Integrated microwave optical aperture conversion front-end chip

Abstract

The present application relates to the field of microwave photonics, and discloses an integrated microwave optical aperture conversion front-end chip. Local oscillator light is efficiently coupled from an optical fiber into the chip through an edge coupler, and the local oscillator light is divided into multiple paths through a cascaded multimode interference coupler, and is input into a ridge waveguide of a lithium niobate electro-optical modulator through a connecting waveguide. The received microwave signal is input into the traveling wave electrode of the electro-optical modulator after low-noise amplification for microwave optical up-conversion, and then the optical signal carrying microwave information is input into the ridge waveguide of the lithium niobate phase shifter through the connecting waveguide for optical delay compensation, and then the optical signal carrying microwave information is emitted through a grating array through the connecting waveguide. The present application combines the advantages of silicon nitride and lithium niobate processes, greatly reduces the volume and power consumption of a microwave optical aperture conversion imaging system, improves the stability of the system, and realizes the miniaturization and integration of the aperture conversion process in the system.

Description

Technical Field

[0001] The present application relates to the field of microwave photonic technology, and in particular to the field of integrated microwave photonic technology. Background Art

[0002] Millimeter wave imaging technology can achieve high-resolution microwave imaging in all weather and all day. It is a technology that uses millimeter waves to illuminate the target and calculate the target microwave image. However, in the face of the increasing imaging resolution and computing resource requirements, the traditional millimeter wave imaging technology faces huge challenges in terms of sensitivity, computing resource overhead, power consumption and system complexity. Microwave photon imaging technology effectively overcomes the technical bottleneck of electronic devices by introducing the advantages of photon technology such as low latency, large bandwidth, and excellent anti-electromagnetic interference. Among them, the microwave photon imaging system based on aperture transformation can achieve real-time forward-looking two-dimensional imaging, and has the characteristics of high sensitivity, low cost, low computing resource overhead and low power consumption.

[0003] Microwave optical aperture transformation imaging system Figure 1 As shown. The system uses a horn antenna array 5 and a microwave antenna array 6 to receive microwave echoes, which are converted to the optical domain by an electro-optical modulator array 7. The converted carrier frequency, i.e., the optical carrier, is provided to the electro-optical modulator array 7 by a laser 1, an optical amplifier 2, a first beam splitter 3, and a second beam splitter 4. In addition to the up-conversion of the carrier frequency to the optical domain, the phase, amplitude, and other information of the microwave wavefront remain unchanged, and then the microwave antenna is replicated by the optical antenna array 15. This process is called aperture transformation. The light waves emitted by the optical antenna array 15 are Fourier transformed by the first beam splitter 9A, the optical filter module 10, and the optical lens 11, and are imaged on the infrared camera 12 located at the focal plane. In the imaging process, a phase control module 8 can also be included to control the output of the electro-optical modulator array 7, and a correction signal can be provided to the phase control module by a phase correction module 14. The input of the phase correction module 14 can come from the reference optical path provided by the first beam splitter 3 and the feedback optical path formed by the first beam splitter 9A, the second beam splitter 9B, and the optical detector 13.

[0004] The core process of the microwave optical aperture transformation imaging system is aperture transformation, which requires that the microwave wavefront can be mapped and transformed into the optical domain with high sensitivity, high gain, and high linearity. The core components for realizing the aperture transformation function include an electro-optic modulator array 7, a phase control module 8, and an optical antenna array 15, wherein the electro-optic modulator array 7 is used to up-convert microwaves into the optical domain, the phase control module 8 is used to compensate for the phase delay caused by environmental disturbances, and the optical antenna array 15 transmits the light waves carrying microwave information into space for subsequent spatial light processing. With the requirements of the application scenarios for the system, integration and miniaturization are the development trends of microwave optical link systems. In order to realize the integration of the aperture transformation function, the most important thing is to solve the large linear dynamic range of a large number of channels and the on-chip design and integration of electro-optic conversion modulation with high modulation efficiency. Currently, the more mature photonic integration platforms include LNOI, SiN, and SOI. SiN and SOI platforms are compatible with CMOS processes, with low waveguide loss, large relative refractive index difference, strong light restriction ability, and small waveguide bending radius, which is conducive to reducing chip size, but there is no significant electro-optic effect, and it is difficult to achieve efficient and high-linear electro-optic modulation. LNOI has an extremely high electro-optic coefficient and fast electro-optic response, which is very suitable for high-speed electro-optic modulation. However, the refractive index difference of LNOI waveguide material is small, the integration density is low, and when the channel waveguide length is long, the loss is high, the yield is low, and the production cost is high. Summary of the invention

[0005] The purpose of this application is to solve the above problems and provide an integrated microwave optical aperture conversion front-end chip to meet the application needs of large-scale array integration in the future.

