JP2006337583A - Organic waveguide type optical modulator and manufacturing method of organic waveguide type optical modulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic waveguide type optical modulator more excellent in productivity and reliability. <P>SOLUTION: The organic waveguide type optical modulator, in which incident light is modulated so that the phase or the intensity of emission light is controlled in accordance with the intensity of an electric field from the external part and a part or the whole region of an optical waveguide having organic material as a core layer is controlled by the electric field from the external part, comprises a branch part 10a for branching the incident light, a modulation part 10b for modulating the branched incident light and a composite part 10c for composing and outputting the modulated light, wherein the modulation part 10b is provided with a plurality of core layers DAST14 with respect to the propagation direction of light. <P>COPYRIGHT: (C)2007,JPO&INPIT

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 electrical signal, and a method for manufacturing the organic waveguide type optical modulator.

  Conventionally, in order to convert an electrical signal into an optical signal in an optical interconnection, there are two methods of externally modulating a CW light (continuous light) from a laser diode by a waveguide type optical modulator and a method using direct modulation of a laser diode. is there. Regarding direct modulation of a laser diode, high-speed modulation of about 10 Gbps is difficult, and an external modulation method is used for higher-speed signals.

  One of the light modulations of the external modulation method is one that uses an electro-optic effect. This 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. The electro-optic effect is caused by the linear electro-optic effect (Pockels effect) due to the second-order nonlinearity and the third-order nonlinearity. There is a 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. 6 shows a Mach-Zehnder type optical modulator using an inorganic ferroelectric crystal LiNbO ₃ (LN; lithium niobate) as an example of a modulator using the electro-optic effect. The optical waveguide part diffuses Ti ions and the like into LN crystal cut out in an appropriate orientation, thereby making a region having a large refractive index a core layer and cladding a buffer layer of LN crystal or silicon oxide film without Ti diffusion. It is a layer. An electric field from the outside is a traveling wave electrode made of a metal such as Au or Cu, and is applied to the signal electrode of the planar stripline. Incident light is branched into two optical waveguides at the Y branch on the entrance side, and the light propagating through the optical waveguide interacts with the microwave applied to the electrodes to cause a phase change. The light causing this phase change is superimposed on the light propagating on the other side at the Y branch on the exit side, and the combined wave causes an intensity change due to the phase change and is converted into an optical signal corresponding to the electrical signal. .

  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, since the dielectric constant of the LN crystal is as large as about ε1 = 43 and ε3 = 28, the effective refractive index nm of the microwave is larger than the refractive index of light n0 = 2.15 (wavelength 1.3 μm), Band limited due to velocity mismatch between wave and 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. An example of a current LN modulator is 5 V drive at 10 Gbps, and is 2 to 3 times larger than 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, since it has a large electro-optic constant, the action length of the modulation section can be shortened, so that there is a possibility that a smaller, lower voltage, and higher speed optical modulator can be realized. In particular, the organic crystal does not require a polarization treatment like an organic polymer, and is stable with no change over time such as polarization relaxation.

  FIG. 7 shows the structural formula of DAST, which is an organic crystal. 4-N, N-dimethylamino-4′-N-methyl-stilbazolium tosylate (hereinafter referred to as DAST) was developed at the Tohoku University Nakanishi Laboratory. It has a large nonlinear optical constant (d11 = 1010 pm / v (λ = 1.3 μm)) and an electro-optic constant (r11 = 75 pm / V (λ = 820 nm)), and has a low dielectric constant (ε = 5. 2), it has attracted attention such as low voltage, high speed optical modulation and detection, and millimeter wave generation.

  Since DAST is an ionic crystal and is soluble in water, methanol, ethanol, propanol, acetone and other solvents except for some non-polar organic solvents such as toluene and hexane, photolithography was used. Patterning is difficult and waveguide formation has been an issue. Therefore, a core groove is formed in the lower clad portion, and an organic crystal DAST showing an electro-optic effect is embedded therein, and chemical mechanical polishing is performed using a solvent that does not deteriorate the characteristics of the DAST to remove DAST other than the groove portion. A waveguide type optical modulator that can be driven at a low voltage and at a high speed by forming DAST in the core portion has been proposed (see, for example, Patent Document 1).

  Thus, by using an organic material having an electro-optic constant larger than that of LN, including DAST, the action length of the modulator that changes the phase of light can be reduced in order to change the electric signal to an optical signal. Miniaturization can be achieved. On the other hand, as for the crystal growth rate of DAST, it is known that the lower the crystal growth rate, the better the optical uniformity of the crystal.

  Therefore, taking advantage of the organic material, an organic waveguide type optical modulator that is smaller, can be driven at a low voltage and at a high speed, and has higher productivity and reliability is required.

