JP4631135B2 - Phaser - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a phase terminal.
[0002]
[Prior art]
In an optical head device for recording / reproducing information on an optical recording medium such as an optical disk such as a CD or DVD and a magneto-optical disk, light emitted from a semiconductor laser, which is a light source, is condensed on the optical recording medium by a lens. It is reflected by the recording medium and becomes return light. This return light is guided to a light receiving element which is a photodetector using a beam splitter, and information on the optical recording medium is converted into an electric signal.
[0003]
Also, CD / DVD compatible optical head devices have been commercialized in order to record / reproduce information on CD and DVD optical discs, which are optical recording media of different standards, using the same optical head device. In an optical disc that uses a medium having a high wavelength dependency with respect to reflection / absorption of light as a recording layer of an optical recording medium and is premised on reproduction such as a CD-R, the semiconductor laser used for the CD has a wavelength of 790 nm. is there. At this time, a semiconductor laser having a wavelength band of 660 nm is used for DVD.
[0004]
By using a monolithic two-wavelength semiconductor laser in which a semiconductor laser having a 790 nm wavelength band and a semiconductor laser having a 660 nm wavelength band are formed in one chip, the emission point position accuracy is high and stable optical head characteristics can be obtained. In addition, the optical head device can be reduced in size and weight by reducing the number of components, and advantages such as simplification of the optical system design can be expected. Therefore, various optical head device configurations using two-wavelength semiconductor lasers can be expected. Has been proposed.
[0005]
In the CD / DVD compatible optical head device using the two-wavelength semiconductor laser of FIG. 4, the emission point 1A (FIG. 4 (a)) of the 660 nm wavelength band and the emission point 1B of the 790 nm wavelength band in the two-wavelength semiconductor laser 1 (FIG. 4). The light emitted from (b)) passes through the beam splitter 4 and becomes parallel light by the collimator lens 5 and is condensed by the objective lens 6 on the optical recording surface of the optical disk 7 such as CD or DVD as an optical recording medium. The The light reflected by the optical recording surface of the optical disc 7 is again collected by the objective lens 6 and the collimating lens 5, reflected by the beam splitter 4, and reaches the photodetector 8A or 8B.
[0006]
[Problems to be solved by the invention]
At this time, as shown in FIGS. 4A and 4B, the positions of the emission point 1A in the 660 nm wavelength band and the emission point 1B in the 790 nm wavelength band on the two-wavelength semiconductor laser 1 are different. The light condensing positions are different, and a light detector 8A for the 660 nm wavelength band and a light detector 8B for the 790 nm wavelength band are required, and the configuration is complicated and the optical head device becomes large. Therefore, there is a method of detecting light in both wavelength bands using a single photodetector (not shown) having a large light receiving area that can cover the light receiving area of the two detectors, but the detection response speed is slow. There is a problem that the apparatus becomes large.
[0007]
As a method for solving the above problem, a method using an optical element that matches the optical axes of the two outgoing lights by using the polarization characteristics of the outgoing lights of the two wavelength bands from the two-wavelength semiconductor laser can be considered. Since the polarization planes of the two outgoing lights are parallel to each other, it is difficult to separate the two outgoing lights.
[0008]
An object of the present invention, different light emission point position, and a two Hisage Kyosu Rukoto the optical element to align the optical axis of the light emitted from the two-wavelength semiconductor laser polarization plane are parallel to each other.