[0006] Some embodiments of the present application provide an integrated microwave optical aperture conversion front-end chip, which includes a substrate layer, including a silicon layer and a first silicon dioxide layer, a silicon nitride layer is located on the substrate layer, including a formed silicon nitride edge coupler, a multimode interference coupler coupled to the edge coupler, a first cascade multimode interference coupler and a second cascade multimode interference coupler of silicon nitride are formed in a first area on the silicon nitride layer, the input end of the first cascade multimode interference coupler is coupled to the multimode interference coupler through a first silicon nitride waveguide, each output end is respectively coupled to a third silicon nitride waveguide, and the input end of the second cascade multimode interference coupler is coupled to Each output end of the multimode interference coupler is respectively coupled to a fourth silicon nitride waveguide; a grating array is formed in the second region of the silicon nitride layer, and the grating array includes a first group of grating couplers and a second group of grating couplers; a gap band is provided between the first region and the second region, and a fifth silicon nitride waveguide, a sixth silicon nitride waveguide, a seventh silicon nitride waveguide and an eighth silicon nitride waveguide are formed in the gap band; a second silicon dioxide layer is located around and above the silicon nitride waveguide to provide a smooth surface for subsequent bonding of a lithium niobate layer; a lithium niobate layer is formed on the second silicon dioxide layer, and a group of first lithium niobate ridge waveguides arranged in parallel are formed on the first part of the lithium niobate layer A first modulator electrode and a second modulator electrode are respectively formed on the first insulating material protective layer formed on both sides and the top of each of the first lithium niobate ridge waveguides, thereby forming a first multi-channel electro-optical modulator; a group of second lithium niobate ridge waveguides arranged in parallel are formed on the second part of the lithium niobate layer, and a third modulator electrode and a fourth modulator electrode are respectively formed on the first insulating material protective layer formed on both sides and the top of each of the second lithium niobate ridge waveguides, thereby forming a second multi-channel electro-optical modulator; a first end of each first lithium niobate ridge waveguide of the first multi-channel electro-optical modulator is coupled to one of the first cascaded multimode interference couplers through the third silicon nitride waveguide output end; the first end of each second lithium niobate ridge waveguide of the second multi-channel electro-optical modulator is coupled to an output end of the second cascaded multi-mode interference coupler through the fourth silicon nitride waveguide; a group of third lithium niobate ridge waveguides arranged in parallel are formed in the third part of the lithium niobate layer, the third lithium niobate ridge waveguides are separated by a second insulating material protective layer, and a first phase shifter electrode and a second phase shifter electrode are respectively formed on the second insulating material protective layer formed on both sides and the top of each third lithium niobate ridge waveguide; the third lithium niobate ridge waveguide in the third part and the first phase shifter electrode and the second phase shifter electrode constitute the first multi-channel phase shifter;A group of fourth lithium niobate ridge waveguides arranged in parallel are formed in the fourth part of the lithium niobate layer, and the fourth lithium niobate ridge waveguides are spaced apart by the second insulating material protective layer, and a third phase shifter electrode and a fourth phase shifter electrode are respectively formed on the second insulating material protective layer formed on both sides and the top of each of the fourth lithium niobate ridge waveguides; the fourth lithium niobate ridge waveguides, the third phase shifter electrode and the fourth phase shifter electrode of the fourth part constitute the second multi-channel phase shifter; wherein the second end of a first lithium niobate ridge waveguide to the first multi-channel electro-optical modulator is coupled to the first multi-channel electro-optical modulator through the fifth silicon nitride waveguide. The first end of each third lithium niobate ridge waveguide of a multi-channel phase shifter; the second end of each third lithium niobate ridge waveguide of the first multi-channel phase shifter is coupled to the first group of grating couplers of the grating array through the seventh silicon nitride waveguide; the second end of a second lithium niobate ridge waveguide of the second multi-channel electro-optical modulator is coupled to the first end of each fourth lithium niobate ridge waveguide of the second multi-channel phase shifter through the sixth silicon nitride waveguide; the second end of each fourth lithium niobate ridge waveguide of the second multi-channel phase shifter is coupled to the second group of grating couplers of the grating array through the eighth silicon nitride waveguide. ;

[0007] In some embodiments, the first portion of the lithium niobate layer and the second portion of the lithium niobate layer are symmetrically arranged; the third portion of the lithium niobate layer and the fourth portion of the lithium niobate layer are symmetrically arranged.

[0008] In some embodiments, the grating array is located in the middle of the first multi-channel phase shifter and the second multi-channel phase shifter in the longitudinal direction.

[0009] In some embodiments, the array arrangement of the grating array is a replica of the microwave antenna array arrangement in equal proportions.

[0010] In some embodiments, in order to utilize the maximum electro-optic coefficient of thin-film lithium niobate, the first lithium niobate ridge waveguide, the second lithium niobate ridge waveguide, the third lithium niobate ridge waveguide and the fourth lithium niobate ridge waveguide are all arranged in parallel along the vertical direction.

[0011] In some embodiments, the electro-optic modulator may be a phase modulator or an intensity modulator.

[0012] In some embodiments, the first lithium niobate ridge waveguide, and / or the second lithium niobate ridge waveguide, and / or the third lithium niobate ridge waveguide, and / or the fourth lithium niobate ridge waveguide includes a lithium niobate ridge waveguide portion, and a tapered first end portion and an inverted tapered second end portion located at both ends of the lithium niobate ridge waveguide portion.

[0013] In some embodiments, the second end of the third silicon nitride waveguide coupled to the first lithium niobate ridge waveguide, and / or the second end of the fourth silicon nitride waveguide coupled to the second lithium niobate ridge waveguide, and / or the second end of the fifth silicon nitride waveguide coupled to the third lithium niobate ridge waveguide, and / or the second end of the sixth silicon nitride waveguide coupled to the fourth lithium niobate ridge waveguide are tapered ends so as to match the positions of the respective inverted tapered lithium niobate ends on both sides of the lithium niobate layer; the first end of the fifth silicon nitride waveguide coupled to the first lithium niobate ridge waveguide, and / or the first end of the sixth silicon nitride waveguide coupled to the second lithium niobate ridge waveguide, and / or the first end of the seventh silicon nitride waveguide coupled to the third lithium niobate ridge waveguide, and / or the first end of the eighth silicon nitride waveguide coupled to the fourth lithium niobate ridge waveguide are inverted tapered ends so as to match the positions of the respective tapered lithium niobate ends on both sides of the lithium niobate layer.

[0014] In some embodiments, the position matching includes partial overlap or no overlap.

[0015] In some embodiments, the first modulator electrode and the second modulator electrode of the first multi-channel electro-optic modulator, and / or the third modulator electrode and the fourth modulator electrode of the second multi-channel electro-optic modulator use traditional rectangular traveling wave electrodes or periodic capacitive traveling wave electrodes.

[0016] In some embodiments, to avoid introducing additional optical delay, the optical path length of each channel is kept consistent from the fiber coupling input to the grating coupling output.

[0017] In some embodiments, in order to avoid light beam confusion and ensure a large field of view, while taking into account both the divergence angle and the large field of view, the array optical antenna distribution is arranged in a non-equidistant manner to suppress grating lobes.

[0018] In some embodiments, the first multi-channel electro-optic modulator and the second multi-channel electro-optic modulator provide a first pad for gold wire bonding to a first metal transmission line on a PCB board, and the first metal transmission line is connected to a first connector; the first multi-channel phase shifter and the second multi-channel phase shifter provide a second pad for gold wire bonding to a second metal transmission line on the PCB board, and the second metal transmission line is connected to a second connector, and the second connector is used to access a low-frequency phase compensation signal.

