JP2002055201A - Optical recording reproducing optical system and optical information recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To significantly increase the recording density for optical information recording and reproducing than a conventional method. SOLUTION: In the optical recording and reproducing optical system to converge the incident light for recording or reproducing information to project the light spot on the recording face of an optical recording medium, a material having >=1.5 cm-1 optical transmission loss coefficient for light at 200 to 375 nm wavelength is used as the material for the optical device constituting the optical recording and reproducing optical system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing optical system used for recording or reproducing information on an optical recording medium such as an optical disk or a magneto-optical disk, and an optical information recording / reproducing apparatus using the same. , MD, DVD
The present invention relates to a technique that is effective when used in a recording / reproducing apparatus using a recording medium such as a recording medium.

[0002]

2. Description of the Related Art Recording / reproducing information on / from an optical recording medium is performed by projecting light onto a recording surface of the optical recording medium. A recording / reproducing optical system is used to perform the spot projection. This recording / reproducing optical system is an SIL (So
It is configured using a light converging lens such as a lid immersion lens, and narrows light emitted from a beam light source such as a semiconductor laser to a small spot and projects it on a recording surface. As a light source for optical recording and reproduction, a near-infrared semiconductor laser having a wavelength of about 780 nm, a red semiconductor laser having a wavelength of about 650 nm, and the like have been conventionally used. Recently, blue semiconductor lasers having a wavelength on the order of 400 nm have also been used.

As a material of a lens constituting an optical recording / reproducing optical system, a borosilicate optical glass such as BK7 has been conventionally known. These glass materials can be used as a lens material for spot converging beam light (wavelength: 400 to 780 nm) emitted from the light source described above. As described above, the conventional optical information recording / reproducing apparatus uses a light source that emits a light beam having a wavelength of 400 to 780 as a recording / reproducing light source, and receives light emitted from the light source to form an optical recording medium. An optical recording / reproducing optical system configured to project a spot on a recording surface has been used. The lens constituting the optical recording / reproducing optical system has been constituted by using the above-mentioned glass.

[0004]

However, it has been found that the above technique has the following problems. First, in the technical field of optical information recording and reproduction using an optical recording medium such as a DVD, it is very important to increase the recording capacity per unit recording area of the recording medium, that is, to increase the recording density. ing. In order to increase the recording density, it is necessary to reduce the spot diameter of the recording / reproducing light. For this purpose, it is necessary to increase the numerical aperture (NA) of an optical system (lens) used to converge the light, or to shorten the wavelength of light used for recording and reproduction. It is known that the minimum light spot diameter that can be stopped down by a certain optical system is roughly proportional to the wavelength of light used and inversely proportional to the numerical aperture of a lens.

Accordingly, in order to realize a high recording density in an optical information recording / reproducing system, it is necessary to increase the numerical aperture of an optical system (lens) and shorten the wavelength of recording / reproducing light. In particular, in order to obtain a significantly higher recording density than before, it is necessary to use at least ultraviolet light having a wavelength of 375 nm or less for recording and reproduction. As described above, recently, as a light source for recording and reproducing optical information, a semiconductor laser having an oscillation wavelength on the order of 400 nm has been used.
Further, as a laser light source that oscillates short wavelength light, wavelength 3
09,248 nm excimer laser and the like. In addition, light having a wavelength of about 265 nm can be generated by using a harmonic of a solid-state laser such as Nd: YAG, Nd: YVO ₄ , and Nd: YLF.

Further, Yb: YAG, Yb: YVO ₄ , Y
b: 25 wavelengths using a harmonic of a solid-state laser such as YLF.
It is possible to create light of 5-260 nm. In order to make the above-mentioned short-wavelength light available for recording and reproduction, the short-wavelength light, particularly ultraviolet light, is efficiently transmitted, and is made of a material having a high refractive index and has a high numerical aperture. An optical recording / reproducing optical system using a lens is required. Here, the conventional optical glass used as the material of the optical system generally has a low ultraviolet light transmittance,
When optical recording and reproduction using ultraviolet light is performed using an optical system made of this glass, a very large light source power is required, which causes a problem that the light source unit becomes large and power consumption increases. .

For example, a typical optical glass, BK
7 is a borosilicate glass, and this glass is 1
When the thickness is 0 mm, the transmittance for light with a wavelength of 375 nm is only about 5%, and the transmittance for light with a shorter wavelength is even lower. In this case, since the reflection loss is about 8%, the light transmission loss coefficient Lk excluding the loss due to the reflection is 2.9 cm ⁻¹ . That is, the optical recording / reproducing optical system constituted by using this glass as a lens material has a wavelength of 37.
It cannot be used at a practical level for optical recording / reproducing with short wavelength light of 5 nm or less. Here, the light transmission loss coefficient Lk is defined as Lk = (1 / d) log (Io / Ii), where d is the thickness of the material, Io is the incident light intensity, and Ii is the outgoing light intensity. Defined by an expression.

