Effect of gradual widening of d/w-ratio on optical performance of photon sieves produced by two maskless lithography techniques: lift-off and chemical etching

The two important parameters, to evaluate the performance of the photon sieves quantitatively, are the intensity and resolution at the focus plane. Both high-intensity and super-resolution depend on the ratio of the diameter (d) of each pinhole to the width (w) of the related Fresnel zone: the d/w ratio. The size deviations in the produced pinholes may adversely affect the optical performance of the photon sieves. The mispositioned and imperfectly-shaped pinholes cause the super-resolution at the focus to be disrupted. The photon sieves are produced by using two sub-methods of maskless lithography: lift-off and wet chemical etching. Although designed to be constant of 1, the d/w ratio was measured to widen gradually for both chemical-etched and lift-off samples. It is revealed the optical performance of the photon sieves may be enhanced as a result of gradual increase of the d/w ratio, compared to the structure of constant d/w ratio.