Supercontinuum (SC) generation towards the mid-infrared (MIR) range is an active field of research and development motivated by a wide range of applications including optical coherence tomography (OCT), material processing, optical sensing and absorption spectroscopy. In this work, we investigate mid-IR SC generation in a cascaded silica and soft-glass fiber system directly pumped with a commercially-available picosecond fiber laser operating in the telecommunications window at 1.55 μm. This all-fiber system is shown to generate a flat broadband mid-IR-SC covering the entire range from 2 to 10 μm with several tens of mW of output power. This technique paves the way for practical and robust broadband SC sources in the mid-IR without the requirement of mid-infrared pump sources or Thulium-doped fiber amplifiers. We also describe a fully-realistic numerical model used to simulate the nonlinear pulse propagation through the cascaded fiber system and use our numerical results to discuss the physical processes underlying the spectral broadening in the cascaded system.
Nonlinear effects are well-known to limit the power scalability of continuous-wave (CW) high power fiber lasers (HPFL). In addition to nonlinear effects than act over the fundamental mode, intermodal nonlinear effects are currently drawing the interest of researchers. Specifically, intermodal nonlinear effects in CW-HPFLs such as degenerate intermodal four-wave mixing (IM-FWM) and stimulated Raman scattering(SRS)-induced intermodal wave-mixing (IM-WM) have been investigated recently; the former generates Stokes and idler at different modes, and the latter transfers power from the fundamental mode to the Raman shifted high-order modes. Here, we report a model that encompasses the aforementioned intermodal couplings in CW-HPFLs and simulate them. More specifically, a model based on multimode generalized nonlinear Schrodinger equations is developed and used to simulate the intermodal couplings in 25/400μm Yb-doped large-mode area fiber amplifiers. Based on the phase-matching condition of IM-FWM, the relation between degenerate IM-FWM frequency shift, modal group velocities, and modal group velocity dispersions is found and applied in the model. By using this model, degenerate IM-FWM and SRS-induced IM-WM, which are intermodal phenomena recently discussed in literatures of CW-HPFLs, are successfully simulated. In addition, a novel intermodal phenomenon is found and discussed, which is the high-order mode second-ordered Stokes resulting from the joint effect of degenerate IM-FWM and SRS-induced intermodal wave-mixing (IM-WM). To the best of our knowledge, this model is the first to include degenerate IM-FWM in the context of CW-HPFLs and reveal the joint effect of the aforementioned intermodal couplings. The result also gives insight of the conditions leading to intermodal couplings.
We investigate Brillouin scattering in hybrid As2Se3 PMMA tapered fiber and demonstrate that Brillouin
frequency shift can be widely tuned over a broad radio-frequency range by varying the core diameter of the
optical tapered fiber.
We use hybrid polymer-chalcogenide optical microwires to realize mid-infrared frequency conversion via the process of
normal dispersion modulation instability (MI). Phase-matching is achieved through a negative fourth-order dispersion
coefficient and leads to the apparition of parametric sidebands located at 2 μm and 3.5 μm, corresponding to a frequency
shift of 30 Thz relative to the pump, which is among the largest reported using normal-dispersion pumped MI in a singlepass
configuration in the mid-IR Stochastic nonlinear Schrödinger equation simulations are in excellent agreement with
experiments.
We demonstrate the generation of dual-wavelength noiselike pulses in an Er3+ fiber laser. A ring cavity configu ration including a polarizer as saturable absorber induces a first series of pulses at the wavelength of 1550 nm via nonlinear polarization rotation. From the Raman gain of these pump pulses emerges a second series of Stokes pulses at 1650 nm. With an adequate control of the polarization states in the cavity, the Stokes pulses contain
67% of the total energy and reach a bandwidth of 84 nm in the U-band.
Fiber optical parametric oscillators are laser sources with multiple longitudinal modes arising from their cavity
length reaching several tens of meters. To reduce the noise due to multimode beating, the spacing between
neighboring modes is increased using a Smith predictor internal control scheme. The Smith predictor utilizes
a model of the dynamic behaviour of the system to deal with pure time delay and eliminate the effect of the
delay in the overall closed-loop system. Applying the smith predictor, the system can be made to operate in a
single-longitudinal mode, removing the excess modes. In this paper a linear model for operation of parametric
oscillator is proposed and based on that transfer function of Smith predictor enhanced parametric oscillator
is established. Numerical analysis of resulting transfer function will lead us toward single-longitudinal mode
operation.
We have modeled the soliton propagation in an As2Se3 microwire coated with PolyMethyl MethAcrylate (PMMA) with
the purpose of optimizing the soliton self-frequency shift (SSFS). We provide the optimal waist diameter and initial
soliton energy required to maximize the wavelength shifting from a wavelength of 2.29 um through a 20 cm long
microwire. In light of the dynamics of a fundamental soliton, we provide the optimal uniform and nonuniform
microwires that maximizes the soliton frequency-shift. Finally, we propose an approach to avoid the dispersive waves
emission by which the soliton energy density maintain at the output of the system.
