Gain-clamping techniques in two-stage double-pass L-band EDFA

Two designs of long-wavelength band erbium-doped fiber amplifier (L-band EDFA) for gain clamping in double-pass systems are demonstrated and compared. The first design is based on ring laser technique where a backward amplified spontaneous emission (ASE) from the second stage is routed into the feedback loop to create an oscillating laser for gain clamping. The gain is clamped at 18.6 d B from -40 to -80 dBm with a gain variation of less than ±0.1 dB and a noise figure of less than 6 dB. Another scheme is based on partial reflection of ASE into the EDFA, which is demonstrated using a narrowband fiber Bragg grating. This scheme achieves a good gain clamping characteristic up to -12 dBm of input signal power with a gain variation of less than ±0.3 dB from a clamped gain of 22 dB. The noise figure of a 1580 nm signal is maintained below 5 dB in this amplifier since this scheme is not based on lasing mechanism. The latter scheme is also expected to be free from the relaxation oscillation problem.     

Dynamic-performance characterization of C-band EDFA using ASE-power peak-selective feedback gain-clamping

We propose and demonstrate a C-band Erbium-doped fiber amplifier (EDFA) using amplified spontaneous emission (ASE) power peaking-selective and feedback to achieve highly stabilized and wide dynamic range gain clamping performances. The gain of 16.20 ± 0.13 dB is obtained with the input signal power dynamic range of 30 dB and the maximum noise figure (NF) was 6.6 dB with the input signal power from −35 to −10 dBm. To investigate the gain variation for the probe signals, we applied a saturation tone signal to simulate 16-channel DWDM signals as it is added (dropped) into (from) EDFA. The gain variation of the proposed scheme at a appropriate ring-cavity loss (VOA = 5 dB) is less than 0.13 dB for the input signal power from −35 to −5 dBm and wavelength from 1530 to 1564 nm.     

Experimental demonstration of output power spectrum clamping for multi-channel backward-pumped distributed fiber Raman amplifiers

Output power spectrum clamping over C+L band (84 channels) is demonstrated experimentally on a standard 100-km single mode backward-pumped distributed fiber Raman amplifier (B-DFRA). The clamping is realized by pump adjustment based on a simple linear relation of individual pump power versus on-off gain level and gain tilt in its spectrum. The average clamping error over all channels are less than 0.32 dB within the experimental range.     

Low noise gain-clamped L-band erbium-doped fiber amplifier by utilizing fiber Bragg grating

A novel gain-clamped long wavelength band (L-band) erbium-doped fiber amplifier (EDFA) is proposedand experimented by using a fiber Bragg grating (FBG) at the input end of the amplifier. This designprovides a good gain clamping and decreases noise effectively. It uses two sections of erbium-doped fiber(EDF) pumped by a 1480-nm laser diode (LD) for higher efficiency and lower noise figure (NF). The gainis clamped at 23 dB with a variation of 0.5 dB from input signal power of -30 to -8 dBm for 1589 nm andNF below 5 dB is obtained. At the longer wavelength in L-band higher gain is also obtained and the gainis clamped at 16 dB for 1614 nm effectively. Because the FBG injects a portion of backward amplifiedspontaneous emission (ASE) back into the system, the gain enhances 5 dB with inputting small signal.     

Characterization of ROF signal based on cascaded optical carrier suppression modulation technique

The paper experimentally demonstrated the optical frequency quadrupling microwave signal generation, a 4 GHz radio frequency (RF) signals up-conversion to 16 GHz in a radio over fiber (ROF) link, using twice optical carrier suppression modulation. The RF signal was mixed with 1.25 Gbps NRZ-OOK data firstly and then modulated by two cascaded single-electrode optical intensity modulators. The obtained 1.25 Gbps/16 GHz ROF signal was transmitted and characterized in the optical fiber link. At BER of 10^?9, low power penalty of 1.0 and 1.4 dB were obtained over a fiber link with a transmission distance of 25 and 50 km.     

碲基掺铒光纤放大器对于渐变输入信号的瞬态响应

为了抑制输出信号功率的瞬态波动,提出了调理脉冲信号边沿变化方式的思想.通过有限差分法数值模拟四能级模型下的粒子数速率-光功率传输方程组,理论研究了宽带碲基掺铒光纤放大器(Erbium-doped Tellurite-based Fiber Amplifier,EDTFA)对于低频脉冲输入信号的瞬态响应.研究表明,相比具有阶跃上升沿的方波脉冲,选择一个合适的渐变上升沿脉冲信号可以有效地抑制EDTFA输出端信号功率的瞬时上冲幅度.在多信道系统中,选择渐变的信道功率上传和下载方式,可以延缓其余信道输出功率的瞬态响应速度,从而为后续增益箍制技术的实施提供了便利.     

