Detector receiving aperture simulation method based on underwater coherent detection technology

Abstract

The invention discloses a detector receiving aperture simulation method based on an underwater coherent detection technology. The method comprises the following steps that the cross spectrum density of signal light reaching a receiving end after passing through an ocean turbulence transmission distance z is calculated; calculating the intermediate frequency signal power of the signal light of the receiving end by using the cross spectrum density of the signal light of the receiving end obtained in the step 1; calculating the optical power of the signal light and the optical power of the local oscillation light at the source field; heterodyne efficiency in the ocean turbulence environment is calculated; and performing numerical simulation on the obtained heterodyne efficiency closed solution through matlab software to obtain the aperture size of the receiving end detector capable of inhibiting the ocean turbulence. According to the method, numerical simulation is carried out on the obtained heterodyne efficiency closed solution, and the appropriate detector aperture capable of effectively inhibiting the ocean turbulence effect is obtained, so that the sensitivity and the signal-to-noise ratio of the detector are improved to the maximum extent.

Description

Technical Field

[0001] The invention belongs to the technical field of underwater wireless optical communication and relates to a detector receiving aperture simulation method based on underwater coherent detection technology. Background Art

[0002] About 70% of the earth's surface is covered by the ocean. In recent years, the strategic position of the ocean in the fields of environment, economy, politics, and military has attracted much attention from all countries. Underwater wireless optical communication technology mainly includes underwater acoustic communication, underwater radio frequency communication, and underwater wireless optical communication. Compared with acoustic wave communication and radio frequency communication, underwater wireless optical communication has many significant advantages such as large communication bandwidth, high transmission rate, low delay, and strong confidentiality. It has become a very promising communication method in the marine environment. Complex underwater channels have brought severe challenges to underwater wireless optical communication. The absorption and scattering of light by particles, microorganisms, and water itself in the ocean turbulence greatly reduces the laser range and imaging contrast. Assuming that only the influence of the ocean turbulence effect on the beam transmission characteristics is considered in the marine environment, random drift, beam expansion, and light intensity flickering will occur after the light wave reaches the receiving end. The ocean turbulence effect greatly reduces the coherence of the laser, making it impossible to capture useful signals using conventional detection methods at the receiving end. In order to realize the detection of weak signal light, coherent detection can be used at the receiving end to extend the communication distance and maximize the sensitivity and signal-to-noise ratio of the detector. However, in the process of using coherent detection to extend the communication distance, it was found that in a certain intensity of ocean turbulence environment, the aperture size of the receiving detector has a crucial influence on improving the sensitivity and signal-to-noise ratio of the receiving detector, which will directly affect the final detection performance of underwater signals.

[0003] Based on this, the present application proposes a detector receiving aperture simulation method based on underwater coherent detection technology. Summary of the invention

[0004] The purpose of the present invention is to provide a detector receiving aperture simulation method based on underwater coherent detection technology. The detector aperture range of the receiving end is obtained through simulation. By setting the detector aperture, the receiver sensitivity and signal-to-noise ratio can be maximized to achieve detection of weak signal light.

[0005] The technical solution adopted by the present invention is a detector receiving aperture simulation method based on underwater coherent detection technology, and the specific steps are as follows:

[0006] Step 1, calculate the cross spectral density of the signal light after it reaches the receiving end after being transmitted through the ocean turbulence for a distance z;

[0007] Step 2: Calculate the intermediate frequency signal power of the receiving end signal light using the cross spectral density of the receiving end signal light obtained in step 1;

[0008] Step 3, calculating the optical power of the signal light and the optical power of the local oscillator light at the source field;

[0009] Step 4, combining the cross spectral density of the signal light at the receiving end obtained in step 2 and the optical power of the signal light and the local oscillator light at the source field calculated in step 3, calculating the heterodyne efficiency in the ocean turbulent environment;

[0010] Step 5: Use MATLAB software to perform numerical simulation on the closed-form solution of heterodyne efficiency and obtain the aperture size of the receiving detector that can suppress ocean turbulence.

[0011] The present invention is also characterized in that:

[0012] The calculation formula of the cross spectral density of the signal light at the receiving end is as follows:

[0013]

[0014] Among them, Γ α (ρ1, ρ2, z) is the cross spectral density of the signal light at the receiving end, r1 and r2 represent a pair of position vectors of the Gauss-Schnell beam at the source plane, ρ1 and ρ2 represent the position coordinates of the Gauss-Schnell beam arriving at the receiving plane after passing through the ocean turbulence, λ represents the wavelength of the signal light, z represents the transmission distance of the signal light, k represents the wave number, k = 2π / λ, i represents an imaginary number, The conjugate complex number representing the random phase factor of the effect of ocean turbulence on spherical waves, Random phase factor representing the effect of ocean turbulence on spherical waves, disturbance caused by ocean turbulence<exp[ψ*(ρ1,r1,z)+ψ(ρ2,r2,z)]> ≈exp[-D ψ (ρ1-ρ2, r1-r2) / 2], where D ψ (ρ1-ρ2, r1-r2) is the wave structure function, and:

