Bragg grating chip

Abstract

This invention relates to a Bragg grating chip, comprising a substrate, a silicon dioxide layer disposed on the substrate, a waveguide disposed on the silicon dioxide layer, and a lattice grating disposed on the side of the waveguide for distributed reflection of light. The lattice grating and at least part of the waveguide are disposed separately. By controlling the distance between the waveguide and the lattice grating, stable effective refractive index perturbation can be achieved, resulting in extremely narrow band (≤0.2nm) filtering performance. The structure is simple, easy to fabricate and control, and exhibits strong consistency and stability.

Description

Technical Field

[0001] This invention relates to a Bragg grating chip, belonging to the field of optoelectronic devices. Background Technology

[0002] Bragg gratings possess the property of reflecting light signals of specific wavelengths, making them suitable for fabricating optical filters, laser resonant cavities, sensors, surface couplers, and other optical devices. When used as narrow-bandpass reflectors in distributed Bragg reflector (DBR) lasers, the desired bandwidth of the Bragg grating's reflection spectrum is extremely narrow, possibly on the order of 0.1-0.3 nm. This requires a very small coupling coefficient between the forward and backward propagation modes within the Bragg grating, meaning the effective refractive index perturbation ΔNeff introduced by the Bragg grating must be very small (referred to as a perturbation, on the order of 1E⁻⁴ to 1E⁻³). Current techniques typically involve etching fringes on the top or sidewalls of the waveguide. However, the effective refractive index is highly sensitive to these fringes; even small surface undulations can cause significant changes in efficiency. Obtaining the desired effective refractive index perturbation requires extremely small surface fringe undulations (around 10 nm), which are difficult to fabricate and cannot be stably controlled, making it challenging to achieve a stable and controllable effective refractive index perturbation.

[0003] Therefore, a scheme is needed to easily obtain Bragg gratings with effective refractive index perturbations. Summary of the Invention

[0004] The purpose of this invention is to provide a Bragg grating chip with very small effective refractive index perturbation, simple and readily available structure, and strong consistency and stability.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a Bragg grating chip, comprising a substrate, a silicon dioxide layer disposed on the substrate, a waveguide disposed on the silicon dioxide layer, and a dot matrix grating disposed on the side of the waveguide for distributed reflection of light, wherein the dot matrix grating and at least a portion of the waveguide are disposed separately.

[0006] Furthermore, the waveguide is a ridge waveguide, which includes a planar layer and a central ridge formed on the planar layer, and the lattice grating is formed on the planar layer and disposed separately from the central ridge.

[0007] Furthermore, the central ridge of the ridge waveguide is rectangular, trapezoidal, or a combination of both.

[0008] Furthermore, the waveguide is a rectangular waveguide or a trapezoidal waveguide, the lattice grating is formed on the silicon dioxide layer, and the waveguide and the lattice grating are disposed separately.

[0009] Furthermore, the dot matrix grating and the waveguide are arranged in parallel.

[0010] Furthermore, the dot matrix grating includes a plurality of grating dots arranged separately, and the shape of the grating dots is one or more of the following: cylindrical, prismatic, frustum, and truncated pyramid.

[0011] Furthermore, the dot matrix grating is disposed on at least one side of the waveguide.

[0012] Furthermore, the waveguide and the lattice grating are made of lithium niobate, silicon, or silicon nitride.

[0013] Furthermore, the dot matrix grating is a uniform grating or a non-uniform grating.

[0014] Furthermore, the Bragg grating chip also includes a cladding layer disposed on the waveguide and the dot matrix grating, the cladding layer being made of silicon dioxide, silicon nitride, or titanium dioxide.

[0015] Furthermore, the Bragg grating chip also includes a metal electrode disposed on the cladding, and the metal electrode is energized to obtain a Bragg grating chip with a tunable center wavelength.

[0016] Furthermore, P-type and N-type impurities are doped into the waveguide, and the metal electrode is energized to obtain a Bragg grating chip with a tunable center wavelength.

[0017] Furthermore, the Bragg grating chip also includes a heating layer disposed on the silicon dioxide layer or cladding layer, and heating the heating layer yields a Bragg grating chip with a tunable center wavelength.

