JPH08334799A - Optical waveguide device - Google Patents

Abstract

PURPOSE: To lessen propagation loss and to prevent the drastic decrease in output light quantity by forming a core layer of an optical waveguide to a layer combined with a specific πconjugation material layer and a polymer layer having excellent transparency, thereby making it possible to utilize the high nonlinear optical effect of an absorption resonance region. CONSTITUTION: The layer 2 of the π conjugation material which alone does not form the optical waveguide as the material has absorption and scattering to the wavelength of the light to be guided and at least the one polymer layer 3 having the excellent transparency are used in combination as the core layer of the optical waveguide. Incident light 5 is confined in the core layer constituted of the π conjugation material layer 2 and the polymer layer 3 and is propagated therein. The light is propagated and is made into exit light 6 but when an electric field is impressed thereon, the refractive index of the π conjugation material layer 2 changes and the effective refractive index changes as the entire part of the waveguide. The way of the propagation of the waveguide is changed by the change and, therefore, the direction of the exit light 6 changes. In actuality, the change in the effective refractive index as the entire part of the optical waveguide is smaller than in the case the core layer is formed of the π conjugation material alone.

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 obtained by using a non-linear optical material in the fields of communication using light and information processing.

[0002]

2. Description of the Related Art Optical modulators and optical switching devices are important as devices used for communication and information processing using light. These are for loading and reading information on the light by modulating the phase and intensity of the light.

Nonlinear optical materials are generally used for such optical modulators and optical switching elements. The nonlinear optical material is a material whose optical constants such as a refractive index and an absorption coefficient change according to the intensity of incident light and an electric field from the outside. The nonlinear optical effect has a quadratic effect and a cubic effect corresponding to the related light order or electric field order. For the above-mentioned applications, the quadratic effect is an electrical- Can only modulate light. On the other hand, in so-called all-optical modulation in which light is controlled by light, it is essential to use a third-order nonlinear optical effect.

The third-order non-linear optical effect includes the following, the electric Kerr effect in which the refractive index changes with an external electric field, the Franz-Keldish effect in which the absorption coefficient changes with an external electric field, and the refraction depending on the external light intensity. There are a Kerr effect in which the rate changes, and a band-filling effect in which the absorption coefficient changes depending on the external light intensity.

As an optical modulator using this nonlinear optical material, an optical modulator formed by a thin film optical waveguide instead of a bulk crystal has already been devised. As an example, JP-A-3-
It is described in detail in Japanese Patent No. 118511 and the like. The main advantages of optical waveguide media when compared to bulk crystals when using optical waveguides are that they can be used at low voltage when using the electro-optic effect, and they can be combined with other devices. Is possible.
Since the light is confined in a small area when the optical waveguide is used, it is also advantageous when the third-order nonlinear optical effect that utilizes the intensity of light is used.

As described above, the optical waveguide type optical modulator has an advantage that the applied voltage is lower than that of the bulk type.
Although widely researched and developed, the use of a nonlinear optical material as a waveguide requires transparency to light. The factor that gives the propagation loss of light in the optical waveguide is that the loss due to the absorption unique to the nonlinear optical material is large, but even if there is no absorption, the influence of scattering caused by various reasons such as microcrystallinity. It can also be said that it is large.

Therefore, in the above publication, the organic thin film portion exhibiting the second-order nonlinear susceptibility χ ⁽²⁾ is the core layer of the optical waveguide, and the second-order nonlinear susceptibility has a refractive index smaller than that of the organic thin film portion. An optical-waveguide-type electro-optical modulator including upper and lower cladding layers showing χ ⁽²⁾ is described.
It is described in the above publication that what is important for producing an optical waveguide device is a low loss for propagating light. Therefore, both the core layer and the clad layer are made of a polymer having high transparency as a main component and an organic material having a large nonlinear optical effect is contained therein.

The propagation loss of the optical waveguide is determined by the light absorption characteristics of the core layer and the cladding layer, the scattering characteristics due to the crystallinity and uniformity in the medium, the smoothness of the interface and the surface, and the like. In a normal organic nonlinear optical material, the nonlinear optical effect is small when it is transparent in the wavelength region to be observed, and the nonlinear optical effect is large in the region of large absorption, that is, χ ⁽²⁾ and χ ⁽³⁾ are When it grows, it is common.

Therefore, as described in the above publication, when a transparent polymer is used as a host and a material having a high light absorption property and a large nonlinear optical effect is contained in the transparent polymer, from the viewpoint of the propagation loss, Since the content rate cannot be increased so much, there is a problem that sufficient performance for performing electro-optical modulation cannot be obtained. Furthermore, since the molecules in the polymer are in a state close to the molecular dispersion, the overall non-linear optical characteristics are at most a simple sum of the non-linear optical characteristics of each molecule. Therefore, there is a problem in that the effect of increasing the nonlinear optical properties, which is exhibited by the formation of a structure such as a microcrystal or an aggregate, of the nonlinear optically active molecule cannot be utilized.

When the nonlinear optical material itself has no absorption, the content of the π-conjugated material as the nonlinear optical material in the transparent polymer as the host polymer can be improved, but phase separation and microcrystals Problems such as instability occur.

The non-linear optical effect is most improved when the host polymer is not used and the non-linear optical material itself is used. However, in many cases, such as when forming a microcrystalline region, scattering becomes large, There is a problem that it cannot be manufactured as an optical waveguide.

