Chaos shift-keying encryption in chaotic external-cavitysemiconductor lasers using a single-receiver scheme

In this letter, we numerically show that chaos shift-keying (CSK) encryption can be achieved by using a single receiver, thus providing a better performance when comparing with the traditional CSK scheme based on two receivers. We analyze the rate equation model for two unidirectionally coupled single-mode external-cavity semiconductor lasers operating in a chaotic regime. The message is encoded in the emitter by slightly varying its injection current. We find that under appropriate conditions, the receiver laser synchronizes to the chaotic emitter, filtering the encoded message and allowing message extraction     

Tuning fidelity of acoustooptically controlled external-cavitysemiconductor lasers

External cavity semiconductor lasers in extended- and ring-cavity configurations were tuned with chirp-compensating pairs of acoustooptic filters. Nanometer-size tuning gaps observed by previous workers were eliminated. The tuning range was approximately 80 nm for the extended cavity and at least 55 nm for the ring cavity. The root-mean-square tuning error was 0.036 nm for the extended cavity and 0.018 nm for the ring cavity. The output could be swept up to 35 mm in as little as 10 msec, limited by the radio-frequency generator. Transmittance measurements made on spare acoustooptic filters using the extended-cavity laser as a swept source were in good agreement with quasi-static measurements made using a grating-tuned laser     

Criteria for synchronization of coupled chaotic external-cavitysemiconductor lasers

We study the synchronization of two unidirectionally coupled single-mode external-cavity semiconductor lasers, that operate in a chaotic regime. A simple theory is developed to obtain synchronization conditions and to analyze the effects of the detuning between the two lasers. We find that numerical simulations are in good agreement with the theory     

All-electronic suppression of mode hopping noise in diode lasers

A simple all-electronic stabilization scheme is presented for suppression of external-cavity mode-hopping noise in diode lasers. This excess noise is generated when the laser is subjected to optical feedback and may degrade the overall performance of optical systems including sensors. Suppression of the noise has been demonstrated to improve the sensitivity of a coherent sensor by more than 23 dB     

折叠腔内腔倍频激光器抑制绿光噪声的研究

使用Jones矩阵法详细研究了V型折叠腔内腔倍频激光器抑制绿光噪声的条件,并用计算结果作了说明。给出了一些典型的V型折叠腔有效调整偏振态以消除和频的配置方式,并与有关实验作了比较。     

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。     

超低频遥控系统的噪声建模与抑制

超低频遥控系统受大气噪声干扰严重,传统的匹配滤波器性能退化明显,为提高超低频遥控系统的可靠性,研究了系统中的噪声建模与抑制技术。通过对实测数据的分析验证了采用对称α稳定（SαS）分布拟合信道噪声的可行性,从分布模型出发,通过仿真研究了Myriad滤波器、局部最优检测器和削波器对超低频大气噪声的抑制效果。结果表明：SαS分布可以作为超低大气噪声的幅度概率分布模型;Myriad滤波器能够以较低的计算复杂度实现对超低频大气噪声的有效抑制。     

Mode-partition noise in fibre lasers

The presence of mode-partition noise in an erbium-doped fibre laser has been experimentally demonstrated. A numerical model has been developed using the Langevin rate equations. Its predictions are in qualitative agreement with the experimental data     

Characteristics of mode-hopping noise and its suppression with the help of electric negative feedback in semiconductor lasers

Some detailed properties of mode-hopping noise in semiconductor injection lasers are reported, and the validity of electric negative feedback as a method of suppressing the noise is demonstrated. Mode-hopping noise was found to be an intrinsic property of the laser, independent of optical feedback (reinjection of the output light) reflected at the surface of an external device. The optical feedback works to shift the operating point of the laser from a stable condition having single-mode operation to an unstable condition revealing the modehopping phenomena. Characteristics of the mode-hopping noise support well the theoretical analysis in which the source of the noise is assumed to be fluctuations of the emission and the electron wave accompanied by spontaneous emission and in which the noise is amplified through mechanism of the mode competition phenomena. Mode-hopping noise was suppressed with the help of the electric negative feedback from the optical detector to the injection current source more effectively than by another reducing method of superposition of the high-frequency current. The suppressed noise level was lower than that at stable single-mode operation.     

Electronic phase-noise suppression in diode lasers

It is shown that active current feedback reduces phase noise in diode lasers by between a factor of 1000 and 30 in the 0?250 Hz region.     