[0009]
[Means for Solving the Problems]
The present invention comprises a thin organic film having birefringence that is fixed on one of the transparent substrates even without low, a diffraction grating, wherein the organic thin film, fast axis, two wavelengths lambda ₁ in the _{λ 2 (λ 1 ≠ λ 2} ), is arranged such polarization is incident is inclined 45 ° to the polarization direction of the mutually parallel linear polarized light, wherein the wavelength lambda ₁ with respect to the linearly polarized light 2 [pi ( m ₁ -1/2) a phase difference of _{(m 1} is a natural number), 2πm _{2 (m 2} for linearly polarized light of the wavelength lambda ₂ is adjusted in the retardation value Ru generate a phase difference of a natural number) The planes of polarization of the two types of linearly polarized light are orthogonal to each other , and the diffraction grating diffracts one of the two types of linearly polarized light and diffracts the other of the light of the two types of wavelengths without diffracting the other. providing a retarder Ru to match the optical axis.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
“First Embodiment”
As shown in FIG. 1, the phase shifter 101 according to the first embodiment of the present invention has an organic thin film 14 sandwiched between a transparent substrate 11 and a transparent substrate 16 and fixed with an adhesive 15. As the transparent substrates 11 and 16, it is preferable to use an optically isotropic medium such as glass or quartz because the transmitted light is not affected by birefringence or the like. As the organic thin film 14, it is preferable to use a birefringent film having an optical axis aligned in the stretching direction by stretching an organic material such as polycarbonate.
[0012]
One of the wavelengths of two different types of linearly polarized light whose polarization planes are parallel to each other is λ ₁ , the other is λ _2, and m ₁ and m ₂ are natural numbers. When light having a wavelength λ ₁ is transmitted through the organic thin film 14, a phase difference of 2π (m ₁ −1/2) is generated, whereas when light having a wavelength λ ₂ is transmitted through the organic thin film 14, a phase difference of 2πm ₂ is generated. The retardation value of the organic thin film 14 is adjusted so that the polarization planes of the two types of linearly polarized light are orthogonal to each other. However, the linearly polarized light having the wavelengths λ ₁ and λ ₂ is incident on the organic thin film 14 with the polarization direction inclined by 45 ° with respect to the fast axis direction (not shown) of the organic thin film 14.
[0013]
For example, a case will be described in which light of wavelength λ ₁ is light in the 660 nm wavelength band for DVD optical disks and light of wavelength λ ₂ is light in the 790 nm wavelength band for CD optical disks. The organic thin film 14 made of polycarbonate having a retardation value (phase difference is 5π) which is 5/2 times the wavelength (m ₁ = 3) with respect to the light of the wavelength λ _{1 has} a fast axis with respect to the incident linear polarization direction. When the linearly polarized light having the wavelength λ ₁ is transmitted through the organic thin film 14 by being inclined by 45 °, the plane of polarization is rotated by 90 °. To contrast the wavelength lambda ₂ of the light, the retardation value of the thin organic film 14 is 2 times the wavelength corresponding to the (m ₂ = 2) (phase difference 4 [pi]) will be, the wavelength lambda ₂ passing through the organic thin film 14 The plane of polarization of linearly polarized light does not rotate. That is, the planes of polarization parallel to each other are orthogonal after passing through the organic thin film 14.
[0014]
When the wavelength λ ₁ is in the 800 nm wavelength band and the wavelength λ ₂ is in the 400 nm wavelength band, the retardation value is ½ times the wavelength (m ₁ = 1) for the light of the wavelength λ ₁ (the phase difference is π ) Is disposed so that the fast axis is inclined by 45 ° with respect to the incident linear polarization direction, the linearly polarized light having the wavelength λ ₁ is rotated by 90 ° when polarized through the organic thin film 14. . On the other hand, the retardation value of the organic thin film 14 is equal to the wavelength (m ₂ = 1) with respect to the light with the wavelength λ ₂ (the phase difference is 2π), and the polarization plane of the linearly polarized light with the wavelength λ ₂ transmitted through the organic thin film 14 is Does not rotate. That is, the planes of polarization parallel to each other are orthogonal after passing through the organic thin film 14.
Here, the natural numbers m ₁ and m ₂ are each preferably about 3, and if it is larger than this, a plurality of organic thin films are stacked, which is not preferable from the viewpoint of productivity.
[0015]
As the organic thin film 14 having birefringence, a film for alignment film applied on the transparent substrate 16 is subjected to a desired alignment treatment, and then a liquid crystal monomer solution as a birefringent material is applied onto the film. Alternatively, a polymer liquid crystal film that has been polymerized and cured by irradiation with light source light for photopolymerization can also be used. In this case, the phaser can be formed without using the adhesive 15.