JP 2003-202533 A

  However, as shown above, since the crystal growth rate of DAST is higher as the crystal growth rate is lower, the optical uniformity of the crystal is better. Therefore, a high-quality DAST crystal is necessary for light modulation in the waveguide portion. When growing to a size (about 10 mm), the crystal growth takes an enormous amount of time, and the productivity deteriorates, leading to an increase in cost. Even when the crystal grows to about 10 nm, the internal stress of the crystal increases as the size of the crystal increases, and cracks are likely to occur due to temperature changes or impacts.

  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 more excellent in productivity and reliability.

  In order to solve the above-described problems and achieve the object, the invention according to claim 1 is directed to modulating the phase or intensity of the outgoing light according to the strength of the electric field from the outside, and the organic material as the core layer. An organic waveguide type optical modulator that controls a part or all of an optical waveguide of an optical waveguide by an external electric field, the branching unit for branching the incident light, and the modulation unit for modulating the branched incident light And a synthesizing unit that synthesizes and outputs the modulated light, and the modulation unit includes a plurality of the core layers in the traveling direction of the light.

  According to the first aspect of the present invention, an organic waveguide type optical modulator is constituted by the branching unit, the modulating unit, and the synthesizing unit, and the core layer is formed only on the modulating unit. It is possible to improve the quality and improve the quality and reliability due to organic crystallinity.

  In the invention according to claim 2, in the branching unit, one waveguide is branched into two waveguides, and the branched waveguides are branched into two, respectively. Four waveguides are formed in parallel with the traveling direction of light in the branched waveguide, and the multiplexing unit multiplexes the four waveguides two by two, and further adds the two waveguides. The waveguide is combined by one waveguide, and the core layer is formed on each of the four waveguides.

  According to the second aspect of the present invention, in the first aspect, the branching portion is configured such that one waveguide is branched into two waveguides, and each of the branched waveguides is branched into two. The modulation unit has an organic material in the core layer, and four waveguides are arranged in parallel with respect to the light traveling direction. The multiplexing unit is combined into two, and each of them is combined. By adopting a configuration in which they are combined into one, it is possible to realize a high-quality organic waveguide type optical modulator that is excellent in productivity and reliability.

  The invention according to claim 3 is characterized in that each of the core layers is composed of one organic single crystal.

  According to the third aspect of the present invention, in the first or second aspect, an organic single crystal having a large electro-optic constant and a low dielectric constant is used as the core layer for the medium having the electro-optic effect, and the core layer is constituted by one single crystal. As a result, it is possible to realize an organic waveguide type optical modulator that is further excellent in reliability, high quality, and low voltage and high speed.

  The invention according to claim 4 is characterized in that the organic material is 4-N, N-dimethylamino-4′-N-methyl-stilbazolium tosylate (DAST).

  According to the invention of claim 4, in claim 1, 2 or 3, 4-N, N-dimethylamino-4'-N-methyl which has a large electro-optic constant, a small dielectric constant and is thermally stable. By using stilbazolium tosylate (DAST) as a medium having an electro-optic effect, it is possible to realize an organic waveguide type optical modulator with a lower voltage and higher speed and higher reliability.

  According to a fifth aspect of the present invention, the organic material is characterized in that the organic waveguide type optical modulator is a Mach-Zehnder type.

  According to the fifth aspect of the present invention, in any one of the first to fourth aspects, the Mach-Zehnder type organic waveguide optical modulator is small and can be driven at a low voltage. An organic waveguide type optical modulator with high cost, high reliability, and high extinction ratio can be realized.

  According to a sixth aspect of the present invention, the modulating unit includes a signal electrode to which a modulation signal is applied above a cladding layer stacked on the core layer, and a ground electrode for applying a ground voltage to the core layer. It is characterized by providing these.

  According to the invention of claim 6, in any one of claims 1 to 5, the signal electrode to which the modulation signal is applied above the cladding layer laminated on the core layer, and the ground voltage applied to the core layer. By providing the ground electrode to be applied, it is possible to modulate the intensity of light by an electric signal.

  The invention according to claim 7 is characterized in that a traveling wave signal electrode is arranged at the center of the branched optical waveguide, and an installation electrode is arranged outside the optical waveguide.

  According to the seventh aspect of the present invention, in the sixth aspect, the traveling wave signal electrode is arranged at the center of the branched optical waveguide, and the ground electrode is arranged outside the optical waveguide, so that each DAST has a reverse direction. An electric field can be applied. As a result, it becomes possible to cause a double phase change by the push-pull operation.

