CN113009626A

CN113009626A - Bragg grating chip

Info

Publication number: CN113009626A
Application number: CN202110433637.XA
Authority: CN
Inventors: 陈亦凡; 严亭
Original assignee: Jiangsu Yirong Photoelectric Technology Co ltd; Suzhou Yirui Optoelectronics Technology Co ltd; Yirui Optoelectronic Technology Anhui Co ltd
Current assignee: Jiangsu Yirong Photoelectric Technology Co ltd; Suzhou Yirui Optoelectronics Technology Co ltd; Yirui Optoelectronic Technology Anhui Co ltd
Priority date: 2021-04-20
Filing date: 2021-04-20
Publication date: 2021-06-22

Abstract

The invention relates to a Bragg grating chip, which comprises a substrate, a silicon dioxide layer arranged on the substrate, a waveguide arranged on the silicon dioxide layer and a lattice grating arranged on the side surface of the waveguide and used for reflecting light in a distributed manner, wherein the lattice grating and at least part of the waveguide are arranged in a separated manner, stable effective refractive index perturbation can be realized by controlling the distance between the waveguide and the lattice grating, and extremely narrow-band (less than or equal to 0.2nm) filtering performance is obtained.

Description

Bragg grating chip

Technical Field

The invention relates to a Bragg grating chip, and belongs to the field of photoelectric devices.

Background

The Bragg grating structure has the property of reflecting light signals with specific wavelength, and can be used for manufacturing optical devices such as optical filters, resonant cavities of lasers, sensors, surface couplers and the like. When the bragg grating is used as a narrow band-pass reflector in a Distributed Bragg Reflector (DBR) laser, it is desirable that the bandwidth of the reflection spectrum of the bragg grating is very narrow, which may be on the order of 0.1-0.3nm, which requires that the coupling coefficient between the forward propagating optical mode and the backward propagating optical mode in the bragg grating is very small, i.e., that the effective refractive index Δ Neff perturbation introduced by the bragg grating is very small (called perturbation, on the order of 1E-4 to 1E-3). In the prior art, the method for preparing the bragg grating generally etches stripes on the top of the waveguide or on the side wall of the waveguide, but the effective refractive index is very sensitive to the stripes, namely, the small surface fluctuation of the waveguide can cause larger effective change. If the expected effective refractive index perturbation is obtained, very small waveguide surface stripe fluctuation (about 10 nm) is needed, and the preparation difficulty of the very small stripe fluctuation is large and the stable control cannot be realized, namely the stable and controllable effective refractive index perturbation is difficult to realize.

Therefore, a solution is needed to easily obtain a bragg grating with effective refractive index perturbations.

Disclosure of Invention

The invention aims to provide a Bragg grating chip which has the advantages of small effective refractive index disturbance, simple and easily-obtained structure and strong consistency and stability.

In order to achieve the purpose, the invention provides the following technical scheme: a Bragg grating chip comprises a substrate, a silicon dioxide layer arranged on the substrate, a waveguide arranged on the silicon dioxide layer, and a lattice grating arranged on the side face of the waveguide and used for reflecting light in a distributed mode, wherein the lattice grating and at least part of the waveguide are arranged in a separated mode.

Further, the waveguide is a ridge waveguide, the ridge waveguide comprises a flat plate layer and a central ridge formed on the flat plate layer, and the lattice grating is formed on the flat plate layer and is arranged away from the central ridge.

Further, the central ridge of the ridge waveguide is rectangular, trapezoidal or a combination of the two.

Further, the waveguide is a rectangular waveguide or a trapezoidal waveguide, the lattice grating is formed on the silica layer, and the waveguide and the lattice grating are arranged in a separated manner.

Further, the lattice grating and the waveguide are arranged in parallel.

Furthermore, the lattice grating comprises a plurality of grating points which are arranged in a separated mode, and the shape of each grating point is one or more of a cylinder shape, a prism shape, a truncated cone shape and a truncated cone shape.

Further, the lattice grating is disposed on at least one side of the waveguide.

Further, the waveguide and the lattice grating are made of lithium niobate, silicon or silicon nitride materials.

Further, the lattice grating is a uniform grating or a non-uniform grating.

Furthermore, the Bragg grating chip also comprises a cladding layer arranged on the waveguide and the lattice grating, and the cladding layer is made of silicon dioxide, silicon nitride or titanium dioxide.

