Design and optimization method of waveguide display sub-wavelength diffraction grating

Abstract

The invention relates to a waveguide display sub-wavelength diffraction grating. The sub-wavelength diffraction grating used for a waveguide display system is designed in order to provide an optimization algorithm which does not require gradient calculation, has multidimensional real number optimization, is discontinuous, does not need to be differentiable, and can be changed with time. A design and optimization method of the waveguide display sub-wavelength diffraction grating comprises the following steps that a grating substrate material, the number of film layers, and the refractive indexof a coating material are determined, and grating parameters involved in optimization are selected; a strict coupled wave analysis theory is adopted to calculate the diffraction efficiency and is combined with a differential evolution algorithm to determine that an evaluation function is the variance of the reflection diffraction first-order diffraction efficiency and the target order diffractionefficiency within the range of a required wavelength or an incident angle; the target order diffraction efficiency is set; and the differential evolution algorithm is used for optimization. The designand optimization method of the waveguide display sub-wavelength diffraction grating is mainly applied to occasions of design and manufacturing of diffraction gratings.

Description

technical field [0001] The invention relates to a waveguide display subwavelength diffraction grating, in particular to a design and optimization method for a waveguide display subwavelength diffraction grating. Background technique [0002] With the continuous development of micro-nano processing technology, subwavelength diffraction gratings, as the core components, have a wide range of application requirements and application prospects in the fields of optical communication, high-energy laser, astrophysics, optical measurement, near-eye waveguide display, polarization imaging, etc. [0003] In waveguide display technology, the coupling method based on sub-wavelength diffraction grating has the advantages of larger exit pupil, more compact, lighter and thinner, and higher transmittance than prism coupling, free-form surface and other coupling methods. Subwavelength diffraction gratings usually only have 0-order and ±1-order diffraction. In the waveguide display system, in ...

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Problems solved by technology

[0009] However, according to the strict coupled-wave analysis theory, there are many influencing factors related to the diffraction efficiency distribution of subwavelength diffraction gratings. have an impact

At present, usually some parameters are set first each time, and then the optimization design is carried out by scanning other parameters to select the optimal parameters. Since the diffraction efficiency is affected by multiple parameters, the grating optimization method of each single variable scanning There are certain limitations and inappropriateness. The parametric scanning method is suitable for the design of simple binary gratings, but it is still not applicable to one-dimensional linear gratings with complex structures such as continuous surface relief gratings and multi-layer dielectric gratings.

Some classic algorithms such as inverse Fourier transform algorithm, simulated annealing algorithm, particle swarm algorithm and genetic algorithm have been introduced to design diffractive optical elements, and the method of combining rigorous coupled wave analysis and genetic algorithm is used to optimize the design of subwavelength diffraction gratings. The random process of generating mutations usually uses new chromosomes generated by disciplined distribution methods such as roulette, but this method is prone to local convergence, resulting in local optimal solutions rather than global optimal solutions

In addition, some optimization methods use the gradient information of the function and require the function to be derivable or continuous, which limits the applicability of the optimization method

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