  According to an eighth aspect of the present invention, there is provided a branching unit that branches the incident, a plurality of modulation units that modulate the branched incident light, and a combining unit that combines and outputs the modulated light. The branching unit, the combining unit, and the plurality of modulation units are separately manufactured and combined to manufacture a method of manufacturing an organic waveguide optical modulator, the core layer of the modulation unit A first step of forming an organic material, the branching section, the combining section, and the plurality of modulating sections are arranged on a support substrate, and are bonded together so that each optical waveguide section is optically connected. And a second step.

  According to the eighth aspect of the invention, in the method of manufacturing an optical modulator in which the branching unit, the combining unit, and the plurality of modulating units are separately manufactured and combined, the organic material is formed on the core layer of the modulating unit. Organic waveguide type light with excellent productivity and reliability by the step of arranging the branching portion, the combining portion, and the plurality of modulating portions on the support substrate and optically bonding the optical waveguide portions. A method for manufacturing the modulator can be realized.

  The invention according to claim 9 is characterized in that it includes a third step of smoothing a surface to be a joint surface of each of the branching portion, the combining portion, and the plurality of modulating portions. .

  According to the ninth aspect of the present invention, in the eighth aspect, the step of smoothing the junction surface between the branching section, the combining section, and the plurality of modulating sections is excellent in reliability. In addition, a method for manufacturing a high-quality organic waveguide optical modulator can be realized.

  An organic waveguide type optical modulator according to the present invention (Claim 1) comprises an organic waveguide type optical modulator composed of a branching unit, a modulating unit, and a combining unit, and a core layer is formed only on the modulating unit. As a result, it is possible to improve productivity with a small amount of organic material and to improve high quality and reliability due to organic crystallinity.

  An organic waveguide type optical modulator according to the present invention (Claim 2) is the organic waveguide type optical modulator according to Claim 1, wherein the branching portion is divided into two waveguides, and the branched waveguide is further divided into two waveguides. Each has two branches, the modulation section has an organic material in the core layer, and four waveguides are arranged in parallel in the light traveling direction, and the two multiplexing sections are one each. By combining each of the optical waveguides with each other, it is possible to provide a high-quality organic waveguide type optical modulator that is excellent in productivity and reliability. Play.

  The organic waveguide type optical modulator according to the present invention (Claim 3) is the medium according to claim 1 or 2, wherein an organic single crystal having a large electro-optic constant and a small dielectric constant is used as the core layer. By using the single crystal, it is possible to provide an organic waveguide type optical modulator that is further excellent in reliability, high quality, low voltage and high speed.

  An organic waveguide type optical modulator according to the present invention (Claim 4) is characterized in that, in Claim 1, 2 or 3, 4-N, which has a large electro-optic constant, a small dielectric constant and is thermally stable. By using N-dimethylamino-4′-N-methyl-stilbazolium tosylate (DAST) as an electro-optic effect medium, it is possible to provide a low-voltage, high-speed and high-reliability organic waveguide optical modulator. There is an effect.

  An organic waveguide type optical modulator according to the present invention (Claim 5) is a Mach-Zehnder type organic waveguide optical modulator according to any one of Claims 1 to 4, and is small and low voltage. Thus, an organic waveguide type optical modulator having a low cost, high reliability, and a high extinction ratio can be provided.

  An organic waveguide type optical modulator according to the present invention (Claim 6) is that the modulation signal is applied above the clad layer laminated on the core layer according to any one of Claims 1 to 5. By providing the signal electrode and the ground electrode for applying a ground voltage to the core layer, there is an effect that the intensity of light can be modulated by an electric signal.

  An organic waveguide type optical modulator according to the present invention (Claim 7) is characterized in that, in Claim 6, the traveling wave signal electrode is arranged at the center of the branched optical waveguide, and the ground electrode is arranged outside the optical waveguide. This makes it possible to apply a reverse electric field to each DAST. As a result, a double phase change can be caused by the push-pull operation, and it is possible to drive at a lower voltage.

  In addition, in the method for manufacturing an organic waveguide type optical modulator according to the present invention (claim 8), a branching unit, a combining unit, and a plurality of modulating units are separately manufactured, and an optical modulator manufactured by combining them is manufactured. In the method, the step of forming an organic material in the core layer of the modulation portion, and the step of optically bonding the optical waveguide portion by arranging the branching portion, the combining portion, and the plurality of modulation portions on the support substrate, There is an effect that it is possible to provide a method for manufacturing an organic waveguide type optical modulator excellent in productivity and reliability.

  According to a ninth aspect of the present invention, there is provided a method for producing an organic waveguide type optical modulator according to the eighth aspect of the present invention. By providing the step, it is possible to provide a method for manufacturing an organic waveguide type optical modulator having excellent reliability and high quality.

  Exemplary embodiments of an organic waveguide type optical modulator and a method for manufacturing the organic waveguide type optical modulator according to the present invention will be explained below in detail with reference to the accompanying drawings.