Weak laser pulse signal amplification based on a fiber Brillouin amplifier

We propose a high-gain and frequency-selective amplifier for a weak optical signal based on stimulated Brillouin scattering in a single mode fiber. To be able to satisfy the needs of high gain and high signal-to-noise ratio laser pulse amplification, different fiber lengths and core diameters are used to fulfill this experiment. In the experiment, a 430 nW(peak power) pulsed signal is amplified by 70 dB with a signal-to-noise ratio of 14 dB. The small size, high gain, low cost, and low noise of the fiber Brillouin amplifier make it a promising weak signal amplification method for practical applications such as lidar.     

基于光纤中交叉相位调制的波长转换器研究

波长转换器在未来的全光网络中将起到重要的作用.通过大量的数值仿真,研究了利用色散位移光纤中的自相位调制效应的波长转换器,首次对各参量,包括输入光信号脉冲的峰值功率,连续波的功率,两束光信号的频率间隔,光纤的色散,光纤的长度以及输入信号的比特率对此波长转换器的性能影响进行了数值研究.结果表明,光纤的色散和输入光信号脉冲的功率在这种波长转换器中起重要作用,而且这种波长转换器可以对高达200Gb/s的信号进行转换.     

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.     

Investigation of slow light enhanced nonlinear transmission for all-optical regeneration in silicon photonic crystal waveguides at 10 Gbit/s

We demonstrate bit error rate improvement, corroborated by eye diagram measurements, of a (10 MHz) amplitude distorted 10 Gbit/s data signal in silicon photonic crystal waveguides. This demonstration exploits a power clamping nonlinear transfer function, provided by slow light enhancement of nonlinear absorption in these waveguides.     

High gain double-pass L-band EDFA with dispersion compensation as feedback loop

We demonstrate an efficient double-pass L-band erbium-doped fiber amplifier (EDFA) incorporating chirped fiber Bragg grating (CFBG). The amplifier structure exploits the characteristics of CFBG to reflect the amplified signal back into the gain medium, filter out the recycled forward amplified spontaneous emission and block the residual 1480 nm pump power. The amplifier configuration has high gain and low noise figures as compared to double-pass EDFA using broadband mirror. The demonstrated amplifier has gain of more than 48 dB and low noise figure of less than 4 dB at low input signal power of −40 dBm.     

高功率宽带射频调制连续激光源

射频强度调制激光作为激光雷达系统的载波可以有效提高系统的抗干扰和抗散射能力,高功率宽带射频强度调制光源是实现高分辨率远距离探测的关键.本文采用在Nd:YAG激光器的耦合腔中插入一对四分之一波片的方法实现了频差调谐范围为30 MHz—1.5 GHz的双频激光输出,结合光纤振荡功率放大技术,将双频信号光功率放大为50 W.耦合腔双频种子源具有良好的功率和频率稳定性,输出功率为9.5 mW时,功率标准差为0.145 mW,稳定性为1.52%,输出双频激光的频差为250 MHz时,拍频的标准差为1.6144 MHz.种子光进行三级光纤功率放大,得到50 W双频激光输出.放大后的双频激光功率波动范围小于0.1 W,双频拍频的标准差为1.777 MHz,很好地保持了放大之前的功率稳定性和双频频差稳定性.     

Intensity dependence of the transient two-wave mixing by population grating in Er-doped fiber

Theoretical analysis of the transient two-wave mixing (TWM) of two continuous waves with rectangular phase modulation counter-propagating through the Er-doped optical fiber is presented. Approximate analytic solutions obtained for undepleted interacting waves of low power (neglecting large-scale saturation of the fiber optical absorption) and of high power (with significant spatially uniform large-scale absorption saturation) are complemented by numerical simulation for a broad region of the recording light power. The experimental dependence of the TWM efficiency on the recording power obtained for a single-mode fiber with ?640 ppm erbium concentration and with initial optical density ≈8.4 at λ = 1526 nm demonstrated the initial, growing and decaying parts predicted theoretically. The maximum experimentally observed relative TWM signal amplitude proved to be approximately 3 times lower than expected.     

Power line monitoring system using fiber optic power supply

We propose a novel power-line-monitoring system using optical fibers for transmitting power as well as signal. The principle is experimentally confirmed with a system composed of a monitoring side with a 1.5-μm laser diode, transmission line of a single mode fiber, and a sensing side having an efficient photovoltaic (PV) cell, electrical junction sensor, and low power liquid crystal optical modulator (LCOM). The PV cell generates the electrical power in the sensing side with a conversion efficiency of 20%. The LCOM is driven with low power of less than 50 μW, modulates the laser light with a signal indicating the power line condition, and transmits the optical signal. The developed sensing unit produces an optical signal having an extinction ratio of 15 dB with low optical power of 1.8 mW. Five systems were in operation for two years, faithfully monitoring the oil pressure in electrical cables every 20 min without incident.     