An example of an optical waveguide type optical modulator using the thin film is a Mach-Zehnder type device. FIG. 7 shows the structure of a Mach-Zehnder device.

That is, in the structure in which the waveguide 16 having the demultiplexing portion and the multiplexing portion is formed on the substrate 15, the optical input 19 incident from the entrance of the waveguide 16 is divided into two branches 17 and 18. The branch 18 which is divided into two parts is provided with a pair of electrodes 21 and the phase of the propagating light is changed by applying an electric field to the part of the branch 18, so that the light from the other branch 17 can be changed. The light output 20 is changed by combining and combining them to change the phase due to the interference effect.

Here, in order to obtain a modulation of 0 to 100% with respect to the optical output, it is necessary that the amounts of light from the branch 17 and the branch 18 are the same amount, and normally, it is the same as the demultiplexing part of the optical waveguide. It is designed to have a symmetrical structure with the multiplexing part. However, as described above, if the nonlinear optical material portion has absorption loss or scattering, such a design reduces the signal level of the entire output light.

FIG. 8 shows a conventional sandwich type optical waveguide. The Mach-Zehnder device shown in FIG. 7 has a parallel electrode structure installed in parallel with the optical waveguide, but here, a simpler sandwich optical waveguide is shown.

The core layer 23, which is the portion of the optical waveguide through which light propagates, is made of a non-linear optical material. The substrate 22 and the buffer layer 24 serve as a clad layer for the optical waveguide. Two
Reference numerals 5 and 26 are electrodes. The buffer layer 24 prevents the loss from becoming large when the core layer 23 of the optical waveguide is in direct contact with the electrode 26, and is unnecessary in the parallel electrode structure used in the Mach-Zehnder type device as shown in FIG. The propagating light 27 in the optical waveguide travels while being totally reflected at an internal reflection angle θ _n1 as schematically shown in the figure.

At this time, the effective refractive index N _eff of the optical waveguide is N _eff = n _n1 sin θ _n1 using the refractive index n _n1 of the π-conjugated material. The change in the effective refractive index N _eff when an electric field is applied to the optical waveguide is N _eff + ΔN _eff = (n _n1 + Δn _n1 ) sin (θ _n1 + Δθ
_n1 ). Since Δθ _n1 is small, it is transformed into the following equation.

ΔN _eff = Δn _n1 sin θ _{n1 In} order to apply this change in refractive index to the optical switching device, the phase change amount Δφ needs to be about 2π radians. This amount of phase change is determined by the wavelength λ of the propagating light and the device length L.
The required device length L is λ / ΔN _eff from the equation Δφ = (2π / λ) ΔN _eff L = 2π.
The change Δn _{n1 in} the refractive index of the nonlinear optical material increases with an electric field or an optical field, but there is a limit to the change and it saturates to some extent. Its saturation level is of the order of 10 ⁻⁴ or less even when this effect is large.

In this case, the device length needs to be about 2 cm. Further, the device length L is limited by the expression L <α ^{−1 with} respect to the absorption coefficient α of the material, from the viewpoint that sufficient output can be obtained even if light is absorbed. From this, the absorption coefficient α needs to be 0.5 cm ⁻¹ or less, and this size is the one that can be obtained only in the almost completely transparent region. However, the non-linear optical effect that causes the large refractive index change Δn _n1 as described above can usually be obtained only in the resonance absorption region where the absorption is large.

[0020]

As described above, the non-linear optical effect, which is a mechanism for changing the refractive index and absorption coefficient of the non-linear optical material, dramatically increases in the absorption region of the material. In general, the effect is shown, but in order to realize the device, if the absorption is large, there is an absorption loss of light propagating through the device, which is disadvantageous.
As described above, in realizing a device, it is general that there is a trade-off relationship between the transparency of the material and the nonlinear optical effect.

Therefore, if an attempt is made to utilize the non-linear optical effect of resonance in the absorption region peculiar to the non-linear optical material, the propagation loss when the optical waveguide is formed becomes large, so that the optical waveguide device cannot be manufactured, or There is a problem that only a device that operates in a transparent wavelength region that exhibits only a small nonlinear optical effect can be manufactured.

Further, even when the nonlinear optical material itself is transparent without showing absorption, the propagation loss of light is increased because the scattering increases due to the formation of the microcrystalline state and becomes opaque.
It could not be used as a device. Further, in a dispersion system using a transparent polymer as a host, there are problems that sufficient performance cannot be obtained due to the small number of molecules and that the effect of increasing the nonlinear optical properties due to the formation of microcrystals or aggregates cannot be utilized. It was

Further, when the optical waveguide is formed by using the π-conjugated system material having the high nonlinear optical effect as described above, the absorption coefficient of the π-conjugated system material becomes large, and even if there is no absorption, the microcrystal is present. There is a problem that the absorption loss of the light propagating through the optical waveguide becomes large, such as the scattering becomes large due to the property. For example, when a Mach-Zehnder device is constructed, there is a problem that the output light amount is significantly reduced.

The present invention has been made in view of the above problems, and is used for an optical modulator, an optical switching element and the like in the fields of communication using light and information processing.
It is an object of the present invention to provide a novel optical waveguide device that has a small propagation loss and does not significantly reduce the amount of output light.

