W. Randall Babbitt

Recovery of spectral features readout with frequency-chirped laser fields

A data-processing technique is proposed for use with conventional frequency-chirped absorption spectroscopy to ensure accurate mapping of spectral features into time-domain signatures with arbitrarily fast readout chirp rates. This technique recovers the spectrum from a signal that is distorted owing to the fast chirp rate and therefore facilitates fast measurement of the spectral features over a broad spectral range with high resolution. Both numerical simulations and experimental results are presented.

Demonstration of optical coherent transient true-time delay at 4 Gbits/s

Multigigabit-per-second true time delay (TTD) was experimentally demonstrated by use of optical coherent transient techniques in a Tm(3+):YAG crystal. A delay accuracy of 1 ps and a delay resolution of 7 ps (both measurement limited) were achieved. The retrieved data retained good fidelity.

Amplification of high-bandwidth phase-modulated signals at 793 nm

Amplification of high-bandwidth phase-modulated optical signals from integrated-optics phase modulators at 793 nm is experimentally demonstrated using an injection-locking technique. Off-the-shelf wide-bandwidth integrated-optics modulators are power limited at 793 nm owing to photorefractive damage of the LiNbO3 waveguides. Typical optical input powers for these devices at this wavelength are less than 10 mW with optical output powers typically less than 1 mW. To amplify the outputs of these modulators, we injected the phase-modulated light into an antireflection-coated 100-mW single-mode diode laser. With the injection-locking technique, small-signal gains of 23 dB are demonstrated with good signal fidelity up to bandwidths of 3 GHz. A bandwidth limitation is found at approximately 3 GHz for sinusoidal phase-modulated signals, above which signal fidelity is seriously degraded. This limitation is significantly less than the measured relaxation oscillations of ∼5.6 GHz, suggesting a new limitation to injection locking of phase-modulated signals. Amplification of binary-phase-shift-keyed-modulated signals to 6 Gbit/s is also demonstrated with no bit errors over the 256-bit test sequences.

Broadband photonic arbitrary waveform generation based on spatial-spectral holographic materials

We discuss an approach for the practical implementation of photonic arbitrary waveform generation of microwave signals. We describe and demonstrate an approach using spatial-spectral (S2) holography in rare earth ion doped crystals that has the potential to achieve extremely wide bandwidths (>40 GHz) using conventional electro-optic phase modulators and low bandwidth (<100 MHz) control electronics. We provide analysis of this approach, show simulations, and perform experimental demonstrations of the technique. We show a pulse compression factor of ~15,000 and demonstrate the largest effective bandwidth of 3.8 GHz to date for pulse compression using S2 holography. We also show control and manipulation of up to 30 independent compressed pulses for the creation of arbitrary waveforms.

Chirped excitation of optically dense inhomogeneously broadened media using Eu 3+ :Y 2 SiO 5

Novel pump-probe experiments provide practical, sensitive diagnostics of media inversion by linearly chirped optical pulses. Maxwell-Bloch simulations and Landau-Zener calculations support the experiments and provide a general prescription for inversion of hole-burning media by chirps.

Optical linear sideband chirp compression for microwave arbitrary waveform generation

A novel approach for the practical implementation of photonic arbitrary waveform generation of microwave signals is explored. Here we describe and demonstrate linear sideband chirp compression over 1 GHz bandwidth with a compression factor of >4000.

Efficient waveform recall in absorbing media

We have found that highly efficient waveform recall is possible in coherent transient systems in which the storage is optically thick. Coherent transients may be used in a variety of information storage and processing applications with advantages over traditional electronic methods. However, it is believed that a serious problem in application of photon echoes in practical systems is the relatively low efficiency of the process. We show in our numerical studies that waveform recall efficiencies greater than unity can be achieved in absorbing media with appropriate choice of absorption length and brief pulse area, even for very weak data pulses. We also present our preliminary experimental results in Barium vapor in which efficiencies of 50% were obtained for both the stimulated and two-pulse photon echoes.

All-optical signal encoder-decoder for secure communications

Direct sequence spread spectrum (DS/SS) is often employed for non-centralized multiple access, and an added degree of system security in coherent optical communications. With advances in coherent optical processing using Spatial- Spectral Holographic (SSH) Devices, it is possible to implement an all optical encoder/decoder for M-ary phase shift keying DS/SS. We address the issue of code selection of length N code sequences drawn from an alphabet consisting of M unit length phasers and designed for a multiuser environment. The codes are selected using very fast simulated re-annealing based on the criterion of minimizing the periodic auto and cross correlation sidelobes. The all optical implementation is discussed.

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.

Nutational stimulated photon echoes

Stimulated photon echoes (SPEs) with time duration comparable to the coherent lifetime and Rabi period have been investigated theoretically and experimentally with an angled beam configuration. The Rabi oscillation effects on both the transmitted field (optical nutation) and the SPE fields are explained by analytic solutions of Maxwell-Bloch equations. The theory also predicts that an echo can exist in the noncausal direction, and this was confirmed by experiments with Tm:YAG crystal.