A global web of optical fibers forms the backbone of the Internet. This network relies on routers that switch the transmitted pulses from one fiber to another, so that information ends up at the desired destination. Currently, data traffic at major interconnections requires routers to first convert the travelling optical pulse into an electrical one, perform a switching operation, and then convert the electrical pulse back to its original form. This process can slow-down systems by a factor of 1000. Until now, the prime difficulty in designing an all-optical network router was finding a means to temporarily store or buffer the packets of information. Researchers have recently proposed a variety of methods for completely stopping light. Unfortunately, inherent limitations prevent their deployment. For instance, previous approaches employed ultra cold or hot gases1 and did not use solid-state materials. Other methods stored the data pulses as acoustical disturbances, which still travelled slowly down the fiber2. We have proposed3 a light-guiding structure that does not require cryogenic temperatures and can efficiently bring an optical pulse to a complete halt. In this approach, light travels inside an engineered solid-state meta-material (MM), that has a negative refractive index. This material was developed4 in 2001 and the scheme is conceptually simple. The device we envisioned is a three-layer waveguiding heterostructure, in which the middle MM layer is surrounded by two regular dielectrics. The center portion tapers from wide to narrow. Because the power-flow direction inside theMM layer is opposite to the one in the dielectric regions, the guided electromagnetic waves are markedly slowed. Figure 1 shows the propagation of a monochromatic ( f = 1THz) p-polarized magnetic-field component. The light enters the device from the wide end and stops at the prearranged critical thickness. Because of theMM’s anomalous frequency dispersion, the longest (red) wavelength components stop at the Figure 1. A white light beam hits the tapered negative refractive index layer (shown in white), which is surrounded by two regular dielectric layers (shown in blue and green). Upon entering the structure, each frequency component, or color, of the beam stops at different thicknesses, forming a trapped rainbow.
A global web of optical fibers forms the backbone of the Internet. This network relies on routers that switch the transmitted pulses from one fiber to another, so that information ends up at the desired destination. Currently, data traffic at major interconnections requires routers to first convert the travelling optical pulse into an electrical one, perform a switching operation, and then convert the electrical pulse back to its original form. This process can slow-down systems by a factor of 1000. Until now, the prime difficulty in designing an all-optical network router was finding a means to temporarily store or buffer the packets of information. Researchers have recently proposed a variety of methods for completely stopping light. Unfortunately, inherent limitations prevent their deployment. For instance, previous approaches employed ultra cold or hot gases1 and did not use solid-state materials. Other methods stored the data pulses as acoustical disturbances, which still travelled slowly down the fiber2. We have proposed3 a light-guiding structure that does not require cryogenic temperatures and can efficiently bring an optical pulse to a complete halt. In this approach, light travels inside an engineered solid-state meta-material (MM), that has a negative refractive index. This material was developed4 in 2001 and the scheme is conceptually simple. The device we envisioned is a three-layer waveguiding heterostructure, in which the middle MM layer is surrounded by two regular dielectrics. The center portion tapers from wide to narrow. Because the power-flow direction inside theMM layer is opposite to the one in the dielectric regions, the guided electromagnetic waves are markedly slowed. Figure 1 shows the propagation of a monochromatic ( f = 1THz) p-polarized magnetic-field component. The light enters the device from the wide end and stops at the prearranged critical thickness. Because of theMM’s anomalous frequency dispersion, the longest (red) wavelength components stop at the Figure 1. A white light beam hits the tapered negative refractive index layer (shown in white), which is surrounded by two regular dielectric layers (shown in blue and green). Upon entering the structure, each frequency component, or color, of the beam stops at different thicknesses, forming a trapped rainbow.
We show how guided electromagnetic waves propagating along an adiabatically tapered negative-refractive-index metamaterial heterostructure can be brought to a complete halt. It is analytically shown that, in principle, this method simultaneously allows for broad bandwidth operation (since it does not rely on group index resonances), large delay-bandwidth products (since a wave packet can be completely stopped and buffered indefinitely) and high, almost 100%, in/out-coupling efficiencies. By nature, the presented scheme invokes solid-state materials and, as such, is not subject to low-temperature or atomic coherence limitations. A wave analysis, which demonstrates the halting of a monochromatic field component travelling along the heterostructure, is followed by a pertinent ray analysis, which unmistakably illustrates the trapping of the associated light-ray and the formation of a double light-ray cone ('optical clepsydra') at the point where the ray is trapped. This method for trapping photons conceivably opens the way to a multitude of hybrid optoelectronic devices to be used in 'quantum information' processing, communication networks and signal processors and may herald a new realm of combined metamaterials and slow light research.
