Linear cavity Brillouin fiber laser with improved characteristics

A configuration for linear cavity Brillouin fiber laser (BFL) generation is demonstrated using a standard single-mode fiber, two optical circulators, a 3 dB coupler, and a 95/5 coupler to allow high efficiency. With a Brillouin pump (BP) power of 13 dBm, the laser peak power is 12.3 dB higher than a conventional linear cavity BFL at an upshifted wavelength of 0.086 nm from the BP wavelength. In addition, it is revealed that the BFL peak power can be higher than the transmitted BP peak power when the BP power exceeds the second Brillouin Stokes threshold power.     

A tunable multi-wavelength Brillouin–erbium fiber laser with fourfold Brillouin frequency spacing

We have experimentally demonstrated a tunable multi-wavelength Brillouin–erbium fiber laser with over 40 GHz spacing utilizing two cascaded double Brillouin-frequency-spacing cavities. In this laser configuration, two segments of 25 km-long single-mode fibers are used as Brillouin gain medium in each ring cavity, and a segment of 8 m-long erbium-doped fiber with 980 nm pump is employed to amplify Brillouin pump (BP). At BP wavelength of 1550 nm, BP power of 8.3 dBm (6.8 mW) and the maximum 980 nm pump power of 27.78 dBm (600 mW), seven output channels with fourfold Brillouin-frequency spacing, and the tuning range of 15 nm from 1545 to 1560 nm are achieved. The proposed multi-wavelength Brillouin–erbium fiber laser has wide applications, such as in microwave signal generation and optical communications.     

Multi-wavelength Brillouin fiber laser using dual-cavity configuration

A simple technique for achieving multi-wavelength tunable multi-wavelength Brillouin fiber laser (BFL) based on dual-pass configuration is demonstrated. The BFL uses a piece of 10 km long non-zero dispersion shifted fiber (NZ-DSF) as a Brillouin gain medium to obtain odd-order Brillouin Stokes waves as an output with the line spacing of 0.16 nm (20 GHz) between each two consecutive waves by employing even-order Brillouin Stokes to improve output performance of the laser. With a BP of 15.3 dBm, at least 15 odd-order Brillouin Stokes and anti-Stokes lines are generated. The laser is room temperature stable, tunable over 50 nm wavelength range and has an optical signal to noise ratio of more than 30 dB at 1560 nm region. This Brillouin fiber laser can operate at any wavelength depending on the Brillouin pump (BP) wavelength used.     

Multi-wavelength generation using a bismuth-based EDF and Brillouin effect in a linear cavity configuration

The generation of a multiple wavelength source using a bismuth-based erbium-doped fiber (Bi-EDF) in a linear cavity configuration is demonstrated. The configuration uses a pair of optical circulators at the input and output ends of the cavity to form a resonator for multi-wavelength generation in conjunction with optical couplers to inject the Brillouin pump (BP) and to tap the output at the two ends. The Brillouin erbium fiber laser (BEFL) comb with a 2.15 m of Bi-EDF has a wavelength spacing of 0.09 nm and operates in long-wavelength (L-) band region. A stable output laser comb of 50 lines is obtained at a BP of 1568.2 nm and 5 dBm and two 1480 nm pumps at 120 mW. The injected BP wavelength and power as well as the 1480 nm pump powers have a great effect on the number of lines and output power of the BEFL. This configuration is compact due to the use of the significantly shorter Bi-EDF as the linear gain medium, and can be made more compact by replacing the single-mode fiber with highly non-linear fibers such as holey fibers.     

Double Brillouin frequency spaced multiwavelength Brillouin-erbium fiber laser with 50 nm tuning range

A 50 nm tuning range multiwavelength Brillouin-erbium fiber laser (MWBEFL) with double Brillouin frequency spacing is presented. Two separated gain blocks with symmetrical architecture, consisted by erbium-doped fiber amplifiers (EDFAs) and Brillouin gain media, are used to generate double Brillouin frequency spacing. The wider tuning range is realized by eliminating the self-lasing cavity modes existing in conventional MWBEFLs because of the absence of the physical mirrors at the ends of the linear cavity. The Brillouin pump (BP) is preamplified by the EDFA before entering the single-mode fiber (SMF), which leads to the reduction of threshold power and the generation enhancement of Brillouin Stokes (BS) signals. Four channels with 0.176 nm spacing are achieved at 2 mW BP power and 280 mW 980 nm pump power which can be tuned from 1525 to 1575 nm.     

