All glass femtosecond laser spinout for photonic quantum computing

All glass femtosecond laser spinout for photonic quantum computing

Technology News |
By Nick Flaherty

Researchers in Switzerland are commercialising a femtosecond laser technology that can be built entirely in glass.

A team at EPFL in Neuchâtel has developed a palm-sized, all-glass GHz femtosecond laser cavity that can be used for the next generation of large scale photonic quantum computers.

The manufactured Yb:KYW oscillator shows self-starting mode-locking with a diffraction-limited beam and outputs a stable train of solitons with 182 fs pulse width at 1.0925 GHz repetition rate, for 725 mW incident pump power. The alignment and lasing are permanently tuned in a contactless way using another femtosecond laser.

The research was funded by the European Research Council under a proof of concept grant as project GigamFemto. The spin-off into a startup called Cassio-P has been supported through the Bridge Proof-of-Concept and EPFL’s Ignition programs.

“We use femtosecond lasers for our research on the non-linear properties of materials and how materials can be modified in their volume,” said Yves Bellouard, head of EPFL’s Galatea Laboratory. “Going through the exercise of painful complex optical alignments makes you dream of simpler and more reliable ways to align complex optics.”

To make a femtosecond laser using a glass substrate, the scientists start with a sheet of glass. “We want to make stable lasers, so we use glass because it has a lower thermal expansion than conventional substrates, it is a stable material and transparent for the laser light we use,” said Bellouard.

A commercial femtosecond laser etches grooves in the glass that allow for the precise placement of the essential components of their laser. Even at micron level precision fabrication, the grooves and the components are not sufficiently precise by themselves to reach laser quality alignment. In other words, the mirrors are not yet perfectly aligned, so at this stage, their glass device is not yet functional as a laser.

The initial etching is therefore designed so that one mirror sits in a groove with micromechanical flexures engineered to locally stir the mirror ­when exposed to femtosecond laser light. In this way, the commercial femtosecond laser is used a second time, this time to align the mirrors, and ultimately create a stable, small scale femtosecond laser.

“This approach to permanently align free-space optical components thanks to laser-matter interaction can be expanded to a broad variety of optical circuits, with extreme alignment resolutions, down to sub-nanometres,” he said.

Ongoing research programs at the Galatea Lab will explore the use of this technology in the context of quantum optical system assembly, pushing the limit of currently achievable miniaturization and alignment accuracy.

The alignment process is still supervised by a human operator, and with practice can take a few hours to achieve. Despite its small size, the laser is capable of reaching approximatively a kiloWatt of peak power and of emitting pulses of less than 200 femtoseconds.;;


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