Abstract

We have previously observed bands, and even a grid, of dark solitons in the cross-section of a laser beam propagating through a self-defocusing material when a diffracting screen was placed at the entrance face of the nonlinear medium. The creation of spatial solitons is attributed to the coupling of diffracted radiation into a self-guiding nonlinear channel. Information encoded as spatial solitons may therefore be transferred in parallel over long distances without the need for large (or any) collection optics. A diffracting screen is a building block of spatial soliton devices. We have found the soliton eigenvalues (each corresponding to the normalized angle and depth of a soliton) for a generalized screen composed of units with two closely spaced opaque regions of width x_A separated by a region of width x_B and arbitrary phase ΦB. If the value of x_B is large, fundamental dark solitons can form when Φ_B = π. On the other hand, when x_B is small, diffractive coupling of radiation from the opaque regions splits the degeneracy of the eigenvalues, much like level-splitting in coupled quantum wells. When a pure phase grating exists (x_A = 0), a single pair of solitons is formed. Numerous applications of spatial dark solitons can be envisioned, including optical interconnecting, limiting, and computing operations.

© 1990 Optical Society of America