Intermodal brillouin laser based on sound field injection and preparation method thereof

Abstract

The application provides an intermodal Brillouin laser based on sound field injection and a preparation method thereof, which comprises a substrate, a corrosion sacrificial layer, a waveguide layer, a straight waveguide, an FP resonant cavity and an interdigital transducer; the corrosion sacrificial layer is arranged on one surface of the substrate; the waveguide layer is arranged on the surface of the corrosion sacrificial layer away from the substrate; the corrosion sacrificial layer is provided with an air cladding; the straight waveguide is arranged on the surface of the waveguide layer away from the air cladding; the FP resonant cavity is formed on the straight waveguide; the interdigital transducer is arranged on the waveguide layer on one side of the FP resonant cavity and is at a certain angle with the straight waveguide and is used for generating sound waves into the FP resonant cavity. The interdigital transducer is used for introducing the sound field into the FP resonant cavity, the injected sound field is relative to the sound field generated by the optical force, the transmission loss existing in the original sound field is compensated, the efficient acousto-optic coupling efficiency is realized, the threshold power of laser generation is reduced, and the requirement for the optical pumping power is further reduced.

Description

Technical Field

[0001] This invention relates to the fields of optical technology, and in particular to an intermodal Brillouin laser based on acoustic field injection and its fabrication method. Background Technology

[0002] Brillouin lasers possess excellent properties such as narrow linewidth, low noise, and high stability, and can generate highly coherent laser sources, showing broad application prospects in high-speed optical communication, lidar, microwave photonics, and quantum mechanics. In recent years, with the rapid development of integrated photonics, the research on monolithic integrated Brillouin lasers has played a crucial role in optical communication systems. The key to generating stimulated Brillouin lasers lies in achieving the excitation and confinement of acoustic and optical fields.

[0003] For example, patent CN114914783A discloses a Brillouin laser based on intermodal Brillouin scattering. This laser uses coherent phonons generated by optical forces to nonlinearly modulate the pump light, producing Stokes light with a certain frequency shift. The Stokes light oscillates under the influence of a resonant cavity, and when the gain exceeds the loss, a Stokes laser is generated. However, phonons generated by optical forces are often inefficient and suffer from transmission losses, significantly reducing the acousto-optic coupling efficiency. Therefore, traditional stimulated Brillouin lasers have a large threshold, requiring a high optical pump power. Furthermore, due to its complex cavity structure, the ring resonant cavity is easily affected by external factors such as temperature and vibration, causing problems such as resonant wavelength drift and unstable output power in the generated laser. Summary of the Invention

[0004] In view of this, the present invention proposes an intermodal Brillouin laser based on acoustic field injection and its fabrication method to solve the problems of low efficiency and transmission loss of phonons generated by optical force in the traditional stimulated Brillouin scattering process, resulting in low acousto-optic coupling efficiency, a large threshold for Brillouin lasers, and a large required optical pump power.

[0005] On one hand, this invention discloses an intermodal Brillouin laser based on acoustic field injection, which includes a substrate, an etched sacrificial layer, and a waveguide layer; wherein,

[0006] The corrosion sacrificial layer is disposed on one of the surfaces of the substrate;

[0007] The waveguide layer is disposed on the surface of the etched sacrificial layer away from the substrate;

[0008] The etched sacrificial layer is provided with an air cladding layer that is in contact with the substrate and the surface of the waveguide layer;

[0009] It also includes straight waveguides, FP resonant cavities, and interdigital transducers; among which,

[0010] The straight waveguide is disposed on the surface of the waveguide layer away from the air cladding;

[0011] The FP resonant cavity is formed on the straight waveguide;

[0012] Interdigital transducers are placed on the waveguide layer on one side of the FP resonant cavity and are at a certain angle to the straight waveguide. They are used to inject sound waves into the FP resonant cavity.

[0013] Based on the above technical solution, preferably, the straight waveguide includes an input straight waveguide, an intermediate straight waveguide, and an output straight waveguide connected in sequence;

[0014] The intermodal Brillouin laser also includes a first Bragg grating and a second Bragg grating. The first Bragg grating is disposed between the input straight waveguide and the intermediate straight waveguide, and the second Bragg grating is disposed between the output straight waveguide and the intermediate straight waveguide. The first Bragg grating, the second Bragg grating, and the intermediate straight waveguide form an FP resonant cavity. The reflectivity of the second Bragg grating is less than that of the first Bragg grating.

