Designing three-dimensional transformation optical media using quasiconformal coordinate transformations

We introduce an approach to the design of three-dimensional transformation optical (TO) media based on a generalized quasiconformal mapping approach. The generalized quasiconformal TO (QCTO) approach enables the design of media that can, in principle, be broadband and low loss, while controlling the propagation of waves with arbitrary angles of incidence and polarization. We illustrate the method in the design of a three-dimensional carpet ground plane cloak and of a flattened Luneburg lens. Ray-trace studies provide a confirmation of the performance of the QCTO media, while also revealing the limited performance of index-only versions of these devices.     

Transformation Optics: From Classic Theory and Applications to its New Branches

In the modern world, the ability to manipulate and control electromagnetic waves has greatly changed people's lives. Novel optical and electromagnetic phenomena and devices will lead to new scientific trends and techniques in the future. The exploration of new theories of optical design and new materials for optical engineering has attracted great attention in recent years. Transformation optics (TO) provides a new way to design optical devices with extraordinary predesigned functions such as invisibility cloaks and electromagnetic wormholes. As the development of artificial electromagnetic media (e.g. metamaterials and metasurfaces) progresses, many of these novel optical devices designed by TO have been experimentally demonstrated and used in specific applications. Starting from the basic theory of transformation optics, we review its applications, extensions, new branches and recent developments in this paper.     

Advances in photonic crystals with MEMS and with semiconductor quantum dots

We discuss photonic crystals (PCs) with a microelectromechanical system (MEMS) and semiconductor quantum dots (QDs) as novel classes of PC devices. Integration of MEMS structures into PC devices enables one to realize several kinds of functional devices, such as modulators, switches, and tunable filters for highly integrated photonic circuits. We describe the basic concept of MEMS-integrated PC devices and show numerical and experimental demonstrations of MEMS-integrated functional PC devices. On the other hand, QDs are promising candidates for active media in PC devices. Spontaneous emission control of QD emission in PC nanocavities is especially important for novel optoelectronic devices and quantum information devices. In PC nanocavities, the interaction between QD excitons and photons is enhanced dramatically. The control of spontaneous emission spectrum and the enhancement of the luminescence intensity of InAs QDs by PC nanocavities are demonstrated at telecommunication wavelengths. The Purcell effect for ensemble and single QDs in PC nanocavities are also discussed.     

Improvement of photovoltaic efficiency using 3D photonic-crystal enhanced light trapping and absorption

The potential of using three-dimensional photonic crystals (PCs) for achieving highly absorptive photovoltaic devices is presented in this study. The diffractive effects of PCs, used as an intermediate layer in the optical collector, on the optical absorption of the photovoltaic structure are theoretically investigated . Different PC configurations implemented in the photovoltaic collectors are modeled, and their absorption enhancements are compared. Longer matter-radiation interaction time for the photovoltaic devices with a PC-based collector results in higher absorption enhancement when compared to the devices using a slab of equivalent volume without a PC structure. The results show that employing simple-cubic (SC) PCs of inverted opal structure facilitates a much stronger enhancement of the absorption efficiency in photovoltaic devices than using the other kinds of PCs. By coupling a SC PC to the intermediate layer of the collector, the enhancement factor across the spectral range (480–1127 nm) could be created by about 2, relative to an ordinary layer of equivalent volume.     

Resonant optical transmission through a one-dimensional photonic crystal adjacent to a thin metal film

We theoretically and experimentally reveal that the large resonant optical transmission (ROT) can be realized through a one-dimensional photonic crystal adjacent to a thin metal film, at a frequency in the original band-gap of the photonic crystal (PC). The influence of periodic number of PC and the thickness of the adjacent metal on the transmission frequency and intensity is studied in detail. An optimum design is given to reach the maximum transmission efficiency, meanwhile a mechanism underlining the ROT phenomenon is proposed. An effective admittance-matching theory is proposed to understand this effect and quantitatively determine the operating frequency, which matches very well with the simulated and measured results. The effects might be very useful to realize some optical filters and sensor devices since the structure is easy for mass production and is matured technically to be prepared in industry.     

