Multi-mode interference coupler loss compensation method and system

Abstract

The invention relates to the field of photon integration, in particular to a loss compensation method and system for a multimode interference coupler. The method comprises the following steps: acquiring data of transmittance, unevenness and optical wavelength of the multimode interference coupler; based on the data, obtaining an effective refractive index of a multimode interference coupler mode; determining the beat length between adjacent modes according to the effective refractive index; through the beat length, loss compensation of the multimode interference coupler is realized. A thermo-optical tuning mechanism is introduced into the multimode interference coupler, and the effective refractive index difference value of transverse electric modes of adjacent orders is dynamically adjusted, so that the beat length is kept at a constant value in the wavelength tuning process, and the loss of the single multimode interference coupler does not change along with the wavelength; the accumulated loss of a light splitting area of the silicon-based optical phased array is remarkably reduced, the working bandwidth of the optical phased array is effectively expanded, and the longitudinal scanning range is greatly widened.

Description

Technical Field

[0001] The present invention relates to the field of photon integration, and in particular to a multimode interference coupler loss compensation method and system. Background Art

[0002] As a new generation of beam control technology, optical phased array (OPA) has important application value in the fields of LiDAR and free-space optical communications. Traditional mechanical scanning systems are limited by moving parts and have inherent defects such as large size and slow speed. Silicon-based OPA achieves non-mechanical beam deflection through electrically controlled phase modulation, but its two-dimensional scanning requires the combination of wavelength tuning and phase control, and faces the problem of increased loss caused by the wavelength sensitivity of the splitter network.

[0003] In the prior art, the self-imaging characteristics of the multimode interference coupler, as the core component of OPA spectrometry, are strongly related to the wavelength. When a tunable laser is used to achieve longitudinal scanning, the wavelength change leads to mode beat length mismatch, causing spectrometry inhomogeneity and increased insertion loss. Especially in a tree structure, the loss of multiple cascaded multimode interference couplers will be exponentially amplified, ultimately limiting the scanning range and system efficiency.

[0004] At present, there is not enough research on loss compensation of multimode interference couplers, and there is no specific method for loss compensation of multimode interference couplers that introduces thermo-optical tuning to keep the ratio of the effective refractive index difference of adjacent modes to the wavelength unchanged. Summary of the invention

[0005] In view of the defects in the prior art, the present invention provides a method and system for compensating loss of a multimode interference coupler.

[0006] In a first aspect, the present invention provides a loss compensation method for a multimode interference coupler, comprising the following steps: obtaining data on transmittance, non-uniformity and light wavelength of the multimode interference coupler; based on the data, obtaining the effective refractive index of the multimode interference coupler mode; determining the beat length between adjacent modes according to the effective refractive index; and achieving loss compensation for the multimode interference coupler through the beat length. The present invention achieves accurate quantification of the input light field characteristics of the multimode interference coupler by acquiring data on the transmittance, non-uniformity and light wavelength of the multimode interference coupler, thereby providing a reliable data basis for its loss compensation; based on experimental data, the effective refractive index of the multimode interference coupler mode is obtained, which overcomes the problem of large deviation between traditional theoretical models and actual devices and significantly improves the accuracy of mode analysis; according to the effective refractive index, the beat length between adjacent modes is determined, which provides a key parameter basis for loss compensation; by utilizing the beat length to compensate for the loss of the multimode interference coupler, the insertion loss caused by energy transfer between modes is effectively suppressed, and the transmission efficiency and performance stability of the device are improved; through multi-parameter collaborative optimization combining experiments and theories, active compensation for the loss of the multimode interference coupler is achieved, which solves the problem of insufficient accuracy of traditional passive compensation methods and provides new ideas for the design and manufacture of high-performance integrated optical devices.