Investigation on stimulated Brillouin scattering characteristics in a highly doped Bismuth-based Erbium-doped fiber

Stimulated Brillouin scattering (SBS) characteristics in a 49 cm long highly doped Bismuth-based Erbium doped fiber (Bi-EDF) is investigated in the ring and linear cavity configurations. At Brillouin pump (BP) power of 6 dBm, the Brillouin laser peak power of the optimized ring Brillouin Erbium fiber laser (BEFL) is obtained at 23 dB higher than the peak power of the conventional linear cavity at an up shifted wavelength of 0.08 nm. This Bi-EDF ring cavity operates at nearly 1563 nm wavelength region, which is up-shifted by 0.08 nm from the Brillouin pump wavelength with the side mode suppression ratios (SMSR) of 29 and 23 dB in the forward and backward directions, respectively.     

布里渊散射谱拟合的混合优化算法

基于布里渊光时域分析仪的全分布式光纤传感系统中,光纤沿途的探测信号含有噪声导致被测量的温度或应变信息难以识别,光谱拟合的精确度对传感信息的识别非常重要。在传感系统低信噪比的情况下,提出了一种提取高精度布里渊散射谱特征的拟合方法,利用小波去噪结合莱文伯-马奈特(LM)算法调节权值后向传输(BP)网络对布里渊散射谱进行特征提取。克服了传统BP神经网络易陷入局部极值的缺点,保证求解的精度。数值仿真表明,该方法适合不同权重比、不同线宽和低信噪比以及大测量范围的情况进行光谱拟合,并且在信噪比为10dB的情况下得到拟合度均超过0.96。实验结果表明,该方法适用于多种泵浦功率情况下的布里渊散射谱的特征提取,优于传统BP神经网络算法且具有较高的拟合精度。     

Tunable multiwavelength Brillouin-erbium ring-cavity fiber laser with short-length photonic crystal fiber

A multi-wavelength Brillouin-erbium ring-cavity fiber laser utilizing 2-m erbium doped fiber (EDF) and 70-m high nonlinear photonic crystal fiber (PCF) is proposed and demonstrated. The output characteristics and also the impacts of pump and Brillouin pump (BP) on the output spectra are investigated in detail. The output number and wavelength location of Brillouin lines are tunable by adjusting the power of 1465 nm pump and BP, and a 5-channel output within 11 nm (1551–1562 nm) tuning range is achieved by choosing appropriate pump power.     

Simple tunable multiwavelength Brillouin/Erbium fiber laser utilizing short-length photonic crystal fiber

We have demonstrated a simple ring cavity tunable multiwavelength Brillouin/Erbium fiber laser (MWBEFL), in which 70 m highly nonlinear photonic crystal fiber (HNL-PCF) is used as the Brillouin gain medium. The fiber laser utilizes recycling mechanism to enhance stimulated Brillouin scattering (SBS). The configuration that consists of only 3 optical components is easy to be integrated and improves the practicality. At the maximum 1480 nm pump power of 110 mW and the Brillouin pump power of 3 dBm, 10 stable output channels with more than 10 dB optical signal to noise ratio (OSNR) and 0.078 nm channel spacing could achieve 10 nm tuning ranges.     

长距离光纤布里渊散射研究

研究了25 km长距离光纤中布里渊散射的功率分布,提出了求解长距离光纤中布里渊散射的耦合强度方程的数值计算方法,与忽略光纤损耗的解析解进行比较,并从实验上加以研究.在此基础上,分析了25 km长距离光纤中布里渊散射过程,得到泵浦波和斯托克斯波沿光纤的功率分布图.     