Furthermore, the Bragg grating chip also comprises a metal electrode arranged on the cladding, and the metal electrode is electrified to obtain the Bragg grating chip with tunable central wavelength.

Furthermore, P-type and N-type impurities are doped into the waveguide, and the metal electrode is electrified to obtain the Bragg grating chip with the tunable central wavelength.

Further, the Bragg grating chip also comprises a heating layer arranged on the silicon dioxide layer or the cladding layer, and the heating layer is heated to obtain the Bragg grating chip with tunable central wavelength.

The invention has the beneficial effects that: the Bragg grating chip comprises a waveguide and a lattice grating which is arranged on the side surface of the waveguide and used for reflecting light in a distributed manner, wherein the lattice grating and at least part of the waveguide are arranged in a separated manner, stable effective refractive index perturbation can be realized by controlling the distance between the waveguide and the lattice grating, and extremely narrow-band (less than or equal to 0.2nm) filtering performance is obtained.

The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood and to implement them in accordance with the contents of the description, the following detailed description is given with reference to the preferred embodiments of the present invention and the accompanying drawings.

Drawings

Fig. 1 is a schematic structural diagram of a bragg grating chip according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view at AA' of FIG. 1;

fig. 3 is a schematic structural diagram of a bragg grating chip according to a second embodiment of the present invention;

fig. 4 is a cross-sectional view at BB' in fig. 3.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In addition, the technical features involved in the different embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

The Bragg grating chip comprises a substrate, a silicon dioxide layer arranged on the substrate, a waveguide arranged on the silicon dioxide layer, and a lattice grating arranged on the side surface of the waveguide and used for reflecting light in a distributed manner.

The lattice grating is arranged apart from at least a portion of the waveguides, and specifically, when the waveguides are ridge waveguides, the ridge waveguides include a slab layer and a central ridge formed on the slab layer, and the lattice grating is formed on the slab layer and arranged apart from the central ridge. When 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 arranged in a separated manner. The central ridge of the ridge waveguide is rectangular, trapezoidal or a combination of the two, but the central ridge can be in other shapes, which is not listed here.

The waveguide and the lattice grating are made of lithium niobate, silicon or silicon nitride material. It should be noted that, when the waveguide and the lattice grating are on the same bragg grating chip, the materials selected by the waveguide and the lattice grating are kept consistent, and the waveguide and the lattice grating are prepared from the same material, so that the process can be obviously simplified. The waveguide may also be made of other materials and other types of waveguides, which are not specifically limited herein and may be selected according to actual needs.

The lattice grating comprises a plurality of grating points which are arranged in a separated mode, the shape of each grating point is one or more of a cylinder shape, a prism shape, a truncated cone shape and a truncated pyramid shape, and the specific shapes of the grating points can be other shapes, which are not listed. The lattice grating is arranged on at least one side surface of the waveguide, namely, the lattice grating can be arranged on any one side surface of the waveguide, or the lattice gratings are arranged on two side surfaces of the waveguide. In addition, in order to obtain the required performance, a plurality of lattice gratings, such as two or three, may be disposed on one side of the waveguide.

The lattice grating is a uniform grating or a non-uniform grating, which is not specifically limited herein, and the specific structure of the lattice grating can be selected according to actual needs.

The number of the lattice gratings, the numerical value of the distance between the lattice gratings and the waveguide, and the size of the grating points are determined by the required size of the effective refractive index disturbance, and the period of the grating points (i.e. the central distance between adjacent grating points) is determined by the required central reflection wavelength, which is not specifically limited herein and can be selected according to the actual needs.

By controlling the distance between the waveguide and the lattice grating, stable effective refractive index perturbation can be realized, extremely narrow band (less than or equal to 0.2nm) filtering performance is obtained, the structure is simple, the preparation difficulty is low, the control is easy, and the consistency and the stability of the obtained Bragg grating are strong. The lattice grating and the waveguide are arranged in parallel, so that light rays are stably transmitted in the waveguide, but the light field distribution of the cross section of the waveguide is periodically disturbed by the lattice grating, and further the effective refractive index is periodically disturbed by the lattice grating.

The material of the substrate may be single crystal silicon, but is not limited thereto, and may be other materials, and is not particularly limited thereto.

