A coupling method of a glass substrate-based single-mode optical fiber and a lead zirconate titanate waveguide
By fabricating an optical waveguide with a gradually changing refractive index on a glass substrate and designing an anti-conical structure in the coupling region of the PZT waveguide, the problem of size mismatch between the PZT waveguide and the optical fiber mode field was solved, resulting in higher coupling efficiency and lower optical power loss.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHAOXING RES INST OF ZHEJIANG UNIV
- Filing Date
- 2023-03-15
- Publication Date
- 2026-07-21
AI Technical Summary
The mode field size mismatch between the PZT waveguide and the optical fiber leads to coupling mismatch, resulting in significant optical power loss.
Using a glass substrate as an interlayer, an optical waveguide with a gradually changing refractive index is fabricated on the glass substrate, and an inverse conical structure is designed in the coupling region of the PZT waveguide. An optically transparent adhesive is used to fix the glass waveguide and the PZT waveguide, thereby achieving evanescent coupling and reducing loss.
This improved the coupling efficiency between the optical fiber and the PZT waveguide, reduced the optical power loss at the interface, and achieved higher coupling efficiency and lower loss.
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Figure CN116360033B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of coupling methods between single-mode optical fiber and lead zirconate titanate waveguide, and particularly to a coupling method between single-mode optical fiber and lead zirconate titanate waveguide based on a glass substrate. Background Technology
[0002] Piezoelectric ceramics are functional ceramics capable of converting mechanical energy and electrical energy into each other, and they have wide applications in resonators, sensors, ultrasonic transducers, drivers, filters, and electronic igniters. Among them, lead zirconate titanate (Pb(Zr1-xTiO3), PZT) ceramics possess excellent piezoelectric and dielectric properties. Due to their good stability, high precision, high energy conversion efficiency, fast response speed, and significantly superior mechanical quality factor, piezoelectric coefficient, and electromechanical coupling constant compared to lead-free piezoelectric ceramics, they are widely used in piezoelectric sensing and actuation fields.
[0003] With the gradual maturation of silicon photonics technology, PZT has begun to be used in the fabrication of photonic devices, mainly optical switches and modulators. In the future, PZT will also be used to fabricate various waveguides. However, the compatibility between PZT waveguides and fiber optic components is limited due to the size mismatch between the mode distributions of the fiber and the PZT waveguide. Fiber optics typically have a mode field size (MFD) of approximately 10 micrometers (μm). The large MFD mismatch between the optical propagation modes in the PZT waveguide and the fiber is called coupling mismatch, which causes significant optical power loss at the interface. To address these issues, a solution is proposed below. Summary of the Invention
[0004] The purpose of this invention is to provide a coupling method between a single-mode optical fiber and a lead zirconate titanate (PZT) waveguide based on a glass substrate, which has the advantages of improving the coupling efficiency between the optical fiber and the PZT waveguide and reducing optical power loss at the interface.
[0005] The above-mentioned technical objective of the present invention is achieved through the following technical solution:
[0006] A coupling method between a single-mode optical fiber and a lead zirconate titanate (PZT) waveguide based on a glass substrate includes a glass substrate, wherein the glass substrate is a glass waveguide, and a PZT waveguide is disposed on the glass substrate. The coupling region of the PZT waveguide has an anti-conical structure, which is used to achieve low-loss power transmission between the glass waveguide and the PZT waveguide. The glass waveguide and the PZT waveguide are fixed by an optically transparent adhesive, which is used to control waveguide separation, wherein the ion-exchanged waveguide is aligned with the PZT waveguide.
[0007] Preferably, the fabrication of the PZT waveguide includes the following steps: depositing and etching PZT material onto silicon dioxide material, and covering it with a buried oxide layer to obtain the PZT waveguide. Preferably, the fabrication of the glass waveguide includes the following steps:
[0008] S1: Cover the glass substrate with a mask and perform photolithography on the glass substrate;
[0009] S2: Cover the glass substrate with the first molten salt to perform primary silver ion exchange;
[0010] S3: Remove the first molten salt and mask, cover the glass substrate with the second molten salt, perform secondary sodium ion exchange, and then remove the second molten salt from the surface of the glass substrate.
