Optical modulation element

Abstract

The present disclosure provides an optical modulation element capable of preventing fine peeling between each structure layer at the outer peripheral end portion of a substrate cut from a wafer. An optical modulation element (1) includes a substrate (10), a waveguide layer (11) formed on the substrate (10), a dielectric layer (12) formed on the waveguide layer (11), and an electrode (4b1) formed on the dielectric layer (12). An outer peripheral end portion (E 12 ) of the dielectric layer (12) exists at an offset region more inward than an outer peripheral end portion (E 10 ) of the substrate (10), and in at least a portion of the offset region, a distance (L 12 ) from the outer peripheral end portion (E 10 ) of the substrate (10) to an outer peripheral end portion (E 12 ) of the dielectric layer (12) is equal to or less than a distance (L 13 ) from the outer peripheral end portion (E 10 ) of the substrate (10) to an outer peripheral end portion (E 13 ) of the electrode (4b1).

Description

Technical Field

[0001] This disclosure relates to an optical modulation element. Background Technology

[0002] With the widespread adoption of the internet, communication volume has increased dramatically, making fiber optic communication extremely important. Fiber optic communication is a communication method that converts electrical signals into optical signals and transmits them through optical fibers. It features wide bandwidth, low loss, and strong noise immunity.

[0003] As methods for converting electrical signals into optical signals, direct modulation using semiconductor lasers and external modulation using optical modulators are known. While direct modulation does not require an optical modulator and is low-cost, it has limitations in high-speed modulation. External optical modulation is used for high-speed and long-distance applications.

[0004] As an optical modulator, a Mach-Zehnder type optical modulator, in which an optical waveguide is formed near the surface of a lithium niobate single-crystal substrate by Ti (titanium) diffusion, has been put into practical use (see Patent Document 1). A Mach-Zehnder type optical modulator is an optical modulator that uses an optical waveguide with a Mach-Zehnder interferometer structure (Mach-Zehnder optical waveguide). A Mach-Zehnder interferometer is a device that splits light emitted from a light source into two beams, which then overlap again to produce interference after passing through different paths. Mach-Zehnder type optical modulators using Mach-Zehnder interferometers have been used to generate various modulated lights, and high-speed optical modulators exceeding 40 Gb / s have been commercialized. However, a major drawback is the total length, which is approximately 10 cm.

[0005] In contrast, Patent Document 2 discloses a Mach-Zehnder type optical modulator using a c-axis oriented lithium niobate film. Compared to optical modulators using a lithium niobate single-crystal substrate, optical modulators using a lithium niobate film can achieve significant miniaturization and lower drive voltage.

[0006] Optical modulation elements using lithium niobate films are formed on a wafer and manufactured by chip-forming the optical modulation elements through a wafer dicing process. Regarding the wafer dicing process, Patent Document 3 describes a method to prevent the optical waveguide layer on the chip end face of the optical modulation element from peeling off by pre-removing the waveguide layer near the dicing line of the substrate.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent No. 4485218

[0010] Patent Document 2: Japanese Patent No. 6456662

[0011] Patent Document 3: Japanese Patent No. 4742779 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] In the existing optical waveguide element described in Patent Document 3, the lower cladding layer, waveguide layer, and upper cladding layer are manufactured by coating a molten or melted polymer material or polymer precursor compound onto a substrate and then curing it by light or heat. In this case, the lower cladding layer cures before the waveguide layer material is coated, therefore it cannot function as an adhesive between the waveguide layer and the substrate surface, and peeling easily occurs at the interface between the lower cladding layer and the waveguide layer during cutting.

[0014] However, when a waveguide layer is formed by epitaxially growing a lithium niobate film on a substrate, waveguide layer peeling is not a major problem. On the other hand, in optical modulation elements where the layer structure is complicated for high performance, there is a problem that the risk of peeling off structural layers other than the waveguide layer increases. That is, in the manufacturing method of the optical modulation element described in Patent Document 3, the measures to prevent peeling off the structural layers are insufficient, and improvement is desired.

[0015] Therefore, the object of this disclosure is to provide an optical modulation element that can reduce the probability of fine peeling of each structural layer at the outer peripheral end of the substrate cut from the wafer.

[0016] Technical solutions for solving the problem

[0017] To address the aforementioned technical challenges, one embodiment of this disclosure provides an optical modulation element characterized by comprising: a substrate; a waveguide layer formed on the substrate; a dielectric layer formed on the waveguide layer; and an electrode formed on the dielectric layer, wherein the outer peripheral end of the dielectric layer exists in a bias region further inward than the outer peripheral ends of the substrate and the waveguide layer, and in at least a portion of the bias region, the distance from the outer peripheral end of the substrate to the outer peripheral end of the dielectric layer is less than or equal to the distance from the outer peripheral end of the substrate to the outer peripheral end of the electrode.

[0018] Invention Effects

[0019] According to this disclosure, it is possible to provide an optical modulation element that can prevent fine peeling between structural layers at the outer peripheral end of a substrate cut from a wafer. Attached Figure Description

[0020] Figure 1 (a) and (b) are general top views showing the structure of the optical modulation element according to the first embodiment of the present disclosure, in particular, Figure 1 (a) is a diagram showing only the waveguide layer. Figure 1 (b) is a diagram showing the overlapping of the electrode layers.

[0021] Figure 2 It is along Figure 1 Approximate cross-sectional views of the optical modulation element along the X1-X1' line in (a) and (b).

[0022] Figure 3 It means along Figure 1 Approximate cross-sectional views of the structure of the optical modulation element near the outer periphery of the substrate of the X2-X2' line in (a) and (b).

[0023] Figure 4 (a) to (c) are general cross-sectional views showing the structure of the optical modulation element according to the second to fourth embodiments of this disclosure.

[0024] Figure 5 (a) to (c) are general cross-sectional views showing the structure of the optical modulation element according to the fifth to seventh embodiments of the present disclosure.

[0025] Figure 6 (a) to (c) are general cross-sectional views showing the structure of the optical modulation element according to the eighth to tenth embodiments of this disclosure.

[0026] Figure 7 (a) to (c) are general cross-sectional views showing the structure of the optical modulation element according to the eleventh to thirteenth embodiments of this disclosure.

[0027] Figure 8 This is a general cross-sectional view showing the structure of the optical modulation element according to the fourteenth embodiment of the present disclosure.

[0028] Figure 9 This is a general top view showing the structure of the optical modulation element according to the fifteenth embodiment of this disclosure. Detailed Implementation

[0029] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0030] Figure 1 (a) and (b) are general top views showing the structure of the optical modulation element according to the first embodiment of the present disclosure, in particular, Figure 1 (a) is a diagram showing only the waveguide layer. Figure 1 (b) is a diagram showing the overlapping of the electrode layers.

[0031] like Figure 1As shown in (a) and (b), the optical modulation element 1 includes: a Mach-Zehnder waveguide 2 formed on a substrate 10, having first and second waveguide portions 2c1 and 2c2 arranged parallel to each other; a first signal electrode 4a disposed along the first waveguide portion 2c1; and a second signal electrode 4b disposed along the second waveguide portion 2c2. The substrate 10 has a rectangular planar shape, having a first side 10a and a second side 10b parallel to the long side direction (Y direction) of the substrate 10, and a third side 10c and a fourth side 10d orthogonal to the long side direction of the substrate 10. The first and second sides 10a and 10b are parallel to the Y direction, and the third and fourth sides 10c and 10d are parallel to the X direction.

[0032] The Mach-Zehnder optical waveguide 2 is an optical waveguide with a structure of a Mach-Zehnder interferometer, comprising: an input waveguide section 2a; a wave-splitting section 2b for splitting the light propagating in the input waveguide section 2a; first and second waveguide sections 2c1 and 2c2 extending from the wave-splitting section 2b and arranged parallel to each other; a wave-combining section 2d for combining the light propagating in the first and second waveguide sections 2c1 and 2c2; and an output waveguide section 2e for propagating the light output from the wave-combining section 2d.

