Optical modulation element, optical modulator, optical modulation module, optical transmission device, and optical transmission system

Abstract

The utility model provides an optical modulation element, an optical modulator, an optical modulation module, an optical transmission device and an optical transmission system. Good optical characteristics can be achieved in the optical modulation element using a convex optical waveguide and segmented electrodes as modulation electrodes. The light modulation element includes: a substrate including a multilayer portion configured as a plurality of layers; an optical waveguide is formed on the optical waveguide layer of the multi-layer part; and a modulation electrode formed by being divided into a plurality of segments along the propagation direction of the light of the optical waveguide, and the interval (L) between the adjacent segments measured in the direction of extension of the optical waveguide is constant. The multilayer portion of the substrate includes an optical waveguide layer, a first support layer in contact with a lower surface of the optical waveguide layer, and a second support layer in contact with a lower surface of the first support layer, and a refractive index n0 of the optical waveguide layer, a refractive index n1 of the first support layer, and a refractive index n2 of the second support layer have relationships of n0 > n1 and n2 > n1.

Description

Technical Field

[0001] The present utility model relates to an optical modulation element, an optical modulator, an optical modulation module, an optical transmission device, and an optical transmission system. Background Art

[0002] In high-speed / high-capacity optical fiber communication systems, optical modulators assembled with optical modulation elements as optical waveguide elements are often used. The optical modulation elements as optical waveguide elements are composed of optical waveguides formed on semiconductor substrates such as InP or substrates with electro-optic effects such as LiNbO3 (hereinafter also referred to as LN), and control electrodes for controlling the light waves propagating in the optical waveguides. Among them, optical modulation elements using LN substrates are widely used in high-speed / high-capacity optical fiber communication systems because of their low light loss and wide-band optical modulation characteristics.

[0003] In recent years, in order to miniaturize the optical modulator itself while achieving further low-voltage driving and high-speed modulation, optical modulators using rib-type optical waveguides or ridge-type optical waveguides (hereinafter collectively referred to as convex optical waveguides) are also being put into practical use. The rib-type optical waveguide or ridge-type optical waveguide is formed by forming a strip-shaped convex portion on the surface of a thinned (or sheet-thinned) LN substrate (for example, with a thickness of 20 μm or less) in order to further enhance the interaction between the signal electric field in the substrate and the waveguide light.

[0004] In addition, in recent years, as a coplanar type modulation electrode, a so-called segmented electrode that divides the electrode into multiple segments along the light propagation direction of the optical waveguide has been proposed to achieve impedance matching between the modulation electrode and the drive circuit and speed integration of the high-frequency propagation speed in the modulation electrode and the light propagation speed in the optical waveguide (Patent Document 1, Patent Document 2, Patent Document 3).

[0005] [Prior Art Documents]

[0006] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2022-148652

[0008] [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-194544

[0009] [Patent Document 3] Japanese Patent Application Laid-Open No. 2020-181173 Summary of the Utility Model

[0010] [Problems to be Solved by the Utility Model]

[0011] The inventors of the present application have found that there is a problem in a convex optical waveguide provided with a segmented electrode as a modulation electrode: even if the convex portions (i.e., ribs or ridges) constituting the optical waveguide are formed with high precision in a wafer process, deviations occur in optical characteristics such as modulation extinction ratio. The factors or solutions to this problem have not been found for a long time.

[0012] An object of the present utility model is to achieve good optical characteristics in an optical modulation element using a convex optical waveguide and a segmented electrode as a modulation electrode.

[0013] [Technical means for solving the problem]

[0014] One aspect of the present utility model is an optical modulation element, including: a substrate including a multilayer portion configured as multiple layers; an optical waveguide layer of the multilayer portion of the substrate, on which an optical waveguide is formed; and a modulation electrode, which is an electrode formed on the optical waveguide layer for controlling light waves propagating in the optical waveguide and is formed by being divided into multiple segments along the light propagation direction of the optical waveguide. In the entire interval or an interval except a part of the electrode, the intervals L measured in the extending direction of the optical waveguide between adjacent segments are constant. The multilayer portion of the substrate includes the optical waveguide layer, a first support layer in contact with the lower surface of the optical waveguide layer, and a second support layer in contact with the lower surface of the first support layer. The refractive index n0 of the optical waveguide layer, the refractive index n1 of the first support layer, and the refractive index n2 of the second support layer have a relationship of n0 > n1 and n2 > n1.

[0015] According to another aspect of the present utility model, the interval L has a relationship of L > 4 × λ / n1 with respect to the wavelength λ of the light wave propagating in the optical waveguide and the refractive index n1 of the first support layer.

[0016] According to another aspect of the present utility model, the thickness t1 of the first support layer has a relationship of t1 < 10 × λ / n1 with respect to the wavelength λ of the light wave propagating in the optical waveguide and the refractive index n1 of the first support layer.

[0017] According to another aspect of the present utility model, the multilayer portion of the substrate further includes a third support layer in contact with the lower surface of the second support layer. The refractive index n0 of the optical waveguide layer, the refractive index n1 of the first support layer, the refractive index n2 of the second support layer, and the refractive index n3 of the third support layer have a relationship of n0 > n1 and n3 > n2 > n1.

[0018] According to another aspect of the present utility model, an absorbing material is disposed on the back surface of the substrate facing the surface of the optical waveguide layer, and the absorbing material absorbs light in the wavelength band of the light wave propagating in the optical waveguide.

[0019] According to another aspect of the present invention, the light-absorbing material is a carbon material, a black resin, or a metal filler.

[0020] According to another aspect of the present invention, the substrate is formed by laminating a plurality of plate bodies, and each of the plate bodies includes one layer or any number of layers selected from the group consisting of the optical waveguide layer and a plurality of support layers including the first support layer and the second support layer.

[0021] Another aspect of the present invention is an optical modulator, including: the optical modulation element according to any one of the above; a housing that houses the optical modulation element; an optical fiber that inputs light to the optical modulation element; and an optical fiber that guides the light output from the optical modulation element to the outside of the housing.

[0022] Another aspect of the present invention is an optical modulation module, including: the optical modulation element according to any one of the above; a housing that houses the optical modulation element; an optical fiber that inputs light to the optical modulation element; an optical fiber that guides the light output from the optical modulation element to the outside of the housing; and a drive circuit that drives the optical modulation element.

[0023] Another aspect of the present invention is an optical transmission device, including: the optical modulator or the optical modulation module; and an electronic circuit that generates an electrical signal for causing the optical modulation element to perform a modulation operation.

[0024] Another aspect of the present invention is an optical transmission system, including: the optical transmission device; and an optical fiber transmission path that transmits the output light of the optical modulation element.

[0025] [Effects of the Utility Model]

[0026] By the present invention, in an optical modulation element using a convex optical waveguide and a segmented electrode as a modulation electrode, good optical characteristics can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 FIG. is a diagram showing the structure of an optical modulator using the optical modulation element of the first embodiment of the present invention.

[0028] Figure 2 FIG. is a plan view of the optical modulation element of the first embodiment.

[0029] Figure 3 FIG. is Figure 2 a side view of the optical modulation element shown.

[0030] Figure 4 FIG. is showing Figure 2 the structure of the modulation section of the optical modulation element shown.

[0031] Figure 5 of (A), Figure 5 of (B) is Figure 4 the V-V sectional view of the modulation section shown in the figure.

[0032] Figure 6 is a side view of the optical modulation element of the second embodiment.

