JPS6187101A - Artificial double refracting medium - Google Patents

Abstract

PURPOSE:To make controllable the magnitude of a main refractive index and double refraction by laminating alternately two kinds of amorphous dielectric materials having different refractive indices at the period substantially smaller than the wavelength of light. CONSTITUTION:Two kinds of the amorphous dielectric materials 1 and 2 which have different refractive indices and are alternately laminated at the period substantially smaller than the wavelength of light are disposed on a substrate 3 and the artificial refracting medium is constituted of the periodic multi-layered films consisting of the materials 1 and 2. The multi-layered films act as the negative uniaxial double refracting medium of which the optical axis is the normal 4 of the layers. The magnitude of the main refractive index and double refraction can be changed simply by changing the ratio of the multi-layered films with the period. The larger double refraction than heretofore is realized with some materials. The artificial constitution of the double refracting medium having optional and desired characteristics is thus made possible by changing the main refractive index and double refraction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an artificial birefringent medium whose principal refractive index and magnitude of birefringence can be controlled.

[Prior art] Conventionally, birefringent crystals have been used as birefringent media, so the principal refractive index and the magnitude of birefringence are fixed as constants unique to the crystal, and there is a drawback that they cannot be artificially controlled. there were.

Furthermore, since birefringent crystals have severe restrictions on lattice matching with the substrate and growth temperature, they have the drawback of being difficult to fabricate on other materials.

Additionally, many birefringent crystals have deliquescent properties.

On the other hand, since amorphous dielectrics are optically isotropic, they have the disadvantage that they cannot be used as birefringent media.

[Objective] The object of the present invention is to solve these drawbacks and provide an artificial birefringent medium in which the principal refractive index and the magnitude of birefringence can be controlled.

[Structure of the Invention] In order to achieve the above object, in the present invention, two types of amorphous dielectric materials having different refractive indexes are alternately laminated at a period sufficiently smaller than the wavelength of light, thereby forming an amorphous dielectric material. An artificial birefringent medium is constructed in which the principal refractive index and the magnitude of birefringence can be controlled by the refractive index and layer thickness of two types of laminated amorphous dielectrics.

[Example] The present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, where ■ and 2
are alternately layered at a period sufficiently smaller than the wavelength of light,
There are two types of amorphous dielectrics having different refractive indexes, and these amorphous dielectrics 1 and 2 are arranged on a substrate 3. The refractive indices of amorphous dielectrics 1 and 2 are nl and 12 (#
n+), and the thickness of each layer is dl and d2, respectively.
It is. In this way, in the present invention, the amorphous dielectrics 1 and 2
The artificial refractive medium is composed of a periodic multilayer film consisting of.

Such periodic operation of the multilayer film is based on the principle described below.

Now, since the period Δ-dl +d2 of such a multilayer film is sufficiently small compared to the wavelength of light, this multilayer film can be regarded as a homogeneous medium for light, and its optical properties are expressed by a dielectric tensor ε. Cartesian coordinates! If +L2 is taken as shown in Figure 1, ε is ε6 = fln, 2+r2n2" ε6 = (ft nI-"+f2 n2-'door<ε
It becomes 0. However, ft "dx /Δ*f2-d2
/Δ-1-f are the ratios of the layer thicknesses of the amorphous dielectrics l and 2, respectively, to the period.

Therefore, this multilayer film operates as a negative uniaxial birefringent medium whose optical axis is the Z axis, that is, the layer normal 4. The principal refractive index no +ne and the magnitude of birefringence Δn for ordinary light and extraordinary light are respectively no 4 = (ft nl”
+(1-ft)nz2)+(1)ne4=(f
tni2+(1-ft)nz-")-"
(2) Δns n□ −n6
(3), 'l, 11 +! 1
It is possible to control by 2. Therefore, even with the same combination of materials, nQ +ne +Δn can be changed simply by changing the ratio fl to the period of the multilayer film.

Furthermore, depending on the material, it is possible to achieve greater birefringence than conventional birefringent crystals.

Alternatively, the dispersion due to the periodic structure can be reduced by making 8 sufficiently smaller than λ.

Furthermore, amorphous 5! j Since dielectrics 1 and 2 are amorphous, there is no need for lattice matching, and they can be fabricated on other materials at low temperatures using sputtering, ECR-type plasma deposition, vapor deposition, etc. It is.

Note that amorphous dielectrics are stable because they are less deliquescent than conventional birefringent crystals.

The artificial birefringence medium of the present invention has controllable optical properties as described above and can be easily fabricated on other materials, so it requires precise refractive index control and requires semiconductors,
It is useful as a birefringent material for optical integrated circuits, which requires combination with different materials such as magneto-optic crystals and electro-optic crystals.

FIG. 2 shows that in the above-described embodiment, an amorphous quartz substrate is used as the substrate 3, and an amorphous dielectric layer 1.2 formed of Ta205 (ditantalum pentoxide) is formed thereon.

nI=2.2), 5i02 (silicon, n
2-1.5) when formed by sputtering method
It shows the relationship between ne +Δn and f.

