Nanometer size field effect transistors can operate as efficient resonant or broadband terahertz detectors, mixers, phase shifters and frequency multipliers at frequencies far beyond their fundamental cut-off frequency. This work is an overview of some recent results concerning the application of nanometer scale field effect transistors for the detection of terahertz radiation.
International audiencePublished experimental results show that single-mode laser light is characterized in the microwave range by a frequency noise which essentially includes a white part and a 1/f (flicker) part. We theoretically show that the spectral density (the line shape) which is compatible with these results is a Voigt profile whose Lorentzian part or homogeneous component is linked to the white noise and the Gaussian part to the 1/f noise. We measure semiconductor laser line profiles and verify that they can be fit with Voigt functions. It is also verified that the width of the Lorentzian part varies like 1/P where P is the laser power while the width of the Gaussian part is more of a constant. Finally, we theoretically show from first principles that laser line shapes are also described by Voigt functions where the Lorentzian part is the laser Airy function and the Gaussian part originates from population noise
We report a detailed experimental and theoretical analysis of a novel type of fibre-optic gyroscope (FOG) that utilizes an air-core photonic-bandgap fibre (PBF) in its sensing coil. The anticipated benefits of using an air-core fibre include dramatically reduced phase bias drift due to temperature (Shupe effect), magnetic field (Faraday effect) and optical nonlinearity (Kerr effect), all of which result from the fact that the fibre mode now propagates in air instead of silica. The reduced Kerr sensitivity, combined with the low theoretical limit of backscattering in air-core fibre, offers the unprecedented potential of ultimately driving this type of FOG with a laser instead of a broadband source, which would yield lower noise and a greater scale-factor stability. We demonstrate some of these anticipated benefits in a PBF FOG with a 235 m coil of air-core fibre interrogated by a broadband Er-doped fibre source. We show that it exhibits a noise limited by the excess noise of the broadband source, as is a conventional gyroscope of the same length (random walk of ∼0.015° h−1/2), but a greatly reduced sensitivity to the Kerr effect (>170), temperature transients (∼6.5), and Faraday effect (>20), compared to a conventional FOG, in quantitative agreement with theory.
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