JP2012181490A - Oxide material having small temperature dependence of optical path length - Google Patents

Abstract

Disclosed is a material having a small temperature dependency of an optical path length that can be used for optical communication and an optical integrated circuit substrate.
A was added LaAlO ₃ in _{SrTiO 3 (Sr 1-X,} La X) (Ti 1-X, Al X) is _{O 3} composite oxide materials, 0 <X <0.80 optical path length in the range of Temperature coefficient (OPD, where OPD = 1 / S · dS / dT = CTE + 1 / n · dn / dT, where S is the optical path length, CTE is the linear thermal expansion coefficient, n is the refractive index, dn / dT Is the temperature coefficient of the refractive index), and particularly in the range of 0.04 <X <0.80, its absolute value is 6 ppm / ° C. or less, and the temperature dependence of the optical path length is extremely small, and optical communication It can be used for filters, optical integrated circuit boards, etc.
[Selection] Figure 4

Description

The present invention relates to a composite oxide material suitable for use in an optical communication device, an optical integrated circuit device, particularly an etalon filter, and a method for producing the same, and an etalon filter substrate and a diffraction grating substrate using the composite oxide material, The present invention relates to an optical integrated circuit substrate.

In optical communication systems and related laser systems, there is a wavelength division multiplexing method as a method for transmitting a large amount of signals at high speed. In this wavelength division multiplexing system, the amount of information transmitted at a time can be increased by transmitting a signal having a wavelength difference as narrow as possible. For this reason, the wavelengths of different channels are very close to each other, and in order to correctly transmit and receive signals of wavelengths close to each other, it is necessary that the characteristics with respect to the wavelengths of signals used for optical communication are stable. is there. An etalon filter is used for the purpose of stabilizing the wavelength of the signal, stabilizing the optical output and selecting the wavelength. An etalon filter has a substrate made of a light transmission medium, and forms a reflection film on both the light incident surface side and the light output surface side of this substrate to reflect the passing light, thereby making the optical signal a standing wave. Thus, the pass band is limited, wavelength multiplexing of a plurality of optical signals is enabled, and optical transmission is facilitated within a predetermined band. Since this filter selectively converts an optical signal having an optical path length that is an integral multiple of the wavelength into a standing wave, its performance greatly depends on the optical path length of the substrate. Therefore, in order to obtain a stable light output, it is important that the material used for the substrate of the etalon filter has a constant optical path length.

However, conventionally known substrate materials have optical path lengths that change with temperature changes. When the optical path length changes, the wavelength of the output optical signal also changes. Therefore, it cannot be used in a wavelength division multiplexing system that transmits a signal having a narrow wavelength difference.

The optical path length and the temperature dependence of the optical path length can be expressed by the temperature coefficient (OPD) in the following (Equation 1).
Optical path length S = n · l
Optical path length temperature coefficient (OPD)
(1 / S) · (dS / dT) = CTE + (1 / n) · (dn / dT) (Formula 1)
Here, l is the thickness of the light transmission medium, CTE is the linear thermal expansion coefficient of the light transmission medium, n is the refractive index of the light transmission medium, and dn / dT is the temperature coefficient of the refractive index.

In order to prevent the temperature change of the optical path length, there are the following methods. The first method is to perform strict temperature control. However, in order to perform strict temperature control, it is necessary to attach a temperature control unit or the like. Therefore, there are problems that the device size becomes large, the cost is high, and the power consumption is necessary.

The second method is to give a thickness change in a direction to cancel the temperature change (dn / dT) of the refractive index. When a temperature change is given to the material, the refractive index and the thickness change, and the optical path length (S = n · l) represented by the product of the refractive index and the thickness changes. Therefore, there is a method of offsetting the temperature change of the refractive index with the thickness change by making the length change negative by sticking a substrate material having a positive dn / dT and a correction member having a negative CTE around the substrate material. It has been proposed (for example, Patent Document 1, Patent Document 2, and Patent Document 3). However, in such a configuration, there is still a problem of an increase in size and cost due to an increase in the number of parts.

