H. Yum

Superluminal ring laser for hypersensitive sensing

The group velocity of light becomes superluminal in a medium with a tuned negative dispersion, using two gain peaks, for example. Inside a laser, however, the gain is constant, equaling the loss. We show here that the effective dispersion experienced by the lasing frequency is still sensitive to the spectral profile of the unsaturated gain. In particular, a dip in the gain profile leads to a superluminal group velocity for the lasing mode. The displacement sensitivity of the lasing frequency is enhanced by nearly five orders of magnitude, leading to a versatile sensor of hyper sensitivity.

Pulse Delay Via Tunable White Light Cavities Using Fiber-Optic Resonators

Previously, we proposed a data buffering system that makes use of a pair of white light cavities. For application to telecommunication systems, it would be convenient to realize such a device using fiber-optic resonators. In this paper, we present the design of such a system, where the white light cavity effect is produced by using stimulated Brillouin scattering. The system consists of a pair of fiber-optic white light cavities placed in series. As in the original proposal, the delay time can be controlled independently of the bandwidth of the data pulses. Furthermore, we show how the bandwidth of the system can be made as large as several times the Brillouin frequency shift. We also show that the net delay achievable in such a buffer can be significantly larger than what can be achieved using a conventional recirculating loop buffer.

Distortion free pulse delay system using a pair of tunable white light cavities

Recently, a tunable bandwidth white light cavity (WLC) was demonstrated by using an anomalously dispersive intra-cavity medium to adjust a cavity linewidth without reducing the cavity buildup factor [G.S. Pati et al., Phys. Rev. Lett. 99, 133601 (2007)]. In this paper, we show theoretically how such a WLC can be used to realize a distortion-free delay system for a data pulse. The system consists of two WLCs placed in series. Once the pulse has passed through them, the fast-light media in both WLCs are deactivated, so that each of these now acts as a very high reflectivity mirror. The data pulse bounces around between these mirrors, undergoing negligible attenuation per pass. The trapped pulse can be released by activating the fast-light medium in either WLC. Numerical simulations show that such a system can far exceed the delay-bandwidth constraint encountered in a typical data buffer employing slow light. We also show that the pulse remains virtually undistorted during the process.

Theoretical description and design of a fast-light enhanced helium-neon ring-laser gyroscope

We describe an enhanced rotation sensor involving an active helium-neon (HeNe) ring laser coupled to a passive enhancement resonator, which has been named a fast-light-enhanced HeNe ring-laser gyroscope (RLG). Theoretical rotation sensitivity enhancements as large as two orders of magnitude are presented. The physical effect responsible for the increased rotational sensitivity is the anomalous dispersion of the enhancement resonator, which produces a larger beat frequency as compared to a standard HeNe ring-laser gyroscope (RLG) as the laser cavity is rotated. We present the layout of the fast-light enhanced HeNe RLG, and we provide the theoretical modeling of the enhanced rotational sensitivity. A design is presented for the red HeNe (632.8 nm). The beat frequency is calculated with respect to rotation rate, which defines the useful range of operation for this highly sensitive RLG. Considerations for practical issues including laser-mirror reflectivity precision, unsaturated laser gain, and cavity-length stability are discussed.

Pump–probe model for the Kramers–Kronig relations in a laser

In this paper, we study theoretically a pump–probe model for the Kramers–Kronig (KK) relations during laser operation. A solution of laser equations reveals that the dispersion profile of a saturated laser gain medium is non-analytical at the boundary between the lasing and the non-lasing spectral region. Such a non-analyticity cannot be explained in terms of the KK relations. In order to interpret this situation, it is important to consider carefully the physical basis of the KK relations. We conclude that the KK relation is expected to apply only to an independent probe applied to the medium, which is under excitation by the pump producing the gain as well as the lasing mode. The absorption/gain and dispersion profiles are then analytical, and satisfy the KK relations. Specifically, these are variants of the so-called Mollow–Ezekiel spectra of probe absorption/gain and dispersion in the presence of a pump, with the exception that in this case the medium is inverted.

Ultra-precise rotation sensing with a superluminal ring laser

We show that group velocity of light far exceeding the vacuum speed can be realized when a medium that produces a narrow band dip in the gain profile is placed inside a ring laser. The dip leads to an effective negative dispersion, which can be tuned to produce a very small group index. The rotational sensitivity of the ring laser is enhanced by a factor equaling the inverse of the group index. For a realistic system, the enhancement factor can be as high as 1.8*105. In order to realize such a device, the background gain can be produced by using, for example, an optically pumped Ti:Sapphire crystal, a semiconductor optical amplifier, or a diode pumped alkali laser. The narrow dip can be produced, for example, by a Rb cell configured for Raman depletion. Here, we present the theoretical model behind such a superluminal laser, and describe a preliminary experiment for realizing such a device.

Visualization of superluminal pulses inside a white light cavity using plane wave spatio temporal transfer functions.

In a white light cavity (WLC), the group velocity is superluminal over a finite bandwidth. For a WLC-based data buffering system we recently proposed, it is important to visualize the behavior of pulses inside such a cavity. The conventional plane wave transfer functions, valid only over space that is translationally invariant, cannot be used for the space inside WLC or any cavity, which is translationally variant. Here, we develop the plane wave spatio temporal transfer function (PWSTTF) method to solve this problem, and produce visual representations of a Gaussian input pulse incident on a WLC, for all times and positions.

Visualization of pulse propagation through an anomalously dispersive intracavity medium

It is well-known that a transfer function method is useful to predict the profile of a pulse after it propagates through an intracavity fast-light medium. However, by using this technique, a behavior of the pulse inside the medium cannot be determined. In this paper, we describe a new theoretical approach to deal with this constraint. In the new method, we find an analytical solution for a monochromatic field of infinite spatial and temporal extents, and add the waves with the weighted amplitude and with the tailored phase to embody a Gaussian input pulse moving toward the cavity. At different time frames, the sum of these waves produces a spatial profile of the pulse before, inside and after the cavity. In particular, the pulse profile can be visualized during a superluminal propagation through the intracavity fast-light medium with zero group index. This model allows us to understand the physical process behind the superluminal propagation through a white light cavity, which is significant to realize a high bandwidth data buffer system overcoming conventional delay bandwidth product(DBP) problem.

Ultra-sensitive Acclerometry Using Anomalous Dispersion in a Sagnac Laser

We show that a zero-area Sagnac ring laser, configured in an L-shape, can perform as an ultrasensitive accelerometer when operated in the so-called superluminal regime by inducing anomalous dispersion with a dipin the gain profile

Fast Light in Optical Fiber for Trap-Door Data Buffering

Constraints encountered in data-buffering via slow light are circumvented by using a trap-door technique based on fast light. We will describe the model and our experimental efforts to realize this buffer using Brillouin gain in optical fiber. Article not Available.