OPTICALLY-INJECTED MULTI-SECTION LASERS FOR CHAOTIC ENCRYPTION SYSTEMS

半导体激光器工作的稳定性对由另一激光器产生的光信号注入到激光腔中或由于输出光的外部反射非常敏感。注入光束与有源腔介质之间的非线性相互作用导致了激光器的混沌运转。虽然这种状态在激光的常规应用中是不受欢迎的，但混沌振荡机制为增强保密光通信和开发新的信号加密技术开辟了一条新的途径，即通过连续调制发射激光设备的动态变量来执行信号编码。同时，具有复合光学腔的多段式半导体激光器，包括被动段和有源段以及多个光栅，具有很高的潜在表现出非常复杂的随机动力学特性。就混沌机制而言，这将导致增强光学密码系统保密性所需的高维混沌。这一特点与商用多段可调谐激光二极管发展的巨大技术进步相结合，使得对这些激光器中的混沌动力学及其在光学加密系统中的潜力进行了全面的研究，从基础和应用的角度都具有重要的意义。这种复合系统的显著特点是，它们通常是由光学参数的非均匀空间变化组成的，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之外，一些光学参数可能是器件操作条件的函数(所谓的功能不均匀)。例如，在复合结构的某些部分，折射率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)等本征现象来改变。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处于同一量级，因此通常的耦合模理论方法在这里不适用。我们将发展一种合适的新的形式和技术来描述电磁波在这样的系统中的传播和相互作用。该方法适用于各种光学非均匀系统，如多电极多节激光器或集成主/被动光子电路。本文研究了多节半导体可调谐激光器在外光注入或光电反馈作用下的随机动力学。为了实现这一目标，我们将发展和应用一种新的一般方法来研究光场的时空特性，包括混沌、噪声以及复合光电子系统中的相关量子和经典效应。在混沌状态下工作的激光有可能被用来替代基于数值算法的经典加密技术。因此，该项目的主要目的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。开发的理论将与最近在我们和其他实验室获得的关于多段激光在光学注入下的同步混沌区域的实验结果进行测试。

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.