[0033] Figure 7 of (A), Figure 7 of (B) is the sectional view of the modulation section of the optical modulation element of the second embodiment.

[0034] Figure 8 is a side view of the optical modulation element of the third embodiment.

[0035] Figure 9 is the sectional view of the modulation section of the optical modulation element of the third embodiment.

[0036] Figure 10 is a diagram showing the structure of the optical modulation module of the fourth embodiment.

[0037] Figure 11 is a diagram showing the structure of the optical transmission device of the fifth embodiment.

[0038] Figure 12 is a diagram showing the structure of the optical transmission system of the sixth embodiment.

[0039] Figure 13 is a plan view showing an example of an existing optical modulation element.

[0040] Figure 14 is Figure 13 the XIV-XIV sectional view of the existing optical modulation element shown in the figure.

[0041] Figure 15 is Figure 13 the XV-XV sectional view of the existing optical modulation element shown in the figure.

[0042] [Explanation of reference numerals]

[0043] 1a, 1b, 1c, 90: Optical modulation element

[0044] 2: Optical modulator

[0045] 3: Housing

[0046] 4: Relay substrate

[0047] 5a, 5b: Signal pins

[0048] 6a: Input optical fiber

[0049] 6b: Output optical fiber

[0050] 7a, 7b: Support members

[0051] 8a, 8b, 8c: Lenses

[0052] 9: Optical unit

[0053] 10: Terminator

[0054] 20a, 20b: Substrates

[0055] 21a, 21b, 21c, 21d: Sides

[0056] 22: Optical waveguide layer

[0057] 23a, 23b: Support layers

[0058] 23a1: First support layer

[0059] 23a2: Second support layer

[0060] 23a3: Third support layer

[0061] 24, 91: Optical substrates

[0062] 25a, 25b, 94: Support substrates

[0063] 26: Optical waveguide

[0064] 27: Input waveguide

[0065] 28: Branch waveguide

[0066] 29a, 29b: Nested Mach-Zehnder type optical waveguides

[0067] 30: Return region

[0068] 31a, 31b: Output waveguides

[0069] 32, 32a, 32b, 32c, 32d, 92: Mach-Zehnder type optical waveguides

[0070] 33a, 33b, 33c: Bias electrodes

[0071] 34, 34a, 34b, 34c, 34d: Modulation sections

[0072] 35: Wire bonding

[0073] 36, 36a1, 36a2, 92a, 92b: Arm waveguides

[0074] 40, 40a, 40b, 93a, 93b: Modulation electrodes

[0075] 40a1, 40b1, 93a1, 93b1: Thermal electrodes

[0076] 40a2, 40b2, 93a2, 93b2: Ground electrodes

[0077] 41a, 96a: Heat transfer paths

[0078] 41b, 41c, 96b, 96c: Ground transfer paths

[0079] 42: Back surface

[0080] 43: Light-absorbing material

[0081] 50: Optical modulation module

[0082] 51: Circuit board

[0083] 52: Driving circuit

[0084] 55: Optical transmission device

[0085] 56: Light source

[0086] 57: Modulator driving section

[0087] 58: Modulation signal generation section

[0088] 60: Optical transmission system

[0089] 61: Optical fiber transmission path

[0090] 62: Optical receiving device Detailed implementation manners

[0091] The inventors of the present application have made diligent studies on the optical property deviation of a convex optical waveguide provided with segmented electrodes as modulation electrodes, and obtained the following insights: The factor of this deviation is the interference of the leakage light generated from the convex optical waveguide at the positions of the respective gap portions between the segments (each part of the electrode divided at regular intervals) constituting the segmented electrodes.

[0092] Figure 13 , Figure 14 , Figure 15 are explanatory diagrams for explaining the factors of the optical property deviation in the existing optical modulation element. Figure 13 is a plan view of an optical modulation element composed of a convex optical waveguide provided with segmented electrodes as modulation electrodes, Figure 14 is Figure 13 a sectional arrow view of the optical modulation element shown in Figure 15 is Figure 13 a sectional arrow view of the optical modulation element shown in

[0093] Refer to Figure 13 , Figure 14 ,Figure 15 , as an example, an existing optical modulation element 90 includes: a Mach-Zehnder type optical waveguide 92 formed on one main surface (upper surface) of an optical substrate 91 which is an LN substrate having a thickness of several micrometers to several tens of micrometers and is composed of a convex optical waveguide; and modulation electrodes 93a and 93b for controlling light waves propagating in each of the two arm waveguides 92a and 92b of the Mach-Zehnder type optical waveguide 92. The other main surface (lower surface) of the optical substrate 91 is joined to a support substrate 94 (see Figure 14 , Figure 15 ). The support substrate 94 is generally a glass plate having a refractive index lower than that of the optical substrate 91.

[0094] The modulation electrode 93a has a heating electrode 93a1 and a ground electrode 93a2 facing each other across the arm waveguide 92a within the main surface of the optical substrate 91. Similarly, the modulation electrode 93b has a heating electrode 93b1 and a ground electrode 93b2 facing each other across the arm waveguide 92b within the main surface of the optical substrate 91.

[0095] The modulation electrodes 93a and 93b are each configured as segmented electrodes divided into a plurality of parts along the light propagation directions of the arm waveguides 92a and 92b, respectively. Specifically, the heating electrode 93a1 and the ground electrode 93a2 constituting the modulation electrode 93a are each divided into a plurality of parts (segments) of the same length along the light propagation direction of the arm waveguide 92a. In addition, the heating electrode 93b1 and the ground electrode 93b2 constituting the modulation electrode 93b are each divided into a plurality of segments of the same length along the light propagation direction of the arm waveguide 92b, and have a structure in which the gaps between the segments are arranged at regular intervals.

[0096] Moreover, the segments of the heating electrode 93a1 and the heating electrode 93b1 are electrically connected to each other through a heat transfer path 96a. In addition, the segments of the ground electrode 93a2 are electrically connected to each other through a ground transfer path 96b, and the segments of the ground electrode 93b2 are electrically connected to each other through a ground transfer path 96c. Thus, the heating electrodes 93a1 and 93b1 connected to each other through the heat transfer path 96a, the ground electrode 93a2 connected to the ground transfer path 96b, and the ground electrode 93b2 connected to the ground transfer path 96c together constitute a coplanar type electrode.

[0097] Moreover, as Figure 15As shown in the cross-sectional view taken along line XV-XV, in the arm waveguide 92a, when a high-frequency signal is transmitted to the modulation electrode 93a, for example, at a portion where the segments of the thermal electrode 93a1 face the segments of the ground electrode 93a2, by applying an electric field to the arm waveguide 92a, the refractive index changes (e.g., increases) by Δn from the refractive index na of the optical substrate 91 (substrate refractive index na). In the gap portions where the segments do not face each other, no electric field is applied to the arm waveguide 92a, so the refractive index remains the substrate refractive index na.

[0098] These portions where the refractive index does not change, which are generated at the positions of the gaps between the segments of the modulation electrode 93a arranged along the arm waveguide 92a, are respectively the refractive index discontinuity points (disorder of refractive index change) along the light propagation direction of the arm waveguide 92a, and become factors causing light leakage from the arm waveguide 92a.

[0099] Moreover, the light leakage generated from each of the portions where the refractive index does not change along the arm waveguide 92a leaks into the support substrate 94 having a refractive index nb lower than that of the optical substrate 91, and is repeatedly reflected between the main surfaces of the support substrate 94, and propagates in the left and right directions shown in the figure while interfering with each other and enhancing each other inside the support substrate 94.

