Photonic Recirculating Delay Line for Analog-to-Digital Conversion
This approach modifies an analog fiber-optic link with a recirculating optical loop.
Aconventional analog fiber-optic link can be augmented with a recirculating optical delay loop so as to realize an optically assisted analogto- digital converter (ADC) that provides improved performance in terms of both speed and resolution using one (slower) electronic ADC (see figure). The overall architecture readily integrates with any electronic ADC system. Moreover, the highspeed ADC performance is fundamentally limited by the performance of the fiber-optic link. The system was constructed on an optical bench. A 1,550-nm, 50-mw diode laser was used as the optical source. The link was modulated using an 18 GHz - LiNbO3 Mach- Zehnder modulator electrically driven with a 1-GHz tone burst. The RFmodulated optical signal was injected into the recirculating delay loop via 3-dB coupler. A loop time delay of roughly 100 nanoseconds was achieved using approximately 22 meters of single mode fiber with fine time delay adjustment (+3 nanoseconds) obtained from a variable delay line. The fundamental ring architecture with unity gain is essentially a laser.
A concern involves the gain dynamics of the loop’s optical amplifier. With little or no light entering the amplifier when the loop gate is open, the turn-on time of the SOA when the light does enter will prevent the total required loop gain from being present when needed. This effect is mitigated by using distributed amplification in the loop. Two optical amplifiers were used in the loop, which allowed for a lower gain in each amplifier and thus a faster turn-on time. Future implementation of the system would perhaps use either more amplifiers or else a continuously distributed amplification scheme.
Upon exiting the loop via the 3-dB coupler, the signal is directed to a 20- GHz PIN photodetector, and the resulting periodic signal is viewed on a highspeed oscilloscope. Since the system was constructed with (connectorized) bulk optical components, this resulted in reduced SNR performance.
This work was done by Henry Zmuda of the University of Florida; Jared Pawloski of the State University of New York, Binghamton; Kristina Norelli of Syracuse University; and Michael Fanto and Thomas McEwen of the Air Force Research Laboratory. For more information, download the Technical Support Package (free white paper) at www.defensetechbriefs.com/tsp under the Photonics category. AFRL-0125
This Brief includes a Technical Support Package (TSP).

Photonic Recirculating Delay Line for Analog-to-Digital Conversion
(reference AFRL-0125) is currently available for download from the TSP library.
Don't have an account?
Top Stories
INSIDERDesign
Clean Sky Demonstrator Fuselage Shows Potential of Thermoplastics in Aircraft...
INSIDERData Acquisition
Blue Origin Rocket Reaches Intended Orbit on First Launch
INSIDERDesign
Can Microvanes Improve Fuel Efficiency for Legacy Air Force Aircraft?
INSIDERSoftware
The Future of Aerospace: Embracing Digital Transformation and Emerging...
NewsElectronics & Computers
Closing Gap to Leverage Enhanced Computational Power for SDV Advancement
Technology ReportUnmanned Systems
AVSC Develops Best Practices for Traceable AV Safety Inspection Protocols
Webcasts
Software
How a Cloud-Based Remote ID System Helps Monitor Random Drone Sightings
AR/AI
AI-Powered Quality Control for Sustainable Automotive Production
Defense
Improving Thermal Management for Aerospace and Defense Electronics
Connectivity
The Road Ahead for Next-Gen E/E Architectures: Trends and...
Aerospace
Department of Defense Contracts Denied: New Cybersecurity Rules...
Software
Leveraging Simulation for Net Zero Emissions in Conventional and...