JP2001201601A - Optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical element with a light path comprising a water resistant material having easily controllable physical properties such as refractive index in place of the conventional a thermal glass used so as to suppress a characteristics change of the optical element due to temperature. SOLUTION: A mixture or composite of 1st and 2nd materials is used as the constituent material of the light path of the optical element and the 1st and 2nd materials are selected in such a way that the refractive indexes of the 1st and 2nd materials have temperature coefficients whose signs are opposite to each other. A mixture or composite of organic and inorganic materials may be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to optical communication, optical measurement,
The present invention relates to a material constituting an optical element used in the field of laser engineering.

[0002]

2. Description of the Related Art In recent years, the development of optical technology has been remarkable along with the development of optical communication and laser. In addition, the required accuracy and performance are also increasing.
As a material for optical components, glass is one of the most important materials as found in optical fibers and optical lenses. Glass has various compositions depending on its use, and has been properly used in various situations. The properties required of such a glass are not only optical transparency, but also its stability is a major factor. Glass is generally relatively excellent in weather resistance and heat resistance,
Depending on the composition, the water resistance may be weak or the thermal properties may be insufficient for the purpose.

One of the characteristics desired for optical materials is stability against temperature. This stability means that the characteristics do not change due to a temperature change, and the fact that the heat resistance of the glass is high does not necessarily mean that the characteristics themselves are stable. In such an optical material, when the temperature changes, the refractive index changes with the temperature,
The length of the element also changes with temperature. The optical path length changes in a form where these two effects overlap. According to Tetsuro Izumiya al "Optical Glass" Kyoritsu Shuppan (1984), the temperature T dependence of the relationship between the thermal expansion coefficient alpha _a and the refractive index n _a of the material, taking into account the optical path length of the space changes due to thermal expansion And is derived as in Equation 1.

[Number 1] _{dn a / dT + (n a} -1) α a = 0

When such a material is used for, for example, a laser medium, the mode of the beam changes.
Further, in an apparatus for adjusting the optical path length, which is constituted by a glass prism in the interferometer, the optical path length is slightly changed due to a change in temperature. According to the above “optical glass”, the temperature change of the optical path length s is ds / dT = ⁶ × 10 ⁻⁶ / ° C. for the glass LSG91H. Such a temperature change of the optical path length causes a large instability especially in an interferometer. In order to eliminate such adverse effects, there is a material called athermal glass. This is a glass for which the above equation 1 is satisfied.

[0005]

However, the constituents of the athermal glass contain a large amount of phosphoric acid, boric acid, and the like due to the selection of elements for satisfying the formula 1, resulting in poor water resistance. To use for a wide range of applications,
I have a problem. In addition, since the composition is limited, it is difficult to control physical properties such as a refractive index, which are characteristics of a glass material.

[0006]

A material constituting an optical path of an optical element is a mixture or a composite of a first material and a second material, and the refractive index of the first material and the refractive index of the second material are sign. Choose the one with the opposite temperature coefficient. Suitable materials include mixtures or composites of organic and inorganic materials.

In this case, the component ratio of the organic material is set to 2 mol% or more and 10 mol% or less. Further, a material mainly composed of hydrocarbons and / or hydrocarbon derivatives is used as the organic material, and SiO ₂ , TiO ₂ , Ge is used as the inorganic material.
O ₂ , Al ₂ O ₃ , ZrO ₂ , B ₂ O ₃ , Na ₂ O, MgO,
A glass material containing at least one of CaO as a component is used.

As a starting material, a mixture of an organic compound and an inorganic compound may be used, but an organic-inorganic composite is more preferably used. In addition, the optical element made of the above-mentioned material has a temperature of 150 ° C. during the manufacturing process.
It is desirable that the heat treatment be performed at a temperature exceeding the above. The optical element is any one of a laser medium, a lens, a prism, a reflection / transmission type diffraction grating, and a beam splitter.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS For example, a lens has a function of refracting light incident from a space outside the lens and forming an image again in the space outside the lens. That is, the lens element functions as an optical system including an external space. Prism, reflection
A transmission type diffraction grating, a beam splitter, a laser medium, and the like are similar optical elements. In such an optical system, when the temperature changes, an optical change is caused by a change in the optical path length due to a change in the refractive index due to the temperature and a change in the physical optical path length due to thermal expansion. Changes in the optical properties occur. For example, when light passing through a simple rectangular parallelepiped optical medium 1 as shown in FIG. 1 is considered, an optical path length S when the refractive index of the medium is n and its total length is L is expressed by Equation 2.
Is defined by

S = nL Note that the optical path length of the optical medium 2 when the temperature changes by ΔT ° C. changes as shown in Expression 3.