[0025]

The present invention is an optical waveguide device obtained by using a nonlinear optical material, wherein an effective electric field is applied to the nonlinear optical material of the core layer of the optical waveguide and / or an external device. In the optical waveguide device capable of modulating the intensity and / or the phase of the propagating light by irradiating or guiding the control light from the optical waveguide to change the optical constant of the nonlinear optical material, the core layer of the optical waveguide is ,
A combination of a π-conjugated material layer having a property of substantially absorbing light with respect to the wavelength of the propagating light and / or a property of having a large light scattering property, and at least one polymer layer having excellent transparency. The present invention relates to an optical waveguide device characterized by being obtained.

Further, in the present invention, the π-conjugated material is thiophene, vinylene, phenylenevinylene, phenylenevinylene, p-phenylene, a substitution product thereof or a combination thereof.
The number of the repeating units is 4 or more, and the number n of the repeating units is 4
It is preferably at least one selected from the group consisting of an oligomer having 10 to 10 or a polymer in which the number n of the repeating units is 20 or more, an unsubstituted phthalocyanine and a metal phthalocyanine.

Further, according to the present invention, in a Mach-Zehnder device in which incident light is demultiplexed, guided to two optical waveguides, and then multiplexed to control the light intensity, one optical waveguide is claimed. Or an optical waveguide having a core layer according to 2, wherein the other optical waveguide is an optical waveguide made of only a polymer material having no non-linear optical characteristic,
Further, the present invention relates to an optical waveguide device characterized in that the ratio of the amount of light split into the two optical waveguides is equal to the ratio of the reciprocal of the light transmittance of both optical waveguides.

[0028]

In the present invention, the core layer of an optical waveguide is combined with a polymer layer having excellent transparency even in a nonlinear optical material which cannot be applied to an optical waveguide by itself because of large waveguide loss due to absorption or scattering. By using such a material, even such a material with large loss can be made into a device.

Further, in the present invention, the π-conjugated material is
Thiophene, vinylene, chenylene vinylene, phenylene vinylene, p-phenylene, substituted products thereof, or a repeating unit of two or more of them, and the number n of the repeating units is 4 to 10 or the number of the repeating units. By using at least one selected from the group consisting of a polymer in which n is 20 or more, an unsubstituted phthalocyanine and a metal phthalocyanine, an optical waveguide can be formed by combining with a polymer layer having better film forming property and high transparency. Easy to form.

Further, in the present invention, in the Mach-Zehnder type device in which incident light is demultiplexed, guided to two optical waveguides, and then multiplexed to control the light intensity, one optical waveguide is used. Only by using a lossy optical waveguide containing only a non-linear optical material, the light amount division into two optical waveguides is made equal to the ratio of the reciprocal of the two transmittances to obtain an efficient optical output.

[0031]

1 is a diagram showing the structure of an optical waveguide according to a first embodiment of the present invention. This first embodiment shows the most basic constitution of the present invention, and operates as an optical waveguide device capable of modulating and switching the light intensity in the optical waveguide.

In FIG. 1, 1 is a substrate, 2 is a π-conjugated material layer provided on the substrate 1, 3 is a polymer layer, and π
The conjugated material layer 2 and the polymer layer 3 operate as a core layer that performs optical confinement as an optical waveguide. 4 is a buffer layer, 5 is incident light, and 6 is outgoing light.

Reference numerals 7 and 8 are control lights for changing the optical constant of the π-conjugated material layer 2, 7 corresponds to the case where light is incident on the entire waveguide, and 8 is incident on the inside of the waveguide. is there. The control by light from the outside may be either 7 or 8, but other methods may be used.

As such a method, for example, there is a method in which the optical waveguide is formed into a channel and light from another adjacent waveguide is incident. Reference numerals 9 and 10 denote electrodes for applying an electric field to the optical waveguide, and these electrodes are of course unnecessary if an external electric field is not used as a control means for the π-conjugated material layer. Therefore, the presence or absence of irradiation light and the necessity of electrodes are determined depending on the control means of the device.
It is also possible to use both the applied electric field and the control light.

As the material for the substrate 1, for example, a semiconductor such as silicon can be used in addition to ordinary glass, and there is no particular limitation.

The nonlinear optical material that can be used in the present invention includes, for example, glass in which semiconductor ultrafine particles are dispersed in addition to the π-conjugated material, but the π-conjugated material is preferable from the viewpoint of forming an optical waveguide.

The π-conjugated material used for the π-conjugated material layer 2 is a material whose optical constants such as a refractive index and an absorption coefficient are changed by external control light or an electric field, that is, a material having a nonlinear optical effect. I wish I had it. In order to use it for an optical waveguide, it is usually necessary that the absorption is small, but the limitation is relaxed in the present invention, and a material having a large nonlinear optical constant due to the resonance absorption effect accompanying light absorption can be used. Is. Therefore, as the applicable material, any π-conjugated material can be used, and a specific example thereof will be shown below.

