We describe the history, guiding mechanism, recent advances, applications, and future prospects for hollow-core negative curvature fibers. We first review one-dimensional slab waveguides, two-dimensional annular core fibers, and negative curvature tube lattice fibers to illustrate the inhibited coupling guiding mechanism. Antiresonance in the glass at the core boundary and a wavenumber mismatch between the core and cladding modes inhibit coupling between the modes and have led to remarkably low loss in negative curvature fibers. We also summarize recent advances in negative curvature fibers that improve the performance of the fibers, including negative curvature that increases confinement, gaps between tubes that increase confinement and bandwidth, additional tubes that decrease mode coupling, tube structures that suppress higher-order modes, nested tubes that increase guidance, and tube parameters that decrease bend loss. Recent applications of negative curvature fibers are also presented, including mid-infrared fiber lasers, micromachining, and surgical procedures. At the end, we discuss the future prospects for negative curvature fibers.

Negative curvature fibers

We report on the fabrication and characterization of rare-earth doped silica fibers manufactured using an in-situ solution doping technique, which is compatible with conventional modified chemical vapor deposition equipment. The in-situ technique permits significantly more doped layers to be deposited, compared to conventional solution doping, and is directly applicable for the fabrication of large core rare-earth doped fibers suitable for high-power fiber sources. Ytterbium-doped aluminosilicate fibers fabricated using the new in-situ doping technique are reported and the results are compared to fibers fabricated using a conventional solution doping method.

MCVD in-situ solution doping process for the fabrication of complex design large core rare-earth doped fibers

We performed numerical simulations to obtain statistical and spectral characteristics of stimulated Brillouin scattering (SBS) initiated by Gaussian noise in single-mode optical fibers. Recently published experimental spectra of SBS power [e.g., Phys. Rev. Lett.85, 1879 (2000)] are explained completely by a one-dimensional SBS model. We give a clear physical insight into the problem and, for what is to our knowledge the first time, reveal how the probability function of Stokes power, the power-correlation function, and the SBS spectra evolve as key parameters of the model vary, leading to a modification of Stokes field statistics.

Statistical properties of stimulated Brillouin scattering in single-mode optical fibers above threshold.

The mid-infrared fiber lasers in the 2–3.5 μm spectral regions have been extensively applied in many application fields, such as biomedicine, telecommunications, military and nonlinear optics. With the improvements of the fiber components, the pumping regimes and other related technologies, the mid-infrared fiber lasers have made significant progress over the past decades and gradually become comparable with or supersede the traditional lasers in terms of certain lasing performance. In this review, from the beginning with the overview of fiber materials for the mid-infrared regions, we briefly summarize and review the latest research progress of mid-infrared continuous-wave (CW) and short pulse fiber lasers, including Tm3+-, Ho3+-doped, Tm3+-Ho3+ co-doped silicate fiber lasers for the 2 μm region and Er3+-, Ho3+-doped, Ho3+-Pr3+ co-doped ZBLAN fiber lasers for the 2.8–3.5 μm region. The advances of saturable absorbers applied in the mid-infrared pulse fiber lasers are also explored. Finally, the future prospects and challenges concerning the further development of mid-infrared fiber lasers are discussed and highlighted.

Recent developments in mid-infrared fiber lasers: Status and challenges

The Bi-doped fiber lasers operating at wavelengths of 1280 nm, 1330 nm, 1480 nm, and 1500 nm with a maximal output power of up to 2 W and a slope efficiency of 14 – 25% have been demonstrated for the first time. We have also investigated the influence of the doping concentration (GeO2 and P2O5) on the optical and laser generation properties of Bi-doped phosphogermanosilicate fibers.

https://iopscience.iop.org/article/10.1002/lapl.200910058/pdf

2 W bismuth doped fiber lasers in the wavelength range 1300 ? 1500 nm and variation of Bi-doped fiber parameters with core composition

A process is described for reproducible deposition of porous layers uniform along the preform axis, and the effect of the nature of the solvent on the infiltration of salt solutions into the porous layer is analyzed in relation to the fabrication of fiber preforms with controlled doping level. Data are presented on the variation of the retention volume in the porous layer with sintering temperature.

