WO2010035642A1 - Optical element and method for producing same - Google Patents

Abstract

An optical element having high light utilization efficiency, wherein fractures of an optical path difference providing structure or antireflective film can be suppressed.  The optical element is characterized by being composed of a thermoplastic resin, by being provided with an optical path difference providing structure on at least one optical surface, and by having a fluorine-containing layer formed by a fluorinating process, wherein a hydrogen atom is substituted by a fluorine atom in a fluorine gas atmosphere, on the optical surface.

Description

Optical element and manufacturing method thereof

The present invention relates to an optical element, and more particularly to an optical element having high light utilization efficiency and having a fine optical path difference providing structure on the surface, and a method for manufacturing the same.

Conventionally, glass is generally used as a constituent material of optical elements (mainly lenses) from the viewpoint of excellent optical characteristics, mechanical strength, etc., but miniaturization of equipment in which the optical elements are used has been reduced. As the process proceeds, it is necessary to reduce the size of the optical element. It is difficult to produce an aspherical shape or a complicated shape with glass, and glass has become an unsuitable material in terms of mass productivity of precision elements.

For this reason, plastic materials that are easy to process are being studied and used. Examples of the plastic material include thermoplastic resins having good transparency (light transmittance) such as polyolefin and acrylic. In addition, such an optical element made of a resin is manufactured by molding. However, in order to suppress the occurrence of aberration due to a temperature change after molding, or an optical element that is compatible with an optical apparatus using a plurality of light sources having different wavelengths. Therefore, an optical path difference providing structure such as a diffraction structure for correcting aberration is often formed.

By the way, the blue laser that has been attracting attention in recent years is much more damaging to the material (resin molding part) that constitutes the optical element than the long-wavelength laser used in optical equipment such as the conventional CD and DVD. It is difficult to produce products that can withstand practical use without relying on expensive materials. As a solution to such a problem, Patent Document 1 discloses an optical element that can withstand the irradiation of a blue laser having a wavelength λ = 405 to 415 nm by appropriately selecting the type of constituent material of the antireflection film. Yes. For example, Patent Document 1 discloses a film made of a fluoride such as aluminum fluoride as an antireflection film.

JP 2005-266780 A

In optical devices that require very high accuracy, such as optical pickup devices, recording media with temperature variations, aberrations due to wavelength differences when multiple different light sources are used (called chromatic aberration), and protective substrate thicknesses are different. A diffraction structure that gives a specific optical path difference to the transmitted light beam on the surface of the optical element as necessary for correction of spherical aberration caused by the thickness of the protective substrate, etc. The optical path difference providing structure may be provided.

On the other hand, in an optical element, when an antireflection film is formed as in Patent Document 1, a film is often formed by a vacuum vapor deposition method as one aspect, but for an optical element provided with an optical path difference providing structure. When the antireflection film is formed by such a method, the following problems are raised. That is, as shown in FIG. 8, the vacuum deposition apparatus 100 includes a vacuum container 102, in which a deposition source 104, a substrate holder 106, and the like are disposed, and the deposition source 104 is heated and held by the substrate holder 106. A vapor deposition material is adhered to the resin molded product 110. In this case, the vapor deposition material adheres to the resin molded product 110 in a directional state. However, since the resin molded product 110 has the unevenness forming the optical path difference providing structure, it becomes a shadow of the convex portion 120. The adhesion amount of the vapor deposition material decreases at the portion, and the film thickness of the antireflection film becomes non-uniform (see the enlarged view in FIG. 8).

As a result, even if an optical path difference providing structure is formed on a resin molded product in order to reduce aberrations and increase the light utilization efficiency, the function of the structure (shape) is impaired and the film thickness of the antireflection film varies. The antireflection effect is also impaired, and as a result, the light utilization efficiency may be reduced. Here, the light utilization efficiency means the ratio of the amount of light that contributes to the formation of spots with respect to the total amount of light before passing through the optical element.

Further, as a problem in handling, since the undulations (dimensions) of the unevenness are very small, the convex portion 120 is easily physically damaged (edge portion is likely to be chipped), and the optical path difference providing structure originally required The effect may be reduced, and improvement has been demanded. In addition, the deposited film having an antireflection function provided on the optical element is also very likely to be chipped at the uneven edge portion, and the antireflection function may be further lowered.

