KR100779693B1 - Wave selection type diffractive optical elements and optical pickup device has them - Google Patents

Abstract

A wavelength selection type diffractive optical device and an optical pickup head device having the same are provided to diffract an incident ray with different wavelength selectively without using an additional polarization device. A wavelength selection type diffractive optical device diffracts one of a lambda 1 wavelength and a lambda 2 wavelength of an incident ray selectively. The wavelength selection type diffractive optical device includes at least one transmissive transparent substrate(10), a first diffraction grating(20) and a second diffraction grating(30). The first diffraction grating is formed on one side of the transparent substrate, and diffracts a light of the lambda 1 wavelength by structural height setting and transmits a light of the lambda 2 wavelength. The second diffraction grating is formed on the other side of the transparent substrate, and transmits the light of the lambda 1 wavelength by structure height setting and diffracts the light of the lambda 2 wavelength.

Description

Wavelength selective diffraction element and optical head device having same {Wave selection type Diffractive optical elements and optical pickup device has them}

1 is a cross-sectional view of a conventional wavelength selective diffraction element;

FIG. 2 is a schematic configuration diagram of an optical head device having the wavelength selective diffraction element of FIG. 1;

3 is a sectional view of a wavelength selective diffraction element according to a first embodiment of the present invention;

4 is a cross-sectional view of a wavelength selective diffraction element according to a second embodiment of the present invention;

5 and 6 are cross-sectional views of the wavelength selective diffraction element according to the third embodiment of the present invention;

7 is a simplified block diagram of an optical head apparatus having the wavelength selective diffraction element of FIGS.

* Explanation of symbols for the main parts of the drawings

  1 Diffraction Element 10 Transparent Substrate

 20: the first lattice 30: the second lattice

 50: adhesive material 60: phase delay layer

100: optical head device 101: dual light source

103: objective lens

The present invention relates to a wavelength selective diffraction element and an optical head apparatus having the same.

An optical head apparatus is used as an apparatus for recording information on or reading information from an information recording surface of an optical recording medium such as an optical disk such as a CD / DVD or a magnetic disk.

In the optical head apparatus, in order to rotate the optical disk while focusing the laser light on the track formed on the information recording surface of the optical disk, the beam of the focused laser light must be kept off the track. In order to realize this, various tracking methods have been developed. Among them, a widely used method is a three-beam method in which a laser beam is divided into two sub-beams, one main-order diffracted light and a first-order diffracted light.

At this time, the diffraction element is used to divide the laser light into a main beam and a sub beam. The diffraction element is provided in the optical path of the laser beam, and diffraction occurs in which the laser beam is divided into one main beam and two sub beams in the diffraction grating region, which is a characteristic structure.

On the other hand, with the development of technology, in recent years, CD and DVD compatible optical head apparatuses for recording or playing back information on two optical discs, CD and DVD, have been widely used.

In the case of a CD-based optical disc such as a general CD-R, a laser beam having a wavelength band of about 780 nm (hereinafter referred to as "CD-based wavelength λ ₂ ") is used. ₁ "laser light.

By the way, in such a CD and DVD compatible optical head device, and λ ₁ laser generator for generating laser light of a DVD-based wavelength (λ ₁₎ as a laser light source, λ which generates the laser light of the CD-based wavelength (λ _{2) Since two} laser generators and three-beam generating diffraction elements corresponding to the respective laser generators must be provided, there is a disadvantage in that the optical head apparatus is enlarged.

Accordingly, in recent years, in order to reduce the size of the optical head device, a two-wavelength semiconductor laser (Dual LD: below) generating laser light of a DVD wavelength λ ₁ and a laser light of a CD wavelength λ ₂ as a laser light source. A dual-beam semiconductor diffractive element corresponding to these two-wavelength semiconductor lasers, which is a laser beam having a DVD wavelength? ₁ or a laser beam having a CD wavelength? ₂ . A wavelength selective diffraction element for selectively generating one laser beam into three beams (main beam and sub beam) is used.

