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Mewhoor, Leckhun Kumar (2017) Dual-layered and wavelength-multiplexed optical barcode for high data storage. Doctoral thesis, London Metropolitan University.
A novel barcode system design to achieve high data storage using more than one layer is introduced theoretically and tested partially in the laboratory. Compared to other existing barcode systems, diffraction gratings are used as core elements in the barcode symbol. As any other barcode system, the novel model requires a source of light, the barcode symbol and photodiode detectors. Theoretical background from optics has been used to design the entire system along with all the positioning of its components. After part-testing the design in laboratory, the barcode system design has been changed to achieve better results.
Experiments have showed that the initial proposed Light Emitting Diode (LED) source light cannot deliver 5mm spot light over a range of 50cm and therefore, white Light Amplification by Stimulated Emission of Radiation (LASER) light has been adopted as replacement. The diffractions from the barcode symbol are captured by detectors built with SI photo diodes, which are designed to detect this range of wavelengths. The barcode symbol is composed of small 5mm by 5mm grating modules and the largest possible symbol size defined is 80 modules (5cmx5cm). Experimental works have proved that intensity of the light can be used to uniquely identify each grating rather than the entire spectrum diffracted. A better design is proposed where the detectors are positioned under the barcode symbol and capture the light intensity of the first diffracted order. Theoretical investigations state that diffraction gratings with different lines per mm diffract different sets of wavelengths spectrum. This characteristic allows a set of unique gratings to be used in the barcode symbol which hence allow data to be represented or stored. Character (Char) sets are defined to help encode and decode data in the barcode symbol.
High data storage has been achieved through the use of two layers. Multiple layers offer the possibility to increase the number of unique sets of gratings which in turn increase the data representation capacity. Using two layers with 16 unique sets of gratings has proved to be able to store around 100 bytes of data. The system has the potential to use more than two layers and using 4 layers with 16 unique gratings per layer will achieve 200 bytes. The thesis has proved through theoretical and experimental work that diffraction gratings can be used in barcode system to represent data and multiple layers adds the benefit of increasing data storage. Further work is also suggested.
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