As a third method, a method in which a material having a positive optical path length temperature coefficient and a material having a negative optical path length temperature coefficient are bonded together or mixed has been proposed. Examples of such a material include a material in which an oxide single crystal material having a negative optical path length temperature coefficient is bonded to an oxide glass material having a positive optical path length temperature coefficient (for example, Patent Document 4), or a positive optical path length temperature. There are materials (for example, Patent Document 5, Patent Document 6, and Patent Document 7) in which inorganic particles having a coefficient are dispersed in a polymer having a negative optical path length temperature coefficient. However, such a material has a problem that reflection and scattering by the material interface increase and transmittance decreases.

As a fourth method, there is a method using a material having a relatively small change in temperature of the optical path length. As such a material having a small optical path length temperature coefficient, quartz glass, quartz, LiNbO ₃ , LiTaO ₃ , LiCaAlF _{6 and the} like have been proposed (for example, Patent Document 8, Patent Document 9, and Patent Document 10). Among the materials described above, materials having optical isotropy include 6.2 ppm / ° C. even in quartz glass having the smallest optical path length temperature coefficient, and quartz, LiNbO ₃ , LiTaO ₃ , and LiCaAlF ₆ are anisotropic materials. There is a problem that the usable orientation is limited. In addition, a crystal material having an optical path length temperature coefficient that is positive and negative depending on the crystal axis is tilted to an angle that cancels the positive and negative changes with respect to the incident light, and a substrate having an orientation that does not substantially change the temperature of the optical path length. Although there is a method to be used (for example, Patent Document 11), there is a problem that polarization dependency occurs due to the use of the tilt of the crystal axis, and the incident direction is limited.

As a fifth method, an air gap type etalon filter using air with a small refractive index temperature change as a substrate has been developed. The air gap type has a structure with no thermal expansion / small air gap and a reflective film on both end faces of the air gap. However, the filter size is smaller than a solid etalon using a solid material for the substrate. There is a disadvantage that it is large. A solid etalon made of a substrate on which a reflective film is formed is easy to construct and is excellent in size and cost. Therefore, there is a demand for a material that can be used for a solid etalon filter and has a small temperature change in optical path length.

JP 2000-352633 A JP-A-9-257567 JP 2001-221914 A JP 2005-10734 A JP 2001-201601 A JP 2006-193398 A WO 2001/113963 JP 2004-226425 A JP 2006-78914 A JP 2006-78915 A JP 2003-270434 A

An object of the present invention is to obtain a material having no optical anisotropy and a change in optical path length due to a temperature change that is 0 or negligibly small. Furthermore, by using this material as a member that requires stability of the optical path length, such as an etalon filter, strict temperature control is not required and downsizing is possible, but a large amount of optical signals can be processed stably. An object of the present invention is to provide an optical device such as an optical communication element and an optical integrated circuit.

As a result of intensive studies and studies to solve the above-mentioned problems, the present inventors have arranged perovskite type (ABO ₃ ) oxide materials having different optical characteristics and arranged at the A site and / or the B site. It has been found that the temperature dependence of the optical path length can be arbitrarily changed by adjusting the combination and blending of the components, and the present invention has been achieved. Specifically, the present invention provides the following.

(1) A perovskite type (ABO ₃ ) oxide material having an absolute value of an optical path length temperature coefficient (OPD) with respect to a wavelength of 1553 nm of 6 ppm / ° C. or less in a temperature range of −20 to 80 ° C. (Where OPD is a characteristic represented by (1 / n) × (dn / dT) + CTE by refractive index n and linear thermal expansion coefficient CTE, and A is Na, K, Rb, Cs, Ag, Ca, One or more selected from Sr, Ba, Zn, Pb, Y, Ln (lanthanoid), Bi, B is selected from Ti, Zr, Hf, Al, Ga, In, Si, Ge, Sn, V, Nb, Ta One or more ingredients)
(2) The oxide material according to (1), wherein the perovskite (ABO ₃ ) oxide contains Sr and La, and Ti and Al.
(3) (Sr _1-X , La _X ) (Ti _1-X , Al _X ) O ₃ (0.04 <X <0.80) The oxide material described.
(4) Doped with one or more components selected from Na, K, Rb, Cs, Ag, Ca, Ba, Zn, Y, Ln ¹ (Ln ¹ is a lanthanoid other than La), Pb, and Bi (3 ) The oxide material described.
(5) The oxide material according to (3) or (4), doped with one or more components selected from Zr, Hf, Ga, In, Si, Ge, Sn, V, Nb, and Ta.
(6) The oxide material according to any one of (1) to (5), which is a single crystal.
(7) An etalon filter substrate including the oxide material according to any one of (1) to (6).
(8) A solid etalon filter including the etalon filter substrate according to (7).
(9) An optical integrated circuit substrate containing the oxide material according to any one of (1) to (6).
(10) A diffraction grating substrate comprising the oxide material according to any one of (1) to (6).

