JPH1054919A - Optical waveguide type polarizer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To constitute an optical waveguide type polarizer while hardly disturbing the crystalline structure of a substrate by adding a first ion having a smaller ion radius than Nb ion to a substrate to constitute an optical waveguide and adding a second ton having a larger ton radius than the first ion to induce a polarizing effect. SOLUTION: On a substrate 1 comprising lithium niobate, an optical waveguide part 2 is formed into a desired waveguide pattern by using a material containing a first ion having a smaller ion radius than the Nb(+5) ion, and further, an auxiliary optical waveguide part 3 is formed in contact with the optical waveguide part 2 by using a material containing a second ion having a larger ion radius than the first ion. As for the first ion, Ti ion (having 0.605Å ion radius against 0.64 A ion radius of Nb ion) is used. As for the second ion, Ni ion (having 0.69Å ton radius) is used. For example, the optical waveguide part 2 with addition of Ti ion and the auxiliary optical waveguide part 3 with addition of Ni ion adjacent to both sides of the waveguide part 2 are formed on the lithium niobate substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide polarizer using an optical waveguide formed on the surface of a ferroelectric substrate, and more particularly to a high-speed polarizer using the optical waveguide on the surface of the ferroelectric substrate. The present invention relates to an optical waveguide polarizer in which a portion having a polarizing action is formed on the same substrate as an electro-optical device such as an optical modulator and can be integrated.

[0002]

2. Description of the Related Art One of the main components of a high-speed optical communication system is an optical modulator based on a ferroelectric crystal having an electro-optic effect. In particular, ions such as Ti are added to a substrate surface of a lithium niobate single crystal, a lithium tantalate single crystal, or a solid solution single crystal having a large electro-optic effect in a desired line shape by a method such as thermal diffusion, and the refractive index is increased. Generally, a high-speed optical modulator configured by combining an optical waveguide formed slightly higher than the surrounding substrate portion and an electrode for electrically modulating the refractive index of the waveguide using an electro-optic effect is used. .

Since these ferroelectric crystals have large optical anisotropy (dependence of the refractive index on the crystal axis), they depend on the polarization direction of a light wave propagating through a waveguide formed along a specific crystal axis. Then, the refractive index felt by the propagating light changes, and the propagation speed changes. When a non-polarized light wave is input to such an optical waveguide element or when the light is output from the element as non-polarized light, a phenomenon unfavorable for stable operation of the element such as a decrease in the extinction ratio of the output light intensity or a drive voltage fluctuation. Occurs. For this reason, it is preferable that the polarization state of the light wave incident on or emitted from the waveguide of the optical modulator is aligned in one direction.

For example, as a structure in which incident light is polarized and guided to the waveguide element, there is a method in which a polarizer is inserted between the incident end face of the waveguide and the incident side optical fiber. In particular, in a mounting method in which an optical fiber is bonded to an end face of a waveguide with a thin film polarizer interposed therebetween, a highly reliable waveguide optical modulator is realized in combination with a sealing technique of a housing. However, in order to further improve the performance of the device, the loss of the propagation light intensity caused by the insertion of the polarizer in the optical path cannot be ignored.

As a conventional method, for example, Japanese Patent Application Laid-Open
As shown in Japanese Patent Application Laid-Open No. 99913, a film having a refractive index equal to or substantially equal to the refractive index of the waveguide is disposed near the optical waveguide, and one polarized light of the guided light is transmitted to the outside of the waveguide through the film. An optical waveguide type polarizer that emits light has been proposed. To emit TE polarized light, a film is arranged beside the waveguide, and to emit TM polarized light, a film is placed under the waveguide. Has been arranged.