光纤光栅与受激布里渊信号的耦合特性

近年来,光纤布拉格光栅传感器与全分布式光纤传感器的融合技术受到了广泛关注,然而光纤布拉格光栅与布里渊信号之间的耦合特性鲜有报道。本文研究了光栅类型、波长、反射率及光纤的光致折射率对受激布里渊信号的影响规律,并探讨了空间分辨率对光纤布拉格光栅定位功能的影响。实验结果表明,在布里渊光时域分析系统中,光纤布拉格光栅处有尖锐的反射峰,而啁啾光栅、长周期光栅及光致折射率变化的光纤处均未出现尖锐的反射峰;光纤布拉格光栅反射率与受激布里渊散射功率谱无关;当光纤布拉格光栅的波长接近1 550 nm时,对受激布里渊频移测量的影响最大;在8 m的长度范围内,光纤布拉格光栅的定位误差约为4 cm,并且与空间分辨率无关。     

Effect of Brillouin slow light on distributed Brillouin fiber sensors

The effect of Brillouin slow light on distributed Brillouin fiber sensors (DBFSs) is studied. We demonstrate Brillouin slow light for a 1.2 ns pulse with peak powers (PS) from 3.3 to 56.2 mW on depletion of the pump power (PP) ranging from 1.3 to 83.2 mW in conventional optical fibers (SMF-28). Experiments show that, when pump power depletion is not negligible, for a given PP the Brillouin gain and delay time of a pulse decrease when PS increases in a long (> or =10 km) sensing fiber. The optimum pump beam depletion resulting from strong interaction of the pump and the probe in the fiber provides accurate temperature and strain information at a high spatial resolution. Our study reveals that at low PP the spatial resolution error caused by the pulse delay for a DBFS with centimeter spatial resolution is less than 5% of the pulse length.     

Flat amplitude multiwavelength Brillouin–Raman random fiber laser with a half-open cavity

In this paper, we experimentally demonstrate a novel configuration of multiwavelength Brillouin–Raman random fiber laser (MBRRFL) utilizing a half-open cavity. The laser resonator is formed by fiber loop mirror at the Brillouin pump (BP) side and random distributed Rayleigh backscattering in a 10 km dispersion compensating fiber. As a result, we are able to obtain a flat amplitude bandwidth of 16.8 nm from 1,550.0 to 1,566.8 nm built-in 210 uniform Brillouin Stokes lines with 0.08 nm spacing and an average OSNR of 13.5 dB. We also studied the influence of BP power and wavelength on the MBRRFL’s performance. Furthermore, comparing with the open cavity configuration, the discrepancies in power level and linewidth between neighboring channels are overcome by using the half-open cavity.     

Optimization of Brillouin pump wavelength location on tunable multiwavelength BEFL

Optimization of Brillouin pump (BP) wavelength location on tunable multiwavelength Brillouin-erbium fiber laser (BEFL) with BP pre-amplified technique is experimentally investigated. The tunable multiwavelength BEFL is achieved by utilization a tunable band-pass filter in a laser cavity. The optimum BP power and BP wavelength location within the filter bandwidth is determined in order to obtain the maximum stable output channels. Optimum distance of launching the BP wavelength is found at 0.80 nm shorter from the center wavelength of the filter bandwidth. 15 stable output channels are achieved from the tunable fiber laser system within the optimum range of BP power which is found to be between 5.2 to 5.7 dBm.     

0.16 nm spaced multi-wavelength Brillouin fiber laser in a figure-of-eight configuration

A stable and compact multi-wavelength Brillouin fiber laser (BFL) operating at room temperature is experimentally demonstrated using a 100 m long photonic crystal fiber (PCF) in conjunction with a figure-of-eight configuration. At a Brillouin pump (BP) level of 15.3 dBm, 7 simultaneous lines with 20 GHz or 0.16 nm line spacing is achieved by removing the odd-order Stokes lines. The anti-Stokes lines are also generated via four wave mixing process in the laser cavity. Compared with the Erbium-based multi-wavelength laser, this BFL has advantages in term of channel spacing and flexibility in the choice of operating wavelength. The output spectrum of the proposed BFL can be tuned by 80 nm, dependent on the availability of an appropriate BP source. The multi-wavelength BFL shows a good stability with power fluctuations of less than 0.5 dB over more than 3 h.     

