光纤陀螺系统中信号光反馈下的激光光源强度噪声特性研究

从建立光纤陀螺激光光源受信号光反馈作用时的等效腔模型出发,对影响光源强度噪声的诸因素进行了理论分析,结果与实验很好符合,并提出了消除信号光反馈对系统性能影响的方法.     

半导体抽运Nd:YAG激光器强度噪声抑制的研究

为了降低半导体抽运固体激光器的弛豫振荡噪声,提高其输出功率的稳定性,采用光电负反馈的方法来抑制半导体抽运的固体激光器的强度噪声,并对激光器强度噪声的理论特性进行了分析。根据理论分析结果设计了比例-积分-微分反馈控制电路,通过运用该反馈电路对激光器进行强度噪声抑制实验,得到了比较理想的实验数据,即当抽运功率为700mW、弛豫振荡峰频率为300kHz时,弛豫振荡峰值处和低频区域强度噪声分别降低了45dB和15dB;当抽运功率为550mW、弛豫振荡峰值为250kHz时,弛豫振荡峰值处和低频区域强度噪声分别降低了40dB和10dB。结果表明,该反馈控制电路能够有效地降低半导体抽运固体激光器的强度噪声,提高激光器输出功率的稳定性。     

利用光电反馈抑制钛宝石激光器低频段的强度噪声

对前置光电负反馈抑制钛宝石激光器强度噪声方法的特性进行了理论分析,表明注入噪声不同时对应的最佳反馈增益不同。利用前置光电负反馈方法,在实验上实现了全固态连续单频可调谐钛宝石激光器低频段的强度噪声抑制,通过调节反馈增益,使激光器的强度噪声抑制程度最大。在分析频率为1.125 MHz处,强度噪声由原来的8.7 dB降低到了1.4 dB,抑制程度达7.3 dB。调节反馈增益和相位延时,可以获得不同分析频率的强度噪声的降低。     

Information capacity of the Poisson channel

The information capacity of the Poisson channel with random or time-varying noise intensity is obtained for time-varying peak and average constraints on the encoder intensity. The channel model is specified, and some definitions from information theory are given. Causal feedback is shown not to increase the channel capacity for the case of nonrandom noise intensity. For random noise intensity, use of causal feedback does increase capacity; the extent of that increase is quantified. Jamming is considered, and the optimal jamming signal is given. Poisson channels with thinning are introduced     

光电反馈抑制掺铒光纤激光器的低频强度噪声

通过光电反馈电路对掺铒光纤激光器的中低频噪声进行了抑制。根据速率方程理论,分析了影响掺铒光纤激光器强度噪声的因素,通过电路仿真分析优化反馈电路参数,重点讨论反馈信号的相位对噪声抑制的影响。实验表明：激光器的低频(小于20KHz)强度噪声平均降低了10dB,中频弛豫振荡峰处（30KHz附近）抑制达35dB,并且克服了光电反馈抑制强度噪声使弛豫振荡峰向高频移动,导致高频噪声增大的问题。优异的噪声特性使光纤激光器在光传感领域具有很高的实用价值。     

Noise analysis of semiconductor lasers within the coherencecollapse regime

The authors present a theoretical analysis of semiconductor laser noise with optical distant feedback. The results show good agreement with numerical simulations. With the analytical model developed, one can easily calculate the relative intensity noise (RIN), the frequency noise, and the spectral linewidth of the semiconductor laser diode. It was found that, because of the decreasing damping frequency, with increasing feedback, the maximum relative intensity noise at the relaxation frequency does not increase monotonically. The maximum RIN is given as the reciprocal value of the damping rate     

Intensity noise of laser diodes with optical feedback

We examine the intensity noise of laser diodes with optical feedback for several feedback conditions. Three stable feedback conditions have been observed, which are defined as follows: an external mirror length shorter than 15 mm, small and large ratios of mirror to laser-front facet reflectivities. Reduction of the external-cavity length, notably to less than 15 mm, stabilized the laser diode and resulted in low intensity noise. A new theoretical treatment of optical feedback is proposed, wherein the feedback field is taken into account in the boundary condition at the feedback coupling laser facet. Theoretical derivations of the intensity noise of external-cavity feedback laser diodes are in good agreement with measured results     

