Spectral behaviour of single- and multi- Fabry-Pérot optical resonators: a theoretical analysis
Creators: name: Yeung, Jerry
Publisher: name: University of Surrey
Year: 2025
Subjects: Fabry-Pérot resonator
Schawlow-Townes linewidth

description: The Fabry-Pérot resonator is a high-finesse interferometer with countless spectroscopic
description: applications. It has been extensively investigated and its spectral properties are well
description: understood. However, these investigations have largely been limited to situations with an
description: electromagnetic field incident upon the resonator from one side only. The effects of external
description: feedback on the spectral properties of Fabry-Pérot-resonator based lasers have been
description: investigated, but the external feedback is inevitably coupled to the operation of the laser and,
description: therefore, occurs only at the laser frequency, i.e., at one of the resonance frequencies of the
description: resonator. In this thesis, we investigate the spectral properties of a Fabry-Pérot resonator when
description: launching light through both end facets. We demonstrate and systematically quantify the novel
description: spectral behavior not observed in a Fabry-Pérot resonator excited from one end facet only. We
description: show that these spectral phenomena also manifest themselves in multi-resonator structures. We
description: propose a potential application of these phenomena by showing that the laser output power of
description: an optically pumped laser with low pump absorption can be enhanced by a factor of two.
description: It has been the general belief for the past sixty years that the Schawlow-Townes laser
description: linewidth is due to amplitude and phase fluctuations induced by spontaneous emission.
description: Recently, it was proposed that, instead, the Schawlow-Townes linewidth is a four-fold
description: approximation of a semi-classical fundamental laser linewidth, which is obtained by
description: performing a Fourier transform on the decay of photons out of the resonator. Most laser models
description: in the literature do not consider frequencies other than the lasing frequency, and most models
description: which consider spontaneous emission incorrectly implement it as a source of random noise. A
description: laser model capable of calculating the fundamental laser linewidth has not yet been developed.
description: In this thesis, we propose a laser model capable of performing ab initio calculations
description: of the laser linewidth in the spectral domain. Spontaneous emission is not implemented as a
description: noise source, but rather as a source of photons that survive on a macroscopic time scale.
description: Spectral selectivity is obtained solely by interference between the light oscillating in the
description: resonator and the light spontaneously emitted by the atoms. Below and above laser threshold,
description: our ab initio calculation delivers the same fundamental laser linewidth as recently predicted.
description: This result independently demonstrates that the fundamental laser linewidth is due to the gain
description: elongating the photon-decay time.