Inhibited Spontaneous Emission in Solid-State Physics and Electronics
ABSTRACT It has been recognized for some time that the spontaneous emission by atoms is not necessarily a fixed and immutable property of the coupling between matter and space, but that it can be controlled by modification of the properties of the radiation field. This is equally true in the solid state, where spontaneous emission plays a fundamental role in limiting the performance of semiconductor lasers, heterojunction bipolar transistors, and solar cells. If a three-dimensionally periodic dielectric structure has an electromagnetic band gap which overlaps the electronic band edge, then spontaneous emission can be rigorously forbidden.
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ABSTRACT: I INTRODUCTION Wavelength Division Multiple Access (WDMA) is one of the ways to exploit the large information transmission capa-city of optical fibres both in independent multi-user envi-ronments and as a part of an existing subscriber network . Demultiplexers utilised for modern optical receivers must meet stringent requirements . The devices with active bandwidth tuning must have a centering time below 1 µs to be functional in networks with high data package transfer rates. Only the acousto-optical type of tuneable filters attains a total tuning range larger than 50 nm, but at the same time the bandwidth of a single channel cannot be below 1 nm . Passive multiplexers with interference channel separation can simultaneously process more than two channels if connected in cascade or if utilizing polygonal prisms, howe-ver both of these methods introduce additional attenuation and increase the price. On the other hand, the passive de-multiplexers utilizing diffraction gratings to separate a large number of channels are more prone to positioning errors . One of the concepts increasingly used in both passive and active microoptical devices for optical communications are the so-called photonic band gap materials or photonic crystals , . These are defined as artificial materials with refractive index periodically varying along one, two or three spatial coordinates with a period comparable to the operating light wavelength. The contrast of the refractive index values between the low-and high-index zones must be sufficiently high (of the order of about 2) to permit forming of photonic band gap (PBG), i.e. of the frequency range in which electromagnetic modes are evanescent . Thus a photonic crystal behaves as an omnidirectional mirror with a high reflection coefficient for the electromagnetic radiation frequencies within the PBG (band-stop filter behaviour). A controlled defect introduced into a PBG lattice results in a localized mode with strongly enhanced transmission (notch-filter behaviour). A recently introduced generalization of photonic band gap materials are nonuniform photonic crystals , . These are PBG materials with spatially dependent crystal lattice properties. The parameters that may be varied include all the geometrical and material parameters of the unit cell, plus doping level/defect properties. Fig. 1 illustrates the concept of nonuniform photonic crystals. It represents a 2D PBG structure of hexagonal dielectric rods ordered in a graphite lattice with the dimensions of the rods uniformly increasing radially from a centre. Surrounding material of the crystal in Fig. 1 is stripped to enable better visibility. Fig. 1. An example of nonuniform two-dimensional honeycombed (graphite-type) photonic crystal lattice In this work we consider the use of nonuniform photonic crystals in passive demultiplexers for optical communications instead of conventional structures with interference channel separation. We show that microoptic demultiplexers with a photonic bandgap material can separate a large number of channels within a wide wavelength range while at the same time retaining a small bandwidth per single channel. II DEMULTIPLEXER SCHEMES We consider the case of a one-dimensional photonic crystal with a photonic bandgap covering one or more of the optical communication windows. The crystal lattice has a built-in defect furnishing a transmission peak (localized mode) at a desired frequency. If the defect thickness is a function of spatial coordinate, i.e. if the defect layer is inhomogeneous (either regarding its thickness or refractive index value), the wavelength of the localized mode transmission peak also becomes position dependent. This means that different regions of the photonic crystal transmit different wavelengths in a controlled manner. This property can be utilized for spatial separation of different channels from a communication signal and their positioning to separate detectors. An advantage of such a concept is that thus obtained multiplexers are monolithically integrated with detector elements.8. Telecommunication Forum TELFOR 2000, Belgrade, Serbia; 11/2000
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ABSTRACT: We analyzed the performance of middle-and longwave infrared semiconductor photodetectors immersed in structures with a photonic bandgap (photonic crystals). The ultimate specific detectivity is determined for a general case of a radiative generation-recombination limited performance. A comparison both with the devices utilizing radiation shields and with standard photonic detectors is given. The performance of an experimental indium antimo-nide photodetector structure enhanced with a 1-D photonic crystal is investigated. As expected, a large enhancement of the background-limited performance appears possible, at least an order of magnitude in comparison to an ideal conventional detector.43rd Yugoslav Conf. ETRAN, Zlatibor, Serbia; 09/1999
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ABSTRACT: Semiconductor-microcavity polaritons are composite quasiparticles of excitons and photons, emerging in the strong coupling regime. As quantum superpositions of matter and light, polaritons have much stronger interparticle interactions compared with photons, enabling rapid equilibration and Bose-Einstein condensation (BEC). Current realizations based on 1D photonic structures, such as Fabry-Pérot microcavities, have limited light-trapping ability resulting in picosecond polariton lifetime. We demonstrate, theoretically, above-room-temperature (up to 590 K) BEC of long-lived polaritons in MoSe2 monolayers sandwiched by simple TiO2 based 3D photonic band gap (PBG) materials. The 3D PBG induces very strong coupling of 40 meV (Rabi splitting of 62 meV) for as few as three dichalcogenide monolayers. Strong light-trapping in the 3D PBG enables the long-lived polariton superfluid to be robust against fabrication-induced disorder and exciton line-broadening.Scientific reports. 12/2014; 4:7432.