In recent years, Volume Bragg gratings (VBGs) have seen widespread use, traditionally inscribed in photo-thermo-refractive glasses. The emergence of femtosecond lasers has enabled VBG inscription in various materials. Silver-containing glasses have drawn attention due to their ability to produce strong Type-A (“A” for Argentum) refractive index changes. We explored the laser writing processes for optimizing the recording inscription of Type-A VBGs. The Gaussian-Bessel beam is employed to produce a single plane grating with 6700 µm3/s throughput while the phase mask approach is investigated to accelerate VBG inscription, allowing record throughput up to 106 µm3/s, paving the way for industrial applications.
This paper reports a second generation of radiation-balanced fiber laser and amplifier cooled internally using anti-Stokes fluorescence by pumping them at 1040 nm. In both devices the gain medium is a single-mode silica fiber with a core heavily doped with Yb3+, initially encapsulated in CaF2 nanoparticles, and co-doped with Al to reduce quenching and increase the cooling efficiency. After optimization of its length (4.1 m) and its output coupler reflectivity (3.3%), the 1065- nm continuous-wave fiber laser has a threshold of 160 mW and a radiation-balanced (no net heat generation) output power of 192 mW, or nearly 70% higher than the previous radiation-balanced fiber laser. At its radiation-balanced point, its optical efficiency is 56.8%. The single-frequency, single-mode fiber amplifier, constructed with the same fiber, was optimum with a length of 6.8 m, and it had a radiation-balanced gain of 20 dB: it amplified an 800-μW signal to 84.2 mW with 433 mW of input pump power. The significance of this result is underscored by the small diameter of the single-mode fiber core (7.8 μm), which makes cooling more challenging. This study further demonstrates the viability of achieving substantial gain and energy extraction in a small-core Yb-doped silica fiber while effectively utilizing anti-Stokes fluorescence to keep it cool.
We report the first demonstration of Volume Bragg grating (VBG) by femtosecond laser writing in silver-containing glasses using type A high refractive index modification supported by the laser-inscribed silver clusters. We present a comparative study between different approaches to achieve high diffraction efficiency in VBG for the VIS-NIR range. The first approach involves direct writing, line-by-line, and plane-after-plane, of the entire structure with a Gaussian beam as well as a Bessel beam. The second method will be considered with the inscription under a periodic phase mask. This work opens the avenue for femtosecond writing VBG with high throughputs compatible for industrialisation
For the last fifteen years, Universite Laval’s SPIE Student Chapter has been building strong links between academia and industry to better prepare its student members to face their future career and to guide them towards industry. With now over fifty companies working in the field of optics and photonics in the Quebec City area alone, this makes it one of the best places in the world for students to visit companies and learn about companies’ expertise, equipment and work environments. In 2017 and for the first time at Universite Laval, the Student Chapter organized a day-long workshop where students had to solve real-world industry-related problems presented by high-end optics-related companies, i.e. an industrial seminar. Now at its fourth edition, a retrospective picture investigating the success of this event can be drawn. Over the years, more than 20 companies from Quebec City’s rich optics and photonics area were invited to present their domain of expertise to students through conferences, product demonstrations and original problem scenarios encountered in the past. As a result, no fewer than 100 students were familiarized with the work of these technology companies. They also exchanged and shared ideas with expert engineers, physicists, chemists, etc., and were given real-world problems to solve. From this process, direct links were created between the employers and the future employees, and a clearer picture was drawn for graduates envisioning an industrial career. Consequently, this event has shown to be beneficial for both students and companies.
The cladding-pumping scheme has made the power scalability of rare-earth-doped fiber lasers up to record levels possible by distributing the pump absorption along much longer fiber lengths. However, in addition to increasing the fiber cost and the cavity losses, a longer cavity length leads to enhanced detrimental nonlinear effects such as stimulated Raman scattering. As a way to reduce the required length of such lasers, we propose here an all-fiber laser architecture that makes use of a femtosecond-written chirped inner-cladding Bragg grating (ICBG) as a residual pump reflector. We report a 73% reflectivity of the pump power propagating in the highly multimode 125 μm-diameter inner cladding of the fiber made out of pure silica. This component was inscribed by using 400 nm femtosecond pulses and the phase-mask technique. Such a reflectivity was reached by optimizing the chirp of the grating and by inserting the fiber inside a hollow capillary with an outside diameter of 1 mm during the inscription. The latter reduces greatly the impact of the fiber’s curvature on the refraction of the writing beam. A larger writing area and consequently a stronger reflectivity could therefore be reached. The presence of this component at the output of a 21 m long erbium-doped silica fiber laser operating at 1.6 μm increased its slope efficiency from 20.5 to 25.1 % with respect to the injected pump power and increased its output from 22.8 to 29 W at 115 W of pump power.
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