Jianxiang Wen

Bismuth and erbium codoped optical fiber with ultrabroadband luminescence across O-, E-, S-, C-, and L-bands

We report the first (to our knowledge) development of a Bi/Er/Al/P codoped germanosilica optical fiber showing ultrabroadband luminescence between 1000 and 1570 nm, covering O-, E-, S-, C-, and L-bands, when pumped by 532, 808, or 980 nm lasers. The fluorescence profiles are found highly pump wavelength dependent, closely associated with different combinations of excitations from both Bi centers and Er ions as active centers. With a proper selection of pump wavelength(s), this Bi/Er codoped fiber could be used as an ultrabroadband gain medium for ultrabroadband amplified spontaneous emission sources, fiber lasers, or amplifiers in telecommunications and in other fields.

Mode converter based on the long-period fiber gratings written in the two-mode fiber

We demonstrated the fabrication of long period fiber gratings written in two-mode fiber as mode converter to realize the mode conversion between LP01 mode and LP11 mode with an efficiency of up to 99.9%.

Refractive index sensitivity enhancement of optical fiber cladding mode by depositing nanofilm via ALD technology

The atomic layer deposition (ALD) technology is introduced to enhance the sensitivity of optical fiber cladding mode to surrounding refractive index (SRI) variation. The highly uniform Al2O nanofilm was deposited around the double cladding fiber (DCF) which presents cladding mode resonant feature. With the high refractive index coating, the cladding mode resonant spectrum was tuned. And the sensitivity enhancement for SRI sensor was demonstrated. Through adjusting the deposition cycles, a maximum sensitivity of 723 nm/RIU was demonstrated in the DCF with 2500 deposition cycles at the SRI of 1.34. Based on the analysis of cladding modes reorganization, the cladding modes transition of the coated DCF was investigated theoretically. With the high performance nanofilm coating, the proposed SRI sensor is expected to have wide applications in chemical sensors and biosensors.

Photoluminescence Characteristics of Bi ( m+ )- Doped Silica Optical Fiber : Structural Model and Theoretical Analysis

The energy levels associated with structural models of different valence states of Bi ions in Bi-doped silica optical fiber are investigated using the density functional theory of quantum-chemical calculation. The Bi5+, Bi3+, and Bi+ local structure models with and without Al ion are analyzed and compared with respect to their fluorescence characteristics. The result reveals that the special fluorescence effect possibly comes from Bi5+ and/or Bi3+ ions. Bi5+ ions may combine with Al ions that activate the luminescence center of Bi5+ ions. Furthermore, the distinctive fluorescence bands are efficiently generated by the coupling effect between Bi5+ and Al3+ ions. The fluorescence of Bi3+ ions may come from the Bi3+ ions with Al-free ion. Fluorescence of Bi+ ions may exist, but its contribution to the fluorescence is nominal.

Gamma irradiation effect on Rayleigh scattering in low water peak single-mode optical fibers

The Rayleigh scattering loss in low water peak single-mode optical fibers under varying Gamma rays irradiation has been investigated. We observed that the Rayleigh scattering coefficient (CR) of the fiber is almost linearly increased with the increase of Gamma irradiation in the low-dose range (< 500 Gy). Based on the electron spin resonance (ESR) spectra analysis, we confirmed that the Rayleigh scattering mainly results from the irradiation-induced defect centers associated with electron transfer or charge density redistribution around Ge and O atoms. This work provides a new interpretation of the optical loss and reveals a new mechanism on irradiation influence on Rayleigh scattering.

Fabrication of Polymer Optical Fibre (POF) Gratings

Gratings inscribed in polymer optical fibre (POF) have attracted remarkable interest for many potential applications due to their distinctive properties. This paper overviews the current state of fabrication of POF gratings since their first demonstration in 1999. In particular we summarize and discuss POF materials, POF photosensitivity, techniques and issues of fabricating POF gratings, as well as various types of POF gratings.

Radiation-induced photoluminescence enhancement of Bi/Al-codoped silica optical fibers via atomic layer deposition.