(First embodiment)
FIGS. 1-1 and 1-2 are explanatory diagrams illustrating the configuration of the organic waveguide type optical modulator according to the first embodiment of the present invention. Here, FIG. 1-1 is a plan view, and FIG. 1-2 is a cross-sectional view taken along the line AA ′ in the DAST portion for changing the phase of light in FIG. Here, DAST is selectively disposed in both branch optical waveguides of a Mach-Zehnder type optical modulator, and the optical path lengths thereof are equal. That is, the organic waveguide type optical modulator 10 has a so-called Mach-Zehnder type configuration in which a modulation unit is arranged in parallel by dividing into two optical paths by Y branching and then synthesized.

  Note that DAST means 4-N, N-dimethylamino-4′-N-methyl-stilbazolium tosylate as described above. DAST is also described as 4-dimethylamino-N-methyl 4 stilbazolium tosylate. Alternatively, trans-4- [4- (dimethylamino)] stbazolium p-toluenesulfate is also described.

  In these figures, reference numeral 10a is a branching part, reference numeral 10b is a modulation part, reference numeral 10c is a multiplexing part, reference numeral 11 is a support substrate, reference numeral 12 is a substrate, reference numeral 13 is a cladding layer, reference numeral 14 is DAST, reference numeral 15 is ground. Reference numeral 16 denotes a traveling wave signal electrode, reference numeral 17 denotes a power source, reference numeral 18 denotes a terminating resistor, and reference numeral 19 denotes an optical waveguide. Hereinafter, these components will be described in detail.

  The bulk crystal of DAST 14 has a rhomboid plate shape that is large in the a and b axis directions and small in the c axis direction. In the case of a DAST thin film crystal, there are a and b axes in the film surface, and the c axis is perpendicular to the film surface. The DAST 14 having such a geometric structure can easily form a and b axes in a plane parallel to the substrate. On the other hand, since the electrooptic constant r11 having the largest DAST is used, it is preferable that the light propagates in the b-axis, an electric field is applied in the a-axis direction, and the polarization plane of the incident light is incident so as to be parallel to the a-axis. . For this reason, the electric field formed by the traveling wave signal electrode 16 and the ground electrode 15 is arranged as shown in FIGS.

  Furthermore, by arranging the traveling wave signal electrode 16 at the center of the branch optical waveguide 16 and the ground electrode 15 outside the branch optical waveguide, an electric field in the opposite direction can be applied to each DAST 14. At this time, the refractive index of the organic crystal DAST 14 which is an electro-optic effect medium selectively disposed in each branched optical waveguide 19 changes in opposite directions. That is, the refractive index of one optical waveguide 19 is increased, and the refractive index of the other optical waveguide 19 is decreased. As a result, the phase of the signal light propagating through the optical waveguide 19 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. Further, the electrode is a traveling wave electrode provided with a 50Ω termination resistor 18 and has an electrode structure that can cope with high-speed light modulation.

  That is, the traveling wave signal electrode 16 is disposed at the center of the branch optical waveguide, and the ground electrode is disposed outside the branch optical waveguide, whereby a reverse electric field can be applied to each DAST 14. As a result, a double phase change can be caused by the push-pull operation, which enables driving at a lower voltage.

  Next, a manufacturing method of the organic waveguide type optical modulator will be described with reference to FIG. First, a method for manufacturing the modulation portion 10b will be described. The substrate 12 on which the modulation portion 10b is manufactured uses a polyimide substrate, and a polyimide resin serving as the cladding layer 13 of the optical waveguide is spin coated on the substrate 12 (step 1). In this embodiment, polyimide resin is used for the clad layer, but it is not particularly limited as long as the refractive index is smaller than the organic material constituting the core layer. For example, epoxy resin and acrylic resin are used. Can be mentioned.

  Subsequently, using the waveguide pattern mask, reactive ion etching using photolithography and oxygen gas is performed to produce a substrate of the modulation portion 10b in which the core groove is formed (step 2). Here, DAST 14 is crystal-grown by a slow cooling method using methanol as a solvent (step 3). With respect to crystal orientation, a DAST single crystal is produced by using a seed crystal so that the waveguide direction is b-axis, the a-axis is in a plane parallel to the substrate, and the c-axis is perpendicular to the substrate. To do.

  At this time, the core portion grew about 5 nm. Since there is DAST that has grown in crystal other than the core groove, after removing unnecessary portion of DAST by polishing, it is cut out to a size suitable for the modulation portion by wire saw, thickness 6μm, length Modulating portions [1] and [2] having a 5 mm DAST core portion are prepared (step 4). In this manufacturing method, by using a plurality of seed crystals for the substrate, it is easy to manufacture a plurality of seed crystals at the same time, and productivity is good.

