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.

We describe a new and unique method for simultaneous determination of the groove depth and duty cycle of binary diffraction gratings. For a near-normal angle of incidence, the +1 and -1 diffracted orders will behave nearly the same as the duty cycle is varied for a fixed grating depth. The difference in their behavior, quantified as the ratio of their respective diffraction efficiencies, is compared to a look-up table generated by rigorous coupled-wave theory, and the duty cycle of the grating is thus obtained as a function of grating depth. Performing the same analysis for the orthogonal probe-light polarization results in a different functional dependence of the duty cycle on the grating depth. By use of both TE and TM polarizations, the depth and duty cycle for the grating are obtained by the intersection of the functions generated by the individual polarizations. These measurements can also be used to assess qualitatively both the uniformity of the grating and the symmetry of the grating profile. Comparison with scanning electron microscope images shows excellent agreement. This method is advantageous since it can be carried out rapidly, is accurate and repeatable, does not damage the sample, and uses low-cost, commonly available equipment. Since this method consists of only four fixed simple measurements, it is highly suitable for quality control in a manufacturing environment.

We report the first experimental realization of total internal reflection (TIR) diffraction gratings. Performance of less than 0.7-dB insertion loss (IL) for both TE and TM polarizations and 0.5-dB polarization-dependent loss (PDL) are predicted over a 50-nm spectral bandwidth with simultaneous fabrication tolerances on the depth and the duty cycle of binary gratings of +/-5% and +/-14%, respectively. Nineteen gratings were fabricated that met these specifications, yielding IL and PDL values less than 0.6 and 0.2 dB, respectively, across the entire 50-nm bandwidth. Measurements made under the Littrow configuration resulted in high efficiency and low PDL across a 100-nm bandwidth, with up to 100% diffraction efficiency within the experimental measurement error.

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