Effective Noise Reduction by Electric Positive and Negative Feedback in Semiconductor Lasers

Semiconductor lasers tend to generate excess intensity noise called the optical feedback noise in addition to the quantum noise. A noise reduction method using an electric positive and negative feedback loop between an optical detector and a semiconductor laser was demonstrated in this paper. The electric positive feedback was set in a high-frequency region, reducing the optical feedback noise, while the electric negative feedback was set in a frequency range lower than the positive-feedback frequency, resulting in the suppression of the quantum noise (optical shot noise). Noise reduction over 100-MHz frequency region and a reduction ability superior to that obtained by the superposition of high-frequency current were confirmed.     

Suppression of the intensity noise in a diode-pumped neodymium:YAGnonplanar ring laser

We investigate the intensity noise properties of a continuous-wave diode pumped Nd:YAG ring-laser system and present results for an active feedback loop that suppresses the relaxation oscillation noise. This system reduces the intensity noise to within 6.1 dB of the quantum noise equivalent level (which is at 1.5×10^-8/√Hz for 1.5 mA) for frequencies between 10 kHz to 300 kHz and to less than 1×10^-7/√Hz for frequencies between 300 Hz and 10 kHz. The technical properties of the optimized feedback system are presented. The theoretical limits of performance for the system are discussed and it is shown that the performance is within 3.1 dB of these limits. We also present data from an optical beat experiment demonstrating that the intensity control system does not introduce any new features into the frequency noise spectrum     

Optoelectronic feedback loop for relaxation oscillation intensitynoise suppression in Tm-Ho:YAG laser

An optoelectronic feedback loop that can be used to effectively reduce the intensity noise of a 2.1 μm Tm-Ho:YAG laser has been designed. The feedback circuit is based on a variable-gain biquadratic bandpass filter with adjustable central frequency and quality factor, providing a high loop gain around the relaxation oscillation frequency of the laser and a closed-loop phase margin larger than 50°. The relaxation oscillation peak in the intensity noise spectrum was completely suppressed in closed-loop operation, and a noise reduction of up to 24 dB was obtained     

Reflection noise in index-guided InGaAsP lasers

We report a detailed study of the excess noise induced in index-guided InGaAsP laser structures by reflection feedback. The phenomena of high-frequency noise (1-5 GHz), low-frequency noise (< 100 MHz), and intensity fluctuations are shown to have a common physical origin in the unusual instability of the coupled laser-external cavity system. After a randomly occurring light intensity drop, the light output recovers in 10-15 steps, each corresponding to an external cavity roundtrip (high-frequency noise); the total recovery time corresponds to the low-frequency noise. The instability, and the subsequent noise, can be suppressed under conditions of very strong feedback such as obtained for lasers with anti-reflection-coated facets. The reflection noise characteristics are shown to be largely independent of the laser structure and structure modifications such as distributed feedback.     

外部光反馈半导体激光器的结构优化研究

通过构建外部光反馈半导体激光器的理论模型,并结合激光器速率方程和噪声理论,讨论并优化了增益芯片和光纤光栅外腔各参数在不同电流下对器件频率噪声和相对强度噪声的影响.模拟结果表明:通过改变电流并对有源区尺寸、光纤光栅结构和耦合效率等参数的调整,在理论上可以将器件的频率噪声降低5×108 Hz左右,相对强度噪声降低8 dB/Hz左右.该研究将为低噪声、窄线宽外部光反馈激光器的实验研究提供理论指导,同时也对其他结构的外腔激光器噪声特性的研究有着借鉴意义.     

