having the convex portion 37 and the filling adhesive 39 is the first diffraction grating.

Then, so as to fill the protrusions 38 made of a polymer liquid crystal of the third transparent substrate 33, using a packed adhesive 40 to bond the adhesive to non surface of the second transparent substrate 32 described above. As the filling adhesive 40, the same adhesive as the filling adhesive 7 of Example 1 (FIG. 1) is used. Here, the diffraction grating having the convex portions 38 and the filling adhesive 40 is the second diffraction grating.

  Further, the polymer liquid crystal film 36 of the fourth transparent substrate 34 and the non-adhered surface of the third transparent substrate 33 face each other and are bonded with a transparent adhesive.

  Here, in producing the three-wavelength diffraction element with a phase plate of this example, as a method of laminating the four transparent substrates, so as to fill the convex portion 37 made of the polymer liquid crystal of the second transparent substrate 32, Filling adhesion so that the polymer liquid crystal film 35 of the first transparent substrate 31 and the polymer liquid crystal film 35 of the third transparent substrate 33 are bonded to each other using the filling adhesive 39 to fill the convex portion 38 made of the polymer liquid crystal of the third transparent substrate 33. After separately preparing the polymer liquid crystal film 36 of the fourth transparent substrate 34 facing each other using the agent 40, the surface of the second transparent substrate 32 having no convex portion 37 made of polymer liquid crystal and Alternatively, a lamination method may be used in which the surface of the third transparent substrate 33 without the convex portion 38 made of polymer liquid crystal is adhered with a transparent adhesive. This is a configuration different from FIG.

  In the diffractive element of this example manufactured in this way, when a laser beam having a wavelength of 405 nm and a linearly polarized light whose polarization direction is perpendicular to the paper surface is transmitted through this element, the polymer liquid crystal film 35 of the first transparent substrate 31 is It functions as a phase plate (first phase plate) having a retardation value of 405 nm, which is the product of the difference between the extraordinary refractive index and the ordinary refractive index of the polymer liquid crystal and its thickness (8.8 μm). Since this retardation value is equal to the wavelength, it passes through without changing the polarization state of the laser light. The first diffraction grating diffracts from the relationship between the difference between the extraordinary light refractive index of the polymer liquid crystal and the refractive index of the filling adhesive 39 and the grating height. At this time, the 0th-order transmittance is about 67% and the first-order diffraction efficiency is about 13.5%. On the other hand, in the second diffraction grating, since the ordinary light refractive index of the polymer liquid crystal and the refractive index of the filling adhesive 40 are equal, they pass straight without being diffracted. The polymer liquid crystal film 36 of the fourth transparent substrate 34 also has a function as a phase plate (second phase plate) having a retardation value of 405 nm, and similarly transmits without changing the polarization state of the laser light.

  When laser light having a wavelength of 780 nm and linearly polarized light whose polarization direction is perpendicular to the paper surface is transmitted through this element, the polymer liquid crystal film 35 serving as the first phase plate functions as a phase plate having a retardation value of 334 nm. And change the polarization state of the laser light. At this time, the intensity of the polarized light component perpendicular to the paper surface is changed to elliptical polarized light having an intensity of 5% and a polarized light component parallel to the paper surface of 95%.

  In the first diffraction grating, the laser light having a polarization component parallel to the paper surface is transmitted straight without being diffracted because the ordinary light refractive index of the polymer liquid crystal is equal to the refractive index of the filling adhesive 39, and in the second diffraction grating, The diffraction is performed from the relationship between the difference between the extraordinary light refractive index of the polymer liquid crystal and the refractive index of the filling adhesive 40 and the grating height. At this time, the 0th order transmittance is about 74%, and the first order diffraction efficiency is about 10%.

  On the other hand, the laser beam having a polarization component perpendicular to the paper surface is diffracted in the first diffraction grating due to the relationship between the ordinary refractive index of the polymer liquid crystal and the refractive index of the filling adhesive 39 and the grating height. At this time, the 0th-order transmittance is about 90% and the first-order diffraction efficiency is about 4%. On the other hand, in the second diffraction grating, the ordinary light refractive index of the polymer liquid crystal and the refractive index of the filling adhesive 40 are substantially equal, so that they pass straight through with almost no diffraction.

