Design of dispersion-compensating fibers based on a dual-concentric-core photonic crystal fiber

A photonic crystal fiber based on a particular periodic arrangement of airholes and pure silica is designed for chromatic dispersion compensation. A two-concentric-core structure is obtained by introducing two different sizes of capillaries (for the airholes) and exhibits very high negative chromatic dispersion [-2200 ps/(nm km) at 1550 nm]. The variation of optogeometric parameters is also investigated to evaluate the tolerance of the fabrication. Finally, the bending influence on the modal characteristics shows that it is possible to tune the phase-matching wavelength over the C band by adjusting the diameter of the fiber.     

Broadband dispersion-compensating photonic crystal fiber

We present a modified dual-core photonic crystal fiber, based on pure silica, with special grapefruit holes in the inner cladding. The fiber has large, broadband negative dispersion, and the dispersion value varies linearly from -380 t o-420 ps/(nm km) in the C band. To decrease the fabrication difficulty, large air holes are adopted. Furthermore, the chromatic dispersion of the fiber is not sensitive to the structure parameters. So the proposed fiber structure can greatly facilitate fiber drawing and can be used for broadband dispersion compensation.     

A global design of an erbium-doped fiber and an erbium-doped fiber amplifier

A global design of an erbium-doped fiber and an open-loop erbium-doped fiber amplifier (EDFA) in a steady-state operation is discussed by applying genetic algorithms. Taking a signal gain and a bandwidth as objective functions, 7 parameters of the EDFA (erbium concentration, core radius, erbium-doped radius, refractive index difference, fiber length, pumping wavelength and signal power) are optimized by solving optical propagation equations, assuming a homogenous two-level active medium and a single-mode propagation. There is evidence to show that the 1480 nm pump utilized in usual EDFAs is not an optimal choice, which should be chosen around 1460 nm. The optimal core radius ranges 0.465–0.548 μm on pumping power 50–200 mW. Under different design objects and with different pumping powers, however, there are different optimal Er-doped concentrations, reflective index differences and fiber lengths. As a single fiber EDFA, 35 dB signal gain or 35 nm bandwidth is obtained with the 7 optimal parameters, 100 mW pumping power and 0.001 mW input signal power.     

Dispersion-free fiber transmission for femtosecond pulses by use of a dispersion-compensating fiber and a programmable pulse shaper

We demonstrate nearly distortionless 2.5-km fiber transmission of sub-500-fs pulses, using a combination of standard single-mode fiber, dispersion-compensating fiber, and a programmable pulse shaper for simultaneous quadratic and cubic dispersion compensation. The dispersion-compensating fiber corrects the bulk of the quadratic and the cubic phases for the single-mode fiber, and the fiber-pigtailed programmable pulse shaper exactly compensates the residual dispersion terms. Together these elements permit complete recompression of pulses, which first broaden by ~400 times in the single-mode fiber.     

基于色散补偿光纤的高速光纤光栅解调方法

本文提出并论证了一种光纤光栅高速解调的新方法, 利用色散补偿光纤的色散效应, 将光纤光栅的波长漂移信息转换成时域信息. 采用脉冲激光器作为光源, 仅需一个光脉冲可获取单根光纤上所有光纤光栅的反射光脉冲, 再根据各个光栅反射回光脉冲的延时变化即可实现波长的解调. 本方法可用于准分布光纤光栅传感网络解调, 系统采用全光纤结构, 无需波长扫描, 大大提高了解调速度. 本文搭建了测试系统进行实验验证, 对3个光纤光栅组成的准分布式传感网络进行了解调, 实验结果表明, 解调出的光纤光栅布喇格波长线性度好, 解调速度最高可达1 MHz, 采样数据取10次平均后解调线性度可达0.9969, 解调误差约为27.8 pm.     

Numerical analysis and optimization of a dual-concentric-core photonic crystal fiber for broadband dispersion compensation

In this article, a novel dual-concentric-core photonic crystal fiber (DC-PCF) for dispersion compensation is presented. The proposed DC-PCF has relatively high negative dispersion over a wide wavelength range, which covers E, S, C, L and U telecommunication wavelength bands. The validity of the proposed design is carried out by employing a 2-D finite difference frequency domain method (FDFD) with perfectly matched layers (PML). By using the numerical method, the dispersion profile of the DC-PCF is optimized in terms of three air-hole diameters to achieve desirable negative dispersion. The influence of the location of ring-core, the number of air-hole rings on dispersion and loss characteristics are also studied.     