Chaos in the coherence collapse of semiconductor lasers

The observation of a quasiperiodic route to chaos in the coherence collapse of a single-mode semiconductor laser subjected to back-reflections from an external cavity is discussed. Also, a simple deterministic model that correlates well with the data is presented     

Chaos synchronization in semiconductor lasers with optoelectronic feedback

Chaos synchronization is experimentally investigated in semiconductor lasers with delayed optoelectronic feedback. Depending on the coupling strength of the driving signal to the receiver, the lasers fall into different regimes of chaos synchronization or modulation. Synchronization happens when the coupling strength to the receiver matches the feedback strength to the transmitter, where the receiver output reproduces the output of the transmitter regardless of the presence of channel distortion or an encoded message. Modulation dominates when the coupling strength is much less than the feedback strength, where the receiver output follows the driving signal. In between, there is no sharp transition between these two regimes but only a mixture of the two phenomena. Driven oscillation is not observed in this optoelectronic feedback system when the coupling strength is increased to a level higher than the feedback strength.     

Mode-partition noise in vertical-cavity surface-emitting lasers

We present a numerical study of the effects of carrier diffusion and spatial hole-burning on the noise characteristics of vertical-cavity surface-emitting lasers (VCSEL's) under both single-mode and multimode operations. In the case of single-mode operation, VCSEL noise characteristics are similar to those of edge-emitting lasers except for a diffusion-induced damping of relaxation oscillations. Under multimode operation, VCSEL's exhibit low-frequency noise enhancement due to mode partition. However, depending on the spatial distributions of the transverse modes excited, the mode-partition noise characteristics can be quite different.     

Low-frequency intensity noise in semiconductor lasers

The observed 1/f noise in the light-output power S _p of four different types of heterostructure lasers is explained in terms of spatially uncorrelated gain fluctuations and spontaneous emission fluctuations. Two possible noise sources are suggested: fluctuations in the absorption coefficient and fluctuations in the number of free carriers. Both models are in agreement with the experimental results obtained from index-guided and gain-guided diodes at wavelengths of 1.3 and 0.8 μm. The dependence S_p ∝P^m has been observed with P the average light-output power and m=3/2 under spontaneous emission, a small transition region with m=5/2, m=4 in the superradiation region, and 0⩽m⩽1 in the laser region     

Polarization-resolved low-frequency noise in GaAlAs lasers

Low-frequency intensity noise displaying 1/fdependency of the light polarized parallel and perpendicular to the junction plane and the correlation between these noise components is investigated in GaAlAs diode lasers. The absolute noise level for the component polarized parallel to the junction (lasing component) rises about 40 dB as the current passes through lasing threshold, while the noise for the orthogonal polarization drops by about 5 dB. The two noise components are well correlated slightly below threshold (coherence function ∼ 0.9), but the coherence function drops rapidly to near zero above threshold. An exception to this behavior occurs in the lasing mode when mode hopping takes place, when the two noise components are well correlated. A qualitative explanation for these phenomena is based on the relation between spontaneous and stimulated emission rates and fluctuations in the intracavity carrier density.     

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.     

光注入多模半导体激光器的混沌及其同步

为了在光纤通信中实现多模同步传输以提高通信容量,构建了一个光注入多模半导体激光器开环混沌通信系统,并利用MATLAB数值仿真了系统的同步性能。结果表明,选取合适的系统参量,多模半导体激光器混沌通信系统能够实现完全同步;发射激光器和接收激光器对应模式可以实现完全同步,而且系统对内部参量失配具有较好的容忍性。     

Electrical mode-hopping noise in external-cavity semiconductor lasers and mode-hopping elimination by a nonoptical control loop

The longitudinal mode-hopping and the associated terminal electrical noise in AlGaAs buried heterostructure lasers in an external-cavity configuration are investigated. It is found that the electrical mode-hopping noise has a1/f-dependence when two external-cavity modes are involved in the mode-hopping. Furthermore, it is found that the optical feedback can suppress the electrical noise significantly below the noise level of the free-running laser. This corresponds to a reduction of the emission line width which is in agreement with the reduction of the electrical noise level. A novel, nonoptical, scheme for active elimination of mode-hopping attributable to thermal drift or mechanical disturbances in CW-operated external-cavity lasers is also proposed and demonstrated. Using this method, where the electrical noise is used as an error signal in a control loop, long-term single external-cavity mode operation and low electrical noise and optical intensity noise levels were maintained.     

He-Ne激光噪声的测量

一、引言 近年来利用激光进行信息处理方面的应用越来越多,如光通讯、激光高速扫描检测及激光唱盘等。这些应用中都需要低噪声激光束,并已出现低噪声的商品激光管。在噪声特性研究中多采用频谱分析仪方法和高响应时间的光电倍增管作为光探测器,但将此装置作为噪声的定量测量仪器显得价格昴贵,数据处理也较繁琐;另外还有光电池和光电二极管作为探测器,用毫伏表或示波器显示噪声大