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Structured photonics for advanced fibre lasers

Periodic Reporting for period 1 - SPAFIL (Structured photonics for advanced fibre lasers)

Reporting period: 2015-07-06 to 2017-07-05

Fiber laser are at the heart of modern photonic technology providing a platform for manufacturing, optical communications, sensing, healthcare, bio-medical and many other applications. Pulsed fiber laser enables cheap, efficient and flexible generation of high energy coherent pulses in a broad range of spectrum, high bandwidth and various pulseshapes. It is vital to improve our understanding of the dynamics of these systems and how they behave in order to fabricate better lasers.

In addition, nanocarbon materials have been discovered to be excellent saturable absorbers. Saturable absorbers are nonlinear passive amplitude modulators used to initiate pulse operation in a laser system. Numerous approaches have been proposed for the integration of nanotubes in fiber systems, these approaches can be divided into those that rely on direct interaction (where the nanotubes are sandwiched between fiber connectors) and those that rely on lateral interaction with the evanescence field of the propagating wave. Evanescence field interaction was proposed to mitigate optically induced thermal damage and to enhance nonlinearity. Tapered fibers in particular offer excellent flexibility to adjust the nonlinearity of nanotube-based devices, but typically suffer from high losses and poor saturable to non-saturable absorption ratio. Fabricating low loss taper fibers will have a great impact in fiber laser technologies as well as other nonlinear fiber optic devices (such as wavelength conversion).
The points below summarize my major studies as a MSC fellow:

0. Recent studies on pulse formation are in a final stage of manuscript preparation but must remain undisclosed until publication.

1. Low-Loss Carbon Nanotube Saturable Absorbers [1]:
The emergence of low-dimensional materials has opened new opportunities in the fabrication of compact nonlinear photonic devices. Single-walled carbon nanotubes were among the first of those materials to attract the attention of the photonics community owing to their high third order susceptibility, broadband operation and ultrafast response. Saturable absorption has become a widespread application for nanotubes in fiber laser technologies. Saturable absorbers are nonlinear passive amplitude modulators used to initiate pulse operation in a laser system. Numerous approaches have been proposed for the integration of nanotubes in fiber systems, these approaches can be divided into those that rely on direct interaction (where the nanotubes are sandwiched between fiber connectors) and those that rely on lateral interaction with the evanescence field of the propagating wave. Evanescence field interaction was proposed to mitigate optically induced thermal damage and to enhance nonlinearity. Tapered fibers in particular offer excellent flexibility to adjust the nonlinearity of nanotube-based devices, but typically suffer from high losses and poor saturable to non-saturable absorption ratio. The fellow proposed a method to fabricate carbon nanotube saturable absorbers with low losses and very large saturable to non-saturable loss ratios.

2. Rogue waves [2]:
During the last two decades, revealing mechanisms of origin waves with anomalous amplitude (rogue waves) have been in focus of researchers from different fields ranging from oceanography to the laser physics. Mode-locked laser, as a test bed system, provided a unique opportunity to collect more data on rogue waves in the form of random pulses (soliton rain) and to clarify mechanisms of rogue wave emergence caused by soliton-soliton and soliton-dispersive wave interactions. we demonstrated for the first time, using an Er-doped laser, experimentally and theoretically that in addition to soliton rain a new type of bright-dark (anomalous spikes-dips) vector rogue waves appears at the time scales of tens of thousands of round-trips driven by polarization instability.

3. Photon-Pair Generation with a 100 nm Thick Carbon Nanotube [3]:
Nonlinear optics based on bulk materials is the current technique of choice for quantum-state generation and information processing. Scaling of nonlinear optical quantum devices is of significant interest to enable quantum devices with high performance. However, it is challenging to scale the nonlinear optical devices down to the nanoscale dimension due to relatively small nonlinear optical response of traditional bulk materials. Here, correlated photon pairs are generated in the nanometer scale using a nonlinear optical device for the first time. The approach uses spontaneous four-wave mixing in a carbon nanotube film with extremely large Kerr-nonlinearity (≈100 000 times larger than that of the widely used silica), which is achieved through careful control of the tube diameter during the carbon nanotube growth. Photon pairs with a coincidence to accidental ratio of 18 at the telecom wavelength of 1.5 µm are generated at room temperature in a ≈100 nm thick carbon nanotube film device, i.e. 1000 times thinner than the smallest existing devices. These results are promising for future integrated nonlinear quantum devices (e.g. quantum emission and processing devices).

4. Two-Dimensional materials [4]:
Light modulation is an essential operation in photonics and optoelectronics. With existing and emerging technologies increasingly demanding compact, efficient, fast and broadband optical modulators, high-performance light modulation solutions are becoming indispensable. The recent realization that 2D layered materials could modulate light with superior performance has prompted intense research and significant advances, paving the way for realistic applications. We cover the state of the art of optical modulators based on 2D materials, including graphene, transition metal dichalcogenides and black phosphorus. We discuss recent advances employing hybrid structures, such as 2D heterostructures, plasmonic structures, and silicon and fibre integrated structures. We also took a look at the future perspectives and discuss the potential of yet relatively unexplored mechanisms, such as magneto-optic and acousto-optic modulation.

[1] Manuscript in final stage of preparation, to be submitted to APL Photonics before July 20th.
[2] Manuscript under review with PRL since May 2017
[3] Manuscript published in Advanced Materials (Adv. Mater. 2017, 29, 1605978)
[4] Manuscript published in Nature Photonics (Nature Photonics 10 (4), 227-238)
I believe this work will influence several research fields:

0. (numbers refer to previous section described work) will influence how scientist interpret and study fiber lasers, thus, it will also allow vast improvements in the fabrication of fiber lasers
1. The fellow developed a method for the fabrication of highly efficient saturable absorbers with controllable saturation fluence that can be used for the fabrication of better lasers and other nanomaterial based nolinear fiber devices.
2. Improved understanding of Rogue will be useful for those working on fiber lasers as well as those working on extreme phenomena in other physical systems.
3. These results are promising for future integrated nonlinear quantum devices (e.g. quantum emission and processing devices).
4. Here, the potential of 2D modulators is outlined, providing numerous directions of research for the future, this will be a highly influential study over the coming years.