Fabrication and characteristics of thin-film optical switches using fluorinated silicon oxide deposited by a liquid-phase technique

Optical switching devices have been studied using thin-film optical waveguides with fluorinated silicon oxide (SiOF) films deposited by a liquid-phase deposition (LPD) technique. This report focuses on the structure of the thermo-optical (TO) switch and its optimization. TO devices with double-and triple-layer structures were fabricated using a material with an organic spin-on-glass (SOG) cladding layer and a liquid-phase deposited (LPD) SiOF core layer. The maximum extinction ratio of 15.97 dB was obtained for the double-layer structure TO devices at the half-wavelength power of 2.78 W, and at the heater area of 0.02 mm². The response time decreased with decrease in the heater area for both double-and triple-layer structures. The response time as short as 6.3 ms was obtained at the heater area of 0.02 mm² for the double-layer structure. For the triple-layer structure, an even shorter response time of 2ms was achieved at the heater area of 0.08 mm², and this was over one order of magnitude smaller than that for the double-layer structure at the same heater area (280 ms).     

Towards athermal optically-interconnected computing system using slotted silicon microring resonators and RF-photonic comb generation

We report that completely athermal design of a slotted silicon waveguide is possible by combining the negative thermo-optic (TO) coefficient of, for example, polymethyl methacrylate (PMMA) with the positive TO coefficient of silicon. When used in a microring resonator structure, the filled overcladding slotted waveguide and the unfilled (air-filled) overcladding slotted waveguide can both achieve athermal characteristics. Simulations indicate a wide range of realizations with proper design parameters of the slotted waveguides, namely, the silicon strip and slot widths. Preliminary experimental results on fabricated devices demonstrate that the temperature dependence is reduced from 91 pm/°C for a regular microring resonator to 52 pm/°C for the PMMA-clad microring resonator. Completely athermal realization is expectable in similar devices with improved fabrication techniques. For the external optical source, we demonstrate a stable 3.5 THz wide (175 modes×20 GHz) optical comb source with nearly flat spectral phase. Adjustable mode spacing and wavelength tunability across the C-band are maintained so that comb lines can be matched to the specified wavelength grid of the computing system. With such schemes, temperature controls of individual optical components in the optically interconnected computing chips become unnecessary, greatly reducing the complexity of the computing system.     

Nanocomposite‐based stretchable optics

Stretchable and conformable optical devices open up very exciting perspectives for the fabrication of systems incorporating diffracting and optical power in a single element. Supersonic cluster beam implantation of silver nanoparticles in an elastomeric substrate grooved by molding allows effective fabrication of cheap and simple stretchable optical elements able to withstand thousands of deformations and stretching cycles without any degradation of their optical properties. The nanocomposite‐based reflective optical devices were characterized both morphologically and optically showing excellent performances and stability compared to similar devices fabricated with standard techniques. The nanocomposite‐based devices can therefore be applied to arbitrary curved nonoptical grade surfaces in order to achieve optical power and to minimize aberrations like astigmatism. The high resilience of the nanocomposite material on which the devices are based allows them to be peeled and reused multiple times.     

半导体激光器同轴封装的高频影响:分析与实验

存高频调制下,封装对半导体激光器的影响非常显著。通过分析封装前后激光器散射参量之间的火系,推导出可用于分析半导体激光器封装高频影响的两种方法：预测法和评价法,从而提供了分析激光器封装的另外两种等价方法。实验中,对同轴（TO）封装的高频特性进行了测试和分析,分析结果与传统比较法的测试结果吻合表明新方法有效。实验表明在10．2GHz以内同轴封装不会降低半导体激光器的频响带宽,即同轴封装的带宽可达10GHz,且发现同轴封装巾电感和电容元件之间的谐振效应对器件的顿响具有补偿作用。两方法可为筛选光电子器件封装提供依据,并为优化封装的设计提供参考。     

Low cost optical detection of DNA hybridization on biochips

The detection of DNA hybridization can be either complicated or require expensive devices. Some methods use a fluorescence signal to investigate hybridization. Here, we present an optical probe based on optical fibers both for illumination and for fluorescence collection. The detection is made with a microspectrophotometer and the signal is then treated with a PC. We also developed the DNA biochips (glass plate with a gold layer functionalized with target DNA) as well as a dedicated microtank which maintains a constant flow of probe DNA over the target one. Finally, the detection of hybridization with this simple and versatile system is presented.     

