An integrated optical diversity receiving device

Abstract

An integrated optical diversity receiving device addresses the high power consumption problem of correcting for phase distortion and beam pointing errors in existing free-space optical communications, belonging to the field of optical communications. The invention comprises: free-space light focused by a lens is received by a multimode / few-mode optical fiber; the multiple modes of light beams received by the multimode / few-mode optical fiber enter a photon lantern; the photon lantern performs mode demultiplexing and is then coupled into a single-mode optical fiber array; each light beam in the single-mode optical fiber array enters a polarization splitter / rotator / combiner through an edge coupler; the polarization splitter / rotator / combiner separates the incoming light beams into transverse electric (TE) and transverse magnetic (TM) modes, then rotates the separated TM polarization state light to a TE polarization state; the rotated TE polarization state light is combined with the separated TE polarization state light before entering an MZI network; the MZI network is used to achieve optical coherent beam combining; and a control circuit controls the combining of the light beams in the MZI network.

Description

Technical Field

[0001] The invention relates to an integrated optical diversity receiving device based on a photon lantern and an integrated optical chip, and belongs to the fields of optoelectronics, integrated optics and optical communications. Background Art

[0002] Free-space optical communication (FSOC) is considered a promising technology to meet the growing demand for high-speed data transmission. FSOC uses optical signals as a carrier to transmit information. However, as light propagates through the atmosphere, the air is affected by factors such as wind and solar heat, resulting in uneven temperature and pressure distributions and random refractive index fluctuations. These variations in the refractive index and propagation path of the light beam in the air can cause random fluctuations in the amplitude and phase of the received signal, leading to wavefront phase distortion and reduced beam coherence. Under the influence of atmospheric turbulence, laser transmission through the atmosphere can produce phenomena such as light intensity flicker and beam drift, reducing the optical power detectable by the receiving detector. This directly impacts communication quality and range. Furthermore, errors in beam aiming and tracking, combined with pointing errors caused by optical alignment accuracy and turbulence-induced fluctuations in the angle of arrival, can also cause fluctuations in received optical power. Therefore, compensating for the effects of atmospheric turbulence and pointing errors has become a key issue in free-space optical communications.

[0003] To correct the effects of phase distortion and beam pointing errors, existing methods include multi-aperture reception or multi-mode reception followed by mode decomposition. These processes are generally accomplished using multiple receiving antennas and multiple detectors, which is difficult to coordinate and results in a bulky system. Subsequent signal processing often requires high-power digital signal processing. Summary of the Invention

[0004] Aiming at the problem of high power consumption when correcting the effects of phase distortion and beam pointing errors in existing free-space optical communications, the present invention provides an integrated optical diversity receiving device based on a photon lantern and an integrated optical chip.

[0005] An integrated optical diversity receiving device of the present invention includes a multimode / few-mode optical fiber, a photon lantern, a single-mode optical fiber array, an MZI network, a control circuit, N sets of edge couplers and a polarization splitter / rotator combiner, where N is the number of light beams in the single-mode optical fiber array;

[0006] The free-space light focused by the lens is received by the multimode / few-mode fiber;

[0007] The beams of multiple modes received by the multimode / fewmode fiber enter the photon lantern;

[0008] The photon lanterns are mode-demultiplexed and then coupled into a single-mode fiber array;

[0009] Each beam in the single-mode fiber array enters a polarization splitter and rotation combiner through an edge coupler;

[0010] The polarization beam splitter and rotation combiner is used to separate the incoming light beam into transverse electric wave (TE) and transverse magnetic wave (TM) modes, and then rotate the separated transverse magnetic wave (TM) polarization state light to the transverse electric wave (TE) polarization state. The rotated transverse electric wave (TE) polarization state light and the separated TE polarization state light are combined and then enter the MZI network.

[0011] The MZI network is used to achieve optical coherent beam combining;

[0012] The control circuit controls the merging of the light beams in the MZI network.