According to the present invention, it is possible to obtain a material whose temperature change of the optical path length is 0 or so small that it can be ignored. When an element or member using this material is used in an optical device such as an optical communication filter or an optical integrated circuit board, a device or device for canceling the change in the optical path length of the material due to a temperature change, such as strict temperature control or thickness control. Therefore, the element and the device using the element can be simplified, reduced in size, and reduced in cost. In addition, since this material has a high refractive index and no optical anisotropy, a member such as a substrate can be miniaturized, and the direction of use is not limited, and the material can be easily processed. As a result, it is possible to provide an optical device such as an optical communication element or an optical integrated circuit that does not require equipment for temperature control and is small in size and excellent in temperature stability and capable of stably processing a large amount of optical signals. .

_{(Sr 1-X, La X} ) (Ti 1-X, Al X) O 3 relationship crystal structure and composition of the single crystal _{(Sr 1-X, La X} ) (Ti 1-X, Al X) O 3 refractive index relationship between the composition of the single crystal Transmittance of (Sr _1-X , La _X ) (Ti _1-X , Al _X ) O ₃ single crystal Relationship between composition of (Sr _1-X , La _X ) (Ti _1-X , Al _X ) O ₃ single crystal and temperature coefficient of optical path length Relationship between composition of (Sr _1-X , La _X ) (Ti _1-X , Al _X ) O ₃ single crystal and average linear thermal expansion coefficient

Hereinafter, although embodiment of this invention is described, this invention is not limited to this.

The oxide material according to the present invention is a perovskite type (ABO ₃ ) oxide, and the absolute value of the optical path length temperature coefficient (OPD) with respect to a wavelength of 1553 nm is 6 ppm / ° C. or less in a temperature range of −20 to 80 ° C. (Where OPD is a characteristic expressed as (1 / n) × (dn / dT) + CTE by the refractive index n and the linear thermal expansion coefficient CTE, and A is Na, K, Rb, Cs , Ag, Ca, Sr, Ba, Zn, Pb, Y, Ln (lanthanoid), Bi or more, B is Ti, Zr, Hf, Al, Ga, In, Si, Ge, Sn, V, One or more components selected from Nb and Ta). The reason why the temperature coefficient of the optical path length, the crystal system, and the composition of the oxide material of the present invention are limited as described above will be described below.

First, regarding the optical path length temperature coefficient (OPD), for example, at 1553 nm, if the absolute value exceeds 6 ppm / ° C., the optical communication device requires extremely precise temperature control. Needs to be 6 ppm / ° C. or less, particularly 5 ppm / ° C., and more preferably 3 ppm / ° C. or less in order to completely eliminate the need for temperature control in high-speed communication at 100 GHz or less.

The wavelength range in which the optical path length temperature coefficient (OPD) is low is not limited to 1553 nm. By designing a material having a low optical path length temperature coefficient at the wavelength of 1553 nm, the wavelength range of 1260 to 1675 nm generally used for optical communication wavelengths is used. The optical path length temperature coefficient can be lowered even for wavelengths in the optical communication wavelength range.

Perovskite-type oxides are mainly used as dielectrics, but it is known that their properties against electromagnetic waves change greatly due to solid solution and doping. Can change the characteristics. Moreover, it is a few materials in which the temperature change of the refractive index and the optical path length exists from positive to negative in the material of the same crystal structure, and each site can contain many components. Therefore, by using a perovskite type oxide having different optical characteristics, adjusting the combination and composition of components arranged at the A site and / or B site, the refractive index and its temperature dependence, linear thermal expansion coefficient It is possible to design materials that control the crystal system. Here, the crystal system of the perovskite oxide material according to the present invention is preferably a cubic crystal having no optical anisotropy.

Among the perovskite oxides, SrTiO ₃ has a cubic perovskite structure and is an optically isotropic material, and the optical path length temperature coefficient is negative −10.5 ppm / ° C. On the other hand, LaAlO ₃ has a rhombohedral perovskite structure which is a pseudo-cubic crystal and has a positive optical path length temperature coefficient. The (Sr, La) (Ti, Al) O ₃ composite oxide in which these two types of oxides are combined can change the temperature dependence of the optical path length from positive to negative, and the temperature of the optical path length is substantially reduced. A material with a coefficient of zero can be obtained.