[0015] D ψ (ρ1-ρ2,r1-r2)=M[(ρ1-ρ2) 2 +(ρ1-ρ2)(r1-r2)+(r1-r2) 2 ] (2)

[0016] Where M represents the ocean turbulence parameter, and the calculation formula is as follows:

[0017]

[0018] Among them, Φ n (κ) uses the Nikishov ocean turbulence refractive index power spectrum, z represents the signal light transmission distance, k represents the wave number, k = 2π / λ, and κ represents the spatial wave number;

[0019] Ocean turbulence refractive index spectrum model Φn (κ) uses the Nikishov ocean turbulence refractive index power spectrum and is expressed as:

[0020]

[0021] where ε is the turbulent kinetic energy dissipation rate, l0 is the inner scale of the ocean turbulence, and χ T is the mean square temperature dissipation rate, e represents the exponent, A T =1.863×10 -2 , A S =1.9×10 -4 , A TS =9.41×10 -3 , ω represents the relative intensity of temperature and salinity changes, with a value of -5 to 0, and δ can be expressed as:

[0022]

[0023] Among them, l0 is the internal scale of ocean turbulence, and m is the spatial wave number;

[0024] Substituting equations (2), (3) and (4) into equation (1), it can be simplified to:

[0025]

[0026] Wherein, the subscript α=L represents the local oscillator light or S represents the signal light; σ α is the beam waist radius of the signal light or the local oscillator light; δα is the transverse coherence length of the signal light or the local oscillator light at z = 0 at the source field;

[0027] make p=ρ1-ρ2,q=ρ1+ρ2,the formula (6) is simplified as follows:

[0028]

[0029] Among them, r c is the average of r1 and r2, r d is the difference between r1 and r2, p is the difference between ρ1 and ρ2, q is the sum of ρ1 and ρ2, subscript α=L represents the local oscillator light or S represents the signal light; σ α is the beam waist radius of the signal light or the local oscillator light; δα is the transverse coherence length of the signal light or the local oscillator light at z = 0 at the source field;

[0030] Use the following formula (8) to calculate r c and r d Integrating, we get formulas (9) and (10):

[0031]

[0032] Among them, a, b, c, e, h, and R represent 6 arbitrary values;

[0033]

[0034] Among them, A α , B α It can be expressed as:

[0035]

[0036] Substituting equations (9) and (10) into equation (7) and simplifying it, we obtain the following equation (12):

[0037]

[0038] Among them, Cα, Dα, Eα It can be expressed as:

[0039]

[0040] In the above formulas (9)-(13), σ α is the beam waist radius of the signal light or the local oscillator light; δα is the transverse coherence length of the signal light or the local oscillator light at z = 0 at the source field, r c is the average of r1 and r2, r d is the difference between r1 and r2, p is the difference between ρ1 and ρ2, q is the sum of ρ1 and ρ2, z represents the signal light transmission distance, k represents the wave number, k = 2π / λ, i represents an imaginary number, and M represents the ocean turbulence parameter.

[0041] The calculation process of the intermediate frequency signal power in step 2 is as follows:

[0042]

[0043] Among them, P IF represents the intermediate frequency signal power. According to formula (12), W L It is expressed as: When α = L, assign the result calculated by formula (12) to W L ; When α = S, the result calculated by formula (12) is conjugated to a complex number and assigned to D is the effective aperture of the detector. The soft-edge aperture is used to replace the hard-edge aperture. The relationship between the soft-edge aperture W and the detector aperture D is D 2 =8W 2 ; From formulas (11) and (13), we can see that A L , C L , D L 、E L , A S , C S , D S 、ES It can be expressed as:

[0044]

[0045] according to The above formula (14) can be simplified as:

[0046]

[0047] Among them, σ L is the beam waist radius of the local oscillator light, σ S is the beam waist radius of the signal light; z represents the transmission distance of the signal light, k represents the wave number, k = 2π / λ, is the angle between vectors ρ1 and ρ2, g, t, s can be expressed as:

[0048]

[0049] in accordance with:

[0050]

[0051] Where: a, p, q, x are arbitrary values, I0 is the Bessel function, and C and D can be expressed by formula (19);

[0052] C=p 2 +q 2 -a 2 , D=2ap (19)

[0053] In formula (16), The integral of ρ2 can be simplified to:

[0054]

[0055] Where q is the sum of ρ1 and ρ2, and I0 is expressed as a Bessel function;

[0056] in accordance with:

[0057]

[0058] Among them, α, β, γ, and x are arbitrary values, and J v ,I v Expressed as an arbitrary function, I v Satisfy the requirements of formula (22);

[0059] I0(0)=1,I p (0)=0,p>0 (22)

[0060] First, integrate ρ2 in equation (16) to obtain:

[0061]

[0062] Substituting formula (23) into formula (20) and simplifying it, we get the following formula (24):

[0063]

[0064] Formula (24) can be simplified as:

[0065]

[0066] Among them, P IF Indicates the intermediate frequency signal power.

