Measuring system for high-order Poincare spherical beam spinning and orbital angular momentum

Abstract

The utility model relates to a high-order Poincare ball beam spinning and orbital angular momentum measuring system, which comprises a high-order Poincare ball beam which sequentially passes through a first diaphragm, a second diaphragm and a first lens and is incident on a prism to generate a reflected beam and a refracted beam, a second lens and a first quadrant detector are sequentially arranged in the direction of refracted light beams, a third lens and a second quadrant detector are sequentially arranged in the direction of reflected light beams, the prism is provided with an interface A and an interface B, high-order Poincare ball light beams are incident and reflected from the interface A, the refracted light beams are output from the interface B, and the interface B is plated with an anti-reflection film. And the included angle between the interface A and the interface B is equal to the refraction angle of the high-order Poincare ball beam. According to the measurement system, the IF displacement of the refracted light beam and the reflected light beam can be measured at the same time, and then the spin angular momentum and the orbital angular momentum of the high-order Poincare sphere light beam can be determined according to the relation between the IF displacement and the angular momentum.

Description

Technical Field

[0001] The utility model relates to the field of high-order Poincare sphere light beam measurement, in particular to a measurement system for the spin and orbital angular momentum of a high-order Poincare sphere light beam. Background Art

[0002] A high-order Poincare sphere beam is a laser mode with complex phase and polarization distribution, and each possible mode corresponds to a point on the high-order Poincare sphere. The center of a high-order Poincare sphere beam is both a polarization singularity and a phase singularity, and can carry quantized spin angular momentum and orbital angular momentum at the same time. This unique physical property makes high-order Poincare sphere beams widely used in optical capture, super-resolution microscopy, space optical communication, laser processing, particle acceleration, precision measurement and other fields. Spin angular momentum and orbital angular momentum play a decisive role in the intensity, polarization and phase distribution of high-order Poincare sphere beams and their transmission characteristics in the medium. Therefore, in the related research and applications of high-order Poincare sphere beams, it is of great significance to measure the spin angular momentum and orbital angular momentum of high-order Poincare sphere beams.

[0003] At present, in the mainstream scheme for measuring the angular momentum of a high-order Poincare sphere beam, two different technologies are required to measure the spin angular momentum and orbital angular momentum respectively. Spin angular momentum is related to the polarization distribution of the beam and can be accurately obtained by measuring the Stokes parameter. The relevant measurement technology is already highly mature. However, orbital angular momentum is related to the phase distribution of the beam. The measurement of orbital angular momentum requires the use of more complex interference or diffraction techniques, such as: (1) interferometry; (2) cylindrical lens diffraction; (3) spatial light modulator. In the first method, the beam to be measured needs to interfere with a plane wave or a spherical wave, and the orbital angular momentum information is obtained by observing the characteristics of the interference fringes. This method not only involves a complex interference device, but also requires the introduction of a plane wave or a spherical wave with good coherence with the beam to be measured. It is difficult to use it to build a stable angular momentum measurement system. In the second method, the beam to be measured needs to pass through a cylindrical lens, and the orbital angular momentum information is obtained by observing the characteristics of the diffraction pattern on the focal plane. Since the diffraction pattern is affected by factors such as optical path alignment and beam quality, it will exhibit complex and unpredictable behaviors, which increases the risk of measurement errors. In the third solution, the spatial phase modulation function of the spatial light modulator is used to offset the vortex phase of the measured light beam, thereby achieving the measurement of orbital angular momentum. However, spatial light modulators are expensive and difficult to promote.

[0004] With the rapid development of applications related to high-order Poincare sphere beams, there is an urgent need for a new angular momentum measurement method for high-order Poincare sphere beams that can simultaneously measure spin angular momentum and orbital angular momentum. Utility Model Content

[0005] In order to make up for the deficiencies of the prior art, the utility model provides a measurement system for the spin and orbital angular momentum of a high-order Poincare sphere light beam, which can simultaneously measure the IF displacement of a refracted light beam and a reflected light beam, and further use the relationship between the IF displacement and the angular momentum to determine the spin angular momentum and orbital angular momentum of the high-order Poincare sphere light beam.

