JP2006243376A - Organic waveguide type optical modulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic waveguide type optical modulator which is small-sized and driven with a low voltage and has high reliability. <P>SOLUTION: The organic waveguide type optical modulator 100 includes: an optical waveguide 3 having a core layer 4 which makes light incidence and emitting possible and which modulates the phase or intensity of the light with an externally controlled electric field and is made of organic crystal, and clad layers 8 and 12 which enclose the core layer 4, and a control electrode modulating the phase or intensity of the light by applying the electric field to the core layer 4. The modulator 100 has a stress relaxing layer 10 formed in the circumference of the core layer 4 between the core layer 4 and clad layers 8 and 12. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an organic waveguide type optical modulator that applies the electro-optic effect of an organic material and modulates the intensity of light by an electric signal.

  With the rapid development of the multimedia society in recent years, the demand for high-capacity high-speed optical communication for transmitting and receiving more information is increasing. At present, electrical signals transmitted from information oscillation sources such as homes and offices via telephone lines are gathered at a relay station for long-distance communication and converted from electrical signals to optical signals. A large number of optical signals are sent to a relay station through optical fibers, where they are converted again into electrical signals and sent to a target information receiving source.

  Such information using optical communication is not only a numerical increase in the number of transmission sources, but also the information to be sent becomes larger like computer data files, image files, and video files, and these are transmitted and received at higher speeds. It is demanded. In addition, an electrical signal from an information transmission source has been converted into an optical signal for higher speed, and a signal amount per unit time is increased by using a shorter optical pulse.

  Due to the increasing demand for large-capacity high-speed optical communication, in recent years, information transmission using light has been proposed not only for trunk networks but also between LANs, network terminals and electronic devices, between boards, and between LSI chips. In particular, in the optical interconnection connecting between devices, between boards, and between LSI chips, the power supply voltage of the mounted LSI chips tends to be lowered. For this reason, a device used for optical interconnection is required to have a low voltage so as not to give noise to the LSI chip. Drivers such as SiGe that modulates light in response to electrical signals are also in the direction of lowering the drive voltage due to the problem of withstand voltage associated with high-speed driving, and this is low due to the low power consumption requirements of the entire system. There is an increasing demand for voltage.

  In this optical interconnection, in order to convert an electric signal into an optical signal, there are a method by direct modulation of a laser diode and a method of externally modulating CW light from the laser diode by a waveguide type optical modulator. However, high-speed modulation of about 10 Gbps is difficult with direct modulation of a laser diode, and external modulation is mainly used for higher-speed signals.

  One of the external modulation optical modulations uses an electro-optic effect. The electro-optic effect is a phenomenon in which the refractive index of the medium changes when an electric field is applied to the optical medium. It is caused by the linear electro-optic effect (Pockels effect) due to the second-order nonlinearity and the third-order nonlinearity. Secondary electro-optic effect (Kerr effect). Practically, the second-order nonlinear constant is several orders of magnitude larger than the third-order nonlinear constant, and therefore an electro-optic effect (Pockels effect) using the second-order nonlinearity is often used.

FIG. 7 is a top view showing a Mach-Zehnder type optical modulator using an inorganic ferroelectric crystal LiNbO ₃ (hereinafter, LN) as an example of a modulator using the electro-optic effect. The optical modulator 80 includes an optical waveguide 83, a control electrode 85, a termination resistor 86, and a high frequency power source 87. The portion of the optical waveguide 83 is formed by diffusing Ti ions or the like into an LN crystal cut out in an appropriate orientation, thereby forming a region having a large refractive index as a core layer, and a buffer of an LN crystal or silicon oxide film without Ti diffusion. The layer is a cladding layer. The electric field from the outside is a traveling wave electrode made of a metal such as Au or Cu, and is applied to the modulation electrode (control electrode 85) of a symmetric or asymmetric planar stripline. Incident light is branched into two ports at the Y branch on the entrance side, and light propagating through the ports interacts with microwaves applied to the electrodes to cause phase modulation. The light that has undergone this phase modulation is combined positively with the light propagating through the other and the Y branch on the exit side, and the combined wave becomes intensity-modulated light due to the phase modulation.

In such a traveling waveform electrode, there is ideally no limitation on the electric circuit band, but in reality, if there is a difference between the modulation signal and the light propagation speed, the band limitation is imposed even if this electrode configuration is adopted. receive. For example, the dielectric constant of LN crystal about epsilon ₁ = 43, in order epsilon ₃ = 28, a large refractive index effective refractive index n _m of the microwave light n ₀ = 2.15 in (wavelength 1.3 .mu.m) On the other hand, it becomes large and is subject to band limitation due to the speed mismatch between the microwave and the light wave. Therefore, to increase the bandwidth, that is, to perform high-speed modulation, it is necessary to reduce the electrode length and the interaction length between the microwave and the light wave.

  However, when the length of the electrode is reduced, the drive voltage for modulation increases, making it difficult to achieve both high speed and low voltage. In an example of a current LN modulator, 5V drive at 10 Gbps is performed, and the size is two to three times as large as the power supply voltage of the LSI chip.

