Writing data using two optical dimensions plus three spatial dimensions – a known technique dubbed ‘5d’ storage – the Southampton team can write at 1,000,000 voxels per second, equivalent to ~230kbyte/s.
They used it to record 6Gbyte into a silica glass substrate, in four squares each 8.8 x 8.8mm, as well as the university logo (see photo). Read-out accuracy was close to 100%.
“The physical mechanism we use is generic,” said researcher Yuhao Lei. “Thus, we anticipate that this writing method could also be used for fast nanostructuring in transparent materials for applications in 3D integrated optics and microfluidics.”
It involves focussing a femtosecond laser to create 500 x 50nm pits, using near-field effects and a second laser to concentrate energy into a sufficiently small space with enough intensity to write the structure – described as “nanolamella-like” – Electronics Weekly has requested clarification.
“Rather than using the femtosecond laser to write directly in the glass, the researchers harnessed the light to produce near-field enhancement, in which a nanolamella-like structure is created by a few weak light pulses, from an isotropic nanovoid generated by a single pulse micro-explosion,” according to Optica, in whose journal the work has been published. “Using near-field enhancement to make the nanostructures minimised the thermal damage that has been problematic for other approaches that use high-repetition-rate lasers.”
Data is stored in the structures (‘slow axis’) orientation in the glass surface (nominal 4th dimension, controlled by write polarisation) as well as its size (5th dimension, by write intensity).
“This approach improves the data writing speed to a practical level, so we can write tens of gigabytes of data in a reasonable time,” said Lei. “The localised, precision nanostructures enable a higher data capacity because more voxels can be written in a unit volume. In addition, using pulsed light reduces the energy needed for writing.”
Although the method could get 500Tbyte of data into a CD-sized patch, it will take a while to write it all.
“With upgrades that allow parallel writing, the researchers say it should be feasible to write this amount of data in about 60 days,”, said Optica.
‘High speed ultrafast laser anisotropic nanostructuring by energy deposition control via near-field enhancement‘ is published in Optica by Optica (formerly OSA). The full paper can be read without payment.
Image credit: Yuhao Lei and Peter G. Kazansky, University of Southampton