Fig. 4.

Open-loop measurement. a The block diagram of the Pound−Drever−Hall (PDH) open-loop measurement setup. An optical probe is used to couple the amplified output of an Agilent 81642A laser into the PDH chip. The output current of the voltage-to-current converter is used to drive a load emulating the impedance of the laser gain section and is monitored using an oscilloscope. b The simulated open-loop PDH read-out current (at $A_i$ = 82 dB) is shown which follows a sinusoidal form as predicted by eq. (1). The measured PDH open-loop read-out signal is also shown which is in close agreement with the simulation for the same operating point setting