title: Solid immersion lens at the aplanatic condition for enhancing the spectral bandwidth of a waveguide grating coupler.
abstract: We report a technique to substantially boost the spectral bandwidth of a conventional waveguide grating coupler by using a solid immersion cylindrical lens at the aplanatic condition to create a highly anamorphic beam and reach a much larger numerical aperture, thus enhancing the spectral bandwidth of a free-space propagating optical beam coupled into a single-mode planar integrated optical waveguide (IOW). Our experimental results show that the broadband IOW spectrometer thus created almost doubles (94% enhancement) the coupled spectral bandwidth of a conventional configuration. To exemplify the benefits made possible by the developed approach, we applied the technique to the broadband spectroscopic characterization of a protein submonolayer; our experimental data confirm the enhanced spectral bandwidth (around 380-nm) and illustrate the potentials of the developed technology. Besides the enhanced bandwidth, the broadband coupler of the single-mode IOW spectrometer described here is more robust and user-friendly than those previously reported in the literature and is expected to have an important impact on spectroscopic studies of surface-adsorbed molecular layers and surface phenomena.
authors.affiliation: Instituto de Física, UFRGS, CP 15051, Porto Alegre, RS 91501-970, Brazil.
authors.forename: Marcelo B
authors.initials: MB
authors.lastname: Pereira
authors.forename: Jill S
authors.initials: JS
authors.lastname: Craven
authors.forename: Sergio B
authors.initials: SB
authors.lastname: Mendes