Case studies

Phase stabilization using the Moku:Pro PID Controller at the University of Münster

Using Multi-instrument Mode to accelerate phase stabilization of highly sensitive, fiber-based systems


The University of Münster is Germany’s fifth-largest university, offering more than 120 diverse fields of study. The University of Münster (WWU) Optical Technologies group, part of the Institute of Applied Physics, conducts research in a variety of fields including nonlinear optics and laser concepts. Ph.D. student Kristin Wallmeier, who specializes in nonlinear microscopy, is working to improve phase stabilization of a two-output pulse train. Kristin’s setup includes a fiber-based oscillator and a subsequent fiber-based optical parametric oscillator. Her goal is to synchronize the fiber-based oscillator, providing the pump of the fiber-based optical parametric oscillator with the output of the fiber-based optical parametric oscillator.

Since her research is highly experimental, she needs a variety of test equipment on any given day for exploratory testing. By using embedded instruments available through Moku:Pro, including the Digital Filter Box and PID Controller in Multi-instrument Mode seen in Figure 1, she is enhancing the phase stabilization of the setup.


Multi-instrument Mode on Moku:Pro: Digital Filter Box, PID Controller, and another Digital Filter Box

Figure 1: Multi-instrument Mode setup with two Digital Filter Boxes and a PID Controller for phase stabilization

Moku:Pro offers up to 14 software-defined instruments, ranging from common bench necessities to unique, essential instruments to streamline even the most experimental lab setups. Using Moku:Pro, Kristin has accelerated her research with a compact solution and flexible test configuration options, as well as an intuitive, iPad-based user interface.

The challenge

Fiber-based systems are highly sensitive to environmental fluctuations such as mechanical vibration and thermal fluctuations. Phase stabilization requires an incredibly stable, fast feedback circuit to correct any changes in the system. The system must be fast enough to restabilize after a disturbance takes place. The system can also be sensitive to noise, so filtering is necessary to achieve clean input and output signals. Without digital filtering options, Kristin would have needed to build analog filters with RC components to ensure she filters out signals that may interfere with the resonant frequency of the piezoelectric actuator that is used to adjust the phase within the feedback circuit.

Before selecting Moku:Pro, Kristin started with an Arduino development board that required her to manually code and develop the features she needed for her research. She quickly determined that the Arduino performance was insufficient when she realized it was too slow to stabilize the feedback loop in her setup. Moku:Pro was a much more efficient solution for her research thanks to its speed enhancements and full suite of preprogrammed, software-defined instrumentation.

The solution

Using the Moku:Pro PID Controller and Digital Filter Box in Multi-instrument Mode (MiM) through the iPad interface, Kristin can accelerate her research and focus more on improving the phase stabilization of the system rather than spending time developing complex test procedures. Kristin first applied digital filters to the input signal to filter out high-frequency components. After using the PID Controller, she further improves signal quality with another Digital Filter Box to remove all high-frequency components that are in the range of the resonant frequency.

“The Digital Filter Box is quite nice because I can just try a lot of different setups without buying all of them and building them in an analog way,” she said.

The easy-to-use PID Controller was Kristin’s main motivation for integrating Moku:Pro into her experiment. When a disturbance occurs, the PID Controller quickly reacts and restabilizes the system, as seen in Figure 2. With the ability to probe multiple points in the signal path, Kristin and her team can use the embedded Oscilloscope to watch the system restabilize the input signal in real time. 

Phase stabilization oscilloscope view in the Moku:Pro PID Controller

Figure 2: Setup of the PID Controller (top) and input signal for the PID Controller (bottom), showing a disturbance of the stabilized phase and the reaction of the system to restabilize

The result

Kristin continues to advance her research by meticulously monitoring her experiment and working to improve the stability of the system. By using the Moku:Pro Digital Filter Box and PID Controller, Kristin has maximized time and cost savings by eliminating the need for do-it-yourself solutions such as building filters with RC components. 

“It’s quite intuitive to set up everything and work with it,” Kristin said. 

Using Moku:Pro has also reduced the need for additional instrumentation. Because of the future-proof nature of the device, she and her team can simply update the software as needed to use new features or instrumentation after they are released. 

“It’s the best, so it doesn’t really make sense to buy another instrument, then another one, and another one,” she added.

Kristin plans to use Moku:Pro for other research in the future, such as stimulated Raman scattering (SRS) microscopy projects utilizing the Lock-in Amplifier, another instrument available through Moku:Pro. 

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