Fast Offset Laser Phase-Locking System
- Friday, 25 April 2008
Phases can be locked within a microcycle; known phase noise can be added.
Figure 1 shows a simplified block diagram of an improved opto- electronic system for locking the phase of one laser to that of another laser with an adjustable offset frequency specified by the user. In comparison with prior systems, this system exhibits higher performance (including higher stability) and is much easier to use. The system is based on a field-programmable gate array (FPGA) and operates almost entirely digitally; hence, it is easily adaptable to many different systems. The system achieves phase stability of less than a microcycle. It was developed to satisfy the phase-stability requirement for a planned spaceborne gravitational-wave-detecting heterodyne laser interferometer (LISA). The system has potential terrestrial utility in communications, lidar, and other applications.NPO-41927), NASA Tech Briefs, Vol. 31, No. 6 (June 2007), page 22. In the present system (as in the previously reported one), beams from the two lasers (here denoted the master and slave lasers) interfere on a photodiode. The heterodyne photodiode output is digitized and fed to the fast phasemeter, which produces suitably conditioned, low-latency analog control signals which lock the phase of the slave laser to that of the master laser. These control signals are used to drive a thermal and a piezoelectric transducer that adjust the frequency and phase of the slave-laser output.
Although the system phase-locks the two lasers to within a microcycle, in the original application, there is an occasional need to analyze the performance of the phasemeter in the presence of noise in the difference between the phases and frequencies between the two lasers. This system includes a subsystem, based on a pseudorandom-number generator, that can add an adjustable amplitude phase noise characterized by a uniform, Gaussian, or 1/ƒ distributions (where ƒ denotes frequency). Figure 2 shows the performance of the phase-locking system, and also noise added by the pseudo-random noise generator to mimic that of free-running lasers.
This work was done by Daniel Shaddock and Brent Ware of Caltech for NASA’s Jet Propulsion Laboratory.
This Brief includes a Technical Support Package (TSP).
Fast Offset Laser Phase-Locking System (reference NPO-44740) is currently available for download from the TSP library.
Please Login at the top of the page to download.