Patent Application
20110217556
The present application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2010-050607 filed on Mar. 8, 2010; the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an optical component and a manufacturing method thereof.
2. Description of the Related Art
Substrates made of resin have been used more commonly in recent years to manufacture optical systems inexpensively and in large quantities. Furthermore, there is a tendency towards making a ratio x of an effective optical diameter E to a radius of curvature R of the substrate larger to make the optical system more compact and smaller.
Optical systems that are typically used in digital cameras or vehicle mounted cameras are used in a wide range of environments, and are therefore required to be more durable against variation in environmental conditions such as temperature and humidity.
An antireflective film needs to be provided on a surface of a resin substrate to improve a transmittance of light and to prevent unnecessary reflection of light within the optical system. However, compared to an antireflective film formed on a glass substrate, the antireflective film formed on the resin substrate has a lower durability and tends to appear shabby because of chapping, cracking, peeling, wrinkling, etc., due to the variation in the environmental conditions such as temperature and humidity. This problem is particularly notable in the antireflective film formed on a substrate that has a larger ratio x of the effective optical diameter E to the radius of curvature R.
An optical element is proposed in Japanese Patent Application Laid-open No. 2004-271653 with a view to providing a solution to the above-described problem. The optical element is designed such that all the stress that is produced in a multilayer film formed on a shaped resin surface is compressive stress. A durability of the multilayer film formed on the resin surface is particularly improved by limiting the compressive stress to 120 Pa·m or less.
An optical component according to the present invention includes an optical thin film formed on a substrate such that an internal stress σ (in units of megapascal (MPa)) satisfies Expression (1) given below when x=|E/R| is in the range of 0 to 3.
σ≦−30x (1)
where E is an effective optical diameter (in units of millimeter (mm)) of the substrate, R is a radius of curvature (in units of mm) of the substrate, and x is an absolute value of a ratio of E to R.
A method of manufacturing an optical component according to the present invention includes forming the optical thin film on the substrate such that the internal stress σ (MPa) satisfies Expression (1) given below when x=|E/R| is in the range of 0 to 3.
σ≦−30x (1)
where E is the effective optical diameter of the substrate (mm), R is the radius of curvature of the substrate (mm), and x is the absolute value of the ratio of E to R.
Exemplary embodiments of an optical component and a manufacturing method thereof according to the present invention are explained below in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments described below.
An optical component 10 according to the present embodiment includes an optical thin film 12 (for example, antireflective film) formed on a resin substrate 11. If an effective optical diameter of the substrate 11 is E (in units of mm) and a radius of curvature of the substrate 11 is R (mm), an internal stress σ (in units of MPa) satisfies Expression (1) given below when an absolute value x=|E/R| of a ratio of E to R is in the range of 0 to 3. A positive internal stress σ indicates a tensile strength and a negative internal stress σ indicates a compressive stress.
σ≦−30x (1)
Ideally, instead of the conditional expression (1), the following conditional expression (1′) should preferably be satisfied.
σ≦−50x (1′)
As shown in
The paraxial radius of curvature is included in the radius of curvature R.
The internal stress σ also satisfies Expression (2) given below.
−30x−300≦σ≦−30x (2)
More ideally, instead of the conditional expression (2), the following conditional expression (2′) should preferably be satisfied.
−50x−250≦σ≦−50x (2′)
The optical thin film 12 may be formed on one surface or on both the surfaces of the substrate 11 according to the specifications of the optical component 10. The optical thin film 12 should preferably be formed by stacking a plurality of films, and at least one of the layers should be formed by an ion assisted deposition method or a plasma assisted deposition method. In the ion assisted deposition method or the plasma assisted deposition method, parameters of the ion assisted deposition method or the plasma assisted deposition method are controlled according to a constituent material of the layer being formed.
Examples of the present embodiment are explained below.
Three substrates L1, L2, and L3 shown in Table 1 are used as resin substrates.
In Table 1, E is the effective optical diameter (mm), D is a lens depth (mm), and R is the paraxial radius of curvature (mm). |E/R| is the absolute value of the ratio of the effective optical diameter E to the paraxial radius of curvature R, and |D/R| is an absolute value of a ratio of the lens depth D to the paraxial radius of curvature R. The lens depth D is a thickness of a part of a lens corresponding to the effective optical diameter E.
As shown in Table 1, the substrate L1 is made of a resin of cycloolefin series, the substrate L2 is made of resin of acrylic series, and the substrate L3 is made of a resin of polycarbonate series. The shape and the material of the substrate are not limited to these, and the substrate L1 and L2, for example, can be made of a resin of polycarbonate series.
Surfaces L11 and L12 of the substrate L1 are opposing faces, surfaces L21 and L22 of the substrate L2 are opposing faces, and surfaces L31 and L32 of the substrate L3 are opposing faces.
A constant temperature and humidity test and a thermal shock test were performed as environment tests. The conditions for environment tests are given below.
(1) Conditions for the constant temperature and humidity test: Exposure to a temperature of 85° C. and humidity of 40% for 1000 hours.
(2) Conditions for the thermal shock test: alternating exposure to temperatures of −40° C. and +85° C. for 30 minutes each, the total 1 hour was repeated for 1000 cycles.
Evaluation of the external appearance after the environment tests was carried out. That is, presence or absence of cracks, wrinkles, chapping, and peeling of the thin film formed on the surface of the resin substrate was visually confirmed by viewing the resin substrate under a stereoscopic microscope made by Olympus Corporation while illuminating the resin substrate obliquely.
As a method for measuring the internal stress, a disc method was used.