The dual wavelength selective diffraction element selectively diffracts any one laser wavelength selected for two kinds of laser wavelengths. The core technique is only for a polarization direction in a specific direction when laser light passes through a diffraction grating formed in the diffraction element. It is to have a diffraction function.

As shown in FIG. 1, the conventional wavelength selective diffraction element 800 includes a first diffraction of λ ₁ and λ ₂ on mutually opposing surfaces of the emission-side transparent substrates 805 and 809 among the plurality of transparent substrates 804, 805, and 809, respectively. The diffraction grating 807a and the second diffraction grating 807b are formed with the adhesive layer 806 interposed therebetween. The polarizing element 801 for converting the polarization of incident light is interposed between the transparent substrates 804 and 805 on the incident side by the adhesive layers 802 and 803.

The orientation direction of the polymer liquid crystal is set so that the first diffraction grating 807a generates diffracted light with respect to λ ₂ which has passed through the transparent substrate 805 and has an ordinary light refractive index at which λ ₁ does not generate diffracted light.

The second diffraction grating 807b generates diffracted light with respect to λ ₁ passing through the transparent substrate 805 and has an ideal optical refractive index such that diffracted light does not occur with respect to λ ₂ . It is set to be orthogonal to the diffraction grating 807a.

In the conventional wavelength selective diffraction element 800 having such a configuration, as shown in FIG. 2, a dual light source 901 for generating laser light and a laser light in the CD and DVD compatible optical head device 900 are provided with an optical disc A. FIG. The optical head device 900 is provided on the optical path between the objective lenses 903 for condensing into each other and independently generates two main beams, one being a zero-order diffraction light and one of the first-order diffraction light, for λ ₁ and λ ₂ . ) Allows recording or playback of information on the corresponding optical disc A of either CD or DVD.

However, in the conventional wavelength selective diffraction element, since the high technology of aligning the birefringence of the polymer liquid crystal in a predetermined direction is used, it is very difficult to manufacture and optical alignment, which is an expensive equipment for the alignment of the polymer liquid crystal in the manufacturing process. Since a device is required and the manufacturing process is complicated, there is a problem that the manufacturing cost of the optical device and the optical head device using the same increase.

In addition, such a conventional wavelength selective diffraction element uses birefringence characteristics, and the polarization states of λ ₁ and λ ₂ must be converted differently before laser light is incident on the diffraction element. Accordingly, there is a problem in that the incident light of different wavelengths can be selectively diffracted only by using a separate polarizer.

Accordingly, an object of the present invention is to provide a wavelength selective diffraction element and an optical head device having the same, which can simplify the manufacturing process and reduce the manufacturing cost, and can selectively diffract incident light having different wavelengths without using a separate polarizing element. To provide.

According to the present invention, there is provided a wavelength selective diffractive element for selectively diffracting any one of lambda ₁ wavelength and lambda ₂ wavelength of incident light in mutually different wavelength bands, comprising: at least one transparent transparent substrate; A first diffraction grating formed on one side of the transparent substrate, the diffraction transmission of light having a wavelength of λ ₁ by a structural height setting, and having a light quantity ratio of transmitting light having a wavelength of λ ₂ ; Is formed on the other side of the transparent substrate, a structured by the height setting for transmitting light of said λ ₁ wavelength other hand, characterized in that it comprises a second diffraction grating with the amount of light that diffracts transmitted light of the λ ₂ wavelength It is achieved by the wavelength selective diffraction element.

Here, the refractive index of the medium of the first diffraction grating and the second diffraction grating is preferably the same.

In this case, the first and the second diffraction grating is effectively formed of any one material of ultraviolet curable resin, thermosetting resin, glass, PC, liquid crystal polymer, PET.

In addition, the thermal expansion coefficient of the material forming the first and second diffraction grating is preferably equal to or larger than the thermal expansion coefficient of the transparent substrate.

In addition, the transparent substrate is provided in a pair, the first diffraction grating and the second diffraction grating are formed on the plate surface of the both transparent substrates, it is effective that the adhesive material is interposed between the both transparent substrates.

In this case, the difference between the refractive index of the medium and the adhesive material between the first diffraction grating and the second diffraction grating is 0.02 to 0.04.