[0013] Preferably, the polarization beam splitter, rotator and combiner comprises a polarization beam splitter, a polarization rotator and an MZI unit;

[0014] Polarization beam splitter, used to separate the incoming light beam into transverse electric wave TE and transverse magnetic wave TM modes;

[0015] A polarization rotator is used to rotate the separated transverse magnetic wave TM polarization state light to a transverse electric wave TE polarization state;

[0016] The rotated transverse electric wave TE polarization state light and the separated TE polarization state light enter the MZI unit. The MZI unit is used to perform optical coherence combining on the two incoming light beams and then enter the MZI network.

[0017] Preferably, the MZI network comprises a plurality of MZI units, each MZI unit comprising two 50:50 beam splitters and two phase shifters;

[0018] Each 50:50 beam splitter has two inputs and two outputs;

[0019] Each MZI unit has two inputs and two outputs. The input of phase shifter No. 1 and one input of 50:50 beam splitter No. 1 serve as the two inputs of the MZI unit. The output of phase shifter No. 1 enters the other input of 50:50 beam splitter No. 1. The two outputs of 50:50 beam splitter No. 1 enter the input of phase shifter No. 2 and one input of 50:50 beam splitter No. 2 respectively. The output of phase shifter No. 2 enters the other input of 50:50 beam splitter No. 2. The two outputs of 50:50 beam splitter No. 2 serve as the two outputs of the MZI unit.

[0020] Several MZI units are combined for input and output, so that multiple beam inputs can be combined into one or more outputs to form an MZI network.

[0021] Preferably, the 50:50 beam splitter is a directional coupler or a multimode interferometer.

[0022] Preferably, the MZI network includes several stages, the number of MZI units in the latter stage is half of the MZI units in the previous stage, one output of each of the two MZI units in the previous stage is respectively connected to the two inputs of an MZI unit in the latter stage, the other output of the MZI unit in the previous stage is connected to a photodetector, and the last stage is one MZI unit.

[0023] Preferably, the control circuit changes the voltage applied to the phase shifter in the MZI network, and when the signal detected by the photodetector in each stage reaches a minimum value, it is determined that the coherent combination of the light beams in each stage has been completed.

[0024] Preferably, the voltage applied to each phase shifter in the MZI network is determined by a gradient descent method or a hill climbing method.

[0025] This embodiment further provides an MZI network, which includes several stages, wherein the number of MZI units in the odd-numbered stages is the same, and the number of MZI units in the even-numbered stages is one less than the number of MZI units in the odd-numbered stages; one output of each of two MZI units in the odd-numbered stages is respectively connected to two inputs of an MZI unit in the next even-numbered stage, and the output of the MZI unit in the odd-numbered stage that is not connected to the next even-numbered stage is connected to the input of the MZI unit in the next odd-numbered stage.

[0026] Preferably, a training set is constructed, including the input and output of the MZI network, and the MZI network is trained using the training set to determine the voltage of each phase shifter in the MZI network.

[0027] Beneficial effects of the present invention:

[0028] Highly integrated and miniaturized: Compared to traditional multi-aperture receivers, this invention utilizes integrated optical technology to integrate edge couplers, polarization splitter / rotator combiners, MZI networks, and transmission waveguides into a single chip. This highly integrated chip structure significantly reduces system size and complexity, making it suitable for portable, lightweight free-space optical communication devices.

[0029] All-optical coherent combining: Traditional free-space optical communications are limited by phase and amplitude fluctuations caused by atmospheric turbulence. This method utilizes phase shifters in an MZI network to achieve coherent combining of multipath optical signals, effectively reducing the impact of atmospheric turbulence on the signals and improving the system's anti-interference capabilities. Furthermore, the all-optical design avoids the use of multiple detectors and power-intensive digital signal processing, thereby improving optical signal processing efficiency.

