JP2009098195A - Optical waveguide device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical waveguide device capable of suppressing generation of a DC drift with a simple construction. <P>SOLUTION: In the optical waveguide device wherein a lower electrode 12 (a first electrode), a lower metal or inorganic oxide layer 13 (a first metal or inorganic oxide layer), a lower clad layer 14 (a first clad layer), an optical waveguide layer 16 (an optical waveguide 17), an upper clad layer 18 (a second clad layer), an upper metal or inorganic oxide layer 19 (a second metal or inorganic oxide layer) and an upper electrode 20 (a second electrode) are sequentially layered on a substrate 10, for example, a layer construction between the optical waveguide layer 16 (the optical waveguide 17) and the lower electrode 12 and a layer construction between the optical waveguide layer 16 (the optical waveguide 17) and the upper electrode 20 are made symmetric in the thickness direction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical waveguide device.

  As a high-speed data network, an optical communication network capable of exchanging a large amount of data at a time has been studied. In an optical communication network, an optical waveguide element that modulates light intensity, phase, wavelength, and the like based on an electrical signal is important.

  As an optical waveguide element, an optical waveguide element that uses an optical waveguide to control optical waveguide light by an electro-optic (hereinafter referred to as “EO”) effect is generally used. Various types of optical waveguide structures have been studied for optical waveguide devices, and various methods for forming optical waveguides have been reported.

As a material used for this optical waveguide element, an inorganic ferroelectric crystal typified by lithium niobate (LiNbO ₃ , hereinafter abbreviated as “LN”) exhibiting a large EO effect has attracted attention. For example, in an optical waveguide element using LN, an impurity such as Ti is diffused on the surface of a single crystal LN substrate having an EO effect so that the refractive index is higher than that of other portions, and the optical waveguide (hereinafter simply referred to as “optical waveguide”). Is sometimes abbreviated as “). This structure is called a diffusion type optical waveguide structure. When a control electrode is formed on the surface of the optical waveguide and a voltage is applied to the electrode to apply an electric field to the optical waveguide, a refractive index change occurs in the optical waveguide layer due to the EO effect, and the light propagating through the optical waveguide This is the principle of control.

  By the way, the DC drift characteristic is typical as one for determining the performance of the optical waveguide device. The phenomenon called DC drift is that the phase of light propagating in the optical waveguide is shifted with the voltage application time even when a constant DC voltage is applied.

  Conventionally, in an inorganic EO element such as LN, space charge is accumulated by continuously repeating modulation at the interface between the electrode and the inorganic oxide, and a DC drift is caused by an internal electric field due to space charge changing with time. Is known to occur. On the other hand, in the EO element using the organic nonlinear material, the DC drift phenomenon itself has hardly been investigated, but from the research by the present inventors, it is clear that the DC drift phenomenon exists also in the organic nonlinear optical material. (For example, see Non-Patent Document 1).

Several techniques have been reported as a solution to this DC drift. For example, in the technique of Patent Document 1, in order to suppress the occurrence of an operating point shift in an optical waveguide element due to a change over time due to DC drift or the like, radiated light emitted from the optical waveguide and signal light leaking from the optical waveguide The interfering light that interferes with each other is monitored, and the operating point of the optical waveguide element is controlled according to the change of the monitored interfering light (see, for example, Patent Document 1).
JP-A-10-221664 S. Nakamura et. al. , OECC / IOOC 2007, 10E1-3, pp. 80-81 (Jury, 2007)

  An object of this invention is to provide the optical waveguide element which can suppress generation | occurrence | production of DC drift with a simple structure.

The invention according to claim 1
An optical waveguide containing an organic nonlinear optical material;
A first electrode disposed on one side of the optical waveguide;
A second electrode disposed on the other surface side of the optical waveguide;
Have
In the optical waveguide element, the layer configuration between the optical waveguide and the first electrode and the layer configuration between the optical waveguide and the second electrode are symmetrical in the thickness direction.

The invention according to claim 2
A first cladding layer disposed between the optical waveguide and the first electrode;
A first metal or inorganic oxide layer disposed between the first electrode and the first cladding layer;
A second cladding layer disposed between the optical waveguide and the second electrode;
A second metal or inorganic oxide layer disposed between the second electrode and the second cladding layer;
The optical waveguide device according to claim 1, further comprising:

The invention according to claim 3
The optical waveguide device according to claim 1, wherein the optical waveguide is a Mach-Zehnder type.

The invention according to claim 4
The optical waveguide device according to claim 1, wherein the optical waveguide is a multimode interference type.

The invention according to claim 5
2. The optical waveguide device according to claim 1, wherein the optical waveguide has a structure protruding in a convex shape toward the first electrode side or the second electrode side.

The invention according to claim 6
2. The optical waveguide device according to claim 1, wherein the optical waveguide has a structure protruding in a convex shape toward both the first electrode side and the second electrode side.

  According to the invention concerning Claim 1, there exists an effect that generation | occurrence | production of DC drift is suppressed with a simple structure.

  According to the invention of claim 2, even when a second metal or inorganic oxide layer is provided between the second cladding layer and the second electrode for the purpose of protecting the second cladding layer, By providing the same first metal or inorganic oxide layer between the first electrode and the first electrode, there is an effect that generation of DC drift is suppressed.

