Optical waveguide element, optical modulator, and optical transmission device

Abstract

The purpose of the present invention is to provide an optical waveguide element in which a Mach-Zehnder type optical waveguide having folded parts is formed and an extinction ratio is improved by suppressing optical crosstalk, an optical modulator including the optical waveguide element, and an optical transmission device including the optical modulator. An optical waveguide element 1A according to the present invention is an optical waveguide element in which an optical waveguide 3 is formed on a substrate 2 having electro-optic effect. The optical waveguide 3 is configured to include a Mach-Zehnder type optical waveguide having folded parts B1, B2, B3, B4. A dummy pattern 110 capable of suppressing optical crosstalk is formed in a region between the adjacently extending optical waveguides 3.

Description

Optical waveguide element, optical modulator, and optical transmitter

[0001] The present invention relates to an optical waveguide element in which a Mach-Zehnder type optical waveguide is formed on a substrate, an optical modulator including the optical waveguide element, and an optical transmitter including the optical modulator.

[0002] In recent years, lithium niobate (LiNbO) with electro-optical effect has been used in the fields of optical communication and optical measurement. ３ Optical modulators are used in which a metal modulation electrode is formed on an optical waveguide element that has an optical waveguide formed on a substrate made of ZnO (hereinafter also referred to as LN) to modulate the light waves propagating in the optical waveguide. Recently, optical waveguide elements and optical modulators have been miniaturized and integrated by forming a Mach-Zehnder optical waveguide. Furthermore, optical waveguide elements and optical modulators have also been shortened by forming a Mach-Zehnder optical waveguide in a folded structure and arranging the optical input / output portions on the same side of the substrate.

[0003] For example, an optical control element described in Patent Document 1 listed below has an input section and an output section of an optical waveguide formed on the same side of a substrate, the optical waveguide has a Mach-Zehnder optical waveguide section in which one optical waveguide branches into two branch waveguides and the two branch waveguides are combined to form one optical waveguide, and is characterized in that the branch waveguide has an even number of folding sections.

[0004] Japanese Patent Application Laid-Open No. 2021-162641

[0005] In optical waveguide devices, miniaturization and integration have led to the arrangement of optical waveguides at short distances. Optical waveguide devices equipped with Mach-Zehnder optical waveguides, particularly those with folded sections, tend to have a large number of waveguides extending in parallel in the width direction. As a result, the distance between adjacent optical waveguides becomes shorter, which can lead to the problem of optical crosstalk, in which light leaking from one optical waveguide (leakage light) mixes with and interferes with another optical waveguide. Furthermore, during etching, the microloading effect can increase variations in processing depth, resulting in poor performance. A solution to this problem is desired.

[0006] The present invention has been made in view of the above-mentioned problems, and aims to provide an optical waveguide element including a Mach-Zehnder type optical waveguide with a folded portion, which suppresses optical crosstalk and improves the extinction ratio, and also aims to provide an optical modulator including the optical waveguide element, and an optical transmitter including the optical modulator.

[0007] In order to solve the above problems, the optical waveguide element, the optical modulator, and the optical transmitter according to the present invention have the following technical features.

[0008] In order to achieve the above object, the optical waveguide element according to the present invention is an optical waveguide element in which an optical waveguide is formed on a substrate having an electro-optic effect, wherein the optical waveguide is configured to include a Mach-Zehnder optical waveguide having a folded portion, and a dummy pattern capable of suppressing optical crosstalk is formed in a region between adjacent extending optical waveguides.

[0009] In addition to the patterns (hereinafter referred to as "actual patterns") necessary for modulating light, the substrate of the optical waveguide element according to the present invention also has dummy patterns formed between adjacently extending actual patterns. According to this configuration, by forming dummy patterns in the regions between adjacently extending optical waveguides, the adjacent optical waveguides are isolated and the dummy patterns can guide or absorb light leaking from the optical waveguides, thereby suppressing optical crosstalk. Light leakage from the optical waveguides is one of the factors that deteriorate the characteristics (e.g., extinction ratio) of the optical waveguide element. However, by guiding or absorbing the leaked light, the dummy patterns can stabilize the characteristics, thereby providing an optical waveguide element with an improved extinction ratio in particular.

[0010] When an optical waveguide element includes a Mach-Zehnder optical waveguide having a folded portion, the shape of the optical waveguide becomes complex and the distance between adjacent optical waveguides becomes short. Therefore, the optical waveguide element is prone to optical crosstalk due to light leakage into adjacent optical waveguides. In contrast, the optical waveguide element according to the present invention can suppress optical crosstalk by forming a dummy pattern in the region between adjacent extending optical waveguides to guide or absorb the leaked light.

[0011] Furthermore, the dummy pattern according to the present invention may be a pattern that allows for characteristic inspection of an optical waveguide element. Characteristic inspection of an optical waveguide element is a necessary process for preventing defective elements from being sent to the assembly process, but the inspection generally requires time and effort. In response to this, by forming the dummy pattern according to the present invention into a pattern tailored to the object to be inspected, the characteristics of the optical waveguide element can be easily measured and evaluated, thereby reducing the time and effort required for characteristic inspection. Furthermore, characteristic inspection using the dummy pattern according to the present invention may be performed in the wafer state or after chip formation. Providing a dummy pattern within the optical waveguide element that allows for characteristic inspection of the optical waveguide element also has the advantage that, if a defect occurs in the optical waveguide element, defect analysis can be easily performed using the dummy pattern.

[0012] Furthermore, forming a dummy pattern according to the present invention on a substrate can be expected to suppress the microloading effect. The microloading effect is a phenomenon in which the etching rate is slower in regions with high pattern density than in regions with low pattern density, or the etching rate slows as the pattern dimensions become thinner, potentially reducing the accuracy of the etching process. In contrast, forming a dummy pattern in a region where the density of the actual pattern formed in the optical waveguide element is low reduces the pattern density deviation (difference in density), potentially mitigating the etching rate difference caused by the microloading effect. In particular, since the density of the actual pattern tends to be relatively low in the inner peripheral region (the inner peripheral side of the curve caused by the folded portion) of a Mach-Zehnder optical waveguide having a folded portion, forming a dummy pattern in this region can reduce the pattern density deviation. This suppresses variations in processing depth during etching, which is expected to stabilize the characteristics of the optical waveguide element.

[0013] In the optical waveguide element according to the present invention having the above configuration, the dummy pattern may be formed in a region between the optical waveguide constituting the optical input section and the optical waveguide constituting the optical output section.

[0014] In the optical waveguide element according to the present invention, the Mach-Zehnder optical waveguide has a folded portion, and the optical waveguide constituting the optical input portion and the optical waveguide constituting the optical output portion may extend substantially parallel to each other. By forming a dummy pattern between the optical waveguides constituting the optical input portion and the optical output portion, optical crosstalk between the input-side optical waveguide and the output-side optical waveguide can be suppressed. Furthermore, since a region where no actual pattern is formed tends to occur between the input-side optical waveguide and the output-side optical waveguide (on the inner side of the curve caused by the folded portion), forming a dummy pattern in this region can alleviate bias in pattern density, suppress the microloading effect, and stabilize the characteristics of the optical waveguide element.

[0015] In the optical waveguide element according to the present invention having the above configuration, the dummy pattern may be formed in a region between a plurality of optical waveguides that constitute the optical output section.

[0016] For example, if two IQ optical modulation units having Mach-Zehnder optical waveguides are arranged in parallel and each of the two IQ optical modulation units generates and outputs a 2-bit optical signal using QPSK (Quadrature Phase Shift Keying) or the like, the optical output unit will have two output optical waveguides. When multiple output optical waveguides are provided in the optical output unit in this manner, optical crosstalk between the multiple output optical waveguides can be suppressed by forming dummy patterns between the multiple output optical waveguides. Furthermore, forming dummy patterns in the regions between the multiple output optical waveguides can alleviate bias in pattern density, suppress the microloading effect, and stabilize the characteristics of the optical waveguide element.

[0017] In the optical waveguide element according to the present invention, in the above configuration, the input and output ends of the dummy pattern may be provided on an end face or an upper face of the substrate.

[0018] According to the above configuration, the input and output terminals of the dummy pattern can be provided on the end face or top face of the substrate and exposed to the outside of the substrate, and the dummy pattern can capture and guide leaked light from the optical waveguide to the outside of the substrate. Furthermore, when inspecting the characteristics of an optical waveguide element using a dummy pattern, the characteristics of the optical waveguide element can be evaluated by inputting light to the input terminal of the dummy pattern and measuring the light output from the output terminal of the dummy pattern.

[0019] In the optical waveguide element according to the present invention having the above configuration, the dummy pattern may have a folded portion.

[0020] According to the above configuration, it is possible to form a dummy pattern having a turn-back portion curved in the same shape as the turn-back portion of the Mach-Zehnder optical waveguide formed in the optical waveguide element.

[0021] In the optical waveguide element according to the present invention, in the above configuration, the optical input end and optical output end of the Mach-Zehnder optical waveguide and the input end and output end of the dummy pattern may be formed on the same side of the substrate.

[0022] According to the above configuration, the input and output ends of the dummy pattern can be formed on the same side as the optical input and output ends of the Mach-Zehnder optical waveguide. When inspecting the characteristics of an optical waveguide element using a dummy pattern, light is input to the input end of the dummy pattern, and the light that passes through the dummy pattern having a folded portion and is output from the output end of the dummy pattern is measured, thereby enabling evaluation of the characteristics of the optical waveguide element that reflects the state of the folded portion.

