Diffractive optical elements for photonic gas sensors

Abstract

Diffractive optical elements are designed and demonstrated as elemental units in photonic gas sensors. Diffraction gratings are written on specially designed photosensitive polymers using photolithographic techniques, as well as on multilayer metal/metal oxide thin film structures. Photonic sensors are implemented using grating structures as the elemental units for the detection of the external agent. These gratings are designed from such materials that show response to the external agent and the sensitivity is increased through the design of the grating. The principle of operation is based on the grating's diffraction efficiency variations due to index of refraction alterations and/or geometrical changes of the grating structure (e.g., groove depth, groove spacing) to external factors. The advantageous characteristics of the presented integrated sensor are the fully reversible behavior at ambient operating conditions, without the need for additional heating or light exposure. Applications of these sensitive photonic sensors so far include water vapor, hydrocarbons, and alcohol detection. The optical designs are based on diffraction efficiency measurements, and incorporate a monochromatic optical source and simple optoelectronic detection components. The photonic sensor integration is based on bulk optics approach.