Another method in which a polarizer is not sandwiched in an optical path
As a separate member installed on the waveguide surface, in this member,
Guide out or absorb polarization in unwanted directions through waveguide
For example, a method such as removal and removal is adopted. Figure 1 shows anisotropic
A conventional example of a waveguide type polarizer using an optical crystal is shown.
Z-plane-cut lithium niobate with diffused waveguide
(Hereinafter, abbreviated as “LN”).
(Nb_TwoO_Five) Deposit a film to form an optical waveguide polarizer
You. At this time, the extraordinary light refractive index n of LN_e(Z-axis direction), always
Light refractive index n_o(In the z-plane) and the refractive index n of the niobium oxide film
_cIs n_o> N_c> N_eThe polarization of the incident light
Of the waves, the TM polarization perpendicular to the substrate surface passes under the niobium oxide film.
Refractive index n when passing _eAnd n_cFeel the large refractive index
Leaks to the niobium oxide side. On the other hand, parallel to the board surface
TE polarization has a refractive index n_oThrough the niobium oxide film
Even if it passes, since the refractive index on the waveguide side is larger,
Propagation while being trapped in As a result, on the output side
Indicates that only the TE polarization is guided. Such an optical waveguide polarizer
Part, for example, near the entrance side of the modulator element.
Then, a polarizer / modulator integrated waveguide is formed.

FIG. 2 shows a conventional example of a waveguide type polarizer using metal cladding. By depositing a metal film on the surface of the waveguide, the electric field of TM polarization of the propagating light is generated in the metal film. An optical waveguide polarizer that allows TE-polarized light to pass therethrough is configured by utilizing the fact that it penetrates deeply and receives large absorption.

[0008]

The conventional method proposed to suppress the loss of propagation light intensity by using an external polarizer, that is, a method of loading an object completely different from the substrate on the surface of the waveguide, Has the following disadvantages.

In the method of absorbing the TM polarization by the metal film, the electric field of the TE polarization, though slightly, penetrates and is absorbed in the metal film, which leads to a loss of the intensity of the propagating light.

In the method of loading a dielectric film or a bulk body whose refractive index has been adjusted by utilizing the refractive index anisotropy of the substrate on the surface of the waveguide, the elastic constant, A significant shift occurs in the coefficient of thermal expansion, and internal stress and strain are introduced into the substrate and the waveguide. When stress or strain is applied to a ferroelectric substrate such as LN, the refractive index changes due to an elastic optical effect, and the speed of propagating light is disturbed.
The element characteristics change.

Further, the difference between the material of the substrate and the material of the baggage body makes it difficult to obtain a high bonding strength for the same reason, and causes a problem in the mechanical reliability of the constituent elements.

Further, in order to achieve the integration of the device, a structure in which the second member is attached to the surface of the device and a height thereof are not preferable. A structure that does not give a discontinuity in the crystal structure to the crystal is desirable. The method described in Japanese Patent Application Laid-Open No. 62-299913 described in the prior art is
Although this method also improves this point, it is necessary to provide a film for guiding the TM polarization under the waveguide in order to radiate the TM polarization outside the waveguide, and this impairs the crystal structure of the substrate crystal. May give continuity.

[0013]

In order to solve the above-mentioned drawbacks, a first ion for forming an optical waveguide and a second ion for guiding a polarization action are added to a substrate. An optical waveguide polarizer is formed without substantially disturbing the crystal structure of the substrate.

In particular, the substrate is made of a ferroelectric crystal of lithium niobate, lithium tantalate, or a solid solution of lithium niobate and lithium tantalate. In these crystals, the added ions contain Nb ions at the Li site ( Nb _Li ), the phenomenon of sequentially replacing Li ions (Li _Li ) at Li sites, and part of the change in the refractive index of the substrate crystal due to the addition of ionic species are caused by the addition of ions through the elastic optical effect of the crystal. The phenomenon caused by the crystal distortion due to the size effect is positively utilized.

According to the present invention, a substrate made of a ferroelectric crystal of lithium niobate, thylium tantalate, or a solid solution of lithium niobate and lithium tantalate is treated with Nb (+
5) an optical waveguide portion made of a material including one or more types of first ions having an ion radius smaller than the ion radius of the ion or Ta (+5) ion in a desired line shape, and at least contacting the optical waveguide portion; And an auxiliary optical waveguide portion formed of a material containing one or more types of second ions having an ion radius larger than the ion radius of the first ions.

