Seaborne photon uplink transmission simulation method based on non-uniform turbulence phase screen

Abstract

The invention discloses an offshore photon uplink transmission simulation method based on a non-uniform turbulence phase screen. The method comprises the following steps: determining initial coordinates and directions of photons and Stokes parameters of incident light; determining a scattering angle and an azimuth angle in a photon scattering event, and judging whether the photons are actually scattered or not according to a scattering phase function; a Stokes parameter after scattering is obtained; selecting a turbulence model and a selection method of subharmonic compensation times, determining a comprehensive power ratio, determining an optimal harmonic frequency by adopting a self-adaptive importance sampling method, generating turbulence phase screens according to a non-uniform distribution mode of the turbulence phase screens, and setting height positions of all the turbulence phase screens; according to the photon coordinates, the photon direction cosine and the random step size, whether the photons intersect with the phase screen or not and reach a receiver plane or not is judged; a determination is made as to whether photons are received by a receiver. According to the invention, the transmission process of polarized light in a marine atmospheric environment is more comprehensively simulated.

Description

Technical Field

[0001] The invention relates to a method for simulating uplink transmission of photons at sea based on a non-uniform turbulence phase screen, and belongs to the technical field of optical communications. Background Art

[0002] As the core link in building an integrated quantum communication network in the air, space, land and sea, the research and application of offshore quantum communication technology is gradually becoming a hot topic in the future communication field. However, the technical challenges faced by the realization of offshore quantum communication technology are also very complex, especially the various environmental factors during the photon transmission process, which has become a key problem restricting its development.

[0003] In the numerical simulation of light propagation, especially for the propagation of light in a path with random turbulence fluctuations, the change of the atmospheric structure function with height is an important factor that cannot be ignored. This change directly affects the distribution of turbulence intensity, so that in actual simulation, if a uniform interval setting is simply adopted, it will not accurately reflect the actual turbulence situation. Phase screens are key elements used in simulations to describe the impact of atmospheric turbulence on light wavefronts, and their position distribution has a direct impact on the authenticity of the simulation results. The correct phase screen setting should be able to reflect the true distribution of atmospheric turbulence with height to ensure the accuracy and reliability of the simulation results. However, in actual operation, how to accurately determine the position and number of phase screens, and how to dynamically adjust the parameters of the phase screen according to the changes in the atmospheric structure function, is still a challenging problem.

[0004] The spectral inversion method is one of the commonly used methods for simulating turbulent phase screens, especially the subharmonic method. The accuracy of generating phase screens using the subharmonic method is related to the harmonic order, and there is an optimal value for the harmonic order. At present, there is still a problem in how to accurately select the optimal harmonic order when generating turbulent phase screens. It is necessary to design a new method for selecting the optimal harmonic order to improve the accuracy of selecting the optimal harmonic order, so as to generate an accurate ocean atmosphere turbulent phase screen. In addition, the influence of the atmospheric environment on the transmitted optical signal is the combined effect of light absorption, scattering, and turbulence effects. The existing method is based on the generalized law of refraction to integrate the turbulence effect into the Monte Carlo simulation framework for simulating absorption and scattering for modeling research. However, this method does not fully consider the change of turbulence intensity with height, and they often use uniform interval settings, which cannot accurately reflect the real turbulence conditions. Summary of the invention

[0005] In order to overcome the above problems existing in the prior art, the present invention proposes a method for simulating uplink transmission of photons at sea based on a non-uniform turbulence phase screen.

