Zengchang Li

Optical amplification of Eu(DBM)3Phen-doped polymer optical fiber

A preform technique is used to prepare a step-index (SI) polymer optical fiber (POF) doped with Eu(DBM)3Phen. The gain (5.7 dB) at 613 nm of the doped SI POF with Eu3+ 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 approximately 0.2 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.

Fabrication of long-period gratings in poly(methyl methacrylate-co-methyl vinyl ketone-co-benzyl methacrylate)-core polymer optical fiber by use of a mercury lamp.

Polymer optical fiber (POF) with a highly photosensitive poly(methyl methacrylate-co-methyl vinyl ketone-co-benzyl methacrylate) core is fabricated. Gratings can be fabricated in the core of a POF with a low-cost mercury lamp. The part of the emission spectrum of the mercury lamp in which the cladding material exhibits photosensitivity is effectively filtered by a 1.5-mm-thick Pyrex glass to ensure that a long-period grating is formed only in the core of a POF. A long-period grating with a 3-dR resonant peak at 1568 nm is fabricated with 0.3 mW/cm2 of UV irradiation over a period of 200 s.

Optical manipulable polymer optical fiber Bragg gratings with azopolymer as core material

Polymer optical fiber (POF) with a core of azopolymer has been fabricated. Based on the photoinduced birefringence of azopolymer materials, a mechanism for writing POF gratings is presented. After writing in azopolymer optical fiber (APOF) by two beams of mutually orthogonal polarizations, a birefringence grating was formed, and then the gratings could be erased almost totally for a short time by the circularly polarized beam at the same wavelength. By manipulating the APOF gratings, the transmittance through APOF at 632.8nm can be adjustable as revealed by the transmittance change during write-erase-write procedure.

Nano-scale study of microstructure of Eu(DBM) 3 phen-doped poly(methyl methacrylate) by near-field scanning microscopy and optical properties

Eu(DBM) 3 phen-doped poly(methyl methacryate) (PMMA) with different doping concentration were prepared. The highest doping concentration sample (10000 ppm) was examined by near-field scanning optical microscopy (NSOM) with a resolution of 50 nm; and the result showed that there were no aggregates larger than 50 nm in the doped polymer. This result was further confirmed by optical properties of the doping material. Concentration quenching was not detected by metastable-state lifetime measurements, indicating that no aggregates existed. According to the fluorescence spectra analysis, the relative intensity ratio (R) of 5 D 0 → 7 F 2 to 5 D 0 → 7 F 1 transition was not shown to be significantly changed with the increasing of Eu 3+ content. The analysis reflected that the local structure and asymmetry in the vicinity of europium ions were not changed, and that the Eu 3+ ions in PMMA were homogeneously dispersed.

Study on the photosensitivity of birefringent grating in copolymer optical fiber with high concentration

A novel copolymer optical fiber with high azobenzene concentration is reported (more than 3.2 mol %). The orientation process of the preform was fitted with corrected bi-exponential equation. Compared with the doped one, the photosensitivity of this kind of copolymer optical fiber preform is analyzed. The influence of azobenzene concentrations and write conditions on photosensitivity of copolymerized PMMA was analyzed. Then, long-period of 120um birefringent grating was fabricated in the single mode fiber with core refractive index of 1.485 (at wavelength of 1.5um), and relative index difference delta of 0.008. The duty cycle is 50%, and the refractive index change in the exposed area is about 4*10-4 for the ordinary or extraordinary ray.

Near-field optical research on the azobenzene polymer films

We report the near-field investigation on azobenzene contained polymer films using scanning near-field optical microscopy. Nanometer scale dots and lines were inscribed on these films, and the topographies and transmitting images of these patterns could be obtained at the same time. The transmitting images were in agreements with the topographies, and it proved that trans-cis isomerization of the azobenzene moieties in the illuminated area induced both surface relief and anisotropy. The experimental results helped to discover the mechanism of the photo induced surface relief and anisotropy, and the agreement between the transmitting images and the topographies could be applied in pure optical writing/reading in high-density data storage.