JPH07306422A - Optical wave guiding method and optical waveguide element - Google Patents

Abstract

PURPOSE:To avert influence by photodamage and to assure the reliability for practicable use of an optical device for which optical waveguides consisting an oxide inorg. ferroelectric substance, such as LiNb03 are used in the case of guiding of signal light including transmission information by using these optical waveguides. CONSTITUTION:This optical waveguide element is 'provided with the one input side waveguide 2a for guiding the signal light L1 and the other input side waveguide 2b for guiding stabilizing light L2 for stabilizing a refractive index change and is so constituted that the signal light L1 is guided in:j the output side waveguide 2c where the refractive index change is held in the satd. state by the stabilizing light L2. The wavelength lambda2 of the stabilizing light L2 is specified to a range of 250 to 1700mn and the wavelength lambda1 of the signal light L1 is specified to a range of 250 to 2000nm. The light intensity I2 of the stabilizing light L2 is specified to >=0.1W/cm<2>.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in, for example, the information processing field or optical measurement and optical communication fields in which information is transmitted by guided light containing transmitted information. The present invention relates to an optical waveguide method and an optical waveguide element capable of ensuring the above reliability.

[0002]

2. Description of the Related Art Recently, optical switches and second harmonic generation (S
As an optical waveguide material for forming an optical functional element such as an HG) element or an optical modulator, an oxide inorganic ferroelectric such as LiNbO ₃ is widely used.

In particular, a LiNbO ₃ single crystal exhibits a large electro-optical effect, and has a relatively large figure of merit M and an electromechanical coupling coefficient as an acousto-optical material, and a thin film optical waveguide with low loss can be easily formed. It has an advantage that it can be manufactured.

As a method of manufacturing an optical waveguide made of LiNbO ₃ , for example, an epitaxial growth method, a sputtering method, an outer diffusion method, a thermal diffusion method, an ion exchange method and the like are known.

However, the above-mentioned inorganic oxide ferroelectrics such as LiNbO ₃ commonly have a phenomenon called optical damage. This phenomenon is a phenomenon in which the refractive index of a substance changes over time when exposed to light, which causes variations in characteristics when the device is assembled and causes instability, and is important for ensuring practical reliability. It is a big barrier.

In particular, an optical waveguide made of Ti-diffused LiNbO ₃ is relatively easy to manufacture and has a strong electro-optic effect, acousto-optic effect and non-linear optical effect, but in the short wavelength region, the optical power level is affected by the above optical damage. Is limited.

Here, the optical damage will be described. Li
When a visible laser beam is applied to an electro-optic crystal such as NbO ₃ or LiTaO ₃ , electrons are excited in the conduction band from the impurity level in the crystal. The excited electrons drift in the + z direction, but fall into the trap level in the middle of the drift. As a result, positively and negatively charged portions are generated in the crystal, and a spatial electric field is generated. This spatial electric field causes a change in the refractive index through the electro-optic effect. The optical damage referred to here means a change in the refractive index due to such light irradiation, and is not structural destruction of the crystal itself.

In order to suppress the occurrence of the above-mentioned optical damage, it has been conventionally considered to select a light propagation direction in a specific direction (for example, Japanese Patent Laid-Open Nos. 3-24505 and 2-17).
9327 and Japanese Unexamined Patent Publication No. 3-120514), as well as studies in the direction of adding other elements (Mg, Zn, Sc, etc.) (for example, Japanese Unexamined Patent Publication No. 5-10).
5590 publication).

Recently, a method of reducing photodamage by heat treatment in ozone has also been reported (see, for example, JP-A-5-105590).

[0010]

However, among the above-mentioned three conventional methods, the method of selecting the propagation direction of light in a specific direction greatly limits the degree of freedom in device design and makes it possible to cope with complicated circuit configurations. Has a problem that its adaptation becomes difficult. Further, the method of adding another element has a problem in that it is difficult to grow a large crystal uniformly.

Moreover, the above three methods have been studied in view of improving the light damage resistance to some extent, and even if the level is lowered by the improvement, the light damage is inherently present, and this influence is completely avoided. You cannot do it.

The present invention has been made in view of the above problems, and an object thereof is to include transmission information by using an optical waveguide made of a material whose refractive index changes by irradiation with light. An object of the present invention is to provide an optical waveguide method capable of avoiding the influence of optical damage in guiding guided light and ensuring the practical reliability of an optical device using the optical waveguide.