[0023] The optical waveguide element according to the present invention has the above-mentioned configuration, and the Mach-Zehnder optical waveguide includes, between an optical input section including an input optical waveguide and an optical output section including first and second output optical waveguides, a parent branch section that branches an optical wave propagating in the input optical waveguide and propagates the optical wave to first and second parent branch waveguides, a first child branch section that branches an optical wave propagating in the first parent branch waveguide and propagates the optical wave to first and second child branch waveguides, and a second child branch section that branches the optical wave propagating in the first parent branch waveguide and propagates the optical wave to first and second child branch waveguides. The optical waveguide may be configured to include a first multiplexing section that combines light waves propagating through the child branch waveguides and propagates the combined light waves to the first output optical waveguide, a second child branching section that branches light waves propagating through the second parent branch waveguide and propagates the combined light waves to the third and fourth child branching waveguides, and a second multiplexing section that combines light waves propagating through the third and fourth child branching waveguides and propagates the combined light waves to the second output optical waveguide, and each of the first to fourth child branching waveguides may have the folding section.

[0024] According to the above configuration, two IQ optical modulation units each having a Mach-Zehnder optical waveguide are arranged side by side, and each of the two IQ optical modulation units can generate and output a 2-bit optical signal by QPSK. Furthermore, by providing a folding section in each of the first to fourth branching waveguides that constitute the Mach-Zehnder optical waveguide, the optical input terminal and two optical output terminals can be formed on the same side of the substrate.

[0025] In the optical waveguide element according to the present invention, in the above configuration, the dummy pattern may be formed at least in a region between the plurality of optical waveguides constituting the optical output portion, and may have a folded portion in any of a region between the first parent branch waveguide and the second parent branch waveguide adjacent to each other, a region between the second child branch waveguide and the third child branch waveguide adjacent to each other, and a region between the first output optical waveguide and the second output optical waveguide adjacent to each other.

[0026] According to the above configuration, a dummy pattern is formed between two IQ optical modulation units having Mach-Zehnder optical waveguides, and a folded portion of the dummy pattern can be provided at any position between the two IQ optical modulation units.

[0027] In the optical waveguide element according to the present invention, in the above configuration, the first output optical waveguide and the second output optical waveguide may be substantially linear.

[0028] According to the above configuration, it is possible to reduce the propagation loss of light in the first output optical waveguide and the second output optical waveguide.

[0029] In the optical waveguide element according to the present invention, in the above configuration, the dummy pattern may be formed so as to be symmetrical with respect to a center line of the folded portion of the Mach-Zehnder optical waveguide.

[0030] According to the above configuration, the bias in pattern density can be alleviated in a balanced manner, and the bias in pattern density can be reduced, and the variation in processing depth during etching processing can be suppressed, which is expected to stabilize the characteristics as an optical waveguide element.

[0031] In the optical waveguide element according to the present invention, in the above configuration, the dummy pattern may be formed to have a portion where it runs substantially parallel to the optical waveguide while maintaining a fixed distance from the optical waveguide.

[0032] According to the above configuration, the dummy pattern can be shaped to match the optical waveguide and run parallel to it, so that the leaked light from the optical waveguide can be reliably captured and optical crosstalk can be more reliably suppressed.

[0033] In order to achieve the above object, an optical modulator according to the present invention is characterized by comprising the above optical waveguide element, a housing that houses the optical waveguide element, an input optical fiber connected to an optical input portion of the optical waveguide element, and an output optical fiber connected to an optical output portion of the optical waveguide element.

[0034] In order to achieve the above object, an optical transmitting device according to the present invention is characterized by having the above optical modulator and an electronic circuit that generates an electrical signal for causing the optical waveguide element to perform a modulation operation.

[0035] According to the present invention, by forming a dummy pattern capable of suppressing optical crosstalk in an optical waveguide element formed with a Mach-Zehnder optical waveguide having a folded portion, it is possible to suppress optical crosstalk and improve the extinction ratio of the optical waveguide element. Furthermore, by performing characteristic inspection of the optical waveguide element using the dummy pattern, it is possible to easily measure and evaluate the characteristics of the optical waveguide element. Furthermore, by forming the dummy pattern on the substrate, it is possible to suppress the microloading effect, suppress variations in processing depth during etching processing, and stabilize the characteristics of the optical waveguide element.

[0036] 1 is a plan view of an optical waveguide element according to a first embodiment of the present invention. FIG. 1 is a cross-sectional view showing an example of the A1-A1 cross section of FIG. 1, illustrating a configuration when there are no irregularities on the substrate other than the optical waveguide and the dummy pattern. FIG. 1 is a cross-sectional view showing another example of the A1-A1 cross section of FIG. 1, illustrating a configuration when there are irregularities on the substrate other than the optical waveguide and the dummy pattern. FIG. 1 is a plan view of an optical waveguide element according to a second embodiment of the present invention. FIG. 1 is a plan view of an optical waveguide element according to a third embodiment of the present invention. FIG. 1 is a plan view of an optical waveguide element according to a fourth embodiment of the present invention. FIG. 1 is a plan view of an optical waveguide element according to a fifth embodiment of the present invention. FIG. 1 is a plan view of an optical waveguide element according to a sixth embodiment of the present invention. FIG. 1 is a plan view of an optical waveguide element according to a seventh embodiment of the present invention. FIG. 1 is a plan view of an optical waveguide element according to an eighth embodiment of the present invention. FIG. 10 is a cross-sectional view showing an example of the A2-A2 cross section of FIG. 10, illustrating a configuration when there are no irregularities on the substrate other than the optical waveguide and the dummy pattern. FIG. 10 is a cross-sectional view showing another example of the A2-A2 cross section of FIG. 10, illustrating a configuration when there are irregularities on the substrate other than the optical waveguide and the dummy pattern. It is a plan view of an optical waveguide element according to a ninth embodiment of the present invention.It is a plan view of an optical waveguide element according to a tenth embodiment of the present invention.It is a plan view showing an optical modulator and an optical transmitting device according to the present invention.

[0037] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The drawings referred to in this specification do not necessarily have accurate scales relative to actual dimensions, and some parts are exaggerated or simplified to schematically illustrate the configuration according to the present invention.

[0038] As exemplified in the first to tenth embodiments, the optical waveguide element according to the present invention is characterized in that an optical waveguide including a Mach-Zehnder optical waveguide having a folded portion is formed on a substrate having an electro-optic effect, and a dummy pattern is formed in a region between adjacent extending optical waveguides. The dummy pattern functions as an optical crosstalk suppression pattern that suppresses optical crosstalk. Furthermore, the dummy pattern may be used as an inspection pattern for inspecting the characteristics of the optical waveguide element, and may be formed at a position that alleviates bias in pattern density so as to alleviate differences in etching rate due to the microloading effect.

[0039] First Embodiment First, a first embodiment of the present invention will be described. Fig. 1 is a plan view of an optical waveguide element 1A according to the first embodiment of the present invention. Figs. 2 and 3 are cross-sectional views showing an example and another example of the A1-A1 cross section of Fig. 1, respectively. In Fig. 1, the optical waveguide element 1A is illustrated so that the width direction of the optical waveguide element 1A is the up-down direction on the paper, the length direction of the optical waveguide element 1A is the left-right direction on the paper, and the thickness direction of the optical waveguide element 1A is the direction perpendicular to the paper.

[0040] The optical waveguide element 1A shown in Figure 1 has a substrate 2 having an electro-optic effect. The substrate 2 having an electro-optic effect can be a substrate made of lithium niobate (LN), lithium tantalate (LT), lead lanthanum zirconate titanate (PLZT), or the like, a substrate made of these materials doped with MgO or the like, a vapor-deposited film made of these materials, or a composite substrate made by bonding these materials to a substrate of a different type. Furthermore, various materials such as semiconductor materials and organic materials can also be used as the substrate 2 of the optical waveguide element 1A.

[0041] The thickness of the substrate 2 is not particularly limited, but may be set to 20 μm or less, preferably 10 μm or less, and more preferably 5 μm or less or 2 μm or less, for example, to improve the electric field efficiency for the optical waveguide 3 formed on the substrate 2. In such cases, a support substrate (reinforcing substrate) 4 may be disposed below the substrate 2 to reinforce its mechanical strength, as shown in FIG. 3 . The support substrate 4 is not particularly limited, but may have a thickness of, for example, 0.2 to 1.0 mm. The support substrate 4 may be directly bonded to the substrate 2 or may be attached to the substrate 2 via a bonding layer (adhesive layer). The material of the support substrate 4 is not particularly limited, but the same material as the substrate 2 can be used, such as semiconductor materials such as LN, glass, and Si.

[0042] An optical waveguide 3 is formed on the substrate 2 of the optical waveguide element 1A. The optical waveguide 3 is a path along which light propagates within the substrate 2. The material of the optical waveguide 3 is not particularly limited, and may be the same material as that of the substrate 2, such as LN, or may be SiO ２ and Al ２ O ３ Alternatively, the optical waveguide 3 may be formed by combining the above materials, for example, by applying a permanent resist onto the substrate 2 made of LN to form a pattern of a spot size converter (SSC).

[0043] The method for forming the optical waveguide 3 on the substrate 2 is not particularly limited, and for example, a convex optical waveguide (rib-type optical waveguide or ridge-type optical waveguide) having a convex portion (rib portion or ridge portion) in a portion corresponding to the optical waveguide 3 may be formed. Alternatively, the optical waveguide 3 may be formed by forming a high refractive index portion made of a high refractive index material such as Ti on the surface of the substrate 2 by thermal diffusion or proton exchange. Furthermore, a composite optical waveguide 3 may be formed by diffusing a high refractive index material into the convex portion of a convex optical waveguide, for example.

