JP2003207613A - Optical element and hologram laser unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical element of a small size having functions of two diffraction gratings and one phaser and further to obtain a hologram laser unit which is integrated with a semiconductor laser, a photodetector and an optical diffraction element, is small in size and prevents the exit return light from a semiconductor laser from affecting the transmission of the semiconductor laser. <P>SOLUTION: The optical element 9 is obtained by superposing two transparent substrates 4 and 5 and laminating the phaser 3 consisting of a thin organic matter film between the transparent substrates 4 and 5 to constitute a laminated plate consisting of the transparent substrates 4 and 5 and the phaser 3 and forming the hologram diffraction grating 1 and the straight diffraction grating 2 on the front and rear 2 surfaces, respectively, of the laminated plate. The hologram laser unit is obtained by integrally forming the semiconductor laser, the photodetector and the optical element 9. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element and a hologram laser unit, and more particularly to an optical element and a hologram laser unit used in an optical head device for recording and reproducing information on an optical recording medium.

[0002]

2. Description of the Related Art A hologram laser unit in which a semiconductor laser, a photodetector and a diffractive optical element are integrated is used in order to downsize an optical head device or reduce the number of optical parts constituting the optical head device. .

[0003]

In particular, as the optical head device for recording information is becoming higher in speed, there is a problem that the oscillation of the semiconductor laser becomes unstable due to the returning light from the optical disk which is the optical recording medium. Has occurred. This problem has been solved by inserting a quarter-wave plate in the optical path of the light from the semiconductor laser toward the optical disc. On the other hand, however, the number of optical components that make up the optical head device increases, and It was an obstacle to the miniaturization of the device. Therefore, there has been a demand for an optical element that reduces the number of optical components and a small light source unit in which the optical element is integrally formed.

[0004]

The present invention has been made to solve the above-mentioned problems, and a plurality of transparent substrates are stacked, and an organic thin film is formed on at least one of adjacent transparent substrates. Provided is an optical element characterized in that a laminated plate including a transparent substrate and a retarder laminated with a retarder sandwiched therebetween is formed, and a diffraction grating is formed on each of the front and back 2 surfaces of the laminated plate. .

Also provided is the above-mentioned optical element in which a polarization-selective diffraction grating is laminated in addition to the retarder.

Furthermore, a hologram laser unit in which at least a semiconductor laser, a photodetector and a diffractive optical element are integrally formed is characterized in that the above optical element is used as the diffractive optical element. A hologram laser unit is provided.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION As a first embodiment of the optical element of the present invention, a plurality of transparent substrates are stacked, and a retarder made of an organic thin film is sandwiched and stacked on at least one of adjacent transparent substrates. A laminated plate including the transparent substrate and the retarder is formed, and a diffraction grating is formed on each of the front and back surfaces 2 of the laminated plate.

The number of transparent substrates may be three or four,
For example, in the case of three sheets, a retarder made of an organic thin film is laminated between two substrates formed by three transparent substrates to form a laminated plate. The diffraction gratings on the two surfaces may have a rectangular cross section, a blazed diffraction grating shape, or any other shape, and the surfaces may have different shapes.

Hereinafter, for simplification, the case where the number of transparent substrates is two and the diffraction gratings on the two surfaces are rectangular in section will be taken as an example, and referring to FIG. One embodiment will be described.

As shown in FIG. 1, an optical element 9 according to the first embodiment of the present invention includes a transparent substrate 4 having a holographic diffraction grating 1 having a rectangular cross section and a curved plane as its surface,
A retarder 3 made of an organic thin film is laminated and fixed between a transparent substrate 5 and a linear diffraction grating 2 having a rectangular cross section and a linear plane.

The holographic diffraction grating 1 and the linear diffraction grating 2 may be directly processed and formed on the transparent substrate 4 and the transparent substrate 5 made of quartz glass or optically isotropic optical glass. After forming a transparent and optically isotropic inorganic thin film such as quartz glass or an organic thin film such as polyimide on the lattice processed surface of 5,
The grating may be processed and formed. The materials forming the holographic diffraction grating 1 and the linear diffraction grating 2 may be different, and the materials forming the transparent substrate 4 and the transparent substrate 5 may be different.

