Optical waveguide element, optical modulation device using the same, and optical transmission apparatus

Abstract

Provided is an optical waveguide element that prevents breakage of a thin plate, particularly breakage of an optical waveguide. The optical waveguide element includes a thin plate (1) having an electro-optic effect and a thickness of 10 μm or less, in which an optical waveguide (2) is formed; and a reinforcing substrate that supports the thin plate. The optical waveguide element is characterized in that the thin plate (1) has a rectangular shape in plan view, a heterogeneous element layer (3) is formed in at least a portion between the outer periphery of the thin plate and the optical waveguide (2), the heterogeneous element layer (3) is formed by disposing an element different from the element constituting the thin plate in the thin plate, and the sum of the lengths of the cleavage planes of the thin plate that cross the formation region of the heterogeneous element layer is 5% or more of the width of the thin plate in the short side direction.

Description

Technical Field

[0001] The present invention relates to optical waveguide elements, optical modulation devices using optical waveguide elements, and optical transmission devices, and particularly to an optical waveguide element comprising: a thin plate having an electro-optic effect and a thickness of 10 μm or less, wherein an optical waveguide is formed on the thin plate; and a reinforcing substrate supporting the thin plate. Background Technology

[0002] In the fields of optical measurement and optical communication, optical waveguide components such as optical modulators using substrates with electro-optic effects are widely used. Moreover, in order to broadband the frequency response characteristics or reduce the driving voltage, the thickness of the substrate is reduced to about 10 μm or less, thereby reducing the actual effective refractive index of the microwaves used as modulation signals, achieving velocity matching between microwaves and light waves, and thus improving the electric field efficiency.

[0003] When using thin plates with a thickness of less than 10 μm, the mechanical strength of the thin plate itself is weak. As shown in Patent Document 1, the reinforcing substrate supporting the thin plate is bonded and fixed.

[0004] However, thin substrates with a thickness of less than 10 μm become very brittle due to reduced toughness. Therefore, even when reinforced with a reinforcing substrate, cracks can still form in the thin substrate, damaging the optical waveguide and increasing light loss. In particular, when cutting chips for various optical waveguide components from a wafer substrate with formed optical waveguides, the thin substrate itself is subjected to mechanical loads, making it prone to breakage.

[0005] Prior art literature

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2010-85789 Summary of the Invention

[0008] Summary of the invention

[0009] The problem that the invention aims to solve

[0010] The problem to be solved by the present invention is to solve the aforementioned problems and provide an optical waveguide element that prevents damage to thin plates, especially optical waveguides, an optical modulation device using the optical waveguide element, and an optical transmission device.

[0011] Solution for solving the problem

[0012] To address the aforementioned issues, the optical waveguide element of the present invention has the following technical features.

[0013] (1) An optical waveguide element comprising: a thin plate having an electro-optic effect and a thickness of 10 μm or less, wherein an optical waveguide is formed on the thin plate; and a reinforcing substrate supporting the thin plate, wherein the optical waveguide element is characterized in that the shape of the thin plate in plan view is rectangular, and at least a portion between the outer periphery of the thin plate and the optical waveguide is formed with a dissimilar element layer, wherein the dissimilar element layer is formed by arranging elements different from the elements constituting the thin plate within the thin plate, and the sum of the lengths of the cleavage surfaces of the thin plate that traverse the region where the dissimilar element layer is formed is at least 5% of the width of the thin plate in the short side direction.

[0014] (2) In the optical waveguide element described in (1) above, the thickness of the heterogeneous element layer is more than half the thickness of the thin plate.

[0015] (3) In the optical waveguide element described in (1) or (2) above, the characteristic is that the heterogeneous element layer is formed by diffusing titanium.

[0016] (4) In the optical waveguide element described in (3) above, the optical waveguide is a diffused waveguide formed by diffusing a high refractive index material, the heterogeneous element layer and the optical waveguide are formed on the same surface of the thin plate, and the thickness from the surface of the thin plate to the highest part of the heterogeneous element layer is set to be thicker than the thickness from the surface of the thin plate to the highest part of the optical waveguide.

