Electronics and photonics have long had a complementary coexistence across multiple application areas. Nonetheless, an ideal partnership of these two realms was made challenging in large part by the enormous frequencies of lightwaves. About two decades ago, this limitation was overcome with the invention of the laser frequency comb. Combs provide a coherent link between electronics and photonics, and because the link is bidirectional, performance attributes previously unique to each can now be shared. Their implementation has been transformative for time keeping, frequency metrology, precision spectroscopy, microwave-generation, ranging and other technologies. More recently still, high-Q nonlinear optical microresonators, have enabled chip-scale frequency combs. I will review efforts to fully integrate comb systems around these new ‘microcombs,’ along with the physical principles of the devices themselves. Finally, I will consider the revolutionary impact this chip-scale unification of the optoelectronic spectrum can have on photonic instrumentation and consumer products.
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