No abstract

Efficient second harmonic generation in integrated platforms is usually achieved by resonant structures, intermodal phase-matching or quasi-phase matching by periodically poling ferroelectric waveguides. However, in all these structures, it is impossible to reconfigure the phase-matching condition in an all-optical way. Here, we demonstrate that a Watt-level laser causes a periodic modification of the second-order susceptibility in a silicon nitride waveguide, allowing for quasi-phase-matching between the pump and second harmonic modes for arbitrary wavelengths inside the erbium band. The grating is long-term inscribed, and leads to a second harmonic generation enhancement of more than 30 dB. We estimate a χ (2) on the order of 0.3 pm/V, with a maximum conversion efficiency of 0.05% W−1. We explain the observed phenomenon with the coherent photogalvanic effect model, which correctly agrees with the retrieved experimental parameters.

We experimentally demonstrate wavelength conversion in the 2 µm region by four-wave mixing in an AsSe and a GeAsSe chalcogenide photonic crystal fibers. A maximum conversion efficiency of −25.4 dB is measured for 112 mW of coupled continuous wave pump in a 27 cm long fiber. We estimate the dispersion parameters and the nonlinear refractive indexes of the chalcogenide PCFs, establishing a good agreement with the values expected from simulations. The different fiber geometries and glass compositions are compared in terms of performance, showing that GeAsSe is a more suited candidate for nonlinear optics at 2 µm. Building from the fitted parameters we then propose a new tapered GeAsSe PCF geometry to tailor the waveguide dispersion and lower the zero dispersion wavelength (ZDW) closer to the 2 µm pump wavelength. Numerical simulations shows that the new design allows both an increased conversion efficiency and bandwidth, and the generation of idler waves further in the mid-IR regions, by tuning the pump wavelength in the vicinity of the fiber ZDW.

Abstract:We report the design of an all-fiber continuous wave Short-Wave Infrared source capable to output up to 700 mW of power at 1940 nm. The source is tunable over wavelength intervals comprised between 1850 nm and 2070 nm depending on its configuration. The output can be single or multimode while the optical signal to noise ratio ranges from 25 and 40 dB. The architecture is based on the integrated association of a fiber optical parametric amplifier and a Thulium doped fiber amplifier.

A nonlinear coefficient of 3.6-4.1 W −1 km −1 and group velocity dispersion of −20 ps 2 ∕km of a commercial corepumped thulium-doped fiber have been evaluated using degenerate four-wave mixing at 2 μm. The anomalous dispersion behavior of the fiber has been confirmed by linear measurements with an all-fiber Mach-Zehnder interferometer (MZI). Additionally, no pump-induced dispersion changes due to excitation of Tm 3 cations have been detected. These characteristics make these fibers attractive for pulsed fiber laser applications. A nonlinearpolarization rotation mode-locked laser involving nonlinear polarization evolution directly in the doped fiber is demonstrated. Thulium-doped fiber (TDF) lasers operating in the 2 μm spectral range have recently attracted significant interest for various applications, covering spectroscopy and atmospheric CO 2 monitoring, material and biological tissues processing, and telecommunications [1][2][3][4][5]. TDFs and a whole range of fiber optics components designed to operate around 2 μm have emerged during the past years and are now widely available, simplifying the implementation of lasers and amplifiers.Thulium-doped fibers can be purchased off the shelf, but some of their characteristics, namely, dispersion and nonlinearity, are rarely studied despite their impact on many applications. 2 μm pulsed lasers have undergone tremendous advances over the past few years, with continuous performance improvements in terms of pulse duration and peak and average powers [4]. Dispersion management of the fiber cavity enables the generation of soliton or similariton (parabolic) pulses [6] when a saturable absorber is included. Solid-state saturable absorbers (SESAMs [6], graphene [7]), or Kerr-nonlinear switching elements (nonlinear optical/amplifying loop mirrors [8]), or combinations of both of them [9], were used to modulate cavity losses. Particularly, nonlinear polarization rotation (NPR) is a straightforward and easy-to-implement effect to lock the cavity [10]. In any case, the dispersion and nonlinearity of the various fibers used in the cavity have a direct impact on the performance of the laser. Even though the realization of powerful lasers (over a few watts) requires the use of doubleclad fibers for pump coupling matters, the 2 μm mode propagates mostly in the core, the diameter of which can be compared to that of an SMF-28 (e.g., 10 μm for Nufern SM-TDF-10P/130-HE). It can therefore experience significant nonlinear effects due to the high field intensity in the doped fiber over a cavity round trip. TDF amplifiers have also become an active topic of research in the telecommunication field since the demonstration of long haul transmission at 2 μm in hollowcore fibers [5]. Due to the impressive bandwidth of such amplifiers (roughly from 1.8 to 2.1 μm [11]), this spectral band is seen as a potential solution to overcome the capacity limit of fiber networks. It is therefore crucial to study the nonlinear and dispersive properties of single core TDF, such as the standard TmDF200 by OF...