RIN transfer measurement and modeling in dual-order Raman fiber amplifiers

A numerical analysis is presented that models the transfer of relative intensity noise (RIN) from the first- and second-order pump lasers to the signal radiation in dual-order Raman fiber amplifiers. Measurements are presented of the first- and second-order RIN transfer functions for co- and counter-propagating fiber amplifiers. The second-order RIN transfer function is similar to that found in single-order Raman fiber amplifiers and the first-order transfer function is approximately 15 dB less than the second-order transfer function. The impact of the RIN transfer from the first- and second-order pump lasers to the signal radiation on the system performance is examined and estimates for the required pump laser RIN levels are presented.     

Output-power-clamped Raman fibre laser with suppression of low-frequency RIN transfer from pump sources

An optical approach is demonstrated for suppressing low-frequency relative intensity noise (RIN) transfer from pump sources to the author's proposed Raman fibre laser (RFL). Low-frequency RIN transfer suppression is accomplished by outputting not the second- but first-order Stokes, which output power is clamped by the lasing second-order Stokes in the cavity and can be easily tuned in a large dynamic range. Thus, this technique fits the RFL for use as pump sources in Raman fibre amplifiers.     

High-power and low-RIN lasers for advanced first- and higher order Raman copumping

We propose a novel high-power (up to 1.9 W) and low relative intensity noise (RIN) laser structure for effective first- and higher order distributed Raman copumping. RIN characterization and bit-error-rate measurements at 10 Gb/s point out RIN-penalty free transmission up to 25 dB of on-off copropagating Raman gain. This new copumping technology can provide sensible span reach enhancement in long-span unrepeated WDM transmission systems in a simple and effective way.     

Relative Intensity Noise Suppression for RF Photonic Links

We propose and experimentally demonstrate a novel technique to reduce laser relative intensity noise (RIN). A RIN suppression servo is usually implemented by inserting an intensity modulator in the optical path and controlling measured light intensity with a closed-loop servo system. We utilize the intensity modulator already present in a photonic link to perform the task of RIN suppression as well as encoding the optical signal with the microwave subcarrier. This technique provides suppression of 10 to 50 dB of laser RIN over a bandwidth of 10 MHz. Furthermore, we implement this technique in an optoelectronic oscillator, significantly improving its phase noise performance due to the reduced effect of RIN on the phase noise of the oscillator.      

Double-cavity Raman fibre lasers with suppressed pump-to-Stokes transfer of low-frequency RIN

Double-cavity Raman fibre lasers with two longitudinally concatenated Stokes cavities are shown to permit the suppression of low-frequency relative-intensity-noise (RIN) transfer from the pump laser to the Stokes output. This concept can provide low-noise Raman fibre lasers for use as pump sources in co-pumped Raman amplifiers.     

Mean Relative Intensity Noise Transfer in Fiber Raman Amplifiers Using Multiple-Wavelength Pumps

We present a numerical analysis of mean relative intensity noise (RIN) transfer in a fiber Raman amplifier (FRA) using multiple-wavelength pumps. For the first time, the RIN transfer is investigated to include pump-to-pump and signal-to-signal RIN transfers, together with the ldquotraditionalrdquo pump, to signal transfer in a multiple-wavelength pumped FRA. We show that for a multiple-wavelength pumped FRA, pump-to-pump and signal-to-signal RIN transfers induce an increase of RIN transfer magnitude. For a multiple-wavelength counter pumped FRA, in additional to the major pump to signal RIN transfer, pump-to-pump RIN transfer is considerable, and signal-to-signal RIN transfer is very small. For a multiple-wavelength co-pumped FRA, both pump-to-pump and signal-to-signal RIN transfers increase RIN transfer magnitude significantly. In addition, for both a co- and counter pumped FRAs, particularly for the co-pumped FRA, the longer wavelength signals experience more RIN transfer than the shorter wavelength signals. Furthermore, the bandwidth of RIN transfer is significantly increased in a multiple-wavelength co-pumped FRA with multiple input signals compared to a single-wavelength co-pumped FRA with an input signal.     

RIN transfer in copumped Raman amplifiers using polarization-combined diodes

Pump-to-signal relative-intensity-noise (RIN) transfer in a forward-pumped Raman amplifier using polarization-combined diodes is measured and analyzed. For the first time, by means of experiment and simulations, we call attention to the impact of the polarized nature of stimulated Raman scattering on RIN transfer. We show that measuring the RIN at the output of a depolarized Raman pump and inserting this figure in the commonly used RIN transfer equation is not sufficient for good signal RIN prediction. Although depolarizing the Raman pump enables polarization-independent signal gain, proper modeling of RIN transfer should include the polarization dependence of the Raman effect and the polarization mode dispersion of the fiber.     

