Enhancement of radiative lifetime in semiconductors using photonic crystals

In this work we present a structure consisting of a semiconductor sample immersed between two one-dimensional photonic crystals, designed with the aim to investigate the possibility to increase radiative lifetime in infrared photodetectors, i.e., to decrease the background radiation limit. Since we used a HgCdTe detector for the detection of CO₂ laser radiation, we formed a defect in the front-side photonic crystal with the transmission peak on 10.6 μm. Our numerical calculations show that the 1-D photonic crystal structures at the front and at the back side of the semiconductor sample significantly increase the radiative lifetime in the photodetector.     

Three-dimensional photonic crystals containing designed defects achieved with two-photon photopolymerization

Two-photon photopolymerization （TPP） with femtosecond laser is a promising method to fabricate threedimensional （3D） photonic crystals （PCs）. Based on the TPP principle, the micro-fabrication system has been built. The 3D woodpile PCs with rod space of 2000 nm are fabricated easily and different defects are introduced in order to form the cross-waveguide and the micro-laser structure PCs. Simulation results of the optical field intensity distributions using finite-difference time domain （FDTD） method are given, which support the designs and implementation of the PC of two types in theory.     

Near-infrared photonic crystals with higher-order bandgaps generated by two-photon photopolymerization

Three-dimensional photonic crystals with bandgaps of 1.5-2.3 mum in wavelength and with gap/midgap ratios of as much as 18% were generated efficiently by two-photon photopolymerization in a liquid resin. From 0.5-1.1-mW femtosecond-pulsed 540-nm light, woodpile structures consisting of 40 layers of elliptically shaped rods spaced at 350-500 nm were fabricated by focusing with a 1.3-N.A. objective. The high degree of correlation in these structures allowed the suppression of infrared transmission by as much as 50% as well as the observation of higher-order bandgaps. We also investigated the decrease in the gap wavelength on reduction of layer spacing, in-plane rod spacing, and rod size.     

Optimization of two-photon absorption enhancement in one-dimensional photonic crystals with defect states

One-dimensional photonic crystals with a defect layer of CdS were fabricated. The observed enhancement of two-photon absorption (TPA) in the CdS layer can be attributed to the intensified optical field confined within the defect layer of the photonic crystal. The results show that the enhancement of TPA coefficient depends basically on the number of periods of the photonic crystal and the defect mode position in the photonic band gap. The observation agrees qualitatively with the expectations of a computation by matrix transfer formulation.     

Thermal emission of macroporous silicon chirped photonic crystals

In this Letter we report on the thermal properties of macroporous silicon photonic crystals with the unit cell gradually varied along the pore axis. We show experimentally that arbitrarily large omnidirectional total-reflectance bands can be produced with such structures. We also demonstrate that those bands can be effectively used to reduce thermal radiation in large spectral bands.     

On the dominant role of two-photon relaxation in photonic crystals in external fields

It is shown that resonant interaction of a coherent wave with impurity atoms leads to filling of levels of an impurity atom that lie in the gap in the photon density of states and do not belong to resonant transitions, while the interaction of impurity atoms with a nonresonant coherent wave results in effective deactivation of the indicated levels. The main mechanism determining the pumping and decay of an impurity level in a gap are two-photon radiative relaxation processes previously investigated by the present author (Zh. éksp. Teor. Fiz. 102, 1126 (1992) [Sov. Phys. JETP 75, 611 (1992)]). Pis’ma Zh. éksp. Teor. Fiz. 70, No. 7, 434–438 (10 October 1999)     

Strongly modified spontaneous emission rates in diamond-structured photonic crystals

The spontaneous emission decay dynamics of nanocrystal quantum dots embedded into biotemplated titania photonic crystals with a diamond-based lattice are investigated. Modification of the decay rate of quantum dot emission over wide frequency bandwidths in the visible by the photonic crystals is observed. Frequency-dependent analysis reveals both inhibition and enhancement of emission with a radiative lifetime variation by more than a factor of 10.     

