Modest Contributions

Some Key Papers

Comment on Nimtz-Stahlhofen experiment (03-13-2008)

Popular presentation on apparent superluminality (09-01-2007)
An equation-free re-interpretation of an experiment by Nimtz and Stahlhofen

Do single photons tunnel faster than light? (08-28-2007)
Presented at the SPIE Conference “The Nature of Light: What Are Photons?” San Diego, CA, August 26, 2007.

Direct space-time observation of pulse tunneling (08-23-2007)
Here we actually look inside a barrier and observe a tunneling pulse. The results support our quasi-static interpretation of tunneling. No evidence of “pulse reshaping” is seen.

Physics Reports review article on tunneling time (12-17-2006)

Meaning of group delay in barrier tunneling (08-18-2007)
We show that the group delay in tunneling is not a traversal time but a lifetime of stored energy or stored probability escaping through both ends of the barrier. Because it is a lifetime associated with both forward (transmitted) and backward (reflected) fluxes, it cannot be used to define a group velocity for forward transit in cases where a wavepacket is mostly reflected. For photonic tunneling barriers the group delay is identical to the dwell time which is also a property of an entire wave function with reflected and transmitted components. Theoretical predictions and experimental reports of superluminal group velocities in barrier tunneling are re-interpreted.

The meaning of group delay in barrier tunneling (New J. Phys. 8, 101 2006) (07-29-2006)
Here we show that the group delay (phase time) in barrier tunneling is not a transit time but the lifetime of stored energy (or stored probability) escaping through both ends of the barrier.

The nature of “superluminal” barrier tunneling (PRL 2003) (09-30-2006)
Here I show that tunneling is a quasi-static phenomenon in which a wavepacket (longer than the barrier) modulates the stored energy (or number of particles) in the barrier.

Physical mechanism for apparent superluminality in barrier tunneling (JSTQE 2003) (11-15-2006)
A more detailed description of my approach to the tunneling time paradox.

Origin of the Hartman Effect (OPtics Express 2002) (07-29-2006)
In barrier tunneling the group delay (phase time) saturates with barrier length. The origin of this effect has been a mystery for decades. Here we show that the origin of the Hartman effect is the saturation of stored energy in the barrier.

Relation between tunneling times for relativistic particles (PRA2004) (11-15-2006)

Delay time and the Hartman effect (PRL 2003b) (11-15-2006)

Nonlinear Photonic Bandgap Structures I (APL 1979) (08-03-2006)
I showed that the presence of an intensity-dependent refractive index can lead to optical bistability and a kind of self-induced transparency in photonic bandgap structures. This work launched the study of nonlinear periodic structures and the transmission resonances known as gap solitons.

Synchronized Chaos (08-03-2006)
We discovered the possibility of synchronized chaotic pulsations in an array of coupled lasers. Spatio-temporal chaos occurs when synchronized chaos breaks down. The first discovery of synchronized chaos in mutually coupled laser oscillators.

Polarization Instabilities (08-03-2006)
This paper launched the field of polarization instabilities. Here I showed that the intensity-dependent refractive index leads to an instability in the polarization state of a light wave in a birefringent fiber.

Stability of Semiconductor Laser Arrays (08-03-2006)
We carried out the first studies of the stability of phase locking in semiconductor laser arrays. Self-pulsations and chaos were predicted.

Gouy Shift and Single-Cycle Pulses I (08-03-2006)
We predicted that the Gouy shift of confined beams would lead to a temporal reshaping of single-cycle pulses.

Gouy Shift and Single-Cycle Pulses II (08-03-2006)
We carried out the first direct observation of the Gouy phase shift using single-cycle terahertz pulses.

Physical origin of Gouy phase shift (Optics Letters 2001) (09-03-2007)
We show explicitly that the Gouy phase shift originates from transverse spatial confinement and the uncertainty principle.

Optimal Design of Fiber Raman Amplifiers (08-03-2006)
With my student Victor Perlin we introduced an optimal design scheme for wideband flat gain fiber Raman amplifiers.

Winful Dissertation: Optical Bistability in Periodic Structures and in Four-Wave Mixing Processes (08-03-2006)
This disssertation provides the first theory of nonlinear periodic structures (also known as photonic bandgap structures). Discovered optical bistability and the nonlinear spatial resonances now known as gap solitons. Also predicted bistability in four-wave mixing processes.

Winful Dissertation Chapter 3 (08-03-2006)
Optical Bistability in Periodic Structures

Winful Dissertation Chapter 4 (08-03-2006)
Bistability in Four-Wave Mixing

Winful Dissertation Appendices and References (08-03-2006)

Pulse compression and solitons in nonlinear periodic structures (08-04-2006)
Here I showed that the negative group velocity dispersion due to a grating embedded in an optical fiber can enable pulse compression and the formation of solitons.