  As an example of the above polishing, polishing is performed using silica abrasive particles using a foamed urethane pad Supreme RN-H (manufactured by Rodel), DAST 14 other than the core groove is removed, and DAST 14 is left only in a specific core groove. be able to.

  In this embodiment, the wire saw is used for cutting, but various precision processing techniques such as laser processing and etching processing can also be used.

  In this embodiment, the DAST core part is formed by a slow cooling method using a seed crystal, but a DAST thin film may be formed by an improved shear method.

  Next, a manufacturing method of the branching portion 10a and the combining portion 10c will be described. A branching portion 10a and a combining portion 10c are produced on a polyimide substrate (step 5). That is, a polyimide resin was spin-coated as a clad layer, and then a reactive ion etching using photolithography and oxygen gas was performed using a waveguide pattern mask to form a core groove. Next, a polyimide resin having a large refractive index serving as a core is formed in the groove to form a low-loss optical waveguide, which is a branching portion 10a and a combining portion 10c.

  The cut surfaces (end surfaces) of the branch portion 10a, the combined portion 10c, and the modulation portions 10b [1] and [2] are further processed to be smooth by polishing. By smoothing the end face in this way, it is possible to reduce the optical loss at the joint surface. The above-mentioned conditions can be applied as the polishing conditions here.

  Subsequently, after the branching portion 10a, the combining portion 10c and the modulation portions 10b [1] and [2] are arranged on the support substrate 11 as shown in FIG. 1, the same polyimide as the lower cladding layer is spin-coated on the upper layer. The upper cladding layer having a thickness of 2 μm was formed. Subsequently, an Au electrode was produced by plating, and a part of the traveling wave signal electrode 16 and the ground electrode 15 having a thickness of 5 μm was produced. Next, the traveling wave signal electrode 16 and the ground electrode 15 were formed in the lead-out portion where the branched optical waveguide 19 intersects, and a 50Ω termination resistor 18 was attached to the end to form a traveling wave electrode. In this way, the Mach-Zehnder type organic waveguide type optical modulator 10 is manufactured (see FIGS. 1-1 and 1-2).

  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 10 thus manufactured, a driving voltage as low as about 1.2 V is obtained. Thus, high-speed and high extinction ratio light intensity modulation could be provided. In addition, it was confirmed that the production cost was reduced by shortening the production time. In addition, it was verified that no cracks or the like were observed in the DAST 14 portion even after continuous use for a long time, and a highly reliable organic waveguide type optical modulator 10 was obtained.

(Second Embodiment)
Next, FIG. 3 shows a configuration and a manufacturing method of an organic waveguide type optical modulator 20 according to the second embodiment different from the organic waveguide type optical modulator 10 described above. This organic waveguide type optical modulator 20 has three modulation portions 20b [1], [2], and [3] with respect to the organic waveguide type optical modulator 10 of FIG. 1-1. Here, in the same manufacturing method as described above, a polyimide substrate is used as a substrate for forming the modulation portion 20b, and a polyimide resin serving as a cladding layer of an optical waveguide is spin-coated on the substrate, and then a waveguide pattern mask is formed. Then, reactive ion etching using photolithography and oxygen gas is performed to form a core groove, and a substrate of the modulation portion 20b is manufactured.

  Here, DAST 14 is crystal-grown by a slow cooling method using methanol as a solvent. With respect to crystal orientation, a DAST single crystal is produced by using a seed crystal so that the waveguide direction is b-axis, the a-axis is in the same plane parallel to the substrate, and the c-axis is perpendicular to the substrate. To do. At this time, the core portion grew about 3 μm. After the DAST 14 other than the core groove is removed by polishing, the modulation portion 20b is cut out by a wire saw, and the modulation portion 20b [1], [2] in which the core portion of the DAST 14 having a thickness of 6 μm and a length of 3 mm is arranged. , [3].

  Subsequently, the branching portion 20a and the multiplexing portion 20c are produced. A branching portion 20a and a combining portion 20c are produced on a polyimide substrate. A polyimide resin was spin-coated as a clad layer, and then a core groove was formed by performing reactive ion etching using photolithography and oxygen gas using a waveguide pattern mask. Next, a polyimide resin having a large refractive index serving as a core is formed in the groove portion to form a low-loss optical waveguide 19, which is a branching portion 20 a and a combining portion 20 c.

  The cut surfaces (end surfaces) of the branching portion 20a, the combining portion 20c, and the modulation portions 20b [1], [2], and [3] are further processed to be smooth by polishing.