On the other hand, between the first diffraction grating and the second diffraction grating, it is more effective to further include a phase delay layer for phase-delaying any one of the lambda ₁ wavelength and the lambda ₂ wavelength.

At this time, the acid delay layer is preferably provided with a phase delay film or a liquid crystal layer having a predetermined phase delay value.

On the other hand, according to another aspect of the present invention, there is provided a dual light source for emitting light having a wavelength of λ _{1 and a} wavelength of λ ₂ , and an object for condensing light having the wavelengths of λ ₁ and λ ₂ on an optical recording medium. A wavelength selective diffraction element disposed in an optical path between the light source and the objective lens, the wavelength selective diffraction element having first and second diffraction gratings for diffractively transmitting light having the λ ₁ wavelength and the λ ₂ wavelength, and the optical recording An optical head apparatus having a photodetector for detecting light of the λ ₁ wavelength and the λ ₂ wavelength reflected from a medium, wherein the wavelength selective diffraction element is the above-mentioned wavelength selective diffraction element. Is achieved.

Here, the spacing between the centers of the first diffraction grating and the second diffraction grating of the wavelength selective diffraction element preferably corresponds to the spacing between two light source centers of the dual light source.

Hereinafter, with reference to the accompanying drawings will be described in detail with respect to the present invention.

3 is a cross-sectional view of the wavelength selective diffraction element according to the first embodiment of the present invention. As shown in the figure, the wavelength selective diffraction element 1 according to the present embodiment includes a single transparent substrate 10, a first diffraction grating 20 formed on both surfaces of the transparent substrate 10, and It includes two times the lattice (30).

The transparent substrate 10 may be formed of a light transmissive transparent material, preferably, a transparent glass plate or a transparent film having excellent strength and heat resistance. The transparent substrate 10 maintains the shape of the diffraction element 1 and serves as a support surface for the first diffraction grating 20 and the second diffraction grating 30.

On the other hand, the first diffraction grating 20 is formed in an uneven shape on one surface of the transparent substrate 10. The first diffraction grating 20 transmits the light of the DVD wavelength λ ₁ by diffraction and transmits the light of the CD wavelength λ ₂ without diffraction by the medium refractive index and the structural height h1 which are predetermined optical structural conditions. Let's do it. The selective diffraction transmission of the light of λ ₁ and λ ₂ of the first diffraction grating 20 results in a light quantity ratio of 10 to 20 with respect to the DVD-based wavelength λ ₁ of which the first diffraction grating 20 has a wavelength band of about 660 nm. In addition, it is possible by having a light quantity ratio of 50 or more with respect to the CD system wavelength (lambda) ₂ which is a wavelength band of about 780 nm.

For example, for the optical structural conditions of the first diffraction grating 20, the refractive index of the medium constituting the first diffraction grating 20 is 1.51, and the height h1 of the first diffraction grating 20 is 1456 nm. When the light intensity ratio is 14.3 for the DVD wavelength λ ₁ in the wavelength band of about 660 nm, and the light intensity ratio is 106 for the CD wavelength λ ₂ in the wavelength band of about 780 nm, the light having the DVD wavelength λ ₁ is diffracted. On the other hand, an example in which light of the CD wavelength λ ₂ is transmitted without diffraction is mentioned.

In addition, the second diffraction grating 30 is also formed on the back surface of the transparent substrate 10 in an uneven shape. In addition, the second diffraction grating 30 also diffracts and transmits the light of the DVD wavelength λ ₁ by the medium refractive index and the structural height h2 which are predetermined optical structural conditions, and the light of the CD wavelength λ ₂ is diffracted. Permeate. The selective diffraction transmission of the light of λ ₁ and λ ₂ of the second diffraction grating 30 has a light quantity ratio of 50 or more with respect to the DVD-based wavelength λ ₁ of which the second diffraction grating 30 has a wavelength band of about 660 nm, It is possible by having the light quantity ratio of 10-20 about CD system wavelength (lambda) ₂ which is a wavelength band of about 780 nm.

