Since the elucidation of total internal reflection by Colladon, Babinet and Tyndall over 150 years ago, bound states of light have been the primary means to transport light, whether on a chip or in optical fibers. We show that light carrying sufficiently high orbital angular momentum can create a centrifugal barrier for itself, thereby enabling guidance even in a regime where a mode is normally considered “cutoff.” We will discuss how this discovery, which has parallels with why binary stars don’t collapse into each other due to gravity, has applications in diverse areas, including classical and quantum communications and computing with high dimensionality, power scaling of fiber lasers by mitigating nonlinearities and nonlinear optics with greater degrees of freedom.

Stimulated Brillouin Scattering (SBS) is a major issue for delivering intense radiation through a fiber and for high-power fiber laser amplifiers. While most SBS-suppression techniques strive to maintain single-mode operation for high beam quality, we experimentally and theoretically demonstrate that coherent excitation of many fiber modes can significantly increase the SBS threshold while maintaining good output-beam quality. By shaping the wavefront of a coherent seed with a spatial light modulator, many fiber modes are excited and the output is focused to a single diffraction-limited spot.

We theoretically and experimentally show coherent pulse stacking (CPS) can accommodate tens-of-fs pulse durations and has negligible stacking fidelity degradation with increased pulse bandwidth. Simulations prove large number of tens-of-fs pulses can be stacked with high pre-pulse contrast. In an experiment, nine spectrally broadened and fiber amplified pulses are stacked using four cascaded cavities. CPS of pulses with different spectral bandwidths, up to 75 nm base-to-base (<50 fs transform-limited duration), are tested, showing negligible stacking degradation due to increased bandwidth. This work provides a path towards high energy, tens-of-fs pulses from ultrafast fiber lasers.

We demonstrate a tunable dual polarization Brillouin fiber laser with a Q-factor of 2.4 billion with an intrinsic relative linewidth of approximately 1 Hz, establishing the potential of such systems for fiber based compact frequency references for precision metrology applications. Mode hops are avoided by implementation of self-injection locking, which also obviates the need for electronic locking of the pump laser frequency to the 100 m length fiber laser cavity. The mode hop free tuning range of an individual laser can be as large a 300 MHz with an integrated linewidth of 20 Hz.

We recently reported on a new form of unidirectional lasing in a fully reciprocal kilometre long fiber ring cavity. It is a threshold like phenomenon where unidirectionality is triggered at full laser operation far above the laser threshold. Directionality is the consequence of asymmetric round trip loss, which arises due to differing nonlinear loss because of Raman scattering for the two directions. Asymmetry can be altered by seeding any direction at Stokes wavelengths to define the final direction of the laser. This was achieved by a simple straight cleaves at WDM outputs, used to tailor the excited spectrum.

We have investigated the laser performance and tunability of a highly Pr3+ doped fluoride glass fiber. Absorption and emission properties as well as laser characteristics in different resonator configurations have been studied. We have achieved 1.3 W output power @ 635nm wavelength with a slope efficiency of 30.6% with respect to the incident pump power. Furthermore, to the best of our knowledge, we present results on wavelength tunability with cladding-pumping on a several meter long Pr3+-doped ZBLAN fiber for the first time.

Mamyshev oscillators are at the forefront of parameter scaling of ultrafast fiber oscillators. This talk focuses on the prospects of Mamyshev oscillators in the spectral 2 µm region based on thulium-doped fibers. Recent studies have reported pulse energies up to 15 nJ at a duration of 140 fs by a large normal dispersive cavity. Moreover, higher order soliton dynamics hold promise to scale the peak power into the MW-class for ultrafast fiber oscillators in the short wavelength mid-infrared.

A compact thulium-doped (Tm) chirped-pulse-amplification (CPA) fiber system is demonstrated that generates 360 fs short pulses centered at a wavelength of 1901 nm with high pulse energies larger than 200 nJ (repetition rate of 9.26 MHz). In an additional second-harmonic generation setup with a periodically poled lithium niobate crystal, pulses centered at 950 nm with a pulse energy of 73 nJ and a transform-limited duration of 300 fs are produced. Such a frequency-doubled Tm-doped CPA system operating around a wavelength of 950 nm can offer an attractive ultrafast source for two-photon microscopy.

We present our progress on developing an innovative compact thulium-based fiber CPA emitting at 2 µm central wavelength. The laser parameters comprise >100 µJ pulse energy at an average power of >30W. The system comes in an industrial-grade platform optimized for long-term operation and its optimized packaging is well suited for the integration in laser machines for materials processing. The laser parameters are ideally suited for processing semiconductors, e.g. silicon by microwelding or cutting of filaments.

