JP2001216675A - Optical head device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain miniaturization by reducing the number of components of an optical head device. SOLUTION: Double refraction organic substance thin film 1 whose retardation value is adjusted so as to generate a prescribed phase difference to exited light which is emitted from a semiconductor laser 11 and transmits a diffraction element 14 is formed on at least one side of surface of two surfaces of a collimator lens 2 or an objective lens 15 composing the optical head device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device for recording and reproducing information on an optical recording medium.

[0002]

2. Description of the Related Art As shown in FIG. 5, a collimator lens 16, an objective lens 15, a phase shifter 17, and a diffractive optical disc for recording / reproducing information on an optical recording medium such as an optical disk such as a CD or DVD or a magneto-optical disk. An optical head device including an optical element such as the element 14 is used.

The optical head device guides light emitted from a semiconductor laser 11 to an optical recording medium 12, and reflects reflected light from the optical recording medium 12 to a diffraction element 14 or a beam splitter (not shown).
Diffracted or deflected by an optical element such as
Is configured to detect reflected light. In addition, phase shifter 1
7 is usually provided between the semiconductor laser 11 and the optical recording medium 12 by itself or integrated with the diffraction element.

[0004] A phase shifter is generally used in a polarization system using polarized light in order to increase the light use efficiency of an optical head device. Also, in a non-polarization type optical head device, a phase shifter may be provided in the optical head device in order to prevent interference between light emitted from a light source such as a semiconductor laser and light returned to the light source. is there.

[0005]

Heretofore, a phaser which has been polished from an inorganic single crystal such as quartz has been used. However, since inorganic single crystals have strong birefringence, the phase difference that occurs when light is incident largely depends on the angle of incidence, and the phase difference between the collimating lens and the objective lens, where the incident light is parallel light, Was not suitable for the installation location. In addition, an optical element made of an inorganic single crystal has a problem in that the number of manufacturing steps is large and the manufacturing is difficult.

The phase shifter made of an organic material is easier to fabricate than an inorganic single crystal such as quartz, but when used as an individual element, the number of parts of the optical head device increases, and the increase in the entire device accompanying this increase. There is a problem that aberration increases. Further, it has been difficult to reduce the size of the device.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and comprises a semiconductor laser,
An optical head device for recording / reproducing information on an optical recording medium, comprising: a collimating lens that collimates the light emitted from the semiconductor laser into a parallel light; and an objective lens that converges the parallel light onto the optical recording medium. A birefringent organic thin film is formed on at least one of both surfaces of the collimating lens or the objective lens, with a retardation value being adjusted so as to generate a predetermined phase difference with respect to the emitted light. An optical head device is provided.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical head device according to the present invention comprises at least a semiconductor laser, a collimator lens for collimating light emitted from the semiconductor laser, and an objective lens for converging parallel light on an optical recording medium. Have. The retardation value is adjusted so that a birefringent organic thin film on one or both surfaces of the collimator lens or the objective lens generates a predetermined phase difference with respect to light emitted from the semiconductor laser. It has been formed.

With the above-described structure, the retarder and the lens can be easily integrated in the manufacturing process unlike the case of the inorganic single crystal because the retarder is an organic thin film. Further, since they are integrated, the size of the device can be reduced as compared with the case where individual optical elements (the retarder and these lenses) are separately incorporated into the optical head device.

Hereinafter, a phaser-integrated lens in which a phaser and a lens are integrated, which is used in the optical head device of the present invention, with reference to the drawings, will be described as an example in which an organic thin film is formed on one surface of the lens. explain.

As shown in FIG. 2, the retarder-integrated collimator lens 3 is formed by forming an organic thin film 1 having birefringence on, for example, one flat surface of the collimator lens 2. Here, reference numeral 11 denotes a semiconductor laser. An anti-reflection film may be applied to the interface between the collimating lens 2 and the air and the interface between the organic thin film 1 and the air. When the anti-reflection coating is applied, the difference in the refractive index between the collimating lens 2 and the air and the organic thin film The surface reflection loss of light hardly occurs due to the difference in the refractive index between air and air. here,
An anti-reflection film is applied (not shown).

