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We present a soliton order preservation mechanism leading to broad tunability with high energy conversion efficiency (ECE) from a fiber-based soliton self-frequency shift (SSFS) system. Here, a pulse compressing fiber, placed before the Raman shifting nonlinear fiber (NLF), acts as a soliton order preserver. Thanks to this passive mechanism, the soliton order at the input of the NLF is preserved within 2.080% is maintained over a tunable range as large as 180 nm in a passive fiber-based SSFS system. Solitons are also tunable up to 320 nm in the wavelength range of1.96-2.28 µm with ECE>50%. Such a soliton order preservation mechanism that enables a high ECE while maintaining a broad soliton tunability is of utmost practical interest for wavelength conversion systems.

We formulate the energy conversion efficiency from a high-order soliton to fundamental solitons by including the influence of interpulse Raman scattering in the fission process. The proposed analytical formula agrees closely with numerical results of the generalized nonlinear Schrodinger equation as well as to experimental results, while the resulting formulation significantly alters the energy conversion efficiency predicted by the Raman-independent inverse scattering method. We also calculate the energy conversion efficiency in materials of different Raman gain profiles such as silica, ZBLAN and chalcogenide glasses (As2S3 and As2Se3). It is predicted that ZBLAN glass leads to the largest energy conversion efficiency of all four materials. The energy conversion efficiency is a notion of utmost practical interest for the design of wavelength converters and supercontinuum generation systems based on the dynamics of soliton self-frequency shift., Comment: To be published in JOSAB

We report a single-end forward-pumped fiber laser with a record high output power of 3 kW. The laser is assembled exclusively from commercially widespread components such as the Yb-doped fiber with core/cladding diameter of 20/400 µm, pump laser diodes at an emission wavelength of 915 nm, and a signal and pump fiber combiner that serves as the pump recycler. The record high power arises from the combination of the 915 nm pumping and pump recycler with an effective reflectivity of 78%, increasing simultaneously the thresholds for stimulated Raman scattering and transverse mode instability (TMI). The length of the oscillator was also varied experimentally from 20 m to 5 m, showing a contrast of up to 19% in the TMI threshold. This shows the importance of accurately partitioning the Yb-doped fiber length in between the oscillator and amplifier sections to minimize the impact of TMI.

Fiber optical parametric oscillators (FOPOs) are compact optical sources of coherent and broadly tunable light compatible with operation in unconventional spectral bands. Highly nonlinear silica fibers have enabled the development of FOPOs in the telecommunication wavelength band, but the strong material absorption of silica glass at wavelengths >2 µm limits its applicability in the mid-infrared (MIR) spectral range. In this work, we overcome this issue and report a FOPO designed entirely out of soft glass fiber. For this purpose, we combine an As2Se3 single-mode fiber coupler, an As2Se3 parametric gain medium, and a low-loss ZBLAN delay fiber to build the first all-fiber laser cavity made of soft glass. Two proof-of-concept FOPOs are presented, one driven by pure parametric gain leading to wavelength-tunable Stokes emission within the range 2.088–2.139 µm, and the other driven by Raman-assisted parametric gain leading to Stokes emission within the range 2.023–2.048 µm. This demonstration is a promising first step toward the development of fully fiberized MIR light sources.

We demonstrate the first saturable absorber made of a chalcogenide multimode fiber assembly, and its use within a resonant fiber cavity to trigger mode-locking. The saturable absorber operates from nonlinear multimode interference in a singlemode-multimode-singlemode fiber structure with lateral offsets at both input and output interfaces. It has a modulation depth of 10% and a peak power saturation intensity $ 55 MW/cm $^2$ . It acts simultaneously as a tunable bandpass filter with a continuous tunability of 61 nm. The saturable absorber triggers a pulsed regime in a fiber laser cavity, leading to mode-locking in a tunable wavelength range of 1834 nm to 1895 nm. The mode-locked fiber laser can be set to generate a pulse train with conventional single pulse pattern or resembling pulse pattern. The all-fiber saturable absorber is a promising component for the fabrication of mode-locked fiber lasers operating in the mid-infrared wavelength range.

We present a reflection mode saturable absorber based on nonlinear multimode interference in a graded index multimode fiber. The saturable absorber provides a modulation depth of 12% at a low saturation intensity of 18.5 MW/cm2. The all-fiber structure and reflection mode design of this saturable absorber makes it an ideal device for the fabrication of fiber lasers with linear resonant cavity. When inserted in a linear laser cavity comprising a thulium doped fiber as the gain medium, the saturable absorber triggers modelocked noise like pulses with a center wavelength of 1905 nm and spectral width of 11.2 nm.

