Large Spontaneous Emission Research Articles

A novel 3D 10-fold interpenetrated homochiral coordination polymer: large spontaneous polarization, dielectric loss and emission studies

A novel 3D acentric coordination polymer, {[Cd2(mpba)2(bpmp)2]·2H2O}n (1) was obtained from hydrothermal reaction of the ligand H2mpba = (S)-4,4′-(2-methylpiprazine-1,4-diyl)bis(methylene)dibenzoic acid and a pyridine-based co-ligand, 4-bis(4-pyridinylmethyl)piperazine (bpmp) with Cd(NO3)2·4H2O. The single crystal X-ray structure of 1 reveals that the complex comprises of a 4-connected dia topology with unusual 10 interpenetrating networks. Interestingly, complex 1 exhibits ferroelectric properties with an electric hysteresis loop, showing a remnant polarization (Pr) of ca. 2.01 μC cm−2 and a coercive field (Ec) of 11 kV cm−1. Permittivity measurements of 1 reveal a high dielectric constant (er ~ 80) and low dielectric loss (tan δ ~ 0.03), which suggests that it could be a useful material for high density data storage. Photoluminescence studies show that complex 1 exhibits emission peaks at around 392 nm in the solid state at room temperature.

Polytypic InP Nanolaser Monolithically Integrated on (001) Silicon

On-chip optical interconnects still miss a high-performance laser monolithically integrated on silicon. Here, we demonstrate a silicon-integrated InP nanolaser that operates at room temperature with a low threshold of 1.69 pJ and a large spontaneous emission factor of 0.04. An epitaxial scheme to grow relatively thick InP nanowires on (001) silicon is developed. The zincblende/wurtzite crystal phase polytypism and the formed type II heterostructures are found to promote lasing over a wide wavelength range.

Lasing in hybrid metal-Bragg nanocavities

We report room-temperature lasing from an optically pumped subwavelength-scale cylindrical InGaAsP pillar surrounded by circular Bragg reflectors on a metal substrate with a dielectric spacer layer. By taking advantage of wide in-plane photonic bandgaps and proper vertical antiresonances, three dielectric Bragg pairs produce a sufficient optical feedback capable of low threshold lasing from the fundamental TE011 mode. A large spontaneous emission coupling into the lasing mode is obtained from the cavity-enhanced Purcell effects and effective suppression of nonlasing modes.

Eu3+ and Sm3+ co-activated aluminum germanate glass channel waveguide as irradiation source for photodynamic therapy

A bright and compact orangish-red fluorescence trace is observed in an Eu3+/Sm3+ co-doped K+Na+ ion-exchanged aluminum germanate (NMAG) glass channel waveguide under excitation with a 488nm Ar+ laser. The excitation wavelength range and the emission intensity of Eu3+ in NMAG glass are remarkably improved by the sensitization of Sm3+, and the energy transfer probability and efficiency are calculated to be 151.2s−1 and 25.3%, respectively. Meanwhile, the energy transferred from Sm3+ can be efficiently utilized to generate intense fluorescence of Eu3+ due to the large spontaneous emission probabilities of the Eu3+: 5D0→7FJ (J=1, 2, and 4) transitions that reach up to 68.9, 364.7, and 152.6s−1, respectively. Enhanced fluorescence in the Eu3+/Sm3+-doped NMAG glass channel waveguide, which matches the excitation band of most photosensitizers, holds great promise for photodynamic therapy.

Electromagnetic Wave Emission from Intrinsic Josephson Junction Stacks: A Review of Theory and Simulation

We review theoretical and numerical research developments in intrinsic Josephson junctions in terms of spontaneous THz electromagnetic-wave emission and report our recent multi-scale simulation scheme to further enhance the radiation power. Starting with theoretical treatments on the couplings among the stacked Josephson junctions, we reveal that solitonic excitation is essential for large spontaneous emission. Finally, we propose an experimental setup, in which an intrinsic Josephson junction is enwrapped by the dielectric materials and reveal that radiation power enhancement occurs by tunning the dielectricity.

Compositional dependence of the 1.8 μm emission properties of Tm3+ ions in silicate glass

The compositional dependence of the 1.8 μm emission properties of Tm3+ ion-doped lead silicate glasses is investigated. Judd–Ofelt parameters are calculated and their variation with different glass modifier ions is obtained. The Judd–Ofelt parameters increase with decreased modifier ionic radius. A large spontaneous emission probability and a large emission cross-section are found to be related with the strength of the modifier ion. Fluorescence spectra are analyzed using rate equations and compared with recorded data. The results are very close, indicating the reliability of this method. Non-radiative probability is deduced by fitting the fluorescence decay curve; it becomes smaller with increased ionic field strength. Energy transfer processes are studied using the extended overlap integral method.

