JPH08262504A - Optical waveguide type optical switch and production of optical waveguide type optical switch - Google Patents

Abstract

PURPOSE: To obtain an opto-thermotic switch capable of stably maintaining a switching state having a specified refractive index by using a ferroelectric material exhibiting the structural phase transition based on a temp. change in a waveguide clad part. CONSTITUTION: Waveguides are formable by quartz or polymer, etc. The clad part 12 is formable by applying a vinylidene fluoride/trifluoroethylene, copolymer (55:45) by spin coating. Two pieces of the channels are heated under the surfaces by energizing a metallic thin-film heater 13 formed in the upper part of the clad part 12, by which the Curie temp. of the clad member material is exceeded, the refractive index of the clad part 12 is greatly changed and the switch of a cut-off type is formed. The ferroelectric material exhibiting the structural phase transition based on the temp. change is used for the waveguide clad part 12 and is held at a temp. above the specific temp., by which the large change in the refractive index of the structural change according to the phase transition is utilized for switching.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical switch for switching an optical path in an optical communication system.

[0002]

2. Description of the Related Art In recent years, with the practical use and expansion of functions of optical communication systems and optical information systems, there has been a demand for an optical switch capable of arbitrarily switching a signal light transmission path at high speed. Such an optical switch is required to have various characteristics such as low loss, high speed switching, high integration, and high reliability, and a waveguide type optical switch satisfying these characteristics is drawing attention.

Waveguide type optical switches include those utilizing the electro-optic effect of LiNbO3, those utilizing the band-filling effect of semiconductors, and those utilizing the thermo-optic effect of quartz (SPIE vol1337, Nonlinear optical switch). propertie
s of organic materials III, 1990).

From the viewpoint of low loss, it is known that a thermo-optical switch using a quartz waveguide is one of the most excellent ones.

This switch utilizes the temperature dependence of the refractive index of quartz, and performs switching by applying heat from the outside to change the refractive index of the heated portion.

[0006]

However, a problem of the thermo-optic switch using the quartz waveguide is that the temperature of the refractive index change region must be kept within a certain temperature range in order to maintain the switching state. That is not the case.

That is, the temperature dependence of the refractive index of quartz used as a switching principle is such that the refractive index continuously changes with a change in temperature. Therefore, in order to maintain a specific refractive index, It is necessary to control the heating temperature of quartz to be constant.

Further, due to the dispersion due to the manufacture of the waveguide,
There is also a problem that control is difficult because the temperature itself for switching also varies.

Therefore, the present invention solves the problem that the temperature of the refractive index change region must be controlled to a certain temperature in order to maintain the switching state as described above, and the temperature is kept above a certain temperature. An object of the present invention is to provide a photothermographic switch that can stably maintain a switching state having a constant refractive index if it is retained.

[0010]

As a means for solving the above-mentioned problems, the inventors of the present invention have proposed that a ferroelectric material exhibiting a structural phase transition due to a temperature change is used in a waveguide clad portion. It is possible to use a large change in the refractive index due to the structural change associated with the phase transition for switching, and the large change in the refractive index due to the structural change needs to be maintained above a specific temperature, and it is necessary to control the temperature within a certain range. Therefore, the present invention was completed and the present invention was completed.

More specifically, the present invention includes at least one waveguide and a cladding arranged around the waveguide, and changes the refractive index of at least a part of the cladding and / or the waveguide in response to temperature changes. The present invention relates to an optical waveguide type optical switch, wherein the change in refractive index is given by a ferroelectric substance.

Further, the present invention is an optical waveguide type optical switch including an on / off switching part including at least an input waveguide, an output waveguide, and the cladding part, the on / off switching being performed according to a temperature change. The present invention relates to an optical waveguide type optical switch, which is characterized in that a refractive index of a part of a clad portion of the above portion is changed to form a waveguide, and the change in the refractive index is given by a ferroelectric substance.

Further, the present invention is an optical waveguide type optical switch including a branch switching section including at least a branch section for branching two or more output waveguides from an input waveguide and the clad section, The invention is characterized in that a refractive index of a part of a clad part of the branch switching part is changed according to a temperature change to change an output optical waveguide, and the change of the refractive index is given by a ferroelectric substance. The present invention relates to an optical waveguide type optical switch.