Here, in order to control the optical path length temperature coefficient (OPD), the ratio of the components arranged at the A site and the B site of the composite oxide is (Sr _1-X , La _X ) (Ti _1-X , Al _X ) O ₃ (0.04 <X <0.80) is preferred. In the range of X ≧ 0.80, the optical path length temperature coefficient does not change depending on the composition, so that it becomes difficult to control the optical path length temperature coefficient. In terms of obtaining a material having a low optical path length, the upper limit of X is preferably smaller than 0.8, more preferably 0.60, and most preferably 0.45. Similarly, the lower limit of X is preferably more than 0.04, more preferably 0.05, and most preferably more than 0.05 because a material having a low optical path length can be obtained.

In particular, when X does not exceed 0.45, the phase transition temperature from cubic crystal to rhombohedral crystal or tetragonal crystal of the composite oxide is lower than −20 ° C., which is the lower limit of the operating temperature, and therefore the operating temperature range. Since the crystal structure at −20 to 80 ° C. is cubic and optical anisotropy does not occur, it is most preferable that X does not exceed 0.45.

If the refractive index is high, the optical path length of the material becomes long, so that the etalon filter element and the optical integrated circuit substrate can be thinned and miniaturized. Therefore, the refractive index should be high. For example, the refractive index with respect to 1553 nm light is 2.1 or more. Is good.

When the crystal system is cubic, it is optically isotropic and can be used without limitation in the direction of use. SrTiO ₃ is −160 ° C. or higher, LaAlO ₃ is cubic at 435 ° C. or higher, and (Sr _1-X , La _X ) (Ti _1-X , Al _X ) O ₃ composite oxide has a large X value. Then, the minimum temperature in the temperature range for maintaining the cubic crystal becomes high, but it becomes cubic at −20 ° C. or higher at X = 0.45, and at room temperature (25 ° C.) or higher at X = 0.5.

In order to adjust the melting point, the crystal system, the lattice constant, etc., the oxide material in the present invention is 1 out of lanthanoids other than Na, K, Rb, Cs, Ag, Ca, Ba, Zn, Y, La, Pb, and Bi. A seed or two or more kinds can be added together. These are components that are mainly substituted and dissolved at the A site, but may be substituted at other sites or infiltrated to the outside of the site.

Furthermore, the oxide material in this invention can add 1 type (s) or 2 or more types from Zr, Hf, Ga, In, Si, Ge, Sn, V, Nb, Ta together. These are components that are mainly substituted and dissolved at the B site, but may be substituted at other sites or infiltrated to the outside of the site. Moreover, you may contain another component in the range which does not disturb the temperature characteristic and transmittance | permeability of an optical path length.

The oxide material in the present invention is transparent, and can be used in the form of transparent / translucent ceramics or single crystals. In particular, since there is no grain boundary and the crystal orientation is uniform, light scattering is small, and a single crystal is preferable because of high transmittance.

Hereinafter, the manufacturing method of the oxide material of this invention is demonstrated. The manufacturing method of the oxide material according to the present invention is known from a powder, a sintered body or a melt, such as FZ method, Bernoulli method, CZ method, EFG method, Bridgman method, μ-PD method, vapor phase growth method, etc. It can be produced as a single crystal of a complex oxide by the single crystal growth method, or can be produced as a translucent ceramic by a production method such as vacuum sintering, pressure sintering, or discharge sintering.

As an example, a case where a single crystal is manufactured using the FZ method will be described. When the oxide of the present invention is produced by the FZ method, (a) a step of preparing a raw material, (b) a step of preparing a raw material rod, (c) a raw material rod is heated and melted, and a single crystal is arranged on the facing seed crystal. There is a process of growing crystals.

