Guosheng Qi

Multi-wavelength optical storage of diarylethene PMMA film

Current commercial optical storage technologies are all based on the heat effect of the recording laser, i.e., heat-mode optical storage. In the present work, photon-mode optical storage using photochromic diarylethene materials was investigated. Two diarylethene derivatives were dispersed into PMMA solution, and spin-coated on a glass substrate with Al reflective layer as the recording layer. Two laser beams of 532 and 650 nm were used in recording and readout simultaneously, and signals with high S/N ratio were detected. Multi-wavelength optical storage was realized with the diarylethene PMMA film.

Signal processing and coding for multiwavelength and multilevel photochromic optical storage

Multi-wavelength and multilevel (MWML) optical storage with photochromic media is a novel technology that can increase storage capacity and transfer rates significantly. Signal processing and coding methods for the MWML storage channel are introduced in this paper. Two-dimensional codes with parallel detection and equalization are studied to increase storage capacity and combat the crosstalk between different wavelength materials. Multilevel amplitude modulation and M-ary runlength-limited (RLL) codes are described and compared for achieving higher coding capacity. The novel MWML recording technology has the potential to be applicable for the next generation optical data storage.

Diarylethene materials for photon-mode optical storage

Photon-mode recording of photochromic materials is regarded as a promising storage system, which has various advantages over the traditional heat-mode recording in terms of its data capacity and data-recording rate. Diarylethenes show good thermal stability and remarkable fatigue resistance, and these properties are indispensable for the applications to optical storage materials. In present work, several diarylethene compounds were synthesized, and a series of optical storage tests were carried out on the sample discs with diarylethenes as the recording materials. The recording based on these photochromic materials was photon-type,and the recorded regions appeared as faded dots. 780, 650 and 532 nm lasers were used for writing on the corresponding discs, and the recorded information were readout by the same lasers respectively. A two-wavelength optical storage was realized on a mixed diarylethene recording layer by two laser beams of 532 nm and 650 nm synchronously. A higher data capacity can thus be expected to reach by using a multi-wavelength optical storage like that. Although the diarylethenes satisfy the minimum demands of optical storage systems, these molecules have one unsolved drawback: the lack of a non-destructive capability. In this work, Electric-locked properties were investigated in a BT3FP-OH thin film; the electric trigger could prevent the photochromic reactions, which provided a practicable non-destructive readout method. Three kinds of diarylethene derivatives linked by solvatochromic dye units wer fabricated; the theoretical investigation showed that reading at the wavelength of about 650-750 nm would destroy the recorded information no longer. Thus a non-destructive method could be constructed on these diarylethene molecules.

Synthesis and multiwavelength optical recording properties of two new photochromic diarylethenes

1,2-bis(2-methyl-5-(2-(1,3-dioxolane))-thien-3-yl)perfluorocyclopentene (1a) and 1,2-bis(2-methyl-5- 4-N,N-dimethyl-phenyl)-thien-3-yl)perfluorocyclopentene (2a) were synthesized and rewritable photo-mode muti-wavelength optical recording by the use of them was performed successfully. In amorphous film photochromic media, two laser beams of 532 nm and 650 nm were used in recording and readout simultaneously, and signals with high S/N ratio were detected. The results show that the reflectivity difference between the recorded dot and unrecorded region is greater than 50%, and above all, there is no crosstalk existing in the two diarylethenes, which it is very important to implement successfully multi-wavelength optical recording. The photochromic properties of them were also discussed.

Multi-level storage based on photochromic recording material

An experiment on the character of photochromic recording material is introduced. Numerical method is used to describe the material character. Based on it, the multi-level experiment demonstrates the availability using photochromic material as recoding medium of 4-level storage system. Finally, a further analysis on optimizing the exposal parameters of different levels of multi-level disc is presented.

Modulation Codes for Multi-wavelength and Multi-Level Photochromic Optical Recording Channel

Multi-wavelength and multi-level optical recording with photochromic materials is a novel way to increase recording density and data transfer rate significantly. Modulation codes for multi-wavelength and multi-level recording channel are discussed. Firstly, two-dimensional (2-D) run-length-limited (RLL) (dx,dy,k;n) codes are introduced for multi-wavelength recording. An example of 2-D RLL(1,1,6;2) code is shown to effectively combat the crosstalk in a two-wavelength recording model. Then, a DC-free four-ary RLL(2,8) code is designed with code rate of 8/10 (bits/symbol), and a partial-response maximum-likelihood (PRML) detector is used for the four-level RLL(2,8) modulation recording channel. We also introduce 2-D RLL(M,1,∞) codes for the joint multi-wavelength multi-level recording channel. Some numerical results on the capacities are derived, and an example of 2-D (5,1,∞) code is constructed via state splitting algorithm. These proposed codes show great potential to be applicable in high-density 2-D and multi-level optical recording channels.

Super-resolution optical mastering system using blue laser and high-numeric-aperture lens

A practical mastering technology was developed using a blue laser optical mastering system with a wavelength of 405 nm, a numeric aperture (NA) of 0.95 and a phase-shift apodizer. The laser is shaped and collimated by a space filter with its diameter 2μm, then is split into two beams by polarizing prism. One beam is used to detection of the optical power, and the other beam is used to write data on the disc. The phase-shift mask is lay between the collimating lens and the polarizing prism to optimizing the intensity distribution of Airy point on the disc. The lens with high NA 0.95 is designed to make the image point of the laser less then the diffraction point. The air-operated focus control device is used to focalize the light on the disc. Based on the technology, the recording spot with its diameter about 223nm is achieved.

Writing process of multiwavelength photochromic storage

Multi-wavelength photochromic storage is a new optical storage method based on the photochromic principle. In this paper, the storage method itself and the mathematic model developed to describe the change of the reflectance in the writing process are discussed. For the photochromic materials, which are sensitive to 650 nm and 532 nm laser respectively and mixed into one layer, the reflectance of the readout laser in the writing process was measured with a 3-wavelength photochromic storage system. The theoretical results of the model agree well with the experimental ones. It is also found that the photochromic optical storage has no threshold.

Capacity of M-ary 2-D RLL constraints for optical recording channels

A new class of M-ary two-dimensional (2-D) run-length limited (RLL) constraints is introduced in this paper. In particular, only RLL d constraints on 2D m /spl times/ n arrays with limited height m are considered. Column vectors of 2-D arrays are used as states in a directed graph. The transfer matrix of the graph is obtained with consideration of non-binary alphabet, and the largest eigenvalue of the transfer matrix is used to calculate the capacity of 2-D (M, d, /spl infin/) RLL constraints on 2-D arrays. Some numerical results are derived for RLL d = 1 and d = 2 constraints. We also present an example of efficient finite-state encoder for d = 1 constraint by state splitting and merging algorithm. The 2-D (M, d, /spl infin/) constrained codes have potential to be applied in advanced 2-D optical recording channels.

Modulation codes for multi-level photochromic optical storage

Multi-level optical storage is a promising approach to increase recording density and data transfer rate significantly without altering optical and mechanical parameters of current optical disc systems. Multi-level amplitude modulation and multi-level run-length limited modulation are two different important recording approaches. In this paper, we discuss and compare these two multi-level modulation principles and corresponding multi-level coding schemes. With advanced coding and signal detection, multi-level run-length limited modulation shows better performances in terms of higher recording density. We present a new 8-ary (1, 3) RLL code constructed by state splitting algorithm for photochromic storage channel. The proposed code has only two coding states and high coding density of 3.0 bits per minimum mark. The encoder/decoder is simple and easy for implementation, which can be applied in future high density multi-level optical storage systems.