  According to the invention of claim 3, even in the Mach-Zehnder type optical waveguide, there is an effect that generation of DC drift is suppressed.

  According to the invention which concerns on Claim 4, even in a multimode interference type optical waveguide, there exists an effect that generation | occurrence | production of DC drift is suppressed.

  According to the invention which concerns on Claim 5, the optical absorption loss by the electrode in an optical waveguide is suppressed, the effective electric field of an optical waveguide element is strengthened, and there exists an effect that reduction of a drive voltage can be aimed at.

  According to the sixth aspect of the invention, it is possible to more effectively reduce the light absorption loss caused by the electrodes in the optical waveguide, increase the effective electric field of the optical waveguide element, and reduce the driving voltage.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

  As shown in FIGS. 1 and 2, the optical waveguide device 100 according to the present embodiment includes a lower electrode 12 (first electrode), a lower metal or an inorganic oxide layer 13 (first metal or inorganic) on a substrate 10. Oxide layer), lower cladding layer 14 (first cladding layer), optical waveguide layer 16 (optical waveguide 17), upper cladding layer 18 (second cladding layer), upper metal or inorganic oxide layer 19 (second metal or An inorganic oxide layer) and an upper electrode 20 (second electrode) are sequentially stacked. In the present embodiment, a case where an optical waveguide, which will be described later, of the optical waveguide element 100 is a Mach-Zehnder interference type will be described. However, the present invention is not limited to such a configuration.

  The substrate 10 will be described. As the substrate 10, various metal substrates (aluminum, gold, iron, nickel, chromium, stainless steel, etc.), various semiconductor substrates (silicon, silicon oxide, titanium oxide, zinc oxide, gallium-arsenic, etc.), glass substrates, plastic substrates ( PET (polyethylene terephthalate), polycarbonate, polyester, polyvinyl chloride, polyvinyl acetate, polymethyl acrylate, polymethyl methacrylate, polyurethane, polyimide, polystyrene, polyamide, etc.) are used. The substrate 10 may be thick and rigid, or it may be thin and flexible.

  Next, the lower electrode 12 will be described. For example, the lower electrode 12 is formed on the entire surface of the substrate 10. Examples of the material constituting the lower electrode 12 include various metals such as Au, Ti, TiN, Pt, Ir, Cu, Al, Al-Cu, Al-Si-Cu, W, and Mo, various oxides (NESA ( Tin oxide), indium oxide, ITO (tin oxide-indium oxide composite oxide), various organic conductors (polythiophene, polyaniline, polyparaphenylene vinylene, polyacetylene) and the like are used.

  The lower electrode 12 is formed by a known method such as a DC magnetron sputtering method, an electron beam evaporation method, an electrolytic plating method, a flash evaporation method, an ion plating method, an RF magnetron sputtering method, an ion beam sputtering method, a laser. -It is formed by thin film growth by a vapor deposition method selected from an ablation method, an MBE method, a CVD method, a plasma CVD method, an MOCVD method, or the like, or a wet process such as a sol-gel method or an MOD method.

  When the substrate 10 is configured as a metal substrate, the lower electrode 12 corresponds to the metal substrate. Such a conductive substrate and the lower electrode 12 are used as electrodes when an electric field is formed between the upper electrode 20 and an optical waveguide layer 16 (optical waveguide 17) made of an organic nonlinear optical material described later. The The upper electrode 20 formed on the upper clad layer 18 is also preferably made of the same material as that of the lower electrode 12.

  Next, the lower metal or inorganic oxide layer 13 will be described. For example, the lower metal or inorganic oxide layer 13 is formed on the entire surface of the lower electrode 12. Examples of the material constituting the lower metal or inorganic oxide layer 13 include various metals (Au, Ti, TiN, Pt, Ir, Cu, Al, Al-Cu, Al-Si-Cu, W, Mo, etc.), Examples include inorganic oxides such as NESA (tin oxide), zinc oxide, indium oxide, and ITO (tin oxide-indium oxide composite oxide). Further, when the lower electrode 12 is patterned, the lower electrode 12 is formed by being patterned so as to be interposed between the lower electrode 12 and the lower cladding layer 14 according to the shape thereof. The thickness of the lower metal or inorganic oxide layer 13 is preferably, for example, from 10 nm to 2 μm, and more preferably from 20 nm to 1 μm.

  The lower metal or inorganic oxide layer 13 is formed by a known method such as DC magnetron sputtering, electron beam evaporation, electrolytic plating, flash evaporation, ion plating, RF magnetron sputtering, ion beam. Formed by thin film growth by vapor phase growth method selected from sputtering method, laser ablation method, MBE method, CVD method, plasma CVD, MOCVD method, etc., or a wet process such as sol-gel method, MOD method, etc.

  Next, the lower cladding layer 14 will be described. The lower cladding layer 14 is formed on the entire surface of the lower metal or inorganic oxide layer 13, for example. As the lower clad layer 14, a material having a lower refractive index than that of the optical waveguide layer 16 laminated on the lower clad layer 14 is used.

The material used for the lower cladding layer 14 is preferably a material that does not cause intermixing when the optical waveguide layer 16 is formed, and is generally known as a thermosetting crosslinked resin, an ultraviolet curable crosslinked resin, or an inorganic material. , Conductive polymers, fluorinated polymers, and the like are used.
Examples of the thermosetting crosslinked resin include polyimide, polyurethane, polybenzocyclobutene, and polyamide. Examples of the ultraviolet curable crosslinking resin include epoxy resin, acrylic resin, and silicone resin. It is done.

