The SMB20 module is an electronic board for use in Optical Phase-Locked Loop (OPLL) applications where the frequency detuning between two laser sources requires tight and quick control.

This board is recommended to process the offset frequency error signal coming from the Phase/Frequency Discriminator module (SMB10). Designed for the high-speed path of the control loop, its output signal is intended to drive the fast frequency actuator device (the slave laser diode in OPLL). In order to avoid saturation of the high-speed loop, a low-frequency path using a piezoelectric actuator may be required (see SMB30 module).

The SMB20 module offers a high performance compensator for the designers allowing a complete control of the loop filter operation. The polarity of the error signal is set either on board or using remote control. The loop gain is adjusted over more than 60 dB using the front panel trimmer or a DC-voltage. The circuit of the high-speed PID has been optimized for speed while two additional integrator stages can boost the loop gain at low frequency. For  lock-acquisition purposes, the integrator output of the fast PID can be precisely controlled by the user. A ramp input is provided to sweep the laser frequency during the open-loop operation while the feedforward input offers a useful control of the fast actuator for frequency jumps or closed-loop measurements.

Like all SM-Series modules, the SMB20 is shipped with the schematic diagrams of its electronic circuitry, providing all required information for advanced users.