Gain dynamics of 14xx-nm-pumped thulium-doped fiber amplifier

Upconversion pumping in the 14xx-nm range gives the thulium-doped fiber amplifier (TDFA) a 3-dB dynamic range of 15 dB, and transient power excursion much lower than the conventional erbium-doped fiber amplifier during dynamic wavelength add-drop, due to the energy transitions inherent to the Tm/sup 3+/ ion. For specific pumping scheme and operating conditions, gain increases with increasing signal input, a behavior significantly different from conventionally optical amplifiers. This phenomenon is studied experimentally and theoretically, and promises to provide insight for gain control algorithms for TDFAs under bursty traffic conditions in a metropolitan area network environment.     

Hybrid fiber amplifiers consisting of cascaded TDFA and EDFA for WDM signals

The detailed gain characteristics of hybrid fiber amplifiers that consist of cascaded thulium-doped fiber amplifiers (TDFAs) and erbium-doped fiber amplifiers (EDFAs) are reported. The experimental results showed that the hybrid amplifiers have gains of over 20 dB with the bandwidth of more than 80 nm in the wavelength range between 1460 and 1560 nm. The low noise figure (NF) below 7 dB was obtained in 1460-1540 nm when placing a TDFA in the first stage followed by an EDFA and in 1480-1560 nm when placing amplifiers in a reversed order. The gain of TDFA and EDFA was optimized for minimizing the gain variation ratio (GVR=(maximumgain-minimumgain)/minimumgain: in the unit of decibels) of the hybrid amplifiers, and it could be minimized to less than 0.4 for the amplifiers that have gain in the wavelength region from 1460 to 1537 nm. The gain-equalization technique was applied, and the hybrid amplifier that had an average gain of 20 dB, a gain excursion of less than 2 dB, an output power of 14.5 dBm, and an NF of less than 7 dB in the 77-nm gain band was achieved.     

Transient gain behavior in 1050/1550-nm dual-wavelength pumped TDFAs

We present an experimental study on transient events in 1050/1550-nm dual-wavelength pumped thulium-doped fiber amplifiers (TDFAs)-a promising candidate for S-band telecommunication applications. For appropriate power ratios of the two pump wavelengths, transient excursions due to signal add-drop are comparable to those in single-wavelength pumped TDFAs. Pump modulation effects, however, more severely impact the signal gain. With our experimental results, it should be possible to develop transient gain suppression control loops for this TDFA type.     

Novel Gain Spectrum Control Method Employing Gain Clamping and Pump Power Adjustment in Thulium-Doped Fiber Amplifier

In this paper, we propose a novel method for controlling the gain spectrum of a thulium-doped fiber amplifier (TDFA) in the S-band. The conventional gain spectrum control method used for a silica erbium-doped fiber amplifier (EDFA) cannot be applied to TDFAs because of the complicated fluctuation of the TDFA gain spectrum. Our proposed method controls the gain spectrum by a combination of gain clamping and pump power adjustment. The algorithm for the method is as simple as that for the conventional EDFA gain spectrum control method. Furthermore, we describe a function for correcting the gain excursion generated by the incorporation of amplified spontaneous emission (ASE) at a signal monitoring photodiode (PD). We achieved a gain excursion of 0.35 dB against a total input signal power of 32 to 2 dBm.     

Tm-doped fiber amplifiers for 1470-nm-band WDM signals

We describe the gain characteristics of thulium-doped fiber amplifiers (TDFA) for wavelength division multiplexing (WDM) signals. We optimized the TDF length and the ratio between the forward and backward pump power to realize efficient amplification. The TDFA achieved a gain of over 20 dB and a noise figure of less than 6 dB in the 1353-1483 nm wavelength region at a total pump power of 300 mW for WDM signals input at a total power of -7 dBm.     

