JPH04230737A - Optical waveguide device - Google Patents

Abstract

PURPOSE:To provide the device which is easily controlled by incoherent light without relying on an electrical method, is not affected by vibrations and is not complicated in device constitution even when a light source for control light is included and facilitates the integration of the elements to the same substrate. CONSTITUTION:This optical waveguide has the substrate 11 which is formed of a material of the refractive index changed by an electrical effect and optical waveguides 12, 13 which are formed in a part on the surface of this substrate 11 and in which signal guided light 15 are propagated. An optical path conversion part having the periodic photovoltaic effect to either one of control light 16 or the guided light is provided in the above-mentioned optical waveguide 13.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide device in which signal light propagating through an optical waveguide can be controlled by other light.

0002

2. Description of the Related Art In recent years, various optical integrated circuits using optical waveguides have been proposed ("Optical Integrated Circuits"; Ohmsha, Nishihara, Haruna, Suhara (authors), 1985). One of the elements used in optical integrated circuits is a grating element. This grating element includes a passive grating element that is structurally built in advance in the optical waveguide, and electro-optic effects, electromagnetic effects, thermo-optic effects, acousto-optic effects, etc. of the material used as the optical waveguide. There is a functional grating that uses This functional grating functions as a deflector, reflector, wavelength filter, coupler, mode converter, etc. for guided light due to its fine periodic structure on the order of the optical wavelength. The passive grating has a fixed function, and the functional grating has a function controlled by electrical signals or the like.

[0003] Furthermore, a functional grating that utilizes a photorefractive effect has been proposed. FIGS. 9A to 9C illustrate the concept. That is, the optical waveguides 2 and 3 are disposed on a substrate 1 so as to intersect with each other, donor type impurities are uniformly introduced and distributed at the intersection 4, and the intersection 4 is given a photorefractive effect, thereby creating an optical waveguide device. is configured. Here, the control light (luminous flux) 5a
, 5b, the waveguide signal 6 is guided along the optical waveguide 2 as shown in FIG. 9(A). Also, the intersection 4
Two coherent beams 5a of short wavelength with energy higher than the energy difference ΔE between the donor level and the conduction band edge.
, 5b are introduced spatially as shown by the arrows in FIG.
A gradient index grating is induced in this portion due to the photorefractive effect. Furthermore, by appropriately selecting the pitch and direction of the interference fringes caused by the irradiated light,
As shown in FIG. 9(C), the signal light 6 propagating through the optical waveguide 2
is diffracted by the grating induced at the intersection 4 and becomes signal light 7 propagating through the optical waveguide 3. An optical switch is realized through the above steps.

FIG. 10 shows an optical switch array. In this method, the optical switches shown in FIG. 9 are arranged in a matrix, and a light valve array 8 made of liquid crystal or the like is placed above the optical switches.
to selectively introduce interference light into the optical switch array,
It operates any optical switch. Furthermore, Figure 1
6a, 6b, 6c in 0 are waveguide signal lights, 7a, 7b, 7
c is a propagating signal light.

[0005] Conventionally, as an optical waveguide technology, "Ph
otorefractive integrated-
optical switch arrays in
LiNbO3” (OPTICS LETTERS
/Vol. 15, No. 1/January 1,19
90) is known.

[0006]

[Problem to be solved by the invention] The above-mentioned passive gray
In optical waveguides, since a periodic structure having a diffraction function is built in advance in the optical waveguide structure, its effect is constant and guided light cannot be actively controlled.

On the other hand, in the above-mentioned functional gratings, guided light is mainly actively controlled by electrical signals applied to electrodes formed on an optical waveguide substrate. However, light modulated by other optical waveguide devices, etc.
When using it as a control signal, or when using spatially modulated light as a control signal, it is necessary to convert the optical signal used in the control section into an electrical signal or the like. Furthermore, it is difficult to spatially introduce electrical signals into the optical waveguide substrate.

[0008] In the case of using photorefractive functional gratings, if vibration or the like is applied during the formation of interference fringes and the interference fringes or the optical waveguide device itself moves, the induced grating This affects the refractive index modulation, etc., making it impossible to obtain the originally expected device operation. For this reason, a structure is required that introduces interference fringes without being affected by vibrations, etc., which complicates the structure.

