This project’s goal was to simplify laser frequency stabilization. A simpler system will have many benefits, including reduction of power consumption, complexity, volume, mass, and risk of failure. To implement the Pound-Drever-Hall (PDH) technique requires both RF modulation and demodulation electronics, including an electro-optic modulator, a photoreceiver of sufficient bandwidth to detect the RF modulation fields, demodulation electronics of sufficient bandwidth, and an RF function generator. For a space mission, this equipment can be costly and power-hungry, in addition to the difficulty of being rated to operate in the harsh space environment.
The need for laser frequency stabilization will occur in many planned missions employing multiple lasers on multiple spacecraft (SIM, LISA, GRACE Follow-on, GRACE C). In addition, many laboratory measurements require laser frequency stabilization. This software-based system obviates the need for RF components (modulator, detector, frequency/function generator, and associated electronics), both in the laboratory and on a spacecraft, to perform laser frequency stabilization in a digitally controlled system.
The code-based (digital) technique was demonstrated for laser frequency stabilization to an optical reference cavity without requiring any RF electronics or RF equipment. The process is coded using LabVIEW and employs field programmable gate arrays (FPGAs) for digital input and output from the photoreceiver and laser, respectively. Instead of employing an external phase-modulator driven by a function generator, the digital code directly modulates the laser’s piezoelectric transducer (PZT).
This work has shown that high laser frequency stability performance can be achieved using optical cavity references, without the need for the traditional PDH RF electronics. This was demonstrated using digital software codes and control, significantly simplifying the analog electronics. This technique reduces mass and power associated with the RF electronics. This software technique is implemented via hardware that will already exist onboard the spacecraft. This also reduces complexity, power consumption, volume, and risk of failure.
This work was done by Glenn DeVine, Brent Ware, Kirk McKenzie, Robert J. Thompson, William M. Klipstein, William M. Folkner, and Robert E. Spero of Caltech for NASA’s Jet Propulsion Laboratory.