| Summary: | 博士 === 國立臺灣科技大學 === 電子工程系 === 94 === This thesis focuses on the design and fabrication of two novel fast tunable lasers for fiber optic communication and multi-gas sensor applications.
The first one based on a novel type of grating reflectors is demonstrated aiming for high-speed wavelength-switching applications. Wavelength selectable laser includes an array of distributed-Bragg-reflection type lasers that are combined with a multimode-interference coupler. In order to cover different wavelength bands with simple fabrication, the grating reflector is formed of two sampling grating subsections on waveguides with different thickness. The resultant Bragg-wavelength detuning from the thickness difference between the two SG subsections causes the maximal refection shift to the high-order reflection peaks. A laser array where each laser covers a different wavelength band is realized by varying from laser to laser the corresponding wavelength position of the second-order peak. Each laser has one-side sampling gratings for allowing one-electrode fast tuning. It can also allow high-reflection facet coating to increase output power. The lasing wavelengths of the four lasers are spaced by about 3.5 nm. Each laser can be tuned to cover at least 3.5nm of wavelength span with better than 30 dB side-mode suppression ratio. Forty 50-GHz-spaced channels can be covered with the four-laser array.
The other one based on 1.5-um and 1.57-um cascaded reflectors is realized for multi-gas sensor system to monitor H2O and CO gas mixtures immediately. With simple fabrication, the new design allows the realization of a widely tunable laser sources that can cover the wavelengths of 1.5-um to 1.57-um. In each wavelength band, the laser can be tuned over 3-nm wavelength range to address the H2O or CO absorption line by current tuning and/or temperature tuning. The characteristics of narrow line-width, good side-mode suppression ratio, and fast wavelength switching can simplify the analysis procedures of gas sensing and thus reduce the cost. By direct absorption method, the novel fast tunable laser has been successfully adopted in diode laser sensor system for monitoring of water vapor concentration.
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