Based on the readout and crosstalk analysis, a kind of multi-channel partial response maximum likelihood (MPRML) detection method which is suitable for photometric multi-wavelength optical disks has been brought forward, the PR mode and parameters have been discussed, and the optimal solution of the method has been given in the paper. Matlab simulation shows that the MPRML method is useful to improve BER performance and the optimal solution is proper. The experiments on the FPGA-based development board also show that MPRML is applicable for photometric multi-wavelength optical disks.
Proc. SPIE. 5643, Advances in Optical Data Storage Technology
KEYWORDS: Signal to noise ratio, Detection and tracking algorithms, Sensors, Remote sensing, Computer programming, Signal processing, Optical recording, Medium wave, Optical storage, Photochromic materials
Multi-wavelength storage is an approach to increase the memory density with the problem of crosstalk to be deal with. We apply Low Density Parity Check (LDPC) codes as error-correcting codes in photochromic dual-wavelength optical storage based on the investigation of LDPC codes in optical data storage. A proper method is applied to reduce the crosstalk and simulation results show that this operation is useful to improve Bit Error Rate (BER) performance. At the same time we can conclude that LDPC codes outperform RS codes in crosstalk channel.
The readout of photochromic multi-wavelength storage was analyzed, and its model was established in this paper, with the disk reflectivity and the recording information distribution optional. The luminous power of the readout was divide into two parts: the part without the disturbance of other materials and the reading crosstalk. The expressions of them were presented, which were useful for the further analysis of the crosstalk and the crosstalk suppression method.
The data are stored in the alternative pits and lands for present optical disk, which is similar to the grating. Accordingly, the grating theory becomes the basis theory for the optical disk. The work presented in this paper focused on several aspects of the following: outlining the optical disk models adopted by the theories in print, analyzing the foundation basis of the models, and bringing forward a model which can be used for the new-fashioned optical storage, multi-wavelength photochromic optical storage. The classical scalar diffraction theory supposed that the effects of the optical disk on the incident beam were introducing the local phase delay that could be described by the optical path difference Δs, and the energy of the incident beam would not be absorbed. The two equations could respectively express the difference of the optical path: (1) Δs=n*Δh and (2) Δs=Δn*h. As the result of the analysis, we concluded that the tradition optical disk model fit for pit-land recording format and the cavity or bubble recording format. For the photochromic optical disk, the recording material, which absorbed the energy of the incident beam, was similar to the amplitude grating. The diffraction theory of this system was presented, and the equations for the readout signal were educed.