Doping of Optical Fiber Preforms via Porous Silica Layer Infiltration with Salt Solutions

An efficient cw single-mode double-clad Nd3+-doped fibre laser is developed which operates at room temperature in a quasi-three level scheme on the 925-nm 4F3/2 — 4I9/2 transition upon diode pump at 805 nm The gain in the laser resonator at 106 μm is strongly suppressed due to a proper choice of the refractive index profile in the fibre core The laser output power above 05 W is obtained with the slope efficiency exceeding 35 %

https://iopscience.iop.org/article/10.1070/QE2003v033n12ABEH002549/pdf

Efficient 0.9-μm neodymium-doped single-mode fibre laser

We have proposed and demonstrated an approach for ensuring quasi-single-mode operation of a cylindrically symmetric hybrid fibre having anomalous dispersion at wavelengths around 1 μm. Basic to this approach are distinctions between spatial fibre mode distributions and the use of a high-loss ring layer in the region of a minimum in the electric field of the operating hybrid mode.

https://iopscience.iop.org/article/10.1070/QEL16129/pdf

Quasi-single-mode hybrid fibre with anomalous dispersion in the 1 μm range

We report for the first time, to the best of our knowledge, on ~1 MW peak power femtosecond pulse delivery through ≈10 m-long air-filled microstructured revolver hollow-core fiber (RHCF) in the telecom spectral band near 1.56 µm wavelength. We have developed a high-power all-fiber master oscillator power amplifier source based on the novel large-mode area erbium-doped double-clad fiber with 980 nm multi-mode diode pumping that emits up to 530 nJ pulses shorter than 400 fs with 1.42 W maximum average power. These pulses have been further launched into low-loss (<30 dB km−1) RHCF with eight non-touched cylindrical capillaries-based cladding and 61 µm core size with more than 80% efficiency. Owing to low dispersion and nonlinearity of the RHCF developed, the output pulse characteristics (spectral and temporal) are close to the input ones for low and moderate pulse energies. However, we have observed significant nonlinear spectral filtering together with pulse shortening (down to 353 fs) at the maximum output average power of 0.94 W. We believe that the system developed may be highly promising for high-precision material processing and other high-energy and high-power laser applications.

1.56 µm sub-microjoule femtosecond pulse delivery through low-loss microstructured revolver hollow-core fiber

A mode-locked all-fiber Er-doped laser based on a figure-eight scheme with a passive nonlinear optical loop mirror and pulse duration of few nanoseconds has been realized for the first time. It has been revealed that the main problem of utilization of standard fibers with anomalous dispersion is the propagation of low-energy optical solitons accompanied by nanosecond pulse break up. Herein, the solution to this problem is discussed and stable laser schemes (i.e. all-polarization maintaining) are realized. A strong influence of the total laser dispersion on the nanosecond laser spectral bandwidth has been found.

https://iopscience.iop.org/article/10.1088/1612-2011/13/3/035104/pdf

Impact of dispersion on the output characteristics of an all-fiber Er-doped nanosecond mode-locked figure-eight laser with passive nonlinear optical loop mirror

A K Senatorov

Papers

Doping of Optical Fiber Preforms via Porous Silica Layer Infiltration with Salt Solutions

Efficient 0.9-μm neodymium-doped single-mode fibre laser

Quasi-single-mode hybrid fibre with anomalous dispersion in the 1 μm range

1.56 µm sub-microjoule femtosecond pulse delivery through low-loss microstructured revolver hollow-core fiber

Impact of dispersion on the output characteristics of an all-fiber Er-doped nanosecond mode-locked figure-eight laser with passive nonlinear optical loop mirror