  As a method of forming the lower clad layer 14 on the lower metal or inorganic oxide layer 13, when a polymer material is used as a material for forming the lower clad layer 14, a general method such as a spin coat method or a dip method is used. A solution coating method is used. When an inorganic material is used as the material for forming the lower cladding layer 14, an electron beam vapor deposition method, a flash vapor deposition method, an ion plating method, an RF (high frequency) -magnetron sputtering method, a DC (direct current) -magnetron. Vapor phase growth selected from sputtering, ion beam sputtering, laser ablation, MBE (molecular beam epitaxy), CVD (vapor phase epitaxy), plasma CVD, MOCVD (organic vapor phase epitaxy), etc. It can be produced by a wet process such as a sol-gel method or a MOD method, but is not limited thereto.

  The film thickness of the lower cladding layer 14 depends on optical waveguide design guidelines such as the wavelength of light incident on the optical waveguide 17 when configured as the optical waveguide element 100, but is preferably in the range of about 1 μm to 20 μm. It is more preferable to use a range of about 1.5 μm to 10.0 μm.

  When the thickness of the lower clad layer 14 is more than 20 μm, the effective voltage applied to the optical waveguide 17 is lowered, so that a sufficient electro-optic (hereinafter referred to as “EO”) effect is obtained. If the thickness is less than 1 μm, light absorption by the lower electrode 12 increases, which may cause a problem of increased light loss.

  Next, the optical waveguide layer 16 will be described. The optical waveguide layer 16 is formed on the surface of the lower cladding layer 14. As the optical waveguide layer 16, a material capable of forming an optical waveguide and having a refractive index higher than that of the lower cladding layer 14 and the upper cladding layer 18 is used. In this embodiment, as the material constituting the optical waveguide layer 16, A polymer (organic nonlinear material) imparted with a nonlinear effect is used. This organic nonlinear material functions as an organic electro-optic material, and by using this material, an electro-optic effect is imparted by using it for the optical waveguide layer 16.

  Organic nonlinear materials include organic nonlinear optical polymers in which an organic compound having nonlinear optical properties is added to a polymer matrix, or structures having nonlinear optical properties in the main chain or side chain of the polymer (hereinafter referred to as “chromophore structure”). A main chain organic nonlinear optical polymer or a side chain organic nonlinear optical polymer.

  As a material constituting the optical waveguide layer 16, it is possible to form the optical waveguide 17, and it is preferable to use the organic nonlinear material which is a material having a refractive index higher than that of the lower clad layer 14. A polymer having a chromophore structure introduced for the purpose of imparting non-linearity to the polymer side chain or main chain is used.

  As the polymer material, acrylic resin, polyimide resin, epoxy resin, polycarbonate resin, polystyrene, polyurethane, polysilane, polybenzocyclobutene, or the like is used.

Although the said chromophore structure will not be specifically limited if it is a well-known thing, What is represented by following Structural formula (1) is preferable.
D-P-A Structural formula (1)
In Structural Formula (1), D represents an atomic group having an electron donating property, P represents a bonding portion, and A represents an atomic group having an electron withdrawing property. As the atomic group having an electron donating property represented by “D” in the structural formula (1), a known group having an electron donating property may be used. It is preferably composed of a group unsaturated bond, an aromatic ring, a heteroaromatic ring, and a combination thereof. The electron donating substituent is not particularly limited as long as it has an electron donating property, but an alkyl group, an alkoxy group, an amino group, and the like are preferable. A part of the alkyl group may be substituted with an alkoxy group or a phenyl group, a part of the alkoxy group may be substituted with an alkoxy group or a phenyl group, and a part of the amino group is an alkyl group. It may be substituted with a group, an alkoxy group, or a phenyl group.

  On the other hand, as the atomic group having an electron-withdrawing property represented by “A”, any known group having an electron-withdrawing property may be used, but an aliphatic unsaturated bond having an electron-withdrawing substituent introduced therein. , Aromatic rings, heteroaromatic rings, and combinations thereof are desirable.

  As the electron-withdrawing substituent, a halogen atom, a halogen-substituted alkyl group, a cyano group, a nitro group, a carbonyl group, and the like are desirable.

  The bond represented by “P” may be any bond that connects “D” and “A” with a covalent bond, but has a conjugate bond that can delocalize electrons. For example, a material having a structure in which “D” and “A” are combined in a π-conjugated system is desirable. Specifically, aliphatic unsaturated bonds, aromatic rings, heteroaromatic rings, and those in which they are bonded to each other are desirable.

  The optical waveguide layer 16 is formed by dissolving a polymer material having the chromophore structure, or a mixture of an organic compound having a chromophore structure and a polymer material, in a solvent for dissolving them, and preparing a coating solution. This is performed by coating the surface of the lower cladding layer 14 and the like with a coating solution.

  As a method for providing the optical waveguide layer 16 by coating, a known method such as spin coating, spray coating, blade coating, dip coating, or the like is used. The removal of the solvent may be performed by heat drying with a blower dryer or the like, or may be dried with a reduced pressure (vacuum) dryer or the like.