[0100] In particular, the segmented electrodes of the modulation electrode 93a are generally divided into several hundreds to several thousands of segments respectively, so the number of gaps between the segments is also several hundreds to several thousands. As a result, in the arm waveguide 92a, the number of light leakages generated from the gaps arranged at equal intervals between the segments is also several hundreds to several thousands, and these light leakages interfere with each other and enhance each other inside the support substrate 94, so light leakage of non-negligible intensity can be generated inside the support substrate 94.

[0101] The above phenomenon also occurs in the arm waveguide 92b formed with the modulation electrode 93b. The light leakage from the arm waveguide 92b interferes with each other and enhances each other inside the support substrate 94, so inside the support substrate 94, the light leakage of non-negligible intensity further increases.

[0102] Moreover, a part of these high-intensity light leakages generated by the interference can enter a part of the arm waveguide 92a, the arm waveguide 92b, and other Mach-Zehnder type optical waveguides 92, and be coupled with the signal light (or modulation light) propagating in the Mach-Zehnder type optical waveguide 92. This light leakage coupled with the signal light (or modulation light) propagating in the Mach-Zehnder type optical waveguide 92 is noise light, which deteriorates optical characteristics such as the extinction ratio of the light modulation operation in the Mach-Zehnder type optical waveguide 92 and causes deviation of the optical characteristics.

[0103] The present utility model is based on the above-mentioned insights into the factors of optical property deviation, and in particular, suppresses the interference of leakage light with each other in the support substrate, suppresses the increase in the intensity of leakage light caused by the interference, thereby reducing the deviation of optical properties in the light modulation operation.

[0104] Hereinafter, embodiments of the present utility model will be described with reference to the drawings.

[0105] [1. First Embodiment]

[0106] First, the first embodiment of the present utility model will be described. Figure 1 FIG. is a diagram showing the structure of a light modulator 2 using a light modulation element 1a according to the first embodiment of the present utility model. The light modulator 2 has a light modulation element 1a and a relay substrate 4 inside a housing 3. The light modulation element 1a has, for example, a Dual Polarization Quadrature Phase-Shift Keying (DP-QPSK) modulator structure. A cover (not shown) as a plate body is finally fixed to the opening of the housing 3, and the inside thereof is hermetically sealed.

[0107] In addition, the light modulator 2 has: a signal pin 5a for inputting a high-frequency electrical signal for modulating the light modulation element 1a; and a signal pin 5b for inputting an electrical signal for adjusting the operating point of the light modulation element 1a and the like.

[0108] Furthermore, the light modulator 2 has an input optical fiber 6a and an output optical fiber 6b on the same surface of the housing 3. The input optical fiber 6a is for inputting light into the housing 3, and the output optical fiber 6b guides the light modulated by the light modulation element 1a to the outside of the housing 3.

[0109] Here, the input optical fiber 6a and the output optical fiber 6b are respectively fixed to the housing 3 via support members 7a and 7b as fixing members. The light input from the input optical fiber 6a is collimated by a lens 8a disposed in the support member 7a and then input to the light modulation element 1a via a lens 8b. However, this is only an example, and the input of light to the light modulation element 1a may also be performed, for example, according to the prior art by introducing the input optical fiber 6a into the housing 3 via the support member 7a and connecting the end face of the introduced input optical fiber 6a to the end face of a substrate 20a (described later) of the light modulation element 1a.

[0110] In addition, the light modulator 2 has an optical unit 9 that performs polarization wave synthesis on two modulated lights output from the light modulation element 1a. The polarization wave synthesized light output from the optical unit 9 is condensed by a lens 8c disposed in the support member 7b and coupled to the output optical fiber 6b.

[0111] The relay substrate 4 transfers the high-frequency electrical signal input from the signal pin 5a and the electrical signals for operation point adjustment and the like input from the signal pin 5b to the optical modulation element 1a through a conductor pattern (not shown) formed on the relay substrate 4. The conductor pattern on the relay substrate 4 is connected to the electrodes of the optical modulation element 1a by wire bonding or the like, for example. In addition, the optical modulator 2 includes a terminator 10 having a specified impedance within the housing 3.

[0112] Figure 2 It is a plan view showing an example of the structure of the optical modulation element 1a. The optical modulation element 1a has a substrate 20a configured in multiple layers. The substrate 20a is, for example, rectangular in plan view and has two left and right sides 21a, 21b extending in the vertical direction of the drawing and facing each other, and upper and lower sides 21c, 21d extending in the left and right direction of the drawing and facing each other. Figure 2 The two left and right sides 21a, 21b extending in the vertical direction of the drawing and facing each other, and the upper and lower sides 21c, 21d extending in the left and right direction of the drawing and facing each other.

[0113] Figure 3 Is Figure 2 It is a side view of the side 21a of the optical modulation element 1a shown. The substrate 20a includes an optical waveguide layer 22 and a support layer 23a. In addition, in the present embodiment, the support layer 23a includes a first support layer 23a1 and a second support layer 23a2. In the present embodiment, as an example, the substrate 20a is formed by laminating a plurality of plate bodies. Specifically, the substrate 20a is formed by laminating an optical substrate 24 and a support substrate 25a. The optical substrate 24 includes the optical waveguide layer 22, and the support substrate 25a includes the support layer 23a composed of the first support layer 23a1 and the second support layer 23a2. The optical substrate 24 is, for example, an X-cut LN substrate having an electro-optic effect that is thinned to a thickness of 20 μm or less (for example, 2 μm). In addition, the support substrate 25a is, for example, a glass substrate including the first support layer 23a1 and the second support layer 23a2 made of glass having different raw materials or compositions.

[0114] In addition, the substrate 20a does not necessarily consist of a plurality of plate bodies as described above. The substrate 20a may be configured as a film body formed in layers on an appropriate substrate. For example, the substrate 20a may be configured to include the first support layer 23a1 and the optical waveguide layer 22 formed in layers on an appropriate plate body constituting the second support layer 23a2 by film formation processes such as sputtering, evaporation, and / or crystal growth.

[0115] The optical modulation element 1a has an optical waveguide 26 formed on the optical waveguide layer 22 of the substrate 20a (in the present embodiment, on the optical substrate 24). Figure 2(the whole shown by the thick dashed line). The optical waveguide 26 is a convex optical waveguide (e.g., a rib optical waveguide or a ridge optical waveguide) formed by a convex portion extending on the optical waveguide layer 22, and performs, for example, coherent multi-value modulation such as over 100 GBaud.

[0116] Referring to Figure 2 , the optical waveguide 26 includes an input waveguide 27 and a branching waveguide 28. The input waveguide 27 receives input light (arrow toward the right in the figure) from the input optical fiber 6a on the upper side of the left edge 21a in the figure of the optical waveguide layer 22, and the branching waveguide 28 branches the input light into two lights with the same light quantity. In addition, the optical waveguide 26 includes two modulation units, namely, the so-called nested Mach-Zehnder type optical waveguides 29a and 29b, which modulate each of the lights branched by the branching waveguide 28.

[0117] The nested Mach-Zehnder type optical waveguide 29a and the nested Mach-Zehnder type optical waveguide 29b reverse the propagation direction of light by 180 degrees in the turning-back region 30 in the right part of the figure of the optical waveguide layer 22, and output the light from the edge 21a of the optical waveguide layer 22 to the left in the figure through the output waveguide 31a and the output waveguide 31b.