In addition, the Bragg grating chip also comprises a cladding layer arranged on the waveguide and the lattice grating, so that the waveguide and the lattice grating are protected, the waveguide and the lattice grating are prevented from being exposed outside, and the service life of the Bragg grating chip is prolonged. The material of the cladding layer is silica, silicon nitride, titanium dioxide, or the like, or a mixture of a plurality of materials, and the cladding layer can be prepared from other materials with strong stability, which are not listed here.

In order to increase the application scenes of the Bragg grating chip, the Bragg grating chip also comprises a metal electrode arranged on the cladding, and for the crystal material with the electro-optic effect, such as lithium niobate and the like, the electric field intensity change caused by the electrification of the metal electrode can change the refractive index of the material, so that the Bragg grating chip with the tunable central wavelength can be obtained, and devices, such as a resonant cavity or a filter and the like with the tunable wavelength can be prepared. In addition, since general materials have a thermo-optic effect, that is, the refractive index changes due to the change of the temperature of the general materials, the bragg grating chip may further include a heating layer disposed on the silica layer or the cladding layer, and the heating layer may be heated to change the refractive index of the general materials, thereby obtaining the bragg grating chip with a tunable central wavelength. In addition, materials such as silicon, lithium niobate and the like have a plasma dispersion effect, namely the refractive index of the materials changes along with the change of the concentration of free carriers in the crystal, so that P-type (for example, boron) and N-type (for example, phosphorus) impurities can be doped on two sides of the ridge of the waveguide of the ridge waveguide through an ion implantation or diffusion process to form a P-i-N type semiconductor physical junction, P-type and N-type regions are respectively connected with a metal electrode, the free carriers are injected or extracted into the waveguide through the electrification of the metal electrode, the refractive index of the materials is controlled, and the Bragg grating with tunable central wavelength is realized.

With respect to the fabrication of bragg grating chips, wherein the silicon dioxide layer and the cladding layer may be grown by Plasma Enhanced Chemical Vapor Deposition (PECVD), Chemical Vapor Deposition (CVD), or Physical Vapor Deposition (PVD).

Preparing the Bragg grating: defining the positions and shapes of the waveguides and the array grating by using an electron beam lithography (electron beam lithography) or an optical lithography (optical lithography); and then, the waveguide and array grating is manufactured by adopting Ion beam milling (Ion beam milling), Reactive Ion Etching (RIE), inductively coupled plasma etching (ICP-RIE), Wet etching (Wet Etch) or Crystal Ion Slicing (Crystal Ion Slicing).

The present invention is further illustrated by the following specific examples.

Embodiment A Bragg grating chip based on rectangular waveguide

Referring to fig. 1 and 2, in the present embodiment, the bragg grating chip includes a single crystal silicon substrate 11, a silica layer 12 on the single crystal silicon substrate 11, a rectangular waveguide 13 and a lattice grating 14 on the silica layer 12, and a cladding layer 15 covering the rectangular waveguide 13 and the lattice grating 14, the lattice grating 14 is located on one side of the rectangular waveguide 13, and a grating point 141 of the lattice grating 14 is a cylindrical structure. The cladding 15 is a silica material, and the material of the cladding 15 is the same as that of the silica layer 12.

Second embodiment Bragg grating chip based on ridge waveguide

Referring to fig. 3 and 4, in the present embodiment, the bragg grating chip includes a single-crystal silicon substrate 21, a silica layer 22 on the single-crystal silicon substrate 21, a ridge waveguide 23 and a lattice grating 24 on the silica layer 22, and a cladding 25 covering the ridge waveguide 23 and the lattice grating 24. The lattice grating 24 is located on one side of the ridge waveguide 23, specifically, the ridge waveguide 23 includes a slab layer 231 and a central ridge 232 formed on the slab layer 231, the lattice grating 24 is located on the slab layer 231 and on one side of the central ridge 232, and the lattice grating 24 and the central ridge 232 are located apart from each other. The grating points 241 of the lattice grating 24 are in a truncated cone shape.

Referring to tables 1, 2 and 3, taking the ridge waveguide as an example, the fringe grating and the lattice grating obtained in the second embodiment of the present application are etched on the ridge waveguide for the comparison analysis of the effective refractive index disturbance. The thickness of the flat plate layer of the ridge waveguide is 180nm, the height of the ridge of the central ridge is 180nm, and the width of the ridge top of the central ridge is 800 nm. The top diameter of the grating point of the lattice grating is 100nm, and the thickness is 180 nm.

