Laser active coherence balancing detection polarization analyzer

[0024] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments, but the protection scope of the present invention should not be limited by this.

[0025] see first figure 1 , figure 1 This is the structural principle block diagram of the laser active coherent balance detection polarization analyzer of the present invention. It can be seen from the figure that the present invention is a laser active coherent balance detection polarization analyzer based on a 90° 2×4 spatial optical bridge, which consists of a laser 1, a local oscillator optical splitting module 2, a polarization state generating module 3, an optical transmitting antenna 4, The echo receiving optical antenna 5 , the echo polarization beam splitting prism 6 , the horizontal vibration processing module 7 , the vertical vibration processing module 8 and the data processor 9 .

[0026] The main optical axis of the laser output of the laser 1 is the local oscillator optical splitting module 2 , the polarization state generating module 3 , and the optical transmitting antenna 4 in sequence. The laser light emitted by the laser 1 is split by the first beam splitting prism 21 of the local oscillator light splitting module 2, and a part of the emitted beam enters the polarization state generating module 3, and is irradiated to the surface of the target 10 through the optical transmitting antenna 4; the other part passes through the second beam splitting. Prism 22, and by adjusting the optical axis angle of the first half-wave plate 23, a local oscillator laser beam in the horizontal vibration direction is formed at its first outgoing end 231, and at the same time by adjusting the optical axis angle of the second half-wave plate 24, at the second outgoing end 231 The end 241 forms a local oscillator laser beam perpendicular to the vibration direction. After the emission beam irradiated on the surface of the target 10 is reflected, the echo beam carrying the target polarization information enters the echo receiving optical antenna 5, and is split by the echo polarization beam splitting prism 6, and formed at the first exit end 61. The target echo beam in the horizontal vibration direction and the second outgoing end 62 form the target echo beam in the vertical vibration direction.

[0027] The local oscillator laser beam and the target echo beam in the horizontal vibration direction are input to the horizontal vibration processing module 7, and pass through the first 90° 2×4 spatial optical bridge 71 to generate four beam outputs with a phase difference of 90° in sequence. , in which the two beams with a phase shift of 180° are photoelectrically detected by the left channel balanced receiver 72 to become a real number signal, which is further converted into a left channel digital signal; the other two beams with a phase shift of 180° are detected by the right channel balanced receiver 73 . The photodetection becomes a real signal, which is further converted into a right channel digital signal. The left channel digital signal and the right channel digital signal are combined by a complex digitizer 74 and converted into a complex signal of the light level component of the echo signal.

[0028]The local oscillator laser beam and the target echo beam in the vertical vibration direction are input to the vertical vibration processing module 8, and pass through the second 90° 2×4 spatial optical bridge 81 to generate four beam outputs with a phase difference of 90° in turn. , in which the two beams with a phase shift of 180° are photoelectrically detected by the left channel balanced receiver 82 and converted into a real number signal, which is further converted into a left channel digital signal; the other two beams with a phase shift of 180° are detected by the right channel balanced receiver 83 . The photodetection becomes a real signal, which is further converted into a right channel digital signal. The left channel digital signal and the right channel digital signal are combined by a complex digitizer 84 and converted into a complex signal of the vertical component of the echo signal light.

[0029] The complex signal of the horizontal component and the vertical component of the echo signal light is expressed by the data processor 9 as the Stokes vector of the echo light field. By adjusting the polarization state generation module 3 to change the polarization state of the emitted light beam, the Stokes vectors of multiple groups of emitted light beams and the echo light field are obtained, and on this basis, the Mueller matrix carrying the target polarization information is obtained by calculation, and finally the target to be measured is obtained. polarization properties.

[0030] The polarization state generating module 3 has two different types of devices. The first is composed of a linear polarizer and a quarter-wave plate. By adjusting the angle of the linear polarizer and the angle between the fast axis of the quarter-wave plate, the outgoing laser light has different polarization states. The second is composed of a polarizer and a phase modulator, and the required laser light of different polarization states is generated by adjusting the voltage acting on the phase delay modulator.

[0031] The transmitting antenna module 4 has a focal length of F 1 The lens is composed of , and the beam waist radius of the laser output can be determined by Calculated. λ is the working wavelength of laser 1, ω 0 is the beam waist radius of laser 1.

[0032] The echo receiving optical antenna 5 includes a focal length of f 1 The first lens 51, the aperture stop 52 and the focal length f 2 the second lens 53. The first lens 51 and the second lens 53 are confocal, and the aperture diaphragm 52 is located at the confocal point for filtering, and the beam reduction ratio is M=f 1 /f 2 Calculated.

[0033] The following uses a target point to explain the imaging principle of the laser active coherent balance detection polarization analyzer of the present invention:

[0034] The detection distance from the system to the target is z, and the coordinate system of the target surface is set to (x k ,y k ), the emission light source selects a polarization-maintaining single-mode laser with a wavelength of λ and a power of P, and its beam waist radius is ω 0. Launching telescope focal length F 1 ,, and its laser beam waist radius can be calculated by: The illumination light field on the target surface is expressed as:

[0035]

[0036] in,

[0037]

[0038]

[0039] The diameter of the illumination spot on the target surface is expressed as: The echo Fresnel diffraction light field that propagates to the receiving telescope system after being reflected by the target is expressed as:

[0040]

[0041] where ρ(x k ,y k ,z)exp[jφ ρ (x k ,y k ,z)] is the reflectivity of the target.

[0042] The transmission distance of the local oscillator beam is z 0 , then the relative time delay of the target is Let f be the echo signal frequency, is the initial phase of the emitted laser, is the phase delay of the target channel, As the phase delay of the local oscillator channel, the echo signal is expressed as:

[0043]

[0044] The local oscillator signal is expressed as:

[0045] For the LO laser beam and target echo beam in the horizontal vibration direction:

[0046]

[0047]

[0048] Therefore, the output of the left-balanced receiver is:

[0049]

[0050] The output of the right balanced receiver is:

[0051]

[0052] Among them, A i represents a constant related to signal strength and detector, represents the initial phase shift. After pluralization,

[0053]

[0054] For the LO laser beam and the target echo beam in the vertical vibration direction:

[0055]

[0056]

[0057] Therefore, the output of the left-balanced receiver is:

[0058]

[0059] The output of the right balanced receiver is:

[0060]

[0061] After pluralization,

[0062]

[0063] Assuming that the amplitude of the local oscillator signal is 1 and the initial phase shift from the signal light is 0, the above-mentioned complex signal containing echo information is simplified to the expression form of the echo light field, and its polarization state can be expressed as:

[0064]

[0065]

[0066] E x ,δ x represent the vibration component and vibration phase along the horizontal direction (x direction), respectively, E y ,δ y Respectively represent the vibration component and phase along the vertical direction (y direction), δ=δ y -δ x represents the phase difference of the two components. Therefore, the Stokes vector of the echo light field can be obtained by the definition formula:

[0067]

[0068]

[0069] S' 2 =2E 0x E 0y cosδ

[0070] S' 3 =2E 0x E 0y sinδ

[0071] Stokes vector of the echo light field The Stokes vector of the outgoing laser beam can be The linear combination of :

[0072]

[0073] The Mueller matrix is ​​expressed as:

[0074] .