JP3467796B2 - Objective lens, optical head device having the same, and method of adjusting optical axis of objective lens - Google Patents

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 used for reading and writing optical discs and the like.

[0002]

2. Description of the Related Art Generally, the optical axis of an objective lens provided in an optical head device for an optical disk must be kept perpendicular to the recording surface of the optical disk at the time of driving the device such as tracking and focusing. I won't. This is because if this optical axis is not held perpendicular to the optical disk surface, optical aberrations such as coma aberration and astigmatism due to the tilt of the objective lens will occur, and light will be utilized due to the effect of this aberration. This is because there is a problem that an error occurs in the extracted information signal or the like.

For this reason, some objective lenses mounted on the optical head device are provided with adjusting means for detecting and correcting the inclination. As an example, as shown in FIG. 4, as the objective lens 41, a so-called molded lens that integrally has a collar portion 43 having a surface perpendicular to the optical axis at the peripheral edge portion of the lens surface portion 42 is used. There is a method in which the light of the collimator 15 is vertically applied to the plane portion of the collar 43 provided on the peripheral edge of the objective lens 41, and the tilt of the lens 41 is sensed by receiving returning reflected light by the collimator 15. . This is a so-called auto-collimation method, and a method of adjusting the optical axis of the lens based on the tilt information of the lens detected here has been conventionally performed.

[0004]

By the way, in the objective lens used in the optical head device, in order to efficiently use a light flux having a wavelength used for reading or the like (hereinafter, referred to as a used wavelength), the lens surface is formed. An antireflection film is provided to improve the transmittance of the wavelength used. This antireflection film is generally formed by a vapor deposition method. Normally, as shown in FIG. 3, the vapor deposition material is blown from below in a vacuum while the lens 31 is held in the vapor deposition holder 20 to perform vapor deposition. To be formed.

Here, since the antireflection film needs to cover the lens surface of the lens 31 accurately, the vapor deposition is performed in order to deposit the lens 31 on the vapor deposition holder 20 with a slight deviation so that the lens surface is not chipped. The aperture of the holder 20 is configured to be larger than the aperture of the lens surface portion (portion d in FIG. 3 ). Therefore, it is generally performed that the antireflection film is partially vapor-deposited on the flat surface of the flange portion provided on the peripheral edge of the lens 31.

For this reason, when auto-collimation for adjusting the optical axis of the objective lens is performed after the antireflection film is vapor-deposited, the anti-reflection film deposited on the collar portion and vapor-deposited causes an influence from the flat portion of the collar portion. There is a problem that the reflectance of reflected light is reduced. This is largely because the antireflection film may improve the transmittance of the inspection light for autocollimation.

Further, since the film is partially formed on the flange portion in a state of protruding from the lens portion, the irradiation region of the inspection light for auto-collimation (the flat surface portion of the flange portion) and this partial film In particular, the edge (the edge protruding from the lens portion) is located in the vicinity and sometimes overlaps. Therefore,
In such a film edge portion, accurate plane reflection may not be performed, and the reflection detection intensity of the autocollimation inspection light may be reduced.

Here, considering only the properties of the film, the reflection for inspection may depend on the type of the antireflection film and the wavelength of the light beam for inspection used in autocollimation (hereinafter referred to as the inspection wavelength). The light reflectance may increase slightly. This is because the inspection wavelength is different from the wavelength used.
This is because the antireflection effect with respect to the inspection wavelength is weakened, and a slight increase in the amount of reflected light may be recognized.