Plasmonic nanoantennas for efficient control of polarization-entangled photon pairs

We suggest a source of polarization-entangled photon pairs based on a cross-shaped plasmonic nanoantenna driven by a single quantum dot. The integration of the nanoantenna with a metal mirror overcomes the fundamental tradeoff between the spontaneous emission (SE) enhancement and the extraction efficiency typical of microcavity- and nanowire-based architectures. With a very high extraction efficiency of entangled photons ($\ensuremath{\approx}$$90%$) at $1.55$ $\ensuremath{\mu}$m and large SE enhancement ($\ensuremath{\approx}$90) over a broad 330-nm spectral range, the proposed design will pave the way toward reliable integrated sources of nonclassical light.

Large spontaneous emission enhancement in plasmonic nanocavities

Researchers demonstrate spontaneous emission enhancements approaching 1,000 for emitters coupled to the gap between a metal wire and a metal substrate. The enhanced emission rate of plasmons in the structures is shown to yield a high internal quantum efficiency, despite the close proximity of lossy metal surfaces.

Monolithic integration of III-V nanowire with photonic crystal microcavity for vertical light emission

A novel photonic structure formed by the monolithic integration of a vertical III-V nanowire on top of a L3 two-dimensional photonic crystal microcavity is proposed to enhance light emission from the nanowire. The impact on the nanowire spontaneous emission rate is evaluated by calculating the spontaneous emission factor β, and the material gain at threshold is used as a figure of merit of this vertical emitting nanolaser. An optimal design is identified for a GaAs nanowire geometry with r = 155 nm and L~1.1 μm, where minimum gain at threshold (gth~13×10³ cm⁻¹) and large spontaneous emission factor (β~0.3) are simultaneously achieved. Modification of the directivity of the L3 photonic crystal cavity via the band-folding principle is employed to further optimize the far-field radiation pattern and to increase the directivity of the device. These results lay the foundation for a new approach toward large-scale integration of vertical emitting nanolasers and may enable applications such as intra-chip optical interconnects.

High Efficient Polarization-Matched InGaN/MgZnO Quantum Well Structures

The optical properties of InGaN/MgZnO quantum wells (QWs) with zero internal field were investigated by using the non-Markovian model with many-body effects. For a given In composition in a well, a Mg composition in a barrier was selected to give a zero internal field in a well. The Mg composition in the barrier to give zero internal field is shown to increase with In composition in the well. The InGaN/MgZnO QW structure has shorter transition wavelength than the InGaN/GaN QW structure because the internal field is negligible for the former case. Also, in the case of a relatively high In composition (x >; 0.15), the InGaN/MgZnO system has a much larger spontaneous emission coefficient than the InGaN/GaN system. This can be explained by the fact that an optical matrix element is largely enhanced due to disappearance of the internal field.

Vertically coupled photonic molecule laser

A photonic molecule semiconductor microdisk laser consisting of three vertically coupled disks of 1.4 μm in diameter is fabricated and optically pumped. Clear mode splitting arising from the strong vertical optical coupling is observed and confirmed by the coupled mode theory. The inter-coupling strength ∼0.40 THz of optical modes between adjacent disks is calculated and agrees well with the experiment. Moreover the multiple stacked microdisk laser has a large spontaneous emission factor (β ∼ 0.72) by fitting the L-L curves and provides some potential functional devices in cavity quantum electrodynamics systems and highly-dense photonic integrated circuits.

Chiral Rashba spin textures in ultracold Fermi gases

Spin-orbit coupling is an important ingredient in many recently discovered phenomena such as the spin-Hall effect and topological insulators. Of particular interest is topological superconductivity, with its potential application in topological quantum computation. The absence of disorder in ultra-cold atomic systems makes them ideal for quantum computation applications, however, the spin-orbit (SO) coupling schemes proposed thus far are experimentally impractical owing to large spontaneous emission rates in the alkali fermions. In this paper, we develop a scheme to generate Rashba SO coupling with a low spontaneous emission extension to a recent experiment. We show that this scheme generates a Fermi surface spin texture for $^{40}\rm{K}$ atoms, which is observable in time-of-flight measurements. The chiral spin texture, together with conventional $s$-wave interactions leads to topological superconductivity and non-Abelian Majorana quasiparticles.