Spontaneous emission in the near field of two-dimensional photonic crystals

We show theoretically that photonic crystal membranes cause large variations in the spontaneous emission rate of dipole emitters, not only inside but also in the near field above the membranes. Our three-dimensional finite-difference time-domain calculations reveal an inhibition of more than five times and an enhancement of more than ten times for the spontaneous emission rate of emitters with select dipole orientations and frequencies. Furthermore, we demonstrate theoretically the potential of a nanoscopic emitter attached to the end of a glass fiber tip as a local probe for mapping the large spatial variations of the photonic crystal local radiative density of states. This arrangement is promising for on-command modification of the coupling between an emitter and the photonic crystal in quantum optical experiments.     

Directional emission from rare earth ions in inverse photonic crystals

Angular distribution of the photoluminescence from trivalent rare earth ions (Eu³⁺) embedded inside a magnesium silicate photonic crystal with an inverse opal structure is experimentally and theoretically studied. The emission at frequencies near the first stop-band of the photonic crystal is shown to exhibit strong angular modulation. The angle-dependent Eu³⁺ photoluminescence is numerically simulated by evaluating the fractional density of optical states in the photonic crystal, with diffuse scattering on structural imperfections taken into account. Experimental data for the emission properties of thin inverse opal films are shown to be in agreement with the simulation results. PACS 42.70.Qs; 78.55.-m     

Spontaneous emission from photonic crystals: full vectorial calculations

Quantum electrodynamics of atom spontaneous emission from a three-dimensional photonic crystal is studied in a full vectorial framework. The electromagnetic fields are quantized via solving the eigenproblem of photonic crystals with use of a plane-wave expansion method. It is found that the photon density of states and local density of states (LDOS) with a full band gap vary slowly near the edge of band gap, in significant contrast to the singular character predicted by the previous isotropic model. Therefore, the spontaneous emission can be solved by conventional Weisskopf-Wigner approximate theory, which yields a pure exponentially decaying behavior with a rate proportional to the LDOS.     

Tailoring self-assembled metallic photonic crystals for modified thermal emission

We predict that modified thermal emission can result from three-dimensional, self-assembled photonic crystals. In previous tungsten structures, known as inverse opals, strong absorption prevented any influence of the periodicity. We consider the origin of this effect and show how to tailor both absorption and surface coupling in experimentally realizable metallic inverse opals. Calculations for tungsten, molybdenum, and tantalum crystals show that their optical properties can be similar to or even better than the tungsten woodpile, where modified thermal emission has already been seen.     

光子晶体中基于有效折射率接近零的光束准直出射

利用平面波展开法(PWM)和时域有限差分法(FDTD)研究了二维正方格子光子晶体靠近禁带边沿附近频率光波的传输特性.研究发现,若有效折射率接近于零,可出现光束从晶体表面准直出射的现象,且光束的出射方向只与晶体表面的取向有关,而与晶格取向无关.这种现象与自准直现象有很大不同.     

Nonperturbative analysis of spontaneous emission in one dimensional special photonic crystals

The retarded spontaneous emission (SpE) process of a two-level atom embedded in realistic one dimensional photonic crystals (1DPC) is investigated with the quantum nonperturbative theory. The atomic transient decay is divided into two processes: the first comes from the natural decay to free space and the second is induced by the reflected field emitted from the atom itself. Due to the multi-reflection in the multi-layer structure, the correct delay time of the induced decay process is hard to calculate in the usual ways. However with the special but practical 1DPC provided, we give the analytic result of the atomic dynamic decay in 1DPC. Our result gives a clear picture to show the process which the atom feels the surrounding.     