[0015] Furthermore, preferably, both the first and second Bragg gratings are dual-period grating series structures, with the short grating period being 460-470nm and the long grating period being 490-500nm.

[0016] Based on the above technical solution, preferably, it further includes an input curved waveguide and an output curved waveguide. The input curved waveguide and the output curved waveguide are disposed on the surface of the waveguide layer away from the air cladding. The input curved waveguide is located on the side of the input straight waveguide and is laterally coupled with the input straight waveguide to form an input asymmetric directional coupler structure. The output curved waveguide is located on the side of the output straight waveguide and is laterally coupled with the output straight waveguide to form an output asymmetric directional coupler structure.

[0017] Based on the above technical solution, preferably, the period of the electrodes of the interdigital transducer is 2.0-2.2 μm, and the tilt angle between the interdigital transducer and the straight waveguide is 6° to 8°.

[0018] Based on the above technical solution, preferably, the input ends of the straight waveguide and the input curved waveguide, and the output ends of the straight waveguide and the output curved waveguide are all provided with focusing apodization grating couplers.

[0019] Based on the above technical solution, preferably, the grating coupler, straight waveguide, first Bragg grating, second Bragg grating, input curved waveguide, and output curved waveguide are all formed by etching the surface of the waveguide layer; wherein...

[0020] The input straight waveguide, intermediate straight waveguide, and output straight waveguide are multimode straight ridge waveguide structures with the same cross-sectional dimensions, and the ridge width of the multimode straight ridge waveguide structure is 2.0-2.3 μm;

[0021] The input curved waveguide and the output curved waveguide are single-mode curved ridge waveguide structures, and the ridge width of the single-mode curved ridge waveguide structure is 0.8-0.9 μm;

[0022] The ridge height of the multimode straight ridge waveguide structure and the single-mode curved ridge waveguide structure is 190-210 nm, and the etching width is 2.0-2.3 μm.

[0023] Preferably, the waveguide layer is made of aluminum nitride, zinc oxide, or lithium niobate, which have a piezoelectric effect; the interdigital transducer is made of aluminum or gold.

[0024] Based on the above technical solution, preferably, multiple etch holes penetrating the waveguide layer are formed on both sides of the straight waveguide, the side of the input curved waveguide and the side of the output curved waveguide away from the straight waveguide. The etch holes are used to penetrate the etch sacrificial layer to form an air cladding.

[0025] On the other hand, this invention discloses a method for fabricating an intermodal Brillouin laser based on acoustic field injection, comprising the following steps:

[0026] S1. Provide a substrate, and grow an etch sacrificial layer on one of the surfaces of the substrate;

[0027] S2. A waveguide layer is grown on the surface of the etched sacrificial layer away from the substrate;

[0028] S3. A mask is formed on the waveguide layer using plasma chemical vapor deposition, and plasma etching is performed to form a grating coupler, a straight waveguide, a first Bragg grating, a second Bragg grating, an input curved waveguide, and an output curved waveguide on the waveguide layer.

[0029] S4. An interdigital transducer was fabricated on the waveguide layer on one side of the resonant cavity using electron beam evaporation and stripping processes.

[0030] S5. Multiple etch holes are formed on the waveguide layers on both sides of the straight waveguide, the side of the input curved waveguide and the side of the output curved waveguide away from the straight waveguide. The etch holes penetrate the waveguide layer and etch the sacrificial layer to form an air cladding.

[0031] The present invention has the following advantages over the prior art:

[0032] (1) The intermodal Brillouin laser based on acoustic field injection disclosed in this invention provides an acoustic field that satisfies the phase-matching condition for the intermodal Brillouin scattering effect in the FP resonator by forming an FP resonator on a straight waveguide and placing an interdigital transducer with an angle on the waveguide layer outside the FP resonator. This injected acoustic field greatly increases the efficiency of the acoustic field generated by optical force. Since the gain value of the Brillouin effect is proportional to the number of participating phonons, the method of injecting the acoustic field significantly improves the gain value of intermodal Brillouin scattering, thereby reducing the threshold power of the Brillouin laser. The number of phonons generated by the interdigital transducer is proportional to the square of the microwave signal power loaded on the interdigital transducer, and is independent of the input power of the pump light, thus reducing the requirement for pump light power. In addition, the electrodes of the interdigital transducer are placed at a certain angle to the straight waveguide to provide longitudinal and transverse acoustic wave vector components for Brillouin scattering, so that the injected acoustic wave satisfies the intermodal phase-matching condition in both the longitudinal and transverse directions, further enhancing the acousto-optic coupling strength. Meanwhile, compared to ring resonators, FP resonators are less susceptible to external factors such as temperature and vibration, and have advantages such as simple structure and stable output.

