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We review our recent work on the generation of novel optical solitons arising from different, high orders of dispersion and combinations thereof. By incorporating a spectral pulse-shaper in a mode-locked laser cavity, we can tailor the net-cavity dispersion, allowing us to access a wide range of new operating regimes corresponding to previously unobserved soliton pulses. We demonstrate the generation of solitons arising between self-phase modulation and any pure, negative even order of dispersion, as well as soliton molecules consisting of multiple solitons with different frequencies but that are temporally coincident.

The authors demonstrate the existence of optical solitons arising from the balance between self-phase modulation and negative, pure, even high-order dispersion using a fiber laser incorporating a spectral pulse shaper.

We investigate theoretically and numerically the self-similar propagation of optical pulses in the presence of gain, positive Kerr nonlinearity, and positive (i.e., normal) dispersion of even order $m$. Starting from a modified nonlinear Schr\"odinger equation, separating the evolution of amplitude and phase, we find that the resulting equations simplify considerably in the asymptotic limit. Exact solutions to the resulting equations indicate that the temporal intensity profile follows a $1\ensuremath{-}{T}^{m/(m\ensuremath{-}1)}$ function with an $m$-dependent scaling relation, with a ${T}^{1/(m\ensuremath{-}1)}$ chirp, where $T$ is the pulse's local time. These correspond to a triangle and a step function, respectively, as $m\ensuremath{\rightarrow}\ensuremath{\infty}$. These results are borne out by numerical simulations, although we do observe indications of nonasymptotic behavior.

We report the generation and characterization of soliton-molecules in dispersion-managed fiber lasers. Solitons at two different frequencies, with common (negative) dispersion, have identical group velocities; these solitons form a bound state with temporal beat fringes.

We report the first laser emitting pure-quartic solitons, temporal optical solitons arising from the balance of Kerr nonlinearity and fourth-order dispersion. We demonstrate that these pulses follow new energy-width scaling.

We study nonlinear pulse propagation in an optical fiber with positive quartic dispersion and gain, and find an exact asymptotic solution. Our solution is confirmed by numerical simulations based on the nonlinear Schrödinger equation.

We report the experimental discovery of new classes of solitons arising from Kerr nonlinearity and negative sixth-; eighth-; and tenth-order dispersion. These pulses demonstrate the use of high-order dispersion for unlocking innovations in nonlinear optics.

We report a fibre laser incorporating an intracavity pulse-shaper that induces a large anomalous net cavity quartic dispersion in which the mode-locked pulses propagate as pure-quartic solitons. We characterize the laser output pulses using a set of spectral and temporal phase resolved measurements and resonant dispersive wave analysis, and find that the results are in excellent agreement with analytic predictions.

Solitons are wave packets that can propagate without changing shape by balancing nonlinear effects with the effects of dispersion. In photonics, they have underpinned numerous applications, ranging from telecommunications and spectroscopy to ultrashort pulse generation. Although traditionally the dominant dispersion type has been quadratic dispersion, experimental and theoretical research in recent years has shown that high-order, even dispersion enriches the phenomenon and may lead to novel applications. In this Tutorial, which is aimed both at soliton novices and at experienced researchers, we review the exciting developments in this burgeoning area, which includes pure-quartic solitons and their generalizations. We include theory, numerics, and experimental results, covering both fundamental aspects and applications. The theory covers the relevant equations and the intuition to make sense of the results. We discuss experiments in silicon photonic crystal waveguides and in a fiber laser and assess the promises in additional platforms. We hope that this Tutorial will encourage our colleagues to join in the investigation of this exciting and promising field.

We describe the fabrication of metamaterial magnifying hyperlenses with subwavelength wire array structures for operation in the mid-infrared (around 3 µm). The metadevices are composed of approximately 500 tin wires embedded in soda-lime glass, where the metallic wires vary in diameter from 500 nm to 1.2 µm along the tapered structure. The modeling of the hyperlenses indicates that the expected overall losses for the high spatial frequency modes in such metadevices are between 20 dB to 45 dB, depending on the structural parameters selected, being promising candidates for far-field subdiffraction imaging in the mid-infrared. Initial far-field subdiffraction imaging attempts are described, and the problems encountered discussed.