Analysis of InGaN-delta-InN quantum wells for light-emitting diodes

The design of InGaN-delta-InN quantum wells (QWs) leads to significant redshift for nitride active region with large electron-hole wave function overlap (Γe_hh) and spontaneous emission rate. The analysis was carried out by using self-consistent six-band k⋅p band formalism. The design of active region consisting of 30 Å In0.25Ga0.75N QW with InN delta-layer leads to large Γe_hh of >50% with emission wavelength in the yellow and red spectral regimes, which is applicable for nitride-based light-emitting diodes.

Photonic crystal nanobeam lasers

Photonic crystal lasers operating at room temperature based on high Q/V nanobeam cavities have been demonstrated. We reported a large spontaneous emission factor (β∼0.97) by fitting the L-L curve with the rate equations.

Optical properties of type-II InGaN/GaAsN/GaN quantum wells

Optical properties of type-II InGaN/GaNAs QW light-emitting diodes are investigated by using the multiband effective mass theory. These results are compared with those of conventional InGaN/GaN QW structures. The type-II InGaN/GaNAs/GaN QW structure shows much larger spontaneous emission and optical gain than that of a conventional QW structure. This can be explained by the fact that, in the case of the type-II QW structure, the effective well width is greatly reduced. A type-II QW structure shows that the peak position at a high carrier density is similar to that (530 nm) at a low carrier density. On the other hand, in the case of a conventional QW structure, the peak position is largely blueshifted at a high carrier density.

High-efficiency staggered 530 nm InGaN/InGaN/GaN quantum-well light-emitting diodes

Optical properties of staggered 530 nm InGaN/InGaN/GaN quantum-well (QW) light-emitting-diodes are investigated using the multiband effective mass theory. These results are compared with those of conventional 530 nm InGaN/GaN QW structures. A staggered InGaN/InGaN/GaN QW structure is shown to have much larger spontaneous emission than a conventional InGaN/GaN QW structure. This can be explained by the fact that a staggered QW structure has much larger matrix element than a conventional QW structure because a spatial separation between electron and hole wave functions is substantially reduced with the inclusion of a staggered InGaN layer. A staggered QW structure shows that the peak position at a high carrier density (530 nm) is similar to that at a noninjection level.

Electronic and optical properties of 530 nm strain-compensated hybrid InGaN/InGaN/ZnO quantum well light-emitting diodes

Electronic and optical properties of 530 nm strain-compensated hybrid InGaN/InGaN/ZnO quantum well (QW) light-emitting diodes (LEDs) using a ZnO substrate are investigated using the multiband effective mass theory. These results are compared to those of conventional InGaN/GaN QW LEDs using a GaN substrate. A strain-compensated QW structure is found to have much larger spontaneous emission than an InGaN/GaN QW structure. This can be explained by the fact that a strain-compensated QW structure has much larger matrix element than an InGaN/GaN QW structure due to the reduction in the internal field.

Very Large Spontaneous-EmissionβFactors in Photonic-Crystal Waveguides

Through a new rigorous Bloch-mode formalism, we theoretically study the generation of photons in single-row-defect photonic-crystal waveguides. In contrast with previous related works relying on a reinforcement of the spontaneous emission (SE) through microcavity effects, we explore situations for which the SE into radiation modes is reduced to a very low level while the SE into the guided mode is maintained at a level comparable to that in the bulk material. Remarkably large SE beta factors in excess of 95% are obtained, and since no resonance effect is involved, this efficiency is achieved over a 40-nm-large spectral interval at lambda approximately 950 nm.

Dynamics of quantum dot photonic crystal lasers

Quantum dot photonic crystal membrane lasers were fabricated and the large-signal modulation characteristics were studied. The authors find that the modulation characteristics of quantum dot lasers can be significantly improved using cavities with large spontaneous emission coupling factor. Their experiments show, and simulations confirm, that the modulation rate is limited by the rate of carrier capture into the dots to around 30GHz in their present system.

Dimension-sensitive optical responses of electromagnetically induced transparency vapor in a waveguide

A three-level EIT (electromagnetically induced transparency) vapor is used to manipulate the transparency and absorption properties of the probe light in a waveguide. The most remarkable feature of the present scheme is such that the optical responses resulting from both electromagnetically induced transparency and large spontaneous emission enhancement are very sensitive to the frequency detunings of the probe light as well as to the small changes of the waveguide dimension. The potential applications of the dimension- and dispersion-sensitive EIT responses are discussed, and the sensitivity limits of some waveguide-based sensors, including electric absorption modulator, optical switch, wavelength sensor, and sensitive magnetometer, are analyzed.