[0007] Optionally, the data of obtaining the transmittance, non-uniformity and light wavelength of the multi-mode interference coupler includes: obtaining data of the wavelength of experimental linear polarized light, wherein the polarization direction of the experimental linear polarized light is consistent with the polarization direction of the transverse electric mode in the multi-mode interference coupler; based on the data, obtaining data of the transmittance and non-uniformity of the multi-mode interference coupler. The present invention ensures that the input light energy is efficiently coupled to the transverse electric mode by precisely controlling the polarization direction of the experimental linear polarized light to be consistent with the polarization direction of the transverse electric mode in the multimode interference coupler, avoids the mode competition loss caused by the excitation of the transverse magnetic mode, and significantly improves the mode purity and light energy utilization rate of the device; dynamically adjusts the temperature of the multimode interference coupler based on a temperature control platform, and compensates for the effective refractive index change caused by wavelength tuning in real time, so that the beat length between adjacent transverse electric modes remains constant in a wide wavelength range, achieves the stability of the self-imaging position and the wavelength insensitivity of the output light field distribution, thereby greatly reducing the additional loss caused by wavelength tuning; by synchronously collecting transmittance and non-uniformity data at different wavelengths, the performance parameters of the multimode interference coupler under the joint regulation of temperature and wavelength are quantified, providing an experimental basis for the optimal design of broadband silicon optical devices.

[0008] Optionally, the acquisition of the effective refractive index of the multimode interference coupler mode based on the data includes: changing the temperature of the multimode interference coupler based on the data; and obtaining the effective refractive index of different orders of transverse electric modes according to the temperature. The present invention realizes the precise utilization of the thermo-optical effect of the waveguide material by actively regulating the operating temperature of the multimode interference coupler, breaking through the technical bottleneck that the device performance is limited by the ambient temperature drift in the traditional fixed temperature working mode; by establishing a dynamic mapping relationship between temperature and the effective refractive index of different orders of transverse electric modes, real-time closed-loop control of the mode effective refractive index difference is realized; by deeply coupling the temperature control parameters with the law of the change of the mode effective refractive index, a compensation algorithm for the mode effective refractive index difference based on temperature tuning is proposed, which greatly reduces the error of the spectral uniformity of the multimode interference coupler; by developing a coordinated control strategy of temperature, refractive index and beat length, the problem of the imbalance of the optimal beat length matching of the device caused by the change of the effective refractive index due to wavelength scanning in the silicon-based optical phased array is successfully solved, resulting in an increase in insertion loss.

[0009] Optionally, obtaining the effective refractive index of different orders of transverse electric modes according to the temperature includes: obtaining the propagation constants of different orders of transverse electric modes according to the temperature; establishing a transverse electric mode effective refractive index calculation model according to the propagation constant; obtaining the effective refractive index of different orders of transverse electric modes through the transverse electric mode effective refractive index calculation model. The present invention realizes the accurate prediction of the propagation characteristics of each order of transverse electric modes in the multimode interference coupler by dynamically correlating the temperature and the mode propagation constant, greatly improves the accuracy of mode analysis, and provides theoretical support for the control of complex light fields; by constructing the effective refractive index calculation model, the synchronous analysis of multi-order mode field characteristics is realized.

[0010] Optionally, the transverse electric mode effective refractive index calculation model satisfies the following expression: in, for The effective refractive index of the order mode, For the The propagation constant of the order mode, The present invention realizes accurate analytical calculation of the effective refractive index of any order transverse electric mode by quantifying the physical relationship between mode propagation constant and wavelength; by independently calculating the propagation constant of each order mode, it breaks through the technical limitation that the traditional effective refractive index measurement is only applicable to the fundamental mode, so that the field distribution control accuracy of the high-order transverse electric mode is improved to the nanometer level; the wavelength and mode effective refractive index mapping database established by this expression is conducive to providing key parameters for the reverse design of multimode interference couplers.

[0011] Optionally, determining the beat length between adjacent modes according to the effective refractive index includes: obtaining the effective refractive index difference of transverse electric modes of different orders according to the effective refractive index, wherein the ratio of the effective refractive index difference to the wavelength of the experimental linear polarized light remains unchanged; determining the beat length between adjacent transverse electric modes according to the effective refractive index difference. The present invention realizes the precise control of the beat length in the multimode interference coupler by establishing a dynamic equilibrium relationship between the effective refractive index difference and the wavelength; by proposing a control criterion of the constant ratio of the effective refractive index difference to the wavelength, the bandwidth limitation of the traditional fixed structure multimode interference coupler is broken; by precisely controlling the effective refractive index difference between adjacent modes, the imaging distortion problem caused by the dispersion of high-order modes in multimode interference is solved; the beat length determination method is conducive to the development of an adaptive compensation algorithm, which significantly reduces the impact of process errors on device performance.

