Compact transverse-magnetic-pass polarizer based on one-dimensional photonic crystal waveguide

Compact, wide bandwidth, multi-channel power dividers based on one-dimensional photonic crystal waveguides

The development of patterned multiquantum well heterostructures in GaAs/AlGaAs waveguides has recently made it possible to achieve exciton-polariton condensation in a topologically protected bound state in the continuum (BIC). Polariton condensation was shown to occur above a saddle point of the two-dimensional polariton dispersion in a one-dimensional photonic crystal waveguide. A rigorous analysis of the condensation phenomenon in these systems, as well as the role of the BIC, is still missing. In the present Letter, we theoretically and experimentally fill this gap by showing that polariton confinement resulting from the negative effective mass and the photonic energy gap in the dispersion play a key role in enhancing the relaxation toward the condensed state. In fact, our results show that low-threshold polariton condensation is achieved within the effective trap created by the exciting laser spot, regardless of whether the resulting confined mode is long-lived (polariton BIC) or short-lived (lossy mode). In both cases, the spatial quantization of the polariton condensate and the threshold differences associated to the corresponding state lifetime are measured and characterized. For a given negative mass, a slightly lower condensation threshold from the polariton BIC mode is found and associated to its reduced radiative losses, as compared to the lossy one.

This paper presents novel designs and simulation results of electro-optic modulators in integrated silicon photonics platforms. The electro-optic modulators described in this paper are based on the modulation of the photonic bandgap in a silicon photonic crystal slab waveguide, consisting of a phase change material (germanium selenide) sandwiched in between silicon layers. Three-dimensional finite difference time domain (FDTD) modeling is employed to simulate two configurations of electro-optic modulators based on mode-gap shifting in photonic crystal slab waveguides—one that is designed for operation with the transverse electric (TE) polarization of light and the other for the transverse magnetic (TM) polarization. When the electric field is applied across the germanium selenide layer surrounded by doped silicon layers, there is a change of phase of the germanium selenide layer. A large refractive index contrast between the two phases of the germanium selenide layer—i.e., between the amorphous phase and the crystalline phase—on application of the electric field is responsible for shifting of the mode gap in the dispersion characteristics of the PhC slab waveguide. Our results show excellent performance of the electro-optic modulators in terms of the high On/Off extinction ratio ( > 37 d B in the TE configuration and > 28 d B in the TM configuration), broadband switching capability ( ∼ 100 n m ), low insertion loss in the On state ( < 2 d B ), high range of tunability (by changing the lattice constant and radius of air holes), and low operating voltage ( < 4 V ). The proposed devices can be used as electro-optic modulators in future nanoscale photonic integrated circuits.

The proposed one-dimensional photonic crystal waveguide structure can be optimized in three steps as outlined below. At first the imaginary part of the Bloch wavevector inside the 1D PC can be made maximum so that the evanescent light field decays most rapidly and thus the confinement factor of a guided mode becomes maximized when the waveguide is completed. This condition uniquely defines the thickness of two layers in 1D PC. Secondly, the omnidirectional mirror condition can be further enforced for the 1D PC to achieve complete inhibition of light escape in the vertical direction. This can be done by ensuring that for a given frequency the point, (ω, ωn0/c), on TM lightline falls in the forbidden bandgap. Lastly, the thickness of the centerguiding layer can be uniquely determined for given frequency and propagation constant, considering structural symmetry and phase matching condition between lights outgoing from and incoming to the guiding layer.

Strongly influenced by the advances in the semiconductor industry, the miniaturization and integration of optical circuits into smaller devices has stimulated considerable research efforts in recent decades. Among other structures, integrated interferometers play a prominent role in the development of photonic devices for on-chip applications ranging from optical communication networks to point-of-care analysis instruments. However, it has been a long-standing challenge to design extremely short interferometer schemes, as long interaction lengths are typically required for a complete modulation transition. Several approaches, including novel materials or sophisticated configurations, have been proposed to overcome some of these size limitations but at the expense of increasing fabrication complexity and cost. Here, we demonstrate for the first time slow light bimodal interferometric behaviour in an integrated single-channel one-dimensional photonic crystal. The proposed structure supports two electromagnetic modes of the same polarization that exhibit a large group velocity difference. Specifically, an over 20-fold reduction in the higher-order-mode group velocity is experimentally shown on a straightforward all-dielectric bimodal structure, leading to a remarkable optical path reduction compared to other conventional interferometers. Moreover, we experimentally demonstrate the significant performance improvement provided by the proposed bimodal photonic crystal interferometer in the creation of an ultra-compact optical modulator and a highly sensitive photonic sensor.

Using cold atoms to simulate strongly interacting quantum systems represents an exciting frontier of physics. However, as atoms are nominally neutral point particles, this limits the types of interactions that can be produced. We propose to use the powerful new platform of cold atoms trapped near nanophotonic systems to extend these limits, enabling a novel quantum material in which atomic spin degrees of freedom, motion, and photons strongly couple over long distances. In this system, an atom trapped near a photonic crystal seeds a localized, tunable cavity mode around the atomic position. We find that this effective cavity facilitates interactions with other atoms within the cavity length, in a way that can be made robust against realistic imperfections. Finally, we show that such phenomena should be accessible using one-dimensional photonic crystal waveguides in which coupling to atoms has already been experimentally demonstrated.