[0019] Some embodiments of the present application also provide an application method of an integrated microwave optical aperture conversion front-end chip 100, a microwave optical aperture conversion imaging system, which includes a horn antenna array, a microwave antenna array, an integrated microwave optical aperture conversion front-end chip, a laser, an optical amplifier, a first beam splitter, a second beam splitter, a first spectroscope, a second spectroscope, an optical filter module, an optical lens, an infrared camera, a light detector, and a phase correction module. The system uses a horn antenna array and a microwave antenna array to receive microwave echoes, which are converted to the optical domain by a lithium niobate multi-channel electro-optical modulator in the integrated microwave optical aperture conversion front-end chip. The converted carrier frequency, i.e., the optical carrier, is provided to the lithium niobate multi-channel electro-optical modulator by a laser, an optical amplifier, and a first beam splitter and a second beam splitter. The light waves emitted by the grating array are Fourier transformed through the optical filter module and the optical lens and imaged on the infrared camera located in the focal plane. In the imaging process, the phase shifter array in the integrated microwave optical aperture conversion front-end chip can also be included to control the output of the lithium niobate multi-channel electro-optical modulator in the integrated microwave optical aperture conversion front-end chip, and a correction signal can be provided to the phase shifter array in the integrated microwave optical aperture conversion front-end chip through a phase correction module, and the input of the phase correction module can come from the reference optical path provided by the first beam splitter and the feedback optical path composed of the first beam splitter, the second beam splitter, and the optical detector. The beneficial effects of the present application include: the integrated microwave optical aperture conversion front-end chip in some embodiments of the present application miniaturizes and integrates the conversion from microwave antenna to optical aperture; the chip in some embodiments of the present application can realize high-speed data transmission with large bandwidth and low loss.

[0020] The integrated microwave optical aperture conversion front-end chip provided in the embodiments of the present application can realize microwave up-conversion to the optical domain, delay error compensation, and microwave optical aperture conversion integrated functions on a single chip, meeting the application requirements of multi-function, array, and miniaturization in microwave optical aperture conversion imaging systems.

[0021] Some embodiments of the present application adopt a heterogeneous integration approach, where the electro-optic modulator and optical phase shifter parts use thin-film lithium niobate material, and the remaining passive parts use silicon nitride material, which can give full play to the advantages of each material and achieve high-speed modulation, low loss, and low power consumption system performance.

[0022] In some embodiments of the present application, the structures of the silicon waveguide and the lithium niobate waveguide at the coupling point are specially designed. The silicon waveguide adopts a conical structure at the coupling point, and the lithium niobate waveguide adopts an inverted conical structure at the coupling point, which can reduce the vertical adiabatic coupling loss when light is coupled from the silicon waveguide to the lithium niobate waveguide. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the microwave optical aperture transformation imaging system.

[0024] Figure 2 It is a schematic diagram of the three-dimensional structure of a microwave optical aperture conversion front-end chip according to an embodiment of the present application.

[0025] Figure 3 It is a planar structural principle diagram of a microwave optical aperture conversion front-end chip according to an embodiment of the present application.

[0026] Figure 4 It is a cross-sectional structural principle diagram of a microwave optical aperture conversion front-end chip according to an embodiment of the present application.

[0027] Figure 5 Schematic diagram of the first type of vertical adiabatic coupling structure in a microwave optical aperture conversion front-end chip according to an embodiment of the present application.

[0028] Figure 6 Schematic diagram of the second type of vertical adiabatic coupling structure in the microwave optical aperture conversion front-end chip according to an embodiment of the present application.

[0029] Figure 7 Schematic diagram of the structure of a microwave optical aperture transformation imaging system based on an integrated microwave optical aperture transformation front-end chip.

[0030] Reference numerals:

[0031] 1 Laser

[0032] 2 optical amplifiers,

[0033] 3First beam splitter

[0034] 4 Second beam splitter

[0035] 5-horn antenna array

[0036] 6 Microwave Antenna Array

[0037] 7Electro-optic modulator array

[0038] 8-optical phase control module

[0039] 9A First beam splitter

[0040] 9B Second beam splitter

[0041] 10 optical filter modules

[0042] 11Optical lens

[0043] 12 Infrared Camera

[0044] 13 Photodetector

[0045] 14 Phase correction module

[0046] 15 optical antenna array

[0047] 100 integrated microwave optical aperture conversion front-end chip

[0048] 10A Edge Coupler

[0049] 20 Multimode Interference Coupler

[0050] 30A first silicon nitride waveguide

[0051] 30B Second silicon nitride waveguide

[0052] 30C Third Silicon Nitride Waveguide

[0053] 30D fourth silicon nitride waveguide

[0054] 30E Fifth Silicon Nitride Waveguide

[0055] 30F Sixth Silicon Nitride Waveguide

[0056] 30G seventh silicon nitride waveguide

[0057] 30H eighth silicon nitride waveguide

[0058] 80A first lithium niobate ridge waveguide

[0059] 80B Second LiNbO3 Ridge Waveguide

[0060] 80C third lithium niobate ridge waveguide

[0061] 80D fourth lithium niobate ridge waveguide

[0062] 40A first cascade multimode interference coupler

[0063] 40B Second Cascade Multimode Interference Coupler

[0064] 50A First Multi-Channel Electro-Optic Modulator

[0065] 50B Second Multi-Channel Electro-Optic Modulator

[0066] 60A First Multi-Channel Phase Shifter

[0067] 60B Second Multi-Channel Phase Shifter

[0068] 70 Grating Array

[0069] L100 Silicon Layer

[0070] L200 first silicon dioxide layer

[0071] L300 Second Silicon Dioxide Layer

[0072] L400 lithium niobate layer

[0073] L500 third silicon dioxide layer

[0074] L600 electrode layer DETAILED DESCRIPTION

[0075] The specific implementation methods of the present application are described in detail below with reference to the accompanying drawings.

[0076] The specific structural and functional details disclosed herein are merely representative and are for the purpose of describing exemplary embodiments of the present application. However, the present application may be implemented in many alternative forms and should not be construed as being limited to the embodiments described herein.