Further, the present invention is an optical waveguide type optical switch including a phase modulation switching section including at least one waveguide and the clad section, wherein one of the clad sections of the phase modulation switching section responds to a temperature change. Characterized by changing the refractive index of the part to modulate the phase of the incident guided light,
The present invention relates to an optical waveguide type optical switch, wherein the change in refractive index is given by a ferroelectric substance.

Further, the present invention includes an internal total reflection switch section including an input waveguide, an output reflection optical waveguide and a transmission waveguide, and a reflection layer, and at least a part of the reflection layer in response to temperature change. The present invention relates to an optical waveguide type optical switch that changes a refractive index, wherein the reflective layer is provided by a ferroelectric substance.

Further, in the present invention, the ferroelectric substance is at least one selected from the group consisting of vinylidene fluoride polymer, vinylidene fluoride-trifluoroethylene copolymer and vinylidene fluoride-tetrafluoroethylene copolymer. It is characterized by including.

Further, the present invention includes the above-mentioned ferroelectric material, wherein the ferroelectric material contains at least a polyvinylidene fluoride-trifluoroethylene copolymer.

The present invention also includes a feature that the temperature change is based on heating by a metal thin film heater.

The present invention will be described in more detail below.

(Waveguide) In the present invention, a waveguide means an optical waveguide in which light propagates, and may be used as a core or a core portion.

The waveguide material usable in the present invention is not particularly limited, and both inorganic materials and organic materials can be preferably used.

Quartz can be particularly preferably used as the inorganic material, and polymer (for example, polymethylmethacrylates) can be particularly preferably used as the organic material.

In the present invention, the method for forming the waveguide is not particularly limited, and general semiconductor processing technology can be used.

For example, when the waveguide is made of inorganic crystal, it is formed by lift-off, when it is made of quartz, it is formed by FHD (flame deposition method), and when it is made of glass, it is formed by ion exchange method. A method such as forming can be preferably used.

(Ferroelectric substance) In the present invention, the ferroelectric substance is a substance which has spontaneous polarization caused by dipole moments pointing in the same direction and which has the property of being inverted by the polarity of the external electric field. Say. When the temperature of the ferroelectric substance is increased, the spontaneous polarization disappears at a certain temperature (Kuriry temperature) and the phase transitions to the paraelectric phase (Kittel, Introduction to Solid State Physics, Maruzen).

The ferroelectric substance that can be used in the present invention is not particularly limited, and both the waveguide portion and the clad portion can be suitably used as the inorganic ferroelectric substance material or the organic ferroelectric substance material.

As the inorganic ferroelectric substance material, for example, KH
2PO4, KH2AsO4, BaTiO3, KNbO3, PbTiO3, LiTaO3, LiNbO3 and the like can be preferably used, as the organic ferroelectric substance material, for example, triglycine sulfate, triglycine selenite, fluorine-based polymer and the like can be preferably used. is there.

From the viewpoints of workability and cost, organic ferroelectric substance materials can be particularly preferably used.

For example, it has been conventionally known that a fluorine-containing organic polymer is a ferroelectric substance, and these can be preferably used in the present invention.

Further, the ferroelectric polymer is not particularly limited as long as it is formed of a polymer of an organic monomer, and various types of copolymers can be used.

Further, in order to adjust heat resistance, mechanical strength, use temperature and the like, it is possible to contain various additives.

For example, a refractive index adjusting agent, an antioxidant, an ultraviolet ray inhibitor and the like.

(Change in Refractive Index Due to Temperature Change) Further, the ferroelectric substance that can be used in the present invention has a so-called stepwise temperature dependence of the refractive index.

In the present invention, that the temperature dependence of the refractive index is stepwise means that the material containing the ferroelectric substance material has a large refractive index at a specific temperature (close to the Curie temperature) and changes stepwise (stepwise). Means to do.

That is, the temperature dependence of the refractive index according to the present invention is not the conventionally known smooth change of the refractive index depending on the temperature of, for example, quartz, but the secondary change due to the structural change of the ferroelectric substance material. It is based on a phase transition, and it is thought that the refractive index changes sharply at a specific temperature (Curie temperature) due to reorientation of polarizable substituents in the molecule (electron・ Photofunctional polymers, 13
1 page, edited by Yoshino, Kodansha Scientific).