[0118] The nested Mach-Zehnder type optical waveguide 29a and the nested Mach-Zehnder type optical waveguide 29b each include two Mach-Zehnder type optical waveguides 32a, 32b and 32c, 32d respectively provided in two waveguide portions constituting a pair of arm waveguides. Hereinafter, the Mach-Zehnder type optical waveguide 32a, the Mach-Zehnder type optical waveguide 32b, the Mach-Zehnder type optical waveguide 32c, and the Mach-Zehnder type optical waveguide 32d are collectively referred to as the Mach-Zehnder type optical waveguide 32. The Mach-Zehnder type optical waveguide 32 each includes two arm waveguides.

[0119] In the upper part of the figure of the optical waveguide layer 22, a bias electrode 33a for adjusting the operating points of the nested Mach-Zehnder type optical waveguide 29a and the nested Mach-Zehnder type optical waveguide 29b is formed at a position upstream of the turning-back region 30 along the propagation direction of the light in the optical waveguide 26. In addition, bias electrodes 33b and bias electrodes 33c for adjusting the respective operating points are provided in the Mach-Zehnder type optical waveguide 32a, the Mach-Zehnder type optical waveguide 32b, the Mach-Zehnder type optical waveguide 32c, and the Mach-Zehnder type optical waveguide 32d.

[0120] In addition, modulation units 34a, 34b, 34c, and 34d shown in the lower part of the illustration of the nested Mach-Zehnder type optical waveguides 29a and 29b that turn back in the turning-back region 30 form modulation electrodes for performing modulation operations on each of the four Mach-Zehnder type optical waveguides 32a, 32b, 32c, and 32d. Hereinafter, the modulation units 34a, 34b, 34c, and 34d are also collectively referred to as the modulation unit 34.

[0121] High-frequency electrical signals for performing modulation operations on each of the Mach-Zehnder type optical waveguides 32 are input from the relay substrate 4 via the wire bonding 35 shown on the right side of the illustration. These high-frequency electrical signals propagate through the modulation electrodes formed in each of the modulation units 34 and are terminated by a termination resistor (not shown) provided in the terminator 10 shown below the illustration.

[0122] To avoid making the figure complex and to make it easy to understand, the Figure 2 does not describe in detail the electrodes formed in the modulation units 34a, 34b, 34c, and 34d. In each of the modulation units 34, segmented electrodes formed by being divided into a plurality of segments along the light propagation direction of the optical waveguide, which are the same as those of the Figure 13 shown prior art, are formed as modulation electrodes.

[0123] As an example, the structure of the modulation electrodes in the modulation unit 34a is shown in the Figure 4 . The modulation electrodes of the other modulation units 34b, 34c, and 34d are also configured in the same manner as the Figure 4 .

[0124] In the Figure 4 , the modulation electrode 40a and the modulation electrode 40b respectively control the optical waves propagating in the arm waveguide 36a1 and the arm waveguide 36a2 of the Mach-Zehnder type optical waveguide 32a.

[0125] The modulation electrode 40a has a thermal electrode 40a1 and a ground electrode 40a2 that face each other with one of the arm waveguides 36a1 sandwiched therebetween within the surface of the optical waveguide layer 22. Similarly, the modulation electrode 40b has a thermal electrode 40b1 and a ground electrode 40b2 that face each other with the other arm waveguide 36a2 sandwiched therebetween within the surface of the optical waveguide layer 22.

[0126] The modulation electrodes 40a and 40b are each configured as segmented electrodes that are divided into a plurality of parts along the light propagation direction of the arm waveguides 36a1 and 36a2. Specifically, the hot electrode 40a1 and the ground electrode 40a2 that make up the modulation electrode 40a are each divided into a plurality of parts (segments) of the same length along the light propagation direction of the arm waveguide 36a1, and the gaps between the segments are arranged at regular intervals. In addition, the hot electrode 40b1 and the ground electrode 40b2 that make up the modulation electrode 40b are each divided into a plurality of segments of the same length along the light propagation direction of the arm waveguide 36a2, and the gaps between the segments are arranged at regular intervals. The number of segments of the hot electrode 40a1, the hot electrode 40b1, the ground electrode 40a2, and the ground electrode 40b2 is, for example, in the thousands. However, the number of the segments can be any number according to the optical modulation characteristics required for the optical modulation element 1a.

[0127] Moreover, the segments of the hot electrode 40a1 and the hot electrode 40b1 are electrically connected to each other through the heat transfer path 41a. In addition, the segments of the ground electrode 40a2 are electrically connected to each other through the ground transfer path 41b, and the segments of the ground electrode 40b2 are electrically connected to each other through the ground transfer path 41c. Thus, the hot electrode 40a1 and the hot electrode 40b1 connected to each other through the heat transfer path 41a, the ground electrode 40a2 connected to the ground transfer path 41b, and the ground electrode 40b2 connected to the ground transfer path 41c together constitute a coplanar electrode.

[0128] Figure 5 of (A), Figure 5 of (B) is Figure 4 the arrow view of the V-V cross-section along the arm waveguide 36a1 of the modulation section 34a shown. In Figure 5 of (A), Figure 5 of (B), the lower part (B) shows the structure of the optical modulation element 1a in the V-V cross-section, and the upper part (A) is a graph showing the refractive index change along the light propagation direction of the arm waveguide 36a1 in the V-V cross-section.

[0129] As Figure 5 shown in (A), in the arm waveguide 36a1, similar to the arm waveguide 92a of the prior art optical modulation element 90 shown in Figure 15 , when a high-frequency signal is transmitted to the modulation electrode 40a, in the portion where the segments of the hot electrode 40a1 face the segments of the ground electrode 40a2, an electric field is applied to the arm waveguide 36a1, and the refractive index changes (e.g., increases) by Δn from the refractive index n0 of the optical waveguide layer 22 (i.e., the optical substrate 24) (substrate refractive index n0). In addition, in the gap portion where the segments do not face each other, no electric field is applied to the arm waveguide 36a1, so the refractive index remains the substrate refractive index n0.

[0130] In the arm waveguide 36a1, the portions where the refractive index does not change (i.e., the portions where the refractive index does not change from the refractive index n0 of the substrate) generated at the positions of the non-facing gap portions of the modulation electrodes 40a are disorders in the refractive index change along the light propagation direction of the arm waveguide 36a1. Moreover, in such disordered portions of the refractive index, similar to the prior art optical modulation element 90, light leakage can occur from the arm waveguide 36a1 formed in the optical waveguide layer 22.

[0131] However, in the present embodiment, in particular, the support layer 23a included in the substrate 20a is composed of two layers, a first support layer 23a1 and a second support layer 23a2, having different refractive indices, so that these light leakages do not interfere with each other. Moreover, the refractive index n0 of the optical waveguide layer 22 in which the optical waveguide 26 is formed, the refractive index n1 of the first support layer 23a1, and the refractive index n2 of the second support layer 23a2 have the relationship of the following formula (1).

[0132] n0 > n1 and n2 > n1 (1)

[0133] Accordingly, the light leakage generated from the arm waveguide 36a1 formed in the optical waveguide layer 22 is incident on the first support layer 23a1 having a refractive index n1 smaller than the refractive index n0 of the optical waveguide layer 22, and then is incident on the second support layer 23a2 having a refractive index n2 larger than the refractive index n1 of the first support layer 23a1.