Further, when the emitted light from the semiconductor laser is perpendicularly incident on the organic thin film 1 and is transmitted therethrough, the organic thin film 1 generates a phase difference of mπ / 2 (m is a natural number) with respect to the transmitted light. This is preferable because interference between light emitted from the light source and return light can be prevented. Here, m is preferably 1 to 5. When m = 1, 3 or 5, the organic thin film acts as a quarter-wave plate, and when m = 2, the organic thin film acts as a half-wave plate. However, when m = 4, it does not act as a phase shifter, so 4 is not considered.

To generate a desired phase difference, the retardation value of the organic thin film 1 is adjusted. That is, assuming that the difference between the ordinary light refractive index and the extraordinary light refractive index of the organic thin film 1 is Δn, the thickness of the organic thin film 1 is d, and the wavelength of the transmitted light is λ, the retardation value is given by Δn · d. between φ and φ
= Δn · d · 2π / λ. Therefore, a desired phase difference can be obtained by adjusting the retardation value for light of a specific wavelength using this equation.

In particular, when the organic thin film 1 has a phase difference of (2p-1) .pi. / 2 (p is a natural number) when light emitted from the semiconductor laser 11 enters the organic thin film 1, (P may slightly deviate from a natural number as long as it functions as a phaser). In this case, when the optical axis direction of the phaser and the oscillation direction of the linearly polarized light of the light emitted from the semiconductor laser have a specific relationship (for example, form an angle of 45 °), the linearly polarized light is incident on the collimating lens. As a result, a phase difference of (2p-1) .pi. / 2 (p is a natural number) is obtained and converted into circularly polarized light. That is, the organic thin film 1 functions as a quarter-wave plate.

In the configuration shown in FIG. 2, the organic thin film 1 is fixed to one surface of the collimating lens 2 using an adhesive. As the organic thin film having birefringence, it is preferable to use (modified) polycarbonate, polyimide, polyether sulfone, or (alicyclic) polyolefin in consideration of heat resistance. (Modified) polycarbonate means a modified polycarbonate in which polyester carbonate is used as a part of a component of the polycarbonate composed of pisphenol A. Alternatively, a polymer liquid crystal can be used.

As the collimating lens, a lens designed to obtain the best wavefront aberration characteristics when integrated with an organic thin film is used. As the adhesive, acrylic, epoxy, urethane, polyester, polyimide, urea, melamine, furan, isocyanate, silicone, cellulose, vinyl acetate,
A vinyl chloride type, a rubber type or a mixture thereof can be used. The adhesive is preferably workable if it is a UV-curing type or a thermosetting type, but is not limited thereto.

In the configuration shown in FIG. 3, an organic thin film 1 having birefringence is fixed to one surface of an objective lens 4 to constitute a phaser-integrated objective lens 5. Here, reference numeral 12 denotes an optical recording medium.

As the organic thin film 1 having birefringence, a UV-curable polymer liquid crystal is used here. The method for forming the organic thin film includes a mold designed in consideration of the shape of the objective lens and the phase difference generated in the organic thin film, and applying a photo-alignment alignment film to the surface of the objective lens 4 on which the organic thin film is formed, Photoalignment treatment is performed by irradiating linearly polarized UV. Thereafter, a liquid crystal monomer which becomes a UV-curable polymer liquid crystal is filled between the mold and the objective lens, and is cured by UV irradiation. As the objective lens 4,
One that is designed to obtain good wavefront aberration characteristics when integrated with the organic thin film 1 is used.

In the above, the case where the organic thin film is formed on one of the two surfaces of the lens has been described, but it may be formed on both surfaces. In this case, the thickness d of the organic thin film may be the sum of the thicknesses of the organic thin films on both surfaces, and the relationship of φ = Δn · d · 2π / λ holds true as it is.

FIG. 4 shows a configuration of an optical head device in which a collimator lens and an objective lens are integrated, and the functions of both lenses are provided in a single objective lens. The phaser-integrated lens according to the present invention is used by being installed in an optical head device that records and reproduces information on an optical recording medium such as an optical disk such as a CD or DVD or a magneto-optical disk. As shown in FIG. 4, the light emitted from the semiconductor laser 11 is
Through the objective lens 4 (integrated collimator lens and objective lens) on which the organic thin film 1 is formed,
It is installed on the optical recording medium 12 so as to be focused. 13 is a photodetector.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a method of manufacturing a phase-integrated collimator lens shown in FIG. 2 to be installed in an optical head device will be described. As the organic thin film 1, a polycarbonate exhibiting birefringence by uniaxial stretching is used, and the organic thin film 1 is fixed to a collimating lens 2 having a focal length of 15 mm and a convex shape on one side with a polyester-based adhesive (not shown). did. The organic thin film 1 has a retardation value of 195 nm,
780n wavelength used for recording / reproducing D-type optical disc
It functions as a quarter-wave plate for the light of m. The thickness of the organic thin film 1 was 50 μm, and an antireflection film was formed on the surface of the organic thin film 1 in order to prevent reflection of light at the interface between air and the organic thin film 1.