S + (dS / dT) LΔT = (n + (dn / dT) ΔT) (L + αLΔT) −1 · αLΔT = nL + (dn / dT) ΔTL + nαLΔT + (dn / dT) ΔTαLΔT) −1 · αLΔT where dn / DT is the temperature coefficient of the refractive index, dS / dT is the temperature coefficient of the optical path length, and α is the linear expansion coefficient. Since these are both values in the 10 ^-6 range, the four items on the left side of Equation 3 can be ignored. The last term is a term that compensates for the optical path length of a space that changes due to expansion of the optical element.

The temperature coefficient dS / dT of the optical path length due to the temperature change (ΔT) is given by the following equation, and Equation 4 is derived. (DS / dT) LΔT = (dn / dT) ΔTL + nαL
ΔT-1 · αLΔT

DS / dT = (dn / dT) + (n−1) αT Therefore, in order to make the optical path length difference zero, Expression 5 must be satisfied.

(Dn / dT) + (n−1) α = 0 Since α is usually a positive number and n of the solid material is larger than 1, the term of dn / dT is required to satisfy Expression 5. Must be negative. Many glass materials have a positive dn / dT. On the other hand, many organic compounds have a negative dn / dT, and the left side of Formula 5 can be negative.

From the above, it can be expected that the use of a mixture of an organic compound and an inorganic compound can eliminate the temperature dependence of the optical path length. The present invention is intended to solve the problem by using a mixture or a composite of an organic material and an inorganic material as a basic material constituting the optical element. Here, the mixture is a material obtained by simply mixing and stirring an organic compound and an inorganic compound. The composite is a material in which an organic component and an inorganic component have a chemical bond such as a covalent bond and a coordinate bond. Hereinafter, a method of determining a theoretical optimum value of the composition ratio x between the organic material and the inorganic material will be described.

(1) For each of the organic material and the inorganic material, the refractive index n _{p of} the organic material alone at room temperature, the refractive index n _i of the inorganic material only at room temperature, the refractive index temperature coefficient dn _p / dT of the organic material only, The refractive index temperature coefficient dn _i / dT of only the material, the linear expansion coefficient α _{p of} only the organic component material, and the linear expansion coefficient α _i of only the inorganic material are obtained by measurement.

(2) The temperature coefficients φ _p and φ _i of the electronic polarization of the organic material and the inorganic material with respect to the above measured values are obtained by using Equation 6 derived from the Lorentz-Lawrence relationship.

Dn _m / dT = [｛( _nm ² −1) ( _nm ² +
1)｝ / 6 _nm ] (φ _m −3α _m ) where m = p for organic materials and m = i for inorganic materials.

(3) The refractive index n _c and the temperature coefficient of the refractive index n _c of the mixture or the composite at room temperature are calculated by the asymptotic asymptotic method using the composition ratio x of the organic material and the inorganic material as variables. _c / dT and the coefficient of linear expansion α _c are obtained, and the number of moles x of the inorganic component of the material constituting the optical element in which Expression 5 is satisfied is determined.