  In contrast, organic crystals and organic polymer materials have a smaller dielectric constant than inorganic materials, and can be expected to improve the speed mismatch. Also, processing such as thinning is relatively easy. In addition, it has a large electro-optic constant, and the working length of the modulation section can be shortened. Therefore, there is a possibility that a small, low voltage and high speed optical modulator can be realized.

  In particular, in the case of organic crystals, it is known that a polarization treatment like an organic polymer is not required, and further, there is no deterioration with time of characteristics such as polarization relaxation and it is stable.

4-dimethylamino-N-methyl-4-stilbazolium tosylate (hereinafter DAST), whose molecular structural formula is shown in FIG. It has been developed and has an extremely large nonlinear optical constant, electro-optic constant (d ₁₁ = 1010 pm / V (λ = 1.3 μm)) and electro-optic constant (r ₁₁ = 75 pm / V (λ = 820 nm)), and an organic crystal Because of its unique low dielectric constant (ε ₁ = 5.2), it has attracted attention such as low voltage, high-speed optical modulation and detection, and generation of millimeter waves. Therefore, for example, in Patent Documents 1 to 3 and the like, a core groove is formed in a lower clad portion, an organic crystal DAST showing an electro-optic effect is embedded therein, and a solvent that does not deteriorate the characteristics of DAST is used. A waveguide type optical modulator that can be driven at a low voltage and at a high speed is proposed by polishing and forming DAST in the core portion by removing DAST other than the groove.

JP 2004-109457 A JP 2004-45891 A JP 2003-202533 A

  In this way, by using an organic material having an electro-optic constant larger than that of LN, including DAST, the action length of the modulation unit (changing the electric signal into an optical signal) that changes the phase of light can be reduced. The size of the vessel can be reduced.

  However, on the other hand, organic crystals such as DAST have the characteristic that volume changes occur due to changes in humidity and heat, especially in light modulators that continuously enter light, when the usage time is long. The effect of heat increases. And when the difference in volume change rate (expansion coefficient) with the adjacent material such as the cladding layer is large at this time, the generation of cracks in the crystal itself or the separation between the crystal part and the cladding layer occurs. It adversely affects device characteristics.

  For this reason, when organic crystals such as DAST are used in the waveguide part (core layer), the problem of volume change rate (thermal expansion coefficient) with the clad layer is solved and the advantages of organic materials are utilized. Further, there is a need for an organic waveguide type optical modulator that can be made smaller, low voltage, and driven at high speed, and that is more reliable.

For such an organic waveguide, a polymer resin such as a polyimide resin is often used for the clad layer in terms of refractive index controllability and ease of manufacture. However, in general, a polymer resin has a low thermal conductivity (thermal conductivity: 0.1 to 4 Wm ⁻¹ K ⁻¹ ), and heat generated from the core layer and the electrode is hardly radiated. In particular, in an optical modulator that continuously receives light, the influence becomes particularly large when the usage time is long. At this time, since the thermal expansion coefficients of the clad layer and the core layer are different, different stresses are generated between the materials, the crystal itself forming the core layer is cracked, and the core layer and the clad layer are separated. There is a phenomenon that adversely affects device characteristics.

  For this reason, when organic crystals such as DAST are applied to the core layer, it is possible to achieve smaller size, lower voltage, and higher speed driving by taking advantage of organic materials in consideration of the effects of heat generation. It is necessary to provide an organic waveguide type optical modulator with excellent reliability.

  The present invention has been made in view of the above, and an object of the present invention is to provide an organic waveguide type optical modulator that is small, low-voltage driven, and highly reliable.

In order to solve the above-described problems and achieve the object, the invention according to claim 1 is an organic crystal that enables the incidence and emission of light and modulates the phase or intensity of light by an externally controlled electric field. In an organic waveguide type optical modulator having an optical waveguide having a core layer and a clad layer surrounding the core layer, and a control electrode that modulates the phase or intensity of light by applying an electric field to the core layer, A stress relaxation layer is formed around the core layer between the core layer and the clad layer.
According to a second aspect of the present invention, there is provided a core layer made of an organic crystal and a clad layer surrounding the core layer, which allows light to enter and exit and modulates the phase or intensity of light by an externally controlled electric field. In an organic waveguide type optical modulator having an optical waveguide having a control electrode that modulates the phase or intensity of light by applying an electric field to the core layer, the cladding layer radiates heat with better thermal conductivity than the cladding layer. It is characterized in that a layer is formed.

According to a third aspect of the present invention, there is provided a core layer made of an organic crystal and a clad layer surrounding the core layer, which allows the incidence and emission of light and modulates the phase or intensity of light by an externally controlled electric field. An organic waveguide type optical modulator having an optical waveguide having a control electrode that modulates the phase or intensity of light by applying an electric field to the core layer, and the periphery of the core layer between the core layer and the cladding layer In addition, a stress relaxation layer is formed, and a heat dissipation layer having better thermal conductivity than the cladding layer is formed in the cladding layer.
According to a fourth aspect of the present invention, in the organic waveguide type optical modulator according to the first or third aspect, the stress relaxation layer is formed around the core layer over the entire circumference.

According to a fifth aspect of the present invention, in the organic waveguide type optical modulator according to any one of the first, third, and fourth aspects, the stress relaxation layer also serves as the cladding layer.
The invention according to claim 6 is the organic waveguide type optical modulator according to any one of claims 1, 3 to 5, wherein a plurality of the stress relaxation layers are formed.
The invention according to claim 7 is the organic waveguide type optical modulator according to any one of claims 1, 3 to 6, wherein the stress relaxation layer made of at least one polyimide resin is provided. It is said.