[0006] The technical solution adopted by the utility model to solve the above technical problems is:

[0007] A system for measuring the spin and orbital angular momentum of a high-order Poincare sphere beam comprises a high-order Poincare sphere beam, wherein the high-order Poincare sphere beam passes through a first aperture, a second aperture and a first lens in sequence and is incident on a prism to generate a reflected beam and a refracted beam, a second lens and a first quadrant detector are arranged in sequence in the direction of the refracted beam, and a third lens and a second quadrant detector are arranged in sequence in the direction of the reflected beam, the prism comprises an interface A and an interface B, the high-order Poincare sphere beam is incident and reflected from the interface A, and the refracted beam is output from the interface B, an anti-reflection film is coated on the interface B, and the vertex angle between the interface A and the interface B is equal to the refraction angle of the high-order Poincare sphere beam.

[0008] Furthermore, the first aperture and the second aperture are used to align the incident high-order Poincare sphere beam to be measured with the optical path, and the first lens is used to transform the waist of the high-order Poincare sphere beam to be measured to the interface A of the prism, and the incident angle of the high-order Poincare sphere beam on the prism interface A is 45 degrees.

[0009] The utility model adopts the above technical solution, and has the advantages that the measurement system of the spin and orbital angular momentum of the high-order Poincare sphere beam can simultaneously measure the IF displacement of the refracted beam and the reflected beam, and then the relationship between the IF displacement and the angular momentum can be used to determine the spin angular momentum and orbital angular momentum of the high-order Poincare sphere beam. In addition, the measurement system also has the advantages of fast measurement speed and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a structural schematic diagram of the measurement system of the utility model;

[0011] Figure 2 Parameter A of UV fused silica glass (a) and N-BK7 glass (b) t , B t , A r and B r Curve that changes with the wavelength of the light to be measured;

[0012] Figure 3 The curves of the prism angle θ of UV fused quartz glass (a) and N-BK7 glass (b) changing with the wavelength of the light to be measured.

[0013] Figure 1 In the figure, 1. High-order Poincare sphere beam, 2. First aperture, 3. Second aperture, 4. First lens, 5. Prism, 6. Second lens, 7. First quadrant detector, 8. Third lens, 9. Second quadrant detector. DETAILED DESCRIPTION

[0014] In order to clearly illustrate the technical features of the present invention, the present invention is described in detail below through specific implementation methods and in conjunction with the accompanying drawings.

[0015] like Figure 1 As shown, in this embodiment, the measurement system of the spin and orbital angular momentum of the high-order Poincare sphere beam includes a high-order Poincare sphere beam 1, and the high-order Poincare sphere beam 1 passes through the first aperture 2, the second aperture 3 and the first lens 4 in sequence and is incident on a prism 5 to generate a reflected beam and a refracted beam. A second lens 6 and a first quadrant detector 7 are arranged in sequence in the direction of the refracted beam, and a third lens 8 and a second quadrant detector 9 are arranged in sequence in the direction of the reflected beam. The prism 5 has an interface A and an interface B. The high-order Poincare sphere beam 1 is incident and reflected from the interface A, and a refracted beam is output from the interface B. The interface B is coated with an anti-reflection film, and the vertex angle between the interface A and the interface B is equal to the refraction angle of the high-order Poincare sphere beam.

[0016] Among them, the first aperture 2 and the second aperture 3 are used to align the incident high-order Poincare sphere beam to be measured with the optical path, and the first lens 4 is used to transform the waist of the high-order Poincare sphere beam to be measured to the interface A of the prism, and the incident angle of the high-order Poincare sphere beam on the prism interface A is 45 degrees.

[0017] The working principle of the above measurement system is as follows:

[0018] When a laser beam is refracted and reflected at the interface of a medium, the center of the beam will shift laterally in the direction perpendicular to the plane of incidence, which is called the Imbert-Fedorov shift, or IF shift for short. Studies have shown that the IF shift of a high-order Poincare sphere beam has a simple mathematical relationship with its spin angular momentum and orbital angular momentum. Using this mathematical relationship, the spin angular momentum and orbital angular momentum of a high-order Poincare sphere beam can be determined by measuring the IF shift of the refracted and reflected beams. The specific process is as follows:

[0019] The beam to be measured can be written as: in, is the circular polarization vector, l is the topological charge, u ±l is the field distribution of the vortex beam, and (Θ, Φ) are the coordinates of the corresponding points of the measured beam on the high-order Poincare sphere.

[0020] The normalized spin angular momentum S and normalized orbital angular momentum L of the measured light beam are given by the following equations:

[0021] It corresponds to the spin angular momentum and orbital angular momentum of a single photon in the measured light beam. From the above, we can see that by measuring the topological charge l and the high-order Poincare sphere coordinates θ, we can calculate the spin angular momentum S and orbital angular momentum L.