[0044] When a convex optical waveguide is formed as the optical waveguide 3, the optical waveguide 3 may be formed by providing a convex portion (convex portion 3a in FIG. 2) that protrudes from the surface of the substrate 2, as shown in the cross-sectional view of Fig. 2, for example. Alternatively, the optical waveguide 3 may be formed on the substrate 2 by forming grooves 3b on both sides of a portion corresponding to the optical waveguide 3 and providing a convex portion (convex portion 3c in FIG. 3) sandwiched between the grooves 3b, as shown in the cross-sectional view of Fig. 3, for example.

[0045] Furthermore, the end of the optical waveguide 3 is configured to allow input and output of light, and for example, the optical waveguide 3 may be exposed to the outside from the end face of the substrate 2, or may have a grating structure or an SSC structure.

[0046] A Mach-Zehnder optical waveguide is formed as the optical waveguide 3 on the substrate 2 of the optical waveguide element 1A. A Mach-Zehnder optical waveguide is a waveguide that has at least one branching section and at least one combining section as basic components. The branching section is a section that branches one optical waveguide into two optical waveguides, and the combining section is a section that connects the two optical waveguides to combine them into one optical waveguide. The branching section and the combining section can be realized by an optical coupler or the like.

[0047] As an example, a multi-stage Mach-Zehnder optical waveguide is formed on the substrate 2 of the optical waveguide element 1A, as shown in Fig. 1. The Mach-Zehnder optical waveguide shown in Fig. 1 has a first child branch 30 and a second child branch 40 provided in the subsequent stage of a parent branch 20. This allows the light waves branched by the parent branch 20 to be further branched by the first child branch 30 and the second child branch 40, respectively.

[0048] An external light wave is input to the input optical waveguide 10 through the optical input end 10a. The optical input end 10a and the input optical waveguide 10 constitute the optical input section of the optical waveguide device 1A. The parent branch section 20 branches the light wave propagating through the input optical waveguide 10 into two branch waveguides (first and second parent branch waveguides) 21 and 22.

[0049] The first child branching section 30 branches the light wave propagating through one branching waveguide 21 branched by the parent branching section 20 into two branching waveguides (first and second child branching waveguides) 31 and 32. As a result, the light wave branched by the parent branching section 20 is further branched by the first child branching section 30. An action section (modulation section) for modulating the optical signal is provided in the portion where the branching waveguides 31 and 32 are formed.

[0050] The first multiplexing section (first multiplexing section) 50 multiplexes (combines) the light waves propagating through the two branching waveguides 31, 32 branched by the first branching section 30. The light waves multiplexed by the first multiplexing section 50 are output to the outside from the output optical waveguide (first output optical waveguide) 70 through the optical output end 70a. The output optical waveguide 70 and the optical output end 70a constitute the optical output section of the optical waveguide device 1A.

[0051] The second child branching section 40 branches the light wave propagating through the other branching waveguide 22 branched by the parent branching section 20 into two branching waveguides (third and fourth child branching waveguides) 41, 42. As a result, the light wave branched by the parent branching section 20 is further branched by the second child branching section 40. An action section (modulation section) for modulating an optical signal is provided in the portion where the two branching waveguides 41, 42 are formed.

[0052] The second multiplexing section (second multiplexing section) 60 multiplexes (combines) the light waves propagating through the two branching waveguides 41, 42 branched by the second branching section 40. The light waves multiplexed by the second multiplexing section 60 are output to the outside from the output optical waveguide (second output optical waveguide) 80 through the optical output end 80a. The output optical waveguide 80 and the optical output end 80a constitute the optical output section of the optical waveguide device 1A.

[0053] The Mach-Zehnder optical waveguide formed on the substrate 2 of the optical waveguide element 1A has a folded portion. A folded portion is a portion folded back so that the propagation direction of the light wave is reversed (approximately 180° opposite). For example, as shown in FIG. 1 , the branch waveguides 31, 32, 41, and 42 formed in the optical waveguide element 1A each have a folded portion (folded portions B1, B2, B3, and B4 in FIG. 1 ) that folds back the optical waveguide 3 so that it is in the opposite direction (approximately 180° opposite). The folded portion may be formed so that the optical waveguide 3 is folded back approximately 180°, and may be, for example, approximately U-shaped, but the shape is not particularly limited. The folded portion may be formed, for example, in a semicircular shape curved with a constant or variable curvature, or may be formed by two bent portions bent approximately 90°, with a straight portion and two quadrants connected to both ends of the straight portion. By folding the optical waveguide 3 at the folding portion in this manner, the propagation direction of the light waves can be reversed, and the optical input end 10a and optical output ends 80a, 80b of the optical waveguide element 1A can also be formed on the same side of the substrate 2.

[0054] The optical waveguide 3 formed on the substrate 2 of the optical waveguide element 1A is a pattern required for modulating light. Although not shown, an electrode pattern made of a common metal material such as gold or copper is also formed on the substrate 2 in order to modulate the light waves propagating through the optical waveguide 3. In this specification, the optical waveguide pattern and electrode pattern required for modulating light are referred to as actual patterns.

[0055] In addition to the actual pattern, a dummy pattern 110 is formed on the substrate 2 of the optical waveguide element 1A.

[0056] The dummy pattern 110 is formed between adjacent extending actual patterns. In the optical waveguide element 1A shown in Fig. 1, the dummy pattern 110 is formed in a region surrounded by the input optical waveguide 10, the branching waveguides 21 and 31, and the output optical waveguide 70.

[0057] The dummy pattern 110 may have the same configuration as the optical waveguide 3. For example, a convex portion (rib portion or ridge portion) may be formed in a portion corresponding to the dummy pattern 110, or the dummy pattern 110 may be formed by forming a high refractive index portion made of a high refractive index material such as Ti on the surface of the substrate 2 by thermal diffusion or proton exchange. Alternatively, the dummy pattern 110 may be formed by diffusing a high refractive index material into the convex portion. The dummy pattern 110 may be formed of the same material as the optical waveguide 3, or may be formed of a material different from the optical waveguide 3.

[0058] As will be described later, the dummy pattern 110 may be used to inspect the characteristics of the optical waveguide element 1A. By giving the dummy pattern 110 the same configuration as the optical waveguide 3, it can be used as an inspection waveguide for measuring optical characteristics. Furthermore, the dummy pattern 110 may be formed using the same shape and material as the electrodes formed on the substrate 2. By giving the dummy pattern 110 the same configuration as the electrodes, it can be used as an inspection electrode for measuring electrical characteristics.

[0059] In the optical waveguide element 1A shown in Fig. 1, the dummy pattern 110 is formed by a convex portion. In this case, the dummy pattern 110 may be formed on the substrate 2 by providing a convex portion (convex portion 110a in Fig. 2) that protrudes from the surface of the substrate 2, as shown in the cross-sectional view of Fig. 2, for example. Alternatively, the dummy pattern 110 may be formed on the substrate 2 by forming grooves 110b on both sides of a portion corresponding to the dummy pattern 110 and providing a convex portion (convex portion 110c in Fig. 3) sandwiched between the grooves 110b, as shown in the cross-sectional view of Fig. 3, for example.

[0060] The dummy pattern 110 is formed at a position sandwiched between adjacently extending optical waveguides 3. In the first embodiment, an aspect in which the dummy pattern 110 is formed between the input optical waveguide 10 and the output optical waveguide 70 is exemplified. By forming the dummy pattern 110 in the region between adjacently extending optical waveguides 3 in this manner, the adjacent optical waveguides 3 can be isolated, and the dummy pattern 110 can capture leaked light from the optical waveguides 3 and guide it to the outside or absorb it. As a result, optical crosstalk, in which leaked light from one optical waveguide 3 mixes with and interferes with the other optical waveguide 3, can be suppressed. The dummy pattern 110 shown in FIG. 1 can suppress optical crosstalk between input light propagating through the input optical waveguide 10 and output light propagating through the output optical waveguide 70.

[0061] The dummy pattern 110 can be formed in any region between adjacently extending optical waveguides 3. In the first embodiment, the dummy pattern 110 is disposed between the input optical waveguide 10 and the output optical waveguide 70, but it may also be disposed, for example, between two branching waveguides branched at a branching portion. The number of dummy patterns 110 is also not particularly limited. Only one dummy pattern 110 may be formed on the substrate 2, or multiple dummy patterns 110 may be formed in the same region or different regions of the substrate 2.

[0062] Furthermore, the dummy pattern 110 may be formed inside the outer periphery of the Mach-Zehnder optical waveguide having a folded portion, with the outer periphery being used as a reference. The outer periphery of the Mach-Zehnder optical waveguide having a folded portion means the outer periphery of the region including the Mach-Zehnder optical waveguide. Note that, in order to ensure symmetry of the cross section, the dummy pattern 110 may be formed both inside and outside the outer periphery of the Mach-Zehnder optical waveguide. The Mach-Zehnder optical waveguide having a folded portion may be a parent Mach-Zehnder formed by a parent branching portion 20, or a child Mach-Zehnder formed by a first child branching portion 30 or a second child branching portion 40.