The change in refractive index due to this structural phase transition is
The value is usually about one digit larger than the change in the refractive index due to the temperature dependence of the refractive index without structural phase transition.

That is, below the temperature of this phase transition (Curie temperature) (ferroelectric phase), a constant refractive index is shown, and above the Curie temperature (paraelectric phase), a constant refractive index greatly different from the above refractive index. Is shown.

When the Curie temperature is further lowered, the refractive index also largely changes and returns to the original value again.

That is, photothermo-optical switching can be performed by changing the refractive index by keeping the temperature higher or lower than the Curie temperature.

Furthermore, the Curie temperature can be set based on the mode of use of the optical waveguide type optical switch.

For example, it can be set depending on the type of the monomer or the copolymerized monomer and the properties of the polymer (for example, molecular weight distribution, degree of branching, stereoregularity, etc.).

For example, in vinylidene fluoride-trifluoroethylene copolymer, it is known that various physical properties such as electrical characteristics can be changed by changing the monomer ratio (electron / optical functional polymer, 131 pages, edited by Yoshino, Kodansha Scientific).

The temperature change of the refractive index of the ferroelectric substance as the switch which can be preferably used in the present invention is as follows. Hereinafter, the Curie temperature is T _C , the refractive index in the ferroelectric phase is n _L below the Curie temperature, and the refractive index in the paraelectric phase is n _L above the Curie temperature.
_{Let H.}

In the present invention, at least 1 from T _C
It is desirable that the refractive index be substantially equal to n _L at a temperature lower by 0 ° C. or be substantially equal to n _H at a temperature 10 ° C. higher than T _C.

[0045] Further, it is more desirable refractive index at least 5 ° C. lower temperature than the T _C is n _L substantially equal, or T _C of at least 5 ° C. higher temperatures in refractive index is equal to n _H substantially .

Here, “substantially equal” means that the difference between the actual refractive index n and the refractive index n _L or n _H in each phase, that is, | n−n _H | or | n _L −n | , | N _L
It is preferably at least 10% or less of -n _H |, and more preferably 5% or less.

In the present invention, it is also desirable that the difference between the two phases of the refractive index of the ferroelectric substance as a switch which can be preferably used is | n _L −n _H | ≧ 10 ⁻⁴ ,
Furthermore, it is more preferable that | n _L −n _H | ≧ 10 ⁻³ . Particularly preferably, | n _L −n _H | ≧ 10 ⁻² .

(Clad part) In the present invention, the clad part means a part which is arranged around the above-mentioned waveguide and enables switching etc. by the difference in refractive index from the waveguide. To do.

In the present invention, the method for forming the above ferroelectric material as the clad portion is not particularly limited.

General processing means can be preferably used. For example, in the case of an inorganic crystal, the crystal itself is used as a clad, and the core is preferably formed by thermal diffusion of metal atoms.

In particular, when an organic ferroelectric polymer is used, it is preferable to dissolve it in an organic solvent and spin coat it.

For example, it is possible to dissolve the mixture containing the polymer and necessary additives in a suitable solvent and form the mixture on the optical waveguide type optical switch element by a method such as spin coating.

(On / Off Switching Section) In the present invention, the mode of the on / off switching section is not particularly limited.

Generally, the input waveguide and the output waveguide are installed in the clad portion with an appropriate distance,
When the cladding portion is not heated, the light from the input waveguide is collected in the cladding portion direction, and the switch is in the off state.

Further, when a part of the clad portion is heated to reach the Curie temperature or higher, the refractive index changes, the clad portion becomes a waveguide, and the switch is turned on.

(Branching part) The branching part of the present invention has a structure in which an input waveguide and at least two or more output waveguides are installed in close proximity to each other, or an output is made from the input waveguide. It does not matter whether the waveguide for is branched.

Generally, when the clad portion of the branch portion has a Curie temperature or lower, light passes through one output waveguide, but when the clad portion of the branch portion is heated to the Curie temperature or higher. In, the change in the refractive index causes switching to the other output waveguide and switching.

(Phase Modulation Switching Section) In the present invention, the structure for phase modulation is not particularly limited.