[0018] The beneficial effects of the present invention are as follows: The Bragg grating chip of the present invention includes a waveguide and a lattice grating disposed on the side of the waveguide for distributed reflection of light. The lattice grating and at least part of the waveguide are disposed separately. By controlling the distance between the waveguide and the lattice grating, stable effective refractive index perturbation can be achieved, resulting in extremely narrow band (≤0.2nm) filtering performance. The structure is simple, easy to manufacture and control, and has strong consistency and stability.

[0019] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the Bragg grating chip shown in Embodiment 1 of the present invention;

[0021] Figure 2 for Figure 1 Cross-sectional view at point AA';

[0022] Figure 3 This is a schematic diagram of the structure of the Bragg grating chip shown in Embodiment 2 of the present invention;

[0023] Figure 4 for Figure 3 Cross-sectional view at BB'. Detailed Implementation

[0024] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0026] The Bragg grating chip of the present invention includes a substrate, a silicon dioxide layer disposed on the substrate, a waveguide disposed on the silicon dioxide layer, and a dot matrix grating disposed on the side of the waveguide for distributed reflection of light.

[0027] The lattice grating and at least part of the waveguide are disposed separately. Specifically, when the waveguide is a ridge waveguide, the ridge waveguide includes a planar layer and a central ridge formed on the planar layer, and the lattice grating is formed on the planar layer and disposed separately from the central ridge. When the waveguide is a rectangular waveguide or a trapezoidal waveguide, the lattice grating is formed on a silicon dioxide layer, and the waveguide and the lattice grating are disposed separately. The central ridge of the ridge waveguide can be rectangular, trapezoidal, or a combination of both, but other shapes are also possible, which will not be listed here.

[0028] The waveguide and lattice grating are made of lithium niobate, silicon, or silicon nitride. It should be noted that when the waveguide and lattice grating are on the same Bragg grating chip, both are made of the same material, which obviously simplifies the manufacturing process. Other materials and waveguide types can also be used; no specific limitations are made here, and the choice can be made according to actual needs.

[0029] A lattice grating comprises a plurality of disjointly arranged grating dots. The shape of the grating dots can be one or more of the following: cylindrical, prismatic, frustum-shaped, and truncated pyramidal. Other specific shapes are also possible, but not listed here. The lattice grating is disposed on at least one side of the waveguide; that is, it can be disposed on any side of the waveguide, or on both sides. Furthermore, to obtain the desired performance, multiple lattice gratings, such as two or three, can be disposed on one side of the waveguide.

[0030] The lattice grating can be either a uniform grating or a non-uniform grating; no specific limitation is made here. The specific structure of the lattice grating can be selected according to actual needs.

[0031] The number of lattice gratings, the distance between the lattice gratings and the waveguide, and the size of the grating dots are determined by the magnitude of the required effective refractive index perturbation. The period of the grating dots (i.e., the center-to-center distance between adjacent grating dots) is determined by the required center reflection wavelength. No specific limitation is made here, and they can be selected according to actual needs.

[0032] By controlling the distance between the waveguide and the lattice grating, stable effective refractive index perturbation can be achieved, resulting in extremely narrow-band (≤0.2nm) filtering performance. This structure is simple, easy to fabricate and control, and the obtained Bragg grating exhibits strong consistency and stability. The lattice grating and waveguide are arranged in parallel to achieve stable light transmission within the waveguide; however, the light field distribution across the waveguide cross-section is periodically perturbed by the lattice grating, thus causing periodic perturbation of the effective refractive index.

[0033] The substrate material can be monocrystalline silicon, but it is not limited to this and can also be other materials, without specific limitations here.

[0034] In addition, the Bragg grating chip also includes a cladding layer disposed on the waveguide and lattice grating to protect them, prevent them from being exposed, and extend the lifespan of the Bragg grating chip. The cladding layer can be made of materials such as silicon dioxide, silicon nitride, or titanium dioxide, or a mixture of multiple materials. The cladding layer can also be prepared from other highly stable materials, which will not be listed here.

