Xiaobo Heng

Optical fiber design with orbital angular momentum light purity higher than 99.9

The purity of the synthesized orbital-angular-momentum (OAM) light in the fiber is inversely proportional to channel crosstalk level in the OAM optical fiber communication system. Here the relationship between the fiber structure and the purity is firstly demonstrated in theory. The graded-index optical fiber is proposed and designed for the OAM light propagation with the purity higher than 99.9%. 16 fiber modes (10 OAM modes) have been supported by a specific designed graded-index optical fiber with dispersion less than 35 ps/(km∙nm). Such fiber design has suppressed the intrinsic crosstalk to be lower than -30 dB, and can be potentially used for the long distance OAM optical communication system.

High spatial resolution distributed fiber strain sensor based on phase-OFDR

A novel method to realize high spatial resolution distributed strain measurement is proposed based on phase demodulation scheme of optical frequency domain reflectometry (OFDR). Strain information can be demodulated directly by analyzing the phase change of Rayleigh backscattered light. Strain location can be obtained with high spatial resolution by cross-correlation method using a wide scanning range of tunable laser source. Based on the above scheme, breakpoint detection with 0.1 mm spatial resolution has been demonstrated, static and dynamic strain up to 100 Hz could be distributedly measured with 10 cm spatial resolution over 200 m sensing fiber, and the minimum measurable strain is about 1 με.

Reduced radiation damage in a multicomponent phosphate glass by Nb^5+ or Sb^3+ doping

An experimental investigation on the effects of Niobium and Antimony (Nb and Sb) on the radiation response of the multicomponent phosphate glass used for higher optical gain single mode fiber has been carried out. The samples were irradiated with γ-rays up to 20 kGy. Optical absorption spectra and Electron Paramagnetic Resonance (EPR) were employed to investigate the radiation-induced-defects. We found that the radiation induced attenuation (RIA) decrease with increasing Nb5+ and Sb3+ doping concentration. Only the phosphorus oxygen hole center (POHC) related EPR signals were observed in the Nb5+-doped samples. Both POHC and phosphorus-oxygen electron centers (POEC) related EPR signals decrease obviously with 1 mol % Sb2O3 doping concentration. These experimental results were interpreted by a model that is based on competition between various defects and Nb- or Sb-ions for the holes and electrons generated by the absorption of γ-rays.

Low-crosstalk orbital angular momentum fiber coupler design

A fiber coupler for low-crosstalk orbital angular momentum mode beam splitter is proposed with the structure of two separate and parallel microfibers. By properly setting the center-to-center distance between microfibers, the crosstalk is less than -20 dB, which means that the purity of the needed OAM mode in output port is higher than 99%. For a fixed overlapping length, high coupling efficiency (>97%) is achieved in 1545-1560 nm. The operating wavelength is tuned to the whole C-band by using the thermosensitive liquid. So the designed coupler can achieve the tunable coupling ratio over the whole C-band, which is a prospective component for the further OAM fiber system.

Gamma radiation induced darkening in barium gallo-germanate glass.

Barium gallo-germanate (BGG) glass is an important glass matrix material used for mid-infrared transmission and mid-infrared fiber laser. In this study, we investigated the γ-ray irradiation induced darkening effect of BGG glass. Optical transmittance spectra, electron paramagnetic resonance (EPR) and thermoluminescence (TL) spectra were employed to investigate the γ-ray irradiation induced defects. Two kinds of Ge-related defects in the irradiated BGG glass, named Ge-related non-bridging oxygen hole center (Ge-NBOHC) and Ge-related electron centers (GEC), were verified. In addition, the absorption bands of the two defects have been separated and the peak absorptivity of Ge-NBOHC and GEC defects is at 375 nm and 315 nm, respectively.