According to an eighth aspect of the present invention, in the organic waveguide type optical modulator according to the second or third aspect, the heat dissipation layer is made of a polymer resin in which a high thermal conductivity material is dispersed.
The invention according to claim 9 is the organic waveguide optical modulator according to claim 2 or 3, characterized in that the heat dissipation layer is made of a carbon material.
According to a tenth aspect of the present invention, in the organic waveguide optical modulator according to the second or third aspect, the heat dissipation layer is made of one of a metal and a metal oxide. The invention according to claim 11 is the organic waveguide optical modulator according to any one of claims 1 to 10, wherein the organic crystal of the core layer is 4-dimethylamino-N-methyl-4-stilba. It is characterized by being zolium tosylate.

  According to the first aspect of the present invention, light can be incident and emitted, and optical characteristics (refractive index) of light can be modulated by an externally controlled electric field, and an organic material can be used as a medium for the electro-optic effect. In the organic waveguide type optical modulator in the core layer, the stress relaxation layer is formed around the core layer between the core layer and the clad layer, which occurs in the core layer due to environmental changes such as temperature and humidity. It is possible to provide an organic waveguide type optical modulator that suppresses deterioration such as cracks and is excellent in reliability.

According to the second aspect of the present invention, light can be incident and emitted, and optical characteristics (refractive index) of light can be modulated by an externally controlled electric field, and an organic material is used as a medium for the electro-optic effect. In the organic waveguide type optical modulator in the core layer, the heat dissipation layer with good thermal conductivity is formed in the cladding layer, so that the heat generated in the core layer is efficiently dissipated, and the temperature rise in the core layer portion. It is suppressed. Therefore, it is possible to provide an organic waveguide type optical modulator that suppresses deterioration such as cracks generated in the core layer due to heat and is excellent in reliability.
According to the third aspect of the present invention, light can be incident and emitted, and optical characteristics (refractive index) of light can be modulated by an externally controlled electric field, and an organic material is used as a medium for the electro-optic effect. In the organic waveguide type optical modulator in the core layer, it suppresses deterioration of cracks and the like generated in the core layer due to environmental changes such as temperature and humidity, and also suppresses deterioration of cracks and the like generated in the core layer due to heat. Thus, an organic waveguide type optical modulator excellent in reliability can be provided.

  According to the invention of claim 4, the stress relaxation layer is formed over the entire circumference around the core layer, so that deterioration such as cracks generated in the core layer due to environmental changes such as temperature and humidity can be prevented. An organic waveguide type optical modulator that can be suppressed in any direction over the entire circumference and has excellent reliability can be provided.

According to the invention of claim 5, the stress relaxation layer also serves as the cladding layer, so that the stress generated in the core layer is relaxed and an organic waveguide type optical modulator excellent in reliability is provided. Can do.
According to the invention of claim 6, since a plurality of stress relaxation layers are formed, the effect of reducing the stress applied to the core layer can be enhanced, and the organic waveguide type optical modulation with higher reliability can be achieved. Can be provided.
According to the invention concerning claim 7, by having the stress relaxation layer made of at least one layer of polyimide resin, it is possible to constitute a highly flexible stress relaxation layer with excellent heat resistance, and to improve reliability. An excellent organic waveguide type optical modulator can be provided.

According to the invention of claim 8, since the heat dissipation layer is made of a polymer resin in which a high thermal conductivity material is dispersed, it is possible to provide an organic waveguide type optical modulator that is easy to manufacture and excellent in reliability. it can.
According to the ninth aspect of the invention, since the heat dissipation layer is made of a carbon material, it is possible to provide an organic waveguide type optical modulator having excellent reliability.
According to the invention of claim 10, since the heat dissipation layer is made of either metal or metal oxide, it is possible to provide an organic waveguide type optical modulator with higher reliability.
According to the invention of claim 11, 4-dimethylamino-N-methyl-4-stilbazolium tosylate having a large electro-optic constant (EO constant), a low dielectric constant, and excellent heat resistance ( By using DAST as an electro-optic effect medium, it is possible to provide a low-voltage, high-speed and high-reliability organic waveguide optical modulator.

  Embodiments of an organic waveguide type optical modulator according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
The organic waveguide type optical modulator of the present embodiment is a waveguide type optical modulator having an organic crystal as a core layer, and a stress relaxation layer is interposed in a part or all of the region between the core layer and the cladding layer. Is. The material constituting the stress relaxation layer can be formed without impairing the function of the optical modulator, has elasticity, and can be provided between the core layer and the cladding layer with a thermal expansion coefficient. For example, polymer materials such as polyimide resin and acrylic resin, silicon rubber, various synthetic rubber resins, and the like are available.

  The thickness of the stress relaxation layer is preferably 0.1 μm to 20 μm, and more preferably about 0.5 μm to 5 μm. If it is too thin, a sufficient stress relaxation effect due to the formation of the stress relaxation layer cannot be obtained. On the other hand, if it is too thick, it is difficult to form a uniform thickness of the stress relaxation layer.