The present invention has been made in view of the above circumstances, and it can be easily controlled by incoherent light without using an electrical method, is not affected by vibration, and includes a light source for control light. The device structure is not complicated even in
It is an object of the present invention to provide an optical waveguide device in which elements can be easily integrated on the same substrate.

0010

[Means for Solving the Problems] The present invention provides a substrate formed of a material whose refractive index changes through electrical action, and an optical waveguide formed on a part of the surface of the substrate through which signal guided light is propagated. An optical waveguide device characterized in that the optical waveguide is provided with an optical path converter having a periodic photovoltaic effect on either the control light or the guided light.

In the present invention, when there is no control light, the refractive index distribution that occurs for the signal guided light propagating in the optical waveguide due to the distribution of the first impurity serving as a donor is The second one does not act as an acceptor.
By doping the impurity with a phase opposite to the concentration modulation of the first impurity, it is possible to make the refractive index of the signal light within the optical waveguide uniform.

In the present invention, short-wavelength light having an energy higher than the energy difference between the energy level of the first impurity as a donor and the lower end of the conductor of the energy band within the material of the optical path converter is controlled. It is possible to irradiate it as light and induce refractive index type grading in the optical waveguide by its photovoltaic effect and electro-optic effect, thereby deflecting or modulating the signal guided light. Here, the control light may be introduced spatially from outside the substrate.

In the present invention, an optical path converter having a periodic photovoltaic effect on either the control light or the guided light is provided in the optical waveguide. Examples include intersections of optical waveguides that intersect. Here, the optical path converter is configured to dope a first impurity, which serves as a donor for either the control light or the guided light, into the optical path converter so that the concentration is modulated at a constant period.
It can be obtained by The optical path conversion section can be obtained in the following two ways.

(1) When the first impurity acts as a donor for the control light: The second impurity, which does not act as a donor or acceptor for the control light and the guided light, converts the optical path of the optical waveguide. The first impurity is doped in a phase opposite to the concentration modulation of the first impurity.

(2) When the first impurity acts as a donor for the guided light: the second impurity, which does not act as a donor or acceptor for the guided light, is doped with a phase opposite to the concentration modulation of the first impurity.

In the present invention, it is preferable that the refractive index of the optical waveguide is 0.03 to 0.05 higher than the refractive index of the substrate. The reason for this is to form a waveguide structure that confines light inside the optical waveguide and to reduce the propagation loss of the optical waveguide.

In the present invention, a case can be considered in which a tapered surface is formed in the optical path changing portion (crossing portion) as shown in FIG. Thereby, the control light propagating through the optical waveguide structure in which the taper portion is formed can be irradiated to the intersection portion having the effect of the present invention located below the taper portion. With this configuration,
It is shown that it is possible to also provide an optical system for control light irradiation on the same substrate on which the device of the invention is formed.

In the present invention, the material constituting the optical waveguide is lithium niobate (LiNbO3).
Z single crystal, ferroelectric materials such as BaTiO3, BSO (B
A paraelectric material such as i12SiO20) or a compound semiconductor such as GaAs can be used.

In the present invention, the first and second impurities include, for example, when the substrate is lithium niobate, Fe as the first impurity and H+ as the second impurity. The first and second impurities can be introduced into the optical waveguide using means such as ion implantation or thermal diffusion.

In the present invention, the intersections of a large number of the optical waveguides may be arranged in a matrix (as shown in FIG. 5). Furthermore, a film whose transmittance to control light is electrically variable may be formed on the intersections formed in a matrix (as shown in FIG. 6). The concept of an optical waveguide device according to the present invention will be illustrated using FIG.

Three-dimensional optical waveguides 12 and 13 are formed on the surface of substrate 11. A cross-shaped clad 14 is formed on the optical waveguides 12 and 13. The cladding 14 is made of a material having an electrical effect, and donor type impurities are periodically distributed in this material as shown in FIG. 2(A).