[0077] It should be understood that, although the terms "first", "second", etc. may be used herein to describe various units, these units should not be limited by these terms. These terms are used only to distinguish one unit from another unit. For example, without departing from the scope of the exemplary embodiments, the first unit may be referred to as the second unit, and similarly the second unit may be referred to as the first unit. The term "and / or" used herein includes any and all combinations of one or more of the listed associated items.

[0078] The terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments. Unless the context clearly indicates otherwise, the singular forms "one", "one" and "one" used herein are also intended to include plural forms. It should also be understood that the terms "include" and / or "comprise" used herein specify the existence of stated features, integers, steps, operations, units and / or components, without excluding the existence or addition of one or more other features, integers, steps, operations, units, components and / or combinations thereof.

[0079] Reference Figure 2 , Figure 3 The core components of the integrated microwave optical aperture conversion front-end chip 100 in the embodiment of the present application include an edge coupler 10A, a multimode interference coupler 20, a first silicon nitride waveguide 30A, a second silicon nitride waveguide 30B, a third silicon nitride waveguide 30C, a fourth silicon nitride waveguide 30D, a fifth silicon nitride waveguide 30E, a sixth silicon nitride waveguide 30F, a seventh silicon nitride waveguide 30G, an eighth silicon nitride waveguide 30H, a first lithium niobate ridge waveguide 80A, a second lithium niobate ridge waveguide 80B, a third lithium niobate ridge waveguide 80C, and a fourth lithium niobate ridge waveguide 80D; a first cascaded multimode interference coupler 40A, a second cascaded multimode interference coupler 40B, a first multi-channel electro-optical modulator 50A, a second multi-channel electro-optical modulator 50B, a first multi-channel phase shifter 60A, a second multi-channel phase shifter 60B, and a grating array 70.

[0080] In some embodiments of the present application, the first cascade multimode interference coupler 40A and the second cascade multimode interference coupler 40B can be respectively formed by cascading five 1X2 multimode interference couplers connected in sequence. Each 1X2 multimode interference coupler is based on the self-imaging principle and can achieve 1:1 light splitting by connecting a single-mode waveguide at a specific position of the multimode waveguide.

[0081] In this article, vertical Figure 2 The V mark in the middle indicates the direction, and the horizontal direction indicates Figure 2 The mark H indicates the direction. The upper edge of the chip is marked as U, the lower edge is marked as B, the left edge is marked as L, and the right edge is marked as R.

[0082] As shown in Figure 1, the edge coupler 10A can be located at one edge of the chip 100, for example, the left edge L is used to couple the optical carrier entering from the optical fiber 300, and the multimode interference coupler 20 divides the optical carrier into a first optical carrier entering the upper branch and a second optical carrier entering the lower branch through the first silicon nitride waveguide 30A and the second silicon nitride waveguide 30B. In the upper branch, the first optical carrier is divided into multiple outputs after passing through the first cascade multimode interference coupler 40A, and is coupled into the first multi-channel electro-optic modulator 50A including the first lithium niobate ridge waveguide 80A arranged vertically in parallel through the third silicon nitride waveguide 30C, and then coupled into the first multi-channel phase shifter 60A including multiple third lithium niobate ridge waveguides 80C arranged vertically in parallel through the fifth silicon nitride waveguide 30E, and then coupled into the first group of grating couplers of the grating array 70 through the seventh silicon nitride waveguide 30G; in the lower branch, The second optical carrier is divided into multiple outputs after passing through the second cascade multimode interference coupler 40B, and then coupled into the second multi-channel electro-optic modulator 50B including a plurality of second lithium niobate ridge waveguides 80B arranged vertically and in parallel through the fourth silicon nitride waveguide 30D, and coupled into the second multi-channel phase shifter 60B including a plurality of fourth lithium niobate ridge waveguides 80D arranged vertically and in parallel through the sixth silicon nitride waveguide 30F, and then coupled from the second multi-channel phase shifter 60B through the eighth silicon nitride waveguide 30H into the second group of grating couplers of the grating array 70. In some embodiments, the grating array 70 is located in the chip region between the first multi-channel phase shifter 60A and the second multi-channel phase shifter 60B, and the array arrangement of the grating array 70 is in a proportional scaling relationship with the microwave antenna array arrangement.

[0083] In some embodiments of the present application, lithium niobate material is used to form a lithium niobate ridge waveguide because lithium niobate material has a strong electro-optic coefficient and a fast electro-optical response speed, and is an important material for high-speed electro-optical modulation. The edge coupler 10A, the multimode interference coupler 20, the first cascade multimode interference coupler 40A, the second cascade multimode interference coupler 40B, the grating array 70, and the first silicon nitride waveguide 30A to the eighth silicon nitride waveguide 30H are made of silicon nitride material. Because the propagation loss of silicon nitride material waveguide has been reduced to below 0.1dB / cm, it is suitable for use as a passive device of an array photonic integrated chip to reduce the overall chip loss. Therefore, the entire chip adopts a heterogeneous integration method to maximize the advantages of each material and optimize the overall performance of the chip.

[0084] During processing, Figure 4 As shown, a first silicon dioxide layer L200 can be formed on a silicon wafer, i.e., a silicon layer L100, which serves as a substrate. Silicon nitride material is deposited and etched on the first silicon dioxide layer L200 to form the above-mentioned first to eighth silicon nitride waveguides 30A to 30H, edge coupler 10A, multimode interference coupler 20, and grating array 70 structures; a second silicon dioxide layer L300 is deposited on the first silicon dioxide layer L200 to provide a smooth surface for subsequent bonding of a lithium niobate film, and a lithium niobate layer L400 is located on the second silicon dioxide layer L300 and is etched on the lithium niobate layer L400 to form a plurality of first lithium niobate ridge waveguides 80A arranged vertically in parallel, a plurality of second lithium niobate ridge waveguides 80B arranged vertically in parallel, a plurality of third lithium niobate ridge waveguides 80C arranged vertically in parallel, and a plurality of fourth lithium niobate ridge waveguides 80D arranged vertically in parallel.

[0085] The spaces between the first lithium niobate ridge waveguides, the spaces between the second lithium niobate ridge waveguides, the spaces between the third lithium niobate ridge waveguides, and the spaces between the fourth lithium niobate ridge waveguides are filled with silicon dioxide material, and then the entire space is covered with silicon dioxide material, thereby forming a third silicon dioxide layer L500, also called a silicon dioxide protective layer.

