Single polymer-variable index for the design and fabrication of variable stop band distributed Bragg reflectors

• Published in: Optical materials 2020-12, Vol.110, p.110509, Article 110509
• Main Authors: Lohithakshan, Lisha C., Geetha, Vishnu, Kannan, Pradeesh
• Format: Article
• Language: English
• Subjects: Distributed Bragg reflectors; High index polymer; Metal oxide-polymer composite; Photonic stop band; Polymer multilayers
• ISSN: 0925-3467; 1873-1252
• DOI: 10.1016/j.optmat.2020.110509

Thin films of variable refractive index from a single polymer were developed by doping titanium dioxide (TiO2) in poly-vinyl alcohol (PVA) by solution processing. Refractive index as high as 1.80 was achieved by increasing the doping levels of TiO2 in PVA. Polymer distributed Bragg reflectors (DBRs) were fabricated by coating titania doped PVA polymer matrix composite (TPMC) and poly methyl methacrylate (PMMA) polymer as alternating high and low index layers respectively. The reflectivity of DBR was increased by increasing number of periods. The experimental results were in agreement with transfer matrix model (TMM) simulations. TMM simulation results showed that, to achieve reflectivity of more than 90%, 20 periods were required for an index contrast of 0.17 and periods reduced to 5 for an index contrast of 0.51. High index contrast of alternative layers will also benefit in having a relatively broad stop band. The present work suggests fabricating flexible polymer DBRs with any desired stop band by simply varying the concentration of TiO2 in PVA without altering any other thin film processing and DBR fabrication parameters. •Thin films of variable refractive index from a single polymer were developed.•Achieved an index of 1.80 by increasing TiO2 doping levels in PVA polymer.•Fabricated all polymer Distributed Bragg Reflectors (DBR).•Proposes simple fabrication procedure to achieve flexible wide stop band DBRs.