Note that the cladding 14 is not necessarily required, and may be formed over the entire surface of the substrate 11. In addition, 15 in the figure indicates waveguide light propagating through the optical waveguide 12;
Reference numeral 6 indicates control light introduced from outside the device to induce grading at the intersection, and reference numeral 17 indicates that when the control light 16 is irradiated, the guided light 15 passes through the intersection 19 and propagates through the optical waveguide 12 as it is. Waveguide output light 18 is waveguide output light that propagates through the optical waveguide 13 after the waveguide light 15 is diffracted by the grading at the intersection 19 when the control light is irradiated.

The optical waveguides 12 and 13 are formed so that the guided light 15 and the diffracted waveguide output light 18 intersect with each other at an angle θ in units of radians. The distribution period of the donor type impurity is the same as the period of the refractive index distribution type grading induced at the intersection 19 by the irradiation of the control light 16, so the pitch is Λ and the wavelength of the guided light 15 is When λ and n are integers, it is set so that COS(θ/2)=nλ/2Λ. As a result, the intersection 19
The above-mentioned grading induced by the grading has a condition that causes the guided light 15 to undergo Bragg diffraction in the direction of the optical waveguide 13.

Next, the light control method of the present invention will be described. When the control light 16 is not irradiated onto the intersection 19 from outside the device as shown in FIG.
Since the waveguide light 15 is not induced, the waveguide light 15 propagates through the optical waveguide 12 as it is, and becomes the waveguide output light 17. Next, when the control light 16 is irradiated onto the intersection 19 from outside the apparatus, the intersection 19 has the structure and effect described above, so that a gradient index grating is induced. By setting this grating under the above conditions, the optical waveguide 1
The guided light 15 propagating through the optical waveguide 2 is diffracted in the direction of the optical waveguide 13 to become the guided output light 18, and the guided light 15, which is signal light, is
The propagation of is switched to the optical waveguide 13.

Furthermore, when the external control light 16 is no longer irradiated, the grating disappears, and the guided light 15 propagates through the optical waveguide 12 as it is without being diffracted, becoming the guided output light 17. The propagation of the guided light 15 that is the signal light propagates from the optical waveguide 13 to the optical waveguide 12 and becomes the guided output light 17, and the propagation of the guided light 15 that is the signal light is switched from the optical waveguide 13 to the optical waveguide 12. As described above, the waveguide direction of the waveguide light 15 is controlled by the control light 16.

FIGS. 2A to 2D show the principle of inducing the gradient index grating at the intersection of FIG. That is, FIG. 1A shows the distribution of the donor type first impurity (Impurity 1) in the X-Y direction at the intersection 19 in FIG.
) is the distribution of carriers generated by light in the X-Y direction, (C) is the electric field distribution due to carrier diffusion in the X-Y direction, and (D) is the distribution of the refractive index induced by this electric field. shows.

By irradiating the intersection 19 with the control light 16,
Carriers are generated by light as shown in FIG. 2(B) from the donor-type first impurity distributed as shown in FIG. 2(A), but due to redistribution due to carrier diffusion etc., the carriers are generated as shown in FIG. 2(C). An electric field distribution is formed, and due to this electric field and the electro-optic effect of the optical waveguide material, a refractive index distribution equal to the distribution period of the first impurity of the donor type is formed as shown in the same figure (D), and the refractive index distribution is It becomes a grating.

When the control light 16 is no longer irradiated to the intersection 19, carriers caused by the light are recombined, so that the electric field distribution disappears, and at the same time, the refractive index distribution disappears, and the grating disappears.

