Jochen Schröder

Optical control of arrays of photorefractive screening solitons

We discuss the creation of an array of 9 x 9 photorefractive spatial screening solitons in a strontium barium niobate crystal. We investigate the waveguide properties of each channel with a beam of different wavelength and find that the waveguides guide the probe beam independently. A supplementary beam is used to influence the paths of the array solitons and to effectively combine two channels by use of mutual attraction of solitons. To our knowledge this is the first all-optical control of an array of photorefractive solitons. Furthermore, we show that in principle image procession is possible with parallel propagation of photorefractive solitons.

Dynamic instability of self-induced bidirectional waveguides in photorefractive media

We report on the experimental observation of a dynamic instability in the interaction of counterpropagating self-trapped beams in a photorefractive strontium barium niobate crystal. While the interaction of copropagating spatial optical solitons exhibits only transient dynamics, resulting in a final steady state, the counterpropagating geometry supports a dynamic instability mediated by intrinsic feedback. Experimental observations are compared with and found to be in qualitative agreement with numerical simulations.

Counterpropagating dipole-mode vector soliton.

We experimentally observed a counterpropagating dipole-mode vector soliton in a photorefractive SBN:60Ce crystal. We investigated the transient formation dynamics and show that the formation process differs significantly from the copropagating geometry. The experimental results are compared with fully anisotropic numerical simulations and show good qualitative agreement.

Complete spatiotemporal characterization and optical transfer matrix inversion of a 420 mode fiber

The ability to measure a scattering mediums optical transfer matrix, the mapping between any spatial input and output, has enabled applications such as imaging to be performed through media which would otherwise be opaque due to scattering. However, the scattering of light occurs not just in space, but also in time. We complete the characterization of scatter by extending optical transfer matrix methods into the time domain, allowing any spatiotemporal input state at one end to be mapped directly to its corresponding spatiotemporal output state. We have measured the optical transfer function of a multimode fiber in its entirety; it consists of 420 modes in/out at 32768 wavelengths, the most detailed complete characterization of multimode waveguide light propagation to date, to the best of our knowledge. We then demonstrate the ability to generate any spatial/polarization state at the output of the fiber at any wavelength, as well as predict the temporal response of any spatial/polarization input state.

Interactions in large arrays of solitons in photorefractive crystals

Large two-dimensional spatial soliton arrays are generated experimentally and numerically in photorefractive media and their waveguiding properties at red and infrared wavelengths are demonstrated. An enhanced stability of solitonic lattices is achieved by exploiting the anisotropy of coherent soliton interaction and by controlling the relative phase between soliton rows. Manipulation of individual solitonic channels is accomplished by the use of separate control beams.

Breaking the Tbit/s Barrier: Higher Bandwidth Optical Processing

The growing demand for broadband communications has inspired many approaches to increasing capacity. Our recent work shows that combining linear and nonlinear optical signal processing can overcome some of the challenges faced by high-symbol rate signals.

Dynamic instability of counterpropagating self-trapped beams in photorefractive media

We present an experimental and numerical investigation of the interaction of bidirectional self-guided beams in photorefractive media. Distinct from copropagating beams, the feedback intrinsic to the counterpropagating geometry renders such configurations unstable beyond a control parameter threshold. The instability is mediated through attractive interaction between the induced waveguides and leads to dynamic states, showing telltale signs of chaotic behaviour. We demonstrate qualitative correspondance between experiment and a saturable Kerr model, investigate the dynamical bifurcation in detail and expand on the consequences of a realistic photorefractive model including nonlocality, anisotropy and self bending.

Eisenbud-Wigner-Smith states and spatial eigenstates in multimode optical fibre

Spatial eigenstates are a familiar part of optical waveguide theory. Such states enter and exit the waveguide as the same spatial state. As illustrated in Fig. 1. In the idealised case, a perfect waveguide, free of mode coupling, perturbations and ignoring chromatic dispersion, these spatial eigenstates also propagate with a single group-delay. However in reality, light propagation in multimode optical fibre is more complicated. Perturbations and mode coupling are such that as the length of propagation increases, it is increasingly unlikely that light can travel from one end of the waveguide to the other, maintaining its spatial state along the entire length of propagation. In this case, a change in wavelength, or fibre length will result in a different set of spatial eigenstates, as illustrated in Fig. 1. The spatial eigenstates become a coincidence of fibre length and wavelength, rather than modes with well-defined propagation constant and group-delay as for the ideal waveguide case. Eisenbud-Wigner-Smith (EWS) states, also known as principal modes [1]-[7], are the eigenstates of the group-delay operator and hence propagate through the fibre associated with a single group delay, and are wavelength independent. However unlike spatial eigenstates, EWS states do not in general have the same spatial state at input and output, as illustrated in Fig. 1. EWS states were first proposed decades ago [1], [6], but were only recently observed experimentally[2]. These states are of significance for their ability to propagate through a scattering medium, yet arrive free of first-order mode dispersion. EWS states are the basis with the least wavelength dependence, and hence also the states with the highest spatial coherence for a given spectral bandwidth at the source. EWS states also identify the maximum and minimum possible propagation delay through the waveguide.

10.3 bits/s/Hz Spectral Efficiency 54×24 Gbaud PM-128QAM Comb-Based Superchannel Transmission Using Single Pilot

We demonstrate transmission of a 14.2 Tbit/s comb-based superchannel using a single shared optical pilot tone. The pilot tone allows for locking the central line between the transmitter and receiver combs, enabling blind carrier recovery and a spectral efficiency of 10.3 bits/s/Hz.

Polarization independent optical injection locking for carrier recovery in optical communication systems

An optical injection locking (IL) system that is independent of the incoming signals polarization is demonstrated for carrier recovery in coherent optical communication systems. A sub-system that enables polarization independence is discussed and experimentally verified. The system is tested over a 20-km test field link using a broad-linewidth laser (40 MHz), and shows the suppression of phase noise when using the carrier recovered by injection locking as the local oscillator.