As gas prices continue to rise and fossil fuels pollute our environment, various alternative fuel sources are being actively pursued. Hydrogen shows considerable promise due to its virtually unlimited supply, energy conversion efficiency, and neutral impact on the environment. However, due to the flammability of hydrogen gas in concentrations as low as 4%, reliable sensors capable of detecting small concentrations of hydrogen with quick response times are a necessity.A novel type of hydrogen sensor utilizing a thin film of palladium deposited on the ridge of an edge-emitting laser has been designed and fabricated. This palladium film is well known to react to hydrogen, forming palladium hydride with optical properties dependent on the hydrogen concentration. This reaction yields a change in complex refractive index and thus also the laser’s output power. The advantages of these sensors are their small size, high sensitivity, wide dynamic range, inline integration, and scalability to arrays. These capabilities surpass most traditional optical sensors, which generally utilize fiber gratings, surface plasmon resonances, or surface reflectance. Although those methods can be effective, the edge-emitting laser sensors are easier to miniaturize, integrate, and array.This thesis is organized into four sections. First, a brief analysis of the rising importance of hydrogen energy sources and various hydrogen sensing mechanisms is presented, followed by an overview of the edge-emitting laser sensor in terms of device design and physical sensing properties. A detailed description of the associated fabrication process is given, along with its test setup. Finally, the device performance with regards to varying concentrations of hydrogen is analyzed, with suggestions for future work and improvements.
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Palladium coated edge-emitting lasers for hydrogen sensing applications
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