In this Ph.D. work rapidly wavelength tunable laser configurations operating in the 1 m range have been investigated. Such lasers are interesting for the so-called optical coherence tomography (OCT) technique, whereof one successful application today is within the field of ophthalmology. In this application, the 1-1.1 m wavelength range is particular suitable for imaging features in the deeper lying layers of the human retina. Ytterbium Doped Fiber Amplifiers (YDFAs) are an attractive and available gain medium for the 1-1.1 m wavelength band. However, the relative long upper state lifetime, imposes a serious limitation on the achievable scanning speed if the YDFA is to be used using for so-called cavity tuned lasers. Another swept wavelength configuration, the so-called lightwave synthesized frequency sweeper, is therefore in this work experimentally and numerically investigated as a possible alternative to cavity tuned lasers. A cavity tuned ring laser, using a semiconductor amplifier is also experimentally investigated as a part of this work. Alone, this source cannot deliver sufficient optical output power for it to be interesting for OCT, but with a proposed sub-sequent YDFA based power booster stage, the source Is not only capable of delivering sufficient power, but it is also possible to shape the lasing spectrum with the booster stage, such that the effective wavelength scanning range the amplified source is improved to that obtained with the cavity tuned laser alone. Apart from OCT, there is a plethora of applications in which tunable lasers can be utilized, one such application is refractive index waveguide sensing. One method, of performing waveguide sensing is through the so-called wavelength-interrogation method, for which the cavity tuned laser has been tested in this project. The large scanning range which can be achieved, with the cavity tuned source allows measurements over large dynamic refractive index ranges.
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Thrane, Lars, Bjarklev, Anders Overgaard, Andersen, Peter E.