Further, in a multi-component glass containing boric acid or silicic acid as a glass network forming component, the ultraviolet absorption derived from these components reaches the upper limit of ultraviolet rays (wavelength around 380 nm). Therefore, the optical recording / reproducing optical system composed of this glass as a lens material cannot be used at a practical level for optical recording / reproducing with short wavelength light having a wavelength of 375 nm or less. Quartz glass is an example of a material that can transmit short-wavelength light such as ultraviolet light. However, quartz glass has a low refractive index, and in order to increase the numerical aperture of a lens made of quartz glass, the radius of curvature of the lens must be reduced. That is, in order to focus light on a small spot, a lens having a small focal length is required. To decrease the focal length of the lens, it is necessary to reduce the radius of curvature of the lens. However, this has the following disadvantages.

That is, in an optical recording / reproducing optical system, an aspheric lens is often used in order to converge light to a spot with high accuracy. However, it is very difficult to accurately obtain the aspheric surface by polishing, and the productivity is poor. Therefore, a lens of a generally used optical recording / reproducing optical system is formed by mold press molding having high productivity. In this case, if an attempt is made to reduce the radius of curvature of the lens in order to increase the numerical aperture of the lens, there is an inconvenience that sagging and warping are likely to occur on the surface formed by the mold press molding. Further, the die used for the press also has a disadvantage that if the radius of curvature of the die surface is small, the processing itself becomes difficult.

The SIL used as an optical element of the optical recording / reproducing optical system is a high-resolution lens suitable for obtaining a high numerical aperture. It is proportional to the ratio n (when the SIL is hemispherical) or its square n ² (when the SIL is hyperhemispherical). Therefore, even in the case of SIL, when the constituent material is quartz glass having a low refractive index, the effect of increasing the aperture cannot be sufficiently obtained.

On the other hand, the lens of the optical recording / reproducing optical system is desirably formed by mold press molding in order to reduce costs and improve mass productivity. In this mold press molding, a technology has been developed in which a preform material obtained by cutting and polishing a glass gob or a glass block is heated and softened, and is subjected to pressure molding with a mold having a highly accurate surface.
The advantage of this technique is that the grinding and polishing steps after molding can be omitted. However, the advantages described above are not utilized unless the mold used for molding can be used repeatedly.
In order to ensure or improve the durability of the mold, it is necessary to minimize the surface deterioration of the mold caused mainly by oxidation,
For this purpose, it is necessary to set the temperature during mold pressing as low as possible.

At present, the upper limit temperature of the mold press is set at 650 to 700 ° C. due to such a restriction factor. On the other hand, since quartz glass has a softening temperature of 1000 ° C. or higher, it is extremely difficult to mold it with a mold press. That is, the optical recording / reproducing optical system made of quartz glass must satisfy the light transmission performance for short wavelength light (375 nm or less), which is one of the necessary conditions for significantly increasing the recording density. Yes, but it lacks other requirements.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical recording / reproducing optical system and an optical information recording / reproducing system capable of significantly increasing the recording density of optical recording / reproduction. An object of the present invention is to provide a recording and reproducing device.

[0014]