Examples of the π-conjugated material include polypyrroles such as polypyrrole, poly (N-substituted pyrrole), poly (3-substituted pyrrole), poly (3,4-disubstituted pyrrole), polythiophene, poly (3). -Substituted thiophene), poly (3,4-disubstituted thiophene), polythiophenes such as polybenzothiophene, polyisothianaphthenes such as polyisothianaphthene, polychenylene vinylenes such as polyphenylene vinylene, poly ( p-
Poly (p-phenylene vinylene) s such as phenylene vinylene), polyaniline, poly (N-substituted aniline),
Poly (3-substituted aniline), poly (2,3-substituted aniline) and other polyanilines, polyacetylene and other polyacetylenes, polydiacetylene and other polydiacetylenes, polyazulene and other polyazylenes, polypyrene and other polypyrenes, polycarbazole , Polycarbazoles such as poly (N-substituted carbazole), polyselenophenes such as polyselenophene, polyfurans such as polyfuran and polybenzofuran, poly (p-phenylene) s such as poly (p-phenylene), poly Polymers such as polyindoles such as indole, polypyridazines such as polypyridazine, polyacenes such as polyacene, and α-sexicenyl and styrylbenzene derived from, for example, thiophene hexamers having the same repeating units as those polymers. Oligomers, such as, metal phthalocyanine, pigments such as non-substituted phthalocyanine, merocyanine dyes, such as dyes such as hemicyanine dyes, and the like.

Among these π-conjugated materials, the π-conjugated material is preferable because it has a good film-forming property and can be easily combined with a polymer layer having high transparency to form an optical waveguide.
Thiophene, vinylene, chenylene vinylene, phenylene vinylene, p-phenylene, substituted products thereof, or a repeating unit of two or more of them, and the number n of the repeating units is 4 to 10 or the number of the repeating units. At least one selected from the group consisting of polymers having n of 20 or more, unsubstituted phthalocyanines and metal phthalocyanines is preferable.

The structural formulas of some of the π-conjugated materials are shown below.

[0041]

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Among the above-mentioned π-conjugated materials, the polymers and oligomers may be used alone or in combination, or a copolymer having two or more kinds of repeating units of these polymers and oligomers may be used. Polymers and oligomers may be used in combination with unsubstituted phthalocyanine and metal phthalocyanine.

The number n of repeating units of the oligomer is preferably 4 to 10, and the number n of repeating units of the polymer is preferably 20 or more.

In the present invention, in the π-conjugated material layer 2,
For example, materials having functional groups such as acrylic acid, acetamide, dimethylamino group, cyano group, carboxyl group, and nitro group, and electrons such as benzoquinone derivatives, tetracyanoethylene and tetracyanoquinodimethane, and their derivatives can be used. A material that serves as an acceptor, such as an amino group, a triphenyl group, an alkyl group,
Materials having functional groups such as hydroxyl groups, alkoxy groups, phenyl groups, substituted amines such as phenylenediamine, anthracene, benzanthracene, substituted benzanthracenes, pyrene, substituted pyrene, carbazole and its derivatives, tetrathiafulvalene and its derivatives, etc. As described above, a material that serves as a donor that is an electron donor may be included (so-called doping).

The method for producing the π-conjugated material layer 2 depends on various properties of the π-conjugated material (regardless of nonlinear optical characteristics), but for example, spin coating method, bar coating method, roll coating method. , Casting method, electrolytic polymerization method,
Vacuum deposition method, Langmuir-Blodgett method, CVD
Any method may be used as long as it is a method for producing an organic thin film, such as a dipping method or a dipping method. However, from the viewpoint of applying the fabricated thin film to an optical waveguide, it is necessary that the homogeneity of the thin film and the surface smoothness are high, and from the viewpoint of improving the nonlinear optical characteristics of the material, the vacuum deposition method is effective. It can be given as one of the methods.

The polymer used for the polymer layer 3 is a highly transparent polymer, for example, 35
The transmittance of light having a wavelength in the range of 0 nm to 1500 nm is 80% to 100%, preferably 85% or more. Examples of such a polymer include acrylic resin and methacrylic resin such as polymethylmethacrylate, polystyrene and the like. Polystyrene resin such as polychloromethylstyrene, polycarbonate resin, polyimide,
Examples include polyvinyl chloride resin and polyester resin.
Acrylic resins, polystyrene resins, polyimide resins, etc. are preferable from the viewpoint of whether or not they affect the conjugated material layer.

As the method for producing the polymer layer 3, for example, spin coating method, bar coating method, roll coating method, casting method, electrolytic polymerization method, vacuum deposition method, Langmuir Blodgett method, CVD method, dipping method, etc. Other methods include encapsulating a liquid phase monomer in a glass substrate or the like and polymerizing it by heating or light irradiation to form a solid phase polymer. In order to form the transparent polymer layer 3 without affecting, it is preferable to use a method of forming a film from a polymer instead of forming a film from a monomer. Further, in order to form a transparent thin film with less scattering, a spin coating method, a bar coating method, a roll coating method, a casting method, a dipping method and the like, which are methods of forming a thin film from a polymer dissolved in a solvent, are preferable.

As the material used for the buffer layer 4, similar to the polymer layer 3 described above, for example, acrylic resin and methacrylic resin such as polymethylmethacrylate, polystyrene resin such as polystyrene and polychloromethylstyrene, polycarbonate resin, polyimide. , Polyvinyl chloride resin, polyester resin, etc., but acrylic resin, polystyrene resin, polyimide resin, etc. are preferable from the viewpoints of transparency, moldability, and presence or absence of influence on the π-conjugated material layer in the thinning process. .

