Wideband frequency tunable optoelectronic oscillator based on a dispersion compensated microwave photonic filter

A wideband tunable optoelectronic oscillator (OEO) based on a dispersion compensated phase modulated microwave photonics filter (MPF) is proposed and experimentally demonstrated. The MPF, consisting of a tunable laser source (TLS), a phase modulator, a fiber Bragg grating Fabry–Perot filter and a photodetector, is used as the oscillating mode selection device. Dual-loop configuration is employed to make sure the OEO operates at a single oscillating mode. Theoretically analysis is carried out to demonstrate the tuning range limitation due to the phase-modulation to intensity-modulation conversion caused by long single mode fiber (SMF). To overcome this disadvantage and expand the signal tuning range, a dispersion compensation fiber is introduced followed by the SMF to compensate the fiber dispersion. By simply adjusting the wavelength of the TLS, an ultra-wideband tunable microwave signal with the frequency tuning range from 2 to 44 GHz is obtained. The phase noise is also investigated and measured to be less than ? 110 dBc/Hz at an offset of 10 kHz within the whole frequency range.     

S波段光纤拉曼放大器中级联受激布里渊散射串扰的实验研究

研究了光纤激光器前向抽运的S波段分布式光纤拉曼放大器中级联的受激布里渊散射(SBS)串扰现象。用窄光谱带宽(<100MHz)的可调谐激光二极管作为信号源,通过S波段分布式光纤拉曼放大器,当被放大的信号功率超过单模光纤受激布里渊散射的阈值时,出现了前向受激布里渊散射,这是传导声波布里渊散射在光纤放大器中放大的现象。随着拉曼放大器抽运功率的提高,在斯托克斯区,出现了两阶受激布里渊散射线,在实验中观测到偶数阶的受激布里渊散射谱线功率大于奇数阶的布里渊一瑞利散射线。当进一步增加拉曼放大器的抽运功率,出现了前向级联的多阶受激布里渊散射现象,拉曼放大器的增益下降,被放大的信号功率转换为受激布里渊散射,噪声变大。受激布里渊散射的串扰破坏了拉曼放大器的特性,使拉曼放大器无法在密集波分复用光纤传输系统中使用,因此需要严格地控制入纤的信号功率和放大器的抽运功率。在实验中还观测到在光纤拉曼放大器中被放大的信号光和受激布里渊散射线两侧的伴线。     

Passive combination of multiple beams in an optical fiber via stimulated Brillouin scattering

We demonstrate passive combination of multiple beams in an optical fiber via stimulated Brillouin scattering (SBS). Four off-axis beams are combined in a long multimode optical fiber using a novel all-optical mount. The combined beam has the high spatial coherence properties of the LP(01) mode owing to the beam cleanup properties of SBS. The threshold for SBS when off-axis pumps are used is shown to be a factor of 13 times higher than for on-axis pump beams. We propose this method would improve the brightness of an array of fiber amplifiers.     

基于多波长激光器的带通微波光子滤波器设计

提出了一种基于多波长光纤激光器的可调谐的带通微波光子滤波器。它以可调谐多波长光纤激光器作为光源,将相位调制器和色散器件相结合,通过在普通单模光纤中相位调制到强度调制的转换效应消除了低频谐振峰实现了带通微波光子滤波器。利用双折射光纤环镜输出谱中的一个窗口对多波长激光信号频谱进行加窗处理,使微波光子滤波器的边瓣抑制比提高了约11dB。通过调节多波长光纤激光器中的偏振控制器可以使输出多波长激光信号的相邻波长间隔得到调节,从而结合普通单模光纤的色散延时作用可以使微波光子滤波器的通带中心频率在7.66GHz范围内调谐。     

Gain and gain-flatness improved photonic crystal fiber Raman amplifier based on a dual-pass amplification configuration with single pump laser

A gain and gain-flatness improved L-band dual-pass Raman fiber amplifier (RFA) utilizing a photonic crystal fiber (PCF) as gain medium is demonstrated. By introducing complementary gain spectra of typical forward and backward pumping single-pass RFA using the same PCF, we finally achieve average net gain level of 22.5 dB with a ±0.8 dB flattening gain in 20-nm bandwidth from 1595 nm to 1615 nm, which is rare in RFAs with only one single pump and no flattening filter. Compared with the single-pass pump configurations, gain level, flatness and bandwidth are greatly improved by using the dual-pass amplification configuration. The limitation of this configuration caused by multi-path interference (MPI) noise and stimulated Brillouin scattering (SBS) is also discussed.     