Accordingly, a main object of the present invention is an optical element having a fine optical path difference providing structure on the surface, which has high light utilization efficiency and can suppress defects in the optical path difference providing structure and the antireflection film. Is to provide.

According to the present invention,
In an optical element made of thermoplastic resin,
An optical path difference providing structure is formed on at least one of the optical surfaces,
The optical surface has a fluorine-containing layer formed by a fluorination treatment in which hydrogen atoms on the surface are substituted with fluorine atoms in a fluorine gas atmosphere.

By forming the fluorine-containing layer, the refractive index of the surface of the thermoplastic resin can be lowered, and by using this as an antireflection film, an antireflection function can be imparted. Further, in this case, since the fluorine-containing layer is formed by fluorination treatment in a fluorine gas atmosphere, compared with the conventional case where an antireflection film is formed by vapor deposition or the like, the shadow of the optical path difference providing structure is reduced. The optical surface is uniformly modified over the entire surface, including the portion to become, and the thickness of the portion that controls the antireflection function (the film thickness of the antireflection film) does not occur. Therefore, the function of the antireflection film is not impaired, and it is possible to suppress a decrease in transmittance and a decrease in light utilization efficiency. In addition, since the C—H bond on the optical surface is replaced (modified) by the fluorination treatment, the portion of the optical surface where the fluorine-containing layer is formed is stronger than the C—H bond. Can be strengthened, and physical loss of the optical path difference providing structure can be suppressed. Accordingly, it is possible to suppress a decrease in the function of the optical path difference providing structure itself, to improve the light utilization efficiency, and to record and reproduce optical information with high accuracy. Furthermore, since the fluorine-containing layer has a function as an antireflection film, the loss of the antireflection film can be suppressed, and the deterioration of the antireflection function can be suppressed.

From the above, it is possible to obtain an optical element having a fine optical path difference providing structure on the surface, having high light utilization efficiency, and suppressing defects in the optical path difference providing structure and the antireflection film.

It is drawing which shows schematic structure of the optical pick-up apparatus used by preferable embodiment of this invention. It is a rough sectional side view of the objective lens used for preferable embodiment of this invention. It is drawing which shows the modification of FIG. It is drawing which shows the modification of FIG. It is drawing which shows the modification of FIG. It is drawing which shows the modification of FIG. It is drawing which shows the modification of FIG. It is drawing for demonstrating a prior art, and is drawing which shows schematic structure of a vacuum evaporation system.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

As shown in FIG. 1, the optical pickup device 1 includes a semiconductor laser oscillator 2 as a light source. The semiconductor laser oscillator 2 emits a blue laser (blue-violet laser) having a specific wavelength (for example, 405 nm) having a wavelength of 380 to 420 nm for BD (Blu-ray Disc). On the optical axis 4 of the blue-violet light emitted from the semiconductor laser oscillator 2, a beam splitter 7, a collimator 3, and an objective lens 10 are sequentially arranged in a direction away from the semiconductor laser oscillator 2. A detector 8 is disposed at a position close to the beam splitter 7 and in a direction perpendicular to the optical axis 4 of the above-described blue-violet light.

In the optical pickup device 1, the laser beam (light) emitted from the laser oscillator 2 passes through the collimator lens 3 and the objective lens 10, and is collected on the information recording surface 6 of the optical disk 5 on the optical axis 4 to be a focused spot. The reflected light from the information recording surface 6 is taken in by the beam splitter 7, and a beam spot is formed again on the light receiving surface of the detector 8.

As shown in FIG. 2, an optical path difference providing structure 20 is formed on the surface (optical surface 11) of the objective lens 10. The optical path difference providing structure 20 is composed of a plurality of annular zones 21 centered on the optical axis 4, the plurality of annular zones 21 have a sawtooth cross section, and the optical surface 11 of each annular zone 21 is discontinuous. It is a surface. The objective lens 10 shown in FIG. 2 is a so-called diffractive lens having a diffractive structure. The diffractive structure is an aspect of the optical path difference providing structure 20, and other structures may be adopted as the optical path difference providing structure 20.