[0033] As shown in the figure, the Mach-Zehnder waveguide 2 extends along the long side of the substrate 10. An input port 2i, serving as one end of the input waveguide 2a, extends out from the third side 10c of the substrate 10, and an output port 2o, serving as one end of the output waveguide 2e, extends out from the fourth side 10d of the substrate 10. The input light from the input port 2i travels through the input waveguide 2a, is split by the wave-splitter 2b, and after traveling through the first and second waveguides 2c1 and 2c2 respectively, is combined by the wave-combiner 2d, and output as modulated light from the output port 2o of the output waveguide 2e.

[0034] The first and second signal electrodes 4a and 4b are provided to apply RF signals to the first and second waveguide portions 2c1 and 2c2, and together with the Mach-Zehnder waveguide 2, they constitute the interaction portion of the optical modulation element 1. The interaction portion of the optical modulation element 1 modulates the light waveguided by the first and second waveguide portions 2c1 and 2c2. The first and second signal electrodes 4a and 4b are linear electrode patterns that overlap with the first and second waveguide portions 2c1 and 2c2 when viewed from above, and their two ends extend to the vicinity of the outer periphery of the substrate 10. That is, one end and the other end of the first signal electrode 4a are led out to the vicinity of the second edge 10b of the substrate 10 via leads 4a3 and 4a4, and one end and the other end of the second signal electrode 4b are also led out to the vicinity of the second edge 10b of the substrate 10 via leads 4b3 and 4b4. One end of each of the first and second signal electrodes 4a and 4b is connected via leads 4a3 and 4b3 to a pair of terminals 4a1 and 4b1 located near the second side 10b of the substrate 10. The pair of terminals 4a1 and 4b1 constitute a signal input port, through which a drive circuit 9a is connected. The other end of each of the first and second signal electrodes 4a and 4b is connected via leads 4a4 and 4b4 to a pair of terminals 4a2 and 4b2 located near the second side 10b of the substrate 10. The pair of terminals 4a2 and 4b2 are interconnected via terminating resistors 9b.

[0035] Differential signals (modulation signals) with the same absolute value but different signs are input to one end of the first and second signal electrodes 4a and 4b. The first and second waveguide sections 2c1 and 2c2 are made of materials with electro-optic effects, such as lithium niobate. Therefore, by applying an electric field to the first and second waveguide sections 2c1 and 2c2, the refractive indices of the first and second waveguide sections 2c1 and 2c2 change by +Δn and -Δn, respectively, thus changing the phase difference between the pair of optical waveguides. The signal light modulated by this phase difference is output from the output waveguide section 2e.

[0036] Figure 2 It is along Figure 1 (a) and (b) are approximate cross-sectional views of the optical modulation element 1 along the X1-X1' line. Additionally, Figure 3 It means along Figure 1 A general cross-sectional view of the structure of the optical modulation element 1 near the outer peripheral end of the substrate 10 of the X2-X2' line in (a) and (b).

[0037] like Figure 2 As shown, the optical modulation element 1 has a multilayer structure in which a substrate 10, a waveguide layer 11, a dielectric layer 12, and an electrode layer 13 are stacked sequentially.

[0038] A waveguide layer 11 made of an electro-optic material, such as lithium niobate, is formed on the main surface of the substrate 10. The waveguide layer 11 has a ridge 11r as a protruding portion and a flat plate portion 11s disposed on both sides of the ridge 11r as a thinner portion. The ridge 11r constitutes a Mach-Zehnder optical waveguide 2 including the first and second waveguide portions 2c1 and 2c2. In this embodiment, the width of the ridge 11r (ridge width) can be set to 0.5 to 5 μm.

[0039] The ridge 11r, which serves as the center of the optical waveguide, is an upward-protruding portion. Compared to the left and right portions, the electro-optic material film in this upward-protruding portion is thicker, thus increasing the effective refractive index. Therefore, it can also confine light in the left and right directions, functioning as a three-dimensional optical waveguide. The shape of the ridge 11r can be any shape capable of waveguided light, and it only needs to be a convex shape where the thickness of the electro-optic material film in the ridge 11r is greater than that of the electro-optic material films on the left and right sides. The ridge 11r can be formed by selectively etching and patterning the electro-optic material film using a mask such as a photoresist formed on it.

[0040] The dielectric layer 12 is formed on at least the upper surface of the ridge 11r to prevent light propagating in the first and second waveguide sections 2c1 and 2c2 from being absorbed by the first and second signal electrodes 4a and 4b. The dielectric layer 12 is preferably made of a dielectric material (dielectric layer) with a refractive index lower than that of the waveguide layer 11 and high transparency; for example, Al2O3, SiO2, LaAlO3, LaYO3, ZnO, HfO2, MgO, Y2O3, etc., can be used. The thickness of the dielectric layer 12 on the upper surface of the ridge 11r only needs to be around 0.2 to 1 μm.

[0041] A thicker dielectric layer 12 reduces light absorption at the electrode, while a thinner layer allows for a higher electric field to be applied to the optical waveguide. Since light absorption at the electrode is a trade-off with the applied voltage, it is necessary to determine an appropriate film thickness based on the desired effect. A higher dielectric constant of the dielectric layer 12 reduces VπL (an indicator of electric field efficiency), while a lower refractive index allows for a thinner dielectric layer 12. Generally, since materials with high dielectric constants also have high refractive indices, it is important to select a material with both high dielectric constant and relatively low refractive index, considering the balance between the two. For example, Al₂O₃, with a relative dielectric constant of approximately 9 and a refractive index of approximately 1.6, is a preferred material. LaAlO₃, with a relative dielectric constant of approximately 13 and a refractive index of approximately 1.7, and LaYO₃, with a relative dielectric constant of approximately 17 and a refractive index of approximately 1.7, are particularly preferred materials.

[0042] Electrode layer 13 includes first and second signal electrodes 4a and 4b. The widths of the first and second signal electrodes 4a and 4b are slightly wider than the ridge widths of the first and second waveguide portions 2c1 and 2c2 formed by the ridge-shaped lithium niobate film. In order to concentrate the electric field from the first and second signal electrodes 4a and 4b into the first and second waveguide portions 2c1 and 2c2, the widths of the first and second signal electrodes 4a and 4b are preferably 1.1 to 15 times the ridge widths of the first and second waveguide portions 2c1 and 2c2, more preferably 1.5 to 10 times.

[0043] The waveguide layer 11 is not particularly limited as long as it is an electro-optic material, but it is preferably made of lithium niobate. This is because lithium niobate has a large electro-optical constant and is suitable as a constituent material for optical devices such as optical modulators. Hereinafter, the structure of this embodiment with the waveguide layer 11 being a lithium niobate film will be described in detail.

[0044] As for the substrate 10, there is no particular limitation as long as the refractive index is lower than that of the lithium niobate film. It is preferable to be a substrate that allows the lithium niobate film to be formed into an epitaxial film, preferably a sapphire single crystal substrate or a silicon single crystal substrate. The crystal orientation of the single crystal substrate is not particularly limited. The lithium niobate film has the property of being easily formed into a c-axis oriented epitaxial film with respect to single crystal substrates of various crystal orientations. The c-axis oriented lithium niobate film has a three-dimensional symmetry. Therefore, it is preferable that the single crystal substrate of the substrate also has the same symmetry. In the case of a sapphire single crystal substrate, a substrate with the c-plane is preferred; in the case of a silicon single crystal substrate, a substrate with the (111) plane is preferred.

[0045] Here, an epitaxial film is a film whose crystal orientation is consistent with that of a substrate or base film relative to the substrate. When the in-plane of the film is defined as the XY plane and the film thickness direction is defined as the Z axis, the crystals are aligned in the X, Y, and Z axis directions. For example, it can be proven to be an epitaxial film by first confirming the peak intensity at the orientation position using 2θ-θ X-ray diffraction, and then confirming the poles.