[0012] Optionally, determining the beat length between adjacent order transverse electric modes based on the effective refractive index difference includes: establishing a beat length calculation model between adjacent order transverse electric modes based on the effective refractive index difference; and determining the beat length between adjacent order transverse electric modes through the beat length calculation model. The present invention achieves quantitative control of the mode coupling length in a multimode interferometer by establishing a beat length calculation model; by dynamically inputting the effective refractive index difference of adjacent order modes into the model, the imaging position offset problem caused by high-order mode interference is solved, and the channel uniformity of the multimode interference coupler is greatly improved; by using the beat length calculation model to guide the asymmetric waveguide structure, the bandwidth limitation of the traditional symmetric multimode interference coupler is broken through.

[0013] Optionally, the beat length calculation model satisfies the following expression: in, is the beat length between adjacent order modes, For the The first mode and The effective refractive index difference of the order modes is, is the wavelength, and The present invention realizes the accurate quantitative characterization of the light field evolution period in the multimode interference device by constructing a beat length calculation model; by revealing the three-way coupling relationship of wavelength, refractive index difference and beat length, dynamic temperature control compensation is realized, which greatly reduces the wavelength-related loss of the multimode interference coupler; by finely calculating the refractive index difference of adjacent modes, the limitation of the existing method that only considers the fundamental mode approximation is broken, so that the design accuracy of the high-order mode interference device reaches the nanometer level.

[0014] Optionally, the achieving loss compensation for the multimode interference coupler by using the beat length includes: establishing a loss analysis model of the multimode interference coupler, wherein the loss analysis model satisfies the following expression: in, is the loss of the multimode interference coupler, is the transmittance of the multimode interference coupler, is the proportionality coefficient, is the non-uniformity of the multimode interference coupler, is the beat length mismatch sensitivity, is the beat length between adjacent order modes, The beat length designed for the device structure; based on the loss analysis model, the beat length between adjacent modes is used to achieve loss compensation for the multimode interference coupler. The present invention achieves accurate diagnosis of the loss mechanism of the multimode interference coupler by establishing a multidimensional loss analysis model of transmittance, non-uniformity, and beat length; by real-time monitoring of the output light field non-uniformity feedback to adjust the beat length, the problem that the existing static compensation method cannot cope with dynamic environmental changes is solved; by closed-loop linkage between loss data and the beat length calculation model, targeted compensation for high-order mode coupling loss is achieved; through the device structure optimization guided by the compensation method, the bandwidth limitation of the traditional symmetrical multimode interference coupler is broken.

[0015] In a second aspect, the present invention provides a multimode interference coupler loss compensation system, comprising a laser, a linear polarizer, a control module, a photodetector, a microscope and a microcontroller, wherein the control module comprises a multimode interference coupler and a temperature control platform, the laser, the linear polarizer, the control module, the photodetector and the microcontroller are arranged along the optical axis, the microscope is arranged in a direction perpendicular to the optical axis and aligned with the control module, and the system uses the multimode interference coupler loss compensation method. Through the coordinated control of integrated lasers, linear polarizers and multi-mode interference couplers, precise matching of the polarization state of the input light is achieved, which greatly improves the excitation efficiency of the transverse electric mode and effectively suppresses the mode competition loss; through the closed-loop feedback design of the temperature control platform and the microcontroller, a dynamic compensation algorithm based on real-time transmittance monitoring is developed to achieve stable control of insertion loss fluctuations; through the multi-parameter joint measurement of microscope imaging and photodetector, nanometer-level precision control of the output light field non-uniformity is achieved, which greatly improves the power uniformity; through the coordinated control of the temperature control platform and the multi-mode interference coupler by the microcontroller, the technical limitations of traditional fixed temperature compensation are broken through. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A flow chart of a multimode interference coupler loss compensation method according to an embodiment of the present invention; Figure 2 It is a structural schematic diagram of a multimode interference coupler loss compensation system according to an embodiment of the present invention; Figure 3Schematic diagram of the structure of a multi-mode interference coupler according to an embodiment of the present invention.

