OPTICALLY-INJECTED MULTI-SECTION LASERS FOR CHAOTIC ENCRYPTION SYSTEMS

半导体激光器的工作稳定性对由另一个激光器产生的光信号或由于输出光的外部反射而注入激光腔非常敏感。注入光束与激活腔介质之间的非线性相互作用导致激光器的混沌运行。虽然这种状态在激光器的通常应用中是不希望的，但是混沌振荡的状态为增强安全光通信和开发用于信号加密的新技术开辟了新的途径，在该信号加密中，通过连续调制发射激光器设备的动态变量来执行信号编码。在各种研究实验室中实现的具有复杂混沌动力学的复杂光学密码系统主要基于相对简单的单段半导体激光二极管。同时，具有复合光学腔的多段半导体激光器，包括被动和主动部分以及多个光栅，具有固有的高潜力，表现出非常复杂的随机动力学性质。就混沌区域而言，这将导致高维混沌，这是提高光学密码系统的机密性所必需的。这一特点与最近在商业多媒体发展方面取得的巨大技术进步相结合，可调谐半导体激光器是一种新型的半导体激光器，它的混沌动力学特性及其在光学加密系统中的应用前景，从理论和应用两个方面都具有重要意义。这种复合系统的显著特点是，它们通常是由具有非均匀空间变化的介质或截面组成的，光学参数，例如折射率、材料增益、光学损耗、非均匀光栅、耦合等。除了这种所谓的结构不均匀性之外，一些光学参数可以是器件操作条件的函数（所谓的功能不均匀性）。例如，可以通过电流注入或通过诸如空间烧孔或增益非线性（增益压缩）的固有现象来修改复合结构的某些部分中的折射率。这里的关键问题是，一般来说，这些变化的特征空间尺度可以与传播光的波长具有相同的量级，因此通常的耦合模理论方法在这里不适用。我们将发展一个适当的新的形式主义和技术来描述电磁波在这样的系统中的传播和相互作用。该方法适用于多电极多段半导体可调谐激光器或集成有源/无源光路等光学非均匀系统，研究了多段半导体可调谐激光器在外部光注入或光电反馈作用下的随机动力学行为。为了实现这一目标，我们将开发和应用一种新的通用方法来研究光场的时空特性，包括复合光电系统中的混沌、噪声以及相关的量子和经典效应。在混沌状态下工作的激光器可以潜在地用作基于数值算法的经典加密技术的替代方案。因此，该项目的主要目标是将多段可调谐激光器应用于同步混沌光学加密系统和通信密码学。所开发的理论将与我们和其他实验室获得的关于多段激光器受光注入的同步混沌状态的最新实验结果进行测试。

Stability of the operation of semiconductor lasers is very sensitive to injection into the laser cavity of the optical signal generated by another laser or due to an external reflection of the output light. The non-linear interaction between the injected beam and the active cavity medium results in the chaotic operation of the laser. Although this state is undesirable in usual applications of lasers, the regime of chaotic oscillations opened a new avenue for enhancement of secure optical communication and development of novel techniques for signal encryption in which signal encoding is performed through continuous modulation of a dynamic variable of the transmitting laser device.Up to now, complex optical cryptosystems with complicated chaotic dynamics implemented in various research laboratories were mainly based on relatively simple single-section semiconductor laser diodes. At the same time, the multi-section semiconductor lasers with composite optical cavities, which include passive and active sections and several gratings, have inherently high potential for exhibiting very complicated stochastic dynamical properties. As far as the chaotic regime is concerned, this will result in the high-dimensional chaos that is required to enhance the confidentiality of optical cryptographic systems. This feature combined with recent tremendous technological progress in the development of commercial multi-section tunable laser diodes makes a comprehensive study of chaotic dynamics in these lasers and their potential for optical encryption systems timely and important from both fundamental and applied point of views.The distinctive feature of the composite systems is that in general they are composed of media or sections with an inhomogeneous spatial variation of the optical parameters, such as refractive index, material gain, optical losses, nonuniform gratings, coupling, etc. In addition to this so-called structural inhomogeneity, some of the optical parameters could be functions of the device operation conditions (so-called functional inhomogeneity). For example, the refractive index can be modified in some parts of the composite structure by current injection or by intrinsic phenomena such as spatial hole burning or gain nonlinearities (gain compression). The key issue here is that in general the characteristic spatial scale of these variations can be of the same order as the wavelength of the propagating light, and because of this the usual coupled-mode theory approach is not applicable here. We will develop an appropriate new formalism and technique to describe the electromagnetic wave propagation and interaction in such systems. This general approach can be applied to various optically inhomogeneous systems, such as multi-electrode multi-section lasers or integrated active/passive photonic circuits.This proposal is devoted to a study of the stochastic dynamics of multi-section semiconductor tunable lasers subject to external optical injection or to optoelectronic feedback. In order to achieve this goal we will develop and apply a new general approach to study spatio-temporal properties of the optical fields, including chaos, noise and related quantum and classical effects in the composite optoelectronic systems. The lasers that operate in chaotic regime can potentially be used as an alternative to classical encryption techniques based on numerical algorithms. Therefore, the main thrust of the project is related to application of multi-section tunable lasers for synchronised chaotic optical encryption systems and communication cryptography.The developed theory will be tested against very recent experimental results on synchronised chaotic regimes of multi-section lasers subject to optical injection obtained in our and other laboratories.