As a method of locally increasing the refractive index of a crystal substrate such as lithium niobate to form an optical waveguide, a method of adding another ion to a crystal and replacing the ion is a known technique. The effects of ions have been studied. Among them, for example, Ti (+4) ion has an effect of increasing the refractive index of both ordinary light and extraordinary light, while Ni (+2) ion, Zn (+2) ion and the like increase the ordinary light refractive index. Although the effect of lowering the extraordinary light refractive index has been found, the reason for such a change in the refractive index is not clear.

Conventionally, it has been common sense to form a Ti-doped waveguide, a Ni-doped waveguide, etc. by using each ion alone, but in the present invention, a plurality of selected ions are added to a substrate. This is characterized in that the polarizer effect is brought out. Further focusing on the size of ions to be added, an effect of reducing extraordinary refractive index can be obtained by adding ions larger than Nb (+5) ions or Ta (+5) ions originally existing in the crystal. Can be This is because, in this crystal, the cations are allowed only in the Z-axis position freedom, that is, displaced in the Z-axis direction to cause polarization. As the polarization decreases, the refractive index decreases. Therefore,
When an ion larger than the Nb (+5) ion partially substituting the Li position of the original crystal is added, the displacement in the Z-axis direction becomes small and the polarization becomes small because the ion size is large. In other words, only the extraordinary light refractive index, which is the refractive index in the polarization direction, that is, the Z direction, decreases.

An ion having an ion radius smaller than the ion radius of the Nb (+5) ion or the Ta (+5) ion is selected as the first ion for mainly deriving the optical waveguide effect.
The ionic radii of the Nb (+5) ion and the Ta (+5) ion are both about 0.64 ° (Shannon, Acta Cr
A32, 751 (1976), Ti (+4) ion (ionic radius 0.605 °) as the first ion
Is raised. The ionic radius of the Li (+1) ion is 0.1.
Since it is 76 °, the first ions are Nb _Li site, Li
Replace _Li sites without causing significant distortion to the crystal. Further, such a first ion increases the ordinary light refractive index and also increases the displacement in the Z-axis direction, and thus has the effect of increasing the extraordinary light refractive index. .

The second ions for inducing the polarization effect include ions larger than the first ions, and more preferably N ions.
An ion larger than b (+5) ion or Ta (+5) ion is selected. Ni (+
2) There are ions (ionic radius 0.69 °), Cu (+2) ions (ionic radius 0.73 °), Zn (+2) ions (0.74 °), and the like, and only the ordinary light refractive index increases due to the above-mentioned effects. The extraordinary light refractive index hardly changes or decreases.

By the effect of the present invention of adding the first ion and the second ion as described above, of the polarization components of the light wave propagating in the optical waveguide formed by the first ion added portion, the polarization component of which the ordinary light refractive index is felt. Only the wave component is guided to the outside of the waveguide, in which the ordinary light refractive index is similarly increased by the addition of the second ion, that is, to the auxiliary optical waveguide, and conversely, the polarized light component that senses the extraordinary light refractive index is extraordinary light refraction around the waveguide. Due to the effect that the rate is reduced by the addition of the second ions as compared with the case where no addition is performed, the ions are more strongly confined in the waveguide and propagated. That is, a specific polarization component can be extracted from the propagating light.

In order to obtain the above-mentioned polarization effect, the portion to which the first ion is added and the portion to which the second ion is added may overlap each other.

When ions larger than Li (+1) ions are substituted in the crystal, for example, some rare earth ions, the crystal distortion becomes too large, and it is necessary to add ions by a diffusion method or the like. Because of the longer process time,
Preferably, the first ion and the second ion are selected from transition metals.