In optical fibre resonators, the balance between anomalous quadratic dispersion and self-phase modulation (SPM) gives rise to optical solitons [1]. These pulses have made a significant impact in a wide range of photonic applications including telecommunications and lasers. However, these conventional soliton-based lasers can only deliver modest pulse energy due to the appearance of Kelly sidebands arising from periodical perturbations in the cavity [2] and a fixed energy-width scaling. Recently, a new class of soliton, arising from the balance of anomalous quartic dispersion and SPM, called pure-quartic soliton (PQS), were observed in a dispersion engineered photonic crystal waveguide [3]. PQSs have huge potential for generating ultrashort pulses with high energy due to their generalized area theorem (E ∼ 1/Δτ3), however they are yet to be observed in fibre platforms [4]. Here we report on the generation of PQS pulses from a passively mode-locked fibre laser incorporating a programmable spectral pulse-shaper that induces a dominant quartic net cavity dispersion. We find that the spectral profile of the generated pulses are in good agreement with the spectral shape of PQSs [3]. We also observe spectral sidebands in this quartic-dispersion cavity, in analogy to the conventional soliton case [2], and find that their positions are in excellent agreement with analytic predictions. These are strong evidences of a novel type of mode-locked laser, the PQS laser, which has the potential to reach dramatically higher energies at short pulse durations than its conventional soliton counterpart [3,4].

The development of new, compact mid-infrared light sources is critical to enable biomedical sensing applications in resource-limited environments. Here, we review progress in fiber-based mid-IR sources, which are ideally suited for clinical environments due to their compact size and waveguide format. We first discuss recent developments in mid-IR supercontinuum sources, which exploit nonlinear optic phenomena in highly nonlinear materials (pumped by ultrashort pulse lasers) to generate broadband spectra. An emerging alternative approach is then presented, based on broadly tunable mid-IR fiber lasers, using the promising dysprosium ion to achieve orders of magnitude higher spectral power density than typical supercontinua. By employing an acousto-optic tunable filter for wavelength tuning, an electronically controlled swept-wavelength mid-IR fiber laser is developed, which is applied for absorption spectroscopy of ammonia (NH3), an important biomarker, with 0.3 nm resolution and 40 ms acquisition time.

We report the generation of pure-quartic solitons from a fiber laser. Quartic cavity dispersion is achieved by an intracavity pulse-shaper. The pulses are characterized through spectral and temporal phase-resolved measurements and resonant dispersive wave analysis.

We study the propagation of ultrashort pulses in optical fiber with gain and positive (or normal) quartic dispersion by self-similarity analysis of the modified nonlinear Schrödinger equation. We find an exact asymptotic solution, corresponding to a triangle-like T 4 / 3 intensity profile, with a T 1 / 3 chirp, which is confirmed by numerical simulations. This solution follows different amplitude and width scaling compared to the conventional case with quadratic dispersion. We also suggest, and numerically investigate, a fiber laser consisting of components with positive quartic dispersion that emits quartic self-similar pulses.

Rare-earth-doped fiber lasers are emerging as promising high-power mid-infrared sources for the 2.6-3.0 {\mu}m and 3.3-3.8 {\mu}m regions based on erbium and holmium ions. The intermediate wavelength range, however, remains vastly underserved, despite prospects for important manufacturing and defense applications. Here, we demonstrate the potential of dysprosium-doped fiber to solve this problem, with a simple in-band pumped grating-stabilized linear cavity generating up to 1.06 W at 3.15 {\mu}m. A slope efficiency of 73% with respect to launched power (77% relative to absorbed power) is achieved: the highest value for any mid-infrared fiber laser to date, to the best of our knowledge. Opportunities for further power and efficiency scaling are also discussed.

We explore the potential of a new mid-infrared laser transition in praseodymium-doped fluoride fiber for emission around 3.4 μm, which can be conveniently pumped by 0.975 μm diodes via ytterbium sensitizer co-doping. Optimal cavity designs are determined through spectroscopic measurements and numerical modeling, suggesting that practical diode-pumped watt-level mid-infrared fiber sources beyond 3 μm could be achieved.

We report the fabrication and characterization of silicon carbide microdisks on top of silicon pillars suited for applications from near- to mid-infrared. We probe 10 μm diameter disks with different under-etching depths, from 4 μm down to 1.4 μm, fabricated by isotropic plasma etching and extract quality factors up to 8400 at telecom wavelength. Our geometry is suited to present high Q single-mode operation. We experimentally demonstrate high-order whispering-gallery mode suppression while preserving the fundamental gallery mode and investigate some requirements for nonlinear optics applications on this platform, specifically in terms of quality factor and dispersion for Kerr frequency comb generation.

We demonstrate an optimized in-band-pumped dysprosium fiber laser with 73% slope efficiency and 1.1 W output at 3.15 μm: the first watt-level fiber source in the 3.0–3.4 μm region and highest ever efficiency mid-IR fiber laser.