For example, the optical structural conditions of the second diffraction grating 30 may be 1.51 (of course, the first diffraction grating having the same refractive index of the medium constituting the second diffraction grating 30 as the first diffraction grating 20). It may have a refractive index different from the refractive index of 20), and when the height h2 of the second diffraction grating 30 is 1339 nm, it has a light quantity ratio of 206 with respect to the DVD system wavelength lambda _{1 which} is a wavelength band of about 660 nm, For example, the CD wavelength λ ₂ having a wavelength range of about 780 nm has a light quantity ratio of 14.5. Thus, the DVD wavelength λ ₁ can be transmitted without diffraction while the CD wavelength λ ₂ is diffracted. .

The light quantity ratio of the first diffraction grating 20 and the second diffraction grating 30 described above is determined based on the following principle.

When the height of each diffraction grating is d, the difference in refractive index between the medium constituting each diffraction grating and air is n, and the wavelength used is λ, the first-order diffracted light and the zero-th order transmitted light are determined by the following equation.

1st order diffracted light

0th transmitted light =

Therefore, the light quantity ratio in the diffraction grating is defined as "0th order transmitted light / 1st diffraction light", and when the refractive index of the medium constituting the diffraction grating is 1.51, the light intensity ratio curve with respect to the grating height for two wavelengths of 660 nm and 780 nm Is shown in Figure 1 below. In the figure below, when the lattice height is 1339nm, the light intensity ratio is about 14.5 at 780nm, but the light intensity ratio is about 206 at 660nm. On the contrary, when the lattice height is 1456 nm, it has a light quantity ratio of 106 at 780 nm and a light quantity ratio characteristic of 14.3 at 660 nm. Accordingly, the 1339 nm high diffraction grating may operate as a 780 nm diffraction grating, and the 1456 nm high diffraction grating may operate as a 660 nm diffraction grating.

Figure-1

The first diffraction grating 20 and the second diffraction grating 30 of the diffraction element 1 each have lattice forming layers on both surfaces of the transparent substrate 10 by spin coating or the like using dendritic polymer. After the coating, the diffraction grating is formed in a concave-convex diffraction grating having a predetermined interval on the surface of the transparent substrate 10 by photolithography, UV embossing, hot embossing, or the like.

At this time, the spacing interval w1 between the centers of the diffraction gratings corresponds to the spacing interval w2 between the centers of both light sources 101a and 101b for emitting the respective light of λ ₁ and λ ₂ from the dual light source 101. By being spaced apart at intervals, the light of λ ₁ and λ ₂ is accurately emitted to the first diffraction grating 20 and the second diffraction grating 30, respectively. Of course, the spacing interval w1 between the centers of the diffraction gratings may be adjusted according to the distance between the light source and the diffraction element, including the spacing w2 between the centers of both light sources of the dual light sources.

In addition, each diffraction grating may be formed of a material such as ultraviolet curable resin, thermosetting resin, glass, PC, liquid crystal polymer, PET, and the like, and the coefficient of thermal expansion of the material constituting each diffraction grating is greater than or equal to that of the transparent substrate. .

As described above, the wavelength selective diffraction element 1 according to the present embodiment adjusts the grating heights h1 and h2 of the first diffraction grating 20 and the second diffraction grating 30 to different wavelengths λ ₁ and λ _2. By having the respective light quantity ratios satisfying the diffraction transmission or transmission conditions with respect to, the λ ₁ and λ ₂ wavelengths can be selectively diffracted in the first diffraction grating 20 and the second diffraction grating 30, respectively.

In particular, even if the first diffraction grating 20 and the second diffraction grating 30 have the same medium refractive index, selective diffraction of λ ₁ and λ ₂ wavelengths is possible only by adjusting the heights h1 and h2 of the diffraction gratings. Therefore, the wavelength selective diffraction element 1 can be manufactured without using a technique such as highly polymer liquid crystal alignment. Thereby, the manufacturing process of the diffraction element 1 is made very simple, and manufacturing cost can be reduced significantly.

