Angular dependent light emission from planar waveguides.

Peter, Jaison; Prabhu, Radhakrishna; Radhakrishnan, P.; Vallabhan, C.P.G.; Nampoori, V.P.N.; Kailasnath, M.

Abstract

We have investigated the angular dependence of amplified spontaneous emission (ASE) and laser emission from an asymmetric and free-standing polymer thin films doped with rhodamine 6G, which is transversely pumped by a pulsed Nd:YAG laser. A semi-leaky waveguide or quasi-waveguide structure has been developed by spin coating technique. In these waveguides, the light was confined by the film/air-film/glass substrate interfaces. At the film/substrate interface, a portion of light will reflect back into the film (guided mode) and the remaining refracted to the substrate resulting in cutoff modes. A blue-shift in ASE has been observed when the pump power was increased from 8 to 20 mW allowing a limited range of tuning of emission wavelength. To study the directionality of the ASE from the waveguide, we have measured the output intensity and FWHM of emission spectra as a function of viewing angle (θ) from the plane parallel to film. From the detailed examination of the output emission spectra, as +θ increases from 0° there has been an initial decrease in output intensity, but at a particular angle ≈10° an increase in output intensity was observed. This additional peak in output intensity as +θ is a clear indication of coexistence of the cutoff mode. We also present a compact solid-state laser based on leaky mode propagation from the dye-doped polymer free-standing film (∼50-μm thickness) waveguide. The partial reflections from the broad lateral surfaces of the free-standing films provided the optical feedback for the laser emission with high directionality. For a pump power of 22 mW, an intense line with FWHM-[less than] 0.2nm was observed at 578nm.

Citation

PETER, J., PRABHU, R., RADHAKRISHNAN, P., VALLABHAN, C.P.G., NAMPOORI, V.P.N. and KAILASNATH, M. 2015. Angular dependent light emission from planar waveguides. Journal of applied physics, 117(1), Article 015301. Available from: https://doi.org/10.1063/1.4905011

• Journal Article Type: Article
• Acceptance Date: Dec 31, 2014
• Online Publication Date: Jan 5, 2015
• Publication Date: Jan 7, 2015
• Deposit Date: Oct 16, 2015
• Publicly Available Date: Oct 16, 2015
• Journal: Journal of applied physics
• Print ISSN: 0021-8979
• Electronic ISSN: 1089-7550
• Publisher: AIP Publishing
• Peer Reviewed: Peer Reviewed
• Volume: 117
• Issue: 1
• Article Number: 015301
• DOI: https://doi.org/10.1063/1.4905011
• Keywords: Planar wave guides; Cutoff mode; Guided mode; Laser modes
• Public URL: http://hdl.handle.net/10059/1312