[0016]
Although the case where the organic thin film is fixed between two transparent substrates has been described above, the organic thin film may be fixed on one transparent substrate. In this case as well, an adhesive may be used, or it may be formed directly on the transparent substrate.
[0017]
Materials for the adhesive 15 include acrylic, epoxy, urethane, polyester, polyimide, urea, melamine, furan, isocyanate, silicone, cellulose, vinyl acetate, vinyl chloride, rubber A system or a mixture thereof can be used. If the adhesive is UV curable or thermosetting, workability is good, but it is not limited thereto. It is necessary to apply the adhesive smoothly and thinly at a constant thickness in order to satisfactorily correct the wavefront aberration of the transmitted light. As a coating method, it is preferable to use a method such as spin coating or roll coating because the workability is excellent and the thickness can be easily controlled.
[0018]
The phase shifter configured as described above has a function of converting linearly polarized light having two different wavelengths whose polarization planes are parallel to each other into linearly polarized light whose polarization planes are orthogonal to each other. Can be separated by the difference in the plane of polarization.
[0019]
“Second Embodiment”
As shown in FIG. 2, the phase shifter 102 of the second embodiment of the present invention comprises an organic thin film portion in which an organic thin film 14 is fixed to a transparent substrate 16 using an adhesive 15, and a sawtooth grating 12. A transparent substrate 11 having an adjusting function is fixed using a filling adhesive 13 so that the organic thin film 14 and the sawtooth lattice 12 face each other. The sawtooth grating 12 has a function of diffracting one of the incident linearly polarized light of two wavelengths and not diffracting the other.
[0020]
The transparent substrates 11 and 16, the organic thin film 14, and the adhesive 15 are the same as those in the first embodiment. That is, as the organic thin film 14, two types of linearly polarized light whose polarization planes are parallel to each other are transmitted through the organic thin film 14 with the polarization direction inclined by 45 ° with respect to the fast axis direction, and then the polarization planes are orthogonal to each other. To do.
[0021]
Here, as shown in FIG. 2B, the optical axis adjustment function refers to a function of adjusting linearly polarized light whose optical axis is obliquely incident on the transparent substrate in the vertical direction. FIG. 2A shows a case of linearly polarized light whose optical axis is perpendicularly incident on the transparent substrate.
[0022]
The sawtooth grating 12 is made of, for example, a polymer liquid crystal made of a birefringent material (ordinary refractive index n _o , extraordinary refractive index _ne ), and is manufactured by the following procedure. A polymer liquid crystal is applied on the transparent substrate 11 so as to have a desired thickness. After aligning the liquid crystal molecules so that the alignment vectors of the liquid crystal molecules in the extraordinary refractive index _ne direction of the polymer liquid crystal are aligned in a specific direction in the plane, and then polymerizing and curing by irradiating light source light for photopolymerization, A sawtooth grating is formed by photolithography and etching techniques. The cross-section of the sawtooth lattice is preferably a right triangle, but may be stepped as shown in FIG. In the case of a staircase, the greater the number of steps in the staircase, the higher the light utilization efficiency. If four or more steps are formed, it is desirable that 70% or more of the first-order diffracted light can be used.
[0023]
Filler adhesive 13 has a refractive index n _s is homogeneous and clear adhesive, for example, the refractive index n _s is selected material so as to be substantially equal to the ordinary refractive index n _o of the liquid crystal polymer 12. The filling adhesive can be appropriately selected from the adhesives described in the first embodiment.
[0024]
The phase shifter configured as described above has a function of converting linearly polarized light having two different wavelengths whose polarization planes are parallel to each other into linearly polarized light whose polarization planes are orthogonal to each other, and having two different wavelengths. While separating light, for example, it does not act as a diffraction grating for linearly polarized light of wavelength λ ₁ , but acts as a diffraction grating for linearly polarized light of wavelength λ ₂ .