[0063] The dummy pattern 110 has a function of suppressing optical crosstalk between adjacent extending optical waveguides 3, and may also be used as an inspection pattern for inspecting the characteristics of the optical waveguide element 1 A. The type of characteristic inspection using the dummy pattern 110 is not particularly limited, and may be used to measure and evaluate, for example, optical characteristics of the optical waveguide 3, such as bending loss and deflection characteristics, or electrical characteristics, such as electrode absorption loss and electrical bandwidth.

[0064] As shown in FIG. 1, the dummy pattern 110 has a linear portion 111 extending in a substantially straight line from one end 111a, a linear portion 112 extending in a substantially straight line from the other end 112a, and an approximately U-shaped folded portion C1 connecting the linear portion 111 and the linear portion 112.

[0065] Note that there is no particular limitation on the lengths of the linear portions 111 and 112. In Fig. 1, the folded portion C1 is disposed near the inside of the folded portion B1 of the branch waveguide 31, but the linear portions 111 and 112 may be shortened to dispose the folded portion C1 at a position closer to one end 111a or the other end 112a.

[0066] The end of the dummy pattern 110 may be provided on an end face of the substrate 2 or on the top surface of the substrate 2. The end of the dummy pattern 110 may be configured to allow input and output of light by, for example, a grating or SSC. In the optical waveguide element 1A shown in FIG. 1 , one end 111 a and the other end 112 a of the dummy pattern 110 are provided between the optical input end 10 a and the optical output end 70 a, and are formed on the same side of the substrate 2.

[0067] When the dummy pattern 110 is used as a test pattern, it is possible to evaluate the basic characteristics of the optical waveguide 3. In the optical waveguide element 1A shown in Fig. 1 , the dummy pattern 110 is configured to include two linear portions 111 and 112 as the optical waveguide 3 and a folded portion C1 connecting the two linear portions 111 and 112.

[0068] When one end 111a and the other end 112a of the dummy pattern 110 are used as an input end and an output end of light, respectively, light input from one end 111a propagates through the dummy pattern 110 having the folded portion C1 and is output from the other end 112a. By measuring the light output from the other end 112a, the characteristics of the linear waveguide having the folded portion can be evaluated.

[0069] In this way, by performing an inspection using the dummy pattern 110, the characteristics of the optical waveguide element 1A can be easily measured and evaluated, and the time and effort required for the characteristic inspection can be reduced. The characteristic inspection using the dummy pattern 110 can be performed in the wafer state or after being formed into chips. Furthermore, since the inspection pattern (dummy pattern 110) is incorporated into the optical waveguide element 1A, even if a defect occurs in the optical waveguide element 1A, defect analysis can be easily performed using the dummy pattern 110.

[0070] Furthermore, the effect of suppressing the microloading effect can be expected by forming the dummy pattern 110 on the substrate 2. When the actual pattern formed on the substrate 2 has a large deviation in pattern density (difference in density), the microloading effect causes local differences in the etching rate, which may result in poor characteristics due to increased variations in processing depth.

[0071] 1, a dummy pattern 110 is formed in the inner region of the Mach-Zehnder optical waveguide having a folded portion (the region on the inner periphery of the curved portion caused by the folded portion). The inner region of the Mach-Zehnder optical waveguide having a folded portion is a region where the density of the actual pattern is relatively low, and by forming the dummy pattern 110 in this region, it is possible to reduce the bias in the pattern density.

[0072] Furthermore, in the cross section of the action portion, the dummy pattern 110 may be formed line-symmetrically with respect to the center line of the folded portion of the actual pattern. As shown in Fig. 1, the folded portion of the actual pattern is a substantially U-shaped portion that connects two optical waveguides 3 that extend substantially parallel to each other, and is line-symmetric with respect to the center line S1 shown in Fig. 1 when the substrate 2 is viewed from above. By forming the dummy pattern 110 line-symmetrically with respect to the center line S1, it is possible to alleviate the bias in pattern density in a balanced manner and reduce the bias in pattern density.

[0073] In this way, by forming the dummy patterns 110 so as to reduce the bias in pattern density, the variation in processing depth during etching processing when manufacturing the optical waveguide element 1A is suppressed, and it is possible to expect the characteristics of the optical waveguide element 1A to be stabilized.

[0074] As described above, the dummy pattern 110 can be said to have multiple functions. As a basic feature of the present invention, the dummy pattern 110 is formed in a region between adjacent extending optical waveguides 3, thereby having the function of suppressing optical crosstalk between the optical waveguides 3. The dummy pattern 110 may also have the function of serving as a test pattern (test waveguide or test electrode) for measuring optical characteristics or electrical characteristics. Furthermore, the dummy pattern 110 may have the function of suppressing the microloading effect by being arranged to alleviate bias in pattern density.

[0075] However, the dummy patterns 110 do not necessarily have to function as inspection patterns or to suppress the microloading effect, and may have only the function of suppressing optical crosstalk. Furthermore, dummy patterns 110 with different functions (for example, dummy patterns 110 that combine the function of suppressing optical crosstalk and the function of inspection patterns, and dummy patterns 110 that only have the function of suppressing optical crosstalk) may be formed on one substrate 2.

[0076] Second Embodiment A second embodiment of the present invention will be described. In the second embodiment, an example will be described in which a dummy pattern is formed in a region between a plurality of optical waveguides that constitute an optical output section. Fig. 4 is a plan view of an optical waveguide element 1B in the second embodiment of the present invention. Descriptions of the same configurations as those in the above-described embodiments will be simplified or omitted, and the same reference numerals will be used.

[0077] The optical waveguide element 1B of the second embodiment has a substrate 2 having an electro-optic effect. The substrate 2 is formed with a Mach-Zehnder optical waveguide having a folded portion as the optical waveguide 3. The Mach-Zehnder optical waveguide formed on the substrate 2 of the optical waveguide element 1B has a shape similar to that of the optical waveguide element 1A described above. As shown in Fig. 4, four branch waveguides 31, 32, 41, and 42 are folded back at folding portions B1, B2, B3, and B4, respectively.

[0078] In addition to the actual patterns, a dummy pattern 120 is formed on the substrate 2 of the optical waveguide element 1B.

[0079] The dummy pattern 120 is formed between adjacent extending real patterns and is formed inside the outer periphery of the Mach-Zehnder optical waveguide having a folded portion. In the optical waveguide element 1B shown in Fig. 4, the dummy pattern 120 is formed in the region sandwiched between the output optical waveguide 70 and the output optical waveguide 80 that constitute the optical output portion.

[0080] In this way, by forming the dummy pattern 120 in the region between adjacently extending optical waveguides 3, it is possible to isolate the adjacent optical waveguides 3, and also to capture leaked light from the optical waveguides 3 by the dummy pattern 120 and guide it to the outside or absorb it. As a result, it is possible to suppress optical crosstalk, in which leaked light from one optical waveguide 3 mixes with and interferes with the other optical waveguide 3. In particular, by forming the dummy pattern 120 between the output optical waveguide 70 and the output optical waveguide 80, it is possible to suppress optical crosstalk between the IQ optical signals, which are output light.

[0081] Furthermore, the dummy pattern 120 having the function of suppressing optical crosstalk may be used as an inspection pattern for inspecting the characteristics of the optical waveguide element 1B.

[0082] As shown in Figure 4, the dummy pattern 120 has a linear portion 121 extending in an approximately straight line from one end 121a, a linear portion 122 extending in an approximately straight line from the other end 122a, and an approximately U-shaped folded portion C2 connecting the linear portion 121 and the linear portion 122.

[0083] There is no particular limitation on the lengths of the linear portions 121 and 122. In Fig. 4, the folded portion C2 is disposed near the first child multiplexing portion 50 and the second child multiplexing portion 60, but the linear portions 121 and 122 may be made longer so that the folded portion C2 is disposed in a range beyond the first child multiplexing portion 50 and the second child multiplexing portion 60.

[0084] One end 121 a and the other end 122 a of the dummy pattern 120 are provided between the optical output terminal 70 a and the optical output terminal 80 a , and are formed on the same side of the substrate 2 .

[0085] When the dummy pattern 120 is used as a test pattern, it is possible to evaluate the basic characteristics of the optical waveguide 3. In the optical waveguide element 1B shown in Fig. 4, the dummy pattern 120 is configured to include two linear portions 121 and 122 as optical waveguides and a folded portion C2 connecting the two linear portions 121 and 122.

[0086] When one end 121 a and the other end 122 a of the dummy pattern 120 are used as an input end and an output end of light, respectively, light input from one end 121 a propagates through the dummy pattern 120 having the folded portion C2 and is output from the other end 122 a. By measuring the light output from the other end 122 a, the characteristics of the substantially linear optical waveguide 3 having the folded portion can be evaluated.

[0087] (Third Embodiment) A third embodiment of the present invention will be described. In the third embodiment, an example will be described in which a dummy pattern is configured to include a folded portion and a bent portion. Fig. 5 is a plan view of an optical waveguide element 1C according to the third embodiment of the present invention. Descriptions of the same components as those in the above-described embodiments will be simplified or omitted, and the same reference numerals will be used.

[0088] The optical waveguide element 1C of the third embodiment has a substrate 2 having an electro-optic effect. The substrate 2 is formed with a Mach-Zehnder optical waveguide having a folded portion as the optical waveguide 3. The Mach-Zehnder optical waveguide formed on the substrate 2 of the optical waveguide element 1C has a shape similar to that of the optical waveguide element 1A described above. As shown in Fig. 5, four branch waveguides 31, 32, 41, and 42 are folded back at folding portions B1, B2, B3, and B4, respectively.

[0089] In addition to the actual pattern, a dummy pattern 130 is formed on the substrate 2 of the optical waveguide element 1C.

