Development of all-optical schemes of quantum communication and information processing implies a precise control of photon pulses—in particular, their spectral and temporal characteristics. Therefore “slow light”, propagating with a velocity much lower than the speed of light in vacuum, has been studied intensively in recent years. GaN and related materials are very promising for different applications in nanophotonics and optoelectronics. The advantages of time-of-flight spectroscopy to determine the parameters of bulk semiconductors, as well as investigation of the fine structure of an excitonic spectrum, are presented
Development of all-optical schemes of quantum communication and information processing implies a precise control of photon pulses—in particular, their spectral and temporal characteristics. Therefore “slow light”, propagating with a velocity much lower than the speed of light in vacuum, has been studied intensively in recent years. GaN and related materials are very promising for different applications in nanophotonics and optoelectronics. The advantages of time-of-flight spectroscopy to determine the parameters of bulk semiconductors, as well as investigation of the fine structure of an excitonic spectrum, are presented
Propagation of light pulses in wide-gap semiconductors, GaN and ZnO, has been studied by time-of-flight spectroscopy. It has been demonstrated that significant light delay exists near an exciton resonance and that this delay is accompanied by pulse distortion and attenuation. Simulation of the pulse shape in the time-energy plane has permitted us to refine excitonic parameters inherent for bulk materials. The time-of-flight studies done over a wide temperature range demonstrate the strong influence of resonant scattering by phonons on the light delay in polar semiconductors. Optical dispersion at exciton resonances in semiconductors results in a delay of light transfer, which is induced by the variation of the group velocity — a phenomenon studied long ago(1-3). Thisdelayhasbeenobservedbytime-of-flightspec- troscopy in different semiconductors (4-6). The current inter- estinsuchretardationisenhancedbecauseitisoneoftheways toobtaintheso-calledslowlight,whichisneededforoptical communication and data processing. Wide-gap semiconduc- tors, like ZnO and GaN, possess strong excitonic resonances thatmakesthemsuitableforsuchapplication. Lightvelocities as low as 6000 km/s in ZnO (4) and 2100 km/s in GaN (5) have been recently measured. In view of these findings, the distortion of a pulse shape has attracted special attention (7). It is worth mentioning that early experiments showed no sig- nificant changes in the shape of a light pulse at the excitonic resonances in GaAs (8) and GaP (9), while the optical dis- persion near the resonances implies a different group velocity and attenuation for the higher- and lower-energy edges of the pulses (10), that inevitably means their distortion in the time- energy plane. The optical pulse modification is also important for a set of optoelectronic devices — high-frequency ones or those, where the light should propagate a long distance. The
The two-level atom can, for good reason, be considered the basic material structure for the study of quantum optics [1]. The two-level atom has played a fundamental role in studies of physical processes, including self-induced transparency (SIT), photon echoes, optical nutation, saturation spectroscopy, and, most recently, slow- and fast-light research. This latter field has recently been the subject of great activity, as researchers have learned how to utilize various physical processes to exert control over the velocity of propagation of light pulses through material systems [2]. This interest stems both from the intellectual intrigue in situations in which the velocity of light can be speeded up or slowed down by many orders of magnitude and the promise that such techniques might be useful for applications in fields such as telecommunications and optical computing [3‐6]. Most of the recent work in this field has made use of the process of electromagnetically induced transparency (EIT) to induce a narrow transparency region in an otherwise highly absorbing optical material [7, 8]. The rapid variation of the refractive index n associated with this transparency window then leads to a strong modification of the group velocity n g in accordance with the standard relation
The ability to manipulate the speed of light has recently become one of the most exciting emergent topics in optics. There are several experimental demonstrations showing the capability to slow down light more than six orders of magnitude in a variety of media, ranging from atomic vapor, solid state crystal, to semiconductors. These results have led to intensive research into new materials, devices, and system studies that examine their impact to new applications. It is believed that we are on the verge of a dramatic change in the way we envision and construct communication, processing and control systems. One direct application of slow and fast light devices is in the area of communications. One grand challenge remaining in information technology today is to store and buffer optical signals directly in optical format. As such, optical signals must be converted to electronic signals to route, switch, or be processed. This resulted in significant latencies and traffic congestions in current networks. In addition, keeping the data in optical domain during the routing process can greatly reduce the power, complexity and size of the routers. To this end, a controllable optical delay line can effectively function as an optical buffer, and the storage is proportional to the variability of the group velocity. In addition to optical buffers, slow and fast light devices can be used as tunable true-time delay elements in microwave photonics, which are important for remotely controlling phased array antenna. Other novel applications include nonlinear optics, optical signal processing, and quantum information processing. There are various approaches that can be used to vary the optical group velocity. Ultraslow or fast group velocity may result from a large material dispersion, waveguide dispersion, or both. In this paper, the authors provide a review of recent progress of slow and fast light using semiconductor devices. Specifically, they will discuss results obtained using semiconductor quantum-well/quantum-dot absorber and optical amplifiers. Slow and fast light are controllable electrically by changing the bias current or voltage as well as optically by changing the pump laser intensity and wavelength. Delay-bandwidth tradeoff and other figures of merits are analyzed
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