[0025]
Further, by forming a diffraction grating on the surface of the transparent substrate 11 in FIG. 2, it is possible to generate three beams for detecting a tracking error when recording / reproducing information on an optical recording medium. In this case, it is preferable that the phase difference based on the grating depth is 2π with respect to λ ₁ or λ ₂ so that only one of the lights having wavelengths λ ₁ and λ ₂ is diffracted. That is, the 2π for lambda ₁ when 2π, and the wavelength lambda ₂ of light is diffracted for the lambda ₂ when only the light of wavelength lambda ₁ is diffracted.
[0026]
As another example of this embodiment, a phase shifter having a phase correction function added to a transparent substrate can be used instead of the above-described optical axis adjustment function. This controls the wavefront of incident linearly polarized light, and a birefringent phase correction unit may be formed on the transparent substrate.
[0027]
“Third Embodiment”
3 includes a monolithic two-wavelength semiconductor laser 1 that emits linearly polarized light having different wavelengths from two light emitting points 1A and 1B, and an optical axis adjustment function for polarized light described in the second embodiment of the present invention. , A beam splitter 4, a collimating lens 5, an objective lens 6, and a photodetector 8, and reproduces information recorded on the optical disc 7 or records information on the optical disc 7.
[0028]
When the linearly polarized light having the wavelength λ ₁ is incident on the phase shifter 102 having the function of adjusting the optical axis of the polarized light, the polarization plane of the linearly polarized light is rotated by 90 ° by the organic thin film portion, and the polymer liquid crystal constituting the sawtooth grating 12 is formed. In contrast, it becomes ordinary light. Therefore, the ordinary refractive index n _o and the refractive index n _s of the filler adhesive 13 of the sawtooth grating 12 are substantially equal (n _o = n _s), straight transmitted without being diffracted.
[0029]
On the other hand, the linearly polarized light having the wavelength λ ₂ that is obliquely incident on the phase shifter and away from the point where the linearly polarized light having the wavelength λ ₁ is incident is the polarization plane of the linearly polarized light even though it is transmitted through the organic thin film portion. Is not rotated and becomes abnormal light with respect to the polymer liquid crystal constituting the sawtooth lattice 12. Therefore, the difference between the refractive index _{n o (n s = n o} ) of the sawtooth extraordinary refractive index of the grating 12 n _e the filling adhesive 13 (n _e -n _o), and depending on the shape of the sawtooth grating 12 + 1st order diffracted light having an efficiency of The + _1st- order diffracted light of wavelength λ ₂ is emitted from the same point as the emission point of the light of wavelength λ ₁ on the phase plate, with the optical axis of the light of wavelength λ ₁ matched.
[0030]
That is, the optical head device equipped with the phase shifter 102 having the function of adjusting the optical axis of polarized light according to the present invention can match the optical axes of linearly polarized light of two different wavelengths emitted from a monolithic two-wavelength semiconductor laser. . Therefore, an optical component that transmits two linearly polarized light can exhibit good optical characteristics with respect to each of the linearly polarized light, and causes extremely high reading errors when reproducing information on the optical disk and writing errors when recording information on the optical disk. Less stable signal detection can be performed.
Furthermore, since only one photodetector is required, the optical head device can be simplified, the number of assembly steps can be reduced, and the device can be reduced in size and weight.
[0031]
“Fourth Embodiment”
In the optical head device of the fourth embodiment, a package (light source unit) having a two-wavelength semiconductor laser, a phase shifter and the like is mounted on the optical head device.
First, the light source unit will be described. For example, a phase shifter 102 having a polarization optical axis adjustment function shown in FIG. 2 may be fixed to a package together with a two-wavelength semiconductor laser to form a light source unit.
[0032]
As shown in FIG. 5, the two-wavelength semiconductor laser 1 that emits two linearly polarized light having wavelengths λ ₁ and λ ₂ and parallel polarization planes from the light emitting point positions 1A and 1B is contained in one metal package 26. The heat sink metal block 28 is fixed. The package 26 is sealed by a light exit window glass 27 for the two-wavelength semiconductor laser 1 of the package 26. A current is supplied to the two-wavelength semiconductor laser 1 through the electrode 29, and the two-wavelength semiconductor laser 1 emits light. The phase shifter 102 having a function of adjusting the optical axis of polarized light is fixed to the outside of the light exit window glass 27 of the package 26 and constitutes one light source unit as a whole.