As an application of such an optical waveguide type polarizer, a waveguide type element utilizing the acousto-optic effect or the electro-optic effect in which the above-mentioned optical waveguide type polarizer is partially or wholly incorporated on the same substrate. Since the optical waveguide is formed by the addition of the first ion, a single operation of adding the first ion to the substrate allows the polarizer portion (hereinafter, referred to as “active device”) to be formed. (Abbreviated as "passive device".) A common optical waveguide is formed in the active device portion, and integration of the waveguide device is facilitated. At this time, the second ions may overlap the active device portion as long as the performance of the active device portion is not adversely affected.

[0024]

DETAILED DESCRIPTION OF THE INVENTION According to the invention of the present application, a substrate made of lithium niobate, which is a ferroelectric crystal, contains at least one first ion having an ion radius smaller than the ion radius of Nb (+5) ion. A material including an optical waveguide portion formed into a desired line shape by a material, and at least one kind of second ions having an ionic radius larger than the ionic radius of the first ion at least in contact with the optical waveguide portion. And an auxiliary optical waveguide formed.

According to the invention of the present application, a substrate made of lithium tantalate, which is a ferroelectric crystal, is provided with one first ion having an ion radius smaller than that of Ta (+5) ion.
An optical waveguide portion formed into a desired line shape by a material included in at least one type, and at least one second ion having an ion radius larger than the ion radius of the first ion in contact with the optical waveguide portion. An auxiliary optical waveguide formed by using the above-mentioned materials is provided.

According to the invention of the present application, a substrate made of a solid solution of lithium niobate and lithium tantalate, which are ferroelectric crystals, is provided with one or more first ions having an ionic radius smaller than the ionic radius of Nb (+5) ions. An optical waveguide portion formed into a desired line shape by a contained material and a second ion having an ionic radius larger than the ionic radius of the first ion are at least in contact with the optical waveguide portion.
And an auxiliary optical waveguide portion formed of at least one kind of material.

According to the present invention, an optical waveguide portion formed of a material containing one or more types of first ions and an auxiliary optical waveguide portion formed of a material containing one or more types of second ions overlap each other. It is characterized by having. The invention of the present application is characterized in that the first ion and the second ion are selected from transition metals. The invention of the present application is characterized in that the first ion is Ti and the second ion is Ni. In the invention of the present application, the first ion is
It is Ti, and the second ion is Cu. The invention of the present application is characterized in that the first ion is Cr and the second ion is Ni. The invention of the present application is
The optical waveguide type polarizer is a waveguide type element utilizing an acousto-optic effect or an electro-optic effect, which is incorporated on the same substrate.

In the present invention, lithium niobate having a congruent composition is generally used as a single crystal ferroelectric substrate to be applied to an element, and the invention of the present application will be described using this substrate as an example. The same effect can be obtained for lithium tantalate and solid solutions of lithium niobate and lithium tantalate.

[0029]

【Example】

Embodiment 1 FIG. 3 shows an embodiment of the waveguide type polarizer of the present invention. z-
An optical waveguide portion 2 in which Ti ions are added to a surface cut lithium niobate substrate 1, and an auxiliary optical waveguide 3 in which Ni ions are added in contact with the optical waveguide portion 2 on both sides of the optical waveguide portion 2. Was formed.

In this embodiment, the optical waveguide portion 2 is
Metallic Ti was vacuum-deposited to a thickness of 740 °, a width of 7 μm, and a length of 60 mm, and heat-treated at 980 ° C. for 20 hours in an oxygen stream to diffuse Ti ions into the substrate.

The deposition thickness, width, and thermal diffusion treatment conditions of metal Ti are examples of conditions for manufacturing an optical waveguide through which light having a wavelength of 1.5 μm can propagate in a single mode.

Next, on both sides in the middle of the Ti diffused optical waveguide portion 2, metal Ni is deposited at a thickness of 500 °, a width of 50 μm, and a length of 5 m.
m, and heat-treated at 850 ° C. for 10 hours in an oxygen stream to diffuse Ni ions into the substrate,
The auxiliary optical waveguide portion 3 was provided so as to be in contact with the i-diffused optical waveguide portion.

