Self-seeded multi-wavelength Brillouin–erbium fibre laser with 20 GHz frequency gap

We demonstrate a self-seeded multi-wavelength Brillouin–erbium fibre laser with double Brillouin frequency gap. The twice channel gap is induced by the gain difference in different directions. Thirty-six stable output channels with 20?GHz frequency gap are obtained when the 980?nm pump power is 300?mW. The factor that induces the double frequency gap is investigated and proved.     

Wavelength-switchable C-band erbium-doped fibre laser incorporating all-fibre Fabry–Perot interferometer fabricated by chemical etching

A switchable and stable triple-wavelength, ring-cavity, erbium-doped fibre laser incorporating an all-fibre Fabry–Perot interferometer (FPI) is designed and experimentally demonstrated. In the proposed fibre laser, the all-fibre FPI is fabricated using the chemical etching method and is used to generate the filter effect. The laser threshold is 88 mW. Switchable single-wavelength lasing at 1529.9, 1545.1 and 1560.2 nm can be realized with a power fluctuation less than 0.64 dB under 20 min of scanning time at room temperature. In addition, the wavelength-switchable dual-wavelength lasers can be tuned by changing the polarization state in the experiment, and the maximum power fluctuations for the 1545.1 and 1560.2 nm lasers are less than 1.19 and 1.57 dB at 26 °C, respectively. Furthermore, a triple-wavelength laser is obtained by adjusting the polarization controller. The results demonstrate that switchable single-, dual-, or triple-wavelength lasers can be generated through the proposed fibre laser.     

An optical fibre tip with double tapers etched by the interfacial layer

We fabricate double-tapered optical fibre tips by the interfacial layer etching method. The optical fibre is first etched by means of meniscus-based etching to obtain one-tapered fibre tip, which is etched again by the interfacial layer between the etchant and the overlay to obtain a double-tapered tip. The formation mechanism of the second taper is analysed. The impacts of the interfacial layer etching time, HF concentration and the overlay on the second cone angle are discussed. The second cone angle can be controlled by the interfacial layer etching time and the overlay. But the HF concentration has few impacts on the second cone angle. The double-tapered fibre tips can be applied for the contactless trapping of particles.     

All-fibre Mach–Zehnder interferometer based on seven-core and coreless fibres for generating stable wavelength-switchable laser

In order to realize a wavelength-tuneable fibre-laser output, a ring-cavity erbium-doped fibre laser based on an all-fibre Mach–Zehnder interferometer (MZI) is proposed and experimentally tested. The MZI consists of a single-mode fibre, two segments of coreless fibre, and a seven-core fibre. For the proposed fibre laser, the length of the gain medium is 4?m and the lasing threshold is 75?mW. By adjusting the loss of the laser cavity, switchable single-wavelength laser emission is realized across the range of 1527.6–1549.9?nm and the wavelength interval is less than 2.4?nm; the peak power difference of each lasing wavelength is less than 7.9?dB. Tuneable dual- and three-wavelength laser outputs were obtained by adjusting the polarization controller. The 3-dB linewidth was less than 0.57?nm. The single- and dual-wavelength laser output power fluctuations were less than 1.4 and 1.7?dB, respectively, when monitored over a period of 30?min.     

Switchable triple-wavelength thulium-doped fibre laser based on a Mach–Zehnder interferometer and fibre ring filter

A switchable triple-wavelength thulium-doped fibre laser based on an all-fibre Mach–Zehnder interferometer and fibre ring filter with a polarization-maintaining fibre is proposed and experimentally demonstrated. In the proposed fibre laser, a Mach–Zehnder interferometer comprising two 1 × 2 optical couplers is inserted into the optical cavity to produce the comb filter effect. The fibre ring filter comprises two optical couplers with a 3:7 splitting ratio and a 2-m-long polarization-maintaining fibre to improve lasing stability. Single-wavelength lasing can be tuned continuously from 1864.4 to 1884.5 nm, and five different modes of dual-wavelength and switchable triple-wavelength lasers can be realized by changing the polarization state. The signal-to-noise ratios of all lasers are more than 33 dB. The maximum power fluctuations and wavelength variations are less than 1.5 dB and 0.3 nm at room temperature, respectively, and the 3 dB bandwidth is less than 0.2 nm. The results demonstrate that stable and switchable single- or dual-wavelength lasers can be generated using the designed fibre laser.     