As the collimating lens 2, a lens designed in consideration of the birefringence (two types of refractive indexes) and the thickness of the organic thin film was used. In addition, an antireflection film was applied to the lens surface to prevent reflection at the interface between the air and the lens (not shown). A polyester UV effect type adhesive was used as the adhesive, and the flat side of the lens was bonded to the surface of the organic thin film on which the antireflection film was not formed.

Next, the collimating lens manufactured as described above was incorporated into an optical head device as shown in FIG. In this embodiment, a wavelength of 780 n for a CD optical disc is used.
m semiconductor lasers 11 were used. This semiconductor laser 11
After being transmitted through the diffraction element 14, the linearly polarized light exiting from is transmitted through the phaser-integrated collimating lens 3 in which the organic thin film 1 is formed on the collimating lens 2, is converted into parallel light, and is further converted into circularly polarized light. The light transmitted through the retarder-integrated collimating lens 3 was collected on the recording surface of the optical recording medium 12 by the objective lens 15.

The reflected return light from the optical recording medium 12 passes through the objective lens 15 and again passes through the phaser-integrated collimating lens 3 to form a linearly polarized light having a vibration direction orthogonal to the vibration direction of the linearly polarized light on the outward path. Was converted to The light transmitted through the phase-integrated collimator lens 3 is diffracted by the diffraction element 14.
And was guided to the photodetector 13.

Since the linearly polarized light transmitted through the collimator lens 3 integrated with the phaser has a vibration direction orthogonal to that of the linearly polarized light emitted from the semiconductor laser 11, no interference occurs between the two linearly polarized lights, and the linearly polarized light is stable. The oscillation output of the laser light thus obtained was obtained. As a result, information could be stably recorded on a writing optical disc such as a CD-R, and the reproduction signal characteristics of a CD optical disc including the CD-R were also good. Further, since the phaser and the collimating lens were integrated, the size of the apparatus could be reduced.

[0026]

As described above, according to the present invention, a phaser-integrated lens in which an organic thin film having birefringence is formed on a lens is incorporated in an optical head device, thereby reducing the number of components of the optical head device. Can be reduced, the size of the optical head device can be reduced, and an optical head device having good characteristics of a reproduced signal from an optical recording medium can be obtained.

[Brief description of the drawings]

FIG. 1 is a conceptual side view showing an example of the configuration of an optical head device according to the present invention incorporating a phaser-integrated objective lens.

FIG. 2 is a cross-sectional view showing an example of the configuration of a phaser-integrated collimator lens according to the present invention.

FIG. 3 is a sectional view showing an example of the configuration of a phaser-integrated objective lens according to the present invention.

FIG. 4 is a conceptual side view showing another example of the configuration of the optical head device of the present invention incorporating a phaser-integrated objective lens.

FIG. 5 is a conceptual side view showing an example of a conventional optical head device.

[Explanation of symbols]

 1: Organic thin film 2, 16: Collimating lens 3: Phaser-integrated collimator lens 4, 15: Objective lens 5: Phaser-integrated objective lens 11: Semiconductor laser 12: Optical recording medium 13: Photodetector 14: Diffraction element 17: Phaser

Claims (2)

[Claims] An optical recording medium comprising: a semiconductor laser; a collimator lens for collimating light emitted from the semiconductor laser; and an objective lens for converging the parallel light on the optical recording medium. In an optical head device performing reproduction, a birefringent organic thin film on at least one of both surfaces of the collimating lens or the objective lens has a retardation value such that a predetermined phase difference is generated with respect to the outgoing light. An optical head device characterized by being adjusted. 2. The optical head device according to claim 1, wherein the predetermined phase difference is mπ / 2 where m is a natural number.