[0086] A first multi-channel electro-optic modulator 50A is formed based on the plurality of first lithium niobate ridge waveguides 80A, a second multi-channel electro-optic modulator 50B is formed based on the plurality of second lithium niobate ridge waveguides 80B, a first multi-channel phase shifter 60A is formed based on the plurality of third lithium niobate ridge waveguides 80C, and a second multi-channel phase shifter 60B is formed based on the plurality of fourth lithium niobate ridge waveguides 80D. For example, a first modulator electrode 501 and a second modulator electrode 502g are formed above the third silicon dioxide layer L500 on both sides of each first lithium niobate ridge waveguide 80A in the first part, i.e., on the upper left and upper right, to form an electrode layer L600, so that a first multi-channel electro-optic modulator 50A is formed in the first part. Similarly, a third modulator electrode and a fourth modulator electrode are formed above the third silicon dioxide layer L500 on both sides of each second lithium niobate ridge waveguide 80B in the second portion, i.e., on the upper left and upper right, respectively, so that a second multi-channel electro-optical modulator 50B is formed in the second portion. A first phase shifter electrode and a second phase shifter electrode are formed above the third silicon dioxide layer L500 on both sides of each third lithium niobate ridge waveguide 80C in the third portion, i.e., on the upper left and upper right, respectively, so that a first multi-channel phase shifter 60A is formed in the third portion. Similarly, a third phase shifter electrode and a fourth phase shifter electrode are formed above the third silicon dioxide layer L500 on both sides of each fourth lithium niobate ridge waveguide 80D in the fourth portion, i.e., on the upper left and upper right, respectively, so that a second multi-channel phase shifter 60B is formed in the fourth portion.

[0087] The ends of the first silicon nitride waveguide 30A to the eighth silicon nitride waveguide 30H form a vertical adiabatic coupling structure with the ends of the first to fourth lithium niobate ridge waveguides for coupling, thereby coupling light upward from the silicon nitride waveguide to the lithium niobate strip waveguide for transmission, or coupling light downward from the lithium niobate ridge waveguide to the corresponding silicon nitride waveguide for transmission.

[0088] For example, the first optical carrier is coupled from the first multi-cascade multimode interference coupler 40A to the first end of the third silicon nitride waveguide 30C, and the second end of the third silicon nitride waveguide 30C forms a first vertical adiabatic coupling structure with the first end of a first lithium niobate ridge waveguide in the first multi-channel electro-optic modulator 50A and the lithium niobate layer. The second optical carrier is coupled from the second multi-cascade multimode interference coupler 40B to the first end of the fourth silicon nitride waveguide 30D, and the second end of the fourth silicon nitride waveguide 30D forms a second vertical adiabatic coupling structure with the first end of the second lithium niobate ridge waveguide in the second multi-channel electro-optic modulator 50B and the lithium niobate layer.

[0089] For another example, a third vertical adiabatic coupling structure exists between the second end of the first lithium niobate ridge waveguide of the first multi-channel electro-optic modulator 50A opposite to the first end, the lithium niobate layer, and the first end of the fifth silicon nitride waveguide 30E; a fourth vertical adiabatic coupling structure exists between the second end of the second lithium niobate ridge waveguide of the second multi-channel electro-optic modulator 50B opposite to the first end, the lithium niobate layer, and the first end of the sixth silicon nitride waveguide 30F. A fifth vertical adiabatic coupling structure exists between the second end of the fifth silicon nitride waveguide 30E opposite to the first end, the lithium niobate layer, and the first end of the third lithium niobate ridge waveguide in the first multi-channel phase shifter 60A; a sixth vertical adiabatic coupling structure exists between the second end of the sixth silicon nitride waveguide 30F opposite to the first end, the lithium niobate layer, and the first end of the fourth lithium niobate ridge waveguide in the second multi-channel phase shifter 60B. For example, a seventh vertical adiabatic coupling structure exists between the second end portion of the third lithium niobate ridge waveguide in the first multi-channel phase shifter 60A that is opposite to the first end portion, the lithium niobate layer, and the first end portion of the seventh silicon nitride waveguide 30G; an eighth vertical adiabatic coupling structure exists between the second end portion of the fourth lithium niobate ridge waveguide in the second multi-channel phase shifter 60B that is opposite to the first end portion, the lithium niobate layer, and the first end portion of the eighth silicon nitride waveguide 30H.

[0090] Among them, from the functional point of view, the above-mentioned first vertical adiabatic coupling structure, the second vertical adiabatic coupling structure, the fifth vertical adiabatic coupling structure and the sixth vertical adiabatic coupling structure belong to the first type of vertical adiabatic coupling structure, and the first optical carrier or the second optical carrier is coupled to the corresponding lithium niobate ridge waveguide after passing through the lithium niobate layer L400 from the lower silicon nitride waveguide; the above-mentioned third vertical adiabatic coupling structure, the fourth vertical adiabatic coupling structure, the seventh vertical adiabatic coupling structure and the eighth vertical adiabatic coupling structure belong to the second type of vertical adiabatic coupling structure. Contrary to the first type of vertical adiabatic coupling structure, the first optical carrier or the second optical carrier is coupled downward from the lithium niobate ridge waveguide of the upper layer to the corresponding silicon nitride waveguide.

[0091] An exemplary configuration of the first vertical adiabatic coupling structure is as follows Figure 5As shown, the third silicon nitride waveguide 30C and the first lithium niobate ridge waveguide are included, and the light wave is gradually coupled from the third silicon nitride waveguide 30C to the first lithium niobate ridge waveguide 80A, wherein the width of the body 301C of the third silicon nitride waveguide 30C gradually decreases toward its second end, forming an inverted tapered second end 302C, and the first lithium niobate ridge waveguide 80A on the lithium niobate layer L400 includes a tapered first end 801A, a strip-shaped main body 802A, and a tapered second end, and the width of the tapered first end 801A gradually increases in the direction toward the strip-shaped main body 802A. The inverted tapered second end 302C of the third silicon nitride waveguide 30C matches the tapered first end 801A of the first lithium niobate strip waveguide at both sides of the lithium niobate layer L400, and the position matching includes, for example, partial overlap or complete overlap in the length direction L. The width of the inversely tapered second end portion 302C in the width direction W is greater than the width of the tapered first end portion 801A of the first lithium niobate strip waveguide.