We demonstrate chalcogenide optical fiber couplers designed with a transmission spectrum response that depends on the input power. The measured switching power is as low as 126 W at a wavelength of 1938 nm.

We report two fiber optical parametric oscillators (FOPO) built entirely out of chalcogenide and fluoride fibers. The FOPOs show Raman assisted and pure parametric oscillation with tunable Stokes emission within 2.023-2.048 μm and 2.088-2.139 μm.

We demonstrate single-mode ZBLAN optical fiber couplers. The controlled tapering procedure leads to coupling ratios of 5%/95% and 14%/86% at a wavelength of 2.2 µm, with insertion losses of 1.6 dB and 1.8 dB, respectively.

We study the impact of inserting a chirped and tilted fiber B ragg grating in between variable lengths of oscillator and amplifier stage of a high-power fiber laser, reaching up to 2 kW in output power.

We present a simple and efficient design of wavelength converter tunable in the wavelength range of 2.10-2.65 μm. Raman solitons at 1.94 μm are frequency shifted in a fluoride fiber with conversion efficiency of 53%-91%.

We report a 78% cladding pump recycler based on a tapered fiber bundle. The conversion efficiency of a 2.2 kW Yb-doped fiber laser is improved by the pump recycler from 66.7% to 73.0%.

We demonstrate a Thulium-doped fiber laser that is Q-switched mode-locked via nonlinear polarization rotation in an As2S3 taper. The laser allows single and multiwavelength pulses, tunable central wavelength and tunable multiwavelength separation.

We experimentally and numerically evaluate the energy distribution of fundamental solitons following a high-order soliton fission process. Under certain conditions, this evaluation significantly diverges from the prediction led by the inverse scattering method.

We demonstrate a mid-infrared compatible tunable bandpass filter that consists of a singlemode-multimode-singlemode fiber structure, made from chalcogenide fibers. Experiments have been carried out using step-index multimode fibers with small core radius, resulting in a continuous wavelength tunability >52 nm and a hop wavelength tunability of 84 nm, via mechanical bending. Core to core lateral offsets at input and output interfaces between singlemode fibers and multimode fiber are optimized to maximize the extinction ratio and set a desired transmission wavelength. Transmission characteristics of the multimode interference effect and design rules of a widely tunable filter are also presented.

We present a precision distance meter that operates from sweeping the repetition rate of an electro-optic (EO) frequency comb. The dynamic range and scan rate of such comb make it possible to measure absolute distances up to hundreds of meters with an accuracy of $\pm 5~\mu \text{m}$ and an acquisition time of 30 ms. The proposed technique requires no fiber stabilization system, making the device simple and cost-effective.

Pulsed laser sources in the spectral window of 2 μm find many applications in engineering and science [1] . Thulium doped fiber lasers (TDFL) are especially attractive for this purpose with their emission in the 1.8-2.1 µm spectral range. The emission spectrum of a TDFL beyond 2.1 µm is also attainable with nonlinear approaches such as soliton self-frequency shift (SSFS) [2] , [3] . Previously, TDFL systems using SSFS have been demonstrated from thulium-doped fiber amplifiers (TDFA) pumped by tens of watts of continuous wave signal, leading to high-power femtosecond pulses (~100 kW, ~100 fs) [4] , [5] . However, such high-power systems are bulky and require external cooling mechanisms, as well as they lead to SSFS for a specific wavelength and pulse intensity. On the other hand, reports of TDFL with SSFS from passive fibers such as Ge-doped fibers require custom-made dispersion engineered fibers [6] . Here, we present a simple, all-fiber system that extends the wavelength reach of a TDFL from a passive, commercially available silica fiber. The system is tunable over 310 nm with an energy conversion efficiency up to 84.6%. To the best of our knowledge, this is the highest energy conversion efficiency ever reported in any SSFS system based on a passive fiber.