[0090] The dummy pattern 130 is formed between adjacent extending real patterns and is formed inside the outer periphery of the Mach-Zehnder optical waveguide having the folded portion. In the optical waveguide element 1C shown in Fig. 5, the dummy pattern 130 is formed in the region sandwiched between the output optical waveguide 70 and the output optical waveguide 80 constituting the optical output portion, and in the region sandwiched between the branch waveguide 32 and the branch waveguide 41.

[0091] In this way, by forming the dummy pattern 130 in the region between adjacently extending optical waveguides 3, it is possible to isolate the adjacent optical waveguides 3, and also to capture leaked light from the optical waveguides 3 by the dummy pattern 130 and guide it to the outside or absorb it. As a result, it is possible to suppress optical crosstalk, which is the interference caused by leaked light from one optical waveguide 3 mixing with the other optical waveguide 3. In particular, by forming the dummy pattern 130 between the output optical waveguide 70 and the output optical waveguide 80, it is possible to suppress optical crosstalk between the IQ optical signals, which are output light.

[0092] Furthermore, the dummy pattern 130 having the function of suppressing optical crosstalk may be used as an inspection pattern for inspecting the characteristics of the optical waveguide element 1C.

[0093] 5, the dummy pattern 130 has a linear portion 131 extending from one end 131a, a linear portion 132 extending from the other end 132a, and a substantially U-shaped folded portion C3 connecting the linear portion 131 and the linear portion 132. The linear portions 131 and 132 have folded portions 131b and 132b, respectively, that are folded at approximately 90° to fit the shape of the Mach-Zehnder optical waveguide.

[0094] The lengths of the linear portions 131 and 132 are not particularly limited, but may be made closer to the waveguide length of the actual pattern by lengthening the linear portions 131 and 132. In Fig. 5, the folded portion C3 is disposed near the folded portion of the Mach-Zehnder optical waveguide, but the linear portions 131 and 132 may be made longer and further provided with a folded portion that is bent at approximately 90°, so that the folded portion C3 may be disposed near the parent branch portion 20, for example.

[0095] The dummy pattern 130 in the third embodiment has a bent portion that is bent at approximately 90 degrees. This allows the dummy pattern 130 to be formed along the actual pattern. Note that the dummy pattern 130 along the actual pattern means that the dummy pattern 130 extends in the substantial extension direction of the actual pattern. In this case, the dummy pattern 130 does not necessarily have to be approximately parallel to the actual pattern. It is preferable that the dummy pattern 130 be formed over at least 10% of the actual pattern, more preferably 40% or more, and even more preferably 70% or more.

[0096] One end 131 a and the other end 132 a of the dummy pattern 130 are provided between the optical output terminal 70 a and the optical output terminal 80 a , and are formed on the same side of the substrate 2 .

[0097] When the dummy pattern 130 is used as a test pattern, it is possible to evaluate the basic characteristics of the optical waveguide 3. In the optical waveguide element 1C shown in Fig. 5, the dummy pattern 130 is configured to include two linear portions 131 and 132 as optical waveguides and a folded portion C3 connecting the two linear portions 131 and 132, and the linear portions 131 and 132 have folded portions 131b and 132b, respectively.

[0098] When one end 131a and the other end 132a of the dummy pattern 130 are used as the input and output ends of light, respectively, light input from one end 131a propagates through the dummy pattern 130, which has the turning portion C3 and the bent portions 131b and 132b, and is output from the other end 132a. By measuring the light output from the other end 132a, it is possible to evaluate the characteristics of the optical waveguide 3, which has turning portions and bent portions that reflect the shape of the actual pattern. Furthermore, for example, a plurality of dummy patterns 130 with different shapes may be formed, and the optical loss of the bent waveguide may be calculated using the plurality of dummy patterns 130.

[0099] (Fourth Embodiment) A fourth embodiment of the present invention will be described. In the fourth embodiment, an example will be illustrated in which a dummy pattern is formed along the shape of an actual pattern. Fig. 6 is a plan view of an optical waveguide element 1D according to the fourth embodiment of the present invention. The same components as those in the above-described embodiments will be denoted by the same reference numerals and descriptions thereof will be simplified or omitted.

[0100] The optical waveguide element 1D of the fourth embodiment has a substrate 2 having an electro-optic effect. The substrate 2 is formed with a Mach-Zehnder optical waveguide having a folded portion as the optical waveguide 3. The Mach-Zehnder optical waveguide formed on the substrate 2 of the optical waveguide element 1D has a shape similar to that of the optical waveguide element 1A described above. As shown in Fig. 6, four branching waveguides 31, 32, 41, and 42 are folded back at folding portions B1, B2, B3, and B4, respectively.

[0101] In addition to the actual patterns, a dummy pattern 140 is formed on the substrate 2 of the optical waveguide element 1D.

[0102] The dummy pattern 140 is formed between adjacent extending real patterns, and is formed inside the outer periphery of the Mach-Zehnder optical waveguide having the folded portion. In the optical waveguide element 1D shown in Fig. 6, the dummy pattern 140 is formed in the region surrounded by the input optical waveguide 10, the branching waveguides 21 and 31, and the output optical waveguide 70 (the region on the inner periphery of the curve formed by the folded portion).

[0103] As shown in FIG. 6 , the dummy pattern 140 has a linear portion 141 extending from one end 141 a, a linear portion 142 extending from the other end 142 a, and a substantially U-shaped folded portion C4 connecting the linear portion 141 and the linear portion 142. The linear portion 141 is bent to match the shape of the optical waveguide 3 that bends at the parent branching portion 20 and the first child branching portion 30. The linear portion 142 is bent to match the shape of the optical waveguide 3 that bends at the first child multiplexing portion 50. The one end 141 a and the other end 142 a are provided between the optical input terminal 10 a and the optical output terminal 70 a and are formed on the same side of the substrate 2. The dummy pattern 140 is formed so as to be partially bent to match the shape of the optical waveguide 3, and is formed so as to run substantially parallel to the actual pattern while maintaining a certain distance therebetween, as shown in FIG. 6 .

[0104] In this way, by forming the dummy pattern 140 in the region between adjacently extending optical waveguides 3, it is possible to isolate the adjacent optical waveguides 3, and also to capture leaked light from the optical waveguides 3 with the dummy pattern 140 and guide it to the outside or absorb it. As a result, it is possible to suppress optical crosstalk, in which leaked light from one optical waveguide 3 mixes with and interferes with the other optical waveguide 3. In particular, by forming the dummy pattern 140 in a shape that matches the optical waveguides 3 and running parallel to them, it is possible to reliably capture leaked light from the optical waveguides 3 and more reliably suppress optical crosstalk.

[0105] Furthermore, the dummy pattern 140 having the function of suppressing optical crosstalk may be used as an inspection pattern for inspecting the characteristics of the optical waveguide element 1D.

[0106] When the dummy pattern 140 is used as a test pattern, the basic characteristics of the optical waveguide 3 can be evaluated. In particular, as shown in FIG. 6 , by forming the dummy pattern 140 to have a shape that matches the optical waveguide 3, the characteristics of the optical waveguide 3 that reflect the bending shape of the optical waveguide 3 can be evaluated. Note that the configuration in this embodiment, in which the dummy pattern 140 is formed to run approximately parallel to the actual pattern while maintaining a certain distance from it, is not limited to the configuration of this embodiment and can also be applied to the dummy patterns of other examples. Furthermore, only a portion of the dummy pattern 140 may be formed to run approximately parallel to the actual pattern while maintaining a certain distance from it. The dummy pattern 140 may be formed, for example, on at least one of the straight portion and the folded portion of the actual pattern.

[0107] Fifth Embodiment A fifth embodiment of the present invention will be described. In the fifth embodiment, an example will be described in which dummy patterns are formed in the shape of a Mach-Zehnder structure. Fig. 7 is a plan view of an optical waveguide element 1E according to the fifth embodiment of the present invention. The same components as those in the above-described embodiments will be denoted by the same reference numerals and descriptions thereof will be simplified or omitted.

[0108] The optical waveguide element 1E of the fifth embodiment has a substrate 2 having an electro-optic effect. The substrate 2 is formed with a Mach-Zehnder optical waveguide having a folded portion as the optical waveguide 3. The Mach-Zehnder optical waveguide formed on the substrate 2 of the optical waveguide element 1E has a shape similar to that of the optical waveguide element 1A described above. As shown in Fig. 7 , four branch waveguides 31, 32, 41, and 42 are folded back at folding portions B1, B2, B3, and B4, respectively.

[0109] In addition to the actual patterns, a dummy pattern 150 is formed on the substrate 2 of the optical waveguide element 1E.

[0110] The dummy pattern 150 is formed between adjacent extending real patterns, and is formed inside the outer periphery of the Mach-Zehnder optical waveguide having the folded portion. In the optical waveguide element 1E shown in Fig. 7, the dummy pattern 150 is formed in the region surrounded by the input optical waveguide 10, the branching waveguides 21 and 31, and the output optical waveguide 70 (the region on the inner periphery of the curve formed by the folded portion).

[0111] As shown in FIG. 7 , the dummy pattern 150 is formed to have a Mach-Zehnder structure shape with a folded portion. The dummy pattern 150 includes a substantially straight line portion 151, a first connection portion 152 that branches from the line portion 151 into two line portions 153 and 154, a second connection portion 155 that joins the two line portions 153 and 154 into the line portion 156, and the substantially straight line portion 156. The line portion 152 has a substantially U-shaped folded portion C5a, and the line portion 153 has a substantially U-shaped folded portion C5b. The end portion 151a of the line portion 151 and the end portion 156a of the line portion 156 are provided between the optical input terminal 10a and the optical output terminal 70a and are formed on the same side of the substrate 2.

