We introduce new figures of merit (FOM's) for resonant optical materials used in recording, storage, and
processing of optically encoded information using coherent optical transients. The goal is to account for maximum
coherence storage time as well as for efficiency of the light matter interaction quantified using the ratio between
the rate of dephasing and the rate of spontaneous radiative decay. Highest FOM values are achieved when the
dephasing rate approaches the fundamental limit set by spontaneous emission under the condition that the total
transition oscillator strength is concentrated between a single pair of energy levels. In this case, the information
(both classical and quantum) can be transferred from the radiation field to the storage medium and back at the
fastest possible rate, while the loss of optically prepared coherence is minimized. We analyze FOM's of some of
the most promising rare-earth-doped crystals at cryogenic temperatures and show that the homogeneous line width
may approach the radiative limit in some cases even when the peak cross section remains below the fundamental
We propose a novel, wideband spectrum analyzer based on spectral hole burning (SHB) technology. SHB crystals contain rare earth ions doped into a host lattice, and are cooled to cryogenic temperatures to allow sub-MHz hole burning linewidths. The signal spectrum is recorded in an SHB crystal by illuminating the crystal with an optical beam modulated by the RF signal of interest. The signal's spectral components excite those rare earth ions whose resonance frequencies coincide with the spectral component frequencies, engraving the RF spectrum into the crystal's absorption profile. Probing this altered absorption profile with a low power, chirped laser while measuring the transmitted intensity results in a time-domain readout of the accumulated RF signal spectrum. The resolution of the spectrum analyzer is limited only by the homogeneous linewidth of the rare earth ions (< 1 MHz when the SHB crystal is cooled to cryogenic temperatures). The spectrum analyzer bandwidth is limited by the inhomogeneous linewidth and by the electro-optic modulator bandwidth, both of which can be > 20 GHz.
Spectral-spatial holographic crystals have the unique ability to resolve fine spectral features (down to kilohertz) in an optical waveform over a broad bandwidth (over 10 gigahertz). This ability allows these crystals to record the spectral interference between spread spectrum waveforms that are temporally separated by up to several microseconds. Such crystals can be used for performing radar range-Doppler processing with fine temporal resolution. An added feature of these crystals is the long upper state lifetime of the absorbing rare earth ions, which allows the coherent integration of multiple recorded spectra, yielding integration gain and significant processing gain enhancement for selected code sets, as well as high resolution Doppler processing. Parallel processing of over 10,000 beams could be achieved with a crystal the size of a sugar cube.
Spectral-spatial holographic processing and coherent integration of up to 2.5 Gigabit per second coded waveforms and of lengths up to 2047 bits has previously been reported. In this paper, we present the first demonstration of Doppler processing with these crystals. Doppler resolution down to a few hundred Hz for broadband radar signals can be achieved. The processing can be performed directly on signals modulated onto IF carriers (up to several gigahertz) without having to mix the signals down to baseband and without having to employ broadband analog to digital conversion.
The pattern matching for fingerprints requires a large amount of data and computation time. Practical fingerprint
identification systems require minimal errors and ultrafast processing time to perform real time verification and
identification. By utilizing the two-dimensional processing capability, ultrafast processing speed and noninterfering
communication of optical processing techniques, fingerprint identification systems can be
implemented in real time. Among the various pattern matching systems, the joint transform correlator (JTC) has
been found to be inherently suitable for real time matching applications. Among the various JTCs, the fringeadjusted
JTC has been found to yield significantly better correlation output compared to alternate JTCs. In this
paper, we review the latest trends and advancements in fingerprint identification system based on the fringeadjusted
JTC. Since all pattern matching systems suffer from high sensitivity to distortions, the synthetic
discriminant function concept has been incorporated in fringe-adjusted JTC to ensure distortion-invariant
fingerprint identification. On the other hand a novel polarization-enhanced fingerprint verification system is
described where a polarized coherent light beam is used to record spatially dependent response of the scattering
medium of the fingerprint to provide detailed surface information, which is not accessible to mere intensity
measurement. It is shown that polarization-enhanced database improves the accuracy of the fingerprint
identification or verification system significantly.
Keywords: Fringe-adjust joint transform correlation, finger print identification, polarization, synthetic
The design, performance analysis and experimental demonstration for an analog, broadband, high performance electro-optical signal processor are presented. The Spatial Spectral (S2) Coherent Holographic Integrating Processor, or S2-CHIP, has been developed recently as a broadband core-component for range and mid-to-high pulse repetition frequency radar-signal processing systems, as well as for lidar and radio astronomy applications. In a range radar system, if the transmit and receive RF waveforms are modulated onto a stable optical carrier, the S2 material will perform the analog correlation of the transmit and receive signals to yield the target’s range, and also coherent integrate multiple return results to increase the signal-to-noise-ratio and provide for target velocity determination. Preliminary experimental results are shown of S2-CHIP range processing using a 1.0 Gb/s data rate with 512-bit BPSK pulses. Good range resolution is observed for delays up to 1.0 microsecond. The ability of the processor’s to handle dynamic coding on the transmit RF waveforms is demonstrated.