JP2003228872A - Opening limiting element and optical head device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a high-performance device by obtaining an opening limiting element capable of materializing high converging performance in one kind of optical system even for two kinds of optical disks having different thicknesses, capable of being easily manufactured with the small number of production processes, having good production yield, and by mounting the opening limiting element on an optical head device executing the recording and reproduction of the optical disk. <P>SOLUTION: The opening limiting element 101 is obtained. The surface of the opening limiting element at its central region A is formed to a protruding part higher than a peripheral region B. The peripheral region B is provided with a wavelength selectivity dielectric substance multilayer film 12-laminated transparent substrate 11. The height (d) of the protruding part is adjusted so that the phases of luminous fluxes may be in phase with each other at the central region A and the peripheral region B with respect to one kind of luminous flux out of two kinds of incident luminous fluxes. The element is installed in an optical path between the light source of the optical head device and an object lens. <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 aperture limiting element and an optical head device, and more particularly to an optical head device for recording and reproducing information on an optical recording medium.

[0002]

2. Description of the Related Art A CD / DVD compatible type optical head device has been commercialized for recording and reproducing CDs or DVDs, which are optical discs of different standards, using the same optical head device. With each optical disc of CD and DVD,
Since the standards such as the wavelength band of light used for recording and reproduction, the thickness of the optical disc, and the recording density are different, it is necessary to change the numerical aperture of the optical system for recording and reproducing a CD and for recording and reproducing a DVD. .

[0003]

DV having a wavelength of 650 nm
In order to perform recording and reproducing of CD using an objective lens having a numerical aperture of about 0.6 designed for D, an aperture limiting element 501 shown in FIG.
A method of switching the numerical aperture for m has been proposed.
The aperture limiting element 501 has a central region C in which a dielectric multilayer film 52 for phase difference adjustment is formed on a transparent substrate 51 and a peripheral region D in which a wavelength selective dielectric multilayer film 53 is formed. . Reference numeral 54 is an antireflection film.

The wavelength-selective dielectric multilayer film 53 is a DVD
It has a function of transmitting the light flux for CD but not the light flux for CD. On the other hand, the dielectric multilayer film 52 for adjusting the phase difference
Has a function of transmitting both the light flux for DVD and the light flux for CD and aligning the phases of the light flux for DVD in the central region C and the peripheral region D.

However, the aperture limiting element 501 is not manufactured in the manufacturing process for forming the central region C and the peripheral region D.
A complex process in which the dielectric multilayer film before and after 0 layer is formed twice, the mask for lift-off is formed twice, and the lift-off is repeated twice is required, and the complicated process is a cause of hindering the yield improvement. An aperture limiting element having a simplified process has been desired.

An object of the present invention is to provide an aperture limiting element which can be easily manufactured with a small number of manufacturing steps and has a high production yield, and an optical head device using the same.

[0007]

The present invention SUMMARY OF] includes a light beam L ₁ having a wavelength lambda _1, the wavelength _{λ 2 (λ 1 ≠ λ 2} ) of the light beam L ₂ of,
An aperture limiting element comprising a wavelength-selective filter region that transmits only one of the light beams and a transparent region that transmits both light beams, wherein the aperture limiting element is the transparent region in a central region of its surface. And a transparent substrate in which a wavelength-selective dielectric multilayer film is laminated as the filter region in the peripheral region of the convex portion or the peripheral region of the surface opposite to the convex portion forming surface, The height of the convex portion is such that the incident light flux L ₁
On the other hand, there is provided an aperture limiting element characterized in that the central region and the peripheral region are adjusted so as to have the same phase.

Also provided is the above-mentioned aperture limiting element in which a wave plate and / or a diffraction grating made of an organic thin film is laminated on the surface of the transparent substrate opposite to the surface on which the convex portion is processed.

[0009] In addition, the wavelength λ ₁ light beam _{L 1} and the wavelength λ
A light source for each emission light beams L ₂ and the _{2 (λ 1 ≠ λ 2)} , an objective lens for converging the light beam L ₁ and the light beam L ₂ to the optical recording medium, and reflected by the condenser to an optical recording medium Luminous flux L
₁ and a photodetector for detecting the light flux L ₂ , wherein the aperture limiting element is arranged in a common optical path between two light sources and an objective lens. Provided is an optical head device.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an aperture limiting element 1 according to the present invention.
1 shows an example of the configuration of an optical head device equipped with 01. An optical head device for recording and reproducing DVD6 and CD7 as an optical recording medium, and as a light source, a semiconductor laser 1A and a CD for emitting a light flux L ₁ having a wavelength λ ₁ for DVD.
And a semiconductor laser 1B that emits a light beam L ₂ having a wavelength of λ ₂ .

