An international consortium led by the UK's National Physical Laboratory has set a new record for comparing ultra-stable lasers at long distances by metering a fibre network. A related research paper was published in the journal Nature Communications.
Using cutting-edge optical frequency standards developed by the German Federal Institute of Physics and Technology and the UK's National Physical Laboratory, the team has been able to demonstrate that measurement accuracy is maintained even over thousands of kilometers of fiber-optic transmission. This metrology fiber optic network is specifically designed to compare optical atomic clocks (which promise to improve the ability to measure time and frequency by orders of magnitude). Just as quartz oscillators are key components in traditional microwave clocks, ultra-stable lasers play a vital role in optical clocks. Similar to the state-of-the-art ultra-stable lasers used in the study, in a way that wiggles in the distance between Earth and the sun less than the width of a hair.
This precision is achieved by using an optical reference cavity that provides an optical standing wave with frequency stability set by the mirror distance. The stability of the optical reference in this study corresponds to the average change in mirror position, is 50 times smaller than the diameter of a proton, and has a cavity length of about half a meter.