As the retarder 3 made of an organic thin film, a film in which birefringence is exhibited by stretching polycarbonate or the like may be used, and the transparent substrate 4 and the transparent substrate 5 are used.
It is also possible to use a polymer liquid crystal thin film formed by subjecting the above to liquid crystal alignment treatment, applying a liquid crystal monomer and curing the same. Further, the retardation value of the phase shifter 3 made of an organic thin film is selected to be, for example, an odd multiple of a quarter wavelength with respect to the center wavelength of the light passing through the optical element 9, so that the optical wave traveling back and forth through the optical element 9 is changed. It is preferable that the vibration directions can be made orthogonal to each other on the forward and return paths.

That is, in the optical element 9 according to the first embodiment of the present invention, when the semiconductor laser is as a light source and the optical disk is above, for example, in FIG. 1, the optical element 9 is reflected by the optical disk to reciprocate the optical element 9. Since the light returning to the semiconductor laser does not interfere with the light emitted from the semiconductor laser,
The semiconductor laser can operate stably.

As a second embodiment of the optical element of the present invention,
In addition to the retarder, it is preferable that a polarization selective diffraction grating is further laminated. This polarization-selective diffraction grating may be stacked on the retarder and laminated between the transparent substrates, or may be separately laminated when there are a plurality of transparent substrates, but the laminated plate can be made smaller. In that case, it is preferable to stack the layers. Hereinafter, the case of stacking layers will be described as an example with reference to FIG.

As shown in FIG. 2, an optical element 10 according to a second embodiment of the present invention includes a transparent substrate 4 having a holographic diffraction grating 1 formed on its surface and a transparent substrate 5 having a linear diffraction grating 2 formed thereon. Then, the retarder 3 made of an organic thin film and the polarization-selective diffraction grating 6 are superposed and laminated. The holographic diffraction grating 1, the linear diffraction grating 2, and the retarder 3 made of an organic thin film can be manufactured by the same process as in the first embodiment.

The retardation value of the retarder 3 made of an organic thin film is the same as that in the first embodiment.
It is preferable to select, for example, an odd multiple of a quarter wavelength with respect to the center wavelength of the light passing through, because the oscillation directions of the light waves that reciprocate in the optical element 10 can be made orthogonal to each other on the outward path and the return path.

The polarization-selective diffraction grating 6 is produced by subjecting the transparent substrate 5 to a usual liquid crystal alignment treatment, applying a liquid crystal monomer and curing it to form a polymer liquid crystal thin film, and processing the polymer liquid crystal thin film into a lattice shape. It is configured by filling the interstitial spaces with an optically isotropic filler having the same refractive index as the ordinary light refractive index. At this time, if the linearly polarized light incident on the optical element 10 is ordinary light, the light is not diffracted even though it is transmitted through the polarization-selective diffraction grating 6, but is transmitted straight through, but the linearly polarized light incident on the optical element 10 is abnormal light. In that case, the light is diffracted.

At this time, the extraordinary light refractive index of the polymer liquid crystal is
n_e, The refractive index of the filler is n_s, Polarization-selective diffraction grating 6
Is d, and the wavelength of light incident on the optical element 10 is λ.
, (N _e-N_s) × d × 2π / λ
The height d is determined so that is λ / 2. That is, the bias
0th order of extraordinary light diffracted by the photoselective diffraction grating 6
The diffracted light component (straight transmission component) becomes 0, which is preferable.

That is, when the optical element 10 according to the second embodiment of the present invention is used, a semiconductor laser is provided as a light source in the lower part of FIG. 2 and an optical disk is provided in the upper part, and outgoing linearly polarized light is incident on the optical element 10 as ordinary light. In this case, since the light reflected by the optical disk and traveling back and forth through the optical element 10 does not return to the semiconductor laser, the semiconductor laser can operate stably.

As an embodiment of the hologram laser unit of the present invention, at least a semiconductor laser, a photodetector, and
This is a hologram laser unit integrally formed with a diffractive optical element. The above optical element is used as this diffractive optical element. An example of the configuration of the hologram laser unit of the present invention is shown in FIG. 3 as a conceptual diagram. The hologram laser unit 11 is one in which the optical element according to the first embodiment of the present invention, the semiconductor laser 7, and the photodetector 8 are integrated. Therefore, the same reference numerals as those shown in FIG. 1 represent the same elements. Further, the optical element of the second embodiment may be used instead of the optical element of the first embodiment.