[0033] (2) By introducing a curved waveguide, an asymmetric directional coupler is formed by evanescent coupling between the curved waveguide and the straight waveguide. This coupler is used for the input of pump light and the output of laser light. The curved waveguide is a single-mode narrow waveguide, and the straight waveguide is a multi-mode wide waveguide. Utilizing the input asymmetric directional coupler structure, not only can TE light be input... 00 The mode can also convert pump light into TE. 10 This mode is something that straight waveguides alone cannot achieve. For output asymmetric directional couplers, the generated TE can be... 00 TE 10 The mode light field is output separately at different ports, so the TE of the laser can be flexibly adjusted by inputting pump light at different ports. 00 / TE 10 The output mode reduces crosstalk between modes during testing. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 A three-dimensional structural diagram of an intermodal Brillouin laser provided in an embodiment of the present invention;

[0036] Figure 2A schematic diagram of the planar structure of an intermodal Brillouin laser provided in an embodiment of the present invention;

[0037] Figure 3 The TE disclosed in this invention 00 Model, TE 10 The field distribution diagram of the mode and the sound field;

[0038] Figure 4 This is a diagram illustrating the intermodal Brillouin laser generation method disclosed in this invention;

[0039] Figure 5 The resonant cavity TE disclosed in this invention 00 Model, TE 10 Mode transmission spectrum;

[0040] Figure 6 The TE in cavity resonant / non-resonant states disclosed in this invention 00 Mode optical field transmission diagram;

[0041] Figure 7 The sound field and TE disclosed in this invention 00 Model, TE 10 Phase matching relationship diagram of the mode optical field;

[0042] Figure 8 This is a graph showing the relationship between the gain value of Stokes light and the radio frequency power of the injected sound field as disclosed in this invention.

[0043] Figure label:

[0044] 1. Substrate; 2. Etched sacrificial layer; 3. Waveguide layer; 20. Air cladding; 4. Straight waveguide; 5. First Bragg grating; 6. Second Bragg grating; 7. Interdigital transducer; 41. Input straight waveguide; 42. Intermediate straight waveguide; 43. Output straight waveguide; 8. Input curved waveguide; 9. Output curved waveguide; 10. Focusing apodization grating coupler; 30. Etched via. Detailed Implementation

[0045] like Figure 1 As shown, combined with Figure 2 The present invention provides an intermodal Brillouin laser based on acoustic field injection, comprising a substrate 1, an etched sacrificial layer 2, a waveguide layer 3, a straight waveguide 4, a first Bragg grating 5, a second Bragg grating 6, and an interdigital transducer 7.

[0046] In this embodiment, the material of the substrate 1 is not particularly limited. Those skilled in the art can choose it arbitrarily according to actual needs. As long as lattice matching is met, the etch sacrificial layer 2 and waveguide layer 3 can be grown on it. As a specific example, the material of the substrate 1 is silicon on insulating substrate 1, abbreviated as SOI.

[0047] An etch sacrificial layer 2 is disposed on one of the surfaces of the substrate 1, and the etch sacrificial layer 2 is grown on the surface of the substrate 1. The material of the etch sacrificial layer 2 is not particularly limited, and those skilled in the art can choose it arbitrarily according to actual needs, as long as the material has selective etching properties with the waveguide layer 3. As a specific example, the material of the etch sacrificial layer 2 is silicon dioxide.

[0048] Waveguide layer 3 is deposited on the surface of corrosion sacrificial layer 2 by physical vapor deposition. The material of waveguide layer 3 is not particularly limited and can be freely selected by those skilled in the art according to actual needs. As a preferred embodiment, the material of waveguide layer 3 is aluminum nitride, zinc oxide or lithium niobate with piezoelectric effect.

[0049] An air cladding 20 is provided in the etched sacrificial layer 2, which is in contact with the surface of the substrate 1 and the waveguide layer 3. The air cladding 20 can be understood as a gap formed by the etching process of the etched sacrificial layer 2, so that the upper and lower surfaces of the waveguide layer 3 are both air cladding 20. The air cladding 20 effectively reduces the leakage of sound waves.

[0050] The straight waveguide 4 is disposed on the surface of the waveguide layer 3 away from the air cladding 20, and is used to transmit pump light, Stokes light and to generate Brillouin scattering effect. The FP resonant cavity is formed on the straight waveguide 4.

