Multilevel Recording in Erasable Phase-Change Media by Light Intensity Modulation

Abstract

Multi-level recording has advantage of increasing the recording density without extensively altering the current optic configuration. In this paper, a new four-level recording phase-change disk using three-recording layers was demonstrated. By modulating the intensity of the laser pulse, marks were chosen to record in any of recording layers, to form four recording regions. Utilizing the property of the phase change media whose amorphous and crystalline states differ largely in refractive indices, each recording region corresponds to different reflectance. For the four-level recording disk, each recording region represents two-bit data, then the recording density of the four-level disk is a factor of two higher than that of a conventional disk recorded by adopting the pulse position modulation (PPM).

Polarization readout analysis for multilevel phase change recording by crystallization degree modulation

“…The detectable differences between polarization rotation angles at different crystallization degree modulated states provide the possibility of recording the multilevel phase change. The multilevel recording can be carried out by pulse width and power modulation, [9] But how can it be read out? After all, an ellipsometer cannot be used as a normal readout system for practical data storage.…”

“…Multilevel phase change recording was first reported by Ovshinsky in his early work [3] and continued refinements later. [4] The intermediate reflectivity or resistivity levels can be obtained by mark size modulation, [5,6] partial crystallization effect, [7,8] stacked structure, [9][10][11][12] etc. Although it is simple in principle, the multilevel recording, such as recording and readout of the multilevel signals in the existing or improved operation systems, remains challenging in its implementation.…”

Towards rewritable multilevel optical data storage in single nanocrystals

“…Multilevel encoding has been demonstrated for instance in polymers but it appears that these systems are subject to significant bleaching with limited number of levels and linearity [6,7]. Multilevel encoding has also previously been demonstrated in optical discs for up to 2 bits per point storage [8,9] and in photoisomeric birefringent polymers using high power femtosecond lasers for the write step [10,11].…”

Multi-level recording of photochromic indolylfulgide

“…In spite of the large number of research publications in this field [12][13][14], few works concerning the multi-level optical storage with photon-mode materials have been reported [15][16][17][18][19][20]. Herein, we describe the multi-level optical recording of indolylfulgide 2-(1-benzyl-3-methyl-2-indolylmethylene)-3-isoproplidene succinic anhaydride (I) in PMMA film depending on variable exposure time, where eight-level recording of amplitude modulation with high SNR readout signals and fast photoconversion speed with regard to a molecule within milliseconds is firstly realized in fulgide film.…”