Fabrication of ultra-high numerical aperture GeO2-doped fiber and its use for broadband supercontinuum generation: publisher's note.

This publisher's note serves to correct Appl. Opt.56, 9315 (2017)APOPAI0003-693510.1364/AO.56.009315.

Manipulation of infrared dispersive waves in customized microstructured optical fibers for 1.7 and 2.0 µm light sources.

We demonstrate the controllable generation of infrared dispersive waves (DWs) from customized, in-house fabricated silica microstructured optical fibers (MOFs) by manipulating the location of zero dispersion wavelength (ZDW) through the structure of the fibers. The highly enriched shaping mechanism of arrested soliton in the MOFs with two ZDWs provides a technique for efficient energy transfer into the targeted eye-safe wavelengths at 1.7 and 2.0 µm by the virtue of DW formation.

Rogue waves in a linear cavity Yb-fiber laser through spectral filtering induced pulse instability.

In this Letter, experimental observation of dissipative rogue waves (DRWs) due to spectral filtering induced pulse instabilities in a mode-locked ytterbium (Yb) fiber laser has been presented. A semiconductor saturable absorber mirror was used to mode-lock the linear cavity laser and a chirped fiber Bragg grating (CFBG) was used for dispersion management, which also acted as a spectral filter and output coupler. Under stable conditions, the cavity delivered dispersion managed dissipative solitons of 447 fs duration and 0.69 nJ pulse energy at 10.19 MHz repetition rate with uniform intensity distribution over a long time span. As the spectral width increased with pump power, random intensity fluctuations were observed in the pulse train due to the filtering effect of the CFBG. Employing a dispersive Fourier transform by stretching the output pulse train in time allowed the existence of DRWs more than 4 times stronger than the significant wave height to be observed. Further increments of pump power led to a stable multi-pulsing state.

Hybrid pumped gain-switched thulium fiber laser at a high repetition rate.

A gain-switched all-fiber thulium laser at 2 µm with high repetition rate has been demonstrated under a hybrid pumping scheme combined of a pulsed pump at 1.56 µm and CW pump at 793 nm. The in-band pulsed pump at 1.56 µm triggers the gain-switching pulses while the CW pump at 793 nm facilitates the energy storage. Therefore, the seed cavity delivers high energy pulses allowing the elimination of multistage amplification. Such hybrid pump configuration is effective for generating gain-switched pulses of high average power with better slope efficiency and pulse width of a few hundreds of a nanosecond. The optimized cavity under such hybrid pump configuration provides output power of 5.92 W from the gain-switched oscillator with slope efficiency of 60% and pulse width of 300 ns at a repetition rate of 344 kHz. Maximum pulse energy of 17.2 µJ and peak power of 53.9 W has been achieved at this repetition rate. Stable gain-switched pulses at reduced pump pulse energy have been achieved by the use of a CW pump at 793 nm. This novel pump configuration facilitates gain switch at higher repetition rates where enough pump pulse energy may not be available. The gain-switched laser also operates at 520 kHz and 1.3 MHz repetition rate by changing the 1.56 µm pulsed pump and cavity length.

Diverse mode of operation of an all-normal-dispersion mode-locked fiber laser employing two nonlinear loop mirrors.

In this paper, we propose an all-normal-dispersion ytterbium-fiber laser with a novel ring cavity architecture having two nonlinear amplifying loop mirrors (NALM) as saturable absorbers, capable of delivering distinctly different pulses with adjustable features. By optimizing the loop lengths of the individual NALMs, the cavity can be operated to deliver Q-switched mode-locked (Q-ML) pulse bunches with adjustable repetition rates, mode-locked pulses in dissipative soliton resonance (DSR) regime or noise-like pulse (NLP) regime with tunable pulse width. The DSR pulses exhibit characteristic narrowband spectrum, while the NLPs exhibit large broadband spectrum. The operation regime of the laser can be controlled by adjusting the amplifier pump powers and the polarization controllers. To the best of the authors' knowledge, this is the first demonstration of a single mode-locked cavity where narrowband DSR pulses and broadband NLPs alongside Q-ML pulse bunches can be selectively generated by employing two NALMs.

Fabrication of ultra-high numerical aperture GeO2-doped fiber and its use for broadband supercontinuum generation.

We report the fabrication, characterization, and application (broadband supercontinuum [SC] generation) of ultra-high numerical-aperture heavily (50 mol. %) GeO2-doped optical fiber, obtained through a modified chemical vapor deposition process and rod-in-tube method. The formation of Ge-related diamagnetic defect centers, such as germanium oxygen defect centers (GeODC) with nonbridging lone electron pairs, confirmed by x-ray photoelectron spectroscopy and optical absorption studies, inducing hypolarizable local dipoles, may be responsible in boosting the nonlinear effects and enhancing stimulated Raman scattering at pumping with high-power pulses, culminating in generation of broadband SC generation. The SC spans toward the Stokes side up to 2.4 µm, under the action of ns-range pulses launched from a smartly Q-switched erbium-doped fiber laser with operation wavelength (1.56 µm) matching the zero-dispersion wavelength of the high GeO2-doped fiber.