As a method for producing the buffer layer 4,
For example, in addition to the spin coating method, bar coating method, roll coating method, casting method, electrolytic polymerization method, vacuum deposition method, Langmuir-Blodgett method, CVD method, dip method, etc., a liquid phase monomer is added to a glass substrate or the like. There is a method of encapsulating and polymerizing it by heating or light irradiation to form a solid phase polymer. In order to form the buffer layer 4 without adversely affecting the underlying polymer layer 2, it is necessary to use a monomer from a monomer. It is preferable to use a method of film formation from a polymer instead of the above film formation. Further, in order to form a transparent thin film with less scattering, a spin coating method, a bar coating method, a roll coating method, a casting method, a dipping method and the like, which are methods of forming a thin film from a polymer dissolved in a solvent, are preferable. When a solvent is used in the process of forming the buffer layer, it is preferable to select a combination in which the solvent does not elute the underlying polymer layer 3.

Each of these materials is not particularly limited, but in order to form an optical waveguide, it is necessary that the refractive index of each layer has the following relationship.

The refractive indexes of the π-conjugated material layer 2 and the polymer layer 3 which are the core layers must be higher than the refractive indexes of the substrate 1 and the buffer layer 4 which are the clad layers.

The size relationship between the refractive index of the π-conjugated material layer 2 and the polymer layer 3 is not particularly limited, but the π-conjugated material layer 2 is used in the guided light absorption region. Since the polymer layer is used in the transparent region, the π-conjugated material layer usually has a higher refractive index than the polymer layer.

There is no particular limitation on the thickness of the substrate 1. However, in the case of the electric field application type, it is preferable that the thickness of the substrate is thin in order to apply the electric field to the π-conjugated material layer. Therefore, an insulating thin film may be provided on a semiconductive substrate such as a semiconductor to serve as the substrate.

The thickness of the π-conjugated material layer 2 is limited by the relationship between the loss when the optical waveguide is formed and the polymer layer. Further, since the polymer layer 3 is integrated with the π-conjugated material layer 2 to form the core layer of the optical waveguide, the π-conjugated material layer 2
It is preferable that the thickness is sufficiently thicker than the thickness.

However, the thickness of the polymer layer 3 is about 1.5 μm to several μm because it is disadvantageous from the viewpoint of device operation if the thickness of the optical waveguide becomes thick and a large number of high-order modes stand. Is preferred.

Further, regarding the combination of film thicknesses for forming a good optical waveguide from the polymer layer 3 and the π-conjugated material layer 2 at this time, it is necessary to consider from the magnitude of the waveguide loss, but the loss is The thickness of the π-conjugated material layer 2 is at least 1 of the thickness of the polymer layer 3 so that it does not become too large.
It is preferably 0% or less. As for the actual thickness,
Usually, about 150 to 2000 angstrom is preferable.

As the material for the electrodes 9 and 10, any material such as metal such as gold or aluminum can be used.
Further, other than metals, it is sufficient that the conductivity is high, and a highly doped conductive polymer, ITO or the like can be used.

Next, the operation and operating principle of the device of this embodiment will be described.

Here, the case where the refractive index changes according to the strength of the electric field from the outside will be described. Figure 2
It shows how light is propagating in the thin film waveguide in the present embodiment. The guided light 11 shown in the figure propagates in the π-conjugated material layer 2 and the polymer layer 3, and the manner of propagation is schematically shown. At this time, if the internal reflection angle in the polymer layer 3 is θ _p and the internal reflection angle in the π-conjugated material layer 2 is θ _n1 , the effective refractive index N of the entire optical waveguide is N.
_eff is written as

N _eff = n _p sin θ _p = n _n1 sin θ _n1 n _p and n _n1 are the polymer layer 3 and the π-conjugated material layer 2 respectively.
Is the refractive index of. When an electric field is applied by the electrodes 9 and 10, the refractive index of the π-conjugated material layer 2 changes. If the change is Δn _n1 , the change in refractive index as an optical waveguide ΔN
The relationship with _eff is as follows using the change Δθ _n1 in the internal reflection angle.

N _eff + ΔN _eff = (n _n1 + Δn _n1 ) sin
(Θ _n1 + Δθ _n1 ) This equation is modified, and since θ _n1 is small, the following equation is obtained.

ΔN _eff = Δn _n1 sin θ _n1 This change in the refractive index can change the phase of the propagating light to modulate the propagating light. However, in the case of constructing an interferometric device, the necessary phase change Δφ is typically Since the amount can be 2π, the required device length L can be obtained from the following equation: Δφ = (2π / λ) ΔN _eff L = 2π. Therefore, L = λ / ΔN _eff . λ is the wavelength of the propagating light.

Here, the device length L is still the absorption coefficient α.
Although the effective length given by gives the upper limit, the electric field confinement factor η in the π-conjugated material layer in the core layer of the waveguide
And L <1 / (ηα) ⁻¹ . This electric field confinement factor η indicates how much of the intensity of light propagating in the core layer of the optical waveguide propagates in the π-conjugated material layer. As a first approximation, the refractive index of the layer forming the core It corresponds almost to the thickness fraction unless it is significantly different. The device length is less restricted by 1 / η compared to the case where the optical waveguide is formed of the π-conjugated material alone. For example, when the π-conjugated material layer is 1000 Å and the polymer layer is 2 μm, the electric field confinement coefficient is about 0.05. In this case, the limitation on the device length is relaxed 20 times as compared with the case where the π-conjugated material alone is manufactured.