  The polymer liquid crystal film 36 which is the second phase plate also has a function as a phase plate having a retardation value of 334 nm, but the fast axis perpendicular to the fast axis of the polymer liquid crystal film 35 (first phase plate). As a result, when passing through the polymer liquid crystal film 36 (second phase plate), the polarization state of the laser light is substantially the same as that before entering the diffraction element of this example, that is, the polarization direction. Becomes linearly polarized light perpendicular to the paper surface and exits the diffraction element of this example.

  At this time, the zero-order transmittance obtained by the diffraction element of this example is about 75%, and the first-order diffraction efficiency is about 9.5%. Note that the first-order diffracted light by the first diffraction grating is unnecessary light. However, the diffraction efficiency is about 0.2%, which is sufficiently small.

  On the other hand, when a laser beam having a wavelength of 660 nm and a linearly polarized light whose polarization direction is perpendicular to the paper surface is transmitted through this element, the polymer liquid crystal film 35 (first phase plate) serves as a phase plate having a retardation value of 343 nm. It has a function and changes the polarization state of the laser beam. At this time, since the retardation value is approximately ½ of the wavelength, it changes to approximately linearly polarized light having a polarization component parallel to the paper surface of 99% or more.

  The substantially linearly polarized light parallel to the paper surface is transmitted straight without being diffracted in the first diffraction grating because the ordinary refractive index of the polymer liquid crystal and the refractive index of the filling adhesive 39 are equal, and in the second diffraction grating, Diffraction occurs from the relationship between the difference between the extraordinary refractive index of the molecular liquid crystal and the refractive index of the filling adhesive 40 and the grating height. At this time, the 0th order transmittance is about 64%, and the first order diffraction efficiency is about 14.6%.

  The polymer liquid crystal film 36 (second phase plate) also has a function as a phase plate having a retardation value of 343 nm, but the phase advance axis orthogonal to the phase advance axis of the polymer liquid crystal film 35 (first phase plate). As a result, when passing through the polymer liquid crystal film 36 (second phase plate), the polarization state of the laser light is substantially the same as that before entering the diffraction element of this example, that is, the polarization direction. Becomes linearly polarized light perpendicular to the paper surface and exits the diffraction element of this example. At this time, the zero-order transmittance obtained by the diffraction element of this example is about 63%, and the first-order diffraction efficiency is about 14.5%.

  The three-wavelength diffractive element with a phase plate of this embodiment is a compatible optical head device for reproducing / recording BD, DVD, and CD with different standards, and includes a 405 nm wavelength band for BD, a 660 nm wavelength band for DVD, a CD In a compatible optical head device equipped with a three-wavelength semiconductor laser that outputs laser light in the 780 nm wavelength band, it can be used as a diffractive element for obtaining three beams for BD and CD tracking. On the other hand, in the case of not performing reproduction / recording of the RAM standard in the DVD, since tracking can be performed without using three beams, diffracted light by the diffractive element of this embodiment is not required, and only 64% 0th order transmitted light is used. .

"Example 6"
This embodiment is a specific example of the fourth embodiment shown in FIG. 6, mark the work made methods below.

  First, an antireflection film is formed on the air-side surface of the first transparent substrate 41 made of glass using a vacuum deposition method. Next, the same polymer liquid crystal film 48 as the polymer liquid crystal film 35 of Example 5 (FIG. 5) is formed on the first transparent substrate 41 made of glass.

  Next, the same convex part 47 as the convex part 18 made of quartz of the third transparent substrate 15 of Example 3 (FIG. 3) is formed on the fourth transparent substrate 44 made of glass, and an antireflection film is formed on the surface thereof. Form a film. Further, a polymer liquid crystal film 49 which is the same as the polymer liquid crystal film 36 of the fourth transparent substrate 34 of Example 5 (FIG. 5) is formed on the surface where the convex portions 47 are not formed.

  Next, the same convex part 45 as the convex part 37 which consists of a polymer liquid crystal of the 2nd transparent substrate 32 of Example 5 (FIG. 5) is formed in the 2nd transparent substrate 42 made from glass. Similarly, the same convex part 46 as the convex part 17 which consists of a polymer liquid crystal of the 2nd transparent substrate 14 of Example 3 (FIG. 3) is formed in the 3rd transparent substrate 43 made from glass.

  The periods and directions of the convex portions 45 and 46 made of polymer liquid crystal and the convex portion 47 made of quartz are different from each other.