Improved Light Extraction of GaN-based LEDs with Nano-roughened p-GaN Surfaces

p-GaN surfaces axe nano-roughened by plasma etching to improve the optical performance of GaN-based light emitting diodes （LEDs）. The nano-roughened GaN present a relaxation of stress. The light extraction of the LEDs with nano-roughened surfaces is greatly improved when compared with that of the conventional LEDs without nano-roughening. PL-mapping intensities of the nano-roughened LED epi-wafers for different roughening times present two to ten orders of enhancement. The light output powers are also higher for the nano-roughened LED devices, This improvement is attributed to that nano-roughened surfaces can provide photons multiple chances to escape from the LED surfaces,     

Evaluation of polycarbonate substrate hologram recording medium regarding implication of birefringence and thermal expansion

In this paper, we evaluate photopolymer media using a polycarbonate (PC) substrate. In holographic data storage medium, substrates that sandwich the photopolymer material are needed to protect the photopolymer material against exogenous shock and open air. An optical glass such as BK-7 is normally used as a substrate, but a PC substrate has a cost advantage and is easy to fabricate compared with optical glass. For holographic recording and reading, however, the high birefringence and high thermal expansion of a PC substrate are significant problems. First, we analyze the degree of degradation of output power by the polarization change and estimate the threshold value of birefringence to record hologram normally. Next, we estimate the temperature tolerance of hologram readout with polycarbonate substrate hologram medium. These analyses results indicate the possible usage of the PC substrate as holographic recording media.     

Analysis of optical characteristics of holey photonic crystal devices with the extended coupled-mode formalism

Presented here is a new approach for analysis of the so-called holey photonic crystals—a class of electro-optical components, in which periodicity of air holes in dielectric media is used for confinement of light. This class includes several kinds of microstructured fibers, semiconductor lasers etc. Accurate evaluation of optical characteristics of those devices is usually a complicated problem due to the large dimensions and the fine structure of their refractive index distribution. Furthermore, usually, only numerical solutions for this class of optical components are available. The overwhelming majority of the physical models, suitable for analysis of holey photonic devices, proceed from the “natural” assumption: the devices are considered as arrays of air holes, surrounded by dielectric material. In this work we propose another model. Namely, we treat them as arrays of dielectric spots (waveguides), embedded in the air (cladding material). This model allows utilization of the extended coupled-mode theory (a relatively new approach designed for analysis of infinite arrays of coupled waveguides and previously considered inapplicable to holey optical components) for calculations of the latter. In this sense, we present a new method for analysis of holey photonic crystals. On the one hand, our method allows analytical evaluation of some optical characteristics of holey optical components (such as the number of photonic bands and bandwidth). On the other hand, accurate numerical computation of the photonic band structure of the holey photonic devices, incorporating a large number of holes, can be done with this technique on a timescale of several minutes.     

High-precision calculation of quasistatic field near a photocathode surface microrelief

In modern photoelectron devices, the problem of the impact of photocathode roughness on a photoelectron beam and the characteristics of the devices is extremely challenging. Through a three-dimensional (3D) field determination near a photocathode surface microrelief, the high-precision dynamics of photoelectrons from a photocathode can be determined and the influence of photocathode surface roughness on photoelectron beam characteristics can be investigated. The combined analytical–numerical method of field determination presented in this paper can be used in the investigations. In contrast with FEM method, the combined analytical–numerical method can calculate the field with a heightened accuracy and in a shorter time using a PC. The method can be applied to both arbitrary surfaces and a class of realistic microrelief surfaces. In the latter, it is possible to accelerate the speed of calculations through analytical developments of the method. For another class of microrelief surfaces, it is possible to formulate an analytical solution for field determination without numerical computations. Typical precisions and computation times of the written code were presented, comparison with a commercial code based on FEM method was done, and features of the method related to numerical instabilities of the code were discussed. A method of eliminating the instabilities was proposed.     