[0134] At this time, the refraction angle θ2 of the light leakage when passing through the boundary surface between the first support layer 23a1 and the second support layer 23a2 is smaller than the incident angle θ1 by a factor of n1 / n2 (<1). Therefore, the diffusion angle of each light leakage incident in the second support layer 23a2 becomes smaller than the diffusion angle of the light leakage in the first support layer 23a1, and the overlap of the light leakages in the second support layer 23a2 is suppressed, thereby suppressing the occurrence of interference between the light leakages.

[0135] The modulation electrodes of the modulation electrodes 40b of the arm waveguide 36a2 and the arm waveguides of the Mach-Zehnder type optical waveguide 32 in the other modulation unit 34 are also configured in the same manner as the modulation electrodes 40a of the arm waveguide 36a1, and the light leakages generated in these arm waveguides are also the same as above, and the overlap of the light leakages in the second support layer 23a2 is suppressed, thereby suppressing the occurrence of interference between the light leakages.

[0136] Hereinafter, the arm waveguides of each Mach-Zehnder type optical waveguide 32 including the arm waveguides 36a1 and 36a2 of the Mach-Zehnder type optical waveguide 32a are collectively referred to as arm waveguides 36. In addition, including the modulation electrodes 40a and 40b provided in the arm waveguides 36a1 and 36a2 in the modulation unit 34a, the modulation electrodes provided in the arm waveguides 36 in each of the modulation units 34 are collectively referred to as modulation electrodes 40.

[0137] By the above action, for the leakage light generated from each of the arm waveguides 36 formed in the optical waveguide layer 22, the mutual enhancement of the intensity caused by the interference between the leakage lights during the propagation in the second support layer 23a2 is suppressed. As a result, even when these leakage lights reach the optical waveguide layer 22 again and are multiplexed with the signal light propagating in the optical waveguide 26, the influence of these leakage lights on the optical characteristics of the optical modulation element 1a is suppressed to be smaller than that of the conventional optical modulation element 90.

[0138] Here, in order to effectively suppress the interference between the leakage lights generated in the arm waveguides 36 of the Mach-Zehnder type optical waveguide 32 formed in the optical waveguide layer 22 by the above action, it is important to suppress the mutual interference of these leakage lights in the first support layer 23a1 before reaching the second support layer 23a2. Specifically, the interference between the leakage lights in the first support layer 23a1 depends on the interval L between the gaps arranged at regular intervals between the respective segments constituting the modulation electrode 40 and / or the thickness t1 of the first support layer 23a1. Here, the interval L between the gaps refers to the distance along the corresponding arm waveguide 36 between the centers in the length direction of each gap.

[0139] More specifically, in order to suppress the interference between the leakage lights in the first support layer 23a1, the interval L of the gaps of the segments constituting the modulation electrode 40 preferably satisfies the following formula (2) with respect to the wavelength λ of the light wave propagating in the optical waveguide 26 and the refractive index n1 of the first support layer 23a1, and more preferably satisfies formula (3).

[0140] L>4×λ / n1 (2)

[0141] L>10×λ / n1 (3)

[0142] In addition, in order to suppress the interference between the leakage lights in the first support layer 23a1, the thickness t1 of the first support layer 23a1 preferably satisfies the following formula (4), and more preferably satisfies formula (5).

[0143] t1<10×λ / n1 (4)

[0144] t1<4×λ / n1 (5)

[0145] In the present embodiment, for example, the wavelength λ of the light wave propagating in the optical waveguide 26 is 1.55 μm, and the interval L of the gaps of the segments constituting the modulation electrode 40 is 50 μm. Further, regarding the optical waveguide layer 22, for example, the thickness t0 in the optical waveguide 26 is 1 μm, and the refractive index n0 at the wavelength λ is 2.2. Further, the first support layer 23a1 is made of SiO2, for example, the thickness t1 is 3 μm, and the refractive index n1 at the wavelength λ is 1.48. Further, the second support layer 23a2 is made of non-alkali glass, for example, the thickness t2 is 300 μm, and the refractive index n2 at the wavelength λ is 1.56. In addition, a semiconductor material such as Si (refractive index 3.5 at the wavelength λ) may be used for the second support layer 23a2 instead of non-alkali glass.

[0146] In addition, the substrate 20a is configured as a multilayer as a whole in the present embodiment, but it is not necessarily configured as a multilayer as a whole. For example, as long as the substrate 20a is configured as a multilayer at least below the modulation unit 34 where the modulation electrode 40 serving as a segmented electrode is formed, the above-described effect or function of suppressing the interference of light leakage can be achieved.

[0147] That is, the substrate 20a includes at least a multilayer portion configured as a multilayer, and in the multilayer portion, it is sufficient to include the optical waveguide layer 22, the first support layer 23a1 in contact with the lower surface of the optical waveguide layer 22, and the second support layer 23a2 in contact with the lower surface of the first support layer 23a1.

[0148] In addition, in the present embodiment and each of the embodiments shown below, the intervals L between the gaps of the adjacent segments of each of the modulation electrodes 40 are not necessarily constant throughout their entire ranges (i.e., their wholes), and it is sufficient that the intervals L between the gaps of the adjacent segments are constant throughout the entire range of the modulation electrode 40 or in a range other than a part thereof. Similarly, the lengths of the segments of each of the modulation electrodes 40 are not necessarily the same throughout their entire ranges, and it is sufficient that the lengths of the segments are constant throughout the entire range of the modulation electrode 40 or in a range other than a part thereof. For example, when the modulation electrode 40 is divided into several hundreds to several thousands of segments, in one or more intervals in the modulation electrode 40, the lengths of the segments and / or the intervals between the gaps of the adjacent segments may be different from those in other intervals.

[0149] [2. Second Embodiment]

[0150] Next, the optical modulation element 1b according to the second embodiment of the present invention will be described. The optical modulation element 1b has the same structure as the optical modulation element 1a, but is different in that the substrate 20b is used instead of the substrate 20a. The optical modulation element 1b can be installed in the optical modulator 2 and used instead of the optical modulation element 1a.

[0151] The top view of the optical modulation element 1b is the same as the top view of the optical modulation element 1a shown in Figure 2 , Figure 4 , and thus the descriptions of Figure 2 and Figure 4 as well as the above descriptions of Figure 2 and Figure 4 are incorporated by reference.

[0152] Figure 6 is a side view obtained by observing the side 21a of the optical modulation element 1b, and is a view corresponding to Figure 3 of the optical modulation element 1a of the first embodiment. Additionally, Figure 7 in (A), Figure 7 in (B) are cross-sectional views of the modulation unit 34a of the optical modulation element 1b along the arm waveguide 36a1, and are views corresponding to Figure 5 in (A), Figure 5 in (B) of the optical modulation element 1a of the first embodiment.

[0153] Furthermore, in Figure 6 and Figure 7 in (A), Figure 7 in (B), for the constituent components that are the same as those shown in Figure 3 and Figure 5 in (A), Figure 5 in (B), the same symbols as those shown in Figure 3 and Figure 5 in (A), Figure 5 in (B) are used to represent them, and the descriptions of Figure 3 and Figure 5 in (A), Figure 5 in (B) are incorporated by reference.

[0154] Referring to Figure 6 and Figure 7 in (A), Figure 7 in (B), the substrate 20b constituting the optical modulation element 1b has the same structure as the substrate 20a, but is different in that it includes a support layer 23b instead of the support layer 23a. The support layer 23b has the same structure as the support layer 23a, but is different in that in addition to including the first support layer 23a1 and the second support layer 23a2, it also includes a third support layer 23a3 that is in contact with the lower surface of the second support layer 23a2. The substrate 20b is formed, for example, by laminating a support substrate 25b including the first support layer 23a1, the second support layer 23a2, and the third support layer 23a3 on the lower surface of the optical substrate 24 instead of the support substrate 25a.