As shown in the enlarged view of FIG. 2, the objective lens 10 is mainly composed of a molding part 50, and a fluorine-containing layer 55 is formed on the surface thereof. The molding part 50 is molded into a lens shape and exhibits essential optical functions such as a light collecting function.

The molded part 50 is made of a thermoplastic resin containing a C—H bond. Examples of the thermoplastic resin include an acrylic resin, a cyclic olefin resin, a polycarbonate resin, a polyester resin, a polyether resin, a polyamide resin, or a polyimide resin, and specific examples include the compounds described in JP-A-2003-73559. The preferable compounds are shown in Table 1 below, and in addition, a cyclic olefin having an alicyclic structure is preferable.

The thermoplastic resins described above are polyolefin resins (polyethylene, polypropylene), cyclic olefin resins (manufactured by ZEON: ZEONEX, Mitsui Chemicals: APEL, JSR: ARTON, Ticona: TOPAS), indene / styrene resins, A polycarbonate resin or the like is preferably used.

The fluorine-containing layer 55 is a layer formed by performing a fluorination treatment on the molded part 50 in a fluorine atmosphere, and has a function of reducing the surface reflectance of the objective lens 10. The fluorine-containing layer 55 has a refractive index with respect to d-line of 1.35 to 1.45, and the value of the refractive index can be measured by the surface reflectance. The thickness of the fluorine-containing layer 55 is preferably 10 to 5000 nm, but is not particularly limited. When the product (nd) of the thickness d of the fluorine-containing layer 55 and the refractive index n is the design wavelength λ, nd≈ Setting the thickness to be λ / 4 is preferable because an antireflection function can be obtained due to the light interference effect. When the layer thickness exceeds 5000 nm, the influence of interference fringes greatly depends on the wavelength of light, and even if an antireflection film is formed thereon, it becomes difficult to exert its function. Conversely, when the layer thickness is less than 10 nm This is because it becomes difficult to sufficiently exert the function of the fluorine-containing layer 55.

The objective lens 10 is not limited to the one having the optical path difference providing structure 20, but may be lenses 10a to 10e having structures 20a to 20d shown in FIGS. 3 to 7, for example.

The optical path difference providing structure 20a in FIG. 3 includes three annular lens surfaces whose optical surfaces 11a are centered on the optical axis 4 (hereinafter, a first annular lens surface 21a, a second annular lens surface 22a, Of the three annular lens surfaces 21a to 23a, the adjacent annular lens surfaces 21a to 23a have different refractive powers.

The first annular lens surface 21a and the third annular lens surface 23a are on the same optical surface 11a, and the second annular lens surface 22a is a surface translated from the optical surface 11a.

In FIG. 3, the first annular lens surface 21a and the third annular lens surface 23a are provided on the same optical surface 11a, but the first and third annular lens surfaces 21a, 23a are the same optical. The second annular lens surface 22a may be a surface that is translated from the optical surface 11a, but may not be a particularly translated surface. Further, the number of the three annular lens surfaces 21a to 23a may be five or at least three.

The optical path difference providing structure 20b in FIG. 4 has a plurality of annular zone-shaped concave portions 21b that cause a phase difference around the optical axis 4 in a concentric manner. The ring-shaped concave portions 21b are formed in five on one surface (upper and lower optical surfaces around the optical axis 4 in FIG. 4) of the optical surface 11b with the optical axis 4 as the center. Adjacent ring-shaped recesses 21b are continuously integrated with each other, and the cross section of each ring-shaped recess 21b as a whole is stepped. Moreover, the optical surface 22b which forms each annular zone-shaped recessed part 21b is a surface translated with respect to the optical surface 11b. The lens 10b shown in FIG. 4 is a so-called phase difference lens.

In FIG. 4, the adjacent ring-shaped recesses 21 b are continuous and integrated, and the entire cross section is stepped, but the ring-shaped recess 21 b is simply provided on the optical surface 11 b individually. (In this case, for example, the lens 10a shown in FIG. 3 has the same structure). In FIG. 4, the annular concave portion 21 b is concentrically formed. However, as shown in FIG. 5, the lens 10 c having the convex portion 23 b on the third annular lens surface 23 a in FIG. (In FIG. 5, the same components as those in FIG. 3 are denoted by the same reference numerals).