We report the fabrication and optical characterization of the first hybrid chalcogenide-polymer microtapers. With this
material combination, the chalcogenide wire induces a large Kerr effect whereas the polymer coating provides sufficient
mechanical robustness and flexibility to the assembly for normal handling as well as limiting the evanescent interaction
with the environment. A few centimeters of such a nonlinear microtaper can replace kilometers of highly nonlinear silica
fiber. Becoming a building block in itself, the hybrid microtaper can also be used to assemble new highly nonlinear
components such as nonlinear couplers.
Hybrid chalcogenide/polysulfone structures are proposed for the implementation of microtapers and nonlinear
couplers. In addition to high mechanical robustness, hybrid microtapers provide design advantages that enable the
implementation of nonlinear couplers with low switching threshold powers.
We experimentally demonstrate the operation of a laser based on self-phase modulation followed by offset spectral
filtering. This laser has three operation modes: a continuous-wave mode, a self-pulsating mode where the laser self
ignites and produces pulses, and a pulse-buffering mode where no new pulse is formed from spontaneous emission noise
but only pulses already propagating or pulses injected in the laser cavity can be sustained. In the self-pulsating and
pulse-buffering modes, the laser is multi-wavelength and continuously tunable over the entire gain band of the
amplifiers. The output pulse width is quasi transform-limited with respect to the spectral-width of the filters used in the
cavity. Overall, this device provides a simple alternative to pulsed laser source and also represents a promising approach
for signal buffering.
Chalcogenide glass based optical waveguides offer many attractive properties in all-optical signal processing because of the large Kerr nonlinearity (up to 420 × silica glass), the associated intrinsic response time of less than 100 fs and low two-photon absorption. These properties together with the convenience of a fiber format allow us to achieve all-optical signal processing at low peak power and in a very compact form. In this talk, a number of non-linear processing tasks will be demonstrated including all-optical regeneration, wavelength conversion and femtosecond pedestal-free pulse compression. In all-optical regeneration, we generate a near step-like power transfer function using only 2.8 m of fiber. Wavelength conversion is demonstrated over a range of 10 nm using 1 m of fiber with 7 ps pulses, peak power of 2.1 W, and 1.4 dB additional penalty. Finally, we will show efficient compression of low-power 6 ps pulses to 420 fs around 1550 nm in a compact all-fiber scheme.
These applications show chalcogenide glass fibers are very promising candidate materials for nonlinear all-optic signal processing.
We report integrated devices in chalcogenide glass for all-optical signal processing, based on pure Kerr (near instantaneous) optical nonlinearities. We demonstrate an integrated 2R optical regenerator operating through a combination of nonlinear self-phase modulation followed by spectral filtering, with a potential to reach bit rates in excess of 1Tb/s. It consists of a low loss As2S3 chalcogenide rib waveguide incorporating a high quality Bragg grating written by an ultra-stable Sagnac interferometer. We achieve a nonlinear power transfer curve using 1.4ps pulses, sufficient for suppressing noise in an amplified link. In addition, we report photonic crystal structures fabricated by focused ion beam (FIB) milling in AMTIR-1 (Ge33As12Se55) chalcogenide glass. We realize high quality free-standing photonic crystal membranes, and observe optical "Fano" resonances in the transmission spectra at normal incidence. We achieve good agreement with theoretical results based on 3D finite difference time-domain calculations. Finally, we achieve resonant evanescent coupling to photonic crystal waveguides via tapered microstructured optical fibre (MOF) nanowires.
In this paper, we show that Bragg gratings can greatly contribute to enhance the performances of today's optical amplifiers.
some of the applications of Bragg gratings in optical amplifiers such as gain equalization, gain stabilization and dispersion
compensation will thus be reviewed.
Gain equalization of an amplifier is performed by introducing spectrally designed Bragg gratings in the
mid-stage of a dual-stage erbium-doped fiber amplifier. The long-haul performances of the amplifier are
evaluated using a 50 km recirculating loop. The results show a clear improvement of the transmission
quality when equalizing the gain.
Gain equalization of an EDFA is performed by introducing spectrally designed all-fiber filters in the mid-stage of a dual-stage fiber amplifier. Two types of filters are studied: a cascade of narrow-band Bragg gratings for discrete equalization of a finite number of channels and a wide-band Bragg grating performing equalization over the whole 1539 nm to 1557 nm range. In future work, it is planned to use the discrete Bragg grating configuration to simultaneously perform Dispersion compensation (D), Equalization (E) and Stabilization of gain (S) and Channel dropping (C) in a dual-stage EDFA. Integration of these functions will result in a high performance amplifier called the DESC-EDFA.
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