[0022] In the measurement system, the first aperture and the second aperture are used to align the incident light beam to be measured with the optical path of the measurement system. The first lens is used to transform the waist of the light beam to be measured to the interface A of the prism. The light beam to be measured passes through the first lens with a wavelength of θ i The angle incident on the interface A of the prism causes reflection and refraction. The refracted beam passes through the second lens and enters the first quadrant detector, and the reflected beam passes through the third lens and enters the second quadrant detector. The second lens and the third lens are used to transform the beam waists of the refracted beam and the reflected beam to the detection surfaces of the two quadrant detectors.

[0023] When the measured light beam undergoes refraction and reflection on the interface A of the prism, an IF displacement occurs in the direction perpendicular to the incident surface. The IF displacement of the refracted light beam and the reflected light beam can be expressed as: δ t =(A t +B t l)cosθ;v r =(A r +B r l)cosΘ. The two quadrant detectors are used to measure the IF shift δ of the refracted beam and the reflected beam respectively t and δ r According to the measured IF displacement δ t and δ r The topological charge l and the high-order Poincare sphere coordinates Θ can be solved, where:

[0024]

[0025] As for the parameter A in the formula t , B t , A r and B r Respectively expressed as:

[0026]

[0027]

[0028]

[0029]

[0030] in: n is the refractive index of the prism material, t p ,t s 、r p and r s are the Fresnel transmission and reflection coefficients, θ i and θ t are the angle of incidence and the angle of refraction respectively, and λ is the wavelength of the light beam to be measured.

[0031] For a specific prism material and wavelength of light to be measured, parameter A t , B t , A r and B r is a fixed value. For common prism materials such as UV fused silica glass and N-BK7 glass, Figure 2 Given the parameter A t , B t , A r and B r Curve of change with the wavelength of the light to be measured (incident angle θ i =45°). For common laser wavelengths, the following table 1 gives the parameter A t , B t , A r and B r The specific value of .

[0032] Table 1 Parameters A corresponding to several common laser wavelengths t , B t , A e and B r Value (incident angle θ i =45°)

[0033]

[0034] In order to avoid the IF displacement of the refracted light beam on the interface B of the prism and to minimize the interference with the propagation direction of the refracted light beam, the interface B needs to be coated with an anti-reflection film, and the vertex angle θ between the interface B and the interface A is equal to the refraction angle θ of the refracted light beam. t :θ=θ t =arcsin(sinθ i / n), thereby ensuring that the refracted beam is perpendicular to the interface B. For common prism materials such as UV fused silica glass and N-BK7 glass, Figure 3 The curve of the change of the prism vertex angle θ with the wavelength of the light to be measured (the incident angle θ i =45°). For common laser wavelengths, Table 2 gives the specific values ​​of the vertex angle θ of the prism.

[0035] Table 2 The values ​​of the prism (I) vertex angle θ corresponding to several common laser wavelengths (incident angle θi =45°)

[0036]

[0037] The above-mentioned specific implementation manner cannot be used as a limitation on the protection scope of the present utility model. For those skilled in the art, any replacement, improvement or change made to the implementation manner of the present utility model falls within the protection scope of the present utility model.

[0038] The matters not described in detail in the present invention are all known technologies to those skilled in the art.

Claims

1. A system for measuring the spin and orbital angular momentum of a high-order Poincare sphere beam, characterized in that: The invention comprises a high-order Poincare sphere beam, wherein the high-order Poincare sphere beam passes through a first aperture, a second aperture and a first lens in sequence and is incident on a prism to generate a reflected beam and a refracted beam, a second lens and a first quadrant detector are arranged in sequence in the direction of the refracted beam, and a third lens and a second quadrant detector are arranged in sequence in the direction of the reflected beam, the prism has an interface A and an interface B, the high-order Poincare sphere beam is incident and reflected from the interface A, and the refracted beam is output from the interface B, an anti-reflection film is coated on the interface B, and the vertex angle between the interface A and the interface B is equal to the refraction angle of the high-order Poincare sphere beam.

2. The high-order Poincare sphere beam spin and orbital angular momentum measurement system according to claim 1, characterized in that: The first aperture and the second aperture are used to align the incident high-order Poincare sphere beam to be measured with the optical path, and the first lens is used to transform the beam waist of the high-order Poincare sphere beam to be measured to the interface A of the prism. The incident angle of the high-order Poincare sphere beam on the prism interface A is 45 degrees.

Images