The optical path difference providing structure 20d in FIG. 6 includes a plurality of diffraction ring zones 21d centered on the optical axis 4, the plurality of diffraction ring zones 21d have a sawtooth cross section, and the optical surface 11d of each diffraction ring zone 21d. Is a discontinuous surface. The cross section of each diffraction ring zone 21d is a stepped form of three steps 22d along the optical axis direction, and the optical surface 12d of each step 22d is a discontinuous surface that is orthogonal to the optical axis 4. .

The lens 10d shown in FIG. 6 may have, for example, a hologram optical element (HOE) 10e having an optical path difference providing structure 20d similar to that shown in FIG. 6 and an objective lens 10f as shown in FIG. . In this case, the hologram optical element 10e uses a flat optical element, and the optical path difference providing structure 20d is provided on the surface of the objective lens 10f of the optical element.

Subsequently, a method for manufacturing the objective lens 10 will be described.

First, the thermoplastic resin is injection-molded into a mold under a certain condition to form a molded part 50 having a predetermined shape. Thereafter, a fluorination treatment is performed on the molding unit 50 to form a fluorine-containing layer 55 on the molding unit 50.

In the fluorination treatment, the molded part 50 is exposed to a fluorine gas atmosphere, and a fluorine-containing layer 55 is formed on the surface thereof. Thereby, the refractive index of the polymer material (thermoplastic resin) can be lowered, and the surface reflectance of the objective lens 10 can be lowered.

By appropriately selecting the fluorine gas concentration in the fluorine gas atmosphere and the temperature and time of exposure to the fluorine gas atmosphere, the layer thickness and fluorination rate of the fluorine-containing layer 55 can be arbitrarily controlled, and the surface reflectance at a desired wavelength Can be reduced.

Here, the fluorine gas atmosphere means being covered with a gas containing fluorine gas, and includes being covered with a mixed gas of fluorine gas and an inert gas such as nitrogen or argon.

Further, the concentration of the fluorine gas in the fluorine gas atmosphere can be appropriately selected according to the material having the desired refractive index and fluorine-containing layer thickness.

The molded part 50 is a polymer made of a thermoplastic resin having a carbon-hydrogen bond, and is not particularly limited as long as it is a polymer having a carbon-hydrogen bond in addition to the above examples. .

In addition, the constituent element of the additive whose addition amount is 5% or less with respect to the total mass, such as an antioxidant, an ultraviolet absorber, and a plasticizer added to the molded part 50 may be other than carbon and hydrogen. .

Further, even when a polymerization auxiliary material such as a catalyst or a reaction terminator used in manufacturing the molded part 50 remains, if the residual amount is less than 1% with respect to the total mass, its constituent elements Is not limited to carbon and hydrogen.

In the present embodiment, the molded part 50 is not particularly limited as long as the above conditions are satisfied. However, when high transparency, high heat resistance, low water absorption, high purity, and low birefringence are added, the cyclic olefin weight is considered. More preferably, it is a coalescence.

By exposing these polymers to fluorine gas of various concentrations diluted with nitrogen gas, for example, at a predetermined temperature and for a predetermined time, the fluorine in the molecule is gradually increased from the surface to the inside of the polymer material. Introduction will occur and the fluorine content of the material will increase.

The penetration depth of fluorine from the material surface and the fluorine content in the material after fluorine treatment vary depending on the concentration of fluorine gas during the fluorine treatment, the fluorine treatment temperature, and the fluorine treatment time.

There are no particular restrictions on these conditions, but when the fluorine concentration is high, when the treatment time is long, when the treatment temperature is high, the penetration depth of fluorine becomes deep, and the fluorine content of the polymer material after fluorine treatment Becomes higher.

Since the refractive index of the fluorinated portion decreases as the fluorine content increases, the low refractive fluorine-containing layer 55 having a desired thickness can be formed by appropriately selecting the fluorine concentration, processing temperature, and processing time. Is possible.

However, when the fluorine concentration is extremely increased or the fluorine treatment is performed at an extremely high temperature and for a long time, the molecule deteriorates. Therefore, as a normal fluorine treatment condition, the fluorine concentration is 1 ppm to 25%, and the treatment temperature is 0 to 100. C. and a treatment time of 0.1 second to 120 minutes are preferred.

Subsequently, the operation of the optical pickup device 1 will be described.