[0030] High stability and reliability: Based on the physical properties of photonic integrated circuits, the chip design of the present invention has excellent temperature stability and mechanical stability, is suitable for working in complex and changeable external environments, and is not easily affected by environmental changes.

[0031] Low-power design: While achieving efficient reception, the present invention realizes low-power integrated optoelectronic device design by optimizing optical chips and phase shifter control.

[0032] High coupling efficiency: Using multi-mode / few-mode optical fiber as the spatial light receiving end, the receiving area is large and the coupling efficiency is high, which increases the receiving sensitivity of the laser communication system. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the principle of the present invention;

[0034] Figure 2 This is a schematic diagram of the principle of the input part of the present invention;

[0035] Figure 3 Schematic diagram of the principle of the polarization beam splitter and rotation combiner of the present invention;

[0036] Figure 4 Schematic diagram of the working principle of the polarization beam splitter of the present invention;

[0037] Figure 5 Schematic diagram of the working principle of the polarization rotator of the present invention;

[0038] Figure 6 Schematic diagram of the principle of the MZI unit;

[0039] Figure 7 Schematic diagram of the principle of MZI network;

[0040] Figure 8 Schematic diagram of the structure of the MZI unit;

[0041] Figure 9 Schematic diagram of the structure of the multi-mode interferometer MMI;

[0042] Figure 10 It is a structural diagram of the MZI network;

[0043] Figure 11 A schematic diagram of another MZI network. DETAILED DESCRIPTION

[0044] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0045] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0046] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0047] An integrated optical diversity receiving device of this embodiment is as follows Figure 1 As shown, it includes an input part and a photonic chip. The input part includes a multi-mode / few-mode optical fiber for receiving the light source, a photon lantern and a single-mode optical fiber array for realizing mode demultiplexing. The free-space light focused by the lens is received by the multi-mode or few-mode optical fiber and excites the high-order mode. The light beam coupled to the multi-mode or few-mode optical fiber will evolve into multiple modes in this part due to the influence of atmospheric turbulence, and will be mode-demultiplexed by the subsequent photon lantern, and the mode in the multi-mode / few-mode optical fiber will be coupled to the single-mode optical fiber array, and then enter the photonic chip through the edge coupler for coherent beam combining.

[0048] Few-mode optical fiber, photon lantern, and single-mode optical fiber array are independent of the photonic chip. Through chip packaging technology, the single-mode optical fiber array is connected to the photonic chip.

[0049] The photonic chip includes an MZI network, a control circuit, N groups of edge couplers and a polarization beam splitter / rotator combiner; a single-mode fiber array is connected to the edge coupler. For each optical path input by the edge coupler, since there are two polarizations in the optical fiber and the edge coupler does not have polarization selectivity, this embodiment deploys a polarization beam splitter / rotator combiner in the chip to decompose the TE and TM modes and convert the TM mode into the TE mode. The processed optical signal is then first polarization-merged through the MZI and then connected to the MZI processing network. The overall structure of the polarization rotation beam splitter / rotator is shown in the figure. Figure 3 As shown, the polarization beam splitter, rotator and combiner includes a polarization beam splitter, a polarization rotator and an MZI unit;

[0050] For polarization beam splitters, it mainly uses the different properties of materials with different polarizations from the input light, and uses a special waveguide structure to achieve spatial separation of light with different polarization states, thereby realizing the manipulation and application of light. The schematic diagram of its working principle is shown in Figure 4As shown, the polarization beam splitter of this embodiment separates the incoming light beam into transverse electric wave TE and transverse magnetic wave TM modes, thereby outputting TE and TM light separately.

[0051] After the polarization beam splitter splits the TE and TM polarized light, in order to achieve efficient use of the received optical power, it is also necessary to merge the generated light of different polarization states. This embodiment mainly rotates the electric field direction of the TM polarized light through the waveguide structure of the polarization rotator, thereby achieving the effect of converting TM polarization into TE polarization. The working principle diagram is shown in the figure. Figure 5 As shown in Figure 2, the polarization rotator in this embodiment achieves conversion from TM polarization to TE polarization through a unique waveguide structure design. Due to the phase difference between the polarization rotator and the two polarization states, this embodiment utilizes an MZI unit to coherently combine the two polarization-rotated beams, outputting TE polarization light that enters the subsequent MZI network for processing.

