Commercially available supercontinuum sources continue to experience a strong growth in a wide range of industrial and scientific applications. In addition, there is a significant research effort focused on extending the wavelength coverage both towards UV and Mid-IR. Broadband sources covering these wavelength regions have received significant attention from potential users, as there is a wide array of applications for which there are few suitable alternative light sources – if any. Our developments in the field of Mid-IR supercontinuum sources have been based on radical approaches; such as soft glasses and novel pumping schemes, whereas shifting the spectrum further towards the UV has been based on sophisticated microstructure fiber designs. Here we present our latest developments in tailoring the power and spectral coverage of spatially coherent broadband supercontinuum sources.
We demonstrate a tunable laser operating in the 1-1.1 &mgr;m wavelength region with a tuning range of 43 nm (FWHM), an
output power of 19 mW and coherence length of 14 mm. The source is based on a master laser consisting of a cavity
tuned ring configuration with a fiber Fabry Perot filter used as a tuning element and a semiconductor amplifier as gain
medium. The output of the master laser is subsequently power boosted using an Ytterbium doped fiber amplifier
(YDFA). In addition to providing a power boost, we demonstrate that by tailoring the gain spectrum of the YDFA it is
possible to increase the FWHM scanning range by 7 nm compared to that of the master laser.
Two swept-wavelength light sources based on Ytterbium doped fibre amplifiers are demonstrated. The filtered output from a superfluorescent source is scanned over 20 nm, and used for topography with an axial resolution of <40 μm. Dynamic properties of a swept-wavelength YDFA based ring laser is investigated. This is the first reported results with dynamically swept sources centered in the 1 μm wavelength range, which is expected to be important for future development of optical coherence tomography systems for retinal imaging.
We present a novel implementation of the lightwave synthesized frequency sweeper (LSFS) based on Ytterbium doped fiber amplifiers. The source can potentially be used for swept source optical coherence tomography (SS-OCT), which has recently been shown to have an improved signal to noise ratio compared to time domain OCT systems, and development of suitable swept wavelength sources is for this reason of utmost importance. Based on Ytterbium doped fiber amplifiers, the source operates in the 1-1.1 μm range, which makes it particular useful for ophthalmic applications of OCT. Previous studies of a LSFS based on Erbium doped fiber amplifiers (EDFAs), which can be operated with noise figures close to the fundamental quantum limit, showed that the scanning range was limited by the buildup of amplified spontaneous emission noise. In spite of Ytterbium doped amplifiers are fundamentally not able to approach the quantum limit, our fundamental experiments show performance comparable to EDFA based systems. The result of the experiments compare well with predictions given by a numerical concatenated amplifier model, hence validating the model and enabling us to use the model for future system optimization.