1064 nm抽运掺铥光纤放大器增益特性的理论研究

从掺铥光纤放大器的速率方程组和光传输方程出发 ,引入光场与掺杂分布的重叠因子 ,利用数值法分别模拟计算了光纤掺杂浓度、长度和抽运功率等参数对放大器增益的影响 ,并计算了一定掺杂浓度和抽运功率下的最佳光纤长度及其对应的增益 ,分析了该类放大器增益随输入信号功率的变化关系 ,并计算了其功率转换效率。     

Segmented-clad fiber design for inherently gain-flattened L/sup +/-band TDFA

We present here an efficient design for high gain, inherently gain-flattened L/sup +/-band thulium-doped fluoride fiber amplifier (TDFA), based on a novel segmented clad fiber refractive index profile. Detailed simulations show that the designed amplifier is able to achieve 20-dB gain, with /spl plusmn/0.7-dB gain ripple over 40-nm bandwidth (1600-1640) nm. Performance comparisons of the proposed module with an L/sup +/-TDFA based on conventional W-fiber designs and on a conventional step-index fiber have also been carried out.     

Novel pumping schemes for fluoride-based thulium-doped fiber amplifier at 690 and 1050 nm (or 1400 nm)

Signal amplification in the S- and S/sup +/-band is demonstrated for the first time by simultaneous pumping of thulium-doped fiber amplifier (TDFA) with 690 and 1050 nm (or 1400 nm). Both pumping schemes are investigated and shown to be highly efficient: Roughly 20 dB of signal gain is available with only 80 mW of 1050 nm plus 42 mW of 690 nm, while signal input power is fixed at -35 dBm. Furthermore, these excitations can take advantage of low-cost readily available pump laser diodes at 690 nm for digital video disk applications. This makes TDFA a promising candidate for coarse wavelength-division-multiplexing applications in metropolitan area network and access network environment.     

Dual-wavelength (1050 nm +1550 nm) pumped thulium-doped fiber amplifier characterization by optical frequency-domain reflectometry

We present experimental results of distributed gain measurements from a dual-pumped (1050 nm +1550 nm) thulium-doped fiber amplifier using optical frequency-domain reflectometry. We show that significant reductions in total pump power and/or fiber length are realized with the addition of a few milliwatts at 1550 nm. For our experimental conditions, the addition of 5 mW of 1550 nm allows for a reduction of 100 mW of pump power at 1050 nm or a reduction of 44% of doped fiber length to reach the same gain as with 1050-nm pumping alone.     

Characterization of efficient dual-wavelength (1050 + 800 nm) pumping scheme for thulium-doped fiber amplifiers

We report on the characterization of a recently introduced dual-wavelength pumping scheme for thulium-doped fiber amplifiers using 800 and 1050 nm. Using a counterpropagating pump configuration, 180 mW of total pump power yielded 27-dB small-signal gain and less than 5-dB noise figure. Furthermore, using optical frequency domain reflectometry, the distributed gain in this configuration was evaluated, allowing for optimization of the doped fiber length.     

An optical fiber amplifier for wide-band wavelength range around1.65 μm

The optical amplification characteristics of a 0.781-μm pumped thulium-doped fiber in the wavelength range of 1.6-1.7 μm are discussed. A maximum net gain of 2.0 dB was obtained for 1.69-μm operation. This optical fiber amplifier is suitable for in-service monitoring and identifying fibers operating at 1.2-1.6 μm     

Laser-diode-pumped highly efficient gain-shifted thulium-dopedfiber amplifier operating in the 1480-1510-nm band

We have developed a gain-shifted thulium-doped fiber amplifier (TDFA) with a high optical efficiency (29%) and a high output power (+21.5 dBm) operating in the 1480-1510-nm wavelength band by employing a novel laser diode pumping scheme of 1.4 and 1.56 μm. The results we obtained confirm the feasibility of applying our gain-shifted TDFA to practical wavelength-division-multiplexing (WDM) networks     

High-resolution distributed-gain measurements in erbium-dopedfibers

For the first time, the distributed gain along erbium-doped fibers was measured with high-resolution reflectometry. The coherent optical frequency-domain reflectometry detection technique intrinsically filters amplified spontaneous emission, allowing precise measurements of Rayleigh backscattering levels and nondestructive determination of the optimum length of the doped fiber for different pump and probe conditions     

Theoretical and experimental investigation of a resonantly pumpedthulium doped fluorozirconate fiber amplifier at around 810 nm

The potential of thulium-doped fluorozirconate fibers to provide an efficient AlGaAs diode pumped traveling wave amplifier at wavelengths around 810 nm is investigated. The authors present calculations and experimental measurements of the small signal gain when excitation is resonant with the upper laser level, with a view to predicting the upper limits of performance for optimized fiber design. The theoretical treatment involves numerical determination of the evolution of pump and signal power (and hence gain) along the length of the fiber as a function of wavelength, spectral lineshapes and lifetimes, and geometrical factors. Amplification over the range 800-830 nm has been achieved in multimoded fiber with a best observed gain of 22 dB at 806 nm     

