Taming rogue waves to create switchable supercontinua

Supercontinuum emission extends from the IR through the visible to the UV. As Robert Alfano and Stanley Shapiro discovered 40 years ago, one can generate supercontinuum pulses by sending bright, narrowband pulses through an optical fiber or other highly nonlinear material. Sometimes, depending on the noise, the process of generating a supercontinuum pulse also begets rare, intense pulses known as rogue waves. The artist’s impression depicts the process. Ordinarily, rogue waves are sporadic and unpredictable, but if they could be produced to order, researchers would have access to bright, amplified pulses of supercontinuum light. UCLA’s Daniel Solli, Claus Ropers, and Bahram Jalali have done just that, at least over a broad range in the IR. Their technique relies on sending in a second seed pulse right after the main pump pulse. The seed pulse is 10 000 times weaker than the pump pulse and, with a central wavelength of 1630 nm, redshifted from the pump pulse by about 100 nm. Adjusting the relative timing of the two pulses has a dramatic effect. When timed optimally, the two pulses always generate a supercontinuum pulse of roguesized magnitude. What’s more, the supercontinuum pulses are uniform in both intensity and spectrum. How does the technique work? Supercontinua begin from a nonlinear process called modulation instability, which produces lobes at either side of the pump pulse spectrum. In the presence of noise, the supercontinuum pulses can vary erratically from pulse to pulse, occasionally yielding a rogue wave. According to the UCLA team’s numerical analysis, seed pulses tame the modulation instability and prompt the controllable formation of rogue waves. Data switching and routing in optical networks are among the applications the UCLA team envisions. (D. R. Solli, C. Ropers, B. Jalali, Phys. Rev. Lett. 101 , 233902, 2008 http://dx.doi.org/10.1103/PhysRevLett.101.233902 .)