[0017] (5) In any of the optical waveguide elements described in (1) to (4) above, the characteristic is that an electrode is formed in the thin plate, and the electrode is formed separately from the heterogeneous element layer.

[0018] (6) An optical modulation device, characterized in that it comprises: an optical waveguide element as described in any of (1) to (5) above; a housing for housing the optical waveguide element; and an optical fiber for inputting light waves from the outside of the housing to the optical waveguide or outputting light waves from the optical waveguide to the outside of the housing.

[0019] (7) In the optical modulation device described in (6) above, the optical modulation device is characterized in that the optical modulation device has an electronic circuit inside the housing that amplifies the modulation signal input to the optical waveguide element.

[0020] (8) An optical transmitting device, characterized in that it comprises: an optical modulation device described in (6) or (7) above; and an electronic circuit that outputs a modulation signal that causes the optical modulation device to perform a modulation operation.

[0021] Invention Effects

[0022] This invention relates to an optical waveguide element comprising: a thin plate having an electro-optic effect and a thickness of 10 μm or less, on which an optical waveguide is formed; and a reinforcing substrate supporting the thin plate. The thin plate, when viewed from above, has a rectangular shape. At least a portion between the outer periphery of the thin plate and the optical waveguide is formed with a dissimilar element layer. This dissimilar element layer is formed by arranging elements different from those constituting the thin plate within the thin plate. The sum of the lengths of the cleavage surfaces of the thin plate extending across the region where the dissimilar element layer is formed is at least 5% of the width of the thin plate in the short side direction. Therefore, even if a crack forms along the cleavage surface of the thin plate from its outer periphery toward the optical waveguide, the dissimilar element layer can prevent the crack from progressing, thereby suppressing damage to the optical waveguide. Attached Figure Description

[0023] Figure 1 This is a top view illustrating a first embodiment of the optical waveguide element of the present invention.

[0024] Figure 2 yes Figure 1 A cross-sectional view at point X-X'.

[0025] Figure 3 This is a top view illustrating a second embodiment of the optical waveguide element of the present invention.

[0026] Figure 4 This is a top view illustrating a third embodiment of the optical waveguide element of the present invention.

[0027] Figure 5 This is a top view illustrating a fourth embodiment of the optical waveguide element of the present invention.

[0028] Figure 6 This is a top view illustrating the fifth embodiment of the optical waveguide element of the present invention.

[0029] Figure 7 It is a diagram illustrating the relationship between the formation region of the heterogeneous element layer and the cleavage plane.

[0030] Figure 8 It is a diagram illustrating the configuration relationship between optical waveguides and heterogeneous element layers.

[0031] Figure 9 This is a diagram showing an example (1) of a wafer forming the optical waveguide element of the present invention.

[0032] Figure 10 This is a diagram showing an example (2) of a wafer forming the optical waveguide element of the present invention.

[0033] Figure 11 This is a diagram showing an example (3) of a wafer forming the optical waveguide element of the present invention.

[0034] Figure 12 This is a diagram illustrating the optical modulation device and optical transmission apparatus of the present invention. Detailed Implementation

[0035] Hereinafter, preferred embodiments of the optical waveguide element of the present invention, the optical modulation device using the optical waveguide element, and the optical transmission apparatus will be described in detail.

[0036] The optical waveguide element of the present invention, such as Figures 1-6 As shown, the device comprises: a thin plate 1 having an electro-optic effect and a thickness of 10 μm or less, on which an optical waveguide 2 (WG) is formed; and a reinforcing substrate 5 supporting the thin plate. The optical waveguide element is characterized in that the shape of the thin plate 1 when viewed from above is rectangular, and at least a portion between the outer periphery of the thin plate and the optical waveguide 2 is formed with a dissimilar element layer 3. The dissimilar element layer 3 is formed by arranging elements different from those constituting the thin plate within the thin plate, and the sum of the lengths of the cleavage surfaces of the thin plate that traverse the region where the dissimilar element layer is formed is at least 5% of the width of the thin plate in the short side direction.

