Researchers at the National Physical Laboratory (NPL) have reduced the power requirements to generate soliton frequency combs, an important tool to measure and read-out the frequencies of optical clocks.
The team demonstrated that the microresonators that generate low power consumption frequency combs can be stabilised with a second auxiliary laser. This significantly reduces the power requirements and increases the stability of soliton frequency combs. The research enabled soliton frequency combs at world record low power levels of only 780 microwatt, which could enable such a frequency comb to run for more than a year using a standard mobile phone battery.
This is a crucial discovery for future optical clocks, where low power consumption frequency combs will be a critical component in allowing them to run for much longer in portable devices than currently available.
The new discovery has been enabled by NPL's research project on dissipative Kerr solitons in microresonators. These solitons correspond to ultrashort pulses of light (less than 100 femtoseconds long) that are generated in tiny optical glass rings, similar to the diameter of a human hair (diameters of ~100 micrometer). The glass ring converts a continuous wave laser into the short soliton pulses.
The frequency spectrum of the train of pulses corresponds to a so-called frequency comb, which consists of many optical frequencies that are precisely spaced (like a rainbow, but with discrete colours and not continuous colour transitions). These optical frequencies can be used like the tick marks on a ruler, not to measure length however, but to measure other optical frequencies. This is an essential tool to read out the frequencies of optical clocks, helping to increase the accuracy of these devices which will in turn improve resilience to GPS outages, gravity sensing, and geodesy. In addition, the microresonator combs can be used for spectroscopy, telecom systems as channel generators and for dimensional metrology.
In particular, the anticipated redefinition of the second to optical frequency standards is expected to generate a strong demand for compact systems with low power consumption. This is especially important for precise navigation devices, for example in self-driving cars and autonomous drones.
Pascal Del'Haye, Principal Research Scientist at NPL, said:
"This new research is an extremely exciting step forward in helping to realise the real potential of compact optical clocks, by removing some of the boundaries posed when regular power sources aren't available."
Shuangyou Zhang, Higher Research Scientist at NPL, said:
"Our new technique for frequency comb generation not only helps to reduce the threshold power but also makes it much easier to access the regime in which the microresonators generate soliton frequency combs. This is especially important for future chip-based turn-key systems."
This research project received funding through the European Commission's Horizon 2020 Marie Sklodowska-Curie Action 748519 'CoLiDR', Horizon 2020 Marie Sklodowska-Curie COFUND action Multiply GA-2015-713694, National Physical Laboratory Strategic Research, European Research Council (ERC) Starting Grant 756966 'CounterLight'. PhD students on the project are supported by EPSRC through the CDT for Applied Photonics (Heriot-Watt University) and the CDTs for Controlled Quantum Dynamics and Quantum Systems Engineering (Imperial College London).
Read the paper, as published in Optica
Sub-milliwatt-level microresonator solitons with extended access range using an auxiliary laser
Shuangyou Zhang et al., OSA Publishing, DOI: https://doi.org/10.1364/OPTICA.6.000206
28 Feb 2019