We demonstrate the realization of a coherent random fiber laser (RFL) in the extremely weakly scattering regime, which contains a dispersive solution of polyhedral oligomeric silsesquioxanes nanoparticles (NPs) and laser dye pyrromethene 597 in carbon disulfide that was injected into a hollow optical fiber. Multiple scattering of polyhedral oligomeric silsesquioxanes NPs greatly enhanced by the waveguide confinement effect was experimentally verified to account for coherent lasing observed in our RFL system. This Letter extends the NPs-based RFLs from the incoherent regime to the coherent regime.

A preform technique is used to prepare a step-index (SI) polymer optical fiber (POF) doped with $\mathrm{Eu}{\left(\mathrm{DBM}\right)}_3\mathrm{Phen}$. The gain (5.7 dB) at 613 nm of the doped SI POF with ${\mathrm{Eu}}^{3+}$ content of 4000 in ${10}^6$ wt., 0.4-mm core diameter, and 30-cm fiber length is observed at ambient temperature by end pumping with a YAG at 355 nm. The input signal light is $\sim 0.2 \mathrm{W}$. The results show the possibility of signal gain in a rare-earth-doped POF amplifier and the potential of a polymer doped with rare-earth ions as an active optical device.

By introducing methanol as a co-solvent into cyclopentanone, solvent effects on structure, photoresponse and speed of gelation of a dicholesterol-linked azobenzene organogel DCAZO2 have been investigated. Optical microscopy (OM) and scanning electron microscopy (SEM) images reveal that the gel fibers form macroscopic aggregates by adding methanol. Minimum gelation concentration (MGC) of the gels decreases with increasing methanol content, while the gel-to-sol transition temperature (T_gel) decreases firstly and increases afterwards. For photoisomerization (corresponding to gel-sol transition), the first stage rate constant k_g1 of the gels decreases with increasing methanol content. The photoisomerization process of the gel with 5% methanol is different from the other five samples, whose first stage rate constant k_g1 is greater than its second stage rate constant k_g2. By increasing methanol content from 0% to 30%, gelation time (corresponding to sol–gel transition) of both heated gel and UV-visible light irradiated gel decreases from 7 h to 5 min and 6 h to 0 min (before visible light irradiation is accomplished), respectively. Solubility parameters and Teas plots of the gelator and mixed solvents are systematically calculated to estimate the gelator-solvent interaction. It is found that gelation requires that the gelator-solvent interaction be neither too strong nor too weak, otherwise solution or precipitate are formed.

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.

A series of new symmetric dicholesterol-linked azobenzene gelators with different spacer lengths have been synthesized. The compounds with spacers of zero, two or six methylene units are denoted as DCAZO0, DCAZO2 and DCAZO6, respectively. A gelation test reveals that a subtle change in the length of the spacer can produce a dramatic change in the gelation behavior of the compounds. DCAZO2 obtains the minimum gelation concentration among the three gelators. For cyclopentanone gel of DCAZO2, the reversible gel–sol transitions by irradiation with UV and visible light are investigated by UV-vis absorption and circular dichroism (CD) spectra, SEM, TEM and XRD analyses. Upon UV irradiation of the gel, trans–cisphotoisomerization of the azobenzene groups occurs, the change in molecular polarity leads to the breaking of van der Waals interactions, resulting in the gel–sol transition. The gel can be recovered by the reverse cis–transphotoisomerization after the exposure to visible light. SEM, TEM and XRD studies reveal that the gelator molecules self-assemble into one-dimensional fibers with diameters 50–100 nm in an anticlockwise direction, which further crossed-linked to form three-dimensional networks.