1.5-µm Cavity-stabilized laser for ultra-stable microwave generation

Based on an extended-cavity diode laser locked to a high-finesse ultra-low thermal expansion Fabry-Perot cavity using the Pound-Drever-Hall (PDH) technique, we are developing an ultra-stable laser at 1.55 μm for the generation of low phase noise microwave. Our target short-term frequency instability is 10^-15 at 1 s. The horizontally-mounted cavity has a resonance width of 8.1 kHz, experimentally determined from the cavity ring-down time. The analysis of the in-loop error signal of the laser stabilization to the cavity shows that the residual servo loop noise contributes only <;10^-15 (@ 1 s) to the laser instability and no additional contribution to the laser linewidth is induced by the PDH stabilization. Consequently, the laser linewidth will be ultimately limited by the cavity noise only. The cavity will be stabilized at its zero coefficient of thermal expansion temperature, which has been experimentally determined to be 22.6°C.