Blue-violet light is emitted from the semiconductor laser oscillator 2 when recording information on the optical disk 5 or when reproducing information recorded on the optical disk 5. The emitted blue-violet light passes through the collimator 3 and is collimated into infinite parallel light, and then passes through the objective lens 10 to form a condensed spot on the information recording surface 6 of the optical disc 5.

The blue-violet light that forms the condensed spot is modulated by the information bit on the information recording surface 6 and reflected by the information recording surface 6. The reflected light is sequentially transmitted through the objective lens 10 and the collimator 3 and then reflected by the beam splitter 7. Thereafter, the reflected light is received by the detector 8 and finally converted into an electric signal by photoelectric conversion.

Thereafter, such an operation is repeatedly performed, and the operation of recording information on the optical disc 5 and the operation of reproducing information recorded on the optical disc 5 are completed.

According to the present embodiment described above, since the optical surface 11 of the objective lens 10 has the fluorine-containing layer 55, the reflectance is low and the antireflection function is maintained. In this case, since the optical surface 11 is subjected to a fluorination treatment and the fluorine-containing layer 55 is formed, the optical surface 11 is uniformly modified over the entire surface, and the thickness of the portion responsible for the antireflection function (antireflection) The situation that the film thickness is not uniform does not occur. Therefore, the function of preventing reflection is not impaired, and it is possible to suppress a decrease in light utilization efficiency.

In addition, since the C—H bond of the optical surface 11 is replaced (modified) by the fluorination treatment, the portion of the optical surface 11 where the fluorine-containing layer 55 is formed is a C—H bond. The binding force is further strengthened, and the optical path difference providing structure 20 can be prevented from being physically lost, and the occurrence of the loss of the antireflection film does not occur. From the above, it is possible to suppress the loss of the optical path difference providing structure 20 and the loss of the antireflection film while maintaining the antireflection function, and high light utilization efficiency can be obtained.

Although the optical element according to the present invention has been described as the objective lens 10, as other optical elements in various forms such as a spherical shape, a rod shape, a plate shape, a cylindrical shape, a tubular shape, a tubular shape, a fibrous shape, a film shape, or a sheet shape. Also good. However, from the viewpoint of reducing the temperature difference between the mold and the inside of the molded product, a shape having a diameter of about 2 to 5 mm and a thickness of about 1 to 3 mm is preferable. Specific examples of such an optical element include the following.

Optical lenses and optical prisms include: camera imaging lenses; microscopes, endoscopes, telescope lenses, and other lenses; total light transmission lenses such as spectacle lenses; CDs, CD-ROMs, WORM (recordable optical disks), MO (Optical optical discs that can be rewritten; magneto-optical discs), pickup lenses for optical discs such as MD (mini discs), DVDs (digital video discs); laser scanning system lenses such as fθ lenses and sensor lenses for laser beam printers; Examples include finder type prism lenses. Examples of optical disc applications include CD, CD-ROM, WORM (recordable optical disc), MO (rewritable optical disc; magneto-optical disc), MD (mini disc), DVD (digital video disc), and the like.

Other optical applications include light guide plates such as liquid crystal displays; optical films such as polarizing films, retardation films and light diffusion films; light diffusion plates; optical cards; liquid crystal display element substrates. Among these, the optical element of the present invention is preferably used as an optical system lens or a laser scanning system lens constituting an optical pickup device requiring low birefringence, and is used as an optical system lens of the optical pickup device. Most preferably, it is used.

As the optical system lens of the optical pickup device, for example, in addition to the objective lens described above, it can be used as an objective lens unit, a coupling lens (collimator), a beam expander, a beam shaper, a correction plate, and the like. Among these, the objective lens unit is a lens group formed by integrally combining a plurality of single lens optical lenses in the optical axis direction, and as at least one single lens optical lens among the plurality of single lens optical lenses. It is preferable to use the optical element of the present invention.

(1) Preparation of Sample Three objective lenses for BD (Blu-ray Disc) were manufactured by injection molding a thermoplastic resin using a fixed mold.

As the thermoplastic resin, ZEONEX 350R, which is a cycloolefin resin material manufactured by Nippon Zeon, was used.

