Matthew R. Fetterman

Ultrafast pulse shaping: amplification and characterization

We demonstrate high-resolution amplified pulse shaping using an acousto-optic modulator (AOM) at a center-wavelength of 795nm. The output pulses have energy of 200mJ/pulse and a transform-limited pulsewidth of 150fs. A spectral modulation of over 40 features is achieved in a single pulse. We characterize the pulses using the STRUT (Spectrally and Temporally Resolved Upconversion Technique). Using predistortion techniques, we demonstrate that the pulses can be shaped in amplitude and phase. We create a complex pulse shape with hyperbolic secant amplitude and hyperbolic tangent frequency sweep, which is useful for applications in adiabatic rapid passage experiments.

Fabrication and analysis of high-contrast InGaAsP-InP Mach-Zehnder modulators for use at 1.55-μm wavelength

A high-contrast ratio, low voltage-length product, multiple quantum well InGaAsP-InP Mach-Zehnder interferometer is demonstrated and analyzed. An on/off ratio of over 40 dB and voltage-length product of 1.8 V-mm were measured, results which are superior to previous reports of similar MQW structures. Using the Lanczos-Helmholtz beam propagation method, we find that the linear and quadratic electrooptic coefficients for InGaAsP quantum wells are r=(3.9/spl plusmn/1.7) pm/V and s=(5.0/spl plusmn/1.5)/spl times/10/sup -19/ m/sup 2//V/sup 2/, respectively. We also demonstrate active optical alignment of the modulator guides using integrated waveguide light emitting diodes.

Spectral interference measurement of nonlinear pulse propagation dynamics in optical fibers

Ultrafast pulse shaping and ultrafast pulse spectral phase-retrieval techniques are used in the spectral interference measurement of nonlinear pulse propagation dynamics in dispersion-shifted optical fiber. Nonlinear responses in both amplitude profile and phase profile of the pulses at zero-dispersion wavelength as well as at nonzero-dispersion wavelength are directly measured. A numerical simulation that uses a third-oder-dispersion-included nonlinear Schrödinger equation gives excellent agreement with the experimental data.

Real-time adaptive amplitude feedback in an AOM-based ultrafast optical pulse shaping system

We demonstrate real-time adaptive amplitude feedback in an AOM-based ultrafast optical pulse shaping system operating at /spl lambda/=1550 nm wavelength for optical communication applications. At the optimized feedback depth, a simple negative feedback algorithm converges in fewer than 10 iterations to within 5% of the target shape. This technique may be very useful for many applications including spectrum-sliced WDM.

Generation of amplified shaped pulses for highly adiabatic excitation

Complex amplified pulses, including al ps, 100 µJ tanh-swept sech pulse for adiabatic inversion, are generated experimentally. STRUT detection verifies the modulation and follows the dynamics induced by such pulses in Rb vapor. Applications to production of spin-polarized gases for medical imaging are discussed.

Propagation of complex shaped ultrafast pulses in highly optically dense samples

We examine the propagation of shaped (amplitude- and frequency-modulated) ultrafast laser pulses through optically dense rubidium vapor. Pulse reshaping, stimulated emission dynamics, and residual electronic excitation all strongly depend on the laser pulse shape. For example, frequency swept pulses, which produce adiabatic passage in the optically thin limit (independent of the sign of the frequency sweep), behave unexpectedly in optically dense samples. Paraxial Maxwell optical Bloch equations can model our ultrafast pulse propagation results well and provide insight.

Altering excitation dynamics in optically dense media using shaped ultrafast laser pulses

Summary form only given. We study the interaction between intense (50 MW peak power), shaped ultrafast laser pulses and optically dense samples of Rb vapor. In particular, we concentrate our attention on laser pulses with a the complex hyperbolic secant envelope, or equivalently, a sech electric field envelope with a tanh frequency sweep. In order to produce and characterize the shaped laser pulses used in our experiments, we exploited several new technologies: amplified, shaped laser pulses were generated using an acousto-optic modulator-based system combined with a chirped-pulse regenerative amplifier. The amplitude and phase of these pulses were then characterized by the STRUT (spectrally and temporally resolved upconversion technique). The STRUT was used to measure the laser pulses both before and after propagating through Rb vapor. Examples of such experimental STRUT images are presented. The complex sech pulse was selected because, in optically thin media, only it and rectangular pulses give complete analytical solutions to the Bloch equations. This shape has been found to generate complete population inversion over a well-defined and amplitude-insensitive bandwidth. In optically dense samples the excited state dynamics are not so straightforward. We have found, both in experiments and theoretically, that the extent and character of the population inversion is related to the frequency sweep of the laser pulses as does the amount of residual excited population after the pulse and any subsequent stimulated emission.

Optical wavelength domain code-division multiplexing using an AOM-based ultrafast optical pulse shaping approach

Optical wavelength domain code-division multiplexing access (WD-CDMA) using an AOM-based ultrafast optical pulse shaping approach is proposed and demonstrated experimentally at 1550 nm. This new multiplexing technique utilizes wavelength domain codes that are essentially different optical spectral patterns in order to achieve CDMA. In addition to the advantages of the conventional CDMA technique, WD-CDMA can make full use of the entire optical bandwidth without requiring faster optical switches or modulators. This approach also drastically reduces sensitivity to fiber dispersion. Experimentally, we demonstrate an optical spectral encoder using ultrafast optical pulse shaping with 16 wavelength bits over an optical bandwidth of 5 THz. The spectrally-encoded optical pulse generated with the spectral encoder is then decoded with different WD-CDMA codes in the spectral domain. Different code-division channels can thus extract their own bit information while sharing the same spectral-encoded laser pulse as their common carrier. These spectral-encoded pulses are shown using the cross- correlation technique to be confined within a time slot of 15 ps. A larger number of WD bits is also achievable with our system.