An integrated chip integrating a thin-film lithium niobate array phase shifter and an optical antenna

Abstract

This application belongs to the field of integrated microwave photonics, and discloses a thin-film lithium niobate array phase shifter and optical antenna integrated chip, which monolithically integrates all multi-channel and large element number devices corresponding to the phase shift module and the optical antenna emission module in the microwave optical aperture transformation imaging system. In the microwave optical aperture transformation imaging system, the received microwave signal is up-converted to the optical domain, and a Fourier lens is used to achieve the spatial positioning of multiple beams. However, the differences in the fiber channel environment will cause changes in the fiber refractive index, resulting in delay drift and affecting the imaging quality. The present invention ensures the stability of the received microwave wavefront during the process of microwave up-conversion to the optical domain through an integrated optical array phase shifter and optical antenna, finally realizing precise spatial positioning, reducing the size of the microwave photon information processing system, lowering the system power consumption, and improving the system stability.

Description

Technical Field

[0001] The present invention belongs to the field of integrated microwave photonics, and particularly relates to a thin-film lithium niobate array phase shifter and optical antenna integrated chip. Background Art

[0002] Millimeter-wave imaging technology can achieve all-weather and all-time high-resolution microwave imaging, which is a technology that uses millimeter waves to irradiate a target and calculates the microwave image of the target. However, in the face of the increasing requirements for imaging resolution and computing resources, 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 bottlenecks of electronic devices by introducing the advantages of photon technology such as low latency, large bandwidth, and excellent electromagnetic interference resistance. Among them, the microwave optical aperture transformation imaging system can achieve real-time forward-looking two-dimensional imaging, with the characteristics of high sensitivity, low cost, low computing resource overhead, and low power consumption.

[0003] The microwave optical aperture transformation imaging system is as Figure 1 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 through an electro-optic modulator array 7. The converted carrier frequency, that is, the optical carrier, is provided to the electro-optic modulator array 7 by a laser 1, an optical amplifier 2, a first beam splitter 3, and a second beam splitter 4. Except for the carrier frequency up-conversion to the optical domain, other information such as the phase and amplitude of the microwave wavefront remains unchanged. Then, the microwave antenna is replicated through an optical antenna array 15, and this process is called aperture transformation. The light wave emitted from the optical antenna array 15 is Fourier-transformed and imaged on an infrared camera 12 located in the focal plane through a first beam splitter 9A, an optical filtering module 10, and an optical lens 11. During this imaging process, a phase control module 8 can also be included to control the output of the electro-optic modulator array 7. A phase correction module 14 can provide a correction signal for the phase control module. 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 composed of the first beam splitter 9A, the second beam splitter 9B, and a photodetector 13.

[0004] In a microwave fiber aperture transformation imaging system, factors such as the temperature, vibration, stress, and differences in thermal effects of the environments where each fiber channel is located affect the refractive index of the fiber, resulting in delay drift and affecting the imaging quality. Therefore, it is necessary to use an integrated optical array phase shifter and optical antenna chip to ensure the stability of the received microwave wavefront during the process of microwave up-conversion to the optical domain, ultimately enabling target imaging. Optical phase shifters and array optical antennas are often discrete devices. Integrating the phase control module 8 and the optical antenna array 15 can separate the microwave antenna array from the backend processing part, facilitating deployment; at the same time, it can greatly reduce the system volume and power consumption and improve system performance. Currently, there is a lack of an integrated solution for optical phase shifters and array optical antennas with a large number of channels, high modulation efficiency, and low coupling loss in a microwave optical aperture transformation imaging system. The difficulties in this integration are as follows: The integration of the phase shifter and the optical antenna often uses silicon-based integration because the silicon-based platform is compatible with the mature complementary metal oxide semiconductor process platform. However, the phase shift methods based on two-photon absorption, high nonlinear effects, and thermo-optical effects of silicon limit the scalability, output beam power, and phase shift speed of the integration of the phase shifter and the optical antenna based on the silicon platform. The advantage of the silicon nitride platform is low propagation loss. However, the scalability and power consumption of the integration of the silicon nitride phase shifter and the optical antenna are also limited by the low thermo-optical coefficient of silicon nitride. Summary of the Invention

[0005] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide an improved integrated chip of an array phase shifter and an optical antenna, which combines the advantages and characteristics of integrated microwave photons and has at least one of the characteristics of miniaturization, integration, high stability, and low loss.