The radiation-induced photoluminescence (PL) properties of Bi/Al-codoped silica optical fibers were investigated. The Bi/Al-related materials were doped into fiber core via atomic layer deposition. The pristine fiber samples were irradiated with different doses, and its absorption and PL properties were studied. A new absorption peak appeared at approximately 580 nm, and the intensity of absorption peaks is increased with the increasing of radiation doses. When the fiber samples were excited with a 532 nm pump, the intensity of the near infrared fluorescence decreased lightly. However, when the fiber samples were excited with a 980 nm pump the intensity of the fluorescence increased significantly with the increase of radiation doses (0-2.0 kGy). The intensity of fluorescence decreased when the radiation doses were increased up to 3.0 kGy. furthermore, the fluorescence intensity of the 1410 nm band increased much more than that the 1150 nm band. In addition, the microstructural characteristics of the Bi/Al-codoped silica optical fibers were analyzed using electron spin resonance (ESR). Many radiation-induced defect centers were present, and the intensity of the ESR signals also increased with the increase of radiation doses. The photoluminescence properties and microstructural characteristics were related in the radiated Bi-related silica optical fibers. A possible underlying mechanism for the radiation-induced photoluminescence enhancement process in the Bi/Al-doped silica fiber is discussed.

Formation and photoluminescence property of PbS quantum dots in silica optical fiber based on atomic layer deposition

The PbS Quantum Dots (QDs)-doped silica optical fiber is fabricated using atomic layer deposition (ALD) technique in combination with modified chemical vapor deposition (MCVD) technology. PbS materials are introduced into the fiber core and then formed to QDs in the optical fiber materials during the preparation process. Its structure features and optical properties are investigated. The element distribution and stoichiometry of the core materials are revealed by μ-X-ray absorption near edge structure (μ-XANES), μ-X-ray fluorescent (μ-XRF) and energy dispersive spectrometer (EDS) analysis. The experiment results indicate that PbS QDs are distributed at the region between core and cladding layers with the concentration about 0.11 mol%. High resolution transmission electron microscopy (HRTEM) further reveals the dispersion of PbS QDs is uniform and its nanocrystalline size is about 2-6 nm. This is basically in agreement with the evolution results with effective-mass method. Additionally, PbS QDs-doped optical fiber pumped with 980 nm exhibits photoluminescence property in the 1050-1350 nm range. The special doping fibers will show application potential in optical fiber amplifiers, fiber lasers and optical sensing.

High Sensitivity Refractometer Based on TiO2-Coated Adiabatic Tapered Optical Fiber via ALD Technology

Atomic layer deposition (ALD) technology is introduced to fabricate a high sensitivity refractometer based on an adiabatic tapered optical fiber. Different thicknesses of titanium dioxide (TiO2) nanofilm were coated around the tapered fiber precisely and uniformly under different deposition cycles. Attributed to the higher refractive index of the TiO2 nanofilm compared to that of silica, an asymmetric Fabry–Perot (F-P) resonator could be constructed along the fiber taper. The central wavelength of the F-P resonator could be controlled by adjusting the thickness of the TiO2 nanofilm. Such a F-P resonator is sensitive to changes in the surrounding refractive index (SRI), which is utilized to realize a high sensitivity refractometer. The refractometer developed by depositing 50.9-nm-thickness TiO2 on the tapered fiber shows SRI sensitivity as high as 7096 nm/RIU in the SRI range of 1.3373–1.3500. Due to TiO2’s advantages of high refractive index, lack of toxicity, and good biocompatibility, this refractometer is expected to have wide applications in the biochemical sensing field.

Generation of the First-Order OAM Modes in Single-Ring Fibers by Offset Splicing Technology

A method of generating the first-order orbital angular momentum (OAM) modes in a single-ring fiber is proposed and demonstrated through an all-fiber structure. The first-order OAM modes (L = ±1) refer to a combination of HE21even mode and HE21odd mode. According to the donut-like shape distribution of the HE21 mode, a standard single-mode fiber can be utilized to excite the HE21 mode in the ring fiber by a lateral-offset splicing. By adjusting the polarization of these two modes, the two first-order OAM modes can be excited separately. Based on this simple structure, the OAM modes can be generated in a broadband wavelength ranging from 1540 to 1580 nm. Moreover, the stable transmission of the generated OAM modes in a 7 m long such ring fiber has been demonstrated.