[0067] The optical power of the signal light at the source field in step 3 can be expressed as:

[0068]

[0069] Among them, P L represents the optical power of the signal light at the source field, ρ = (ρ1, ρ2) represents the position coordinates of the Gauss-Schnell beam arriving at the receiving plane after passing through the ocean turbulence, W represents the soft edge aperture, D represents the detector aperture,

[0070] According to formula (12), we can see that W L It is expressed as: When α = L, assign the result calculated by formula (12) to W L , A L It is expressed as formula (16):

[0071] The calculation process of the optical power of the local oscillator light at the source field is as follows:

[0072]

[0073] Among them, P S represents the optical power of the local oscillator light at the source field, ρ = (ρ1, ρ2) represents the position coordinates of the Gauss-Schnell beam arriving at the receiving plane after passing through the ocean turbulence, and W represents the soft-edge aperture.

[0074] The calculation process of heterodyne efficiency in step 4 is as follows:

[0075] The heterodyne efficiency in the ocean turbulence environment can be expressed as:

[0076]

[0077] Among them, η het is the heterodyne efficiency in a turbulent ocean environment;

[0078] Substituting equations (25), (26) and (27) into equation (28), the heterodyne efficiency in the ocean turbulence environment can be calculated by simplification, namely:

[0079]

[0080] Wherein, ρ = (ρ1, ρ2) represents the position coordinates of the Gauss-Schnell beam arriving at the receiving plane after being transmitted through the ocean turbulence, k represents the wave number, k = 2π / λ, and s, g, and t can be expressed by formula (17).

[0081] The invention provides a detector receiving aperture simulation method based on underwater coherent detection technology, and obtains heterodyne efficiency by establishing a detection mathematical model of partially coherent Gauss-Scherr light beams in ocean turbulence, such as the process of steps 1 to 4, and numerically simulates the obtained closed-form solution of the heterodyne efficiency through MATLAB software to obtain the aperture size of the receiving-end detector that can suppress ocean turbulence.

[0082] The beneficial effects of the present invention are as follows: the detector receiving aperture simulation method based on the underwater coherent detection technology of the present invention utilizes the generalized Huygens-Fresnel diffraction principle and the heterodyne detection mathematical model of partially coherent light beams, and further obtains the heterodyne efficiency of the partially coherent Gaussian-Scherrer light beams under ocean turbulence by calculating the cross spectral density after the partial Gaussian-Scherrer light beams are transmitted over a distance z in ocean turbulence. The obtained closed-form solution of the heterodyne efficiency is numerically simulated to obtain a suitable detector aperture that can effectively suppress the ocean turbulence effect, thereby maximizing the sensitivity and signal-to-noise ratio of the detector. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] Figure 1 It is a flow chart of underwater coherent detection of the present invention;

[0084] Figure 2 This is a detector receiving aperture simulation method based on underwater coherent detection technology in the present invention, and a graph showing the variation of heterodyne efficiency with transmission distance under different detector apertures D. DETAILED DESCRIPTION

[0085] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0086] The detector receiving aperture simulation method based on underwater coherent detection technology of the present invention specifically includes the following steps:

[0087] Step 1, calculate the cross spectral density of the signal light after it reaches the receiving end after being transmitted through the ocean turbulence for a distance z;

[0088] The calculation formula of the cross spectral density of the signal light at the receiving end is as follows:

[0089]

[0090] Among them, Γ α (ρ1, ρ2, z) is the cross spectral density of the signal light at the receiving end, r1 and r2 represent a pair of position vectors of the Gauss-Schnell beam at the source plane, ρ1 and ρ2 represent the position coordinates of the Gauss-Schnell beam arriving at the receiving plane after passing through the ocean turbulence, λ represents the wavelength of the signal light, z represents the transmission distance of the signal light, k represents the wave number, k = 2π / λ, i represents an imaginary number, The conjugate complex number representing the random phase factor of the effect of ocean turbulence on spherical waves, Random phase factor representing the effect of ocean turbulence on spherical waves, disturbance caused by ocean turbulence<exp[ψ*(ρ1,r1,z)+ψ(ρ2,r2,z)]> ≈exp[-D ψ (ρ1-ρ2, r1-r2) / 2], where D ψ (ρ1-ρ2, r1-r2) is the wave structure function, and:

[0091] D ψ (ρ1-ρ2,r1-r2)=M[(ρ1-ρ2) 2 +(ρ1-ρ2)(r1-r2)+(r1-r2) 2 ] (2)

[0092] Where M represents the ocean turbulence parameter, and the calculation formula is as follows:

[0093]

[0094] Among them, Φ n (κ) uses the Nikishov ocean turbulence refractive index power spectrum, z represents the signal light transmission distance, k represents the wave number, k = 2π / λ, and κ represents the spatial wave number;

[0095] Ocean turbulence refractive index spectrum model Φ n (κ) uses the Nikishov ocean turbulence refractive index power spectrum and is expressed as:

[0096]

[0097] where ε is the turbulent kinetic energy dissipation rate, l0 is the inner scale of the ocean turbulence, and χ T is the mean square temperature dissipation rate, e represents the exponent, A T =1.863×10 -2 , A S =1.9×10 -4 , A TS =9.41×10 -3 , ω represents the relative intensity of temperature and salinity changes, with a value of -5 to 0, and δ can be expressed as:

[0098]

[0099] Among them, l0 is the internal scale of ocean turbulence, and m is the spatial wave number;

[0100] Substituting equations (2), (3) and (4) into equation (1), it can be simplified to:

[0101]

[0102] Wherein, the subscript α=L represents the local oscillator light or S represents the signal light; σ α is the beam waist radius of the signal light or the local oscillator light; δα is the transverse coherence length of the signal light or the local oscillator light at z = 0 at the source field;

[0103] make p=ρ1-ρ2,q=ρ1+ρ2,the formula (6) is simplified as follows:

[0104]

[0105] Among them, r c is the average of r1 and r2, r d is the difference between r1 and r2, p is the difference between ρ1 and ρ2, q is the sum of ρ1 and ρ2, subscript α=L represents the local oscillator light or S represents the signal light; σ α is the beam waist radius of the signal light or the local oscillator light; δα is the transverse coherence length of the signal light or the local oscillator light at z = 0 at the source field;

[0106] Use the following formula (8) to calculate r c and r d Integrating, we get formulas (9) and (10):

[0107]

[0108] Among them, a, b, c, e, h, and R represent 6 arbitrary values;

[0109]

[0110] Among them, A α , B α It can be expressed as:

[0111]

[0112] Substituting equations (9) and (10) into equation (7) and simplifying it, we obtain the following equation (12):

[0113]

[0114] Among them, C α , D α、E α It can be expressed as:

[0115]

[0116] In the above formulas (9)-(13), σ α is the beam waist radius of the signal light or the local oscillator light; δα is the transverse coherence length of the signal light or the local oscillator light at z = 0 at the source field, r c is the average of r1 and r2, r d is the difference between r1 and r2, p is the difference between ρ1 and ρ2, q is the sum of ρ1 and ρ2, z represents the signal light transmission distance, k represents the wave number, k = 2π / λ, i represents an imaginary number, and M represents the ocean turbulence parameter.

[0117] Step 2: Calculate the intermediate frequency signal power of the receiving end signal light using the cross spectral density of the receiving end signal light obtained in step 1;

[0118] The specific process is as follows:

[0119]

[0120] Among them, P IF represents the intermediate frequency signal power. According to formula (12), W L It is expressed as: When α = L, assign the result calculated by formula (12) to W L ; When α = S, the result calculated by formula (12) is conjugated to a complex number and assigned to D is the effective aperture of the detector. The soft-edge aperture is used to replace the hard-edge aperture. The relationship between the soft-edge aperture W and the detector aperture D is D 2 =8W 2 ; From formulas (11) and (13), we can see that A L , C L , D L 、E L , A S , C S , D S 、E S It can be expressed as:

[0121]

[0122] according to The above formula (14) can be simplified as:

[0123]

[0124] Among them, σ L is the beam waist radius of the local oscillator light, σ S is the beam waist radius of the signal light; z represents the transmission distance of the signal light, k represents the wave number, k = 2π / λ, is the angle between vectors ρ1 and ρ2, g, t, s can be expressed as:

[0125]

[0126] in accordance with:

[0127]

[0128] Where: a, p, q, x are arbitrary values, I0 is the Bessel function, and C and D can be expressed by formula (19);

[0129] C=p 2 +q 2 -a 2 , D=2ap (19)

[0130] In formula (16), The integral of ρ2 can be simplified to:

[0131]

[0132] Where q is the sum of ρ1 and ρ2, and I0 is expressed as a Bessel function;

[0133] in accordance with:

[0134]

[0135] Among them, α, β, γ, and x are arbitrary values, and J v ,I v Expressed as an arbitrary function, I v Satisfy the requirements of formula (22);

[0136] I0(0)=1,I p (0)=0,p>0 (22)

[0137] First, integrate ρ2 in equation (16) to obtain:

[0138]

[0139] Substituting formula (23) into formula (20) and simplifying it, we get the following formula (24):

[0140]

[0141] Formula (24) can be simplified as:

[0142]

[0143] Among them, P IF Indicates the intermediate frequency signal power.

[0144] Step 3, calculating the optical power of the signal light and the optical power of the local oscillator light at the source field;

[0145] The optical power of the signal light at the source field can be expressed as:

[0146]

[0147] Among them, P L represents the optical power of the signal light at the source field, ρ = (ρ1, ρ2) represents the position coordinates of the Gauss-Schnell beam arriving at the receiving plane after passing through the ocean turbulence, W represents the soft edge aperture, D represents the detector aperture,

[0148] According to formula (12), we can see that W L It is expressed as: When α = L, assign the result calculated by formula (12) to W L , A L It is expressed as formula (16):

[0149] The calculation formula of the optical power of the local oscillator light at the source field is as follows:

[0150]

[0151] Among them, P S represents the optical power of the local oscillator light at the source field, ρ = (ρ1, ρ2) represents the position coordinates of the Gauss-Schnell beam arriving at the receiving plane after passing through the ocean turbulence, and W represents the soft-edge aperture.

