New chip-based frequency combs demonstrate potential for portable atomic clocks
The world would look radically different without rulers and measuring tapes that fit into a pocket. Carpenters, fashion designers and engineers rely on these trusty tools to check the size of everything from a wooden board to a fabric swatch. But physicists who work with light lack that same convenience for one of the basic measurements of their craft. They routinely need to measure and compare…
Researchers have developed a compact, portable optical frequency comb that could revolutionize the way physicists measure and compare light frequencies. These frequency combs, which produce a rainbow of different frequencies of light at regular intervals, are crucial for many experiments and measurements that rely on light. Traditionally, large lab setups have been used to create these combs, but the new device, developed by a joint team of researchers from the Joint Quantum Institute (JQI) and international collaborators, is now small enough to fit on a portable chip.
The new chip-based frequency comb eliminates the need for bulky equipment and allows for easy adaptation to various practical measurement tasks. This breakthrough has potential applications in portable atomic clocks, which could help map underground mineral deposits and enable navigation systems that don't rely on GPS satellite signals. The researchers describe their advances and the performance of the compact device in an article published in Nature.
The key to the new frequency comb's success is a phenomenon called parametrically driven cavity solitons (PDCSs), which involve circulating light from two lasers around a tiny ring called a microresonator. If the ring is the right shape and the light is injected into it in the right way, the circulating light generates a string of pulses that can be used as a frequency comb.
However, previous attempts to use chip-based PDCSs have been complicated and difficult to control and stabilize, making them impractical for many applications.
The researchers overcame these challenges by combining PDCSs with a synchronization technique that stabilized the optical frequency combs. This combination, dubbed SParCS (self-aligned parametrically-driven cavity soliton), produces a pristine ruler with a single set of tick marks for measuring frequencies. The compact, portable frequency comb is a significant step forward in enabling the use of optical frequency combs in deployable atomic timekeeping, one of their most demanding and important applications.
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