[0046] Specifically, when performing measurements using 2θ-θ X-ray diffraction, the intensity of all peaks outside the target plane must be less than 10% of the maximum peak intensity of the target plane, preferably less than 5%. For example, in a c-axis oriented epitaxial film of lithium niobate, the peak intensity outside the (00L) plane is less than 10% of the maximum peak intensity of the (00L) plane, preferably less than 5%. (00L) is a general term for equivalent planes such as (001) or (002).

[0047] Secondly, poles need to be visible in pole determination. Under the condition of confirming the peak intensity at the first orientation position mentioned above, this only indicates orientation in one direction. Even if the first condition is met, in cases of inconsistent in-plane crystal orientation, the intensity of X-rays at a specific angular position is not high, and poles cannot be seen. Since LiNbO3 has a trigonal crystal structure, there are three poles in a single crystal of LiNbO3(014).

[0048] In the case of lithium niobate films, epitaxial growth is known to be performed in a so-called bicrystalline state where the crystals are symmetrically bonded after rotating 180° around the c-axis. In this case, two of the three poles are symmetrically bonded, resulting in a total of six poles. Furthermore, when a lithium niobate film is formed on a silicon single-crystal substrate with the (100) plane, since the substrate is four-fold symmetrical, 4 × 3 = 12 poles are observed. In addition, in this disclosure, lithium niobate films epitaxially grown in a bicrystalline state are also included in the epitaxial film.

[0049] The lithium niobate film has the composition LixNbAyOz. A represents elements other than Li, Nb, and O. X is 0.5–1.2, preferably 0.9–1.05. y is 0–0.5. z is 1.5–4, preferably 2.5–3.5. Elements representing A can be K, Na, Rb, Cs, Be, Mg, Ca, Sr, Ba, Ti, Zr, Hf, V, Cr, Mo, W, Fe, Co, Ni, Zn, Sc, Ce, etc., or combinations of two or more.

[0050] The thickness of the lithium niobate film is preferably 2 μm or less. This is because if the film thickness is greater than 2 μm, it is difficult to form a high-quality film. On the other hand, if the lithium niobate film is too thin, the light confinement within the lithium niobate film weakens, and light leaks to the substrate 10 or the dielectric layer 12. Even when an electric field is applied to the lithium niobate film, there is concern that the change in the effective refractive index of the optical waveguide will be smaller. Therefore, the lithium niobate film is preferably at least about 1 / 10 of the wavelength of the light used.

[0051] As a method for forming lithium niobate films, sputtering, CVD, sol-gel methods, etc., are preferred. If the c-axis of lithium niobate is oriented perpendicular to the main surface of the substrate 10, then by applying an electric field parallel to the c-axis, the optical refractive index changes proportionally to the electric field strength.

[0052] When using sapphire as a single-crystal substrate, lithium niobate films can be epitaxially grown directly on the sapphire single-crystal substrate. When using silicon as a single-crystal substrate, lithium niobate films are formed by epitaxial growth via a cladding layer (not shown). As the cladding layer, a material with a refractive index lower than that of lithium niobate films and suitable for epitaxial growth is used. For example, when Y₂O₃ is used as the cladding layer, high-quality lithium niobate films can be formed.

[0053] In addition, as a method for forming lithium niobate films, a method of thinly grinding and slicing a lithium niobate single-crystal substrate is also known. This method has the advantage of obtaining the same properties as single crystals and is applicable to this disclosure.

[0054] like Figure 2 and Figure 3 As shown, the outer peripheral end E of the dielectric layer 12 12 Located at the outer peripheral end E of the substrate 10 and waveguide layer 11 10 Further inward, a bias region consisting of a stepped structure 10s is formed near the outer peripheral end of the substrate 10. The lower layer of the stepped structure 10s is the upper surface of the waveguide layer 11, and the upper layer is the upper surface of the dielectric layer 12. The dielectric layer 12 is cut together with the substrate 10 and the waveguide layer 11, thereby creating a bias region at the outer peripheral end E of the dielectric layer 12. 12 Position and outer peripheral end E of substrate 10 10 When aligned, fine peeling of the dielectric layer 12 can easily occur on the cross-section of the substrate 10. Moisture can enter from the peeled portion, further developing the peeling of the dielectric layer 12 and reducing the reliability of the optical modulation element 1. However, in this embodiment, the outer peripheral end E of the dielectric layer 12... 12 The location is located at the outer peripheral end E of the substrate 10 and the waveguide layer 11. 10 In the case of being further inward, it is possible to prevent minor peeling of the dielectric layer 12 when cutting the substrate 10. Additionally, in this embodiment, the outer peripheral end E of the dielectric layer 12... 12 The location is located at the outer peripheral end E of the substrate 10 and the waveguide layer 11. 10 Even when the element is positioned further inside, it is possible to suppress the generation of minute peeling of the dielectric layer 12 when an impact is applied to the optical modulation element 1, thereby obtaining an optical modulation element 1 with high reliability.

[0055] like Figure 1As shown in (b), the stepped structure 10s (bias region) near the outer peripheral end of the substrate 10 is provided on the first side 10a and the second side 10b of the substrate 10, which are parallel to the extension direction of the optical waveguide, and is not provided on the third side 10c and the fourth side 10d of the substrate 10. This is because the optical input port 2i and the optical output port 2o of the Mach-Zehnder optical waveguide 2 are respectively located on the third side 10c and the fourth side 10d of the substrate 10.

[0056] When the dielectric layer 12 covering the ridge 11r of the waveguide layer 11 is absent at the optical input port 2i and optical output port 2o, the light confinement is weakened, and the characteristics of the optical waveguide are significantly reduced. On the other hand, the front end face of the optical waveguide is required to be extremely flat. Therefore, the end face is ground on the third side 10c and the fourth side 10d of the substrate 10. At this time, the minor peeling of the dielectric layer 12 is also removed. Therefore, it is not necessary to provide a step structure 10s on the third side 10c and the fourth side 10d. However, it is not necessary to provide a step structure 10s. The step structure 10s can be provided throughout the outer peripheral region of the substrate 10, except for the formation positions of the optical input port 2i and the optical output port 2o of the Mach-Zehnder optical waveguide 2. That is, as long as the outer periphery of the substrate 10, at least near the formation positions of the optical input port 2i and the optical output port 2o, is an area excluding the formation of the step structure 10s. For example, the area excluding the formation can also be set to a range of 3 times the waveguide width. That is, an exclusion region is formed on both sides of the optical input port 2i and the optical output port 2o with the width of the waveguide.

[0057] As long as minor peeling of the dielectric layer 12 is avoided as much as possible when cutting the substrate 10, the outer peripheral end E of the dielectric layer 12 12 Relative to the outer peripheral end E of the substrate 10 10 offset L 12 There are no specific limitations, and the method varies depending on the cutting method of the substrate 10. When using a cutting method with large variations in cutting allowance or low precision in the cutting position, it is necessary to increase the offset L. 12 When using a cutting method with small variation in cutting allowance or high precision in cutting position, the offset L can be reduced. 12 For example, when using a cutting blade, the blade wears down due to repeated use, resulting in a smaller cutting allowance. Therefore, the outer peripheral end E of the dielectric layer 12 is determined by considering the cutting allowance and positional accuracy when cutting the substrate 10. 12 offset L 12 .