[0006] The technical solution adopted by the present invention to solve the technical problem is: a method for simulating uplink transmission of photons at sea based on a non-uniform turbulence phase screen, comprising the following steps: Step 1, establish a spatial rectangular coordinate system, assume that the light source is located at the origin of the spatial rectangular coordinate system, the zenith direction is the positive direction of the z-axis, set the simulation parameters, and determine the system initialization; Step 2: Determine the scattering angle θ and azimuth angle of the photon scattering event based on the Monte Carlo simulation method of random sampling and scattering phase function. , update the Stokes parameters; Step 3, select the turbulence model and the selection method of the subharmonic compensation order, determine the comprehensive power ratio, use the adaptive importance sampling method to determine the optimal harmonic order, generate the turbulence phase screen according to the non-uniform distribution pattern of the turbulence phase screen, and set the height position of all turbulence phase screens; Step 4, calculate the random step length of the photon; Step 5, according to the photon coordinates, the photon direction cosines and the random step length, calculate the new position of the photon after one movement, and determine whether the photon intersects the phase screen, reaches the receiver plane, and is received by the receiver according to the new position; Step 6: If the photon intersects with the phase screen, the coordinates of the intersection of the photon and the phase screen are calculated, and the photon coordinates, direction, Stokes vector and photon weight are updated; if the photon does not intersect with the phase screen, it is determined whether the photon reaches the receiver plane, if not, the coordinates, direction, weight and Stokes vector of the photon after the collision are updated; Step 7, judge the size of the photon weight and the predetermined threshold. If yes, calculate the coordinate position and direction of the current photon on the receiver plane to determine whether the photon is received by the receiver. If yes, record the coordinate position, Stokes vector and weight information of the photon; if not, do not record and the tracking is terminated; Step 8, loop through steps 4 to 7 until the photon is received by the receiver.

[0007] The above-mentioned method for simulating the uplink transmission of photons at sea based on the non-uniform turbulence phase screen, the step 1 specifically comprises: determining the initial position coordinates of the photons , initial direction , polarization state weight and the initial Stokes vector parameters of the incident photon Determine the polarization state, where is the total intensity of the incident wave, is the phase difference between the x and y directions of the incident wave; ± 45° linear polarized light component; Indicates the proportion of circular polarization in polarized light.

[0008] The above-mentioned method for simulating the uplink transmission of photons at sea based on the non-uniform turbulence phase screen, the step 2 specifically comprises: obtaining the scattering phase function according to the scattering angle and azimuth angle generated by random sampling , generating a A pseudo-random number uniformly distributed between , if satisfied , it is considered that the photon is scattered and the random angle generated is the scattering angle and azimuth of this scattering, and a new transmission direction is generated to continue transmission, and the new photon vector, go to step 3, otherwise reselect.

[0009] The scattering phase function is: ; The photon scattering angle for A random number between for A random number between , is the Mie scattering matrix The elements of the Mie scattering matrix for: ; New directions for photon transmission for: If the direction of motion of the photon deviates from the z-axis, the updated transmission direction of the photon is: ; When the direction of motion of the photon approaches the z-axis, the transmission direction of the photon is updated to: ; In the above-mentioned method for simulating the uplink transmission of photons at sea based on the non-uniform turbulence phase screen, the step 3 specifically comprises: Step 3.1, select the ocean-atmosphere turbulence power spectrum , which has the following form: ; in, is the spatial wave number, and Divided into internal and external scales of turbulence, represents the outer scale wave number parameter, represents the inner scale wave number parameter, is the atmospheric refractive index structure constant, i.e., the optical turbulence intensity profile; Step 3.2, select the marine atmospheric environment Function distribution model; Step 3.3, use the turbulent refractive index spectrum and the complex Gaussian random number matrix to generate the complex random field in the phase space, and perform inverse Fourier transform to obtain the spatial distribution of the two-dimensional phase : ; in, , and represent the discrete spatial frequencies in the x and y directions respectively, , and represent the grid size in the x and y directions respectively; Then represents a complex random matrix with Gaussian random distribution and mean zero; is the interval of the phase screen on the z-axis; Step 3.4, use the low frequency harmonic compensation method to correct the phase screen Perform low frequency compensation to generate a new phase screen , the expression is: ; in, is the phase screen low-frequency compensation term, p is the subharmonic order, is the harmonic order, and the subharmonic frequency interval ; Step 3.5, the selection method of subharmonic compensation order, uses the adaptive importance sampling method to calculate the preliminary optimal harmonic order N p—origin ; Step 3.6: Repeat steps 3.1 to 3.5 to generate all phase screens.

[0010] In the above-mentioned method for simulating the uplink transmission of photons at sea based on the non-uniform turbulence phase screen, the step 3.5 is specifically as follows: A. Select the comprehensive power ratio, the value range is [0,1]; B. Determine the outer scale of atmospheric turbulence L0(h), which satisfies the following formula: ;

[0011] in, is the reference height The outer scale of turbulence at is an empirical parameter; C. The initial importance function satisfies: ;

[0012] is the ocean-atmosphere turbulence power spectrum, and D is the phase screen size.