[0155] In addition, similar to the substrate 20a, the substrate 20b does not necessarily consist of multiple plate bodies. The substrate 20b may also be configured as a film body formed in layers on a suitable substrate. For example, the substrate 20b may also be configured to include a second support layer 23a2, a first support layer 23a1, and an optical waveguide layer 22 formed in layers on a suitable plate body constituting the third support layer 23a3 through film formation processes such as sputtering, evaporation, and / or crystal growth.

[0156] Similar to Figure 5 (A) of Figure 5 and (B) of Figure 7 (A) of Figure 7 in (B) of

[0157] In the optical modulation element 1b, the support layer 23b included in the substrate 20b is composed of three layers: a first support layer 23a1, a second support layer 23a2, and a third support layer 23a3 with different refractive indices. Moreover, the refractive index n0 of the optical waveguide layer 22 in which the optical waveguide 26 is formed, the refractive index n1 of the first support layer 23a1, the refractive index n2 of the second support layer 23a2, and the refractive index n3 of the third support layer 23a3 have the relationship of the following formula (6).

[0158] n0 > n1, n2 > n1, and n3 > n2 > n1 (6)

[0159] Thus, the leakage light generated from the arm waveguide 36a1 formed in the optical waveguide layer 22 is refracted in the direction in which the diffusion of the leakage light narrows twice when passing through the boundary surface between the first support layer 23a1 and the second support layer 23a2 and when passing through the boundary surface between the second support layer 23a2 and the third support layer 23a3. Therefore, the diffusion angle of each leakage light incident into the third support layer 23a3 is smaller than the diffusion angle in the second support layer 23a2 of the optical modulation element 1a of the first embodiment, and the overlap between the leakage lights is further suppressed, thereby more effectively suppressing the occurrence of interference between the leakage lights.

[0160] The above-described effect is similarly produced in each of the arm waveguides 36 of the Mach-Zehnder type optical waveguides 32 in the arm waveguide 36a2 and other modulation units 34.

[0161] Through the above effects, for the leakage light generated from the arm waveguide 36 formed in the optical waveguide layer 22, the increase in the leakage light intensity caused by the interference between the leakage lights during propagation in the third support layer 23a3 is further suppressed compared with the optical modulation element 1a of the first embodiment. As a result, even when these leakage lights reach the optical waveguide layer 22 again and are multiplexed with the signal light propagating in the optical waveguide 26, the influence of the leakage lights on the optical characteristics of the optical modulation element 1b is suppressed to be smaller than that of the conventional optical modulation element 90.

[0162] In addition, for the optical modulation element 1b, the preferred conditions for the interval L along the corresponding arm waveguide 36 of the gap between the segments constituting the modulation electrode 40 and the thickness t1 of the first support layer 23a1 are also as shown in the above formulas (2) to (5).

[0163] In this embodiment, for example, the wavelength λ of the light wave propagating in the optical waveguide 26 is 1.55 μm, and the interval L of the gap between the segments constituting the modulation electrode 40 is 50 μm. In addition, for the optical waveguide layer 22, for example, the thickness t0 in the optical waveguide 26 is 1 μm, and the refractive index n0 at the wavelength λ is 2.2. In addition, the first support layer 23a1 is made of SiO2, for example, the thickness t1 is 3 μm, and the refractive index n1 at the wavelength λ is 1.48. In addition, the second support layer 23a2 is made of non-alkali glass, for example, the thickness t2 is 200 μm, and the refractive index n2 at the wavelength λ is 1.56. In addition, the third support layer 23a3 is made of Si, the thickness t3 is 300 μm, and the refractive index n3 at the wavelength λ is 3.5.

[0164] In addition, in this embodiment, similar to the substrate 20a of the first embodiment, as long as the substrate 20b is formed as a multilayer at least below the modulation portion 34 where the modulation electrode 40 serving as a segmented electrode is formed, it can exhibit the above-mentioned function or effect of suppressing the interference of leakage light.

[0165] That is, the substrate 20b at least includes a multilayer portion formed as a multilayer, and in the multilayer portion, as long as it includes the optical waveguide layer 22, the first support layer 23a1 in contact with the lower surface of the optical waveguide layer 22, the second support layer 23a2 in contact with the lower surface of the first support layer 23a1, and the third support layer 23a3 in contact with the lower surface of the second support layer 23a2.

[0166] [3. Third Embodiment]

[0167] Next, the light modulator 1c of the third embodiment of the present invention is described. The light modulator 1c has the same structure as the light modulator 1a, but a light absorbing material is disposed on the back surface of the substrate 20a facing the surface of the light waveguide layer 22, and the light absorbing material absorbs light in the wavelength band of the light wave propagating in the light waveguide 26. The light modulator 1c can be installed in the light modulator 2 for use instead of the light modulator 1a.

[0168] The top view of the light modulator 1c is Figure 2 , Figure 4 The top view of the light modulation element 1a shown is the same, so reference is made to Figure 2 and Figure 4 As well as the above Figure 2 and Figure 4 Description.

[0169] Figure 8 is a side view of the light modulator 1c when observing the side 21a thereof, and is similar to the side view of the light modulator 1a according to the first embodiment. Figure 3 In addition, Figure 9 3 is a cross-sectional view of the modulation section 34a of the optical modulation element 1c along the arm waveguide 36a1, and is similar to the optical modulation element 1a of the first embodiment. Figure 5 In addition, Figure 9 In the graph of the refractive index of the arm waveguide 36a1, Figure 5 The same, therefore, is omitted.

[0170] In addition, Figure 8 and Figure 9 In Figure 3 and Figure 5 (A) Figure 5 The same components as those shown in (B) are used as Figure 3 and Figure 5 (A) Figure 5 The same symbols as those shown in (B) are used to represent the above Figure 3 and Figure 5 (A) Figure 5 Description of (B).

[0171] Reference Figure 8 and Figure 9, in the optical modulation element 1c, an absorbing material 43 is disposed on the entire surface of the back surface 42 of the substrate 20a facing the surface of the optical waveguide layer 22, and the absorbing material 43 absorbs light in the wavelength band of the light wave propagating in the optical waveguide 26. Thus, in the optical modulation element 1c, the leakage light generated from the arm waveguide 36 of the optical waveguide layer 22 is absorbed by the absorbing material 43 and attenuated when it propagates in the second support layer 23a2 and reaches the back surface 42. As a result, in the optical modulation element 1c, the intensity of the leakage light that reaches the optical waveguide layer 22 again is significantly reduced, and the influence of these leakage lights on the optical characteristics of the optical modulation element 1c is more effectively suppressed compared with the conventional optical modulation element 90.

[0172] The absorbing material 43 can be, for example, a carbon material such as carbon black, a black resin such as cashew oil, or a metal filler such as Ag. These absorbing materials 43 can be, for example, coated on the back surface 42 of the substrate 20a using an appropriate resin as an adhesive and hardened, and thus disposed on the back surface 42.

[0173] In addition, in the present embodiment, the absorbing material 43 is disposed on the entire surface of the back surface 42 of the substrate 20a, but it can also be coated on a part of the back surface 42. For example, as long as the absorbing material 43 is disposed at least in the range corresponding to the lower part of the modulation portion 34 of the modulation electrode 40 that forms the segmented electrode on the back surface 42, the attenuation effect of the leakage light can be achieved.

