Micro-ring resonator and preparation method thereof

Abstract

The invention relates to a micro-ring resonator and a preparation method thereof, and belongs to the technical field of integrated photonic device and semiconductor manufacturing. The micro-ring resonator comprises a micro-ring structure and a bus waveguide, the material of the micro-ring resonator comprises Al < x > Ga < 1-x > As, and x is greater than 0.4. The micro-ring resonator provided by the invention is an integrated O-band micro-ring resonator, has the characteristics of high efficiency, miniaturization and integration, and has a considerable quality factor compared with the existing silicon nitride and lithium niobate micro-ring resonators, and meanwhile, the threshold value of the generated optical frequency comb is as low as the micro-watt magnitude. The micro-ring resonator is made of the AlGaAs material with the Al component larger than 0.4, loss caused by the two-photon absorption (TPA) phenomenon is effectively reduced, and the generation efficiency and stability of the optical frequency comb are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of integrated photonic devices and semiconductor manufacturing, and in particular relates to a microring resonator and a preparation method thereof. Background Art

[0002] With the rapid development of technologies such as optical communications, optical computing, and artificial intelligence, the demand for optical data routing, switching networks, and information processing hardware continues to grow. In the short-distance environment of data centers and high-performance computers, it is expected that O-band wavelength division multiplexing (WDM) architecture will be deployed, which requires multi-wavelength laser light sources. Traditional uniformly spaced multi-wavelength semiconductor laser arrays have high processing requirements, multiple lasers occupy a large area, and require multiple drivers at the same time, which takes up a lot of resources. The optical frequency comb is an effective method to generate multi-wavelength lasers with equal intervals (free spectral range, FSR). Among them, coupling a single tunable laser with a microring resonator and utilizing the nonlinearity of the microring material, especially utilizing the Kerr effect (Kerr) and four-wave mixing (FWM) process to generate an optical frequency comb is one of the most common methods currently.

[0003] Silicon Nitride (SiN x ) microrings have the advantage of providing high Q factors and low-loss resonant cavities, which are essential for generating optical frequency combs with extremely narrow linewidth and high stability. Thin-film lithium niobate (TFLN) microrings can generate optical frequency combs with lower pump powers due to their high nonlinear coefficients, which is very beneficial for applications that require high efficiency and tunable optical frequency combs. Aluminum gallium arsenide (AlGaAs) materials can also achieve similar nonlinear coefficients to SiN due to their higher nonlinear coefficients than thin-film lithium niobate. x Microrings have comparable high quality factors, so AlGaAs microrings have lower thresholds.

[0004] However, AlGaAs materials have two-photon absorption (TPA) phenomenon depending on the rate component, which increases the loss. The AlGaAs-OI microring resonators reported so far mainly work in the communication C band, and their Al component is usually greater than 0.18 and less than 0.25, while the communication O band requires the Al component to be greater than 0.4, which is experimentally difficult to prepare. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems existing in the above-mentioned prior art and to provide a microring resonator and a preparation method thereof.

[0006] The present invention is achieved through the following technical solutions:

[0007] In a first aspect, the present invention provides a microring resonator, comprising a microring structure and a bus waveguide, wherein the material of the microring resonator comprises Alx Ga 1-x As, where x>0.4.

[0008] The microring resonator provided by the present invention is an integrated O-band microring resonator, which has the characteristics of high efficiency, miniaturization and integration. Compared with the existing silicon nitride and lithium niobate microring resonators, it has a comparable quality factor, and the threshold for generating an optical frequency comb is as low as microwatt level. The microring resonator of the present invention adopts AlGaAs material with an Al component greater than 0.4, effectively reducing the loss caused by the two-photon absorption (TPA) phenomenon, and improving the generation efficiency and stability of the optical frequency comb.

[0009] Specifically, the microring resonator is located on an insulator, the confined light field is mainly distributed in an AlGaAs waveguide, and the microring waveguide has anomalous dispersion in the O band to achieve the generation of a Kerr optical frequency comb.

