Generation of 3.5 nJ femtosecond pulses from a continuous-wave laser without mode locking

Using time-lens compression in a loop configuration, we generate 516 fs pulses at 3.5 nJ pulse energy from a continuous-wave 1.55 mum source without mode locking. Just as a spatial lens can expand or focus a beam in space, so can a time-lens broaden or compress a pulse in time. By placing a time-lens in a loop, we maximize the efficiency of bandwidth generation by using one time-lens driven at low power to emulate a stack of many lenses. Our system is compact, is all fiber, and allows large tuning of the repetition rate and continuous tuning of the pulse width and center wavelength.