The light beams L ₁ and L ₂ emitted from the semiconductor lasers 1A and 1B are respectively beam splitters 2 and 3.
After being transmitted through the collimating lens 4, the aperture limiting element 101, and the objective lens 5, the DVD 6
Alternatively, the light is focused on CD7. The light reflected by the DVD 6 or the CD 7 is finally focused on the photodetector 8. Further, 9 is a phase plate, and by using a quarter-wave plate, it is possible to prevent return light of the same polarization direction to the semiconductor laser 1B at the time of recording information on the CD 7 and stabilize the oscillation characteristics of the semiconductor laser 1B. You can

FIG. 2 shows (a) a sectional view and (b) a plan view of the aperture limiting element 101 according to the first embodiment of the present invention.
On the lower surface of the transparent substrate 11, a convex portion having a step d is directly processed, and the convex portion is a central region A, and a portion (recessed portion) lower than the central region A by d is a peripheral region B.
Further, the antireflection film thickness is d _a in the central region A film 13
But the wavelength selectivity of the dielectric multilayer film 12 is formed thickness is d _f in the peripheral region B. An antireflection film 14 is also formed on the upper surface of the transparent substrate 11. As the transparent substrate 11, an optically isotropic material such as glass or quartz glass can be used.

Further, as the antireflection films 13 and 14, a dielectric multilayer film of about 4 layers which allows the light flux L ₁ for DVD and the light flux L ₂ for CD to pass by 98% or more and is easily manufactured is used. As the wavelength-selective dielectric multilayer film 12, a transmittance of 90% or more for the light flux L ₁ of the wavelength λ ₁ for DVD and a transmittance of 20% or less for the light flux L ₂ of the wavelength λ ₂ for CD. A dielectric multi-layer film having about 20 layers can be used. However, the transmittance of the light flux L ₂ for CD is C
To prevent unnecessary light from being collected on the information recording surface of D, 10
% Or less is preferable. Therefore, by forming the wavelength-selective dielectric multilayer film 12 in the peripheral region B, the aperture limiting element 101 can limit the diameter of the light flux L ₂ for CD to the diameter of the central region A.

In the optical head device equipped with the aperture limiting element 101 of the present invention shown in FIG.
The numerical aperture is set to 0. 0 without limiting the diameter of the light flux L ₁ for DVD.
The light flux of 6 can be condensed on the DVD 6, while the diameter of the light flux L ₂ for CD is limited, and the light flux having a numerical aperture of 0.45 to about 0.5 can be condensed on the CD 7, so that the DVD 6 and the CD 7
Even with optical discs having different thicknesses, recording and reproduction can be stably realized by using a single objective lens.

Next, a method of manufacturing the aperture limiting element 101 of the present invention will be described with reference to FIG. First, as shown in FIG. 3A, the antireflection film 1 is formed on both surfaces of the transparent substrate 11.
3 and 14 are formed by a vacuum evaporation method or a sputtering method, a photoresist 15 is laminated on the antireflection film 13 as shown in FIG. 3B, and patterned using a photolithography technique. Then, as shown in FIG. 3C, the antireflection film 13 and the transparent substrate 11 are etched by a dry etching method.

Further, as shown in FIG. 3D, the remaining photoresist 15 is used as it is as a mask for lift-off, and the wavelength-selective dielectric multilayer film 12 is formed by a vacuum deposition method or a sputtering method. After forming the film, the photoresist 15 is peeled off with a peeling liquid or the like, so that the aperture limiting element 101 of FIG.

Here, the aperture limiting element 10 shown in FIG.
The step difference d of ₁ is determined so that the optical path length for the light passing through the central area A and the optical path length for the light passing through the peripheral area B of the light flux L ₁ for DVD are equal. That is, the thickness d _a of the antireflection film _13, the refractive index n of the thickness d _f, and the transparent substrate 11 at the wavelength of the light flux for CD for receiving an aperture limiting wavelength selective dielectric multilayer film 12, an antireflection film Using the average refractive index n _{a of} 13 and the average refractive index n _f of the wavelength-selective dielectric multilayer film 12, d = {(n _f −1) ·
d _f - is determined as _{(n a -1) · d a} } / (n-1).

Here, the average refractive index means the sum of the products of the refractive index of each layer constituting the multilayer film and the thickness of each layer divided by the thickness of the multilayer film.

According to the method of manufacturing the aperture limiting element 101 of the present invention, there is one step of forming a dielectric multilayer film of about 20 layers,
High productivity with a simple dry etching process and one lift-off process, and high yield.
An aperture limiting element can be produced.