[0010] Preferably, the number of the bus waveguides is 1-2, one end of the bus waveguide is input, and the other end is output.

[0011] Preferably, the microring resonator comprises a microring waveguide and a coupling waveguide, and the microring waveguide and the coupling waveguide are each independently at least one of a strip waveguide, a ridge waveguide or a multilayer waveguide.

[0012] Preferably, the radius of the microring resonator satisfies the formula:

[0013] Where FSR is the frequency interval, c is the speed of light, R is the radius of the microring, and n is g is the group refractive index of the mode.

[0014] Specifically, the radius of the microring resonator can be designed according to the required frequency interval.

[0015] Preferably, the input end and the output end of the bus waveguide are both tapered waveguides with gradually changing widths, the input end is coupled to the microring waveguide via evanescent waves, and the output end is coupled to the underlying waveguide via evanescent waves.

[0016] In a possible embodiment, the bus waveguide of the microring resonator has tapered waveguides with gradually changing widths at both ends, the widths of the strip waveguides at the input and output ends decrease linearly, the input end is coupled to the microring waveguide by evanescent waves, and the output end is also coupled to the waveguide of the lower layer by evanescent waves, thereby achieving efficient optical coupling.

[0017] In a second aspect, the present invention provides a method for preparing the microring resonator, comprising the following steps:

[0018] (1) Al on substrate A x Ga 1-xA layer of Al2O3 or SiN is deposited on the surface of the As layer x , and then bonding the deposited surface to the integrated photonic chip; the substrate A includes a protective layer and an Al x Ga 1-x As layer;

[0019] (2) Remove the protective layer to obtain an Al x Ga 1-x As layer integrated photonic chip;

[0020] (3) Photolithography and plasma etching were performed on the Al x Ga 1-x The micro-ring resonator was prepared in the As layer. x Ga 1-x As microring resonator integrated onto an integrated photonic chip.

[0021] The preparation method of the present invention adopts an etching process to etch away the protective layer, thereby solving the problem of high surface roughness of the prepared AlGaAs layer film with an Al component greater than 0.4, which is beneficial to reducing the loss of the aluminum gallium arsenide waveguide and the microring, improving the quality factor of the microring, and reducing the threshold for generating an optical frequency comb. The preparation method of the present invention includes the steps of providing a substrate, depositing a protective layer, chip bonding, substrate thinning and etching, and microring structure processing. The microring resonator finally formed has a high quality factor, a smaller device volume, and a higher integration, and the threshold pump power is as low as the microwatt level, while improving the efficiency and stability of optical frequency comb generation.

[0022] Preferably, in step (1), the Al x Ga 1-x The thickness of the As layer is 450nm-550nm.

[0023] Preferably, the substrate A comprises, from bottom to top, a gallium arsenide substrate, an AlGaAs layer with an Al content greater than 0.75, a gallium arsenide layer and an Al x Ga 1-x As layer.

[0024] Preferably, the method for preparing the substrate A comprises the following steps: sequentially obtaining an AlGaAs layer having an Al content greater than 0.75, a gallium arsenide layer and an Al layer on the surface of a gallium arsenide substrate by molecular beam epitaxy or metal organic compound chemical vapor phase epitaxy. x Ga 1-x As layer.

[0025] Specifically, the gallium arsenide substrate is a commercial substrate. In view of the fact that the AlGaAs thin film with a high Al content is prone to high roughness during the preparation process, the present invention sequentially deposits an AlGaAs layer with an Al content greater than 0.75, a gallium arsenide layer and a target Al content on the surface of the gallium arsenide substrate.x Ga 1-x As layer, AlGaAs layer with Al composition greater than 0.75 and target Al x Ga 1-x A thin GaAs layer is inserted between the As layers. When the protective layer is subsequently removed by chemical wet etching or plasma etching, the target Al x Ga 1-x Roughness of the As layer film surface.