[0013] D. Generate initial wave number samples , the initial wave number samples are from the lower bound and upper bound The probability density function of the uniform distribution is The definition is as follows: ; E. Calculate the cumulative power spectrum : ; in, is the wave number sample The weight of , N is the total number of wave number samples generated; F. Normalize the weights: ; G. Record the initial optimal harmonic order , that is, the first satisfaction The wave number position of is the target value of comprehensive power ratio (set according to actual needs); H. Repeat D~G and use Gaussian kernel density estimation method to update the importance function , until its variance is less than the specified tolerance or the maximum number of iterations is reached; I. According to actual needs Round off to get the final optimal harmonic order: When the accuracy of the phase screen is required to be high, choose to round up: = ;

[0014] When the running speed requirement is high, choose to round down: = .

[0015] In the above-mentioned method for simulating the uplink transmission of photons at sea based on the non-uniform turbulence phase screen, the step 4 specifically comprises: Step 4.1, according to the marine atmospheric environment Function distribution model, for the height range with strong turbulence and large rate of change, the equal Rytov index interval phase screen distribution method is selected to set the phase screen position, that is, the Rytov index between phase screens is set to a constant a, and the frequency interval of adjacent phase screens is set to The calculation method is: ;

[0016] Further obtain the position of the i-th phase screen : ;

[0017] is the position of the i-1th phase screen; Step 4.2: For areas with weak turbulence intensity and relatively slow rate of change, select the uniformly spaced phase screen distribution method to set the phase screen position, that is, the phase screen spacing satisfies: ,in is the height range where the turbulence intensity changes relatively slowly. The total number of phase screens set for this area; Step 4.3, repeat steps 4.1 to 4.2 to obtain the locations of all atmospheric turbulence phase screens.

[0018] In the above-mentioned simulation method for uplink transmission of photons at sea based on non-uniform turbulence phase screen, the specific calculation formula for the new position of the photon after one movement in step 5 is as follows: ; ; in is the new position of the photon after it moves, is the position of the photon before it moves, is the angular cosine in the propagation direction z; L is the random free step length of the photon; For is a pseudo-random number uniformly distributed between , and (aa+bb) is the atmospheric attenuation coefficient.

[0019] In the above-mentioned method for simulating the uplink transmission of photons at sea based on the non-uniform turbulence phase screen, the step 6 specifically comprises: If the photon intersects the phase screen and does not reach the receiver plane, then Calculate the coordinates of the photon's intersection with the phase screen for: ; in, and are the coordinates and directions before passing through the photon phase screen, is the position of the phase screen in the z-axis direction; When a photon passes through a phase screen, its transmission direction changes. It is expressed as: ; In the formula, is the light wave number; After a photon passes through the phase screen, the photon coordinates before the next scattering occurs It is expressed as: ; Update the direction of the photon : If the direction of motion of the photon deviates from the z-axis, the updated transmission direction of the photon is: ; If the direction of motion of the photon is close to the z-axis, the updated transmission direction of the photon is: ; Update Photon New The vector is: ; In the formula and are the scattering angle and azimuth of the nth scattering of the photon, respectively, and the rotation matrix for: ; Update photon coordinates : .

[0020] In the above-mentioned method for simulating the uplink transmission of photons at sea based on the non-uniform turbulence phase screen, the step 7 is specifically as follows: determining whether the transmission is terminated, generating a A pseudo-random number uniformly distributed between ,like If the value is less than or equal to the weight, the photon continues to transmit until it is received, confirms and records the received photon parameters and saves the data, including: the number of scattering times, the total number of received photons, the number of received scattered photons, and the polarization state of the photon; otherwise, the photon transmission is terminated and the next photon is emitted; the photon weight Updated as follows: ; In the formula, is the photon weight before updating.