[0092] The first type of vertical adiabatic coupling structure and the second type of vertical adiabatic coupling structure may have the same configuration or different configurations. In an embodiment of the same configuration, the exemplary configuration of the second vertical adiabatic coupling structure is as follows: Figure 6 As shown, it includes a first lithium niobate ridge waveguide 80A and a fifth silicon nitride waveguide 30E, and the light wave is gradually coupled from the first lithium niobate ridge waveguide 80A to the fifth silicon nitride waveguide 30E, wherein the width of the body 301E of the fifth silicon nitride waveguide 30E gradually decreases toward its first end 302E to form a tapered second end 302E, and the first lithium niobate strip waveguide 80A on the lithium niobate layer L400 includes a tapered first end, a strip-shaped main body 802A and an inverted tapered second end 803A, and the width of the inverted tapered second end 803A gradually increases in the direction toward the strip-shaped main body 802A.

[0093] Similarly, the tapered second end 302E of the fifth silicon nitride waveguide 30E matches the inverted tapered second end 803A of the first lithium niobate ridge waveguide 80A at both sides of the lithium niobate layer L400, and the position matching includes, for example, partial overlap or complete overlap in the length direction L. In the width direction W, the width of the tapered first end 302E is greater than the width of the inverted tapered second end 803A of the first lithium niobate ridge waveguide 80A.

[0094] In the above, the cone and the reverse cone only represent the difference in the direction of the cone. For example, the cone means that the width of the waveguide gradually decreases in the direction of light propagation, while the reverse cone means that the width of the waveguide gradually increases in the direction of light propagation.

[0095] In addition, the total length of the waveguides of each channel on an integrated microwave optical aperture conversion front-end chip in the present application is consistent to achieve high-fidelity mapping conversion from microwave to optical domain. The channel refers to the total path from the multimode interference coupler 20 to a grating coupler of the grating array.

[0096] The chip 100 can be integrally mounted on the PCB board 200, and the pads of the first multi-channel electro-optic modulator 50A and the second multi-channel electro-optic modulator 50B on the chip 100 are gold-wire bonded to the first metal transmission line on the PCB board 200, and the first metal transmission line is connected to the first connector, and the first connector is used to apply a microwave signal (electrical signal) to the chip 100. The first connector can be, for example, an SMPM interface connector. The pads of the first multi-channel phase shifter 60A and the second multi-channel phase shifter 60B on the chip 100 are gold-wire bonded to the pads on the PCB board 200 and the second metal transmission line on the PCB board 200, and the second metal transmission line is connected to the second connector, and the second connector is used to access the phase compensation signal, such as an SMPM interface connector or other connectors.

[0097] The working principle of the chip 100 is to efficiently couple the optical carrier in the optical fiber 300 into the chip 100 through the edge coupler 10A, and then input the optical carrier with equal power into the first multi-channel electro-optical modulator 50A and the second multi-channel electro-optical modulator 50B respectively through the multi-mode interference coupler 20, the first cascade multi-mode interference coupler 40A, and the second cascade multi-mode interference coupler 40B, and the microwave signal is input to the pads of the electrodes of the first multi-channel electro-optical modulator 50A and the second multi-channel electro-optical modulator 50B through the SMPM interface connector 210 on the PCB board 200. After the microwave signal is modulated by the electro-optical modulator, the microwave signal can be up-converted into the optical domain.

[0098] Subsequently, the optical signal modulated by the first multi-channel electro-optic modulator 50A is input to the first multi-channel phase shifter 60A via its first lithium niobate ridge waveguide 80A, and the optical signal modulated by the second multi-channel electro-optic modulator 50B is input to the second multi-channel phase shifter 60B via its second lithium niobate ridge waveguide 80B, and after a phase delay error compensation signal is applied to it, it enters the grating array 70. Finally, the optical antenna coupled to the grating array 70 transmits the light carrying the microwave signal for subsequent optical processing.

[0099] The chip in the embodiment of the present application greatly reduces the volume of the microwave optical aperture transformation imaging system and reduces the power consumption of the system. The integrated chip integrates multiple channels of multiple discrete devices into one chip, and the size of the chip is only on the order of millimeters.

[0100] The chip in the embodiment of the present application adopts a heterogeneous integration method, taking advantage of the low loss of silicon nitride waveguide, significantly reducing the overall microwave photonic system loss, thereby reducing power consumption. At the same time, by taking advantage of the large electro-optic coefficient and fast electro-optic response of lithium niobate waveguide, the modulator bandwidth of each channel can theoretically reach greater than 70 GHz.

[0101] This application combines the advantages of microwave photonics and photonic integration technology, and combines the semiconductor process characteristics of SiN and LNOI to invent and develop an integrated microwave optical aperture transformation front-end chip, which integrates the electro-optic modulator array, phase control module, and optical antenna array in the microwave optical aperture transformation imaging system into a single chip, and realizes microwave optical domain aperture transformation. It can greatly reduce the volume of the microwave optical aperture transformation imaging system, reduce system power consumption, and improve system stability, thereby meeting the future large-scale array integration application requirements.

[0102] The present application can realize the integrated functions of microwave up-conversion to the optical domain, delay error compensation, and microwave optical aperture transformation on a single chip, meeting the application requirements of multi-function, array, and miniaturization in microwave optical aperture transformation imaging systems.

[0103] In the embodiment of the present application, the optical waveguide length of each channel of the chip is equal, which can achieve a fidelity mapping change from the microwave antenna to the optical aperture.

[0104] The vertical adiabatic coupling structure of the chip in the embodiment of the present application greatly reduces the coupling loss of light waves between each silicon nitride waveguide and each lithium niobate ridge waveguide.

