Moku offers a Laser Lock Box (LLB) to lock a laser onto a cavity using a variety of locking methods. The output signal of the LLB is typically a control signal output from the fast and/or slow PID controllers. The error signal used for the locking process is what is passed into the PID controllers. However, there may be applications that require the output of the error signal itself.

To output the error signal, a second LLB is required to replicate the settings of the primary LLB to generate the same error signal. However, the PID controllers will be configured so that the error signal passes through to the output. Multi-Instrument mode is therefore required to deploy 2 LLBs side-by-side:

The LLB in slot 1 is the primary LLB used to lock the laser, while the LLB in slot 2 is used specifically for outputting the error signal. The input signal (Input 1) is routed to each of the LLB's main input. Output 1 is the output of the fast PID controller of the primary LLB, while Output 2 is the error signal coming from the second LLB. 

To make sure the same error signal is generated in each LLB, the demodulation sources will need to be identical as well. To do this, ensure both LLBs are setup as shown in the figure below:

The only difference between the two LLBs is the PID controller settings. Set the primary LLB PID controller as it would normally be configured to achieve the desired lock. In the second LLB, the fast PID controller should be set so that only the Proportional gain is enabled and set with a gain of 0 dB:

With this setup, Output 2 of the device will now output the LLB error signal.