Another object of the present invention is to guide a guided light containing transmission information when the substrate and / or the optical waveguide is made of a material whose refractive index changes by irradiating light. You can avoid the effects of light damage when
An object of the present invention is to provide an optical waveguide element capable of ensuring the practical reliability of an optical device using the optical waveguide.

Another object of the present invention is to provide an optical waveguide.
When a substrate and / or an optical waveguide is made of an oxide inorganic dielectric material such as LiNbO ₃ which can have a strong electro-optic effect, acousto-optic effect, and non-linear optical effect, guided light including transmission information is guided. An object of the present invention is to provide an optical waveguide element capable of avoiding the influence of optical damage at the time of making it possible and ensuring the practical reliability of an optical device using an optical waveguide made of an oxide-inorganic dielectric.

[0015]

According to the present invention, as shown in FIG. 1, for example, an optical waveguide 2 made of a material whose refractive index changes by irradiation with light is used to include transmitted information. the guided light L ₁ in the optical waveguide method for guiding, by the second guided light L _2, in a state saturated with refractive index change △ n of the optical waveguide 2, so as to guiding the first guided wave L ₁ To

In this case, it is preferable that the light intensity I ₂ of the second guided light L ₂ in the optical waveguide 2 be 0.1 W / cm ² or more. In addition, the wavelength λ ₂ of the second guided light L ₂ is set to 2
The wavelength is in the range of 50 to 1700 nm, and the wavelength λ ₁ of the _first guided light L ₁ is in the range of 250 to 2000 nm.

The optical waveguide element according to the present invention is, for example, as shown in FIG. 1, a first optical waveguide for guiding a _first guided light L ₁ containing transmission information on a substrate 1. Two
a and the second guided light L ₂ is provided a second optical waveguide 2b for guided, a third optical waveguide whose refractive index change △ n is saturated by the second guided light L ₂ The first guided light L ₁ is configured to be guided in 2c.

In this case, the substrate 1 and / or the optical waveguide 2
Is composed of an oxide inorganic dielectric. Specifically, the oxide inorganic dielectric is LiNbO ₃ .

[0019]

In the optical waveguide method according to the present invention, first, the second guided light L ₂ is guided through the optical waveguide 2 made of a material whose refractive index changes by irradiation with light. As a result, optical damage occurs in the optical waveguide 2 and the refractive index changes, but the refractive index change Δn is the second guided light L ₂
Becomes saturated. In this state, the _first guided light L ₁ containing the transmission information is guided.

In this case, since the refractive index change Δn due to the generated optical damage is in a saturated state, it maintains a substantially constant value Δns regardless of the elapse of the light irradiation time t. It becomes possible to guide the _first guided light L ₁ whose refractive index change Δn is equivalently stabilized. As a result, the adverse effect of the optical damage, that is, the device characteristics are deteriorated,
Also, it is possible to avoid the adverse effect that the light intensity is limited, and it is possible to improve the life, stability of characteristics, and reliability of the optical waveguide device.

Further, while positively causing optical damage by the second guided light L ₂ , the refractive index change Δn is saturated to stabilize the refractive index change Δn.
A certain degree of optical damage inherent in the waveguide material is allowed, and the restrictions on crystal growth, waveguide fabrication, etc. are greatly eased.

Moreover, it is not the conventional method of avoiding the optical damage by selecting the polarization direction or the waveguide direction of the light as a specific direction, and the optical damage caused by the optical damage does not depend on the polarization direction or the waveguide direction of the light. Since the influence can be avoided, it is not necessary to consider the installation condition of the optical waveguide and the constraint on the optical path, and it is possible to sufficiently cope with the complication of the element structure due to the multifunctionalization. This is extremely advantageous in increasing the functionality of electronic equipment having an optical transmission system.

Here, the second guided light in the waveguide 2
L₂Light intensity of₂0.1 W / cm ²What I did above is
Below this, saturation of the refractive index change Δns does not occur, and
Inability to eliminate instability due to damage or saturation
If it happens, it will take some time to reach saturation.
This is because it works.

Further, the wavelength λ ₂ of the _second guided light L ₂ is set to 25
The range of 0 to 1700 nm is set because a small coherent light source does not exist below this range and optical damage hardly occurs above this range. The wavelength λ ₁ of the _first guided light L ₁ is set to 250 to 2000 nm because
This is because there is no small coherent light source in the wavelength range other than this.