Next, in the case where a refractive index distribution occurs for the guided light 15 due to the distribution of donor type impurities before the intersection 19 is irradiated with the control light 16, the refractive index of the intersection 19 is made uniform. The method will be explained with reference to FIG. The figure is
The first donor mold in the X-Y direction at the intersection 19 in FIG.
The distribution of impurities (shown in Figure 3 (A)), the distribution of the refractive index caused by it (shown in Figure 3 (B)), and the distribution of the second impurity (Impurity 2) introduced to correct the refractive index distribution (shown in Figure 3 (B)). C)
), the resulting refractive index distribution (shown in (D) in the same figure), and the overall refractive index distribution (shown in (E) in the same figure) that integrates the effects of the first and second impurities. control light 16
For the light having the wavelength of the guided light 15, a second impurity that does not become a donor or acceptor is introduced into the intersection with a concentration and distribution as shown in FIG. The refractive index of the portion 19 can be made uniform. If a difference in refractive index between the intersection 19 and the other parts of the optical waveguides 12 and 13 occurs with respect to the guided light 15, and this poses an obstacle to the propagation of the guided light, the second impurity is removed from the optical waveguide 12 other than the intersection 19. , 13 and can be uniformly introduced and distributed to make the refractive index of the portion equal to that of the intersection. Note that the distribution of the first and second impurities is not limited to that shown in FIGS. 2 and 3, and may be distributed in a stepwise manner or with a varying period, for example.

Furthermore, in order to prevent the waveguide light 15 from inducing the gradient index grating at the intersection 19, the waveguide light 15 absorbs the energy of the donor of the first impurity of the donor type.
The control light 16 emits long wavelength light with an energy lower than the energy difference between the level and the lower part of the conductor.
A short wavelength light having a higher energy than the energy difference of the impurities is used.

Furthermore, the optical waveguide device according to the present invention is shown in FIG.
The present invention is not limited to the configuration shown in FIG. 11, but may be a configuration shown in FIG. 11 or 12, for example. FIG. 11 shows a first substrate 11 made of a material having an electrical effect like the substrate 11.
A core 20 serving as an optical waveguide having a slightly higher refractive index than those of these substrates is interposed between the second substrate 11b. FIG. 12 shows a structure in which the second substrate is not provided and is in direct contact with air.

[0032]

[Embodiments] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 4 shows a device configuration for realizing an optical switch. Substrate 21 is formed from lithium niobate single crystal. A three-dimensional optical waveguide 2 whose refractive index is approximately 0.03 to 0.05 higher than the refractive index of the substrate 21.
2 and 23 are formed on the surface of the substrate 21 so as to cross each other. The optical waveguides 22 and 23 are formed by thermally diffusing titanium patterned on the substrate 21 by a lift-off method or the like. Here, the optical waveguides 22, 23
First and second impurities patterned by electron beam drawing or the like are introduced into the intersection 61 by thermal diffusion or the like. Here, the first impurity is Fe, and the second impurity is H
+. The light source 24 is installed on the end face of the optical waveguide 22. The light source 24 is made of a compound semiconductor,
Guided light 25 can be excited in the optical waveguide 22. The light receiving elements 28 and 29 are installed on the other end surface of the optical waveguide 22 and on the end surface of the optical waveguide 23. The light receiving elements 28 and 29 have a function of detecting the guided lights 26 and 27 that have propagated through the optical waveguides 22 and 23, respectively.

A light source 31 made of a compound semiconductor is placed on the intersection 61 with a buffer layer 30 made of SiO2 having a smaller refractive index than the optical waveguides 22 and 23 interposed therebetween. Note that other materials with a small refractive index may be used instead of SiO2. The light source 31 has an appropriate film thickness so as to irradiate the intersection 61 of the optical waveguides 22 and 23 with its emitted light, which is control light. The distribution of the donor-type first impurity introduced into the intersection of the optical waveguides 22 and 23 is such that the refractive index grating induced by the control light irradiation from the light source 31 optically guides the guided light 25. It is set to have the above-mentioned conditions for causing diffraction to the wave path 23.

Next, the operation of the entire apparatus will be explained. Signal waveguide light 2 excited in the optical waveguide 22 by the light source 24
5, when the control light is not irradiated by the light source 31, the grating does not exist at the intersection 61 of the optical waveguides 22 and 23 below the light source 31, so the light propagates through the optical waveguide 22 as it is, and the light is received. The light enters the element 28 and is detected. Furthermore, when the control light is irradiated by the light source 31, a gradient index grating is induced at the intersection 61, propagates through the optical waveguide 23 through diffraction, enters the light receiving element 29, and is detected. be done. As described above, the optical path of the signal waveguide light can be switched by turning the control light ON/OFF. Note that the substrate 21 may be formed using a sputtering method or the like on a substrate made of a material different from the waveguide material, such as silicon single crystal, for example. Optical waveguide 22, 2
A material having a refractive index smaller than that of the optical waveguide can also be provided as a cladding layer on the upper part of the optical waveguide. (Embodiment 2) FIG. 7 shows another device configuration for realizing an optical switch. Note that the same members as those in FIG. 4 are given the same reference numerals, and the description thereof will be omitted.