[0051] The interdigital transducer 7 is disposed on the waveguide layer 3 on one side of the FP resonant cavity and is at a certain angle to the straight waveguide 4, and is used to inject sound waves into the resonant cavity.

[0052] In some preferred embodiments, the interdigital transducer 7 is made of aluminum or gold. In this embodiment, the waveguide layer 3 can be a piezoelectric material, and the interdigital transducer is formed on the waveguide layer. The interdigital transducer and the waveguide layer work together to convert electrical energy into acoustic energy.

[0053] By employing the above technical solution, a FP resonant cavity is formed on a straight waveguide, and an interdigital transducer with an angle is placed on the waveguide layer outside the FP resonant cavity. This provides an acoustic field that satisfies the phase-matching condition for the intermodal Brillouin scattering effect in the FP resonant cavity. This injected acoustic field significantly increases the efficiency compared to optically generated acoustic fields. Since the gain of the Brillouin effect is proportional to the number of participating phonons, the injected acoustic field method greatly enhances the gain of intermodal Brillouin scattering, thereby reducing the threshold power of the Brillouin laser. The number of phonons generated by the interdigital transducer is proportional to the square of the microwave signal power applied to the interdigital transducer, and is independent of the input power of the pump light, thus reducing the power requirement for the pump light. In addition, the electrodes of the interdigital transducer are placed at a certain angle to the straight waveguide to provide longitudinal and transverse acoustic wave vector components for Brillouin scattering, ensuring that the injected acoustic wave satisfies the intermodal phase-matching condition in both the longitudinal and transverse directions, further enhancing the acousto-optic coupling strength. Meanwhile, compared to ring resonators, FP resonators are less susceptible to the influence of external factors such as temperature and vibration, and have advantages such as simple structure and stable output.

[0054] As some preferred implementations, by setting the period and angle of the interdigital transducer electrodes, the frequency of the acoustic wave generated is equal to the frequency difference between different modes of optical fields in the optical waveguide, and the propagation wave vector of the acoustic wave is equal to the wave vector difference between different modes of optical fields, that is, the phase matching condition is met, so as to generate a large acousto-optic coupling efficiency, thereby reducing the threshold of the laser.

[0055] Preferably, in this embodiment, the period of the electrodes of the interdigital transducer is 2.0-2.2 μm, and the tilt angle between the interdigital transducer and the straight waveguide is 6° to 8°.

[0056] The interdigital transducer proposed in this invention is placed at a certain angle to the straight waveguide to provide a longitudinal acoustic wave vector component for Brillouin scattering, thereby completing the energy conversion between optical field modes. The acoustic wave q generated by the interdigital transducer is divided into a longitudinal wave vector component q1 and a transverse wave vector component q2. Where n1 and n2 are the effective refractive indices of the core and cladding materials for sound wave propagation, respectively, λ is the operating wavelength, and w is the width of the straight waveguide; additionally, the angle of the interdigitated transducer is set to θ = tan -1 (q1 / q2), period Λ=2π / q, it can be seen that the angle θ and period Λ of the interdigital transducer need to be accurately designed so that the generated acoustic waves satisfy the intermodal phase matching condition in both the longitudinal and transverse directions in order to produce a large acousto-optic coupling efficiency, thereby reducing the threshold of the laser.

[0057] In this embodiment, the straight waveguide 4 includes an input straight waveguide 41, an intermediate straight waveguide 42, and an output straight waveguide 43 connected in sequence.

[0058] This embodiment illustrates a preferred implementation of the FP resonant cavity. Specifically, the intermodal Brillouin laser further includes a first Bragg grating 5 and a second Bragg grating 6. The first Bragg grating 5 is disposed between the input straight waveguide 41 and the intermediate straight waveguide 42, and the second Bragg grating 6 is disposed between the output straight waveguide 43 and the intermediate straight waveguide 42. The first Bragg grating 5, the second Bragg grating 6, and the intermediate straight waveguide 42 form an FP resonant cavity.

[0059] The resonant cavity disclosed in this embodiment uses Bragg gratings at both ends as two reflecting mirrors, and the light wave is reflected back and forth between the mirrors multiple times to form multi-beam interference. Most existing Brillouin laser resonant cavities are ring resonant cavities, but due to their complex cavity structure, they are easily affected by external factors such as temperature and vibration, which causes problems such as resonant wavelength drift and unstable output power in the generated laser. In contrast, the FP resonant cavity with Bragg grating structure, as a simple linear cavity, has refractive index modulation that is not easily affected by temperature, has strong thermal stability, and has the advantages of simple and compact structure and stable output.

