Photonic crystal fibers (PCFs) have emerged as a promising platform for a wide range of applications due to their unique properties and design flexibility. These fibers consist of a periodic array of microstructured air holes that run along the length of the fiber, which enables precise control over the propagation of light. Of particular interest are hollow core fibers, which are characterized by a central void that enables light to be confined within the hollow core. As research and development in this field continue to advance, photonic crystal fibers are poised to play a pivotal role in the next generation of optical communication and sensing systems.

The students task is to provide a comprehensive overview of PCFs with a focus on characterizing their distinctive linear and nonlinear properties. 

Possible literature:

• Philip St.J. Russell, "Photonic-Crystal Fibers," J. Lightwave Technol. 24, 4729-4749 (2006)
• Benabid, F., and P. J. Roberts. "Linear and nonlinear optical properties of hollow core photonic crystal fiber." Journal of Modern Optics 58.2 (2011): 87-124.

• lecture: Optical Communication Systems

Optical communication systems rely on various modulation techniques to encode information onto light signals for transmission. Intensity modulation (IM) is a basic method of varying the intensity of a light wave according to the signal to be transmitted. IM can be performed, for example, with a directly modulated laser (DML) or an electro-absorption modulator (EAM). However, IM with a DML or an EAM unintentionally induces phase modulation. Understanding this phenomenon is crucial as it affects signal quality and transmission efficiency. The student's task is to understand why this unintended phase modulation is generated and to analyze its impact on the communication system.

The following literature can be helpful:

• ZHANG, Kuo, et al. Performance comparison of DML, EML and MZM in dispersion-unmanaged short reach transmissions with digital signal processing. Optics express, 2018
• KOBAYASHI, Soichi, et al. Direct frequency modulation in AlGaAs semiconductor lasers. IEEE Transactions on Microwave Theory and Techniques, 1982
• KREHLIK, P. Directly modulated lasers in negative dispersion fiber links. Opto-Electronics Review, 2007
• AMRO, Mohammad Yousif; SENIOR, John M. Chirp control of an electroabsorption modulator to be used for regeneration and wavelength conversion at 40 Gbit/s in all-optical networking. Photonic Network Communications, 2005

During the internship, the student will be researching the application of Neural Network-based signal predistortion to mitigate the effects of fiber chromatic dispersion in direct detection systems.

• basic Python skills beneficial