Showing papers on "Photonic crystal published in 1992"

Existence of a photonic band gap in two dimensions

Abstract: A systematic theoretical investigation is undertaken in order to identify a two‐dimensional periodic dielectric structure that has a complete in‐plane photonic band gap for both polarizations. Of the various structures studied, only a triangular lattice of air columns is found to have the desired band‐gap properties. Microwave transmission experiments are performed to test the theoretical predictions.

Measurement of photonic band structure in a two-dimensional periodic dielectric array.

Abstract: The photonic band structure in a two-dimensional dielectric array is investigated using the coherent microwave transient spectroscopy (COMITS) technique. The array consists of alumina-ceramic rods arranged in a regular square lattice. The dispersion relation for electromagnetic waves in this photonic crystal is determined directly using the phase sensitivity of COMITS. The experimental results are compared to theoretical predictions obtained using the plane-wave expansion technique. Configurations with the electric field parallel and perpendicular to the axis of the rods are investigated.

Photonic band gaps in two-dimensional square and hexagonal lattices.

Abstract: Two-dimensional square and hexagonal lattices exhibit photonic band gaps common to s- and p-polarized waves. These gaps occur from an overlap of the gaps between the first and second p bands and higher s bands. A dielectric structure with a hexagonal lattice of air holes requires a lower index contrast to generate a band gap and gives rise to larger gaps than a square lattice. Furthermore, square and hexagonal lattices of dielectric rods in air do not give rise to band gaps even when asymmetry is introduced to lift the degeneracies.

Low-loss dielectric resonant devices having lattice structures with elongated resonant defects

Abstract: A dielectric resonator comprising a resonant defect structure diposed in a lattice structure formed of a plurality of multi-dimensional periodically arranged dielectric elements confines electromagnetic energy within a frequency band in the photonic band gap. The frequency band of the confined electromagnetic energy is tunable. The unique structure of the dielectric resonator leads to reduced power dissipation losses when used in microwave and millimeter wave components. Accordingly, the dielectric resonator may be used to produce high quality resonant cavities, filters and power generators.

Photonic band gaps

Abstract: Many major discoveries in physics this century originate from the study of waves in periodic structures. Examples include X-ray and electron diffraction by crystals, electronic band structure and holography. Analogies between disciplines have also led to fruitful new avenues of research. An exciting example is the recent discovery of three-dimensionally periodic dielectric structures that exhibit what is called a "photonic band gap" (PBG), by analogy with electronic band gaps in semiconductor crystals. Photons in the frequency range of the PBG are completely excluded so that atoms within such materials are unable to spontaneously absorb and re-emit light in this region; this has obvious beneficial implications for producing highly efficient lasers. Given that electrons and photons obey almost the same differential wave equation, the idea of a PBG is clearly far from crazy. It does, however, demand a radical rethink of how light behaves in periodic structures.

Photonic band gap materials and method of preparation thereof

Abstract: The invention concerns materials which exhibit photonic band gaps in the near infrared and visible regions of the optical spectrum and methods of preparation of such materials

Performance of a PET detector module utilizing an array of silicon photodiodes to identify the crystal of interaction

Abstract: Summary form only given, as follows. A multilayer PET (positron emission tomography) detector module consisting of an array of 3 mm square by 30 mm deep BGO (bismuth germanate) crystals coupled on one end to a single photomultiplier tube and on the opposite end to an array of 3 mm square silicon photodiodes has been investigated. The photomultiplier tube provides an accurate timing pulse and energy discrimination for all the crystals in the module, while the silicon photodiodes identify the crystal of interaction. When a single BGO crystal is excited with 511 keV photons, a photodiode signal centered at 500 electrons (e/sup -/) with a width of 375 e/sup -/ FWHM at an operating temperature of +25 degrees C is measured. When a four-crystal/photodiode module is excited with a collimated beam of 511 keV photons, the photodiode array correctly identifies the crystal of interaction roughly 50% of the time. This misidentification rate is higher than predicted by signal to noise arguments, and is thought to be due to insufficient beam collimation and Compton interactions in the module. The misidentification rate can be greatly reduced, and an 8*8 crystal/photodiode module constructed, by using thicker depletion layer photodiodes or cooling to 0 degrees C. >

Photonic band gaps in periodic dielectric structures: The scalar-wave approximation.

