Suppression Of Spontaneous Emission Research Articles

Room temperature enhancement and inhibition of spontaneous emission in semiconductor microcavities

We have fabricated planar semiconductor microcavities with metallic mirrors in which we have observed both enhancement and inhibition of spontaneous emission, at room temperature. Our results are quantitatively accounted for by modeling the band-to-band emission as arising from point dipoles. Observation of these cavity quantum electrodynamics effects in room temperature semiconductor structures opens the way to optoelectronic devices with controlled spontaneous emission.

Quantum interference in the fluorescence of a molecular system

It has been observed experimentally [H.R. Xia, C.Y. Ye, and S.Y. Zhu, Phys. Rev. Lett. {\bf 77}, 1032 (1996)] that quantum interference between two molecular transitions can lead to a suppression or enhancement of spontaneous emission. This is manifested in the fluorescent intensity as a function of the detuning of the driving field from the two-photon resonance condition. Here we present a theory which explains the observed variation of the number of peaks with the mutual polarization of the molecular transition dipole moments. Using master equation techniques we calculate analytically as well as numerically the steady-state fluorescence, and find that the number of peaks depends on the excitation process. If the molecule is driven to the upper levels by a two-photon process, the fluorescent intensity consists of two peaks regardless of the mutual polarization of the transition dipole moments. If the excitation process is composed of both a two-step one-photon process and a one-step, two-photon process, then there are two peaks on transitions with parallel dipole moments and three peaks on transitions with antiparallel dipole moments. This latter case is in excellent agreement with the experiment.

Coherent control of spontaneous emission in a four-level system

In this article we study the potential for coherently control spontaneous emission in a four-level scheme. Our control parameter is the relative phase of two laser fields having the same angular frequency. We investigate in detail the trapping conditions, the population dynamics and the behaviour of the (long time) spontaneous emission spectrum, which are now phase dependent. Inhibition of spontaneous emission and extreme spectral narrowing are shown as the relative phase is varied. Our results are interpreted using a dressed state analysis of the dynamics.

Spontaneous emission properties of a quasi-continuum

We study the spontaneous emission properties of two distinct quasi-continua sets of levels of atomic and molecular systems so close in energy that they behave in some respect as a continuum, yet preserving some aspects of the discrete level structure, depending on the timescales of interest. The first quasi-continuum considered consists of N degenerate excited levels that decay to a single ground level, while the second consists of a pair of energy separated quasi-continua of N degenerate excited levels that decay to the same ground level. We find that the first quasi-continuum can trap population in the system and can completely inhibit spontaneous emission, depending on the initial conditions. For the second quasi-continuum, no population trapping is possible but partial inhibition of spontaneous emission via `dark' lines in the spectrum can occur. Our results are compared with those obtained from the V -type system.

Single-domain spectroscopy of self-assembled photonic crystals

We show how optical microscopy can be used to study the optical properties of a single crystalline domain in a self-assembled photonic crystal. By measuring spatially resolved reflection and emission spectra from a synthetic opal, inhomogeneities due to averaging over inherent disorder can be avoided. From “defect-free” reflection and emission spectra, the intrinsic photonic band structure can be extracted and inhibition of spontaneous emission can be verified.

Applications of active arrayed-waveguide gratings in dynamic WDM networking and routing

We describe how active arrayed-waveguide gratings (AWGs) may find a diverse range of applications in future dynamic wavelength division multiplexed (WDM) networking and routing. Our initial simulations indicate that these applications include dynamic signal power and erbium-doped fiber amplifier (EDFA) gain equalization with a dynamic range of 12 dB, and interchannel amplified spontaneous emission (ASE) suppression by more than 20 dB; optical add/drop multiplexing with passband-flattened channels and suppressions of 15 dB; and dynamic dispersion compensation of up to /spl plusmn/300 ps/nm.

Quantum interference in a driven two-level atom

We show that a dynamical suppression of spontaneous emission, predicted for a three-level atom [S.-Y. Zhu and M. O. Scully, Phys. Rev. Lett. 76, 388 (1996)] can occur in a two-level atom driven by a polychromatic field. We find that the quantum interference, responsible for the cancellation of spontaneous emission, appears between different channels of transitions among the dressed states of the driven atom. We discuss the effect for bichromatic and trichromatic (amplitude-modulated) fields and find that these two cases lead to the cancellation of spontaneous emission in different parts of the fluorescence spectrum. Our system has the advantage of being easily accessible by current experiments.