[0035] To broaden the application scenarios of Bragg grating chips, they also include metal electrodes disposed on the cladding. For crystalline materials with electro-optic effects, such as lithium niobate, the change in electric field intensity caused by energizing the metal electrodes can alter the refractive index of the material, thereby obtaining a Bragg grating chip with a tunable center wavelength. This allows for the fabrication of devices such as wavelength-tunable resonant cavities or filters. Furthermore, since most materials exhibit thermo-optic effects, meaning their refractive index changes with temperature, Bragg grating chips can also include a heating layer disposed on the silicon dioxide layer or cladding. Heating this heating layer can change the refractive index of the material, resulting in a Bragg grating chip with a tunable center wavelength. Furthermore, materials such as silicon and lithium niobate exhibit plasma dispersion, meaning their refractive index varies with the concentration of free carriers within the crystal. Therefore, P-type (e.g., boron) and N-type (e.g., phosphorus) impurities can be doped into both sides of the waveguide ridge using ion implantation or diffusion processes to form a "PiN" type semiconductor physical junction. The P-type and N-type regions are then connected to metal electrodes, and free carriers are injected or extracted into the waveguide by energizing the metal electrodes. By controlling the refractive index of the material, a Bragg grating with a tunable center wavelength can be achieved.

[0036] Regarding the fabrication of Bragg grating chips, the silicon dioxide layer and cladding can be grown by plasma-enhanced chemical vapor deposition (PECVD), chemical vapor deposition (CVD), or physical vapor deposition (PVD).

[0037] Fabrication of Bragg gratings: The position and shape of the waveguide and array grating are defined using electron beam lithography or optical lithography; then, the waveguide and array grating are fabricated using ion milling, reactive ion etching (RIE), inductively coupled plasma etching (ICP-RIE), wet etching, or crystal ion slicing.

[0038] The present invention will be further described below with reference to specific embodiments.

[0039] Example 1: Bragg grating chip based on rectangular waveguide

[0040] See Figure 1 and Figure 2In this embodiment, the Bragg grating chip includes a single-crystal silicon substrate 11, a silicon dioxide layer 12 on the single-crystal silicon substrate 11, a rectangular waveguide 13 and a dot grating 14 on the silicon dioxide layer 12, and a cladding 15 covering the rectangular waveguide 13 and the dot grating 14. The dot grating 14 is located on one side of the rectangular waveguide 13, and the grating dots 141 of the dot grating 14 are cylindrical. The cladding 15 is made of silicon dioxide, and the material of the cladding 15 is the same as that of the silicon dioxide layer 12.

[0041] Example 2: Bragg grating chip based on ridge waveguide

[0042] See Figure 3 and Figure 4 In this embodiment, the Bragg grating chip includes a single-crystal silicon substrate 21, a silicon dioxide layer 22 on the single-crystal silicon substrate 21, a ridge waveguide 23 and a dot grating 24 on the silicon dioxide layer 22, and a cladding 25 covering the ridge waveguide 23 and the dot grating 24. The dot grating 24 is located on one side of the ridge waveguide 23. Specifically, the ridge waveguide 23 includes a planar layer 231 and a central ridge 232 formed on the planar layer 231. The dot grating 24 is located on the planar layer 231 and on one side of the central ridge 232, and the dot grating 24 and the central ridge 232 are separated. The grating dots 241 of the dot grating 24 have a frustum-shaped structure.

[0043] Please refer to Tables 1, 2, and 3 for a comparative analysis of the effective refractive index perturbation using a ridge waveguide as an example, etched with a striped grating and a lattice grating obtained in Embodiment 2 of this application. The ridge waveguide has a planar layer thickness of 180 nm, a central ridge height of 180 nm, and a ridge top width of 800 nm. The lattice grating has a top dot diameter of 100 nm and a thickness of 180 nm.

[0044] Table 1. Bragg gratings with side-etched fringes of ridge waveguides

[0045] Appearance Fluctuations 10nm Fluctuations 20nm Fluctuation 100nm Effective refractive index perturbation 0.0012 0.0025 0.0133

[0046] Table 2. Bragg gratings with etched fringes on the top surface of the ridge waveguide.

[0047] Appearance Fluctuations 10nm Fluctuations 20nm Effective refractive index perturbation 0.0066 0.0135

[0048] Table 3 shows Bragg gratings with dot matrix gratings on one side of the ridge waveguide.