  Next, the polymer liquid crystal film 48 of the first transparent substrate 41 is bonded face-to-face using a filling adhesive 50 so as to fill the convex portions 45 made of the polymer liquid crystal of the second transparent substrate 42. As the filling adhesive 50, the same adhesive as the filling adhesive 6 of Example 1 (FIG. 1) is used. Next, the surface of the second transparent substrate 42 that is not bonded is bonded using the filling adhesive 51 so as to fill the convex portions 46 made of the polymer liquid crystal of the third transparent substrate 43. As the filling adhesive 51, the same one as the filling adhesive 7 of Example 1 (FIG. 1) is used. Here, the diffraction grating having the convex portion 45 and the filling adhesive 50 is the first diffraction grating, and the diffraction grating having the convex portion 46 and the filling adhesive 51 is the second diffraction grating.

  Further, the polymer liquid crystal film 49 of the fourth transparent substrate 43 and the non-bonded surface of the third transparent substrate 43 face each other and are bonded with a transparent adhesive.

  Here, in producing the three-wavelength diffractive element with a phase plate of this example, as a method of laminating the four transparent substrates, the second transparent substrate 42 is filled so as to fill the convex portions 45 made of polymer liquid crystal. A filling adhesive 51 is used so that the polymer liquid crystal film 48 of the first transparent substrate 41 is adhered to the first transparent substrate 41 with the adhesive 50 and the convex portion 46 made of the polymer liquid crystal of the third transparent substrate 43 is filled. After preparing separately the polymer liquid crystal film 49 of the fourth transparent substrate 44 bonded to each other, the surface of the second transparent substrate 42 without the convex portions 45 made of polymer liquid crystal and the third transparent substrate A lamination method may be used in which a surface having no convex portion 46 made of 43 polymer liquid crystal is adhered with a transparent adhesive. This is a configuration different from that of FIG.

  In the three-wavelength diffractive element with a phase plate manufactured in this way in this way, when the laser beam having a wavelength of 405 nm and the polarization direction is linearly polarized light perpendicular to the paper surface is transmitted through the element, the polymer of the first transparent substrate 41 The liquid crystal film 48 has a function as a phase plate (first phase plate) having a retardation value 405 nm that is a product of the difference between the extraordinary refractive index and the ordinary refractive index of the polymer liquid crystal and the thickness thereof. Since this retardation value is equal to the wavelength, it passes through without changing the polarization state of the laser light. The first diffraction grating diffracts from the relationship between the difference between the extraordinary light refractive index of the polymer liquid crystal and the refractive index of the filling adhesive 50 and the grating height. At this time, the 0th-order transmittance is about 67% and the first-order diffraction efficiency is about 13.5%. On the other hand, in the second diffraction grating, since the ordinary light refractive index of the polymer liquid crystal and the refractive index of the filling adhesive 51 are equal, they pass straight without being diffracted. The polymer liquid crystal film 49 also has a function as a phase plate (second phase plate) having a retardation value of 405 nm, and similarly transmits the laser light without changing the polarization state. Furthermore, in the diffraction grating (third diffraction grating) of the fourth transparent substrate 44, the difference between the optical path length of the concave portion and the optical path length of the convex portion is 810 nm, which is twice the wavelength. The depth is determined, and the light passes straight without being diffracted.

  On the other hand, when a laser beam having a wavelength of 660 nm and a linearly polarized light whose polarization direction is perpendicular to the paper surface is transmitted through this element, the polymer liquid crystal film 48 (first phase plate) serves as a phase plate having a retardation value of 343 nm. It has a function and changes the polarization state of the laser beam. At this time, since the retardation value is approximately ½ of the wavelength, it changes to approximately linearly polarized light having a polarization component parallel to the paper surface of 99% or more.

  In the first diffraction grating, the linear refractive index of the polymer liquid crystal and the refractive index of the filling adhesive 50 are substantially equal in the first diffraction grating, so that almost straight polarized light parallel to the paper surface is transmitted straight through without being diffracted. In the second diffraction grating, The height of the convex portion is determined so that the difference between the optical path length of the concave portion and the optical path length of the convex portion is 660 nm which is equal to the wavelength, and the light passes straight without being diffracted.

  The polymer liquid crystal film 49 which is the second phase plate also has a function as a phase plate having a retardation value of 343 nm, but the fast axis perpendicular to the fast axis of the polymer liquid crystal film 48 (first phase plate). As a result, when passing through the polymer liquid crystal film 49 (second phase plate), the polarization state of the laser light is substantially the same as that before entering the diffraction element of this example. The third diffraction grating diffracts from the relationship between the difference in refractive index between the convex quartz and the concave air and the grating height. At this time, the 0th order transmittance is 69%, and the first order diffraction efficiency is 12.6%.

