1.7 W holmium-doped fluoroindate fiber laser at 3920 nm.

A monolithic fiber laser emitting 1.7 W at 3920 nm is experimentally demonstrated in a Ho3+:InF3 fiber. The cavity comprises a pair of highly reflective fiber Bragg gratings written in the active fiber with the femtosecond phase-mask scanning technique and is spliced to the pump diode with a robust silica-to-fluoride fiber splice. This work is an important step toward high-power all-fiber laser operating in the vicinity of 4 µm.

Towards real-time active imaging of greenhouse gases using tunable mid-infrared all-fiber lasers.

We report a tunable all-fiber laser emitting a maximum output power of 2.55 W around 3240 nm. The fiber laser cavity based on a fluoride fiber doped with dysprosium ions yields an efficiency of 42% according to the in-band launched pump power at 2825 nm. Due to a custom piezoelectric fiber Bragg grating (FBG) package, mechanical strains applied to the narrowband FBG used as the input cavity coupler allowed for fast tuning of the emission wavelength over a spectral range of 1.5 nm. This laser was deployed in the field in northern Québec (Canada) to assess its performances for remote sensing of methane in the presence of a significant amount of water vapor, i.e., over a hydroelectric reservoir. The preliminary results acquired during this field campaign confirm the great potential of the proposed approach for the development of a real-time active imaging system of greenhouse gases.

Visible femtosecond fiber laser.

Femtosecond fiber lasers have revolutionized the industry of laser technology by providing ultrashort pulses of high brightness through compact, affordable, and reliable setups. In this work, we extend the scope of application of such sources by reporting, to our knowledge, the first femtosecond fiber laser operating in the visible spectrum. The passively mode-locked ring cavity is based on nonlinear polarization evolution in a single-mode Pr3+-doped fluoride fiber and runs in an all-normal dispersion regime. Compressed pulses at 635 nm have a duration of 168 fs, a peak power of 0.73 kW, and a repetition rate of 137 MHz.

Enhancing Evanescent Wave Coupling of Near-Surface Waveguides with Plasmonic Nanoparticles.

Evanescent field excitation is a powerful means to achieve a high surface-to-bulk signal ratio for bioimaging and sensing applications. However, standard evanescent wave techniques such as TIRF and SNOM require complex microscopy setups. Additionally, the precise positioning of the source relative to the analytes of interest is required, as the evanescent wave is critically distance-dependent. In this work, we present a detailed investigation of evanescent field excitation of near-surface waveguides written using femtosecond laser in glass. We studied the waveguide-to-surface distance and refractive index change to attain a high coupling efficiency between evanescent waves and organic fluorophores. First, our study demonstrated a reduction in sensing efficiency for waveguides written at their minimum distance to the surface without ablation as the refractive index contrast of the waveguide increased. While this result was anticipated, it had not been previously demonstrated in the literature. Moreover, we found that fluorescence excitation by waveguides can be enhanced using plasmonic silver nanoparticles. The nanoparticles were also organized in linear assemblies, perpendicular to the waveguide, with a wrinkled PDMS stamp technique, which resulted in an excitation enhancement of over 20 times compared to the setup without nanoparticles.

Toward low-loss mid-infrared Ga2O3-BaO-GeO2 optical fibers.

The development of efficient and compact photonic systems in support of mid-infrared integrated optics is currently facing several challenges. To date, most mid-infrared glass-based devices are employing fluoride or chalcogenide glasses (FCGs). Although the commercialization of FCGs-based optical devices has rapidly grown during the last decade, their development is rather cumbersome due to either poor crystallization and hygroscopicity resilience or poor mechanical-thermal properties of the FCGs. To overcome these issues, the parallel development of heavy-metal oxide optical fiber from the barium-germanium-gallium oxide vitreous system (BGG) has revealed a promising alternative. However, over 30 years of fiber fabrication optimization, the final missing step of drawing BGG fibers with acceptable losses for meters-long active and passive optical devices had not yet been reached. In this article, we first identify the three most important factors that prevent the fabrication of low-loss BGG fibers i.e., surface quality, volumic striae and glass thermal-darkening. Each of the three factors is then addressed in setting up a protocol enabling the fabrication of low-loss optical fibers from gallium-rich BGG glass compositions. Accordingly, to the best of our knowledge, we report the lowest losses ever measured in a BGG glass fiber i.e., down to 200 dB km-1 at 1350 nm.

Monolithic silica fiber laser operating at 585 nm.

We report, to the best of our knowledge, the first monolithic silica fiber laser operating in the visible. The laser cavity is based on a dysprosium-doped aluminosilicate fiber bounded by a pair of fiber Bragg gratings operating at 585 nm. The yellow laser signal reaches a record output power of 147 mW. Although the pump irradiation causes photodarkening, significant reduction of the photoinduced absorption losses is demonstrated via a photobleaching process with visible light.