RIN transfer analysis in pump depletion regime for Raman fibreamplifiers

A numerical analysis is presented that models the relative intensity noise transferred from a Raman pump to a signal laser in an optical fibre. The analysis is valid in both the pump-depletion and nondepletion regimes. The RIN requirements for a 0.1 dB Q-penalty in the pump depletion regime are similar to those in the nondepletion regime, exhibiting a RIN requirement reduction of only 3-4 dB/Hz     

Characteristics of gain and pump-to-signal RIN transfer in a dual-pump SOPA with Raman effect

We investigate the spectra of the gain and pump-to-signal relative intensity noise (RIN) transfer in silicon optical parametric amplifier (SOPA) with Raman effect, and draw a conclusion that Raman effect makes the spectra narrower from 260 nm to 180 nm. A maximum gain also appears at 1622 nm. Moreover, the effects of the related parameters in SOPA on the gain and the pump-to-signal RIN transfer characteristics are also discussed. The high gain (16 dB) and low pump-to-signal RIN transfer (7 dB) can be obtained by using the appropriate parameters of pump and silicon waveguide.     

窄线宽低噪声可调谐非平面环形激光器

针对空间相干光通信和探测等应用,对非平面环形激光器的线宽、噪声和调谐特性进行了系统的实验研究。单频输出功率达到752mW,光光效率42%,斜率效率54%。采用延时自外差拍频法测试了激光线宽,其随泵浦功率的增加而增大,输出功率小于200 mW 时,线宽小于1 kHz,在最高输出功率下线宽为2.3 kHz。激光强度噪声主要由弛豫振荡引起,相对强度噪声（RIN）随着泵浦功率的提高而降低。在1.78W 泵浦功率下,RIN 达到-93 dB/Hz。采用温度和压电两种方式进行了激光调谐。温度调谐范围达到62 GHz。压电调谐范围达到130MHz,响应带宽100 kHz。     

Dual-order Raman pump

This letter presents the design of a dual-order Raman fiber laser to be used as a pump for distributed Raman amplification. In particular, noise figure, gain ripple, and tunability are measured and analyzed in comparison to first-order Raman amplification. The tradeoff between noise figure improvement and increased nonlinear penalty is also discussed.     

Relative intensity noise in cascaded-Raman fiber lasers

Pump-to-Stokes and Stokes-to-Stokes relative intensity noise (RIN) transfer is discovered now for cascaded Raman fiber lasers (RFLs) with multimode laser pumping. We report on the first experimental study of this effect observed with two-stage phosphosilicate RFL and also propose its analytical explanation. It is shown that the peaks of radio-frequency (RF) spectrum associated with longitudinal mode beating in the pump laser cavity almost uniformly transfer to the first and second Stokes RF-spectra, thus increasing RIN of the RFL in megahertz-frequency domain.     

Performance limitations of high-power DFB fiber lasers

In this letter, we experimentally study several different configurations of high-power single-frequency sources based on distributed-feedback fiber laser (DFB FL). In particular, we have compared two schemes in terms of pumping efficiency, relative intensity noise (RIN) and optical signal-to-noise ratio (OSNR): directly pumped DFB FLs pumped by a high-power fiber-based pump source (stand-alone DFB FL) and a combination of a DFB FL and a power amplifier (amplified DFB FL). At the output powers below 40 mW, a stand-alone DFB FL has the highest OSNR (> 63 dB) and the lowest RIN (< -165 dB/Hz). The net efficiency of a stand-alone DFB FL can be doubled by using an amplified DFB FL at the expense of degraded OSNR and RIN. It is also shown that RIN below -160 dB/Hz and OSNR > 60 dB can be achieved by an amplified DFB with output power greater than 1 W.     

Influence of Pump-to-Signal RIN Transfer on Noise Figure in Silicon Raman Amplifiers

The effect of the relative intensity noise (RIN), transferred from the pump to the signal, in 1-cm-long chip scale silicon Raman amplifiers is investigated in the presence of nonlinear losses. We show that due to the short waveguide length, the reduction in fluctuations that normally occurs due to “walk-off” between pump and signal waves in fiber amplifiers is inefficient in chip scale Raman amplifiers. In the counterpropagating pump configuration, which leads to minimum frequency RIN transfer, fluctuations up to 1.5 GHz are transferred from the pump to the signal. As a case study, the noise figure degrades by as much as 11 dB in the silicon waveguide with the free carrier life time of 0.1 ns, when it is pumped with a laser with a RIN value of $-$125 dB/Hz.      

