K.D. Merkel

Coherent integration of 0.5 GHz spectral holograms at 1536 nm using dynamic biphase codes

Spectral hole-burning-based optical processing devices are proposed for coherent integration of multiple high-bandwidth interference patterns in a spectral hole-burning medium. In this implementation, 0.5 GHz spectral holographic gratings are dynamically accumulated in Er3+:Y2SiO5 at 4.2 K using a 1536 nm laser frequency stabilized to a spectral hole, along with commercial off-the-shelf components. The processed data, representing time delays over 0.5–2.0 μs, were optically read out using a frequency-swept probe; this approach makes possible the use of low-bandwidth, large-dynamic-range detectors and digitizers and enables competitive processing for applications such as radar, lidar, and radio astronomy. Coherent integration dynamics and material advances are reported.

Accumulated programming of a complex spectral grating

A complex spectral grating is accumulated by repeated application of a pair of low-power optical programming pulses to a short-term persistent inhomogeneously broadened transition in Tm:YAG at 4.5 K and then probed to investigate the buildup dynamics. The necessary frequency stability is obtained by locking a cw Ti:sapphire laser to a regenerating transient spectral hole in the same transition. Grating accumulation is demonstrated for both a periodic spectral grating, representing a true-time delay, and a complex spectral grating, permitting correlation-based pattern recognition. This work is a step toward demonstrating an optical coherent transient continuously programmed continuous processor.

Variable-time-delay optical coherent transient signal processing.

A technique is proposed and experimentally demonstrated that achieves simultaneous optical pattern waveform storage and programmable time delay for continuous real-time signal processing by use of optical coherent transient technology. We achieve variable-time-delay and broadband signal processing by frequency shifting of two chirped programming pulses, the chirp rate of one being twice that of the other, without using brief reference pulses and without changing the timing of the programming sequence. We demonstrate the technique experimentally in Tm(3+): YAG at 5 K for 40-MHz chirps by performing temporal signal convolution with true-time delays that vary over a 250-ns range.

Microwave spectral analysis using optical spectral hole burning

A microwave spectrum analyzer capable of capturing multi-GHz spectra with sub-MHz resolution and unity probability of intercept based on optical spectral hole burning materials is proposed and initial demonstrations presented.

Continuous waveform variable true-time delay by optical coherent transients

Abstract We experimentally demonstrate for the first time variable delay of a continuous optical waveform using a spectral-spatial grating programmed with two, temporally overlapping frequency chirped pulses. Variation in the programmed time delay is achieved from 375 ns to 625 ns by frequency shifting of the chirped programming pulses. A box input beam geometry is used so that the emitted output signal is phase matched and isolated from all the input pulses. Experiments were performed in Tm3+:YAG at 5 K on the transition at 793 nm.

Range-Doppler Imaging Using an Analog Optical Signal Processor with Agile Waveform Sets

A range-Doppler radar signal processor based upon a spatial-spectral holographic analog optical signal processor is discussed. Such a system has a variety of advantages over conventional range-Doppler signal processors including increased instantaneous bandwidths (> 20 GHz), enhanced dynamic range over those bandwidths, and the ability to process a variety of wideband radar waveforms directly at the radar carrier frequency without down conversion. Range-Doppler ambiguity functions are measured showing range resolution < 15 cm, Doppler resolution < 130 Hz, and > 15 dB enhanced imaging due to agile waveform sets.

Analog optical signal processing of baseband codes in Tm:YAG up to 10 Gb/s

Aspects of analog signal processing are explored using baseband codes from 1 to 10 Gb/s modulated onto a 378 THz optical carrier and processed by spectral holographic techniques in Tm:YAG. Results include processing of signals buried in additive noise, variation of time delays over 5 /spl mu/s, and material signal losses as low as /spl sim/1 dB//spl mu/s.

Broadband Photonic Signal Processing of LIDAR Noise Waveforms

We present a novel broadband photonic signal processor, capable of sensing and processing a wide variety of waveforms including analog optical noise, for coherent LIDAR range processing. The device relies on the spectral and spatial sensing capabilities of rare-earth ion doped crystals to perform correlative signal processing. The processed results are extracted using a highly-coherent, actively-stabilized low - power frequency-swept laser, allowing broadband information to be detected and digitized at low bandwidths with high dynamic range. Time-of-flight resolution of ∼450 ps, signal-to-noise ratios of > 40 dB and up to 1us delays are demonstrated using 8 ms long waveforms. The optical noise waveforms are created by modulating RF noise onto the carrier, using up to 6 Gbps pseudo noise coding and 2 GHz analog noise waveforms.

Real-time wideband optical processing of S-and X-band signals for advanced radar systems

Real-time, wideband (>1 GHz) analog signal processing is experimentally demonstrated utilizing electro-optical devices and spectrally selective optical materials. Broadband signals are processed directly at S-band and X-band carrier frequencies without any down conversion.

Recovery technique for chirped readout of spectral features

A data processing technique is proposed for use with conventional absorption spectroscopy at arbitrarily fast frequency chirp rates to map spectral features accurately into time-domain signatures. Numerical simulations and experimental results are presented.