Thermal noise limited ultra-stable laser at 1555 nm

We present the designs and performances of cavity-stabilized lasers at 1555 nm, which are built as the frequency source for a transportable photonic microwave generation system. The frequency instability reaches the thermal noise limit of 10 cm-long vertically held cavity of 7×10 −16 at 1 s averaging time, and the beat signal of the two lasers reveals a remarkable linewidth of 185 mHz.