Fiber-optic gyroscope Y-branch modulator chip based on silicon-based lithium tantalate film material

Abstract

The invention discloses a fiber-optic gyroscope Y-branch modulator chip based on a silicon-based lithium tantalate film material, and belongs to the technical field of optoelectronic integration. Comprising a substrate supporting layer, a dielectric layer, a thin film lithium tantalate waveguide core layer, a metal layer and a waveguide upper wrapping layer from bottom to top. And the fiber-optic gyroscope Y-branch modulator is prepared on a thin film lithium tantalate waveguide core layer. The optical fiber gyroscope Y-branch modulator comprises a first optical fiber coupling area, a first 1 * 2 coupler, a polarization area, a second 1 * 2 coupler, a modulation area and a second optical fiber coupling area which are connected in sequence. Compared with a conventional lithium niobate Y-branch device, the lithium niobate Y-branch device has a smaller device size and a higher integration level, and has a wider application scene in the future.

Description

Technical Field

[0001] The invention belongs to the technical field of optoelectronic integration, and in particular relates to a fiber optic gyroscope Y-branch modulator chip based on silicon-based lithium tantalate thin film material. Background Art

[0002] Lithium tantalate crystal (LiTaO3, LT for short) is a negative uniaxial crystal with a non-centrosymmetric lattice structure, a wide wavelength transmission range, and excellent thermoelectric, piezoelectric, ferroelectric, electro-optical and nonlinear optical properties. Therefore, LT is considered to be an excellent multifunctional material with high research value and development prospects in the application of optical and acoustic devices. At present, traditional lithium tantalate materials have been widely used in electronic communication equipment such as filters, resonators, acoustic transducers, and in many high-end communication fields such as mobile phones, walkie-talkies, WeChat communications, aerospace, etc., demonstrating mature development and excellent material properties. Compared with lithium niobate crystal (LiNbO3, LN for short), lithium tantalate has the advantages of small photorefractive damage, weak birefringence, low dielectric loss, and weak drift of low-frequency carrier signals. This makes thin-film lithium tantalate a strong competitor of thin-film lithium niobate in some fields.

[0003] With the advancement of technology, smart-cut technology has gradually matured. Recently, LTOI wafers made by smart-cut technology have gradually entered the market. Compared with LNOI wafers, due to special technical means, LTOI wafers have higher production efficiency, lower cost and greater commercialization potential. The traditional fiber gyro Y-branch modulator chip solution uses lithium niobate crystals to achieve on-chip beam splitting and polarization functions. However, with the gradual maturity of LNOI technology, the use of LNOI to make Y-branch waveguides has gradually become a popular solution. However, due to the limitations of the material itself, the DC drift of LN in DC and low-frequency alternating electric fields is very strong, which seriously affects the application of LN materials in the field of low-speed modulation. The current common practice is to compensate for the drift signal of lithium niobate through a feedback system, but this operation increases the complexity of the system. The use of LT materials can solve this problem from the root. When loaded with low-frequency signals, LT has stronger stability. Summary of the invention

[0004] The present invention aims to solve the deficiencies of the prior art and proposes a fiber optic gyroscope Y-branch modulator chip based on silicon-based lithium tantalate thin film material, comprising: a substrate support layer, a dielectric layer, a thin film lithium tantalate waveguide core layer, a metal layer and a waveguide upper cladding layer from bottom to top;

[0005] The fiber optic gyroscope Y-branch modulator is prepared on the thin film lithium tantalate waveguide core layer;

[0006] The substrate support layer serves as a chip support;

[0007] The waveguide upper cladding layer is used to protect the thin film lithium tantalate waveguide core layer, and is also used together with the dielectric layer to provide a high refractive index contrast for the thin film lithium tantalate waveguide core layer;

[0008] The metal layer is used for electro-optical modulation.

[0009] Further preferably, the Y-branch modulator is divided into: a waveguide area and a modulation area;

[0010] The waveguide region is composed of a substrate support layer, a dielectric layer, a thin-film lithium tantalate waveguide core layer and a waveguide upper cladding layer connected in sequence;

[0011] The modulation area is connected to the waveguide area, and is composed of a substrate support layer, a dielectric layer, a thin-film lithium tantalate waveguide core layer, a metal layer and a waveguide upper cladding layer which are connected in sequence.

