Zhoushun Zhang

Supramolecular bisazopolymers exhibiting enhanced photoinduced birefringence and enhanced stability of birefringence for four-dimensional optical recording

Extremely stable, high-density information storage media were prepared by the connection of two azobenzene groups via hydrogen bonding to form supramolecular bisazopolymers. The supramolecular bisazopolymers contain 4-((4-hydroxyphenyl)diazenyl)benzonitrile (AzoCN) as a hydrogen bonding donor and poly(6-(4-(pyridin-4-yldiazenyl)phenoxy)hexyl methacrylate) (pAzopy) as a hydrogen bonding acceptor. High quality films of the supramolecular bisazopolymers pAzopy/(AzoCN)x (x = 0.25, 0.5, 0.75, 1.0) with different molar ratios of donor/acceptor were prepared by spin-casting. The supramolecular bisazopolymers spontaneously form lamellar structures with a periodic thickness of 7.1 nm. These samples exhibit optically induced birefringence. The birefringence and proportion of remnant birefringence increase from 0.0265 to 0.1 and 50.5% to 108%, respectively, as the content of AzoCN in the samples increases, which indicates a larger proportion of AzoCN enhances both the birefringence and its stability. We also use an azopolymer without pyridine groups (pAzoCH3) and AzoCN to do a control experiment, which shows that pAzoCH3/(AzoCN)1.0 do not show significant enhanced birefringence and its stability. The enhancements in pAzopy/(AzoCN)x are because of the unique structure of the supramolecular bisazopolymers. A new laser direct writing system has been developed for optical recording on the azopolymers. The pAzopy/(AzoCN)1.0 film is significantly better at image recording than the pAzopy film, because the optically recorded images on the pAzopy/(AzoCN)1.0 film are very clear after storage for four months whereas the optically recorded images on the pAzopy one disappear after just one day. Four-dimensional optical recording has been achieved by integrating the polarization and the intensity of the laser and the two dimensions of a plane. An information density of about 0.93 Gbit cm−2 could be optically recorded on the pAzopy/(AzoCN)1.0 film, which is about 20 times the information density of a normal DVD.

Two-photon-induced polarization-multiplexed and multilevel storage in photoisomeric copolymer film

We present a two-photon-induced polarization-multiplexed and multilevel data storage method with a bisazobenzene copolymer film. A polarization-adjustable femtosecond pulsed laser is used as writing beam to induce anisotropy, and the recorded information is retrieved by a CCD sensor from the film with corresponding polarized illumination. It is found that the optical axis of bisazobenzene molecules can be reoriented under two-photon excitation by the polarized femtosecond laser via a photoisomerization process. Polarization-multiplexed and multilevel storage is demonstrated by using this method. The capability to combine both advantages of these distinct techniques makes it a novel approach to obtain higher optical data density.

High signal-to-noise ratio multi-dimensional storage using femtosecond pulsed laser

Recently multi-dimensional data storage has been intensively researched. Four-dimensional storage can be achieved by combining ultra-fast laser based multilayer recording and polarization-multiplexed technology. One of the obstacles is the readout crosstalk between different layers and polarization states. In this paper, we report on the high signal-to-noise ratio (SNR) four-dimensional data storage using femtosecond pulsed laser. Different polarization-encoded patterns are recorded by tightly focusing a polarized femtosecond laser beam (800nm, 80MHz, 80fs) in the same portion of multilayer film, and retrieved by placing the sample between two orthogonal polarizers. Compared with other readout methods, the recorded patterns are read out with a higher signal-to-noise ratio in the absence of crosstalk.Recently multi-dimensional data storage has been intensively researched. Four-dimensional storage can be achieved by combining ultra-fast laser based multilayer recording and polarization-multiplexed technology. One of the obstacles is the readout crosstalk between different layers and polarization states. In this paper, we report on the high signal-to-noise ratio (SNR) four-dimensional data storage using femtosecond pulsed laser. Different polarization-encoded patterns are recorded by tightly focusing a polarized femtosecond laser beam (800nm, 80MHz, 80fs) in the same portion of multilayer film, and retrieved by placing the sample between two orthogonal polarizers. Compared with other readout methods, the recorded patterns are read out with a higher signal-to-noise ratio in the absence of crosstalk.