However, since the purpose of use is originally to increase the transmission efficiency with respect to the length (reduction of the reflection efficiency), the improvement of the reflectance with respect to the inspection wavelength is extremely small (about 2 to 3%), The reflected light that improves the collimation inspection efficiency cannot be obtained. Further, in the conventional objective lens, the film is formed only on a very small part of the irradiation area (the flat surface portion of the collar) of the auto-collimation inspection light, so that the reflection efficiency is further increased. In addition, as mentioned above, when combined with the problem of irregular reflection due to partial film formation, practical improvement in reflection efficiency can hardly be expected, and the strength is sufficient for inspection and adjustment of autocollimation. It is not possible to obtain reflected light having

In order to avoid the above-mentioned inconvenience, as disclosed in JP-A-3-168937, a light reflection increasing film is formed on the flat surface of the flange portion, in addition to the antireflection film deposited on the curved surface of the lens. It has been proposed to deposit. Further, if a particular quantity of reflected light is desired, a reflection increasing film such as Al may be deposited.

However, there are the following problems in forming the reflection increasing film only on such a flat surface of the brim portion. First, since the vapor deposition material and the holder diameter are different between the vapor deposition of the antireflection film on the lens surface portion and the vapor deposition of the reflection increasing film on the collar portion, it is necessary to perform the vapor deposition work separately. Further, when depositing the reflection enhancing film on the lens collar, the lens surface must be covered to prevent the reflection enhancing film from being attached to the lens surface at the center of the lens. Different shielding means are required.

For this reason, when performing two vapor deposition operations,
After vacuuming once to deposit one of the films, it is necessary to open the vapor deposition device and set the lens and the shielding means again, and to evacuate again from the beginning to perform the next vapor deposition work. Therefore, as a work process for manufacturing a lens, the number of processes at the time of vapor deposition is doubled, and further, different means are required, so that work time, labor, etc. are required, throughput is lowered, and manufacturing cost is very high. is there.

The present invention has been made in order to solve the above-mentioned problems, and as an optimum objective lens for an optical head device, it maintains the conventional transmission efficiency with respect to the used wavelength, and also the reflection efficiency with respect to the inspection wavelength. It is an object of the present invention to devise an objective lens which can be sufficiently improved and which is easy to manufacture, and to provide an optical head device using the same.

[0014]

In order to achieve the object of the present onset for the above purpose achievement
In the clear, the lens surface and the flat surface provided on the lens periphery
An objective lens having:
On the surface, for the light when the optical axis inspection adjustment of the lens optical axis
It has a function as a reflection increasing film,
Anti-reflection against the light used in the device equipped with the lens
The wavelength selection film that functions as a film is formed uniformly
An objective lens is provided.

According to a second aspect of the invention, in the optical head device according to the first aspect, the wavelength selection film is
It is characterized in that it becomes an antireflection film for the light of the first wavelength and an antireflection film for the light of the second wavelength.

According to the invention described in claim 2, in claim 1,
In the described objective lens, the wavelength selection film is a multi-layer.
It is characterized by comprising a film. Invention according to claim 3
Then, in the objective lens described in claim 1 or 2,
The plane portion is provided substantially perpendicular to the optical axis of the lens.
It is characterized by According to the invention described in claim 4,
The objective lens according to any one of claims 1 to 3, including the flat portion.
It is characterized by having a brim-shaped peripheral portion. In claim 5
In the invention described, it is stated in any one of claims 1 to 4.
An optical head device equipped with an objective lens
To do. According to the invention described in claim 6,
It is the method of adjusting the optical axis of the objective lens that is described
The reflected light from the flat surface
Is performed.

[0017]

Since the present invention is constructed as described above, it has the following effects. First, the objective lens of the optical head device according to the present invention has a lens surface having a predetermined aperture and a brim-shaped peripheral portion having a plane portion perpendicular to the lens optical axis. This is because auto-collimation for inspecting and adjusting the optical axis of the objective lens in the optical head device is performed by a method similar to the conventional method. That is, also in the present invention, at the time of auto-collimation, the reflected light obtained by vertically irradiating the inspection light of the inspection wavelength to the collar-shaped peripheral portion having the plane portion perpendicular to the lens optical axis as in the conventional method. By detecting the, the arrangement state of the objective lens is sensed.