In general, a part of the waveguide is heated to a Curie temperature or higher to change the refractive index difference between the waveguide and the cladding to perform modulation.

It is also possible to provide a plurality of modulation switching parts by appropriately selecting the constituent components of the clad part, or by providing different clad parts so as to have partially different Curie temperatures.

(Internal Total Reflection Switch Section) In the present invention, the structure of the internal total reflection switch section is not particularly limited.

Generally, when a ferroelectric material is used as the reflective layer and the reflective layer is maintained at the Curie temperature or lower, all the incident light is reflected due to the difference in refractive index between the incident optical waveguide and the reflective layer. Then, the light passes through the reflected output waveguide.

On the other hand, when the reflective layer is heated to the Curie temperature or higher, the refractive index of the reflective layer changes greatly, and all the incident light is transmitted through the reflective layer due to the difference in refractive index between the incident optical waveguide and the reflective layer. It will pass through the transmission output waveguide.

(Vinylidene Fluoride, Vinylidene Fluoride-Trifluoroethylene Copolymer, Vinylidene Fluoride-Tetrafluoroethylene Copolymer) The organic polymer as the organic ferroelectric according to the present invention has been conventionally known. Those that can be suitably used are not particularly limited.

Vinylidene fluoride polymers, vinylidene fluoride-trifluoroethylene copolymers and vinylidene fluoride-tetrafluoroethylene copolymers are well known and can be particularly preferably used in the present invention.

In the present invention, these polymers may be used alone or in a mixture with other polymers.

In the present invention, the monomer ratio of the above copolymer is important especially when controlling the Curie temperature.

For example, in the case of vinylidene fluoride-trifluoroethylene copolymer, the Curie temperature is 70 to 80 ° C.
However, a monomer ratio of 1: 1 is suitable for adjusting the Curie temperature.

(Metallic thin film heater for heating) The material constituting the heating heater usable in the present invention is not particularly limited as long as it is a conductive material.

From the viewpoint of workability and cost, Al
(Aluminum), Ti (titanium) and the like can be used particularly preferably.

The shape of the heating heater is not particularly limited as long as it can keep the clad portion to be heated above the Curie temperature.

The forming method is not particularly limited.

For example, the heater may be embedded in the surface to be formed. More specifically, a concave portion having the shape of a heater is formed (or a predetermined surface is formed so as to give the concave portion in advance), and all or a part of the conductive material such as Al constituting the heater is formed as described above. You may fill in the recessed part formed in.

(Waveguide type optical switch) Generally, as shown in FIG. 5, a lower clad portion 52 is formed on a suitable substrate 51 (for example, Si), and a waveguide 53 is further formed thereon. It can be manufactured by forming the upper clad portion 54 on the substrate and further forming the required metal film heater 55 for heating.

Hereinafter, some possible modes of the waveguide type optical switch using the temperature change of the refractive index due to the phase transition accompanied by the structural change according to the present invention will be shown below. However, the embodiments of the optical switch in which the present invention can be used are not limited to these.

A refractive index distribution control type on / off type switch can be formed as shown in FIG. Here, the waveguide 11 may be formed of quartz, polymer, or the like. The clad portion 12 can be formed by applying a vinylidene fluoride-trifluoroethylene copolymer (55:45) by spin coating.

The two channels shown in FIG. 1 are heated below the surface of the metal thin film heater 13 having the clad portion formed on the upper side thereof, so that the Curie temperature of the material of the clad portion is exceeded and the refraction of the clad portion is increased. The rate changes greatly and a cut-off type switch is formed.

When a vinylidene fluoride-trifluoroethylene copolymer (55:45) is used as the cladding, the Curie temperature is about 70 ° C.

Also, a directional coupler type switch can be formed as shown in FIG. Here, the waveguide 63 may be formed of quartz or polymer or the like. The clad portion 64 is made of vinylidene fluoride-trifluoroethylene copolymer (5
5:45) may be applied by spin coating. A metal thin film heater 65 is formed on the surface of the clad portion at the coupling portion of the waveguide.

When the metal thin film heater is energized, the refractive index of the clad portion in the coupling portion is greatly changed, the coupling constant in the coupling region is changed, and the output path is switched.