[0012] Further preferably, the waveguide upper cladding on both sides of the waveguide in the modulation zone is etched to a preset depth to improve the modulation efficiency of the Y waveguide modulation zone; the etching depth is 400nm to 800nm.

[0013] Further preferably, the waveguide region comprises: a first optical fiber coupling region, a first 1×2 coupler, a polarizing region, a second 1×2 coupler and a second optical fiber coupling region;

[0014] The first optical fiber coupling region comprises port 1 and port 2, which are respectively used to connect to an external broadband light source and an external photodetector;

[0015] The first 1×2 coupler and the second 1×2 coupler are used to combine and split the light source;

[0016] The polarizing zone is used to generate single polarized light, and the polarizing zone is selected from a metal polarizer that selectively absorbs TM mode or a polarization beam splitter based on a waveguide structure;

[0017] The second optical fiber coupling region comprises a port 3 and a port 4, which are respectively connected to polarization-maintaining optical fibers.

[0018] Further preferably, the modulation area is used to perform electro-optical modulation on the single polarized light, and electrodes are prepared on both sides of the waveguide;

[0019] The modulation rate is not higher than 2 GHz; the modulation zone waveguide is widened by a tapered waveguide, and the width of the widened waveguide ranges from 1.5um to 4um.

[0020] Further preferably, the electrodes on both sides of the waveguide are coplanar lumped electrodes or traveling wave electrodes, the electrode design is a push-pull design, and the overall structure is a Mach-Zehnder interference type optical waveguide modulator structure.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] Compared with the current traditional lithium niobate Y branch, the present invention has the following advantages: (1) the thin-film lithium tantalate Y branch device has a smaller size and a higher degree of integration, which can reduce the device volume of the Y branch and enable it to have a wider range of application scenarios in the future; (2) the thin-film lithium tantalate Y branch integrates the beam splitter connecting the input light and the detector onto the chip, reducing the device cost; (3) the ion implantation polarization is adopted, and the thin-film lithium tantalate Y branch adopts a special waveguide structure for polarization, which has a more obvious polarization effect and a purer mode; (4) the electrical drift phenomenon of the Y branch waveguide on the lithium tantalate under low-frequency signals is smaller and can be almost ignored, which is more suitable for use in Y branch devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0024] Figure 1 A top view of the structure of a fiber optic gyroscope Y-branch modulator based on lithium tantalate thin film material according to an embodiment of the present invention;

[0025] Figure 2 A top view of a thin-film lithium tantalate waveguide core layer according to an embodiment of the present invention;

[0026] Figure 3 Schematic diagrams of cross sections of embodiments of the present invention; (a) is a schematic diagram of a cross section of a waveguide region; (b) is a schematic diagram of a cross section of a modulation region;

[0027] Figure 4 Schematic diagram of electrode design according to an embodiment of the present invention.

[0028] Description of reference numerals:

[0029] a-waveguide region; b-modulation region; c-first fiber coupling region; d-first 1×2 coupler; e-polarizing region; f-second 1×2 coupler; g-second fiber coupling region. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] Embodiment 1:

[0033] The present embodiment provides an optical fiber gyroscope Y-branch modulator chip based on silicon-based lithium tantalate thin film material, comprising: a substrate support layer, a dielectric layer, a thin-film lithium tantalate waveguide core layer, a metal layer and a waveguide upper cladding layer from bottom to top; the optical fiber gyroscope Y-branch modulator is prepared on the thin-film lithium tantalate waveguide core layer; the substrate support layer serves as a chip support; the waveguide upper cladding layer is used to protect the thin-film lithium tantalate waveguide core layer, and is also used together with the dielectric layer to provide a high refractive index contrast for the thin-film lithium tantalate waveguide core layer; the metal layer is used for electro-optical modulation.