Next, in the optical waveguide element according to the present invention, the first guided light L ₁ containing the transmission information is guided to the first optical waveguide 2a, and the second optical waveguide 2b.
Then, the second guided light L ₂ is guided. At this time, the second guided light L guided through the second optical waveguide 2b
₂ causes optical damage to the third optical waveguide 2c and changes the refractive index in the waveguide 2c. The refractive index change Δn is saturated by the second guided light L ₂ . . Then, the _first guided light L ₁ guided through the first optical waveguide 2a is guided through the third optical waveguide 2c whose refractive index change Δn is saturated by the second guided light L ₂ . become.

In this case, the refractive index change Δn due to the optical damage generated in the third optical waveguide 2c is equal to the second guided light L
_Since it is in a saturated state due to ₂ , the constant value Δns is maintained irrespective of the elapse of the light irradiation time t, and the first derivative in which the refractive index change Δn is equivalently stabilized. It becomes possible to guide the wave light L ₁ . As a result, the adverse effect of the optical damage, that is, the device characteristics are deteriorated,
Also, it is possible to avoid the adverse effect that the light intensity is limited, and it is possible to improve the life, stability of characteristics, and reliability of the optical waveguide device.

Further, while the optical damage is positively generated by the second guided light L ₂ , the refractive index change Δn is saturated to stabilize the refractive index change Δn.
A certain degree of optical damage inherent in the waveguide material is allowed, and the restrictions on crystal growth, waveguide fabrication, etc. are greatly eased.

Moreover, this is not a conventional method of avoiding optical damage by selecting a specific polarization direction or waveguide direction of light, and is not dependent on the polarization direction or waveguide direction of light. Since the influence can be avoided, it is not necessary to consider the installation condition of the optical waveguide and the constraint on the optical path, and it is possible to sufficiently cope with the complication of the element structure due to the multifunctionalization. This is extremely advantageous in increasing the functionality of electronic equipment having an optical transmission system.

Here, the substrate 1 and / or the optical waveguide 2 are
In the case of being composed of an oxide inorganic dielectric material such as LiNbO ₃ , a large electro-optical effect is generally exhibited, and a merit index M which is relatively large as an acousto-optic material is also obtained.
And has an electromechanical coupling coefficient, and has an advantage that a low loss thin film optical waveguide can be easily manufactured.
Due to the occurrence of optical damage, the refractive index of the substrate 1 and / or the optical waveguide 2 changes over time, which causes characteristic variations and instability when the device is assembled, and in the short wavelength region, due to the effect of optical damage. The problem arises that the optical power level is limited.

However, in the present invention, the second optical waveguide 2b
To guide the _second guided light L ₂ for making the refractive index change Δn into a saturated state, and change the refractive index change Δn of the third optical waveguide 2c through which the _first guided light L ₁ is guided. Since the saturation state is adopted, the influence caused by the change Δn in the refractive index due to the optical damage as described above is reduced, and the practical reliability can be secured.

Therefore, the effect of the optical waveguide 2 composed of an oxide inorganic dielectric material such as LiNbO ₃ (relatively easy to manufacture, having a strong electro-optic effect, acousto-optic effect and non-linear optical effect) is sufficiently obtained. It can be exhibited, and the application range of the optical waveguide composed of the oxide-inorganic dielectric can be expanded.

[0032]

EXAMPLES Examples of an optical waveguide element for realizing the optical waveguide method according to the present invention (hereinafter, simply referred to as an optical waveguide element according to the example) will be described below with reference to FIGS.
Before describing the specific configuration of the optical waveguide device according to the example, the principle of the optical waveguide method according to the present invention will be described below.

The optical waveguide method according to the present invention is based on the recognition that it is impossible to completely suppress the intrinsic optical damage, and reverses the conventional idea of the optical damage so that the optical damage is sufficiently suppressed. It is based on the concept of utilizing a stable equilibrium state after the occurrence of.

Specifically, the optical waveguide method according to the present invention is
These are utilized based on the elucidation and confirmation of the following four phenomena of the light damage phenomenon.

(1) First, as shown in FIG. 3, the change Δn in the refractive index due to light damage changes with the elapse of the light irradiation time t.
First, it changes almost linearly toward the saturated refractive index change Δns, approaches the saturated refractive index change Δns while drawing a non-linear curve with the knee point as a boundary, and further changes this saturated refractive index change Δns. As an asymptote, it has a characteristic of extending almost parallel to the time axis. The time dependency of the refractive index change Δn can be expressed in an exponential function form as shown in the following equation (1).

Δn (t) = Δns {1-exp (-t / τ)} (1) where τ is the transit time of the light wave propagating in the crystal.

(2) As for the refractive index change Δn, as shown in FIG. 4, the portion where it changes linearly becomes steeper as the light intensity is larger, and the time until it approaches the saturated refractive index change Δns. It has the property of being shorter.

