REAL-TIME OBSERVATION OF THE OPTICAL SAGNAC EFFECT IN ULTRAFAST BIDIRECTIONAL FIBRE LASERS
M Chernysheva, S Sugavanam, S Turitsyn
APL Photonics 5, 016104 (2020)
The optical Sagnac effect sets fundamentals of the operating principle for ring laser and fiber optic gyroscopes, which are preferred instruments for inertial guidance systems, seismology, and geodesy. Operating at both high bias stability and angular velocity resolutions demands special precautions like dithering or multimode operation to eliminate frequency lock-in or similar effects introduced due to synchronization of counterpropagating channels. Recently, to circumvent these limitations, ultrashort pulsed radiation was suggested to supersede conventional continuous wave operation. Despite the ultrafast nature of ultrashort pulse generation, the interrogation of the Sagnac effect relies on highly averaging measurement methods. Here, we demonstrate the novel approach to the optical Sagnac effect visualization by applying real-time spatio-temporal intensity processing and time-resolved spectral domain measurements of ultrashort pulse dynamics in rotating the bidirectional ring fiber laser cavity. Our results reveal the high potential of application of novel methods of optical Sagnac effect measurements, allowing enhancement of rotation sensitivity and resolution by several orders of magnitude.
BUILD-UP DYNAMICS IN BIDIRECTIONAL SOLITON FIBER LASERS
I Kudelin, S Sugavanam, and M Chernysheva
Photonics Research 8(6) 776-780 (2020)
Bidirectional ultrafast fiber lasers present an attractive solution, enabling the generation of two mutually coherent ultrashort pulse trains in a simple and turnkey system. Still, the lack of a comprehensive numerical model describing steady-state bidirectional generation, and even less ultrafast soliton breakdowns and collisions, is obstructing the achievement of the performance compared with unidirectional lasers. In this paper, we have experimentally investigated real-time build-up dynamics of counter-propagating solitons in an ultrafast ring Er-doped fiber laser via the dispersive Fourier transform methodology. We parade that counter-propagating pulses experience independent build-up dynamics from modulation instability, undergoing breathing dynamics and diverging subordinate pulse structure formation and annihilation to a stable bidirectional pulse train. Yet, the interaction of pulses in the cavity presents the key underlying phenomenon driving formation evolution distinct from unidirectional pulse build-up. Our findings will provide physical foundations for bidirectional ultrafast fiber laser design to carry forward their application.
AUTOFLUORESCENCE GUIDED WELDING OF HEART TISSUE BY LASER PULSE BURSTS AT 1550 NM
K Litvinova, M Chernysheva, B Stegemann, F Leyva
Biomedical Optics Express 11(11) 6271-6280 (2020)
Wound healing and other surgical technologies traditionally solved by suturing and stapling have recently been enhanced by the application of laser tissue welding. The usage of high energy laser radiation to anastomose tissues eliminates a foreign body reaction, reduces scar formation, and allows for the creation of watertight closure. In the current work, we show that an ultrafast pulsed fibre laser beam with 183 µJ·cm−2 energy fluence at 1550 nm provides successful welding of dissected chicken heart walls with the tensile strength of 1.03±0.12 kg·cm−2 equal to that of native tissue. The welding process was monitored employing fluorescence spectroscopy that detects the biochemical composition of tissues. We believe that fluorescence spectroscopy guided laser tissue welding is a promising approach for decreasing wound healing times and the avoiding risks of postoperative complications.
PULSE-ONSET DYNAMICS IN A BIDIRECTIONAL MODE-LOCKED FIBRE LASER VIA INSTABILITIES
I Kudelin, S Sugavanam, M Chernysheva
Communications Physics 3, 202 (2020)
Real-time observation of the emergence of coherent structures from noise via instabilities is of particular interest across disciplines ranging from biology to astrophysics. In the context of photonics, ultrafast fibre lasers provide an ideal test-bed for experimental observation of dynamical instabilities and generation of coherent structures of ultrashort pulses. Here we present experimentally obtained switch-on dynamics of counter-propagating ultrashort pulses in a bidirectional mode-locked fibre laser with delayed pulse formation via Q-switched and modulation instabilities, pronounced central wavelength drift, with the multiple-pulse formation. We define a localisation parameter using the round-trip resolved autocorrelation function to quantify the extent of the pulse formation, indicating an energy interchange between coherent features and background radiation. Furthermore, we report the formation of synchronised and unsynchronised dispersion waves. Our results reveal the complexity of the establishment of coherent features and their interaction with background radiation, contributing further towards the understanding of nonlinear systems in general.
