This thesis focuses on selected fundamental aspects of fiber-based supercontinuum ligh sources and presents two case studies of highresolution optical interferometry. Most commonly, supercontinuum light is generated by pulsed laser sources, so that strong intensity fluctuations are inherent in the emitted light. For applications, which require broadband continuouswave illumination, a new concept of a broadband light source based on dispersive stretching of supercontinuum light pulses is presented. This concept was found to be able to provide intensity fluctuations below 1 % in the output light. Supercontinuum generation in multimode fibers involves two major aspects that make it differ from continuum generation in singlemode fibers; much higher powers can be obtained without damaging the fiber and different spectral properties become accessible with the higher-order modes. To explore these possibilities, a numerical solver for simulation studies of supercontinuum generation in multimode fibers was developed. First, the solver was used to demonstrate the polarization dynamics of the supercontinuum generated by two degenerate fiber modes in a non-birefringent microstructured fiber. Next, the operation of the solver was verified by comparing the simulated and measured supercontinua produced in a suspended-core fiber. The influence of the higher-order modes became apparent already at lower pump powers. As a case study of applications where broadband light sources are needed, an interferometer was developed to characterize surface vibrations in micro-mechanical resonators. The measurement principle was based on phase-shifting white-light interferometry (PS-WLI) with stroboscopic illumination. An analysis method was developed which made it possible to detect vibration amplitudes below 100 picometers. Further, it was found that for the best performance of PS-WLI an optimal spectral width of the illuminating light source is required, which in the presented setup was closely matched by a simple green light-emitting diode (LED). The pulse duration obtained from the LED allowed imaging out-of-plane vibration fields in a micromechanical plate resonator at frequencies up to 14 MHz, which is about 10 MHz higher than what has previously been reported. In principle, the achieved amplitude detection limit could allow even higher frequencies. Additionally, a simple interferometric gas refractometer based on a hollow-core photonic band-gap fiber was developed and characterized. Using a tunable laser source, spectrally resolved measurements of both the refractive index and the absorption coefficient of gaseous analytes could be measured with high sensitivity. With this device, the refractive index of an airacetylene mixture was measured with a resolution of 4•10-7 RIU (refractive index units) in the spectral range from 1525 nm to 1545 nm.
|Translated title of the contribution||Novel light sources and high-resolution interferometric applications|
|Publication status||Published - 2013|
|MoE publication type||G5 Doctoral dissertation (article)|
- supercontinuum generation
- multimode fibers
- white-light interferometry