Periodic gradient grating and method for measuring vortex beam

Abstract

The invention discloses a method for measuring vortex beam through a periodic gradient grating. The method is characterized in that the number of a pitch line of first-stage diffraction spot transmitted through the periodic gradient grating is treated as the order of an orbit angular momentum state of the vortex beam; the direction of the pitch line represents the positive and negative of the orbit angular momentum state of the vortex beam; when the periodic gradient factor of the grating is positive and the direction of the pitch line of the spot at the left side of the first-stage diffraction spot is consistent with the direction of a symmetric axis of the grating, the order of the orbit angular momentum state of the vortex beam to be measured is positive. With the adoption of the method, the vortex beam of the orbit angular momentum state at any order can be measured, and thus a great progress is made by being compared with the prior art; meanwhile, when the direction of the incident vortex beam is deviated from the grating center, the position of the first-stage diffraction spot of a diffraction pattern can correspondingly rotate about the zero-stage diffraction spot, and the generated diffraction pattern does not influence the measurement of the order of the orbit angular momentum state; therefore, the requirement of the periodic gradient grating on the collimation of an optical system is reduced, and an optical path can be adjusted easily.

Description

technical field [0001] The invention relates to the field of optoelectronic technology, in particular to a period-gradient grating for measuring vortex beams and a measuring method. Background technique [0002] Vortex beams are a type of beams that have attracted much attention in recent years. Different from general beams with flat and spherical wavefronts, vortex beams have a continuous spiral phase, the beam center phase is uncertain, and there are phase singularities. The center intensity to zero. Vortex beams have gradually become a hot research topic in academia because of their considerable application prospects. Especially the Laguerre-Gaussian beam is a kind of vortex beam commonly used by people. It has a spiral phase structure of φ=ilθ, each photon carries The orbital angular momentum state of . The orbital angular momentum state makes the light beam have another modulation method in the field of optical communication besides the intensity, phase, frequency,...

AI Technical Summary

Problems solved by technology

However, many applications currently require vortex beams to have higher orders and more superposition states, so that the above measurement methods cannot be applied well; first, the amplitude diffraction grating uses the first-order diffraction order, and the two directions The composite amplitude grating generates a total of 9 diffraction orders, so once the composite grating structure is fixed, it can only measure up to 9 vortex beams with different orbital angular momentum states

Secondly, because the range of the OAM state of the vortex beam measured by the composite fork-shaped amplitude grating is closely related to the fork index of the two-direction fork-shaped grating (the number of the OAM state of the vortex beam measured by the composite fork-shaped amplitude grating is The sum of cross indices in two directions), in order to increase the maximum range of measurement, it is necessary to increase the cross indices in both directions, but with the increase of the cross index, it brings considerable difficulties to the production process, and generates The first-order diffraction spot is also worse

Finally, the traditional compound fork-shaped amplitude grating has high requirements on the collimation of the optical path, and the irradiation beam needs to hit the central finger of the fork-shaped grating to accurately obtain the diffraction pattern

Therefore, the composite fork grating measurement method has certain limitations

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