[0006] The present invention provides an integrated chip integrating a thin-film lithium niobate array phase shifter and an optical antenna, which integrates the phase control module and the optical antenna array in the microwave optical aperture transformation imaging system. In this way, the microwave antenna and the backend processing module can be separated and placed at a distance, which is convenient for deployment and reduces propagation loss. The system uses a horn antenna array and a microwave antenna array to receive microwave echoes, converts them to the optical domain through an electro-optic modulator array, and inputs the optical wave carrying microwave information into the integrated chip of the thin-film lithium niobate array phase shifter and the optical antenna through an optical fiber. The integrated chip includes a silicon substrate, a silica base layer located on the silicon substrate, a lithium niobate waveguide layer located on the silica base layer, a silica cladding layer on the lithium niobate waveguide layer, and a metal electrode layer on the silica cladding layer; the lithium niobate waveguide layer includes a lithium niobate flat layer and a lithium niobate strip waveguide layer, and a lithium niobate ridge waveguide including a multi-channel end-face coupler and a thin-film lithium niobate phase shifter array is formed in the lithium niobate waveguide layer; wherein each channel of the multi-channel end-face coupler includes a first inverted conical waveguide portion formed in the lithium niobate flat layer, a second inverted conical waveguide portion formed in the lithium niobate flat layer and continuously arranged and aligned with the first inverted conical waveguide portion, and a third inverted conical waveguide portion formed in the lithium niobate strip waveguide layer corresponding to the second inverted conical waveguide portion; the thin-film lithium niobate phase shifter array includes a plurality of lithium niobate phase shifters, and each lithium niobate phase shifter is coupled to one of the multi-channel end-face couplers; the lithium niobate phase shifter is formed based on a lithium niobate ridge waveguide, and the lithium niobate ridge waveguide includes a planar waveguide portion continuously arranged with the second inverted conical waveguide portion in the lithium niobate flat layer and a strip waveguide portion continuously arranged and aligned with the third inverted conical waveguide portion in the lithium niobate strip waveguide layer; wherein the lithium niobate phase shifter further includes a ground electrode in the metal electrode layer above the silica cladding layer on the first side of the strip waveguide portion and a signal electrode in the metal electrode layer above the silica cladding layer on the second side of the strip waveguide portion; wherein, the lithium niobate phase shifter is configured to change the refractive index of the lithium niobate ridge waveguide by applying a voltage on the signal electrode, and further change the phase of the optical wave passing through the lithium niobate ridge waveguide; the number of channels of the multi-channel end-face coupler is equal to the number of lithium niobate phase shifters. An array of optical antennas is formed in the lithium niobate waveguide layer, and each optical antenna unit is an optical antenna designed by an inverse algorithm with four etching depths of thin-film lithium niobate. The lithium niobate phase shifter is connected to the thin-film lithium niobate optical antenna in the array of optical antennas through an output waveguide, and the optical wave is efficiently emitted into free space through the thin-film lithium niobate optical antenna for subsequent three-dimensional spatial optical processing.

[0007] In some embodiments, the multi-channel end-face coupler is located above the integrated chip of the thin-film lithium niobate array phase shifter and the optical antenna, the array optical antenna is located below the integrated chip of the thin-film lithium niobate array phase shifter and the optical antenna, and the thin-film lithium niobate phase shifter array is placed vertically.

[0008] In some embodiments, for any lithium niobate phase shifter, the relationship between the change in the refractive index of the lithium niobate ridge waveguide and the voltage applied to the signal electrode of the lithium niobate phase shifter is: , where is the change in the refractive index of the lithium niobate ridge waveguide, is the refractive index of the lithium niobate ridge waveguide without voltage applied, is the voltage applied to the signal electrode, is the spacing between the ground electrode and the signal electrode, is the electro-optic coefficient of the lithium niobate material.

