Far-infrared band-pass grid filters

Michael E. MacDonald; Erich N. Grossman

doi:10.1117/12.262759

18 December 1996 Far-infrared band-pass grid filters

Michael E. MacDonald, Erich N. Grossman

Proceedings Volume 2842, Millimeter and Submillimeter Waves and Applications III; (1996) https://doi.org/10.1117/12.262759
Event: SPIE's 1996 International Symposium on Optical Science, Engineering, and Instrumentation, 1996, Denver, CO, United States

Abstract

The spectral performance of bandpass grid filters centered at terahertz frequencies is presented. The filters are composed of a periodic array of cross-shaped apertures in an evaporated metal film on a thin dielectric substrate. A commercial Fourier-transform spectrometer is used to measure spectral transmittance. Results are presented for filters using gold films of different thickness. The peak transmittance is correlated with the DC surface resistance R_s of the film, which is probed using an in situ test structure on the fabricated filters. This is true even though the gold films all have a thickness several times the classical skin depth at the resonant frequency. Measurements of R_s and peak transmittance at 77 K show an equivalent correlation, indicating that some of the loss is due to the finite conductivity of the gold film. The dielectric substrate causes a downward shift in the center frequency of the filter proportional to the dielectric constant and thickness of the substrate. The center frequency shifts rapidly with increasing dielectric thickness and reaches an asymptotic value reduced from the freestanding case by the square root of the mean dielectric constant. Measurements are compared to a finite-difference time domain model, which accurately predicts the center frequency, but does not account for losses. The performance of these filters, along with their simple fabrication, makes them useful frequency- selective elements at far-IR wavelengths.

Citation Download Citation

Michael E. MacDonald and Erich N. Grossman "Far-infrared band-pass grid filters", Proc. SPIE 2842, Millimeter and Submillimeter Waves and Applications III, (18 December 1996); https://doi.org/10.1117/12.262759

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