[0060] Using a Bragg grating as the reflector of the FP resonant cavity allows for better selection of the laser excitation wavelength, because only light fields that satisfy the Bragg resonance condition will be reflected and oscillate and amplify in the resonant cavity.

[0061] In some preferred embodiments, both the first Bragg grating 5 and the second Bragg grating 6 are dual-period gratings in series, with a short grating period of 460-470 nm and a long grating period of 490-500 nm. The purpose of designing the dual-period gratings is to simultaneously reflect TE wavelengths near 1550 nm. 00 and TE 10 Light field mode.

[0062] The first Bragg grating 5 and the second Bragg grating 6, together with the intermediate straight waveguide 42, form an FP resonant cavity. The cavity length is adjusted so that the integer multiples between the longitudinal modes match the frequency shift of the Brillouin scattering, i.e., the Brillouin frequency shift is an integer multiple of the longitudinal mode spacing. As the cavity length increases, the number of resonance peaks increases, and the TE... 00 TE 10 The spacing between the resonant peaks will decrease the FSR. When the FSR is exactly equal to the Brillouin frequency shift, both modes are in resonance and the acousto-optic conversion efficiency is at its maximum.

[0063] In order to convert pump light into TE 00 or TE 10The intermodal Brillouin laser in this embodiment also includes an input curved waveguide 8 and an output curved waveguide 9. The input curved waveguide 8 and the output curved waveguide 9 are disposed on the surface of the waveguide layer 3 away from the air cladding 20. The input curved waveguide 8 is located on one side of the input straight waveguide 41 and is laterally coupled to the input straight waveguide 41 to form an input asymmetric directional coupler structure for inputting TE. 00 / TE 10 The pump light, with its output curved waveguide 9 located on one side of the output straight waveguide 43, is laterally coupled to form an output asymmetric directional coupler structure for outputting TE. 00 / TE 10 Pump light.

[0064] To achieve the input and output of pump light, this embodiment also provides focusing-type apodization grating couplers 10 at the input ends of the straight waveguide 4 and the input curved waveguide 8, and at the output ends of the straight waveguide 4 and the output curved waveguide 9. The focusing-type apodization grating coupler 10 has a larger coupling efficiency and operating bandwidth compared to the strip vertical coupler. In this embodiment, the focusing-type apodization grating coupler 10 is formed by etching on the surface of the waveguide layer 3. Specifically, its etching depth is 150-200 nm, its etching width is 280-300 nm, the etching width gradually increases along the waveguide length, the etching width variation is 50-60 nm, and the number of gratings is 15-20.

[0065] In this embodiment, the pump light is coupled to the input asymmetric directional coupler through the focusing apodization grating coupler 10. After passing through the first Bragg grating 5, part of the pump light enters the region of the intermediate straight waveguide 42. The acoustic wave generated by the interdigital transducer 7 modulates it with Brillouin scattering, generating frequency-shifted Stokes light. The Stokes light is continuously resonantly amplified in the resonant cavity. When the gain value is greater than the total loss, Brillouin laser is generated and passes through the second Bragg grating 6 with weaker reflectivity, and finally outputs laser at the output asymmetric directional coupler port.

[0066] In this embodiment, the grating coupler, straight waveguide 4, first Bragg grating 5, second Bragg grating 6, input curved waveguide 8, and output curved waveguide 9 are all formed by etching the surface of waveguide layer 3; wherein...

[0067] The input straight waveguide 41, the intermediate straight waveguide 42, and the output straight waveguide 43 are multimode straight ridge waveguide structures with the same cross-sectional dimensions, while the input curved waveguide 8 and the output curved waveguide 9 are single-mode curved ridge waveguide structures.

[0068] In this embodiment, the height and width of the cross-sections of both the straight-ridge waveguide and the curved-ridge waveguide require special design. The width of the ridge region determines the number of supported modes (single-mode or multi-mode). A larger ridge region allows for the simultaneous existence of multiple pump modes in the straight-ridge waveguide. The etching width of the ridge region on the surface of waveguide layer 3 determines the frequency of the acoustic field. The TE supported by the straight-ridge waveguide is simulated using the finite element method. 00 Pattern and TE 10 And the sound field distribution diagram as follows Figure 3 As shown.