Here, both 5i02 and Ta2o5 are transparent in a wide wavelength range from visible to near infrared, that is, have low loss, and have a relatively large difference in refractive index, so that a large birefringence can be obtained. Furthermore, since 5i02 and Ta205 are mechanically stable, they can be manufactured in the same process, and a mixture can be formed in any ratio, so that when laminated, the adhesion of the interface between the two is good.

In FIG. 2, the solid line 5. Broken line 6. The dash-dotted lines 7 are nQ, +16, respectively. It is a theoretical value of Δn, and it is an experimental value, which was measured in the vicinity of λ to 840 nm for an artificial birefringent medium with A m35nta and a total number of 100 layers. These experimental values are in good agreement with the theoretical values, and fl
This shows that nQ one +Δn can be controlled by .

In this experiment, a birefringence of ΔnmO, 13 was obtained at f1=o, 52, but this value is smaller than Δrl of calcite (CaCO3), which is a typical birefringent crystal used conventionally.
This is a large value on par with 0.17, indicating that the present invention is useful also in terms of the magnitude of birefringence.

Figure 3 shows the measurement results of the dispersion characteristics of the above-mentioned artificial birefringent medium. By making 8 sufficiently smaller than the input, the dispersion is extremely large over a wide range of input of 30.5 to 2.0 #Lm. It shows that it has become smaller.

In the above embodiment, Ta205 is used as the amorphous dielectric 1.
Similar results can be obtained by using diniobium pentoxide NbzOs (nt·2.2), which has properties similar to Ta205, instead of Ta205.

Furthermore, in the above embodiment, the amorphous dielectric 1 or 2
) Alternatively, if a mixture of 5i02 and Ta2Q5 or Nb2O5 is used as 1 and 2, "l +12" can be freely changed according to the mixture ratio, so "
By setting + +"2 off to an appropriate value, an artificial birefringence medium having a desired "O+"e + Δn can be constructed.

Furthermore, in the above embodiments, the amorphous dielectric 1 or 2) or 1 and 2 may be 5iNx (refractive index 1.
7-3.5) or 5iOx (0 to X≦2) (refractive index!
, 5 to 3.5), depending on the composition ratio
Change +n2 to any desired value. Because you can
By setting ``1'' and n2off to appropriate values, an artificial birefringent medium having a desired ``Oone +Δn'' can be constructed.

In addition, in the above-mentioned embodiment, the case where the number of cycles of the multilayer film was 100 was shown, but sufficient effects can be obtained if the number of layers is several cycles or more.

[Effect] As explained above, the principal refractive index nQ one and the magnitude of birefringence Δn of the artificial birefringent medium of the present invention can be determined by the refractive index and layer thickness of the amorphous dielectric material. By changing these, there is an advantage that a birefringent medium having any desired characteristics can be artificially constructed.

In addition, since the artificial birefringent medium of the present invention is amorphous, it has the advantage of not requiring crystal growth and can be easily produced on other materials, and has the advantage of not being deliquescent.

Therefore, if the artificial refractive medium of the present invention is used in an optical integrated circuit, it will come into contact with other materials such as semiconductors, electro-optic crystals, and magneto-optic crystals to form a birefringent medium whose refractive index is matched to that of other materials, allowing light to pass through. It has the advantage of being able to control polarization.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the present invention, FIG. 2 is a characteristic curve diagram showing an example of the dependence of the principal refractive index and birefringence on the layer thickness ratio f1 of the present invention, and FIG. FIG. 2 is a characteristic curve diagram showing an example of the dispersion characteristics of the principal refractive index for ordinary light according to the present invention. l...Amorphous dielectric. 2...Amorphous dielectric, 3...Substrate. 4... Layer normal, 5... Principal refractive index (ordinary light). 6... Principal refractive index (extraordinary light), 7... Magnitude of birefringence. 1.2-1--Amorphous dielectric material 3-----1 substrate 4-----1 method butterfly Fig. 2 0 0.2 0.4 0.6 0.8
1.0λ (J, 1m)

Claims (1)

[Scope of Claims] 1) An artificial birefringent medium characterized in that it is constructed by alternately laminating two types of amorphous dielectric materials with different refractive indexes at a period sufficiently smaller than the wavelength of light. 2) The artificial birefringent medium according to claim 1, wherein the two types of amorphous dielectrics are silicon dioxide and ditantalum pentoxide or diniobium pentoxide. . 3) In the artificial birefringent medium according to claim 1, at least one of the two types of amorphous dielectrics is silicon dioxide, ditantalum pentoxide, or pentoxide, the refractive index of which can be controlled by changing the mixing ratio. An artificial birefringent medium characterized by being a mixture with diniobium. 4) In the artificial birefringent medium according to claim 1, at least one of the two types of amorphous dielectrics is silicon nitride or silicon oxide whose refractive index can be controlled by changing the composition ratio. An artificial birefringent medium characterized by using.