[0058] The dielectric layer 12 preferably covers the upper surface of the waveguide layer 11 over the widest possible area. The dielectric layer 12 serves to protect the waveguide layer 11 as a whole; therefore, the area on the upper surface of the waveguide layer 11 not covered by the dielectric layer 12 should preferably be as small as possible. Therefore, the outer peripheral end E of the dielectric layer 12... 12 offset L 12 Ideally, the width W of the substrate 10 in the direction of the bias direction of the dielectric layer 12 should be as small as possible (refer to...). Figure 2 (less than 10%)

[0059] In this embodiment, Figure 1 The terminal portions 4a1, 4b1, 4a2, and 4b2 shown constitute the outer peripheral end E of the electrode layer 13. 13 The outer peripheral end E of electrode layer 13 13 Located at the outer peripheral end E of the dielectric layer 12 12 Further inward, at the outer peripheral end E of electrode layer 13 13 Offset L relative to substrate 10 13 The outer peripheral end E of dielectric layer 12 12 offset L 12 In other words, the outer peripheral end E of the dielectric layer 12 12 Located at the outer peripheral end E of the substrate 10 10 and the outer peripheral end E of electrode layer 13 13 Between, from the outer peripheral end E of the substrate 10 10 To the outer peripheral end E of dielectric layer 12 12 Distance L 12 The offset of dielectric layer 12 is less than that from the outer peripheral end E of substrate 10. 10 To the outer peripheral end E of electrode layer 13 13 Distance L 13 (Offset of electrode layer 13). Here, in this embodiment, it extends up to the outer peripheral end E of electrode layer 13. 13 Distance L 13 It is the distance from the second side 10b of the substrate 10 to the end face of the second side 10b of the substrate 10 on the terminal portions 4a1, 4b1, 4a2, 4b2, up to the outer peripheral end E of the dielectric layer 12. 12 Distance L 12 This is the distance from the first side 10a of the substrate 10 to the end face of the dielectric layer 12 on the side of the first side 10a of the substrate 10, located in the step structure 10s (bias region) on the first side 10a of the substrate 10. It is also the distance from the second side 10b of the substrate 10 to the end face of the dielectric layer 12 on the side of the second side 10b of the substrate 10, located in the step structure 10s (bias region) on the second side 10b of the substrate 10. Furthermore, the offset L of the dielectric layer 12... 12It can also be related to the offset L of electrode layer 13 13 The same applies. Alternatively, the offset L of the dielectric layer 12 may exist in the area near the outer periphery of the substrate 10 where electrodes such as the terminal portion 4a1 are not provided. 12 The offset L greater than electrode layer 13 13 The region. In any case, the outer periphery E of the dielectric layer 12 is also expected. 12 Existing at the outer peripheral end E of substrate 10 10 The bias region further inward is provided at least in the formation region of the interaction portion of the electrodes.

[0060] In this embodiment, the outer peripheral end E of the waveguide layer 11 11 Position and outer peripheral end E of substrate 10 10 Alignment, not present at the outer peripheral end E of substrate 10 10 Further inside. This is because the waveguide layer 11, which is made of lithium niobate film, is formed by epitaxial growth. The bonding strength between the substrate 10 and the waveguide layer 11 is very high. Therefore, even if the waveguide layer 11 is cut together with the substrate 10, the probability of fine peeling at the interface is low.

[0061] As described above, the optical modulation element 1 of this embodiment is manufactured by forming multiple optical modulation elements on a wafer that serves as an assembly substrate, and then dicing each optical modulation element. Regarding the dielectric layer 12, after forming the waveguide layer 11 on the wafer that serves as the substrate 10, it is selectively formed in areas other than the cutting allowance using a mask. Then, the electrode layer 13 is formed. Thus, the dielectric layer 12 is not present on the cutting line; therefore, the dielectric layer 12 is not cut along with the substrate 10, and no fine peeling of the dielectric layer 12 occurs. Therefore, the reliability of the optical modulation element 1 can be improved.

[0062] Figure 4 (a) to (c) are general cross-sectional views showing the structure of the optical modulation element according to the second to fourth embodiments of this disclosure.

[0063] like Figure 4 As shown in (a), the optical modulation element 1 of the second embodiment is characterized in that it further comprises a protective layer 14 covering the upper surface of the dielectric layer 12 and the upper surface and side surfaces (exposed surfaces) of the electrode layer 13. Like the dielectric layer 12, the outer peripheral end E of the protective layer 14 is... 14 The position is located at the outer peripheral end E of the substrate 10. 10 Further inwards. Additionally, the outer periphery E of the protective layer 14... 14 Position and outer peripheral end E of dielectric layer 12 12 Alignment. That is, the outer peripheral end E of the protective layer 14 14 offset L 14 With the outer peripheral end E of dielectric layer 1212 offset L 12 Equal. The other structures are the same as in the first embodiment.

[0064] The protective layer 14 serves to protect the dielectric layer 12 and the electrode layer 13. The material of the protective layer 14 is not particularly limited, but a material with a dielectric constant higher than that of air is preferred. By using this protective layer 14 to cover the exposed surfaces of the first and second signal electrodes 4a and 4b, the effective refractive index can be increased, and the bandwidth can be improved through speed matching of light and electricity. Furthermore, the outer peripheral end E of the protective layer 14... 14 The position is located at the outer peripheral end E of the substrate 10. 10 Located further inside, the protective layer 14 is not cut along with the substrate 10. Therefore, it is possible to prevent minor peeling of the protective layer 14 when cutting the substrate 10.

[0065] like Figure 4 As shown in (b), the optical modulation element 1 of the third embodiment is characterized in that the outer peripheral end E of the protective layer 14 14 The position is located at the outer peripheral end E of the dielectric layer 12. 12 Further inward. That is, the outer peripheral end E of the protective layer 14. 14 offset L 14 The outer peripheral end E of dielectric layer 12 12 offset L 12 The other structures are the same as in the second embodiment. When different material layers are removed simultaneously by reactive ion etching or the like, fine peeling sometimes occurs between the layers, reducing the reliability of the optical modulation element. However, in this embodiment, the outer peripheral end E of the protective layer 14 is... 14 Located at the outer peripheral end E of the dielectric layer 12 12 If the protective layer 14 is placed further inside and the protective layer 14 and the dielectric layer 12 are not removed at the same time, it is possible to prevent minor peeling of the protective layer 14.

[0066] like Figure 4 As shown in (c), the optical modulation element 1 of the fourth embodiment is characterized in that the outer peripheral end E of the protective layer 14 14 The location is at the outer peripheral end E of the dielectric layer 12. 12 Further outward, the outer peripheral end face of the dielectric layer 12 and a portion of the upper surface of the waveguide layer 11 (a portion of the lower layer of the stepped structure 10s) are covered by the protective layer 14. That is, the outer peripheral end E of the protective layer 14 14 offset L 14 The outer peripheral end E of the dielectric layer 12 12 offset L 12The other structures are the same as in the third embodiment. According to this embodiment, in addition to the effects of the third embodiment, the outer peripheral end face of the dielectric layer 12 can also be protected.

[0067] Figure 5 (a) to (c) are general cross-sectional views showing the structure of the optical modulation element according to the fifth to seventh embodiments of the present disclosure.

[0068] like Figure 5 As shown in (a), the optical modulation element 1 of the fifth embodiment is characterized in that the dielectric layer 12 is composed of multiple material layers with different elements or compositions, and the outer peripheral end of one material layer exists in a region that is more inward than the outer peripheral ends of the other material layers. In this embodiment, the dielectric layer 12 has a three-layer structure consisting of a lower layer 12a, an intermediate layer 12b, and an upper layer 12c, and the outer peripheral ends E of these three layers are... 12a E 12b E 12c The position is located at the outer peripheral end E of the substrate 10. 10 Further inwards. Additionally, the outer periphery E of the upper layer 12c. 12c The location is at the outer periphery end E of the lower layer 12a. 12a and the outer peripheral end E of the intermediate layer 12b 12b Further inward. The outer periphery E of the intermediate layer 12b 12b Position and outer peripheral end E of lower layer 12a 12a Alignment. Therefore, the outer peripheral end E of the upper layer 12c. 12c offset L 12c The outer peripheral end E of the intermediate layer 12b is larger than 12b offset L 12b E, the outer periphery of the intermediate layer 12b 12b offset L 12b With the outer peripheral end E of the lower layer 12a 12a offset L 12a Equal. The other structures are the same as in the first embodiment.