[0037] The substrate 1 used as the optical waveguide element of the present invention can be a substrate with electro-optic effect, such as lithium niobate (LN), lithium tantalate (LT), or PLZT (lead lanthanum zirconate titanate). In particular, the present invention can be effectively applied to LN substrates with X-plates formed along the surface of a wafer.

[0038] The optical waveguide formed on the substrate 1 can be formed by diffusing Ti or the like to the substrate surface using methods such as thermal diffusion or proton exchange. Furthermore, the portion of the substrate corresponding to the optical waveguide can be etched into a convex rib-shaped waveguide by etching the portion of the substrate 1 other than the optical waveguide or by forming grooves on both sides of the optical waveguide.

[0039] To achieve velocity matching between the microwave and light waves in the modulation signal, the thickness of substrate 1 is set to 10 μm or less, more preferably 5 μm or less. To improve the mechanical strength of substrate 1, such as... Figure 2 As shown, a reinforcing substrate 5 is bonded and fixed to the substrate 1 via an adhesive layer 4, such as resin, on the back side of the substrate (thin plate) 1. The reinforcing substrate 5 is made of a material with a coefficient of thermal expansion similar to that of the substrate 1, such as an LN substrate. Furthermore, when the substrate (thin plate) 1 and the reinforcing substrate 5 are directly bonded without using the adhesive layer 4, the thickness of the substrate 1 can be set to 1 μm or less, preferably 0.7 μm or less.

[0040] The optical waveguide element of the present invention is characterized in that, as Figure 1 , Figures 3-6As shown, at least a portion between the outer periphery of the thin plate 1 and the optical waveguide 2 is formed into a dissimilar element layer 3, in which elements different from those constituting the thin plate are disposed within the thin plate. Preferably, materials such as Ti, MgO, or Zn, which can form dissimilar element layers in the substrate through thermal diffusion, are used as the material constituting the dissimilar element layer.

[0041] In the foreign element layer 3, the foreign element is dissolved in the crystalline substrate with an electro-optic effect through thermal diffusion. This suppresses dislocation movement and strengthens the material (solid solution strengthening). Furthermore, the presence of the foreign element layer 3 suppresses the formation of cracks in the thin sheet caused by thermal stress or shear stress during the manufacturing process. In addition, by diffusing the foreign element, the cleavage planes of materials such as LN are locally disrupted, so even if cracks form, they will not extend along the cleavage direction, preventing damage to the optical waveguide.

[0042] Figure 1 , Figures 3-6 This is a diagram illustrating the formation pattern of dissimilar element layers when viewed from above in an optical waveguide element. Figure 1 The diagram shows a layer 3 of dissimilar elements arranged over a large area from the outer periphery of the thin plate 1 to the optical waveguide 2. Figure 3 The diagram shows a layer 3 of dissimilar elements arranged around the outer periphery of a thin plate 1 that is prone to cracking. Figure 4 The diagram shows a dissimilar element layer 3 arranged along the long side of the thin plate 1, which suppresses the effects of cracks that are easily generated when cutting the chip along the long side.

[0043] Figure 5 and Figure 6 It is a diagram in which the heterogeneous element layer 3 is discretely arranged, such that a portion of the heterogeneous element layer 3 necessarily exists along the direction of propagation of the cleavage surface A generated in the thin plate 1.

[0044] The configuration pattern of heterogeneous element layer 3 can not only be as Figure 5 Region AR1 is arranged regularly with a fixed spacing, and can be arranged in an irregular pattern, concentrated at locations that are particularly protected by the heterogeneous element layer 3, as shown in region AR2. Furthermore, if there is no waveguide along the direction of the cleavage plane A, the heterogeneous element layer can be omitted, as in region AR3.