[0034] Combination Figure 1 , Figure 2 , Figure 3 In this embodiment, the Y-branch modulator is divided into: a waveguide area (a) and a modulation area (b); the waveguide area (a) is composed of a substrate support layer, a dielectric layer, a thin film lithium tantalate waveguide core layer and a waveguide upper cladding layer connected in sequence; the modulation area (b) is connected to the waveguide area (a), and is composed of a substrate support layer, a dielectric layer, a thin film lithium tantalate waveguide core layer, a metal layer and a waveguide upper cladding layer connected in sequence. The bending of the curved part is a circular arc, an Euler curve, a c4 curve, a Bessel curve, etc. The thickness of the thin film lithium tantalate waveguide core layer: 300nm~420nm; the waveguide width: 0.5um~1.0um; wherein, the waveguide upper cladding layer on both sides of the waveguide of the modulation area (b) is etched to a preset depth to improve the modulation efficiency of the Y waveguide modulation area (b); the etching depth is 400nm~800nm.

[0035] Specifically, the waveguide region (a) includes: a first fiber coupling region (c), a first 1×2 coupler (d), a polarizing region (e), a second 1×2 coupler (f) and a second fiber coupling region (g); the first fiber coupling region (c) includes port 1 and port 2, which are respectively used to connect an external broadband light source and an external photodetector; the first 1×2 coupler (d) is used to combine the light sources; the polarizing region (e) is used to generate single-polarized light, and the polarizing region (e) uses a metal polarizer that selectively absorbs TM mode or a polarization beam splitter based on a waveguide structure; the second 1×2 coupler (f) is used to split the light source; the second fiber coupling region (g) includes port 3 and port 4, which are respectively connected to polarization-maintaining fibers.

[0036] The modulation area (b) is used for electro-optical modulation of single polarization light, and electrodes are prepared on both sides of the waveguide; the modulation rate is less than 1GHz; the waveguide in the modulation area (b) is widened by a tapered waveguide, and the width of the widened waveguide ranges from 1.5um to 4um. The electrodes on both sides of the waveguide are coplanar lumped electrodes or traveling wave electrodes, and the electrode design is a push-pull design. The overall structure is a Mach-Zehnder interference type optical waveguide modulator structure.

[0037] The waveguide cross-sections of the first fiber coupling region (c), the first 1×2 coupler (d), the polarizing region (e), the second 1×2 coupler (f), the modulation region (b) and the second fiber coupling region (g) are convex or rectangular.

[0038] Embodiment 2:

[0039] The working process / principle of the Y-branch modulator provided by the present invention includes:

[0040] The fiber gyro Y-branch modulator chip based on silicon-based lithium tantalate thin film material contains a total of four ports, which can be on the same side or on different sides. Among them, the first fiber coupling area (c) contains port 1 and port 2, which are connected to the broadband light source and the photodetector (PD) respectively; the second fiber coupling area (g) contains port 3 and port 4, which are connected to the polarization-maintaining fiber respectively. The input light is input from port 1 and enters a section of the on-chip polarization area (e) through the first 1×2 coupler (d); in the polarization area (e), the TM mode light and the TE high-order mode light in the waveguide cannot be bound by the waveguide, so it is impossible to form a stable transmission mode in the waveguide. There is only pure TE0 mode in the polarization area (e). Then it enters the second 1×2 coupler (f), which is used to divide the input light into two beams and enter the modulation area (b). The area with electrodes on both sides of the polarization area (e) is the modulation area (b), which is used to realize signal modulation of the input light, and the modulation rate is below 1GHz. In the modulation area (b), the waveguide can be appropriately widened through a tapered waveguide to improve the modulation efficiency; the width of the wide waveguide after widening is 1.5um~4um. After that, the light is output from port 3 and port 4 and enters the polarization-maintaining fiber ring. The light output from port 3 and port 4 undergoes a period of interference in the polarization-maintaining fiber ring and returns to the chip from port 4 and port 3 respectively. At this time, the modulation area (b) modulates again, and the light returning from the polarization-maintaining fiber ring passes through the modulation area (b) and enters the second 1×2 coupler (f), and beam combining is realized. The beam-combined light passes through the polarization zone (e) and enters the first 1×2 coupler (d), and is output from port 1 and port 2 respectively. Port 2 is connected to a photodetector to detect the signal.

