The unit applies the imported highly linear DFB laser of low noise, big transmission capability and small nonlinear distortion. It is completed with reliable APC (Automatic Power Control) circuit for light power output, ATC (Automatic Temperature Control) for thermo-electric cooler, MGC (Manual Gain Control) and AGC (Automatic Gain Control) function for input radio frequency, which ensure the optimum performance of the whole set and the stable operation of the laser all through its service life.