PhD defence by Rasmus Dybbro Engelsholm

Title: Low Noise Supercontinuum Lasers for Optical Coherence Tomography Systems

Supervisors

Principal supervisor:  Prof. Ole Bang, DTU Fotonik

Co-supervisor: Christos Markos, DTU Fotonik


Evaluation Board

Assoc. Prof Jesper Lægsgaard, DTU Fotonik

Dr. Peter Horak, University of South Hampton, UK

Assoc. Prof. Ryszard Buczyński, University of Warsaw (UW), Poland


Master of the Ceremony

Assoc. Prof. Christos Markos

Abstract:

Supercontinuum sources have wide ranging applications due to their exceptional brightness, spatial coherence and broad spectral coverage. Within the field of spectral domain optical coherence tomography they are especially interesting, as their spectral broadness enable imaging with sub-micrometer resolution. This can in turn be used for skin and eye disease diagnostics as well as non-destructive quality testing of a large range of products. However, the high relative noise of supercontinuum sources decreases image quality in terms of higher background noise and lower contrast, compared to other, less broad, sources. A part of this thesis deals with ways to quantify the noise in relation to optical coherence tomography across measurement methods.

A section of this thesis is the step by step derivation of the generalized nonlinear Schrödinger equation, including tapering, multiple modes and mode profile dispersion. A numerical scheme for solving the equation was then implemented and tested. The numerical model was used to understand how undertapering can reduce supercontinuum relative intensity noise near the spectral edges. The model was also used to investigate low noise supercontinuum generation in all normal dispersion fibers. Both Raman scattering and polarization modulation instability was shown to deteriorate the noise properties. An optimized at and close to dispersion photonic crystal fiber design was proposed, and steps were taken to reduce confinement loss. The fiber was subsequently investigated with pumping at 1064nm through an initial step of soliton fission. While it was found to be an improvement upon current commercial sources, the noise was due to interference fringes not as low as expected.


Tidspunkt

fre 30 nov 18
13:30 - 16:30

Arrangør

DTU
DTU Fotonik

Kontaktperson

Hvor

Lyngby Campus

Bld. 341, aud. 22