[0112] In this way, by forming the dummy pattern 150 in the region between adjacently extending optical waveguides 3, it is possible to isolate the adjacent optical waveguides 3 and also to capture the leaked light from the optical waveguides 3 and guide it to the outside or absorb it by the dummy pattern 150. As a result, it is possible to suppress optical crosstalk, in which leaked light from one optical waveguide 3 mixes with and interferes with another optical waveguide 3.

[0113] Furthermore, the dummy pattern 150 having the function of suppressing optical crosstalk may be used as an inspection pattern for inspecting the characteristics of the optical waveguide element 1E.

[0114] The dummy pattern 150 functions as an optical waveguide to propagate light waves. Light input from the end 151a of the dummy pattern 150 branches at the first connection portion 152, propagates through the linear portion 153 having the folded portion C5a and the linear portion 154 having the folded portion C5b, and is combined at the second connection portion 155 and output from the end 156a. By measuring the light output from the end 156a, the characteristics of the Mach-Zehnder optical waveguide having the folded portion can be evaluated.

[0115] 7, the dummy pattern 150 is formed so as to be symmetrical with respect to the center line S1 of the folded portion of the actual pattern. By forming the dummy pattern 150 so as to be symmetrical with respect to the center line S1 in this manner, the bias in the pattern density can be alleviated in a balanced manner, and the bias in the pattern density can be reduced. As a result, when manufacturing the optical waveguide element 1E, variations in the processing depth during etching due to the microloading effect are suppressed, and the characteristics of the optical waveguide element 1E can be expected to be stabilized.

[0116] Sixth Embodiment A sixth embodiment of the present invention will be described. In the sixth embodiment, an example will be described in which the ends of the dummy patterns are provided on the upper surface of the substrate. Fig. 8 is a plan view of an optical waveguide element 1F in the sixth embodiment of the present invention. The same components as those in the above-described embodiments will be denoted by the same reference numerals and descriptions thereof will be simplified or omitted.

[0117] The optical waveguide element 1F of the sixth embodiment has a substrate 2 having an electro-optic effect. The substrate 2 is formed with a Mach-Zehnder optical waveguide having a folded portion as the optical waveguide 3. The Mach-Zehnder optical waveguide formed on the substrate 2 of the optical waveguide element 1F has a shape similar to that of the optical waveguide element 1A described above. As shown in Fig. 8, four branch waveguides 31, 32, 41, and 42 are folded back at folding portions B1, B2, B3, and B4, respectively.

[0118] In addition to the actual patterns, a dummy pattern 160 is formed on the substrate 2 of the optical waveguide element 1F.

[0119] The dummy pattern 160 is formed between adjacent extending real patterns and is formed inside the outer periphery of the Mach-Zehnder optical waveguide having a folded portion. In the optical waveguide element 1F shown in Fig. 8, the dummy pattern 160 is formed in the region sandwiched between the output optical waveguide 70 and the output optical waveguide 80 constituting the optical output portion, the region sandwiched between the branch waveguide 32 and the branch waveguide 41, and the region sandwiched between the branch waveguide 21 and the branch waveguide 22.

[0120] The dummy pattern 160 is composed of a linear portion 161. As shown in Fig. 8, the linear portion 161 is formed so as to bend at approximately 90° at bending portions 161b and 161c in accordance with the shape of the folded portion of the Mach-Zehnder optical waveguide.

[0121] The end of the dummy pattern 160 may be provided on an end surface of the substrate 2 or on the upper surface of the substrate 2. Here, one end 161a of the linear portion 161 constituting the dummy pattern 160 is disposed between the branching waveguide 21 and the branching waveguide 22 and is provided on the upper surface of the substrate 2. On the other hand, the other end 161d of the linear portion 161 is disposed between the optical output terminal 70a and the optical output terminal 80a and is provided on the end surface of the substrate 2.

[0122] In this way, by forming the dummy pattern 160 in the region between adjacently extending optical waveguides 3, it is possible to isolate the adjacent optical waveguides 3 and also to capture the leaked light from the optical waveguides 3 and guide it to the outside or absorb it by the dummy pattern 160. As a result, it is possible to suppress optical crosstalk, in which leaked light from one optical waveguide 3 mixes with and interferes with another optical waveguide 3.

[0123] Furthermore, the dummy pattern 160 having the function of suppressing optical crosstalk may be used as an inspection pattern for inspecting the characteristics of the optical waveguide element 1F.

[0124] The Mach-Zehnder optical waveguide formed in the optical waveguide element 1F has a folded portion formed by arranging two bending portions that are bent at approximately 90 degrees. The dummy pattern 160 also has bending portions 161b and 161c that are bent at approximately 90 degrees, and the number of bending portions is set to be the same as that of the optical waveguide 3, which is the actual pattern.

[0125] One end 161a of the linear portion 161 can be configured to allow light input from, for example, a grating. Light input from one end 161a of the linear portion 161 propagates through the linear portion 161 having the bent portions 161b and 161c, and is output from the other end 161d of the linear portion 161. By measuring the light output from the other end 161d, it is possible to estimate the bending loss in the optical waveguide 3, which is the actual pattern.

[0126] Seventh Embodiment A seventh embodiment of the present invention will be described. In the seventh embodiment, an aspect in which a plurality of dummy patterns are provided will be illustrated. Fig. 9 is a plan view of an optical waveguide element 1G according to the seventh embodiment of the present invention. The same components as those in the above-described embodiments will be denoted by the same reference numerals and descriptions thereof will be simplified or omitted.

[0127] The optical waveguide element 1G of the seventh embodiment has a substrate 2 having an electro-optic effect. A Mach-Zehnder optical waveguide having a folded portion is formed on the substrate 2 as the optical waveguide 3. The Mach-Zehnder optical waveguide formed on the substrate 2 of the optical waveguide element 1G has a shape similar to that of the optical waveguide element 1A described above. As shown in Fig. 9, four branch waveguides 31, 32, 41, and 42 are configured to be folded back at folding portions B1, B2, B3, and B4, respectively.

[0128] In addition to the actual patterns, dummy patterns 170 and 173 are formed on the substrate 2 of the optical waveguide element 1G.

[0129] The dummy pattern 170 is formed between adjacent extending real patterns, and is formed inside the outer periphery of the Mach-Zehnder optical waveguide having the folded portion. In the optical waveguide device 1G shown in Fig. 9, the dummy pattern 170 is formed in the region surrounded by the input optical waveguide 10, the branching waveguides 21 and 31, and the output optical waveguide 70 (the region on the inner periphery of the curve formed by the folded portion).

[0130] The dummy pattern 173 is formed between adjacent extending real patterns and is formed inside the outer periphery of the Mach-Zehnder optical waveguide having a folded portion. In the optical waveguide device 1G shown in Fig. 9, the dummy pattern 173 is formed in a region sandwiched between the output optical waveguide 70 and the output optical waveguide 80 that constitute the optical output portion.

[0131] In this way, by forming the dummy patterns 170, 173 in the region between adjacently extending optical waveguides 3, the adjacent optical waveguides 3 can be isolated from each other, and the dummy patterns 170, 173 can capture leaked light from the optical waveguides 3 and guide it to the outside or absorb it. As a result, optical crosstalk, in which leaked light from one optical waveguide 3 mixes with and interferes with the other optical waveguide 3, can be suppressed. The dummy pattern 170 can suppress optical crosstalk between the input optical waveguide 10 and the output optical waveguide 70. The dummy pattern 173 can suppress optical crosstalk between the output optical waveguide 70 and the output optical waveguide 80.

[0132] Furthermore, the dummy patterns 170 and 173 having the function of suppressing optical crosstalk may be used as inspection patterns for inspecting the characteristics of the optical waveguide device 1G.

[0133] 9 , the dummy pattern 170 has a linear portion 171 extending in a substantially straight line from one end 171 a, a linear portion 172 extending in a substantially straight line from the other end 172 a, and a substantially U-shaped folded portion C7 a connecting the linear portion 171 and the linear portion 172. The one end 171 a and the other end 172 a of the dummy pattern 170 are provided between the optical input terminal 10 a and the optical output terminal 70 a, and are formed on the same side of the substrate 2.

[0134] 9 , the dummy pattern 173 has a linear portion 174 extending in a substantially straight line from one end 174a, a linear portion 175 extending in a substantially straight line from the other end 175a, and a substantially U-shaped folded portion C7b connecting the linear portion 174 and the linear portion 175. The one end 174a and the other end 175a of the dummy pattern 173 are provided between the light output terminal 70a and the light output terminal 80a, and are formed on the same side of the substrate 2.

[0135] When the dummy patterns 170 and 173 are used as test patterns, the basic characteristics of the optical waveguide 3 can be evaluated. The multiple dummy patterns 170 and 173 may be set under different conditions. For example, by setting the multiple dummy patterns 170 and 173 to different waveguide lengths, it is possible to calculate the propagation loss of light that depends on the waveguide length. Furthermore, the multiple dummy patterns 170 and 173 may have the same waveguide length but different input and output terminal structures. For example, if one end 171 a of one dummy pattern 170 has an SSC structure and one end 174 a of the other dummy pattern 173 has a grating structure, it is possible to predict the coupling loss of the SSC and the grating.

