Call/Recall, Inc has developed a series of efficient and stable 2-photon recording materials using photochromic fluorescence compounds that are well suited for 3-D optical memory. One of the goals of this blog will be to summarize recent experimental results obtained with our Write Once Read Many (WORM) optical volumetric systems and provide some technical background.
One type of WORM media used is composed of photoacid generator (AG) and dye precursor (DP) molecules, uniformly dispersed in polymer host, such as PMMA. These media are thermally stable in both write and read forms and capable of >106 read times. An acid, produced by two-photon excitation of AG molecules, reacts with DP to form strongly fluorescent dye. We have used several onium salts as photoacid generators, including commercially available triarylsulfonium salts and others specially designed and synthesized in our laboratory. Several dye precursors that generate Rhodamine and Oxazine type fluorescent dyes have been used and new ones developed. Recently, reversible two-photon recordable media have also been demonstrated. Our new materials are capable of write/read/erase, non-destructive readout and enable faster data rates.
The unwritten photochromic molecules are dispersed in a PMMA polymer matrix enabling the media to be low cost and molded by either compression or injection molding. The recording efficiency depends on several factors including the two-photon absorption cross section of the unwritten form, and the temporal and spatial photon density inside the media. A 3-d bit is recorded in the volume of the media only at regions with sufficient temporal and spatial photon density. High temporal photon density is achieved using picosecond pulsewidth laser systems having several nJ/pulse energy, and high spatial photon density is achieved through the use of tightly focused laser beams for recording using objective lenses having numerical apertures (NA) in the 0.5-1.0 range. Recording occurs only within a small volume around the focus of the laser beam due to two-photon response and follows the 3-D point spread function irradiance distribution of the focused recording laser beam. The recording response of the material follows the square of the optical system point spread function (PSF) resulting in a recorded bit size that is 30% less than the Rayleigh criterion PSF. The recorded bits are read by fluorescence when excited by a 635nm red laser diode in a single-photon absorption process within the written spot volume.
Considerable progress has also been made fabricating large, 120 mm diameter WORM disks to be used in high capacity information storage that demonstrate capability to store 300 GB to >1TB level per disk. An advanced objective lens is integrated into the recording test-stand and initial experiments show at least a 10x increase in recording speed with excellent experimental results observed at 20Mbit/s data rate, and will be tested at 16x and higher in anticipation of single channel recording and readout data rates in the 50-75Mbit/s data rate with recently developed more sensitive materials making the single channel data rates comparable to existing disk storage formats. An array format, common to every high-end data storage device, is under development will be used to achieve > 300Mbit/s in future prototypes.
One type of WORM media used is composed of photoacid generator (AG) and dye precursor (DP) molecules, uniformly dispersed in polymer host, such as PMMA. These media are thermally stable in both write and read forms and capable of >106 read times. An acid, produced by two-photon excitation of AG molecules, reacts with DP to form strongly fluorescent dye. We have used several onium salts as photoacid generators, including commercially available triarylsulfonium salts and others specially designed and synthesized in our laboratory. Several dye precursors that generate Rhodamine and Oxazine type fluorescent dyes have been used and new ones developed. Recently, reversible two-photon recordable media have also been demonstrated. Our new materials are capable of write/read/erase, non-destructive readout and enable faster data rates.
The unwritten photochromic molecules are dispersed in a PMMA polymer matrix enabling the media to be low cost and molded by either compression or injection molding. The recording efficiency depends on several factors including the two-photon absorption cross section of the unwritten form, and the temporal and spatial photon density inside the media. A 3-d bit is recorded in the volume of the media only at regions with sufficient temporal and spatial photon density. High temporal photon density is achieved using picosecond pulsewidth laser systems having several nJ/pulse energy, and high spatial photon density is achieved through the use of tightly focused laser beams for recording using objective lenses having numerical apertures (NA) in the 0.5-1.0 range. Recording occurs only within a small volume around the focus of the laser beam due to two-photon response and follows the 3-D point spread function irradiance distribution of the focused recording laser beam. The recording response of the material follows the square of the optical system point spread function (PSF) resulting in a recorded bit size that is 30% less than the Rayleigh criterion PSF. The recorded bits are read by fluorescence when excited by a 635nm red laser diode in a single-photon absorption process within the written spot volume.
Considerable progress has also been made fabricating large, 120 mm diameter WORM disks to be used in high capacity information storage that demonstrate capability to store 300 GB to >1TB level per disk. An advanced objective lens is integrated into the recording test-stand and initial experiments show at least a 10x increase in recording speed with excellent experimental results observed at 20Mbit/s data rate, and will be tested at 16x and higher in anticipation of single channel recording and readout data rates in the 50-75Mbit/s data rate with recently developed more sensitive materials making the single channel data rates comparable to existing disk storage formats. An array format, common to every high-end data storage device, is under development will be used to achieve > 300Mbit/s in future prototypes.
The very first full disk recording of 253GB has been performed in two-photon 3-d optical data storage materials in anticipation of recording even more on the next disk, as demonstrated by the bit densities shown in experimental recordings using recording energies of 50nJ per bit projected to be at nJ/bit recording energy per bit very soon. Full disk recordings of 500GB, 750GB, and 1TB are planned out for this year and updates will be posted as work progresses.
2 comments:
I work in the optical drive industry as the Manager of Product Development. I wondered if there an image of the current drive size? What about estimated drive dimensions once finished?
Very interesting product, keep up the good work!
Thanks,
Murray Ellis II
Hi Murray,
Thanks for the great questions and feedback. There are some layouts in the technical section of our homepage and pictures in some of our published references, but will add more soon to make them easier to find. The drive dimensions when finished will be similar to the optical head design layout on the technical section of our homepage which is similar in size to existing optical head footprints. It's our goal to keep the footprint of the head as small as possible and may evolve slightly from what you see there. I'm looking forward to sharing more as we're preparing to record a full 1TB of data in a standard format disk size of 120mm diameter 1.2mm thick disk very soon.
Thanks,
Ed Walker
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