Jinggang Peng

Theoretical study and experimental fabrication of high negative dispersion photonic crystal fiber with large area mode field

We present a systematic process of theoretical design and experimental fabrication of the large mode area and large negative dispersion photonic crystal fiber. An easily fabricated fiber structure is proposed. The influence of structure parameters deviations from the design on the chromatic dispersion are evaluated and a design rule is given. Finally our fabricated fiber and test results are demonstrated. The measured effective area of inner core mode is 40.7 mum(2) which is the largest effective area of high negative dispersion photonic crystal fibers that have been experimentally fabricated. The measured peak dispersion is -666.2ps/(nm.km) and the bandwidth is 40nm.

Ce-Tb-Mn co-doped white light emitting glasses suitable for long-wavelength UV excitation

We report on a new kind of white light emitting glass suitable for long-wavelength ultraviolet excitation by simultaneously emitting blue, green and red fluorescence, which is fabricated by melting of Ce(3+)-Tb(3+)-Mn(2+) co-doped borosilicate glass. The spectroscopic properties of singly, doubly and triply doped glasses have been reported and the energy transfer from Ce(3+) to Tb(3+) and Mn(2+) has also been investigated. By adjusting the concentration of different co-dopants, we obtained the ideal white light emitting borosilicate glass with the color coordinate (x = 0.318, y = 0.333).

Tailoring of clusters of active ions in sintered nanoporous silica glass for white light luminescence

To tailor clusters of active ions in glasses is laborious but critical for obtaining high efficient luminescence. Here, we present a facile method to tailor clusters of active ions by using one kind of porous host, the nanoporous silica glass. The white light-emitting glasses were prepared by sintering of nanoporous silica glasses impregnated with Ce3+, Tb3+, Mn2+ and Al3+ ions. The combination of blue, green and red emissions of Ce3+, Tb3+ and Mn2+ ions in the glasses under ultraviolet light excitation create white light emissions. The fluorescence of the glasses under long-wavelength ultraviolet excitation are dependent on energy transfer processes between the active ions; and the Al3+ plays a key role in adjusting of the energy transfer processes.

Enhanced green luminescence in Ce-Tb-Ca codoped sintered porous glass.

We report on a new kind of green-emitting high silica luminous glass, which is fabricated by sintering of Ce(3+)-Tb(3+) co-doped porous glass. The spectra show that there are energy transfer between Ce(3+) and Tb(3+), and cross-relaxation between (5)D(3) and (5)D(4) energy level of Tb(3+). The energy transfer process can be adjusted by addition of Ca(2+) into the Ce(3+)-Tb(3+) co-doped porous glass, and the transfer rate can be enhanced about four times than that of Ce(3+)-Tb(3+) co-doped porous glass. The role of Ca(2+) has been discussed, and the fluorescence decay curve reveals that the Ca(2+) play an important role in energy transfer.

Investigation on radiation resistance of Er/Ce co-doped silicate glasses under 5 kGy gamma-ray irradiation

Various Er/Ce co-doped SiO2-Al2O3-CaO glasses are prepared by the melt-quenching method. The radiation resistance of Er/Ce co-doped glasses is investigated under 5 kGy gamma-ray irradiation. The absorption spectra, up-conversion spectra, fluorescence intensity and lifetime of Er/Ce co-doped glasses before and after irradiation are measured and analyzed in details. The radiation induced absorption (RIA) of the Er/Ce co-doped silicate glasses can be suppressed due to Ce ions co-doping. The fluorescence intensity and lifetime of Er/Ce co-doped glasses have no apparent change after irradiation. Furthermore, the possible mechanism of Ce effect on the radiation resistance improvement is discussed. The result indicates that Er doped glasses with an optimal Ce concentration introduction can be used as active medias for radiation-resistant materials in harsh radiation environments.