Relative intensity noise of multiwavelength fibre laser

Relative intensity noise of a six-channel multiwavelength distributed Fabry-Perot fibre laser is compared to the noise of a singlemode distributed feedback fibre laser. The noise characteristics of individual channels are similar to that of the singlemode laser, offering a low-cost and compact solution for wavelength multiplexing applications without noise penalty.     

LD抽运1319nm单频激光器的调谐和噪声抑制研究

研究了LD抽运单块非平面行波环行腔Nd:YAG激光器的调谐特性,通过控温法实现了1319nm单频激光的宽范围调谐,调谐范围14GHz。实验研究了影响1319nm单频激光器功率噪声主要因素,测量了激光功率噪声谱,并通过光电反馈抑制弛豫振荡功率噪声,弛豫震荡中心频率噪声抑制了30dB,提高了测量精度。     

Chaos control and noise suppression in external-cavitysemiconductor lasers

Feedback-induced chaos and intensity noise enhancement in a laser diode with external optical feedback are studied by computer simulations. The enhancement of relative intensity noise (RIN) that is often observed in experiments is considered as a result of the feedback-induced deterministic chaos and the intensity noise suppression is treated from the viewpoint of chaos control. Especially, the conventional noise suppressing technique known as a high-frequency injection modulation is turned into a problem of stabilizing chaos through parameter modulations. We developed an analytical method which allows to optimize the modulation frequency from the linear stability analysis of the dynamical model that describes the laser diode with external feedback. The robustness of the modulation with respect to the modulation frequency and depth is verified and the results suggest the feasibility of applying our method to actual noise suppression. The RIN in the low-frequency region (up to 100 MHz) is shown to be reduced to the solitary laser level when the feedback-induced chaos is effectively controlled with the optimized modulation frequency     

外部微扰反馈对Bragg声光双稳系统混沌的控制

针对Bragg路声光双稳系统的混沌态,提出了利用外部微扰反馈的方法对其进行控制。数值分析表明,适当选择反馈强度可将原本混沌的系统控制到各种不同的周期轨道上,同时计算了噪声对系统状态演化的影响。结果表明,系统对小幅度噪声具有一定抗干扰能力。     

用于精密测量的低噪声激光器研究进展（特邀）

激光精密测量的测量精度主要受限于光场噪声和各种技术噪声,在去耦合技术噪声后,光场量子噪声成为限制其测量精度的主要因素。文中针对全固态单频激光器强度噪声特性,阐述强度噪声的主要来源及其对功率噪声谱的影响,回顾了传统直流反馈控制、光学交流耦合反馈控制和量子压缩器三种强度噪声抑制技术。通过回顾相关技术的发展历程,总结了强度噪声抑制技术的当前发展水平和未来发展趋势——三种技术相结合的抑噪方案是解决高灵敏度探测的重要途径。     

Measurements and theory of correlation between terminal electricnoise and optical noise in a two-section semiconductor laser

The correlation between the terminal voltage noise and the intensity and frequency noise is characterized experimentally and theoretically for a two-section distributed Bragg reflector (DBR) laser. An all-electric feedback scheme for noise reduction is proposed and analyzed theoretically     

非平面环形腔激光器的强度噪声及其抑制

采用全量子理论对单块非平面环形腔Nd:YAG激光器的强度噪声特性进行了研究,通过理论分析和仿真发现,单块非平面环形腔激光器的弛豫振荡主要由真空起伏、偶极起伏和内腔损耗引起,抽运噪声和自发辐射对弛豫振荡的影响相对较小。同时,从理论上对强度噪声的光电负反馈抑制进行了分析和仿真,为实验上噪声抑制电路的设计提供了一定的理论基础。参考此理论电路,设计了可以获得较好的相位超前和低噪声宽带宽增益放大的噪声抑制电路,在实验上获得了良好的噪声抑制效果。当弛豫振荡峰为311kHz时,弛豫振荡峰处的强度噪声被抑制了39dB,在整个频谱范围内获得了低于-115dB/Hz的噪声水平。