[0105] In summary, the technical solution adopted in some embodiments of the present application is an integrated microwave optical aperture conversion front-end chip, including a silicon wafer; a silicon dioxide layer located on the silicon wafer, the two together form a substrate, and a silicon-based optical waveguide layer located on the silicon dioxide layer, wherein the silicon-based optical waveguide layer includes an edge coupler, a multimode interference coupler, a single-mode input waveguide connecting the multimode interference coupler and a high-speed electro-optical modulator, an output waveguide connecting an optical phase shifter and a grating coupler, and a grating coupler. There is a gap band between the multimode interference coupler and the grating coupler; a silicon dioxide layer is filled around the silicon-based optical waveguide layer and the gap band; a lithium niobate electro-optical modulator includes a lithium niobate layer located on the gap band, a lithium niobate ridge waveguide located on the lithium niobate layer, and a modulator electrode located on the silicon dioxide protective layer at the upper left and upper right of the lithium niobate ridge waveguide; a lithium niobate electro-optical phase shifter includes a lithium niobate layer located on the gap band, a lithium niobate ridge waveguide located on the lithium niobate layer, and a phase shifter electrode located on the silicon dioxide protective layer at the upper left and upper right of the lithium niobate ridge waveguide; the silicon dioxide protective layer is located on the lithium niobate layer and filled around the lithium niobate ridge waveguide.

[0106] In some embodiments of the present application, the first multi-channel phase shifter and the first multi-channel electro-optic modulator are placed in parallel; the second multi-channel phase shifter and the second multi-channel electro-optic modulator are placed in parallel. In this way, the maximum electro-optic coefficient in the anisotropic lithium niobate crystal in each of the first, second, third, and fourth lithium niobate strip waveguides and the lithium niobate layer can be utilized to improve the modulation efficiency. Specifically, the lithium niobate crystal is anisotropic, so the electro-optic coefficient of the lithium niobate crystal in different directions is different. For example, at a wavelength of 1550nm, r13=8.6pm / V, r22=3.4pm / V, r51=28pm / V, and r33=30.8pm / V. In order to utilize the maximum electro-optic coefficient r33, an x-cut wafer is generally selected, an electric field is applied along the Z-axis direction, and the working mode is propagated along the y-axis. When the first and second multi-channel phase shifter arrays are placed in parallel with the first and second multi-channel electro-optic modulator arrays, the crystal tangents of the two are consistent, and the maximum modulation efficiency can be obtained. However, if the phase shifter array and the electro-optic modulator array are placed vertically, the tangents of the lithium niobate crystal waveguides of the two are different, and one of them has an electro-optic coefficient that is not r33, and the maximum modulation efficiency cannot be obtained.

[0107] In some embodiments, the position matching includes partial overlap or no overlap.

[0108] In some embodiments, the first modulator electrode and the second modulator electrode of the first multi-channel electro-optic modulator, and / or the third modulator electrode and the fourth modulator electrode of the second multi-channel electro-optic modulator adopt traditional rectangular traveling wave electrodes or periodic capacitive traveling wave electrodes. The periodic capacitive traveling wave electrodes can break the mutual restriction between the half-wave voltage and the electro-optic bandwidth, and realize high electro-optic bandwidth modulation while maintaining a low half-wave voltage.

[0109] In some embodiments, to avoid introducing additional optical delay, the optical path length of each channel is kept consistent from the fiber coupling input to the grating coupling output.

[0110] In some embodiments, in order to avoid light beam confusion and ensure a large field of view, while taking into account both the divergence angle and the large field of view, the array optical antenna distribution is arranged in a non-equidistant manner to suppress grating lobes.

[0111] The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not intended to be limited to the embodiments shown herein, but to conform to the widest scope consistent with the principles and novel features disclosed herein.

[0112] Furthermore, while advantages associated with certain embodiments of the technology have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the technology. Therefore, the present disclosure and associated technology may include other embodiments not expressly shown or described herein. Therefore, the present disclosure is limited only by the appended claims.

Claims

1. An integrated microwave optical aperture conversion front-end chip, characterized in that: include A substrate layer, comprising a silicon layer and a first silicon dioxide layer, wherein a silicon nitride layer is located on the substrate layer, and comprises a formed silicon nitride edge coupler (10A), a multimode interference coupler (20) coupled to the edge coupler (10A), a first cascade multimode interference coupler (40A) and a second cascade multimode interference coupler (40B) of silicon nitride formed in a first region on the silicon nitride layer, wherein an input end of the first cascade multimode interference coupler (40A) is coupled to the multimode interference coupler (20) via a first silicon nitride waveguide (30A), and each output end is respectively coupled to a third silicon nitride waveguide (30C), The input end of the second cascade multimode interference coupler (40B) is coupled to the multimode interference coupler (20) through a second silicon nitride waveguide (30B), and each output end is respectively coupled to a fourth silicon nitride waveguide (30D); a grating array is formed in the second region of the silicon nitride layer, and the grating array (70) includes a first group of grating couplers and a second group of grating couplers; a gap band is provided between the first region and the second region, and a fifth silicon nitride waveguide (30E), a sixth silicon nitride waveguide (30F), a seventh silicon nitride waveguide (30G) and an eighth silicon nitride waveguide (30H) are formed in the gap band; The second silicon dioxide layer is located around and above the first silicon nitride waveguide to the eighth silicon nitride waveguide to provide a smooth surface for subsequent bonding of the lithium niobate layer; A lithium niobate layer (L400) is formed on the second silicon dioxide layer, a group of first lithium niobate ridge waveguides (80A) arranged in parallel are formed on the first part of the lithium niobate layer, and a first modulator electrode and a second modulator electrode are respectively formed on the first insulating material protective layer formed on both sides and the top of each of the first lithium niobate ridge waveguides (80A), thereby forming a first multi-channel electro-optical modulator (50A); a group of second lithium niobate ridge waveguides (80B) arranged in parallel are formed on the second part of the lithium niobate layer, and a third modulator electrode and a fourth modulator electrode are respectively formed on the first insulating material protective layer formed on both sides and the top of each of the second lithium niobate ridge waveguides (80B), thereby forming a second multi-channel electro-optical modulator (50B); The first end of each first lithium niobate ridge waveguide (80A) of the first multi-channel electro-optic modulator (50A) is coupled to an output end of the first cascaded multimode interference coupler (40A) through the third silicon nitride waveguide (30C); the first end of each second lithium niobate ridge waveguide (80B) of the second multi-channel electro-optic modulator (50B) is coupled to an output end of the second cascaded multimode interference coupler (40B) through the fourth silicon nitride waveguide (30D); A group of third lithium niobate ridge waveguides (80C) arranged in parallel are formed in the third part of the lithium niobate layer, the third lithium niobate ridge waveguides (80C) are separated by a second insulating material protective layer, and a first phase shifter electrode and a second phase shifter electrode are respectively formed on the second insulating material protective layer formed on both sides and the top of each third lithium niobate ridge waveguide; the third lithium niobate ridge waveguide (80C) in the third part and the first phase shifter electrode and the second phase shifter electrode constitute a first multi-channel phase shifter (60A); A group of fourth lithium niobate ridge waveguides (80D) arranged in parallel are formed in the fourth part of the lithium niobate layer, the fourth lithium niobate ridge waveguides (80D) are separated by the second insulating material protective layer, and a third phase shifter electrode and a fourth phase shifter electrode are respectively formed on the second insulating material protective layer formed on both sides and the top of each fourth lithium niobate ridge waveguide (80D); the fourth lithium niobate ridge waveguide (80D) in the fourth part, the third phase shifter electrode and the fourth phase shifter electrode constitute a second multi-channel phase shifter (60B); wherein the second end of a first lithium niobate ridge waveguide (80A) of the first multi-channel electro-optic modulator (50A) is coupled to the first end of each third lithium niobate ridge waveguide of the first multi-channel phase shifter (60A) through the fifth silicon nitride waveguide (30E); the second end of each third lithium niobate ridge waveguide of the first multi-channel phase shifter (60A) is coupled to the first group of grating couplers of the grating array (70) through the seventh silicon nitride waveguide (30G); The second end of a second lithium niobate ridge waveguide (80B) of the second multi-channel electro-optic modulator (50B) is coupled to the first end of each fourth lithium niobate ridge waveguide of the second multi-channel phase shifter (60B) through the sixth silicon nitride waveguide (30F); the second end of each fourth lithium niobate ridge waveguide (80D) of the second multi-channel phase shifter (60B) is coupled to the second group of grating couplers of the grating array (70) through the eighth silicon nitride waveguide (30H).