FIG. 4 is a sectional view of an aperture limiting element 201 which is a second embodiment of the present invention. Aperture limiting element 201
In place of the antireflection film 14 in the aperture limiting element 101 of the first embodiment of FIG. 2, an element 16 such as a phase plate or a diffraction grating for controlling the state of light is provided on the transparent substrate provided with the antireflection film 18. It is a configuration sandwiched by 17. 4 that are the same as those in FIG. 2 indicate the same elements.

When the aperture limiting element 102 of the second embodiment is mounted on an optical head device, the number of elements constituting the optical head device can be reduced and the optical head device can be downsized, which is preferable.

FIG. 5 is an optical layout diagram showing an optical head device equipped with the aperture limiting element 301 of the third embodiment of the present invention, which is an optical head device for recording and reproducing DVD6 and CD7. 41B is a unit in which a semiconductor laser 1A for DVD and a photodetector 8A are integrated.
Is a hologram unit in which a semiconductor laser 1B for CD, a photodetector 8B, and a hologram element 10 having no polarization dependence are integrated and integrated. When the unit is used in the optical head device, the optical head device can be downsized. The reference numerals in FIG. 5 that are the same as those in FIG. 1 and have no description mean the same elements as those in FIG.

The aperture limiting element 301 is, for example, as shown in FIG. 6, a polarization hologram grating 1 instead of the antireflection film 14 in the aperture limiting element 101 of the first embodiment shown in FIG.
9, phase plate 20, transparent substrate 21 provided with antireflection film 22
Are laminated in this order. Reference numerals 11 and 1 in FIG.
2 and 13 mean the same elements as the reference numerals in FIG.

The retardation value generated by the phase plate 20 is selected so as to be 5/4 wavelength for the light flux L ₁ for DVD and one wavelength for the light flux L ₂ for CD.
By this selection, the light beam L ₁ is transmitted to the polarization hologram grating 19
With this function, the light travels straight through without being diffracted by the aperture limiting element 301 on the outward path, but is diffracted by the aperture limiting element 301 on the return path after the reflection of the DVD 6 and is focused on the photodetector 8A. On the other hand, the light beam L ₂ can pass through the aperture limiting element 301 without being diffracted by the polarization hologram grating 19 in both the forward and backward passes.

As the polarization hologram grating 19, for example, a polymer liquid crystal is processed by a technique of photolithography and etching to form a hologram grating having an uneven cross section, and then the ordinary refractive index or extraordinary light refraction of the polymer liquid crystal is performed. It is possible to use one in which the concave portion of the hologram grating is filled with an optically isotropic material having the same ratio.

In the optical head device equipped with the aperture limiting element 301 of the third embodiment of the present invention shown in FIG. 5, by using the aperture limiting element 301, the optical device equipped with the aperture limiting element 101 shown in FIG. Similar to the head device, CD and DVD recording and reproduction can be stably realized by using a single objective lens. Further, the aperture limiting element 301 has a polarization hologram grating 19 and a phase plate 20 laminated (FIG. 6) to give one element an aperture limiting function, a beam splitter function, and a polarization control function. As compared with the illustrated optical head device, a smaller optical head device can be realized.

[0027]

EXAMPLE This example is an example of an optical head device for recording and reproducing information on DVD and CD, which will be described with reference to FIG. As a light source, the wavelength λ ₁ (= 66 for DVD
Semiconductor laser 1A for emitting a light beam L ₁ of 0 nm) and a CD
And a semiconductor laser 1B that emits a light beam L ₂ having a wavelength λ ₂ (= 780 nm) for use with the aperture limiting element 101 between the collimator lens 4 and the objective lens 5.
Was installed.

As the beam splitter 2, the light flux L
_{For 1} , the beam splitter used is a half mirror and totally transmits the light flux L ₂ . As the beam splitter 3, a beam splitter that totally transmits the light beam L ₁ and serves as a half mirror for the light beam L ₂ is used. Further, a quarter-wave plate which is a phase plate 9 is also mounted in order to prevent light returning to the semiconductor laser 1B when recording information on the CD 7 and stabilize the oscillation of the semiconductor laser 1B.

The aperture limiting element 101 (FIG. 2) was manufactured by the manufacturing method shown in FIG. First, as shown in FIG. 3A, the antireflection films 13 and 14 having a reflectance of 0.5% or less with respect to the light flux L ₁ and the light flux L ₂ are formed on both surfaces of the transparent substrate 11.
Is formed by a vacuum deposition method, a photoresist 15 is laminated on the antireflection film 13 as shown in FIG. 3B, and patterned by using a photolithography method. Then, as shown in FIG. Thus, the antireflection film 13 and the transparent substrate 11 were etched by the dry etching method.

