Chip-based devices known as frequency combs, which measure the frequency of light waves with unparalleled precision, have revolutionized time keeping, the detection of planets outside of our solar system and high-speed optical communication.
Now, scientists at the National Institute of Standards and Technology (NIST) and their collaborators have developed a new way of creating the combs that promises to boost their already exquisite accuracy and allow them to measure light over a range of frequencies that was previously inaccessible. The extended range will enable frequency combs to probe cells and other biological material.
The new devices, which are fabricated on a small glass chip, operate in a fundamentally different way from previous chip-based frequency combs, also known as microcombs.
Top: In the new comb system, two pump lasers shape each tooth, producing a frequency comb that could theoretically be sharper than a comb produced by a single laser. Bottom: The interaction between the two lasers randomly produces solitons in two different phases, which can be understood as a soliton pulse having either a positive or negative sign.
Credit: S. Kelley/NIST
A frequency comb acts as a ruler for light. Just as the uniformly-spaced tick marks on an ordinary ruler measure the length of objects, the uniformly-spaced frequency spikes on a microcomb measure the oscillations, or frequencies, of light waves.
Researchers typically employ three elements to build a microcomb: a single laser, known as the pump laser; a tiny ring-shaped resonator, the most important element; and a miniature waveguide that transports light between the two. Laser light that’s injected into the waveguide enters the resonator and races around the ring. By carefully adjusting the frequency of the laser, the light within the ring can become a soliton—a solit ..
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