SHORT-WAVE IR ULTRAFAST FIBER LASER SYSTEMS: CURRENT CHALLENGES AND PROSPECTIVE APPLICATIONS
D C Kirsch, S Chen, R Sidharthan, Y Chen, S Yoo, M Chernysheva
Ultrashort pulse generation at the short-wave infrared (SWIR) wavelength ranges from 1.6 to 2.5μm2.5μm and together with benefits of the all-fiber design has transformed lasers into an essential tool for industrial, technological, scientific, environmental, and medical applications. With the development of pumping sources and fiber components, ultrafast SWIR fiber lasers have drawn exceptional research and industrial attention over the last decade, resulting in the achievement of comparable performance or even surpassing well-established near-IR sources. Exceptionally compact, highly stable, cost-effective, and maintenance-free ultrafast fiber lasers operating at the SWIR range are currently well on the way to be commercially employed. This invited Perspective article gives a comprehensive overview of the most significant achievements enabling ultrafast generation at SWIR, including up-to-date gain fibers and saturable absorbers, nonlinear process, and laser architectures. This article highlights the perspectives and strategies for further maturing of the field of SWIR fiber lasers and pathways for the improvement of the performance, overcoming existing bottlenecks and challenges toward reducing pulse durations, tunability of repetition rate, and power upscaling. The advancement of the ultrafast SWIR laser development is projected until the landscape of existing technologies, driven by these ultimate sources, and potential applications, emerging on the horizon.
SHORT BROADBAND FIBER GRATINGS WITH LOW GROUP DELAY
M Becker, I Chiamenti, T Elsmann, M Chernysheva
Journal of Lightwave Technology (2021)
Fiber Bragg gratings (FBGs) are essential optical components, which due to their design flexibility offer numerous prospects for a wide range of applications in fiber laser, sensor, and telecommunication technologies. Here we demonstrate that a phase mask interferometer driven by a deep-ultraviolet femtosecond laser enables inscription of FBGs with top-hat spectral reflection bandwidth. FBGs with the bandwidth of 2 nm have been achieved with inscription of several superimposed narrow FBGs with bandwidth less than 0.2 nm. The induced refractive index modulation profile of the superimposed gratings has been investigated with two measurement methods, namely, optical frequency domain reflectometry and the layer-peeling method. The analysis has shown that the spatial modulation index profile follows a sinc profile and has a very narrow central peak of less than 0.4 mm. Importantly, the FBGs provide low group delay values in comparison to their chirped counterparts. Additionally, the small center structure makes such gratings ideal for fiber sensing with high local resolution. The demonstrated FBG inscription method, developed initially to fabricate optical reflectors for infrared laser systems, can be translated to other applications, such as biophotonics, telecommunications, sensing and astrophysics.
FIRST-ORDER FIBRE BRAGG GRATING INSCRIPTION IN INDIUM FLUORIDE FIBRE USING UV/VIS FEMTOSECOND LASER AND TWO-BEAM INTERFEROMETRY
I Chiamenti, T Elsmann, A Reupert, O Kara, M Becker, L Wondraczek, M Chernysheva
Optics Letters (2021)
Fibre gratings are among key components in fibre-based photonics systems and, particularly, laser cavities. In latter, they can play multiple roles, such as those of mirrors, polarisers, filters or dispersion compensators. In this Letter, we present the inscription of highly reflective first-order fibre Bragg gratings (FBGs) in soft indium fluoride-based (InF3) fibres using a two-beam phase-mask interferometer and a femtosecond laser. We demonstrate an enhanced response of InF3-based fibre to a visible (400 nm) inscription wavelength compared to ultraviolet irradiation at 266 nm. In this way, FBGs with a reflectivity of over 99.7% were inscribed at around 1.9 µm with the bandwidth of 2.68 nm. After thermal annealing at 393 K, the Bragg wavelength demonstrates stable thermal shift of 20 pm/K in the temperature range spanning from 293 to 373 K. These observations suggest a potential extension of InF3 fibre-based laser components to an operational range of up to 5 µm.