Microresonator-Based Optical Frequency Combs: A Time Domain Perspective
Technical Report,01 Jul 2012,31 Dec 2015
Purdue University West Lafayette United States
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Optical frequency combs are promising for a variety of applications. Comb generation based on nonlinear wave mixing in optical microresonators offers promise to replace traditional mode-locked laser combs and to substantially shrink the size of comb sources to the chip-level for applications outside of specialized research laboratories. In this project we studied comb generation in microresonators formed in silicon nitride films on siliconchips. Our most important contribution has been to convincingly demonstrate that in addition to the anomalous dispersion microresonator devices commonly studied, comb generation can and does occur in normal dispersion microresonators and is made possible by interactions between different spatial modes in the few-moded waveguides from which the microresonators are fabricated. Time domain measurements show for the first timethat under normal dispersion, combs can take the form of mode-locked dark pulses. Comb generation from normal dispersion micoresonators offers potential for operation deep into the visible spectrum where normal dispersion dominates, may be compatible with thinner, lower loss films,and may provide opportunities for higher power at the cost of reduced optical bandwidth.