A dual modality optical fiber sensor

We propose and demonstrate a fibre optic system based on bi-tapered silica fibre that can simultaneously measure strain and fibre curvature. Both modalities on the signal can be extracted with no measurable crosstalk between them. The experimental signal has a pure phase modulation when strain is applied to the tapered fibre optic section of the sensor and the signal shows only intensity modulation when an un-tapered fibre section is bent. High sensitivity is achieved from the experimental results for strain and bending losses and the estimation of measurement errors is 0.2 and 0.1%, respectively. This system offers low-cost, compactness and it can be adapted for structural health monitoring.     

Broadband amplifier and high performance tunable laser with an extinction ratio of higher than 60 dB using bismuth oxide-based erbium-doped fiber

A Bi₂O₃-based erbium-doped fiber (Bi-EDF) ring laser with a 70?nm tunable range is demonstrated with a 49?cm long Bi-EDF in which tuning range can be extended to larger than 100?nm using an optical switch to alter the length of Bi-EDF in the laser cavity. With an extinction ratio of better than 60?dB throughout the entire tuning range, the measured FWHM of laser lines are measured to be 0.09?nm. In addition, the common amplification parameters are measured and studied in detail for various pumping configurations.     

TiCN作为可饱和吸收体的2.8 μm被动调Q锁模光纤激光器

本文报道了一种基于材料可饱和吸收的2.8 μm被动调Q锁模掺铒氟化物光纤激光器。通过将TiCN颗粒作为可饱和吸收体直接涂覆于反射腔镜,并结合氟化物光纤垂直端面的输出耦合,实现了具有较低激光阈值和紧凑腔结构的2.8 μm脉冲光纤激光器。该激光器在泵浦功率达到330 mW时,开始出现调Q锁模脉冲。随着泵浦功率持续增大,调Q脉冲包络重复频率从14.34 kHz增加至32.57 kHz,对应的脉冲宽度从10.51 μs减小至5.40 μs。在650 mW的泵浦功率下,获得最大平均输出功率25.83 mW,斜率效率为7.2%。     

A generation of 2 μm Q-switched thulium-doped fibre laser based on anatase titanium(IV) oxide film saturable absorber

We demonstrate a Q-switched thulium-doped fibre laser operating at approximately 1935 nm wavelength using anatase titanium(IV) oxide (TiO₂) embedded in polyvinyl alcohol as the passive newly saturable absorber (SA). The film has absorption loss of 3.5 dB and modulation depth of 33%. It is sandwiched between two fibre ferrules in a ring laser cavity to produce self-started pulse train with a repetition rate that is tuned from 30.12 to 36.96 kHz as the 1552-nm pump power is increased from 289 to 485 mW. At maximum pump power, the laser produced a Q-switching pulse train with pulse duration, output power, pulse energy and peak power of 1.91 μs, 11 mW, 0.3 μJ and 146 mW, respectively. These results show that the TiO₂ is a new potential SA material for pulsed laser applications.     

Wavelength switchable L-band erbium-doped fiber laser employing C-band EDFA as gain medium

A new structure for the L-band multiwavelength switchable erbium-doped fiber laser is proposed. Overlapping laser cavities are formed by cascading fiber Bragg gratings as reflectors in a ring structure with a C-band EDFA as a common gain medium. The proposed laser is made to be wavelength-switchable by individually adjusting the loss of each overlapping cavity. Instead of using an L-band EDFA as the gain medium in the L-band fiber laser, we have experimentally demonstrated that by tailoring the gain of the C-band EDFA to have a significant gain tilt in the L-band, a lasing power efficiency of 26% can be achieved over a wide range of switchable lasing wavelengths. Following this optimal design, the side-mode suppression ratio and the minimal separation between two switchable lasing wavelengths were found to be over 42 dB and 0.33 nm, respectively.     

Phase equilibria diagrams,crystal growth peculiarities and Raman investigations of lead and sodium-bismuth tungstate–molybdate solid solutions

In this paper a comprehensive study of lead and sodium-bismuth tungstate–molybdate solid solutions was carried out, including the clarification of their structural peculiarities and phase diagrams of PbMoO₄–PbWO₄ and NaBi(MoO₄)₂–NaBi(WO₄)₂ systems, the study of spontaneous Raman spectra of these compounds, as well as preliminary experiments on single crystals growth of lead tungstate–molybdate. The linewidths, peak and integral intensities of the totally symmetric Raman vibrations of solid solutions were estimated in comparison with known SRS-active crystals. The conditions of the Czochralski growth of optically transparent lead tungstate–molybdate mixed crystals were found and SRS effect was observed in these crystals when pumping by 12 ns 1064 nm laser pulses.