(3) Further, as shown in FIG. 5, the saturated refractive index change Δns has a time-dependent characteristic (see FIG. 3) in the refractive index change Δn as the light intensity I increases. Similarly, it first changes into a substantially linear shape, and then
It has the characteristic that it gradually rises while drawing a non-linear curve at point e) and reaches a saturation state at a certain light intensity It. Change in saturated refractive index in saturated condition △
Above a light intensity It, ns is substantially constant regardless of the light intensity I.

7 to 9 show the LiNb used in this example.
The experimental data of an O ₃ waveguide are shown. FIG. 7 is 5 mol /%
Light intensity of change in saturation refractive index Δns of LiNbO ₃ waveguide produced by growing LiNbO ₃ single crystal film on Mg-doped LiNbO ₃ single crystal by liquid phase epitaxial growth, especially due to optical damage of TE mode Δns It shows dependence.

Among them, the curve a shows the characteristics of the LiNbO ₃ waveguide produced by the liquid phase epitaxial growth method using the solution containing 0.25 mol% of vanadium (V), and the curve b shows the characteristic of boron (B). 0.3mo in the solution
The characteristics of a LiNbO ₃ waveguide produced by a liquid phase epitaxial growth method using a solution containing 1% iron (Fe) are shown, and a curve c shows 0.7 mol in a solution of boron (B).
The characteristics of a LiNbO ₃ waveguide manufactured by a liquid phase epitaxial growth method using a solution containing 20% magnesium (Mg) are shown.

FIG. 8 shows Li prepared by the Ti thermal diffusion method.
The characteristics of the NbO ₃ waveguide are shown. The curve d shows the dependency of the saturated refractive index change Δns due to the TM mode optical damage on the light intensity, and the curve e shows the saturation refractive index change Δ due to the TE mode optical damage. The light intensity dependence of ns is shown.

FIG. 9 shows L produced by the proton exchange method.
It shows the light intensity dependence of the saturation refractive index change Δns of the iNbO ₃ waveguide due to the optical damage particularly in the TM mode,
Curve f shows the characteristics when the crystal is annealed at a high temperature after the proton exchange, and curve g shows the characteristics when the high temperature annealing is not performed after the proton exchange.

Of these various characteristic curves a to f, FIG.
LiNbO prepared by the liquid phase epitaxial method
_{The three} waveguides are in a saturated state when the light intensity is around 100 (W / cm ² ), and show a constant saturation refractive index change Δns when the light intensity is higher than that.

LiNbO by the Ti thermal diffusion method shown in FIG.
_{In the three} waveguides, especially in the TE mode, the light intensity is saturated near about 10 ⁴ (W / cm ² ), and when the light intensity is higher than that, a constant saturation refractive index change Δns (=
1.7 × 10 ⁻⁴ ) is shown. In the TM mode, the change in the saturation change rate Δns exceeds the upper limit value of the input dynamic range of the photodetector used in this experiment, so no reliable characteristic is obtained, but the characteristic indicated by the broken line is shown. Expected.

LiNb by the proton exchange method shown in FIG.
Each of the O ₃ waveguides has a saturation change rate Δns.
However, since it exceeds the upper limit of the input dynamic range of the photodetector used in this experiment, no reliable characteristics have been obtained, but it is expected that the characteristics shown by the broken line are exhibited.

(4) Further, the saturated refractive index change Δns shows a tendency that as the wavelength λ of light increases, the magnitude of the light intensity I entering the saturated state increases as shown in FIG. However, there is no change in the saturated refractive index change Δns. That is, the saturated refractive index change Δns does not depend on the wavelength of light.

Thus, the refractive index change Δn due to optical damage
Is a saturated state when the light intensity I exceeds a certain value (light intensity It) and the value (saturation value Δns) at that time does not depend on the wavelength λ of the light. In the example, light having a light intensity higher than the light intensity It that enters the saturation state stabilizes the change in the refractive index of the LiNbO ₃ waveguide while intentionally causing optical damage to the LiNbO ₃ waveguide. _By guiding in _three waveguides, stable device characteristics are realized.

Next, two concrete structural examples of the optical waveguide device according to the above-mentioned embodiment (hereinafter, referred to as an optical waveguide device according to the first embodiment and an optical waveguide device according to the second embodiment for convenience). Will be described with reference to FIGS. 1 and 2.