  At this time, the zero-order transmittance obtained by the diffraction element of this example is about 68%, and the first-order diffraction efficiency is about 12.5%.

  When a laser beam having a wavelength of 780 nm and linearly polarized light whose polarization direction is perpendicular to the paper surface is transmitted through this element, the polymer liquid crystal film 48 (first phase plate) functions as a phase plate having a retardation value of 334 nm. And change the polarization state of the laser light. At this time, the intensity of the polarized light component perpendicular to the paper surface is changed to elliptical polarized light having an intensity of 5% and a polarized light component parallel to the paper surface of 95%.

  In the first diffraction grating, the polarized light component parallel to the paper surface is transmitted straight without being diffracted because the ordinary refractive index of the polymer liquid crystal and the refractive index of the filling adhesive 50 are equal, and in the second diffraction grating, the polymer component is polymerized. Diffraction occurs from the relationship between the difference between the extraordinary light refractive index of the liquid crystal and the refractive index of the filling adhesive 51 and the grating height. At this time, the 0th order transmittance is about 73% and the first order diffraction efficiency is about 11%.

  On the other hand, the laser beam having a polarization component perpendicular to the paper surface is diffracted in the first diffraction grating due to the relationship between the difference between the ordinary light refractive index of the polymer liquid crystal and the refractive index of the filling adhesive 50 and the grating height. At this time, the 0th-order transmittance is about 90% and the first-order diffraction efficiency is about 4%. On the other hand, in the second diffraction grating, since the ordinary light refractive index of the polymer liquid crystal and the refractive index of the filling adhesive 51 are substantially equal, they pass through straightly without being diffracted.

  The polymer liquid crystal film 49 (second phase plate) also has a function as a phase plate having a retardation value of 334 nm, but the fast axis perpendicular to the fast axis of the polymer liquid crystal film 48 (first phase plate). As a result, when passing through the polymer liquid crystal film 49 (second phase plate), the polarization state of the laser light is substantially the same as that before entering the diffraction element of this example. Further, in the third diffraction grating, the height of the convex portion is determined so that the difference between the optical path length of the concave portion and the optical path length of the convex portion is 780 nm which is equal to the wavelength. It goes straight through.

  At this time, the zero-order transmittance obtained by the diffraction element of this example is about 74%, and the first-order diffraction efficiency is about 10.5%. Note that the first-order diffracted light by the first diffraction grating is unnecessary light. However, the efficiency is about 0.2%, which is sufficiently small.

  The diffraction element of this example is a compatible optical head device for reproducing / recording BD, DVD and CD with different standards, and has a 405 nm wavelength band for BD, a 660 nm wavelength band for DVD, and a 780 nm wavelength band for CD. In a compatible optical head device equipped with a three-wavelength semiconductor laser that outputs laser light, it can be used as a diffractive element for obtaining three BD, DVD, and CD tracking beams.

  The three-wavelength diffractive element or the three-wavelength diffractive element with a phase plate of the present invention is formed by forming a diffraction grating made of a birefringent resin, and a diffraction grating made of a phase plate and an inorganic medium. This has the effect that the diffraction efficiency and the diffraction direction can be selectively controlled with respect to light of a plurality of wavelengths even though it is a single diffraction element. By using this diffraction element, a compatible optical head device equipped with a three-wavelength semiconductor laser that is expected to be small and light can be realized.

Diffraction element for three wavelengths according to the first embodiment of the present invention It is a modification of the diffraction element for 3 wavelengths of 1st Embodiment of this invention, and the diffraction element of Example 2 Diffraction element for three wavelengths according to the second embodiment of the present invention It is a modification of the diffraction element for 3 wavelengths of 2nd Embodiment of this invention, and the diffraction element of Example 4 The diffraction element for three wavelengths with a phase plate of 3rd Embodiment of this invention The diffraction element for three wavelengths with a phase plate of 4th Embodiment of this invention A compatible optical head device equipped with the three-wavelength diffraction element with phase plate according to the third embodiment of the present invention