  The optical waveguide layer 16 is formed between the lower electrode 12 and the upper electrode 20 in an optical waveguide (hereinafter sometimes referred to as an action part) located between the lower electrode 12 and the upper electrode 20. In order for the generated electric field to work effectively, the optical waveguide layer 16 is preferably thin, preferably 5.0 μm or less, and more preferably 3.5 μm or less.

  When the thickness of the optical waveguide layer 16 is thicker than 5.0 μm, the voltage value applied to the action portion of the optical waveguide 17 in order to cause a desired phase change in the light propagating through the action portion is higher. It may be difficult to achieve a low driving voltage because voltage application of a voltage value is required. In addition, the minimum of the film thickness of the optical waveguide layer 16 is about 1.0 micrometer.

  The optical waveguide 17 formed in the optical waveguide layer 16 is configured, for example, as shown in FIGS. 1 and 2 such that the optical waveguide 17 is a ridge type (a shape in which the optical waveguide 17 protrudes convexly toward the upper cladding layer 18). In this case, the ridge type optical waveguide 17 may be formed by forming a ridge by a dry etching method.

In the present embodiment, the case where the optical waveguide 17 formed in the optical waveguide layer 16 is a Mach-Zehnder type as shown in FIGS. 1 and 2 will be described.
In the Mach-Zehnder type optical waveguide 17, an incident optical waveguide portion 17C into which light is incident and an outgoing optical waveguide portion 17D that emits the incident light are formed as one optical path, and two optical paths 17A (hereinafter referred to as “optical paths”) are formed. And may be referred to as an arm portion 17A) and an optical path 17B (hereinafter also referred to as an arm portion 17B). For this reason, the light incident on the incident optical waveguide portion 17A is divided into two optical paths (the arm portion 17A and the arm portion 17B), and then propagates through the arm portion 17A and the arm portion 17B. The light is merged at the portion 17D and emitted to the outside of the optical waveguide 17.

The ridge width and height of the optical waveguide 17 (the width and height of the optical waveguide 17) vary depending on the combination of the refractive index of the optical waveguide 17 and the thickness and thickness of the optical waveguide layer 16, but the ridge height. The (step) is generally preferably in the range of 50 nm to 3000 nm, and more preferably in the range of 500 nm to 2000 nm. If the ridge height is less than 50 nm, a sufficient refractive index difference cannot be obtained between the optical waveguide 17 and each of the upper cladding layer 18 and the lower cladding layer 14, and light can be confined in the optical waveguide 17. It may disappear.
On the other hand, if the ridge height exceeds 3000 nm, it may become a multi-mode and the function of the target element cannot be fully exhibited. The ridge width is preferably in the range of 1 μm to 15 μm, and more preferably in the range of 3 μm to 10 μm.

  The optical waveguide 17 can take a large difference in refractive index between the upper cladding layer 18 and the lower cladding layer 14 by adopting the ridge structure as described above. Therefore, the absorption loss due to the electrodes can be suppressed and the effective electric field of the element can be increased, so that the drive voltage can be reduced.

  Next, the upper cladding layer 18 will be described. The upper cladding layer 18 is formed, for example, on the entire surface of the optical waveguide layer 16. The upper cladding layer 18 is formed by forming the optical waveguide 17 by forming the ridge in the optical waveguide layer 16 and then covering the optical waveguide layer 16 with a material having a refractive index lower than that of the optical waveguide layer 16.

  The material used for the upper clad layer 18 is preferably a material that does not intermix with the optical waveguide layer 16 when the upper clad layer 18 is formed, and the material used for the lower clad layer 14 described above is used. Further, as the means for forming the upper clad layer 18, the method used for the formation of the lower clad layer 14 described above is similarly used. The film thickness of the upper cladding layer 18 is preferably in the range of 1 μm to 20 μm, and more preferably in the range of 1.5 μm to 10.0 μm.

  In the optical waveguide device 100, it is usually necessary to make the refractive indexes of the upper cladding layer 18 and the lower cladding layer 14 smaller than the refractive index of the optical waveguide layer 16. In the present embodiment, the difference in refractive index between the optical waveguide layer 16 and the upper cladding layer 18 and the lower cladding layer 14 depends on the use of the optical waveguide element 100. For example, when used as a single mode optical waveguide, The difference in refractive index between the optical waveguide layer 16, the upper cladding layer 18 and the lower cladding layer 14 is preferably in the range of 0.01% to 3%.

  Next, the upper metal or inorganic oxide layer 19 will be described. The upper metal or inorganic oxide layer 19 is formed on the surface of the upper cladding layer 18, for example. The upper metal or inorganic oxide layer 19 is formed by patterning so as to be interposed between the upper cladding layer 18 and the upper electrode 20 in accordance with the shape and arrangement position of the upper electrode 20. This upper metal or inorganic oxide layer 19 is formed for the purpose of protecting the upper cladding layer 18 when the upper electrode 20 is formed (at the time of lift-off), and is formed on the entire surface of the upper cladding layer 18 at one end. After the electrode 20 is formed, the layers other than the upper electrode 20 formation region are removed by an etching process or the like. The material and forming method of the upper metal or inorganic oxide layer 19 are the same as those of the lower metal or inorganic oxide layer 13.

