CN114090957A - Method for controlling orbital angular momentum of random light beam by using non-uniform disturbance - Google Patents
Method for controlling orbital angular momentum of random light beam by using non-uniform disturbance Download PDFInfo
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- CN114090957A CN114090957A CN202111382722.4A CN202111382722A CN114090957A CN 114090957 A CN114090957 A CN 114090957A CN 202111382722 A CN202111382722 A CN 202111382722A CN 114090957 A CN114090957 A CN 114090957A
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Abstract
The invention discloses a method for controlling random light beam orbital angular momentum by using non-uniform disturbance. The method comprises the following steps: the laser generates a stable laser beam, and the size of the light spot of the laser beam is adjusted to enable the laser beam to cover the holographic image; loading a digital hologram with non-uniform random vortices on a spatial light modulator; generating a hologram having non-uniform random disturbances by varying a random function; by varying the angle parameter in the random function matrix
The angular momentum value of the low coherence beam trajectory can be controlled.
Description
Technical Field
The invention provides a method for controlling orbital angular momentum of a random light beam by using non-uniform disturbance. The method can regulate and measure the orbital angular momentum of the vortex light beam in the non-uniform disturbance environment, and can be applied to the fields of sensing atmospheric turbulence, free space communication systems, channel multiplexing in optical communication, optical detection and the like.
Background
The optical vortex is a spiral distribution wave with phase singularities, and the light intensity distribution diagram of the optical vortex is a hollow ring-shaped structure in a life ring shape. The optical vortex has a helical phase-twisted wavefront, represented by the exponential term exp (il θ), where θ is the rotational azimuth, l represents the topological charge, the counterclockwise torsional topological charge is unity, and the clockwise torsional topological charge is negative. Among the vortex beams that have been widely studied are the laguerre-gaussian beam, the higher order bessel beam, and the super-geometric gaussian beam.
The regulation and control and the measurement of the orbital angular momentum of the optical vortex have important significance for the application of vortex beams. The regulation and measurement of the fully coherent vortex beam are complete. The measurement and regulation of the orbital angular momentum of the Partially Coherent Vortex Beam (PCVB) is still insufficient. PCVB is a low coherence beam with a strongly distorted helical phase. This makes the wavefront phase based conditioning and measurement scheme ineffective. Further, the light intensity distribution of the PCVB loses the distribution characteristic of the phase odd points. Therefore, it is also difficult to identify the PCVB beam orbital angular momentum information based on the characteristics of the light intensity distribution.
In the prior art, studies on PCVB mainly consider isotropic coherence collapse, and studies on PCVB which collapses unevenly in all directions are lacking. Because the non-uniform coherence destruction is closer to a real disturbance environment, the measurement and regulation of the non-uniform PCVB have important significance for improving the vortex sensing precision in atmospheric turbulence, realizing a free space communication system and OAM channel multiplexing and optical detection in optical communication and the like.
There are two main approaches in the prior art for achieving non-uniform modulation of the vortex beam. First, the literature (Alperin S N, Niederiter R D, Gopinath J T, et al.Quantitive measurement of the organic and regular movement of light with a single, static lenses [ J ]. Optics Letters,2016,41(21): 5019-: an inclined cylindrical lens is used to generate non-uniformly distorted light, and then the topological number of the light beam is identified through the singularity feature in the light intensity distribution. The method is simple in device and can also be applied to measurement of fractional order topological charge, but cannot be used for low-coherence vortex beams. Second, the literature (Chen J, Liu X, Yu J, et al. Simultaneous determination of the sign and the identity of the cosmetic charge of a partial coherent vortex beam [ J ]. Applied Physics B,2016,122(7):1-12.) proposes: two vertically placed cylindrical lenses are used for asymmetrically regulating and controlling the PCVB light intensity, and then the topological charge value of the PCVB light intensity is obtained by observing the distribution characteristics of the beam space correlation function. The method can regulate and measure the orbital angular momentum of the PCVB, but the device is complicated, and the treated PCVB light beam is isotropically destroyed in coherence, so that the spatial distribution function of the PCVB light beam cannot be regulated.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a method for controlling random light beam orbital angular momentum by using non-uniform disturbance, so that the light beam orbital angular momentum can be regulated and controlled under the condition of non-uniform coherence damage, and the measurement and the regulation and the control of the non-uniform disturbance vortex light orbital angular momentum can be feasible.
In order to achieve the above object, the technical scheme adopted by the invention provides a method for controlling random light beam orbital angular momentum by using non-uniform disturbance, which comprises the following steps: the laser generates a stable laser beam, a computer is used for preparing a hologram of a non-uniform random vortex light beam, and the size of the light spot of the laser light beam is adjusted to enable the light spot to completely cover the holographic picture on the spatial light modulator; selecting the first-order diffracted light reflected by the spatial light modulator by using an aperture diaphragm; making the first-order diffracted light enter a cylindrical lens forming an angle of 45 degrees with the horizontal plane; the light beam passing through the cylindrical lens is incident to a camera, and the angular momentum value of the light beam track is obtained through calculation after photographing and recording; continuously changing angle parameters in a random function matrix in digital holography placed in a spatial light modulator by using a computer, and recording the average light intensity distribution under the corresponding angle parameters by using a camera; the quantitative relation between the angle parameter and the orbital angular momentum value of the light beam can be obtained through calculation, so that the measurement and the regulation of the orbital angular momentum are realized;
the spatial correlation function of the non-uniform random vortex rotation is as follows:
wherein W (r)1,r2) Is a spatial point r1And r2Cross spectral density function of r0Is the position of the disturbance point on the cross-section of the optical axis, P (r)0) Is a random probability density function, r1And r2Is any two spatial positions on the cross section of the optical axis, U is the wave function of the light field,
is the conjugate of the light field wave function; the spatial light field generated by the hologramIn 1, with r0Is the center of the disturbance; probability density function P (r) of the center of disturbance0) Is a multivariable normal random function in the xy plane, the variance matrix of which is
Wherein c isxRoot mean square of disturbance range in x direction, cyThe disturbance range in the y direction is root mean square, rho is disturbance correlation in the x direction and the y direction, and the variance matrix sigma meets a semi-positive definite condition.