[0052] The MZI network of this embodiment includes several MZI units, such as Figure 6 As shown, each MZI unit includes two 50:50 beam splitters and two phase shifters;

[0053] Each 50:50 beam splitter has two inputs and two outputs;

[0054] Each MZI unit has two inputs and two outputs. The input of phase shifter No. 1 and one input of 50:50 beam splitter No. 1 serve as the two inputs of the MZI unit. The output of phase shifter No. 1 enters the other input of 50:50 beam splitter No. 1. The two outputs of 50:50 beam splitter No. 1 enter the input of phase shifter No. 2 and one input of 50:50 beam splitter No. 2 respectively. The output of phase shifter No. 2 enters the other input of 50:50 beam splitter No. 2. The two outputs of 50:50 beam splitter No. 2 serve as the two outputs of the MZI unit.

[0055] The aforementioned photonic chips can be based on any mature material system, including but not limited to SOI, SiN, GaAs, lithium niobate, and others. The 50:50 beam splitter can be based on a directional coupler (DC) or a multimode interferometer (MMI) coupler, and the phase shifter can utilize the material's thermo-optical effect, electro-optical effect, or carrier injection. PDs can be integrated on-chip, or optical fibers can be used to connect the photonic chip to an off-chip PD. These two MZI network designs are by no means the only two.

[0056] By utilizing the light beam processing characteristics of the MZI unit and cooperating with the photonic detector (PD), a corresponding MZI network can be designed to combine multiple light beam inputs into one output, such as Figure 7 As shown, the MZI network consists of several stages. The number of MZI units in each subsequent stage is half that of the previous stage. One output of each of the two MZI units in the previous stage is connected to the two inputs of an MZI unit in the next stage, and the other output of the MZI unit in the previous stage is connected to a photodetector. The final stage consists of a single MZI unit. A control circuit varies the voltage applied to the phase shifters in the MZI network. When the signal detected by the photodetector in each stage reaches a minimum, the coherent combining of the beams in each stage is determined to be complete.

[0057] Specific design:

[0058] Given the MZI unit structure, such as Figure 8 The MZI unit has a 2-input, 2-output structure, where two beams of input light enter the MZI unit through input_1 and input_2, and the two output ports are output_1 and output_2. One of the output ports should be connected to a PD to confirm coherent combining.

[0059] Specifically, after passing through electrically controlled thermal phase shifter 312, the light from input_1 is adjusted to have the same phase as input_2, or a phase difference of π (this phase difference varies depending on the structure of the MMI). It then enters a two-input, two-output multi-mode interferometer (MMI) 313. This MMI is designed so that when the phase difference between the two beams is π, the output intensity at the output ends is equal. When the phase difference is an integer multiple of π / 2, the output is primarily from one of the two arms. Therefore, when the phase difference between the two beams entering MMI 313 is an integer multiple of π, MMI 313 splits the two beams into two equal-intensity outputs. One of the optical signals then enters electrically controlled thermal phase shifter 314, where its phase difference with the other arm is adjusted to an integer multiple of π / 2. The signal then enters MMI 314 for coherent combining. As mentioned above, when the output of the external PD on the output reaches the minimum value, it is considered that coherent combining has been successfully achieved.

[0060] Specifically speaking of structural parameters, the length of thermal phase shifter No. 1 312 is 260 μm, and it uses TiN material as the heating electrode. The two ends are powered by copper electrodes and the vertical distance from the waveguide is 2000 nm. The structures of multi-mode interferometer No. 1 313 and multi-mode interferometer No. 2 315 are the same. Figure 9As shown, the four arms of the multimode interferometer have identical structural parameters: input / output lengths of 30 μm, a width of 500 nm at the thinner end, and a width of 1500 nm at the thicker end. The central multimode interference region is 42.7 μm long and 6 μm wide. The entire MMI is etched from a 220 nm thick layer of silicon.

