P. Tchofo Dinda

Impact of fourth-order dispersion in the modulational instability spectra of wave propagation in glass fibers with saturable nonlinearity

We analyze the modulational instability (MI) of light waves in glass fibers with a local saturable nonlinear refractive index. We identify and discuss the salient features of the effect of the fourth order of the fiber dispersion, in the MI spectra. Particularly, we find that in fibers with negative sign of the second-order dispersion and positive sign of the fourth-order dispersion (FOD), the two existing types of MI processes, called processes of type I, which generate a single pair of sidebands, and processes of type II, which lead to two pairs of sidebands, become highly sensitive to the magnitude of the FOD, both quantitatively and qualitatively. We demonstrate the existence of a critical FOD and two branches of critical pump powers, from which we construct the global map of the MI behaviors in the system, including clear delimitations of the respective domains of the existence of MI processes of types I and II.

Polarization switching and suppression of stimulated Raman scattering in birefringent optical fibers

We analyze stimulated Raman scattering in normally dispersive highly birefringent fibers under dual-frequency, orthogonal polarization pumping. Experiments show that stimulated Raman scattering can be suppressed in anyone of the fiber axes by two distinct processes prevailing at large and small group-velocity mismatches (GVM’s), respectively, between the pumps. For a relatively large GVM, parametric four-wave mixing is the dominant process for the suppression of Raman–Stokes radiation. On the other hand, for a small GVM, the Raman–Stokes light is suppressed along the polarization direction of the highest-frequency pump, through a mechanism associated with the orthogonal component of the Raman gain. The sign of the GVM between the pumps allows for selecting the particular fiber axis where suppression of the Raman–Stokes radiation is desired. This selection is achieved by simply tuning the frequency spacing between the pumps.

A collective variable approach for dispersion-managed solitons

We present a method to express the generalized nonlinear Schr¨ odinger equation, for pulse propagation in dispersion managed fibre-optic links, in terms of pulse parameters, called collective variables (CVs), such as pulse width, amplitude, chirp and frequency. The CV equations of motion are derived by imposing a set of constraints on the CVs, to minimize the soliton dressing during propagation.

Observation of modulational instability induced by velocity-matched cross-phase modulation in a normally dispersive bimodal fiber

We demonstrate experimentally the existence of cross-phase-modulation-induced modulational instability in the absence of group-velocity mismatch between the interacting nonlinear dispersive waves. The experiment is performed by means of a normally dispersive isotropic bimodal fiber. The group-velocity mismatch between the fundamental and the first-order modes that constitute the two interacting waves is controlled by wavelength tuning. A strong power dependence of the modulational instability spectra is observed near the condition of group-velocity matching.

Analytical method for designing dispersion-managed fiber systems.

Using the equations of motion of pulse width and chirp, we present an analytical method for designing dispersion-managed (DM) fiber systems without optical losses. We show that the initial Gaussian pulse considered for the analytical design of periodically amplified DM fiber systems with losses will propagate as a proximity fixed point. Then averaging the DM soliton fields obtained from the slow dynamics of the proximity fixed point will yield the exact fixed point.

Modulational instability in fiber systems with periodic loss compensation and dispersion management

In this paper we study modulational instability in a Kerr fiber taking into account the combined effects of periodic power variations and dispersion management. It is shown that periodic dispersion management and periodic amplification produce nonconventional MI sidebands which are essentially independent of each other. In addition, we show that the amplifier spontaneous emission noise tends to inhibit the growth of sidebands, for a sufficiently long propagation distance.

Suppression of soliton self-frequency shift by upshifted filtering

We consider the effects of stimulated Raman scattering on ultrashort light pulses propagating in long-haul fiber transmission lines. We propose an efficient method for suppressing the soliton self-frequency shift by use of upshifted filters without any compromise in signal-to-noise ratio and with the pulse stability preserved.

Analytical design of densely dispersion-managed optical fiber transmission systems with Gaussian and raised cosine return-to-zero Ansatze

We propose an easy and efficient way to analytically design densely dispersion-managed fiber systems for ultrafast optical communications. This analytical design is based on the exact solution of the variational equations derived from the nonlinear Schrodinger equation by use of either a Gaussian or a raised-cosine (RC) Ansatz. For the input pulses of dispersion-managed optical fiber transmission systems we consider a RC profile and show that RC return-to-zero pulses are as effective as Gaussian pulses in high-speed (160-Gbits/s) long-distance transmissions.

Experimental demonstration of 160-GHz densely dispersion-managed soliton transmission in a single channel over 896 km of commercial fibers

We experimentally demonstrate the first 160-GHz densely dispersion-managed soliton transmission in a single channel at 1550 nm over nearly 900 km using commercially available non-zero dispersionshifted fibers. This performance has been achieved by using a 16 km-long recirculating loop configuration and an appropriate design of the dispersion map.

Impact of the material absorption on the modulational instability spectra of wave propagation in high-index glass fibers

We examine the behavior of modulational instability (MI) in several classes of high-index glass fibers that are being developed to obtain very high nonlinearities and soften the conditions of generation of highly efficient light sources, namely, telecommunication fibers, air-silica microstructured fibers, tapered fibers, and nonsilica glass fibers. We perform a comparative assessment of their respective performances in MI processes on the basis of three major performance criteria: the level of the input pump power, the fiber length, and the magnitude of the frequency drifts. Indeed, we show that the effectiveness of MI processes in such fibers is not merely influenced by the strength of the nonlinearity, but is also strongly determined by the linear attenuation of waves in the fiber material. In those high-index glass fibers, this attenuation acts as a strong perturbation, causing a frequency drift of the MI sidebands. However, we show that this frequency drift can be totally suppressed by means of a technique based on the concept of a photon reservoir, which feeds in situ the process of MI by continually supplying it the amount of photons absorbed by the fiber.