  This stress relaxation layer can be formed by a method such as a spray coating method, a wet method, or a spin coating method. For example, in the case of a polyimide resin, it can be formed by a method of applying a polyimide resin composition containing a solvent at an arbitrary thickness and removing the solvent by overheating under normal pressure or reduced pressure.

  The stress relaxation layer may be formed as a single layer or a multilayer. For example, when an organic crystal to be a core layer is produced by a solution method, the material used for the stress relaxation layer is restricted by the resistance to the solvent used, but in this case, the layer in contact with the core layer By selecting the material, it is possible to easily achieve both the solvent resistance and the stress relaxation effect.

As the organic crystal, any organic material that has been used conventionally and has a large nonlinear optical constant compared to inorganic materials represented by KH ₂ PO ₄ , LiNbO _{3 and the} like can be used. For example, 4-dimethylamino-N -Methyl-4-stilbazolium tosylate (4-dimethyl-4-stilbazolium tosylate: DAST), 2-methyl-4-nitroaniline (MNA), metanitroaniline (mNA), 3-methyl -4-nitropyridine-1-oxide (POM), urea, methyl 2-cyano-3- (2-methoxyphenyl) -2-propenoate (CMP methyl), L-arginine phosphate monohydrate (LAP), 4- (N, N dimethylamino) -3-acetamidonitrobenzene (D N), 3,5-dimethyl-1- (4-nitrophenyl) pyrazole (DMNP), 4'-nitrobenzylidene-3-acetamino-4-methoxyaniline (MNBA), and the like. Here, 4-dimethylamino-N-methyl-4-stilbazolium tosylate is preferable because it has a very large nonlinear optical constant and electro-optical constant and has a low dielectric constant specific to organic crystals. .

Embodiment 2. FIG.
The organic waveguide type optical modulator of the present embodiment is a waveguide type optical modulator having an organic crystal as a core layer, and is provided with a heat dissipation layer containing a high thermal conductivity material. This heat dissipation layer can be formed without impairing the function of the optical modulator, and has only to have higher thermal conductivity than the polymer resin (thermal conductivity: 0.1 to 4 Wm ⁻¹ K ⁻¹ ) constituting the cladding layer. The high heat conductive material to be configured includes carbon materials such as fullerene, carbon nanotube, diamond, and carbon fiber (thermal conductivity: 1000 to 2000 Wm ⁻¹ K ⁻¹ ), metals such as Au, Ag, Al, and Cu. (Thermal conductivity: 80 to 400 Wm ⁻¹ K ⁻¹ ) or metal oxides (thermal conductivity: 20 to 40 Wm ⁻¹ K ⁻¹ ) such as ZnO, MgO, and Al ₂ O ₃ can be used. Examples of the polymer resin that disperses (mixes at a uniform rate) such a high thermal conductive material include polyimi resins, epoxy resins, acrylic resins, and silicon resins.

The heat dissipation layer can be formed of a polymer resin in which a high thermal conductivity material is dispersed by a method such as a spray coating method, a wet method, or a spin coating method. For example, in the case of a polyimide resin, there may be mentioned a method in which a polyimide resin composition containing a solvent is applied at an arbitrary thickness by a spin coating method, and the solvent is removed by overheating under normal pressure or reduced pressure.
Further, the heat dissipation layer may be formed of a single layer or a multilayer.

Hereinafter, a configuration and a manufacturing method of the present invention will be described based on examples.
[Example 1]
FIG. 1 is a schematic top view of an organic waveguide type optical modulator according to a first embodiment of the present invention. 2 is a cross-sectional view taken along the line AA in FIG. The optical modulator 100 includes an optical waveguide 3, a control electrode 5 (signal electrode 5 a and ground electrode 5 b), a substrate 2, a termination resistor 6, and a high frequency power source 7. In this embodiment, DAST is selectively arranged in the modulation part of two optical waveguides 3 formed in parallel, and the optical path lengths of the two DASTs are made equal.

The bulk crystal of DAST has a rhomboid plate shape that is large in the a and b axis directions and small in the c axis direction. Appl. Phys. Lett. , Vol. 74 (1999) 635, the DAST thin film crystal also has a and b axes in the film plane, and the c axis is perpendicular to the film. DAST having such a geometric structure can easily form a and b axes in the plane parallel to the substrate. On the other hand, in order to use the largest electro-optic constant r ₁₁ of DAST, the light is propagated in the b-axis, an electric field is applied in the a-axis direction, and the polarization plane of incident light is incident so as to be parallel to the a-axis. Good. Therefore, the electric field formed by the traveling wave signal electrode and the ground electrode is arranged as shown in FIGS. 1 and 2 so that the electric field is parallel to the substrate.

  Further, a traveling wave signal electrode 5a is disposed at the center of each branch optical waveguide 3, and a ground electrode 5b is disposed outside the branch optical waveguide 3, thereby applying a reverse electric field to each pair of DASTs. can do. At this time, the refractive index of the organic crystal DAST, which is an electro-optic effect medium selectively disposed in each of the branched waveguides 3, changes in the opposite direction. That is, the refractive index is increased in one optical waveguide 3 and the refractive index is decreased in the other optical waveguide 3.

