The nonlinear response of amorphous silicon waveguides is reported and compared to silicon-on-insulator (SOI) samples. The real part of the nonlinear coefficient γ is measured by four-wave-mixing and the imaginary part of γ is characterized by measuring the nonlinear loss at different peak powers. The combination of both results yields a two-photon-absorption figure of merit of 4.9, which is more than 7 times higher than for the SOI samples. Time-resolved measurements and simulations confirm the measured nonlinear coefficient γ and show the absence of slow free-carrier effects versus ns free-carrier lifetimes in the SOI samples.

Abstract:We present an experimental technique to characterize backscattering in silicon microring resonators, together with a simple analytical model that reproduces the experimental results. The model can extract all the key parameters of an add-drop-type resonator, which are the loss, both coupling coefficients and backscattering. We show that the backscattering effect strongly affects the resonance shape, and that consecutive resonances of the same ring can have very different backscattering parameters.

Abstract:We present the characterization of the ultrafast nonlinear dynamics of a CMOS-compatible horizontal-slot waveguide with silicon nanocrystals. Results are compared to strip silicon waveguides, and modeled with nonlinear split-step calculations. The extracted parameters show that the slot waveguide has weaker carrier effects and better nonlinear figure-of-merit than the strip waveguides.

Single-wall carbon nanotube deposition on the cladding of optical fibers has been carried out to fabricate an all-fiber nonlinear device. Two different nanotube deposition techniques were studied. The first consisted of repeatedly immersing the optical fiber into a nanotube supension, increasing the thickness of the coating in each step. The second deposition involved wrapping a thin film of nanotubes around the optical fiber. For both cases, interaction of transmitted light through the fiber core with the external coating was assisted by the cladding mode resonances of a tilted fiber Bragg grating. Ultrafast nonlinear effects of the nanotube-coated fiber were measured by means of a pump-probe pulses experiment. © 2011 OCIS codes: 060.3735, 060.4370, 160.4236.Single-wall carbon nanotubes (SWNTs) have found innovative applications in the optical field due to their nonlinear properties in the near IR. Depending on the chirality of SWNTs, they can be either metallic or semiconducting, the latter being the desired behavior for nonlinear optical performance. Many optical applications could benefit from using SWNTs as nonlinear materials, such as noise suppression, wavelength conversion, and passive mode-locking [1][2][3]. A challenge when designing SWNT-based devices is incorporating the nanotubes in such a way as to enhance their interaction with light. One common method involves dispersing SWNTs in a solvent and spraying the solvent onto substrates in order to produce a nanotube film in the middle of a light beam [3]. Some inherent drawbacks in these configurations are the need for alignment and focusing stages, low SWNT burn thresholds, and low nonlinear interaction length. Solutions that overcome these challenges are based on SWNT deposition onto optical fibers. Tapered, D-shaped, and hollow optical fibers have been proposed to take advantage of the evanescent field interaction with SWNTs, distributing that interaction along the fiber length [4-6]. Nevertheless, manufacturing and handling these kinds of fibers is quite complex and delicate. In this work we propose for the first time SWNT deposition on standard optical fiber cladding for nonlinear applications. Interaction of light propagating through the fiber core with the outer SWNT coating is achieved via cladding mode resonances in a tilted fiber Bragg grating (TFBG). Two nanotube deposition methods have been carried out: dip-coating of the optical fiber in a SWNT suspension and wrapping of a SWNT film around the optical fiber. A TFBG is a kind of grating in which the index modulation planes are not orthogonal to the fiber axis but form a particular tilt angle. This inclination enhances the coupling of light from core mode to counterpropagating cladding mode resonances. Consequently, the grating transmission response is a multinotch response consisting of numerous cladding mode resonances in addition to the core mode resonance [see Fig. 1(a)]. The transverse mode profile of cladding modes spreads to the cladding of the fiber and interacts with the outer mediu...

An accurate technique to characterize chromatic dispersion and its slope versus wavelength is reported. The method is based on a heterodyne Mach-Zehnder interferometer, which is immune to thermal phase noise by using a counterpropagating reference beam. Chromatic dispersion profiles are obtained over a broad wavelength region even in short waveguides with considerable loss. Conventional strip silicon waveguides as well as slotted geometries are considered. Theoretical simulations are also presented for comparison, which show good agreement with the experimental results.