Femtosecond tunable solitons up to 4.8 µm using soliton self-frequency shift in an InF3 fiber.

A tunable ultrashort soliton pulse source reaching up to 4.8 µm is demonstrated based on a 2.8 µm femtosecond fiber laser coupled to a zirconium fluoride fiber amplifier followed by a small core indium fluoride fiber. This demonstration is extending by 300 nm the long wavelength limit previously reported with soliton self-frequency shift (SSFS) sources based on fluoride fibers. Our experimental and numerical investigation highlighted the spectral dynamics associated with the generation of highly redshifted pulses in the mid-infrared using SSFS enhanced by soliton fission. This study is intended at providing a better understanding of the potential and limitations of SSFS based tunable femtosecond fiber sources in the 3-5  µm spectral range.

Modified astigmatic beam technique for laser writing.

The ultrafast laser writing of optical waveguides and devices is increasingly ubiquitous among the photonics community, mostly for its flexibility and three-dimensional fabrication capability. The well-known astigmatic beam technique is the simplest method to inscribe near-circular cross-section waveguides. In this paper, we report on a significant enhancement to the widely used astigmatic beam technique that makes it more flexible and yields a more circular waveguide cross section. By simply superposing a long-focus lens before the laser inscription objective lens, we demonstrate that the normalized squared radial deviation from a perfectly circular waveguide cross section can be reduced to <4×10-4, which is a significant improvement compared to >0.1 typically obtained using the standard astigmatic beam technique, or >0.7 with a Gaussian beam. The modified technique also makes it easy to use the full power delivered by the laser, which is not usually the case with the standard technique. A technique to optimize the waveguide shape prior to the inscription by in situ laser-induced plasma emission imaging is also discussed.

Probing the dispersive properties of optical fibers with an array of femtosecond-written fiber Bragg gratings.

We propose an efficient method to determine the effective refractive index of step-index optical fibers from the visible to the mid-IR and thus allowing to infer their dispersive properties over a broad spectral range. The validity of the method, based on the writing of an array of fiber Bragg gratings (FBGs) with known periods using the fs scanning phase mask technique, is first confirmed with a standard silica fiber, then applied to various fluoride glass fibers to determine their effective refractive index and dispersion over more than three octaves, i.e. from 550 to 4800 nm.

Recent developments in lanthanide-doped mid-infrared fluoride fiber lasers [Invited].

Mid-infrared fiber sources, emitting between 2.5 µm and 5.0 µm, are interesting for their great potential in several application fields such as material processing, biomedicine, remote sensing and infrared countermeasures due to their high-power, their diffraction-limited beam quality as well as their robust monolithic architecture. In this review, we will focus on the recent progress in continuous wave and pulsed mid-infrared fiber lasers and the components that bring these laser sources closer to a field deployment as well as in industrial systems. Accordingly, we will briefly illustrate the potential of such mid-infrared fiber lasers through a few selected applications.

Dysprosium-doped silica fiber as saturable absorber for mid-infrared pulsed all-fiber lasers.

We report on a mid-infrared Q-switched erbium-doped all-fiber laser using a dysprosium-doped silica fiber as saturable absorber for the first time in this wavelength range. Moreover, we demonstrate the use of a highly reflective chirped fiber Bragg grating written in a silica fiber as the input coupler for such lasers. This Q-switched all-fiber laser generates a stable pulse train centered at 2798 nm with a maximum average power of 670 mW at a repetition rate of 140 kHz with a pulse duration of 240 ns and a pulse energy of 4.9 µJ.

15†W monolithic fiber laser at 3.55†µm.

We report a dual-wavelength-pumped all-fiber continuous-wave (CW) laser operating at 3.55 µm that reached an output power of 14.9 W, which is, to the best of our knowledge, a record. The laser cavity, made of an erbium-doped fluoride fiber and bounded by two fiber Bragg gratings (FBGs), operates at an overall optical efficiency of 17.2% and a slope efficiency of 51.3% with respect to the 1976 nm launched pump power. The all-fiber design of the cavity not only allows for significant power scaling of the laser output, but also improves its long-term stability at high output power. The cavity design was set according to a numerical optimization that showed very good agreement with the experimental results.

Ultrafast laser writing of arbitrary long low-loss waveguides in optical fibers.

We propose an innovative femtosecond laser writing approach, based on a reel-to-reel configuration, allowing the fabrication of arbitrary long optical waveguides in coreless optical fibers directly through the coating. We report few meters long waveguides operating in the near-infrared (near-IR) with propagation losses as low as 0.055 ± 0.004 dB/cm at 700 nm. The refractive index distribution is shown to be homogeneous with a quasi-circular cross section, its contrast being controllable via the writing velocity. Our work paves the way for the direct fabrication of complex arrangements of cores in standard and exotic optical fibers.

Dual stage fiber amplifier operating near 3 µm with milijoule-level, sub-ns pulses at 5 W.