Tuning and switching of the spontaneous emission in one-dimensional photonic crystals

If the modal density available to an excited atom is varied on the time scale of its lifetime, then we can expect the natural process of spontaneous emission (SE) to become dynamically manipulable. We consider various experimental possibilities and focus on an atom embedded in a photonic crystal designed to have a band edge in the vicinity of the frequency of the emitted light. Specifically, we calculate the rate of SE by erbium ions (radiating at the wavelength 1.54 μm) implanted in a one-dimensional silicon/silica photonic crystal. The semiconductor layers are assumed to be strongly doped; by tuning the impurity density the free carrier concentration changes and the photonic bands shift. As a result, the SE rate exhibits significant dependency on the level of charge injection.     

Dynamics of spontaneous emission from SiN with two-dimensional photonic crystals

We investigated the dynamics of spontaneous emission from a photonic crystal etched into a SiN slab. After fitting the decay curves of the emission to double exponential functions, we divided the dynamic process of the spontaneous emission into a fast process and a slow process. It was observed that the presence of the photonic crystal increased the proportion of the fast decay component, and consequently, the emission rate and time-integrated emission intensity were also enhanced. These enhancements were a result of the coupling of the guide modes to the leaky modes of the photonic crystal slab waveguide.     

Analysis of directional emission via surface modes on photonic crystals

Directional emission of light exiting a photonic crystal waveguide by a coherent action of radiative surface modes was recently demonstrated [E. Moreno et al., Phys. Rev. B 69 (2004) 121402], and subsequently the substantial enhancement of the directional emission was achieved by engineering the surface and adjusting relevant parameters [S.K. Morrison et al., Appl. Phys. Lett. 86 (2005) 081110]. Here we present the analysis of surface modes causing directional emission by the plane wave expansion method and the finite-difference time-domain method. Then we numerically investigate the effects of surface termination on directional emission. We find another surface termination condition with a positive surface displacement. Our surface termination is more effective than the original structure, and nearly as effective as the termination for the enhancement. Besides, our termination is simpler than that for the enhancement. We confirm its effectiveness in the far-field beam profile and radiation intensity distribution of directional emission from our termination.     

Phase control of spontaneous emission from a double-band photonic crystals

Through picture of dressed states, this paper investigates the spontaneous emission spectrum from a microwave-driven three-level atom embedded in a double-band photonic crystals. The physical dynamics of the phase dependent phenomenon is analysed by comparing two models `upper level coupling' and `lower level coupling'. When the phase is changed from 0 to $\pi$, the variety of spontaneous emission spectra from either of the two models are inverse to each other, in which the relative height and width of peaks are determined by the density of states in photonic crystals.     

Spontaneous emission from a ladder three-level atom in anisotropic photonic crystals

We investigate the spontaneous radiation from a ladder three-level atom embedded in a three-dimensional anisotropic photonic crystal with an external driving field. The properties of the spontaneous emission are dependent strongly on the relative position of the middle level from the band edge. Due to the Autler-Townes splitting by the action of the driving field, the external driving field can also affect the properties of the spontaneous emission. The population exchanged between the upper and the middle levels decreases as the detuning of the external driving field frequency from the corresponding transition frequency increases. The properties of the emission field can be changed or so much as controlled by choosing suitable intensity of the external driving field. The emission spectrum is more complex, and dependent on the location of the observer in this case.     

二维光子晶体中极化原子自发辐射的开关效应

利用二维光子晶体的各向异性，结合原子的偶极辐射能量分布特点，提出通过改变原子的极化方向，可以使其自发辐射寿命显著地缩短或者延长，实现开关控制．发现在某些空间位置上，极化原子寿命的改变可高达33倍．     

Switching control of spontaneous emission by polarized atoms in two-dimensional photonic crystals

We calculate the lifetime distribution function of an assembly of polarized atoms in two-dimensional (2D) photonic crystals (PCs) at different polarization orientations of atomic dipole moments. We reveal a switching effect of atomic spontaneous emission (SE) and find a significant change of atomic lifetime, up to a factor of 33, by tuning the polarized orientation of the atoms. These observations suggest that the tuning of the polarized orientation of atoms provides a new way for the effective control of atomic SE processes in 2D PCs.