[0033]
Alternatively, the light source unit may include a photoelectric conversion element in which a photodetector, an electric signal processing circuit, an amplifier circuit, and the like are integrated in a package. Thereby, further miniaturization and integration can be realized.
[0034]
A beam splitter hologram that guides the return light reflected by the optical recording medium to the photodetector may be further laminated and integrated with the phase shifter 102 having a polarization optical axis adjustment function. Accordingly, a light source unit in which a plurality of functions are combined can be realized, so that the number of parts can be reduced and the size can be reduced.
[0035]
In the optical head device in which the light source unit having the above-described configuration is mounted, two linearly polarized light beams having wavelengths λ ₁ and λ ₂ from the same light emitting point position on the upper surface of the phase shifter 102 having a polarization optical axis adjusting function. Since the light source unit can be used as a two-wavelength light source, it can be handled in the same manner as a conventional single-wavelength light source.
[0036]
In addition, the optical head device on which the light source unit is mounted eliminates the trouble of optical axis alignment such as a two-wavelength semiconductor laser and a phase shifter, simplifies the assembly process of the optical head device, improves productivity, It is preferable because it can be reduced in size and weight.
[0037]
【Example】
"Example 1"
Example 1 is a specific example of the phase shifter of the second embodiment shown in FIG. A polycarbonate organic thin film 14 having a retardation value of 1650 nm with respect to light in a 660 nm wavelength band for a DVD optical disk was fixed to the transparent substrate 16 having a refractive index of 1.5 by an acrylic adhesive 15. This retardation value was a value of m ₁ = 3, and the generated phase difference was 5π. For linearly polarized light in the 790 nm wavelength band for CD optical disks, the retardation value corresponds to the value of m ₂ = 2 and the generated phase difference is 4π.
[0038]
Because of these phase differences, linearly polarized light in the 660 nm wavelength band rotates the plane of polarization by 90 °, and linearly polarized light in the 790 nm wavelength band does not rotate the plane of polarization, so light in two wavelength bands whose polarization planes are parallel to each other is polycarbonate. After passing through the manufactured organic thin film 14, the plane of polarization was orthogonalized. However, two types of linearly polarized light of a 660 nm wavelength band and a 790 nm wavelength band were incident on the organic thin film 14 with the polarization direction inclined by 45 ° with respect to the fast axis direction of the organic thin film 14.
[0039]
On the other hand, a polyimide for alignment film was applied in the form of a film on the transparent substrate 11 having a refractive index of 1.5, followed by rubbing alignment treatment, and then a polymer liquid crystal film was formed on the film. Refractive index of the polymer liquid crystal, an extraordinary refractive index after photopolymerization curing n _e of about 1.6, the ordinary refractive index n _o was about 1.5. For the light of 790 nm wavelength band for CD optical disk obliquely incident on the phase shifter, the polymer liquid crystal is obtained by alternately repeating three times of photolithography and etching so as to obtain a desired diffraction angle and diffraction efficiency. A transparent substrate having the function of adjusting the optical axis of polarized light was fabricated by processing into a sawtooth lattice 12 having eight stages. On the other hand, it does not have a diffraction effect for light in the 660 nm wavelength band.
[0040]
As thin organic film 14 and the sawtooth grating 12 face each other, the refractive index n _s is fixed using a transparent filler adhesive 13 of substantially equal acrylic and ordinary refractive index n _o of the liquid crystal polymer, the optical axis adjustment of the polarization A phase shifter 102 having a function was manufactured.
[0041]
"Example 2"
The phase shifter 102 having the function of adjusting the optical axis of polarized light produced in Example 1 was placed between the two-wavelength semiconductor laser 1 of the optical head device and the objective lens 6 as shown in FIG. In this optical head device, the optical axis of the optical system optimally designed for the light of 660 nm wavelength band for DVD optical disks can be made to coincide with the optical axis of the light of 790 nm wavelength band for CD optical disks. . Then, using the photodetector 8 having a small light receiving area shared during recording / reproduction of CD-type and DVD-type optical discs, good reproduction / recording was possible for DVD-type and CD-type optical discs.