Highly Efficient S-Band Thulium-Doped Fiber Amplifier Employing High-Thulium-Concentration Doping Technique

In the paper, we describe in detail a highly efficient S-band thulium-doped fiber amplifier (TDFA) employing a high-thulium-concentration doping technique. A TDFA with a dual-pass configuration is superior to a TDFA with a single-pass configuration with regard to power-conversion efficiency, whereas it is inferior with regard to noise figure (NF). We propose a cascaded configuration consisting of a single- and double-pass configuration, which provides high efficiency and a low NF. The configuration generated no interference noise, which can result from multipass interference (MPI) with a double-pass configuration. We achieved gains exceeding 26 dB and NFs of less than 7 dB in the 1480-1510-nm wavelength region (30-nm bandwidth). Furthermore, an 8 times 10-Gb/s transmission experiment also confirmed that there was no MPI-induced excess noise.     

新型高掺铥硅酸盐玻璃光纤及其光纤激光的研究

具有高稀土离子掺杂浓度的有源光纤一直以来是高性能单频光纤激光器的核心,选用硅酸盐玻璃材料制作高掺杂有源光纤可以有效提升光纤增益。通过高温熔融工艺制备了铥离子掺杂浓度为8 wt.%的高掺杂硅酸盐玻璃,测试了其光谱特性和荧光寿命,并根据McCumber理论计算玻璃的受激发射截面。采用管棒法制备光纤预制棒,拉制出尺寸为7/125 μm的高掺铥硅酸盐玻璃光纤。基于低损耗的异质光纤熔接,测试了该光纤的增益特性,并分别采用2 cm和8 cm的新型掺铥光纤搭建线形腔光纤激光器,获得百毫瓦的1950 nm激光输出。研究表明,在8 wt.%的高浓度掺杂下,铥离子在文中的新型硅酸盐光纤基质中具备良好的发光能力,这种国产高掺杂玻璃光纤在实现高性能单频光纤激光器方面具有明显优势。     

48% power conversion efficiency in single pump gain-shiftedthulium-doped fibre amplifier

A new pumping scheme (1.2 μm+1.4 μm) is demonstrated for a gain-shifted thulium-doped fibre amplifier (TDFA), leading to record efficiency of 48% using one single pump dual-wavelength laser     

Tm-doped mode-locked fiber lasers

Ultrashort pulse fiber lasers are increasingly used in various areas for scientific as well as industrial purposes. In contrast to ultrashort pulse lasers based on ytterbium- and erbium-doped fibers, the dispersion of silica fibers in the amplification band of thulium-doped fibers around 2 μm is typically anomalous, which has fundamental impact on the pulse propagation. In this paper, mode-locked thulium-doped fiber lasers operating in different pulse propagation schemes are presented. The transfer of various concepts into the 2 μm wavelength range, which have been successfully applied for pulse parameter scaling in the 1 and 1.5 μm spectral region, are discussed on the basis of experimental and numerical results.     

S—波段光纤放大器及其研究进展

介绍了实现S-波段放大的3种光纤放大器；掺铥光纤放大器（TDFA）、增益位移TDFA（GSTD-FA）和光纤喇曼放大器，就其原理、结构、特点和发展现状进行了综述。     

1.4-μm-band gain characteristics of a Tm-Ho-doped ZBLYAN fiberamplifier pumped in the 0.8-μm band

The gain characteristics of a 1.4-μm-band thulium-holmium-doped ZBLYAN fiber amplifier are described. Signal gain is obtained over the whole 1.4-μm band for a pump power level of 73.5 mW. A maximum signal gain of 18 dB is achieved at a signal wavelength of 6.46 μm for a pump power of 150 mW at 0.79 μm. The noise figure is 5.6 dB in the signal wavelength region from 1.45-1.50 μm. From a comparison of the gain characteristics of thulium-holmium-doped ZBLYAN fibers and thulium-doped ZBLYAN fibers, it is proved that holmium ions play an effective role in increasing the gain and widening the gain spectrum