[0069] In some preferred embodiments, the interdigital transducer 7, the straight waveguide 4, the input curved waveguide 8, and the output curved waveguide 9 are not on the same horizontal plane. The straight waveguide and the curved waveguide are all ridge waveguide structures, not strip structures, so they are not on the same plane as the electrode transducer. The ridge waveguide can better confine the sound field and the light field at the same time, with low loss and enhanced acousto-optic coupling efficiency.

[0070] As some preferred embodiments, the ridge width of the multimode straight ridge waveguide structure is 2.0-2.3 μm; the ridge width of the single-mode curved ridge waveguide structure is 0.8-0.9 μm; the ridge height of the multimode straight ridge waveguide structure and the single-mode curved ridge waveguide structure is 190-210 nm, the etching depth is 150-200 nm, and the etching width is 2.0-2.3 μm.

[0071] The input asymmetric directional coupler has two input ports, located at the input end of the single-mode bent waveguide and the input end of the multimode straight waveguide 4, respectively; at the same time, the output asymmetric directional coupler has two output ports, located at the output end of the single-mode bent waveguide and the output end of the multimode straight waveguide 4, respectively; different laser modes can be obtained by inputting / outputting at different ports, so laser generation is divided into two methods.

[0072] As one approach, TE is input at port 41 of the input straight waveguide. 00 The pump light of the mode passes through the TE of the first Bragg grating 5. 00 The pump light is directly injected into the acoustic field modulation, generating TE. 10 The mode sideband light is resonantly amplified by the resonant cavity to form TE. 10 The mode laser is output at the output port 43 of the output straight waveguide. See details below. Figure 4 The image above;

[0073] As another approach, input TE at the 8-port of the input curved waveguide 00 The pump light of the mode is evanescently coupled to the input straight waveguide 41 to form a TE. 10 The mode light field, injected into the sound field will TE 10 Energy of the mode light field scattered into TE 00Single-sideband light is used to achieve inter-mode energy conversion and single-sideband signal amplification, followed by TE. 00 The mode edge band light is amplified by resonance under the action of the resonant cavity, forming TE. 00 The mode laser is output at the output port 43 of the output straight waveguide. See details below. Figure 4 See the image below.

[0074] The curved waveguide structure proposed in this invention is evanescently coupled with a straight waveguide 4 to form an asymmetric directional coupler, used for pump light input and laser output. The curved waveguide is a single-mode narrow waveguide, and the straight waveguide 4 is a multi-mode wide waveguide. Utilizing this input asymmetric directional coupler structure, not only can TE light be input... 00 The mode can also convert pump light into TE. 10 This mode is something that straight waveguide 4 alone cannot achieve. For the output asymmetric directional coupler, the generated TE can be... 00 TE 10 The mode light field is output separately at different ports, so the TE of the laser can be flexibly adjusted by inputting pump light at different ports. 00 / TE 10 The output mode reduces crosstalk between modes during testing.

[0075] Tunable laser output in two modes has significant application value in many fields due to its unique field and phase distribution, such as laser cutting and precision machining. Compared with single laser mode output, it has greater flexibility and selectivity, providing more possibilities for the application of laser technology.

[0076] Figure 5 TE in a resonant cavity composed of Bragg gratings 00 / TE 10 The transmission spectral lines, using TE 00 Model and TE 10 The extremely small FSR between modes enables inter-band energy conversion, improving conversion efficiency while further reducing device size.

[0077] Figure 6 The above figure shows the effect of TE when the resonant cavity is in the resonant state. 00 Pattern reflection, Figure 6 The figure below shows the optical field transmission in the non-resonant state of the resonant cavity. The figure indicates that only wavelengths satisfying the Bragg grating resonance condition are reflected, while other wavelengths are directly transmitted. Therefore, the Bragg grating has strong filtering characteristics, generating single-mode laser light of a specific wavelength.

[0078] In this example, the injected acoustic field generated by the interdigital transducer 7 modulates the Brillouin sideband light. The longitudinal acoustic wave vector direction is set to be opposite to the optical field propagation direction, and the frequency of the injected acoustic field is equal to the TE in the waveguide. 00 Model and TE10 The phase matching relationship between the light field and the sound field due to the difference in mode frequencies is as follows: Figure 7 As shown.