[0136] 9, the dummy pattern 170 is formed so as to be line-symmetrical with respect to the center line S1 of the folded portion of the actual pattern. By forming the dummy pattern 170 so as to be line-symmetrical with respect to the center line S1 in this manner, the bias in the pattern density can be alleviated in a balanced manner, and the bias in the pattern density can be reduced. As a result, when manufacturing the optical waveguide element 1G, variations in the processing depth during etching due to the microloading effect are suppressed, and the characteristics of the optical waveguide element 1G can be expected to be stabilized.

[0137] Eighth Embodiment An eighth embodiment of the present invention will be described. In the eighth embodiment, an example will be described in which a test pattern including a test waveguide and a test electrode is used as a dummy pattern. Fig. 10 is a plan view of an optical waveguide element 1H according to the eighth embodiment of the present invention. The same components as those in the above-described embodiments will be described briefly or omitted, and the same reference numerals will be used.

[0138] The optical waveguide element 1H of the eighth embodiment has a substrate 2 having an electro-optic effect. A Mach-Zehnder optical waveguide having a folded portion is formed on the substrate 2 as the optical waveguide 3. The Mach-Zehnder optical waveguide formed on the substrate 2 of the optical waveguide element 1H has a shape similar to that of the optical waveguide element 1A described above. As shown in Fig. 10, four branch waveguides 31, 32, 41, and 42 are folded back at folding portions B1, B2, B3, and B4, respectively.

[0139] In addition to the actual patterns, dummy patterns 180, 183a, 183b, and 183c are formed on the substrate 2 of the optical waveguide element 1H.

[0140] The dummy pattern 180 has a function of propagating light waves as a test waveguide. As shown in Fig. 10 , the dummy pattern 180 has a linear portion 181 extending in a substantially straight line from one end 181a, a linear portion 182 extending in a substantially straight line from the other end 182a, and a substantially U-shaped folded portion C8 connecting the linear portion 181 and the linear portion 182. The one end 181a and the other end 182a of the dummy pattern 180 are provided between the optical input terminal 10a and the optical output terminal 70a, and are formed on the same side of the substrate 2.

[0141] On the other hand, dummy patterns 183a, 183b, and 183c function as inspection electrodes that modulate light waves by applying a high-frequency electrical signal to dummy pattern 180. Dummy patterns 183a, 183b, and 183c as inspection electrodes are arranged so as to sandwich linear portion 181 and linear portion 182 that constitute dummy pattern 180, as shown in FIG.

[0142] The dummy pattern 180 serving as the inspection waveguide can be configured, for example, by a convex portion formed on the substrate 2. The dummy patterns 183a, 183b, and 183c serving as the inspection electrodes are made of a metal material such as gold or copper that is used as an electrode.

[0143] The dummy pattern 180 may be formed on the substrate 2 by providing a convex portion (convex portion 180a in FIG. 11 ) that protrudes from the surface of the substrate 2, as shown in the cross-sectional view of FIG. 11 . Alternatively, the dummy pattern 180 may be formed on the substrate 2 by forming grooves 180b on both sides of a portion corresponding to the dummy pattern 180 and providing a convex portion (convex portion 180c in FIG. 12 ) that is sandwiched between the grooves 180b, as shown in the cross-sectional view of FIG. 12 . The three dummy patterns 183a, 183b, and 183c are provided at positions adjacent to the convex portions (convex portion 180a or convex portion 180c) of the two linear portions 181 and 182, as shown in FIGS. 11 and 12 , and are arranged so as to sandwich the linear portions 181 and 182.

[0144] When the dummy patterns 180, 183a, 183b, and 183c are used as test patterns, it is possible to perform a characteristic test (for example, measurement of absorption loss by electrodes) related to the modulation operation of the optical waveguide element 1H. It is preferable to set the positional relationship and separation distance between the test waveguide and the test electrode so that they are the same as the positional relationship and separation distance between the active parts of the actual pattern that actually performs the modulation operation.

[0145] The dummy patterns 180, 183a, 183b, and 183c are arranged to isolate adjacent optical waveguides 3, which also has the effect of suppressing optical crosstalk. Furthermore, the dummy pattern 180 is formed so as to be symmetrical with respect to the center line S1 of the folded portion of the actual pattern, as shown in Fig. 10, which also has the effect of suppressing the microloading effect.

[0146] Ninth Embodiment A ninth embodiment of the present invention will be described. In the ninth embodiment, an aspect in which a plurality of test patterns are provided as dummy patterns will be illustrated. Fig. 13 is a plan view of an optical waveguide element 1I according to the ninth embodiment of the present invention. Descriptions of configurations similar to those of the above-described embodiments will be simplified or omitted, and the same reference numerals will be used.

[0147] The optical waveguide element 1I of the ninth embodiment has a substrate 2 having an electro-optic effect. A Mach-Zehnder optical waveguide having a folded portion is formed on the substrate 2 as the optical waveguide 3. The Mach-Zehnder optical waveguide formed on the substrate 2 of the optical waveguide element 1I has a shape similar to that of the optical waveguide element 1A described above. As shown in Fig. 13, four branch waveguides 31, 32, 41, and 42 are configured to be folded back at folding portions B1, B2, B3, and B4, respectively.

[0148] In addition to the actual patterns, dummy patterns 180, 183a, 183b, and 183c are formed on the substrate 2 of the optical waveguide element 11. The dummy patterns 180, 183a, 183b, and 183c have the same configuration as in the eighth embodiment described above, and can be used as test patterns.

[0149] In addition to the dummy patterns 180, 183a, 183b, and 183c, dummy patterns 190, 193a, 193b, and 193c that can be used as inspection patterns are formed on the substrate 2 of the optical waveguide element 1I.

[0150] The dummy pattern 190 has a function of propagating light waves as a test waveguide. As shown in Fig. 13, the dummy pattern 190 has a linear portion 191 extending in a substantially straight line from one end 191a, a linear portion 192 extending in a substantially straight line from the other end 192a, and a substantially U-shaped folded portion C9 connecting the linear portion 191 and the linear portion 192. The one end 191a and the other end 192a of the dummy pattern 190 are provided between the optical output terminal 70a and the optical output terminal 80a, and are formed on the same side of the substrate 2.

[0151] On the other hand, dummy patterns 193a, 193b, and 193c function as inspection electrodes that modulate light waves by applying a high-frequency electrical signal to dummy pattern 190. Dummy patterns 193a, 193b, and 193c as inspection electrodes are arranged so as to sandwich linear portion 191 and linear portion 192 that constitute dummy pattern 190, as shown in FIG.

[0152] Dummy patterns 194, 195, 196a, 196b, and 196c that can be used as inspection patterns are further formed on the substrate 2 of the optical waveguide element 1I.

[0153] The dummy patterns 194, 195 have the function of propagating light waves as test waveguides. As shown in Fig. 13, the dummy patterns 194, 195 are formed to extend substantially parallel to each other between the output optical waveguide 70 and the output optical waveguide 80. Both ends of the dummy patterns 194, 195 are designed to allow light to be input and output from the top surface of the substrate 2.

[0154] On the other hand, dummy patterns 196a, 196b, and 196c function as inspection electrodes that modulate light waves by applying high-frequency electrical signals to dummy patterns 194 and 195. Dummy patterns 196a, 196b, and 196c as inspection electrodes are arranged so as to sandwich dummy patterns 194 and 195 therebetween, as shown in FIG.

[0155] In this way, by providing a plurality of test patterns including test waveguides and test electrodes, it is possible to perform characteristic tests (particularly, measurement of the electrical band) related to the modulation operation of the optical waveguide element 11. Although it depends on the measurement method, when measuring the electrical band, it is preferable to use a two-stage electrode configuration.

[0156] The dummy patterns 180, 183a, 183b, 183c, dummy patterns 190, 193a, 193b, 193c, and dummy patterns 194, 195, 196a, 196b, 196c are all arranged to isolate adjacent optical waveguides 3, which also has the effect of suppressing optical crosstalk. Furthermore, the dummy pattern 180 is formed so as to be symmetrical with respect to the center line S1 of the folded portion of the actual pattern, as shown in FIG. 13, which also has the effect of suppressing the microloading effect.

[0157] (Tenth Embodiment) A tenth embodiment of the present invention will be described. In the tenth embodiment, an example will be illustrated in which dummy patterns that can be used as test patterns and dummy patterns that cannot be used as test patterns are mixed. Fig. 14 is a plan view of an optical waveguide element 1J in the tenth embodiment of the present invention. Descriptions of configurations similar to those of the above-described embodiments will be simplified or omitted, and the same reference numerals will be used.

[0158] The optical waveguide element 1J in the tenth embodiment has a substrate 2 having an electro-optic effect. The substrate 2 is formed with a Mach-Zehnder optical waveguide having a folded portion as the optical waveguide 3. The Mach-Zehnder optical waveguide formed on the substrate 2 of the optical waveguide element 1J has a shape similar to that of the optical waveguide element 1A described above. As shown in Fig. 14, four branch waveguides 31, 32, 41, and 42 are folded back at folding portions B1, B2, B3, and B4, respectively.

[0159] In addition to the actual pattern, a dummy pattern 200 and dummy patterns 211, 212, and 213 are formed on the substrate 2 of the optical waveguide element 1J.

[0160] The dummy pattern 200 is formed between adjacent extending real patterns, and is formed inside the outer periphery of the Mach-Zehnder optical waveguide having the folded portion. In the optical waveguide element 1J shown in Fig. 14, the dummy pattern 200 is formed in the region surrounded by the input optical waveguide 10, the branching waveguides 21 and 31, and the output optical waveguide 70 (the region on the inner periphery of the curve formed by the folded portion).