[0017] Reference numerals 1 is a laser, 2 is a linear polarizer, 3 is a control module, 4 is a photodetector, 5 is a microscope, and 6 is a microcontroller. DETAILED DESCRIPTION

[0018] The specific embodiments of the present invention will be described in detail below. It should be noted that the embodiments described herein are only for illustration and are not intended to limit the present invention. In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is obvious to those of ordinary skill in the art that these specific details do not need to be adopted to implement the present invention. In other examples, in order to avoid confusing the present invention, known circuits, software or methods are not specifically described.

[0019] Throughout the specification, references to "one embodiment," "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "in one embodiment," "in an embodiment," "an example," or "an example" appearing in various places throughout the specification do not necessarily all refer to the same embodiment or example. In addition, particular features, structures, or characteristics may be combined in one or more embodiments or examples in any suitable combination and / or subcombination. In addition, it should be understood by those of ordinary skill in the art that the figures provided herein are for illustrative purposes and that the figures are not necessarily drawn to scale.

[0020] See also Figure 1 , an embodiment of the present invention provides a multimode interference coupler loss compensation method, the method comprising the following steps: S1. Obtain the data of wavelength, transmittance and inhomogeneity of the experimental linearly polarized light.

[0021] In one embodiment, a tunable laser is first used to emit a 1500 nm laser, and the wavelength tunable range of the tunable laser is 1500 nm to 1600 nm.

[0022] Furthermore, the laser is passed through a linear polarizer and the polarization angle is adjusted to generate the linear polarized light required for the experiment, referred to as experimental linear polarized light. The polarization direction of the incident light of the linear polarizer needs to be adjusted to be consistent with the polarization direction of the transverse electric (TE) mode in the multimode interference coupler to maximize the TE mode excitation.

[0023] Furthermore, starting from 1500nm, the laser wavelength is gradually increased by a fixed wavelength of 1nm until 1600nm. At the same time, at each wavelength point, the following parameters are recorded: One is the wavelength value, which is obtained by directly reading the output wavelength of the laser; The second is transmittance, which is measured by a photodetector through the output optical power of the multimode interference coupler and calculated in combination with the input optical power. The calculation expression is as follows: in, is the transmittance of the multimode interference coupler, is the output optical power, is the input optical power, is the wavelength; The third is the non-uniformity, which is obtained by measuring the relative standard deviation of the power distribution of multiple output ports at the output end of the multi-mode interference coupler. The calculation formula is as follows: in, is the non-uniformity of the multimode interference coupler, also called the relative standard deviation of the power distribution, is the total number of output ports at the output end of the multimode interference coupler, is the average power of each port, For the The power of each output port.

[0024] It should be noted that there are two key points in the above process: 1. By rotating the linear polarizer, the polarization direction of the incident light is consistent with the dominant direction of the TE mode of the multimode interference coupler, which can be verified by maximizing the transmittance.

[0025] 2. If the transmittance of the photodetector changes periodically with the polarization angle, it indicates that there is a mixture of TE mode and transverse magnetic mode (TM) mode. At this time, the polarization angle needs to be optimized to suppress the TM mode, which will cause mode competition and additional loss.

[0026] S2. Based on the data, obtain the effective refractive index of the multimode interference coupling device mode.

[0027] Among them, S2 includes the following steps: S21. Based on the data, change the temperature of the multi-mode interference coupling device.

[0028] In one embodiment, a high-precision temperature control platform is used to heat / cool the multimode interference coupling device, and the temperature adjustment range covers the device working range, which is Among them, 5 For intervals, change the temperature stepwise and keep each temperature point stable for at least 1 min.

[0029] Furthermore, the device temperature is monitored in real time by a temperature sensor, and the data is fed back to a microcontroller, which is used to perform micro-control on the multi-mode interference coupling device to ensure alignment of the laser.

[0030] This method achieves precise temperature control over a wide range by adopting a high-precision temperature control platform; real-time monitoring and dynamic compensation of device temperature are achieved through a closed-loop feedback system constructed through temperature sensors and microcontrollers.

[0031] S22. Based on the temperature, obtain propagation constants of transverse electric modes of different orders.

[0032] Symmetrical multimode interference couplers use the principle of self-imaging, that is, when the input light field enters the multimode waveguide, its electric field distribution can be decomposed into the linear superposition of multiple guided modes supported by the multimode waveguide. The propagation constant of each guided mode is different, resulting in phase differences with propagation distance. At a specific propagation length, the phase difference of each mode satisfies the integer multiple relationship. At this time, the light field re-coherently superimposes to form a periodic reproduction of the input light field.