We describe one-dimensional (1D) fractal photonic crystal waveguides (FPCWs), i.e., photonic crystal waveguides (PCWs) etched with a self-similar distribution of grooves. The transmission properties of these new types of photonic waveguides are described. It is shown that the FPCW transmission spectrum has self-similarity properties associated with the fractal distribution of grooves. Furthermore, FPCWs exhibit sharp localized transmissions peaks that are approximately equidistant inside the photonic band gap.

A silicon-organic hybrid electro-optic (EO) modulator based on one-dimensional photonic crystal slot waveguides is proposed and demonstrated. Effective EO coefficient up to 490 pm/V is observed as a result of the slow group velocity in the proposed structure.

We have measured the intensity of Raman scattering light, which is due to optical phonons, as a function of excitation laser wavelength for the guide-mode band of ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$-based photonic-crystal-slab line-defect waveguide. As a result, we find that the Raman scattering efficiency is pronouncedly enhanced as the signal wavelength approaches the band edge. Comparison of the result with theoretical prediction reveals that the enhancement should reflect increase of the photon density of states in a divergent manner, which is characteristic of a one-dimensional system.

We have designed and simulated compact photonic crystal (PC) slab waveguide based wave plate. We have numerically investigated the optical path of the TE-like and TM-like waves propagating through a triangular based photonic crystal (PC) slab waveguide. The PC slab waveguide is formed by removing one row of the air holes along &Ggr;K direction. The plane wave expansion and three-dimensional finite-difference time domain (3D-FDTD) methods were employed for the design and simulation of the PC slab waveguide. The thickness of 0.75<i>a</i>, <i>a</i> is the lattice constant, for the PC slab waveguide provides both TE-like and TM-like modal guiding within the normalized frequency band of 0.26-0.268. Spatial Fourier transform (SFT) of the electromagnetic field distribution in the propagation direction was used for the analysis of the dispersion properties of the guided modes of the PC slab waveguide. It was found that the effective refractive indices of the TM-like modes were substantially larger than that of the TE-like modes. The large birefringence of this structure suggests that the PC slab waveguide is useful for the construction of compact wave plates. The birefringence larger than 12.6 % within the modal guiding frequency band was achieved for the PC slab waveguide. Thus, the PC slab waveguide with the length of 6 &mgr;m provides first-order half wave plate within the normalized frequency band of 0.26-0.268.

Theoretical research and simulation of GaAs nanowire arrays in reflection-type photon-enhanced thermionic emission solar converters

A novel subwavelength transparent metal structure consisting of a periodic connected slot antennas nanohole array in a gold film is proposed in this work. The transmission characteristics of the structure are investigated by the three-dimensional finite-difference time-domain (3D FDTD) method. A broad transmission band with bandwidth more than 300 nm and maximum transmission intensity more than 90 % is achieved via the localized surface plasmons at the edges of nanoholes, the surface plasmon polaritons (SPPs) on the surface of the gold film, and Fabry–Ferot resonances of surface plasmons in the nanoholes. The transmission properties can be tailored by changing the geometrical parameters and dielectric materials filled in the holes. These results indicate that our structure has potential applications in optical devices such as plasmonic filters, sensors, and so on.

In this work, by using three-dimensional finite-difference time-domain (3D FDTD) method, the effect of conventional nano-patterned sapphire substrate (NPSS) on the optical crosstalk and the light extraction efficiency (LEE) for InGaN/GaN-based flip-chip micro light-emitting diodes (µ-LEDs) are systematically studied. We find that the conventional NPSS is not suitable for µ-LEDs. It is because the inclined mesa sidewall for µ-LEDs possesses a good scattering effect for µ-LEDs, but the introduced conventional NPSS causes part of the light be off escape cone between sapphire and air and become the guided light. To suppress the guided light and improve the optical crosstalk, a thick air layer between the n-GaN layer and the sapphire substrate can be used as a light filter to prevent the guided light from propagating into the sapphire. However, in reality, it is challenging to make the aforementioned air layer from point of fabrication view. Therefore, we propose the air-cavity patterned sapphire substrate (AC-PSS) as the light filter. Our results show that the crosstalk ratio can be decreased to the value even lower than 10%. The LEE can also be enhanced simultaneously due to combination effects of the filtering effect of the AC-PSS and the scattering effect of the inclined mesa sidewall.

In this paper, output near fields of nanowires with different optical and structure configurations are calculated by using the three-dimensional finite-difference time-domain (3D FDTD) method. Then a nanowire with suitable near field distribution is chosen as the probe for scanning dielectric and metal nanogratings. Scanning results show that the resolution in near-field imaging of dielectric nanogratings can be as low as 80nm, and the imaging results are greatly influenced by the polarization direction of the incident light. Compared with dielectric nanogratings, metal nanogratings have significantly enhanced resolutions when the arrangement of gratings is perpendicular to the polarization direction of the incident light due to the enhancement effect of the localized surface plasmons (SPs). Results presented here could offer valuable references for practical applications in near-field imaging with nanowires as optical probes.

We present exact analytical solutions to the ideal one-dimensional planar photonic crystal waveguides (1-D PPCWs) that consist of a central core and infinite number of cladding layers symmetrically placed around the core. We show that these exact solutions allow one to distinguish clearly between light guidance due to total internal reflection and light guidance due to the photonic crystal effect. We also compare structures with finite and infinite cladding layers and provide results for the propagation characteristics and the modal field distributions.