Abstract: Using a plane-wave expansion method we have computed the band structure for a scalar wave propagating in periodic lattices of dielectric spheres (dielectric constant e, ) in a uniform dielectric background (e&). All of the lattices studied (simple cubic, bcc, fcc, and diamond) do possess a full band gap. The optimal values of the filling ratio f of spheres and of the relative dielectric contrast for the existence of a gap are obtained. The minimum value of the relative dielectric contrast for creating a gap is also obtained. These results are applicable to the problem of classical-wave propagation in composite media and relevant to the problem of classical-wave localization. I. INTRODUCTION Recently, there has been growing interest' in the studies of the propagation of electromagnetic (EM) waves in three-dimensional (3D) periodic andlor disordered dielectric structures (photonic band structures). The reasons for this interest are both fundamental and practical. The possibility of the observation of Anderson localization of EM waves in disordered dielectric structures, where the strong el-el interaction effects entering the electron-localization problem are absent, is of fundamental interest. ' Also in analogy to the case of electron waves propagating in a crystal, classical EM waves traveling in periodic dielectric structures will be described in terms of photonic bands with the possibility of the existence of frequency gaps where the propagation of EM waves is forbidden. The potential applications of such photonic band gaps are very interesting. It has been suggested that the inhibition of spontaneous emission in such gaps can be utilized to substantially enhance the performance of semiconductor lasers and other quantum electronic devices. Photonic band-gap materials can also find applications in frequency-selective mirrors, bandpass filters and resonators. Moreover, electromagnetic interaction governs many properties of atoms, molecules and solids. The absence of EM modes inside the photonic gap can lead to unusual physical phenomena. For example, atoms or molecules embedded in such a material can be locked in excited states if the photons to be emitted to release the excess energy have frequency within the forbidden gap. In addition, John has proposed that Anderson localization of light near a photonic band gap might be achieved by weak disordering of a periodic arrangement of spheres. It is therefore, very important to obtain structures with a frequency gap where the propagation of EM waves is forbidden for all wave vectors. Yablonovitch and Gmitter have demonstrated the soundness of the basic idea of photonic bands in 3D periodic structures in an experiment using microwave frequencies, where the periodic structures can be fabricated by conventional machine tools. In addition, a photonic gap in a face-centeredcubic (fcc) dielectric structure was reported. During the same period, theoretical studies of the propagation of EM waves in 3D periodic structures began. ' At first, the photonic band structures have been examined theoretically in the scalar-wave approximation ' in which the vector nature of the EM field is ignored. It soon became apparent' " that not so many aspects of the experimental photon bands in periodic dielectric structures can be understood in terms of scattering of scalar waves. However, the scalar-wave approach is directly applicable to the scattering of acoustic waves, an area of equally active interest and to the localization of acoustic waves. ' ' Recently, by expanding the EM fields with a plane-wave basis set, Maxwell's equations were solved exactly, ' taking the vector nature of the EM field fully into account. Comparison of the calculated' ' results of the fcc structure with experiment indicated that, while the experimental data and theory agree very well over most of the Brillouin zone, there are two symmetry points (8' and U) where the experiment indicates a gap, while calculations show that propagating modes exist. It is now believed that the fcc structure does not possess a full photonic band gap in the lowest bands, instead there is a region of low density of states rather than a forbidden frequency gap.

3-dimensional photonic band structure

Abstract: Three-dimensionally periodic dielectric structures, (photonic crystals), possessing a forbidden gap for electromagnetic wave propagation, (a photonic bandgap), are now known. If the perfect 3-dimensional periodicity is broken by a local defect, then local electromagnetic modes can occur within the forbidden bandgap. The addition of extra dielectric material locally, inside the photonic crystal, produces ‘donor’ modes. Conversely, the local removal of dielectric material from the photonic crystal produces ‘acceptor’ modes. It will now be possible to make high-Q electromagnetic cavities of volume ∼ 1 cubic wavelength, for short wavelengths at which metallic cavities are useless. These new dielectric cavities can cover the range all the way from millimeter waves, down to ultraviolet wavelengths.

Photonic Band Gap structures: A new approach to accelerator cavities

Abstract: We introduce a new accelerator cavity design based on Photonic Band Gap (PBG) structures. The PBG cavity consists of a two‐dimensional periodic array of high dielectric, low loss cylinders with a single removal defect, bounded on top and bottom by conducting sheets. We present the results of both numerical simulations and experimental measurements on the PBG cavity.

Applications of Photonic Band Gap Structures

Abstract: Imagine a material that would exclude all electromagnetic radiation in 4π steradians over a range of frequencies. The center frequency of the exclusion gap could be determined by the experimenter to be anywhere from the optical to the microwave region. The width of the gap would be large, at least 20% of the center frequency. Radiation outside that gap would be transmitted through the material, while radiation in the gap would be reflected. In-gap radiation generated inside the material would be trapped. Uses for such a material would be manifold, from filtering and noise suppression to modification of the electromagnetic vacuum and suppression of spontaneous emission. Such a material has recently been created: the photonic band gap crystal.