[0069] Preferably, the lower layer 12a is made of SiO2. By making the lower layer 12a a SiO2 film, the portion in contact with the waveguide layer 11 can be made with a low refractive index, which can enhance the light confinement of the optical waveguide.

[0070] Preferably, the intermediate layer 12b is composed of a compound containing at least La, Al, Si, and O. By setting the intermediate layer 12b to LaAlSiO, the dielectric layer 12 can be made to have a high dielectric constant, thereby reducing the driving voltage of the optical modulation element.

[0071] Preferably, the upper layer 12c is composed of a compound containing Si, In, and O. By making the upper layer 12c a SiInO film, a low dielectric constant is achieved near the electrode, which reduces losses. In addition, DC drift can be suppressed and the reliability of the optical modulation element can be improved.

[0072] As mentioned above, when different material layers are removed simultaneously by reactive ion etching or similar methods, fine delamination can easily occur between the layers. However, in this embodiment, the outer peripheral end E of the upper layer 12c... 12c Located at the outer periphery end E of the intermediate layer 12b 12b and the outer peripheral end E of the lower layer 12a 12a Further inside, the upper layer 12c, the middle layer 12b, and the lower layer 12a are not removed at the same time, thus preventing the fine peeling of the upper layer 12c.

[0073] like Figure 5 As shown in (b), the optical modulation element 1 of the sixth embodiment is characterized in that the dielectric layer 12 has a three-layer structure consisting of a lower layer 12a, an intermediate layer 12b, and an upper layer 12c, and the outer peripheral end E of the intermediate layer 12b is shown in (b). 12b and the outer peripheral end E of the upper layer 12c 12c The position is located at the outer periphery end E of the lower layer 12a. 12a Further inwards. The outer periphery E of the upper layer 12c. 12c The position of the outer periphery of the intermediate layer 12b, E 12b Alignment, outer peripheral end E of lower layer 12a 12a The position is located at the outer peripheral end E of the substrate 10. 10 Further inwards. Therefore, the outer peripheral end E of the upper layer 12c. 12c offset L 12c With the outer peripheral end E of the intermediate layer 12b 12b offset L 12b Equal to, and greater than the outer peripheral end E of the lower layer 12a 12a offset L 12a Other structures and the fifth embodiment ( Figure 5 The same as (a)).

[0074] In this embodiment, the outer peripheral end E of the upper layer 12c 12c and the outer peripheral end E of the intermediate layer 12b 12b Located at the outer periphery end E of the lower layer 12a 12a Further inside, the upper layer 12c and the middle layer 12b are not removed at the same time as the lower layer 12a, thus preventing the fine peeling of the middle layer 12b.

[0075] like Figure 5As shown in (c), the optical modulation element 1 of the seventh embodiment is characterized in that the dielectric layer 12 has a three-layer structure consisting of a lower layer 12a, an intermediate layer 12b, and an upper layer 12c, and the outer peripheral end E of the intermediate layer 12b is shown in (c). 12b The position is located at the outer periphery end E of the lower layer 12a. 12a Further inward, also, the outer periphery E of the upper layer 12c 12c The position is located at the outer periphery end E of the intermediate layer 12b. 12b Further inward. Therefore, the outer peripheral end E of the intermediate layer 12b 12b offset L 12b The outer peripheral end E of the lower layer 12a is larger than 12a offset L 12a The outer peripheral end E of the upper layer 12c 12c offset L 12c The outer peripheral end E of the intermediate layer 12b is larger than 12b offset L 12b The other structures are the same as in the fifth embodiment.

[0076] In this embodiment, the outer peripheral end E of the upper layer 12c 12c Located at the outer periphery end E of the intermediate layer 12b 12b Further inward, the upper layer 12c and the intermediate layer 12b were not removed simultaneously, thus preventing minor peeling of the upper layer 12c. In addition, the outer peripheral end E of the intermediate layer 12b was... 12b Located at the outer periphery end E of the lower layer 12a 12a Further inside, the intermediate layer 12b and the lower layer 12a are not removed at the same time, thus preventing the fine peeling of the intermediate layer 12b.

[0077] Figure 6 (a) to (c) are general cross-sectional views showing the structure of the optical modulation element according to the eighth to tenth embodiments of this disclosure.

[0078] like Figure 6 As shown in (a), the optical modulation element 1 of the eighth embodiment is characterized in that the dielectric layer 12 has a three-layer structure consisting of a lower layer 12a, an intermediate layer 12b, and an upper layer 12c, and the outer peripheral ends E of these three layers are shown. 12a E 12b E 12c The position is located at the outer peripheral end E of the substrate 10. 10 Further inward, the outer periphery E of the upper layer 12c 12c The location is located at the outer periphery end E of the intermediate layer 12b. 12b and the outer peripheral end E of the lower layer 12a 12a Further outward, the upper layer 12c covers the outer periphery E of the lower layer 12a. 12aThe side surface (outer peripheral end face) and the outer peripheral end E of the intermediate layer 12b 12b The side surface (outer peripheral end face). Therefore, the outer peripheral end E of the upper layer 12c. 12c offset L 12c The outer peripheral end E of the intermediate layer 12b is smaller than the middle layer 12b 12b offset L 12b E, the outer periphery of the intermediate layer 12b 12b offset L 12b With the outer peripheral end E of the lower layer 12a 12a offset L 12a Equal. The other structures are the same as in the fifth embodiment. According to this embodiment, in addition to the effects of the fifth embodiment, the outer peripheral end faces of the intermediate layer 12b and the lower layer 12a can also be protected.

[0079] like Figure 6 As shown in (b), the optical modulation element 1 of the ninth embodiment is characterized in that the outer peripheral end E of the intermediate layer 12b 12b The location is at the outer periphery end E of the lower layer 12a. 12a Further outward, the outer periphery of the upper 12c, E 12c The location is located at the outer periphery end E of the intermediate layer 12b. 12b Further outwards. Therefore, the outer peripheral end E of the upper layer 12c. 12c offset L 12c The outer peripheral end E of the intermediate layer 12b is smaller than 12b offset L 12b E, the outer periphery of the intermediate layer 12b 12b offset L 12b The outer peripheral end E of the lower layer 12a is smaller than 12a offset L 12a The other structures are the same as in the eighth embodiment. In this embodiment, the outer peripheral end faces of the intermediate layer 12b and the lower layer 12a can also be protected.

[0080] like Figure 6 As shown in (c), the optical modulation element 1 of the tenth embodiment is characterized in that the outer peripheral end E of the intermediate layer 12b 12b The position is located at the outer periphery end E of the upper layer 12c. 12c Further outward, the outer periphery of the upper 12c, E 12c The location is at the outer periphery end E of the lower layer 12a. 12a Further outwards. Therefore, the outer peripheral end E of the intermediate layer 12b. 12b offset L 12b The outer peripheral end E of the upper layer 12c is smaller than that of the upper layer. 12c offset L 12c The outer peripheral end E of the upper layer 12c 12coffset L 12c The outer peripheral end E of the lower layer 12a is smaller than 12a offset L 12a The other structures are the same as in the eighth embodiment. According to this embodiment, the outer peripheral end face of the lower layer 12a can be protected.

[0081] Figure 7 (a) to (c) are general cross-sectional views showing the structure of the optical modulation element according to the eleventh to thirteenth embodiments of this disclosure.

