Coupled nonlinear cavities: new avenues to ultrashort pulses

Much of science consists of exploring the very big and the very small, be it in space or in time. This chapter describes how a new method for the production of ultrashort pulses of light emerged recently. This technique utilizes optical nonlinearity in a resonator coupled to the laser resonator for enhancement of mode locking. The chapter concentrates on a relatively recent method to produce ultrashort pulses that relies on optical nonlinearity, typically provided by a fiber, incorporated into the laser feedback. It outlines the historical development of this method and present recent results, including some from our lab. Nonlinearity is a leitmotiv of laser physics, and it is not a new idea to shape pulses by nonlinear techniques.