[0161] 14, the dummy pattern 200 has a linear portion 201 extending in a substantially straight line from one end 201a, a linear portion 202 extending in a substantially straight line from the other end 202a, and a substantially U-shaped folded portion C10 connecting the linear portion 201 and the linear portion 202. The one end 201a and the other end 202a of the dummy pattern 200 are provided between the optical input terminal 10a and the optical output terminal 70a, and are formed on the same side of the substrate 2.

[0162] 14, the dummy pattern 211 is formed to extend substantially linearly between the branching waveguides 21 and 22. The dummy patterns 212 and 213 are formed to extend substantially parallel to each other between the output optical waveguides 70 and 80.

[0163] The dummy pattern 200 is arranged to isolate adjacent optical waveguides 3, and has the effect of suppressing optical crosstalk. Furthermore, the dummy pattern 200 is configured to be able to propagate light waves as a test waveguide, and can be used as a test pattern for inspecting the characteristics of the optical waveguide element 1J.

[0164] The dummy patterns 211, 212, and 213 are also arranged to isolate adjacent optical waveguides 3, and have the effect of suppressing optical crosstalk. However, the dummy patterns 211, 212, and 213 are not configured to be able to propagate light waves as test waveguides, and therefore cannot be used as test patterns for inspecting the characteristics of the optical waveguide element 1J.

[0165] In this way, the optical waveguide element 1J may include a mixture of the dummy pattern 200 that can be used as an inspection pattern and the dummy patterns 211, 212, and 213 that can also be used as inspection patterns.

[0166] An optical modulator and an optical transmitter according to the present invention will be described below. Fig. 15 is a plan view showing an optical modulator 300 and an optical transmitter 400 according to the present invention. The present invention can provide an optical modulator and an optical transmitter using the optical waveguide elements 1A to 1J in each of the above-described embodiments. Note that Fig. 15 shows, as an example, an optical modulator 300 and an optical transmitter 400 having the optical waveguide element 1A in the first embodiment.

[0167] An optical modulator 300 shown in Fig. 15 includes an optical waveguide element 1A, a housing 301, an input optical fiber 302, and an output optical fiber 303. Although not shown in Fig. 15, a modulation electrode, a bias electrode, and the like for modulating an optical signal are provided on the substrate 2 of the optical waveguide element 1A.

[0168] In the optical modulator 300, an optical waveguide element 1A is housed in a housing 301. An input optical fiber 302 is connected to the optical input portion of the optical waveguide element 1A, and an output optical fiber 303 is connected to the optical output portion. In this manner, by connecting the optical waveguide element 1A in the housing 301 to the outside of the housing 301 with an optical fiber, a compact optical modulator 300 can be provided. Note that a spatial optical system may be interposed between the optical input portion and optical output portion of the optical waveguide element 1A and the input optical fiber 302 and output optical fiber 303. Furthermore, the above-described optical waveguide element 1A has two optical output ends 70a, 80a. In this case, the optical modulator 300 may have a polarization combining unit 304 and be configured to polarization combine light output from the two optical output ends 70a, 80a and guide the combined light to the output optical fiber 303.

[0169] 15 , an optical transmitting device 400 can be configured by connecting an electronic circuit 401 that generates a modulated signal (electrical signal), which is a high-frequency signal for performing a modulation operation, to the optical modulator 300. An amplifier circuit 402 may be provided to amplify the modulated signal generated by the electronic circuit 401. The electronic circuit 401 and the amplifier circuit 402 may be disposed outside the housing 301 of the optical modulator 300, but disposing them inside the housing 301 can achieve efficient transmission of the modulated signal and a compact optical transmitting device 400.

[0170] Furthermore, the optical transmitter 400 may be configured to include a light source, and the light emitted by the light source may be input to the optical input section of the optical waveguide element 1 A. In this way, the light output from the light source is modulated by the optical modulator 300, and the modulated light can be output from the optical transmitter 400.

[0171] The above-described embodiments are provided to facilitate understanding of the present invention and are not intended to limit the present invention. The components disclosed in the above-described embodiments are intended to encompass all design modifications and equivalents that fall within the technical scope of the present invention. Furthermore, the present invention also encompasses technical ideas obtained by appropriately combining the concepts exemplified in the respective embodiments.

[0172] 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H, 1I, 1J Optical waveguide element 2 Substrate 3 Optical waveguide 3a, 3c, 110a, 110c, 180a, 180c Convex portion 3b, 110b, 180b Groove 4 Support substrate (reinforcing substrate) 10 Input optical waveguide 10a Optical input end 20 Parent branching section 21 Branching waveguide (first parent branching waveguide) 22 Branching waveguide (second parent branching waveguide) 31 Branching waveguide (first child branching waveguide) 32 Branching waveguide (second child branching waveguide) 41 Branching waveguide (third child branching waveguide) 42 Branching waveguide (fourth child branching waveguide) 30 First child branching section 40 Second child branching section 50 First child multiplexing section (first multiplexing section) 60 Second child multiplexing section (second multiplexing section) 70 Output optical waveguide (first output optical waveguide) 70a, 80a, 80b Optical output end 80 Output optical waveguide (second output optical waveguide) 110,120,130,140,150,160,170,173,180,183a,183b,183c,190,193a,193b,193c,194,195,196a,196b,196c,200,211,212,213 Dummy pattern 111, 112, 121, 122, 131, 132, 141, 142, 151, 152, 153, 154, 156, 161, 171, 172, 174, 175, 181, 182, 191, 192, 201, 202 Linear portions 111a, 121a, 131a, 141a, 161a, 171a, 174a, 181a, 191a, 201a One end portion 112a, 122a, 132a, 142a, 161d, 172a, 175a, 182a, 192a, 202a Other end portion 131b, 132b, 161b, 161c Bent portions 151a, 156a End portion 152 First connection section 155 Second connection section 300 Optical modulator 301 Housing 302 Input optical fiber 303 Output optical fiber 304 Polarization combining section 400 Optical transmitter 401 Electronic circuit 402 Amplification circuit B1, B2, B3, B4, C1, C2, C3, C4, C5a, C5b, C7a, C7b, C8, C9, C10 Folded section S1 Center line

Claims

1. An optical waveguide element in which an optical waveguide is formed on a substrate having an electro-optical effect, the optical waveguide being configured to include a Mach-Zehnder type optical waveguide having a turning portion, and a dummy pattern capable of suppressing optical crosstalk being formed in a region between the adjacent and extending optical waveguides.

2. The optical waveguide element according to claim 1, wherein the dummy pattern is formed in a region between an optical waveguide constituting an optical input portion and an optical waveguide constituting an optical output portion.

3. The optical waveguide element according to claim 1, wherein the dummy pattern is formed in a region between a plurality of optical waveguides constituting an optical output portion.

4. The optical waveguide element according to any one of claims 1 to 3, wherein an input end and an output end of the dummy pattern are provided on an end face or an upper surface of the substrate.

5. The optical waveguide element according to any one of claims 1 to 3, wherein the dummy pattern has a turning portion.

6. The optical waveguide element according to claim 5, wherein an optical input end and an optical output end of the Mach-Zehnder type optical waveguide, and an input end and an output end of the dummy pattern are formed on the same side of the substrate.

7. The Mach-Zehnder type optical waveguide has, between an optical input portion including an input optical waveguide and an optical output portion including first and second output optical waveguides, a main branching portion that branches a light wave propagating through the input optical waveguide and propagates it to first and second main branching waveguides, a first sub-branching portion that branches a light wave propagating through the first main branching waveguide and propagates it to first and second sub-branching waveguides, a first combining portion that combines light waves propagating through the first and second sub-branching waveguides and propagates them to the first output optical waveguide, a second sub-branching portion that branches a light wave propagating through the second main branching waveguide and propagates it to third and fourth sub-branching waveguides, and a second combining portion that combines light waves propagating through the third and fourth sub-branching waveguides and propagates them to the second output optical waveguide, and the first to fourth sub-branching waveguides each have the turning portion. The optical waveguide element according to any one of claims 1 to 3.

8. The dummy pattern is formed at least in a region between a plurality of optical waveguides constituting the light output unit, and has a folded-back portion in any one of a region between the first parent branch waveguide and the second parent branch waveguide adjacent to each other, a region between the second child branch waveguide and the third child branch waveguide adjacent to each other, and a region between the first output optical waveguide and the second output optical waveguide adjacent to each other. The optical waveguide element according to claim 7.

9. The optical waveguide element according to claim 8, wherein the first output optical waveguide and the second output optical waveguide are substantially linear.

10. The dummy pattern is formed to be line-symmetric with respect to the center line of the folded-back portion of the Mach-Zehnder type optical waveguide. The optical waveguide element according to any one of claims 1 to 3.

11. The dummy pattern is formed to have a portion that runs substantially parallel to the optical waveguide while maintaining a certain distance from the optical waveguide. The optical waveguide element according to any one of claims 1 to 3.

12. An optical modulator comprising: the optical waveguide element according to any one of claims 1 to 3; a housing that houses the optical waveguide element; an input optical fiber connected to the light input unit of the optical waveguide element; and an output optical fiber connected to the light output unit of the optical waveguide element.

13. An optical transmission device comprising: the optical modulator according to claim 12; and an electronic circuit that generates an electrical signal for causing the optical waveguide element to perform a modulation operation.

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