[0082] like Figure 7 As shown in (a), the optical modulation element 1 of the eleventh embodiment is characterized in that it is Figure 4 (b) and Figure 5 The combination of embodiments shown in (a) further includes a protective layer 14 covering the upper surface of the dielectric layer 12 and the upper surface of the electrode layer 13. The dielectric layer 12 is composed of a lower layer 12a, an intermediate layer 12b, and an upper layer 12c. The outer peripheral end E of the upper layer 12c 12c The location is at the outer periphery end E of the lower layer 12a. 12a and the outer peripheral end E of the intermediate layer 12b 12b Further inwards. Additionally, the outer periphery E of the protective layer 14... 14 The location is at the outer peripheral end E of the upper layer 12c of the dielectric layer 12. 12c Further inwards. Therefore, the outer peripheral end E of the upper layer 12c. 12c offset L 12c The outer peripheral end E of the intermediate layer 12b is larger than 12b offset L 12b and the outer peripheral end E of the lower layer 12a 12a offset L 12a The outer peripheral end E of the protective layer 14 14 offset L 14 The outer peripheral end E of the upper layer 12c is larger than 12c offset L 12c According to this embodiment, the same effects as those of the third and fifth embodiments can be achieved.

[0083] like Figure 7 As shown in (b), the optical modulation element 1 of the twelfth embodiment is characterized in that it is Figure 4 (a) and Figure 5 The combination of embodiments shown in (a) further includes a protective layer 14 covering the upper surface of the dielectric layer 12 and the upper surface of the electrode layer 13. The dielectric layer 12 is composed of a lower layer 12a, an intermediate layer 12b, and an upper layer 12c. The outer peripheral end E of the upper layer 12c 12c The location is at the outer periphery end E of the lower layer 12a. 12aand the outer peripheral end E of the intermediate layer 12b 12b Further inwards. Additionally, the outer periphery E of the protective layer 14... 14 The position of the upper layer 12c of dielectric layer 12 is at the outer peripheral end E. 12c Alignment. Therefore, the outer peripheral end E of the upper layer 12c. 12c offset L 12c The outer peripheral end E of the intermediate layer 12b is larger than 12b offset L 12b and the outer peripheral end E of the lower layer 12a 12a offset L 12a The outer peripheral end E of the protective layer 14 14 offset L 14 With the outer peripheral end E of the upper layer 12c 12c offset L 12c Equal. According to this embodiment, the same effect as that of the second and fifth embodiments can be achieved.

[0084] like Figure 7 As shown in (c), the optical modulation element 1 of the thirteenth embodiment is characterized in that it is Figure 4 (c) and Figure 5 The combination of embodiments shown in (a) further includes a protective layer 14 covering the upper surface of the dielectric layer 12 and the upper surface of the electrode layer 13. The dielectric layer 12 is composed of a lower layer 12a, an intermediate layer 12b, and an upper layer 12c. The outer peripheral end E of the upper layer 12c 12c The location is at the outer periphery end E of the lower layer 12a. 12a and the outer peripheral end E of the intermediate layer 12b 12b Further inwards. Additionally, the outer periphery E of the protective layer 14... 14 The location is located at the outer peripheral end E of the lower layer 12a of the dielectric layer 12. 12a and the outer peripheral end E of the intermediate layer 12b 12b Further outward, the protective layer 14 covers the outer peripheral end faces of the lower layer 12a, the middle layer 12b, and the upper layer 12c. Therefore, the outer peripheral end E of the protective layer 14... 14 offset L 14 The outer peripheral end E of the lower layer 12a is smaller than 12a offset L 12a and the outer peripheral end E of the intermediate layer 12b 12b offset L 12b According to this embodiment, the same effects as those of the third and fifth embodiments can be achieved.

[0085] Figure 8 This is a general cross-sectional view showing the structure of the optical modulation element according to the fourteenth embodiment of the present disclosure.

[0086] like Figure 8 As shown, the optical modulation element 1 of the fourteenth embodiment is characterized in that the outer peripheral end E of the waveguide layer 11 11 Existing at the outer peripheral end E of substrate 10 10 Further inward. The outer periphery E of waveguide layer 11 11 offset L 11 The outer peripheral end E of the dielectric layer 12 12 offset L 12 The other structures are the same as in the first embodiment.

[0087] When the waveguide layer 11 is formed by bonding or other methods without epitaxy, fine peeling can easily occur at the interface when the waveguide layer 11 is cut together with the substrate 10. However, if the waveguide layer 11 is not provided along the cutting line of the substrate 10, fine peeling of the waveguide layer 11 can be prevented when cutting the substrate 10. Furthermore, even when the waveguide layer 11 is formed by epitaxy, fine peeling of the waveguide layer 11 can be reliably prevented when cutting the substrate 10.

[0088] In this embodiment, the outer peripheral end E of the dielectric layer 12 12 Existing at the outer periphery of waveguide layer 11, E 11 Further inward, the outer peripheral end E of the dielectric layer 12 can also be... 12 The location is at the outer periphery end E of waveguide layer 11. 11 Further outwards. That is, the outer periphery E of waveguide layer 11. 11 offset L 11 It can also be larger than the outer peripheral end E of dielectric layer 12 12 offset L 12 In this case, the outer peripheral end face of the waveguide layer 11 is covered by the dielectric layer 12.

[0089] Figure 9 This is a general top view showing the structure of the optical modulation element according to the fifteenth embodiment of this disclosure.

[0090] like Figure 9 As shown, the optical modulation element 1 of the fifteenth embodiment is characterized in that the Mach-Zehnder waveguide 2 has a single-folding structure. More specifically, the first and second waveguide portions 2c1 and 2c2 of the Mach-Zehnder waveguide 2 have: a first straight portion 2S1, a curved portion 2U that changes the travel direction of the first straight portion 2S1 by 180 degrees, and a second straight portion 2S2 that is arranged parallel to the first straight portion 2S1.

[0091] The substrate 10 has a first side 10a and a second side 10b parallel to the long side direction (Y direction), and a third side 10c and a fourth side 10d orthogonal to the long side direction of the substrate 10. The optical input port 2i and the optical output port 2o are both disposed on the third side 10c of the substrate 10. The first and second waveguide portions 2 of the first straight section 2S1... c1 2c2 travels parallel to each other from the third side 10c to the fourth side 10d. The first and second waveguide sections 2 of the curved section 2U. c1 2c2 is formed into a concentric semicircle to change the direction of travel of the first straight section 2S1 by 180 degrees. The first and second waveguide sections 2 of the second straight section 2S2... c1 2c2 moves parallel to each other from the fourth side 10d to the third side 10c.

[0092] The first and second signal electrodes 4a and 4b are continuously formed along the first straight section 2S1, the curved section 2U, and the second straight section 2S2 of the Mach-Zehnder waveguide 2. By forming the signal electrodes as long as possible not only along the straight sections but also along the curved sections, the driving voltage can be reduced. In optical modulation elements, the length of the main body's long side is a significant practical technical challenge, but by folding the optical waveguide back as shown in the figure, this long side can be significantly shortened, achieving both low driving voltage and miniaturization. In particular, the optical waveguide formed by the lithium niobate film exhibits low loss even when the radius of curvature of the curved section 2U is reduced to approximately 50 μm, making it suitable for this embodiment.

[0093] In the optical modulation element 1 of this embodiment, the optical input port 2i and optical output port 2o of the Mach-Zehnder waveguide 2 are led out from the third side 10c of the substrate 10. Therefore, no step structure 10s is provided on the third side 10c. Step structures 10s are provided on the other three sides 10a, 10b, and 10d. In the case of such a structure in which the Mach-Zehnder waveguide 2 is folded back once or an odd number of times, the lead-out direction of the optical output port 2o is the same as that of the optical input port 2i. Therefore, it is sufficient to set only one side (the third side 10c) as the area excluding the formation of the step structure 10s, and provide the step structure 10s on the remaining three sides (the first side 10a, the second side 10b, and the fourth side 10d). This can prevent the fine peeling of the dielectric layer 12 when cutting the substrate 10.

