Linewidth in Widely Tunable Digital Supermode Distributed Bragg Reflector Lasers: Comparison Between Theory and Measurement

A transfer-matrix-based model is presented for calculating the linewidth of a widely tunable distributed Bragg reflector (DBR) laser as a function of its tuning currents. This model is used to calculate the linewidth of a digital supermode (DS)-DBR laser across its tuning range and compared to linewidth measurements under the same conditions. Excellent agreement is obtained with all the fine structure seen in the measurement being reproduced by the model. This suggests that the dominant factors which determine the complex structure of the linewidth are simple ones such as loss, threshold gain and optical power rather than complex details of the carrier dynamics