Tunable multi-wavelength fiber laser based on a polarization-maintaining erbium-doped fiber and a polarization controller

A stable and tunable multi-wavelength fiber laser with a polarization-maintaining erbium-doped fiber (PM-EDF) and a polarization controller (PC) is proposed and demonstrated. A homemade PM-EDF incorporated in the ring cavity is used as the gain medium. Simultaneous multi-wavelength oscillation is achieved at room temperature. The theory of the PM-EDF and PC to suppress the wavelength competition is described in detail. The 3 dB bandwidth is less than 0.01 nm. The power fluctuation and wavelength shift are measured to be less than 0.5 dB and 0.05 nm over 32 min. The wavelength tuning between single-, double-, triple-, and four-wavelength is realized.     

Visible continuum generation using a femtosecond erbium-doped fiber laser and a silica nonlinear fiber

Supercontinuum extending to visible wavelengths is generated in a hybrid silica nonlinear fiber pumped at 1560 nm by a femtosecond, erbium-doped fiber laser. The hybrid nonlinear fiber consists of a short length of highly nonlinear, germano-silicate fiber (HNLF) spliced to a length of photonic crystal fiber (PCF). A 2 cm length of HNLF provides an initial stage of continuum generation due to higher-order soliton compression and dispersive wave generation before launching into the PCF. The visible radiation is generated in the fundamental mode of the PCF.     

Novel split-band erbium-doped fiber amplifier

In this paper we design a 120 nm bandwidth erbium-doped fiber amplifier using a seed light injection method for the first time. It is shown that when the wavelength of the seed light varies from 1520 to 1570 nm, the gain at 1610 nm reaches maximum near 1553 nm and increases as the seed light power. Based on the method, a novel split-band EDFA configuration is designed. The split-band architecture employs a 1550/1610 nm waveband multiplexer/demultiplexer and two independent sub-bands which pass in parallel through separate branches of the optical amplifier. The signals at independent sub-bands are combined and flattened before output, resulting in a broadband gain-flattened optical amplifier with 120 nm bandwidth.     

Design of dispersion-compensating Bragg fiber with an ultrahigh figure of merit

We report a novel idea for achieving highly efficient dispersion-compensating Bragg fiber by exploiting a modified quarter-wave stack condition. Our Bragg fiber yielded an average dispersion of approximately -1800 ps/(nm km) across the C band for the fundamental TE mode and an ultrahigh figure of merit of approximately 180,000 ps/(nm dB), which is at least 2 orders of magnitude higher than that of conventional dispersion-compensating fibers. The proposed methodology could be adopted for the design of a dispersion compensator across any desired wavelength range.     

铋基掺铒光纤放大器宽带放大特性的理论研究

研制了铋酸盐基质掺铒玻璃43Bi2O3-30B2O3-27SiO2,测试分析了玻璃中Er3+离子的光谱性质。结合获得的Er3+离子光谱参数,建立了一个以该铋基掺铒玻璃作为放大器增益介质时Er3+离子跃迁的三能级理论模型,研究了铋基掺铒玻璃光纤放大器(Bi-EDFA)的信号放大特性。研究显示,单波长输入情形下,Bi-EDFA具有大于40dB的信号增益和75nm的3dB波长带宽。同时,相比于硅基掺铒光纤放大器(Si-EDFA),Bi-EDFA具有优异的多波长信号宽带放大和低噪声特性,低噪声系数(~5.5dB)可维持至1610nm波长之外。结果表明,铋基掺铒玻璃光纤放大器是一种单位长度增益极高和宽带放大能力的小型化掺铒光纤放大器,适合于WDM系统的集成化需求。     

A twin-core erbium-doped fiber amplifier

We propose a twin-core erbium-doped optical fiber amplifier. It has the advantage over the conventional single core erbium-doped fiber amplifier in that it has a flat gain characteristic over a wide bandwidth, i.e. within 30 nm. By adjusting the pump power launched into one of the cores, the gain characteristic can be tuned.     

Transmission capacity of erbium-doped fiber amplifiers as a criterion for quality of erbium-doped optical fibers

A new criterion—transmission capacity in the unsaturated gain regime—is proposed for comparing the quality of glasses for erbium-doped fiber amplifiers, considered as an element of an optical communication system. It is shown that, according to the criterion for the highest transmission capacity, amplifiers based on alumino-phosphate-silicate and zinc-sodium-germanate-silicate fibers are preferred for systems with separate C and L bands, respectively. In broadband systems, the highest transmission capacity is observed in amplifiers based on tellurite fibers.     

Switchable triple-wavelength erbium-doped fiber laser using a single fiber Bragg grating in polarization-maintaining fiber

A stable and narrow wavelength spacing multiwavelength erbium-doped fiber laser is proposed and demonstrated. The laser can produce simultaneous dual- and triple-wavelength lasing oscillations with a narrow wavelength spacing of less than 0.1 nm via using a single fiber Bragg gratings written in polarization-maintaining (PM) fiber. By adjusting polarization controller, the wavelength spacing of dual-wavelength lasing oscillations can be tuned to as small as 0.032 nm. The maximum amplitude variation for every lasing wavelength is less than 0.5 dB. The room-temperature operation principle is based on the polarization hole burning and deeply saturated effect in an ordinary erbium-doped fiber ring laser (EDFRL). The laser has the advantages of simple all-fiber configuration, low cost, high stability and operating at room temperature.     