[0026] Preferably, the thickness of the AlGaAs layer having an Al component greater than 0.75 is 480 nm-520 nm, and the thickness of the gallium arsenide layer is 45 nm-55 nm.

[0027] Preferably, in step (1), the deposition method includes at least one of magnetron sputtering deposition and atomic layer deposition (ALD).

[0028] Preferably, in step (1), the deposited Al2O3 or SiN x The thickness does not exceed 50nm; specifically, the deposited Al2O3 or SiN x The thickness is 4.5nm-5.5nm.

[0029] Preferably, in step (1), a layer of Al2O3 or SiN is deposited on the surface of the integrated photonic chip. x , and then bond the deposited surface to the deposited surface of substrate A.

[0030] Preferably, in step (1), the bonding method includes at least one of bonding adhesive bonding and direct bonding.

[0031] Preferably, in step (2), the etching method includes at least one of mechanical grinding, chemical solution corrosion, chemical wet etching, and plasma etching.

[0032] Preferably, in step (2), the operation of removing the protective layer is: firstly reducing the thickness of the gallium arsenide substrate by mechanical grinding or chemical solution etching, and then removing the remaining gallium arsenide substrate by chemical wet etching; then removing the AlGaAs layer with an Al content greater than 0.75 by chemical wet etching; and then removing the gallium arsenide layer by plasma etching to obtain a gallium arsenide layer containing Al. x Ga 1-x As layer integrated photonic chip.

[0033] The present invention uses multiple selective etching processes to peel off the protective layer layer by layer, and the selectivity of each layer is very large, so that when removing the material of the protective layer, Al x Ga1-x The surface roughness of the As layer film effectively controls its surface quality, reduces the loss of the microring resonator, and improves its quality factor and the efficiency and stability of optical frequency comb generation.

[0034] Specifically, the thickness of the gallium arsenide substrate is first reduced by mechanical grinding or chemical solution etching, and then the remaining gallium arsenide substrate is removed by chemical wet etching, such as citric acid plus hydrogen peroxide or ammonia plus hydrogen peroxide; then the AlGaAs layer with an Al component greater than 0.75 is removed by chemical wet etching, such as hydrofluoric acid; and then the gallium arsenide layer is removed by plasma etching, and more precise etching control and better surface quality are achieved through selective etching to obtain Al-containing x Ga 1-x As layer integrated photonic chip.

[0035] Preferably, the method for preparing the microring resonator further comprises step (4): depositing Al2O3 and silicon oxide in sequence on the surface of the microring resonator.

[0036] Specifically, the step (4) is: depositing a layer of Al2O3 by ALD to stabilize the defect state generated by etching and reduce the loss of the microring resonator, and finally depositing silicon oxide on the top by chemical vapor deposition to form a cladding layer.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) Compared with silicon nitride (SiN x ) and thin film lithium niobate (TFLN), the microring resonator of the present invention has a higher refractive index. Under the condition of achieving the same free spectral range (FSR), the device size is smaller, the device density is higher, and the integration is higher.

[0039] (2) The microring resonator of the present invention has an ultra-low threshold pump power as low as tens of microwatts, has higher energy efficiency, and is beneficial to reducing the energy consumption of the chip.

[0040] (3) The preparation method of the microring resonator of the present invention solves the problem of high surface roughness of the prepared film with an Al component greater than 0.4 through multiple selective etching processes, which is beneficial to reducing the loss of the AlGaAs waveguide and the microring, improving the quality factor of the microring, and lowering the threshold for generating an optical frequency comb.

[0041] (4) The microring resonator of the present invention is suitable for the fields of high-density optical communication, optical computing and artificial intelligence, and provides a new solution for the next generation of photonic integration technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Schematic diagram of top view and schematic diagram of cross section of a microring resonator of an embodiment;

[0043] Figure 2 Two substrates required for preparing the embodiment;

[0044] Figure 3 To obtain Al x Ga 1-x Flowchart of integrated photonic chip of As layer;

[0045] Figure 4 Schematic diagram of the preparation of microring resonator.