Spontaneous emission extraction and Purcell enhancement from thin-film 2-D photonic crystals

Electromagnetic band structure can produce either an enhancement or a suppression of spontaneous emission from two-dimensional (2-D) photonic crystal thin films. We believe that such effects might be important for light emitting diodes. Our experiments were based on thin-film InGaAs-InP 2-D photonic crystals at ambient temperature, but the concepts would apply equally to InGaN thin films, for example. We show that the magnitude of Purcell enhancement factor, F/sub p//spl sim/2, for spatially extended band modes, is similar to that for a tiny mode in a three dimensional (3-D) nanocavity. Nonetheless, light extraction enhancement that arises from Zone folding or Bragg scattering of the photonic bands is probably the more important effect, and an external quantum efficiency >50% is possible. Angle resolved photoluminescence from inside the photonic crystal gives a direct spectral readout of the internal 2-D photonic band dispersion. The tradeoffs for employing various photonic crystal structures in high efficiency light-emitting diodes are analyzed.

Analysis of dynamical suppression of spontaneous emission

It has been shown recently [see, for example, S.-Y. Zhu and M. O. Scully, Phys. Rev. Lett. {\bf 76}, 388 (1996)] that a dynamical suppression of spontaneous emission can occur in a three-level system when an external field drives transitions between a metastable state and {\em two} decaying states. What is unusual in the decay scheme is that the decaying states are coupled directly by the vacuum radiation field. It is shown that decay dynamics required for total suppression of spontaneous emission necessarily implies that the level scheme is isomorphic to a three-level lambda system, in which the lower two levels are {\em both} metastable, and each is coupled to the decaying state. As such, the total suppression of spontaneous emission can be explained in terms of conventional dark states and coherent population trapping.

3-Dimensional Photonic Crystals at Optical Wavelengths

Different experimental strategies towards the 3-dimensional photonic crystals operating at optical wavelength are classified. The detailed discussion is devoted to the recent progress in photonic crystals fabricated by template method — the photonic band gap materials on the base of opal. The control of photonic properties of opal-based gratings is achieved through impregnating the opal with high refractive index semiconductors and dielectrics. Experimental study demonstrated the dependence of the stop band behaviour upon the type of impregnation (complete or partial) and showed a way for approaching complete photonic band gap. The photoluminescence from opal- semiconductor gratings revealed suppression of spontaneous emission in the gap region with following enhancement of the emission efficiency at the low-energy edge of the gap.

Emission from Organized Molecular Systems with the Order of Emissive Wavelength

Emissive behaviors from the systems with the sizes of the order of visible wavelength are described. Control of electrically-pumped emission from thin-film electroluminescent devices by use of one-dimensional planer cavities is demonstrated. Photoluminescence behaviors from organic dielectric stacks with buried emissive centers prepared by vacuum-vapor deposition were examined. Photoluminescence from self-organized three-dimensional ordered arrays of polystyrene small particles with luminescent dyes is also studied. In both systems, inhibition of spontaneous emission due to photonic gaps were observed.

Wide-range tunable semiconductor lasers using asymmetric dual quantum wells

Using asymmetric dual quantum wells for the laser material, the semiconductor lasers are broadly tunable. In a grating coupled ring cavity, the semiconductor laser is continuously tunable from 766 to 856 nm using a 400-μm semiconductor laser amplifier in the cavity. This letter also demonstrates that the grating coupled ring cavity could well eliminate the amplified stimulated emission noise and about 40-dB amplified spontaneous emission (ASE) suppression ratio is obtained over the entire tuning range.

Suppression of spontaneous emission for a two-dimensional honeycomb photonic bandgap structure estimated using a new effective-index model

The suppression of spontaneous emission introduced by a two-dimensional honeycomb-rod photonic bandgap structure is evaluated using the plane-wave expansion theory. An analysis of the out-of-plane angle dependency on the photonic bandgaps through the application of a new effective refractive-index model is presented. The in-plane properties for structures characterized by a rod dielectric constant in the range from 1.0 to 15.0, air background, and a filling fraction in the range from 0.07 to 0.4 are analyzed, and a structure with a relative in-plane bandgap of 10% is chosen. The out-of-plane angle analysis is performed for this structure, and it is found that propagation for modes within a narrow frequency interval is inhibited for a solid angle of 2.16 /spl pi/, covering 54% of the spontaneous emission from a narrow-linewidth point source.

Spontaneous emission control in semiconductor microcavities with metallic or Bragg mirrors

We present a systematic study of the modification of the spontaneous emission of a point dipole in a planar semiconductor microcavity, bounded by different types of mirrors. Numerical evaluations of the spontaneous emission rate indicate that semiconductor cavities bounded by Bragg mirrors display only a weak modification of spontaneous emission, while significant enhancement and inhibition of spontaneous emission should be observed in cavities bounded by metallic mirrors.