In recent years, chirped and tilted fiber gratings (CTFBG) have become promising all-fiber components for the suppression of Stimilated Raman Scattering (SRS) in high power fiber lasers (HPFLs). A CTFBG acts as a smooth wideband filter with an engineered central wavelength. It can be used to couple SRS light from fiber core mode to fiber cladding modes [1] . However, a CTFBG may fail to achieve SRS suppression because of the residual core-to-core Bragg reflection that typically attains −20 dB [2] , [3] . Moreover, the chirp direction with respect to light flow has an impact on the reflected spectrum of a CTFBG, and thus one direction must be advantageous over the other. Here, we report the impact of the tilt angle and chirp direction of a CTFBGs inserted at the output of a HPFL. Several CTFBGs are compared, with tilt angles spanning 4 ◦ − 6 ◦ and for both chirp directions. We conclude that CTFBGs optimal for SRS suppression should be oriented with SRS entering from the long wavelength chirp side, as well as their tilt angle should be close to 5 ◦ .

Brillouin fiber lasers (BFLs) are most often used as optical signal processing devices to reduce laser noise and increase coherence length [1] . BFLs made of silica typically require hundreds of meters of cavity length to provide the sufficient gain, leading to multi-mode operation. Hence, additional filtering applies to suppress the higher order modes. Realizing single-mode BFLs with small footprint and low threshold power requires a nonlinear medium with a large nonlinearity gain. Chalcogenide (ChG) fibers are excellent candidates for this purpose, with their nonlinearity that is 2-3 orders of magnitude larger than silica. So far, a few BFLs using ChG fibers have been proposed [2] – [4] . However, the proposed BFLs include a resonant cavity formed with standard optical fibers and optical fiber couplers (OFC) that are made of silica glass. Recently, ChG OFCs have been proposed [5] – [6] , providing the possibility to fabricate all-ChG fiber devices. Here, we propose the first all-ChG BFL, as well as the first all-ChG ring cavity. The proposed BFL is single-mode thanks to the short cavity length. The same cavity is also compatible with a wide spectral range of wavelengths owing to the all-ChG ring cavity structure, from the telecommunication band up to the mid-infrared.

Pulsed fiber lasers in the 2 μm wavelength window have become important tools in spectroscopy, medical surgery, and material processing [1] . Passive saturable absorbers (SA) based on multimode interference (MMI), graphene, and carbon nanotubes have been proposed to induce modelocking into thulium-doped fiber lasers (TDFLs) [2] – [4] . Of particular interest is the MMI-SA which also enables wavelength tunability while preserving compatibility with a broad range of wavelengths [5] . Most SAs operate in transmission, thus naturally leading to TDFLs in ring configuration. However, SAs that operate in a reflection mode are also highly desirable for compatibility with linear laser cavities because of their simple architecture. Here, we present an all-chalcogenide (ChG) fiber-based MMI-SA that operates in reflection mode. The MMI-SA induces modelocked pulses in an all-fiber linear cavity TDFL. Because of its ChG composition and simplicity, this architecture of all-fiber MMI-SA is compatible over a broad range of wavelengths, from the telecommunication band to the mid-infrared.

We derive an analytical formulation of Raman-induced frequency shift experienced by a soliton. The resulting formulation is a high-order extension of Gordon's formula for soliton self-frequency shift that includes propagation losses, self-steepening, and dispersion slope.

We experimentally demonstrate that a supercontinuum becomes further broadened by using a dispersion varying nonlinear medium. Compared to constant dispersion designs, a power enhancement of 4.3 dB and bandwidth extension of 262 nm are obtained.

We report an effective pump recycler for industrial kilowatt fiber lasers. The pump recycler is a ( 6 + 1 ) × 1 tapered fiber bundle, with signal ports of Ge-doped fiber (GDF) with core/cladding diameters of 20/400 µm and pump fiber ports (PFPs) with core/cladding diameters of 135/155 µm. By splicing PFPs in pairs, 77.9% of the residual pump light reaching the pump recycler is sent back to the cladding of the GDF. The insertion of a pump recycler increases the power conversion efficiency (PCE) of a fiber laser using an Yb-doped fiber (YDF) from 61.0% to 70.5%, with a maximum output power of 2.78 kW. The laser with a 20 m long YDF and pump recycler compares well to another laser using a 40 m long YDF without pump recycler. In both cases, the PCE is comparable but the laser with a 20 m long YDF and pump recycler benefits from reduced stimulated Raman scattering (SRS), thus enabling an 80% increase in Raman threshold. By giving access to short YDF length, the tapered fiber bundle represents an effective pump recycler since it enables reducing SRS while keeping a large PCE.