(A) The process of preparing a raw material has the following means, for example.
(1) The starting material is weighed to a desired ratio.
(2) Mix and grind the weighed raw materials.
(3) Calcination of the mixture.
(4) The calcined powder is pulverized.
The raw material may be in the form of oxide, hydroxide, carbonate, nitrate, sulfate, various alkoxides, and the like. In mixing and pulverization, an organic solvent such as pure water or alcohol can be added to form wet pulverization, and a ball mill, a planetary mill, or the like may be used. In order to sufficiently react the raw material mixed powder, methods such as (3) calcination and (4) repeated pulverization several times, and controlling the atmosphere during calcination can be used singly or in combination. When salts are used as the raw material, the reaction of the raw material is promoted by setting the atmosphere to gas flow or reduced pressure, and the raw material calcined powder can be obtained efficiently. The calcination temperature is preferably 1000 ° C. or more, and the calcination time is preferably 1 hour or more.

(B) The process of preparing the raw material rod includes, for example, the following processes.
(1) The raw material is molded.
(2) Sinter the compact.
As a forming method, a uniaxial press, a cold isostatic press (CIP), a hot press (HP), a hot isostatic press (HIP), extrusion, injection, casting, or the like can be used. In the hot press and hot isostatic press, molding and sintering can be performed simultaneously. The mold used for molding can be made of rubber, metal, ceramics, or the like. The sintering temperature is preferably 1500 ° C. or higher, and the sintering time is preferably 1 hour or longer.

(C) The process of heating and melting the raw material rod to grow a single crystal on the seed crystal includes, for example, the following processes.
(1) A raw material rod and a seed crystal are arranged opposite to each other at both ends of the heating unit.
(2) The tip of the raw material rod is heated and melted and brought into contact with the seed crystal.
(3) The heating and melting part (melting zone) is moved to the raw material rod side, and a single crystal is grown on the seed crystal.
(4) Separate the grown single crystal from the raw material rod and seed crystal.
A refractory metal wire can be used for fixing the raw material rod and the seed crystal, and platinum rhodium wire is preferred particularly in an oxidizing atmosphere.

The seed crystal is a LaAlO ₃ single crystal or sintered rod, a sintered rod having the same composition as the raw material, a grown (Sr, La) (Ti, Al) O ₃ single crystal, or a SrTiO ₃ single crystal or sintered rod. Can be used.

In the SrTiO ₃ -LaAlO ₃ system, the composition of the melting zone is different from that of the raw material rod and the grown single crystal, so the single crystal composition immediately after the start of growth is not stable. By disposing a solvent between them, a single crystal having a desired composition can be grown from the initial growth stage. The solvent here is an amount of the solvent composition that is the same volume as the volume of the molten zone being grown, or the amount of strontium aluminate calculated to become a solvent composition of the molten zone volume when mixed and melted with the raw material rod. The solvent composition is a self-flux containing more Al and / or Sr than the single crystal composition.

During the growth of the single crystal, the raw material rod and / or the seed crystal can be rotated and stirred, and the growth crystal having a thickness different from that of the raw material rod can be obtained by changing the moving speed of the raw material rod and the seed crystal relative to the heating part. Is possible.

  For physical property adjustment, lanthanoids other than Na, K, Rb, Cs, Ag, Ca, Ba, Zn, Y, La, Pb, Bi, Zr, Hf, Ga, In, Si, Ge, Sn, V, Nb, When adding Ta etc., it can add in the process of preparing (a) raw material powder and / or (b) preparing a raw material stick | rod.

The method of the present invention is not limited to the method described above. For example, the raw material rod does not have to be a sintered body, and if a (Sr, La) (Ti, Al) O ₃ -based single crystal obtained by growth is used as a raw material rod and a seed crystal, It becomes easy to obtain a high-quality single crystal.

When the Bernoulli method is used as another method for producing a single crystal, the method includes (a) a step of preparing raw material powder, and (b) a step of growing the single crystal by gradually depositing the raw material powder on a seed crystal through a flame. Can do. For the step (a), the means described above in the FZ method can be used, and for the step (b), known means in the Bernoulli method can be used.

When the CZ method is used as another method for producing a single crystal, for example, a top seed CZ method using a self-flux or a double crucible CZ method can be selected. In the CZ method, (a) a step of preparing a raw material and a flux, (b) a step of putting the raw material and a flux into a crucible to form a heated melt, (c) a seed crystal is brought into contact with the heated melt and crystallized while rotating. A step of pulling up. For the step (a), the means described above in the FZ method can be used, and for the steps (b) and (c), known means in the CZ method can be used, and the crystal can be pulled up while supplying the raw materials. it can.