[0009] In some embodiments, for any lithium niobate phase shifter, the relationship between the phase change of the light wave passing through the lithium niobate ridge waveguide and the voltage applied to the signal electrode is: , where, is the phase change of the light wave after passing through the lithium niobate ridge waveguide, is the electro-optic overlap factor, is the length of the lithium niobate ridge waveguide, is the wavelength of the transmitted light, is the refractive index of the lithium niobate ridge waveguide without voltage applied, is the electro-optic coefficient of the lithium niobate material, is the voltage applied to the signal electrode, is the spacing between the ground electrode and the signal electrode.

[0010] In some embodiments, for the array optical antenna, any one of the optical antenna units has the same structure, and different etching depth combinations are selected according to the etching depth of the actual processing technology, and it is designed by using the direct binary search reverse algorithm. The optical antenna unit has high coupling efficiency and good robustness.

[0011] In some embodiments, to avoid beam confusion and ensure a large field of view, while taking into account the divergence angle and the large field of view, for the distribution of the array optical antenna, non-equidistant arrangement can be used to suppress grating lobes.

[0012] In some embodiments, the lithium niobate waveguide layer is formed from a lithium niobate wafer with x-cut y-propagation or z-cut x-propagation or z-cut y-propagation.

[0013] In some embodiments, the multi-channel end-face coupler includes thirty channels for coupling the light propagating in thirty optical fibers into the thin-film lithium niobate phase shifter array, which is composed of thirty lithium niobate phase shifters; the array optical antenna is composed of thirty identical thin-film lithium niobate optical antennas.

[0014] Some embodiments of the present application further provide a microwave optical aperture transformation imaging system, which includes a horn antenna array, a microwave antenna array, an electro-optic modulator array, an integrated chip of a thin-film lithium niobate array phase shifter and an optical antenna, a laser, an optical amplifier, a first beam splitter, a second beam splitter, a first beam splitter mirror, a second beam splitter mirror, an optical filtering module, an optical lens, an infrared camera, a photodetector, and a phase correction module. The system uses the horn antenna array and the microwave antenna array to receive microwave echoes, and up-converts them to the optical domain through the electro-optic modulator array. The converted carrier frequency, that is, the optical carrier, is provided to the electro-optic modulator array by the laser, the optical amplifier, the first beam splitter, and the second beam splitter. The optical wave is transmitted through the optical fiber to the integrated chip of the thin-film lithium niobate array phase shifter and the optical antenna, and the optical wave emitted by the optical antenna array in the integrated chip of the thin-film lithium niobate array phase shifter and the optical antenna is Fourier-transformed and imaged on the infrared camera located at the focal plane through the optical filtering module and the optical lens. During this imaging process, it may also include that the phase shifter array in the integrated chip of the thin-film lithium niobate array phase shifter and the optical antenna controls the output of the electro-optic modulator array, and the phase correction module can provide a correction signal for the phase shifter array in the integrated chip of the thin-film lithium niobate array phase shifter and the optical antenna. 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 mirror, the second beam splitter mirror, and the photodetector.

[0015] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in: the present invention monolithically integrates all the multi-channel and large-element-number devices corresponding to different functional modules, greatly reducing the size of the microwave optical aperture transformation imaging system, reducing the system power consumption, improving the system stability, and making the microwave optical aperture transformation imaging system convenient and flexible to deploy. The present invention performs phase shifting on the transmitted light based on the thin-film lithium niobate phase modulator structure, and the electro-optic response is in the nanosecond order and has a linear electro-optic effect. Even in extremely harsh environments, it can accurately compensate the time delay of the transmitted light in each channel in real time to ensure stable target imaging. The present invention designs the optical antenna unit based on the reverse algorithm, selects different etching depth combinations, and realizes low coupling loss and large process tolerance. The chip in the present application can realize the miniaturization of multi-channel delay error compensation in the system under the trend of the microwave optical aperture transformation imaging system continuously developing towards large and multi-element numbers. This chip can play a key role in microwave photon front-end signal processing and has high application value. Description of the Drawings

[0016] Figure 1 is a schematic diagram of the principle of a microwave optical aperture transformation imaging system.

