A driving force in the rapidly developing field of photonic crystals has been the photonic bandgap, a range of energies where the propagation of light is completely forbidden. The photonic bandgap allows the design of photonic lattices that localize, guide and bend light at sub-micron length scales, providing opportunities for the creation of miniature optical devices and integrated optical circuits to help drive the revolution in photonics. A less well known attribute of photonic crystals is their theoretical ability to slow light to a velocity of zero. This phenomenon can be achieved at the high and low energy edges of photonic stopgaps where the photonic bands are flat and light exists as a standing wave commensurate with the photonic lattice and travels at a group velocity of zero, referred to as “slow photons” herein. It has been shown theoretically that the probability of harvesting slow photons scales inversely with their group velocity. This means that a number of well known photon driven processes and devices in chemistry and physics can be enhanced by capturing this unique property of slow photons. In this paper we will look at slow photons mainly through the eye of chemistry and highlight some recent developments in this exciting and emerging field that demonstrate the potential of slow photons in materials chemistry and nanochemistry.
A driving force in the rapidly developing field of photonic crystals has been the photonic bandgap, a range of energies where the propagation of light is completely forbidden. The photonic bandgap allows the design of photonic lattices that localize, guide and bend light at sub-micron length scales, providing opportunities for the creation of miniature optical devices and integrated optical circuits to help drive the revolution in photonics. A less well known attribute of photonic crystals is their theoretical ability to slow light to a velocity of zero. This phenomenon can be achieved at the high and low energy edges of photonic stopgaps where the photonic bands are flat and light exists as a standing wave commensurate with the photonic lattice and travels at a group velocity of zero, referred to as “slow photons” herein. It has been shown theoretically that the probability of harvesting slow photons scales inversely with their group velocity. This means that a number of well known photon driven processes and devices in chemistry and physics can be enhanced by capturing this unique property of slow photons. In this paper we will look at slow photons mainly through the eye of chemistry and highlight some recent developments in this exciting and emerging field that demonstrate the potential of slow photons in materials chemistry and nanochemistry.
The problem of slowing down light by orders of magnitude has been extensively discussed in the literature. Such a possibility can be useful in a variety of optical and microwave applications. Many qualitatively different approaches have been explored. Here we discuss how this goal can be achieved in linear dispersive media, such as photonic crystals. The existence of slowly propagating electromagnetic waves in photonic crystals is quite obvious and well known. The main problem, though, has been how to convert the input radiation into the slow mode without losing a significant portion of the incident light energy to absorption, reflection, etc. We show that the so-called frozen mode regime offers a unique solution to the above problem. Under the frozen mode regime, the incident light enters the photonic crystal with little reflection and, subsequently, is completely converted into the frozen mode with huge amplitude and almost zero group velocity. The linearity of the above effect allows the slowing of light regardless of its intensity. An additional advantage of photonic crystals over other methods of slowing down light is that photonic crystals can preserve both time and space coherence of the input electromagnetic wave.
Unluckily, light is inherently difficult to control, not to mention how hard it is to store it.This is not only due to its speed, but also to the very nature of its basic unit, the photon, being massless and having no electric charge.A number of ingenious and diverse schemes to diminish the speed of light in a controllable fashion has been proposed, giving rise to the intriguing field of slow light.All slow light schemes are based in the same basic principle, in www.intechopen.comAdvanced Photonic Sciences 54 spite of their interdisciplinary nature: the existence of a single sharp resonance or multiple resonances (Khurgin & Tucker, 2009).As it will be justified, photonic crystal devices are, to our understanding, the most promising approach for the development of practical photonic devices based on slow light.This chapter begins by reviewing the motivation and principles of slow light, followed by a description and assessment of the different techniques to diminish the speed of light and the applications of this phenomenon.In a subsequent section the particularly promising approach of slow-light photonic crystal arrangements will be addressed.In that section, together with the fundamentals of photonic band gap materials, their simulation methods and fabrication techniques, simulations results and analysis on our designs of slow-light photonic crystal arrangements will be presented.The chapter will be concluded with an assessment of photonic band gap engineered materials as a technology for developing slowlight based devices for telecommunications and microwave photonics applications.