In addition, the wavelength selective diffraction element 1 according to the present invention adjusts the heights h1 and h2 of the first diffraction grating 20 and the second diffraction grating 30 to transmit diffraction at wavelengths λ ₁ and λ ₂ , or Since the respective light quantity ratios satisfy the transmission conditions, the respective λ ₁ and λ ₂ wavelengths can be selectively diffracted regardless of the polarization state of the λ ₁ and λ ₂ wavelengths without using a separate polarizing element.

As shown in FIG. 7, the diffraction element 1 according to the present invention having such an optical structural condition uses a dual light source 101 and a laser light to generate a laser light in the CD and DVD compatible optical head device 100. A main beam which is provided on an optical path between the objective lens 103 focused on the optical disk a, and which is zero order diffracted light for λ ₁ and λ ₂ in the first diffraction grating 20 and the second diffraction grating 30, respectively; By independently generating the two sub-beams, which are the first diffracted light, the optical head device 100 can record or reproduce information on any one of the corresponding optical disks a of CD or DVD.

4 is a cross-sectional view of the wavelength selective diffraction element 1 according to the second embodiment of the present invention. As shown in this figure, the wavelength selective diffraction element 1 according to the present embodiment has a first diffraction grating 20 and a second diffraction grating 30 disposed on a pair of transparent substrates 10 spaced apart from each other. It is formed and has a structure in which the adhesive material 50 is filled between both transparent substrates (10). Thereby, the structural stability of the diffraction element 1 can be ensured.

At this time, any one of the first diffraction grating 20 and the second diffraction grating 30 is formed on the plate surface of one transparent substrate 10 between the two transparent substrate 10, the other is the other transparent substrate 10 It may be formed on the outer side of the. Of course, the first diffraction grating 20 and the second diffraction grating 30 may be formed on opposite surfaces of both transparent substrates 10.

Here, the optical structural conditions of the first diffraction grating 20 and the second diffraction grating 30 are the same as those of the diffraction element 1 of the first embodiment described above, and thus description thereof is omitted.

On the other hand, the difference between the refractive index (n2) of the adhesive material 50 is filled between the two transparent substrate 10 and the refractive index (n1) of the first diffraction grating 20 and the second diffraction grating 30 is 0.02 to 0.04 It is preferable. This is not only difficult to form the diffraction grating when the difference between the refractive index n2 of the adhesive material 50 and the refractive index n1 of the first diffraction grating 20 and the second diffraction grating 30 is 0.02 or less, This is because the problem of the accuracy of the structural shape of the diffraction grating is reduced.

5 and 6 are cross-sectional views of the wavelength selective diffraction element 1 according to the third embodiment of the present invention. As shown in the figure, the wavelength selective diffraction element 1 according to the present embodiment has a first diffraction grating 20 and a second diffraction grating 30 disposed on a pair of transparent substrates 10 spaced apart from each other. And a phase delay layer 60 is formed between the two transparent substrates 10.

Here, since the optical structural conditions of the first diffraction grating 20 and the second diffraction grating 30 are the same as those of the diffraction element 1 of the above-described embodiments, description thereof will be omitted.

On the other hand, the phase delay layer 60 is provided in the form of a film, as shown in Figure 5, having an appropriate phase delay value (OPD) value, it is interposed between the transparent substrate 10 by the adhesive material 50 or As shown in FIG. 6, the liquid crystal layer is formed of a liquid crystal polymer (LCP) and may be interposed between both transparent substrates 10.

The phase delay layer 60 can change the polarization of λ ₁ and λ ₂ incident at different wavelengths by a pre-adjusted phase delay value. For example, the polarization direction can be rotated by 90 degrees with respect to the λ ₁ wavelength having a wavelength of 660 nm, and the phase delay value OPD can be selected for the λ ₂ wavelength having a wavelength of 780 nm without any phase delay. Of course, the phase delay for polarization rotation about the λ ₁ wavelength and the λ ₂ wavelength may be reversed.

The wavelength selective diffraction element 1 having such a phase delay layer 60 has a wavelength of λ ₁ and λ ₂ when λ ₁ and λ ₂ wavelengths incident in the same polarization direction pass through the phase delay layer 60. By changing the polarization of any one of the, the polarization direction of λ ₁ and λ ₂ to be installed on the optical path of the CD and DVD compatible optical head device 100 using the two-wavelength dual light source 101 is generated Can be.

