Waveguide patterning on thin film and self-assembled photonic crystals

Abstract

Waveguide (WG) structures are patterned on polymeric thin films and on three-dimensional colloidal photonic crystals (PhC). Different techniques such as direct laser writing, electron beam lithography (EBL), optical lithography and femto-second laser writing are used to pattern the WG structures on PPR, polymethyl methacrylate (PMMA) and SU-8 photoresists. All these techniques are found to be successful in writing the WG structures on thin films. Air channel WGs are formed by EBL and direct laser writing techniques on PMMA and PPR, respectively. The air channel is further infiltrated with a higher index zinc oxide by sol-gel chemistry for guidance of light by total internal reflection. The structure written on SU-8 by optical lithography and on PMMA thin film by femto second laser writing resulted in the ridged WG structures where the guidance is possible by total internal reflection. The WG writing is also successfully carried out by electron beam lithography and femto second laser writing on PhCs fabricated from PMMA and polystyrene colloidal particles using inward growing self-assembly method. Unlike the earlier WG structures, the light guidance is possible due to photonic band gap effect in PhC WG, only for the wavelengths that lie within the stop band of the PhC. The quality of the written structures is characterized using images from scanning electron microscope, atomic force microscope and optical microscope. For optical characterization, a diode laser beam is successfully guided through the WG structure fabricated on PMMA PhC by EBL and on SU-8 thin film by optical lithography method.