[0021] The beneficial effects of the present invention are: 1. The present invention can simultaneously consider the absorption, scattering and turbulence effects in the marine atmospheric environment, select the marine atmospheric turbulence power spectrum model, atmospheric absorption and scattering model, and propose the use of power spectrum inversion method and vector Monte Carlo method to jointly construct a simulation model for photon transmission in the marine atmospheric environment, which can realize the simultaneous study of the influence of atmospheric turbulence and attenuation effects on light transmission characteristics.

[0022] 2. The present invention proposes to improve the accuracy of power ratio calculation based on the ocean-atmospheric turbulence power spectrum model, taking into account the relationship between the outer scale of turbulence and height, and combining the adaptive importance sampling method to dynamically adjust and optimize, thereby affecting the accuracy of the selection of the optimal harmonic order. At the same time, according to the requirements for phase screen accuracy and operating speed, a suitable rounding method is selected to ensure that the calculation results are optimized while meeting the requirements.

[0023] 3. Based on the selection of appropriate turbulence power spectrum model and photon absorption and scattering model, the present invention integrates the mixed distribution pattern of multi-layer turbulence phase screen, and appropriately designs mathematical models for the interaction of polarized light with atmospheric aerosol particles and multi-layer turbulence phase screen, thereby proposing a simulation method suitable for synchronously studying the light spot information and polarization state change characteristics on the vertical transmission path of atmospheric polarized light. This method can flexibly adapt to different application scenarios and provide a more accurate and efficient simulation method for the study of marine atmospheric turbulence effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0025] Figure 1 It is a schematic diagram of the principle of the present invention; Figure 2 The present invention is an overall flow chart; Figure 3 Specific distribution of the turbulent phase screen in the z-axis direction in the embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0027] See also Figure 1 As shown, the present invention is based on a method for simulating uplink transmission of photons at sea based on a non-uniform turbulence phase screen, comprising the following steps: Step 1, the simulation system is initialized; the light source is assumed to be located at the origin of the spatial rectangular coordinate system, the zenith direction is the positive direction of the z-axis, the light transmission distance S is 500m~100km, and the atmospheric window wavelength is selected to simulate the vertical transmission channel of the laser atmosphere; the photon number N0 is 10 3 ~10 8 , determine the initial position coordinates of the photon , initial direction , the phase screen distribution mode in the Z-axis direction is a non-uniform distribution mode, Figure 3 In the embodiment, the height of the transmitting end from the sea level is 0 km, and the optical transmission distance S=50 km, the zenith angle is , the specific distribution of turbulent phase screens in the z-axis direction. In the figure, the first section is from the near sea surface to the quadrilateral mark point. This section uses equal Rytov index intervals to distribute the phase screens in this interval, and 6 phase screens are distributed; then, the pentagonal mark point and the hexagonal mark point divide the remaining interval into three sections, and the three sections are independently and evenly spaced to distribute phase screens. The number of phase screens distributed is 6, 4 and 15, that is, 31 phase screens are used to equivalent the atmospheric turbulence in the altitude of 0 km~50 km. The size of the phase screen is 0.5~3 m× 0.5~3 m; the azimuth is the angle between the projection of the photon scattering direction on the XOY plane and the positive half axis of the X axis; the scattering angle θ is the angle between the photon propagation direction and the positive half axis of the X axis; the atmospheric attenuation coefficient c is set to 0.5 m -1 , the atmospheric scattering coefficient is bb = 0.26 m -1 , the atmospheric absorption coefficient is aa=0.24 m -1 , the initial weight of the photon is W0=1.

[0028] Step 2: Determine the scattering angle θ and azimuth angle of the photon scattering event based on the Monte Carlo simulation method of random sampling and scattering phase function. First, the scattering angle and azimuth are generated by random sampling to obtain the scattering phase function , generating a A pseudo-random number uniformly distributed between , if satisfied , it is considered that the photon is scattered and the random angle generated is the scattering angle and azimuth of this scattering, and a new transmission direction is generated to continue transmission, and the new photon vector; otherwise reselect.

[0029] The photon scattering phase function is as follows: ; in, , , is the component of the incident photon state, and the Stokes vector of the incident wave is expressed as ; Photon scattering angle for The random number of photon scattering angle; photon azimuth for A random number between , is the Mie scattering matrix The elements of ; parameter , , , The scattering amplitude and get: ; in, and The size of is related to the photon radius and the photon complex refractive index.