[0033] In one embodiment, the propagation constants of transverse electric modes of different orders are obtained by measuring the temperature of the multimode interference coupling device using an interference fringe method and a mode matching method.

[0034] Specifically, for the interference fringe method, if the output end of the multi-mode interference coupling device presents multi-beam interference, the propagation constant difference of different order transverse electric modes is calculated by the fringe spacing, and the calculation expression of the propagation constant difference is as follows: in, For the The propagation constant of the order transverse electric mode, For the The propagation constant of the order transverse electric mode, is the spacing of the interference fringes.

[0035] Furthermore, the modes of the multimode interference coupling device are simulated by the finite difference method, and the propagation constants are obtained by fitting the experimental data. and .

[0036] This method achieves accurate measurement of the propagation constants of each order of transverse electric modes in multimode interference couplers by combining the dual verification methods of the interference fringe method and the finite difference method, breaking through the technical bottleneck of insufficient accuracy of existing measurement methods; by establishing a quantitative relationship model between the propagation constant difference and the interference fringe spacing, the complex mode analysis is transformed into an intuitive fringe spacing measurement problem, which greatly reduces the experimental difficulty of high-order mode characteristic analysis; through the coordinated fitting of finite difference method simulation and experimental data, the mode distortion problem caused by process errors in actual devices is solved, so that the calculation accuracy of the propagation constant reaches the theoretical design level; through the linkage mechanism of temperature control and propagation constant measurement, dynamic monitoring of phase evolution in the multimode interference process is realized, so that the performance stability of the device in a temperature-changing environment is improved by more than ten times.

[0037] S23. According to the propagation constant, the effective refractive index of transverse electric modes of different orders is obtained.

[0038] In one embodiment, a transverse electric mode effective refractive index calculation model is established according to the propagation constant, and the transverse electric mode effective refractive index calculation model satisfies the following expression: in, for The effective refractive index of the order mode, For the The propagation constant of the order mode, is the wavelength.

[0039] Furthermore, the effective refractive indices of transverse electric modes of different orders are obtained through the transverse electric mode effective refractive index calculation model.

[0040] This method achieves accurate conversion from mode transmission characteristics to refractive characteristics by establishing an effective refractive index calculation model, thus opening up the key link between theoretical simulation and experimental measurement. By uniformly calculating the effective refractive indices of different-order modes, it breaks through the limitation of existing methods that can only analyze fundamental mode characteristics, and achieves accurate control of high-order mode interference effects. By dynamically introducing wavelength parameters into the calculation process, it achieves real-time compensation for dispersion effects, significantly improving the performance stability of broadband optical devices.

[0041] S3. Determine the beat length between adjacent modes based on the effective refractive index.

[0042] In one embodiment, firstly, according to the effective refractive index, the effective refractive index difference of different order transverse electric modes is obtained, and the effective refractive index difference satisfies the following relationship: in, is the effective refractive index difference of different order transverse electric modes, for The effective refractive index of the order transverse electric mode, for The effective refractive index of the order transverse electric mode, .

[0043] Further, according to the above relationship of effective refractive index difference, the effective refractive index difference between adjacent transverse electric modes is obtained. In this embodiment, the adjacent transverse electric modes are Model and mold.

[0044] It should be noted that when the temperature of the multimode interference coupler is changed, the effective refractive indexes of different-order transverse electric modes will change, which will in turn cause the effective refractive index difference between adjacent-order transverse electric modes to change.

[0045] Furthermore, based on the effective refractive index difference, a beat length calculation model between adjacent order transverse electric modes is established, and the beat length calculation model satisfies the following expression: in, is the beat length between adjacent order transverse electric modes, is the effective refractive index difference of adjacent order transverse electric modes, is the wavelength.

[0046] Furthermore, based on the beat length calculation model, by adjusting the wavelength of the experimental linear polarized light and the temperature of the multimode interference coupler, so that It is always a fixed value, that is, the best matching value, an almost completely unchanged value.