[0017] Figure 2 This is a schematic diagram of the overall structure of the integrated thin-film lithium niobate array phase shifter and optical antenna chip in the embodiment of the present application.

[0018] Figure 3 is a schematic cross-sectional structure diagram of the thin-film lithium niobate phase shifter in the embodiment of the present application.

[0019] Figure 4 This is a schematic diagram of the structure of the input waveguide and the ridge waveguide of one channel in the multi-channel end-face coupler in the embodiment of the present application.

[0020] Figure 5 This is a schematic diagram of the cross-sectional structure of the optical antenna unit in the embodiment of the present application.

[0021] Figure 6 This is a schematic diagram of the structure of a microwave optical aperture transformation imaging system based on an integrated thin-film lithium niobate array phase shifter and optical antenna chip.

[0022] Explanation of reference numerals: 20 Integrated thin-film lithium niobate array phase shifter and optical antenna chip, 201 Multi-channel end-face coupler, 202 Thin-film lithium niobate phase shifter, 203 Array optical antenna, 301 Silicon substrate layer, 302 Silicon dioxide base layer, 303 Lithium niobate flat layer, 304 Lithium niobate strip waveguide layer, 305 Silicon dioxide coating layer, 306 Ground electrode, 307 Signal electrode, 401 First inverted conical waveguide part, 402 Second inverted conical waveguide part, 403 Flat waveguide part, 404 Third inverted conical waveguide part, 405 Strip waveguide part. Detailed implementation manners

[0023] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] The present invention provides an integrated thin-film lithium niobate array phase shifter and optical antenna chip 20, which includes a silicon substrate 301, a silicon dioxide base layer 302, a lithium niobate flat layer 303, a lithium niobate strip waveguide layer 304, a silicon dioxide coating layer 305, and a metal electrode layer that are sequentially arranged from bottom to top.

[0025] Among them, the silica substrate layer 302 is located on the silicon substrate 301, the lithium niobate planar layer 303 is located on the silica substrate layer 302, and the lithium niobate strip waveguide layer 304 is located on the lithium niobate planar layer 303, including a plurality of lithium niobate strip waveguide parts separated by silica materials. The lithium niobate planar layer 303 and the lithium niobate strip waveguide layer together form a lithium niobate waveguide layer. The lithium niobate strip waveguide parts are obtained by injecting helium (He) ions into a lithium niobate crystal, followed by thin-film bonding, annealing, peeling, and etching. The lithium niobate waveguide layer includes a multi-channel end-face coupler 201, a thin-film lithium niobate phase shifter array 202, and an array of optical antennas 203. The silica cladding layer 305 is located around and above the lithium niobate strip waveguide 304, that is, it includes the silica spacer layer that separates the lithium niobate strip waveguides and the silica cover layer that entirely covers the lithium niobate strip waveguides and the silica spacer layer. One of the functions of the silica cladding layer 305 is to protect the lithium niobate ridge waveguide, and another function is to prevent the ground electrode 306 and the signal electrode 307 in the thin-film lithium niobate phase shifter array 202 from being too close to the lithium niobate ridge waveguide and causing additional absorption loss to the light wave.

[0026] In this embodiment, the lithium niobate waveguide layer is formed from a lithium niobate wafer with x-cut y-propagation or z-cut x-propagation or z-cut y-propagation.

[0027] As Figure 2 shown, as described above, the lithium niobate waveguide layer includes a multi-channel end-face coupler 201, a thin-film lithium niobate phase shifter array 202, and an array of optical antennas 203 connected in sequence. The multi-channel end-face coupler 201 may include, for example, 30 channels, each connected to a lithium niobate phase shifter in the thin-film lithium niobate phase shifter array 202 through an input waveguide. The thin-film lithium niobate phase shifter array 202 includes lithium niobate phase shifters matching the number of channels of the multi-channel end-face coupler 201, such as 30 lithium niobate phase shifters.