The operation of the device of this embodiment is as follows. In FIG. 1, incident light 5 propagates while being confined in a core layer composed of a π-conjugated material layer 2 and a polymer layer 3. As a method of introducing light, a method such as prism coupling or grating coupling is used in addition to the end face coupling introduced from the end face of the waveguide. Light propagates and becomes emitted light 6, but when an electric field is applied, the π-conjugated material layer 2
And the effective refractive index of the waveguide as a whole changes. This change changes the propagation state of the waveguide, so that the direction of the emitted light changes.

When incident light is polarized in the direction of 45 °, the incident wave is polarized in the in-plane direction of the substrate.
The E mode and the TM mode polarized in the direction perpendicular to the substrate are propagated separately, and finally both are combined, so that generally elliptically polarized light is obtained. At this time, when an electric field is applied to the electrodes 9 and 10 to change the refractive index of the π-conjugated material layer 2 in the core layer, the effective refractive index changes and TE is decomposed into three waves.
The refractive index for the mode light and the TM mode light changes. As a result, the polarization state of the propagating light changes, so that it operates as phase modulation. Further, the intensity of light can be modulated by using an analyzer.

In practice, the change ΔN _{eff in} the effective refractive index of the optical waveguide as a whole is smaller than that in the case where the π-conjugated material alone is used. However, the degree of reduction is not so small as the electric field confinement coefficient η. Therefore, as the restriction on the absorption coefficient of the π-conjugated material forming the optical waveguide is reduced, it is possible to use a material having a large π-conjugated material absorption. Therefore, it is possible to utilize a large non-linear optical effect due to the resonance absorption effect as compared with the related art.

FIG. 3 is a diagram showing a second embodiment of the present invention. Here, although the structure is similar to that of the first embodiment, with respect to the electrode for applying an electric field to the π-conjugated material layer 2, the upper electrode 10 is a parallel electrode type and the π-conjugated material layer 2 is used. To prevent the incident light 5 from propagating through the electrode 10. Therefore, in that structure, since the upper electrode does not directly participate in the light propagating portion, the buffer layer 4 provided in the first embodiment is unnecessary in order to avoid loss due to the electrode. This electrode structure is often used in field effect transistors, and an electric field can be efficiently applied to the π-conjugated material layer.

Here, as the π-conjugated material used for the π-conjugated material layer 2, the above-mentioned materials can be used.

Next, the operation of this embodiment will be described. Incident light 5 is introduced into the core layer composed of the π-conjugated material layer 2 and the polymer layer 3 by the method already described. At this time, 7 is irradiated as control light from the upper surface of the device to the portion where the light is propagating. This control light is transmitted through the π-conjugated material layer 2
Absorbs and resonates with and exhibits a large nonlinear optical effect. Specifically, the refractive index of the π-conjugated material layer 2 changes due to the Kerr effect, and the effective refractive index N _eff changes with respect to the guided light. This changes the phase of the propagating light.

In this embodiment, an electric field is applied in advance, charge pairs are generated by irradiation with control light, and charge separation is performed by the electric field, whereby charges can be accumulated at the interface between the substrate 1 and the π-conjugated material layer 2. Since the non-linear optical effect is also produced by this accumulated charge, the waveguiding mode of the guided light can be changed. In this case, even if the control light irradiation is pulsed, this change is memorized because the charge accumulation is preserved. An optical switching operation having such a memory effect is also possible.

FIG. 4 is a diagram showing the structure of a Mach-Zehnder device according to the third embodiment of the present invention. An optical waveguide is branched into two on the substrate and combined. Further, FIG. 5 shows a structure of a cross section taken along the line AA in FIG. As a manufacturing method, first, the π-conjugated material layer 2 is provided on the substrate. At this time, the π-conjugated material layer 2 is formed only on one branch 13 of the optical waveguide branches. In this device, since the waveguide is a channel type, a π-conjugated material thin film is formed only in the optical waveguide portion by using a lithography method. Next, a thin film is formed so that the polymer layer 3 has a shape of an optical waveguide. Here, since the effect of light irradiation is used as the nonlinear optical effect, the electrode structure is unnecessary. Finally, in order to form a channel waveguide in which the optical waveguide is embedded in the side cladding layer 12, the whole is embedded with a polymer. Any embedding method may be used, but for example, a method of surrounding the periphery with an ultraviolet curable monomer or oligomer and curing it by ultraviolet irradiation is used.

Further, in this optical waveguide, the branch 13 having the π-conjugated material layer 2 has a larger loss than the branch 14, so that the amounts of light of the two branches are the same when they are combined. In order to do so, the division ratio of the light quantity at the first Y branch was set as follows. That is, the transmittance of the branch 13 is T (13) and the transmittance of the branch 14 is T (13).
Assuming that (14), the light amount to the branch 13 and the light amount to the branch 14 are set to be 1 / T (13): 1 / T (14). By doing so, the amount of light from each branch where they are combined becomes the same.

When light is actually incident on this element, the output light 6 obtained without irradiating the control light 7 has the same output light intensity as when the entire optical waveguide has the same structure as the branch 14. It was about the same. Further, when the control light 7 was applied, the effective refractive index in the branch 13 changed, the phase of the branch 13 changed, and the light interfered with the light from the branch 14, and the output light intensity became almost zero.

The present invention will be described in more detail below, but the present invention is not limited to these examples.