Explanation of symbols

1, 2, 3, 8, 9, 13, 14, 15, 21, 22 Transparent substrate 31, 32, 33, 34, 41, 42, 43, 44 Transparent substrate 4, 5, 10, 11, 16, 17 Convex Part 23, 24, 37, 38, 45, 46 Convex part 15, 18, 25, 47 Convex part 6, 7, 12, 19, 20, 26, 39, 40, 50, 51 Filling adhesive 35, 36, 48 , 49 Phase plate 53 Three-wavelength semiconductor laser 52 Three-wavelength diffractive element with phase plate according to the third embodiment of the present invention 54 Polarizing beam splitter 55 Collimator lens 56 1/4 wavelength plate 57 Objective lens 58 Optical recording medium 59 Optical detector

Claims (4)

A first diffraction grating in which a first convex portion made of a resin exhibiting birefringence and a first concave portion made of a resin exhibiting optical isotropy are in contact with each other to form a concave-convex shape having a periodic cross section;
A second diffraction grating in which a second convex portion made of a resin exhibiting birefringence and a second concave portion made of a resin exhibiting optical isotropy are in contact with each other to form a concavo-convex shape having a periodic cross section;
A third diffraction grating having a periodic concavo-convex portion or a third convex portion made of an inorganic material,
For incident light of three different wavelengths λ ₁ , light of wavelength λ ₂ and light of wavelength λ ₃ (λ ₁ <λ ₂ <λ ₃ ) ,
Wherein the first diffraction grating is configured to diffract the wavelength lambda ₁ of the light, to transmit the wavelength lambda ₂ of the light and the wavelength lambda ₃ of the light, the refractive index of the first convex portion and / or The height as well as the refractive index of the first recess are adjusted,
The second diffraction grating is configured to transmit the wavelength lambda ₁ of light and the wavelength lambda ₂ of light, so as to diffract the wavelength lambda ₃ of the light, the refractive index of the second protrusions and / or The height as well as the refractive index of the second recess are adjusted ,
The third diffraction grating transmits the light having the wavelength λ ₁ and the light having the wavelength λ ₃ and refracts the light having the wavelength λ ₂ and diffracts the light having the wavelength λ _2. rate and / or height is adjusted Tei Ru 3-wavelength diffraction element. A first diffraction grating in which a first convex portion made of a resin exhibiting birefringence and a first concave portion made of a resin exhibiting optical isotropy are in contact with each other to form a concave-convex shape having a periodic cross section;
A second diffraction grating in which a second convex portion made of a resin exhibiting birefringence and a second concave portion made of a resin exhibiting optical isotropy are in contact with each other to form a concavo-convex shape having a periodic cross section;
Two phase plates provided to sandwich the first diffraction grating and the second diffraction grating; and
A third diffraction grating having a periodic concavo-convex portion or a third convex portion made of an inorganic material,
For incident light of three different wavelengths λ ₁ , light of wavelength λ ₂ and light of wavelength λ ₃ (λ ₁ <λ ₂ <λ ₃ ),
The first diffraction grating diffracts the light of the wavelength λ ₁ and transmits the light of the wavelength λ _{2 and} the light of the wavelength λ ₃ and / or the refractive index of the first convex portion. The height as well as the refractive index of the first recess are adjusted,
The second diffraction grating transmits the light of the wavelength λ ₁ and diffracts the light of the wavelength λ ₃ , and the refractive index and / or height of the second convex portion, and the second The refractive index of the recess of the
The two of the phase plate, a phase difference of 2π with respect to the wavelength lambda ₁ of light, a phase difference of substantially π to the wavelength lambda ₂ of the light, and the wavelength lambda ₃ have a phase difference of substantially π to light,
The third diffraction grating transmits the light having the wavelength λ ₁ and the light having the wavelength λ ₃ and refracts the light having the wavelength λ ₂ and diffracts the light having the wavelength λ _2. rate and / or height that is tuned phase fitted with three-wavelength diffraction element. A light source that emits light of _three different wavelengths λ ₁ , light of wavelength λ ₂ , and light of wavelength λ ₃ (λ ₁ <λ ₂ <λ ₃ ) , and an object that focuses the light of each wavelength on the optical recording medium and the lens is condensed and a photodetector for detecting light reflected by the optical recording medium, an optical head device for reproducing and / or recording information of the optical recording medium,
3-wavelength diffraction element or a phase fitted with 3 optical head device diffraction element for wavelength that are placed according to claim 2 according to the optical path, in claim 1 between the light source and the objective lens. The wavelength λ ₁ Is a 405 nm wavelength band for BD, and the wavelength λ ₂ Is a 660 nm wavelength band for DVD, and the wavelength λ ₃ 4. The optical head device according to claim 3, which is a 780 nm wavelength band for CD.

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