D. E. Leaird

Observation of spatial optical solitons in a nonlinear glass waveguide

We report the observation of spatial optical solitons due to the Kerr nonlinearity in a planar glass waveguide and present measurements of the nonlinear response obtained by placing a pinhole at the output of the waveguide. For input intensities greater than that required for the fundamental soliton, we observe breakup of the output owing to the effect of two-photon absorption.

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.

Experimental observation of spatial soliton interactions

We report the experimental observation of interaction forces between two fundamental spatial optical solitons in a nonlinear glass waveguide. Both attraction and repulsion were observed, depending on the relative phase between the solitons.

Femtosecond spectral holography

Storage, recall, and processing of shaped femtosecond waveforms are achieved by performing spectral holography within a femtosecond pulse shaping apparatus. Time reversal, as well as correlation and convolution, of femtosecond temporal signals is demonstrated. Applications of this technique to matched filtering, dispersion compensation, encryption and decoding and femtosecond waveform synthesis are also discussed. The work extends the powerful principles of holographic signal processing, which have been used extensively for pattern recognition and filtering of two-dimensional spatial signals, to the femtosecond time domain. >

Generation of terahertz-rate trains of femtosecond pulses by phase-only filtering.

We describe a simple linear filtering technique for transforming individual femtosecond light pulses into terahertzrepetition-rate bursts of femtosecond pulses. By using phase-only filtering, high efficiency is achieved. Pulse repetition rates approaching 6 THz are obtained.

Mode-locked dark pulse Kerr combs in normal-dispersion microresonators

Kerr frequency combs from microresonators are now extensively investigated as a potentially portable technology for a variety of applications. Most studies employ anomalous dispersion microresonators that support modulational instability for comb initiation, and mode-locking transitions resulting in coherent bright soliton-like pulse generation have been reported. However, some experiments show comb generation in normal dispersion microresonators; simulations suggest the formation of dark pulse temporal profiles. Excitation of dark pulse solutions is difficult due to the lack of modulational instability in the effective blue-detuned pumping region; an excitation pathway has been demonstrated neither in experiment nor in simulation. Here we report experiments in which dark pulse combs are formed by mode-interaction-aided excitation; for the first time, a mode-locking transition is observed in the normal dispersion regime. The excitation pathway proposed is also supported by simulations.

Femtosecond multiple-pulse impulsive stimulated Raman scattering spectroscopy

Optical control of elementary molecular motion through impulsive stimulated Raman scattering is enhanced by means of timed sequences of femtosecond pulses that are produced by pulse-shaping techniques. In particular, terahertz-rate trains of femtosecond pulses are used for repetitive impulsive excitation of individual phonon modes in an α-perylene molecular crystal. When the pulse repetition rate is matched to the desired phonon frequency, mode-selective vibrational amplification is achieved. A comparison of data acquired with the transient-grating and the pump–probe experimental geometries reveals the timing dynamics of the induced phonon oscillations with respect to the driving femtosecond pulse sequence.

Line-by-line pulse shaping control for optical arbitrary waveform generation

We demonstrate line-by-line pulse shaping control for optical arbitrary waveform generation (O-AWG). Independent manipulation of individual spectral lines from a mode-locked frequency comb leads to synthesis of user-specified ultrafast optical waveforms with unprecedented frequency resolution.

Use of femtosecond square pulses to avoid pulse breakup in all-optical switching

The authors report measurements of ultrafast all-optical switching in dual-core fiber nonlinear couplers. By performing the measurements with square optical pulses, the pulse breakup which occurs in experiments performed by using conventional bell-shaped pulses is minimized. Compared to measurements performed by using conventional bell-shaped pulses, the measurements yield decreased switching power, a sharper switching transition, and improved power transfer. It is concluded that square pulse switching can be utilized to enhance the switching performance of any ultrafast all-optical switching device triggered by instantaneous intensity. >

Spectral holography of shaped femtosecond pulses.

Storage and subsequent recall of shaped femtosecond waveforms is achieved by performing spectral holography within a femtosecond pulse-shaping apparatus. Readout of the spectral hologram by using a short reference pulse yields both real and time-reversed reconstructions of the original signal. Convolution and correlation operations are achieved by using shaped pulses for readout. These experiments demonstrate the possibility of nonlinear spectral filtering and signal processing of femtosecond optical waveforms.