The present invention provides the following means as means for solving the above-mentioned problems. First solution: In an optical recording / reproducing optical system for narrowing down light incident for recording or reproducing information and projecting a spot on a recording surface of an optical recording medium, an optical element constituting the optical recording / reproducing optical system Is an optical recording / reproducing optical system comprising a material having a light transmission loss coefficient Lk defined by the following equation (1) of 1.5 cm ^-1 or less for light having a wavelength of 200 to 375 nm. Lk = (1 / d) log (Io / Ii) (1) where d is the thickness of the optical element [cm], Io is the incident light intensity, and Ii is the outgoing light intensity. -Second solution: In the optical recording / reproducing optical system of the first means, a first lens for condensing light incident for recording or reproducing information, and the same optical axis as the first lens. A second lens disposed on the first lens for receiving light collected by the first lens and focusing on a recording surface of a recording medium, wherein the first lens and the second lens are respectively And a material having a light transmission loss coefficient Lk defined by the above formula (1) of 1.5 cm ^-1 or less for light having a wavelength of 200 to 375 nm. Third solution: In the optical recording / reproducing optical system according to the first or second means, at least one of the first lens and the second lens receives light having a wavelength of 200 to 375 nm by the following formula (2). ) Is made of a material having a refractive index n that satisfies condition (1). n ≧ 1.44 + 8.23 / (λ−124) (2) where n is a refractive index and λ is a wavelength [nm]. Fourth solution: In the optical recording / reproducing optical system according to any one of the first to third means, at least one of the first lens and the second lens is made of a phosphate-based or fluorophosphate-based glass. It is characterized by consisting of. Fifth solution: In the optical recording / reproducing optical system according to any one of the first to fourth means, at least one of the first lens and the second lens includes Ce, Pt, Cr, and C.
It is characterized by being made of glass containing at least one ion selected from u, Fe and Ni at 100 ppm or less. Sixth solution: In the optical recording / reproducing optical system according to any one of the first to fifth means, at least one of the first lens and the second lens is made of a fluorophosphate glass having the following composition. It is characterized by becoming. ^{P 5+: 0.5~30 [cat%]} ( cation display, the same applies ^{hereinafter) Al 3+: 8~40 Mg 2+:} 0~20 Ca 2+: 0~35 Sr 2+: 0~50 Ba 2 ⁺ : 0 to 65 Na ⁺ and / or Li ⁺ : 0 to 5 at least selected from Y, La and rare earth elements (elements having an atomic number of 57 to 71 excluding Pm), which are divalent to tetravalent metals. One kind of ion: 0 to 10%, and the anion ratio [F] / ([F] + [O]) is 0.05
~ 0.99. -Seventh solution: In the optical recording / reproducing optical system according to any one of the first to fifth means, at least one of the first lens and the second lens is made of a fluorophosphate glass having the following composition. It is characterized by becoming. Al (PO ₃ ) ₃ : 0 to 35 [wt%] Ba (PO ₃ ) ₂ : 0 to 25 Mg (PO ₃ ) ₂ : 0 to 15 Ca (PO ₃ ) ₂ : 0 to 15 Sr (PO ₃ ) ₂ : 0-15 However, phosphorus pentoxide total P ₂ O ₅ in terms _{of: 1~25 AlF 3: 10~25 BaF 2} : 10~35 MgF 2: 0~15 CaF 2: 0~30 SrF 2: 0~35 Na ₂ O and / or NaF: 0 to 5 Li ₂ O and / or LiF: 0 to 5 Y, La, rare earth element (atomic numbers 57 to 71 excluding Pm)
At least one oxide selected from the group consisting of: and / or fluorides thereof: 0 to 7.5. Eighth Solution: In the optical recording / reproducing optical system according to any one of the first to fifth means, at least one of the first lens and the second lens has a phosphate glass having the following composition. It is characterized by consisting of. ^{P5 +} : 65 to 85 [cat%] (cation indication, the same applies hereinafter) Al3 ⁺ : 2 to 10 Mg2 ⁺ : 0 to 30 Ca2 ⁺ : 0 to 30 Sr2 ⁺ : 0 to 30 Ba2 ⁺ : 0 to 40 Zn ²⁺ : 0 to 8 Na ⁺ and / or K ⁺ : 0 to 8 provided that the total amount of Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ²⁺ and Zn ²⁺ : 18 to 40; At least one selected from the group consisting of Y, La, and rare earth elements (elements having an atomic number of 57 to 71 excluding Pm), which are divalent to tetravalent metals: 0 to 8%. Ninth solution: In the optical recording / reproducing optical system according to any one of the first to fifth means, at least one of the first lens and the second lens is a phosphate glass having the following composition. It is characterized by consisting of. _{P 2 O 5: 40~85 [wt} %] Al 2 O 3: 2~10 MgO: 0~20 CaO: 0~25 SrO: 0~40 BaO: 0~60 ZnO: 0~8 Na 2 O and / or K ₂ O: Less than six However, MgO, CaO, SrO, BaO , the total content of ZnO: 8~60, Y, La, at least one oxide selected from rare earth elements: 0-20. Tenth solution: In the optical recording / reproducing optical system according to any one of the first to ninth means, at least one of the first lens and the second lens is a lens formed by a mold press molding method. It is characterized by the following. Eleventh solution: In the optical recording / reproducing optical system according to any one of the first to tenth aspects, a transmission loss with respect to a light beam having a wavelength of 200 to 375 nm is 35% or less in the entire optical system. Twelfth solution: a light source that emits a beam light having a wavelength of 200 to 375 nm as light for recording or reproducing information, an optical recording / reproducing optical system according to any one of the first to twelfth means, and light emitted from the light source. An optical information recording / reproducing apparatus comprising a light guiding means for guiding the light to the optical recording / reproducing optical system.

According to the above-described solution, the wavelength of 200 to
Recording and reproduction of optical information with 375 nm light can be performed efficiently, thereby achieving the object of significantly increasing the recording density of optical recording information recording and reproduction as compared with the related art.

[0016]

FIG. 1 is a diagram showing a configuration of an optical information recording / reproducing system 30 according to an embodiment of the present invention.
1 is a diagram showing an overall outline of an optical information recording / reproducing apparatus 1 using an optical recording / reproducing optical system according to an embodiment of the present invention.
Hereinafter, an optical recording / reproducing optical system and an optical information recording / reproducing apparatus according to an embodiment of the present invention will be described with reference to these drawings.