[0079] In this embodiment, the pump light is Brillouin modulated by the injected acoustic field, transferring the energy of the pump light to the Stokes light to generate a gain value. Therefore, the gain value of the Stokes light is proportional to the microwave drive RF power. Figure 8 This relates the gain of the Stokes beam to the RF power of the injected sound field. When the gain of the Stokes beam is greater than the loss, laser generation occurs. The threshold power is relatively small compared to the Brillouin laser that generates the sound field by optical force.

[0080] To achieve the air cladding 20 on the etched sacrificial layer 2, this embodiment provides multiple etched holes 30 penetrating the waveguide layer 3 on both sides of the straight waveguide 4, and on the side of the input curved waveguide 8 and the output curved waveguide 9 away from the straight waveguide 4. The etched holes 30 are used to penetrate the etched sacrificial layer 2 to form the air cladding 20. Preferably, the etched holes 30 are strip-shaped holes with a width of 50-60 μm and an interval of 3-5 μm between adjacent slots.

[0081] This invention also discloses a method for fabricating an intermodal Brillouin laser based on acoustic field injection, characterized by the following steps:

[0082] S1. Taking silicon substrate 1 as an example, an etching sacrificial layer 2 is grown on one of the surfaces of silicon substrate 1. For example, silicon dioxide is selected as the etching sacrificial layer 2. The thickness of the etching sacrificial layer 2 is not specifically limited, but is preferably 100-200nm, so as to ensure that the waveguide layer 3 does not contact the silicon substrate 1 after the etching sacrificial layer 20 is etched out.

[0083] S2. A waveguide layer 3 is grown on the surface of the etched sacrificial layer 2 away from the substrate 1. In this embodiment, the waveguide layer 3 is made of aluminum nitride. Aluminum nitride and the air cladding 20 have a large refractive index difference, which has a strong confinement effect on the light field. The waveguide layer 3 is also deposited on the surface of the etched sacrificial layer 2 by plasma chemical vapor deposition. The thickness of the waveguide layer 3 is preferably 300-400nm to ensure that the optical waveguide can be etched.

[0084] S3. A mask is formed on the waveguide layer 3 using plasma chemical vapor deposition. Then, a grating coupler, a straight waveguide 4, a first Bragg grating 5, a second Bragg grating 6, an input curved waveguide 8, and an output curved waveguide 9 are formed on the waveguide layer 3 using photolithography. The pattern is then transferred sequentially onto the chromium and silicon dioxide masks and the AlN waveguide using electron beam lithography and plasma etching to form the ridge waveguide structure, including the straight waveguide 4, the curved waveguide, the Bragg grating, and the grating coupler. The grating coupler generally uses a 2nm high-precision exposure, while the straight waveguide 4 and the curved waveguide use a lower 4nm or 8nm exposure precision.

[0085] S4. An interdigital transducer 7 is fabricated on the waveguide layer 3 on one side of the resonant cavity using electron beam evaporation and stripping processes. A metal interdigital transducer 7 and a metal marker are fabricated on the aluminum nitride waveguide layer 3. The metal interdigital transducer 7 is generally made of aluminum, and the metal marker is generally made of gold. The number of interdigital transducer 7 pairs is 10-20. An adhesion layer Cr is provided between the metal marker Au and the aluminum nitride waveguide layer 3 to improve the adhesion performance between the metal marker Au and the waveguide layer 3. The thickness of Au is set to 10-20 nm, and the thickness of Cr is set to 80-100 nm.

[0086] S5. Multiple etch holes 30 are formed on the waveguide layer 3 on both sides of the straight waveguide 4, the input curved waveguide 8, and the side of the output curved waveguide 9 away from the straight waveguide 4. The etch holes 30 etch the sacrificial layer 2 to form an air cladding 20. The etch solution is passed through the etch holes 30 to etch the sacrificial layer 2 to obtain the air cladding 20, thus fabricating a suspended ridge waveguide laser. The etch holes 30 are strip-shaped holes, preferably 40-50 μm in length and 1-2 μm in width, to facilitate the passage of the etch solution.