We report a 2800 nm Er3+-doped fluoride fiber amplifier that delivers 1 mJ pulses with an average power of 5 W and pulse duration of 1 ns at 5 kHz repetition rate. To the best of our knowledge, this is the highest pulse energy achieved from a fluoride-fiber-based system operating near 3 µm, and the W-level average power and short pulse lengths make the system a promising tool for biomaterials processing.

From near-UV to long-wave infrared waveguides inscribed in barium fluoride using a femtosecond laser.

Depressed-cladding waveguides (DCWs) of various sizes were inscribed in barium fluoride, allowing single-mode operation in the entirety of its transmission window (λ=0.2-12µm). Using femtosecond laser pulses at 515 nm, type I laser modified tracks were overlapped to form circular waveguides, whose cross-sectional geometry and numerical aperture were tailored to accommodate 0.405, 2.85, and 10.6 µm light. The mode profile, propagation loss, refractive index profile, and numerical aperture of the optimized waveguides were analyzed and compared with theory. We particularly demonstrate the challenging inscription of a large DCW for single-mode operation at 10.6 µm with propagation loss of <0.63dB/cm.

Smartphone Screen Integrated Optical Breathalyzer.

One third of fatal car accidents and so many tragedies are due to alcohol abuse. These sad numbers could be mitigated if everyone had access to a breathalyzer anytime and anywhere. Having a breathalyzer built into a phone or wearable technology could be the way to get around reluctance to carry a separate device. With this goal, we propose an inexpensive breathalyzer that could be integrated in the screens of mobile devices. Our technology is based on the evaporation rate of the fog produced by the breath on the phone screen, which increases with increasing breath alcohol content. The device simply uses a photodiode placed on the side of the screen to measure the signature of the scattered light intensity from the phone display that is guided through the stress layer of the Gorilla glass screen. A part of the display light is coupled to the stress layer via the evanescent field induced at the edge of the breath microdroplets. We demonstrate that the intensity signature measured at the detector can be linked to blood alcohol content. We fabricated a prototype in a smartphone case powered by the phone's battery, controlled by an application installed on the smartphone, and tested it in real-world environments. Limitations and future work toward a fully operational device are discussed.

2.3 W monolithic fiber laser operating in the visible.

We report, to the best of our knowledge, the first monolithic visible fiber laser pumped by a pigtailed diode. The robust cavity design proposed is based on a highly reflective fiber Bragg grating spliced to a double-clad praseodymium-doped fiber. The laser signal generated at 635.5 nm is single-mode, has a FWHM bandwidth of 0.16 nm, and reaches a maximum cw output power of 2.3 W. This demonstration breaks ground for the development of reliable high-power visible fiber lasers.

Direct-laser-written integrated mid-IR directional couplers in a BGG glass.

The development of coherent sources and other optical components for the mid-infrared has been hampered by the lack of sturdy materials that can withstand high power radiation or exposition to harsh environment. BGG glasses are robust materials transmitting over the 2.5-5 µm region. We report here the direct femtosecond laser fabrication of efficient directional couplers integrated in a BGG glass chip. The photonic components are characterized from 2.1 to 4.2 µm and compared to similar structures inscribed in silica glass samples. At 2.85 µm, a 99% relative cross transmission is reported in BGG glass. The experimental measurements are in good agreement with the coupled mode theory for wavelengths up to 3.5 µm.

Fuseless side-pump combiner for efficient fluoride-based double-clad fiber pumping.

We report a novel technique for side-pumping fluoride-based double-clad fibers, allowing a record coupling efficiency of 93% and a maximum power handling near 100 W at 981 nm. Our simple technique is based on wrapping a silica taper around a fluoride fiber and, therefore, does not require any complex fusion between these two dissimilar fibers. Under passive cooling, pump combiners made of undoped and erbium-doped fluoride fibers were successfully operated during several hours at respective incident powers of 91 and 44 W. Heat management issues and active cooling strategies are also discussed. This innovative combiner is a keystone towards the development of compact and robust high-power mid-infrared fiber lasers and amplifiers.

1.4 W in-band pumped Dy3+-doped gain-switched fiber laser at 3.24 µm.

In this Letter, we report, to the best of our knowledge, the first demonstration of an in-band pumped gain-switched Dy3+-doped fiber laser operating at 3.24 µm. The monolithic cavity bounded by two fiber Bragg gratings was pumped by a gain-switched Er3+-doped fiber system. It produced stable nanosecond pulses in a single-pulse regime on its entire operating range from 20 kHz to 120 kHz. A record average power of 1.43 W was achieved for a repetition rate of 120 kHz, and a record pulse energy of 19.2 µJ was achieved at 60 kHz. These results represent a significant improvement in Dy3+-doped pulsed fiber laser performances and open the way to applications in the fields of remote sensing and material processing.