[0045] The longer the heterogeneous element layer 3 is along the cleavage plane A of the thin plate 1, the more effectively it can prevent the crack from progressing. Figure 7 This diagram illustrates dissimilar element layers discretely arranged along cleavage plane A. In this invention, when the sum of the lengths (L1, L2) of the cleavage planes traversing the dissimilar element layers, as described later, is more than 5% of the width in the short side direction of the thin plate, the propagation of cracks along the cleavage plane can be effectively suppressed to a certain extent.

[0046] like Figure 2 As shown, in order to prevent light waves propagating in the optical waveguide from being scattered or absorbed due to the presence of the heterogeneous element layer, the spacing G between the heterogeneous element layer 3 and the optical waveguide 2 can be set to be greater than or equal to the mode field diameter (MFD) of the light waves propagating in the optical waveguide.

[0047] Furthermore, regarding the thickness of the dissimilar element layer 3, if the thickness of the dissimilar element layer 3 is the same as or greater than the thickness of the portion of the thin plate 1 where the cleavage surface is formed (i.e., the portion where the dissimilar element layer is not formed), the generation of cracks at the cleavage surface can be effectively suppressed. Therefore, the thickness t1 of the dissimilar element layer 3 can be set to be more than half the thickness t0 of the thin plate. Of course, it is more preferable to form the dissimilar element layer 3 along the entire thickness direction of the thin plate 1.

[0048] Figure 8 This is a diagram showing examples of heterogeneous element layers 3 configured for various optical waveguide WGs. Figure 8 (a) and Figure 2 Similarly, a dissimilar element layer 3 is disposed on the same surface as the diffused waveguide WG. In this structure, when titanium is used in the dissimilar element layer 3, it is possible to form the dissimilar element layer 3 simultaneously with the thermal diffusion of titanium in the optical waveguide. However, in order to set the mechanical strength of the dissimilar element layer to be higher than that of the optical waveguide portion, the amount of titanium formed on the surface of the thin plate before thermal diffusion (the amount of titanium per unit area) in the dissimilar element layer can be greater than that in the optical waveguide, effectively making the thickness of the dissimilar element layer thicker than that of the optical waveguide. Figure 8 As shown in (f), in this case, the upper surface of the heterogeneous element layer 3 and the optical waveguide WG becomes a convex shape protruding from the surface of the thin plate, and the height of this convex portion of the heterogeneous element layer is higher than the height of the convex portion of the optical waveguide by an amount represented by the symbol Δ. It should be noted that, even when the elements that diffuse thermally are different in the optical waveguide and the heterogeneous element layer, setting the height of the heterogeneous element layer to be higher than the height of the optical waveguide can more stably suppress the arrival of cracks into the optical waveguide.

[0049] like Figure 8 As shown in (b), the surface forming the optical waveguide WG and the surface forming the heterogeneous element layer 3 can also be set as different surfaces (opposite to each other) of the thin plate 1. When the thickness of the thin plate is 10 μm or less, especially 5 μm or less, elements that thermally diffuse from one surface can easily reach the vicinity of the opposite surface, thus enabling the formation of a heterogeneous element layer with higher uniformity. Even in cases such as Figure 8 (b) In the case that optical waveguides and heterogeneous element layers are formed on different surfaces, sufficient crack suppression effect can also be obtained.

[0050] Figure 8(c) and (d) show the case where a ribbed optical waveguide is formed as the optical waveguide WG. This case is also similar to... Figure 8 Similarly to (a) and (b), the heterogeneous element layer 3 can be formed on the same surface as the optical waveguide WG or on a different surface (surfaces opposite to each other). Furthermore, it can also be as follows: Figure 8 (e) shows that a dissimilar element layer 3 is formed over the entire back surface of the thin plate 1. In this case, the formation area of ​​the dissimilar element layer 3 covers the entire thin plate, thus uniformly improving the mechanical strength of the thin plate. It should be noted that a diffusion waveguide of Ti or the like can also be formed on the protrusion of the ribbed waveguide as the structure of the optical waveguide WG.

