Tridirectional Gratings as Improved Couplers for QWIPs

Tridirectional diffraction gratings have been proposed to provide optical coupling to quantum-well infrared photodetectors (QWIPs) in focal-plane arrays. The tridirectional gratings would be improved versions of the bidirectional (rectangular-pattern) gratings described in "Cross-Grating Coupling for Focal-Plane Arrays of QWIPS" (NPO-19657), NASA Tech Briefs, Vol. 22, No. 1 (January 1998), page 6a. The tridirectional gratings would comprise metal patches or holes arranged in a pattern of closely packed regular hexagonal cells (see figure), with dimensions chosen to optimize diffraction patterns to maximize coupling within narrow spectral bands of interest.