[0047] This method achieves quantitative control of the light field evolution period in the multimode interference coupler by establishing an accurate calculation model of the beat length, reducing the error of the existing empirical design method to the theoretical limit; through the coordinated compensation mechanism of dynamically adjusting the wavelength and temperature, the beat length is stably maintained within a wide wavelength range, completely solving the performance degradation problem of traditional devices caused by wavelength changes; by regulating the refractive index difference of adjacent order transverse electric modes, the phase matching accuracy in the multimode interference process is improved to a new level, making the self-imaging quality reach a nearly ideal state; through the closed-loop feedback system of temperature, wavelength, and beat length, the intelligent locking of the working point of the multimode interference device is achieved, significantly improving the reliability of the device in complex environments.

[0048] S4. Through the beat length, loss compensation of the multimode interference coupler is achieved.

[0049] In existing symmetrical multimode interference couplers, the position of self-imaging is usually , ensuring that a uniformly distributed double image is formed at its output end. However, in the two-dimensional OPA scanning, as the wavelength changes, the optimal matching beat length of the symmetrical multimode interference coupler will change accordingly, resulting in an increase in loss. As the loss of a single device increases, the loss of the entire spectroscopic area will increase geometrically, resulting in a limited bandwidth of the silicon-based OPA, which further limits the scanning range.

[0050] In one embodiment, a loss analysis model of a multimode interference coupler is first established, and the loss analysis model satisfies the following relationship: in, is the loss of the multimode interference coupler, also called multidimensional loss or total loss, is the basic loss, satisfying the following expression: in, is the transmittance of the multimode interference coupler, For uneven loss, the following relationship is satisfied: in, is the proportionality coefficient, which is calibrated through experiments. is the non-uniformity of the multimode interference coupler, is the beat length mismatch loss, which satisfies the following relationship: in, is the beat length between adjacent order transverse electric modes, The beat length designed for the device structure, is the beat length mismatch sensitivity, for a symmetrical multimode interference coupler, It can be approximated as: in, is the multimode waveguide width, is the waveguide scattering loss, which is included in In loss.

[0051] Furthermore, the above loss analysis model is sorted out to obtain: It should be noted that the basic loss is inherent in the device and has nothing to do with the design parameters, and is mainly caused by material and process defects; the uneven loss is the additional loss caused by the uneven power distribution of each channel at the output end; the beat length mismatch loss is the loss caused by the actual beat length deviating from the design value, and this loss varies with the wavelength.

[0052] Further, the fixed value obtained in step S3 Substituting into the above loss analysis model, we can see that Not with wavelength The reason is that by changing the effective refractive index of the device (thermo-optic effect) through the temperature control platform, the change of the effective refractive index difference between adjacent modes can be dynamically compensated, so that It remains constant during wavelength tuning, thus compensating for beat length mismatch loss and reducing the overall loss.

[0053] In a specific embodiment, the loss compensation method of the multimode interference coupler is applied to a silicon-based OPA, and the loss in the light-splitting region is reduced geometrically, effectively increasing the wavelength bandwidth, thereby further increasing the range of the longitudinal scanning.

[0054] It should be noted that the scanning principle of silicon-based OPA is based on the phase interference control of light waves, and its one-dimensional scanning realizes the linear deflection of the light beam through phase modulation. The one-dimensional OPA consists of a single-row waveguide array, and each waveguide unit is equipped with an independent phase modulator, such as a thermo-optic effect or electro-optic effect modulator. After the laser is evenly distributed to each waveguide through the beam splitter, the optical path difference of adjacent waveguides is changed by adjusting the phase value of each unit. According to the principle of multi-slit interference, the main lobe direction of far-field interference enhancement is determined by the phase difference, which satisfies the formula: in, is the wavelength, is the phase difference between adjacent waveguides, is the waveguide spacing, is an angle. Two-dimensional scanning requires independent control of the light beam in both the horizontal and vertical dimensions. In the horizontal dimension, the phase difference between waveguides is used for control, and the principle is the same as that of one-dimensional scanning. In the vertical dimension, the wavelength change of the tunable laser is used to change the output angle of the grating coupler through the dispersion effect. Its scanning range is limited by the wavelength tuning bandwidth. In the structure of silicon-based OPA, the cascade type splitter occupies a large part, and because it splits light in a tree-like manner, in one In the silicon-based OPA, there is A splitter, with With the increase of the optical splitter, the number of optical splitters will increase geometrically. Among these optical splitters, the most commonly used is the multimode interference coupler. The symmetrical multimode interference coupler has the characteristics of low insertion loss, low cost, high process tolerance and high uniformity.