  As a result, the phase of the signal light propagating through the optical waveguides 3 and 3 branched into two is advanced on the one hand and the phase is delayed on the other hand. For this reason, a double phase change can be caused by the push-pull operation, which enables driving at a lower voltage. Moreover, the length of the core layer 4 made of an organic material can be shortened by configuring the branch portion as in this embodiment, so that the manufacturing time can be shortened and the quality can be improved. Further, the electrode 5 is a traveling wave electrode provided with a terminal resistance of 50Ω, and has an electrode structure that can cope with high-speed light modulation.

FIG. 3 is a schematic process diagram of the manufacturing process of the organic waveguide type optical modulator of this embodiment. A method of manufacturing the organic waveguide type optical modulator 100 will be described with reference to FIG.
Formation of Cladding Layer First, in this example, a silicon substrate was used as the base substrate 2 as shown in FIG. Then, an acrylic resin was spin coated on the basic substrate 2 to form the substrate-side clad layer 8. In this embodiment, acrylic resin is used as the material for the substrate-side cladding layer 8, but the material for the substrate-side cladding layer 8 is particularly suitable if it has a lower refractive index than the organic material for the core layer described later. For example, epoxy resin, polyimide resin, high molecular resin such as silicon resin, silicon, quartz, and the like can be used.

Formation of Core Groove Next, as shown in FIG. 3B, the substrate-side cladding layer 8 is subjected to reactive ion etching using photolithography and oxygen gas using a waveguide pattern mask to obtain a width. A core groove 8a having a thickness of 10 μm and a depth of 10 μm was produced.

-Formation of Stress Relaxation Layer Next, as shown in FIG. 3C, in order to form the in-groove stress relaxation layer 10, the substrate-side clad layer 8 in which the core groove 8a is formed is formed by spray coating. A polyimide resin layer having a refractive index larger than that of the core layer was formed by coating with a thickness of about 2 μm. In this way, the core groove 8a having the bottom surface and the inner surface covered with the polyimide resin layer was obtained. Thus, by enclosing the core layer 4 with the polyimide resin having a higher refractive index than the core layer 4, the stress between the core layer 4 and the cladding layer 8 can be relieved, and a low-loss optical waveguide Can be formed.

-Formation of a core layer Next, the polyimide resin formed in parts other than the core groove 8a was removed using lithography and etching. Thereafter, as shown in FIG. 3D, DAST constituting the core layer 4 was crystal-grown in the core groove 8a by a slow cooling method using methanol as a solvent. At this time, the crystal orientation is set by the seed crystal so that the waveguide direction is the b-axis, and in the same plane parallel to the substrate 2, the a-axis and the vertical direction to the substrate 2 are the c-axis. Single crystals were grown. At this time, the DAST single crystal grew about 10 mm in the core groove 8a. Further, since DAST having grown crystals exists also in portions other than the core groove 8a, unnecessary portions of DAST were removed by polishing. In this way, a core layer 4 in which two DASTs are arranged in parallel was formed. Note that in this manufacturing method, by using a plurality of seed crystals for the substrate, a plurality of core layers can be easily manufactured at the same time, and productivity can be improved.

  Moreover, as an example of the above-described polishing method, there is a method of polishing using silica abrasive particles using a foamed urethane pad Supreme RN-H (Rodel). By this method, DAST other than the core groove 8a can be removed and easily left only in the core groove 8a.

  Further, in this example, the core layer 4 made of DAST was formed by a slow cooling method using a seed crystal. Phys. Lett. , Vol. 74 (1999) 635, the core layer 4 may be formed by an improved shear method.

Formation of Stress Relaxation Layer Next, polyimide resin was spray coated so as to cover the core layer 4 to form an electrode-side stress relaxation layer 11 having a thickness of about 2 μm. Thereafter, the same acrylic resin as that of the substrate-side clad layer 8 was spin-coated on the upper layer of the electrode-side stress relaxation layer 11 to form an electrode-side clad layer 12 having a thickness of 10 μm.

  The thermal expansion coefficient of the polyimide resin forming the in-groove stress relaxation layer 10 and the electrode side stress relaxation layer 11 is larger than that of the DAST crystal forming the core layer 4, and the acrylic forming the electrode side cladding layer 12 and the substrate side cladding layer 8. Since it is smaller than the resin, it is possible to relieve the stress between layers caused by thermal changes.

Formation of control electrode Next, an Au electrode was prepared by plating, and a part of the traveling wave type signal electrode 5 (5a) and the ground electrode 5 (5b) having a thickness of 5 μm constituting the control electrode 5 were prepared. Next, a signal electrode and a ground electrode were also formed at the lead-out portion that intersected with the branched optical waveguide 3, and a 50Ω termination resistor 6 was attached to the end to form a traveling wave electrode. As described above, the organic waveguide type optical modulator 100 shown in FIGS. 1 and 3 was produced.

  When a modulation signal is input between the electrodes through the coaxial cable while the laser light having a wavelength of 1.3 μm is incident on the organic waveguide type optical modulator 100 thus manufactured, the voltage is about 1.2V. It was possible to provide high-speed and high extinction ratio light intensity modulation with a low driving voltage. In addition, cracks and the like were not observed in the core layer 4 portion even after 200 hours of continuous use, and a highly reliable organic waveguide type optical modulator could be realized.

