Dong Yoon Oh, Scott Diddams, Ki Youl Yang, Kerry J. Vahala, Connor Fredrick, Gabriel Ycas
Short duration, intense pulses of light can experience dramatic spectral broadening when propagating through lengths of optical fiber. This continuum generation process is caused by a combination of nonlinear optical effects including the formation of so-called dispersive waves. Optical analogues of Cherenkov radiation, these waves allow a pulse to radiate power into a distant spectral region. In this work, efficient dispersive wave generation of visible to ultraviolet light is demonstrated in silica waveguide arrays on a silicon chip. Conversion efficiency is nearly 40% and lithographic control of the dispersive-wave phase-matching condition tunes the emission to wavelengths as short as 265nm. The emission is also confirmed to be highly coherent by application of the devices to offset frequency measurement of a mode-locked frequency comb. A chip containing hundreds of engineered waveguides enables a mode-locked laser to attain unprecedented tunable spectral reach for spectroscopy, bio-imaging, tomography and metrology.
Frequency comb, nonlinear waveguide, super continuum