[0030] New directions for photon transmission as follows: If the direction of motion of the photon deviates from the z-axis, the updated transmission direction of the photon is: ; When the direction of motion of the photon approaches the z-axis, the transmission direction of the photon is updated to: ; Update the Stokes parameters and scattering angles: ; Among them, and are the nth scattering angle and azimuth of the photon, respectively, and the rotation matrix for: .

[0031] Step 3, generate the ocean-atmosphere turbulence phase screen; the method is as follows: Step 3.1, select the ocean-atmosphere turbulence power spectrum , which has the following form: ; In the formula is the spatial wave number, and Divided into internal and external scales of turbulence, represents the outer scale wave number parameter, represents the inner scale wave number parameter, is the atmospheric refractive index structure constant, i.e., the optical turbulence intensity profile. In this example, the The function distribution model satisfies: ; in is the height from sea level.

[0032] Step 3.2: Use the turbulent refractive index spectrum and the complex Gaussian random number matrix to generate the complex random field in the phase space, and then perform an inverse Fourier transform to obtain the spatial distribution of the two-dimensional phase. : ; In the formula, and represent the discrete spatial frequencies in the x and y directions respectively, ,in and represent the grid size in the x and y directions respectively; Then represents a complex random matrix with Gaussian random distribution and mean zero; is the spacing of the phase screen on the z-axis.

[0033] Step 3.4, use the low frequency harmonic compensation method to correct the phase screen Perform low frequency compensation to generate a new phase screen , the expression is: ; In the formula, is the phase screen low-frequency compensation term, p is the subharmonic order, is the harmonic order, and the subharmonic frequency interval .

[0034] Step 3.5, the selection method of subharmonic compensation order, uses the adaptive importance sampling method to calculate the preliminary optimal harmonic order N p—origin The steps are as follows: A. Select the comprehensive power ratio, the value range is [0,1], B. Determine the outer scale of atmospheric turbulence L0(h), which satisfies the following formula: ; in, is the reference height The outer scale of turbulence at It is an empirical parameter. For the marine atmosphere environment, 𝛽 is usually between 0.12 and 0.15, but it can increase to between 0.15 and 0.20 under unstable conditions.

[0035] C. Assume that the initial importance function satisfies: ; is the ocean-atmosphere turbulence power spectrum, and D is the phase screen size.

[0036] D. Generate initial wave number samples , the initial wave number samples are from the lower bound and upper bound The probability density function of the uniform distribution is The definition is as follows: ; E. Calculate the cumulative power spectrum : ; in, is the wave number sample The weight of , N is the total number of wave number samples generated.

[0037] F. Normalize the weights: .

[0038] G. Record the initial optimal harmonic order , that is, the first satisfaction The wave number position of The target value of the comprehensive power ratio (set according to actual needs) 。

[0039] H. Repeat D~G and use Gaussian kernel density estimation method to update the importance function , until its variance is less than the specified variance tolerance or the maximum number of iterations is reached.

[0040] I. According to actual needs Round off to get the final optimal harmonic order : When the accuracy of the phase screen is required to be high, choose to round up: = .

[0041] When the running speed requirement is high, choose to round down: = .

[0042] Step 3.6: Repeat steps 3.1 to 3.5 to generate all phase screens.

[0043] Step 4, in the numerical simulation of light propagation in the non-uniform turbulent path, a phase screen distribution mode is set, and the specific implementation method is as follows: Step 4.1, according to the marine atmospheric environment Function distribution model, for the height range with strong turbulence and large change speed, the equal Rytov index interval phase screen distribution method is selected to set the phase screen position, that is, the Rytov index between phase screens is set to a constant a, and the frequency interval of adjacent phase screens is set to The calculation method is: ;

[0044] Further obtain the position of the i-th phase screen : ; is the position of the i-1th phase screen.

[0045] Step 4.2: For areas with weak turbulence intensity and relatively slow change speed, select the uniformly spaced phase screen distribution method to set the phase screen position, that is, the phase screen spacing satisfies: ,in is the height range where the turbulence intensity changes relatively slowly. The total number of phase screens set for this region.

[0046] Step 4.3, repeat steps 4.1 to 4.2 to obtain the locations of all atmospheric turbulence phase screens.

