Skip to main content

The Single Optical Fibre Scalpel

Periodic Reporting for period 1 - THESIS (The Single Optical Fibre Scalpel)

Reporting period: 2018-10-01 to 2020-09-30

Modern laser microsurgery requires compact ultrafast laser sources and miniature fibre-optic probes. The aim of this project is to develop a scanner-free and ultra-thin single multimode optical fibre scalpel to perform image-guided high-precision microsurgery. In this project, we will tackle the key challenges in the field of laser microsurgery: i) The lack of robust and compact ultrafast laser sources; ii) bulky laser-pulse delivery probes; and iii) the lack of simultaneous high-resolution imaging modalities to guide the surgery. In this proposed research, we developed a new dissipative-soliton-resonance (DSR) ultrafast fibre laser and tried to integrate the DSR laser to the single multimode fibre imaging system. It is expected to make new advancements and discoveries in a number of emerging topics at the forefront of Photonics, such as DSR ultrafast fibre laser technology, single multimode fibre imaging, and ultrafast laser microsurgery. In addition, the results arising from nonlinear imaging of the biological tissue and ultrafast-laser-tissue interaction will inform clinical and biomedical research on biomaterials properties and disease pathology. These are central to the research theme priority of personalising health and care in Horizon 2020 - producing knowledge that will be applied in the area of health and medicine. The commercial value of the new ultrafast fibre-based light sources and the medical instrument for in-vivo endoscopic imaging and microsurgery will also be explored during this project.
Overall objectives: we aim to develop a novel single MMF ultrafast laser scalpel functioning as both a high resolution imaging probe and a high-precision microsurgery laser knife. This single MMF laser scalpel will be scanner-free, lensless, ultra-thin, high-resolution, low cost and with a precision to target single cells. We will also develop a new DSR ultrafast laser source, and then integrate it with the single MMF laser scalpel. This DSR source will enable both ultrafast nonlinear imaging and tissue ablation simultaneously with tuneable parameters such as pulse width, pulse energy, centre wavelength and repetition rate.
1) We experimentally investigated the properties of dissipative-soliton-resonance (DSR) pulses in a fiber laser. Pulse breaking of the DSR pulses was accompanied by the multipulse state and harmonic mode-locking pulses evolving from the original DSR pulse. Narrowing of the DSR pulse with the increase in the pump power was observed for the very first time. Further results show that these unusual evolutions of DSR pulses could be attributed to the changes in several laser parameters resulting from the increasing pump power under specific operating conditions.
2) We experimentally demonstrated period doubling of DSR pulses in a fiber laser and numerically duplicated it. DSR pulse narrowing with pump power increasing under the period-doubling state was also experimentally observed.
3) We report on the experimental observation of the period doubling of multiple DSR pulses in an all-normal-dispersion fibre laser. The typical DSR performance of a linear pulse duration change, versus the variation of pump power, can be maintained when the period doubling of multiple DSR pulses appears.
4) We experimentally demonstrated a type of tunable and switchable harmonic h-shaped pulse generation in a thulium-doped fiber (TDF) laser passively mode locked by using an ultralong nonlinear optical loop mirror. The total cavity length was ∼3.03 km, the longest ever built for a TDF laser to our best knowledge. The produced h-shaped pulse can operate either in a fundamental or in a high-order harmonic mode-locking (HML) state depending on pump power and intra-cavity polarization state (PS).
5) We report on DSR and its transformation into a type of burst-like emission in a holmium-doped fiber laser in the large normal dispersion regime. It is revealed that this burst-like emission could be caused by a type of peak-power depressing effect, which results from the competition between DSR and soliton formation.
6) We report on experimental generation and evolution of circumstance-susceptible, narrow-bandwidth, h-shaped pulse in a TDF laser. Our results substantiate the experimental revelation of such a type of particular-profile pulse in the normal dispersion regime, demonstrating some new evolution features facilitated by the dispersionrelevant circumstance-susceptibility.
7) We reviewed possible generation and propagation of various soliton molecules (SMs) in fiber systems. SMs can survive either in fibers or fiber lasers. A dispersion-managed (DM) fiber link is the only platform for SM demonstration, while various fiber lasers can support different SMs. The fundamental unit of SMs can be conventional solitons generated in an anomalous dispersion regime, stretched pulses in DM fiber lasers, parabolic pulses, or gain-guided solitons in a normal dispersion regime. We demonstrated a new kind of SM with nanosecond soliton separation.
8) Raman-scattering-assisted noise-like pulse (NLP) generation was achieved by using an appropriate segment of high nonlinearity fiber in an erbium-doped fiber laser. Broadband spectrum with 203 nm 3-dB bandwidth was obtained, which, to the best of our knowledge, is the broadest bandwidth achieved for NLPs. The broadband operation is the result of tailored cavity design, which optimizes various effects including the Raman scattering effect to maximize the bandwidth of NLPs. Further broadening the NLP spectrum up to 294 nm was achieved by using spectral filtering outside the cavity with a polarization beam splitter.
9) We report on scalar soliton rains (SRs) shedding from vector square-wave noise-like pulse (NLP) by introducing a microfiber-knot-resonator (MKR) into an erbium-doped fiber (EDF) laser. It was found that the SRs existed only along a particular polarization direction, whereas the NLPs could be found in any pair of orthogonal polarization directions, despite some differences in pulse peak power.
10) Period doubling eigenstates of solitons generated in a fiber laser mode-locked by the nonlinear polarization rotation are numerically explored in detail. We found that, apart from the synchronous evolution between the two polarization components, there exists asynchronous development depending on the detailed operation conditions. In addition, period doubling of one polarization component together with period-one of another polarization component can be achieved.
Overview of the results: 6 publications in leading journals such as Photonics Research, Optics Express, and Photonics Journal are presented.
Properties of DSR pulses have been explored in detailed. The physical mechanism of the limitation on DSR pulse energy boost have been identified. It is expected that engineering work on getting rid of the limitation can help further improving pulse energy achievable.
Extreme performance of fiber lasers, such as noise-like pulse with 203 nm bandwidth, were achieved. The physical mechanism and possible strategies to overcome the bandwidth limitation effects are examined, which pave a way for achieving better performance beyond the state of the art in future.