Flat dielectric grating reflectors with focusing abilities.pdfVIP

LETTERS PUBLISHED ONLINE: 2 MAY 2010 | DOI: 10.1038/NPHOTON.2010.116 Flat dielectric grating reflectors with focusing abilities David Fattal , Jingjing Li, Zhen Peng, Marco Fiorentino and Raymond G. Beausoleil * Sub-wavelength dielectric gratings have emerged recently as a pattern). Transmissive gratings are also possible and will be promising alternative to distributed Bragg reflection dielectric described elsewhere. stacks for broadband, high-reflectivity filtering applications. To understand the phase front modification provided by a non- Such a grating structure composed of a single dielectric layer periodic SWG mirror, we start by considering the complex reflec- with the appropriate patterning can sometimes perform as tion coefficient r0(l) of a particular periodic SWG mirror, as well as 30 or 40 dielectric distributed Bragg reflection layers, shown in Fig. 1a. The wavelength-dependent reflectance and while providing new functionalities such as polarization phase shift of the mirror can be easily obtained using either the control and near-field amplification. In this Letter, we introduce finite-element method (FEM) or rigorous coupled wave analysis an interesting property of grating mirrors that cannot be rea- (RCWA)12. In the particular case of Fig. 1a, the grating is a set of lized by their distributed Bragg reflection counterpart: we linear silicon grooves with a period of 0.76 mm on a quartz substrate, show that a non-periodic patterning of the grating surface and is illuminated at normal incidence with a TM-polarized plane can give full control over the phase front of reflected light