Daniel J. Gauthier

Stored Light in an Optical Fiber via Stimulated Brillouin Scattering

We describe a method for storing sequences of optical data pulses by converting them into long-lived acoustic excitations in an optical fiber through the process of stimulated Brillouin scattering. These stored pulses can be retrieved later, after a time interval limited by the lifetime of the acoustic excitation. In the experiment reported here, smooth 2-nanosecond-long pulses are stored for up to 12 nanoseconds with good readout efficiency: 29% at 4-nanosecond storage time and 2% at 12 nanoseconds. This method thus can potentially store data packets that are many bits long. It can be implemented at any wavelength where the fiber is transparent and can be incorporated into existing telecommunication networks because it operates using only commercially available components at room temperature.

The speed of information in a 'fast-light' optical medium.

One consequence of the special theory of relativity is that no signal can cause an effect outside the source light cone, the space-time surface on which light rays emanate from the source. Violation of this principle of relativistic causality leads to paradoxes, such as that of an effect preceding its cause. Recent experiments on optical pulse propagation in so-called ‘fast-light’ media—which are characterized by a wave group velocity υg exceeding the vacuum speed of light c or taking on negative values—have led to renewed debate about the definition of the information velocity υi. One view is that υi = υg (ref. 4), which would violate causality, while another is that υi = c in all situations, which would preserve causality. Here we find that the time to detect information propagating through a fast-light medium is slightly longer than the time required to detect the same information travelling through a vacuum, even though υg in the medium vastly exceeds c. Our observations are therefore consistent with relativistic causality and help to resolve the controversies surrounding superluminal pulse propagation.

Broadband SBS Slow Light in an Optical Fiber

In this paper, we investigate slow light via stimulated Brillouin scattering (SBS) in a room temperature optical fiber that is pumped by a spectrally broadened laser. Broadening the spectrum of the pump field increases the linewidth Deltaomegap of the Stokes amplifying resonance, thereby increasing the slow-light bandwidth. One physical bandwidth limitation occurs when the linewidth becomes several times larger than the Brillouin frequency shift OmegaB so that the anti-Stokes absorbing resonance substantially cancels out the Stokes amplifying resonance and, hence, the slow-light effect. We find that partial overlap of the Stokes and anti-Stokes resonances can actually lead to an enhancement of the slow-light delay-bandwidth product when Deltaomegapsime1.3OmegaB. Using this general approach, we increase the Brillouin slow-light bandwidth to over 12 GHz from its nominal linewidth of ~30 MHz obtained for monochromatic pumping. We controllably delay 75-ps-long pulses by up to 47 ps and study the data-pattern dependence of the broadband SBS slow-light system

Applications of Slow Light in Telecommunications

Exotic effects such as slow light, fast light and even stored light have been observed in the laboratory. Now, optical scientists are turning their attention toward developing applications of slow light, including controllable optical delay lines, optical buffers and true time delay methods for synthetic aperture radar.

Controlling the Velocity of Light Pulses

Blod Blod. It is now possible to exercise a high degree of control over the velocity at which light pulses pass through material media. This velocity, known as the group velocity, can be made to be very different from the speed of light in a vacuum c. Specifically, the group velocity of light can be made much smaller than c, greater than c, or even negative. We present a survey of methods for establishing extreme values of the group velocity, concentrating especially on methods that work in room-temperature solids. We also describe some applications of slow light.

Distortion management in slow-light pulse delay

We describe a methodology to maximize slow-light pulse delay subject to a constraint on the allowable pulse distortion. We show that optimizing over a larger number of physical variables can increase the distortion-constrained delay. We demonstrate these concepts by comparing the optimum slow-light pulse delay achievable using a single Lorentzian gain line with that achievable using a pair of closely-spaced gain lines. We predict that distortion management using a gain doublet can provide approximately a factor of 2 increase in slow-light pulse delay as compared with the optimum single-line delay. Experimental results employing Brillouin gain in optical fiber confirm our theoretical predictions.

High-dimensional quantum cryptography with twisted light

Quantum key distribution (QKD) systems often rely on polarization of light for encoding, thus limiting the amount of information that can be sent per photon and placing tight bounds on the error rates that such a system can tolerate. Here we describe a proof-of-principle experiment that indicates the feasibility of high-dimensional QKD based on the transverse structure of the light field allowing for the transfer of more than 1 bit per photon. Our implementation uses the orbital angular momentum (OAM) of photons and the corresponding mutually unbiased basis of angular position (ANG). Our experiment uses a digital micro-mirror device for the rapid generation of OAM and ANG modes at 4 kHz, and a mode sorter capable of sorting single photons based on their OAM and ANG content with a separation efficiency of 93%. Through the use of a seven-dimensional alphabet encoded in the OAM and ANG bases, we achieve a channel capacity of 2.05 bits per sifted photon. Our experiment demonstrates that, in addition to having an increased information capacity, multilevel QKD systems based on spatial-mode encoding can be more resilient against intercept-resend eavesdropping attacks.

Enhancing the Spectral Sensitivity of Interferometers using Slow-Light Media

We demonstrate experimentally that the spectral sensitivity of an interferometer can be greatly enhanced by introducing a slow-light medium into it. The experimental results agree very well with theoretical predictions that the enhancement factor of the spectral sensitivity is equal to the group index n(g) of the slow-light medium.

The restitution portrait: A new method for investigating rate-dependent restitution

Introduction: Electrical restitution, relating action potential duration (APD) to diastolic interval (DI), was believed to determine the stability of heart rhythm. However, recent studies demonstrate that stability also depends on long‐term APD changes caused by memory. This study presents a new method for investigation of rate‐ and memory‐dependent aspects of restitution and for assessment of mapping models of APD.

12-GHz-Bandwidth SBS Slow Light in Optical Fibers

We increased the bandwidth of SBS slow light in an optical fiber to 12.6 GHz. We delayed 75-ps pulses by up to 47 ps and studied the data pattern dependence of the broadband SBS slow-light system.