It is known that light can be slowed down in the vicinity of resonances in dispersive materials.5 In order to reduce the group velocity (vg) of light coherently, there are primarily two major approaches employing either electronic or optical resonances. In the electronic scheme, drastic slowing down and complete stopping of light pulses can be accomplished by converting optical signals into electronic coherences.6-9 The use of electronic states to coherently store the optical information, however, imposes severe constraints in the scheme, including narrow bandwidth, limited working wavelengths and strong temperature dependence. While promising steps have been taken towards slowing light in solidstate media and semiconductor nanostructures operating at room temperature,10 it still remains a great challenge to implement such schemes on-a-chip incorporating optoelectronic devices.9 Besides, only a few special and delicate electronic resonances available in nature possess the required properties. As a result, there has been great interest in pursuing alternative approaches utilizing optical resonances in photonic structures, such as microcavities,11photonic crystals,12 semiconductor waveguide ring resonators,13etc. In 2007, researchers in UK proposed a tapered structure based on metamaterial with negative refractive index.14 Theoretically, this structure should be able to slow light to a standstill. The material would halt each frequency of light, and hence color, at slightly different places, to make so called “trapped rainbow” (see Fig. 9.1), which opened a new and attractive approach to stopping light.
A competent method for slowing and completely stopping light, based on wave propagation along an adiabatically tapered negative-refractive-index metamaterial heterostructure, is presented. It is analytically shown that, in principle, this method simultaneously allows for broad bandwidth operation (since it does not rely on group index resonances), large delay-bandwidth products (since a wave packet can be completely stopped and buffered indefinitely) and high, almost 100%, in/out-coupling efficiencies. Moreover, by nature, the presented scheme invokes solid-state materials and, as such, is not subject to low-temperature or atomic coherence limitations. A wave analysis, which demonstrates the halting of a monochromatic field component travelling along the heterostructure, is followed by a corresponding ray analysis that illustrates the trapping of the associated light-ray and the formation of a double light-ray cone ('optical clepsydra'). This method for trapping photons conceivably opens the way to a multitude of hybrid, optoelectronic devices to be used in 'quantum information' processing, communication networks and signal processors, and may herald a new realm of combined metamaterials and slow light research.
Recently there has been a considerable interest in metamaterial waveguide structures capable of dramatically slowing down or, even, completely stopping light. Here, we shall explain in some detail the working principle behind the deceleration and/or stopping of light in metamaterial structures, and review the various, metamaterial-enabled, methods that have been proposed thus far towards achieving such a goal. Further, we will concisely describe how one can construct zero-loss metamaterials over a continuous and broad (but not infinite) range of frequencies, which is an essential prerequisite for any slow-light system. Moreover, it will be explained that inside such waveguide structures light can in principle be stopped (zero group velocity, vg = 0) even in the presence of losses. By nature, metamaterialenabled schemes for stopping/storing light invoke solid-state materials and, as such, are not subject to low-temperature or atomic coherence limitations. Furthermore, these methods simultaneously allow for broad bandwidth operation, since they do not rely on group index resonances; large delay-bandwidth products, since a wave packet can, in principle, be completely stopped and buffered indefinitely; and (for the case, in particular, where a negative-index metamaterial is used) high, almost 100%, in/out-coupling efficiencies. Thus, we conclude that these methods for trapping photons, which can be realised using existing technology, could open the way to a multitude of hybrid optoelectronic devices to be used in 'quantum information' processing, communication networks and signal processors and may conceivably herald a new realm of combined metamaterials and slow light research.
We review recent theoretical and experimental in progress in the realisation of slow and stopped light by the 'trapped rainbow' principle in optical metamaterials featuring negative electromagnetic parameters (permittivity/permeability and/or refractive index). We explain how and why these structures can enable complete stopping of light even in the presence of disorder and, simultaneously, dissipative losses. Using full-wave numerical simulations we show that the incorporation of thin layers made of an active medium adjacently to the core layer of a negative-refractive-index waveguide can completely remove dissipative losses - in a slow-light regime where the effective index of the guided wave is negative.
We introduce an efficient method for slowing and stopping/storing light, which is based on wave propagation along a slowly axially varying, adiabatically tapered, negative refractive index metamaterial heterostructure. We analytically show that the present method can, in principle, simultaneously allow for broad bandwidth operation (since it does not rely on group index resonances), large delay-bandwidth products (since a wave packet can be completely stopped and buffered indefinitely) and high, almost 100%, in/out-coupling efficiencies. Moreover, by nature, the presented scheme invokes solid-state materials and, as such, is not subject to low-temperature or atomic coherence limitations. This method for trapping photons conceivably opens the way to a multitude of hybrid, optoelectronic devices to be used in 'quantum information' processing, communication networks and signal processors, and may herald a new realm of combined metamaterials and slow light research.