[0094] In the case of an even number of foldbacks in the Mach-Zehnder waveguide 2, and Figure 1As shown in the case without folding, the lead-out direction of the light output port 2o is opposite to that of the light input port 2i. Therefore, it is sufficient to set only the two sides from which they are led out (the third side 10c and the fourth side 10d) as the area excluding the formation of the step structure 10s, and set the step structure 10s on the remaining two sides (the first side 10a and the second side 10b). This can prevent the fine peeling of the dielectric layer 12 when cutting the substrate 10.

[0095] As explained above, in the optical modulation element 1 of this embodiment, the optical input port 2i and the optical output port 2o of the Mach-Zehnder waveguide 2 are led out from the third side 10c of the four sides of the substrate 10, and a stepped structure 10s is provided on the remaining three sides. Therefore, it is possible to prevent the fine peeling of the dielectric layer 12 on these three sides.

[0096] The preferred embodiments of this disclosure have been described above, but this disclosure is not limited to the above embodiments. Various changes can be made without departing from the spirit of this disclosure, and these changes are also included within the scope of this disclosure.

[0097] The technology disclosed herein includes the following structural examples, but is not limited thereto.

[0098] One embodiment of the optical modulation element disclosed herein is characterized by comprising: a substrate, a waveguide layer formed on the substrate, a dielectric layer formed on the waveguide layer, and an electrode formed on the dielectric layer. The dielectric layer has an outer peripheral end located in a bias region further inward than the outer peripheral end of the substrate. In at least a portion of the bias region, the distance from the outer peripheral end of the substrate to the outer peripheral end of the dielectric layer is less than or equal to the distance from the outer peripheral end of the substrate to the outer peripheral end of the electrode. Accordingly, by utilizing the dielectric layer to cover a wide area of ​​the substrate for protection, and by preventing the dielectric layer from being cut along with the substrate during substrate cutting, fine peeling of the dielectric layer at the outer peripheral end of the substrate can be prevented. Furthermore, the generation of fine peeling of the dielectric layer when subjected to impact on the optical modulation element can be suppressed, resulting in an optical modulation element with high reliability.

[0099] Alternatively, the optical modulation element may also include a protective layer formed at least on the electrode and dielectric layers, with the outer periphery of the protective layer located in a region further inward than the outer periphery of the substrate and waveguide layer. This structure not only suppresses electrode degradation but also increases the effective electrical refractive index and improves the bandwidth of the optical modulation element. Furthermore, it reduces the probability of fine peeling of the protective layer at the outer periphery of the substrate during substrate cutting.

[0100] Alternatively, the outer periphery of the protective layer may be located in a region further inward than the outer periphery of the dielectric layer. Alternatively, the outer periphery of the protective layer may be located in a region further outward than the outer periphery of the dielectric layer, in which the protective layer covers the end face of the dielectric layer. When different material layers are removed simultaneously by reactive ion etching or similar methods, fine peeling may occur between the layers, reducing the reliability of the optical modulation element. However, by positioning the outer periphery of the protective layer differently from the outer periphery of the dielectric layer and removing both through separate processes, fine peeling of the protective layer can be prevented.

[0101] Alternatively, the dielectric layer may have multiple material layers with different elements or compositions, with the outer periphery of at least one material layer located in a region further inward than the outer periphery of at least one of the other material layers. In this way, by multiplying the dielectric layer and changing the material according to the position of the layers, the performance of the optical modulation element, such as reducing the driving voltage, can be improved. Furthermore, by differentiating the positions of the outer periphery of the multiple material layers and removing them through different processes, fine peeling of the material layers can be prevented.

[0102] Alternatively, the dielectric layer may have multiple material layers with different elements or compositions, with the outer periphery of the upper layer existing in a region further inward than the outer periphery of the lower layer. This structure prevents fine peeling of the upper layer.

[0103] Alternatively, the dielectric layer may have multiple material layers with different elements or compositions, where the outer periphery of the upper layer exists in a region further outward than the outer periphery of the lower layer, in which the upper layer covers the end face of the lower layer. This structure prevents fine peeling of the upper layer and protects the end face of the lower layer.

[0104] Alternatively, the dielectric layer may have multiple material layers with different elements or compositions, including an upper layer, a lower layer, and an intermediate layer located between the upper and lower layers, with the outer periphery of the upper layer existing in a region further inward than the outer periphery of the intermediate and lower layers. This structure improves the characteristics of the waveguide layer and electrodes and prevents fine delamination of the upper layer.

[0105] Alternatively, the dielectric layer may have multiple material layers with different elements or compositions, including an upper layer, a lower layer, and an intermediate layer located between the upper and lower layers, with the outer periphery of the upper and intermediate layers existing in a region further inward than the outer periphery of the lower layer. This structure prevents fine peeling of the intermediate layer.

[0106] Alternatively, the dielectric layer may have multiple material layers with different elements or compositions, including an upper layer, a lower layer, and an intermediate layer located between the upper and lower layers. The outer periphery of the upper layer is located further outward than the outer periphery of the intermediate and lower layers, and in this region, the upper layer covers the end faces of the intermediate and lower layers. This structure prevents fine peeling of the intermediate and upper layers.

[0107] Alternatively, the dielectric layer may have multiple material layers with different elements or compositions, including an upper layer, a lower layer, and an intermediate layer located between the upper and lower layers. The outer periphery of the upper layer is located in a region further outward than the outer periphery of the lower layer, and the outer periphery of the intermediate layer is located in a region further outward than the outer periphery of both the upper and lower layers. This structure prevents micro-peeling of the intermediate and upper layers and protects the end faces of the lower and intermediate layers.

[0108] Alternatively, the upper layer can be composed of compounds containing Si, In, and O, the middle layer of which is composed of compounds containing at least La, Al, Si, and O, and the lower layer of which is composed of SiO2. This structure reduces the transmission loss and driving voltage of the optical waveguide, enabling high-performance optical modulation elements. Furthermore, while the probability of micro-peeling of each structural layer during substrate cutting increases when the dielectric layer is multilayered, this can be prevented by removing the dielectric layer beforehand from near the cutting location.

[0109] Alternatively, the outer periphery of the waveguide layer may be located in a region further inward than the outer periphery of the substrate. When the waveguide layer is formed by bonding or other methods, peeling of the waveguide layer is prone to occur during substrate cutting. However, when the outer periphery of the waveguide layer is located further inward than the outer periphery of the substrate, fine peeling of the waveguide layer can be reliably avoided.

[0110] Alternatively, the optical input and output ports of the optical waveguide formed on the waveguide layer can be located at the outer periphery of the substrate. A stepped structure, formed by the outer periphery of the dielectric layer being located further inward than the outer periphery of the substrate, is positioned in a region other than near the respective locations of the optical input and output ports. In this case, the stepped structure preferably extends to all edges of the periphery except for the edge where the optical input and output ports are located. This prevents micro-peeling of the dielectric layer while ensuring the functionality of the optical input and output ports of the optical waveguide.

[0111] The waveguide layer can be composed of a lithium niobate film or an epitaxial film of lithium niobate. This structure allows for significant miniaturization of optical modulation elements and reduction of driving voltage. Furthermore, even when the waveguide layer is cut along with the substrate, the probability of fine peeling of the waveguide layer can be reduced.

[0112] Alternatively, the offset of the dielectric layer can be less than 10% of the width of the substrate in the same direction as the offset direction of the dielectric layer. In this way, if the offset of the dielectric layer is less than 10% of the width of the substrate, the dielectric layer can protect a wide area of ​​the substrate and can prevent the dielectric layer from being cut off together with the substrate during the substrate cutting process, and can prevent fine peeling of the dielectric layer at the outer peripheral end of the substrate.

[0113] Alternatively, the bias region can be provided at least in the formation region of the interaction portion of the electrode. By biasing the outer peripheral end of the dielectric layer in the formation region of the interaction portion, it is possible to prevent the dielectric layer from being cut off together with the substrate during the substrate cutting process, and to prevent fine peeling of the dielectric layer at the outer peripheral end of the substrate.