TABLE 1 Bragg Grating of laterally etched stripes of a ridge waveguide

Morphology of	Undulation 10nm	Undulation 20nm	Undulation 100nm
				Effective refractive index perturbation	0.0012	0.0025	0.0133

TABLE 2 Bragg Grating of Top etched stripe of Ridge waveguide

Morphology of	Undulation 10nm	Undulation 20nm
			Effective refractive index perturbation	0.0066	0.0135

TABLE 3 Bragg grating with lattice grating on one side of ridge waveguide

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

In order to control the change amount of the effective refractive index disturbance within 1E-3, the required surface stripe etching deviation control magnitude is about 8nm for the Bragg grating directly etching the stripe on the side surface of the waveguide; for the Bragg grating directly etching the stripe on the top surface of the waveguide, the required surface stripe etching deviation control magnitude is about 1-2 nm; for the lattice grating, the deviation control magnitude of the required lattice grating and waveguide spacing is about 80-140 nm. Therefore, the Bragg grating with etched stripes on the surface has stronger process sensitivity compared with the lattice grating. In the current process, the 10 nm-level stripe on the surface of the waveguide is extremely difficult to control stably, which results in poor performance consistency and stability of the surface etched Bragg grating chip. For the lattice grating, the deviation control of the 50 nm-order distance is relatively easy to realize, so that stable effective refractive index perturbation can be easily realized by controlling the distance between the grating lattice and the waveguide, and the actual requirement is met.

In summary, the bragg grating chip of the present invention includes a waveguide and a lattice grating disposed on a side surface of the waveguide for distributively reflecting light, the lattice grating is disposed apart from at least a portion of the waveguide, and by controlling a distance between the waveguide and the lattice grating, a stable effective refractive index perturbation can be achieved, and a very narrow band (not more than 0.2nm) filtering performance can be obtained.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. A Bragg grating chip is characterized by comprising a substrate, a silicon dioxide layer arranged on the substrate, a waveguide arranged on the silicon dioxide layer, and a lattice grating arranged on the side face of the waveguide and used for reflecting light in a distributed mode, wherein the lattice grating and at least part of the waveguide are arranged in a separated mode.

2. A bragg grating chip as claimed in claim 1, wherein the waveguide is a ridge waveguide including a slab layer and a central ridge formed on the slab layer, the lattice grating being formed on the slab layer and being located apart from the central ridge.

3. A bragg grating chip as claimed in claim 2, wherein the central ridge of the ridge waveguide is rectangular, trapezoidal, or a combination thereof.

4. A bragg grating chip as claimed in claim 1, wherein said waveguide is a rectangular waveguide or a trapezoidal waveguide, said lattice grating is formed on said silica layer, and said waveguide and said lattice grating are disposed apart from each other.

5. A bragg grating chip as claimed in claim 1, wherein the lattice grating and the waveguide are disposed in parallel.

6. A bragg grating chip as claimed in claim 1, wherein the lattice grating includes a plurality of grating points arranged in a spaced-apart relationship, the grating points having one or more of a cylindrical shape, a prismatic shape, a truncated circular shape, and a truncated pyramidal shape.

7. A bragg grating chip as claimed in claim 1, wherein the lattice grating is disposed on at least one side of the waveguide.

8. A bragg grating chip as claimed in claim 1, wherein the material of said waveguide and said lattice grating is lithium niobate, silicon or silicon nitride material.

9. A bragg grating chip as claimed in claim 1, wherein the lattice grating is a uniform grating or a non-uniform grating.

10. A bragg grating chip as claimed in claim 1, wherein said bragg grating chip further comprises a cladding layer disposed over said waveguide and said lattice grating, said cladding layer being formed of a material selected from the group consisting of silicon dioxide, silicon nitride, and titanium dioxide.

11. A bragg grating chip as claimed in claim 10, wherein said bragg grating chip further comprises a metal electrode disposed on said cladding layer, said metal electrode being energized to provide a bragg grating chip having a tunable center wavelength.

12. A bragg grating chip as claimed in claim 11 wherein said waveguide is doped with P-type and N-type impurities and said metal electrode is energized to provide a bragg grating chip having a tunable center wavelength.

13. A bragg grating chip as claimed in claim 10, wherein said bragg grating chip further comprises a heating layer disposed on said silica layer or cladding layer, heating said heating layer resulting in a bragg grating chip having a tunable center wavelength.