双波长全光自动增益箝制掺铒光纤放大器的实验研究

提出了结构简单的光纤布喇格光栅（FBG）双波长全光自动增益箝制方案,并进行了相关实验.结果表明,在三种不同的箝制波长组合1535.64nm+1562.68nm、1530.48nm+1562.68nm、1530.48 nm+1551.36 nm条件下,1540 nm信号的输出增益大小和输入信号功率动态范围几乎一致.对应此三种箝制波长组合,环路内的损耗分别为：14.7 dB、15 dB、15 dB.由此证明,在相同泵浦条件和环路损耗条件下,此三种不同箝制波长组合具有近似相同的箝制效果.而1551.36 nm+1562.68 nm箝制波长组合得到的结果相差甚远.此结果说明,在设计双波长全光自动增益箝制掺铒光纤放大器（OAGC-EDFA）时,为了取得足够大的信号增益,两箝制波长的波长间隔应尽量较大.     

Simulation analysis of crosstalk among channels with fiber Raman amplifiers at 10 Gb/s

We have investigated the effects of crosstalk in fiber Raman amplifiers (FRAs) by propagating signals through the Raman fiber. We have observed that quality factor reduces for lesser channel spacing. We have able to propagate the signals in two channels with spacing of 20 GHz and quality factor above 25 dB was obtained. The effect of signal input power and injected pump power on crosstalk and signal interference ratio (SIR) has analyzed. It is observed that the signal gain and the injected pump power should be limited to the value well below the threshold of Raman amplification to ensure small crosstalk and high SIR. The effect of Raman fiber length on crosstalk is also studied and it is observed that for high values of Raman fiber length, SIR reduces considerably.     

1018nm光源及光纤激光同带抽运实验研究

设计了级联式全光纤1018nm光源。该光源采用两级级联放大方案,实现了对低功率1018nm种子光的放大,获得了4.2W的最大输出功率,并分析了影响放大效率的因素。以获得的1018nm激光为抽运源,进行了1070nm信号光的同带抽运放大器实验研究,测量了放大器的输出特性。在纤芯抽运实验中,获得了明显的放大效果和较高的功率转换效率。进行了瓦量级包层同带抽运的实验研究,分析了导致包层抽运实验中功率转换效率偏低的原因并提出了解决方案。     

长波段掺铒光纤放大器用掺铒光纤的设计考虑

本文分析了长波段掺铒光纤放大器(EDFA)的增益系数与Er³⁺离子浓度的关系.研制了铝共掺杂的高浓度掺铒光纤,以缩短长波段掺铒光纤的长度.用两级泵浦实现了L-波段EDFA.光纤放大器的掺铒光纤总长18m,在1570nm波长处的小信号增益为42.26dB,输出功率为17.5dBm.我们认为,较低的浓度淬灭效应归因于光纤中较高的A1掺杂浓度.当总的输入信号功率为-3dBm时,在1570至1600nm间的7路WDM信号的增益不平坦度仅为0.68dB..     

Optimally gain-flattened and dispersion-managed C + L-band hybrid amplifier using a single-wavelength pump laser

We propose a hybrid C-band erbium-doped fiber amplifier (EDFA) and L-band Raman fiber amplifier (RFA) using a single pump laser diode. The optimum pump sharing ratio to EDFA/RFA is 1/10 with a total pump power of 660 mW. Using multiple fiber Bragg gratings (FBGs) with various reflectivities at different positions along the dispersion compensation fiber, the optimum dispersion compensation and power equalization for C + L-band channels are simultaneously realized. With an input power of −20 dBm/ch, the signal power variation among the channels is reduced from 9.8 dB to less than ±0.5 dB. Two pump reflectors are introduced to increase the pumping efficiency.     

Pulse amplification characteristics of multimode fiber amplifier

Under small signal situation, the analytical expression for describing the output signal emitted from an Yb³⁺-doped fiber amplifier with a Gaussian input pulse signal is deduced, by full considering both fiber guided modes’ propagation constant and filling factor, which depend on the signal frequency. Pumped by continue wave (CW) source, the analytical expressions of the small signal gain and each guided mode's output power are obtained. Based on these analytical expressions, the various intensity distributions of output pulses amplified by the fiber amplifier with different Gaussian input pulse widths are analyzed.