2. The integrated microwave optical aperture conversion front-end chip according to claim 1, characterized in that: The first portion of the lithium niobate layer and the second portion of the lithium niobate layer are symmetrically arranged; the third portion of the lithium niobate layer and the fourth portion of the lithium niobate layer are symmetrically arranged.

3. The integrated microwave optical aperture conversion front-end chip according to claim 1, characterized in that: The grating array (70) is located in the middle of the first multi-channel phase shifter (60A) and the second multi-channel phase shifter (60B) in the longitudinal direction; the array arrangement of the grating array (70) is replicated in proportion to the microwave antenna array arrangement.

4. The integrated microwave optical aperture conversion front-end chip according to claim 1, characterized in that: The first lithium niobate ridge waveguide (80A), the second lithium niobate ridge waveguide (80B), the third lithium niobate ridge waveguide (80C) and the fourth lithium niobate ridge waveguide (80D) are all arranged in parallel along a vertical direction.

5. The integrated microwave optical aperture conversion front-end chip according to claim 1, characterized in that: The first multi-channel electro-optical modulator, and / or the second multi-channel electro-optical modulator is a phase modulator or an intensity modulator; the first modulator electrode and the second modulator electrode of the first multi-channel electro-optical modulator, and / or the third modulator electrode and the fourth modulator electrode of the second multi-channel electro-optical modulator adopt traditional rectangular traveling wave electrodes or periodic capacitive traveling wave electrodes.

6. The integrated microwave optical aperture conversion front-end chip according to claim 4, characterized in that: The first lithium niobate ridge waveguide, and / or the second lithium niobate ridge waveguide, and / or the third lithium niobate ridge waveguide, and / or the fourth lithium niobate ridge waveguide include a lithium niobate ridge waveguide portion, and a conical first end portion and an inverted conical second end portion located at both ends of the lithium niobate ridge waveguide portion.

7. The integrated microwave optical aperture conversion front-end chip according to claim 6, characterized in that: The second end of the third silicon nitride waveguide (30C) coupled to the first lithium niobate ridge waveguide, and / or the second end of the fourth silicon nitride waveguide (30D) coupled to the second lithium niobate ridge waveguide, and / or the second end of the fifth silicon nitride waveguide (30E) coupled to the third lithium niobate ridge waveguide, and / or the second end of the sixth silicon nitride waveguide (30F) coupled to the fourth lithium niobate ridge waveguide are tapered ends so as to match the positions of the inverted tapered lithium niobate ends on both sides of the lithium niobate layer; The first end of the fifth silicon nitride waveguide (30E) coupled to the first lithium niobate ridge waveguide, and / or the first end of the sixth silicon nitride waveguide (30F) coupled to the second lithium niobate ridge waveguide, and / or the first end of the seventh silicon nitride waveguide (30G) coupled to the third lithium niobate ridge waveguide, and / or the first end of the eighth silicon nitride waveguide (30H) coupled to the fourth lithium niobate ridge waveguide, are inverted tapered ends so as to match the positions of the tapered lithium niobate ends on both sides of the lithium niobate layer.

8. The integrated microwave optical aperture conversion front-end chip according to claim 7, characterized in that: The position matching includes partial overlap or complete non-overlap; from the fiber coupling input to the grating coupling output, the optical path of each channel remains consistent.

9. The integrated microwave optical aperture conversion front-end chip according to claim 1, characterized in that: It also includes an array optical antenna coupled to the grating array (70), wherein the array optical antenna is arranged in a non-equidistant manner to suppress grating lobes.

10. The integrated microwave optical aperture conversion front-end chip according to claim 1, characterized in that: The first multi-channel electro-optic modulator (50A) and the second multi-channel electro-optic modulator (50B) provide a first pad for gold wire bonding with a first metal transmission line on a PCB board (200), and the first metal transmission line is connected to a first connector; the first multi-channel phase shifter (60A) and the second multi-channel phase shifter (60B) provide a second pad for gold wire bonding with a second metal transmission line on the PCB board (200), and the second metal transmission line is connected to a second connector, and the second connector is used to access a low-frequency phase compensation signal.

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