  In the present embodiment, the in-groove stress relaxation layer 10 and the electrode-side stress relaxation layer 11 are provided as means for relaxing the stress between layers generated by thermal change, but only one of them is provided. Even if it is, a predetermined effect can be obtained.

[Example 2]
FIG. 4 is a schematic process diagram of the manufacturing process of the organic waveguide type optical modulator of Example 2, and FIG. 4E shows a longitudinal section of the completed organic waveguide type optical modulator. In FIG. 4E, the organic waveguide type optical modulator 110 of this embodiment has a core groove 13a formed on a base substrate 13 made of silicon resin, and is made of acrylic resin in the core groove 13a. A first in-groove stress relieving layer 18 also serving as a side cladding layer is formed, and a second in-groove stress relieving layer 20 made of polyimide resin is further formed on the inside thereof. A core layer 4 made of DAST is formed. Other configurations are the same as those of the first embodiment.

A method of manufacturing the organic waveguide type optical modulator 110 will be described with reference to FIG.
Formation of Core Groove As shown in FIG. 4A, a silicon substrate was used as the base substrate 13 in this example. Then, as shown in FIG. 4B, photolithography using a waveguide pattern mask and reactive ion etching using CF ₄ gas are performed on the basic substrate 13, and the two are arranged in parallel. A core groove 13a having a thickness of 24 μm and a depth of 17 μm was formed.

Formation of Stress Relaxation Layer Next, in order to form the first in-groove stress relaxation layer 18, acrylic resin was coated on the base substrate 13 with a thickness of about 5 μm by a spray coating method. Next, in order to form the second in-groove stress relaxation layer 20, a polyimide resin was coated with a thickness of about 2 μm. Since the acrylic resin has a wide selection range, it is easy to select an appropriate elasticity for the relaxation layer, and since the refractive index can be easily adjusted, the function as a cladding layer can be easily achieved. Therefore, it is possible to relieve the stress generated in the core layer as the heat changes. However, since the solvent resistance to methanol used for crystal production is not good, a polyimide resin excellent in solvent resistance is configured as the second stress relaxation layer 10.

-Formation of a core layer Next, the acrylic resin layer and polyimide resin layer which were formed in parts other than the core groove 13a were removed using lithography and etching. In this way, the first in-groove stress relaxation layer 18 also serving as the cladding layer and the second in-groove stress relaxation layer 20 were formed. Then, the core layer 4 made of DAST was formed inside the second in-groove stress relaxation layer 20 by the same method as in Example 1.

Formation of Stress Relaxation Layer Next, an acrylic resin was coated on the substrate with a thickness of about 10 μm by spray coating to form an electrode side stress relaxation layer 22 that also serves as an electrode side cladding layer.

-Formation of control electrode Next, the control electrode 5 was formed by the same method as in Example 1. The organic waveguide type optical modulator 110 was produced as described above.

  When a modulation signal is input between the electrodes through the coaxial cable while the laser light having a wavelength of 1.3 μm is incident on the organic waveguide type optical modulator 110 thus manufactured, the voltage is as low as about 1.2V. It was possible to provide high-speed and high extinction ratio light intensity modulation with the driving voltage. In addition, cracks and the like were not observed in DAST even after 300 hours of continuous use, and a highly reliable organic waveguide type optical modulator could be realized.

[Comparative example]
In the same production method as in Example 1, a silicon substrate was used as a substrate, and a polystyrene resin serving as a cladding layer of an optical waveguide was spin-coated on the substrate. Furthermore, using a Mach-Zehnder waveguide pattern mask, reactive ion etching using photolithography and oxygen gas was performed to form a core groove.

  Next, a polyimide resin having a large refractive index to be a core layer is formed in the groove portion to form a low-loss optical waveguide. Further, using lithography and etching, the polyimide resin that becomes a portion for selectively forming DAST was removed, and the core groove was formed again. Here, DAST is crystal-grown by slow cooling using methanol as a solvent in the same manner as in Example 1, DAST other than the core groove is removed, and a DAST core having a thickness of 6 μm, a width of 6 μm, and a length of 10 mm is formed on the branched optical waveguide. A branched optical waveguide with a portion was prepared.

  In this manner, as in Example 1, an electrode side cladding layer made of polystyrene resin, formation of a traveling waveform signal electrode and a ground electrode, and a terminal resistance of 50Ω are formed in this order, and a Mach-Zehnder type organic waveguide optical modulator is formed. Was made. When a modulation signal is input between electrodes via a coaxial cable while a laser beam having a wavelength of 1.3 μm is incident, a traveling wave electrode is used at a driving voltage as low as about 1.2 V, so that high-speed light intensity is obtained. Although the modulation could be confirmed, cracks occurred in the DAST crystal due to long-term use for about 150 hours, and the optical loss increased.

[Example 3]
FIG. 5 is a schematic process diagram of the manufacturing process of the organic waveguide type optical modulator of Example 3, and FIG. 5D shows a longitudinal section of the completed organic waveguide type optical modulator.
5D, in the organic waveguide type optical modulator 120 of this embodiment, a heat dissipation layer 21 made of carbon fiber-containing polyimide resin is formed on a base substrate 23 made of silicon resin, and this heat dissipation is further performed. A clad layer 27 made of polyimide resin and having a thickness of 13 μm is formed on the layer 21, a core groove 27 a having a depth of 10 μm is formed in the clad layer 27, and the core layer 4 made of DAST is formed in the core groove 27 a. The clad layer 32 made of polyimide resin is further formed above the core layer 4. Other configurations are the same as those of the first embodiment.