[0152] Step 4, combining the cross spectral density of the signal light at the receiving end obtained in step 2 and the optical power of the signal light and the local oscillator light at the source field calculated in step 3, calculating the heterodyne efficiency in the ocean turbulent environment;

[0153] The specific process is as follows:

[0154] The heterodyne efficiency in the ocean turbulence environment can be expressed as:

[0155]

[0156] Among them, η het is the heterodyne efficiency in a turbulent ocean environment;

[0157] Substituting equations (25), (26) and (27) into equation (28), the heterodyne efficiency in the ocean turbulence environment can be calculated by simplification, namely:

[0158]

[0159] Wherein, ρ = (ρ1, ρ2) represents the position coordinates of the Gauss-Schnell beam arriving at the receiving plane after being transmitted through the ocean turbulence, k represents the wave number, k = 2π / λ, and s, g, and t can be expressed by formula (17).

[0160] Step 5: Use MATLAB software to perform numerical simulation on the closed-form solution of heterodyne efficiency and obtain the aperture size of the receiving detector that can suppress ocean turbulence.

[0161] The simulation process in step 5 is described by the following example:

[0162] Embodiment 1:

[0163] The MATLAB simulation parameters are set as follows: light source wavelength λ = 532.8nm, coherence length of signal light in the source field δ s =0.02m, coherence length of the local oscillator light in the source field δ L =0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 150m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, detector receiving aperture D=0.02m, heterodyne efficiency η het is 0.15.

[0164] Embodiment 2:

[0165] The MATLAB simulation parameters are set as follows: light source wavelength λ = 532.8nm, coherence length of signal light in the source field δ s =0.02m, coherence length of the local oscillator light in the source field δ L =0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 150m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, detector receiving aperture D=0.01m, heterodyne efficiency η het is 0.4.

[0166] Embodiment 3:

[0167] The MATLAB simulation parameters are set as follows: light source wavelength λ = 532.8nm, coherence length of signal light in the source field δ s =0.02m, coherence length of the local oscillator light in the source field δ L =0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 150m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, detector receiving aperture D=0.03m, heterodyne efficiency η het is 0.08.

[0168] Embodiment 4:

[0169] The MATLAB simulation parameters are set as follows: light source wavelength λ = 532.8nm, coherence length of signal light in the source field δ s =0.02m, coherence length of the local oscillator light in the source field δ L =0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 150m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, detector receiving aperture D=0.05m, heterodyne efficiency η het is 0.05.

[0170] Embodiment 5:

[0171] The MATLAB simulation parameters are set as follows: light source wavelength λ = 532.8nm, coherence length of signal light in the source field δ s =0.02m, coherence length of the local oscillator light in the source field δ L =0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L=0.02m, ocean transmission distance z = 150m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, detector receiving aperture D=0.06m, heterodyne efficiency η het is 0.05.

[0172] Embodiment 6:

[0173] The MATLAB simulation parameters are set as follows: light source wavelength λ = 532.8nm, coherence length of signal light in the source field δ s =0.02m, coherence length of the local oscillator light in the source field δ L =0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 150m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, detector receiving aperture D=0.07m, heterodyne efficiency η het is 0.02.

[0174] Through the above-mentioned embodiments 1 to 6, it can be seen that under certain conditions, the heterodyne efficiency shows a decreasing trend with the increase of the receiving aperture. Therefore, when the light source wavelength λ=532.8nm and the coherence length δ of the signal light in the source field is s =0.02m, coherence length of the local oscillator light in the source field δ L =0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 150m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, when the detector receiving aperture is 0.01-0.05, the heterodyne efficiency is larger, and the effect of suppressing ocean turbulence is better.

[0175] Embodiment 7:

[0176] The MATLAB simulation parameters are set as follows: light source wavelength λ = 532.8nm, coherence length of signal light in the source field δ s =0.02m, coherence length of the local oscillator light in the source field δ L =0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 50m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, detector receiving aperture D=0.01m, heterodyne efficiency η het is 0.65.

[0177] Embodiment 8:

[0178] The MATLAB simulation parameters are set as follows: light source wavelength λ = 532.8nm, coherence length of signal light in the source field δ s =0.02m, coherence length of the local oscillator light in the source field δ L =0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 50m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, detector receiving aperture D=0.02m, heterodyne efficiency η het is 0.35.

[0179] Embodiment 9:

[0180] The MATLAB simulation parameters are set as follows: light source wavelength λ = 532.8nm, coherence length of signal light in the source field δ s =0.02m, coherence length of the local oscillator light in the source field δ L=0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 50m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, detector receiving aperture D=0.03m, heterodyne efficiency η het is 0.25.