In the case of the EFG method as another method for producing a single crystal, (a) a step of preparing a raw material, (b) a step of charging the raw material into a crucible to form a heated melt, (c) a die immersed in the heated melt The step of bringing the seed crystal into contact with the melt sucked up by the step of pulling up the crystal can be included. For the step (a), the means described above in the FZ method can be used, and for the steps (b) and (C), known means in the EFG method can be used.

In the case of the Bridgman method as another method for producing a single crystal, a raw material dropping Bridgman method or the like can be used, (a) a step of preparing the raw material, (b) putting the raw material into a crucible, and contacting the seed crystal And (c) a step of heating and melting a contact portion between the raw material and the seed crystal, melting the raw material, and growing a single crystal while cooling from the seed crystal side. For the step (a), the means described above in the FZ method can be used, and for the step (b), known means in the Bridgman method can be used. In the step (b), the solvent described by the FZ method may be disposed between the raw material and the seed crystal.

In the case of a vapor phase growth method as another method for producing a single crystal, (a) a step of preparing a raw material, (b) a step of forming and sintering the raw material to prepare a target, (c) a target being vaporized, and a substrate A step of laminating the single crystal to grow a single crystal can be included. For the steps (a) and (b), the means described above in the FZ method can be used, and for the step (c), known means in the vapor phase growth method can be used. For example, two or more targets separated from components such as SrTiO ₃ and LaAlO ₃ may be used.

In the method for producing an oxide material according to the present invention, an infrared ray, a carbon heater, a metal heater, a high frequency, or the like can be used as a heat source, and a preheating heater or an after heater may be used as necessary. The atmosphere during production is not particularly limited, but an inert atmosphere is preferable when a carbon or metal heater is used. In the single crystal of the present invention, the transmittance of the material may be reduced depending on the manufacturing atmosphere, but the transmittance can also be improved by performing annealing treatment on the obtained oxide material. The annealing treatment is desirably an oxidizing atmosphere and 1000 ° C. or higher.

(Examples and Comparative Examples)
Examples and Comparative Examples were prepared by the following procedure. SrCO ₃ (manufactured by high purity chemical, 3N), TiO ₂ (manufactured by high purity chemical, 4N), La ₂ O ₃ (manufactured by high purity chemical, 4N) or La (OH) ₃ (manufactured by high purity chemical, 4N), Al Starting powder of ₂ O ₃ (Iwatani Chemical Industries, RA-40, 4 Nup) or Al (OH) ₃ (High Purity Chemical, 4N) was weighed and mixed in ethanol at 1500 ° C. For 5 hours and then wet pulverized in ethanol. The obtained calcined powder was further fired and pulverized, and dried to obtain a raw material powder.

The obtained raw material powder was filled into an elongated rubber tube, pressed at 3 t / cm ² with hydrostatic pressure for 1 minute, and formed into a round bar shape with a diameter of 3-6 mm. This molded body was sintered in the atmosphere at 1500-1700 ° C. for 3-10 hours to obtain a raw material rod.

Using the obtained raw material rod, crystal growth was performed with an infrared condensing device (FZ-T-800H manufactured by Crystal System Co., Ltd.). A 20% Rh-Pt line was used for setting the raw material rod and the seed crystal. The seed crystal used was a (Sr _1-X , La _X ) (Ti _1-X , Al _X ) O ₃ sintered body having the same composition, and the composition, growth rate, and growth atmosphere of the single crystal are shown in Table 1. Stirring was performed by rotating the seed crystal and the raw material bar in reverse.

Grown _{(Sr 1-X, La X} ) (Ti 1-X, Al X) for _{O 3} single crystal, the crystal structure XRD (Philips X'pert-MPD), composition electron probe microanalyzer (JEOL ( JXA-8200 manufactured by Co., Ltd.), refractive index is Metricon prism coupler 2010, transmittance is spectrophotometer (U-4100 manufactured by Hitachi High-Technologies Corporation), average linear thermal expansion coefficient is thermal dilatometer (TD5030SA manufactured by Bruker) The optical path length temperature coefficient (OPD) was evaluated by a method of measuring the change due to the temperature of the interference light on both end surfaces subjected to parallel plane polishing in the range of -20 to 80 ° C. Table 2 shows the crystal system, growth orientation, OPD, refractive index at 1553 nm, and average linear thermal expansion coefficient.