[0087] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An intermodal Brillouin laser based on acoustic field injection, comprising a substrate (1), an etched sacrificial layer (2), and a waveguide layer (3); wherein, The corrosion sacrificial layer (2) is disposed on one of the surfaces of the substrate (1); The waveguide layer (3) is disposed on the surface of the etched sacrificial layer (2) away from the substrate (1); An air cladding (20) is provided in the corrosion sacrificial layer (2) that is in contact with the surfaces of the substrate (1) and the waveguide layer (3); Its features include: a straight waveguide (4), an FP resonant cavity, and an interdigital transducer (7); wherein, The straight waveguide (4) is disposed on the surface of the waveguide layer (3) away from the air cladding (20); The FP resonant cavity is formed on the straight waveguide (4); Interdigital transducers (7) are placed on the waveguide layer (3) on one side of the FP resonant cavity and are at a certain angle to the straight waveguide (4) to inject sound waves into the FP resonant cavity; The straight waveguide (4) includes an input straight waveguide (41), an intermediate straight waveguide (42) and an output straight waveguide (43) connected in sequence; The intermodal Brillouin laser also includes a first Bragg grating (5) and a second Bragg grating (6). The first Bragg grating (5) is disposed between the input straight waveguide (41) and the intermediate straight waveguide (42), and the second Bragg grating (6) is disposed between the output straight waveguide (43) and the intermediate straight waveguide (42). The first Bragg grating (5), the second Bragg grating (6) and the intermediate straight waveguide (42) form an FP resonant cavity. The reflectivity of the second Bragg grating (6) is less than that of the first Bragg grating (5). The first Bragg grating (5) and the second Bragg grating (6) are both dual-period grating series structures, with a short grating period of 460-470nm and a long grating period of 490-500nm; It also includes an input curved waveguide (8) and an output curved waveguide (9), which are disposed on the surface of the waveguide layer (3) away from the air cladding (20). The input curved waveguide (8) is located on the side of the input straight waveguide (41) and is laterally coupled to the input straight waveguide (41) to form an input asymmetric directional coupler structure. The output curved waveguide (9) is located on the side of the output straight waveguide (43) and is laterally coupled to the output straight waveguide (43) to form an output asymmetric directional coupler structure. The period of the electrodes of the interdigital transducer (7) is 2.0-2.2 μm, and the tilt angle between the interdigital transducer (7) and the straight waveguide (4) is 6°~8°; the input end of the straight waveguide (4) and the input curved waveguide (8), and the output end of the straight waveguide (4) and the output curved waveguide (9) are all provided with focusing apodization grating couplers (10); The grating coupler (10), straight waveguide (4), first Bragg grating (5), second Bragg grating (6), input curved waveguide (8), and output curved waveguide (9) are all formed by etching the surface of the waveguide layer (3); among them, The input straight waveguide (41), the intermediate straight waveguide (42), and the output straight waveguide (43) are multimode straight ridge waveguide structures with the same cross-sectional dimensions, and the ridge width of the multimode straight ridge waveguide structure is 2.0-2.3 μm; The input curved waveguide (8) and the output curved waveguide (9) are single-mode curved ridge waveguide structures, and the ridge width of the single-mode curved ridge waveguide structure is 0.8-0.9μm; The ridge height of the multimode straight ridge waveguide structure and the single-mode curved ridge waveguide structure is 190-210 nm, and the etching width is 2.0-2.3 μm; Multiple etch holes (30) are provided on both sides of the straight waveguide (4), the side of the input curved waveguide (8) and the side of the output curved waveguide (9) away from the straight waveguide (4) in the waveguide layer (3). The etch holes (30) are used to pass through the etch sacrificial layer (2) to form an air cladding (20).

2. The intermodal Brillouin laser based on acoustic field injection as described in claim 1, characterized in that: The waveguide layer is made of aluminum nitride, zinc oxide or lithium niobate with piezoelectric effect; the interdigital transducer (7) is made of aluminum or gold.

3. A method for fabricating an intermodal Brillouin laser based on acoustic field injection as described in any one of claims 1-2, characterized in that, The steps include the following: S1. Provide a substrate (1) and grow an etch sacrificial layer (2) on one of the surfaces of the substrate (1); S2. A waveguide layer (3) is grown on the surface of the etched sacrificial layer (2) away from the substrate (1); S3. A mask is formed on the waveguide layer (3) by plasma chemical vapor deposition and plasma etching is performed to form a grating coupler (10), a straight waveguide (4), a first Bragg grating (5), a second Bragg grating (6), an input curved waveguide (8), and an output curved waveguide (9) on the waveguide layer (3). S4. An interdigital transducer (7) is fabricated on the waveguide layer (3) on one side of the resonant cavity using electron beam evaporation and stripping processes. S5. Multiple etch holes (30) are provided on both sides of the straight waveguide (4), the side of the input curved waveguide (8) and the side of the output curved waveguide (9) away from the straight waveguide (4) of the waveguide layer (3). The etch holes (30) pass through the etch holes (30) and etch the sacrificial layer (2) to form an air cladding (20).

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