In FIG. 2, an optical information recording / reproducing apparatus 1 comprises:
Near field recordin (NFR)
g) A magneto-optical disk recording / reproducing device using a recording / reproducing method called a technique, which is configured to record / reproduce information on / from a magneto-optical disk 2 which is an optical recording medium.

The disk 2 is driven to rotate by a spindle motor (not shown). In order to record / reproduce information on the rotationally driven disk 2, a rotating arm 4 having a floating type head 3 mounted on the tip thereof, and the rotating arm 4 is rotationally driven about a rotating shaft 5. The boil coil motor 5a has a wavelength of 200 as light for recording or reproducing information.
A light source 6 that emits a light beam of about 375 nm;
Light guide means (light guide mirrors) 71 and 72 for guiding the light emitted from the optical recording / reproducing optical system are provided. An optical recording / reproducing optical system 30 according to the present invention is formed on the flying head 3. The flying head 3 is also called an optical pickup.

As shown in FIG. 1, an optical recording / reproducing optical system 30
Is composed of a first lens (objective lens) 31 and a second lens (SIL) 32. First lens 3
1 collects light from the light source 6 (see FIG. 2). The second lens 32 is an SIL, is arranged on the same optical axis as the first lens 31, receives the light condensed by the first lens 31, and records the light on the recording surface 2 a of the disk (recording medium) 2. Focus on.

FIG. 3 is a diagram showing the structure of the tip portion of the rotating arm 4. As shown in FIG. 3, a flexure beam 41 is attached to the rotating arm 4, and a floating optical head 3 is attached to the tip of the beam 41. FIG. 4 is a diagram showing the flying optical head 3. The optical recording / reproducing optical system 30 and the magnetic coil 33 are mounted on the flying optical head 3. The optical diameter 30 of the optical recording / reproducing optical system includes a first lens (objective lens) 31 and a second lens (SI
L) 32. The first lens 31
The light from the light source 6 is collected. The second lens 32 is S
An IL, which is arranged on the same optical axis as the first lens 31, receives light collected by the first lens 31, and focuses on a recording surface of the disk (recording medium) 2. The magnetic coil 33 is provided for performing recording by a magneto-optical recording method.

Here, at least one of the first lens 31 and the second lens 32 forming the optical recording / reproducing optical system 30 has a transmission loss coefficient Lk of 1.5 cm for light having a wavelength of 200 to 375 nm. It is composed of ^-1 or less material. When the light transmission loss coefficient Lk is 1.5 cm ^-1 or less, even if the total lens thickness of the entire optical system, that is, the optical path length of the light passing through the material is about 5 mm, the internal transmission is 50% or more. Rate is obtained. In this case, the optical power can be effectively used, and the size of the mounted light source can be reduced.

Further, the light transmission loss coefficient Lk is set to 0.8 cm.
^{If -1} or less, the internal transmittance can be increased to 67% assuming that the total lens thickness is 5 mm.
Therefore, the material of the lenses 31 and 32 has a wavelength of 20.
The light transmission loss coefficient Lk of light for 0 to 375 nm is 0.
More preferably, it is 8 cm ^-1 or less.

It is preferable that at least one of the lenses 31 and 32 is made of a material having a refractive index n that satisfies the following expression (2) for light having a wavelength of 200 to 375 nm. n ≧ 1.44 + 8.23 / (λ−124) (2) (n is the refractive index of the material, and λ is the wavelength [nm] of light incident on the lens material)

Further, n> 1.44 + 8.23 / (λ
-124), that is, a material having a higher refractive index than quartz.

When optical glass is used as the material of the lenses 31 and 32, phosphate glass or fluorophosphate glass can be used. In this case, a group that is suitable for use is a group having a significantly high refractive index, which satisfies at least the condition of the above formula (2) and further has a refractive index exceeding the refractive index of quartz glass such as a numerical aperture. Desirable to significantly increase performance factors. In addition, glass systems such as silicate and borosilicate, which are often used for optical glass, have an ultraviolet absorption edge peculiar to the glass system on the long wavelength side compared to phosphate glass or fluorophosphate glass. So
It is difficult to use as it is.

The present invention discloses the use of phosphate glass and fluorophosphate glass as an effective solution to the above-mentioned problem. When the composition of these glasses is out of the range specified in the above solution, the stability against crystallization of the glass is not sufficient, or the chemical durability of the obtained glass is not sufficient, and There is a problem that it is difficult to obtain a suitable glass or is not suitable for long-term practical use.

In the case of fluorophosphate glass, P and O are components that form a glass network structure skeleton. Al is considered to have a similar effect. Excessive amounts of these components cause problems such as an excessively high softening temperature, while excessive amounts result in problems such as low glass-forming ability, apt to generate crystals, and deterioration of durability. Alkali and alkaline earth metals are components that improve the glass-forming ability and solubility of this type of glass. Sr and B among alkaline earths
a is a component useful for increasing the refractive index of glass. If these components are too large or too small, the glass forming ability is deteriorated.