[0046] Description of reference numerals:

[0047] 101-AlGaAs micro-ring structure, 102-bus waveguide, 103-input coupling region, 104-output coupling region, 105 is the lower input silicon waveguide, 106 is the lower output silicon waveguide; 107, 108, 109 below are the cross-sectional views of region 103 from left to right; 201-GaAs substrate, 202-AlGaAs layer with a composition greater than 0.75, 203-GaAs layer, 204-Al x Ga 1-x As layer, x>0.4, 205-atomic layer deposited Al2O3 layer, 206-integrated photonic chip; 301-mask of micro-ring and bus waveguide obtained after exposure and development. DETAILED DESCRIPTION

[0048] To better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be understood by those skilled in the art that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0049] Unless otherwise specified, the experimental methods used in the examples are all conventional methods; the materials, reagents, etc. used, unless otherwise specified, can be obtained from commercial channels.

[0050] The following is a further description of the specific implementation of the present invention through specific examples in conjunction with the accompanying drawings. Those skilled in the art can understand the implementation method and application advantages of the present invention based on the contents disclosed in this specification.

[0051] The accompanying drawings are only used for illustrative purposes and should not be construed as limiting the present invention. For ease of description, some components in the accompanying drawings may be omitted or not enlarged or reduced according to general proportions, and do not represent the size of actual devices.

[0052] The schematic top view of the microring resonator of the present invention is as follows Figure 1As shown, the present invention provides an integrated O-band microring resonator, the structure in the plane includes a microring structure (101) and a bus waveguide (102), one end of the bus waveguide is an input (103), and the other end is an output (104).

[0053] Specific as Figure 1 As shown, the integrated O-band microring resonator provided by the present invention supports TE fundamental mode input in the bus waveguide 102, and outputs in TE mode in the bus output waveguide 102. The transmission direction of the optical wave mode is Figure 1 In this embodiment, the pump light is input from the silicon waveguide (105), and in the 103 region, the laser is coupled from the lower silicon waveguide to the upper Al waveguide in the form of an evanescent wave through a tapered waveguide with a gradually changing width. x Ga 1-x As bus waveguide, 103 area from left to right, silicon waveguide and Al x Ga 1-x The relative width of the As waveguide changes as shown in 107, 108, and 109. The width of the silicon waveguide gradually decreases, and the width of the Al x Ga 1-x The As waveguide gradually widens, while the opposite is true in the 104 region.

[0054] In this embodiment, a method for preparing a microring resonator includes the following steps:

[0055] (1) Provide a sheet containing Al x Ga 1-x As (x> 0.4) layer substrate A, such as Figure 2 Left: From bottom to top, the materials are GaAs substrate (201), 500nm AlGaAs layer (202) with Al content greater than 0.75, 50nm GaAs layer, and 500nm thick Al x Ga 1-x As (x>0.4) layer, providing an integrated photonic chip, such as Figure 2 right;

[0056] (2) Depositing a 5 nm layer of Al2O3(205) on the surfaces of both substrates using magnetron sputtering or atomic layer deposition (ALD);

[0057] (3) The upper surface of substrate A is fixed to the integrated photonic chip by bonding adhesive or direct bonding, such as Figure 3 (a);

[0058] (4) Reduce the thickness of the GaAs substrate by mechanical grinding or chemical solution etching to retain a thickness of 50 μm, such as Figure 3 (b);

[0059] (5) Using chemical wet selective etching, the etching solution is citric acid solution: hydrogen peroxide = 3:1, to remove the remaining gallium arsenide substrate, and the etching is stopped until the AlGaAs layer with an Al composition greater than 0.75, such as Figure 3 (c);

[0060] (6) Using chemical wet selective etching, hydrofluoric acid is used to remove the AlGaAs layer with an Al content greater than 0.75, until the gallium arsenide layer is reached, such as Figure 3 (d);

