Spinning from Nature:Engineered Preparation and Application of High-Performance Bio-Based Fibers

Many natural fibers are lightweight and display remarkable strength and toughness.These properties originate from the fibers’hierarchical structures,assembled from the molecular to macroscopic scale.The natural spinning systems that produce such fibers are highly energy efficient,inspiring researchers to mimic these processes to realize robust artificial spinning.Significant developments have been achieved in recent years toward the preparation of high-performance bio-based fibers.Beyond excellent mechanical properties,bio-based fibers can be functionalized with a series of new features,thus expanding their sophisticated applications in smart textiles,electronic sensors,and biomedical engineering.Here,recent progress in the construction of bio-based fibers is outlined.Various bioinspired spinning methods,strengthening strategies for mechanically strong fibers,and the diverse applications of these fibers are discussed.Moreover,challenges in reproducing the mechanical performance of natural systems and understanding their dynamic spinning process are presented.Finally,a perspective on the development of biological fibers is given.

Pulse Propagation with Self-Phase Modulation in Nonlinear Chiral Fiber and Its Applications

From Maxwell＇s equations and Post＇s formalism, a generalized chiral nonlinear Schr6dinger equation （CNLSE） is obtained for the nonlinear chiral fiber. This equation governs light transmission through a dispersive nonlinear chiral fiber with joint action of chirality in linear and nonlinear ways. The generalized CNLSE shows a modu- lation of chirality to the effect of attenuation and nonlinearity compared with the case for a conventional fiber. Simulations based on the split-step beam propagation method reveal the role of nonlinearity with cooperation to chirality playing in the pulse evolution. By adjusting its strength the role of chirality in forming solitons is demonstrated for a given circularly polarized component. The application of nonlinear optical rotation is also discussed in an all-optical switch.

Cadmium Selenide Polymer Microfiber Saturable Absorber for Q-Switched Fiber Laser Applications

We demonstrate the generation of a Q-switching pulse train in an erbium-doped fiber laser （EDFL） cavity using a newly developed cadmium selenide （CdSe） based saturable absorber （SA）. The SA is obtained by embedding CdSe nanomaterials into a polymethyl methacrylate （PMMA） microfiber. It is incorporated into an EDFL cavity to generate a Q-switched laser operating at 1533.6nm. The repetition rates of the produced pulse train are tunable within 37–64kHz as the pump power is varied from 34mW to 74mW. The corresponding pulse width reduces from 7.96μs to 4.84μs, and the maximum pulse energy of 1.16nJ is obtained at the pump power of 74mW.

Application of Remote Radio Head over Fiber Technology

The Remote Radio Head (RRH) over Fiber system is a new distributed network coverage mode.It processes the baseband parts concentratively by separating the baseband and Radio Frequency (RF).It moves the RF modules using fibers from the Base Stations (BSs) to the remote RF units.These RF modules are placed on the stations to be covered.This solution saves many equipment rooms required by conventional solutions.Meanwhile,it supports RRH over a large number of fibers through high-capacity macro BSs to realize the conversion between capacity and coverage.In addition,the RRH system also supports the coverage in other situations,such as high-speed railways and ultra-long distance.It is one of the most widely used technologies in the 3G network.

A Novel Fiber Bragg Grating with Triangular Spectrum and Its Application in Strain Sensor

A novel fiber Bragg grating with triangular spectrum is presented. A strain sensor based on this fiber grating is proposed. Experiments showed that the sensor has advantages of high sensitivity, wider measuring range and immunity to fluctuation of the light source power.

Tunable Fiber Gratings and Their Applications

Some practical research topics on tunable fiber gratings in author's group are presented, including tuning speed, tuning range, tuning characteristics of gratings in HB fiber, and the tunability of the line-width. The applications of fiber gratings in communication and sensing are also discussed.

Recent Advances in Holey Fibers and Their Applications

Transmission loss of holey fiber is found to depend on its structure, and to be caused by Rayleigh scattering at glass surface. Under this loss dependence, most promising is optical wiring application, for which fiber designs to realize bend-insensitivity and single-modedness are presented.