Single-longitudinal-mode erbium-doped fiber laser based on a fiber Bragg grating Fabry-Perot filter

A novel single-longitudinal-mode (SLM) erbium-doped fiber laser with a simple linear cavity based on a fiber Bragg grating Fabry-Perot filter (FBG-FPF) and a narrowband (～0.06 nm) FBG is proposed and demonstrated experimentally. Two uniform FBGs form the FBG-FPF, which has two ultranarrow transmission bands with a bandwidth of 0.12 pm and a wavelength spacing of 0.095 nm. By slightly tuning the central wavelength of the narrowband FBG, SLM lasing at 1549.658 or 1549.563 nm (corresponding to the two transmission peaks of the FBG-FPF) is achieved with a laser output power of ～4 mW, when the pump power is ～75 mW.     

High-energy single-transverse-mode Q-switched fiber laser based on a multimode large-mode-area erbium-doped fiber

We demonstrate that appropriately designed doped multimode fibers provide robust single-mode output when used within a fiber laser cavity. Using a novel large-mode-area fiber, we demonstrate what we believe to be record single-mode (M(2) <1.2) pulse energies of >0.5 mJ from a Q -switched fiber laser and even higher pulse energies (as high as 0.85 mJ) with slightly compromised spatial-mode quality (M(2)<2.0) . This approach offers significant scope for extending the range of single-mode output powers and energies that are achievable from fiber-laser-amplifier systems.     

Coherent combining of tunable erbium-doped fiber lasers by a single-mode fiber feedback loop

We experimentally demonstrate the coherent combining of two tunable erbium-doped fiber lasers by using a single-mode fiber feedback loop configuration. A single-mode fiber is arranged in the feedback loop to filter the far-field pattern, and the energy of desired in-phase mode is collected and injected into the resonators of two component fiber lasers. The coherently combined laser is tunable over a wide spectrum ranging from 1536 to 1569 nm, which means that the combining scheme is compatible with wavelength tuning. The effects and necessity of whether adopting polarization controlling measures or not in component lasers are investigated in detail. The results indicate that adding polarization controlling can improve the array＇s coherence, whereas it will decrease the output power and efficiency simultaneously.     

Optimization of erbium-doped fiber MOPA laser

An erbium-doped fiber laser (EDFL) constructed in a master oscillator and power amplifier (MOPA) configuration is analyzed. The pump powers for the fiber cavity laser and the booster amplifier stages are managed properly to achieve maximal pump conversion efficiency. Our design achieves a pump conversion efficiency of 91.4%, corresponding to a quantum efficiency of 96.6%, for a 1565.8 nm MOPA laser pumped by a total power of 300 mW at 1480 nm. The optimized MOPA laser shows a 25% enhancement in the pump conversion efficiency, compared to a non-MOPA fiber laser. A side lobe suppression ratio of 48 dB for the optimized MOPA laser is observed.     

Bismuth-based erbium-doped fiber as a gain medium for L-band amplification and Brillouin fiber laser

Bismuth-based erbium-doped fiber (Bi-EDF) is demonstrated as an alternative medium for optical amplification and nonlinear applications. The bismuth glass host provides the opportunity to be doped heavily with erbium ions to allow a compact optical amplifier design. The bismuth-based erbium-doped fiber amplifier (Bi-EDFA) is demonstrated to operate at wavelength region from 1570 to 1620 nm using only a 215 cm long of gain medium. The maximum gain of 15.8 dB is obtained at signal wavelength of 1610 nm with the corresponding noise figure of about 6.3 dB. A multi-wavelength laser comb is also demonstrated using a stimulated Brillouin scattering in the 215 cm long Bi-EDF assisted by the 1480 nm pumping. The laser generates more than 40 lines of optical comb with a line spacing of approximately 0.08 at 1612.5 nm region using 152 mW of 1480 nm pump power.     

Figure-eight actively-passively mode-locked erbium-doped fiber laser

The advantages of using nonlinear optical loop mirror (NOLM) to compress pulse with slight amplitude fluctuation and reflected energy loss are analyzed in theory. Experimentally the NOLM is placed in an actively mode-locked erbium-doped fiber ring laser to form a figure-eight actively and passively mode-locked fiber laser. 12 ps mode-locked pulses centered at 1.543 μm were obtained with the modulation frequency of 2.498748700 GHz. 3.715 mW output power is achieved with 50 mW pump power.