Thorlabs' DSC1 Compact Digital Servo Controller is designed to lock or stabilize an optical system to an input voltage signal by providing real-time voltage feedback determined by a user-selected control algorithm. Featuring 100 kHz of bandwidth and an input and output voltage range of ±4 V, this digital servo controller is able to actively lock with high-frequency devices like current-modulated lasers, piezo actuators, acousto-optic modulators (AOMs), electro-optic modulators (EOMs), fiber stretchers, voice coils, or fast steering mirrors. 

• Digital Servo Controller with 100 kHz Bandwidth
• Servo Lock, Peak Lock, and Ramp Function Modes
• Ideal for Frequency Stabilizing Lasers
• Compact Housing with a Touchscreen Interface

The controller has three modes that offer complementary functionality: Servo Lock mode, Peak Lock mode, and Ramp mode. 

When using the Servo Lock mode, the output voltage can be modulated with a PID (proportional, integral, derivative) algorithm to maintain a set input voltage. All the parameters of the algorithm can be tuned for the specific system. For example, the output of a system can be intensity stabilized by measuring the power with a photodiode, feeding the signal from the photodiode into the servo controller, and having the servo controller output control an intensity modulator such as an acousto-optic modulator (AOM), electro-optic modulator, or lithium niobate amplitude modulator. Changing the set point in the servo controller will cause the system to adjust to and then maintain that new set point. Additionally, the servo controller could stabilize the frequency of a laser with a side-of-fringe lock using Servo Lock mode. In a side-of-fringe lock, the set point could be placed part-way up a resonance peak from a Fabry Perot cavity or an absorption peak from an atom or molecule.

The Peak Lock mode will lock a system to a local maximum or minimum in the input voltage using dither-locking, also known as extremum seeking control or lock-in demodulation servo. It does this by modulating the system at a chosen frequency, the dither frequency, then digitally demodulating the signal to create an error function that can be minimized. By locking a system to a maximum or minimum feature in the input voltage, the performance of a system can be tightly controlled. For example, a laser can be frequency locked to a molecular absorption line in a dilute gas like acetylene or to the maximum transmission mode of a Fabry-Perot cavity with inherent immunity to drift or perturbations in laser power. 

The digital servo controller software provides a simple and powerful interface for the DSC1 controller. The input voltage can be displayed in either the frequency or time domain.

In the Ramp mode, the digital servo controller can linearly sweep the output voltage over a defined range and display the resultant input signal as a function of voltage, like an oscilloscope. This can resolve features like an interferogram from an interferometer as well as providing a direct view of the response of the system over an applied voltage range. For example, if the servo controller sweeps the frequency of a laser passing through a gas absorption cell, the transmission spectrum of the gas can be observed.

Features

• High-Speed PID Control with up to 100 kHz Bandwidth
• Laser Lock Box Capable of Frequency Stabilizing Lasers
• Compact 130 mm Wide Enclosure Powered by USB Type-C
• Full Functionality Accessible through the Touchscreen 
• Three Modes:
• Servo Lock - Lock to a Specified Input Voltage
• Peak Lock - Dither Locking, also known as Peak Locking, Extremum Seeking Control, or Lock-In Stabilization
• Ramp - Linearly Sweep the Output Voltage Over a Defined Range
• Digital Servo Controller Software Provides Tools for Additional Analysis of Signals (See the Software Tab to Download)
• Servo Lock Mode: Displays the Input Voltage in the Time or Frequency Domain
• Peak Lock Mode: Displays the Demodulated Input Voltage in the Time or Frequency Domain
• Ramp Mode: Displays the Input Voltage as a Function of the Ramped Output Voltage like an Oscilloscope
• Can be Used to Fully Control the Digital Servo Controller

Applications

• Single Frequency Laser or Cavity Locking
• Interferometer Stabilization
• Fourier Transform Spectroscopy
• Saturable Absorption Spectroscopy
• Dichroic Atomic Vapor Laser Locking (DAVLL)
• Active Beam-Pointing Stabilization
• Laser Power Stabilization
• Laser Repetition Rate Locking
• External Cavity Diode Lasers (ECDLs)
• Fiber Phase or Path-Length Stabilization
• Enhancement Cavity Locking for CW SHG Cavities
• Intensity Stabilization (Noise-Eating) with AOMs
• Motion Control