The optical waveguide device A _{1 according} to the first embodiment shown in FIG. 1 shows the simplest device configuration example to which the principle according to the above embodiment is applied, and is applied to an SHG device, a phase modulator or the like. It is possible. The optical waveguide device A ₁ shown in FIG. 1 will be described. The optical waveguide device A _{1 according} to the first embodiment is one example of the substrate ₁ made of, for example, Z-cut LiNbO ₃ crystal when the ridge type is taken as an example. For example, a Ti thermal diffusion method and a dry etching method are applied to the main surface to form a waveguide layer (optical waveguide) 2 made of Ti: LiNbO ₃ crystal on a substrate 1.

The optical waveguide 2 formed on the substrate 1 is
The two waveguides 2a and 2b formed on the input side and the one waveguide 2c formed on the output side are connected in the middle and have a substantially Y-shaped plane. Then, of the two waveguides 2a and 2b on the input side, the signal light (wavelength λ
₁ , the light intensity I ₁ ) L ₁ is guided, and the stabilized light (wavelength λ ₂ , light intensity I ₂ > It) L ₂ for stabilizing the change in the refractive index is guided to the other waveguide 2b. It has become so.

The optical waveguide device A _{1 according} to the first embodiment has a linear waveguide 2c on the output side of the substrate 1.
A planar electrode 3 to which a modulation voltage is applied is loaded in a portion near the output side waveguide 2 of the optical waveguide device A _1.
An optical filter 4 that transmits light (modulated signal light) mL ₁ having a wavelength λ ₁ is spatially separated from c.

The operation of the optical waveguide device A _{1 according to} the _first embodiment will now be described. First, the signal light L ₁ guided through one of the input-side waveguides 2a is coupled (branched).
, The stabilizing light L guided through the other input waveguide 2b
₂ is combined and interfered with _2, and is guided through the output side waveguide 2c as the combined signal light L ₁₂ having high light intensity.

The stabilized light L ₂ having a large light intensity is guided through the input side waveguide 2b, so that these waveguides 2b
And the light damage occurs 2c, the light intensity I ₂ of the stable Kahikari L ₂ is a light intensity It least bring △ ns saturated refractive index change, the refractive index change due to optical damage occurred △
n is a substantially constant value Δn regardless of the elapse of the light irradiation time t.
s will be maintained. Therefore, the combined signal light L ₁₂ obtained by multiplexing and interfering the stabilizing light L ₂ is equivalently the light with the stabilized refractive index change Δn.

The combined signal light L ₁₂ guided through the output side waveguide 2c undergoes a phase change by the modulation voltage applied to the planar electrode 3 and is guided through the output side waveguide 2c as the modulated combined signal light mL _12. Will be done. This modulated combined signal light mL ₁₂ changes its refractive index due to the stabilizing light component L ₂ .
Since n is in a saturated state, the light intensity is not limited by the influence of light damage even if high frequency modulation is performed by the modulation voltage. The output waveguide 2c a guided modulated synthesized signal light mL ₁₂ is the subsequent stage of the optical filter 4, is stabilized Kahikari component L ₂ is removed, only the modulated component mL ₁ of the signal light L ₁ is the next stage It will be sent later.

Next, the optical waveguide device A _{2 according} to the second embodiment.
This will be described with reference to FIG. In addition, the same code | symbol is described about the thing corresponding to FIG. 1, and the overlapping description is abbreviate | omitted.

Optical waveguide device A according to the second embodiment
Reference numeral ₂ denotes a branching interference type optical modulator (Mach-Zehnder type optical modulator). Also in this case, like the optical waveguide device A _{1 according} to the first embodiment, when a ridge type is taken as an example, For example, a Ti thermal diffusion method and a dry etching method are applied to one main surface of the substrate 1 made of Z-cut LiNbO ₃ crystal to form a waveguide layer (waveguide) 2 made of Ti: LiNbO ₃ crystal on the substrate 1. Consists of

The waveguide 2 formed on the substrate 1 has a shape in which the optical waveguide shape of the optical waveguide element A _{1 according} to the first embodiment, particularly the shape of the output side waveguide 2c, is branched into two. Is formed in. Specifically, _one waveguide 2c ₁ extending from the coupling point of the input-side waveguides 2a and 2b to the output side
Is branched into two waveguides (first and second waveguides 2c ₂ and 2c ₃ ) at a branch point on the input side in the middle, and further,
The first and second waveguides 2c ₂ and 2c ₃ are combined at the branch point on the output side to form a single waveguide 2c ₄ , which has a branch interference type shape.

