Abstract: A laser system includes a semiconductor laser having a laser driver coupled thereto. An output of the semiconductor laser is optically coupled to an input of an optical splitter that provides outputs including or coupled to a first branch having a first branch fiber coupled to a feedback reflector which provides a cavity boundary that defines a passive secondary cavity for the semiconductor laser, and a second branch including a back reflection reduction device. The roundtrip attenuation from an output facet of the laser to the feedback reflector is from ?30 dB to ?80 dB. The laser driver provides sufficient drive stability so that a frequency variation of the semiconductor laser is less than one free spectral range (FSR) of the secondary cavity. An output of said system is taken after the back reflection reduction device.