Full parameter extraction of a temperature-insensitive quantum well DFB laser using an optical injection technique

Distributed feedback lasers are key ingredients of high-speed, high-capacity integrated photonic chips. In this work, we extract the linewidth enhancement factor above threshold by measuring the transitional points in the optical-injection stability map from a quantum well distributed feedback laser with a temperature-controlled mismatch between the lasing and optical gain peaks. This unique measurement technique allows the simultaneous extraction of important parameters influencing the linewidth, particularly the photon lifetime. When the current is higher than twice threshold and 50 ℃, the linewidth enhancement factor is smaller than that at 10 ℃. This effect is attributed to the increasing differential gain at the lasing peak position, which is a result of the larger optical mismatch. We also measured the spectral linewidth at different temperatures, which then yields the spontaneous emission factor, n_sp. Due to the low linewidth enhancement factor at high temperatures, a large photon lifetime, and a modest increase in n_sp, the linewidth does not drastically increase with pump current and stays below 100 kHz at 50 ℃. Overall, the stability of the linewidth enhancement factor combined with the large optical mismatch brings a relative temperature insensitivity, which is of paramount importance for applications requiring high-temperature operation and improved coherent light.