[0042]
In the optical head device, the same effect can be obtained even if a phase shifter 102 having a function of adjusting the optical axis of polarized light is installed between the objective lens 6 and the photodetector 8. Although it is difficult for light in the 790 nm wavelength band for CD optical discs to pass through the optimal optical axis in a collimator lens or objective lens, it is possible to adjust the optical axis of linearly polarized light just before the photodetector. Also, the photodetector 8 having a small light receiving area shared when recording and reproducing both the CD and DVD optical disks can be used.
[0043]
【The invention's effect】
As described above, the phase shifter of the present invention can make two kinds of linearly polarized light having different polarization planes parallel to each other and orthogonal to each other. Further, by adding a linearly polarized light diffraction function to the above phaser, the optical axes of the two linearly polarized light incident perpendicularly and obliquely to the phaser can be matched.
[0044]
Furthermore, by mounting a phaser with a diffraction function on an optical head device having a two-wavelength semiconductor laser, the optical axes of the two linearly polarized light can be matched, so that each optical component in the device is excellent. It is possible to realize an optical head device that can exhibit stable optical characteristics and can perform stable signal detection with very few read errors when reproducing information on the optical disk and writing errors when recording information on the optical disk. Further, since only one photodetector is required, the optical head device can be simplified, the number of assembly steps can be reduced, and the device can be reduced in size and weight.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a phase shifter according to a first embodiment of the present invention.
2A and 2B are cross-sectional views of a phase shifter according to a second embodiment of the present invention, in which FIG. 2A is a cross-sectional view showing a state in which an optical axis of one linearly polarized light is perpendicularly incident on a transparent substrate, and FIG. Sectional drawing which shows a mode that the optical axis of becomes obliquely incident on a transparent substrate.
FIG. 3 is a conceptual diagram of an optical head device according to a third embodiment .
4A and 4B are conceptual diagrams of a conventional optical head device, in which FIG. 4A is a conceptual diagram showing a state in which linearly polarized light is emitted from an emission point 1A of a two-wavelength semiconductor laser, and FIG. The conceptual diagram which shows a mode that polarized light radiate | emits .
FIG. 5 is a conceptual diagram of a light source unit (package) in an optical head device according to a fourth embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 101: Phaser 102: Phaser 11, 16 which has the function of adjusting the optical axis of polarized light, 16: Transparent substrate 12: Sawtooth grating 13: Filling adhesive 14: Organic substance thin film 15: Adhesive 1: Two-wavelength semiconductor laser 1A, 1B: Light emitting point 4: Beam splitter 5: Collimating lens 6: Objective lens 7: Optical disk 8A, 8B: Photo detector 26: Package 27: Light exit window glass 28: Metal block 29 for heat sink 29: Electrode

Claims (2)

An organic thin film having birefringence fixed on at least one transparent substrate, and a diffraction grating,
The organic thin film has a fast axis of two wavelengths λ ₁ and λ ₂ (λ ₁ ≠ λ ₂ ), and the polarization plane is incident at an angle of 45 ° with respect to the polarization direction of linearly polarized light parallel to each other. is arranged, for the wavelength lambda ₁ of the linearly polarized light _{2π (m 1 -1/2) (m} 1 is a natural number) 2.pi.m ₂ is a phase difference of, with respect to the wavelength lambda ₂ of the linearly polarized light _{(m 2} Is adjusted to a retardation value that generates a phase difference of (natural number), and the planes of polarization of the two types of linearly polarized light are orthogonal to each other,
The diffraction grating is a phase shifter that diffracts one of the linearly polarized light of the two wavelengths and matches the optical axes of the light of the two wavelengths without diffracting the other. The diffraction grating is a sawtooth grating in cross-section at right angles triangular or stepped, made of a birefringent material having an ordinary refractive index n _o and extraordinary refractive index n _e,
The phaser according to claim 1, wherein a filling adhesive having a uniform refractive index n _s equal to the ordinary refractive index n _o fills the sawtooth grating .

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