Calvin Harrington

Correlation of single-mode fiber radiation response and fabrication parameters

Statistically significant correlations have been established between certain fabrication parameters of matched clad, single-mode optical fiber waveguides and their response to an ionizing radiation dose of 2000 rad. The reCOVE:ry data measured at -35 degrees C following exposure have been fit to nth-order kinetic behavior where the adjustable parameters are the initial and permanent incremental losses (A(o) and A(f), respectively), the half-life of attenuation tau, and the order of kinetics n. The set of fibers chosen for analysis had Ge-doped silica cores. In fibers with Ge-F-doped silica clads, A(o) correlates with the concentration of Ge-doped into the fiber core; A(f) correlates with the ratio of oxygen to reagents used during core deposition; and tau and n correlate with a two-way interaction of core oxygen and fiber draw speed. In P-F-doped clad fibers, the P concentration has been found to correlate with the order of the kinetics of recovery.

From spectral holeburning memory to spatial-spectral microwave signal processing

Many storage and processing systems based on spectral holeburning have been proposed that access the broad bandwidth and high dynamic range of spatial-spectral materials, but only recently have practical systems been developed that exceed the performance and functional capabilities of electronic devices. This paper reviews the history of the proposed applications of spectral holeburning and spatial-spectral materials, from frequency domain optical memory to microwave photonic signal processing systems. The recent results of a 20 GHz bandwidth high performance spectrum monitoring system with the additional capability of broadband direction finding demonstrates the potential for spatial-spectral systems to be the practical choice for solving demanding signal processing problems in the near future.

Broadband multi-emitter signal analysis and direction finding using a dual-port interferometric photonic spectrum analyzer based on spatial-spectral materials

A broadband signal analyzer that can determine the power spectra and direction of all spectrally non-overlapping emitters for a two antenna system is proposed and demonstrated. A spectrum analyzer (SA) based on spatial-spectral (S2) materials has previously been demonstrated that can monitor broadband signals (over several tens of gigahertz (GHz)) with sub-megahertz (MHz) resolution in real-time (sub-millisecond updates). Here, a dual-channel S2 SA is used to monitor the two outputs of a dual-drive dual-port optical Mach-Zehnder interferometer, where the RF inputs to the interferometer are driven by microwave signals with various time delayed components, emulating the outputs of a two-element antenna array receiving signals from emitters with various bandwidths, formats, and center frequencies. The sensitivity of the optical power spectra of the two output ports to the time delay of each resolvable frequency component of the signals enables the determination of energy and direction of each resolvable frequency component of multiple emitters. A simple post-processing technique is used to estimate the angle of arrival (AoA) and power spectrum of each emitter. The interferometric technique works on a variety of signals including short bursts of variable bandwidth frequency agile microwave signals. The systems direction finding (DF) and SA capabilities enable it to simultaneously monitor multiple types of emitters. With the current system architecture, tone bursts, spread-spectrum waveforms, and chirped waveforms over 5 GHz of bandwidth were demonstrated. Sub-picosecond resolution (sub-0.5 degree angular resolution on bore-site for signals with a 3.8 GHz carrier frequency) was demonstrated for signals with a 19 dB signal-to-noise ratio (SNR) at 1 MHz spectral resolution. The theoretical and measured resolutions are shown to be in good agreement.

Frequency resolved angle and time difference of arrival estimation with spatial spectral holography

Correlative power spectrum and spectral phase mapping via readout of a fiber interferometer with spatial-spectral materials is analyzed and demonstrated to enable precise frequency resolved time delay and angle of arrival estimation with microwave signals.

Demonstrations of analog-to-digital conversion using a frequency domain stretched processor

Proof-of-concept analog-to-digital conversion demonstrations are presented for a photonics based frequency-domain, stretched processor. Here 800 MHz bandwidths and >26 dB dynamic range are shown, with models suggesting 10-bit performance over 20 GHz bandwidths.

Continuous wideband spectrum analysis over 10 GHz bandwidth with 61 dBc spur-free dynamic range

The latest performance results for a novel radio frequency (RF) sensor technology are presented for continuous monitoring of RF spectrum with large instantaneous bandwidth. The photonic approach relies on a spatial spectral (S2) holographic light absorbing crystal. The S2 spectrum analyzer as presently demonstrated operates on instantaneous bandwidths (IBW) over 10 GHz, in this case from 0.5-10.5 GHz, and is being extended to IBW of 40 GHz. The device presently outputs 100,000,000 frequency energy/time measurements per second, each measurement being the result of continuous monitoring spectrum analysis with energy amplitude assigned on a frequency and time grid from a continuous digital data stream at 500 MegaBytes per second. For these measurements, we have observed 61 dBc spur free dynamic range (SFDR) over the full IBW of 10 GHz. With low-noise RF gain we have observed RF sensitivity levels of -110 dBm for continuous RF tones with >59 dB two-tone SFDR. The resolution bandwidth (RBW) for the signals over a 10 GHz IBW can be as low as 100 kHz (100,000 frequencies per frame) at a 1 kHz frame rate (FR), and then increases with increased FRs that can vary from 1-200 kHz. All parameters of IBW, RBW and FR are fully reconfigurable on-the-fly for adaptive spectrum analysis, and the S2 device is also upgradeable to direction finding and other signal processing functions.

Spatial-spectral holographic real-time correlative optical processor with >100 Gb/s throughput

The demonstration of an all-optical, ultra-high-speed, time-domain signal correlator based on spatial-spectral holographic (SSH) technology is described. The fully programmable signal correlator demonstration operates asynchronously and continuously on signals with up to 32 GHz of bandwidth and correlative filter length exceeding a time-bandwidth product of 104, for the equivalent of teraflop-scale processing. Experimental demonstrations are presented that show both digital and analog correlation capability using phase-shift keyed modulation formats to search plain text ASCII data sources for arbitrary phrases at continuous line rate throughputs up to 200 Gbps with minimal latency. These high-bandwidth demonstrations were enabled by improvements in the photonic supporting components and cryogenic SSH for RF and microwave signal processing methods. Potential application of the SSH real-time correlator for high-bandwidth analog or multi-level format signals is discussed.

Efficient spectral and correlative processing with spatial-spectral holography

Spatial-spectral holographic (SSH) materials function as a coherent frequency domain resource for high-performance spectral and correlative processing. Real-time matched filtering of 25 GHz bandwidth signals is demonstrated including simple text searches. Despite cryogenic cooling, SSH processing can be efficient for large scale processing systems.

Demonstration of Analog-to-Digital Conversion Using Spatial-Spectral Holography

Proof-of-concept demonstrations for an optical approach to broadband analog-to-digital conversion are shown with 800 MHz bandwidth and >26 dB dynamic range. Models suggest that this frequency-domain stretched processor could achieve 10-bit performance over 20 GHz bandwidths.