[0018] Incidentally, the flange-like rim portion is formed at the peripheral portion of the lens surface, yet as long as it has a perpendicular plane part to the lens optical axis, over necessarily all around the periphery of the lens surface portion Need not be formed. It is preferable that the flat portion is provided at three or more positions on the peripheral edge of the lens, and the inspection can be performed by the autocollimation on the flat portion.

Further, the lens surface portion and the flange-shaped peripheral portion do not necessarily have to be integrated, but the plane portion of the flange-shaped peripheral portion is always kept perpendicular to the lens optical axis. There is a need. In addition, it is preferable to use a molded lens in which these are integrally configured.

Next, the objective lens of the present invention is provided with a wavelength selection film, but the wavelength selection film may be any one as long as it has an antireflection effect for at least the used wavelength. This is because the general optical head device uses a light flux having a wavelength different from the used wavelength and the inspection wavelength, and the reflection efficiency is improved depending on the wavelength due to the existence of the wavelength selection film for the inspection wavelength.

However, as in the invention described in claim 2, it is an antireflection film for the light of the first wavelength and a reflection increasing film for the light of the second wavelength. Is preferred. For the light of the first wavelength, the used wavelength used for reading and writing of the optical disk used in the optical head device according to the present invention is selected, and for the light of the second wavelength, it is used during the auto-collimation of the objective lens. Select the inspection wavelength of the inspection light.

In other words, according to the used wavelength of the optical head device and the selected wavelength, conditions are set such that the anti-reflection film is used for the used wavelength and the reflection increasing film is used for the inspection wavelength. A film designed with a suitable material and thickness is formed on the objective lens as a wavelength selection film.

Here, in a general optical head device, the inspection wavelength of the auto-collimation for inspecting and adjusting the optical axis of the objective lens is usually performed using visible light, and the semiconductor laser (LD) when the optical head is used is used. The oscillation wavelength is usually the near infrared wavelength. Therefore, a vapor deposition film having such a property as a reflection increasing film for such visible light and an antireflection film for near infrared wavelength may be selected.

With this wavelength selection film, the used wavelength incident on the objective lens is efficiently transmitted through the lens surface portion and guided to the optical disk, while the inspection wavelength at the time of autocollimation is efficiently reflected by the flange-shaped peripheral portion. Therefore, it is possible to easily detect the optical axis adjustment of the objective lens.

Further, in the present invention, such a wavelength selection film is provided so as to uniformly cover the lens surface of the objective lens and the flange-shaped peripheral portion, and as shown in the conventional example, the antireflection film and the reflection film are provided. Instead of providing the increasing film separately, a film having both functions is uniformly provided as a wavelength selection film on the objective lens.

As described above, the wavelength selection film serves as a reflection increasing film for the inspection wavelength and an antireflection film for the used wavelength, and is at least the flat surface portion of the lens surface portion and the flange-shaped peripheral portion. It is formed by uniformly vapor-depositing these portions so as to cover (the inspection light reflection portion at the time of autocollimation).

Here, the material and film thickness of the wavelength selection film,
It is possible to obtain a wavelength-selective film consisting of a single-layer film by appropriately selecting the used wavelength and the inspection wavelength used for the optical head device, but when the used wavelength or the inspection wavelength is limited, As in the invention described in 3, the wavelength selection film may be a multi-layered film including two or more layers.

Even in the case of forming a plurality of layers, since the region where the wavelength selection film is formed is the same region in each film layer, even when performing the vapor deposition work a plurality of times, it is only necessary to change the vapor deposition material or the like. Good. Further, it is effective to form a multilayer film if only wavelength selection efficiency is pursued, but the vapor deposition film of at least about two layers can sufficiently achieve the object of the present invention. In this case, unlike the conventional example, since the present invention can be formed by simply stacking two layers and vapor-depositing them, the manufacturing cost is slightly increased, and an optical head device of low cost can be realized as a whole. Is.

