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Processing Systems with Optical Delay

Periodic Reporting for period 1 - ProDelSys (Processing Systems with Optical Delay)

Reporting period: 2018-06-01 to 2020-05-31

The primary goal of my project “ProDelSys - Processing systems with optical delay” was to enhance my professional skills in laser physics, fibre optics and general nonlinear-wave theory. This had to be done via a research programme focused on developing of all-optical processing systems based on ultra-short pulse fibre lasers with optical delay or feedback. Ultra-short pulse fibre lasers are highly desirable and are deployed as light sources due to their flexibility, simplicity and cost-efficiency. They can be used as light sources for spectroscopy including chemical, and biochemical analysis, sensing, instrument calibration, optical clocking, and medicine.

The ultra-short pulse fibre lasers were proposed to be realised by mode-locking using an optical delay line (thus the title of the project). However, science is a living thing and constantly develops depending on the achieved results and the application requirements. So, the plans slightly changed and I was involved in the development and analysis of nonlinear dynamics of two types of ultra-short fibre lasers mode-locked by a saturable absorber instead of a delay line. The first laser was a Bismuth fibre laser to be used in medicine. The other one was an Erbium fibre laser. It was used to better understand laser behaviour and to use this knowledge by engineers and scientists for laser development and applications.

Two schemes for photonic fibre-based neural networks were proposed. Once fully implemented and their dynamics understood, these schemes can be used in telecommunication for signal detection and restoration as well as for signal classification. This will enable faster and more stable optical information transmission which will be profitable for the whole society. The society will also profit from the fibre-based sensors on which I worked during my Fellowship. The first sensor is to be used for various spectroscopic applications, the second one for low-invasive real-time diagnostics of cancer. The fibre-based scheme that I proposed to generate broad optical spectra in the mid-infrared range can enhance the progress of spectroscopic applications.

The results of this project that were achieved in collaboration with scientists and engineers from 7 European countries enhance the European leadership in photonics and produce a new generation of photonic systems and devices supporting the European vision for a high-technology economy to promote European social and economic cohesion and prosperity.
-technology economy to promote European social and economic cohesion and prosperity.
As proposed in the project plan, I was involved in the development of a passively mode-locked Bismuth fibre laser to be used for such medical applications as the reduction of skin acne, closure of the wounds, or to study biochemical processes in cells. Using mathematical modelling and computer simulations, suitable pulsing regimes of this laser were identified in the normal and anomalous laser cavity dispersion regimes. The results were presented at the international conference SPIE Photonics Europe. I developed a mathematical model for a mode-locked fibre laser using delay differential equations to combine the mathematical concepts of semiconductor optics with the concepts from fibre optics. Further, to enhance the implementation of AI technologies, I participated in the development of two photonic neural networks for optical signal recognition and restoration. Several problems to be solved in future were identified concerning these neural networks. For instance, a sophisticated scheme of the network training needs to be developed to make it fully autonomous from the training on a PC (as it is being done at the moment). I also took part in the development of a novel fibre sensor for various spectroscopic applications by experimentally testing its performance and identifying groups of biochemical elements and tissues for which it can be used.

I introduced a fibre-based scheme for generation of a broad optical spectrum (often called a supercontinuum) spreading from around 1500nm to 2500nm. It can be deployed for infrared spectroscopy in chemistry, food industry, artwork conservation, and medical diagnostics. The results were presented as posters and conference proceedings at international conferences CLEO/Europe-EQEC and OFC. Further, I analysed and evaluated light intensity data experimentally obtained with an Erbium-doped fibre laser that is passively mode-locked with carbon nanotubes. This data showed that fast and slow instabilities in the cavity induce various nonlinear waves. This contributes to the understanding of complex nonlinear laser dynamics. The results were presented at the international conference CLEO/Europe-EQEC and published as a journal paper in Laser Physics Letters. Also, I participated in the development of a novel fibre sensor that, in combination with artificial intelligence and machine learning technologies, would allow for low-invasive real-time diagnostics and determination of cancer boundaries directly during surgeries. Using machine learning techniques, I analysed the optical spectra that were taken in-situ by this novel sensor and was able to detect samples that indicated a cancerous tissue. A publication of these results as a journal paper is being prepared (as for July 2020). The sensor itself is in the further development phase to improve its characteristics and effectiveness.
The studies on mode-locked fibre lasers contribute towards the innovation in laser physics and laser development. They open the opportunity to use fibre lasers for applications in medicine and deepen the understanding of complex laser dynamics. The development of a mathematical model for fibre mode-locked lasers that is based on delayed differential equations connects the mathematical modelling in semiconductor and fibre optics and unifies mathematical concepts used in photonics.

The results achieved on photonic neural networks contribute to European policies. Since such neural networks are expected to consume less energy than their electronic counterparts, they will enhance sustainable technologies. Enabling signal restoration, recognition, and classification in telecommunication, they will contribute to the integration of digitalisation in all industrial technologies and societal challenges. If used for pattern recognition in communication signal transmission, they will also be useful for cybersecurity.

The fibre-based scheme for generation of a broad optical spectrum can be used for infrared spectroscopy in chemistry, food industry, artwork conservation, and medical diagnostics. Also, it allows for a deeper understanding of nonlinear effects in optical fibres.

The work on novel fibre sensors contributes towards the technological development in spectroscopy, biology, and medicine. Specifically, the fibre sensor for low-invasive real-time cancer boundary detection will allow for more precise and accurate surgeries on cancers and, thus, increase the chances of patients’ cure.

The beneficiaries of my project, apart from myself, will be scientists in the fields of optics, photonics, physics, applied mathematics, engineers developing and producing optical devices, medical doctors and their patients, companies working in the food industry or artwork conservation. Also, these will be young generations of students to whom I will transfer the knowledge and skills gained during my Fellowship.