Jason D. McKinney

Photonic synthesis of broadband microwave arbitrary waveforms applicable to ultra-wideband communication

We demonstrate photonic synthesis of broadband radio-frequency (RF) waveforms suitable for ultra-wide bandwidth (UWB) systems via open-loop reflection-mode dispersive Fourier transform optical pulse shaping. Using this technique, we synthesize broadband burst, monocycle and pulsed waveforms with RF bandwidths ranging from /spl sim/1-8 GHz. Through appropriate optical waveform design, we demonstrate direct control over the shape of the RF spectrum - a capability that enables us to tailor our RF waveforms to conform to the low-power UWB spectral criteria.

Millimeter-wave arbitrary waveform generation with a direct space-to-time pulse shaper

By using tailored pulse sequences from a novel, 1.5-microm direct space-to-time pulse shaper driving a high-speed photodetector, we have achieved, for the first time to our knowledge, millimeter-wave arbitrary waveform generation at center frequencies approaching 50 GHz. By appropriately designing the driving optical pulse sequences, we demonstrate the ability to synthesize strongly phase- and frequency-modulated millimeter-wave electrical signals on a cycle-by-cycle basis.

Characterization and imaging in optically scattering media by use of laser speckle and a variable-coherence source

We demonstrate the application of laser-speckle statistics formed by a variable-coherence source illuminating a scattering medium, for determining the scattering parameter mu;(s)>(?) of a diffusion model for the medium. Furthermore, we apply this technique to visualize laterally localized inhomogeneities embedded within a highly scattering sample.

Photonically assisted generation of arbitrary millimeter-wave and microwave electromagnetic waveforms via direct space-to-time optical pulse shaping

We present our work in optical generation of arbitrarily shaped millimeter-wave electromagnetic waveforms. Through a novel technique, which utilizes tailored optical pulse sequences from a direct space-to-time pulse shaper to drive a high-speed optical-to-electrical converter, we generate amplitude-equalized, arbitrarily phase- and frequency-modulated waveforms at center frequencies approaching 50 GHz. In addition, we demonstrate the extension of this technique to generation of arbitrary electromagnetic waveforms in the low-gigahertz range, through dispersive stretching of the pulse shaper output. In the dispersively stretched configuration, the duration of our electrical waveforms is tuned through simple alignment changes in our pulse-shaping apparatus.

Compensation of the effects of antenna dispersion on UWB waveforms via optical pulse-shaping techniques

To our knowledge, we present the first experimental demonstration of compensation of antenna dispersion effects on impulsive ultra-wideband (UWB) signals. By extracting the RF spectral phase from a time-domain impulse response measurement of a pair of ridged TEM horn antennas, we utilize a photonic-synthesis technique for arbitrary electromagnetic signal waveforms to generate a signal matched to the antenna pair. We demonstrate that the received waveform is compressed and exhibits reduced ringing levels, as compared to the impulse response of the system. Our technique is reprogrammable and we believe the technique will be applicable to a variety of antennas operating in the UWB communications band of 3.1-10.6 GHz.

Photonic microwave arbitrary waveform generation using a virtually imaged phased-array (VIPA) direct space-to-time pulse shaper

We present the first direct space-to-time pulse shaper using a virtually imaged phased array as the spectral disperser. We use this pulse shaper to demonstrate generation of 10-50-GHz arbitrary microwave waveforms with time apertures as large as 1.0 ns and peak-to-peak amplitudes as high as 400 mV.

Direct space-to-time pulse shaping at 1.5 /spl mu/m

We present a novel direct space-to-time pulse shaper, operating in the 1.5-/spl mu/m optical communications band which enables generation of continuous optical pulse sequences at a rate of /spl sim/100 GHz. The apparatus includes several novel features, such as the use of a diffractive optical element for spatial patterning, fiber coupled input/output, and a telescopic configuration which collectively enable generation of nearly equal amplitude optical pulse sequences over a time aperture in excess of 100 ps. We also present a mathematical description of the temporal and frequency modulation behavior of our apparatus, in addition to continuous 100-GHz optical pulse sequences generated in our system.

Engineering of the radio-frequency spectra of ultrawideband electromagnetic waveforms via optical pulse shaping techniques

Through optical pulse shaping in the Fourier domain, we demonstrate engineering of ultrawideband radio-frequency spectra. Apodization and modulation of our optical waveforms enable generation of RF spectra that fill the 3.1 - 10.6 GHz frequency band.

Engineering of the passband function of a generalized spectrometer.

To our knowledge, we demonstrate a new scheme for passband engineering of a grating spectrometer. Through spatial masking of the input beam and translation of the optical components we present shaping, shifting, and scaling of the passband in optical frequency. Specifically, we demonstrate the relationship between the applied spatial masking function and the spectrometer passband may be tuned from an exact Fourier transform to a direct scaling through longitudinal displacement of the spectrometer lens and sampling slit and that this operation is independent of the choice of spectrometer center frequency.

A programmable Fresnel transform pulse shaper.

We demonstrate the first reprogrammable Fresnel transform pulse shaper based on a modified direct space-to-time pulse shaping apparatus. In our approach, the pulse shaping lens and mask are implemented by a dual-layer liquid crystal spatial light modulator. The input mask subsequently undergoes a free-space Fresnel transform which causes quadratic dispersion of the output temporal waveform. When used as a spectrometer, we demonstrate that the passband function of the apparatus (determined by the Fourier transform of the input spatial mask) may be chosen to exhibit a user-defined scale. Here we present the theory of operation, as well as experimental verification in both the time- and frequency-domains.