FIG. 6 shows a fourth embodiment of the present invention. Α-Sexcenyl (thiophene hexamer) was deposited as a π-conjugated material layer 2 on a glass substrate by vacuum vapor deposition to a thickness of 50 nm. Then, the thickness of 1.
A 5 μm polymer layer 3 was provided. The optical waveguide was a slab type, and its propagation length was 2 cm.

As the incident light 5, a semiconductor laser having a wavelength of 630 nm was used, and linearly polarized light of 45 ° was made incident by the end face coupling method. Since this wavelength is slightly over the absorption region of α-sexicenyl and the scattering is not small, it is impossible to use this material alone as an optical waveguide.

As the emitted light 6, the light from the end face was condensed and detected by the lens system, and it was confirmed that the thin film element was operating as a device. At this time, the refractive index of the glass substrate is 1.5, and the refractive index of the α-sexicenyl film is 1.
8. Since the soluble polyimide film had a refractive index of 1.6, it was found that a guided mode having an effective refractive index of 1.5 to 1.6 was obtained. The emitted light was separated by a beam splitter into a horizontal polarization component and a vertical polarization component, and then the phase shift of both components was measured.

Further, as the control light 7, light having a wavelength of 520 nm, which is an absorption region of α-sexicenyl, was applied to the entire optical waveguide. Also at this time, the phase shift between the vertically polarized component and the horizontally polarized component of the emitted light 6 was measured. As a result, there was a difference in the phase shift between when the control light 7 was irradiated and when the control light 7 was not irradiated, and it was found that the element of this example operates as a phase modulation element for propagating light.

Next, a fifth embodiment of the present invention will be described with reference to FIG. As the substrate 1 and the lower electrode 9 in FIG. 1, a thermal oxide film (silicon oxide film) is used in this embodiment.
A silicon substrate marked with was used. The silicon oxide film corresponds to the substrate 1, and the silicon substrate corresponds to the electrode 9. Here, the silicon substrate is a substrate having high conductivity due to high doping, and the thickness of the thermal oxide film is 15
It is 0 nm.

A layer having a thickness of 100 nm was formed thereon by vacuum evaporation using the α-sexicenyl used in the fourth example as the π-conjugated material layer 2. Next, soluble polyimide was provided as the polymer layer 3 by a spin coating method to a thickness of 3 μm. Next, a polymethylmethacrylate layer was formed as the buffer layer 4 to a thickness of 500 nm by spin coating. Further, gold was provided as an upper electrode thereon by vacuum evaporation to a thickness of 500 nm.

The refractive index of the silicon oxide film is 1.45, α
-The sexexenyl film was 1.80, the soluble polyimide film was 1.56, and the polymethylmethacrylate film was 1.49, and it was found that the core layer composed of the α-sexicenyl layer and the soluble polyimide layer functions as a waveguide.

A laser having a wavelength of 510 nm was used as the incident light 5, and the light was guided into the optical waveguide by prism coupling.
The wavelength of 510 nm corresponds to the absorption edge of α-sexicenyl, and the above structure made it possible to form an optical waveguide. At this time, an electric field was applied between the silicon substrate and the upper electrode. As for the electric field, the upper electrode was grounded and −20 V was applied to the silicon substrate. By the application of this electric field, absorption of light with a wavelength of 510 nm occurred in the α-sexicenyl layer, and the intensity of the emitted light 6 decreased. Thus, it was found that the light intensity can be modulated by applying an electric field.

Next, a sixth embodiment of the present invention will be described with reference to FIG.
Will be explained. In FIG. 4, on the substrate 1 made of quartz glass, α-sexicenyl was used as the π-conjugated material layer 2, and a thin film was formed so as to serve as an optical waveguide in a portion of the branch 13 excluding the branching portion and the multiplexing portion. The thickness of the α-sexicenyl layer was set to 60 nm, and polychloromethylstyrene was used as a polymer layer thereon to form a film having a thickness of 1.5 μm. The pattern was formed by lithography. Here, since polychloromethylstyrene operates as a resist, it was produced by utilizing the characteristic that the solubility in a solvent changes by irradiating this pattern. Finally, the side cladding layer 12 was produced by embedding the periphery with an ultraviolet curable resin. As a result, a Mach-Zehnder type interference device could be manufactured.

Next, a seventh embodiment of the present invention will be described with reference to FIG.
Will be explained. In FIG. 6, a polyphenylene vinylene (PVT) film was provided as a π-conjugated material layer 2 on a substrate 1 made of glass. The PTV film can be obtained by spin coating a solution of a soluble precursor and then performing heat treatment. Here, the thickness is 60 nm. afterwards,
In the same manner as in the fourth embodiment, a polymer layer 3 having a thickness of 1.5 μm was provided by a spin coating method using a γ-butyl lactone solution of soluble polyimide. The optical waveguide was a slab type, and its propagation length was 2 cm. A semiconductor laser having a wavelength of 830 nm was used as the incident light 5, and linearly polarized light of 45 ° was made incident by the end face coupling method. This wavelength is
Although it is not the light absorption region of PTV, the scattering is large, and PTV
Optical waveguiding was not possible with the film formed alone. The emitted light 6 from the device is detected by collecting the light from the end face with a lens system, but since the polarization characteristic is changed by the irradiation of the control light 7, the element of this embodiment propagates the light. It was found that it operates as a phase modulation element of.