[0028] Y, La and rare earth elements are particularly useful components for increasing the refractive index, but if these components are excessive, the glass forming ability is degraded. Fluorine is one of the factors that improve the ultraviolet light transmission performance of this type of glass. This is presumed from the fact that when comparing an oxide composed of the same cation and a fluoride, the fluoride is superior in ultraviolet transmittance. However, the content ratio between oxygen and fluorine greatly affects the glass-forming ability, and out of an appropriate range, the glass-forming ability deteriorates.

In the case of phosphate glass, P is a component forming a glass network structure skeleton. It is considered that Al also has an effect of structurally assisting the PO skeleton. Alkaline earth metals are components that improve the glass forming ability and the solubility of this type of glass. Among alkaline earths, Sr and Ba are components useful for increasing the refractive index of glass. Excessive or excessive amounts of these components deteriorate the glass-forming ability. Y, La and rare earth elements are particularly useful components for increasing the refractive index. However, when these components are excessive, the glass forming ability is deteriorated.

An important factor that determines the ultraviolet transmittance is absorption by trace impurities. Examples of ions that cause ultraviolet absorption include Ce, Pt, Cr, Cu, Fe, and Ni. These ions, when present in the glass, even on the order of ppm, cause absorption in the ultraviolet. In particular, Fe is an impurity whose absorption intensity is high and is easily mixed in from the atmosphere during handling of the raw material powder and the like, so that its elimination is the most important matter.

In the present invention, as an effective solution to the above-mentioned problem, ions contained in the lens material are specified. This solution is characterized in that the content of each ion of Ce, Pt, Cr, Cu, Fe, and Ni is set to 100 ppm or less. Further, the total amount of these ions is more preferably 100 ppm or less. Especially 1 ppm of Fe ion
It is preferred that: Further, absorption by Fe ions in the ultraviolet region is due to Fe ³⁺ ions, and Fe ²⁺
Has only a small absorption in this region, and therefore, it is effective to carry out the glass in a reduced state when producing the glass by melting, as a means for increasing the ultraviolet transmittance. As this reduction method,
Examples include contacting a neutral or reducing gas such as nitrogen or carbon dioxide gas with the glass melt, and introducing a reducing agent such as carbon powder / starch or bromide / iodide into the batch.

In addition, unless deviating from the object of the present invention, a component such as K, Cs, B, Si, Cl or the like which does not have a remarkable absorption in the wavelength region of 200 nm or more is attached to the fluorophosphate glass. It is possible to adjust the solubility of glass, refractive index, glass transition point, durability, workability, and the like. Also, as long as it does not depart from the purpose of the present invention, phosphate glass,
2% of alkali elements, B, Si, halogen elements, etc.
It is possible to adjust the solubility, refractive index, glass transition point, durability, workability, and the like of glass by attaching a component having no significant absorption in a wavelength region of 00 nm or more.

In order to thermally deform quartz glass, 10
Although a high temperature of 00 ° C or higher is required, the softening temperature of phosphate glass and fluorophosphate glass is much lower than that, and if an appropriate composition is selected, a glass having a softening temperature of 700 ° C or lower can be produced. It is easy to do. Further, if the crystallization resistance, the durability, and the like are adjusted by adjusting the appropriate composition, mold press molding can be performed.

Here, the smaller the light spot diameter narrowed down at the recording surface position, the higher the recording density can be made. The diameter of the light spot narrowed down at the recording surface position is inversely proportional to the numerical aperture of the lens system and proportional to the wavelength. Therefore, for example, the light source wavelength is changed from 400 nm to 275 nm.
Then, the recording density can be improved twice or more. Further, the recording density can be further improved by increasing the numerical aperture of the lens, but this can be achieved by using a high refractive index glass material. According to the above embodiment, the above object can be achieved more effectively.

Example 1 Composition (wt%) shown in Table 1
(Shown) was prepared. After blending and mixing using high-purity raw materials, 925 ° C using a platinum crucible
And then homogenized by defoaming, stirring, etc., cast into an appropriate mold, and subjected to a slow cooling step.

[Table 1]

In addition, this composition is defined as cation% (cat%).
When displayed, it is as shown in Table 2. Note that the anion ratio F / [F + O] is 0.64.

[Table 2]

The refractive index of this glass was 1.535 for light having a wavelength of 262 nm. This sufficiently satisfies the conditions specified in the solution of the present invention. Since the refractive index of pure quartz glass is about 1.500 in this wavelength range, S
Using the glass of this embodiment as an IL lens material is more advantageous in terms of resolution. The light transmission loss coefficient Lk at a wavelength of 262 nm was 0.5 cm ^-1 . This allows
For example, when the lens thickness is 5 mm, the light transmission loss of the entire optical system can be reduced to about 30%.
Regarding the ion content, Ce,
When the amount of each of Pt, Cr, Cu, Fe, and Ni is 2, 2
5,2,3,0.5,1 ppm, the total content is 33.
It was found to be 5 ppm.