The effect of the provision of the Ti diffusion optical waveguide portion 2 and the Ni diffusion auxiliary optical waveguide portion 3 will be described below. FIG. 5 is a diagram showing a relationship between an optical waveguide portion in which Ti, Ni and Ti + Ni are diffused into an LN substrate, an extraordinary light refractive index of the LN substrate, and a diffusion temperature.

FIG. 5 shows another z-plane cut lithium niobate substrate in which metal Ti is vacuum-deposited at a thickness of 740 ° and heat-treated in an oxygen stream at 980 ° C. for 20 hours.
The metal Ni is vacuum-deposited at a thickness of 500 ° so as to partially overlap the portion where the ions are diffused, the surface where the substrate is exposed, and the Ti ion diffusion portion.
A portion where Ni ions were diffused in the substrate by heat treatment at 0 ° C. for 10 hours was provided, and a Ti ion diffusion portion measured at room temperature (（: diffusion temperature of 980 ° C.), nothing after diffusion of Ti ions at 980 ° C. Non-diffused substrate portion (●), Ni ion diffusion portion treated at various temperatures (○), and Ni and Ti
Is the value of the extraordinary light refractive index of the portion where both ions are diffused (used in the description of the other embodiment 2: □).

FIG. 6 shows the case where Ti,
FIG. 4 is a diagram showing the relationship between the ordinary light refractive index of the optical waveguide portion in which Ni and Ti + Ni are diffused, the LN substrate, and the diffusion temperature.

The refractive index of the Ti diffused optical waveguide portion shown in FIG.
The refractive index of the Ni-diffusion-assisted optical waveguide portion in FIG. 3 corresponds to “▲” in FIGS. 5 and 6, and the Ni-diffusion portion diffused at 850 ° C. so as not to overlap the Ti-diffusion portion, ie, “ ○: 850 ° C. ”.

From the measurement results of FIGS. 5 and 6, by diffusing and adding Ni ions into the substrate, the extraordinary light refractive index of the substrate is reduced (comparison of ● and FIG. 5), and the ordinary light refractive index is reduced. It can be seen that they rise (comparison between ● and ○ in FIG. 6).

In the embodiment shown in FIG. 3, the extraordinary light refractive index difference between the Ti ion diffusion optical waveguide portion and the Ni ion diffusion auxiliary optical waveguide portion (FIG. 5A and ○: difference between 850 ° C.)
The polarization component which is larger than the difference from the non-added substrate portion (the difference between ▲ and ● in FIG. 5) and has an extraordinary optical refractive index in the optical waveguide portion with the auxiliary optical waveguide portion (FIG. 3). In the example of the z-plane cut lithium niobate substrate, TM polarization) is strongly confined.

Conversely, the polarization component that senses the ordinary light refractive index due to the increase in the ordinary light refractive index in the Ni ion diffusion assisting waveguide portion (T-plane in the example of the z-plane cut lithium niobate substrate in FIG.
The confinement of (E-polarized wave) becomes loose, and the TE-polarized wave component leaks from the optical waveguide portion to the auxiliary waveguide portion.

With such an effect, TM polarized light could be preferentially propagated by the waveguide polarizer shown in the embodiment of FIG.

Embodiment 2 FIG. 4 shows another embodiment of the present invention. The z-plane cut lithium niobate substrate 1 was formed by partially overlapping an optical waveguide portion 2 to which Ti ions were added and an auxiliary optical waveguide 3 to which Ni ions were added in the middle of the optical waveguide portion 2. In this embodiment, the optical waveguide portion 2 is made of a metal Ti having a thickness of 740.
Å, vacuum-deposited to a width of 7 μm and a length of 60 mm, and heat-treated in an oxygen stream at 980 ° C. for 20 hours to form T on the substrate.
It was formed by diffusing i-ions.