[0114] For example, in the above embodiment, an optical modulator having a pair of optical waveguides formed by epitaxially growing a lithium niobate film on the substrate 10 was described. However, this disclosure is not limited to this structure, and an optical modulator with optical waveguides formed by electro-optic materials such as barium titanate or lead zirconate titanate can also be used. In addition, as the waveguide layer 11, semiconductor materials, polymer materials, etc., that have electro-optic effects can also be used.

[0115] Symbol Explanation

[0116] 1. Optical modulation element

[0117] 2. Mach-Zehnder waveguide

[0118] 2a Input waveguide section

[0119] 2b Wavelength Division

[0120] 2d combiner

[0121] 2e Output waveguide section

[0122] 2i optical input port

[0123] 2o Optical output port

[0124] 2S1 First Straight Section

[0125] 2S2 Second Straight Section

[0126] 2U bend

[0127] 4a First signal electrode

[0128] 4a1 Terminal section

[0129] 4a2 Terminal Section

[0130] 4a3 Lead-out section

[0131] 4a4 lead-out

[0132] 4b Second signal electrode

[0133] 4b1 Terminal section

[0134] 4b2 Terminal section

[0135] 4b3 Lead-out section

[0136] 4b4 Lead-out section

[0137] 9a drive circuit

[0138] 9b Terminating Resistor

[0139] 10 substrate

[0140] 10a First side of substrate

[0141] The second side of the 10b substrate

[0142] The third side of the 10c substrate

[0143] The fourth side of the 10d substrate

[0144] 10s Step Structure

[0145] 11 Waveguide layer

[0146] 11r Spine

[0147] 11s Flat Panel

[0148] 12 Dielectric layer

[0149] 12a Lower layer

[0150] 12b Intermediate Layer

[0151] 12c upper layer

[0152] 13 Electrode Layer

[0153] 14 Protective Layer

[0154] E 10 outer peripheral end of substrate

[0155] E 11 outer periphery of waveguide layer

[0156] E 12 The outer periphery of the dielectric layer

[0157] E 12a The outer periphery of the lower layer

[0158] E 12b The outer periphery of the intermediate layer

[0159] E 12c The outer periphery of the upper layer

[0160] E 14 outer periphery of the protective layer

[0161] L 11 Waveguide layer offset

[0162] L 12 offset of dielectric layer

[0163] L 12a Lower layer offset

[0164] L 12b offset of intermediate layer

[0165] L 12c upper layer offset

[0166] L 14 Offset of protective layer

Claims

1. An optical modulation element, characterized in that, have: substrate; A waveguide layer is formed on the substrate; A dielectric layer is formed on the waveguide layer; as well as Electrodes, which are formed on the dielectric layer, The outer peripheral end of the dielectric layer exists in a bias region that is further inward than the outer peripheral ends of the substrate and the waveguide layer. In at least a portion of the bias region, the distance from the outer peripheral end of the substrate to the outer peripheral end of the dielectric layer is less than the distance from the outer peripheral end of the substrate to the outer peripheral end of the electrode.

2. The optical modulation element according to claim 1, wherein, It also includes: a protective layer, which is formed at least on the electrode and the dielectric layer, with the outer peripheral end of the protective layer existing in a region that is more inner than the outer peripheral end of the substrate and the waveguide layer.

3. The optical modulation element according to claim 2, wherein, The outer peripheral end of the protective layer exists in a region that is more inward than the outer peripheral end of the dielectric layer.

4. The optical modulation element according to claim 2, wherein, The outer peripheral end of the protective layer exists in a region further outward than the outer peripheral end of the dielectric layer, in which the protective layer covers the end face of the dielectric layer.

5. The optical modulation element according to any one of claims 1 to 4, wherein, The dielectric layer is composed of multiple material layers with different elements or compositions, and the outer periphery of at least one material layer exists in a region that is more inward than the outer periphery of at least one other material layer.

6. The optical modulation element according to any one of claims 1 to 4, wherein, The dielectric layer has multiple material layers with different elements or compositions. The outer peripheral end of the upper layer of the plurality of material layers exists in a region that is more inward than the outer peripheral end of the lower layer.

7. The optical modulation element according to any one of claims 1 to 4, wherein, The dielectric layer has multiple material layers with different elements or compositions. The outer peripheral end of the upper layer of the plurality of material layers exists in a region further outward than the outer peripheral end of the lower layer, in which the upper layer covers the end face of the lower layer.

8. The optical modulation element according to any one of claims 1 to 4, wherein, The dielectric layer has multiple material layers with different elements or compositions. The plurality of material layers include an upper layer, a lower layer, and an intermediate layer located between the upper layer and the lower layer. The outer peripheral end of the upper layer exists in a region that is more inward than the outer peripheral ends of the middle layer and the lower layer.

9. The optical modulation element according to any one of claims 1 to 4, wherein, The dielectric layer has multiple material layers with different elements or compositions. The plurality of material layers include an upper layer, a lower layer, and an intermediate layer located between the upper layer and the lower layer. The outer periphery of the upper layer and the middle layer exists in a region that is more inward than the outer periphery of the lower layer.

10. The optical modulation element according to any one of claims 1 to 4, wherein, The dielectric layer has multiple material layers with different elements or compositions. The plurality of material layers include an upper layer, a lower layer, and an intermediate layer located between the upper layer and the lower layer. The outer peripheral end of the upper layer exists in a region further outward than the outer peripheral ends of the middle layer and the lower layer, in which the upper layer covers the end faces of the middle layer and the lower layer.

11. The optical modulation element according to any one of claims 1 to 4, wherein, The dielectric layer has multiple material layers with different elements or compositions. The plurality of material layers include an upper layer, a lower layer, and an intermediate layer located between the upper layer and the lower layer. The outer periphery of the upper layer is located further outward than the outer periphery of the lower layer. The outer periphery of the intermediate layer exists in a region that is further outward than the outer periphery of the upper layer and the outer periphery of the lower layer.

12. The optical modulation element according to claim 8, wherein, The upper layer is composed of compounds containing Si, In, and O, the middle layer is composed of compounds containing at least La, Al, Si, and O, and the lower layer is composed of SiO2.

13. The optical modulation element according to claim 9, wherein, The upper layer is composed of compounds containing Si, In, and O, the middle layer is composed of compounds containing at least La, Al, Si, and O, and the lower layer is composed of SiO2.

14. The optical modulation element according to claim 10, wherein, The upper layer is composed of compounds containing Si, In, and O, the middle layer is composed of compounds containing at least La, Al, Si, and O, and the lower layer is composed of SiO2.

15. The optical modulation element according to claim 11, wherein, The upper layer is composed of compounds containing Si, In, and O, the middle layer is composed of compounds containing at least La, Al, Si, and O, and the lower layer is composed of SiO2.

16. The optical modulation element according to any one of claims 1 to 4, wherein, The outer peripheral end of the waveguide layer exists in a region that is more inward than the outer peripheral end of the substrate.

17. The optical modulation element according to any one of claims 1 to 4, wherein, The optical input port and optical output port of the optical waveguide formed in the waveguide layer are disposed at the outer peripheral end of the substrate. The stepped structure formed by the outer peripheral end of the dielectric layer being located further inward than the outer peripheral end of the substrate is disposed in the area other than the respective locations of the optical input port and the optical output port.

18. The optical modulation element according to any one of claims 1 to 4, wherein, The waveguide layer is composed of a lithium niobate film.

19. The optical modulation element according to any one of claims 1 to 4, wherein, The offset of the dielectric layer is less than 10% of the width of the substrate in the same direction as the offset direction of the dielectric layer.

20. The optical modulation element according to any one of claims 1 to 4, wherein, The bias region is at least located in the formation region of the interaction portion of the electrode.

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