[0055] The advantage of this method is that it introduces thermo-optical tuning into the multimode interference coupler to change its Model and The difference in the effective refractive index of the modes changes with wavelength. It is always a constant value, that is, it does not affect the loss of a single multimode interference coupler.

[0056] See also Figure 2 , Figure 2 The schematic diagram of the structure of a multimode interference coupler loss compensation system in an embodiment of the present invention. The system includes a laser 1, a linear polarizer 2, a control module 3, a photodetector 4, a microscope 5 and a microcontroller 6. The laser 1, the linear polarizer 2, the control module 3, the photodetector 4 and the microcontroller 6 are arranged along the optical axis, and the microscope 5 is arranged in a direction perpendicular to the optical axis and aligned with the control module 3. The system uses the multimode interference coupler loss compensation method.

[0057] In this embodiment, the laser 1 is a tunable laser with a wavelength range of 1500nm-1600nm, which is used to generate initial laser.

[0058] The linear polarizer 2 is used to change the polarization angle of the initial laser light to generate the linear polarized light required for the experiment.

[0059] The microcontroller 6 is used to receive, adjust and output the linear polarized light required for the experiment to ensure that the laser is aligned with the multi-mode interference coupler in the control module 3 .

[0060] The control module 3 includes a multi-mode interference coupler and a temperature control platform. The multi-mode interference coupler is located on the temperature control platform. The multi-mode interference coupler is used for beam power equalization. The structure is as follows: Figure 3 As shown, the narrow waveguides on both sides are used to input and output optical signals, which are coupled with the multimode waveguide in the middle through the evanescent field. The wider part is used to support multiple propagation modes, and power distribution is achieved through the interference of these modes. The length of the multimode waveguide is a key parameter, which determines the interference effect between different modes. By adjusting the length, the splitting ratio and output characteristics of the coupler can be controlled. Evenly distributed electrodes are added to the multimode waveguide area in the middle; the temperature control platform is used to start under the drive of the control signal, heat the multimode interference coupler, and change the temperature of the multimode interference coupler.

[0061] The photodetector 4 is used to collect the transmittance and non-uniformity of the multi-mode interference coupler when the wavelength and voltage change.

[0062] The microscope 5 is used to magnify the multimode interference coupler to achieve naked eye resolution, facilitate optical fiber alignment, light adjustment and storage of device structure images.

[0063] In summary, the present invention provides a method for compensating loss of a multimode interference coupler. By acquiring data on the transmittance, non-uniformity and wavelength of light of the multimode interference coupler, the present invention realizes accurate quantification of the input light field characteristics of the multimode interference coupler, and provides a reliable data basis for its loss compensation. Based on experimental data, the effective refractive index of the multimode interference coupler mode is obtained, which overcomes the problem of large deviation between the traditional theoretical model and the actual device, and significantly improves the accuracy of mode analysis. According to the effective refractive index, the beat length between adjacent modes is determined, so that the beat length maintains a constant value during the wavelength tuning process, and the loss of a single multimode interference coupler does not change with the wavelength, which significantly reduces the cumulative loss of the silicon-based optical phased array splitting area, effectively expands the working bandwidth of the optical phased array, and greatly improves the longitudinal scanning range. By using the beat length to compensate for the loss of the multimode interference coupler, the insertion loss caused by energy transfer between modes is effectively suppressed, and the transmission efficiency and performance stability of the device are improved. Through the multi-parameter collaborative optimization combining experiments and theories, active compensation for the loss of the multimode interference coupler is realized, which solves the problem of insufficient accuracy of the traditional passive compensation method, and provides new ideas for the design and manufacture of high-performance integrated optical devices. A multimode interference coupler loss compensation system provided by the present invention achieves precise matching of the polarization state of the input light through the coordinated control of an integrated laser, a linear polarizer and a multimode interference coupler, greatly improves the excitation efficiency of the transverse electric mode, and effectively suppresses the mode competition loss; through the closed-loop feedback design of a temperature control platform and a microcontroller, a dynamic compensation algorithm based on real-time transmittance monitoring is developed, and stable control of insertion loss fluctuations is achieved; through the multi-parameter joint measurement of microscope imaging and photodetector, nanometer-level precision control of the output light field non-uniformity is achieved, and the power uniformity is greatly improved; through the coordinated control of the temperature control platform and the multimode interference coupler by the microcontroller, the technical limitations of traditional fixed temperature compensation are broken through.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