A method for manufacturing the organic waveguide type optical modulator 120 will be described with reference to FIG.
Formation of heat dissipation layer and cladding layer First, in Example 3, a silicon substrate is used as the base substrate 23 as shown in FIG. Then, on the base substrate 23, a carbon fiber-containing polyimide resin was formed to a thickness of 10 μm by a spin coating method to form a heat dissipation layer 21. Next, a polyimide resin serving as the substrate-side cladding layer 27 is formed on the heat dissipation layer 21 to a thickness of 13 μm by spin coating.

-Formation of Core Groove Next, as shown in (b), the substrate-side cladding layer 27 is subjected to reactive ion etching using photolithography and oxygen gas using a waveguide pattern mask to obtain a width of 10 μm, A core groove 27a having a depth of 10 μm was produced.

-Formation of core layer Next, as shown in (c), the DAST constituting the core layer 4 was crystal-grown in the core groove 27a by a slow cooling method using methanol as a solvent. At this time, the crystal orientation is set by the seed crystal so that the waveguide direction is the b-axis, the a-axis is in a plane parallel to the substrate 23, and the c-axis is the vertical direction to the substrate 23. DAST single crystals were grown. At this time, the DAST single crystal grew about 10 mm in the core groove 27a. Further, since DAST having crystal growth exists also in the portion other than the core groove 27a, unnecessary portions of DAST were removed by polishing. In this way, a core layer 4 in which two DASTs are arranged in parallel was formed.

Formation of Cladding Layer Next, the same polyimide resin as the substrate-side cladding layer 27 previously formed is spin-coated on the upper layer of the core layer 4 to form an electrode-side cladding layer 32 having a thickness of 10 μm. Next, the control electrode 5 was formed on the electrode-side cladding layer 32 by the same method as in Example 1. The organic waveguide type optical modulator 120 was produced as described above.

  When a modulation signal is input between the electrodes via the coaxial cable while the laser light having a wavelength of 1.3 μm is incident on the organic waveguide type optical modulator 120 thus manufactured, the voltage is about 1.2 V. It was possible to provide high-speed and high extinction ratio light intensity modulation with a low driving voltage. In addition, cracks and the like were not observed in DAST even after continuous use for 200 hours, and a highly reliable organic waveguide type optical modulator could be realized.

[Example 4]
FIG. 6 is a schematic process diagram of the manufacturing process of the organic waveguide type optical modulator of Example 4, and FIG. 6D shows a longitudinal section of the completed organic waveguide type optical modulator.
In FIG. 6D, in the organic waveguide type optical modulator 130 of the present embodiment, a heat dissipation layer 31 made of alumina-containing polyimide resin is formed on a base substrate 23 made of silicon resin. A clad layer 27 made of polyimide resin having a thickness of 10 μm is formed on 31, a core groove 27 a having a depth of 10 μm is formed in the clad layer 27, and a core layer 4 made of DAST is formed in the core groove 27 a. In addition, a clad layer 32 made of polyimide resin is further formed above the core layer 4. Other configurations are the same as those of the third embodiment.

A method of manufacturing the organic waveguide type optical modulator 130 will be described with reference to FIG.
Formation of heat dissipation layer and cladding layer First, in Example 4, a silicon substrate is used as the base substrate 23 as shown in FIG. Then, an alumina-containing polyimide resin was formed to a thickness of 10 μm on the base substrate 23 by a spin coating method to form a heat dissipation layer 31. Next, a polyimide resin serving as the substrate-side clad layer 27 is formed on the heat dissipation layer 21 to a thickness of 10 μm by spin coating.

-Formation of Core Groove Next, as shown in (b), the substrate-side cladding layer 27 is subjected to reactive ion etching using photolithography and oxygen gas using a waveguide pattern mask to obtain a width of 10 μm, A core groove 27a having a depth of 10 μm was produced.
Formation of core layer Next, as shown in (c), the DAST constituting the core layer 4 is crystal-grown by the same method as in Example 1, and the same as the substrate-side clad layer 27 previously formed thereon. A polyimide resin was spin-coated to form an electrode-side cladding layer 32 having a thickness of 10 μm. Next, the control electrode 5 was formed on the electrode-side cladding layer 32 by the same method as in Example 1. The organic waveguide type optical modulator 130 was produced as described above.

  When a modulation signal is input between the electrodes via the coaxial cable while the laser light having a wavelength of 1.3 μm is incident on the organic waveguide type optical modulator 130 thus manufactured, the voltage is about 1.2 V. It was possible to provide high-speed and high extinction ratio light intensity modulation with a low driving voltage. In addition, cracks and the like were not observed in DAST even after continuous use for 200 hours, and a highly reliable organic waveguide type optical modulator could be realized.

[Comparative example]
In the same manufacturing method as in Example 3, a polyimide substrate is used as a substrate, and a polyimide resin serving as a cladding layer of an optical waveguide is spin-coated on the substrate. Furthermore, using a Mach-Zehnder waveguide pattern mask, reactive ion etching using photolithography and oxygen gas was performed to form a core groove.

