Guanghao Zhu

Simultaneous spatial and temporal focusing of femtosecond pulses

We experimentally demonstrate the concept of simultaneous spatial and temporal focusing of femtosecond pulses. Our technique has the potential to significantly reduce background excitation which fundamentally limits the imaging depth in scattering biological specimens.

Simultaneous spatial and temporal focusing for axial scanning

We show theoretically and experimentally that simultaneous spatial and temporal focusing can scan the temporal focal plane axially by adjusting the group velocity dispersion in the excitation beam path. When the group velocity dispersion is small, the pulse width at the temporal focal plane is transform-limited, and the amount of shift depends linearly upon the dispersion. By adding a meter of large mode area fiber into the system, we demonstrate this axial scanning capability in a fiber delivery configuration. Because a transform-limited pulse width is automatically recovered at the temporal focal plane, simultaneous spatial and temporal focusing negates the need for any dispersion pre-compensation, further facilitating its integration into a fiber delivery system. A highly promising application for simultaneous spatial and temporal focusing is an axial scanning multiphoton fluorescence fiber probe without any moving parts at the distal end and without dispersion pre-compensation.

Compensation of self-phase modulation in fiber- based chirped-pulse amplification systems

We demonstrate a simple, all-fiber technique for removing nonlinear phase due to self-phase modulation in fiber-based chirped-pulse amplification (CPA) systems. Using a LiNbO3 electro-optic phase modulator to emulate a negative nonlinear index of refraction, we are able to remove 1.0 π rad of self-phase modulation acquired by pulses during amplification and eliminate nearly all pulse distortion. Our technique is high speed, removes nonlinear phase on a pulse-to-pulse basis, and can be readily integrated into existing CPA systems.

Experimental demonstration of postnonlinearity compensation in a multispan DPSK transmission

We demonstrate significant performance improvement in 10-Gb/s multispan differential phase-shift keying transmissions by employing postnonlinearity compensation (PNC) for both dispersion-managed soliton and quasi-linear transmission. Measurements of timing misalignment tolerance as well as bandwidth requirement of the PNC unit show that the PNC technique is robust and practical, and can be easily extended to higher bit-rate transmissions.

Compensation of self-phase modulation in fiber-based chirped-pulse amplification systems

We demonstrate a simple, all-fiber technique for removing nonlinear phase on a pulse-to-pulse basis in a fiber-based CPA system. Removal of 1.0 pi of nonlinear phase is achieved.

Background Reduction with Two-Color Two-Beam Multiphoton Excitation

By comparing axial excitation profiles, we present experimental proof which demonstrates that two-color two-beam multiphoton excitation offers a better signal to background ratio than conventional single beam multiphoton excitation.

Nonlinear distortion free fiber-based chirped pulse amplification with self-phase modulation up to 2π

By using an electo-optic phase modulator to realize nonlinear phase pre-compensation, we demonstrate nonlinear distortion free fiber-based chirped pulse amplification with accumulated self-phase modulation up to 2.0 π radians.

Experimental demonstration of postnonlinearity compensation in a multi-span DPSK transmission

We demonstrate performance improvement in a multi-span 10 Gb/s DPSK transmission by employing postnonlinearity compensation. Significant improvements in BER were obtained for both dispersion managed soliton and quasi-linear transmission.

Simultaneous spatial and temporal focusing for remote axial scanning in wide field imaging

We show theoretically and experimentally that simultaneous spatial and temporal focusing can scan the temporal focal plane axially by adjusting the group velocity dispersion, allowing for remote axial scanning