[0051] In optical waveguide components such as optical modulators, control electrodes, such as signal electrodes, ground electrodes, or DC bias electrodes, are placed on or near the upper side of the waveguide to modulate or control the bias point of light propagating in the waveguide. If such electrodes are placed on a thin plate, and the difference between the thermal expansion coefficient of the electrodes and that of the thin plate, especially the dissimilar element layer, is large, electrode peeling from the dissimilar element layer formation region and increased internal stress in the dissimilar element layer formation region can occur. In the worst case, partial substrate breakage may occur in the dissimilar element layer. Therefore, the dissimilar element layer formation region and the electrode formation region can be configured separately. It should be noted that the present invention does not hinder the formation of electrodes on the dissimilar element layer to a extent that electrode peeling and substrate breakage as described above do not occur.

[0052] Figures 9-11 This is a diagram showing the pattern of the region where the heterogeneous element layer is formed in the wafer state. The wafer 10 can be in any state before or after the thin plate is processed. In order to suppress wafer breakage due to thermal stress during thermal diffusion, optical waveguides and heterogeneous element layers can be formed before the thin plate is processed.

[0053] exist Figure 9 In this process, a heterogeneous element layer 3 is formed only in the chip portion (C1, C2) constituting the optical waveguide element to suppress the propagation of cracks originating from the periphery of wafer 10 into the interior of the chip portion. Figure 10 In this process, the heterogeneous element layer is extended throughout the wafer to suppress the generation and progression of cracks across the entire wafer. Furthermore, in... Figure 11 In order to facilitate the final cutting of the chip portions (C1, C2) constituting the optical waveguide element from the wafer 10, the heterogeneous element layer 3 is not formed in the vicinity 30 surrounding each chip portion (C1, C2), thus making the wafer cutting easier.

[0054] To verify the effectiveness of the present invention, the following experiment was conducted to measure the crack (crack) initiation rate.

[0055] After depositing a full-surface Ti film on an LN substrate (wafer), optical waveguides and heterogeneous element layers are formed using photolithography. Heating causes the optical waveguides and heterogeneous element layers to thermally diffuse into the LN substrate. Then, optical waveguide elements (chips) are cut out. The ratio of the number of chips with cracks reaching the optical waveguides to the number of cut-out chips is quantified as the "crack generation rate."

[0056] In addition, all optical waveguide substrates are fabricated with the following values, which are configured to bond thin optical waveguide substrates to a 500μm thick reinforcing substrate via an adhesive with a thickness of 30μm.

[0057] The thickness of the thin plate is t0 = 10 μm, the thickness of the heterogeneous element layer is t1 = 10 μm, the width of the short side of the chip (rectangular) is W0 = 2000 μm, and the MFD of the optical waveguide is Φ10 μm.

[0058] In Example 1, using Figure 1 The pattern of the formation region of the heterogeneous element layer is shown, and the gap G between the optical waveguide and the heterogeneous element layer is set to 30 μm.

[0059] In Example 2, using Figure 3 The pattern of the heterogeneous element layer formation area shown is formed with a width of 100 μm along the periphery of the thin plate.

[0060] In Example 3, using Figure 4 The pattern shown is formed by creating a heterogeneous element layer with a width W1 of 100 μm.

[0061] In Example 4, using Figure 5 The pattern shown has a width of 100 μm for the dissimilar element layer along the long side of the thin plate, and a spacing of 50 μm between adjacent dissimilar element layers. It should be noted that the cleavage angle θ of the X-cut thin plate is 60 degrees.

[0062] In Comparative Example 1, no heterogeneous element layer was formed.

[0063] In Comparative Example 2, using Figure 4 The pattern shown has a heterogeneous element layer with a width W1 of 20 μm.

[0064] Table 1 shows the test results.

[0065] [Table 1]

[0066]

[0067] According to the results in Table 1, as shown in Examples 1 to 4, when a dissimilar element layer is formed on the periphery of the thin plate, the crack generation rate, which was approximately 10% previously as shown in Comparative Example 1, can be suppressed to less than half. In particular, when comparing Example 3 with Comparative Example 2, it can be confirmed that when the width of the dissimilar element layer is 5% or more relative to the width of the short side of the chip, the generation and progression of cracks can be suppressed more effectively.