  Next, after the branching portion 20a, the combining portion 20c and the modulating portions 20b [1], [2], [3] are arranged on the support substrate as shown in FIG. 3, the same polyimide as the lower cladding layer is formed on the upper layer. An upper clad layer having a thickness of 2 μm was formed by spin coating. Next, a traveling wave signal electrode 16 and a ground electrode 15 were formed. Au electrodes were produced by plating, and a traveling wave signal electrode 16 having a thickness of 5 μm and a part of the ground electrode 15 were produced. Next, the traveling wave signal electrode 16 and the ground electrode 15 were formed at the lead-out portion that intersected with the branched optical waveguide, and a 50Ω termination resistor 18 was attached to the terminal to form a traveling wave electrode. Thus, the Mach-Zehnder type organic waveguide type optical modulator 20 is manufactured (see FIG. 3).

  When a modulation signal is input between the electrodes via the coaxial cable while a laser beam having a wavelength of 1.3 μm is incident on the organic waveguide type optical modulator 20, the driving voltage is as low as about 1.2V. It was verified that the organic waveguide type optical modulator 20 having a high speed and a high extinction ratio can be obtained. In addition, the manufacturing cost is reduced because the manufacturing time is shortened. In addition, even when used continuously for a long time, the occurrence of cracks or the like is not observed in the DAST 14 portion, and a highly reliable organic waveguide type optical modulator 20 is realized.

(Comparative example)
In the same manufacturing method as in the first embodiment, a polyimide substrate is used as the substrate 12, and a polyimide resin serving as a cladding layer of the optical waveguide 19 is spin-coated on the substrate 12. 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 as a core is formed in the groove to form a low-loss optical waveguide. Further, using lithography and etching, polyimide that becomes a portion for selectively forming DAST 14 is removed, and a core groove is formed again.

  Here, DAST14 was crystal-grown by the slow cooling method using methanol as a solvent in the same manner as in the first embodiment. With respect to crystal orientation, a DAST single crystal is produced by using a seed crystal over 720 hours so that the waveguide direction is the b-axis, the a-axis is in a plane parallel to the substrate 12, and the vertical direction to the substrate is the c-axis. . At this time, it was confirmed that the core portion grew about 10 mm. The DAST 14 other than the core groove is removed in the same manner as in the first embodiment, and a branch optical waveguide portion is prepared in which the core portion of the DAST 14 having a thickness of 6 μm and a length of 10 mm is arranged on the branch optical waveguide.

  As in the first embodiment, a Mach-Zehnder type organic waveguide optical modulator 20 is formed by sequentially forming an upper clad layer made of polyimide resin, formation of a traveling waveform signal electrode and a ground electrode, and a termination resistor 18 of 50Ω. To do.

  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 after a long period of use, and the optical loss increased. In this case, the production time is about three times that of the first embodiment, and the productivity is not good.

(Third embodiment)
FIGS. 4-1 and FIGS. 4-2 are explanatory drawings which show the structure of the organic waveguide type optical modulator 30 concerning the 3rd Embodiment of this invention. 4A is a plan view, and FIG. 4B is a cross-sectional view of the DAST portion AA ′ for changing the phase of light in FIG. 1-1. Here, the DAST 14 is selectively disposed in both branch optical waveguides of a Mach-Zehnder type optical modulator, and the optical path lengths thereof are equal. That is, the organic waveguide type optical modulator 10 has a so-called Mach-Zehnder type configuration in which a modulation unit is arranged in parallel by dividing into two optical paths by Y branching and then synthesized.

  Here, it is assumed that the DAST 14 is selectively disposed in the branching optical waveguides of the modulation parts configured in parallel, and the optical path lengths are 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. In the case of a DAST thin film crystal, there are a and b axes in the film plane, and the c axis is perpendicular to the film. The DAST 14 having such a geometric structure can easily form the a and b axes in the plane parallel to the substrate. On the other hand, since the largest electro-optic constant r11 of DAST 14 is used, it is preferable that the light propagates 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. For this reason, the electric field formed by the traveling wave signal electrode and the ground electrode is arranged as shown in FIGS.

  Furthermore, by arranging the traveling wave signal electrode 16 at the center of each branch optical waveguide and the ground electrode 15 outside the branch optical waveguide, a reverse electric field can be applied to each pair of DASTs 14. At this time, the refractive index of the organic crystal DAST 14 which is an electro-optic effect medium selectively disposed in each branched optical waveguide 19 changes in opposite directions. That is, the refractive index of one optical waveguide 19 is increased, and the refractive index of the other optical waveguide 19 is decreased. As a result, the phase of the signal light propagating through the optical waveguide 19 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. Further, by forming the branch portion as in the present invention, the length of the core layer made of an organic material can be shortened, and the manufacturing time can be shortened and the quality can be improved. Further, the electrode is a traveling wave electrode provided with a 50Ω termination resistor 18 and has an electrode structure that can cope with high-speed light modulation.

