Silicon-erbium-doped lithium niobate heterogeneous integrated waveguide amplifier and integration method thereof

Abstract

The invention discloses a heterogeneous integrated waveguide amplifier and an integration method. The waveguide amplifier comprises an end face coupler, a silicon-erbium-doped lithium niobate heterogeneous waveguide, a low-loss adiabatic conical coupler and an Euler bent waveguide. The silicon-based waveguide forms an end face coupler and an Euler bending waveguide; the silicon-erbium-doped lithium niobate heterogeneous waveguide forms an amplification waveguide and a low-loss adiabatic conical coupler. The integration method comprises the following steps: etching a silicon wafer to form a silicon-based waveguide; and the silicon-erbium-doped lithium niobate heterogeneous waveguide is formed by bonding an erbium-doped lithium niobate wafer. Erbium-doped lithium niobate is used as a gain medium to realize on-chip C-waveband signal light amplification; the waveguide amplifier is formed through the silicon-erbium-doped lithium niobate heterogeneous waveguide, etching of lithium niobate is avoided, and therefore the waveguide amplifier is compatible with the CMOS technology. Flexible heterogeneous integration between an active material and a passive material is realized through a bonding process from an erbium-doped lithium niobate wafer to a silicon wafer. By flexibly amplifying the on-chip signal light, the invention has important significance for realizing large-scale integration in the future.

Description

Technical Field

[0001] The invention belongs to the field of photon heterogeneous integration, in particular to a silicon-erbium-doped lithium niobate heterogeneous integrated waveguide amplifier and an integration method thereof. Background Art

[0002] With the application and development of optoelectronic integration in the fields of optical communications, photonic artificial intelligence, lidar, etc., on-chip optical signal transmission loss caused by optical multiplexing technology and device insertion loss has become an important factor limiting the scale of integration and system performance. One of the effective solutions is to use rare earth element-doped waveguide amplifiers to achieve on-chip gain. Compared with other optical amplifiers, erbium-doped optical amplifiers have the characteristics of low loss, low noise, low dispersion, and high gain amplification in the communication band. In addition, lithium niobate is a mature matrix material for doping rare earth elements as a gain medium to achieve optical gain. Therefore, the erbium-doped lithium niobate heterogeneous integrated waveguide amplifier, as an optical device for realizing optical signal compensation, provides an important solution to solve the limitation of loss on the scale of integration.

[0003] Recently, research on on-chip optical waveguide amplifiers based on different platforms has demonstrated the feasibility and broad prospects of on-chip signal light amplification. For example, based on the silicon nitride platform, a high-performance erbium-doped silicon nitride waveguide amplifier was prepared by erbium ion implantation (Liu Y, Qiu Z, Ji X, et al. A photonic integrated circuit–based erbium-doped amplifier [J]. Science, 2022, 376 (6599): 1309-1313.); based on the lithium niobate platform, an erbium-doped lithium niobate waveguide amplifier was prepared on a lithium niobate thin film wafer on an insulator by using photolithography-assisted chemical mechanical etching technology (Liang Y, Zhou J, Liu Z, et al. A high-gain cladded waveguide amplifier on erbium doped thin-film lithium niobate fabricated using photolithography assisted chemo-mechanical etching [J]. Nanophotonics, 2022, 11 (5): 1033-1040.). This device can make full use of the superior electro-optical properties, nonlinearity and gain characteristics of lithium niobate.

[0004] However, the optical waveguide amplifiers in the prior art are mostly applied to lithium niobate integrated platforms or silicon nitride integrated platforms, and cannot be directly applied to silicon-based integrated platforms due to material compatibility issues, while silicon materials themselves cannot achieve effective light amplification. Therefore, it is urgent to study a waveguide amplifier that can be applied to silicon-based material platforms.

