Matthew S. Bigelow

Propagation of smooth and discontinuous pulses through materials with very large or very small group velocities

We investigate the propagation of optical pulses through two different solid- state optical materials, ruby and alexandrite, for which the group velocity can be very small (vgc )o r superluminal (vgc or negative). We find that for smooth pulses the fractional delay or advancement is maximized through the use of pulses with durations comparable to the response time of the physical process—coherent population oscillations—that leads to these extreme group velocities. However, we find that the transmitted pulse shape becomes distorted unless the pulse is much longer or much shorter than this response time. We also investigate the transmission of pulses that possess an abrupt change in pulse amplitude. We find that, to within experimental accuracy, this nearly discontinuous jump propagates at the usual phase velocity of light c/n ,e ven though the smoothly varying portions of the pulse propagate at the group velocity.

Ultra-slow and superluminal light propagation in solids at room temperature

Slow and superluminal group velocities can be observed in any material that has large normal or anomalous dispersion. While this fact has been known for more than a century, recent experiments have shown that the dispersion can be very large without dramatically deforming a pulse. As a result, the significance and nature of pulse velocity is being reevaluated. In this review, we discuss some of the current techniques used for generating ultra-slow, superluminal, and even stopped light. While ultra-slow and superluminal group velocities have been observed in complicated systems, from an applications point of view it is highly desirable to do have this done in a solid that can operate at room temperature. We describe how coherent population oscillations can produce ultra-slow and superluminal light under these conditions.

Tunable all-optical delays via Brillouin slow light in an optical fiber

We have demonstrated that stimulated Brillouin scattering can be used to generate all-optical slow-light pulse delays of greater than a pulse length for pulses as short as 16 ns in a single-mode fiber. Since the induced delay is generated for wavelengths detuned from the pump field by the Brillouin frequency, tuning near an electronic resonance of the material is not required and thus delays can be induced at telecommunication wavelengths. This represents a significant improvement over previous demonstrations of slow light in solids and is an important step towards developing an all-optical tunable delay line for telecommunications. In addition, these results strongly suggest that analogous delays can be achieved using stimulated Raman scattering at telecommunication data rates.

Transient stimulated Brillouin scattering dynamics in polarization maintaining optical fiber

Summary form only given. We experimentally investigate SBS in polarization-maintaining (PM) fiber with square optical pulses having a duration short compared to the fiber transit time, and show that just above threshold, SBS is generated over the entire length of the fiber. We also present measurements of the SBS threshold for pulse durations short compared to the SBS phonon lifetime (/spl sim/16 ns) and show detailed measurements of the pulse distortion on the pulse transmitted through the fiber.

A multi-channel tunable source for atomic sensors

We have designed and completed initial testing on a laser source suitable for atomic interferometry from compact, robust, integrated components. Our design is enabled by capitalizing on robust, well-commercialized, low-noise telecom components with high reliability and declining costs which will help to drive the widespread deployment of this system. The key innovation is the combination of current telecom-based fiber laser and modulator technology with periodicallypoled waveguide technology to produce tunable laser light at rubidium D1 and D2 wavelengths (and expandable to other alkalis) using second harmonic generation (SHG). Unlike direct-diode sources, this source is immune to feedback at the Rb line eliminating the need for bulky high-power isolators in the system. In addition, the source has GHz-level frequency agility and in our experiments was found to only be limited by the agility of our RF generator. As a proof-of principle, the source was scanned through the Doppler-broadened Rb D2 absorption line. With this technology, multiple channels can be independently tuned to produce the fields needed for addressing atomic states in atom interferometers and clocks. Thus, this technology could be useful in the development cold-atom inertial sensors and gyroscopes.

Ultra‐Slow and Superluminal Light Propagation in a Room‐Temperature Solid

We review some of the current techniques used for generating ultra‐slow, superluminal, and even stopped light. While ultra‐slow and superluminal group velocities have been observed in complicated systems, from an applications point of view it is highly desirable to do have this done in a solid that can operate at room temperature. We describe how coherent population oscillations can produce ultra‐slow and superluminal light under these conditions.

SUPERLUMINAL AND ULTRA-SLOW LIGHT PROPAGATION IN ROOM-TEMPERATURE SOLIDS

In recent years there has been great interest in techniques that can lead to a modification of the propagation velocity of light pulses through optical materials [1,2]. Interest stems both from the intrinsic interest in the ability to control the velocity of light over large ranges and from the potential for applications such as controllable delay lines, optical data storage devices, optical memories, and devices for quantum information. Much of this recent work has made use of the process [3] of electromagnetically induced transparency (EIT) to modify the absorptive and refractive properties of a material both to produce the good transparency needed to propagate pulses over long distances and to produce a rapid variation of refractive index needed to produce slow light. We have recently introduced a new method for achieving ultra-slow light propagation [4]. Our method produces slow light in room temperature solids. Like EIT, our method makes use of the concept of quantum coherence, but uses a different effect known as coherent population oscillations [5,6]. In particular, we apply pump and probe fields to our ruby crystal, and the population of ground-state chromium ions is induced to oscillate coherently at the resulting beat frequency. These oscillations lead to a decreased absorption of the probe beam, and consequently (by the Kramers-Kronig relations) to a steep spectral variation of the refractive index with a positive slope. Since the group index is given by n n dn d g = + ω ω / , this process produces a large positive value of the group index. We have also studied light propagation in alexandrite [7], which at certain wavelengths acts as an inverse saturable absorber. In this case, coherent population oscillations lead to increased absorption of the probe beam and consequently a steep variation of the refractive index with negative slope and thus a negative value of the group

Optically Tunable "Slow" Light in Waveguides

We demonstrate a technique for generating tunable all-optical delays as long as 20 ns in single-mode fibers at telecommunication wavelengths using stimulated Brillouin scattering. This process represents a step towards implementing slow-light in telecommunication systems.

Information velocity-in ultraslow and fast light media

We consider the effect of large normal or anomalous dispersion on the information velocity. We also experimentally study how pulse shapes are distorted as the pulse bandwidth becomes comparable to the region of steep dispersion

Ultraslow and superluminal light propagation in room temperature solids

We have observed ultraslow propagation in ruby and superluminal propagation in alexandrite enabled by the process of coherent population oscillations. Novel applications are allowed by the ability to control the velocity of light.