  Next, the upper electrode 20 will be described. The upper electrode 20 is formed on the surface of the upper metal or inorganic oxide layer 19. For example, when an electric field is formed between the upper electrode 20 and the lower electrode 12, the phase of the light propagating through the region of the optical waveguide 17 located in the formed electric field is changed and the optical waveguide 17 is also changed. It is provided at a position where the intensity of the light incident on the light is modulated and emitted. In the present embodiment, the upper electrode 20 is composed of two electrode pairs.

  Specifically, as shown in FIGS. 1 and 2, when the optical waveguide 17 is of a Mach-Zehnder type, the upper electrode forming each pair of the upper electrodes 20 includes the arm portion 17 </ b> A and the arm portion of the optical waveguide 17. A pair of upper electrode 20A and upper electrode 20B is provided in a region corresponding to one or both of 17B.

  That is, the counter electrode constituting the upper electrode 20 applies a voltage between the counter electrode of the upper electrode 20 and the lower electrode 12, thereby modulating the light incident on the optical waveguide 17 as a result. Are provided in a region where the light can be emitted.

  In the example shown in FIGS. 1 and 2, the upper electrode 20 </ b> A of the upper electrode 20 </ b> A and the upper electrode 20 </ b> B that form a pair is applied with a voltage between the upper electrode 20 </ b> A and the lower electrode 12. The upper electrode 20B is provided at a position where an electric field can be formed on the arm portion 17B of the optical waveguide 17 when a voltage is applied between the upper electrode 20B and the lower electrode 12. It has been.

  In the present embodiment, as described above, the upper electrode 20A and the upper electrode 20B constituting the pair constituting the upper electrode 20 are positioned at positions corresponding to the arm portions 17A of the optical waveguide 17 and the optical waveguide 17, respectively. Although the case where it is provided at a position corresponding to the arm portion 17B will be described, the intensity of light incident on the optical waveguide 17 when a voltage is applied between the upper electrode 20 and the lower electrode 12 forming a pair. It is only necessary to be provided at a position where the light that is modulated is emitted from the optical waveguide 17 and is not limited to such a form.

  For example, both the upper electrode 20A and the upper electrode 20B may be configured to be provided at positions corresponding to either the arm portion 17A or the arm portion 17B of the optical waveguide 17.

  Further, in the present embodiment, in order to simplify the description, the case where the upper electrode 20 is configured by a pair of electrodes will be described, but a configuration in which a plurality of pairs of upper electrodes are provided may be used. Needless to say.

  The upper electrode 20 is formed by a known method such as a DC magnetron sputtering method, an electron beam evaporation method, an electrolytic plating method, a flash evaporation method, an ion plating method, an RF magnetron sputtering method, an ion beam sputtering method, a laser. -It is formed by thin film growth by a vapor deposition method selected from an ablation method, an MBE method, a CVD method, a plasma CVD method, an MOCVD method, or the like, or a wet process such as a sol-gel method or an MOD method.

  The optical waveguide device 100 manufactured in this way is processed into a chip shape (element shape) by cutting to complete the device. A dicer or the like is used for cutting. The element shape generally refers to a rectangular shape, but includes a case of processing into a rhombus shape or a trapezoid shape for the purpose of reducing the return light at the light input / output end face.

In order to develop a nonlinear optical effect in the optical waveguide 17 of the optical waveguide element 100, it is necessary to align the molecular orientation by poling.
This poling treatment is a process of applying the electric field in the state heated to the glass transition temperature (Tg) or higher after the film formation, and performing the alignment treatment to thereby form the organic nonlinear material constituting the optical waveguide 17 and the optical waveguide layer 16. This refers to a process of removing the electric field after lowering the temperature to Tg or lower while maintaining the orientation in the polarization direction or the polarization direction of the chromophore portion of the organic nonlinear material having the chromophore.

  As such a poling treatment, an electric field is applied by a method in which an organic nonlinear material is directly sandwiched between two or more electrodes (electrode poling), a medium such as a liquid between the organic nonlinear material and the electrode. And a method of applying an electric field to the organic nonlinear material by an indirect method by corona discharge (corona poling).

  The poling temperature is preferably equal to or higher than the glass transition temperature. Specifically, it is desirable to maintain the poling temperature within a range of 100 ° C. to 200 ° C. for about 0.2 hours to 10 hours. When the polling temperature is raised stepwise from room temperature to the final temperature, the rising temperature of each step is preferably in the range of 5 ° C to 50 ° C, and the time of each step is preferably about 10 minutes to 120 minutes, It may be the same or different throughout. The rate of temperature increase when the temperature is continuously increased is preferably about 0.1 ° C./min to 20 ° C./min, and may be combined with the step of increasing the temperature stepwise.

  This step may be performed at any time after the optical waveguide layer is formed, but if heating is required in a later step, the nonlinear optical effect is reduced. It is preferable to perform polarization alignment treatment.

  The optical waveguide element 100 configured as described above is used as an optical modulation element that modulates light or an optical switch that performs switching.

  Next, the operation of the optical waveguide device 100 configured as described above will be described.

  The light incident from the incident optical waveguide portion 17C of the optical waveguide 17 is branched and propagated to the arm portion 17A and the arm portion 17B, and then propagates through the outgoing optical waveguide portion 17D and is emitted from the optical waveguide 17.