[0005] The present invention is proposed based on this background, and aims to realize a silicon-erbium-doped lithium niobate heterogeneous integrated waveguide amplifier through the bonding process of erbium-doped lithium niobate wafer to silicon wafer. The amplifier can combine silicon-based passive optical path and erbium-doped lithium niobate optical amplification, and can flexibly amplify on-chip signal light; and there is no need to etch lithium niobate, and it has the advantage of CMOS process compatibility, providing important technical support for the realization of large-scale integrated systems in the future. Summary of the invention

[0006] In order to overcome the deficiencies of the above-mentioned prior art, the present invention proposes a silicon-erbium-doped lithium niobate heterogeneous integrated waveguide amplifier, which uses erbium-doped lithium niobate as a gain medium and uses a silicon-erbium-doped lithium niobate heterogeneous waveguide to form a gain waveguide, thereby achieving on-chip C-band signal light amplification while avoiding etching of lithium niobate. The present invention adopts a method of bonding erbium-doped lithium niobate wafers to silicon wafers, which can simultaneously give play to the optical amplification advantages of erbium-doped lithium niobate and the compatibility advantages of silicon material CMOS processes. By flexibly amplifying on-chip signal light, it is of great significance for the realization of large-scale integrated systems in the future.

[0007] The technical solution of the present invention is as follows:

[0008] A silicon-erbium-doped lithium niobate heterogeneous integrated waveguide amplifier, characterized in that: the structures of the waveguide amplifier from left to right are end coupler, silicon-erbium-doped lithium niobate heterogeneous waveguide, low-loss adiabatic tapered coupler, Euler bending waveguide and silicon-based waveguide. The end coupler is used for on-chip input of C-band signal light and 1480nm pump light; the silicon-erbium-doped lithium niobate heterogeneous waveguide is used to control the distribution of pump light field and signal light field to achieve signal light amplification; the low-loss adiabatic tapered coupler is used to connect the silicon-erbium-doped lithium niobate heterogeneous waveguide and the Euler bending waveguide, and the Euler bending waveguide connects the low-loss adiabatic tapered coupler and the silicon-based waveguide through a small bending radius.

[0009] End coupler for on-chip input of C-band signal light and 1480nm pump light;

[0010] A silicon-erbium-doped lithium niobate heterogeneous waveguide, connected to the end coupler, is used to control the distribution of the pump light field and the signal light field and realize the amplification of the signal light;

[0011] A tapered coupler connected to the silicon-erbium-doped lithium niobate heterogeneous waveguide;

[0012] An Euler bending waveguide connected to the tapered coupler, connecting the tapered coupler and the silicon-based waveguide via a small bending radius;

[0013] A silicon-based waveguide connected to the Euler bending waveguide for further signal transmission;

[0014] The silicon-based waveguide constitutes the end face coupler, and the silicon-erbium-doped lithium niobate heterogeneous waveguide and the silicon-based waveguide constitute the tapered coupler.

[0015] Preferably, the silicon-erbium-doped lithium niobate heterogeneous waveguide is formed by bonding a silicon thin film layer and an erbium-doped lithium niobate layer via a silicon oxide buffer layer, wherein the silicon thin film layer has a thickness of 90 nm and a width of 500 nm, and the erbium-doped lithium niobate layer has a thickness of 600 nm.

[0016] Preferably, in the silicon-erbium-doped lithium niobate heterogeneous waveguide, the overlap factor of the pump light and the signal light is greater than 95%, and the signal light accounts for more than 75% of the optical field energy in the erbium-doped lithium niobate.

[0017] Preferably, the bending radius of the Euler bending waveguide is less than 10 μm, the tapered coupler adopts a tapered structure with a gradually changing width, and the tapered length of the tapered coupler is greater than 100 μm. The pump light and the signal light pass through the thermal tapered coupler to achieve transmission between the silicon-erbium-doped lithium niobate heterogeneous waveguide and the Euler bending waveguide. The signal light and the pump light are transmitted to the next section of the silicon-based waveguide or the silicon-erbium-doped lithium niobate heterogeneous waveguide by a 90° bend in the Euler bending waveguide.

[0018] The integration method of the above heterogeneous integrated waveguide amplifier includes bonding of erbium-doped lithium niobate wafer to silicon wafer, waveguide etching, thin film deposition, and chemical mechanical polishing. The steps are as follows:

[0019] 1) preparing an SOI wafer and an Er:LNOI wafer, wherein the SOI wafer comprises a silicon substrate, a silicon oxide isolation layer and a silicon thin film layer from bottom to top; and the Er:LNOI wafer comprises a silicon substrate, a silicon oxide isolation layer and an erbium-doped lithium niobate layer from bottom to top; the silicon oxide isolation layer has a thickness of several microns, and the silicon thin film layer or the erbium-doped lithium niobate layer has a thickness of hundreds of nanometers;