The third optical waveguide 41 is provided on the substrate 21 along the optical waveguide 23 in order to introduce control light to the intersection 61 of the optical waveguides 22 and 23. Here, the optical waveguide 41 is made of lithium niobate, Si3
It is formed by forming a film of a material such as N4 on the substrate 21 by a sputtering method or the like, and patterning this film using a technique such as a lift-off method. The optical waveguide 41
has a tapered surface 42 on the intersection 61,
It is processed using the RIE method or the like so that the control light 43 is emitted to the intersection 61 located below. An optical fiber 44 is coupled to the end face of the optical waveguide 41 so as to introduce control light from the outside. Next, the operation of the device will be explained.

Control light 43 is optical fiber 4
4, propagates through the optical waveguide 41, and passes through the optical waveguide 2.
The optical waveguide becomes tapered at the intersection 61 of 2 and 23,
The light is radiated to the intersection 61, and a gradient index grating is induced in the intersection 61. The other operations are the same as in the first embodiment. With this device, it is easy to introduce control light from the outside. (Embodiment 3) FIG. 8 shows the configuration of a device realizing an optical modulator.

In the third embodiment, the induced refractive index gradient grating is formed by the first impurity so that the guided light 25 is diffracted and becomes the guided light 51 which propagates in the opposite direction in the optical path conversion section 62. has been introduced. Note that the light source 24
An optical isolator may be provided between the optical waveguide 22 and the optical waveguide 22 to stabilize the operation of the light source. Also, without using the light source 24, using an optical fiber or the like from outside the device,
Guided light 25 may be introduced into the optical waveguide 22. Furthermore, the control light may be introduced spatially from outside the apparatus without providing the light source 24, or an optical fiber may be used.

Next, the operation of the apparatus having the above configuration will be explained. The guided light 25 excited to the optical waveguide 22 by the light source 24 is transmitted to the light source 3 when the light source 31 does not irradiate the control light.
Since there is no refractive index gradient grading in the lower part of the optical waveguide 2 which has undergone the above treatment, the optical waveguide 2
2 and becomes output light 52. Furthermore, when the control light is irradiated by the light source 31, a gradient index grating is induced in the portion of the optical waveguide 22 below the light source 31, and the guided light 25 is diffracted, causing the optical waveguide to pass through the optical waveguide. 22 becomes the guided light 51 that propagates in the opposite direction, and the output light 52 is not output. As described above, guided light can be modulated by control light. (Embodiment 4) FIG. 5 shows the configuration of an apparatus for realizing an optical switching array.

The present device is an optical switching element shown in Example 1, in which two optical waveguides are configured to be perpendicular to each other and are arranged in a matrix on the same substrate 21. Therefore, the material, manufacturing method, arrangement of each element, and modification of each element are the same as in the first embodiment. Note that it goes without saying that the number of arrays is not limited to 3×3. Next, the operation of the above device will be explained.

The operation of each switching element is the same as in the first embodiment. Among the control light light sources 31a to 31i,
The light source 31 can be set to emit light by setting a suitable one.
The guided light from a to 31f is transmitted to any light receiving element 28a to
It can lead to 28f. In addition, 24a to 2 in the figure
4f is a light source. Note that it is also possible to form the optical switching elements according to the second embodiment into an array as in the fourth embodiment.

