Applications of ultra-long Raman lasers in Photonics

拉曼散射是影响电磁辐射通过物质传播的基本过程。1928年，c·v·拉曼首次报道了这种效应，并因此获得了1930年的诺贝尔奖。1972年，在单模光纤中首次观察到受激拉曼散射。在光学中的受激拉曼散射（SRS）过程中，一个光子在通过物质介质传输时放弃其能量，产生一个波长更高的新光子，该光子对应于同时通过光纤的其他辐射，加上一些以振动态（声子）的形式被光纤吸收的剩余能量。这些振动状态的能量取决于材料的特性，因此能量从较低波长转移到较高波长（增益谱）的方式是特定介质的特征。对于硅纤维，当能量从泵浦转移到频率低约13.2太赫兹的辐射时，拉曼转换效率达到最大值。近年来，光纤中拉曼效应的开发为光子学中的许多重要应用打开了大门，这些应用对光子学和通信工业产生了直接的影响。仅仅依靠材料的特性就可以将能量从一个频率转移到另一个频率，这是一个非常强大和有吸引力的可能性，例如，在拉曼光纤激光器、分布式放大器和频率转换器的创造中已经得到了转化。在前面提到的应用中，分布式放大可能是未来电信行业具有更高短期效应潜力的技术，因为它似乎是部署未来高容量光通信链路的关键，这要归功于它提高系统性能和扩大工作波长范围的能力。最近，我们已经证明了拉曼效应可以用来将长光纤通信链路作为一个整体转换成超长激光器，在这个过程中创造了现存最长的腔激光器。通过这种超长激光传输信息时，拉曼增益分布接近理想，并且信号在传输过程中不会受到功率变化的影响，这在降噪和提高系统性能方面具有重要的好处。无损传输一直是光通信的长期梦想目标，它将减少线路中的噪声，并为非线性物理和应用数学领域的研究创造令人兴奋的可能性。但超长激光器是非常有趣的设备，它不仅可以用作几乎无损的通信通道，还可以用作光源。超长拉曼激光传输跨度代表了一个简单但相当激进的新概念，近年来由于其众多潜在的应用和与概念本身相关的令人兴奋的潜在物理学，引起了人们的极大兴趣。作为这个想法的发起者，首席研究员和阿斯顿大学的光子学研究小组非常适合扩展和推进它的任务。这项建议的经费将证明是非常宝贵的，可用于获得将这项原始研究提高到下一个水平所需的人力和基本设备。

Raman scattering is a fundamental process that affects electromagnetic radiation when this is transmitted through matter. The effect was first reported in 1928 by C. V. Raman, who was awarded the 1930 Nobel Prize for his discovery, and in 1972 stimulated Raman scattering was observed for the first time in single-mode optical fibres. In the process of stimulated Raman scattering (SRS) in optical, a photon that is being transmitted through the material medium gives up its energy to create a new photon at a higher wavelength corresponding to some other radiation simultaneously travelling through the fibre, plus some residual energy which is absorbed by the fibre in the form of vibrational states (phonons). The energy of these vibrational states is dependent on the material properties, so the way the energy is transferred from the lower wavelengths to the higher wavelengths (gain spectrum) is a characteristic of the particular medium. For a silica fibre, the maximum Raman conversion efficiency is achieved when the energy is transferred from the pump to radiation with frequency about 13.2 THz lower.In recent years, the exploitation of the Raman effect in optical fibre has opened the door to many important applications in photonics that have had an immediate impact in the photonics and communications industry. The possibility of shifting energy from one frequency to another by relying solely on the properties of the material is a very powerful and attractive one that has translated, for example, in the creation of Raman fibre lasers, distributed amplifiers and frequency converters. Of the previously mentioned applications, distributed amplification is perhaps the technology with the potential for a higher short-term effect in the future of telecomms industry, as it seems to hold the key for the deployment of future high-capacity optical communication links, thanks to its ability to increase system performance and expand the range of operating wavelengths. Recently, we have demonstrated that the Raman effect can be used to transform long fibre optic communication links as a whole into ultra-long lasers, creating in the process the longest cavity laser in existence. When transmitting information through such an ultra-long laser, Raman gain distribution is close to ideal, and the signal is spared from suffering power variations during transmission, which can bring important benefits in terms of noise reduction and improved system performance.Lossless transmission has been a long-term dream goal of optical communications that would bring with it a reduction of the noise in the line, as well as create exciting possibilities for research in the fields of nonlinear physics and applied mathematics. But ultra-long lasers are very interesting devices that can be used not only as virtually lossless communication channels, but also as light sources.Ultra-long Raman laser transmission spans represent a simple but quite radical new concept that has attracted much interest in recent times, both due to their numerous potential applications and to the exciting underlying physics associated with the concept itself.As originators of the idea, the principal investigator and the Photonics Research Group at Aston University are perfectly suited to the task of expanding and advancing it. The funding of this proposal would prove invaluable for acquiring the manpower and basic equipment required to take this original research to the next level.