Compensation Of The Laser Wavelength Drift In Collinear Holographic Storage System

With the rapid development of digital technology and digital products, today’s society has entered the era of big data,the sharply increased information has put forward higher requirements for data storage system. Traditional magnetic storage systems, such as disks and magnetic tapes, are widely used in daily life. However, these storage devices have a disadvantage of short storage life-time. The flash memory based on the semiconductor technology has high transmission speed and large storage density. But the cost and life-time have hindered the pace of progress. Traditional optical disc systems, such as CD and DVD, have a long life-time, but the storage density has reached the theoretical limitations. Thus it can be seen that in the future, these storage devices will not become the mainstream of this era.Holographic optical storage system with large storage capacity and high transmission rate,is gradually becoming the powerful candidate for the next generation of storage devices. Traditional holographic optical storage technology,called 2-axis system device cannot achieve commercialization due to the complex structure and the property of prone to be affected by the environment vibration. Collinear holographic storage technology is a novel type of optical storage technology which has large density and ultrahigh speed. Compared to the 2-axis holographic storage system, it is simple and robust to environmental vibration. It is proposed to accelerate commercialization process for the optical holographic storage technology.The collinear holographic storage system has a wide wavelength tolerance, which makes it possible that semiconductor laser can be used in the system. However, because of the output wavelength instability of semiconductor laser, the wavelength of the laser used in the recording process and the reproduction process may not be consistent. So it will cause bit error rate of the reconstructed image. This thesis mainly focuses on how to compensate the wavelength drift of laser to reduce the bit error rate of the reconstructed image. Method which can be used to compensate the laser wavelength drift has been proposed. It is the focal length compensation method, and according to this method, the experiment system has been designed. Then the focal length compensation method is verified by the simulation and the accuracy of the focal length compensation method is obtained by numerical simulation. At the same time another application of focal length compensation method has also been demonstrated. The focal length compensation method is also adapted to decrease the bit error rate of the reconstructed image caused by the material shrinkage. The numerical simulation is also carried out and some preliminary results have been achieved.