A novel dual-wavelength fiber Bragg grating and its application in fiber ring laser

A novel method for fabricating dual-wavelength fiber Bragg gratings (FBGs) by using one phase mask is developed. The method is based on a double-exposure technique. Our technique lends itself to writing gratings with controllable reflectivity and separation of two Bragg wavelengths. A grating with two equal transmission peaks of 20.25 dB is obtained by this method and the separation of the two Bragg wavelengths is about 0.8 nm. With the grating, we demonstrate a dual-wavelength erbium-doped fiber ring laser whose interval of the two peaks is 0.8 nm. The laser’s peak powers can get 3.1 mW above and have a good stability.

Laser Trimming for Adjustment of Grating Offset in Phase-Shifted Fiber Grating Coupler for All-Optical Switching Application

We theoretically investigated laser trimming to adjust grating offset in phase-shifted fiber grating coupler (FGC) for all-optical switching application. It was clarified that the trimming made the extinction ratio higher in all-optical FGC switch.

All-fiberized and narrow-linewidth 5 kW power-level fiber amplifier based on a bidirectional pumping configuration

In this paper,an all-fiberized and narrow-linewidth 5 kW power-level fiber amplifier is presented.The laser is achieved based on the master oscillator power amplification configuration,in which the phase-modulated single-frequency laser is applied as the seed laser and a bidirectional pumping configuration is applied in the power amplifier.The stimulated Brillouin scattering,stimulated Raman scattering,and transverse mode instability effects are all effectively suppressed in the experiment.Consequently,the output power is scaled up to 4.92 kW with a slope efficiency of as high as approximately 80%.The 3-dB spectral width is about 0.59 nm,and the beam quality is measured to be M^(2)~1.22 at maximum output power.Furthermore,we have also conducted a detailed spectral analysis on the spectral width of the signal laser,which reveals that the spectral wing broadening phenomenon could lead to the obvious decrease of the spectral purity at certain output power.Overall,this work could provide a reference for obtaining and optimizing high-power narrow-linewidth fiber lasers.

kW-class high power fiber laser enabled by active long tapered fiber

Compared with traditional uniform fibers, tapered fiber has numerous unique advantages, such as larger mode area,higher pump absorption, suppression to nonlinear effects, and maintaining good beam quality. In this manuscript, we have constructed an all-fiberized fiber amplifier which is based on a piece of ytterbium-doped tapered double-clad fiber(T-DCF). The fiber amplifier is operated under continuous wave(CW) regime at 1080 nm wavelength. The M2 factor of the amplifier at 1.39 k W output power is ～1.8. The maximum output power of the system reached 1.47 k W, which, to the best of our knowledge, is the highest output power of long tapered fiber based fiber laser system. Our result successfully verifies the potential of power scalability and all-fiberized capability of long tapered fiber, and the performance of our system can be further enhanced by fiber design optimization.

302 W triple-frequency,single-mode,linearly polarized Yb-doped all-fiber amplifier

Stimulated Brillouin scattering(SBS) effect is currently the major limitation for the power scaling of singlefrequency/narrow linewidth fiber laser systems. A single-mode linearly polarized all-fiber amplifier system is set up to investigate SBS effect in triple-frequency high-power amplifiers. With this amplifier, up to 302 W output power with 83% slope efficiency is achieved and the SBS threshold is scaled up to 12 d B. To the best of our knowledge, this is the highest output power of multifrequency laser from a single-mode polarization maintaining fiber. Good spectral properties and high brightness make this laser source available for the application of second harmonic generation, coherent beam combining.

Development and prospect of high-power Yb^(3+) doped fibers

Ytterbium-doped fibers have become the optimum gain media of high-power fiber lasers thanks to a simple energy structure, which strongly reduces the excited state absorption, and a low quantum defect and a high optic–optic conversion efficiency, which means the low thermal load. In this paper, we take a review of the current state of the art in terms of Yb^(3+)doped fibers for high-power fiber lasers, including the development of the fabrication techniques. The research work to overcome the challenges for Yb3+doped fibers, which affect the stability of output power and beam quality, will be demonstrated. Direction of further research is presented and the goal is to look for a fiber design, to boost single fiber output power, stabilize the laser power and support robust single-mode operation.