Then, like the optical waveguide device A _{1 according} to the first embodiment, the two waveguides 2a and 2 on the input side are provided.
b, signal light (wavelength λ ₁ , light intensity I
₁ ) Stabilized light (wavelength λ ₂ , light intensity I ₂ > I) in which L ₁ is guided and the refractive index change is stabilized in the other waveguide 2 b.
t) L ₂ is guided.

In the optical waveguide device A _{2 according} to the second embodiment, the planar electrode 3 to which the modulation voltage is applied is loaded on the portion of the substrate 1 which is close to the first waveguide 2c _2. Consists of

The operation of the optical waveguide device A _{2 according to} the _second embodiment will now be described. First, the signal light L ₁ guided through one input side waveguide 2a is combined and interfered with the stabilizing light L ₂ guided through the other input waveguide 2b at the coupling portion, and a combined signal with high optical intensity is obtained. Waveguide 2c as light L _12
It will guide _one .

The stabilized light L ₂ having a large light intensity is guided through the input side waveguide 2b, so that the waveguide 2b
And the light damage occurs 2c, the light intensity I ₂ of the stable Kahikari L ₂ is a light intensity It least bring △ ns saturated refractive index change, the refractive index change due to optical damage occurred △
Is a substantially constant value Δns regardless of the elapse of the light irradiation time t.
Will be maintained. Therefore, the combined signal light L ₁₂ obtained by multiplexing and interfering the stabilizing light L ₂ is equivalently the light with the stabilized refractive index change Δn.

Combined signal light L guided through the waveguide 2c _1
12 is bisected at the branch point on the input side. Of the bisected synthetic signal light L _12, the combined signal light L ₁₂ guided through first waveguide 2c ₂ is subjected to the phase change by the modulation voltage applied to the planar electrode 3, modulated synthesized signal The light mL ₁₂ is guided through the first waveguide 2c ₂ . On the other hand, the combined signal light L ₁₂ guided through the second waveguide 2c ₃ is
No modulation is applied, and the second reference light signal L ₁₂
Will be guided through the waveguide 2c ₃ .

The modulated combined signal light mL ₁₂ guided through the first waveguide 2c ₂ and the reference combined signal light L ₁₂ guided through the second waveguide 2c ₃ at the branch point on the output side. Modulated combined signal light mL ₁₂ that is combined / interfered and contains the phase difference component Δφ
As a result, the light is guided through the output side waveguide 2c ₄ , and the output light intensity changes corresponding to the phase difference component Δφ included in the modulated combined signal light mL ₁₂ . In this case, since the refractive index change Δn of the modulated combined signal light mL ₁₂ is saturated by the stabilizing light L ₂ , even if the modulated voltage is high frequency modulated by the modulation voltage, the light intensity is limited due to the influence of optical damage. There is nothing to be done. This output side waveguide 2c
_In the modulated combined signal light mL ₁₂ guided by 4, the stabilizing light component L ₂ is removed by the optical filter 4 in the subsequent stage, and only the modulation component mL ₁ of the signal light L _{1 including} the phase difference component Δφ is obtained. Will be sent to the next and subsequent stages.

As described above, in the optical waveguide elements A ₁ and A _{2 according to} the first and second embodiments, the signal light L is fed to one of the two input side waveguides 2a and 2b. ₁ is guided, and the stabilizing light L ₂ whose light intensity is equal to or higher than the light intensity It that causes the saturation refractive index change Δns is guided in the other waveguide 2b, and these signal light L ₁ and the stabilizing light L ₂ are guided. Since the light that is combined and interfered with L ₂ is used as the signal light L ₁ , the change in the refractive index due to the optical damage that occurs Δ
n is a substantially constant value Δn regardless of the elapse of the light irradiation time t.
Since s is maintained, it is possible to equivalently guide the signal light L ₁ whose refractive index change Δn is stabilized. As a result, it is possible to avoid the adverse effects caused by the influence of optical damage, that is, the adverse effects that the device characteristics are deteriorated and the light intensity is limited, and the life, stability of the characteristics, and the reliability of the optical waveguide device are improved. be able to.

In the above embodiment, the signal light L₁
Wavelength λ₁And stabilizing light L₂Wavelength λ ₂To be different from
Therefore, using the optical filter 4, the output side waveguide 2c
Modulated synthetic signal light mL that guides light₁₂Easy to stabilize light L
₂Various optical parts that can be eliminated
Stabilized light L for products and photoelectric conversion elements₂Is mixed and dried
True signal light L that has not been propagated₁Modulation component of mL₁Only
Can be sent, especially when the input
Avoid complicated design changes such as changing the Mick Range
be able to.

