Jeffrey I. Hirsh

All-dielectric high-efficiency reflection gratings made with multilayer thin-film coatings

We made a high-efficiency ref lection grating by coating a nine-layer quarter-wave system of ZnS/Na(3)AlF(6) directly onto a surface-relief grating in photoresist. Eff iciencies of 70% and 84% were measured at the firstorder Littrow mount with the laser beam incident from the air side and from the substrate side, respectively. The experimental results are in qualitative agreement with theoretical predictions. The key to further improvement in the diffraction eff iciency is to improve the contour conformation of the coated dielectric layers.

1- to 100-channel waveguide beam splitter and TE to TM polarization converter

This paper describes a channel waveguide beam splitter (CWBS) in which a single laser beam can be split into many beams using glass stripe waveguides and localized surface relief gratings. The grating element situated on top of individual 90 degree(s) T-branches couples a fraction of the backbone light down a side channel and acts as a miniature mode converter. Single-mode TE light in the backbone is converted into single-mode TM light in the side channel. The laser wavelength used in these experiments was 830 nm. Each individual grating was only a few microns in length and so the grating acceptance exhibited a large bandwidth. The total excess loss coupling the input waveguide optical power partially into 100 waveguide branches was only 0.25 dB.