The grating plane pattern of the holographic diffraction grating 1 in the optical element of the first embodiment is incident on this optical element from above in FIG.
The first-order diffracted light diffracted by is designed so as not to pass through the linear diffraction grating 2. At this time, if the total thickness of the transparent substrate 4 and the transparent substrate 5 is 1.5 mm or less, the holographic diffraction grating 1 has a grating pitch of 1 μm or less, which makes processing difficult. Therefore, the total thickness of the transparent substrate 4 and the transparent substrate 5 is 1.5 mm to 2.5 mm.
It is preferable to set the distance between these because the holographic diffraction grating 1 can be easily processed and the optical element does not become large.

According to the hologram laser unit 11 of the present invention, the oscillation characteristics are not disturbed by the returning light to the semiconductor laser, so that the hologram laser unit 11 can operate stably.

[0023]

EXAMPLES A method of manufacturing the optical element of this example will be described based on the optical element shown in FIG. After forming the holographic diffraction grating 1 on the surface of the transparent substrate 4 made of glass by using photolithography and etching, an antireflection film was applied to this surface. Similarly, after forming the linear diffraction grating 2 on the surface of the transparent substrate 5 made of glass,
Similarly, an antireflection film was applied to this formation surface. Next, as the phase shifter 3 formed of an organic thin film, a thin film obtained by uniaxially stretching polycarbonate to generate a retardation value corresponding to a quarter wavelength with respect to the center wavelength of light transmitted through the optical element 9 is irradiated with ultraviolet rays. A curable adhesive was used to sandwich and fix the transparent substrate 4 and the transparent substrate 5 on the back surfaces of the respective lattice-processed surfaces.

Next, as a result of assembling a hologram laser unit using this optical element 9 as shown in FIG.
In the hologram laser unit 11, the optical element 9 functions, and the laser beam is stably oscillated and operates well without the emission of the semiconductor laser being disturbed by the reflected return light from the optical disk (not shown).

[0025]

As described above, according to the present invention, a retarder made of an organic thin film having a retardation value of, for example, a quarter wavelength is sandwiched between two transparent substrates having a diffraction grating formed on the surface thereof. The optical element consists of two diffraction gratings and one
It is possible to realize a compact optical element that also has the functions of two quarter-wave plates.

A small unit is realized in the hologram laser unit of the present invention equipped with this optical element,
Further, when this unit is mounted in the optical head device, the diffraction grating of the optical element functions and the laser light oscillation is not disturbed by the reflected return light from the optical disk to the semiconductor laser that is the light source, and stable operation is possible. . Further, the number of constituent parts of the optical head device can be reduced and the device can be downsized.

[Brief description of drawings]

FIG. 1 is a sectional view showing a configuration of an optical element according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a configuration of an optical element according to a second embodiment of the present invention.

FIG. 3 is a conceptual diagram showing an example of the configuration of a hologram laser unit of the present invention.

[Explanation of symbols]

1: Holographic diffraction grating 2: Linear diffraction grating 3: Phaser 4, 5: transparent substrate 6: Polarization-selective diffraction grating 7: Semiconductor laser 8: Photodetector 9, 10: Optical element 11: Hologram laser unit

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H049 AA03 AA13 AA43 AA45 AA66                       BA05 BA07 BA25 BA42                 5D119 AA01 AA04 FA05 FA30 JA22                       JA23 JA31                 5D789 AA01 AA04 FA05 FA30 JA22                       JA23 JA31                 5F089 BA04 BB02 CA20 GA05

Claims (3)

[Claims] 1. A plurality of transparent substrates are stacked, a retarder made of an organic thin film is sandwiched between at least one of adjacent transparent substrates, and a laminated plate including the stacked transparent substrates and the retarder is formed. An optical element having a diffraction grating formed on each of the front and back surfaces 2 of the laminated plate. 2. The optical element according to claim 1, further comprising a polarization-selective diffraction grating laminated in addition to the retarder. 3. A semiconductor laser, a photodetector, and
A hologram laser unit integrally formed with a diffractive optical element, wherein the optical element according to claim 1 or 2 is used as the diffractive optical element.