Stimulated Brillouin scattering slow-light-based fiber-optic temperature sensor

We propose and experimentally demonstrate a method for temperature sensing using stimulated Brillouin scattering (SBS)-based slow light. The approach relies on temperature dependence of the Brillouin frequency shift in a fiber, hence the time delay of an input probe pulse. By measuring the delay, temperature sensing can be realized. We achieve temperature measurement in a 100 m single-mode fiber (SMF) using a cw pump. The main temperature-sensing range is ～18°C from the room temperature, limited by the SBS gain bandwidth. To apply the technique for measurement of a shorter fiber segment, a pulsed pump is used to introduce SBS slow light. Temperature sensing is achieved in a 2 m SMF with a main sensing range of around ～25°C. The scheme is easily implemented, exhibits a relatively high temperature sensitivity with a resolution better than 1.0°C, and is potentially applicable for distributed sensing.     

High-Q, tunable, photonic microwave single passband filter based on stimulated Brillouin scattering and fiber Bragg grating filtering

We experimentally demonstrate a single passband, photonic microwave bandpass filter scheme based on stimulated Brillouin scattering (SBS) in optical fiber. A single side band (SSB)-modulated probe and a single frequency, tunable pump beam that have been produced by the combination of conventional Mach-Zehnder modulators and fiber Bragg grating filters, are used for the generation of SBS phenomenon in a 1-km long highly nonlinear dispersion-shifted optical fiber. Using the proposed scheme a single microwave passband with a ∼26 MHz bandwidth is readily achieved over a radio frequency tuning range from 1.3 to 9.3 GHz. The maximum Q-factor is measured to be ∼360.     

光纤中受激Brillouin散射动态弛豫振荡特性及其抑制方法

为了避免在高功率光纤放大器和光纤相位共轭镜等实际应用中因受激Brillouin散射（SBS）造成的光纤损伤,根据描述SBS动态弛豫振荡特性的振幅耦合方程,利用有限差分的数值模拟方法研究了光纤中SBS的动态弛豫振荡特性,并对其抑制进行了初步探讨.得到了光纤中SBS弛豫振荡在不同的脉冲上升时间的时空三维图;同时利用方波和脉冲光作抽运光进行了相应实验研究,实验结果与理论模拟结果符合很好.结果表明,增大抽运光脉冲上升时间可以有效抑制因SBS而产生的弛豫振荡,进而避免因其造成的光纤损伤. 关键词： 受激Brillouin散射 动态弛豫振荡特性 有限差分法     

Measurement of modulation index and half-wave voltage of an electro-optical phase modulator with a dispersion-based phase filter

In this paper, a novel method based on the use of an optical phase filter is proposed to evaluate the modulation index, as well as the half-wave voltage of an optical phase modulator. When a phase modulated signal propagates along the length of a dispersive fiber, the fiber dispersion acts as an optical phase filter and spectrally alters the relative phasing of the phase modulated signal, causing the phase modulation to become intensity modulation, which allows the swept frequency measurement of phase modulators by using a vector network analyzer. The modulation index and half-wave voltage as a function of the modulation frequency are experimentally measured for a commercial phase modulator, which agree well with the results obtained using the widely accepted optical spectrum analysis method. The proposed method requires only a length of dispersive fiber and works without any small-signal approximation, which is applicable for different driving levels and operating wavelengths with the same setup.     