793 nm pump induced photo-bleaching of photo-darkened Yb 3+ -doped fibers

We report on the strong photo-bleaching of the photo-darkening (PD) induced loss under the cladding pump of a 793 nm laser diode (LD) in double clad Yb-doped fibers. Up to 68% PD loss at 810 nm was bleached. The bleaching rates under different powers show that the higher pump power corresponds to the more bleached loss within the same time. Moreover, repeatable processes of PD and photo-bleaching were observed when alternately pumped with 915 and 793 nm LDs. Furthermore, it was found that simultaneously pumping the fiber with 915 and 793 nm LDs can suppress about 80% PD loss, compared with pumping the fiber only with 915 nm LD. The mechanism of photo-bleaching under 793 nm pump was also discussed.

A hollow beam supercontinuum generation by the supermode superposition in a GeO 2 doped triangular-core photonic crystal fiber

A GeO2 doped triangular-core photonic-crystal fiber (PCF) is designed and fabricated to allow the generation of a hollow beam through a nonlinear-optical transformation by femtosecond pulses at 1040 nm from a high power Yb-doped PCF laser oscillator. The hollow beam supercontinuum is obtained at far field by adjusting incident light polarization to excite the high order supermode, behaving as a mode convertor. The supercontinuum ranging from 540 to 1540 nm is achieved with an average power of 1.04 W.

Yb³⁺-doped large core silica fiber for fiber laser prepared by glass phase-separation technology.

We report on the preparation and optical characteristics of an Yb(3+)-doped large core silica fiber with the active core prepared from nanoporous silica rod by the glass phase-separation technology. The measurements show that the fiber has an Yb(3+) concentration of 9811 ppm by weight, a low background attenuation of 0.02 dB/m, and absorption from Yb(3+) about 5.5 dB/m at 976 nm. The laser performance presents a high slope efficiency of 72.8% for laser emission at 1071 nm and a low laser threshold of 3 W within only 2.3 m fiber length. It is suggested that the glass phase-separation technology shows great potential for realizing active fibers with larger core and complex fiber designs.

All fiber M-Z interferometer for high temperature sensing based on a hetero-structured cladding solid-core photonic bandgap fiber.

We proposed and experimentally demonstrated a high temperature fiber sensor using a hetero-structured cladding solid-core photonic bandgap fiber (HCSC-PBGF) for the first time to our knowledge. A hetero-structured cladding solid-core photonic bandgap fiber is designed and fabricated that supports vibrant core mode and cladding mode transmission. Then, an all fiber M-Z interference sensor is constructed by splicing single mode fiber at both ends of HCSC-PBGF without any other micromachining. The transmission characteristics of HCSC-PBGF are analyzed with a full-vector beam propagation method and a full-vector finite element method, and the simulation results are consistent with experiment results. The sensitivity of this fiber sensor is as high as 0.09 nm/°C when operating from room temperature to 1000 °C, and the fringe contrast keeps stable and clear. It is obvious that this all fiber sensor will have great application prospects in fiber sensing with the advantages of a compact structure, high sensitivity, and cost-effectiveness.

Mitigation of photodarkening effect in Yb-doped fiber through Na^+ ions doping

In this work, Na+ ions doping into the Yb-doped fiber is proposed to improve the photo-darkening resistance. The results show that the photo-darkening induced excess loss at equilibrium state at 633nm, 702 nm, 810 nm, and 1041 nm is 115.54dB/m, 86.87dB/m, 25.51 dB/m, 2.92 dB/m, respectively, when co-doping with Na+ ions. More than 30% excess loss is reduced comparing to the Yb-doped fiber without Na+ ions. The mechanism of Na+ ions doping to mitigate the PD excess loss is discussed. Besides, we measured the laser efficiency of Yb/Al/Na co-doped fiber to be 76.1%. This result remains almost the same with Yb-doped fiber and proves that the addition of Na+ ions do not deteriorate the fiber slope efficiency. The background loss of the two fibers also stays close. The results indicate this method is promising in high power fiber laser development.