Guided mode resonance (GMR) gratings are used as filters due to the narrow bandwidth and high efficiency at the resonance wavelength. In this paper, a two-dimensional gradient-period GMR grating with rectangular array structure is proposed. Ta2O5, HfO2 and SiO2 are selected as grating materials. Double reflection peaks are obtained by matching the guide modes in two orthogonal planes of diffraction to different wavelengths. The rigorous coupled wave analysis (RCWA) are used to analyze the resonance characteristics of two-dimensional GMR grating. By comparing the resonance behavior, the resonance wavelengths of two-dimensional GMR grating can be approximated as the superposition of two one-dimensional GMR gratings, the periods of the two one-dimensional gratings are respectively equal to those of the two-dimensional GMR grating along x and y direction (Λx and Λy). Thus, we can control the two resonance wavelengths by changing the periods of Λx, Λy. According to the result of design, when the two resonance peaks are both in the spectrum range of 850nm-1050nm, the efficiencies of the two peaks are greater than 90%, and full width at half-maximum (FWHM) less than 1.5nm. This two-wavelength tunable filter will be a good two-dimensional displacement sensor. The effects of duty cycle, groove depth and other parameters on the resonance wavelength are also studied.
Crossed-grating, as the standard element for metrology in two-dimensional precision positioning system, has been widely used in precision machine tools, highly sophisticated manufacturing and machining system. The technical indicators of crossed-grating, such as its diffraction efficiency and the efficiency equilibrium of the TE or TM polarized light are relevant to the microstructure of crossed-grating. While the structure of crossed-grating is determined by the microstructure of holographic photoresist grating. For exploring the evolution of microstructure of crossed holographic photoresist grating. In this paper, a new method for obtaining the variation curve of groove depth with exposure volume (the contrast curve of photoresist)is proposed, this method does not need a series of repeated experiments and is easy to operate compared with previous step experiments. The contrast curve of photoresist under different developing conditions (such as developer concentration and developing time) are analyzed. In addition, the top-view groove profile of crossed holographic photoresist grating under different process conditions are revealed too. The above research results provides a theoretical basis for the process parameters in holographic recording and developing of crossed holographic photoresist grating.
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