Monolithically integrated, high coherence frequency comb generation through on-chip gain switching

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McCarthy, John T.
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University College Cork
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As the number of internet users continuous to increase, methods of developing new forms of communication networks are being widely considered. Optical frequency comb sources have the potential to reduce or eliminate the spectrally inefficient guard bands that are currently used to prevent cross-talk between adjacent channels. With their common laser source and fixed phase relation, frequency combs can offer to not only to replace the hundreds of lasers being used to generate hundreds of channels, but also reduce the present day separation between channels. This thesis demonstrates on-chip frequency combs that are generated through gain switching. Simulation analysis is carried out to investigate the effects of experimental parameters on the quality of gain switched combs and extensive experimental analysis is carried out to examine the experimental conditions required to enhance the quality of these combs. Typically a two laser design is used where a gain switched Fabry–Pérot laser is phase locked to a single mode laser creating a primary-secondary configuration. Different coupling techniques were investigated and developed, with stable combs being generated as a result of bidirectional coupling, and greater comb enhancement being demonstrated using mutually coupled techniques. Utilising both the combs generated through mutual coupling and the knowledge of on-chip, stable, bidirectionally coupled combs, the conditions required to generate an enhanced comb with additional comb lines are developed. Methods of on-chip comb line filtering are demonstrated for the purpose of future de-multiplexing systems. Finally, a new method of frequency comb generation through on-chip gain switching, without the previously required additional optical injection, is analysed and developed. The versatile design and ease of integration of these comb sources shows great promise for future generation designs and optical networks.
Frequency combs , Gain switching , Monolithic integration
McCarthy, J. T. 2023. Monolithically integrated, high coherence frequency comb generation through on-chip gain switching. PhD Thesis, University College Cork.
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