Next, on both sides of the Ti-diffused optical waveguide portion 2, metal Ni is vacuum-deposited to a thickness of 500 mm, a width of 107 μm (including an overlap with the optical waveguide portion) and a length of 5 mm, and this is subjected to an oxygen gas flow. Medium, heat treatment at 900 ° C. for 10 hours to diffuse Ni ions into the substrate,
Auxiliary optical waveguide portion 3 was formed so as to partially overlap.

The effects of the Ti diffusion optical waveguide portion 2 and the Ni diffusion auxiliary optical waveguide portion 3 will be described with reference to FIGS.

The refractive index of the portion of the Ti diffusion optical waveguide not overlapping with the Ni auxiliary optical waveguide 3 of FIG. 4 corresponds to “相当”, and the refractive index of the Ni diffusion auxiliary optical waveguide 3 of FIG.
Ni diffused at 850 ° C so as not to overlap with the diffusion part
This corresponds to an ion diffusion portion, that is, “○: 900 ° C.”.
Further, the refractive index of the portion where both waveguide portions overlap is “□:
900 ° C. ”.

From the measurement results shown in FIGS. 5 and 6, the Ti ion-diffused optical waveguide portion to which Ni ions are overlapped is added, as compared with the optical waveguide portion to which only Ti ions are added.
The extraordinary refractive index slightly decreased (comparison between ▲ and □ in Fig. 5),
It can be seen that the ordinary light refractive index slightly increases (comparison between FIG. 6A and FIG. 6D).

Although there is a change in the refractive index of the optical waveguide portion due to such superposition, (Ti + Ni) in the embodiment of FIG.
Abnormal light refractive index difference between the ion diffusion optical waveguide portion and the Ni ion diffusion auxiliary optical waveguide portion (FIG. 5 □: 900 ° C. and ○: 90)
The difference of 0 ° C.) is larger than the difference between the Ti ion diffusion optical waveguide portion and the non-doped substrate portion (the difference between ▲ and ▲ in FIG. 5). ,
The confinement of the polarization component (the TM polarization in the example of the z-plane cut thylium niobate substrate in FIG. 4) that senses the extraordinary light refractive index is strong.

Conversely, the increase in the ordinary refractive index in the Ni ion diffusion assisting optical waveguide portion causes the polarization component (the TE polarized wave in the example of the z-plane cut lithium niobate substrate shown in FIG. 4) to feel the ordinary refractive index. The confinement is loosened, and the TE polarization component easily leaks from the optical waveguide to the auxiliary optical waveguide.

With such an effect, the TM-polarized light could be preferentially propagated also in the optical waveguide type polarizer shown in the embodiment of FIG.

Embodiment 3 Another embodiment of the present invention, which is a modification of FIG. 4, is shown. x-
A surface cut lithium niobate substrate was fabricated using a combination of a Ti ion diffusion optical waveguide portion and a Ni ion diffusion auxiliary optical waveguide portion superposed thereon.

The optical waveguide was manufactured by evaporating metal Ti having a thickness of 740 ° in the y-axis direction of the substrate over a width of 7 μm and a length of 30 mm, and diffusing it in oxygen at a temperature of 980 ° C. for 20 hours.

Further, over the length of 10 mm from one end of the substrate, metal Ni is applied to the surface of the optical waveguide portion and the substrate portion.
00Å vacuum-deposited, in oxygen at 900 ° C for 10 hours,
An auxiliary optical waveguide portion was manufactured.

As a result of polishing both ends of the Ti ion diffusion optical waveguide portion, light was incident from the side where Ni ions were not added (incident light intensity was 800 μW), and the intensity of output light was monitored at the other end. The output light intensity in the TE polarization state is 2
The output light intensity in the 1 μW, TM polarized state was 7 μW, and it was confirmed that the TE polarized light propagated preferentially.

