Dual-Frequencies Diffractive Lenses at Millimeter Wavelengths

The analysis and comparison of two novel kinds of focusing elements as reflectors

“…As shown in Figure 8a, the intensity of three-order SP at the focus at each harmonic wavelength is lightened linearly with increasing value of m in Eq. (14). The intensity of three-order FZPCP is lower than that of three-order SP at higher harmonic wavelength.…”

“…For multiorder FZPCP, the diffraction efficiency at each harmonic frequency becomes lower with increasing values of m in Eq. (14), which means the highest diffraction efficiency occurs at the longest harmonic wavelength. For multiorder SP, the diffraction efficiency at each harmonic wavelength remains unchanged regardless of the order M. Moreover, the thickness of multiorder SP can be increased freely to enhance the bandwidth.…”

“…The total thickness is M (an integer) times thicker than the first diffracted order phase-correcting Fresnel zone plates. Multiorder diffractive elements have been used to construct broadband or multispectral optical systems [10][11][12][13][14][15].…”