[0028] Each lithium niobate phase shifter includes a lithium niobate ridge waveguide formed in the lithium niobate waveguide layer, a ground electrode 306 on the silica cladding layer in the upper left of the lithium niobate ridge waveguide, and a signal electrode 307 on the silica cladding layer in the upper right. The ground electrode 306 and the signal electrode 307 are disposed on the metal electrode layer. By changing the refractive index of the lithium niobate ridge waveguide through the electric field applied to the above two electrodes of the thin-film lithium niobate phase shifter array 202, the optical wave phase passing through the lithium niobate ridge waveguide is further changed. Each lithium niobate phase shifter in the thin-film lithium niobate phase shifter array 202 is connected to a thin-film lithium niobate optical antenna in the array optical antenna 203 through an output waveguide, and the optical wave is emitted into free space through the thin-film lithium niobate optical antenna of the array optical antenna 203. The number of thin-film lithium niobate optical antennas in the array optical antenna 203 can match the number of lithium niobate phase shifters, which is 30 in this embodiment.

[0029] The multi-channel end-face coupler 201 is located above the integrated chip 20 of the thin-film lithium niobate array phase shifter and optical antenna. The array optical antenna 203 is located below the integrated chip 20 of the thin-film lithium niobate array phase shifter and optical antenna. The thin-film lithium niobate phase shifter array 202 is placed along the x-axis direction. Such a design is to separate the electrical input / output interfaces and optical input / output interfaces of the integrated chip 20 of the thin-film lithium niobate array phase shifter and optical antenna, so as to avoid mutual interference and facilitate subsequent chip packaging.

[0030] As Figure 3 shown, in the cross-sectional view of the thin-film lithium niobate phase shifter array 202, the optical wave exists in the lithium niobate ridge phase-shifting waveguide composed of the lithium niobate slab layer 303 and the lithium niobate strip waveguide layer 304. The ground electrode 306 is grounded, and a delay error compensation voltage signal is input into the signal electrode 307. The electric field between the above two electrodes will change the refractive index of the lithium niobate ridge phase-shifting waveguide, thereby changing the phase of the transmitted light.

[0031] For any lithium niobate phase shifter, the relationship between the change in the refractive index of the lithium niobate ridge waveguide and the voltage applied to the signal electrode of the lithium niobate phase shifter is:

[0032]

[0033] Where is the change in the refractive index of the lithium niobate ridge waveguide, is the refractive index of the lithium niobate ridge waveguide without voltage application, is the voltage applied to the signal electrode, is the distance between the ground electrode and the signal electrode, is the electro-optic coefficient of the lithium niobate material.

[0034] For any lithium niobate phase shifter, the relationship between the phase change of the light wave passing through the lithium niobate ridge waveguide and the voltage applied to the signal electrode is as follows:

[0035]

[0036] Wherein, is the phase change of the light wave after passing through the lithium niobate ridge waveguide, is the electro-optic overlap factor, is the length of the phase shifter, is the wavelength of the transmitted light, is the refractive index of the lithium niobate ridge waveguide when no voltage is applied, is the electro-optic coefficient of the lithium niobate material, is the voltage applied to the signal electrode, is the distance between the ground electrode and the signal electrode.

[0037] Thus, when the required phase delay is calculated, the delay error compensation voltage signal required to be applied to the signal electrode 307 can be calculated according to the above formula.

