CN113155296A - Device for measuring fractional order correlation vortex light beam topological load - Google Patents
Device for measuring fractional order correlation vortex light beam topological load Download PDFInfo
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Abstract
The invention discloses a device for measuring fractional order correlation vortex light beam topological charge. The method comprises the following steps: the laser generates fractional order correlated vortex rotation, and the size of a light beam spot is adjusted to cover the holographic phase plate; measuring a cross spectral density function (CCF) of fractional order associated vortex optical rotation, and observing the position of a Fractional Topological Charge (FTC) notch on an associated vortex optical cross section to be measured in the function space; loading a digital holographic phase plate on the spatial light modulator and adjusting the azimuth angle of the digital holographic phase plate to enable a CCF gap generated by the digital holographic phase plate to be overlapped with an FTC gap of the associated vortex to be detected; using a small aperture diaphragm to select first-order diffraction light reflected by the spatial light modulator; changing the phase difference of the digital holographic phase plate; enabling the superposed position of the FTC notch and the phase plate notch in the CCF to be detected to present: appearance of a notch-disappearance of a notch-appearance of a notch; and calculating the decimal part of the FTC by using the phase differences corresponding to the three phenomena, and combining the integral topological charge part to obtain the final value of the associated vortex optical rotation fractional order topological charge.
Description
Technical Field
The invention provides a device for measuring fractional order correlation vortex light beam topological charge. The device can measure the decimal part of the topological charge value in the fractional order correlated vortex optical beam, and can be applied to the fields of optical image coding, optical communication, particle manipulation, optical trapping, optical detection and the like.
Background
Optical vortices are helically distributed waves with phase singularities, with dark regions in the middle of the intensity distribution. The helical phase-distorted wavefront is represented by the exponential term exp (il θ), where θ is the rotation azimuth and l represents the topological charge. Under paraxial propagation conditions, each photon in an optical vortex has
Topology ofWherein
Representing planck constants. Laguerre-gaussian, higher order bessel and hypergeometric gaussian beams are some well-known vortex beams.
The vortex states of the vortex bundle may be considered fractional order on an integer value basis, where fractional order vortex states are a superposition of the integer vortex bundle state basis. Fractional order Vortex optical rotation (Fractional Vortex) has a spiral phase structure, the central light intensity is zero, a light spot has a unique radial gap and contains the characteristics of determining topological charges (OAM) and the like, and the characteristics enable the Fractional order Vortex optical rotation to have wide application prospects in the fields of nonlinear optics, biomedicine, optical communication and the like.
The associated vortex light is a random light field of light vortex passing through atmospheric turbulence, the light source is closer to a light source of a real environment, and the application of the light source in actual production and life has important significance. We refer to such random beams as partially coherent vortex rotation (PCVB). The fractional order partial coherent vortex optical rotation greatly improves the bearing capacity of vortex optical information because of containing a topological charge fraction part, and is a new direction of optical image coding and optical communication.
At present, there are several methods for measuring fractional order topological charge (FTC). For example, the FTC is measured by obtaining an interference intensity pattern between a vortex beam and its conjugate beam by a cascaded Mach-Zehnder interferometer; another method is to measure the FTC of the vortex beam using a dynamic angle double slit method. The optical paths used by these methods are complex, are difficult to implement in practical applications, and are mostly only suitable for one specific vortex beam.
The documents Hosseini-Saber M A, Akhlaghi E A, Saber A. differential based vortex beam fractional polar charge measurement [ J ]. Optics Letters,2020,45(13): 3478-. The method uses a phase plate with a certain thickness to measure the topological charge fraction part of the fractional order vortex light beam by controlling the inclination angle of the phase plate. However, the method relies on the diffraction intensity distribution characteristics of the vortex beam, and can only measure the topological charge of the complete coherent vortex rotation. Under the disturbance environment, the coherence of the light field is reduced, and the structural characteristics of the light intensity diffraction pattern disappear. Therefore, this method cannot measure the topological charge fraction part of fractional order correlated vortex rotation. In addition, the inclination angle and the rotation angle of the phase plate used in the technology are easily influenced by environmental disturbance, the quantization control is not easy to realize, large experimental error is easy to generate, and the measurement accuracy is influenced. The above is the main problem that the fractional order vortex optical topological charge measurement is not solved at present.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a device for measuring the topological charge of a fractional order correlated vortex light beam. The device provided by the invention writes the phase plate into the holographic film, and quantificationally controls the correlation function space distribution of the emergent light field by changing the azimuth angle and the phase difference of the holographic film. And measuring the topological charge of the fractional order correlation vortex rotation by using the distribution characteristics of the light field second order correlation function.