[0047] Step 5, the calculation method of the random free step length of the generated photon is as follows: ; For A pseudo-random number uniformly distributed between , (aa+bb) is the atmospheric attenuation coefficient.

[0048] Furthermore, the new position of the photon after one movement is as follows: ; in is the new position of the photon after it moves, is the position of the photon before it moves, is the cosine of the angle in the propagation direction z.

[0049] Step 6, according to the photon coordinates , photon direction cosines With the random step size L, it is determined whether the photon intersects the phase screen, reaches the receiver plane and is within the aperture and field of view of the detector; Step 6.1: If the photon does not intersect the phase screen and does not reach the receiver plane, it is considered that the photon can continue to transmit and the following steps are performed: Determine the scattering angle of a photon scattering event using a Monte Carlo simulation method based on random sampling and scattering phase function and azimuth , and judge whether the photon is actually scattered based on the scattering phase function; obtain the Stokes vector after scattering: The scattering angle and azimuth angle are generated by random sampling to obtain the scattering phase function : ; in, , , is the component of the incident photon state, and the Stokes vector of the incident wave is expressed as ; Photon scattering angle for The random number of photon scattering angle; photon azimuth for A random number between , is the Mie scattering matrix The elements are: ; parameter , , , The scattering amplitude and get: ; in, and The size of is related to the photon radius and the photon complex refractive index.

[0050] Generate a A pseudo-random number uniformly distributed between , if satisfied , it is considered that the photon is scattered and the random angle generated is the scattering angle and azimuth of this scattering, and a new transmission direction is generated to continue transmission, and the new photon vector; otherwise, transmission continues in the original direction.

[0051] New directions for photon transmission as follows: If the direction of motion of the photon deviates from the z-axis, the updated transmission direction of the photon is: ; When the direction of motion of the photon approaches the z-axis, the transmission direction of the photon is updated to: ; Update Photon New The vector is: ; In the formula and are the nth scattering angle and azimuth of the photon, respectively, and the rotation matrix for: .

[0052] Step 7: If the photon intersects the phase screen and does not reach the receiver plane, then Step 7.1, calculate the coordinates of the intersection of the photon and the phase screen for: ; in, and are the coordinates and directions before passing through the photon phase screen, is the position of the phase screen in the z-axis direction; Step 7.2: When a photon passes through the phase screen, its transmission direction changes. According to the generalized Snell's law, the new direction of the photon is It is expressed as: ; In the formula, is the light wave number.

[0053] Step 7.3, after the photon passes through the phase screen, the photon coordinates before the next scattering occurs It is expressed as: .

[0054] Step 7.4, update the direction of the photon : If the direction of motion of the photon deviates from the z-axis, the updated transmission direction of the photon is: ; If the direction of motion of the photon is close to the z-axis, the updated transmission direction of the photon is: .

[0055] Step 7.5, Update Photon to new The vector is: ; In the formula and are the scattering angle and azimuth of the nth scattering of the photon, respectively, and the rotation matrix for: .

[0056] Step 7.6, Photon Weights Updated as follows: ; In the formula, is the photon weight before updating.

[0057] Step 8: Determine whether the transmission is terminated, as follows: Generate a A pseudo-random number uniformly distributed between ,like If it is less than or equal to the weight, the above process steps 5 to 7 are executed repeatedly until the photon is received, and the received photon parameters are confirmed and recorded and the data is saved, including: the number of scattering times, the total number of received photons, and the polarization state of the photons; otherwise, the photon tracking stops and the next photon is emitted.

[0058] The above embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art may make various modifications or equivalent substitutions to the present invention within the essence and protection scope of the present invention, and such modifications or equivalent substitutions shall also be deemed to fall within the protection scope of the present invention.