  Next, a method for manufacturing the organic waveguide type optical modulator 30 will be described with reference to FIG. First, a method for manufacturing the modulation portion 30b will be described. A polyimide substrate is used as a substrate for forming the modulation portion 30b, and a polyimide resin serving as a cladding layer of the optical waveguide 19 is spin-coated on the substrate 12 (step 1). In this embodiment, polyimide resin is used for the clad layer, but it is not particularly limited as long as the refractive index is smaller than the organic material constituting the core layer. For example, epoxy resin and acrylic resin are used. Can be mentioned.

  Next, using the waveguide pattern mask, reactive ion etching using photolithography and oxygen gas is performed to produce a substrate of the modulation portion 30b in which the core grooves formed in parallel are formed (step 2).

  Here, DAST 14 is crystal-grown by a slow cooling method using methanol as a solvent. With respect to crystal orientation, a DAST single crystal is produced by using a seed crystal so that the waveguide direction is b-axis, the a-axis is in a plane parallel to the substrate, and the c-axis is perpendicular to the substrate. did. At this time, it was confirmed that the core portion grew about 5 mm. Since there is crystal grown DAST 14 in the portion other than the core groove, after removing the unnecessary portion DAST 14 by polishing, the wire saw is cut to a size suitable for the modulation portion, and the thickness is 10 μm and the length. A modulation part in which four DAST core parts of 5 mm having exactly the same crystal orientation were arranged in parallel was produced (steps 4 and 5). In this manufacturing method, by using a plurality of seed crystals for the substrate, it is easy to manufacture a plurality of seed crystals at the same time, and productivity is improved.

  An example of the above polishing is to perform polishing using silica abrasive particles using a urethane foam pad, Supreme RN-H Rodale, to remove DAST14 other than the core groove and leave DAST14 only in a specific core groove Can do.

  In this example, the wire saw is used for cutting, but various precision processing techniques such as laser processing and etching processing can also be used. In this example, the DAST core portion is formed by the slow cooling method using the seed crystal, but the DAST thin film may be formed by the improved shear method.

  Subsequently, a manufacturing method of the branch portion 30a and the multiplexing portion 30c will be described. A branched portion 30a and a combined portion 30c were produced on a polyimide substrate. A polyimide resin was spin-coated as a clad layer, and then a core groove was formed by performing reactive ion etching using photolithography and oxygen gas using a waveguide pattern mask. Next, a polyimide resin having a large refractive index serving as a core was formed in the groove portion to form a low-loss optical waveguide 19 to obtain a branching portion 30a and a combining portion 30c (Step 5).

  The cut surfaces (end surfaces) of the branch portion 30a, the combined portion 30c, and the modulation portion 30b were further smoothed by polishing. By smoothing the end face, it is possible to reduce the optical loss at the joint face. The above-mentioned conditions can be applied as the polishing conditions here.

  Next, after the branching portion 30a, the combining portion 30c and the modulating portion 30b are arranged on the support substrate as shown in FIG. 4-1, the same polyimide as the lower clad layer is spin-coated on the upper layer and formed to have a thickness of 2 μm. The upper cladding layer was used. Then, an Au electrode was produced by a plating method, and a traveling wave signal electrode 16 having a thickness of 5 μm and a part of the ground electrode 15 were produced. Next, the traveling wave signal electrode 16 and the ground electrode 15 were formed at the lead-out portion that intersected with the branched optical waveguide, and a 50Ω termination electrode 18 was attached to the end to form a traveling wave electrode. Thus, the organic waveguide type optical modulator 30 shown in FIGS. 4-1 and 4-2 was manufactured.

  Providing high-speed and high extinction ratio light intensity modulation at a low drive voltage of about 1.2 V 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. I was able to. In addition, the manufacturing time is shortened, and the manufacturing cost can be reduced by simplifying the joint surfaces of the branch portion 30a, the modulation portion 30b, and the multiplexing portion 30c. In addition, no cracks or the like were observed in the DAST portion even after continuous use for a long time, and a highly reliable organic waveguide type optical modulator 30 could be realized.

(Comparative example)
In the same manufacturing method as described above, 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 as a core is formed in the groove to form a low-loss optical waveguide. Further, using polyimide and etching, polyimide that becomes a portion for selectively forming DAST 14 was removed, and a core groove was formed again. Here, DAST14 was crystal-grown by the slow cooling method using methanol as a solvent in the same manner as described above. With respect to the crystal orientation, a DAST single crystal was produced by using a seed crystal over 720 hours so that the waveguide direction was the b-axis, the a-axis was in a plane parallel to the substrate, and the c-axis was the direction perpendicular to the substrate. At this time, the core portion grew about 10 mm. The DAST 14 other than the core groove was removed in the same manner as described above to produce a branched optical waveguide portion in which a DAST core portion having a thickness of 6 μm and a length of 10 nm was arranged on the branched optical waveguide.