Penalty-free 10 Gbit/s single-channel co-pumped distributed Ramanamplification using low RIN 14xx nm DFB pump

A penalty-free 10 Gbit/s single-channel transmission with co-pumped distributed Raman amplification using a novel high power, low relative integrity noise (RIN), multimode 14xx nm distributed feedback pump is reported. No penalty from pump to signal RIN transfer was observed with co-pumped Raman gains up to 6 dB large effective area fibre (LEAF). In contrast, 0.5 dB penalty was observed with a fibre Bragg grating stabilised pump at 6 dB of Raman gain     

双向时分复用光纤时间传递链路噪声分析

研究分析了双向时分复用(BTDM)光纤时间传递链路 的主要噪声及产生机理,建立了基于BTDM光纤时间传递 的链路噪声模型。仿真分析了激光器强度噪声、光放大器增益与个数、接收机带宽等对BTDM 光纤时间传 递接收信噪比(SNR)的影响。结果表明,BTDM光纤时间传递 接收SNR在光放大器达到最优增益时最大,且最 大SNR随光放大器个数的增加而增加并趋于稳定;相同长度光纤链路,光放大器个数越多 ,在一定范围 内,激光器相对强度噪声对BTDM光纤时间传递链路接收SNR 影响更大,接收机带宽对BTDM光纤时 间传递接收信号抖动的影响越小;BTDM光纤时间传递接收SNR随定时信号前 光持续时间的增加而减小,并趋于WDM方案的SNR。     

Effect of pump laser noise on an erbium-doped fiber-amplified signal

The effect of pump laser noise on erbium-doped fiber-amplifier (EDFA) output was investigated using an optically pumped semiconductor laser (OPSL) as a high-power pump. Measurements included pump and amplified signal relative intensity noise (RIN) in frequency and time domains as well as gain spectral measurements and 10-Gb/s Q-factor tests, all under several levels of backreflection to the pump laser. Time-domain low-frequency noise (<50 kHz) was observed to increase with increasing backreflection. With 150-mW OPSL output power and -28 dB backreflection, temporal RIN was /spl sim/3.4% for the pump and /spl sim/2.2% for the amplified signal. At a maximum pump power of 450 mW, RIN was 1.4% and 1.1%, respectively. The measured Q-factor of 12.5 dB at 10 Gb/s showed less than 0.5-dB penalty compared to a back-to-back system measurement of 13 dB. Power budget and operating specifications of an OPSL-pumped multicoil EDFA were also evaluated.     

Experimental Investigation and Analytical Modeling of Excess Intensity Noise in Semiconductor Class-A Lasers

Excess intensity noise in a low-noise single-frequency class-A VECSEL is experimentally investigated over the frequency range 10 kHz-18 GHz. An analytical model is derived, based on multimode Langevin equations, to describe the observed laser excess noise over the whole bandwidth. From 50 MHz to 18 GHz, class-A operation leads to a shot noise limited relative intensity noise (RIN), namely -155 dB/Hz for 1-mA detected photocurrent, except at harmonics of the cavity free spectral range (FSR). At these frequencies, the excess noise is shown to be due to the amplified spontaneous emission contained in the nonlasing side modes. The measured levels of excess noise correspond to side mode suppression ratios (SMSRs) ranging from 70 to 90 dB, in agreement with the model. At low frequencies, 10 kHz-50 MHz, the observed excess noise spectrum has the expected Lorentzian shape. Its bandwidth increases with the pumping rate to an upper limit given by the cavity photon lifetime. Below this cutoff frequency, we show that the pump RIN is the dominant source of noise, while it is filtered by the laser dynamics above. Finally, our model permits to design a semiconductor class-A laser with an intensity noise limited to the shot noise level over the whole 10 kHz-18 GHz bandwidth.     

百瓦级1.2/1.5 μm双波长金刚石拉曼激光器（特邀）

具有高功率、高光束质量的双波长激光器在精密光谱、共振干涉测量和激光雷达等领域有着重要的应用。但是受到激光工作物质固有的光谱和增益特性制约,通过传统的粒子数反转激光器难以直接获得高功率的双波长激光输出,因此通常需要结合非线性光学频率变换技术将常规的单一波长高功率激光拓展至一个或若干个特殊波段。受激拉曼散射作为一种三阶非线性效应,具有频移大、自相位匹配和光束净化等优点,是实现高效率、高光束质量波长转换有效手段。利用具有宽光谱透过范围（>0.23 μm）、超高热导率（>2 000 W·m?1·K?1）和大拉曼频移（1 332 cm?1）等优异特性的金刚石晶体作为拉曼增益介质,通过外腔振荡结构实现了1 μm泵浦光直接向1.2 μm和1.5 μm双波长激光的高效转换,在最高稳态泵浦功率414 W的条件下获得了1.2 μm和1.5 μm功率分别为72 W和110 W的输出。该研究为实现高功率的双波长激光输出开辟了新的途径。     

High-power CW linearly polarized all-fiber Raman laser

We demonstrate a high-power continuous-wave linearly polarized all-fiber Raman laser. The maximum Stokes output power of 4.7 W at 1120-nm wavelength with conversion slope efficiency of 87% was achieved. It is shown that Raman laser threshold greatly depends on pump polarization degree while Raman laser polarization depends on the design of Raman converter rather than on polarization of the pump laser. Slope efficiency was found to be independent on pump polarization degree.