介电界面系统的电-声子相互作用

本文应用体极化电荷和面极化电荷产生的宏观电势导出了极化本征矢量遵从的积分和微分方程。证明了极化本征矢量应按正文中的正交归一关系(18)归一化,并导出了双层界面系统的极化本征模的哈密顿量及其与荷电粒子相互作用哈密顿量的算符表示形式。证明了电子与P-偏振SO声子的相互作用可用电子与有效频率为ωeff,±SO的SO声子的相互作用耦合常数α±SO表征;电子与P-偏振LO声子相互作用在性质上是电子与它所在的介质的体LO声于的相互作用,但被面效应减弱了。     

Electrical field analysis of metal‐surface plasmon resonance using a biaxially strained Si substrate

Electrical field components of metal‐surface plasmon resonance were analyzed in detail. Both longitudinal optical (LO) and transverse optical (TO) phonon modes of a biaxially strained Si layer can be excited by surface‐enhanced Raman spectroscopy (SERS). The z to y polarization ratio in SERS measurements was calculated to be 0.78 using the intensity ratio of TO to LO phonon modes. The electrical field components of SERS were also calculated by the finite‐difference time‐domain method. Copyright © 2014 John Wiley & Sons, Ltd.     

Deterministic aperiodic nanostructures for photonics and plasmonics applications

This review focuses on the optical properties and device applications of deterministic aperiodic media generated by mathematical rules with spectral features that interpolate in a tunable fashion between periodic crystals and disordered random media. These structures are called Deterministic Aperiodic Nano Structures (DANS) and can be implemented in different materials (linear and nonlinear) and physical systems as diverse as dielectric multilayers, optical gratings, photonic waveguides and nanoparticle arrays. Among their distinctive optical properties are the formation of multi‐fractal bandgaps and characteristic optical resonances, called critical modes, with unusual localization, scaling and transport properties. The goal of the paper is to provide a detailed review of the conceptual foundation and the physical mechanisms governing the complex optical response of DANS in relation to the engineering of novel devices and functionalities. The discussion will mostly focus on passive and active planar structures with enhanced light‐matter coupling for photonics and plasmonics technologies.     

Efficient tunable negative refraction photonic crystal achieved by an elliptic rod lattice with a nematic liquid crystal

Photonic crystals (PCs) have many potential applications because of their ability to control light-wave propagation. We have investigated the electromagnetic wave propagation inside an elliptic rod PC slab by means of finite-difference time-domain simulations. The band structure of the PC composed of elliptic rod in the square and triangular lattices is studied by solving Maxwell's equations using the plane wave expansion method. Numerical simulations show that the refractive angle can be tuned greatly by rotating the directors of elliptic rod in the PC slab. Furthermore, an optical switch based on elliptic rod PC structures with nematic liquid crystals was proposed. In the on/off switching system, the partial band gap can be controlled when the normalized operation frequency is 0.28. The modulation induced by liquid crystals created a sharp switching in the photonic devices. Such a mechanism of negative refraction PCs should open up a new application for designing components in photonic integrated circuits.     

Extraordinary refraction and dispersion in two-dimensional photonic-crystal slabs

Studies of the refraction and dispersion properties of two-dimensional (2D) photonic-crystal (PC) slab waveguides are reported. The photonic band structure is strongly modified in a slab PC, and only a small number of bands satisfy the guiding conditions imposed by the lack of translation symmetry in the direction perpendicular to the slab; however, it was found that a significant number of the guided modes retain the giant refraction and strong dispersion properties discovered previously in pure 2D PCs. A small change in incident angle resulted in a dramatic change in refraction angle. Furthermore, the dispersion surface exhibited a strong dependence on the frequency, resulting in a superprism effect similar to what has been predicted for pure 2D PCs. In the silicon-based slab PC studied, refraction angles as high as nearly 70 degrees were predicted for incident angles of less than 7 degrees , and frequency components differing by 3% were separated by 15 degrees . The demonstration of giant refraction and superprism phenomena in slab waveguide PCs open the possibility of developing new classes of optical devices that can, for example, be used to develop 2D optical integrated circuits for communications and computing.     

Raman study of confined TO phonons in GaAs/AlAs superlattices grown on GaAs (311)A and B surfaces

The use of Raman scattering in different polarization geometries makes it possible to observe the splitting of transverse optical (TO) phonon modes confined in GaAs/AlAs superlattices grown on faceted GaAs (311)A surfaces. The frequencies of TO modes with atomic displacements in the direction along the facets were observed to be higher than in the transverse one. Increased splitting, up to 3.5 cm ^− 1, was observed for (311)A superlattices when the average thickness of the GaAs layers was 6 monolayers or less. The splitting was absent in superlattices grown on (311)B surfaces under the same conditions. The effect of splitting is reputed to be caused by corrugation of GaAs/AlAs (311)A interfaces and formation of lateral superlattices or arrays of quantum wires, depending on the GaAs layer thickness.