High repetition rate gain-switched 1.94 µm fiber laser pumped by 1.56 µm dissipative soliton resonance fiber laser.

A dissipative soliton resonance (DSR) mode-locked Er:Yb fiber laser has been used to pump a thulium fiber laser to generate gain-switched pulses at high repetition rates. Here 412 ns long DSR pulses with a center wavelength of around 1.56 µm at a repetition rate of 410 kHz have been fed to a thulium fiber laser, resulting in generation of gain-switched pulses at 1.94 µm. The minimum pulse width achieved was 256 ns with an average power of 4.6 W at 66% slope efficiency. Gain-switched pulses at 520 kHz and 750 kHz were generated through changing the pump pulse repetition rate by modifying the DSR cavity. To the best of our knowledge, this is the first demonstration of a high repetition rate gain-switched thulium fiber laser pumped by a DSR mode-locked fiber laser. As DSR pulses can be generated with high seed average power and energy independent of the operating wavelength regime as well as mode-locking technique, the proposed method can be applied to generate gain-switched pulses at high repetition rates and various wavelengths without the need of any optical or electrical modulators.

Near-infrared supercontinnum generation in single-mode nonlinear Yb(3+)-doped fiber amplifier.

Near-infrared supercontinnum (SC) generation, accompanied with several emission bands at visible and ultraviolet, is experimentally investigated in an all-fiber single-mode Yb(3+)-doped silica fiber MOPA. The seed is an all-normal-dispersion mode-locked Yb(3+)-doped single-mode fiber laser using a nonlinear polarization evolution mechanism. With the pump power of several hundreds of milliwatts, SC spanning of 1010 nm to 1600 nm was generated in a 20-m single-mode germano-zirconia-silica Yb(3+)-doped fiber amplifier. The intensive nonlinear effects, namely stimulated Raman scattering, four wave mixing, and self-phase modulation, enable the SC generation in the small-core fiber amplifier without the use of photonic crystal fibers or tapered fibers. Such a compact and cost-effective SC generation system enables applications in optical coherent tomography, optical metrology, and nonlinear microscopy.

Picosecond fiber MOPA pumped supercontinuum source with 39 W output power.

We report a picosecond fiber MOPA pumped supercontinuum source with 39 W output, spanning at least 0.4-2.25 microm at a repetition rate of 114.8 MHz. The 2m long PCF had a large, 4.4 microm diameter core and a high-delta design which led to an 80% coupling efficiency, high damage threshold and rapid generation of visible continuum generation from the picosecond input pulses. The high and relatively uniform power density across the visible spectral region was approximately 31.7 mW/nm corresponding to peak power density of approximately 12.5 W/nm for the 21 ps input pulses. The peak power density was increased to 26.9 W/nm by reducing the repetition rate to 28 MHz. This represents an increase in both average and peak power compared to previously reported visible supercontinuum sources from either CW pumped or pulsed-systems.

Generation of supercontinuum and its theoretical study in three-ring silica microstructured optical fibers.

We report supercontinuum generation in nonlinear microstructured optical fibers (MOFs) especially fabricated in a two-step stack and draw process having three rings of airholes. High air-filling fraction (>0.9) is obtained in a simple and straightforward way during the drawing process which is essential to enhance nonlinearity. Two of the fabricated samples are characterized and zero dispersion wavelength is tailored to achieve efficient pumping in the anomalous group velocity dispersion regime. The characteristics of the supercontinuum band as observed experimentally show good agreement with the predicted numerically simulated results, where soliton mediated dispersive waves are distinctly observed.

Design of all-solid leakage channel fibers with large mode area and low bending loss.

We investigate a novel design for all-solid large mode area (LMA) leakage channel fibers (LCFs) for high-power Yb-doped fiber lasers and amplifiers, based on a single down-doped-silica rod ring surrounding a seven-cell pure-silica core, aiming for effectively single-mode behavior and low bending loss characteristics. Through detailed numerical simulations based on the finite element method (FEM), we find that the proposed all-solid LMA-LCFs, having a seven-cell core and two different sizes of down-doped rods, can achieve sufficient differential mode loss and much lower bending loss, as compared with a previously-reported LCF with a one-cell core and six large down-doped-silica rods.

Characterization of porous core layer for controlling rare earth incorporation in optical fiber.

The porous core layer deposited by modified chemical vapour deposition process has been analyzed in terms of thickness, pore size distribution, homogeneity and characteristics of the soot particles to investigate their variation with deposition temperature and input vapour composition. The compositions selected were SiO(2), SiO(2)-GeO(2) and SiO(2)-P(2)O(5). Rare earth ions were incorporated into the deposit by a solution doping technique. The analysis of deposited microstructures was found to provide a quantitative indication about the rare earth incorporation and its variation with respect to process conditions. Thus the characterization provides a method of controlling rare earth doping and ultimate preform/fiber properties.