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We developed a new holmium-doped triple-clad fiber (Ho-3CF), reducing the clad diameter to improve the overlap between pump and doped-core, and the holmium concentration to reduce the influence of ion clustering on the laser efficiency. We illustrate here the performance of this fiber in a laser oscillator configuration. The laser emission is centered at 2.12 $\mu$m by a fiber Bragg grating, and the active fiber is pumped in the clad by a 1.94 $\mu$m thulium-doped fiber laser. The slope efficiency reaches 73% with respect to absorbed power (60% considering coupled power), for a maximum signal power of 62 W delivered on a quasi single spatial mode (M$^2$=1.2). To the best of our knowledge, this slope efficiency is the highest reported for a high power clad-pumped fiber laser emitting at a wavelength higher than 2.1 $\mu$m. We also analyze experimentally the impact of the pump Numerical Aperture (NA), at the input of the Ho-3CF, on the laser efficiency. Finally, we use our numerical simulation to comment on the best choice of pump wavelength.

The ultrashort pulse laser operation is crucially defined by engaging explicit modulators. Conventionally, they are laborious to incorporate into an all-fibre design or involve the design of sophisticated cavities. We exploit Thulium-doped fibre as the gain and simple, highly integrated saturable absorber with a modulation depth of 23% and a high thermal damage threshold. Hence, pulses as short as 350fs carrying 1nJ energy at a repetition rate of 45MHz have been demonstrated. The laser average output power showed long-term stability with ~1%. The utilised concept of all-fibre saturable absorber provides technological grounds for a down-scaled, highly integrated laser architecture., Comment: 4 pages, 4 figures, letter, preprint

Broadband wavelength tuneability can ensure a new level of versatility for laser systems and extend areas of their applications. Principle limitations of achieving wide tuning wavelength ranges are generally defined by the spectral bandwidth of the gain and traditional tuneability techniques, relying on electrically controlled or bulk filters, reducing laser efficiency and generation stability. In this work, we present nearly 90 nm tuneability in ultrafast Tm-doped fibre laser within the span from 1873 to 1962 nm by implementing variable feedback for efficient control of the excitation level of the active medium and, hence, the gain spectrum. The highest laser efficiency is observed with 20% feedback, generating 580-fs soliton pulses at 1877 nm central wavelength with 1.5 nJ output pulse energy. By combining the nonlinear Shrodinger equation and population inversion rate equations for the gain medium, the developed numerical model helps to unveil nonlinear pulse evolution under the influence of dynamically varying gain spectrum. The resulting laser system presents a compact and straightforward approach to achieve laser generation with a broad range tuneability of wavelength and operation regimes, which is not impaired by the limitations on laser stability or power performance and can be translated to other wavelength ranges.

We realize a fiber Bragg grating InGaN based laser diode emitting at 400 nm and demonstrate its high coherency. Thanks to the fabrication of a narrow band fiber Bragg grating in the near-UV, we can reach single-mode and single-frequency regimes for the self-injection locked diode. The device exhibits 44 dB side-mode-suppression-ratio and mW output power. Detailed frequency noise analysis reveals sub-MHz integrated linewidth and 16 kHz intrinsic linewidth. Such a narrow linewidth laser diode in the near-UV domain with a compact and low-cost design could find applications whenever coherency and interferometric resolutions are needed.

We report on our realization of a high power holmium doped fiber laser, together with the validation of our numerical simulation of the laser. We first present the rare absolute measurements of the physical parameters that are mandatory to model accurately the laser-holmium interactions in our silica fiber. We then describe the realization of the clad-pumped laser, based on a triple-clad large mode area holmium (Ho) doped silica fiber. The output signal power is 90 W at 2120 nm, with an efficiency of about 50% with respect to the coupled pump power. This efficiency corresponds to the state of the art for clad-pumped Ho-doped fiber lasers in the 100 W power class. By comparing the experimental results to our simulation, we demonstrate its validity, and use it to show that the efficiency is limited, for our fiber, by the non-saturable absorption caused by pair induced quenching between adjacent holmium ions., Comment: 14 pages, 7 figures

We have developed a Watt-level single-frequency tunable fiber laser in the 915-937 nm spectral window. The laser is based on a neodymium-doped fiber master oscillator power amplifier architecture, with two amplification stages using a 20 mW extended cavity diode laser as seed. The system output power is higher than 2 W from 921 to 933 nm, with a stability better than 1.4 percent and a low relative intensity noise., Comment: 4 pages, 4 figures