[0049] Spacing between ridge waveguide and lattice grating 400nm 500nm 600nm Effective refractive index perturbation 0.0027 0.0015 0.0008

[0050] To control the variation in effective refractive index perturbation within 1E-3, for Bragg gratings with stripes directly etched on the waveguide side, the required surface stripe etching deviation control is on the order of approximately 8 nm; for Bragg gratings with stripes directly etched on the waveguide top surface, the required surface stripe etching deviation control is on the order of approximately 1–2 nm; and for the lattice grating of this invention, the required deviation control between the lattice grating and the waveguide spacing is on the order of approximately 80–140 nm. Therefore, surface-etched striped Bragg gratings are more process-sensitive than lattice gratings. In current manufacturing processes, 10 nm-level stripes on the waveguide surface are extremely difficult to stably control, resulting in poor consistency and stability of the surface-etched Bragg grating chip performance. However, for lattice gratings, deviation control of spacing on the order of 50 nm is relatively easy to achieve. Therefore, by controlling the spacing between the grating lattice and the waveguide, stable effective refractive index perturbation can be easily achieved, meeting practical requirements.

[0051] In summary, the Bragg grating chip of the present invention includes a waveguide and a lattice grating disposed on the side of the waveguide for distributed reflection of light. The lattice grating and at least part of the waveguide are disposed separately. By controlling the distance between the waveguide and the lattice grating, stable effective refractive index perturbation can be achieved, resulting in extremely narrow band (≤0.2nm) filtering performance. The structure is simple, easy to fabricate and control, and exhibits strong consistency and stability.

[0052] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0053] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A Bragg grating chip, characterized in that, The device includes a substrate, a silicon dioxide layer disposed on the substrate, a waveguide disposed on the silicon dioxide layer, and a lattice grating disposed on the side of the waveguide for distributed reflection of light. The lattice grating and at least a portion of the waveguide are disposed separately. When the spacing deviation between the lattice grating and the waveguide is any value between 80nm and 140nm, the perturbation change of the effective refractive index is within 1E-3.

2. The Bragg grating chip as described in claim 1, characterized in that, The waveguide is a ridge waveguide, which includes a flat plate layer and a central ridge formed on the flat plate layer. The lattice grating is formed on the flat plate layer and is disposed away from the central ridge.

3. The Bragg grating chip as described in claim 2, characterized in that, The central ridge of the ridge waveguide is rectangular, trapezoidal, or a combination of both.

4. The Bragg grating chip as described in claim 1, characterized in that, The waveguide is a rectangular waveguide or a trapezoidal waveguide, and the lattice grating is formed on the silicon dioxide layer. The waveguide and the lattice grating are disposed separately.

5. The Bragg grating chip as described in claim 1, characterized in that, The dot matrix grating and the waveguide are arranged in parallel.

6. The Bragg grating chip as described in claim 1, characterized in that, The dot matrix grating includes a plurality of grating dots arranged separately, and the shape of the grating dots is one or more of the following: cylindrical, prismatic, frustum, and prismatic.

7. The Bragg grating chip as described in claim 1, characterized in that, The dot matrix grating is disposed on at least one side of the waveguide.

8. The Bragg grating chip as described in claim 1, characterized in that, The waveguide and the lattice grating are made of lithium niobate, silicon, or silicon nitride.

9. The Bragg grating chip as described in claim 1, characterized in that, The dot matrix grating is either a uniform grating or a non-uniform grating.

10. The Bragg grating chip as described in claim 1, characterized in that, The Bragg grating chip also includes a cladding layer disposed on the waveguide and the dot matrix grating, wherein the cladding layer is made of silicon dioxide, silicon nitride, or titanium dioxide.

11. The Bragg grating chip as described in claim 10, characterized in that, The Bragg grating chip also includes a metal electrode disposed on the cladding, and the metal electrode is energized to obtain a Bragg grating chip with a tunable center wavelength.

12. The Bragg grating chip as described in claim 11, characterized in that, The waveguide is doped with P-type and N-type impurities, and the metal electrode is energized to obtain a Bragg grating chip with a tunable center wavelength.

13. The Bragg grating chip as described in claim 10, characterized in that, The Bragg grating chip also includes a heating layer disposed on the silicon dioxide layer or cladding layer, and heating the heating layer yields a Bragg grating chip with a tunable center wavelength.

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