Research into slow light began theoretically in 1880 with the paper [1] of H A Lorentz, who is best known for his work on relativity and the speed of light. Experimental work started some 60 years later with the work of S L McCall and E L Hahn [2] who explored non-linear self-induced transparency in ruby. This field of research has burgeoned in the last 10 years, starting with the work of L Vestergaard Hau and coworkers on slow light via electromagnetically induced transparency in a Bose–Einstein condensate [3]. Many groups are now able to slow light down to a few metres per second or even stop the motion of light entirely [4]. Today, slow light – or more often `slow and fast light' – has become its own vibrant field with a strongly increasing number of publications. In broad scope, slow light research can be categorized in terms of the sort of physical mechanism used to slow down the light. One sort of slow light makes use of material dispersion. This dispersion can be the natural dispersion of the ordinary refractive index or can be the frequency dependence of some nonlinear optical process, such as electromagnetically induced transparency, coherent population oscillations, stimulated light scattering, or four-wave mixing processes. The second sort of slow light makes use of the wavelength dependence of artificially structured materials, such as photonic crystals, optical waveguides, and collections of microresonators. Material systems in which slow light has been observed include metal vapours, rare-earth-doped materials, Raman and Brillioun gain media, photonic crystals, microresonators and, more recently, metamaterials. A common feature of all of these schemes is the presence of a sharp single resonance or multiple resonances produced by an atomic transition, a resonance in a photonic structure, or in a nonlinear optical process. Current applications of slow light include a series of attractive topics in optical information processing, such as optical data storage, optical memories, quantum information devices, and optical communication systems in which the use of slow light will allow all-optical processing with less wasted heat. To implement these applications, devices such as buffers, memories, interferometers and switches that utilize slow light need to be developed. Future challenges include the need for improved coupling of light into slow light modes, overcoming propagation losses, and mitigating the influence of large dispersion of the group velocity. The collection of papers in this special issue of Journal of Optics features a broad spectrum of articles that highlight actual developments in many of the material types and schemes described above. It represents therefore an excellent up to date snapshot of the current state of the field of slow light research. References [1] Lorentz H A 1880 Uber die Beziehung zwischen der Fortpflanzung des Lichtes und der Körperdichte Wiedemann Ann. 9 641–64 [2] McCall S L and Hahn E L 1967 Self-induced transparency by pulsed coherent light Phys. Rev. Lett. 18 908–11 [3] Vestergaard Hau L, Harris S E, Dutton Z and Behroozi C H 1999 Nature 397 594 [4] Philips D F, Fleischhauer A, Mair A, Walsworth R L and Lukin M D 2001 Storage of light in atomic vapor Phys. Rev. Lett. 86 783–6
Slow light with a markedly low group velocity is a promising solution for optical buering and advanced time-domain optical signal processing.It is also anticipated to enhance linear and nonlinear eects and so miniaturize functional photonic devices because slow light compresses optical energy in space.Photonic crystal waveguide devices generate on-chip slow light at room temperature with a wide bandwidth and low dispersion suitable for short pulse transmission.This paper rst explains the delay-bandwidth product, fractional delay, and tunability as crucial criteria for buering capacity of slow light devices.Then the paper describes experimental observations of slow light pulse, exhibiting their record high values.It also demonstrates the nonlinear enhancement based on slow light pulse transmission.
Recent experimental and theoretical results on the optical properties of globular photonic crystals coauthored by the author are presented. The dispersion relation for electromagnetic waves in a 1D photonic crystal that simulates the properties of a selected direction in the globular photonic crystal is calculated. The spectral ranges that are characterized by the anomalous slowing of electromagnetic waves in the photonic crystal and correspond to the stop-band edges are determined. A method for the measurement of the transmission and reflection spectra of the broadband radiation in photonic crystals is proposed. The method enables one to find the characteristics of the stop bands. The features of the secondary emission that emerges in opals due to the UV and visible excitation are reported. The conditions for the low-threshold lasing in opals filled with rareearth elements are presented. The experimental results on the induced-globular light scattering are demonstrated. Such a scattering implies the coherent excitation of vibrational states of the globules in a globular photonic crystal. A new phenomenon (slow light scattering) which involves the excitation of slow photons (slowtons) that correspond to the stop-band edges of the photonic crystal is observed. The conditions for the measurement of the slow light scattering in opals excited using the ruby and nitrogen lasers are experimentally determined. The experimental and theoretical results open up the prospects for low-threshold nonlinear optical processes in material media.
Light showing extremely slow propagation (known as "slow light") can produce various effects such as compression of optical signals, buffering, convolution integral calculation, beam forming, enhancement of optical absorption, gain, non-linearity, and so on. To generate such light, very large material and structural dispersions are used. Photonic crystal waveguides are good candidates for many device applications since they can easily generate slow light at room temperature. This paper discusses the potential of slow light devices while explaining some critical issues, such as the delay-band product and the dispersion compensation.