title: Real-time high-resolution heterodyne-based measurements of spectral dynamics in fibre lasers.
abstract: Conventional tools for measurement of laser spectra (e.g. optical spectrum analysers) capture data averaged over a considerable time period. However, the generation spectrum of many laser types may involve spectral dynamics whose relatively fast time scale is determined by their cavity round trip period, calling for instrumentation featuring both high temporal and spectral resolution. Such real-time spectral characterisation becomes particularly challenging if the laser pulses are long, or they have continuous or quasi-continuous wave radiation components. Here we combine optical heterodyning with a technique of spatio-temporal intensity measurements that allows the characterisation of such complex sources. Fast, round-trip-resolved spectral dynamics of cavity-based systems in real-time are obtained, with temporal resolution of one cavity round trip and frequency resolution defined by its inverse (85 ns and 24 MHz respectively are demonstrated). We also show how under certain conditions for quasi-continuous wave sources, the spectral resolution could be further increased by a factor of 100 by direct extraction of phase information from the heterodyned dynamics or by using double time scales within the spectrogram approach.
authors.affiliation: Aston Institute of Photonic Technologies, Aston University, Birmingham, B4 7ET, United Kingdom.
authors.forename: Srikanth
authors.initials: S
authors.lastname: Sugavanam
authors.affiliation: Aston Institute of Photonic Technologies, Aston University, Birmingham, B4 7ET, United Kingdom.
authors.forename: Simon
authors.initials: S
authors.lastname: Fabbri
authors.affiliation: Aston Institute of Photonic Technologies, Aston University, Birmingham, B4 7ET, United Kingdom.
authors.forename: Son Thai
authors.initials: ST
authors.lastname: Le
authors.affiliation: Institute of Automation and Electrometry SB RAS, 1 Ac. Koptyug Ave., Novosibirsk, 630090, Russia.
authors.forename: Ivan
authors.initials: I
authors.lastname: Lobach
authors.affiliation: Institute of Automation and Electrometry SB RAS, 1 Ac. Koptyug Ave., Novosibirsk, 630090, Russia.
authors.forename: Sergey
authors.initials: S
authors.lastname: Kablukov
authors.affiliation: Zecotek Photonics, Inc., 1120-21331 Gordon Way, Richmond, BC V6W 1J9, Canada.|Novosibirsk State University, 630090, Novosibirsk, Russia.
authors.forename: Serge
authors.initials: S
authors.lastname: Khorev
authors.affiliation: Aston Institute of Photonic Technologies, Aston University, Birmingham, B4 7ET, United Kingdom.|Institute of Automation and Electrometry SB RAS, 1 Ac. Koptyug Ave., Novosibirsk, 630090, Russia.|Novosibirsk State University, 630090, Novosibirsk, Russia.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Churkin