[0011] S4: Separate the glass substrate using a laser;
[0012] Through the above steps, an optical waveguide with a gradually changing refractive index is formed on the top of the glass substrate.
[0013] Preferably, the inverted conical structure is characterized by the PZT portion extending horizontally and its width gradually decreasing towards the glass waveguide direction, thus presenting an inverted conical shape.
[0014] Preferably, the evanescent coupling region is designed by calculating the continuous supermode overlap integral along the taper of the inverted cone structure as a measure of the change in MFD mismatch loss; the taper shape of the inverted cone structure is obtained by applying a constant mode mismatch loss along the taper length; the taper design needs to take into account the supermode overlap integral of TE and TM modes.
[0015] Preferably, the buried oxide layer material of the PZT waveguide is silicon dioxide.
[0016] Preferably, the PZT waveguide has a rectangular cross-sectional profile.
[0017] Preferably, in the glass waveguide, the electric field is concentrated at the high refractive index region of the refractive index gradient region.
[0018] Preferably, the glass waveguide can be directly coupled to the optical fiber, and at the overlapping edge with the PZT waveguide, it is evanescently coupled to the PZT waveguide.
[0019] Ideally, the adhesive bonding line thickness needs to be strictly controlled, and the stability of the adhesive refractive index over time and temperature changes is also required to maintain high coupling efficiency.
[0020] As a preferred option, the refractive index contrast (the difference between the maximum refractive index at the center of the waveguide and the minimum refractive index at the periphery) of the glass waveguide needs to be designed. A higher refractive index contrast can reduce bending loss and a smaller minimum bending radius, which can also achieve a denser waveguide arrangement.
[0021] The beneficial effects of this invention are as follows:
[0022] This application consists of a glass waveguide and a tapered PZT waveguide evanescently coupled together.
[0023] The first part is the glass waveguide. The glass waveguide manufacturing process involves multiple steps, mainly four: photolithography; primary silver ion exchange; reference protection, mask removal, and secondary ion exchange; and laser separation. Through these steps, a refractive index-gradient optical waveguide is formed on the top of the glass. The optical quality of the top surface of the glass substrate carrying the ion-exchanged (IOX) waveguide is ideally suited for coupling with the evanescent modes of the PZT waveguide.
[0024] The second part is the PZT waveguide. PZT material is deposited and etched on silicon dioxide material and covered by a thin silicon dioxide layer to form the PZT waveguide. An anti-conical structure is designed in the coupling region.
[0025] An optically transparent adhesive is used to provide mechanical contact and control waveguide separation between the glass waveguide and the PZT waveguide, wherein the ion-exchange waveguide and the PZT waveguide are aligned.
[0026] Low-loss power transfer between the PZT and the glass waveguide is achieved by reducing the width of the PZT waveguide through thermal adiabatic treatment. The continuous supermode overlap integral along the taper is calculated as a measure of the variation in MFD mismatch loss, thus designing the evanescent coupling region. The taper shape is obtained by applying a constant mode mismatch loss along the taper length. The taper design must consider the supermode overlap integrals of both TE and TM modes.
[0027] The advantage of this structure is that direct coupling between the PZT waveguide and the optical fiber results in excessive loss. The glass waveguide, as an intermediary layer, can be evanescently coupled to the PZT waveguide or directly coupled to the single-mode optical fiber, and it has a higher power tolerance. Attached Figure Description
[0028] Figure 1 This is a schematic diagram illustrating the coupling mismatch between the PZT waveguide and the optical fiber in an embodiment.
[0029] Figure 2 This is a three-dimensional conceptual diagram illustrating the coupling method between a single-mode optical fiber and a PZT waveguide based on a glass substrate, as shown in the embodiment.
[0030] Figure 3 for Figure 2 Cross-sectional view of the thermally adiabatic coupling region;
[0031] Figure 4 The following is a detailed process diagram for manufacturing a glass waveguide as an example.
