Adiabatically tapered microstructured mode converter for selective excitation of the fundamental mode in a few mode fiber.

We propose a new technique to selectively excite the fundamental mode in a few mode fiber (FMF). This method of excitation is made from a single mode fiber (SMF) which is inserted facing the FMF into an air-silica microstructured cane before the assembly is adiabatically tapered. We study theoretically and numerically this method by calculating the effective indices of the propagated modes, their amplitudes along the taper and the adiabaticity criteria, showing the ability to achieve an excellent selective excitation of the fundamental mode in the FMF with negligible loss. We experimentally demonstrate that the proposed solution provides a successful mode conversion and allows an almost excellent fundamental mode excitation in the FMF (representing 99.8% of the total power).

Bragg-scattering conversion at telecom wavelengths towards the photon counting regime.

We experimentally study Bragg-scattering four-wave mixing in a highly nonlinear fiber at telecom wavelengths using photon counters. We explore the polarization dependence of this process with a continuous wave signal in the macroscopic and attenuated regime, with a wavelength shift of 23 nm. Our measurements of mean photon numbers per second under various pump polarization configurations agree well with the theoretical and numerical predictions based on classical models. We discuss the impact of noise under these different polarization configurations.

Numerical analysis of directional coupling in dual-core microstructured optical fibers.

In this paper, we present a numerical analysis of the coupling coefficients in dual-core air-silica microstructured optical fibers with pi/6 symmetry. The calculations are based on an especially fitted application of the coupled mode theory for microstructured optical fibers. This method is compared with three other techniques, the supermode method, the beam propagation method and the equivalent fiber model, and is shown to be very computationally efficient. Our studies enable us to derive a formula linking the coupling coefficients to core separation according to the wavelength, the pitch and the hole diameter of the fiber structure.

Demonstration of a true single-shot 100 GHz-bandwidth optical oscilloscope at 1053-1064 nm.

We demonstrate an innovating design to validate and to optimize the real-time performance of an all-optical oscilloscope at 1053-1064 nm. A unique broadband pulse is generated by means of frequency beats and of proper optical-shaping, which helps us to evidence a signal bandwidth of 100 GHz and a dynamics range in excess of 25 dB. Gain-narrowing and dispersion effects due to the replication of the input pulse are shown to be the first limitations in the broadband capabilities.