N _c ² = (V _c + 2R _c ) / (V _c -R _c )

[Equation 8] _{V c = V i x + V} p (1-x)

R _c = R _ix + R _p (1-x)

Α _c = [α _i · V _i x / ｛V _p (1-x) + V _{i
x}] + [α p ·} V p (1-x) / {V p (1-x) + V i
x｝]

Equation 11] _{φ c = [φ i · V} i x / {V p (1-x) + V i
_{x}] + [φ p ·} V p (1-x) / {V p (1-x) + V i
x｝]

Equation 12] _{dn c / dT = [{(} n c 2 -1) (n c 2 +
1)｝ / 6n _c ] (φ _c −3α _c ) where φ _c is the temperature coefficient of electronic polarization of the material forming the optical element, V _c is the molecular volume of the material forming the optical element,
V _p is the molecular volume of only the organic component material, V _i is the molecular volume of the inorganic component material only, R _c is the molecular refraction of the material constituting the optical element, R _p is the molecular refraction of the organic component material only, R _i is This is molecular refraction of only the inorganic component material. The composition ratio x determined as described above is a standard for adjusting actual materials as shown in the following examples.

The composition ratio, that is, the mole fraction, as used herein, is defined by the ratio of the number of constituent atoms by distinguishing the inorganic component from the organic component based on the following criteria. The concentration of the inorganic component is determined by the number of metal elements (Si, Ti, Zr, Al, Zn, In, Sn, etc.) and the number of oxygen atoms bonded thereto.
Organic components are elements other than the inorganic components (C, H, Cl,
F, Br, I, O, etc.). However, substances which decompose and volatilize even if they are contained during the preparation are not considered as components, but only the remaining components. For example, C ₂ H ₅ OH generated by hydrolysis of the solvent ethanol and Si—OC ₂ H ₅ is not considered as a component if it volatilizes. The organic component contained in the inorganic compound is calculated as an organic component.
For example, all CH ₃ -Si a CH ₃ group, Ph-Si of Ph (phenyl) group, CH ₂ = CH group CH ₂ = CH-Si are counted as organic components.

[0016]

EXAMPLE The material to be mixed was SiO as an inorganic material.
The material produced was performed using a photopolymerizable monomer as a ₂ and an organic material. Although a photopolymerizable monomer was used here,
This is not particularly important and was selected in terms of ease of fabrication. In order to uniformly mix these materials, a reaction mainly based on the sol-gel method is used.
₂ (Refractive index: about 1.42) Tetraethoxysilane (TEOS) as the source, 2-ethoxy as the photopolymerizable monomer
Hydroxy-3-phenoxypropyl acrylate (C
_{H 2 = CHCOOCH 2 C (OH} ) HCHO-C 6 H 5: H
FPA) was used. The refractive index of the HFPA polymer is about 1.55. The ratio of organic to inorganic components is TE
It was determined by the weight ratio of SiO ₂ to HFPA after OS hydrolysis. In this embodiment, the inorganic component is 0% to 100%.
% And examined the effect.

First, a TEOS reaction solution as a base of an inorganic component was prepared in the following procedure. , TEOS, 90g, T
HF, 20cc, i-PA, 100cc, H 2 O, 1
Mix 5.6 cc, HCl and 7.2 cc,
The reaction was performed for 30 minutes. Thereafter, a predetermined amount of HFPA is mixed, and 3,3 ′, 4,4′- is further used as a photopolymerization initiator.
Tetra (t-butylperoxycarbonyl) benzophenone (BTTB: manufactured by NOF) is 10% by weight based on the solid content, and a ketocoumarin dye (3,3-carbonylbis (7-diethylaminocoumarin) as a visible light sensitizer; KCD) was mixed at 0.5% by weight with respect to the solid content. Thereafter, the reaction product is cast and dried to about 1
Thin sections with a thickness of from 00 to 200 μm were obtained. In addition, when the organic component was small, it was very fragile, so that it was dried slowly for about one week, and coated with an inert material such as gold to prevent it from adhering to the material to be cast. Finally, Ar laser 514.
The material was uniformly irradiated with light of 5 nm to polymerize the monomer.

Thereafter, a heat treatment was performed at 160 ° C. to obtain a target material. By performing the heat treatment at a temperature exceeding 150 ° C. in this manner, water or alcohols added as a solvent in the process of adjusting the reaction solution can be volatilized, and these can be prevented from remaining in the material. . Accordingly, it is possible to suppress volatilization of these solvents after the element is formed and to suppress the material from shrinking, and it is possible to reduce a temperature change of the optical element. However, it is necessary to set the heating temperature according to the organic component so that the organic component in the material created by heating is not decomposed. Generally, at most 400 ° C. or less.