[0068] Furthermore, in this invention, the aforementioned optical waveguide elements can also be used to construct optical modulation devices and optical transmission devices. For example... Figure 12 As shown, the substrate 1 of the optical waveguide element of the present invention can be housed in a housing SH, such as a metal, and the outside of the housing can be connected to the optical waveguide element 1 via an optical fiber F, thereby providing a compact optical modulation device MD. Of course, not only can the incident or emitting portion of the optical waveguide of the substrate 1 be optically connected to the optical fiber via a space optical system, but the optical fiber can also be directly connected to the substrate 1.

[0069] An electronic circuit (digital signal processor DSP) that outputs a modulation signal So to modulate an optical modulator MD is connected to the optical modulator MD, thereby constructing an optical transmission device OTA. The modulation signal S applied to the optical control element needs to amplify the DSP's output signal So; therefore, a driver circuit DRV is used. The driver circuit DRV and the digital signal processor DSP can be configured outside the housing SH, or they can be configured inside the housing SH. In particular, configuring the driver circuit DRV inside the housing further reduces the propagation loss of the modulation signal from the driver circuit.

[0070] Industrial availability

[0071] As described above, according to the present invention, it is possible to provide an optical waveguide element that prevents damage to thin plates, particularly optical waveguides.

[0072] Explanation of reference numerals in the attached figures

[0073] 1. Substrates (thin plates) exhibiting electro-optic effects

[0074] 2 Optical waveguide

[0075] 3. Layer of different elements

[0076] 4. Adhesive layer

[0077] 5. Reinforced substrate

[0078] MD optical modulation device

[0079] OTA optical transmission device

[0080] SH casing

Claims

1. An optical waveguide element comprising: a thin plate having an electro-optic effect and a thickness of 10 μm or less, wherein an optical waveguide is formed on the thin plate; and a reinforcing substrate supporting the thin plate, wherein the optical waveguide element is characterized in that... The thin plate has a rectangular shape when viewed from above. At least a portion of the outer periphery of the thin plate and the optical waveguide is formed into a dissimilar element layer. This dissimilar element layer is formed by arranging elements different from those constituting the thin plate within the thin plate, such that a portion of the dissimilar element layer necessarily exists along the direction of propagation of the cleavage plane of the thin plate. Furthermore, the sum of the lengths of the cleavage plane of the thin plate traversing the region where the dissimilar element layer is formed is at least 5% of the width of the thin plate in the short side direction.

2. The optical waveguide element according to claim 1, characterized in that, The thickness of the heterogeneous element layer is more than half the thickness of the thin plate.

3. The optical waveguide element according to claim 1 or 2, characterized in that, This heterogeneous element layer is formed by diffusing titanium.

4. The optical waveguide element according to claim 3, characterized in that, The optical waveguide is a diffused waveguide formed by diffusing a high refractive index material. The heterogeneous element layer and the optical waveguide are formed on the same surface of the thin plate. The thickness from the surface of the thin plate to the highest part of the heterogeneous element layer is set to be thicker than the thickness from the surface of the thin plate to the highest part of the optical waveguide.

5. The optical waveguide element according to claim 1 or 2, characterized in that, An electrode is formed on the thin plate, and the electrode is formed separately from the heterogeneous element layer.

6. An optical modulation device, characterized in that, It comprises: an optical waveguide element as described in any one of claims 1 to 5; a housing for housing the optical waveguide element; and an optical fiber for inputting light waves from the outside of the housing to the optical waveguide or outputting light waves from the optical waveguide to the outside of the housing.

7. The optical modulation device according to claim 6, characterized in that, The optical modulator has an electronic circuit inside the housing that amplifies the modulation signal input to the optical waveguide element.

8. An optical transmitting device, characterized in that, It comprises: the optical modulation device as described in claim 6 or 7; and electronic circuitry that outputs a modulation signal that causes the optical modulation device to perform a modulation operation.

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