Micro-optical spatial and spectral elements

Abstract

Interference filters have a defect layer incorporated within a photonic crystal structure and generate a narrow transmission notch within a wide stop band. In this paper, we propose and demonstrate wavelength-tunable spatial filters by introducing diffractive optical elements in the defect layer. The spectral transmission through the device was a function of the local defect layer thickness under broadband illumination. For each wavelength, the spatial transmission followed the contours of equal defect layer optical thickness. The devices were implemented by depositing a one-dimensional photonic crystal with a centrally integrated defect layer on a silicon substrate using plasma-enhanced chemical vapor deposition. The defect layer was lithographically patterned with charge 2, 8-level vortex structures. The spectral transmission peak and linewidth was characterized by separately illuminating each zone of diffractive element using a tunable laser source and compared with model simulations. The spatial transmission through the device was imaged onto a CCD camera. Triangular wedge-shaped zones with wavelength-dependent orientations were observed. These novel devices with spectrally tunable spatial transmission have potential applications in pupil filtering, hyperspectral imaging, and engineered illumination systems.