The disturbance parameter of the variance matrix sigma is
By varying the angle parameter in the random function matrix
The orbital angular momentum value of the non-uniform random vortex rotation can be periodically and quantitatively changed;
due to the application of the technical scheme, the method for controlling the orbital angular momentum of the random light beam by utilizing the non-uniform disturbance has the following advantages:
1. the invention provides a method for controlling orbital angular momentum of a random light beam by using non-uniform disturbance.
2. The optical path of the device adopted by the invention can digitally regulate and control the disturbance in different directions, and the orbital angular momentum can be accurately measured and is easy to regulate and control; the light path structure is simple, the experimental accuracy is improved, the orbital angular momentum information can be directly acquired through light intensity, and the method has application value in the fields of optical communication, atmospheric turbulence sensing and the like.
Drawings
Fig. 1 is a schematic structural diagram of an apparatus for controlling random beam orbital angular momentum by using non-uniform disturbance according to an embodiment of the present invention.
Detailed Description
The present invention will be further described in detail with reference to the following examples, which are illustrative of the present invention and are preferred forms of application of the present invention, but the present invention is not limited to the following examples.
As shown in fig. 1, it is a schematic structural diagram of an apparatus for controlling random beam orbital angular momentum by using non-uniform disturbance according to this embodiment: it comprises a laser 1; a spatial light modulator 2; a computer 3; an aperture diaphragm 4; a cylindrical lens 5; a camera 6; a computer 7;
in this embodiment, a hologram of a non-uniform random vortex beam is prepared in the computer 3; by varying the random function P (r)0) Angle parameter contained in medium sigma matrix
To produce a holographic plate with non-uniform random perturbations; connecting the computer 3 with a spatial light modulator 2; turning on the laser 1 to generate a stable laser beam; adjusting the size of the light spot of the laser 1 to enable the laser 1 to completely cover the holographic picture of the spatial light modulator 2; selecting first-order diffracted light in the reflected light beams of the spatial light modulator 2 by using an aperture stop 4; the first order diffracted light passes through a cylindrical lens 5 forming an angle of 45 degrees with the horizontal plane; the average light intensity distribution after passing through the cylindrical lens 5 is photographed by a camera 6; calculating orbital angular momentum through a computer 7; altering angular parameters in a hologram in a spatial light modulator 2
And recording each using the camera 6
Mean intensity distribution at value; the orbital angular momentum under each angle is calculated by the computer 7, and finally, the angle parameter can be measured
Quantitative relation with the orbital angular momentum value of the light beam; by this relationship, the angle of the low coherence beam trajectory can be controlledAnd (4) a momentum value.
Claims (2)
1. A method for controlling orbital angular momentum of a low coherent light beam by using non-uniform disturbance is characterized by comprising the following steps: laser beams are emitted into a spatial light modulator, and non-uniform random vortex optical rotation is generated through a hologram loaded by the spatial light modulator; the spatial correlation function of the non-uniform random vortex rotation is as follows:
wherein W (r)1,r2) Is a spatial point r1And r2Cross spectral density function of r0Is the position of the disturbance point on the cross-section of the optical axis, P (r)0) As a function of random probability density, r1And r2Is any two spatial positions on the cross section of the optical axis, U is the wave function of the light field,
is the conjugate of the light field wave function; the hologram generates a spatial light field of r0Is the center of the disturbance; probability density function P (r) of the center of disturbance0) Is a multivariable normal random function in the xy plane, the variance matrix of which is
Wherein c isxRoot mean square of disturbance range in x direction, cyThe disturbance range in the y direction is root mean square, rho is disturbance correlation in the x direction and the y direction, and the variance matrix sigma meets a semi-positive definite condition.
2. The method of claim 1, wherein the method comprises the following steps: the disturbance parameter of the variance matrix sigma is
By varying the angle parameter in the random function matrix
The orbital angular momentum value of the non-uniform random vortex rotation can be periodically and quantitatively changed; record each
Average light intensity distribution under the value, and angle parameter can be measured by calculation
Quantitative relation with the orbital angular momentum value of the light beam; by this relationship, the angular momentum value of the low coherence beam trajectory can be controlled.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114675416A (en) * | 2022-03-29 | 2022-06-28 | 中国计量大学 | Method for generating anti-turbulence-disturbance multimode high-order vortex rotation by using distortion disturbance |
| CN114722354A (en) * | 2022-06-10 | 2022-07-08 | 苏州大学 | Method, device and storage medium for calculating flux density of normalized orbital angular momentum |
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2021
- 2021-11-22 CN CN202111382722.4A patent/CN114090957A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114675416A (en) * | 2022-03-29 | 2022-06-28 | 中国计量大学 | Method for generating anti-turbulence-disturbance multimode high-order vortex rotation by using distortion disturbance |
| CN114675416B (en) * | 2022-03-29 | 2023-12-29 | 中国计量大学 | Method for generating multimode Gao Jieguo optical rotation resisting turbulence disturbance by utilizing torsion disturbance |
| CN114722354A (en) * | 2022-06-10 | 2022-07-08 | 苏州大学 | Method, device and storage medium for calculating flux density of normalized orbital angular momentum |
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