Self-swept holmium fiber laser near 2100 nm

Observation of four self-sweeping regimes in a single-mode bi-directional ytterbium-doped fiber ring laser

In this work, for the first time, four self-sweeping regimes in a single-mode bi-directional ytterbium-doped fiber ring laser are observed by adjusting the polarization controller (PC): normal self-sweeping, reverse self-sweeping, mixed state, and wavelength stop state. In addition, regulating the PC can artificially selectively make the laser operate in normal self-sweeping or reverse self-sweeping within a certain pump power range, and their self-sweeping characteristics (e.g., sweeping rate, sweeping range, etc.) and intensity dynamics are investigated in detail, respectively. In conclusion, we can flexibly regulate the sweeping direction and sweeping characteristics of the bi-directional self-sweeping fiber ring laser in a simple approach by adjusting the PC, which is potentially valuable for its practical application.

Heat treatment and fiber drawing effect on the luminescence properties of RE-doped optical fibers (RE = Yb, Tm, Ho)

We investigate the influence of various optical fiber fabrication processes on the fluorescence decay of RE ions commonly used in fiber lasers and amplifiers, i.e. Yb³⁺, Tm³⁺ and Ho³⁺. Optical fiber preforms were prepared using the MCVD method combined with Al₂O₃ nanoparticle doping and subjected to subsequent heat treatment processes such as preform elongation and fiber drawing. The fluorescence decay of RE ions was measured in multiple stages of optical fiber preparation: in an original preform, in an elongated preform (cane), in a standard fiber, and in an overcladded fiber. It was found that heat treatment processing of the preforms generally leads to a faster fluorescence decay, which can be explained by the diffusion of dopants and clustering of RE ions. The fiber drawing exhibited a greater effect compared to preform elongation, which was ascribed to a faster cooling rate of the process. In general, the heat treatment of RE-doped silica glass preforms leads to the decline of fluorescence decay.

Dual-longitudinal-mode CW self-sweeping operation in Er-doped fiber laser

A new type of sweeping operation-dual-mode continuous-wave (CW) self-sweeping-is demonstrated in an erbium-doped fiber laser with a sweeping range of 2.8 nm in a region of 1605 nm. The laser generates two adjacent longitudinal modes of equal intensity, but at some moments of time, one of the modes with lower frequency begins to vanish and a new one with even higher frequency starts to grow. As a result, the self-sweeping of lasing frequency with CW intensity dynamics is observed.

Active Optical Fibers and Components for Fiber Lasers Emitting in the 2-μm Spectral Range

Laser sources emitting in the infrared range at around 2 µm are attracting great interest for a variety of applications like processing of transparent thermoplastic polymers in industry as well as plenty of applications in medicine, spectroscopy, gas sensing, nonlinear frequency conversion to the mid-infrared, to mention a few. Of late, fiber lasers compared to other kinds of lasers benefit from their all-fiber design, leading to a compact, robust, and well thermally manageable device. Particularly, thulium- and holmium-doped fiber lasers are the first choice in fiber lasers emitting light around 2 µm. In this paper, we give an overview of our recent results in the research on thulium- and holmium-doped optical fibers, fiber lasers, and related research topics in the 2-µm spectral range. In particular, we present, to our knowledge, the first results of improvement of pump absorption in double-clad fibers thanks to the fiber twist frozen during drawing. Finally, a brief demonstration of material processing by thulium all-fiber laser operating at 2 µm is presented.

Observation of reverse self-sweeping effect in an all-polarization-maintaining bidirectional ytterbium-doped fiber laser

In this article, we report, to the best of our knowledge, the first observation of the reverse self-sweeping phenomenon in an all-polarization-maintaining bidirectional ytterbium-doped fiber laser. Conventional behaviors, including the dependence of sweeping range, sweeping rate and average pulse repetition rate on the pump power, can be observed in our fiber laser. Two couplers with ratio of 50/50 and 10/90 are respectively employed as the output coupler in fiber laser, which generates the reverse self-sweeping phenomenon for comparison.

Single-frequency self-sweeping Nd-doped fiber laser

We experimentally demonstrate for the first time, to the best of our knowledge, a Nd-doped fiber laser with wavelength self-sweeping. The main feature of the laser is the generation of periodic microsecond pulses, where each of them contains practically only single longitudinal mode radiation with a linewidth of about 1 MHz. The laser frequency changes from pulse to pulse with high linearity by one intermode beating frequency of the laser ∼7.1  MHz. The laser generates a linearly polarized radiation near wavelength of 1.06 μm with a self-sweeping range of up to 1.8 nm.

Broad-range self-sweeping single-frequency linearly polarized Tm-doped fiber laser

We experimentally demonstrate a linearly polarized Tm-doped fiber laser with sweeping range up to 26 nm in the region of 1.92 μm. The main feature of the laser is generation of periodic microsecond pulses in which each contains practically only single longitudinal mode radiation. The laser frequency changes from pulse to pulse with high linearity by one intermode beating frequency of the laser ∼8  MHz. The developed source is applied to measure spectrum of water absorption lines in air.

Michelson mode selector for spectral range stabilization in a self-sweeping fiber laser

We report on spectral range stabilization in a self-sweeping laser by adding a narrowband fiber Bragg grating (FBG) to the output mirror in the Michelson configuration. The effects of FBG reflectivity and optical path difference in the Michelson interferometer on the laser spectral dynamics are investigated. Optimization of the interferometer allows us to demonstrate broadband (over 16 nm) self-sweeping operation and reduction of the start and stop wavelength fluctuations by two orders and one order of magnitude (∼100 and 15 times) for start and stop bounds, respectively (down to several picometers). The proposed approaches significantly improve quality of the spectral dynamics and facilitate application of the self-sweeping lasers.

All-fiber Brillouin optical spectrum analyzer based on self-sweeping fiber laser

We proposed and demonstrated an all-fiber scheme for optical spectrum measurement based on stimulated Brillouin scattering and frequency self-sweeping laser without external driver and frequency tunable elements. The resolution and measuring range of proposed analyzer is measured to be 23 MHz and 5 THz respectively. The ways for improvement of the device characteristics are discussed.

Focus issue introduction: Advanced Solid-State Lasers (ASSL) 2016

The editors introduce the focus issue on "Advanced Solid-State Lasers (ASSL) 2016", which is based on the topics presented at a conference of the same name held in Boston, USA, from October 30 to November 3, 2016. This focus issue, jointly prepared by Optics Express and Optical Materials Express, includes 20 contributed papers (14 for Optics Express and 6 for Optical Materials Express) selected from the voluntary submissions from attendees who presented at the conference and have extended their work into complete research articles. We hope this focus issue provides a useful link to the variety of topical discussions held at the conference and will contribute to the further expansion of the associated research areas.