Abstract

Considerable effort has been devoted to the development of all-optical switches in the last several years,¹ with a view to using these switches in ultrafast telecommunications. In spite of having a very low nonlinear refractive index coefficient (n₂ = 3 × 10⁻²⁰ m²/W), fused silica fibre is probably the best material medium for such switches owing to its extremely low loss (~0.2 dB/km). A severe challenge in using fused silica fibre is designing devices that can take full advantage of the low loss property, since the device length needs to be maximised in order to minimise the switching power. The nonlinear optical loop mirror (NOLM) has proved to be very effective in this respect, and devices as long as 9km have been successfully tested by our group. The NOLM operates on the principle of nonlinear interference between counterpropagating modes of a single fibre. In this letter we report successful all-optical switching with a device which also allows long lengths of fibre to be utilised.

© 1991 Optical Society of America