This work focuses on optimizing the pump power and tunable filter to achieve mode-locking operation in an all-fiber Mamyshev oscillator. Based on the Tm-doped Mamyshev oscillator, we have a clear understanding of the effect of pump power and wavelength of the bandpass filter on its operation mode, such as mode-locking, pulse splitting, multi-pulse train with random distribution and amplification of the seed. Our study provides valuable insights and directions for how to optimize the pump power and tunable filter to achieve mode-locking in a complex Mamyshev oscillator based on the existing non-mode-locking state. Funding: Villum Fonden (project no. 00037822: Table-Top Synchrotrons) and Innovation Fund Denmark (project no. 2105-00039B: Hypersort).

By coherently seeding a multimode fiber amplifier with a tailored spatial wavefront, it is possible to generate the target output profile in the presence of thermo-optical nonlinearity and gain saturation. We prove numerically that such wavefront exists with a modified phase-conjugation approach. An optical beam with target profile and power is launched from the distal end to proximal end of a multimode waveguide with absorption, and the exiting wavefront is phase-conjugated and sent back to the waveguide with loss switched to gain of equal magnitude. The target output beam is obtained with enhanced threshold for transverse mode instability due to multimode excitation.

Antiresonant hollow-core fibers (AR-HCFs) have opened up exciting possibilities for high-energy and high-power laser delivery, thanks to their exceptionally low nonlinearities and high damage thresholds. Here, we discuss our recent work on high power laser transmission in AR-HCFs. We use a 5 ring nested AR-HCF our experiments, which provides robust single-mode performance with M2 of 1.045. This effectively mitigates nonlinear effects, as evidenced by the absence of measurable nonlinear distortions in the delivered laser beam. Our results could pave the way for high-brightness narrow-linewidth fiber delivery systems for a wide range of applications.

We experimentally demonstrate a single-frequency Yb-doped multimode fiber amplifier (~76 modes) with a focused Gaussian output beam and enhanced stimulated-Brillouin-scattering (SBS) threshold. With few-mode excitation, the SBS threshold output power (57 W) is already an order of magnitude higher than that for a single-mode fiber amplifier of the same length. The output beam, however, is slightly speckled. To achieve high beam quality, we optimize the input wavefront to focus output light to a single diffraction-limited spot and simultaneously achieve much higher SBS threshold (up to 105 W), because forming a tight output focus requires coherent amplification of many modes.

Spectral Beam Combining (SBC) is a useful tool for power scaling of optical systems as well as for multiplexing in communications. We will give an overview of different concepts for SBC and compare them regarding channel count, spectral properties and power handling. For this regard, we will present our examples of these concepts, ranging from a 20kW spectral combiner for high power application over systems in the 100W-range for free-space communications in different spectral regions down to miniaturized combiner concepts for multi-W applications to reduce the footprint.

A fiber connector solution has long been sought for application flexibility and serviceability of kW class single mode fiber lasers. Laser manufacturers and systems integrators currently accept a loss of brightness to perform fiber coupling at high power. Coherent has recently demonstrated repeatable kW-class power transmission through a fiber connector with insertion loss similar to that of a splice and near-diffraction-limited beam quality at the output. Additionally, we show high-efficiency coupling of an LMA fiber source to a hollow core delivery fiber. Connector specifications, performance data, and design trades will be discussed as they relate to various anticipated applications.

We report an environmentally insensitive, all-fiberized, polarization-maintained (PM), self-starting, mode-locked Tm fiber laser cavity enabled by a single-wall carbon nanotube (SWNT) saturable absorber. This produces dissipative solitons at 1876 nm, with a repetition rate of 19.2 MHz, and a maximum average power of 21.5 mW, corresponding to a pulse energy of 1.1 nJ. The output pulse has a duration of 4.2 ps and can be compressed to 391 fs using a grating-based compressor. To the best of our knowledge, this is the first demonstration of an all-fiberized, all-PM, dissipative-soliton, mode-locked thulium fiber laser using a SWNT saturable absorber.

Gain dynamics play a crucial role in the design of laser oscillators and amplifiers. In order to expand the understanding of gain dynamics into the spectral 2 μm region, this study presents the experimental characterization of transfer functions in thulium-doped fiber amplifiers associated with the 3F4 → 3H6 transition that governs emission in this spectral range. The transfer functions for both the signal and pump are thoroughly investigated, providing detailed information on their magnitude and phase. We find a damped high-pass and a low-pass filtering behaviour for the respective signal and pump transfer function of thulium-ions in silica glass.

We experimentally and numerically demonstrate a simple and general technique to reduce the noise of modulational instability and soliton-based broadband supercontinuum lasers at the pulse-to-pulse level. Because of the requirement of low cost and high average power, such supercontinuum lasers constitute 99% of today’s commercially available supercontinuum lasers. The technique relies on adding a short normal dispersion fiber to force the spectrally and temporally distributed solitons to spectrally broaden through self-phase modulation (SPM) and thereby overlap to average out the noise. We experimentally demonstrate that this SPM technique provides significant noise reduction over a broad bandwidth.