[0061] The MZI network is composed of the above MZI units through a specific topological structure. Here we provide a binary tree network structure, such as Figure 10 As shown. Specifically, the input optical signals 111 and 211, 311 and 411, 511 and 611, 711 and 811 respectively enter the first-stage multimode interferometer MZI shown by number 911, and the phase is adjusted by adjusting the two phase shifters in the MZI unit to achieve the function of coherent merging of the light beams. Through the electrical signal intensity output by the four integrated photodetectors (PD), this embodiment can know whether the coherent merging of the light beams is completed. Specifically, when the PD output reaches the minimum value, this embodiment considers that the light beam is output to the other output end of the MZI unit, achieving the coherent merging function of this level. At the same time, the output of the MZI network of this level exists as the input of the MZI network of the next level. Through the three-stage MZI network of the first stage 911, the second stage 112, and the third stage 132, as well as the PD detection outputs of the first layer 101, the second layer 122, and the third layer 142, this embodiment can achieve the function of coherently merging 8 input signals into one output signal.

[0062] The combined effect of the MZI network is identified and controlled by the control circuit of this embodiment. Specifically, the phase shift size is adjusted by adjusting the voltage applied to the thermally controlled phase shifter of the MZI. Figure 10 For the MZI network shown, a power of 60mW can achieve a phase shift of 0 to 2π. This implementation verifies the MZI's effectiveness by monitoring the PD's output voltage. When the PD output voltage reaches its minimum, coherent combining is achieved. Specifically, by varying the voltage applied to the phase shifter, the corresponding PD output is obtained. Using specific algorithms, such as gradient descent or hill climbing, the minimum PD output value can be found.

[0063] This embodiment also provides an MZI network, such as Figure 11As shown, the MZI network consists of several stages, with the same number of MZI units in odd-numbered stages and one less in even-numbered stages. One output of each of the two MZI units in an odd-numbered stage is connected to the two inputs of an MZI unit in the next even-numbered stage, while the output of any MZI unit in an odd-numbered stage not connected to the next even-numbered stage is connected to the input of an MZI unit in the next odd-numbered stage. This MZI network can be used as an optical neural network. The training set is constructed using the light output from the grating array and the light output from a diversity receiving photonic chip for spatial optical communications. The training set is used to train the optical neural network and determine the voltage level of each phase shifter in each MZI network. The resulting optical neural network can achieve optical coherent beam combining.

[0064] The optical signal received in this embodiment adopts optical coherent combining to avoid photoelectric conversion and digital signal processing to circumvent the efficiency and frequency issues caused by them. This embodiment adopts an integrated design, and all optical devices are integrated on an optical chip through micro-nano technology, which greatly reduces the required space. In addition, thanks to the existing packaging technology, the input and output of the chip do not require a complicated assembly process, which improves the stability and reliability of the system. This embodiment uses multi-mode or few-mode optical fiber for spatial light reception, with high coupling efficiency and low alignment difficulty. This embodiment coherently combines the two polarizations in the optical fiber in real time and dynamically to improve signal processing efficiency.

[0065] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely illustrative of the principles and applications of the invention. It should be understood that many modifications may be made to the illustrative embodiments, and that other arrangements may be devised, without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in ways other than those described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be employed in conjunction with other described embodiments.