FIG. 6 shows control light sources 31a to 31a on the device.
31i, a suitable buffer layer 63 is placed on the top surface of the device.
A light valve array 64 made of liquid crystal or the like corresponding to the intersection of each optical waveguide is provided through the light guide, and a light source 66 disposed above the device emits uniform light 65 to the light valve array 6.
A modification example in which the control light is modulated by 4 is shown. (Example 5)

FIG. 13 shows the configuration of a device realizing a self-switching element. Embodiment 5 has a configuration in which light having an energy higher than the energy level difference between the first impurity doped in the intersection 61 and the lower end of the conductor is used as the waveguide signal light 6. It has become.

The waveguide signal light 6 travels straight through the optical waveguide 2 after reaching the intersection 61, but there is a predetermined delay time difference from the time the waveguide signal light reaches the intersection 61, and the waveguide signal light is refracted at the intersection 61. The rate distribution type grating is induced, and the course of the waveguide signal light 6 is changed to become the waveguide signal output light 7.

As described above, according to the fifth embodiment, a self-switching element by the guided signal light is formed depending on the time length of the guided signal light and the signal irradiation. Therefore, the described control light becomes unnecessary, and the device configuration is simplified.

[0046]

Effects of the Invention As detailed above, according to the present invention, it is easily controlled by incoherent light without using an electrical method, is not affected by vibration, and when a light source of control light is included. Also, it is possible to provide an optical waveguide device whose device structure is not complicated and whose elements can be easily integrated on the same substrate.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the concept of an optical waveguide device according to the present invention.

FIG. 2 is a distribution diagram showing donor-type first impurities, carriers, electric field distribution, and refractive index as viewed from the X-Y direction of the device in FIG. 1;

FIG. 3 is a distribution diagram showing the donor-type first impurity, refractive index distribution, and second impurity as seen from the X-Y direction of the device in FIG. 1;

FIG. 4 is a perspective view of the optical switch according to the first embodiment.

FIG. 5 is a perspective view of an optical switch according to Example 4.

FIG. 6 is a perspective view of an optical switch showing a modification of the fourth embodiment.

FIG. 7 is a perspective view of an optical modulator according to a second embodiment.

FIG. 8 is a perspective view of an optical switch according to Example 3.

FIG. 9 is a conceptual diagram of a functional grating using a photoelective effect.

FIG. 10 is a conceptual diagram of an optical switch array.

11 is an explanatory diagram showing a concept of a device different from the optical waveguide device of FIG. 1. FIG.

12 is an explanatory diagram showing a concept of a device different from the optical waveguide device of FIG. 1. FIG.

FIG. 13 is a perspective view of a self-switching element in Example 3.

[Explanation of symbols]

11, 21...Substrate, 14...Intersection, 15, 25, 26...
Waveguide light, 16... Control light, 17... Waveguide output light, 18... Diffraction waveguide output light, 24, 24a to 24f, 31, 31a to
31i... Light source, 28, 28a to 28f, 29... Light receiving element, 30, 61... Buffer layer.

Claims (5)

[Claims] 1. A substrate comprising a substrate made of a material whose refractive index is changed by electrical action, and an optical waveguide formed on a part of the surface of the substrate, through which signal waveguide light is propagated, and a control light or waveguide. An optical waveguide device characterized in that the optical waveguide is provided with an optical path converter having a periodic photovoltaic effect on either one of the wave lights. 2. A first impurity serving as a donor for either the control light or the guided light is doped in the optical path converting section so that the concentration thereof is modulated at a constant period. The optical waveguide device according to claim 1. 3. The first impurity serves as a donor for the control light, and serves as a donor for the control light and the guided light.
Alternatively, a second impurity that does not act as an acceptor is
3. The optical waveguide device according to claim 2, wherein the optical path conversion portion of the optical waveguide is doped with the first impurity in a phase opposite to the concentration modulation of the first impurity. 4. The first impurity acts as a donor for the guided light, and the second impurity, which does not act as a donor or acceptor for the guided light, acts as a donor for the guided light. 3. The optical waveguide device according to claim 2, wherein the optical waveguide device is doped in a phase opposite to the concentration modulation of the first impurity. 5. The control light is light having an energy higher than the energy difference between the energy level of the first impurity as a donor and the lower end of the conductor of the energy band within the material of the optical path conversion section. The optical waveguide device according to claim 2.