[0032] Reference numerals: 201, Fiber optic interface; 202, Glass waveguide; 204, PZT waveguide; 203, Thermal coupling; 301, Buried oxide layer; 302, Silica material; 303, PZT material; 304, Adhesive; 305, Ion-exchanged glass waveguide; 306, Core. Detailed Implementation
[0033] The following description is merely a preferred embodiment of the present invention, and the scope of protection is not limited to this embodiment. All technical solutions falling within the scope of the present invention should be protected by the present invention. Identical components are indicated by the same reference numerals.
[0034] like Figure 1 The diagram illustrates a typical photonic chip design for coupling a PZT waveguide 204 to an optical fiber. The design includes an inverted tapered waveguide serving as an edge coupler, meeting requirements for lower loss, polarization independence, broadband bandwidth, and lower cost. Due to manufacturing limitations or design requirements, the edge of the tapered waveguide (tip) within the chip is typically a few micrometers away from the chip edge at the fiber interface 201. The design also includes cladding layers, such as SiO2 layers, below and above the tapered waveguide, serving as the propagation medium along the tapered waveguide or at its ends. Propagation along the tapered waveguide in the SiO2 amplifies the waveguide mode, which continues to propagate in the SiO2 medium at the tip before reaching the optical fiber. However, the lack of lateral confinement in the SiO2 layer causes stray output light from the tip to be scattered within the cladding. The high refractive index of the Si substrate causes a significant portion of the output light from the tip to penetrate into the substrate, which greatly reduces the chip-to-fiber coupling efficiency.
[0035] The embodiments provided herein are designed to improve coupling efficiency and reduce coupling mismatch between PZT waveguide 204 and optical fiber (or other suitable optical waveguides with an MFD comparable to that of optical fiber). These embodiments include adding a glass waveguide 202 to reduce coupling loss at the interface between the PZT waveguide 204 and the optical fiber. The glass waveguide 202 is added as an interface between the waveguide and the optical fiber. This design improves coupling efficiency by maximizing or increasing the recovery portion between the optical propagation modes supported by the waveguide and the optical fiber.
[0036] The present invention will be further described below with reference to the accompanying drawings.
[0037] Figure 2 This is a coupling structure diagram of a single-mode optical fiber and a PZT waveguide, which is mainly divided into three parts: the optical fiber interface 201, the glass waveguide 202, and the PZT waveguide 204. The overlapping part of the glass waveguide 202 and the PZT waveguide 204 is the thermal coupling 203, which is the key part of this invention. Its cross-section is shown below. Figure 3 As shown in the figure. Among them, the PZT waveguide 204 is inverted conical in shape, as shown by the dashed line.
[0038] Figure 3This is a cross-sectional view of the coupling section between the glass waveguide and the PZT waveguide. The upper part is the PZT waveguide 204, formed by the deposition and etching of PZT material 303 on silicon dioxide material 302 and covered by a thin silicon dioxide layer, with a rectangular cross-sectional profile. The lower part is the glass waveguide 202, whose refractive index gradually changes at the top center (core 306), with the highest refractive index at the center and gradually decreasing towards the periphery. The upper and lower parts are connected by adhesive 304.
[0039] The specific principle is as follows:
[0040] Glass waveguide 202 can be directly coupled to optical fiber (MFD mismatch is very small). Therefore, fiber-to-glass waveguide 202 coupling can be directly achieved by connecting optical fiber through optical fiber interface 201. Then, glass waveguide 202 and PZT waveguide 204 are evanescently coupled at the overlapping portion. Glass waveguide 202 has low insertion loss, and as an interface added between PZT waveguide 204 and optical fiber, it can reduce coupling loss at the interface between PZT waveguide 204 and optical fiber, and significantly improve coupling efficiency.
[0041] First, the glass waveguide 202 is manufactured through multiple processing steps, mainly including the following four steps: (1) photolithography; (2) primary silver ion exchange; (3) reference protection, mask removal, and secondary ion exchange; (4) laser separation. The process flow diagram is shown below. Figure 4 As shown. Using these steps, an optical waveguide with a gradually changing refractive index can be fabricated. At the same time, the refractive index contrast of the glass waveguide 202 (the difference between the maximum refractive index at the center of the core 306 and the minimum refractive index at the periphery) needs to be designed. A higher refractive index contrast can reduce bending loss, and a smaller minimum bending radius can achieve a denser waveguide arrangement.