In the above embodiment, the stabilizing light L
_Since the refractive index change Δn is stabilized while the optical damage is positively generated in ₂ , the optical damage inherent in the waveguide material is allowed to some extent, and crystal growth or The restrictions on the fabrication of waveguides are greatly eased. Moreover, it avoids the influence of optical damage without depending on the polarization direction or the waveguide direction of light, instead of the conventional method of avoiding the optical damage by selecting the polarization direction or the waveguide direction of light as a specific direction. Therefore, it is not necessary to consider the installation condition of the optical waveguide device and the constraint on the optical path, and it is possible to sufficiently cope with the complication of the device structure due to the multifunctionalization.
This is extremely advantageous in increasing the functionality of electronic equipment having an optical transmission system.

The optical waveguide devices A ₁ and A _{2 according to} the first and second embodiments are merely examples, and in addition, traveling wave optical modulators, balance bridge optical modulators, single sideband modulators, etc. Electro-optical control devices such as phase control devices, uniform Δβ directional couplers, inverting Δβ directional couplers, distributed wavelength coupling devices such as optical wavelength filters, and collinear devices such as mode converters and variable wavelength filters. Shaped device,
It is also applicable to acousto-optic control devices such as coplanar devices such as Bragg modulators and Bragg deflectors, and optical bistable elements (non-linear elements) such as waveguide bistable devices.

As a condition when applied to the above-mentioned various devices, the target optical waveguide material is a material that causes optical damage, typically an oxide inorganic ferroelectric, and specifically, The above LiNbO ₃ , LiTaO ₃ , and K
It is composed of TiOPO ₄ , KNbO _{3, and the} like.

As the method of forming the optical waveguide, impurities (for example, titanium (Ti)) diffusion, out-diffusion method, LPE are used.
(Liquid phase epitaxial) method, ion exchange method, laser ablation, sputtering method, sol-gel method and the like.

In particular, although the ridge type optical waveguide is mainly described in the first and second embodiments, it is also applicable to a buried type, (dielectric) loaded type, (metal) loaded type and the like. Specifically, for example, in the case of the embedded type, LiNbO ₃ crystal is used as the substrate and Ti:
There are examples of forming a waveguide layer by embedding LiNbO _3, and examples of using a LiNbO ₃ crystal as a substrate and embedding H +: LiNbO ₃ by a selective proton exchange method to form a waveguide layer.

Then, the signal light L ₁ guided through the optical waveguide
Has a wavelength λ ₁ of 250 to 2000 nm. This is because there is no small coherent light source in the wavelength range other than this.

[0072] On the other hand, the wavelength λ ₂ of stability Kahikari L ₂ is, 250
˜1700 nm. This is because below this, there is no small coherent light source, and above this, almost no optical damage occurs. Further, the light intensity I ₂ of the stabilizing light L ₂ is set to 0.1 W or more per square centimeter. This is because below this, saturation of the change Δns in the saturated refractive index does not occur, destabilization due to optical damage cannot be eliminated, or even if saturation occurs, it takes time to reach the saturated state.

In the above embodiment, the signal light L ₁
The stabilizing light L ₂ and the stabilizing light L ₂ are made to enter the optical waveguide from different optical paths. However, the signal light L ₁ itself has the role of the stabilizing light L ₂ , and the saturation of the saturated refractive index change Δns is taken into consideration. It is also conceivable to develop such as device design.

[0074]

As described above, according to the optical waveguide method of the present invention, an optical waveguide made of a material whose refractive index is changed by irradiating light is used to include transmission information.
In the optical waveguide method of guiding the guided light, the first guided light is guided in a state where the change in the refractive index of the optical waveguide is saturated by the second guided light. It is possible to guide the first guided light whose refractive index change is stabilized. As a result, it is possible to avoid the adverse effects caused by the influence of optical damage, that is, the adverse effects that the device characteristics are deteriorated and the light intensity is limited, and the life, stability of the characteristics, and the reliability of the optical waveguide device are improved. be able to.

Further, in the optical waveguide method according to the present invention, in the above method, the light intensity of the second guided light in the waveguide is set to 0.1 W / cm ² or more, so that the refractive index change Δns It is possible to avoid the problem that the saturation does not occur and the instability due to the optical damage cannot be eliminated, and the inconvenience that it takes time to reach the saturated state.

Further, in the optical waveguide method according to the present invention, in the above method, the wavelength of the second waveguide light is 250 to 170.
Since the range is 0 nm, it is possible to avoid the problem that a small coherent light source cannot be used and the inconvenience that optical damage hardly occurs.