  Next, a polyimide resin having a large refractive index to be a core layer is formed in the groove portion to form a low-loss optical waveguide. Further, using lithography and etching, the polyimide resin that becomes a portion for selectively forming DAST was removed, and the core groove was formed again.

  Here, as in Example 3, DAST was crystal-grown by a slow cooling method using methanol as a solvent to remove DAST other than the core groove, and a DAST core having a thickness of 10 μm, a width of 10 μm, and a length of 10 mm was formed on the branched optical waveguide. A branched optical waveguide having a portion disposed thereon is formed, and an upper clad layer made of polyimide resin, formation of a traveling waveform signal electrode and a ground electrode, and a termination resistance of 50Ω are formed in this order, and a Mach-Zehnder type organic waveguide optical modulator is formed. Produced. When a modulation signal is input between the electrodes via a coaxial cable while a laser beam having a wavelength of 1.3 μm is incident on the organic waveguide type optical modulator, it proceeds at a driving voltage as low as about 1.2V. Although a high-speed light intensity modulation could be confirmed because of using a wave electrode, cracks occurred in the DAST crystal after a long time of use for about 150 hours, and the light loss increased.

  This is suitable for an organic waveguide type optical modulator used in an optical interconnection connecting between devices, between boards, and between LSI chips.

1 is a schematic top view of an organic waveguide type optical modulator of Example 1 according to the present invention. FIG. 2 is a cross-sectional view taken along the line AA in FIG. 1. 6 is a schematic process diagram of a manufacturing process of the organic waveguide type optical modulator of Example 1. FIG. 6 is a schematic process diagram of a manufacturing process of an organic waveguide type optical modulator of Example 2. FIG. 12 is a schematic process diagram of a manufacturing process of the organic waveguide type optical modulator of Example 3. FIG. 6 is a schematic process diagram of a manufacturing process of an organic waveguide type optical modulator of Example 4. FIG. It is a top view showing a Mach-Zehnder type optical modulator using an inorganic ferroelectric crystal LN. It is a figure which shows the structural formula of the organic crystal DAST.

Explanation of symbols

2, 13, 23 Substrate (basic substrate)
3 Branch optical waveguide 4 Core layer 5 Control electrode 6 Termination resistor 7 High frequency power supply 8, 27 Substrate side clad layer (clad layer)
10 In-groove stress relaxation layer (stress relaxation layer)
11 Electrode side stress relaxation layer (stress relaxation layer)
12 Electrode side cladding layer (cladding layer)
18 First groove stress relaxation layer (stress relaxation layer: also used as substrate side cladding layer)
20 Second groove stress relaxation layer (stress relaxation layer)
21, 31 Heat dissipation layer 22 Electrode side stress relaxation layer (stress relaxation layer: electrode side cladding layer)

Claims (11)

An optical waveguide having a core layer made of an organic crystal and capable of modulating the phase or intensity of light by an externally controlled electric field and allowing the light to enter and exit, and a cladding layer surrounding the core layer, and the core layer An organic waveguide type optical modulator having a control electrode that modulates the phase or intensity of light by applying an electric field to
An organic waveguide type optical modulator, wherein a stress relaxation layer is formed around the core layer between the core layer and the clad layer. An optical waveguide having a core layer made of an organic crystal and capable of modulating the phase or intensity of light by an externally controlled electric field and allowing the light to enter and exit, and a cladding layer surrounding the core layer, and the core layer An organic waveguide type optical modulator having a control electrode that modulates the phase or intensity of light by applying an electric field to
An organic waveguide type optical modulator, wherein a heat dissipation layer having better thermal conductivity than the cladding layer is formed on the cladding layer. An optical waveguide having a core layer made of an organic crystal and capable of modulating the phase or intensity of light by an externally controlled electric field and allowing the light to enter and exit, and a cladding layer surrounding the core layer, and the core layer An organic waveguide type optical modulator having a control electrode that modulates the phase or intensity of light by applying an electric field to
A stress relaxation layer is formed around the core layer between the core layer and the cladding layer,
An organic waveguide type optical modulator, wherein a heat dissipation layer having better thermal conductivity than the cladding layer is formed on the cladding layer. The organic waveguide type optical modulator according to claim 1, wherein the stress relaxation layer is formed around the entire circumference of the core layer. The organic waveguide type optical modulator according to any one of claims 1, 3, and 4, wherein the stress relaxation layer also serves as the cladding layer. The organic waveguide type optical modulator according to any one of claims 1 to 3, wherein a plurality of the stress relaxation layers are formed. The organic waveguide type optical modulator according to claim 1, wherein the stress relaxation layer is made of at least one layer of polyimide resin. The organic waveguide optical modulator according to claim 2, wherein the heat dissipation layer is made of a polymer resin in which a high thermal conductivity material is dispersed. The organic waveguide optical modulator according to claim 2, wherein the heat dissipation layer is made of a carbon material. The organic waveguide type optical modulator according to claim 2 or 3, wherein the heat dissipation layer is made of either metal or metal oxide. The organic waveguide type optical modulation according to any one of claims 1 to 10, wherein the organic crystal of the core layer is 4-dimethylamino-N-methyl-4-stilbazolium tosylate. vessel.

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