Although the obtained output light intensity was weak, this is because in the case where the optical waveguide portion and the auxiliary optical waveguide portion overlap each other as in this embodiment, FIGS. As described with reference to FIG. 6, the first ion (T
i) Due to the additional addition of the second ion (Ni) into the additional optical waveguide, the refractive index of the optical waveguide part is partially changed, and the configuration of the first embodiment (FIG. 3) in which the auxiliary optical waveguide part is in contact is used. compared,
It is considered that the purpose of the present invention is to weaken the effect of confining the polarized light that senses the extraordinary light refractive index, and also that the light wave propagating through the optical waveguide is liable to be scattered in this portion due to the change in the refractive index of the multiple ion addition portion. Can be

Therefore, in this embodiment, it is necessary to select an ion doping condition that causes little change in the refractive index of the overlapping portion. Alternatively, the configuration shown in FIG. 3 is more preferable.

Example 4 A waveguide polarizer having the same configuration as that shown in FIG. 3 was formed on a lithium niobate (LN) substrate by using Ti (4+) as a first ion and a second ion as a second ion.
It was manufactured using Cu (2+) for ions.

Metal Cu is vacuum-deposited at a thickness of 500 ° on the surface of the z-plane cut and x-plane cut substrate provided with the optical waveguide portion and thermally diffused at 850 ° C. and 900 ° C. for 10 hours in an oxygen stream. did. Table 1 shows the ordinary light and extraordinary light refractive indices of the Cu ion diffusion auxiliary optical waveguide portion. Table 1 also shows the refractive index measured for the corresponding non-added substrate.

In the auxiliary optical waveguide portion by addition of Cu (2+) ions, similarly to the case of addition of Ni (2+), the ordinary light refractive index increases, and conversely, the extraordinary light refractive index decreases, and the extraordinary light refractive index decreases. A polarizer that preferentially propagates polarized light whose refractive index is felt was obtained.

[0058]

[Table 1]

Example 5 A waveguide polarizer having the same configuration as that of FIG. 3 was formed on a lithium niobate substrate by using Cr (3+) (ionic radius: 0.615 °) as a first ion and Ni as a second ion. (2
+).

For the optical waveguide portion, metal Cr is vacuum-deposited on a substrate at a thickness of 700 ° and a width of 7 μm, and is deposited in an oxygen gas stream.
It was manufactured by diffusion treatment at 000 ° C. for 10 hours.

The refractive index of the Cr ion-diffused optical waveguide portion is higher than the refractive index of the substrate, as in the case of the Ti ion-diffused optical waveguide, in both the ordinary refractive index and the extraordinary refractive index.
Similar results to Example 1 for i-ion diffusion were obtained.

However, C, which can be selected as the first ion,
r (3+), Fe (3+), etc. are different from Ti (4+)
The valence of ions is easily changed by the energy (in the case of a short wavelength) of the incident light wave, and a drift phenomenon of the output light intensity, so-called “optical damage” of the crystal, occurs.
There is no problem in application to an element that propagates light having a wavelength of 3 to 1.5 μm). However, when light having a shorter wavelength is propagated, it is difficult to obtain stable element characteristics, which is not preferable.

In the above embodiments, a lithium niobate substrate has been described. However, a lithium tantalate substrate and a solid solution substrate of both can be manufactured in the same manner, and substantially the same effects can be obtained.

However, in the case of a lithium niobate substrate or a solid solution substrate containing more lithium niobate, the Curie temperature is higher than that of a lithium tantalate substrate.
When ion addition is performed using a thermal diffusion method, diffusion temperature conditions can be widely selected, which is preferable.

For lithium tantalate, it is necessary to select diffusion conditions at 650 ° C. or less. When a forced method such as ion implantation is used as the ion adding means,
This is not the case.

Further, the first and second embodiments in the above embodiment are described.
Regarding the ions, instead of metal Ti serving as the first ion,
Ti oxide may be deposited in a desired line shape. Instead of Ni as the second ion, a desired amount of Ni oxide may be deposited on the entire surface of the substrate.