The technical scheme for realizing the aim of the invention is to provide a device for measuring the topological charge of the fractional order correlated vortex light beam, which comprises the following steps:
(1) the laser generates fractional order correlated vortex rotation, and the size of a light beam spot is adjusted to enable the light beam spot to completely cover the holographic phase plate; measuring a cross spectral density function (CCF) of a fractional order correlation vortex light field, and observing the position of an FTC notch on the cross section of a light beam to be measured in the function space; loading a digital holographic phase plate on the spatial light modulator and adjusting the azimuth angle of the digital holographic phase plate to ensure that a CCF gap generated by the digital holographic phase plate is superposed with an FTC gap of PCVB;
(2) selecting the first-order diffracted light reflected by the spatial light modulator by using an aperture diaphragm; changing the phase difference of the digital holographic phase plate; the superposition position of the FTC notch and the phase plate notch in the CCF of the light field to be detected shows the following changes: when the three changes occur, the phase difference loaded by the digital holographic phase plate is recorded and recorded as phi1, phi2 and phi 3; using the formula:
calculating a decimal part l' of the FTC; the combined integer topological charge portion is the final value of the fractional order topological charge associated with the vortex rotation.
The invention has the beneficial effects that:
1. the invention provides a device for measuring fractional order correlation vortex light beam topological charge.
2. The light path of the device adopted by the invention can be digitally controlled, and the phase adjustment quantification is controllable. The optical path has a simple structure, reduces experimental errors caused by rotating the phase plate, improves the accuracy and feasibility of experiments, and has application value in the fields of optical communication, imaging and the like.
Drawings
Fig. 1 is a schematic structural diagram of an apparatus for measuring fractional order correlated vortex optical topological charges provided in an embodiment of the present invention.
Fig. 2 is a diagram of a rotated azimuthal holographic phase plate.
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 a device for measuring fractional order correlated vortex beam topological charge provided in this embodiment: it comprises a laser 1; a spatial light modulator 2; a computer 3; an aperture diaphragm 4; a continuous shooting camera 5; a computer 6;
as shown in FIG. 2, which is a schematic diagram of the digital holography phase plate provided in this embodiment, a portion contains phase information, and b portion does not contain phase information, the phase plate can rotate by an angle of rotation of
Is measured.
In this embodiment, holographic phase plate images with different azimuth angles are prepared in the computer 3; connecting a computer 3 with the spatial light modulator 2; turning on the laser 1 to generate fractional order correlated vortex rotation; adjusting the size of the light spot of the laser 1 to enable the laser 1 to completely cover the holographic phase plate of the spatial light modulator 2; adjusting the azimuth angle of the holographic phase plate on the spatial light modulator 2 through the computer 3, and observing a CCF gap generated by the digital holographic phase plate and an FTC gap of PCVB in a CCF space; adjusting the azimuth angle of the holographic phase plate until a CCF gap generated by the digital holographic phase plate is superposed with an FTC gap generated by PCVB; selecting first-order diffracted light in the reflected light beam of the spatial light modulator 2 by using the aperture diaphragm 4; controlling the continuous shooting camera 5 to shoot through the computer 6 to obtain an image with the superposed gaps, and recording the azimuth angle of the holographic phase plate at the moment; changing the phase difference of the holographic phase plate under the azimuth angle, changing the diffraction pattern in the CCF space, and recording the CCF pattern under the phase difference; repeating the photographing step, and storing the CCF patterns under different phase differences; along with the change of the phase difference, the superposition position of the FTC notch and the phase plate notch in the CCF pattern of the light field to be detected shows the following changes: appearance of a notch-disappearance of a notch-reappearance of a notch; recording the phase difference corresponding to the picture with the phenomenon, and calculating the decimal part l' of the FTC by a formula (1.1); the combined integer topological charge portion is the final value of the fractional order topological charge associated with the vortex rotation.