光纤中双宽带抽运SBS慢光及其脉冲展宽减小的理论研究

提出了一种单模光纤中采用双宽带抽运实现宽带受激布罩渊散射(SBS)慢光的方法.给出了双宽带抽运的SBS慢光及其脉冲展宽的理论模型.色散分析发现,两抽运光间存在一个最佳的频率间隔,可有效地减少由于群速度色散所引起的脉冲展宽.理论计算表明,该方案所获得的SBS增益带宽和信号脉冲群延迟分别提高到了相同条件下单宽带抽运的1.7倍和2倍.     

窄线宽纳秒脉冲光纤拉曼放大器的理论模型和数值分析

窄线宽纳秒脉冲光纤拉曼放大器在非线性频率变换、遥感探测和量子信息等领域有广泛的应用前景.综合考虑受激拉曼散射(stimulated Raman scattering,SRS)、受激布里渊散射(stimulated Brillouin scattering,SBS)、自相位调制(self-phase modulation)和交叉相位调制(cross-phase modulation)等非线性效应,建立了窄线宽纳秒脉冲光纤拉曼放大器的非线性动力学模型.仿真分析了放大器中脉冲激光的时频演化特性,对比研究了抽运脉冲宽度、光纤长度和信号光功率等因素对放大器性能的影响.研究发现,上述因素会影响放大器的SRS阈值、SBS阈值、输出激光线宽、激光转换效率等.例如,当脉冲宽度为800 ns时,SBS随着抽运功率的增加而发生,限制了激光功率的提升;减短抽运脉宽可以抑制SBS,但是输出激光的线宽易于展宽到数百MHz以上;增加光纤长度可以获得更低的SRS阈值和更高的转换效率,但是SBS效应和光谱展宽程度也随之增强.系统搭建中需要平衡各非线性效应,选择合适的系统参数.研究内容可以为窄线宽纳秒脉冲光纤拉曼放大器的设计搭建提供参考.     

一种新型自激发布里渊掺铒光纤激光器

利用级联的受激布里渊效应,自激发布里渊掺铒光纤激光器可以实现常温下的多波长激光输出。通过在自激发掺铒光纤激光器中引入一个高双折射萨尼亚克(Sagnac)环形滤波器,调节萨尼亚克环形滤波器的偏振控制器(PC),实现了可调谐多波长输出,同时在实验中观测到双布里渊多波长带的现象。研究了这种光纤激光器中萨尼亚克环形滤波器的带宽和980 nm抽运光功率对输出波长数的影响,在萨尼亚克环形滤波器的带宽为83.3 nm以及980 nm抽运光功率为260 mW时,得到了52个间隔为0.088 nm的多波长激光输出。     

Long-distance fiber sensor system based on the second-order Raman pump and amplification

We demonstrate a novel technique to realize a long-distance fiber sensor system based on the second-order Raman pump and amplification. With the second-order Raman pump and amplification, a gain spectrum around 1582-nm is achieved. It serves as not only the optical source for the remote fiber sensor but also the filter to intensity modulated the wavelength shift of the fiber sensor. A long-distance fiber strain sensor system is demonstrated by adopting a fiber Fabry?CPérot sensor. Experimental results show that the wavelength shift of the sensor in response to the strain is simultaneously intensity modulated by the steep slope with a high sensitivity, while it is temperature insensitive. With the side gain spectrum served as a quasi-linear filter, the sensor can also be quasi-linearly intensity-modulated.     

入射偏振对有线电视光发射机受激布面渊散射抑制性能的影响

受激布里渊散射 (SBS)的抑制性能是光纤调幅有线电视外调制发射机的关键指标之一。从理论上分析了入射偏振分别为TE与TM模时 ,对发射机受激布里渊散射抑制性能的影响。分析计算显示 :入射光偏振态模式为TE模最佳。还对入射偏振态偏离TE模的情形进行了分析 ,表明为保证发射机对受激布里渊散射抑制性能 ,入射光偏离TE模的角度应小于 10°。     

A photonic approach for microwave/millimeter-wave frequency measurement using stimulated brillouin scattering in single mode fiber

A photonic approach for microwave/millimeter-wave (MMW) frequency measurement is proposed and demonstrated based on stimulated Brillouin scattering (SBS) of a 20-km standard single mode fiber (SSMF). After the MMW signal is modulated to a laser source with two sidebands using optical carrier suppression (OCS) modulation, its frequency can be easily measured by monitoring the SBS-induced amplification with a power meter. Due to the 1-pm resolution of a tunable pump laser source, a frequency measurement range of 1–40 GHz is demonstrated in our experiment with a frequency resolution of 125 MHz. We believe the frequency measurement range can be further extended to satisfy photonic radar front-end processing application.     

