Semiconductor DFB or DBR lasers with narrow linewidths are of outmost importance for a variety of applications, the most important ones being communication and LIDAR. Conventional single mode lasers based on quantum wells have linewidths of the order of one to a few MHz; reducing the linewidth requires the addition of an external feedback, and a stabilization scheme by means of some control circuitry which enables to reach linewidths of about 100 kHz.
A much better solution is a diode laser chip that can provide very narrow linewidths without the need for complex external additions. Recent works suggest that such lasers are possible provided that the gain medium comprises quantum dots (QDs). This paper describes the spectral properties of state of the art 1550 nm InAs/InP QD DFB lasers grown by solid source MBE and comprising five highly uniform dot layers. The linewidth of these lasers was tested using delayed self-heterodyne as well as by beating against a highly stabilized optical frequency comb. The lasers exhibit linewidths of the order of 20 kHz at room temperature and below 70 kHz at 80 degrees C.