[0038] Figure 4The figure shows a schematic diagram of the input waveguide structure of the multi-channel end-face coupler 201. The multi-channel end-face coupler 201 includes a first tapered waveguide portion 401 located in the lithium niobate slab layer 303, a second tapered waveguide portion 402 that is continuously arranged and aligned with the first tapered waveguide portion 401, and a third tapered waveguide portion 404 located in the lithium niobate strip waveguide layer 304 corresponding to the position of the second tapered waveguide portion 402. The end-face coupler is coupled to the lithium niobate ridge waveguide. Among them, the second tapered waveguide portion 402 and the slab waveguide portion 403 are connected as a whole. The third tapered waveguide portion 404 is continuously arranged and aligned with the strip waveguide portion 405 on its larger-size side and thus connected as a whole. "Tapered" in this article means that the dimension of the waveguide in the Y direction gradually increases along the X direction towards the lithium niobate ridge waveguide, and the dimension in the Z direction does not change. "Aligned" means that the dimensions in the Y direction are equal. "Strip" means that the dimension of the waveguide in the Y direction does not change along the X direction, and the dimension in the Z direction does not change either. In this embodiment, the upper and lower surfaces of all waveguides are flat. The specific process of coupling includes: First, the optical field of the optical fiber is coupled into the first tapered waveguide portion 401. Secondly, the double-layer tapered waveguide composed of the third tapered waveguide portion 404 and the second tapered waveguide portion 402 adiabatically couples the mode field in the first tapered waveguide 401 into the lithium niobate ridge phase-shifting waveguide. The first tapered waveguide portion 401 has a first taper, the second tapered waveguide portion 402 has a second taper greater than the first taper, and the third taper of the third tapered waveguide portion 404 on the second tapered waveguide portion 402 is much smaller than the second taper of the second tapered waveguide portion 402, for example, one-third of the second taper. The length of the second tapered waveguide portion 402, that is, the dimension in the X direction, is basically equal to the length of the third tapered waveguide portion 404, but the width, that is, the dimension in the Y direction, is greater than the width of the third tapered waveguide portion 404. The length of the slab waveguide portion 403, that is, the dimension in the X direction, is basically equal to the length of the strip waveguide portion 405.

[0039] Because there is a size difference of about 10 times between the optical fiber and the waveguide, there is a mode mismatch of light waves in the optical fiber and the waveguide. The combined tapered waveguide structure formed by the multi-channel end-face coupler 201 in this embodiment and the formed double-layer tapered waveguide structure allow the optical mode to gradually transition, reducing the reflection loss and scattering loss caused by sudden changes in the cross-section, improving the coupling efficiency, and reducing the coupling loss. In addition, the waveguides of the multi-channel end-face coupler 201 and the ridge waveguides of the phase shifters use the same lithium niobate material, making the process simpler.

[0040] Figure 5The figure shows a schematic diagram of the cross-sectional structure of an optical antenna after optimizing the binary search reverse algorithm. The coupling region of the optical antenna is equally divided into N pixel bars along the light propagation direction. Each pixel bar has the same width, and the height of the pixel bars in the initial structure is randomly selected between 0 nm and 600 nm to explore more design variables. After initialization, the height of each pixel bar is changed in turn, and the quality factor of the optical antenna structure is calculated and compared. If the quality factor is improved, the new height is retained; otherwise, the original height is restored. After each iteration, the pixel bar state is set to the height corresponding to the best quality factor to ensure that the final structure only contains four depths. The iterative process is continuously repeated until the quality factor converges to complete the optimization.

[0041] Figure 6 This embodiment also provides an application of an integrated chip 20 of a thin-film lithium niobate array phase shifter and an optical antenna. The application includes a horn antenna array 5, a microwave antenna array 6, an electro-optic modulator array 7, an integrated chip 20 of a thin-film lithium niobate array phase shifter and an optical antenna, a laser 1, an optical amplifier 2, a first beam splitter 3, a second beam splitter 4, a first beam splitter 9A, a second beam splitter 9B, an optical filtering module 10, an optical lens 11, an infrared camera 12, a photodetector 13, and a phase correction module 14. The system uses the horn antenna array 5 and the microwave antenna array 6 to receive microwave echoes, and converts them to the optical domain through the electro-optic modulator array 7. The converted carrier frequency, that is, the optical carrier, is provided to the electro-optic modulator array 7 by the laser 1, the optical amplifier 2, the first beam splitter 3, and the second beam splitter 4. The optical wave is transmitted through an optical fiber to the integrated chip 20 of the thin-film lithium niobate array phase shifter and the optical antenna. The optical wave emitted by the optical antenna array in the integrated chip 20 of the thin-film lithium niobate array phase shifter and the optical antenna is Fourier-transformed and imaged on the infrared camera 12 located in the focal plane through the optical filtering module 10 and the optical lens 11. During this imaging process, it can also include that the phase shifter array in the integrated chip 20 of the thin-film lithium niobate array phase shifter and the optical antenna controls the output of the electro-optic modulator array 7. The phase correction module 14 can provide a correction signal for the phase shifter array in the integrated chip 20 of the thin-film lithium niobate array phase shifter and the optical antenna. 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 composed of the first beam splitter 9A, the second beam splitter 9B, and the photodetector 13.