[0020] 2) patterning the silicon thin film layer described in step 1) in the planned area to obtain the silicon thin film layer structure in the end coupler, curved waveguide, silicon-based waveguide and silicon-erbium-doped lithium niobate heterogeneous waveguide;

[0021] 3) depositing a silicon oxide buffer layer on the patterned silicon thin film layer using plasma enhanced chemical vapor deposition technology on the wafer obtained in step 2);

[0022] 4) using plasma enhanced chemical vapor deposition technology on the erbium-doped lithium niobate wafer described in step 1) to deposit a silicon oxide buffer layer on the erbium-doped lithium niobate layer;

[0023] 5) chemically mechanically polishing the silicon oxide buffer layers obtained in step 3) and step 4) to reduce surface roughness;

[0024] 6) performing a direct bonding process on the SOI wafer and the Er:LNOI wafer obtained in step 5) through a silicon oxide buffer layer, and then performing annealing;

[0025] 7) The wafer-to-wafer bonded body obtained in step 6) is subjected to chemical mechanical polishing to remove the silicon substrate of the Er:LNOI wafer.

[0026] The technical effects of the present invention are as follows:

[0027] 1. The present invention regulates the light field distribution of signal light and pump light in silicon-erbium-doped lithium niobate heterogeneous waveguide by changing the structure of silicon waveguide. When the light field is distributed in the silicon waveguide, it is suitable for realizing highly compact curved waveguides; when most of the light field is distributed in erbium-doped lithium niobate, it is suitable for realizing high-gain signal light amplification, providing a loss compensation solution for large-scale integration.

[0028] 2. The present invention prepares a waveguide amplifier through a heterogeneous integration method of wafer-to-wafer bonding, which can avoid etching of lithium niobate materials and is compatible with mature CMOS processes, reducing process difficulty.

[0029] 3. The wafer-to-wafer bonding heterogeneous integration method proposed in the present invention can bond heterogeneous material wafers in the planned area of ​​4-inch and above wafers by wafer-to-wafer bonding, providing a flexible heterogeneous integration solution for photonic integration systems of multi-material platforms.

[0030] 4. The present invention divides the amplifying waveguide into a gain part and a bending part. The gain part uses a heterogeneous waveguide to achieve compatibility with the CMOS process, and the bending part uses an Euler bending waveguide to reduce the device size. This provides an effective solution to overcome the problems of poor compatibility and large device size of waveguide amplifiers. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the structure of the silicon-erbium-doped lithium niobate heterogeneous integrated waveguide amplifier of the present invention, wherein (a) is a top view and (b) is a cross-sectional view.

[0032] Figure 2 Schematic diagram of the performance of the heterogeneous integrated waveguide amplifier of the present invention, including: (a) 1531nm signal light field distribution diagram; (b) 1480nm pump light field distribution diagram; (c) gain variation with pump power of different waveguide structures.

[0033] Figure 3 This is a process flow chart of the heterogeneous integrated waveguide amplifier of the present invention. DETAILED DESCRIPTION

[0034] The present invention is described in detail below in conjunction with the accompanying drawings, and detailed implementation methods and structures, as well as device performance, are given, but the protection scope of the present invention is not limited to the following embodiments.

[0035] See also Figure 1 , Figure 1 FIG. 1 is a schematic diagram of the structure of the silicon-erbium-doped lithium niobate heterogeneous integrated waveguide amplifier of the present invention. Figure 1 As shown in (a), a silicon-erbium-doped lithium niobate heterogeneous integrated waveguide amplifier includes, from left to right, an end coupler 1, a silicon-erbium-doped lithium niobate heterogeneous waveguide 2, a low-loss adiabatic tapered coupler 3, an Euler bent waveguide 4, and a silicon-based waveguide 5. The end coupler 1 is used for on-chip input of signal light and pump light; the silicon-erbium-doped lithium niobate heterogeneous waveguide 2 is used to regulate the distribution of the pump light field and the signal light field to achieve signal light amplification; the low-loss adiabatic tapered coupler 3 is used to connect the silicon-erbium-doped lithium niobate heterogeneous waveguide and the Euler bent waveguide, and the Euler bent waveguide 4 connects the low-loss adiabatic tapered coupler and the silicon-based waveguide through a small bending radius. Figure 1 As shown in (b), the silicon-erbium-doped lithium niobate heterogeneous integrated waveguide amplifier includes, from bottom to top, a SOI silicon substrate layer 6, a SOI silicon oxide isolation layer 7, a SOI silicon thin film layer 8, a SOI silicon oxide buffer layer 9, an Er:LNOI silicon oxide buffer layer 10, an Er:LNOI erbium-doped lithium niobate layer 11 and a silicon oxide upper cladding layer 12. The silicon oxide buffer layer has a thickness of 10 to 100 nm.