We demonstrate the first all-chalcogenide Brillouin fiber laser. The laser is composed of an As2S3 optical fiber for nonlinear amplification and of an As2Se3 optical fiber coupler to form a resonant ring cavity.

We present an all-fiber saturable absorber based on multimode interference (MMI-SA) in a chalcogenide fiber. Results show the nonlinear saturation profile, and mode-locking upon insertion of the MMI-SA in a thulium-doped fiber laser cavity.

We report a 2 kW monolithic Yb-doped fiber laser with Raman filtering within the resonant cavity. The laser is based on commercially widespread 20 µm-core double-cladding fibers and laser diodes at a wavelength of 915 nm.

We demonstrate the highest energy conversion efficiency of 84.6% from a soliton self-frequency shift system based on a passive silica fiber. The soliton is tunable over 310 nm in the spectral range 1.96-2.27 µm.

We derive an analytical expression that predicts the Raman-induced frequency shift experienced by a soliton. By including fiber losses, dispersion slope, and self-steepening, the resulting expression is a high-order extension of Gordon’s formula.

Mid-infrared (MIR) fiber based optical sources, such as wavelength converters that are based on soliton-self frequency shift (SSFS), parametric processes or supercontinuum sources are attractive for their compactness and mechanical stability [1] – [3] . Of particular interest, wavelength converters based on SSFS can generate widely tunable, high quality ultrashort pulses from a dispersion engineered nonlinear fiber paired with a suitable pulsed source [4] . There have been a few reports of SSFS in silica [5] , fluoride [6] and tellurite [7] fibers. Among soft glass fibers, chalcogenide (ChG) fibers (e.g As 2 Se 3 , As 2 S 3 ) are particularly attractive for SSFS in the MIR due to their compatibility with this spectral range as well as their high optical nonlinearity. In addition, the tapering of a ChG fiber down into a microwire provides an enhanced nonlinear optical effect, thus allowing low pump power operation from a compact device. In the past, Cheng et al. reported SSFS tunable in the spectral range of 2.98-3.41 μm (12.7 THz) in AsSe 2 fibers from pulses with an energy of 1.8 nJ [8] . In this work, we report SSFS that is widely tunable within the spectral range of 2.03-2.60 μm (39.2 THz) from a pump pulse energy as low as 64 pJ. Such a frequency detuning is realized from dispersion engineering of an As 2 S 3 microtaper. To the best of our knowledge, this is the lowest pump energy ever used to obtain wideband SSFS.

We derive an analytical formulation of the Raman-induced frequency shift experienced by a fundamental soliton. By including propagation losses, self-steepening, and dispersion slope, the resulting formulation is a high-order (HO) extension of the well-known Gordon's formula for soliton self-frequency shift (SSFS). The HO-SSFS formula closely agrees with numerical results of the generalized nonlinear Schrödinger equation, but without the computational complexity and required computation time. The HO-SSFS formula is a useful tool for the design and validation of wavelength conversion systems and supercontinuum generation systems.

We report the effective suppression of Raman emission in a monolithic ytterbium-doped fiber laser by the insertion of a chirped and tilted fiber Bragg grating (CTFBG) directly within the gain fiber of the laser. In comparison with a non-compensated filtered laser cavity for which the Raman threshold occurs at an output power of 1.54 kW, the insertion of a CTFBG within the gain medium leads to an increase in the Raman threshold by 260 W. We also demonstrate that the insertion of a CTFBG in between a laser cavity and a passive beam delivery fiber leads to an increase in the Raman threshold by 100 W with respect to the non-compensated case.

We report the first supercontinuum source using a tapered microstructured As 2 S 3 fiber by pumping at a wavelength of 1.938 μm. The all-fiber source leads to a supercontinuum spanning from 1.50 μm to 2.65 μm with an average power of 14.5 mW.

We demonstrate the operation of an optical fiber coupler with nonlinear response. The tapered coupler is made of As 2 Se 3 glass and the coupling ratio is controlled by the input power.

We present an all-fiber saturable absorber based on the multimode interference effect of a chalcogenide glass fiber. Experimental results show a modulation depth of 9.4% at a wavelength of 1940 nm.

We derive an analytic expression for the Ramaninduced frequency shift of a fundamental soliton in an optical fiber, beyond the well-known Gordon formula. Resulting from the moment method the expression quantifies the soliton frequency shift as a function of fiber and pulse parameters.