The internal stress σ is determined by Expression (3) given below:
σ=Esb2/[6(1−Vs)rd] (3)
where Es is Young's modulus, Vs is Poisson's ratio, b is a thickness of the substrate, d is a thickness of the optical thin film, and r is the radius of curvature of the substrate.
Specifically, a silicon wafer having a diameter of 4 inches and the thickness b of 525 micrometers (μm) is set in a chamber with the substrate, and the optical thin film is formed on the silicon wafer (on the mirror surface side). A deformation amount of the silicon wafer substrate was measured immediately after film formation.
To measure the thickness of the optical thin film, the following method was adopted. A straight line was drawn with a permanent marker on a glass flat plate. The silicon wafer and the glass flat plate were simultaneously set inside the chamber, and film was deposited. After the film was deposited, the part marked by the permanent marker was removed with ethanol to create a level difference. The level difference was measured and the value obtained was regarded as the film thickness.
Concrete examples and comparative examples are explained below in detail.
An antireflective film that serves as an optical thin film of several layers of a low refractive index material SiO2, and a high refractive index material Ta2O5 was deposited on both the surfaces of the resin substrate. The antireflective film has a four-layer structure with alternating Ta2O5 and SiO2 layers, the first layer on the substrate side being that of Ta2O5.
A plasma gun was used to perform plasma irradiation during the deposition of the SiO2 and Ta2O5 layers of the antireflective film using the plasma assisted deposition method.
The ion assisted deposition method can be used in place of the plasma assisted deposition method. In the ion assisted deposition method or the plasma assisted deposition method, the parameters (for example, gas flow amount, irradiation duration, and applied power) should preferably be controlled according to a constituent material of the layer being formed.
The low refractive index material SiO2 can be of any shape. It can be granular, sintered pellet or molten ring. A mixture with Al2O3 can also be used as long as the main component is SiO2.
TiO2 or Nb2O5 can be used in place of Ta2O5 as a high refractive index material. Similar to the low refractive index material, the high refractive index material also can be of any shape.
An antireflective film that serves as an optical thin film of several layers of a low refractive index material SiO2, and a high refractive index material TiO2 was deposited on both the surfaces of the resin substrate. The antireflective film has a five-layer structure with alternating TiO2 and SiO2 layers, the first layer on the substrate side being that of TiO2.
A plasma gun was used to perform plasma irradiation during the deposition of the SiO2 layer of the antireflective film using the plasma assisted deposition method.
The ion assisted deposition method can be used in place of the plasma assisted deposition method. In the ion assisted deposition method or the plasma assisted deposition method, the parameters (for example, gas flow amount, irradiation duration, and applied power) should preferably be controlled according to a constituent material of the layer being formed.
The low refractive index material SiO2 can be of any shape. It can be granular, sintered pellet or molten ring. A mixture with Al2O3 can also be used as long as the main component is SiO2.
Ta2O5 or Nb2O5 can be used in place of TiO2 as a high refractive index material. Similar to the low refractive index material, the high refractive index material also can be of any shape. A mixture with La can also be used as long as the main component is TiO2.
An antireflective film that serves as an optical thin film of several layers of a low refractive index material SiO2, a high refractive index material TiO2, and a topmost layer of MgF2 was deposited on both the surfaces of the resin substrate. The antireflective film has a seven-layer structure with alternating SiO2 and TiO2 layers, the first layer on the substrate side being that of SiO2 and the topmost layer being that of MgF2.
A plasma gun was used to perform plasma irradiation during the deposition of the SiO2 layer of the antireflective film using the plasma assisted deposition method.
The ion assisted deposition method can be used in place of the plasma assisted deposition method. In the ion assisted deposition method or the plasma assisted deposition method, the parameters (for example, gas flow amount, irradiation duration, and applied power) should preferably be controlled according to a constituent material of the layer being formed.
The low refractive index material SiO2 can be of any shape. It can be granular, sintered pellet or molten ring. A mixture with Al2O3 can also be used as long as the main component is SiO2. The material of MgF2 can also be of any shape.
Ta2O5 or Nb2O5 can be used in place of TiO2 as a high refractive index material. Similar to the low refractive index material, the high refractive index material also can be of any shape. A mixture with La can also be used as long as the main component is TiO2.
The structure of the film in the Comparative Example 1 is similar to that of Concrete Example 1. However, a vapor deposition method was used instead of the plasma assisted deposition method. The value of the internal stress σ was 20 MPa.
A structure of the film in the Comparative Example 2 is similar to that of Concrete Example 2. However, the vapor deposition method was used instead of the plasma assisted deposition method. The value of internal stress σ was 20 MPa.
A structure of the film in the Comparative Example 3 is similar to that of Concrete Example 3. However, the vapor deposition method was used instead of the plasma assisted deposition method. The value of internal stress σ was 30 MPa.
As can be surmised from
In
The deterioration of appearance occurs in instances that are above and to the right of the dashed line in
Furthermore, in the comparative examples, cracks had already started appearing after lapse of 250 hours in the environment test. On the contrary, in the concrete examples, in the instances where the deterioration of appearance did not occur, a chronological change of the internal stress σ after 1000 hours from the start of the environment test was within 100 MPa compared to the initial value.
Thus, as described above, the present invention provides an optical component that includes an optical thin film deposited on a resin substrate, and that has an improved durability against the variations in the environmental conditions such as temperature and humidity.
An optical component and a manufacturing method thereof according to the present invention has an effect of improving a durability of an optical thin film formed on a resin substrate against variations in environmental conditions such as temperature and humidity.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-050607 | Mar 2010 | JP | national |