[0036] like Figure 2 The performance schematic diagram of the heterogeneous integrated waveguide amplifier of the present invention is shown. The waveguide amplifier uses a 90nm thick, 500nm wide silicon waveguide and a 600nm thick erbium-doped lithium niobate to form a silicon-erbium-doped lithium niobate heterogeneous waveguide. Figure 2 (a) is the 1531nm signal light field distribution diagram, Figure 2 (b) is the 1480nm pump light field distribution diagram. The light field energy distribution in lithium niobate is greater than 75% for both, and the overlap factor of pump light and signal light is as high as 95%, which shows that the signal light and pump light have good interaction, which is conducive to achieving high gain. Figure 2 (c) The gain performance under different waveguide widths was compared, and the limitation of the waveguide width caused by the write field splicing error in the processing was comprehensively considered. A silicon waveguide with a width of 550nm was selected as the silicon-erbium-doped lithium niobate heterojunction amplifier waveguide.

[0037] like Figure 3The process flow chart of the heterogeneous integrated waveguide amplifier of the present invention includes bonding of erbium-doped lithium niobate wafer to silicon wafer, waveguide etching, thin film deposition, and chemical mechanical polishing. The steps are as follows:

[0038] 1) preparing an SOI wafer and an Er:LNOI wafer, wherein the SOI wafer comprises a silicon substrate, a silicon oxide isolation layer and a silicon thin film layer from bottom to top; and the Er:LNOI wafer comprises a silicon substrate, a silicon oxide isolation layer and an erbium-doped lithium niobate layer from bottom to top; the silicon oxide isolation layer has a thickness of several microns, and the silicon thin film layer or the erbium-doped lithium niobate layer has a thickness of hundreds of nanometers;

[0039] 2) patterning the silicon thin film layer described in step 1) in the planned area by using an EBL process and a silicon etching process to obtain the silicon thin film layer structure in the end coupler, the curved waveguide, the silicon-based waveguide and the silicon-erbium-doped lithium niobate heterogeneous waveguide;

[0040] 3) using plasma enhanced chemical vapor deposition technology on the wafer obtained in step 2) to deposit a silicon oxide buffer layer of about 75 nm on the patterned silicon thin film layer;

[0041] 4) using plasma enhanced chemical vapor deposition technology on the erbium-doped lithium niobate wafer described in step 1) to deposit a silicon oxide buffer layer of about 75 nm on the erbium-doped lithium niobate layer;

[0042] 5) chemically mechanically polishing the silicon oxide buffer layers obtained in step 3) and step 4) to reduce surface roughness;

[0043] 6) aligning the SOI wafer and the Er:LNOI wafer obtained in step 5) and performing a direct bonding process through a silicon oxide buffer layer, and then annealing after completion;

[0044] 7) The wafer-to-wafer bonded body obtained in step 6) is subjected to chemical mechanical polishing to remove the silicon substrate of the Er:LNOI wafer.

[0045] The present invention precisely controls the light field distribution in erbium-doped lithium niobate through the structural design of silicon waveguides. At the same time, the amplifying waveguide is divided into a gain part and a bending part. The gain part uses a heterogeneous waveguide to achieve compatibility with CMOS technology, and the bending part uses an Euler bending waveguide to reduce the device size, thereby providing an effective solution to overcome the problems of poor compatibility and large device size of waveguide amplifiers.