Claims

1. An integrated optical diversity receiving device, characterized in that: It includes multi-mode / few-mode optical fibers, photonic lanterns, single-mode optical fiber arrays, MZI networks, control circuits, N sets of edge couplers and polarization splitter / rotator combiners, where N is the number of beams in the single-mode optical fiber array. The free-space light focused by the lens is received by the multimode / few-mode fiber; The beams of multiple modes received by the multimode / fewmode fiber enter the photon lantern; The photon lanterns are mode-demultiplexed and then coupled into a single-mode fiber array; Each beam in the single-mode fiber array enters a polarization splitter and rotation combiner through an edge coupler; The polarization beam splitter and rotation combiner is used to separate the incoming light beam into transverse electric wave (TE) and transverse magnetic wave (TM) modes, and then rotate the separated transverse magnetic wave (TM) polarization state light to the transverse electric wave (TE) polarization state. The rotated transverse electric wave (TE) polarization state light and the separated TE polarization state light are combined and then enter the MZI network. The MZI network is used to achieve optical coherent beam combining; The control circuit controls the merging of the light beams in the MZI network.

2. The integrated optical diversity receiving device according to claim 1, wherein: The polarization beam splitter, rotator and combiner includes a polarization beam splitter, a polarization rotator and an MZI unit; Polarization beam splitter, used to separate the incoming light beam into transverse electric wave TE and transverse magnetic wave TM modes; A polarization rotator is used to rotate the separated transverse magnetic wave TM polarization state light to a transverse electric wave TE polarization state; The rotated transverse electric wave TE polarization state light and the separated TE polarization state light enter the MZI unit. The MZI unit is used to perform optical coherence combining on the two incoming light beams and then enter the MZI network.

3. An integrated optical diversity receiving device according to claim 1 or 2, characterized in that: The MZI network includes several MZI units, each of which includes two 50:50 beam splitters and two phase shifters; Each 50:50 beam splitter has two inputs and two outputs; Each MZI unit has two inputs and two outputs. The input of phase shifter No. 1 and one input of 50:50 beam splitter No. 1 serve as the two inputs of the MZI unit. The output of phase shifter No. 1 enters the other input of 50:50 beam splitter No.

1. The two outputs of 50:50 beam splitter No. 1 enter the input of phase shifter No. 2 and one input of 50:50 beam splitter No. 2 respectively. The output of phase shifter No. 2 enters the other input of 50:50 beam splitter No.

2. The two outputs of 50:50 beam splitter No. 2 serve as the two outputs of the MZI unit. Several MZI units are combined for input and output, so that multiple beam inputs can be combined into one or more outputs to form an MZI network.

4. The integrated optical diversity receiving device according to claim 3, wherein: The 50:50 beam splitter is a directional coupler or a multimode interferometer.

5. The integrated optical diversity receiving device according to claim 3, wherein: The MZI network consists of several stages. The number of MZI units in the next stage is half of that in the previous stage. One output of each of the two MZI units in the previous stage is connected to the two inputs of an MZI unit in the next stage. The other output of the MZI unit in the previous stage is connected to a photodetector. The last stage consists of one MZI unit.

6. The integrated optical diversity receiving device according to claim 5, characterized in that: The control circuit changes the voltage applied to the phase shifter in the MZI network. When the signal detected by the photodetector in each stage reaches a minimum value, it is determined that the coherent combination of the light beams in each stage has been completed.

7. The integrated optical diversity receiving device according to claim 6, characterized in that: The voltage applied to each phase shifter in the MZI network is determined by a gradient descent method or a hill climbing method.

8. The integrated optical diversity receiving device according to claim 3, characterized in that: The MZI network includes several stages, the number of MZI units in the odd-numbered stages is the same, and the number of MZI units in the even-numbered stages is one less than the number of MZI units in the odd-numbered stages; one output of each of the two MZI units in the odd-numbered stages is respectively connected to the two inputs of an MZI unit in the next even-numbered stage, and the output of the MZI unit in the odd-numbered stage that is not connected to the next even-numbered stage is connected to the input of the MZI unit in the next odd-numbered stage.

9. The integrated optical diversity receiving device according to claim 8, characterized in that: A training set is constructed, including the input and output of the MZI network. The MZI network is trained using the training set to determine the voltage of each phase shifter in the MZI network.

Images