[0042] Secondly, low-loss power transfer between the PZT and the glass waveguide 202 is achieved by reducing the width of the PZT waveguide 204 through thermal insulation. As the waveguide width decreases, mode constraint decreases, the effective cross-section increases, and the effective refractive index decreases, allowing light to couple into the glass waveguide 202. Therefore, the PZT material 303 extends horizontally and gradually decreases in width towards the glass waveguide 202, exhibiting an inverted cone shape. The continuous supermode overlap integral along the cone is calculated as a measure of the MFD mismatch loss variation, thus designing the evanescent coupling region. The cone shape is obtained by applying a constant mode mismatch loss along the cone length. The cone design must consider the supermode overlap integrals of the TE and TM modes.
[0043] Finally, an optically transparent adhesive 304 is used to provide mechanical contact and control waveguide separation between the glass waveguide 202 and the PZT waveguide 204, with the ion-exchange waveguide and PZT waveguide 204 aligned. It is important to note that coupling loss is highly sensitive to waveguide separation; therefore, the thickness of the adhesive 304 bonding line must be strictly controlled. Furthermore, the stability of the adhesive 304's refractive index over time and temperature changes must be ensured to maintain high coupling efficiency.
[0044] The specific embodiments described above further illustrate the technical problems, technical solutions, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A coupling device for a single-mode optical fiber and a lead zirconate titanate waveguide based on a glass substrate, characterized in that, The device includes a glass substrate, which is a glass waveguide. A PZT waveguide is disposed on the glass substrate. The coupling region of the PZT waveguide has an inverted conical structure. The inverted conical structure is formed by the PZT portion extending horizontally and gradually decreasing in width towards the glass waveguide, presenting an inverted cone shape. The inverted conical structure is used to achieve low-loss power transmission between the glass waveguide and the PZT waveguide. The glass waveguide and the PZT waveguide are fixed by an optically transparent adhesive, which is used to control waveguide separation. The ion-exchange waveguide is aligned with the PZT waveguide. The glass waveguide fabrication Includes the following steps: S1: Cover the glass substrate with a mask and perform photolithography on the glass substrate; S2: Cover the glass substrate with the first molten salt to perform primary silver ion exchange; S3: Remove the first molten salt and mask, cover the glass substrate with the second molten salt, perform secondary sodium ion exchange, and then remove the second molten salt from the surface of the glass substrate. S4: Separate the glass substrate using a laser; Through the above steps, an optical waveguide with a gradually changing refractive index is formed on the top of the glass substrate.
2. The coupling device for a single-mode optical fiber and a lead zirconate titanate waveguide based on a glass substrate according to claim 1, characterized in that, The fabrication of the PZT waveguide includes the following steps: PZT waveguides are fabricated by depositing and etching PZT material onto silicon dioxide material and then covering it with a buried oxide layer.
3. The coupling device for a single-mode optical fiber and a lead zirconate titanate waveguide based on a glass substrate according to claim 1, characterized in that, The evanescent coupling region is designed by calculating the continuous supermode overlap integral along the taper of the inverted cone structure as a measure of the variation in MFD mismatch loss; the taper shape of the inverted cone structure is obtained by applying a constant mode mismatch loss along the taper length.
4. The coupling device for a single-mode optical fiber and a lead zirconate titanate waveguide based on a glass substrate according to claim 2, characterized in that, The buried oxide layer material of the PZT waveguide is silicon dioxide.
5. The coupling device for a single-mode optical fiber and a lead zirconate titanate waveguide based on a glass substrate according to claim 1, characterized in that, The PZT waveguide has a rectangular cross-sectional profile.
6. The coupling device for a single-mode optical fiber and a lead zirconate titanate waveguide based on a glass substrate according to claim 1, characterized in that, In the glass waveguide, the electric field is concentrated at the high refractive index region in the region of gradual refractive index change.
7. The coupling device for a single-mode optical fiber and a lead zirconate titanate waveguide based on a glass substrate according to claim 1, characterized in that, The glass waveguide is coupled to the optical fiber, and at the overlapping edge with the PZT waveguide, it is evanescently coupled to the PZT waveguide.