Claims

1. A silicon-erbium-doped lithium niobate heterogeneous integrated waveguide amplifier, characterized in that: include: End coupler for on-chip input of C-band signal light and 1480nm pump light; A silicon-erbium-doped lithium niobate heterogeneous waveguide, connected to the end coupler, is used to control the distribution of the pump light field and the signal light field and realize the amplification of the signal light; A tapered coupler connected to the silicon-erbium-doped lithium niobate heterogeneous waveguide; An Euler bending waveguide connected to the tapered coupler, connecting the tapered coupler and the silicon-based waveguide via a small bending radius; A silicon-based waveguide connected to the Euler bending waveguide for further signal transmission; The silicon-based waveguide constitutes the end face coupler, and the silicon-erbium-doped lithium niobate heterogeneous waveguide and the silicon-based waveguide constitute the tapered coupler.

2. The silicon-erbium-doped lithium niobate heterogeneous integrated waveguide amplifier according to claim 1, characterized in that: The silicon-erbium-doped lithium niobate heterogeneous waveguide is formed by bonding a silicon thin film layer and an erbium-doped lithium niobate layer through a silicon oxide buffer layer, wherein the silicon thin film layer has a thickness of 90nm and a width of 500nm, and the erbium-doped lithium niobate layer has a thickness of 600nm.

3. The silicon-erbium-doped lithium niobate heterogeneous integrated waveguide amplifier according to claim 1, characterized in that: In the silicon-erbium-doped lithium niobate heterogeneous waveguide, the overlap factor of pump light and signal light is greater than 95%, and the light field energy of the signal light in the erbium-doped lithium niobate accounts for more than 75%.

4. The silicon-erbium-doped lithium niobate heterogeneous integrated waveguide amplifier according to claim 1, characterized in that: The bending radius of the Euler bending waveguide is less than 10 μm, the tapered coupler adopts a tapered structure with a gradually changing width, and the tapered length of the tapered coupler is greater than 100 μm. The pump light and the signal light pass through the thermal tapered coupler to achieve transmission between the silicon-erbium-doped lithium niobate heterogeneous waveguide and the Euler bending waveguide. The signal light and the pump light are bent 90° in the Euler bending waveguide and transmitted to the next section of the silicon-based waveguide or the silicon-erbium-doped lithium niobate heterogeneous waveguide.

5. A method for integrating the silicon-erbium-doped lithium niobate heterogeneous integrated waveguide amplifier according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: Step 1) providing an SOI wafer and an Er:LNOI wafer, wherein the SOI wafer comprises a silicon substrate, a silicon oxide isolation layer and a silicon thin film layer from bottom to top; the Er:LNOI wafer comprises a silicon substrate, a silicon oxide isolation layer and an erbium-doped lithium niobate layer from bottom to top; the silicon thin film layer and the erbium-doped lithium niobate layer have a thickness of several hundred nanometers; Step 2) patterning the silicon thin film layer of the SOI wafer to form a silicon thin film layer of an end coupler, an Euler bending waveguide, a silicon-based waveguide, and a silicon-erbium-doped lithium niobate heterogeneous waveguide; Step 3) depositing a silicon oxide buffer layer on the patterned silicon thin film layer obtained in step 2) and the erbium-doped lithium niobate layer of the Er:LNOI wafer in step 1), and performing chemical mechanical polishing; Step 4) bonding the SOI wafer to the Er:LNOI wafer through a silicon oxide buffer layer and annealing; Step 5) removing the silicon substrate of the Er:LNOI wafer by chemical mechanical polishing to complete the preparation of the heterogeneous integrated waveguide amplifier.

6. The method for integrating the silicon-erbium-doped lithium niobate heterogeneous integrated waveguide amplifier according to claim 5, characterized in that: In the step 3), the silicon oxide buffer layer is located between the silicon thin film layer and the erbium-doped lithium niobate layer, has a thickness of 10 nm to 100 nm, and is formed by plasma enhanced chemical vapor deposition technology.

7. The method for integrating the silicon-erbium-doped lithium niobate heterogeneous integrated waveguide amplifier according to claim 5, characterized in that: The patterning process in step 2) is implemented by combining electron beam lithography with silicon etching process.

8. The method for integrating the silicon-erbium-doped lithium niobate heterogeneous integrated waveguide amplifier according to claim 5, characterized in that: The silicon-erbium-doped lithium niobate heterogeneous waveguide can be a strip waveguide or a slot waveguide structure.

9. The method for integrating a lithium heterogeneous integrated waveguide amplifier according to claim 5, characterized in that: This integration method is also applicable to heterogeneous integration of silicon nitride and erbium-doped lithium niobate.

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