  In the optical waveguide device 100, when no voltage is applied between the upper electrode 20 and the lower electrode 12 from a voltage application unit (not shown), the light is incident on the incident optical waveguide unit 17C, and the arm unit 17A and the arm unit The light propagating through 17B is converged to single mode light while interfering with each other at the joint portion (joint portion with the output optical waveguide portion 17D) of these arm portions. At this time, since no electric field is formed in the arm portion 17A and the arm portion 17B, there is no phase difference in the light propagating through these arm portions, so that the output optical waveguide portion 17D Light having the same intensity as the light incident on 17C is emitted.

  As described above, since the optical waveguide 17 is formed of a material having an electro-optic effect, a voltage is applied between the upper electrode 20 and the lower electrode 12, and an electric field is formed in the optical waveguide 17. Then, the refractive index of light propagating through the region where the electric field is formed in the optical waveguide 17 changes, and the phase changes. Therefore, when a voltage is applied to the lower electrode 12 and the upper electrode 20 from a voltage application unit (not shown) and an electric field is formed between the lower electrode 12 and the upper electrode 20, the applied voltage is reduced. In accordance with the voltage value, the refractive index of light propagating through a region corresponding to the formed electric field in the optical waveguide 17 changes, and light having an intensity different from the intensity of the light incident on the optical waveguide 17 is transmitted. The light is emitted from the waveguide 17.

  Specifically, when a voltage is applied between the upper electrode 20 and the lower electrode 12 from a voltage application unit (not shown), the voltage is incident on the incident optical waveguide unit 17C and propagates through the arm unit 17A and the arm unit 17B. The light is converged while interfering with each other at the joint portion (joint portion with the output optical waveguide portion 17D) of these arm portions. At this time, since the electric field is formed in the arm part 17A and the arm part 17B, a phase difference corresponding to the electric field is generated in the light propagating through these arm parts, and the incident optical waveguide part 17C is emitted from the output optical waveguide part 17D. Light having an intensity different from that of the light incident on the light is emitted. That is, when a voltage is applied between the upper electrode 20 and the lower electrode 12 from a voltage application unit (not shown), the intensity of light is continuously modulated according to the applied voltage. By repeating this operation and operating the device continuously, accumulation of space charge occurs in the interface light on the upper electrode 20 (interface on the waveguide layer side) and the interface on the lower electrode 12 (interface on the optical waveguide layer side). An internal electric field is generated.

  In the optical waveguide device 100 of the present embodiment, as described above, the lower metal or the inorganic oxide is disposed between the optical waveguide layer 16 (optical waveguide 17) and the lower electrode 12 in order from the lower electrode 12 side. The layer 13 and the lower clad layer 14 are sequentially laminated, and the upper clad layer 18 and the upper metal or the upper metal or the metal are sequentially disposed between the optical waveguide layer 16 (the optical waveguide 17) and the upper electrode 20 from the optical waveguide layer 16 side. The inorganic oxide layer 19 is sequentially laminated. That is, the layer configuration between the optical waveguide layer 16 (optical waveguide 17) and the lower electrode 12 and the layer configuration between the optical waveguide layer 16 (optical waveguide 17) and the upper electrode 20 are symmetrical in the element thickness direction. In the element thickness direction, in other words, the layer configuration from the optical waveguide layer 16 (optical waveguide 17) to the two electrodes (lower electrode 12 and upper electrode 20) is the same in the element thickness direction. The “same” means that the types of layers are preferably the same, and desirably the constituent materials and the layer thickness are also the same.

  Therefore, in the optical waveguide device 100 of the present embodiment, the interface between the upper electrode 20 (interface on the optical waveguide layer side) and the interface of the lower electrode 12 (interface on the optical waveguide layer side) are applied when a charged voltage is applied (during driving). Since the energy levels at the junction interface are the same, the space charge accumulation generated at the interface is the same and is canceled out, so that the occurrence of DC drift is suppressed.

  In particular, in the present embodiment, when the upper electrode 20 is formed (lifted off), in view of the necessity of forming the upper metal or inorganic oxide layer 19 on the upper clad layer 18, the optical waveguide layer 16 (optical In order that the layer configuration between the waveguide 17) and the lower electrode 12 and the layer configuration between the optical waveguide layer 16 (optical waveguide 17) and the upper electrode 20 are symmetrical in the element thickness direction, A lower metal or inorganic oxide layer 13 is formed between the electrode 12 and the lower cladding layer 14 to suppress DC drift. Further, the present invention is not limited to this configuration, depending on the purpose between the optical waveguide layer 16 (optical waveguide 17) and the lower electrode 12, and between the optical waveguide layer 16 (optical waveguide 17) and the upper electrode 20, depending on the purpose. Even if it is necessary to provide a functional layer, by providing a functional layer having a similar configuration between the other, a symmetric layer configuration in the element thickness direction is realized, and DC drift is suppressed.

In this embodiment, the case where the optical waveguide 17 is a ridge type has been described. However, as shown in FIG. 3A, the optical waveguide 17 protrudes toward the lower cladding layer 14 (lower electrode 12). You may comprise the reverse ridge type of the shape.
As a method for forming the inverted ridge type optical waveguide 17, a known method using a semiconductor process technique such as reactive ion etching (RIE), wet etching, photolithography, electron beam lithography, or the like, is previously applied to the lower cladding layer. Then, the lower cladding layer 14 is processed to form a trench, and the optical waveguide layer 16 is formed thereon, thereby forming an inverted ridge type optical waveguide.