光纤中的瞬态SBS过程的数值分析与探讨

 通过数值方法得到了光纤中的瞬态SBS过程中耦合波和声场的强度分布图，从而分析了光纤中瞬态SBS的发生过程以及光纤长度、泵浦脉宽等因素对SBS反射率及阈值的影响，据此提出了一种新的光纤相位共轭器。     

Experimental comparison of a Kerr nonlinearity figure of merit including the stimulated Brillouin scattering threshold for state-of-the-art nonlinear optical fibers

We introduce a new figure of merit (FOM) including the input pump power limit associated with stimulated Brillouin scattering (SBS) for evaluation of the Kerr nonlinearity efficiency of optical fibers. The new FOM is expressed as gammaL(eff)P(SBS) (gamma is a nonlinearity parameter, L(eff) is effective length, and P(SBS) is the SBS threshold), while the conventional FOM is given by gammaL(eff). Using the new FOM, we perform an efficiency comparison among four types of state-of-the-art nonlinear optical fiber: a Bi2O3-based nonlinear fiber, a silica-based holey fiber, a highly nonlinear dispersion-shifted fiber, and a conventional dispersion-shifted fiber. The Bi2O3-based nonlinear fiber is found to have the best Kerr nonlinearity efficiency owing to the superior nonlinear property of the Bi2O3 glass compared with that of the silica.     

相位调制边带失衡问题研究

 高功率激光系统中一般利用相位调制器对单纵模激光进行频谱展宽以避免受激布里渊散射，当后继系统中的滤波器存在中心波长偏差时，则会导致相位调制产生的边带失衡，使光信号出现较为严重的高频起伏。基于前端系统模拟平台对此问题进行了数值模拟研究，结果表明滤波后的高频起伏随滤波器带宽变窄和中心波长偏差增大而加剧。分析表明0.2 nm带宽的滤波器出现0.05 nm左右的波长偏差时，将引起24.3%左右的顶部起伏。实验中根据分析将滤波器带宽从0.2 nm加大到0.4 nm，成功将脉冲顶部起伏从25.2%减小到了4.4%，对前端系统的研制起到了很好的指导作用。     

Stimulated Brillouin Scattering Enhancement Factor Improvement in a 11.6-GHz-Linewidth 1.5-kW Yb-Doped Fiber Amplifier

The stimulated Brillouin scattering(SBS) threshold enhancement factor in a pure white noise linewidth broadening Yb-doped fiber amplifier(YDFA) with a short large mode area fiber is theoretically and experimentally studied.We demonstrate a 1064.08 nm,11.6 GHz linewidth,1.5kW output power YDFA with an SBS threshold enhancement of ~57(26 W SBS threshold with single frequency seed).The output beam is near-diffraction limited with a beam quality factor of M~2 = 1.15 and a slope efficiency of up to 87%.No SBS or stimulated Raman scattering effects are observed in the whole power range.Further power scaling is limited by the available pump power in our system.     

High-Q microwave photonic filter with self-phase modulation spectrum broadening and third-order dispersion compensation

We propose and experimentally demonstrate a scheme of high-Q microwave photonic filter （MPF） using the techniques of self-phase modulation （SPM） spectrum broadening and third-order dispersion （TOD） compensation. The optical pulses from a mode-locking laser are spectrally broadened by the SPM in the highly nonlinear fiber. A wideband optical frequency comb with 365 spectral lines within 10-dB power variation from the highest spectral power is obtained. By applying a cubic phase modulation via a waveshaper, the effect of TOD which broadens the MPF passband is eliminated. The final implemented MPF has a Q-value as high as 296 and a tuning range of 700 MHz.