[0181] Embodiment 10:

[0182] The MATLAB simulation parameters are set as follows: light source wavelength λ = 532.8nm, coherence length of signal light in the source field δ s =0.02m, coherence length of the local oscillator light in the source field δ L =0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 50m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, detector receiving aperture D=0.04m, heterodyne efficiency η het is 0.18.

[0183] Embodiment 11:

[0184] The MATLAB simulation parameters are set as follows: light source wavelength λ = 532.8nm, coherence length of signal light in the source field δ s =0.02m, coherence length of the local oscillator light in the source field δ L =0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 50m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, detector receiving aperture D=0.05m, heterodyne efficiency η het is 0.15.

[0185] Embodiment 12:

[0186] The MATLAB simulation parameters are set as follows: light source wavelength λ = 532.8nm, coherence length of signal light in the source field δ s =0.02m, coherence length of the local oscillator light in the source field δ L =0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 50m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, detector receiving aperture D=0.06m, heterodyne efficiency η het is 0.12.

[0187] Embodiment 13:

[0188] The MATLAB simulation parameters are set as follows: light source wavelength λ = 532.8nm, coherence length of signal light in the source field δ s =0.02m, coherence length of the local oscillator light in the source field δ L =0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 50m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, detector receiving aperture D=0.07m, heterodyne efficiency η het is 0.11.

[0189] Through the above-mentioned embodiments 7 to 13, it can be seen that under certain conditions, the heterodyne efficiency shows a decreasing trend with the increase of the receiving aperture. Therefore, when the light source wavelength λ=532.8nm and the coherence length δ of the signal light in the source field is s =0.02m, coherence length of the local oscillator light in the source field δ L=0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 50m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, when the detector receiving aperture is 0.01-0.05, the heterodyne efficiency is larger, and the effect of suppressing ocean turbulence is better.

[0190] Embodiment 14:

[0191] The MATLAB simulation parameters are set as follows: light source wavelength λ = 532.8nm, coherence length of signal light in the source field δ s =0.02m, coherence length of the local oscillator light in the source field δ L =0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 250m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, detector receiving aperture D=0.01m, heterodyne efficiency η het is 0.3.

[0192] Embodiment 15:

[0193] The MATLAB simulation parameters are set as follows: light source wavelength λ = 532.8nm, coherence length of signal light in the source field δ s =0.02m, coherence length of the local oscillator light in the source field δ L =0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 250m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, detector receiving aperture D=0.02m, heterodyne efficiency η het is 0.08.

[0194] Embodiment 16:

[0195] The MATLAB simulation parameters are set as follows: light source wavelength λ = 532.8nm, coherence length of signal light in the source field δ s =0.02m, coherence length of the local oscillator light in the source field δ L =0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 250m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, detector receiving aperture D=0.03m, heterodyne efficiency η het is 0.05.

[0196] Embodiment 17:

[0197] The MATLAB simulation parameters are set as follows: light source wavelength λ = 532.8nm, coherence length of signal light in the source field δ s =0.02m, coherence length of the local oscillator light in the source field δ L =0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 250m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, detector receiving aperture D=0.04m, heterodyne efficiency η het is 0.03.

[0198] Embodiment 18:

[0199] The MATLAB simulation parameters are set as follows: light source wavelength λ = 532.8nm, coherence length of signal light in the source field δ s =0.02m, coherence length of the local oscillator light in the source field δ L=0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 250m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, detector receiving aperture D=0.05m, heterodyne efficiency η het is 0.02.

[0200] Embodiment 19:

[0201] The MATLAB simulation parameters are set as follows: light source wavelength λ = 532.8nm, coherence length of signal light in the source field δ s =0.02m, coherence length of the local oscillator light in the source field δ L =0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 250m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, detector receiving aperture D=0.06m, heterodyne efficiency η het is 0.02.

[0202] Embodiment 20:

[0203] The MATLAB simulation parameters are set as follows: light source wavelength λ = 532.8nm, coherence length of signal light in the source field δ s =0.02m, coherence length of the local oscillator light in the source field δ L =0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 250m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, detector receiving aperture D=0.07m, heterodyne efficiency η het is 0.02.

[0204] Through the above-mentioned embodiments 14 to 20, it can be seen that under certain conditions, the heterodyne efficiency shows a decreasing trend with the increase of the receiving aperture. Therefore, when the light source wavelength λ=532.8nm and the coherence length δ of the signal light in the source field is s =0.02m, coherence length of the local oscillator light in the source field δ L =0.02m, signal beam waist radius σ s =0.01m, local oscillator beam waist radius σ L =0.02m, ocean transmission distance z = 250m, ocean turbulence kinetic energy dissipation rate ε = 1×10 -2 m 2 / s 2 , the inner scale of ocean turbulence l0 = 0.01m, the mean square temperature dissipation rate χ T =1×10 -7 K 2 / s, temperature-salinity contribution ratio ω=-3, when the detector receiving aperture is 0.01-0.05, the heterodyne efficiency is relatively large, which has a significant effect on suppressing ocean turbulence.