We demonstrate the generation of 70-fs pulses (∼7 optical-cycles) from a mid-infrared mode-locked Ho:ZBLAN fiber laser using nonlinear compression with step-index chalcogenide fiber. Experiments are supported by numerical modelling, confirming the scalability of this approach.

We report the femtosecond laser inscription of a 45◦ tilted fibre Bragg grating (TFBG) into ZBLAN fibre. Integrating this TFBG into a mid-IR fibre laser cavity resulted in 20.5 dB output polarization extinction ratio.

We report the fabrication of fiber Bragg gratings (FBGs) in passive as well as doped fibers utilizing the femtosecond laser line-by-line technique. Narrow-linewidth linear gratings as well as broadband chirped gratings were inscribed into silica- and fluoride-glass optical fibers. Polarization-dependent characteristics of non-tilted and of 45°-tilted gratings are analyzed and the possibility of direct inscription into coated (i.e. non-stripped) fibers is demonstrated.

Output pulses from an ultrafast holmium-praseodymium co-doped fiber ring laser are spectrally broadened in different highly nonlinear chalcogenide fibers. Moderate levels of broadening are achieved in step-index fibers and the effect is utilized for nonlinear pulse compression. Much larger broadening factors can be observed in suspended-core fibers and polymer-protected robust all-chalcogenide microwires. Under optimized conditions, an ultra-broadband supercontinuum spanning from 2 – 12 μm is generated.

We demonstrate a $\hbox{Ho}^{3+}$ , $\hbox{Pr}^{3+} $ co-doped fluoride fiber laser that produces an output power of 7.2 W, a 150-nm tuning range, and a narrow linewidth of $ nm using a power-scalable $\hbox{Yb}^{3+} $ fiber-laser-pumped 1150-nm Raman fiber laser as the excitation source. The maximum output power is achieved at a slope efficiency of 29%, with wavelength tuning between 2825 and 2975 nm that overlaps with the OH absorption region in many mid-infrared transparent glasses. The system is used to provide accurate measurements of the background scattering loss and the degree of water incorporation in the rare-earth-doped core of commercial double-clad fluoride fiber; the high power allows accurate core loss measurements for quite lossy fibers. Furthermore, the spectral location of the OH absorption feature was observed to be dependent on glass composition shifting from 2872 nm in undoped ZBLAN to 2896 nm upon $\hbox{Ho}^{3+}\hbox{Pr}^{3+}$ co-doping, whereas $\hbox{As}_{2}\hbox{S}_{3} $ glass was observed to have an OH peak location of 2911 nm.

Mode-locked fiber lasers emitting short pulses of light at wavelengths of 2 μm and longer are reviewed. Rare-earth doped silica and fluoride fiber lasers operating in the mode-locked regime in the mid-IR (2–5 μm) have attracted attention due to their usefulness to spectroscopy, nonlinear optics, laser surgery, remote sensing and ranging to name a few. While silica fiber lasers are fundamentally limited to emission wavelengths below 2.2 μm, fluoride fiber lasers can reach to nearly 4 μm. The relative infancy of fluoride fibers as compared to silica fibers means the field has work to do to translate the mode-locking techniques to systems beyond 2 μm. However, with the recent demonstration of a stable, mode-locked 3 μm fiber laser, the possibility of achieving high performance 3 μm class mode-locked fiber lasers looks promising.

We propose and demonstrate a simple route to few-optical-cycle pulse generation from a mid-infrared fiber laser through nonlinear compression of pulses from a holmium-doped fiber oscillator using a short length of chalcogenide fiber and a grating pair. Pulses from the oscillator with 265-fs duration at 2.86 {\mu}m are spectrally broadened through self-phase modulation in step-index As2S3 fiber to 141-nm bandwidth and then re-compressed to 70 fs (7.3 optical cycles). These are the shortest pulses from a mid-infrared fiber system to date, and we note that our system is compact, robust, and uses only commercially available components. The scalability of this approach is also discussed, supported by numerical modeling., Comment: Published in Optics Letters

We report on our research into fluoride fiber-based 3 µm class laser sources. Using holmium as the gain medium, record-high peak power levels are achieved in mode-locked laser systems that emit ultrashort pulses in the water vapor transmission window around 2.9 µm. Highly nonlinear and dispersion-engineered hybrid chalcogenide-polymer microwires are utilized to extend the frequency range of those sources further into the mid-infrared. In addition, dysprosium- doped fibers are employed to demonstrate continuous-wave lasers that are tunable between 3 and 3.5 µm.