In this work, we present a compact size and highly efficient nanosecond pulsed 1550nm single mode fiber laser that can operate from -40C to +95C. The laser generates 2 to 10 ns pulses at a repetition rate of hundreds kHz to a few MHz with hundreds to kilowatt peak power. The design of this laser is optimized to achieve over 10% wall-plug efficiency at room temperature with an ultra-low ASE noise less than 1%. The performance is also well maintained with less than 30% EO (electrical-optical) efficiency degradation at extreme temperatures and demonstrates high reliability consistent with deployment into harsh environments.The robust performance makes the laser an ideal source for lidar and sensing applications, along with other medical, scientific, and industrial applications.

In recent years, the demand for high-power, polarization maintaining single mode lasers operating in the 1.55 µm wavelength band significantly increased due to technological advances in free space communication, coherent LiDAR, quantum computing, and remote sensing. These applications benefit from the compactness, robustness, and efficiency of diode-pumped Erbium Ytterbium-doped fiber amplifiers (EYDFAs) and triggered the development of EYDFs with enhanced performance. In this work, we demonstrate a new single-mode PM EYDF with robust single-mode operation beyond 20 W output power and discuss the remaining challenges to scale the power further and how we plan to mitigate those.

In this communication, we report for the first time on a homemade 55 µm core VLMA “Yb-free” Er-doped aluminosilicate double-clad fiber manufactured by the REPUSIL powder sintering technology and its implementation within two different laser configurations emitting around 1560 nm, both pumped at 976 nm. First, a free-running free-space CW oscillator delivers up to 40 W of average power with optical-to-optical efficiency of 30 % and near-diffraction-limited beam, despite the large core size. In a second experiment, the fiber is used as the main amplifier of a MOPA system delivering up to 10 nJ pulses at GHz repetition rate.

Mid-infrared supercontinuum lasers are spatially coherent and can cover a wide spectral range of 2-10 μm. This makes them useful in many important applications, such as spectroscopy and optical coherence tomography. 2.8 μm ultrafast lasers are an important emerging pump wavelength for mid-infrared supercontinuum sources. We present our work on MHz repetition rate 2.8 μm erbium-doped ZBLAN fiber lasers using a MOPA architecture to boost the output power. Performing pulse break-up in a highly Germania-doped silica fiber and pumping this spectrum into a highly nonlinear sulfide fiber, we demonstrate both the noise and bandwidth achievable with the novel fiber cascade. We acknowledge funding from Villum Fonden (2021 Villum Investigator project no. 00037822: Table-Top Synchrotrons).

We developed two Ytterbium-doped rod-type effective singlemode fibers based on new hexagonal FA-LPF design, exhibiting MFD of 47μm and 67μm. Both fibers can deliver 150W of 1030nm signal for 250W of pump power, characterized in a MOPA set-up for different nanosecond pulse durations and repetition rate with excellent beam quality (M² ⪅ 1.1). Using the 47μm MFD fiber, TMI threshold has been measured for signal power slightly higher than 200W. Using the 67μm MFD fiber, we performed, through a third harmonic generation, the creation of 51W signal power at 343nm for 8ns temporally square pulse at 400 kHz repetition rate.

Exceeding the multi-kW power level with thulium-doped fiber lasers has not been achieved using a single thulium-doped fiber laser. One solution to overcome this limit is the coherent beam combination. We focus on an active phase control with tiled aperture configuration. The setup consists in an amplified seed laser split in three channels. These channels are controlled in phase and amplified again before being launched free space and combined. A SPGD algorithm controls the channel’s phase to provide combination. Rise time below 0.5 ms were achieved with a residual amplitude noise lower than λ/30.

We report on the development of FastLas, a scalable and versatile Ultra-Short Pulse (USP) laser compression technology. This system compresses down to a 50-20 fs range, USP lasers with pulse widths from 900 fs to 200 fs, energies from a few μJ to 1 mJ, average power from 100 mW to 100 W, and wavelengths from 343 nm in UV to 1.8μm in IR. It utilizes a gas-filled hollow-core photonic crystal fiber to broaden and compress any USP laser spectrum. As a result, FastLas presents an adaptable pulse compression solution, offering potential for applications in various industrial and scientific fields.

Hollow-Core Photonic Crystal Fiber (HCPCF) technology has revolutionized Ultra-Short Pulse (USP) laser beam delivery. Industry-grade USP laser beam delivery system (BDS) modules, developed by GLOphotonics, however, display polarization fluctuations during movement. To overcome this, we've developed a BDS module maintaining constant polarization irrespective of motion. This BDS uses an inhibited-coupling HCPCF with an injected beam from a 1030 nm wavelength USP laser. Demonstrating a 97% transmission rate and stable linear polarization (34dB of polarization extinction ratio (PER)), it showed less than 3% power fluctuation and less than 1% polarization fluctuation during movement. This marks a significant advancement in BDS applications.