[0042] In this embodiment, the delay error compensation voltage signal applied calculated by the phase correction module 14 can obtain the phase delay required for each channel of light through the stochastic parallel gradient descent algorithm (SPGD algorithm) or the heterodyne method, and then calculate the delay error compensation voltage signal according to the relationship between the phase change of the transmitted light and the voltage applied to the above electrodes of the phase shifter, and apply it to the signal electrode 307, so as to achieve the delay alignment between channels and ensure the stability of coherent imaging.

[0043] An integrated chip combining a thin-film lithium niobate array phase shifter and an optical antenna according to an embodiment of the present invention has at least the following beneficial effects:

[0044] Through careful layout, the present invention integrates different functions of different devices with multiple channels onto one chip, which can greatly reduce the volume of the sensing system or optical interconnection in the data center in wireless communication, reduce the system power consumption, reduce the system weight, and has a wide range of applications. The present invention uses thin-film lithium niobate as the material for the phase shifter, end-face coupler, and optical antenna. Compared with the method of heterogeneous integration of silicon or silicon nitride and lithium niobate, the process flow is simple, the practicability is strong, and the stability is high. Compared with the method of using the thermo-optic effect or carrier diffusion effect of traditional silicon materials for phase shifting, the electro-optic effect of thin-film lithium niobate has a faster response time and better linearity. Therefore, the present invention has high industrial utilization value.

[0045] Finally, the above embodiments are merely examples for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A thin-film lithium niobate array phase shifter and optical antenna integrated chip for use in a microwave optical aperture transformation imaging system, characterized in that: The thin-film lithium niobate array phase shifter and optical antenna integrated chip includes a silicon substrate, a silicon dioxide base layer on the silicon substrate, a lithium niobate waveguide layer on the silicon dioxide base layer, a silicon dioxide coating layer on the lithium niobate waveguide layer, and a metal electrode layer on the silicon dioxide coating layer; The lithium niobate waveguide layer includes a multi-channel end-face coupler, a thin-film lithium niobate phase shifter array and an array optical antenna connected in sequence; the lithium niobate waveguide layer includes a lithium niobate planar layer and a lithium niobate strip waveguide layer; wherein each channel of the multi-channel end-face coupler includes a first inverted tapered waveguide portion formed on the lithium niobate planar layer, a second inverted tapered waveguide portion formed on the lithium niobate planar layer and continuously arranged and aligned with the first inverted tapered waveguide portion, and a third inverted tapered waveguide portion formed on the lithium niobate strip waveguide layer and corresponding to the second inverted tapered waveguide portion; The thin-film lithium niobate phase shifter array comprises a plurality of lithium niobate phase shifters, each of which is coupled to one of the multi-channel end-face couplers; the lithium niobate phase shifter is formed based on a lithium niobate ridge waveguide, and the lithium niobate ridge waveguide comprises a planar waveguide portion disposed on the lithium niobate planar layer and continuously disposed with the second inverted tapered waveguide portion, and a strip waveguide portion disposed on the lithium niobate strip waveguide layer and continuously disposed with and aligned with the third inverted tapered waveguide portion; The lithium niobate phase shifter further comprises a ground electrode disposed in the metal electrode layer above the silicon dioxide cladding layer on the first side of the strip waveguide portion and a signal electrode disposed in the metal electrode layer above the silicon dioxide cladding layer on the second side of the strip waveguide portion; wherein the lithium niobate phase shifter is configured to change the refractive index of the lithium niobate ridge waveguide by applying a voltage to the signal electrode, thereby changing the phase of the light wave passing through the lithium niobate ridge waveguide; The silicon dioxide cladding layer includes a silicon dioxide spacer layer separating the lithium niobate strip waveguide and a silicon dioxide cap layer entirely covering the lithium niobate strip waveguide and the silicon dioxide spacer layer; The lithium niobate phase shifter is connected to the thin-film lithium niobate optical antenna in the array optical antenna through an output waveguide, and the light wave is emitted into free space through the thin-film lithium niobate optical antenna; For the array optical antenna, any of the optical antenna units has the same structure, and according to the etching depth of the actual processing technology, different initial etching depth combinations are selected, and a direct binary search inverse algorithm is used for design; The coupling region of the optical antenna unit is divided into N pixel strips equidistantly along the light propagation direction, each pixel strip has the same width, and the pixel strip height of the initial structure of the optical antenna unit is randomly selected between 0 nm and 600 nm.