Silicon carbide (SiC) is a well-known material in the field of high temperature and high voltage electronics thanks to a high thermal conductivity, high electric field breakdown strength and high maximum current density [1]. Simultaneously with a strong inertness and a low thermal expansion, this makes silicon carbide a good material for extreme condition sensing [2]. The fact that the cubic structure (3C) of SiC can be grown on silicon makes it compatible with most of the silicon technology. At the same time, silicon carbide exhibits some good optical properties particularly promising for non-linear photonics from the near to the mid infrared range [3-4]. Its high refractive index (n∼2.6 at λ = 1.5μm) allows a good light confinement. Studies on other crystallographic structures [5] suggest that 3C-SiC may exhibit good non-linear properties with a nonlinear index comparable to silicon and nonlinear loss — often detrimental to non-linear processes — virtually inexistent thanks to wide its bandgap [6]. In this work, we report the linear optical and thermal characterization of silicon carbide microdisks on a silicon substrate designed for non-linear operations from near to mid-infrared wavelength.

We demonstrate record performance in a mid-IR ultrafast fiber laser by using holmium instead of erbium as the active gain medium. The 2.9 μm laser emits 180 fs pulses with 37 kW peak power.

We demonstrate a holmium-doped fluoride fiber laser that emits 37 kW peak power pulses with 180 fs pulse durations at 3 µm. The 100 nm redshift of holmium gain relative to erbium allows for minimal interaction with atmospheric water absorption resulting in a significant increase in performance for 3 µm class ultrafast fiber lasers.

We demonstrate supercontinuum spanning from 2.2 to 4.6 µm in a dispersion-engineered, As2Se3 microwire using a mode-locked holmium fiber laser operating at 2.9 µm. The output spectrum is > 50 times broader than the input laser spectrum.

We develop a computational model of a holmium-based laser which produces robust mode-locking at 2.9 microns with peak powers in the tens of kilowatts, far exceeding current fiber laser performance at 1.5 microns.

I will review our work on nonlinear waveguides for supercontinuum generation in the mid-infrared focusing on the nonlinear properties and waveguide performance of chalcogenide, silicon and silicon-germanium devices

We demonstrate a compact silicon-on-sapphire (SOS) strip waveguide sensor for mid-IR absorption spectroscopy. This device can be used for gas and liquid sensing, especially to detect chemically similar molecules and precisely characterize extremely absorptive liquids that are difficult to detect by conventional infrared transmission techniques. We reliably measure concentrations up to 0.25% of heavy water (Dsub2/subO) in a Dsub2/subO-Hsub2/subO mixture at its maximum absorption band at around 4 μm. This complementary metal-oxide-semiconductor (CMOS) compatible SOS Dsub2/subO sensor is promising for applications such as measuring body fat content or detection of coolant leakage in nuclear reactors.

The mid-infrared (mid-IR) spectral region holds great promise for new laser-based sensing technologies, based on measuring strong mid-IR molecular absorption features. Practical applications have been limited to date, however, by current low-brightness broadband mid-IR light sources and slow acquisition-time detection systems. Here, we report a new approach by developing a swept-wavelength mid-infrared fiber laser, exploiting the broad emission of dysprosium and using an acousto-optic tunable filter to achieve electronically controlled swept-wavelength operation from 2.89 to 3.25 {\mu}m (3070-3460 cm^-1). Ammonia (NH3) absorption spectroscopy is demonstrated using this swept source with a simple room-temperature single-pixel detector, with 0.3 nm resolution and 40 ms acquisition time. This creates new opportunities for real-time high-sensitivity remote sensing using simple, compact mid-IR fiber-based technologies., Comment: Invited article for APL Photonics

We report the direct femtosecond laser inscription of type-I fiber Bragg gratings (FBGs) into the core of soft-glass ZBLAN fibers. We investigate and compare various fabrication methods such as single pass (line by line), double pass, and stacking (plane by plane) to create the highest reflectivity FBGs (99.98%) for mid-infrared (mid-IR) applications. In addition, we experimentally demonstrate how the parameters that influence the coupling coefficient, i.e., refractive index modulation and overlap factor, can be controlled in these gratings to specifically tailor the FBG properties. The performance of the direct-written type-I gratings after 6 h of annealing is further analyzed, and the reflectivity increases by approximately 10 dB. To the best of our knowledge, this is the first demonstration of temperature-stable mid-IR FBGs with highest coupling coefficient (464 m−1) and lowest loss (

We present fabrication, simulation and characterization of silicon carbide microdisk on silicon pillar aiming at non-linear operation from near-infrared to mid-infrared. We report experimental Q factor of 1800 at telecom wavelength.

