Showing papers on "Photonic crystal published in 1990"

Quantum electrodynamics near a photonic band gap: Photon bound states and dressed atoms.

Abstract: It is shown that in dielectrics exhibiting a complete photonic band gap, quantum electrodynamics predicts the occurrence of bound states of photons to hydrogenic atoms. When the atomic transition frequency lies near a photonic band edge, the excited atomic level experiences an anomalous Lamb shift and splits into a doublet. One member of this doublet exhibits resonance fluorescence whereas the other level is dressed by the emission and reabsorption of near-resonant photons whose amplitude decays exponentially from the vicinity of the atom.

Two-atom resonant radiative coupling in photonic band structures.

Abstract: Radiative coupling between identical atoms sharing an excitation is studied in media where dispersion creates photonic band gaps, i.e., forbidden bands of light propagation for all directions and polarizations. Photonic band gaps can exist in media whose dielectric index exhibits strong three-dimensionally periodic modulations (``photonic crystals'') or in bands of polaritonic media. It is shown that the resonant dipole-dipole interaction as well as cooperative fluorescence of two-atom systems can be strongly enhanced or suppressed, to the extent of being essentially eliminated, by one of the following mechanisms: (a) dependence on location of the atoms within a unit cell of a photonic crystal, i.e., sensitivity to the spatial variation of the field normal modes; (b) dependence on the density of normal modes in allowed bands and on the density of virtual (evanescent) modes in band gaps. The ability to suppress the dipole-dipole interactions at interatomic separations characterizing quasimolecules would have far-reaching implications on their dissociative or collisional dynamics, spectroscopy, and rates of energy transfer.

Photonic band structure: the face-centered-cubic case

Abstract: We employ the concepts of band theory to describe the behavior of electromagnetic waves in three-dimensionally periodic face-centered-cubic (fcc) dielectric structures. This can produce a “photonic band gap” in which optical modes, spontaneous emission, and zero point fluctuations are all absent. In the course of a broad experimental survey, we have found that most fcc dielectric structures have “semimetallic” band structure. Nevertheless, we have identified one particular dielectric “crystal” that actually has a “photonic band gap.” This dielectric structure consisting of 86% empty space, requires a refractive-index contrast of greater than 3:1, which happens to be readily obtainable in semiconductor materials.

Semiconductor photonic integrated circuit for high-density WDM light source

Abstract: Recent progress in semiconductor optical devices and their fabricatin technique has brought about a possibility to develope various kinds of semiconductor photonic integrated circuits (SPICs) [1,23. We report, here, a 1.5um range four-channel light source SPIC, which consists of four wavelength-tunable LDs and four light intensity modulators and two waveguide couplers, aming at high-density WDM optical system application. The SPIC! is shown schematically in Fig.1. Wavelength-tunable three section DBR LD [3], Franz-Keldysh electro-absorption intensity modulator 141 and Y-branch waveguide were employed as each device structure. The SPIC wafer was grown with four MOVPE steps and one LPE step. Wavelength-tunable DBR LDs consisted of a 600pm long active region, a phase control region (lOOpm), and a DBR region (150pm). The active region included a four-well InGaAs/InGaAsP MQW active layer [5]. Modulators were 300pm long. Coupler waveguides were 300pm long and bent in a 1 mm radius. A 0.3pm thick non-doped optical confinement layer (1.35pm wavelength composition) was grown selectively by MOVPE, except for the active region. This layer acts as an absorber in the modulator region. Semi-insulating buried-hetero structure [6] was formed for transverse optical and current confinement, as well as for sufficient electrical isolation between these optical elements. The front end (coupler side) was antireflection coated with SiN film. DBR LDs operated with 37-55 mA threshold currents and maximum output power values were 2-3 mW from the front end under CW conditions. Figure 2 shows extinction ratio versus applied voltage characteristics for the modulators. Over 1 OdB extinction ratios were obtained at -5V applied voltage in all the modulators. Calculated modulator capacitance was 2 pF. 3 GHz modulation bandwidth was obtained experimentally. Wavelength tuning characteristics are shown in Fig.3. Lasing wavelengths were tuned over 80%l semi-continuously, by adjusting both DBR region current (IDBR) and phase con~trol current (I PC). Simultaneous four-channel wavelength control to govem 5A, 1OA and 2 0 a channel spacing was demonstrated successfully, as shown in Fig.4. 2.5Gb/s modulation was carried out with 5 V D P NRZ signal. A clear modulated light output waveform was obtained as shown in Fig.S(a). Figure 5(b) shows a time-averaged spectrum for modulated light. A CW spectrum was shown simultaneously , where lasing wavelength was detuned by 3 8, for easy comparisov. The modulated light spectrum at -3OdB level to the peak was found to be only 0.12A wider than the CW spectrum. This result implies the applicability of the present SPIC for high-density WDM systems with narrow channel spacing, which is hard to be achieved by LD direct modulation scheme. The c.hanne1 spacing will be reduced ideally to six times the bit-rate (for example, 1.25A in the case of 2.5-Gb/s modulation) without substantial spectral interference between adjacent channels. In conclusion, an SPIC for high density WDM systems was developed. Successful channel spacing control in wide wavelength range, and very low chirping 2.5Gb/s intensity modulation, were demonstrated.

Two-Dimensional Array Microlasers for Photonic Switching

Abstract: Electrically-driven microlasers are shown to be attractive devices for photonic chip-to-chip communication or as elements of a photonic switch. Picosecond optical techniques allow us to study properties of microresonators with submicron diameters.

Microlasers for Photonic Switching and Interconnection

Abstract: Vertical-cavity, surface-emitting lasers have great potential owing to their inherent two-dimensional geometry and very small gain nedium volumes which are essential to low threshold currents. Possible applications are optical switching/computing, photonic interconnection, high/low power laser sources, image processing, optical neural networks, etc. Driven by these high promises, there have been numerous reports on vertical cavity surface emitting laser diodes using InGaAs/GaAs/A1As, GaAs/AlGaAs structures16. In this paper, we report characteristics of discrete InGaAs microlasers and monolithic two-dimensional arrays of microlasers. The advantages of optics for communications of data over distances longer than nearby gates have been argued previously7. We proposed and demonstrated a photonic interconnect scheme using microlasers with planar optics which will be robust, accurate, and easily alignable.

Photonic band structure of optical rings

Abstract: Concepts borrowed from the electronic band structure can be used to describe the behavior of lightwaves in a periodic dielectric medium. An example of such a medium is an optical ring resonator with a backscattering element, e.g., an etalon. Here the periodicity is topological, the periodicity length being the circumference of the ring.1,2

Improved mass-transported GaInP/GaAs lasers

Abstract: Buried-heterostructure (BH) lasers have been fabricated in GaInP/GaAs doubleheterostructure (DH) wafers using mass transp~rt. (Figure 1 shows a cross section of the BH structure obtained after mass transport.) This work1 was the first demonstration of masstransport fabrication techniques applied to lasers emitting in the 800to 900-nm wavelength range (h z 890 nm was observed for the GaAs active regions). It was also the first demonstration of organometallic-vapor-phase-epitaxy (OMVPE) of DH lasers in this material system, where the wide bandgap layers consisted of Gao51In0.49P rather than the conventional AlGaAs alloys. OMVPE should provide significant advantages over hydride vapor phase2 and liquid phase3 epitaxy which have previously been used to grow GaInP/GaAs lasers.