2. The thin-film lithium niobate array phase shifter and optical antenna integrated chip according to claim 1, characterized in that: The number of the multi-channel end face couplers is equal to the number of the lithium niobate phase shifters.

3. The thin-film lithium niobate array phase shifter and optical antenna integrated chip according to claim 1, characterized in that: The multi-channel end-face coupler is located above the thin-film lithium niobate array phase shifter and optical antenna integrated chip, the array optical antenna is located below the thin-film lithium niobate array phase shifter and optical antenna integrated chip, and the thin-film lithium niobate phase shifter array is placed vertically.

4. The thin film lithium niobate array phase shifter and optical antenna integrated chip according to claim 1, characterized in that: For any lithium niobate phase shifter, the relationship between the change in the refractive index of the lithium niobate ridge waveguide and the voltage applied to the signal electrode of the lithium niobate phase shifter is: ,in is the refractive index change of the lithium niobate ridge waveguide, is the refractive index of the lithium niobate ridge waveguide when no voltage is applied, is the voltage applied to the signal electrode, is the distance between the ground electrode and the signal electrode, is the electro-optic coefficient of lithium niobate material.

5. The thin-film lithium niobate array phase shifter and optical antenna integrated chip according to claim 1, characterized in that: For any lithium niobate phase shifter, the relationship between the phase change of the light wave passing through the lithium niobate ridge waveguide and the voltage applied to the signal electrode is: ,in, is the phase change of the light wave after passing through the lithium niobate ridge waveguide, is the electro-optic overlap factor, is the length of the lithium niobate ridge waveguide, is the wavelength of the transmitted light, is the refractive index of the lithium niobate ridge waveguide when no voltage is applied, is the electro-optic coefficient of lithium niobate material, is the voltage applied to the signal electrode, is the distance between the ground electrode and the signal electrode.

6. The thin-film lithium niobate array phase shifter and optical antenna integrated chip according to claim 1, characterized in that: After the initialization is completed, the height of each pixel strip is changed in turn, and the quality factor of the optical antenna unit structure is calculated and compared; if the quality factor is improved, the new height is retained, otherwise the original height is restored; after each round of iteration, the pixel strip state is set to the height corresponding to the best quality factor; Ensure that the final optical antenna unit structure contains only four depths; repeat the iterative process until the quality factor converges and the optimization is completed.

7. The thin-film lithium niobate array phase shifter and optical antenna integrated chip according to claim 1, characterized in that: In order to avoid beam confusion and ensure a large field of view, while ensuring that the phase information carried by the microwave signal is converted to the optical domain without distortion and taking into account both the divergence angle and the large field of view, the array optical antenna distribution adopts a non-equidistant arrangement.

8. The thin-film lithium niobate array phase shifter and optical antenna integrated chip according to claim 1, characterized in that: The lithium niobate waveguide layer is formed by an x-cut y-transmission or z-cut x-transmission or z-cut y-transmission lithium niobate wafer.

9. The thin-film lithium niobate array phase shifter and optical antenna integrated chip according to claim 1, characterized in that: The multi-channel end-face coupler includes thirty channels for coupling light propagating in thirty optical fibers into the thin-film lithium niobate phase shifter array, wherein the thin-film lithium niobate phase shifter array is composed of thirty lithium niobate phase shifters; the array optical antenna is composed of thirty identical thin-film lithium niobate optical antennas.

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