When a vinylidene fluoride-trifluoroethylene copolymer (55:45) is used as the cladding, the Curie temperature is about 70 ° C.

The phase control type switch utilizing the change in refractive index according to the present invention is also possible.

In the branch buffer type modulator switch as shown in FIG. 3, the waveguide 32 may be made of quartz or polymer. The clad portion 31 can be formed by applying a vinylidene fluoride-trifluoroethylene copolymer (55:45) by spin coating.

When the metal thin film heater 33 is energized, the temperature of the clad under the heater exceeds the Curie temperature,
The refractive index changes greatly, and the phase change of the guided light is obtained.

When a vinylidene fluoride-trifluoroethylene copolymer (55:45) is used as the clad portion, the Curie temperature is about 70 ° C.

Further, as shown in FIG. 4, a switch of total internal reflection type (TIR) can be formed.

The waveguide 43 can be made of quartz or polymer. A layer 45 of vinylidene fluoride-trifluoroethylene copolymer (55:45) is provided at the intersection of the two waveguides to reflect or transmit incident light. A heater 46 made of a metal thin film is provided in the vicinity of the intersection of the vinylidene fluoride-trifluoroethylene copolymer (55:45) layer.

When the metal thin film heater is energized, the layer of vinylidene fluoride-trifluoroethylene copolymer (55:45) in the vicinity of the intersection is heated, and when the Curie temperature is exceeded, the refractive index greatly changes and the incident light is transmitted. The light is totally reflected.

When the vinylidene fluoride-trifluoroethylene copolymer (55:45) is used as the reflection / transmission part, the Curie temperature is about 70 ° C.

[0090]

In the present invention, by using a ferroelectric material as the cladding material, a stepwise refractive index based on a second-order phase transition accompanied by a structural change from the ferroelectric phase to the paraelectric phase at the transition temperature (Curie temperature) A change occurs, which enables an optical waveguide switch that switches depending on whether the transition point temperature (Curie temperature) rises or falls.

[0091]

Embodiments of the present invention will be described in detail below with reference to the attached drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

(Directional Coupler Switch) A 2 × 2 directional coupler switch shown in FIG. 6 was produced.

A quartz film was formed as a lower clad layer 62 on the single crystal silicon wafer 61 by a general flame deposition method under the following conditions.

Further, two waveguide core portions 63 having the shape shown in the drawing were formed on the surface of the lower clad 62 by the flame deposition method similarly.

On the upper surface of the obtained core portion, a solution of vinylidene fluoride-trifluoroethylene copolymer (vinylidene fluoride mole fraction 55%) in dimethylformamide (2
0%) spin coating the upper clad layer 6
4 was formed. In this case, 5% of fluorine-substituted PMMA (polymethylmethacrylate) was added to the polymer as a refractive index adjusting agent.

The refractive index of this upper cladding layer at room temperature (25 ° C.) was 1.447.

The Curie temperature of this polymer is about 70.
° C.

Furthermore, the temperature above the Curie temperature (about 95
(° C.), the refractive index was 1.442.

Further, a thin film heater 65 was formed in a region covering the upper part of the coupling portion where two waveguides approach each other (target; metallic titanium, sputter gas; argon, pressure; 2 × 10 ⁻¹ Pa). ).

The resistance value and energization amount of the heater were set so that the cladding of the joint could be heated to 90 to 100 ° C.

When the heater of the obtained 2 × 2 directional coupler switch was not energized, when light was incident from the input port, the light was emitted from the output port A.

On the other hand, when the heater was energized to heat the upper clad layer, after about 0.5 seconds, the output light was emitted from the output port B.
It switched to. Even if the heater was energized and heating was continued, the output did not change.

After that, when the heater was turned off, about 0.5 seconds later, the light was emitted from the output port again.

(Internal Total Reflection Switch) The internal total reflection switch shown in FIG. 4 was produced.

A quartz film was formed on a crystalline silicon wafer 41 by a flame deposition method under the following conditions, for each of the substrate having the incident optical waveguide core and the reflecting optical waveguide and the two substrates having the transmitting optical waveguide. .

A thin film 45 of vinylidene fluoride-trifluoroethylene copolymer (vinylidene fluoride mole fraction 55% and a polymer containing a refractive index matching agent) was formed on these two substrates.
It was sandwiched and the optical waveguide for incidence and the optical waveguide for transmission were attached so as to be a straight line.