Further, as shown in FIG. 3D, the remaining photoresist 15 is used as it is as a lift-off mask, and the wavelength-selective dielectric multilayer film 12 having the structure shown in Table 1 is ion-assisted deposited. After being formed by the method, the photoresist 15 was peeled off with a peeling solution to fabricate the aperture limiting element 101 of FIG.

[0031]

[Table 1]

Here, the aperture limiting element 10 of FIG.
The etching step d of 1 is the thickness d _{a of the} antireflection film 13 =
0.3 [mu] m, the wavelength selectivity of the dielectric multilayer film 12 thickness _{d f}
= 1.8 μm and the refractive index n = 1.45 of the transparent substrate 11 and the average refractive index n _a = 1.87 of the antireflection film 13 at the wavelength of the light flux for CD subject to aperture restriction, and the wavelength-selective dielectric. The average refractive index n _f = 1.77 of the multilayer film 101 was used and determined according to the following equation. _{d = {(n f -1)} · d f - (n a -1) · d a} /
(N-1) = 2.5 [mu] m As described above, the aperture restriction is made by a simple process including one film forming process of the dielectric multilayer film of about 20 layers, one dry etching process, and one lift-off process. In the optical head device equipped with the element 101, high converging performance can be realized with one optical system for optical disks having different thicknesses such as DVD and CD, and good recording / reproducing characteristics are shown.

[0033]

As described above, according to the present invention, the number of manufacturing steps is one, which is one step of forming a dielectric multilayer film of about 20 layers, one dry etching step, and one lift-off step. In addition, it is possible to obtain an aperture limiting element that can be manufactured in accordance with the present invention and has a high production yield. Further, by mounting the aperture limiting element in the optical head device, the aperture of the light flux is effectively limited according to two different wavelengths. It is possible,
With respect to DVD and CD having different thicknesses, the respective light fluxes can be condensed, and information can be recorded and reproduced well.

[Brief description of drawings]

FIG. 1 is an optical layout diagram of an optical head device equipped with an aperture limiting element according to a first embodiment of the present invention.

2A and 2B are diagrams showing a configuration of an aperture limiting element according to a first embodiment of the present invention, in which FIG. 2A is a sectional view and FIG.

FIG. 3 is a conceptual diagram showing a method of manufacturing the aperture limiting element according to the first embodiment of the present invention.

FIG. 4 is a sectional view showing the structure of an aperture limiting element according to a second embodiment of the present invention.

FIG. 5 is an optical layout diagram of an optical head device equipped with an aperture limiting element according to a third embodiment of the present invention.

FIG. 6 is a sectional view showing the configuration of an aperture limiting element according to a third embodiment of the present invention.

FIG. 7 is a sectional view showing a configuration of a conventional aperture limiting element.

[Explanation of symbols]

101, 201, 301, 501: Aperture limiting element 1A, 1B: Semiconductor laser 2, 3: Beam splitter 4: Collimating lens 5: Objective lens 6: DVD 7: CD 8, 8A, 8B: Photodetector 9: Phase plate 10: Hologram element having no polarization dependence 41A: Unit 41B: Hologram unit 11, 17, 21, 51: transparent substrate 12: Wavelength selective dielectric multilayer film 13, 14, 18, 22, 54: Antireflection film 15: Photoresist 16: Element that controls the state of light 19: Polarization hologram grating 20: Phase plate 52: Dielectric multilayer film for phase adjustment 53: Wavelength-selective dielectric multilayer film A, C: central area B, D: peripheral area

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Claims (3)

[Claims] _1. A light flux L ₁ of wavelength λ ₁ and a wavelength λ ₂ (λ ₁ ≠
A wavelength-selective filter region that transmits only one of the light beams L ₂ of λ ₂ ) and a transparent region that transmits both light beams. , A dielectric multilayer film having a wavelength-selective dielectric multilayer film as a filter region in a peripheral region of a convex region or a peripheral region opposite to a convex-forming surface in the central region of the surface thereof. The aperture limiting element is characterized in that the height of the convex portion is adjusted so that the phase of the incident light flux L ₁ is aligned in the central region and the peripheral region. 2. The aperture limiting element according to claim 1, wherein a wave plate and / or a diffraction grating made of an organic thin film is laminated on the surface of the transparent substrate opposite to the surface on which the convex portion is processed. Wherein the light flux with wavelength lambda _{1 L 1} and the wavelength λ ₂ (λ ₁ ≠ λ
₂ ) a light source for emitting a light beam L ₂ and a light beam L ₁
An optical head device comprising: an objective lens for condensing the light flux L ₂ on an optical recording medium; and a photodetector for detecting the light flux L ₁ and the light flux L ₂ condensed and reflected by the optical recording medium, An optical head device, wherein the aperture limiting element according to claim 1 or 2 is arranged in a common optical path between two light sources and an objective lens.