‘Quiet’ light

The other approach is to make an external-cavity laser whose cavity satisfies the fundamental physical requirements for a narrow linewidth laser, including the ability to hold billions of photons for a long time and support very high internal optical power levels. “The key to making our sub-Hz Brillouin laser on a photonic integrated chip was to use a technology developed at UC Santa Barbara—photonic integrated circuits built with waveguides that are extremely low loss, on par with the optical fiber,” Blumenthal explained. “These low-loss waveguides, formed into a Brillouin laser ring cavity on the chip, have all the right ingredients for success: They can store an extremely large number of photons on the chip, handle extremely high levels of optical power inside the optical cavity and guide photons along the waveguide much as a rail guides a monorail train.”

Source: phys.org