Plane waves in periodic, quadratically nonlinear slab waveguides: stability and exact Fourier structure

We consider the propagation of broad optical beams through slab waveguides with a purely quadratic nonlinearity and containing linear and nonlinear long-period quasi-phase-matching gratings. An exact Floquet analysis on the periodic, plane-wave solution shows that the periodicity can drastically alter the growth rate of the modulational instability but that it never completely removes the instability. The results are confirmed by direct numerical simulation, as well as through a simpler, approximate theory for the averaged fields that accurately predicts the low-frequency part of the spectrum.Comment: 10 Pages, 13 figures (some in two parts) new version has some typos removed and extra references and explanation adde

Two-Particle Parasitic Effects in Rare-Earth Doped Waveguides

This paper discusses Er-doped optical waveguides implemented in glass materials. The emphasis is put on physical limitations posed by concentration dependent nonlinear effects and on methods for their characterization. Examples of recently demonstrated, best performance integrated active devices are also given

Alternating cascade of spectrally different erbium-doped fiber amplifiers for link-loss-insensitive long-haul WDM transmission

This paper numerically investigates a cascade of erbium-doped fiber amplifiers (EDFA's) with different spectral characteristics in an alternating scheme. Thereby, in a transmission band with appropriate spectral properties (1544-1550 nm), the sensitivity of optically amplified long-haul WDM transmission links on the span loss between amplifiers can be reduced to that of single-channel systems. This may be as much as an order of magnitude better than in a traditional, nonalternating, WDM cascade. While passive bandpass filters are necessary to control the wavelength range, there is no need for any active gain equalization or feed-back control. The gain in the cascade can also to some extent automatically adjust to compensate for a spectral tilt of the loss, We show that the range of this automatic loss tilt compensation can be increased, up to three times its original value, by enhancing the difference of the net gain that signals at different wavelengths experience in EDFA's of different types

Steady-State and Switch-Off Behavior of Upconversion in Er-Doped Fibers

By measuring the metastable and the upconverted fluorescence in Er-doped fibers we determine rate of homogeneous upconversion as a function of the population inversion. The results confirm the prediction of our statistical model that at the same population inversion the upconversion rates under the steady-state and the switch-off conditions are different. The larger rate of the steady state upconversion is attributed to the pump enhanced redistribution of the excitation energy

Analysis of gain improvements through a pump reflector in Er³⁺-doped optical amplifiers in the presence of concentration quenching

We numerically examine the small-signal gain improvements possible when the pump light is reflected in erbium-doped amplifiers suffering from concentration quenching caused by homogeneous and inhomogeneous energy-transfer upconversion. For an unquenched amplifier, the improvement is larger for a pump power of 20 mW than it is at 100 mW. On the other hand, at a pump power of 100 mW, the reflector is found to be efficient for a quenched amplifier, with a maximum improvement of 6.5 dB. We also find that the reflector is more efficient at 1.535 μm than it Is at 1.550 μm, under all examined operating conditions

Analysis and design of a tunable wavelength-selective add-drop in liquid crystals on Silicon

We propose an optical disk microresonator embedded in liquid crystals and providing tunability via an external electric field bias. All the loss mechanisms in the tunable add-drop are taken into account via a 3D+time parallellized FDTD code

Widely tunable directional coupler filters with 1D photonic crystal

International audienceWe present two concept examples for adding a wide range tunability to Si/SiO/sub 2/ devices involving a photonic crystal element. They are based on a directional coupler filter of two different geometries, where one of the arms is a Bragg reflection waveguide (BRW) used for the bandwidth improvement. The tuning relies on changing the properties of the BRW core. As an illustration we consider the smectic A* liquid crystal as the core material and show that ca 100 nm tuning range is achievable by the core index variations of 0.006 under applying electric field of 5 V/μm