Using the glass of Example 1, lenses 31 and 32 of FIG. 1 were produced. In this case, the lens was formed by mold press molding. The mold is made of cemented carbide,
A Pt-Rh-Au-Ir thin film coated on the surface was used. The preform glass as the material to be molded was roughly polished into a sphere. Pressing was performed at 525 ° C. in a vacuum, and the product was taken out after cooling. In the case of pressing under normal pressure, gas was confined near the center of the lens by the pressing, and the molding surface was disturbed. Pressing in a vacuum could prevent this.

(Example 2) An optical recording / reproducing optical system was constructed using the glass material of Example 1 for the objective lens 31 and quartz glass for the SIL 32, respectively. The quartz glass has a light transmission loss coefficient Lk of 0.35c at a wavelength of 262 nm.
m ⁻¹ and the refractive index were 1.501 (1.499: calculated value). This quartz glass was formed by a grinding and polishing process. At this time, the light transmission loss of the entire optical system was 20%, and the convergent spot diameter was about 1.5 times that of the first embodiment, but this is a range that can be sufficiently used for practical use.

Example 3 A (phosphoric acid) glass having the composition shown in Table 3 (wt%) was prepared. This glass is prepared and mixed using high-purity raw materials, heated and melted at 1250 ° C for 3 hours using a quartz glass crucible, homogenized by defoaming, stirring, etc., and then cast into an appropriate mold. And obtained through a slow cooling step.

[Table 3]

When this composition is expressed in terms of cation%, the results are as shown in Table 4.

[Table 4]

The refractive index of this glass is 1.560 at a wavelength of 350 nm, which sufficiently satisfies the conditions specified by the solution of the present invention. Since the refractive index of pure silica glass in this wavelength range is about 1.476, it has been found that the use of the glass of Example 3 as the SIL lens material is more advantageous in terms of resolution. Further, this glass was mold press-moldable at 650 ° C. or lower. The light transmission loss coefficient at a wavelength of 350 nm is 0.35.
cm ^-1 . Thus, for example, when the lens thickness is 5 mm, the light transmission loss of the entire optical system is only 16%.
Becomes Regarding the ion content, according to ICP emission spectrometry, the mixing amounts of Ce, Pt, Cr, Cu, Fe, and Ni were 2, 0.2, 2, 3, 0.5, and 1 ppm, respectively.
The total content was found to be 8.7 ppm.

Examples 4 to 8 In each of Examples 4 to 8, a fluorophosphate glass having a composition shown in Table 5 was produced. In the same table, (4) shows the composition produced in Example 4, (5) shows the composition produced in Example 5, (6) shows the composition produced in Example 6, (7) shows the composition produced in Example 7, and (8) shows the composition produced in Example 8. . Example 4
In Nos. To 8, after mixing and mixing to a predetermined composition using a high-purity raw material, a platinum crucible was used at 950 to 1100 ° C. for 3 hours.
It was heated and melted for a long time, homogenized by defoaming, stirring, etc., cast into an appropriate mold, and produced through a slow cooling step. As raw materials, aluminum metaphosphate, barium metaphosphate, carbonate compounds of constituent elements, oxide compounds, and fluorides were used. Of course, the raw materials are not limited to these, and can be arbitrarily selected as long as they give the final composition. For example, raw materials such as pyrophosphate and nitrate can be used.

Table 5 shows 275 as representative values of the transmittance and the refractive index in the ultraviolet region of each glass.
The loss coefficient and the refractive index in nm are given. It was found that each glass had high ultraviolet transmission characteristics and a high refractive index.

[Table 5] The softening points of the glasses produced in Examples 4 to 8 were all 600 ° C. or less, and mold press molding at 650 ° C. or less was possible.

(Examples 9 to 13) In Examples 9 to 13, phosphate glasses having the compositions shown in Table 6 were produced. In the same table, (9) is Example 9, (10) is Example 10, (11) is Example 11, and (12) is Example 1.
2 and (13) show the compositions prepared in Example 13, respectively. In Examples 9 to 13, using a quartz glass crucible after mixing and mixing to a predetermined composition using a high-purity raw material,
Perform heating and melting at 1100 to 1300 ° C for 3 hours,
After homogenization by defoaming, stirring, etc., it was cast into an appropriate mold and produced through a slow cooling step. As raw materials, aluminum metaphosphate, barium metaphosphate, oxide compounds and carbonate compounds of constituent elements were used. Of course, the raw materials are not limited to these, and can be arbitrarily selected as long as they give the final composition. For example, raw materials such as pyrophosphate and nitrate can be used.