FIG. 1 shows the relationship between the composition and lattice constant of (Sr _1-X , La _X ) (Ti _1-X , Al _X ) O ₃ single crystal, and FIG. 2 shows the relationship between the composition and refractive index. Lattice constant and refractive index decreases in accordance with the LaAlO ₃ amount is LaAlO ₃ and SrTiO ₃ in the single-crystal sample obtained was confirmed to be a solid solution. Moreover, although the transmittance | permeability curve of the Example was shown in FIG. 3, it has confirmed that there was no absorption in the wavelength of the 1260-1675 nm range used for all optical communication, and this material can be utilized as an optical communication member.
Further, FIG. 4 shows the relationship between the composition of the (Sr _1-X , La _X ) (Ti _1-X , Al _X ) O ₃ single crystal and the temperature dependence of the optical path length with respect to 1553 nm. The temperature dependence of the optical path length can be adjusted in the range of 0 <X <0.80. As X increases, the optical path length temperature dependence increases in the positive direction, particularly when 0.04 <X ≦ 0.60. It has been found that the absolute value of the temperature coefficient of the optical path length decreases in the range. On the other hand, it was found that the temperature dependence of the optical path length is negatively large in the comparative example with X = 0 to 0.04, and is too large in the comparative example with X = 0.81 to 1.00. FIG. 5 shows the average linear thermal expansion coefficient of the (Sr _1-X , La _X ) (Ti _1-X , Al _X ) O ₃ single crystal at −30 to 70 ° C. and the crystal system of the sample at room temperature (25 ° C.). It was. From this figure, it can be confirmed that the relationship between X and average linear thermal expansion is different at X = 0.5. This indicates that a single crystal phase transition occurs at a composition around X = 0.5 in the temperature range of −30 to 70 ° C. From this result and the relationship between the value of X shown in Table 2 and the crystal system, it is more preferable that X ≦ 0.5 in order to be a cubic single crystal without optical anisotropy. I understand. In particular, it can be seen from FIG. 5 that X <0.45 indicates that there is a phase transition at a temperature lower than −30 to 70 ° C. of the measurement temperature range in the average linear thermal expansion coefficient measurement, and −20 to 80 which is the use temperature range of the etalon filter. It can be easily predicted to maintain cubic crystals at ° C.

As shown in the above experimental results, the oxide material of the present invention, particularly the oxide single crystal material, has a very small temperature coefficient of optical path length, and is used for optical devices such as optical communication filters and optical integrated circuits. It was confirmed that it was suitable as a substrate material. In addition, since the material according to the present invention has a high refractive index, the substrate itself can be made thin, and since there is no optical anisotropy, the direction of use of the material is not limited and the degree of processing freedom is high.

Claims (10)

A perovskite (ABO ₃ ) oxide material characterized in that an absolute value of an optical path length temperature coefficient (OPD) for a wavelength of 1553 nm is 6 ppm / ° C. or less in a temperature range of −20 to 80 ° C. (Where OPD is a characteristic represented by (1 / n) × (dn / dT) + CTE by refractive index n and linear thermal expansion coefficient CTE, and A is Na, K, Rb, Cs, Ag, Ca, One or more selected from Sr, Ba, Zn, Pb, Y, Ln (lanthanoid), Bi, B is selected from Ti, Zr, Hf, Al, Ga, In, Si, Ge, Sn, V, Nb, Ta One or more ingredients) 2. The oxide material according to claim 1, wherein the perovskite (ABO ₃ ) oxide contains Sr and La, and Ti and Al. 3. _3. The oxide material according to claim 1, wherein (Sr _1-X , La _X ) (Ti _1-X , Al _X ) O ₃ (0.04 <X <0.80). . 4. The composition according to claim 3, doped with one or more components selected from Na, K, Rb, Cs, Ag, Ca, Ba, Zn, Y, Ln ¹ (Ln ¹ is a lanthanoid other than La), Pb, and Bi. Oxide material. The oxide material according to claim 3 or 4, doped with one or more components selected from Zr, Hf, Ga, In, Si, Ge, Sn, V, Nb, and Ta. 6. The oxide material according to claim 1, which is a single crystal. An etalon filter substrate comprising the oxide material according to claim 1. A solid etalon filter comprising the etalon filter substrate according to claim 8. An optical integrated circuit substrate comprising the oxide material according to claim 1. A diffraction grating substrate comprising the oxide material according to claim 1.