EPFL scientists have managed to crystallize light within optical on-chip microresonators in the form of periodic pulse trains.
These periodic pulse trains are said to boost the performance of optical communication links and advance ultrafast LiDAR with sub-micron precision.
According to the scientists, optical microresonators convert laser light into ultrashort pulses travelling around the resonator’s circumference.
These pulses – also known as dissipative Kerr solitons – can propagate in the microresonator maintaining their shape.
When solitons exit the microresonator, the output light takes the form of a pulse train – a series of repeating pulses with fixed intervals.
EPFL’s invention ensures that the repetition rate of the pulses is determined by the microresonator size.
According to the scientists, smaller sizes enable pulse trains with high repetition rates, reaching hundreds of gigahertz in frequency.
Once perfected, these can be used to boost the performance of optical communication links or become a core technology for ultrafast LiDAR with sub-micron precision.
Though this technology appears groundbreaking, it nevertheless suffers from ‘light-bending losses’ or loss of light caused by structural bends in its path.
A well-known problem in fiber optics, light-bending loss also means that the size of microresonators cannot drop below a few tens of microns.
According to the scientists, this very much limits the maximum repetition rates achievable for pulses.
Researchers from the EPFL lab of Tobias J. Kippenberg have now found a way to bypass this limitation and uncouple the pulse repetition rate from the microresonator size by generating multiple solitons in a single microresonator.
The scientists discovered a way of seeding the microresonator with the maximum possible number of dissipative Kerr solitons with precisely equal spacing between them.
This new formation of light can be thought of as an optical analogue to atomic chains in crystalline solids; the scientists have thus called them ‘perfect soliton crystals’ (PSCs).
PSCs can coherently multiply the performance of the resulting pulse train – not just its repetition rate, but also its power – thanks to interferometric enhancement and the high number of optical pulses.
According to EPFL researcher Maxim Karpov, the new pulse trains could prove useful for spectroscopy and distance measurement applications.
It could also double up as a source of low-noise terahertz radiation with a chip-size footprint.
Image and content: Second Bay Studios/EPFL