Frequency and linewidth dependence of distributed-feedback resonators on thermal chirp

• Published in: 2017 19th International Conference on Transparent Optical Networks (ICTON) pp. 1 - 5
• Main Authors: Kores, Cristine C., Ismail, Nur, Geskus, Dimitri, Dijkstra, Meindert, Bernhardi, Edward H., Pollnau, Markus
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01.07.2017
• Subjects: Bragg gratings; Chirp; chirped gratings; coupled mode theory; distributed-feedback resonators; Gratings; narrow linewidth; Optical waveguides; Resonators; Transmission line matrix methods; Waveguide lasers
• ISSN: 2161-2064
• DOI: 10.1109/ICTON.2017.8025100

We present an analysis of the spectral characteristics of distributed-feedback (DFB) laser resonators with thermally chirped distributed mirrors. Such DFB resonators have the interesting capability of producing a linewidth as narrow as a few kHz. The investigated devices are ytterbium-doped amorphous Al 2 O 3 channel waveguides with a periodic Bragg grating inscribed into its SiO 2 top cladding. The resonance in the spectral response of the resonator results from a distributed λ/4 phase-shift produced by increasing the waveguide width. Its frequency is determined by the period of the Bragg grating, whereas its linewidth is determined by the intrinsic losses and the outcoupling losses of the resonator. When such a device is optically pumped to achieve gain and eventually lasing, the grating period becomes thermally chirped, thereby influencing the spectral characteristics of the resonator. We investigate experimentally and via simulations the frequency and linewidth of the resonance in the presence of a thermally induced linear chirp on the grating profile. Experiments and simulations show good quantitative agreement.