Next, a semiconductor laser beam having a wavelength of 830 nm was made incident and guided to this device. Light having a wavelength of 830 nm is not absorbed but has a large scattering due to the microcrystalline property of α-sexicenyl, and it is difficult to use it as a single layer as an optical waveguide as it is, but as in this example, a core layer combined with a transparent polymer is used. By making it possible, an optical waveguide can be realized. A laser having a wavelength of 480 nm was used as the control light. When the control light 7 was not emitted, the output could be taken out as the emitted light, but when the control light 7 was emitted, the intensity of the emitted light decreased and became zero.

[0086]

As described above, in the optical waveguide device according to the present invention, the core layer of the optical waveguide absorbs or scatters the wavelength of the guided light and therefore does not form an optical waveguide by itself. By using a material layer and at least one polymer layer having excellent transparency in combination, it becomes possible to use a nonlinear optical effect having a large absorption resonance region, which has heretofore not been applicable to an optical waveguide device.
It is an optical waveguide device that has a small propagation loss and does not significantly reduce the amount of output light.

In the present invention, the π-conjugated material is
Thiophene, vinylene, chenylene vinylene, phenylene vinylene, p-phenylene, substituted products thereof, or a repeating unit of two or more of them, and the number n of the repeating units is 4 to 10 or the number of the repeating units. By using at least one selected from the group consisting of a polymer in which n is 20 or more, an unsubstituted phthalocyanine and a metal phthalocyanine, an optical waveguide is formed by a combination with a polymer layer having good film-forming property and high transparency. Cheap.

Furthermore, in the optical waveguide device of the present invention, only one of the two branches in the Mach-Zehnder device is transparent to the π-conjugated material layer having absorption and loss but having a large nonlinear optical effect due to resonance or the like. An optical waveguide in which a core layer consisting of a polymer layer is formed is used, and the optical waveguide of the other branch has a structure in which only the transparent polymer layer is used as the core layer. In the device that modulates the intensity of the output light after combining by changing the, the split of the light quantity into the two branch waveguides is made equal to the ratio of the reciprocal of the two transmittances. This is an optical waveguide device in which the amount of light of the same intensity can be obtained from two branches in consideration of the loss due to the material, and the intensity of emitted light can be made zero during operation.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of an optical waveguide device according to a first embodiment and a fifth embodiment of the present invention.

FIG. 2 is a diagram showing a structure of a cross section taken along the line AA of the optical waveguide device in the first example of the present invention.

FIG. 3 is a diagram showing a structure of an optical waveguide device according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a structure of a Mach-Zehnder device in a third embodiment and a sixth embodiment of the present invention.

FIG. 5 is a diagram showing a structure of a Mach-Zehnder device taken along line AA in a third embodiment and a sixth embodiment of the present invention.

FIG. 6 is a diagram showing a structure of an optical waveguide device according to a fourth embodiment of the present invention.

FIG. 7 is a diagram showing a structure of a conventional Mach-Zehnder type optical waveguide device.

FIG. 8 is a diagram showing a cross-sectional structure of a conventional optical waveguide device.

[Explanation of Codes] 1 substrate, 2 π-conjugated material layer, 3 polymer layer, 4
Buffer layer, 5 incident light, 6 emitted light, 7 control light,
8 control light, 9 lower electrode, 10 upper electrode, 11 propagating light, 12 side cladding layer, 13 branch (including π-conjugated material layer) branch, 14 branch, 15 substrate, 16 waveguide, 17 branch, 18 branch, 19 Incident light, 20 Emitted light, 21 Electrode pair, 22 Substrate, 23 Core layer, 24
Clad layer, 25 lower electrode, 26 upper electrode, 27
Propagating light.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyuki Fuchigami 8-1-1 Tsukaguchi Honcho, Amagasaki City Mitsubishi Electric Corporation Material Device Research Center (72) Inventor Makoto Tsunoda 8-1-1 Tsukaguchi Honcho, Amagasaki Mitsubishi Electric Device Co., Ltd. Material Device Research Center

Claims (3)

[Claims] 1. An optical waveguide device obtained by using a nonlinear optical material, wherein an effective electric field is applied to the nonlinear optical material of the core layer of the optical waveguide and / or control light from the outside is irradiated or guided. In the optical waveguide device capable of modulating the intensity and / or the phase of the propagating light by changing the optical constant of the nonlinear optical material by oscillating, the core layer of the optical waveguide is adjusted to the wavelength of the propagating light. On the other hand, it is possible to combine a π-conjugated material layer having a property of substantially absorbing light and / or a property of having a large light scattering property, and at least one polymer layer having excellent transparency. Optical waveguide device. 2. The π-conjugated material has thiophene, vinylene, phenylene vinylene, phenylene vinylene, p-phenylene, a substitution product thereof or two or more of these repeating units, and the number n of the repeating units is 4. 10. The optical waveguide device according to claim 1, which is at least one selected from the group consisting of an oligomer of 10 to 10 or a polymer in which the number n of the repeating units is 20 or more, an unsubstituted phthalocyanine and a metal phthalocyanine. 3. A Mach-Zehnder device that splits incident light, guides it to two optical waveguides, and then multiplexes the light to control the light intensity. Optical waveguide having a core layer, the other optical waveguide is an optical waveguide made only of a polymer material having no non-linear optical characteristics, and the ratio of the amount of light divided into the two optical waveguides is An optical waveguide device characterized by being equal to the ratio of the reciprocal of the transmittance of.