Multispectral and large bandwidth achromatic imaging with a single diffractive photon sieve.

Abstract

Conventional photon sieves suffer from large chromatic aberration due to diffractive nature and can image only at a single designed wavelength with near zero bandwidth. Here, a novel photon sieve that can image achromatically and simultaneously at multiple wavelengths with wide spectral bandwidth is proposed and demonstrated experimentally. The multispectral achromatic imaging with a single diffractive photon sieve is implemented with harmonic diffraction and wavefront coding, in which harmonic diffraction makes different diffracted orders of multiple harmonic wavelengths on a common focus while wavefront coding through the coded distribution of the pinholes expands the bandwidth of diffracted imaging. Numerical simulations show that when four spectral bands centered at 437.5, 500, 583.3, and 700 nm in the visible range is designed with a cubic wavefront coding parameter α = 30π and a harmonic diffraction order of 5, the bandwidth at the corresponding wavelength band can reach ± 8, ± 9, ± 11 and ± 14 nm respectively, and the total working bandwidth of the harmonic diffraction wavefront coded photon sieve reaches ~84 nm compared with 0.39 nm of the conventional one. Experimental validation was performed using an UV-lithography fabricated wavefront coded photon sieve of a focal length of 500 mm and a diameter of 50 mm at a designed wavelength of 700 nm. The results show excellent agreement with the theoretical predictions.