Claims

1. A loss compensation method for a multimode interference coupler, characterized in that: The method comprises the following steps: Obtain data on transmittance, non-uniformity and wavelength of light of multimode interference coupler; Based on the data, obtaining an effective refractive index of a mode of a multimode interference coupler; determining a beat length between adjacent modes according to the effective refractive index; The beat length is used to achieve loss compensation for the multimode interference coupler.

2. The loss compensation method of a multimode interference coupler according to claim 1, characterized in that: The method of obtaining the data of transmittance, non-uniformity and optical wavelength of the multimode interference coupler comprises: Acquiring data on the wavelength of experimental linear polarized light, wherein the polarization direction of the experimental linear polarized light is consistent with the polarization direction of the transverse electric mode in the multimode interference coupler; Based on the data, data on transmittance and non-uniformity of the multi-mode interference coupler are obtained.

3. The loss compensation method of a multimode interference coupler according to claim 1, characterized in that: The obtaining, based on the data, an effective refractive index of a multimode interference coupler mode comprises: Based on the data, changing the temperature of the multimode interference coupler; According to the temperature, effective refractive indices of transverse electric modes of different orders are obtained.

4. The loss compensation method of a multimode interference coupler according to claim 3, characterized in that: The obtaining of effective refractive indices of transverse electric modes of different orders according to the temperature comprises: According to the temperature, the propagation constants of transverse electric modes of different orders are obtained; According to the propagation constant, a transverse electric mode effective refractive index calculation model is established; The effective refractive indexes of transverse electric modes of different orders are obtained by using the transverse electric mode effective refractive index calculation model.

5. The loss compensation method of a multimode interference coupler according to claim 4, characterized in that: The transverse electric mode effective refractive index calculation model satisfies the following expression: in, for The effective refractive index of the order mode, For the The propagation constant of the order mode, is the wavelength.

6. The loss compensation method of a multimode interference coupler according to claim 1, characterized in that: Determining the beat length between adjacent modes according to the effective refractive index comprises: According to the effective refractive index, an effective refractive index difference of transverse electric modes of different orders is obtained, and the ratio of the effective refractive index difference to the wavelength of the experimental linear polarized light remains unchanged; The beat length between adjacent order transverse electric modes is determined according to the effective refractive index difference.

7. The loss compensation method of a multimode interference coupler according to claim 6, characterized in that: Determining the beat length between adjacent order transverse electric modes according to the effective refractive index difference comprises: According to the effective refractive index difference, a beat length calculation model between adjacent order transverse electric modes is established; The beat lengths between adjacent order transverse electric modes are determined by the beat length calculation model.

8. The loss compensation method of a multimode interference coupler according to claim 7, characterized in that: The beat length calculation model satisfies the following expression: in, is the beat length between adjacent order modes, For the The first mode and The effective refractive index difference of the order modes, is the wavelength, and Adjacent order.

9. The loss compensation method of a multimode interference coupler according to claim 1, characterized in that: The method of realizing loss compensation of the multimode interference coupler by using the beat length includes: A loss analysis model of a multimode interference coupler is established, and the loss analysis model satisfies the following expression: in, is the loss of the multimode interference coupler, is the transmittance of the multimode interference coupler, is the proportionality coefficient, is the non-uniformity of the multimode interference coupler, is the beat length mismatch sensitivity, is the beat length between adjacent order modes, The beat length designed for the device structure; Based on the loss analysis model, the beat length between adjacent modes is utilized to achieve loss compensation for the multimode interference coupler.

10. A loss compensation system for a multimode interference coupler, the system using a loss compensation method for a multimode interference coupler according to any one of claims 1 to 9, characterized in that: The system includes a multimode interference coupler, a laser, a linear polarizer, a temperature-controlled platform, a photodetector, a microscope and a microcontroller.

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