  The optical waveguide 17 can take a large difference in refractive index between the upper cladding layer 18 and the lower cladding layer 14 by adopting an inverted ridge structure. Therefore, the absorption loss due to the electrodes can be suppressed and the effective electric field of the element can be increased, so that the drive voltage can be reduced.

  Further, in the present embodiment, the case where the optical waveguide 17 is a ridge type has been described. However, as shown in FIG. 3B, the optical waveguide 17 includes the upper clad layer 18 (upper electrode 20) side and the lower portion. You may comprise in the forward / reverse ridge type | mold of the shape which protruded convexly to both the clad layer 14 (lower electrode 12) side.

The forward / reverse ridge type optical waveguide 17 is formed by combining the ridge type and reverse ridge type formation methods.
When the optical waveguide 17 is a forward / reverse ridge type, it is possible to obtain a larger refractive index difference between the upper clad layer 18 and the lower clad layer 14 than the ridge type and the reverse ridge side. Therefore, the absorption loss due to the electrodes can be suppressed and the effective electric field of the element can be increased, so that the drive voltage can be reduced.

  In the present embodiment, the case where the optical waveguide 17 formed in the optical waveguide layer 16 is a Mach-Zehnder type is described. However, the shape of the optical waveguide 17 is not limited to such a shape, and the optical waveguide 17 is X X-cross type that crosses the shape, multi-mode interference type that allows the multi-mode propagation by spreading the optical waveguide 17 in the horizontal direction (see FIG. 4), or a combination of these optical waveguide patterns Are not limited to the Mach-Zehnder type.

For example, when the optical waveguide 17 is configured as a multimode interference type, as shown in FIG. 4, the optical waveguide 21 formed in the optical waveguide layer 16 includes an incident optical waveguide portion 21A and a multimode interference type optical waveguide 21B. And the output optical waveguide portion 21C and the output optical waveguide portion 21D.
When the electric field is formed between the upper electrode 20 and the lower electrode 12, the phase of the light propagating through the region of the optical waveguide 17 located in the formed electric field is changed. At the same time, it may be provided at a position where the intensity of the light incident on the optical waveguide 17 is modulated and emitted.

  For example, as shown in FIG. 4, at a position corresponding to the multimode interference optical waveguide 21B and intersecting the light propagation direction from the incident optical waveguide portion 21A toward the outgoing optical waveguide portion 21C and the outgoing optical waveguide portion 21D. Any configuration is possible as long as one of the paired upper electrodes (upper electrode 20A) and the other (upper electrode 20B) are provided on both sides of the center line in the direction of the direction.

  Hereinafter, the details of the invention will be described more specifically with reference to examples. Needless to say, the present invention is not limited to the following examples.

Example 1
First, as a solution of the nonlinear optical material, cyclohexanone, tetrahydrofuran, polysulfone, and DR1 (Disperse Red 1), 77 parts by weight, 9 parts by weight, 10 parts by weight, respectively, with the total weight of all the materials as 100 parts by weight, And 4 parts by mass of a solution (hereinafter referred to as PS solution) was prepared. Nμ / _{M W} of the non-linear optical materials made from this solution was approximately 0.007. When the refractive index in the thin film of this material was measured by the prism coupling method, it was confirmed to be 1.63.

  On the surface of a silicon substrate (diameter: 50.8 mm, thickness: 0.5 mm), Au is provided as a lower electrode with a thickness of 500 nm by a sputtering method, and then Ti is deposited as a metal layer on the lower electrode surface by a sputtering method to a thickness of 30 nm. did.

Next, an acrylic ultraviolet curable resin having a refractive index of 1.54 was applied as a lower clad layer to the surface of the metal layer, and an ultraviolet ray was irradiated to produce a 3.5 μm thick resin cured film.
Subsequently, the adjusted nonlinear optical material solution (PS solution) is applied as an optical waveguide layer, cured by leaving it in an environment of 120 ° C. for 60 minutes, and then subjected to reactive ion etching (RIE) followed by photolithography. A Zehnder type optical waveguide was formed. The film thickness of the optical waveguide layer was 3.3 μm, the ridge height of the optical waveguide was 0.7 μm, and the width was 5 μm.

  Next, the acrylic ultraviolet curable resin having a refractive index of 1.54 to be an upper clad layer is applied on the formed optical waveguide layer, and cured by irradiating with ultraviolet rays in the same manner as the lower clad layer. An upper clad layer made of a resin cured film having a thickness of 5 μm was produced.

On this upper cladding layer, Ti is sputtered as a protective layer at the time of lift-off (when a mask is formed in a region where the upper electrode is not formed and the upper electrode is formed using this mask and then the mask is removed). 30 nm.
On this protective layer, a resist was applied, an upper electrode pattern was formed by photolithography, and gold was sputtered and lifted off to form an upper electrode.
At this time, a rectangular parallelepiped upper electrode having a thickness of 1.0 μm is formed in each of the regions corresponding to the two arm portions of the optical waveguide formed in the Mach-Zehnder type, and these are defined as upper electrodes to be paired. It was.

  The obtained wafer stack was held in an environment of 140 ° C. and subjected to a poling treatment for 30 minutes using a corona poling device having a wire voltage of 4.5 KV and a grid voltage of 1 KV, thereby performing an alignment treatment.

