Design and fabrication of large-mode-area multicore chalcogenide fiber with low bending loss.

Multicore fiber (MCF) has a larger mode-area (LMA) compared to traditional single-core fiber, making it easy to get a mode area of more than 3000 µm2 with an optimized MCF structure. Here, a fine-structured 19-core fiber based on chalcogenide glass was fabricated using a combined method involving extrusion, drilling, and rod-in-tube for the first time. The fiber has a minimum transmission loss of 1.8 dB/m at 6.7 µm. When the bending radius exceeds 6 cm, a low bending loss of about 0.6 dB appears, and the experimental data are in good agreement with the simulation results. In addition, the supermode characteristics of the 19-core fiber are analyzed from both perspectives of simulation and experiment, and these results are perfectly in good agreement. We believe it opens a new way to develop high-power and bend-resisting fiber with such kind of multicore structure.

High-Q lasing in Nd3+-doped phosphate glass microsphere resonators.

Nd3+-doped glasses are the most widely used laser gain media. However, Nd3+-doped non-silica microsphere lasers generally have lower quality (Q) factors due to the presence of non-radiative energy-loss impurities in traditional glass systems. In this work, we report the first, to the best of our knowledge, Nd3+-doped phosphate glass microsphere laser with the highest Q-factor of 1.54 × 106 among all Nd3+-doped non-silica glass microsphere lasers. Whispering gallery modes in the 1020-1120-nm band can be obtained for a typical microsphere with a diameter of 82.57 µm. When the pump power exceeds the threshold of 0.17 mW, single- and multi-mode microsphere lasing can be generated under 808-nm laser diode (LD) pumping. Typical Q-factors of the phosphate glass microspheres can reach 106, which is at least an order of magnitude higher than those of other Nd3+-doped non-silica glass microsphere lasers. The Nd3+-doped phosphate glass microsphere laser reported in this work can be considered as an active optical/photonic device with low pump thresholds.

Single-mode suspended large-core chalcohalide fiber with a low zero-dispersion wavelength for supercontinuum generation.

Chalcogenide glass possesses outstanding advantages, such as supercontinuum generation, but its nonlinear applications were limited by large zero-dispersion wavelength (ZDW). Traditional suspended-core fibers can shift the ZDW to near IR with a tiny core size of less than 5 µm but a large evanescent wave loss exists in these fibers. In this paper, we prepared a novel suspended-core fiber (SCF) based on chalcohalide glasses for the first time via the extrusion method, in which the ZDW of the fundamental mode in the fiber with a core size of larger than 30 µm was successfully shifted to 2.6 µm. We also calculated confinement loss (CL) of propagation modes and fundamental mode energy ratio in the fiber. We found that the minimum CL ratio of the high order modes (LP11) to the CL of the fundamental mode is 124, indicating that the single-mode operation condition is satisfied when the wavelength is more than 4.6 µm. The lowest transmission loss is 1.2 dB/m at 6.5 µm. An ultra-broad supercontinuum spectrum, covering from 1.6 to 12 µm was generated in this suspended-core fiber pumped by a 5 µm femtosecond laser. Such a wide SC in the chalcogenide SCF is due to the large core size. All these results demonstrate the potential to use the large core SCF in the application of a mid-IR laser.

High-efficiency tunable femtosecond solitons generation from 1.9 to 2.35 µm in a thulium-doped fiber amplifier via precise seed-pulse management.

We demonstrate the tunable Raman femtosecond solitons generation with a record-breaking power of 1.2 W at 2.3 µm and an ever-reported highest Raman soliton energy conversion efficiency of 99% via precise seed-pulse management in the thulium-doped single-mode fiber amplifier. We find that the central wavelength and the chirp of the incident pulses could dramatically affect the red-shifted soliton energy, locations, conversion efficiency, and the threshold power in fundamental Raman soliton generation. For the first time, we experimentally illustrated how the seed pulse with Kelly sidebands could affect the Raman solitons generation in this amplifier, and obtained the detailed regularity between the parameters of incident pulses and the properties of the generated solitons. This work provides useful guidance for Raman soliton-based high-power mid-infrared femtosecond laser fabrication.

Se-H-free As2Se3 fiber and its spectral applications in the mid-infrared.

The complete removal of the impurities like Se-H in Se-based chalcogenide glasses has been challenging in the development of highly transparent chalcogenide glass fiber. In this paper, several purification methods, including dynamic distillation, static distillation, and combined distillation method, were adopted with an aim of purifying arsenic selenide glass with ultra-low content of the impurities. The experimental results demonstrated that the Se-H can be completely eliminated in the arsenic selenide glass host and fiber without the introduction of any chloride. We further explored the applications of such low loss and Se-H-free chalcogenide glass fiber in the mid-infrared. It was found that, using such a Se-H free fiber, a flattened supercontinuum spectrum above the -30 dB level from 1.2 to 13 µm was generated from the Se-H free fiber with a 5.5 µm laser pumping. The sensitivity was found to be improved 5.1 times for CO2 gas in the 3 to 6 µm wavelength range.

High-sensitivity micro-strain sensing using a broadband wavelength-tunable thulium-doped all-fiber structured mode-locked laser.

We demonstrate a thulium-doped mode-locked fiber laser with ultra-broadband wavelength tunability for micro-strain sensing based on the multimode interference (MMI) effect in single-mode-multimode-single-mode (SMS) fiber configuration. The homemade SMS device with high performance is fusion spliced in the laser cavity, and the developed dispersion precisely managed the all-fiber structured mode-locked picosecond laser with a record-breaking wavelength tuning range from 1976 to 1916 nm while exerting axial strain on this SMS device. We experimentally explored the regularity between the strain and the central-wavelength shift of the mode-locked pulse, and for the first time to the best of the authors' knowledge, achieved the precise in-line axial strain measurement from 0 to 5385 µÉ› by using the tunable ultrafast-laser-based sensor, and sensitivity is up to -11.5 pm/µÉ›. With high compactness and durability, this sensor has advantages in real-time dynamic measurement over other passive devices, thus will undoubtedly find various application scenarios.

Generation of watt-level supercontinuum covering 2-6.5 µm in an all-fiber structured infrared nonlinear transmission system.

We demonstrate a watt-level mid-infrared supercontinuum source, with the spectrum covering the infrared region from 2 to 6.5 µm, in an all-fiber structured laser transmission system. To further improve the SC spectral bandwidth, power and system compactness in the follow-up As2S3 fiber, we theoretically and experimentally explored some knotty problems that would potentially result in the As2S3 fiber end-facet failure and low SC output power during the high-power butt-coupling process and proposed an optimal coupling distance on the premise of the safety of As2S3 fiber end face. In addition, we also built a multi-pulse pumping model for the first time to more precisely estimate the SC spectral evolution in As2S3 fiber. This work will give an important reference to someone who is working on the all-fiber structured, high-power mid- and far-infrared supercontinuum source.