Further, the thin film heater 46 is formed on the region of the vinylidene fluoride-trifluoroethylene copolymer thin film in the vicinity of the reflecting portion composed of the incident optical waveguide, the reflective optical waveguide, and the transmissive optical waveguide by vapor deposition of titanium metal. Was formed.

The resistance value and energization amount of the heater were set so that the cladding of the joint could be heated to 90 to 120 ° C.

When the heater of the obtained internal total reflection type switch was not energized, when light was incident from the incident optical waveguide, the light was emitted from the reflective optical waveguide core.

On the other hand, when the heater was energized and heated, the output light was switched to the output from the transmission optical waveguide after about 0.5 seconds. Even if the heater was energized and heating was continued, the output light did not change.

Then, when the heater was turned off, the light was emitted from the reflection optical waveguide again after about 0.5 seconds.

[0112]

According to the structure of the present invention, a ferroelectric material exhibiting a structural phase transition due to a temperature change is used in a waveguide clad portion, and is maintained at a certain temperature or higher, so that a large structural change due to the phase transition occurs. The refractive index change can be used for switching.

[Brief description of drawings]

FIG. 1 is a diagram showing an aspect of a configuration of an optical waveguide type optical switch having an on / off switching unit.

FIG. 2 is a diagram showing an aspect of a configuration of an optical waveguide type optical switch having a branch switching unit.

FIG. 3 is a diagram showing two modes (A, B) of a configuration of an optical waveguide type optical switch having a phase modulation switching section.

FIG. 4 is a diagram showing an aspect of a configuration of an optical waveguide type optical switch having an internal total reflection switch section.

FIG. 5 illustrates a process of forming a directional coupler switch.

FIG. 6 shows a 2 × 2 directional coupler switch.

[Explanation of symbols]

1 ... Waveguide, 2 ... Reference waveguide, 4 ... Heating electrode, 11 ...
Metal thin film heater, 1 ... Clad part, 2 ... Reflective layer, 4 ...
SiO2, 11 ... Lower clad layer, 2 ... Reflective layer, 4 ... S
i02, 11 ... Upper clad layer.

Claims (8)

[Claims] 1. An optical waveguide type light including at least one waveguide and a clad portion arranged around the waveguide, and changing the refractive index of at least a part of the clad and / or the waveguide according to a temperature change. An optical waveguide type optical switch, wherein the change in refractive index is given by a ferroelectric substance. 2. An optical waveguide type optical switch including an on / off switching section including at least an input waveguide, an output waveguide, and the cladding section, wherein the cladding section of the on / off switching section responds to a temperature change. The optical waveguide type optical switch according to claim 1, wherein a refractive index of a part of the optical waveguide is changed to form a waveguide. 3. An optical waveguide type optical switch including a branch switching part including at least a branch part for branching two or more output waveguides from an input waveguide, and a clad part. 2. The optical waveguide type optical switch according to claim 1, wherein the refractive index of a part of the cladding portion of the branch switching portion is changed to change the output optical waveguide. 4. An optical waveguide type optical switch including a phase modulation switching section including at least one waveguide and the clad section, wherein a refractive index of a part of the clad section of the phase modulation switching section according to temperature change. Is changed to modulate the phase of the incident guided light, and the optical waveguide type optical switch according to claim 1. 5. An internal total reflection switch section including an input waveguide, an output reflection optical waveguide and a transmission waveguide, and a reflection layer, wherein the refractive index of at least a part of the reflection layer is changed according to temperature change. An optical waveguide type optical switch, wherein the reflective layer is provided by a ferroelectric substance. 6. The ferroelectric material contains at least one selected from the group consisting of a vinylidene fluoride polymer, a vinylidene fluoride-trifluoroethylene copolymer, and a vinylidene fluoride-tetrafluoroethylene copolymer. The waveguide type optical switch according to claim 1 or 5. 7. The waveguide type optical switch according to claim 1, wherein the ferroelectric substance contains at least a polyvinylidene fluoride-trifluoroethylene copolymer. 8. The optical waveguide type optical switch according to claim 1, wherein the temperature change is based on heating by a metal thin film heater.