  In the same manner as described above, an upper clad layer made of polyimide resin, formation of traveling wave signal electrode 16 and ground electrode 15, and 50Ω termination resistor 18 are formed in this order, and Mach-Zehnder type organic waveguide type optical modulator 30 is manufactured.

  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 after a long period of use, and the optical loss increased. Further, the production time is about three times as long as that of the above-described embodiment, and the productivity is not good.

  As described above, the organic waveguide optical modulator and the method for manufacturing the organic waveguide optical modulator according to the present invention are useful for optical interconnection and the like, and in particular, information processing, optical measurement, and optical fiber communication systems. Suitable for modulators in

It is a top view which shows the structure of the organic waveguide type optical modulator concerning the 1st Embodiment of this invention. It is A-A 'sectional drawing in the DAST part which performs the phase change of the light in FIGS. 1-1. It is explanatory drawing which shows the manufacturing method (process) of the organic waveguide type optical modulator concerning the 1st Embodiment of this invention. It is a top view which shows the structure of the organic waveguide type optical modulator concerning the 2nd Embodiment of this invention. It is a top view which shows the structure of the organic waveguide type optical modulator concerning the 3rd Embodiment of this invention. FIG. 4A is a cross-sectional view taken along line A-A ′ in a DAST portion that changes the phase of light in FIG. 4A. It is explanatory drawing which shows the preparation methods (process) of the organic waveguide type optical modulator concerning the 3rd Embodiment of this invention. It is a top view which shows the structure of the conventional organic waveguide type | mold optical modulator. It is explanatory drawing which shows DAST which is an organic material by structural formula.

Explanation of symbols

10, 20, 30 Organic waveguide type optical modulator 10a, 20a Branching portion 10b, 20b Modulating portion 10c, 20c Combined portion 11 Support substrate 12 Substrate 13 Clad layer 14 DAST
DESCRIPTION OF SYMBOLS 15 Ground electrode 16 Signal electrode 17 Power supply 18 Termination resistor 19 Optical waveguide

Claims (9)

Organic waveguide type that modulates the phase or intensity of outgoing light according to the strength of the electric field from the outside, and controls part or all of the optical waveguide with an organic material as a core layer by the electric field from the outside An optical modulator,
A branching unit that branches the incident light, a modulation unit that modulates the branched incident light, and a combining unit that combines and outputs the modulated light,
The said modulation | alteration part is equipped with the said several core layer with respect to the advancing direction of light, The organic waveguide type optical modulator characterized by the above-mentioned. In the branch portion, one waveguide is branched into two waveguides, and each of the branched waveguides is branched into two,
In the modulation unit, four waveguides are formed in parallel with respect to the traveling direction of light in the branched waveguide,
The multiplexing unit combines the four waveguides two by two, and further combines the two waveguides by one waveguide.
The organic waveguide type optical modulator according to claim 1, wherein the core layer is formed on each of the four waveguides.   3. The organic waveguide type optical modulator according to claim 1, wherein each of the core layers is composed of one organic single crystal.   4. The organic waveguide optical modulator according to claim 1, wherein the organic material is 4-N, N-dimethylamino-4′-N-methyl-stilbazolium tosylate (DAST). 5.   The organic waveguide optical modulator according to claim 1, wherein the organic waveguide optical modulator is a Mach-Zehnder type. The modulator is
A signal electrode to which a modulation signal is applied above a cladding layer laminated on the core layer;
A ground electrode for applying a ground voltage to the core layer;
The organic waveguide type optical modulator according to claim 1, further comprising:   7. The organic waveguide optical modulator according to claim 6, wherein a traveling wave signal electrode is disposed at the center of the branched optical waveguide, and an installation electrode is disposed outside the optical waveguide. A branching unit that branches the incident; a plurality of modulation units that modulate the branched incident light; and a combining unit that combines and outputs the modulated light, and the branching unit and the multiplexing unit A method for producing an organic waveguide type optical modulator in which a part and a plurality of modulation parts are separately produced and combined,
A first step of forming an organic material in the core layer of the modulator;
A second step of arranging the branching unit, the combining unit and the plurality of modulating units on a support substrate, and bonding the optical waveguide portions so as to be optically connected;
A method for producing an organic waveguide type optical modulator, comprising:   9. The organic waveguide type according to claim 8, further comprising a third step of smoothing a surface to be a joint surface between the branching portion, the multiplexing portion, and the plurality of modulation portions. A method for manufacturing an optical modulator.

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