[0205] The above simulation process is expressed through diagrams, such as Figure 2 As shown, Figure 2 It is the change of heterodyne efficiency with the detector receiving aperture under different transmission distances; it can be seen from the figure that the heterodyne efficiency shows a decreasing trend with the increase of the receiving aperture, and the rate of decline is faster as the transmission distance increases. This is because the larger the detector aperture D, the longer the transmission distance, the more signal light affected by ocean turbulence is received, and the light intensity after coherence with the local oscillator light is more affected by ocean turbulence, resulting in a more significant decrease in heterodyne efficiency. It can be seen from this that the larger the detector aperture, the higher the heterodyne efficiency.

[0206] The detector receiving aperture simulation method based on underwater coherent detection technology of the present invention has a detection process as follows: Figure 1 As shown, it includes a signal laser at the horizontal transmitting end and a local oscillator laser at the vertical transmitting end; the signal light (linearly polarized light) is emitted by the beam expansion and collimation system, reaches the receiving end after being transmitted in the ocean turbulent medium for a distance z, and is coherently mixed with the local oscillator light (linearly polarized light) (the influence of the ocean turbulence on the polarization state of the signal light is not considered for the time being), and after coherent superposition, it reaches the surface of the receiving detector through a self-focusing lens to output an intermediate frequency (difference frequency) electrical signal.

[0207] The functions of the device during the detection process are as follows:

[0208] Signal light laser: The signal light laser is a narrow line width laser with a wavelength of λ=532.8nm;

[0209] Local oscillator laser: The local oscillator laser is a narrow linewidth laser with a wavelength of λ = 532.8nm;

[0210] Optical mixer: The receiving end signal light is coherently mixed with the local oscillator light;

[0211] Photodetector: Converts photocurrent into an electrical signal.

Claims

1. A detector receiving aperture simulation method based on underwater coherent detection technology, characterized in that: The specific steps are as follows: Step 1, calculate the cross spectral density of the signal light after it reaches the receiving end after being transmitted through the ocean turbulence for a distance z; Step 2: Calculate the intermediate frequency signal power of the receiving end signal light using the cross spectral density of the receiving end signal light obtained in step 1; Step 3, calculating the optical power of the signal light and the optical power of the local oscillator light at the source field; Step 4, combining the cross spectral density of the signal light at the receiving end obtained in step 2 and the optical power of the signal light and the local oscillator light at the source field calculated in step 3, calculating the heterodyne efficiency in the ocean turbulent environment; Step 5: Use MATLAB software to perform numerical simulation on the closed-form solution of heterodyne efficiency and obtain the aperture size of the receiving detector that can suppress ocean turbulence.

2. The detector receiving aperture simulation method based on underwater coherent detection technology according to claim 1 is characterized in that: The calculation formula of the cross spectral density of the signal light at the receiving end is as follows: Among them, Γ α (ρ1, ρ2, z) is the cross spectral density of the signal light at the receiving end, r1 and r2 represent a pair of position vectors of the Gauss-Schnell beam at the source plane, ρ1 and ρ2 represent the position coordinates of the Gauss-Schnell beam arriving at the receiving plane after passing through the ocean turbulence, λ represents the wavelength of the signal light, z represents the transmission distance of the signal light, k represents the wave number, k = 2π / λ, i represents an imaginary number, The conjugate complex number representing the random phase factor of the effect of ocean turbulence on spherical waves, Random phase factor representing the effect of ocean turbulence on spherical waves, disturbance caused by ocean turbulence<exp[ψ*(ρ1,r1,z)+ψ(ρ2,r2,z)]> ≈exp[-D ψ (ρ1-ρ2, r1-r2) / 2], where D ψ (ρ1-ρ2, r1-r2) is the wave structure function, and: D ψ (ρ1-ρ2,r1-r2)=M[(ρ1-ρ2) 2 +(ρ1-ρ2)(r1-r2)+(r1-r2) 2 ] (2) Where M represents the ocean turbulence parameter, and the calculation formula is as follows: Among them, Φ n (κ) uses the Nikishov ocean turbulence refractive index power spectrum, z represents the signal light transmission distance, k represents the wave number, k = 2π / λ, and κ represents the spatial wave number; Ocean turbulence refractive index spectrum model Φ n (κ) uses the Nikishov ocean turbulence refractive index power spectrum and is expressed as: where ε is the turbulent kinetic energy dissipation rate, l0 is the inner scale of the ocean turbulence, and χ T is the mean square temperature dissipation rate, e represents the exponent, A T =1.863×10 -2 , A S =1.9×10 -4 , A TS =9.41×10 -3 , ω represents the relative intensity of temperature and salinity changes, with a value of -5 to 0, and δ can be expressed as: Among them, l0 is the internal scale of ocean turbulence, and m is the spatial wave number; Substituting equations (2), (3) and (4) into equation (1), it can be simplified to: Wherein, the subscript α=L represents the local oscillator light or S represents the signal light; σ α is the beam waist radius of the signal light or the local oscillator light; δα is the transverse coherence length of the signal light or the local oscillator light at z = 0 at the source field; make r d =r1-r2, p=ρ1-ρ2, q=ρ1+ρ2, formula (6) is simplified as follows: Among them, r c is the average of r1 and r2, r d is the difference between r1 and r2, p is the difference between ρ1 and ρ2, q is the sum of ρ1 and ρ2, subscript α=L represents the local oscillator light or S represents the signal light; σ α is the beam waist radius of the signal light or the local oscillator light; δα is the transverse coherence length of the signal light or the local oscillator light at z = 0 at the source field; Use the following formula (8) to calculate r c and r d Integrating, we get formulas (9) and (10): Among them, a, b, c, e, h, and R represent 6 arbitrary values; Among them, A α , B α It can be expressed as: Substituting equations (9) and (10) into equation (7) and simplifying it, we obtain the following equation (12): Among them, C α , D α 、E α It can be expressed as: In the above formulas (9)-(13), σ α is the beam waist radius of the signal light or the local oscillator light; δα is the transverse coherence length of the signal light or the local oscillator light at z = 0 at the source field, r c is the average of r1 and r2, r d is the difference between r1 and r2, p is the difference between ρ1 and ρ2, q is the sum of ρ1 and ρ2, z represents the signal light transmission distance, k represents the wave number, k = 2π / λ, i represents an imaginary number, and M represents the ocean turbulence parameter.