  By cutting out the wafer-like laminate formed in this way with a dicer, the length in the longitudinal direction (the length in the light propagation direction of the optical waveguide) is 35 mm, and the length in the width direction is A chip having a thickness of 8 mm and a thickness of 0.51 mm was obtained.

With respect to the obtained optical waveguide element, a laser beam having a wavelength of 1.55 μm is made incident at an intensity of 1 mW from the light incident side of the optical waveguide through an optical fiber for light input / output, and the optical waveguide element is used in an environment of 70 ° C. Applying a triangular wave having a frequency of 10 Hz, a maximum value of +10 V, and a minimum value of −10 V between one electrode of the two upper electrodes of the waveguide element and the lower electrode, driving characteristics for 500 hours evaluated. The outgoing light is measured by an optical power meter (manufactured by Anritsu Co., Ltd., MT9812B + MU931124A) through an optical fiber, a modulation characteristic curve is obtained from the relationship between applied voltage and outgoing light intensity, and half-wave voltage derived from this characteristic: Vπ The maximum light output voltage: Vt was determined at each measurement time, and then the drift amount: ΔΦ was defined by the following formula (1). In the following formula (1), Vt1 represents the maximum light output voltage immediately after the start of voltage application, and Vt2 represents the maximum light output voltage after 500 hours have elapsed from the start of voltage application.
ΔΦ = ΔV / Vπ = (Vt1−Vt2) / Vπ (1)

  As a result, even for 500 hours of driving, the drift amount: ΔΦ after 500 hours from the start of voltage application was 1.1 rad, based on the maximum optical output voltage 5 minutes after the start of voltage application. The DC drift amount ΔV is 8.3 V from the formula (1), and is about 11 V (1.5 times the half-wave voltage) in terms of 10000 hours in a 25 ° C. environment, DC drift is suppressed, and DC drift compensation It became clear that compensation was possible with a DC power supply circuit for use.

  Moreover, the method of converting into 10,000 hours from the DC drift amount in 500 hours was performed as follows. From the DC drift amount at 500 ° C. at 70 ° C., the drift amount at 10000 hours in a 70 ° C. environment was estimated as 20 times the amount. The temperature dependency was determined by estimating the drift amount at 25 ° C. with the activation energy of DC drift in the organic nonlinear optical material being 0.52 eV (from Non-Patent Document 1).

(Comparative Example 1)
An optical waveguide device was obtained in the same manner as in Example 1 except that no metal layer (Ti layer) was formed on the lower electrode, and the drive characteristics were evaluated. As a result, for 500 hours driving, DC drift amount ΔΦ is 73.5 rad, ΔV is 558 V, about 38 V (5 times half-wave voltage) in terms of 10,000 hours under 25 ° C. environment, The DC drift is larger than that of the embodiment, and it is difficult to perform long-term operation compensation by the DC power supply circuit for DC drift compensation.

It is a perspective view which shows the structure of the optical waveguide element which concerns on this embodiment. It is A-A 'sectional drawing of the perspective view shown in FIG. 1 of the optical waveguide element which concerns on this embodiment. (A) and (B) are schematic views corresponding to a cross-sectional view taken along the line B-B 'of the perspective view shown in FIG. 1 in the optical waveguide device according to the present embodiment, and are schematic views showing a different form from FIG. It is a schematic diagram which shows the aspect different from the form shown in FIG.1 and FIG.2 in the optical waveguide element in this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Substrate 12 Lower electrode 13 Lower metal or inorganic oxide layer 14 Lower cladding layer 16 Optical waveguide layer 17 Optical waveguide 17A, 17B Arm portion 17C Incident optical waveguide portion 17D Outgoing optical waveguide portion 18 Upper cladding layer 19 Upper metal or inorganic oxide Layers 20, 20A, 20B Upper electrode 21 Optical waveguide 21A Incident optical waveguide portion 21B Multimode interference optical waveguide 21C Outgoing optical waveguide portion 21D Outgoing optical waveguide portion 100 Optical waveguide device 100 Optical waveguide device

Claims (6)

An optical waveguide containing an organic nonlinear optical material;
A first electrode disposed on one side of the optical waveguide;
A second electrode disposed on the other surface side of the optical waveguide;
Have
An optical waveguide element in which a layer configuration between the optical waveguide and the first electrode and a layer configuration between the optical waveguide and the second electrode are symmetrical in the thickness direction. A first cladding layer disposed between the optical waveguide and the first electrode;
A first metal or inorganic oxide layer disposed between the first electrode and the first cladding layer;
A second cladding layer disposed between the optical waveguide and the second electrode;
A second metal or inorganic oxide layer disposed between the second electrode and the second cladding layer;
The optical waveguide device according to claim 1, further comprising:   The optical waveguide device according to claim 1, wherein the optical waveguide is a Mach-Zehnder type.   The optical waveguide device according to claim 1, wherein the optical waveguide is a multimode interference type.   2. The optical waveguide device according to claim 1, wherein the optical waveguide has a structure protruding in a convex shape toward the first electrode side or the second electrode side.   2. The optical waveguide device according to claim 1, wherein the optical waveguide has a structure protruding in a convex shape toward both the first electrode side and the second electrode side.

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