As described above, by forming the wavelength selection film uniformly on the objective lens, a sufficiently strong reflected light can be obtained from the flat surface of the flange-shaped peripheral portion when the lens optical axis is adjusted. When the optical head device is used, the effect of the antireflection film works, and it can be used without light loss. Further, it is possible to suppress the occurrence of flare and ghost, which must be taken care of in such an optical head device.

[0030]

The present invention will be described in more detail with reference to the following examples. FIG. 1 shows an objective lens used in an optical head device according to an embodiment of the present invention. This objective lens is composed of a molded lens 1 having a lens surface portion 2 composed of a biconvex surface in the center portion and a flange-shaped peripheral portion 3 integrally formed in the peripheral portion. Here, although the lens surface S _1a forming the lens surface portion 2 is a spherical surface, the lens surface S _1b is formed of an aspherical surface in order to suppress the aberration with respect to the wavelength used. The peripheral portion 3 has a flat surface portion S ₂ perpendicular to the optical axis of this lens.
Is equipped with.

In this embodiment, CaF is used as the lens substrate.
K (low dispersion glass manufactured by Sumita Optical Co., Ltd.) is used, and the wavelength selection film 4 is formed so as to uniformly cover one surface of the objective lens. The wavelength selection film 4 is formed by vapor deposition of a two-layer film including a first film layer 5 and a second film layer 6 . Incidentally, these vapor deposition means are not particularly limited,
A commonly used method may be applied.

In the optical head device (not shown) using this objective lens 1, the wavelength when the optical head is used is
Using the luminous flux of λ ₁ (= 830 nm), the wavelength used by the collimator used when adjusting the optical axis of the lens is λ ₂ (= 54
A light flux of 6 nm) is used. The refractive index of the molded lens 1 is n (λ ₁ ) = 1.43049 and n (λ ₂ ) = 1.
43527.

Next, two embodiments of the present invention will be described. First, in the first embodiment, the first film layer of the wavelength selection film 4 is made of Al ₂ O ₃ , its thickness is 0.127 μm, the second film layer is made of ZrO ₂ , and its thickness is 0.103 μm.
m. Moreover, in the second embodiment, the first film layer of the wavelength selection film 4 is made of SiO ₂ , its thickness is 0.194 μm, the second film layer is made of TiO ₂ , and its thickness is 0.025.
μm.

FIG. 2 shows the spectral reflectance of the objective lens (wavelength selection film) of these examples. As is clear from this figure, the operating wavelength of the optical head λ ₁ (= 830 nm)
In contrast, in any of the examples, the reflectance is almost 0.
%, And it can be seen that almost all the luminous flux of the used wavelength is transmitted and can be used efficiently. Furthermore, by suppressing reflection of the wavelength used by the objective lens, flare and ghosts are suppressed when using the optical head.

On the other hand, the wavelength used by the collimator λ ₂ (= 5
46 nm), the reflectance is 16.
It is 7%, and similarly in the second embodiment, it is 21.9%. Here, when the flat surface portion S ₂ of the peripheral edge portion 3 is not coated at all, the reflectance with respect to the used wavelength λ ₂ is 3.3%, and by providing the wavelength selection film 4, the reflectance is about 5 times. It can be seen that the increase is ~ 7 times.

Therefore, in the collimator of the optical head device, when adjusting the optical axis of the lens, the reflected light having a sufficiently strong intensity can be obtained from the flat surface of the brim-shaped peripheral portion. This reflectance is sufficient as the detection intensity of the inspection light in the collimator, and the lens without the film (reflectance 3.3
%), The amount of reflected light detected was small, and there was a problem in performing accurate adjustment, but in the present embodiment, such a problem does not occur.

Further, when a wavelength selection film considering only the reflection efficiency with respect to the wavelength used is provided (for example, a single layer film having a reflectance of 100%), the reflectance is expected to be improved depending on the wavelength selection film. It is advisable to select an available wavelength as appropriate and use it as the inspection wavelength.