Claims

1. A simulation method for uplink photon transmission at sea based on non-uniform turbulence phase screen, characterized in that: The steps include: Step 1, establish a spatial rectangular coordinate system, assume that the light source is located at the origin of the spatial rectangular coordinate system, the zenith direction is the positive direction of the z-axis, set the simulation parameters, and determine the system initialization; Step 2: Determine the scattering angle θ and azimuth angle of the photon scattering event based on the Monte Carlo simulation method of random sampling and scattering phase function. , update the Stokes parameters; Step 3, select the turbulence model and the selection method of the subharmonic compensation order, determine the comprehensive power ratio, use the adaptive importance sampling method to determine the optimal harmonic order, generate the turbulence phase screen according to the non-uniform distribution pattern of the turbulence phase screen, and set the height position of all turbulence phase screens; Step 4, calculate the random step length of the photon; Step 5, according to the photon coordinates, the photon direction cosines and the random step length, calculate the new position of the photon after one movement, and determine whether the photon intersects the phase screen, reaches the receiver plane, and is received by the receiver according to the new position; Step 6: If the photon intersects with the phase screen, the coordinates of the intersection of the photon and the phase screen are calculated, and the photon coordinates, direction, Stokes vector and photon weight are updated; if the photon does not intersect with the phase screen, it is determined whether the photon reaches the receiver plane, if not, the coordinates, direction, weight and Stokes vector of the photon after the collision are updated; Step 7, judge the size of the photon weight and the predetermined threshold. If yes, calculate the coordinate position and direction of the current photon on the receiver plane to determine whether the photon is received by the receiver. If yes, record the coordinate position, Stokes vector and weight information of the photon; if not, do not record and the tracking is terminated; Step 8, loop through steps 4 to 7 until the photon is received by the receiver.

2. The method for simulating uplink transmission of photons at sea based on a non-uniform turbulence phase screen according to claim 1 is characterized in that: The step 1 specifically includes: determining the initial position coordinates of the photon , initial direction , polarization state weight and the initial Stokes vector parameters of the incident photon Determine the polarization state, where is the total intensity of the incident wave, is the phase difference between the light intensity in the x and y directions of the incident wave; It is ±45° linear polarized light component; Indicates the proportion of circular polarization in polarized light.

3. The method for simulating uplink transmission of photons at sea based on non-uniform turbulence phase screen according to claim 1 is characterized in that: The step 2 specifically includes: generating a scattering angle and an azimuth angle according to random sampling to obtain a scattering phase function , generating a A pseudo-random number uniformly distributed between , if satisfied , it is considered that the photon is scattered and the random angle generated is the scattering angle and azimuth of this scattering, and a new transmission direction is generated to continue transmission, and the new photon vector, go to step 3, otherwise reselect; The scattering phase function is: ; The photon scattering angle for A random number between for A random number between , is the Mie scattering matrix The elements of the Mie scattering matrix for: ； New directions for photon transmission for: If the direction of motion of the photon deviates from the z-axis, the updated transmission direction of the photon is: ; When the direction of motion of the photon approaches the z-axis, the transmission direction of the photon is updated to: 。 4. The method for simulating uplink transmission of photons at sea based on non-uniform turbulence phase screen according to claim 1 is characterized in that: The step 3 specifically includes: Step 3.1, select the ocean-atmosphere turbulence power spectrum , which has the following form: ; in, is the spatial wave number, and Divided into internal and external scales of turbulence, represents the outer scale wave number parameter, represents the inner scale wave number parameter, is the atmospheric refractive index structure constant, i.e., the optical turbulence intensity profile; Step 3.2, select the ocean atmosphere environment Function distribution model; Step 3.3, use the turbulent refractive index spectrum and the complex Gaussian random number matrix to generate the complex random field in the phase space, and perform inverse Fourier transform to obtain the spatial distribution of the two-dimensional phase : ; in, , and represent the discrete spatial frequencies in the x and y directions respectively, , and represent the grid size in the x and y directions respectively; Then represents a complex random matrix with Gaussian random distribution and mean zero; is the interval of the phase screen on the z-axis; Step 3.4, use the low frequency harmonic compensation method to correct the phase screen Perform low frequency compensation to generate a new phase screen , the expression is: ; in, is the phase screen low-frequency compensation term, p is the subharmonic order, is the harmonic order, and the subharmonic frequency interval ; Step 3.5, the selection method of subharmonic compensation order, uses the adaptive importance sampling method to calculate the preliminary optimal harmonic order N p—origin ; Step 3.6: Repeat steps 3.1 to 3.5 to generate all phase screens.

