Experimental and theoretical study of the optical frequency comb generated by gain-switching of semiconductor lasers

• Autores: Alejandro Rosado Pérez
• Directores de la Tesis: Ignacio Esquivias Moscardó (dir. tes.), José Manuel García Tijero (codir. tes.)
• Lectura: En la Universidad Politécnica de Madrid ( España ) en 2020
• Idioma: español
• Tribunal Calificador de la Tesis: Salvador Balle i Monjo (presid.), Paloma Rodríguez Horche (secret.), Vicente Durán Bosch (voc.), Ana Quirce Teja (voc.), Cristina De Dios Fernández (voc.)
• Programa de doctorado: Programa de Doctorado en Tecnologías de la Información y las Comunicaciones: Materiales y Dispositivos por la Universidad Politécnica de Madrid
• Materias:
  • Física
    • Óptica
      • Láseres
  • Ciencias tecnológicas
    • Tecnología electrónica
      • Dispositivos semiconductores
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• Resumen

  • The research work carried out within the framework of this PhD has focused on the generation of Optical Frequency Combs (OFC) in semiconductor lasers using the gain-switching (GS) technique. The work has been mainly experimental, although simulations have been used to contribute to a better understanding of the internal physics of the OFCs generation process. Various types of lasers have been used, specially distributed feedback (DFB) lasers and discrete mode lasers (DML). An exhaustive experimental characterisation of the properties of the OFCs generated by GS in a full range of operating conditions has been performed. Two ranges of repetition frequencies have been explored: the GHz range with applications in optical communications, and the range of hundreds of MHz for application in spectroscopy. The effect of the optical injection (OI) on the properties of the OFCs has been investigated, and interesting results have been obtained, such as the improvement or deterioration of the quality of the spectra depending on the GS and OI conditions. The optimal operating conditions to generate high quality OFCs at the different frequencies considered have been found. In order to improve the understanding of the different physical processes involved in the generation of the OFCs generated by GS, a simulation tool based on the rate equation model for semiconductor lasers has been developed, with detailed treatment of the noise sources. For a correct simulation of the OFCs the values of a set of internal laser parameters is are required. They were obtained through an original procedure based on the measurement of the relative intensity noise (RIN) spectra. Using this procedure, the uncertainty in the simulated results has been reduced, since it allows to extract more parameters than other procedures due to an adequate analytical treatment of the RIN equations. The simulations have completely reproduced the temporal and spectral response of different lasers in a wide range of electrical and optical injection conditions. From the simulations, the predominant physical processes that contribute to the generation of OFCs, dynamic "chirp" at high repetition frequencies, and adiabatic "chirp" at low frequencies, have been identified. It has been shown that it is possible to improve the characteristics of low frequency OFCs by driving the laser with electric pulses, instead of using sinusoidal driving. High quality 100 MHz OFCs (up to 866 tones in 10 dB) with good carrier-to-noise (CNR) ratio have been generated. It has also been shown that step-recovery diodes (SRDs) can be used as a source of electrical pulses to generate OFCs, thus reducing the cost and size of the equipment involved, while maintaining the quality of the OFCs. The role of the “jitter” of the electrical source in the quality of the OFCs has been studied theoretically and experimentally. Finally, the OFCs generated by gain-switching and optical injection have been used to measure the absorption spectra of different elements, using three different architectures: heterodyne detection, and dual-comb spectroscopy and a new implementation of this technique. In this implementation the dual-comb is generated from a single GS laser by alternating the repetition frequency. Promising results for the application of these OFCs in gas spectroscopy have been obtained.