[0174] In addition, when the optical modulation element 1c is mounted on the frame 3, the optical modulation element 1c can be fixed to the frame 3 by, for example, providing an adhesive layer between the surface of the absorbing material 43 disposed on the back surface 42 of the substrate 20a and the surface of the back surface 42 where the absorbing material 43 is not coated and the frame 3.

[0175] [4. Fourth Embodiment]

[0176] Next, a fourth embodiment of the present invention will be described. This embodiment is an optical modulation module 50 including the optical modulation element 1a of the first embodiment. Figure 10 is a diagram showing the structure of the optical modulation module 50 of the present embodiment. In Figure 10 for the constituent components that are the same as those of the optical modulator 2 of the first embodiment shown in Figure 1 the same reference numerals as those shown in Figure 1 are used to represent them, and the description of Figure 1 is incorporated by reference.

[0177] The optical modulation module 50 has the same as Figure 1It has the same structure as the optical modulator 2 shown, but is different in that it includes a circuit board 51 instead of the relay board 4. The circuit board 51 includes a drive circuit 52. The drive circuit 52 generates a high-frequency electrical signal for driving the optical modulation element 1a based on, for example, a modulation signal supplied from the outside via the signal pin 5a, and outputs the generated high-frequency electrical signal to the optical modulation element 1a.

[0178] The optical modulation module 50 having the above structure includes the optical modulation element 1a in the same manner as the optical modulator 2 of the first embodiment. Therefore, similarly to the optical modulator 2, the influence of light leakage from the arm waveguide 36 provided with the modulation electrode 40 as a segmented electrode on the optical characteristics of the optical modulation element 1a can be reduced, thereby realizing a good optical modulation operation.

[0179] In addition, in the present embodiment, the optical modulation module 50 is provided as an example to include the optical modulation element 1a, but it may also be provided to include the optical modulation element 1b of the second embodiment or the optical modulation element 1c of the third embodiment.

[0180] [5. Fifth Embodiment]

[0181] Next, a fifth embodiment of the present invention will be described. This embodiment is an optical transmission device 55 equipped with the optical modulator 2 of the first embodiment. Figure 11 It is a diagram showing the structure of the optical transmission device 55 of this embodiment. The optical transmission device 55 has an optical modulator 2, a light source 56 that emits light to the optical modulator 2, a modulator drive unit 57, and a modulation signal generation unit 58. In addition, the optical modulation module 50 of the fourth embodiment can be used instead of the optical modulator 2 and the modulator drive unit 57. Further, the optical modulator 2 may include the optical modulation element 1b or the optical modulation element 1c instead of the optical modulation element 1a.

[0182] The modulation signal generation unit 58 is an electronic circuit that generates an electrical signal for causing the optical modulator 2 to perform a modulation operation. Based on transmission data provided from the outside, it generates a high-frequency signal, that is, a modulation signal, for causing the optical modulator 2 to perform an optical modulation operation in accordance with the modulation data, and outputs it to the modulator drive unit 57.

[0183] The modulator drive unit 57 amplifies the modulation signal input from the modulation signal generation unit 58 and outputs four sets of high-frequency electrical signals for driving each of the modulation electrodes 40 provided in the four Mach-Zehnder type optical waveguides 32 of the optical modulation element 1a included in the optical modulator 2.

[0184] These high-frequency electrical signals are input to the signal pin 5a of the optical modulator 2 to drive the optical modulation element 1a. As a result, the light output from the light source 56 passes through the optical modulator 2 and is, for example, DP-QPSK modulated, becoming modulated light and being output from the optical transmission device 55.

[0185] In the optical transmission device 55, since the optical modulator 2 or the optical modulation module 50 including the optical modulation element 1a, the optical modulation element 1b, or the optical modulation element 1c is used, good modulation characteristics can be achieved and good optical transmission can be performed.

[0186] [6. Sixth Embodiment]

[0187] Next, a sixth embodiment of the present invention will be described. This embodiment is an optical transmission system 60 that uses the optical transmission device 55 of the fifth embodiment. Figure 12 FIG. shows the structure of the optical transmission system 60 of this embodiment. The optical transmission system 60 includes: the optical transmission device 55 of the fifth embodiment; an optical fiber transmission path 61 that transmits the output light of the optical transmission device 55, that is, the modulated optical signal; and an optical reception device 62 that receives the optical signal transmitted by the optical fiber transmission path 61. Since the optical transmission system 60 transmits an optical signal by using the optical transmission device 55 including the optical modulator 2 or the optical modulation module 50 including the optical modulation element 1a, the optical modulation element 1b, or the optical modulation element 1c, it has good optical transmission performance.

[0188] [7. Other Embodiments]

[0189] Regarding the optical waveguide layer 22 for forming the optical waveguide 26, in the first to third embodiments, it is provided to be included in the optical substrate 24 that is an LN substrate, but it may not necessarily be composed of LN. The optical waveguide layer 22 may also be composed of a semiconductor material such as InP.

[0190] In the above embodiments, the substrate 20a and the substrate 20b that are configured as multi-layers are provided to be formed by laminating a plurality of plate bodies. However, this is an example, and as described above, the substrate 20a and the substrate 20b may also be composed of film bodies formed in a layer shape on an appropriate substrate.

[0191] In the above embodiments, the substrate 20a is provided to laminate the optical substrate 24 that is a plate body constituting the optical waveguide layer 22 and the support substrate 25a that is a plate body constituting the first support layer 23a1 and the second support layer 23a2. However, the optical substrate 24 and the support substrate 25a are an example of the plate bodies constituting the substrate 20a, and the distribution of the layers included in each of the plurality of plate bodies is arbitrary. That is, when the substrates such as the substrate 20a and the substrate 20b are formed by laminating a plurality of plate bodies, each plate body may include one layer or any number of multiple layers among the optical waveguide layer 22 and the plurality of support layers such as the first support layer 23a1.

[0192] In addition, the present utility model is not limited to the structure of the described embodiment and can be implemented in various forms without departing from its main idea.

[0193] [8. Structure supported by the above embodiment]

[0194] The above embodiment supports the following structure.

[0195] (Structure 1) An optical modulation element, comprising: a substrate including a multilayer portion configured as multiple layers; an optical waveguide layer of the multilayer portion of the substrate, on which an optical waveguide is formed; and a modulation electrode which is an electrode formed on the optical waveguide layer for controlling light waves propagating in the optical waveguide and is formed by being divided into multiple segments along the light propagation direction of the light in the optical waveguide, and in the entire interval of the electrode or an interval except for a part thereof, the intervals L measured in the extending direction of the optical waveguide between adjacent segments are constant, the multilayer portion of the substrate includes the optical waveguide layer, a first support layer in contact with the lower surface of the optical waveguide layer, and a second support layer in contact with the lower surface of the first support layer, and the refractive index n0 of the optical waveguide layer, the refractive index n1 of the first support layer, and the refractive index n2 of the second support layer have the relationship of n0 > n1 and n2 > n1.

[0196] With the optical modulation element of Structure 1, it is possible to suppress the situation where the leakage light from the optical waveguide due to the gaps between the segments of the segmented electrode, that is, the modulation electrode of the optical waveguide, formed by being divided into multiple segments along the light propagation direction of the light in the optical waveguide is enhanced by interference with each other. Thus, in the optical modulation element of Structure 1, the influence of such leakage light on the optical characteristics of the optical modulation element can be reduced, thereby achieving good optical characteristics.