Low-loss dielectric resonant devices

Abstract: A dielectric resonator comprising a resonant defect structure (38) disposed in a lattice structure formed of a plurality of multi-dimensional periodically arranged dielectric elements (30) confines electromagnetic energy within a frequency band in the photonic band gap. The frequency band of the confined electromagnetic energy is tunable. The unique structure of the dielectric resonator (29) leads to reduced power dissipation losses when used in microwave and millimeter wave components. Accordingly, the dielectric resonator may be used to produce high quality resonant cavities, filters and power generators.

High-speed and low-drive-voltage MQW EA-modulator integrated DFB laser with semi-insulating BH structure

Abstract: EA-modulator integrated DFB lasers have become one of the key devices in multigigabit long-distance lightwave communications. [1, 2] Recently, a new method of integrating photonic devices has been proposed, using the in-plane local bandgap energy control of the MQW structures during simultaneous selective area growth (SAG) by MOCVD. [3, 4] This technique offers a high optical coupling efficiency as well as reproducible fabrication, which are essential in such optical integrated devices. This paper describes an MQW EA-modulator integrated with a DFB laser, fabricated by SAG and a semi-insulating BH process, aimed at a high on/off ratio and high-speed operation.

The Single-Mode Light-Emitting-Diode

Abstract: A single-mode light-emitting-diode (LED) can have many of the favorable coherence properties of lasers, while being a more reliable, threshold-less, device. Progress in electromagnetic micro-cavities, such as those formed by photonic band structure, allow all the spontaneous emission (of an LED) to be funneled into a single electromagnetic mode. It is shown that the internal spontaneous emission quantum efficiency in GaAs/AlGaAs double heterostructures can be as high as 99.7%, and consequently, the external quantum efficiency and the shot-noise suppression in such single-mode LEDs can be comparable to those of semiconductor lasers, but at much lower injection level.

Fast and Sensitive Two-Terminal Double-Heterojunction Optical Thyristors

Abstract: A new Two-Terminal Double-Heterojunction Optical Thyristor is presented, that combines good optical sensitivity and fast turn-off. This is obtained by bandgap and doping engineering of the PnpN structure: the optical sensitivity is achieved by using a low doping for the outer, wide bandgap, thyristor layers; the fast turn-off, on the other hand, is obtained by adapting the doping levels and thicknesses of the inner thyristor layers such that the n-layer is punched through when a critical reverse bias is applied to the device. The optical sensitivity is 5 to 100 pJ, the turn-off time is RC-limited and typically less than 10 ns, the data transmission rate in differential configuration is at least 5×104 bit/s. As the structure remains a two-terminal device, integration into large arrays - for massively parallel data transmission - is possible.

Band offsets in heavily doped p type GeSi/Si(100) strained layers: Applications to design of Long Wave-length InfraRed (LWIR) detectors

Abstract: We show that the effect of heavy B doping modifies considerably the valence band offsets of the layers as well as the calculated cut-off wave-lengths of LWIR detectors.

Lateral bandgap engineering for InP-based photonic integrated circuits

Abstract: It is demonstrated that both SMG (shadow masked growth) and SG (selective growth) together with the use of QWs (quantum wells) can change the bandgap of InP-based materials laterally over the substrate. The thickness change that can be obtained with both techniques and the corresponding deviation from stoichiometry are competitive. The authors present the basic principle of both techniques and the basic characteristics (thickness and composition change). They have fabricated a multiwavelength laser array using SMG with a wavelength span of 130 nm around 1550 nm. >

Organic photonics: materials and devices strategy for computational and communication systems

Abstract: It is pointed out that passive and electroactive organic optical materials open new possibilities for fabricating enhanced and novel photonic devices. Low deposition temperatures and benign chemistry permit multiple-layer structures and integration of the organic materials directly with semiconductor electronics. The electrooptical properties of the active organics are comparable to or larger than conventional semiconductor and crystalline ceramic materials, and allow replacement of these materials with the electrooptical organics. The fabrication and optical characteristics of optical organics make possible the formation of monolithic packages applicable to control of signals in computational and communication systems. Photonic multichip modules, hybrid optical/electronic nonlinear systems, and phased-array optics are technologies that can be realized more effectively with organic photonics. >

High-Speed Integrated Quantum Well Self-Electrooptic Effect Device

Abstract: The novel high-speed integrated SEED-like bistable element with the light controlled shape of the power transfer characteristics is proposed.

Photonic superguiding state

Abstract: The present paper establishes the photonic superguiding theory in polar crystals with a high nonlinearity. In the quantum theory it is shown that photons can feel an attractive effective interaction by exchanging of virtual phonons. Such an interaction leads to the superguiding state, in which photons with opposite wave vectors and spins are bound into pairs. The photon pairs travel without scattering attenuations. In the classical theory we prove that the crystals exhibiting the photonic superguiding state are the self-defocusing media in which temporal bright solitons can propagate. The optical solitons do not suffer from dispersion. If the photons propagating in a waveguide enter the superguiding state, the waveguide exhibits both an ultralow energy loss and a high transmission rate.