Catherine Baskiotis

Mid-infrared ZBLAN fiber supercontinuum source using picosecond diode-pumping at 2 µm

We present the first demonstration of mid-IR supercontinuum generation directly pumped with picosecond pulses from a Thulium fiber-amplified gain-switched laser diode at 2 µm. We achieve more than two octaves of bandwidth from 750 - 4000 nm in step-index ZBLAN fiber with Watt-level average power and spectral flatness of less than 1.5 dB over a 1300 nm range in the mid-IR from 2450 - 3750 nm. The system offers high stability, power-scaling capability to the 10 W regime, and demonstrates an attractive route towards relatively inexpensive, versatile and practical sources of high power broadband mid-IR radiation.

Mode area scaling with multi-trench rod-type fibers

We propose a novel all-solid rod-type fiber structure that presents a cylindrical symmetry and low refractive-index contrasts. Effectively single-mode propagation for the fundamental mode is ensured thanks to resonant couplings between Higher Order Modes (HOMs) and cladding modes. Numerical simulations demonstrate the possibility of achieving a fundamental mode effective area as large as 5000 µm² at a wavelength of 1.06 μm in fibers ensuring a high leakage loss ratio (>100) between the HOMs and the fundamental mode while keeping the fundamental mode leakage losses at a level lower than 0.2dB/m. Further scaling to an effective area of 12,200 µm2 at 1.06 μm in an effectively single-mode fiber is also presented by exploiting the power delocalization of several HOMs on top of the high-leakage loss filtering.

Accurate modal gain control in a multimode erbium doped fiber amplifier incorporating ring doping and a simple LP_01 pump configuration

We experimentally validate a numerical model to study multimode erbium-doped fiber amplifiers (MM-EDFAs). Using this model, we demonstrate the improved performance achievable in a step index MM-EDFA incorporating a localized erbium doped ring and its potential for Space Division Multiplexed (SDM) transmission. Using a pure LP₀₁ pump beam, which greatly simplifies amplifier construction, accurate modal gain control can be achieved by carefully tuning the thickness of the ring-doped layer in the active fiber and the pump power. In particular, by optimizing the erbium-ring-doped structure and the length of active fiber used, over 20dB gain for both LP₀₁ and LP₁₁ signals with a maximum gain difference of around 2 dB across the C band are predicted for a pure LP₀₁ pump beam delivering 250 mW power at 980 nm.

Large Mode Area Multi-Trench Fiber With Delocalization of Higher Order Modes

Multi-trench fiber (MTF) is a novel large mode area fiber design for high power fiber laser applications. This fiber design allows very high suppression of the higher order modes by offering high losses and delocalizing them out of the core. MTFs allow the core refractive index to be higher than the surrounding cladding as compared to other structures such as photonic crystal fibers, photonic bandgap fibers, and Bragg fibers. This feature of MTFs dramatically reduces the complexity associated with doped fiber fabrication. The MTF design is an all-solid structure with cylindrical symmetry, which provides easy cleaving and splicing with other fibers. In this paper, we present the first experimental demonstration of the MTF. S2 measurements indicate single mode operation with very high suppression of the higher order modes.

Bending performance of large mode area multi-trench fibers.

Bending performance of the Multi-trench Fibers (MTFs) has been investigated using the Finite Element Method. Numerical investigations show that MTFs can provide low-loss effective single mode operation under bent configuration, thanks to the resonant coupling of the Higher order Modes (HOMs). Large ratio between the HOMs and the Fundamental Mode (FM) losses can be ensured, although the ratio drops with increasing Effective Area (A(eff)) of the FM. MTFs provide better losses ratio between the HOMs and the FM in comparison with other fibers like step-index, W-type, and parabolic fibers.

Minimizing differential modal gain in cladding-pumped EDFAs supporting four and six mode groups

We employ a Genetic Algorithm for the purpose of minimization of the maximum differential modal gain (DMG) over all the supported signal modes (at the same wavelength) of cladding-pumped four-mode and six-mode-group EDFAs. The optimal EDFA designs found through the algorithm provide less than 1 dB DMG across the C-band (1530-1565 nm) whilst achieving more than 20 dB gain per mode. We then analyze the sensitivity of the DMG to small variations from the optimal value of the erbium doping concentration and the structural parameters, and estimate the fabrication tolerance for reliable amplifier performance.

First demonstration of single trench fiber for delocalization of higher order modes

We demonstrate an ytterbium-doped single-trench fiber ensuring a high losses ratio (~1000) and low power fraction (~0.7) between the higher-order-modes and fundamental-mode with excellent bend robustness and 85% laser efficiency at a wavelength of 1040nm.

Large mode area hybrid multi-trench fiber for spectral filtering

We present a multi-trench-fiber, in which high-index-rods are included along one of its axis. Numerical simulation shows excellent filtering of higher-order-modes (>10dB/m) at 1060nm and Stimulated-Raman-Scattering (>60dB/m) at 1116nm for Aeff (>520µm2) with good bend-robustness.

SiN-assisted flip-chip adiabatic coupler between SiPh and Glass OPCBs

We demonstrate, for the first time to our knowledge, a SiN-assisted in-plane adiabatic coupler between SiPh and onboard glass waveguides. Our numerical study is founded on an actual graded index glass waveguide developed by Fraunhofer-IZM. The Silicon taper profile and the optimal length are extracted employing the supermode theory and the adiabatic theorem. Fabrication and assembly issues are investigated, resulting to an optimized coupler design that exhibits a theoretical Si-to-glass loss below 0.1dB over the entire C-band. The proposed solution can be realized utilizing standard passive flip-chip assembly equipment and is, therefore, cost-effective, easy to be fabricated, and well-suited for compact packaging.

LMA effectively single-mode thulium doped fibre with normal dispersion at wavelengths around 2um

During the last few years, an increasing interest in Large Mode Area fibre operating around a wavelength of 2μm for high-power fibre laser applications has been observed. For most pulsed laser applications, it is desirable to operate the fibre in the normal dispersion regime to avoid the limiting effects of modulational instability (MI)/soliton formation [1]. However, it is very difficult to achieve normal dispersion in conventional step-index large mode area fibres operating around a wavelength of 2μm due to the fact that the dispersion of their fundamental mode is mainly dominated by the material dispersion of silica, which is anomalous and very high around this wavelength (e.g.: ~44ps/(nm.km) at 1930nm, cf. Fig. 1.(b)).