Table 6 shows 300 n as representative values of the transmittance and the refractive index of each glass in the ultraviolet.
The loss coefficient and the refractive index at m are shown. It was found that each glass had high ultraviolet transmission characteristics and a high refractive index.

[Table 6] The softening points of the glasses produced in Examples 9 to 13 were all 650 ° C or less, and mold press molding at 700 ° C or less was possible.

Comparative Example An optical recording / reproducing optical system of the same type as that shown in FIG. 4 was produced in the same manner as in Example 1 except that SIL was produced using BK7. At a wavelength of 262 nm, the light transmission loss coefficient of BK7 with an optical path length of 5 mm is approximately 1
The refractive index was 0 cm ^-1 and the refractive index was 1.56. The spot diameter could not be measured.

As described above, the present invention has been described based on the typical embodiments and examples. However, the present invention can have various aspects other than those described above. For example, in addition to the spherical lens, an aspherical lens, a Fresnel lens, a grating lens, a hologram lens, or the like can be used as the objective lens. When these lenses are used, there is an advantage that the element can be made thinner.

Examples of the optical recording medium include a phase change type optical recording medium for recording information by a phase change of a recording layer, a read-only optical recording medium on which information is written in advance by emboss pits, and an MO or MD. And other magneto-optical recording media. When a magneto-optical recording medium is used, a magnetic coil for recording is mounted on the optical head 3 as shown in FIG. In addition, for example, it can be used in an exposure step of mastering for creating a master of a recording medium.

[0050]

As is apparent from the above description, the optical recording / reproducing optical system according to the present invention has a light transmission loss coefficient Lk defined by the above-mentioned formula (1) of 1 to 1.0 for light having a wavelength of 200 to 375 nm. By using an optical element made of a material having a size of 5 cm ^-1 or less, the recording density of optical recording information recording / reproducing can be significantly increased as compared with the related art. Further, the optical information recording / reproducing apparatus of the present invention can significantly increase the recording density of the optical recording information recording / reproducing than before by using the optical recording / reproducing optical system including the optical element.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of an optical recording / reproducing optical system according to the present invention.

FIG. 2 is a schematic perspective view showing the entire configuration of an optical information recording / reproducing apparatus according to the present invention.

FIG. 3 is a side view showing a part of the device shown in FIG. 2;

FIG. 4 is a cross-sectional view showing an optical head portion of the device shown in FIG.

[Explanation of symbols]

 Reference Signs List 1 optical information recording / reproducing device 2 optical recording medium 2a recording surface 3 floating head 30 optical recording / reproducing optical system 31 first lens (objective lens) 32 second lens (SIL) 33 magnetic coil 4 rotating arm 5a boil coil Motor 6 Light source 71, 72 Light guide means (light guide mirror)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H087 KA13 PA02 PA17 PB02 QA02 QA05 QA13 QA14 QA21 QA33 QA41 4G062 AA04 BB09 CC04 DA01 DB01 DB02 DB03 DB04 DB05 DC01 DD05 DD06 DD07 DE01 DE02 DE03 DF01 EA01 EA02 EB01 EC02 EC03 ED01 ED02 ED03 ED04 EE01 EE02 EE03 EE04 EF01 EF02 EF03 EF04 EF05 EG01 EG02 EG03 EG04 EG05 EG06 FA01 FB01 FC01 FD01 FE01 HFF H01 FJ01 FJ01 H02 F02G01H02 FJ03 FK01 HH13 HH14 HH15 HH17 HH20 JJ01 JJ03 JJ05 JJ07 JJ10 KK01 KK02 KK03 KK04 KK05 KK06 KK07 KK08 KK10 MM02 MM04 NN16 5D090 AA01 BB02 BB05 BB10 FF11 KK06 LL01 5D119 AA23BA01

Claims (12)

