Saraswati Behera

Single-step optical realization of bio-inspired dual-periodic motheye and gradient-index-array photonic structures.

This Letter demonstrates a single-step optical realization method for hexagonal and square lattice-based dual periodic motheye and gradient-index-array photonic structures over large areas. Computed phase mask of gradient interference patterns are used as inputs to a phase-only spatial light modulator (SLM), and the first-order diffracting beams are coherently superposed with the help of a 2f-2f Fourier filtering setup to avoid complex optical geometry for generation and control of individual beams. The simulated interference patterns are verified experimentally through a CMOS camera. The fabricated micro-structures on a positive photoresist are shown to have a major periodicity of 638 μm and minor periodicity of 25.2 μm, with the air hole diameter varying from 22.7 to 6.9 μm along the X and Y axes. The depth of the fabricated structure gradually varies from 4.203 μm at the center to 1.818 μm at the corner. These structures may be scaled down to submicron features that can show improved anti-reflection properties for solar energy harvesting and GRIN lens for optical wavelength region.

N-single-helix photonic-metamaterial based broadband optical range circular polarizer by induced phase lags between helices

In this work, we have designed a photonic-metamaterial based broadband circular polarizer using N=4 phase-lagged aluminum single helices arranged in a square array as a unit cell. The effect of phase differences between the helices in an array on the optical performance of the structure is studied, and a comparative study is done with that of multi-intertwined helices. It is observed that the proposed metamaterial structure shows circular polarization sensitivity over a broad optical wavelength range (≈450-900  nm), with improved optical performance in average extinction ratio and broad positive circular dichroism in comparison to multiple intertwined helices. The induced phase lag between the helices in a square-array based unit cell reduces the linear birefringence and leads to the recovery of circular space symmetry in the structure.

Submicrometer photonic structure fabrication by phase spatial-light-modulator-based interference lithography.

We present a large-area and single-step fabrication approach based on phase spatial light modulator (SLM)-assisted interference lithography for the realization of submicrometer photonic structures on photoresist. A multimirror beam steering unit is used to reflect the SLM-generated phase-engineered beams leading to a large angle between interfering beams while also preserving the large area of the interfering plane beams. Both translational and rotational periodic submicrometer structures are experimentally realized. This approach increases the flexibility of interference lithography to fabricate more complex submicrometer photonic structures and photonic metamaterial structures for future applications.

Plasmonic metamaterial based unified broadband absorber/near infrared emitter for thermophotovoltaic system based on hexagonally packed tungsten doughnuts

In this paper, we report a simple and effective design of a polarization independent and wide incident angle plasmonic metamaterial based unified broadband absorber and thermal emitter consisting of hexagonally packed tungsten doughnuts (hexa-rings) for thermophotovoltaic system. The proposed design shows more than 85% of absorption over 0.3 to 2.18 μm, that is, over the broad spectral range from the ultraviolet to the near infrared (NIR), and 100% absorption and thermal emission at 2.18 μm. Further, the NIR plasmonic absorption and thermal emission peak is tuned from the spectral range 2.18 to 3 μm for different low bandgap photovoltaic materials by varying the design parameters such as inner and outer ring radius, instead of varying any other design parameters in the proposed design. The possibility of the realization of hexa-doughnut structures through a single-step phase engineered interference lithography technique is also demonstrated through the realization of micro/nanostructure samples over large...

Design and fabrication of woodpile photonic structures through phase SLM-based interference lithography for omnidirectional optical filters

In this Letter, we report a large-area and single-step optical fabrication technique based on phase engineering interference lithography that is scalable and reconfigurable for the realization of submicrometer scale periodic face-centered cubic inverse woodpile photonic structures. The realized inverse woodpile structure on positive having four number axial layers with 740 nm spatial and 1046 nm axial periodicities shows 10% reflectance and 90% transmittance at 776 nm wavelength that can further be improved for the addition of axial layers. The realized structure can be transferred to crystalline silicon for realizing a bandpass/rejection near-infrared filter in a reflection/transmission mode. Further, woodpile structures based on low-contrast silicon nitride (Si3N4) are designed as selective narrow frequency filters at 1310 and 1550 nm wavelengths for telecommunication applications and omnidirectional red-green-blue filters for display devices by tuning the design parameters.

Hexagonal periodic motheye photonic structure as broadband anti-reflector

Design of motheye photonic structure as anti-reflector over 400–1100 nm broad wavelength range is reported, whose template is realized by single-step phase-engineered interference lithography approach.

Tapered-double-helix Photonic Metamaterial Based Broadband Circular Polarizer for Optical Wavelength Range

We have designed a photonic-metamaterial structure using tapered-double-helices and have done FDTD based theoretical study on its optical properties. Broadband circular polarization is observed within 457–1080 nm with improved optical properties.

Effect of helical phase on the optical performance of photonic metamaterial based broadband circular polarizer

Broadband circular polarizer based on nanophotonic metamaterial helices is designed and effect of the helical phase between intertwined helices is studied. The proposed structure increases the average extinction ratio above fifty percent.