Further, in the optical waveguide method according to the present invention, in the above method, the wavelength of the first guided light is 250 to 200.
Since the range is 0 nm, it is possible to avoid the disadvantage that a small coherent light source cannot be used.

Further, according to the optical waveguide of the present invention, the first optical waveguide for guiding the first guided light containing the transmission information and the second guided light are guided on the substrate. And a second optical waveguide for causing the first guided light to be guided in the third optical waveguide whose optical refractive index is saturated by the second guided light. The change in the refractive index due to the optical damage generated in the third optical waveguide guided by the first guided light is saturated by the second guided light, and the change in the refractive index occurs regardless of the elapsed time of the light irradiation. It will maintain an almost constant value. That is, it becomes possible to equivalently guide the first guided light whose refractive index change is stabilized to the third optical waveguide, which causes a harmful effect due to the influence of optical damage, that is, device characteristics are deteriorated and light intensity is reduced. It is possible to avoid the adverse effect of being limited, and the life of the optical waveguide device,
It is possible to stabilize the characteristics and improve the reliability.

In the optical waveguide element according to the present invention, in the above structure, the substrate and / or the optical waveguide is made of an oxide inorganic dielectric material. Specifically, since LiNbO ₃ is used as the oxide inorganic dielectric, the effect of the optical waveguide formed of the oxide inorganic dielectric (relatively easy to manufacture, strong electro-optic effect, acousto-optic effect and nonlinear effect) is obtained. (Having an optical effect) can be sufficiently exerted, and the utilization range of the optical waveguide composed of the oxide-inorganic dielectric can be expanded.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of an optical waveguide device for realizing an optical waveguide method according to the present invention.

FIG. 2 is a configuration diagram showing a second embodiment of an optical waveguide device for realizing the optical waveguide method according to the present invention.

FIG. 3 is a characteristic diagram showing the time dependence of a refractive index change Δn due to optical damage of an optical waveguide.

FIG. 4 is a characteristic diagram showing a light intensity dependency of a refractive index change Δn due to optical damage of an optical waveguide.

FIG. 5 is a characteristic diagram showing a light intensity dependence of a saturated refractive index change Δns.

FIG. 6 shows the change in saturated refractive index when the wavelength of light is changed.
It is a characteristic view which shows the light intensity dependence of ns.

FIG. 7 is a characteristic diagram showing experimental results (optical intensity dependence of saturation refractive index change Δns) of an optical waveguide manufactured by the LPE method.

FIG. 8 is a characteristic diagram showing experimental results (optical intensity dependence of saturation refractive index change Δns) of an optical waveguide manufactured by a Ti thermal diffusion method.

FIG. 9 is a characteristic diagram showing experimental results (optical intensity dependence of saturation refractive index change Δns) of an optical waveguide manufactured by the proton exchange method.

[Explanation of symbols]

A _1, A ₂ optical waveguide device 1 substrate 2 waveguide 2a, 2b input waveguide _{2c, 2c 1, 2c 2,} 2c 3, 2c 4 output waveguide 3 planar electrode 4 optical filter L ₁ signal light L ₂ stable Light L ₁₂ Combined signal light mL ₁₂ Modulated signal light

Claims (7)

[Claims] 1. An optical waveguide method for guiding a first guided light containing transmission information by using an optical waveguide made of a material whose refractive index is changed by irradiating light, wherein the second guided light is used. An optical waveguide method in which the first guided light is guided while the change in the refractive index of the optical waveguide is saturated. 2. The optical waveguide method according to claim 1, wherein the light intensity of the second guided light in the waveguide is 0.1 W / cm ² or more. 3. The wavelength of the second guided light is 250 to 17
It is 00 nm, The optical waveguide method of Claim 1 or 2 characterized by the above-mentioned. 4. The wavelength of the first guided light is 250 to 20.
It is 00 nm, The optical waveguide method of Claim 1, 2 or 3 characterized by the above-mentioned. 5. A first optical waveguide for guiding a first guided light containing transmission information and a second optical waveguide for guiding a second guided light on a substrate. An optical waveguide device comprising the above-mentioned first guided light guided through a third optical waveguide whose refractive index change is saturated by the second guided light. 6. The optical waveguide element according to claim 5, wherein the substrate and / or the optical waveguide is made of an oxide inorganic dielectric. 7. The optical waveguide device according to claim 6, wherein the oxide inorganic dielectric material is LiNbO ₃ .