基于径向基函数神经网络的传感布里渊散射谱特征提取

基于布里渊效应的分布式光纤传感器以其可在沿光纤中同时获得被测量场时间和空间上的连续分布信息,成为当前国际的研究热点。根据光纤中布里渊散射谱的传输特点和高精度特征提取的要求,提出了利用莱文伯-马夸特(L-M)算法调节权值的径向基函数神经网络(RBFN)对布里渊散射谱进行特征提取。通过与反向传播(BP)神经网络、五次多项式曲线拟合法和三次样条插值法进行预测比较,在中心频率为11.213GHz,权重比为4∶1的仿真散射谱模型中,本方法相对误差最小,仅0.0015179%,温度相对误差仅为0.152℃,且拟合度较好。在不同脉宽和不同温度下的同一检测系统中,前者的综合评价指标优于其他三种拟合方法。数值分析和实验研究均表明径向基函数神经网络适用于对布里渊散射谱进行拟合,有效提高了预测精度。     

基于光子晶体光纤中受激布里渊散射的光载波抑制

设计了一种基于光子晶体光纤中受激布里渊散射的载波滤波器.该滤波器利用两个环形器和一段光子晶体光纤构成了一个环形腔,这种腔结构有效地降低了光纤中受激布里渊散射的阈值.理论分析了光子晶体光纤载波滤波器对提高光调制深度和射频增益的影响.利用25 m的高非线性光子晶体光纤作为受激布里渊增益介质,当入射载波功率为70 mW时,微波光子信号的射频增益为5.38 dB,实验结果与理论计算相吻合.     

Influence of laser linewidth on performance of Brillouin optical time domain reflectometry

The effects of optical sources with different laser linewidths on Brillouin optical time domain reflectometry (BOTDR) are investigated numerically and experimentally. Simulation results show that the spectral linewidth of spontaneous Brillouin scattering remains almost constant when the laser linewidth is less than 1 MHz at the same pulse width; otherwise, it increases sharply. A comparison between a fiber laser (FL) with 4-kHz linewidth at 3 dB and a distributed feedback (DFB) laser with 3-MHz linewidth is made experimentally. When a constant laser power is launched into the sensing fiber, the fitting linewidths of the beat signals (backscattered Brillouin light and local oscillator (LO)) is about 5 MHz wider for the DFB laser than for the FL and the intensity of the beat signal is about a half. Furthermore, the frequency fluctuation in the long sensing fiber is lower for the FL source, yielding about 2 MHz less than that of the DFB laser, indicating higher temperature/strain resolution. The experimental results are in good agreement with the numerical simulations.     

基于宽带光源和自外差检测的布里渊光时域反射温度传感系统

为简化系统结构、减小相干瑞利噪声对系统性能的影响,提出了一种采用宽带光源的瑞利和布里渊散射自外差检测布里渊光时域反射温度传感系统.分析了瑞利和布里渊自外差检测原理,研究了布里渊频移和自外差信号功率与光纤温度和应变的关系.设计并搭建采用宽带光源的自外差检测布里渊光时域反射温度传感系统,获得了常温下沿光纤分布的自外差信号功率谱及不同温度时加温段光纤的功率谱,验证了布里渊频移和自外差信号相对功率变化随温度的线性增加关系.通过实验数据获得的布里渊频移和相对功率变化的温度系数分别为1.07±0.01MHz/℃和(0.37±0.09)%/℃.本文的研究结果为基于瑞利和布里渊自外差检测布里渊光时域反射传感系统的温度和应变同时测量提供了理论和实验依据.     

Broadly tunable multiwavelength fiber laser with bismuth-oxide EDF using large effective area fiber

A multiwavelength laser comb using 2.49 m Bismuth-oxide erbium-doped fiber (Bi-EDF) with different lengths of large effective area fiber (LEAF) in a ring cavity configuration is realized. The Bi-EDF is used as the linear gain medium and LEAF is used as the non-linear gain medium for stimulated Brillouin scattering. Out of the four different lengths, the longest length of 25 km LEAF exhibits the widest tuning range of 44 nm (1576 to 1620 nm) in the L-band at 264 mW pump power and 5 mW Brillouin pump power. In addition, a total of 15 output channels are achieved with total average output power of −8 dBm from this laser structure. All Brillouin Stokes signals exhibit high peak power of above −20 dBm per signal and their optical signal-to-noise ratio of greater than 15 dB.