[0197] (Structure 2) The optical modulation element according to Structure 1, wherein the interval L has the relationship of L > 4 × λ / n1 with respect to the wavelength λ of the light wave propagating in the optical waveguide and the refractive index n1 of the first support layer.

[0198] With the optical modulation element of Structure 2, it is possible to suppress the mutual enhancement caused by the interference between the leakage lights, thereby achieving better optical characteristics.

[0199] (Structure 3) The optical modulation element according to Structure 1 or 2, wherein the thickness t1 of the first support layer has the relationship of t1 < 10 × λ / n1 with respect to the wavelength λ of the light wave propagating in the optical waveguide and the refractive index n1 of the first support layer.

[0200] With the optical modulation element of Structure 3, it is possible to suppress the mutual enhancement caused by the interference between the leakage lights in the first support layer, thereby achieving better optical characteristics.

[0201] (Structure 4) The optical modulation element according to any one of Structures 1 to 3, wherein the multilayer portion of the substrate further includes a third support layer in contact with the lower surface of the second support layer, and the refractive index n0 of the optical waveguide layer, the refractive index n1 of the first support layer, the refractive index n2 of the second support layer, and the refractive index n3 of the third support layer have a relationship of n0 > n1 and n3 > n2 > n1.

[0202] With the optical modulation element of Structure 4, the support layer is composed of three layers, thereby further suppressing the mutual enhancement caused by the interference between leakage lights, and thus achieving better optical characteristics.

[0203] (Structure 5) The optical modulation element according to any one of Structures 1 to 4, wherein an absorbing material is disposed on the back surface of the substrate facing the surface of the optical waveguide layer, and the absorbing material absorbs light in the wavelength band of the light wave propagating in the optical waveguide.

[0204] With the optical modulation element of Structure 5, for the intensity of the leakage light reaching the back surface of the substrate, it can be reduced by the absorbing material disposed on the back surface, thereby effectively reducing the influence of the leakage light on the optical characteristics of the optical modulation element and achieving better optical characteristics.

[0205] (Structure 6) The optical modulation element according to Structure 5, wherein the absorbing material is a carbon material, a black resin, or a metal filler.

[0206] With the optical modulation element of Structure 6, the intensity of the leakage light reaching the back surface of the substrate can be effectively reduced, thereby achieving better optical characteristics as an optical modulation element.

[0207] (Structure 7) The optical modulation element according to any one of Structures 1 to 6, wherein the substrate is formed by laminating a plurality of plate bodies, and each plate body includes one layer or any number of layers of the optical waveguide layer and a plurality of support layers including the first support layer and the second support layer.

[0208] With the optical modulation element of Structure 7, a substrate including an optical waveguide layer for forming an optical waveguide and a plurality of support layers can be easily formed.

[0209] (Structure 8) An optical modulator, comprising: the optical modulation element according to any one of Structures 1 to 7; a housing for housing the optical modulation element; an optical fiber for inputting light to the optical modulation element; and an optical fiber for guiding the light output from the optical modulation element to the outside of the housing.

[0210] With the optical modulator of Structure 8, since the optical modulation element of any one of Structures 1 to 7 is used, an optical modulator with good optical characteristics can be achieved.

[0211] (Structure 9) An optical modulation module, comprising: an optical modulation element according to any one of Structures 1 to 7; a housing that houses the optical modulation element; an optical fiber that inputs light to the optical modulation element; an optical fiber that guides the light output from the optical modulation element to the outside of the housing; and a drive circuit that drives the optical modulation element.

[0212] With the optical modulation module of Structure 9, since the optical modulation element according to any one of Structures 1 to 7 is used, an optical modulation module having good optical characteristics can be realized.

[0213] (Structure 10) An optical transmission device, comprising: an optical modulator according to Structure 8 or an optical modulation module according to Structure 9; and an electronic circuit that generates an electrical signal for causing the optical modulation element to perform a modulation operation.

[0214] With the optical transmission device of Structure 10, since an optical modulator or an optical modulation module using the optical modulation element according to any one of Structures 1 to 7 is used, good optical transmission characteristics can be realized.

[0215] (Structure 11) An optical transmission system, comprising: an optical transmission device according to Structure 10; and an optical fiber transmission path that transmits the output light of the optical modulation element.

[0216] With the optical transmission system of Structure 11, since an optical transmission device using the optical modulation element according to any one of Structures 1 to 7 is used, good optical transmission characteristics can be realized.

Claims

1. A light modulation element, characterized in that: include: a substrate including a multi-layer portion configured as a plurality of layers; The optical waveguide layer of the multilayer portion of the substrate is formed with an optical waveguide; as well as The modulation electrode is an electrode for controlling the light wave propagating in the optical waveguide formed on the optical waveguide layer, and is formed by being divided into a plurality of segments along the propagation direction of the light in the optical waveguide. In the entire section or the section excluding a part of the modulation electrode, the interval L between the gaps between the adjacent segments measured in the extending direction of the optical waveguide is constant, The multilayer portion of the substrate includes the optical waveguide layer, a first support layer in contact with a lower surface of the optical waveguide layer, and a second support layer in contact with a lower surface of the first support layer, The refractive index n0 of the optical waveguide layer, the refractive index n1 of the first supporting layer, and the refractive index n2 of the second supporting layer have The relationship is n0>n1 and n2>n1.

2. The light modulation element according to claim 1, wherein: The interval L has a relationship of L>4×λ / n1 with respect to the wavelength λ of the light wave propagating in the optical waveguide and the refractive index n1 of the first supporting layer.

3. The light modulation element according to claim 1, wherein: The thickness t1 of the first supporting layer has a value of about the wavelength λ of the light wave propagating in the optical waveguide and the refractive index n1 of the first supporting layer. The relationship of t1<10×λ / n1.

4. The light modulation element according to claim 1, wherein: The multilayer portion of the substrate further comprises a third support layer connected to the lower surface of the second support layer, The refractive index n0 of the optical waveguide layer, the refractive index n1 of the first supporting layer, the refractive index n2 of the second supporting layer, and the refractive index n3 of the third supporting layer have The relationship is n0>n1 and n3>n2>n1.

5. The light modulation element according to claim 1, wherein: A light absorbing material is disposed on the back surface of the substrate facing the front surface of the optical waveguide layer, and the light absorbing material absorbs light in a wavelength band of light waves propagating through the optical waveguide.

6. The light modulation element according to claim 5, wherein: The light absorbing material is carbon material, black resin or metal filler.

7. The light modulation element according to claim 1, wherein: The substrate is formed by stacking a plurality of plates. The plate bodies respectively include the optical waveguide layer and one or any number of multiple supporting layers including the first supporting layer and the second supporting layer.

8. An optical modulator, characterized in that: include: The light modulating element according to claim 1; A frame housing the light modulating element; an optical fiber for inputting light to the light modulation element; as well as An optical fiber guides the light output from the light modulation element to the outside of the housing.

9. An optical modulation module, characterized in that: include: The light modulating element according to claim 1; A frame housing the light modulating element; an optical fiber for inputting light to the light modulation element; An optical fiber for guiding the light output by the light modulation element to the outside of the frame; as well as The driving circuit drives the light modulation element.

10. An optical transmitting device, characterized in that: include: The optical modulator according to claim 8 or the optical modulation module according to claim 9; as well as The electronic circuit generates an electrical signal for causing the light modulation element to perform a modulation operation.

11. An optical transmission system, characterized in that: include: The optical transmitting device as claimed in claim 10; and an optical fiber transmission path for transmitting the output light of the optical modulation element.

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