Further, instead of metal Cu serving as the second ion, a desired amount of Cu oxide may be deposited on the entire surface of the substrate.

Instead of metal Cr serving as the first ion, Cr
Oxide may be deposited in the desired line shape.

The order of the addition process may be reversed or simultaneous, but it is desirable to add ions requiring high temperature for the diffusion process first.

[0070]

As described above, by adding the first ions and the second ions, of the polarization components of the light wave propagating in the optical waveguide formed by the first ion-added portion, the polarization component having the ordinary refractive index is felt. Only the wave component is guided out of the waveguide whose ordinary light refractive index has been increased by the addition of the second ion. Conversely, the polarization component that senses the extraordinary light refractive index has the extraordinary light refractive index around the waveguide of the second ion. Due to the effect reduced by the addition as compared with the case without the addition, the light is more strongly confined and propagated in the waveguide. That is, a specific polarization component can be extracted from the propagating light.

[Brief description of the drawings]

FIG. 1 shows an optical waveguide polarizer using an anisotropic optical crystal (conventional example).

FIG. 2 shows an optical waveguide polarizer using a metal cladding (conventional example).

FIG. 3 shows an embodiment of an optical waveguide polarizer according to the present invention.

FIG. 4 shows another embodiment of the optical waveguide polarizer according to the present invention.

FIG. 5 is a diagram showing a relationship between an extraordinary light refractive index of an optical waveguide portion and a diffusion temperature.

FIG. 6 is a diagram showing the relationship between the ordinary light refractive index of the optical waveguide portion and the diffusion temperature.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Optical waveguide part 3 Auxiliary optical waveguide part

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Junichiro Ichikawa 585 Tomimachi, Funabashi-shi, Chiba Sumitomo Osaka Cement Co., Ltd.

Claims (9)

[Claims] 1. A material comprising one or more first ions having an ionic radius smaller than the ionic radius of Nb (+5) ions on a substrate made of lithium niobate which is a ferroelectric crystal,
An optical waveguide portion formed in a desired line shape, and a material containing at least one kind of second ions having an ionic radius larger than the ionic radius of the first ion at least in contact with the optical waveguide portion. An optical waveguide type polarizer comprising: 2. A material comprising one or more first ions having an ionic radius smaller than the ionic radius of Ta (+5) ions on a substrate made of lithium tantalate which is a ferroelectric crystal,
An optical waveguide portion formed in a desired line shape, and a material containing at least one kind of second ions having an ionic radius larger than the ionic radius of the first ion at least in contact with the optical waveguide portion. An optical waveguide type polarizer comprising: 3. A material in which a substrate made of a solid solution of lithium niobate and lithium tantalate, which are ferroelectric crystals, contains one or more first ions having an ionic radius smaller than the ionic radius of Nb (+5) ions. By
An optical waveguide portion formed in a desired line shape, and a material containing at least one kind of second ions having an ionic radius larger than the ionic radius of the first ion at least in contact with the optical waveguide portion. An optical waveguide type polarizer comprising: 4. An optical waveguide portion formed of a material containing one or more types of first ions and an auxiliary optical waveguide portion formed of a material containing one or more types of second ions overlap each other. Claim 1 characterized by the above-mentioned.
An optical waveguide polarizer according to any one of the preceding claims. 5. The optical waveguide polarizer according to claim 1, wherein the first ion and the second ion are selected from transition metals. 6. The optical waveguide polarizer according to claim 5, wherein the first ion is Ti and the second ion is Ni. 7. The optical waveguide polarizer according to claim 5, wherein the first ion is Ti and the second ion is Cu. 8. The optical waveguide polarizer according to claim 5, wherein the first ion is Cr, and the second ion is Ni. 9. The optical waveguide device according to claim 1, wherein the optical waveguide polarizer is a waveguide device utilizing an acousto-optic effect or an electro-optic effect, which is incorporated on the same substrate. Polarizer.