In this review we consider the basic elements of tapering chalcogenide optical fibers for the generation of extreme spectral broadening through supercontinuum generation. Creating tapered nanofiber devices in chalcogenide fiber, which has an intrinsic nonlinearity that is two orders of magnitude higher than silica, has resulted in the demonstration of octave-spanning spectra using record low power. We first present a brief theoretical understanding of the tapering process that follows from the basic principle of mass conservation, and a geometric construction tool for the visualization of the shape of tapered fibers. This is followed by a theoretical treatment of dispersion engineering and supercontinuum generation in a chalcogenide nanofiber. In the final section, we cover the experimental implementation of the chalcogenide nanofiber and demonstrate an octave-spanning spectrum created with 150 W of peak power.

In this work silicon pillar waveguides have been proposed to exploit the entire transparent window of silicon. These geometries posses a broad and at dispersion (from 2 to 6 μm) with four zero dispersion wavelengths. We calculate supercontinuum generation spanning over two octaves (2 to >8 μm) with long wavelengths interacting weakly with the lossy substrate. These structures have higher mode confinement in the silicon - away from the substrate, which makes them substrate independent and are promising for exploring new nonlinear phenomena and highly sensitive molecular sensing over the entire silicon's transparency range

We report the direct femtosecond laser inscription of a 45° tilted fiber Bragg grating (TFBG) into fluoride fiber, creating an in-fiber mid-infrared polarizer. Utilizing a 16 mm long intracavity TFBG, we demonstrate a 2.862 μm Ho3+Pr3+:ZBLAN fiber laser with 21.6 dB output polarization extinction ratio (PER), up to 0.37 W output power and 31.3% slope efficiency. In addition, we experimentally demonstrate that the laser PER is a linear function of grating length. Our results show that fluoride TFBGs are a promising route to replace bulk polarizers in mid-IR laser cavities, paving the way to all-fiber mid-infrared laser systems.

Cascaded stimulated Brillouin scattering (SBS) is a complex nonlinear optical process that results in the generation of several optical waves that are frequency shifted by an acoustic resonance frequency. Four-wave mixing (FWM) between these Brillouin shifted optical waves can create an equally spaced optical frequency comb with a stable spectral phase, i.e. a Brillouin frequency comb (BFC). Here, we investigate phase-locking of the spectral components of BFCs, considering FWM interactions arising from the Kerr-nonlinearity as well as from coupling by the acoustic field. Deriving for the first time the coupled-mode equations that include all relevant nonlinear interactions, we examine the contribution of the various nonlinear processes to phase-locking, and show that different regimes can be obtained that depend on the length scale on which the field amplitudes vary.

We demonstrate an octave spanning, 1.9–6.2 μm supercontinuum generation in a low loss silicon on a sapphire (SOS) nanowire. The supercontinuum is achieved by pumping in the low-loss window of SOS near 3.7 μm.

We demonstrate externally photo-induced partially-reversible tuning of the resonance of a microdisk made of AMTIR-1 (Ge(33)As(12)Se(55)). We have achieved for the first time, to the best of our knowledge, both positive and negative shift in a microresonator with external tuning. A positive resonance shift of 1 nm and a negative resonance shift of 0.5 nm on a single microdisk has been measured. We have found that this phenomenon is due to initial photo-expansion of the microdisk followed by the photo-bleaching of the AMTIR-1. The observed shifts and the underlying phenomenon is controllable by varying the illumination power (i.e. the low power illumination suppresses the photobleaching process). We measure a loaded quality factor of 1.2x10(5) at 1550nm (limited by the measuring instrument). This holds promise for non-contact low power reversible-tunning of photonic circuit elements.

We demonstrate a fiber laser emitting 497fs pulses near 3µm using a mid-IR transparent fluoride fiber doped with Erbium. The potential of this laser as a source for a mid-IR fiber-based frequency comb is explored.

Tuning of a diode-cladding-pumped cascade Ho3+-doped fluoride fiber laser is demonstrated using a single plane ruled diffraction grating. At the maximum available pump power, a tuning range 2955-3021 nm, an output power of >;500 mW, and a bandwidth of

We report the development of a widely tunable all-fiber mid-infrared laser system based on a mechanically robust fiber Bragg grating (FBG) which was inscribed through the polymer coating of a Ho3+-Pr3+ co-doped double clad ZBLAN fluoride fiber by focusing femtosecond laser pulses into the core of the fiber without the use of a phase mask. By applying mechanical tension and compression to the FBG while pumping the fiber with an 1150 nm laser diode, a continuous wave (CW) all-fiber laser with a tuning range of 37 nm, centered at 2870 nm, was demonstrated with up to 0.29 W output power. These results pave the way for the realization of compact and robust mid-infrared fiber laser systems for real-world applications in spectroscopy and medicine.