Atoms in micron-sized metallic and dielectric waveguides

Over the past ten years, our group has investigated the effects of confinement on atoms inside metallic micron–sized cavities in order to elucidate some basic phenomena in the field of cavity quantum electrodynamics (QED). The first of these was the inhibition of spontaneous emission from an atom inside a cavity. This was followed by a laser spectroscopic measurement of the van der Waals interaction between a single Rydberg atom and a gold cavity, which showed that a simple electrostatic model of the atom–cavity interaction is correct when the cavity is small enough. More recently, the retarded Casimir–Polder force was measured between a ground state sodium atom and a large cavity, demonstrating that the van der Waals potential fails at long enough range and that the vacuum fluctuations of the field then have an important role in the interaction of the atom with the cavity. Our group is now pushing forward these investigations to study cavities whose walls have losses and dispersion, where the theory of cavity QED is significantly more complicated. With real surfaces, we have to deal with the complex dielectric response e(ω) of the material, which exhibits frequency–dependent absorption and dispersion. One particularly interesting case is when a downward transition in the atom is resonant with an excitation of the cavity walls. This opens a new branch for the atomic decay: as an alternative to creating a photon within the space surrounded by the cavity walls the atomic decay can now create an electromagnetic excitation of the walls themselves. Another novel feature of our experiments is that the Bohr frequencies of the atom are close to the kT/h, where T is room temperature. We therefore expect to be able to measure effects associated with QED at finite temperature; in other words, to study how the blackbody radiation affects our experiments. By conducting experiments with real surfaces, we hope to elucidate and perhaps simplify the theoretical models used to describe these systems.

Optimization of DSF- and SOA-based phase conjugators by incorporating noise-suppressing fiber gratings

We compare the performance of dispersion-shifted-fiber (DSF) and semiconductor-optical-amplifier (SOA) based laser phase conjugators for a 10-Gb/s nonreturn-to-zero system with respect to conversion efficiency, noise figure, and distortion. Fiber gratings are used for signal extraction and amplified spontaneous emission (ASE) suppression, allowing closer wavelength spacing and reducing the conjugation noise figure by up to 12 dB. Despite the higher SOA conversion efficiency, both conjugators give similar noise figures with ASE suppression. However, the DSF-based conjugator has the advantage of distortion tolerance at higher input power.

Green's functions for Maxwell's equations: application to spontaneous emission

We present a new formalism for calculating the Green's function for Maxwell's equations. As our aim is to apply our formalism to light scattering at surfaces of arbitrary materials, we derive the Green's function in a surface representation. The only requirement on the material is that it should have periodicity parallel to the surface. We calculate this Green's function for light of a specific frequency and a specific incident direction and distance with respect to the surface. The material properties entering the Green's function are the reflection coefficients for plane waves at the surface. Using the close relationship between the Green's function and the density of states (DOS), we apply our method to calculate the spontaneous emission rate as a function of the distance to a material surface. The spontaneous emission rate can be calculated using Fermi's Golden Rule, which can be expressed in terms of the DOS of the optical modes available to the emitted photon. We present calculations for a finite slab of cylindrical rods, embedded in air on a square lattice. It is shown that the enhancement or suppression of spontaneous emission strongly depends on the frequency of the light.

Modification of Spontaneous Emission from Periodic Array of Spherical Polystyrene Particles Containing Fluorescent Molecules

AbstractEmissive behavior of dye molecules embedded in the systems with the size of visible wavelength were studied. The structures consisted of close-packed arrays of spherical dielectric particles with diameter of submicrometer were fabricated. Photoluminescence from selfassembled arrays of dye-doped polystyrene microspheres were examined. In this systems, partial suppression of spontaneous emission by ordered structures were observed. Electricallypumped emission from organic light emitting diodes with highly ordered arrays of silica microspheres were attempted.

Inhibition of spontaneous emission from quantum-well magnetoexcitons.

We propose a method for tailoring the radiative properties of two-dimensional magnetoexcitons. First, we show that the magnetoexciton-photon coupling is purely bilinear in the strong-magnetic-field limit, implying that optical nonlinearities appear through the breakdown of bosonic commutation relations at high densities. The dispersion curve of magnetoexcitons may be modified or engineered using external electric or optical fields. We show that the application of an in-plane electric field will render the ground-state magnetoexcitons stable against radiative recombination, as a result of the momentum conservation. Based on this effect, we propose a particular geometry which should allow for the investigation of condensation effects and superfluidity in direct-band-gap semiconductors. \textcopyright{} 1996 The American Physical Society.

Quantum Zeno effect on atomic excitation decay in resonators.

A unified theory of two-level atom coupling to vacuum field reservoirs with arbitrary mode-density spectra is used to demonstrate that the quantum Zeno effect on excitation decay of the atom (and, correspondingly, inhibition of spontaneous emission) is observable in open cavities and waveguides, using a sequence of evolution-interrupting pulses on a nanosecond scale.