In order to further enhance the effect of the present invention, if a wavelength selection film having three or more vapor-deposited films is formed, the reflectance with visible light is further increased, and the adjustment work becomes easier. And needless to say, it can be done accurately. Here, when only a single layer of the antireflection film for the used wavelength is provided, the reflectance for the inspection wavelength is 2.7%, and the detection intensity is too weak to use the reflected light for inspection adjustment. is there. However, it is possible to improve the reflectance of the inspection wavelength while maintaining the transmittance of the wavelength of use by changing the wavelength of use or the wavelength of inspection at any time or by constructing the wavelength selection film with multiple layers. Become.

[0039]

As described above, according to the present invention, since the wavelength selection film is provided on the objective lens of the optical head device, the transmittance for the used wavelength is improved and the reflectance for the inspection wavelength is improved. ing.

Therefore, there is an advantage that the light flux to be used can be efficiently used, and the optical axis of the objective lens can be easily and accurately adjusted by autocollimation, and the accuracy of reading and writing in the optical head device is improved. There are advantages.

That is, the wavelength selection film of the present invention has properties of selectively preventing reflection and increasing reflection depending on the wavelength of the light beam to be irradiated, and the strong reflection light from the flat surface of the flange-shaped peripheral portion causes The optical axis is adjusted accurately and efficiently, and at the same time, it serves as an anti-reflection film for LD light when the optical head device is used, so flare and ghost for the used wavelength can be suppressed and the LD light can be effectively used. It is possible.

In addition, since the wavelength selection film may be formed by uniformly depositing one kind of vapor deposition film on the lens surface portion and the flat surface portion of the flange-shaped peripheral portion simultaneously at the same time, different means may be used as in the prior art. It is possible to save the labor of coating with, to improve the throughput in manufacturing the objective lens and the optical head device, and to significantly reduce the manufacturing cost.

As described above, according to the present invention, the wavelength selection film is uniformly provided on the objective lens to prevent the reflection which is indispensable when the optical head device is used, and at the same time, the strongly reflected light is obtained when the optical axis inspection is adjusted. In addition to satisfying the requirement of the opposite property that the user wants to obtain, it also has the excellent advantage that it has the advantage of both advantages and advantages that the manufacturing cost is further reduced.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of an objective lens used in an optical head device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between reflectance and wavelength in the above example.

FIG. 3 is an explanatory diagram showing a conventional vapor deposition method for an antireflection film.

FIG. 4 is an explanatory diagram showing a method of adjusting an optical axis in an optical head device.

[Explanation of symbols]

1 ... objective lens, 2 ... lens surface, 3 ... flanged periphery, 4 ... wavelength selective film, 5 ... first film layer, 6 ... second film layer, S ₁ ... lens curved surface, S ₂ ... flat portion ( Vertical plane to the optical axis).

Claims (6)

(57) [Claims] 1. An objective lens having a lens surface and a flat surface portion provided on a peripheral edge of the lens, wherein an objective lens is provided on the lens surface and the flat surface portion for light at the time of optical axis inspection adjustment of a lens optical axis. Is an objective lens in which a wavelength selection film having a function as a reflection increasing film and having a function as an antireflection film with respect to light used in a device equipped with the objective lens is uniformly formed. 2. The objective lens according to claim 1, wherein the wavelength selection film is a multilayer film. 3. The objective lens according to claim 1, wherein the plane portion is provided substantially perpendicular to the lens optical axis. 4. The objective lens according to claim 1, further comprising a brim-shaped peripheral portion including the flat portion. 5. An optical head device comprising the objective lens according to any one of claims 1 to 4. 6. The optical axis adjusting method for an objective lens according to claim 1, wherein the optical axis of the objective lens is autocollimated by reflected light from the flat surface portion. Adjustment method.