Abstract
Researchers at the University of Central Florida have invented
a chip-scale optical-to-RF link technology that clears a path for integrated
photonics. Using a novel harmonic multitone injection locking technique, the
invention down-converts frequency combs from the optical domain (>120GHz to
THz) into the microwave domain (10s of GHz), where it can be easily
photo-detected and controlled. Thus, as a timing signal generator or optical
clock, the new technology provides enhanced timing precision for Position, Navigation
and Timing (PNT) applications, such as secure communications in military
GPS-denied environments. It may also provide a precise timing reference for
high-bandwidth coherent telecommunications or a wavelength reference for
metrology. Compared to existing technologies, the invention is simpler, since
it relies on the natural phase-lock effect from the optical injection locking
process instead of electronic phase-locked loops. It is also more robust, since
it inherits from the stability of the injection locking process. Finally, the
system is more efficient, since it requires little optical power for the
harmonic injection locking process.
Technical Details
With its unique harmonic multi-tone injection locking
technique, the invention expands the concept of optical injection locking, in
which a slave laser is synchronized to a master laser.
The figure illustrates the new technique involving a widely-spaced optical frequency comb
(OFC) at nf_rep and a slave
mode-locked laser (MLL) at f_rep. The master OFC injects multiple tones into the slave
MLL at a harmonic of the fundamental repetition rate (f_rep), thereby down-converting a set of
millimeter-wave or THz range separated optical tones into the GHz/microwave
domain. When the multiple tones of the master laser coincide with adjacent comb
lines of the MLL, the repetition rate stability from the master is transferred
to the slave, as well. The technique effectively reduces the linewidth of the
individual axial modes, stabilizes the repetition rate, and reduces the RF
spectrum phase noise. The architecture is compatible with current fabrication
processes and offers a SWaP (size, weight and power) system with a dramatic
increase in accuracy and robust, long-term stability.
Benefit
Compatible with current fabrication processes and offers a SWaP systemProvides a dramatic increase in accuracySimple, efficient, robust and stableMarket Application
Military defensePNT applications where microsecond accuracy is needed or when another timing reference (such as GPS) is not availableTelecommunicationsWavelength reference for metrologyPublications
Harmonic Injection Locking for a Direct Optical to RF Link
Conference on Lasers and Electro-Optics (CLEO), 2018, Optical Society of America, 2018, paper JTh2A.167
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