[0061] (7) Using fluorine-based plasma, selectively etch away the gallium arsenide layer until Al x Ga 1-x As (x>0.4) layer, Al x Ga 1-x As (x>0.4) thin film layer is prepared on the integrated photonic chip, such as Figure 3 (e);

[0062] (8) Photolithography on Al x Ga 1-x The photoresist mask for preparing micro-ring structure and bus waveguide on As (x>0.4) thin film layer, such as Figure 4 (a); and plasma dry etching is used to form a micro-ring structure and a bus waveguide, such as Figure 4 (b); Finally, a 5 nm thick Al2O3 layer was deposited by ALD, and silicon oxide was deposited on the top to form a cladding layer by chemical vapor deposition to obtain a microring resonator ( Figure 4 The Al2O3 layer in the middle has been omitted).

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A microring resonator, characterized in that: The micro-ring resonator comprises a micro-ring structure and a bus waveguide, wherein the material of the micro-ring resonator comprises Al x Ga 1-x As, where x>0.

4.

2. The microring resonator according to claim 1, characterized in that: The number of the bus waveguides is 1-2, one end of the bus waveguide is input, and the other end is output.

3. The microring resonator according to claim 1, characterized in that: The microring resonator comprises a microring waveguide and a coupling waveguide, wherein the microring waveguide and the coupling waveguide are each independently at least one of a strip waveguide, a ridge waveguide or a multilayer waveguide.

4. The microring resonator according to claim 1, characterized in that: The radius of the microring resonator satisfies the formula: Where FSR is the frequency interval, c is the speed of light, R is the radius of the microring, and n is g is the group refractive index of the mode.

5. The method for preparing a microring resonator according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) Al on substrate A x Ga 1-x A layer of Al2O3 or SiN is deposited on the surface of the As layer x , and then bonding the deposited surface to the integrated photonic chip; the substrate A includes a protective layer and an Al x Ga 1-x As layer; (2) removing the protective layer to obtain a x Ga 1-x As layer integrated photonic chip; (3) Photolithography and plasma etching were performed on the Al x Ga 1-x Microring resonators were fabricated in the As layer.

6. The method for preparing a microring resonator according to claim 5, characterized in that: In the step (1), the Al x Ga 1-x The thickness of the As layer is 450nm-550nm.

7. The method for preparing a microring resonator according to claim 5, characterized in that: The substrate A includes, from bottom to top, a gallium arsenide substrate, an AlGaAs layer with an Al content greater than 0.75, a gallium arsenide layer and an Al x Ga 1-x As layer.

8. The method for preparing a microring resonator according to claim 7, characterized in that: The thickness of the AlGaAs layer with an Al component greater than 0.75 is 480nm-520nm, and the thickness of the gallium arsenide layer is 45nm-55nm.

9. The method for preparing a microring resonator according to claim 7, characterized in that: In the step (2), the operation of removing the protection is: firstly reducing the thickness of the gallium arsenide substrate by mechanical grinding or chemical solution etching, and then removing the remaining gallium arsenide substrate by chemical wet etching; then removing the AlGaAs layer with an Al content greater than 0.75 by chemical wet etching; and then removing the gallium arsenide layer by plasma etching to obtain a gallium arsenide layer containing Al x Ga 1-x As layer integrated photonic chip.

10. The method for preparing a microring resonator according to claim 5, characterized in that: Satisfy at least one of the following: (1) In step (1), the deposition method includes at least one of magnetron sputtering deposition and atomic layer deposition (ALD); (2) In the step (1), the deposited Al2O3 or SiN x The thickness does not exceed 50nm; (3) In step (1), the bonding method includes at least one of bonding adhesive bonding and direct bonding; (4) In step (2), the etching method includes at least one of mechanical grinding, chemical solution corrosion, chemical wet etching, and plasma etching.

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