5. The method for simulating uplink transmission of photons at sea based on non-uniform turbulence phase screen according to claim 4 is characterized in that: The step 3.5 is specifically as follows: A. Select the comprehensive power ratio, the value range is [0,1]; B. Determine the outer scale of atmospheric turbulence L0(h), which satisfies the following formula: ; in, is the reference height The outer scale of turbulence at is an empirical parameter; C. The initial importance function satisfies: ; is the ocean-atmosphere turbulence power spectrum, and D is the phase screen size; D. Generate initial wave number samples , the initial wave number samples are from the lower bound and upper bound The probability density function of the uniform distribution is The definition is as follows: ； E. Calculate the cumulative power spectrum : ; in, is the wave number sample The weight of , N is the total number of wave number samples generated; F. Normalize the weights: ； G. Record the initial optimal harmonic order , that is, the first satisfaction The wave number position of is the target value of comprehensive power ratio (set according to actual needs); H. Repeat D~G and use Gaussian kernel density estimation method to update the importance function , until its variance is less than the specified tolerance or the maximum number of iterations is reached; I. According to actual needs Round off to get the final optimal harmonic order: When the accuracy of the phase screen is required to be high, choose to round up: = ; When the running speed requirement is high, choose to round down: = 。 6. The method for simulating uplink transmission of photons at sea based on a non-uniform turbulence phase screen according to claim 1 is characterized in that: The step 4 specifically includes: Step 4.1, according to the marine atmospheric environment Function distribution model, for the height range with strong turbulence and large rate of change, the equal Rytov index interval phase screen distribution method is selected to set the phase screen position, that is, the Rytov index between phase screens is set to a constant a, and the frequency interval of adjacent phase screens is set to The calculation method is: ; Further obtain the position of the i-th phase screen : ; is the position of the i-1th phase screen; Step 4.2: For areas with weak turbulence intensity and relatively slow rate of change, select the uniformly spaced phase screen distribution method to set the phase screen position, that is, the phase screen spacing satisfies: ,in is the height range where the turbulence intensity changes relatively slowly. The total number of phase screens set for this area; Step 4.3, repeat steps 4.1 to 4.2 to obtain the locations of all atmospheric turbulence phase screens.

7. The method for simulating uplink transmission of photons at sea based on non-uniform turbulence phase screen according to claim 1 is characterized in that: The specific calculation formula for the new position of the photon after one movement in step 5 is as follows: ; ; in is the new position of the photon after it moves, is the position of the photon before it moves, is the angular cosine in the propagation direction z; L is the random free step length of the photon; For is a pseudo-random number uniformly distributed between , and (aa+bb) is the atmospheric attenuation coefficient.

8. The method for simulating uplink transmission of photons at sea based on non-uniform turbulence phase screen according to claim 1 is characterized in that: The step 6 specifically includes: If the photon intersects the phase screen and does not reach the receiver plane, then Calculate the coordinates of the photon's intersection with the phase screen for: ; in, and are the coordinates and directions before passing through the photon phase screen, is the position of the phase screen in the z-axis direction; When a photon passes through a phase screen, its transmission direction changes. It is expressed as: ; In the formula, is the light wave number; After a photon passes through the phase screen, the photon coordinates before the next scattering occurs It is expressed as: ; Update the direction of the photon : If the direction of motion of the photon deviates from the z-axis, the updated transmission direction of the photon is: ; If the direction of motion of the photon is close to the z-axis, the updated transmission direction of the photon is: ; Update Photon New The vector is: ; In the formula and are the scattering angle and azimuth of the nth scattering of the photon, respectively, and the rotation matrix for: ; Update photon coordinates : 。 9. The method for simulating uplink transmission of photons at sea based on a non-uniform turbulence phase screen according to claim 1, characterized in that: The step 7 is specifically as follows: determining whether the transmission is terminated, generating a A pseudo-random number uniformly distributed between ,like If the value is less than or equal to the weight, the photon continues to transmit until it is received, confirms and records the received photon parameters and saves the data, including: the number of scattering times, the total number of received photons, the number of received scattered photons, and the polarization state of the photon; otherwise, the photon transmission is terminated and the next photon is emitted; the photon weight Updated as follows: ; In the formula, is the photon weight before updating.

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