The optical surface on the incident surface side (light source side) of the above-mentioned objective lens is provided with a diffractive structure for correcting spherical aberration caused by a temperature change as an optical path difference providing structure. 2 is a diffractive structure having a sawtooth cross section as shown in FIG.

The above objective lens has good shape transfer and light utilization efficiency of 69.8%.

Thereafter, one of the three objective lenses was fluorinated, and this was designated as “Sample 1”.

Fluorination treatment was performed under the conditions of a fluorine concentration of 5%, a treatment temperature of 25 ° C., and a treatment time of 1 minute.

The remaining two objective lenses were vapor-deposited to form 150 nm and 300 nm fluoride films on their surfaces. An objective lens having a fluoride film thickness of 150 nm was designated as “Sample 2”, and an objective lens having a fluoride film thickness of 300 nm was designated as “Sample 3”.

In the vapor deposition process, after evacuating the vacuum degree to 2 × 10 ⁻² Pa or less in a vacuum vapor deposition apparatus, the vapor deposition material is heated and evaporated by an electron gun to form a silicon oxide film on the lens surface. did. The lens temperature during vapor deposition was 80 ° C., and the film formation speed was 1 nm / sec.
(2) Sample evaluation (2.1) Measurement of light utilization efficiency The light utilization efficiency of each of samples 1 to 3 was measured using a Zygo interferometer (wavelength 405 nm). The measurement results are shown in Table 2.
(2.2) Measurement of light utilization efficiency after wiping test Using a cleaning paper soaked with IPA (isopropyl alcohol), the surface of each sample 1 to 3 on which a fluorine-containing layer and a fluoride film are formed Was wiped (wiping test was carried out), and the light utilization efficiency (decrease amount) after the wiping test was measured. During the wiping test, a force of 30 g load was applied to the cleaning paper, and the number of wiping was 50 times. A Zygo interferometer (wavelength 405 nm) was used to measure the amount of decrease in light utilization efficiency.

Table 2 shows the decrease in light utilization efficiency after the wiping test for each of samples 1 to 3.

(3) Summary As shown in Table 2, when the light utilization efficiency is compared, the light utilization efficiency of sample 1 is higher than that of samples 2 and 3. Comparing the light utilization efficiency after the wiping test, it can be seen that Sample 1 has a smaller amount of decrease than Samples 2 and 3, and the physical loss of the optical path difference providing structure and the loss of the antireflection film are suppressed. From the above, it can be seen that it is useful to form a fluorine-containing layer by fluorination treatment in order to suppress the decrease in light utilization efficiency and the loss of the optical path difference providing structure.

1 Optical pickup device 2 Semiconductor laser oscillator (light source)
DESCRIPTION OF SYMBOLS 3 Collimator lens 4 Optical axis 5 Optical disk 6 Information recording surface 7 Beam splitter 8 Detector 10, 10a, 10b, 10c, 10d, 10f Objective lens (optical element)
11, 11a, 11d, 12d, 22b Optical surface 20, 20a, 20b, 20c, 20d Optical path difference providing structure 21a First annular lens surface (annular lens surface)
22a Second annular lens surface (annular lens surface)
23a Third annular lens surface (annular lens surface)
23b Ring-shaped convex part 50 Molding part 55 Fluorine-containing layer 100 Vacuum deposition apparatus 102 Vacuum vessel 104 Deposition source 106 Substrate holder 110 Resin molded product 120 Convex part

Claims (5)

In an optical element made of thermoplastic resin,
An optical path difference providing structure is formed on at least one of the optical surfaces,
The optical element has a fluorine-containing layer formed by a fluorination treatment in which hydrogen atoms are replaced with fluorine atoms in a fluorine gas atmosphere. The optical element according to claim 1,
The optical element, wherein the thermoplastic resin has an alicyclic structure. The optical element according to claim 1 or 2,
The optical element, wherein the optical path difference providing structure is a diffractive structure. The optical element according to any one of claims 1 to 3,
An optical element used as an objective lens of an optical pickup device. In the method of manufacturing an optical element made of a thermoplastic resin,
An optical path difference providing structure is formed on at least one of the optical surfaces,
The method of manufacturing an optical element, wherein the optical surface is formed with a fluorine-containing layer by fluorination treatment in which hydrogen atoms are replaced with fluorine atoms in a fluorine gas atmosphere.

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