Claims (2)
1. A device for measuring fractional order correlation vortex light beam topological load is composed of a laser (1), a spatial light modulator (2), a computer (3), an aperture diaphragm (4), a continuous shooting camera (5) and a computer (6); the method is characterized in that:
(A) preparing holographic phase plate images for generating different azimuth angles in a computer (3); connecting the computer (3) with a spatial light modulator (2) and loading the prepared hologram into the spatial light modulator (2); opening a laser (1) to generate fractional order correlated vortex optical rotation, and adjusting the spot size of an emergent beam of the laser (1) to enable the laser to completely cover a holographic phase plate of a spatial light modulator (2); adjusting the azimuth angle of a holographic phase plate on the spatial light modulator (2) through the computer (3) to enable a cross density spectrum function (CCF) notch generated by the digital holographic phase plate to coincide with a Fractional Topological Charge (FTC) notch of a partially coherent vortex rotation (PCVB);
(B) selecting first-order diffracted light in reflected light of the spatial light modulator (2) by using an aperture diaphragm (4); the first-order diffraction light reflected by the spatial light modulator (2) enters a continuous shooting camera (5), and the continuous shooting camera (5) is controlled by the computer (6) to shoot to obtain an image with superposed gaps; recording the azimuth angle of the holographic phase plate at the moment; changing phase plate holographic plates with different phase differences in the computer (3) to generate diffraction patterns with different phases, repeating the photographing step, and storing the patterns;
(C) changing the phase difference of the digital holographic phase plate; the superposition position of the FTC notch and the phase plate notch in the CCF of the light field to be detected shows the following changes: appearance of a notch-disappearance of a notch-reappearance of a notch; recording the phase difference loaded by the digital holographic phase plate when the three changes occur, and calculating the decimal part of the FTC; the combined integer topological charge portion is the final value of the fractional order topological charge associated with the vortex rotation.
2. The apparatus of claim 1, wherein the apparatus is configured to measure the topological charge of the fractional order correlated vortex beam, and further configured to: in the device, the computer (3) controls the digital holographic phase plate generated by the spatial light modulator (2), the computer (3) is used for adjusting the azimuth angle of the holographic plate to enable a CCF notch generated by the holographic phase plate to be superposed with an FTC notch of PCVB, and then the holographic plate with different phase differences at the azimuth angle is replaced to take a picture.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113655625A (en) * | 2021-09-03 | 2021-11-16 | 西华大学 | Light beam device with atmospheric turbulence resistance |
| CN114964527A (en) * | 2022-05-10 | 2022-08-30 | 苏州大学 | Method and device for measuring topological charge of partial coherence fractional order vortex light beam |
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2021
- 2021-05-31 CN CN202110596850.2A patent/CN113155296A/en active Pending
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113655625A (en) * | 2021-09-03 | 2021-11-16 | 西华大学 | Light beam device with atmospheric turbulence resistance |
| CN113655625B (en) * | 2021-09-03 | 2023-09-05 | 西华大学 | Device for light beam with anti-atmospheric turbulence capability |
| CN114964527A (en) * | 2022-05-10 | 2022-08-30 | 苏州大学 | Method and device for measuring topological charge of partial coherence fractional order vortex light beam |
| CN114964527B (en) * | 2022-05-10 | 2023-06-02 | 苏州大学 | Partial coherence fractional order vortex beam topology charge number measurement method and device |
| WO2023216438A1 (en) * | 2022-05-10 | 2023-11-16 | 苏州大学 | Method and apparatus for counting topological charges of partially coherent fractional-order vortex beam |
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