Doppler wind lidar using a MOPA semiconductor laser at stable single-frequency operation

A compact master-oscillator power-amplifier semiconductor laser (MOPA-SL) is a good candidate for a coherent light source (operating at 1550 nm) in a Doppler wind Lidar. The MOPA-SL requires two injection currents: I_dfb for the distributed-feedback (DFB) laser section (master oscillator) and I_amp for the tapered amplifier section. The specified maximum current values are 0.7 A and 4.0 A for I_dfb and I_amp. Although the MOPA-SL has been proven capable of producing single-frequency CW output beam, stable operation at this spectral condition has also been known to highly depend on the drive currents to the laser. This was done by observing the spectral characteristic of the laser using an optical spectrum at different drive current combinations. When using the laser for a Doppler wind Lidar application, a combination of (I_dfb, I_amp) which is close to the center of an identified stable single-frequency regime is used. The current settings for the laser result in a highly stable Lidar as shown by a 5-day long continuous measurement of the Doppler shift produced by a constantly rotating diffusely reflecting target.