As described above, the wavelength selective diffraction element according to the present invention can selectively diffract incident light having different wavelengths by differently adjusting the lattice heights of the first diffraction grating and the second diffraction grating. A wavelength selective diffraction element and an optical head device having the same can be manufactured without using a technique.

Thereby, the manufacturing process of a diffraction element becomes very simple, and manufacturing cost can be reduced significantly.

In addition, since the heights of the first diffraction grating and the second diffraction grating are adjusted to have respective light quantity ratios satisfying the diffraction transmission or transmission conditions with respect to the λ ₁ and λ ₂ wavelengths, λ is not required without using a separate polarizing element. ₁ and there regardless of the polarization state of the wavelength λ ₂ can be selectively diffract each wavelength λ ₁ and λ _2.

Thereby, the manufacturing process and manufacturing cost of the diffraction element and the optical head apparatus having the same are further reduced.

As described above, according to the present invention, a wavelength selective diffraction element and an optical head having the same can be easily manufactured and reduce the manufacturing cost, and can selectively diffract incident light of different wavelengths without using a separate polarizing element. The device is provided.

Claims (10)

A wavelength selective diffraction element for selectively diffracting any one of lambda ₁ wavelength and lambda ₂ wavelength of incident light in mutually different wavelength bands, At least one transparent transparent substrate; It is formed at one side of the transparent substrate, and the first grating by a structural height setting with the amount of light which the other hand, the light transmission of the wavelength λ ₂ of light is transmitted through a diffraction of the wavelength λ _1; Is formed on the other side of the transparent substrate, a structured by the height setting for transmitting light of said λ ₁ wavelength other hand, characterized in that it comprises a second diffraction grating with the amount of light that diffracts transmitted light of the λ ₂ wavelength Wavelength selective diffraction element. The method of claim 1, And the refractive index of the medium of the first diffraction grating and the second diffraction grating is the same. The method of claim 2, The first and second diffraction grating is a wavelength selective diffraction element, characterized in that formed of any one material of ultraviolet curable resin, thermosetting resin, glass, PC, liquid crystal polymer, PET. The method of claim 3, And the thermal expansion coefficient of the material forming the first and second diffraction gratings is greater than or equal to the thermal expansion coefficient of the transparent substrate. The method of claim 4, wherein The transparent substrate is provided in a pair, the first diffraction grating and the second diffraction grating are formed on the plate surface of the both transparent substrates, A wavelength selective diffraction element characterized in that an adhesive material is interposed between the two transparent substrates. The method of claim 5, The wavelength selective diffraction element of claim 1, wherein the difference between the refractive index of the medium and the adhesive material of the first diffraction grating and the second diffraction grating is 0.02 to 0.04. The method of claim 5, And a phase delay layer between the first diffraction grating and the second diffraction grating to delay a phase of any one of the wavelengths λ ₁ and λ ₂ . The method of claim 7, wherein The gas acid delay layer is a wavelength selective diffraction element, characterized in that provided with a phase delay film or a liquid crystal layer having a predetermined phase delay value. A dual light source that emits light having a wavelength of λ _{1 and a} wavelength of λ ₂ , and an objective lens for condensing light of the λ ₁ and λ ₂ wavelengths on an optical recording medium, and an optical path between the light source and the objective lens. the installation, the first and second said λ ₁ wavelength and λ ₂ wavelengths and a wavelength-selectable diffraction element having a diffraction grating, reflected by the optical recording medium, for selectively diffracting transmitted by the λ ₁ wavelength and the light of said λ ₂ wavelength In the optical head device having a photodetector for detecting light, The wavelength selective diffraction element is an optical head device, characterized in that the wavelength selective diffraction element of any one of the first to eighth. The method of claim 9, And an interval between the centers of the first diffraction grating and the second diffraction grating of the wavelength selective diffraction element corresponds to a spacing between two light source centers of the dual light sources.

Images