Fabrication of helical photonic structures with submicrometer axial and spatial periodicities following “inverted umbrella” geometry through phase-controlled interference lithography

Abstract

In this Letter we report for the first time, to the best of our knowledge, a phase spatial light modulator (SLM)-based interference lithography (IL) approach for the realization of hexagonally packed helical photonic structures with a submicrometer scale spatial, as well as axial, periodicity over a large area. A phase-only SLM is used to electronically generate six phase-controlled plane beams. These six beams from the front side and a direct central backside beam are used together in an "inverted umbrella" geometry setup to realize the desired submicrometer axial periodic chiral photonic structures through IL. The realized structures with 650 nm spatial and 353 nm axial periodicities on negative photoresist can be used as an optical filter and refractive index sensor, as evidenced from the FDTD-based simulation study on its optical properties. Further, the fabricated templates can be transferred to metals such as silver or aluminum for the realization of a metamaterial-based broadband circular polarizer ranging from 1 to 3.5 μm of near-infrared spectra.

Applications of asymmetric 2D and 3D gold Fano resonators and optical realization approach

“…Figures 9(j)-(l) present the 3D asymmetric spiral PhCs (XYZ, XY, XZ plane) formed due to the interference of 6 + 1 phase engineered plane beams with the phase offset as mentioned in equation ( 3) with the weight factor defined by table 1(j). The corresponding symmetric spiral structure possible through interference as reported in previous literatures [26,27] is presented in figures 9(m)-(o) for comparison. This study reveals that the cross-section of the realized asymmetric spiral is a rectangle (ellipse) instead of a hexagon (circle) in case of the symmetric ones.…”

“…Square spiral PhCs have shown better bandgap than the circular spirals and its fabrication was possible mostly through GLAD (nano structure) which is multi-step, time consuming, as well as a costly fabrication technique [23]. These 3D printed prototypes of the rectangular/square spiral PhCs through phasecontrolled interference technique enable the possibility of the realization of rectangular spirals of any geometry such as spiral diameter, spiral pitch, spatial and axial periodicity in a single step following the technique presented by Behera et al [25,26].…”

Engineering Plasmonic Hybridization toward Advanced Optical Sensors

“…Unlike photolithography, LIL does not use any physical mask and hence is free of the diffraction limit. The angle of interference can manipulate the interference pattern, the number of beams, [240,241] as well as by the polarization, [242] intensity, [241] and phases [243,244] of the interfering beams. For a simple case of twobeam interference, the periodicity is defined by Λ = 𝜆/(2sin𝜃) with Λ min = 𝜆/2.…”

Study of polarization effects in phase-controlled multi-beam interference lithography towards the realization of sub-micron photonic structures

“…With further modification, it is possible to realize and fabricate even submicron-sized architectures such as chiral helices [36] and woodpile [37] photonic structures by incorporating higher interference angles in the conventional umbrella geometry through a custom-designed reflective component. Practically applicable structures of such chiral helical design with reduced pitch have been obtained by incorporating an 'inverted-umbrella' geometry [38]. In a regular umbrella geometry of 'n + 1' beams, the azimuthally oriented 'n' side beams lying on the surface of an imaginary cone as well as the central beam, all are incident from the same hemisphere on to the recording medium.…”

“…Thus an effective study with a vector approach is indeed required by considering the polarization states of the final interfering beams. In this article, two of the previously reported cases of woodpile [37] and chiral helical [38] photonic structures are analyzed through scalar and vector approaches that have provided an insight into the possibilities and limitations of this PCIL method. Further, the effect of polarization states of the incoming beam onto the final interference pattern for different cases of azimuthal and radial configurations are investigated apart from the inherent linear case, and suitable modifications as per requirement are proposed.…”