This material was set as an experimental sample 6 in a Mach-Zehnder interferometer comprising a half mirror 5, a first mirror 3, a second mirror 4 and a photodetector 7 shown in FIG. It was heated by an element (not shown). The incident light 10 is incident upon heating and the photodetector 7
Was measured, and the degree of deviation of the optical path length was measured. The thickness of the sample used for the measurement was 150 μm. The temperature was varied from room temperature to 60 ° C. The change rate of the optical path length is calculated from the change of the interferometer, and the result is shown in FIG.
Shown in When Formula 1 or Formula 5 was satisfied, it was found that the organic component was in the range of 10 to 2%.

In this embodiment, the change in the optical path length was checked by the interferometer. This is for the purpose of evaluating the material and is not directly related to the application. This is a material that is basically used for producing lenses.

As a starting material of an organic compound for forming this material, all carbon compounds except carbon oxides and metal carbonates, especially compounds having a hydrocarbon group can be applied. The photopolymerizable monomer is not limited to the above HFPA, and various monomers containing a vinyl group, an acryl group, a methacryl group, an allyl group, and the like can be used. As a starting material for the inorganic compound, metal halides, metal complexes, and the like can be used in addition to the metal alkoxide represented by TEOS.

However, when a specific organic compound and an inorganic compound are mixed, phase separation and whitening may occur due to poor compatibility. For example, when the organic compound does not contain a functional group (for example, an amide bond, an imide bond, a urethane bond, or the like) that easily bonds to a hydroxyl group such as a silanol group generated in a process of generating an inorganic compound, Problem arises. On the other hand, when an organic-inorganic composite in which an organic compound and an inorganic compound are bonded at the time of a raw material is used, there is an effect that compatibility is improved. As such an organic-inorganic composite, it is preferable to use vinyl silane, acryl silane, methacryl silane, or the like.

[0023]

The present invention provides a material for an optical element useful for compensating for temperature fluctuations in the optical path length in an optical system composed of an optical element and a space. The characteristics of the entire optical system including an optical element made of the material of the present invention, for example, a prism, a lens, and a reflection / transmission type diffraction grating are not affected by temperature. Therefore, it is not necessary to newly prepare a temperature compensating means, and a highly reliable optical element can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an optical path length and a temperature change of the optical path length.

FIG. 2 is an arrangement diagram of an interference optical system for measuring an optical path length change.

FIG. 3 is a diagram showing the relationship between the optical path length temperature dependency and the composition obtained from an interferometer experiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical medium 2 Optical medium when temperature rises 3 Mirror 4 Mirror 5 Half mirror 6 Experimental sample 7 Photodetector 10 Incident light

Claims (8)

[Claims] An optical element including a solid material and a space made of air or vacuum in an optical path, wherein a material constituting an optical path of the optical element is a mixture or a composite of first and second materials. An optical element, wherein the two materials have opposite signs of temperature coefficient of refractive index. 2. The optical element according to claim 1, wherein the first material is an organic material, and the second material is an inorganic material. 3. The composition ratio of the organic material is 2 mol% or more and 1 or more.
The optical element according to claim 2, wherein the content is 0 mol% or less. 4. The optical element according to claim 1, wherein the organic material is a material mainly composed of hydrocarbons and / or hydrocarbon derivatives. 5. The method according to claim 1, wherein the inorganic material is SiO ₂ , TiO ₂ , Ge.
O ₂ , Al ₂ O ₃ , ZrO ₂ , B ₂ O ₃ , Na ₂ O, MgO,
The optical element according to claim 1, wherein the optical element is a glass material containing at least one of CaO as a component. 6. The optical element according to claim 1, wherein the composite is synthesized using a starting material as an organic-inorganic composite. 7. The optical element according to claim 1, wherein a heat treatment is performed at a temperature exceeding 150 ° C. in a manufacturing process. 8. The optical element according to claim 1, wherein the optical element is any one of a laser medium, a lens, a prism, a reflection / transmission type diffraction grating, and a beam splitter.