3. The detector receiving aperture simulation method based on underwater coherent detection technology according to claim 1 is characterized in that: The calculation process of the intermediate frequency signal power described in step 2 is as follows: Among them, P IF represents the intermediate frequency signal power. According to formula (12), W L It is expressed as: When α = L, assign the result calculated by formula (12) to W L ; When α = S, the result calculated by formula (12) is conjugated to a complex number and assigned to D is the effective aperture of the detector. The soft-edge aperture is used to replace the hard-edge aperture. The relationship between the soft-edge aperture W and the detector aperture D is D 2 =8W 2 ; From formulas (11) and (13), we can see that A L , C L , D L 、E L , A S , C S , D S 、E S It can be expressed as: according to The above formula (14) can be simplified as: Among them, σ L is the beam waist radius of the local oscillator light, σ S is the beam waist radius of the signal light; z represents the transmission distance of the signal light, k represents the wave number, k = 2π / λ, is the angle between vectors ρ1 and ρ2, g, t, s can be expressed as: in accordance with: Where: a, p, q, x are arbitrary values, I0 is the Bessel function, and C and D can be expressed by formula (19); C=p 2 +q 2 -a 2 ,D=2ap (19) In formula (16), The integral of ρ2 can be simplified to: Where q is the sum of ρ1 and ρ2, and I0 is expressed as a Bessel function; in accordance with: Among them, α, β, γ, and x are arbitrary values, and J v ,I v Expressed as an arbitrary function, I v Satisfy the requirements of formula (22); I0(0)=1,I p (0)=0,p>0 (22) First, integrate ρ2 in equation (16) to obtain: Substituting formula (23) into formula (20) and simplifying it, we get the following formula (24): Formula (24) can be simplified as: Among them, P IF Indicates the intermediate frequency signal power.

4. The detector receiving aperture simulation method based on underwater coherent detection technology according to claim 3 is characterized in that: The optical power of the signal light at the source field described in step 3 can be expressed as: Among them, P L represents the optical power of the signal light at the source field, ρ = (ρ1, ρ2) represents the position coordinates of the Gauss-Schnell beam arriving at the receiving plane after passing through the ocean turbulence, W represents the soft edge aperture, and D represents the detector aperture. According to formula (12), it can be seen that W L It is expressed as: When α = L, assign the result calculated by formula (12) to W L , A L It is expressed as formula (16): The optical power of the local oscillator light at the source field is as follows: Among them, P S represents the optical power of the local oscillator light at the source field, ρ = (ρ1, ρ2) represents the position coordinates of the Gauss-Schnell beam arriving at the receiving plane after passing through the ocean turbulence, and W represents the soft-edge aperture.

5. The detector receiving aperture simulation method based on underwater coherent detection technology according to claim 4 is characterized in that: The calculation process of the heterodyne efficiency described in step 4 is as follows: The heterodyne efficiency in the ocean turbulence environment can be expressed as: Among them, η het Heterodyne efficiency in a turbulent ocean environment; Substituting equations (25), (26) and (27) into equation (28), the heterodyne efficiency in the ocean turbulence environment can be calculated by simplification, namely: Wherein, ρ = (ρ1, ρ2) represents the position coordinates of the Gauss-Schnell beam arriving at the receiving plane after being transmitted through the ocean turbulence, k represents the wave number, k = 2π / λ, and s, g, and t can be expressed by formula (17).

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