[Claims] In an optical recording / reproducing optical system for narrowing down light incident for recording or reproducing information and projecting a spot on a recording surface of an optical recording medium, an optical element constituting the optical recording / reproducing optical system includes: An optical recording / reproducing optical system comprising a material having a light transmission loss coefficient Lk defined by the following equation (1) of 1.5 cm ^-1 or less for light having a wavelength of 200 to 375 nm. Lk = (1 / d) log (Io / Ii) (1) where d is the thickness of the optical element [cm], Io is the incident light intensity, and Ii is the outgoing light intensity. 2. The optical recording / reproducing optical system according to claim 1, wherein a first lens for condensing light incident for recording or reproducing information, and on the same optical axis as the first lens. And a second lens that receives the light collected by the first lens and focuses on the recording surface of the recording medium, wherein the first lens and the second lens are respectively An optical recording / reproducing optical system comprising a material having a light transmission loss coefficient Lk defined by the above formula (1) of 1.5 cm ^-1 or less for light having a wavelength of 200 to 375 nm. 3. The optical recording / reproducing optical system according to claim 1, wherein at least one of the first lens and the second lens receives light having a wavelength of 200 to 375 nm by the following formula (2). An optical recording / reproducing optical system comprising a material having a refractive index n satisfying the following condition: n ≧ 1.44 + 8.23 / (λ−124) (2) where n is a refractive index and λ is a wavelength [nm]. 4. The optical recording / reproducing optical system according to claim 1, wherein at least one of said first lens and said second lens is made of phosphate-based or fluorophosphate-based glass. An optical recording / reproducing optical system, comprising: 5. The optical recording / reproducing optical system according to claim 1, wherein at least one of the first lens and the second lens includes Ce, Pt, Cr, and C.
An optical recording / reproducing optical system comprising a glass containing at least one ion selected from u, Fe, and Ni at 100 ppm or less. 6. The optical recording / reproducing optical system according to claim 1, wherein at least one of the first lens and the second lens is made of a fluorophosphate glass having the following composition. An optical recording / reproducing optical system, comprising: ^{P 5+: 0.5~30 [cat%]} ( cation display, the same applies ^{hereinafter) Al 3+: 8~40 Mg 2+:} 0~20 Ca 2+: 0~35 Sr 2+: 0~50 Ba 2 ⁺ : 0 to 65 Na ⁺ and / or Li ⁺ : 0 to 5 at least selected from Y, La and rare earth elements (elements having an atomic number of 57 to 71 excluding Pm), which are divalent to tetravalent metals. One kind of ion: 0 to 10%, and the anion ratio [F] / ([F] + [O]) is 0.05
~ 0.99. 7. The optical recording / reproducing optical system according to claim 1, wherein at least one of the first lens and the second lens is made of a fluorophosphate glass having the following composition. An optical recording / reproducing optical system, comprising: Al (PO ₃ ) ₃ : 0 to 35 [wt%] Ba (PO ₃ ) ₂ : 0 to 25 Mg (PO ₃ ) ₂ : 0 to 15 Ca (PO ₃ ) ₂ : 0 to 15 Sr (PO ₃ ) ₂ : 0-15 However, phosphorus pentoxide total P ₂ O ₅ in terms _{of: 1~25 AlF 3: 10~25 BaF 2} : 10~35 MgF 2: 0~15 CaF 2: 0~30 SrF 2: 0~35 Na ₂ O and / or NaF: 0 to 5 Li ₂ O and / or LiF: 0 to 5 Y, La, rare earth element (atomic numbers 57 to 71 excluding Pm)
At least one oxide selected from the group consisting of: and / or fluorides thereof: 0 to 7.5. 8. The optical recording / reproducing optical system according to claim 1, wherein at least one of the first lens and the second lens is made of a phosphate glass having the following composition. An optical recording / reproducing optical system, comprising: ^{P5 +} : 65 to 85 [cat%] (cation indication, the same applies hereinafter) Al3 ⁺ : 2 to 10 Mg2 ⁺ : 0 to 30 Ca2 ⁺ : 0 to 30 Sr2 ⁺ : 0 to 30 Ba2 ⁺ : 0 to 40 Zn ²⁺ : 0 to 8 Na ⁺ and / or K ⁺ : 0 to 8 provided that the total amount of Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ²⁺ and Zn ²⁺ : 18 to 40; At least one selected from the group consisting of Y, La, and rare earth elements (elements having an atomic number of 57 to 71 excluding Pm), which are divalent to tetravalent metals: 0 to 8%. 9. The optical recording / reproducing optical system according to claim 1, wherein at least one of the first lens and the second lens is made of a phosphate glass having the following composition. An optical recording / reproducing optical system, comprising: _{P 2 O 5: 40~85 [wt} %] Al 2 O 3: 2~10 MgO: 0~20 CaO: 0~25 SrO: 0~40 BaO: 0~60 ZnO: 0~8 Na 2 O and / or K ₂ O: Less than six However, MgO, CaO, SrO, BaO , the total content of ZnO: 8~60, Y, La, at least one oxide selected from rare earth elements: 0-20. 10. The optical recording / reproducing optical system according to claim 1, wherein at least one of said first lens and said second lens is a lens formed by a mold press molding method. An optical recording / reproducing optical system, characterized in that: 11. The optical recording / reproducing optical system according to claim 1, wherein a transmission loss with respect to a light beam having a wavelength of 200 to 375 nm is 35% or less in the entire optical system. Recording / playback optical system. 12. A light source that emits a light beam having a wavelength of 200 to 375 nm as light for recording or reproducing information, an optical recording / reproducing optical system according to any one of claims 1 to 11, and light emitted from the light source. An optical information recording / reproducing apparatus, comprising: a light guiding means for guiding the light to the optical recording / reproducing optical system.