Single step optical realization of 3D photonic bandgap submicrometer periodic structures for thermophotovolatics

3D photonic structures show photonic bandgap in all three directions and for all states of polarization of the incident electromagnetic wave due to the presence of wavelength scale periodic features in three dimensions.... [ view full abstract ]

3D photonic structures show photonic bandgap in all three directions and for all states of polarization of the incident electromagnetic wave due to the presence of wavelength scale periodic features in three dimensions. Basically woodpile and inverse opal kind of structures show complete photonic bandgap and can be used in thermophotovoltaic (TPV) system as frequency selective absorbers that increases the conversion efficiency without using a concentrator [1]. Here, we report a single step optical fabrication approach to realize 3D woodpile submicrometer periodic photonic structures with nano-scale features over large area. We have followed a phase SLM assisted technique [2] to avoid the generation of multiple beams and to manipulate the phase of the side beams. A multi-mirror (four mirrors) custom made assembly that is housed in a 3D printed mount is used to allow large angle interference of the generated phase engineered beams. The umbrella geometry and experimental setup to realize the woodpile photonic structures are presented in the attached Fig. 1. SEM image of the experimentally realized woodpile photonic structures over large area is presented in Fig. 2. Spatial periodicity of the realized structure is approximately 600 nm.  The bandgap and optical properties of the designed structure are studied using Lumerical solution's FDTD simulation software to propose its applications. The fabricated structure can be used as a frequency absorber for long wavelength photons when transferred to a suitable material.

Fig. 1: Optical realization of woodpile photonic structure (a) umbrella geometry of 4+1 beams (b) experimental setup; LCOS: Liquid crystal on silicon; SLM: Spatial Light Modulator.

Fig. 2: SEM image of the experimentally realized woodpile structure on positive photoresist over large area.

Reference
[1] M. Florescu, H. Lee, I. Puscasu, M. Pralle L. Florescu, D.Z Ting and J. P. Dowling , "Improving solar cell efficiency using photonic band-gap materials", Solar Energy Materials and Solar Cells 91, 1599-610 (2007).
[2] S. Behera, M. Kumar and J. Joseph, "Submicrometer photonic structure fabrication by phase spatial-light-modulator-based interference lithography", Opt. Lett. 41, 1893-6 (2016).