[0041] In order to realize the function of the electrode crossing the waveguide, a layer of waveguide upper cladding material is covered on the waveguide layer to prevent light loss caused by direct contact between the metal and the waveguide; the preset thickness of the waveguide upper cladding is: 900nm~1400nm. The waveguide upper cladding is etched to a certain depth on both sides of the waveguide in the modulation area (b) to improve the modulation efficiency of the Y waveguide modulation area (b); the preset waveguide upper cladding etching depth is: 400nm~800nm, and then the waveguide upper cladding material continues to grow to protect the electrode. In the area outside the modulation area (b), the waveguide upper cladding does not need to be etched to a certain depth, and the metal electrode can cross from the top of the waveguide. Due to the protection of the waveguide upper cladding, the light absorption in the waveguide is less. The electrode design adopts the GSG push-pull lumped electrode design, such as Figure 4 The electrodes on both sides of the waveguide are ground (G) electrodes, and the middle of the waveguide is the signal (S) electrode. The RF signal is input through the S electrode. The G electrodes on both sides are grounded and are used to modulate the optical signal in the Y-branch modulator chip. A layer of waveguide upper cladding material is covered above the electrode to protect the electrode.

[0042] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A fiber optic gyroscope Y-branch modulator chip based on silicon-based lithium tantalate thin film material, characterized in that: include: From bottom to top: substrate support layer, dielectric layer, thin-film lithium tantalate waveguide core layer, metal layer and waveguide upper cladding layer; The fiber optic gyroscope Y-branch modulator is prepared on the thin film lithium tantalate waveguide core layer; The substrate support layer serves as a chip support; The waveguide upper cladding layer is used to protect the thin film lithium tantalate waveguide core layer, and is also used together with the dielectric layer to provide a high refractive index contrast for the thin film lithium tantalate waveguide core layer; The metal layer is used for electro-optical modulation.

2. The fiber optic gyroscope Y-branch modulator chip based on silicon-based lithium tantalate thin film material according to claim 1, characterized in that: The Y-branch modulator is divided into: a waveguide area and a modulation area; The waveguide region is composed of a substrate support layer, a dielectric layer, a thin-film lithium tantalate waveguide core layer and a waveguide upper cladding layer connected in sequence; The modulation area is connected to the waveguide area, and is composed of a substrate support layer, a dielectric layer, a thin-film lithium tantalate waveguide core layer, a metal layer and a waveguide upper cladding layer which are connected in sequence.

3. The fiber optic gyroscope Y-branch modulator chip based on silicon-based lithium tantalate thin film material according to claim 2, characterized in that: The waveguide upper cladding on both sides of the waveguide in the modulation zone is etched to a preset depth to improve the modulation efficiency of the Y waveguide modulation zone; the etching depth is 400nm to 800nm.

4. The fiber optic gyroscope Y-branch modulator chip based on silicon-based lithium tantalate thin film material according to claim 2, characterized in that: The waveguide region includes: a first optical fiber coupling region, a first 1×2 coupler, a polarizing region, a second 1×2 coupler and a second optical fiber coupling region; The first optical fiber coupling region comprises port 1 and port 2, which are respectively used to connect to an external broadband light source and an external photodetector; The first 1×2 coupler and the second 1×2 coupler are used to combine and split the light source; The polarizing zone is used to generate single polarized light, and the polarizing zone is selected from a metal polarizer that selectively absorbs TM mode or a polarization beam splitter based on a waveguide structure; The second optical fiber coupling region comprises a port 3 and a port 4, which are respectively connected to polarization-maintaining optical fibers.

5. The fiber optic gyroscope Y-branch modulator chip based on silicon-based lithium tantalate thin film material according to claim 4, characterized in that: The modulation area is used to perform electro-optical modulation on the single polarized light, and electrodes are prepared on both sides of the waveguide; The modulation rate is not higher than 2 GHz; the modulation zone waveguide is widened by a tapered waveguide, and the width of the widened waveguide ranges from 1.5um to 4um.

6. The fiber optic gyroscope Y-branch modulator chip based on silicon-based lithium tantalate thin film material according to claim 5, characterized in that: The electrodes on both sides of the waveguide are coplanar lumped electrodes or traveling wave electrodes, the electrode design is a push-pull design, and the overall structure is a Mach-Zehnder interference optical waveguide modulator structure.

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