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The internal quantum efficiency of organic light-emitting diodes (OLEDs) has reached nearly 100%, and thus further improvement in the external quantum efficiency can be achieved only through outcoupling enhancement. However, light propagation in OLEDs for achieving high outcoupling has mainly been controlled not by the internal organic semiconductor layers but by external optical elements, which inevitably increase process cost. Here, a method is proposed for outcoupling enhancement that actively controls the refractive index of a hole transport layer (HTL) in OLEDs using a stably evaporable perfluororesin, which has a low refractive index and high amorphousness. The co-deposition of the perfluororesin with a hole transport material lowers the refractive index of the HTL to 1.56 at 550 nm without deteriorating the electrical properties. Owing to the nano-sized pillar-like phase separation between the perfluororesin and the hole transport material, the path of charge transport is retained. Using the low-index co-deposited HTL, a 1.22-fold enhancement of the outcoupling efficiency of a phosphorescent OLED is demonstrated. The proposed method can be generally applied to OLEDs to significantly enhance their outcoupling efficiency without increasing process cost. The results show the potential of active refractive index control as a major strategy for achieving further high-efficiency OLEDs.

Cholesteric liquid crystals are tunable self-assembled photonic bandgap materials. Because of their unusual properties and potential for applications in photonics, their optical properties have rec...

Controlling the direction of light propagation, or light switching, enables the addressing of individual optical elements in high-density and complex photonic integrated devices. Light switching is...

Resonance lineshapes of a side-coupled waveguide-microring resonator (MRR) is crucial for the performances of MRR-based on-chip photonic devices. Much efforts have been made to modify the resonance lineshapes to other types, such as asymmetric Fano profiles. However, complex photonic structures are required to integrate with waveguide-MRR. Here, we model the light propagation in a waveguide-MRR into the interactions of a discrete resonance mode and a continuum waveguiding mode and propose the phase delay between the two states plays great roles in controlling the resonance lineshape into symmetric Lorentzian dips, Lorentzian peaks, and Fano lineshapes with arbitrary asymmetric factors. We experimentally verify this by fabricating silicon waveguide-MRR with an air-hole inserted in the bus-waveguide section coupled with the MRR, where the air-hole with varied dimensions could control the phase delay. The results not only have potentials to strengthen the performances of MRR-based devices, but also provide a simple strategy to control resonance lineshapes in other optical resonators, including photonic crystal cavity, microtoroid, etc.

Interaction between nanoparticles and optical resonators contributes to the conceptual and experimental demonstration of nanoparticle sensors and scattering-induced coupling between two counter-pro...

The goal of this thesis is to steer light deep inside otherwise opaque media. Opaque media are those that strongly interact with light, leading to low transmission and high scattering or reflection. We perform experimental studies on samples that interact with light in different manners. The opaque samples range from randomly distributed nanoparticles that scatter light in all directions to 3D periodically ordered photonic crystals with a forbidden range of light frequencies, a full photonic band gap, and even superperiodic structures, namely 3D arrays of coupled resonating cavities in a 3D band gap. In presence of multiple scattering, the wavefront shaping phase modulation technique is used to focus light behind or inside the medium. We apply this technique to photonic crystals with a forbidden energy gap for light that have intrinsic fabrication disorder that results in multiple scattering. By adding periodically repeated cavities in 3D band gap crystals, we finally present a novel controlled wave transport in superperiodic media, where light hops from cavity to cavity within an otherwise forbidden photonic band gap.

Recently, near-field optical tweezers integrated on a chip based on silicon on insulator (SOI) have attracted more attention and are promising for biological and chemical analyses. Here we propose a low-loss tapered Si waveguide with a high intensity gradient in the electric field to trap microparticles whose diameters vary from 1 μm to 5 μm. The high transmittance allows for cascading the traps along the direction of light propagation. Optical forces in all three dimensions are analyzed around a high-stiffness potential well obtained.

The concept of silicon photonics beyond the singlemode regime is proposed to help solve the issue of propagation losses and random phase errors for light propagation along silicon photonic waveguides. It shows the great potential for enhancing the performance of photonic devices. A review for recent progresses is given in this paper.

We study the propagation of light through a three-dimensional (3D) superlattice of cavities that is embedded in a 3D photonic band gap. In such a superlattice of cavities, light propagation takes place as a result of inter-cavity coupling. Light supported by the cavity modes takes certain preferred high-symmetry paths inside the structure, hence known as ‘Cartesian light’ [1] .

An active ultra-compact plasmonic waveguide composed of a subwavelength slit and perforated in vanadium dioxide (VO 2 ) followed by a metallic layer is proposed and numerically analyzed. Refractive index variation of VO 2 by external stimuli provides a feasible way for tuning the optical properties of the waveguide. Varying the refractive index of VO 2 corresponds with changing the phase of VO 2 to the metallic state (“on” state). Consequently, the entire structure becomes a typical metal–insulator–metal (MIM) waveguide that routes the incident light through the slit. In addition, during the “off” state, the incident light thereby propagates in the slit and VO 2 medium and mitigates rapidly. By adding a MIM waveguide attached to the Fabry–Perot (FP) cavity, spectrally wide stopband and passband filtering features in telecommunication frequency regime are demonstrated. Tailoring the resonance wavelength can be performed through the geometrical parameters. Such active plasmonic waveguides with high transmission, coupling, and compact size can be utilized in future fully integrated all plasmonic chip technology.

We demonstrate an integrated electro-optic frequency circulator on thin-film lithium niobate. Our device operates at telecommunications wavelengths, exhibiting fre-quency conversion and isolation of 37.3 dB, with insertion loss of 3.8 dB.

We study the resonant frequency gap in the short-range order photonic system. The decay rate measurements are performed for an emitter embedded in these structures to validate the changes in the local density of states.

Multimode silicon photonics is promising to further increase the link capacity of optical interconnects thus attract more and more attention. Moreover, the introduction of higher-order modes also greatly enhances the flexibility for the design of on-chip photonic devices, showing great potential in some emerging applications. Currently multimode silicon photonic devices have been tremendously investigated. This paper gives a tutorial review for the recent progresses in this field.

Flexible and high-efficiency thermoelectric devices can be achieved by relying on three-dimensional nanostructures fabricated by proximity-field nanopatterning (PnP) process. In this study, the phase shift mask, which generates the light diffraction in the photoresist, has been studied. To enhance device performance, the size limitation of the mask for this process was investigated as well as how the mask affects the device performance in light propagation simulations. Results show that decreasing the nanostructure size by altering the periodicity from 0.60 µm to 0.30 µm results in 50 % filling factor (FF). To summarize, the mask periodicity 0.30 µm is the size limitation performed by simulation, and the mask periodicity 0.40 µm is an exciting candidate for future work.

We theoretically investigate the optical second-order sideband generation (OSSG) in an optical parity-time (PT) symmetric system, which consists of a passive cavity trapping the atomic ensemble and an active cavity. Compared with the double-passive system, it is found that near the exceptional point (EP), the efficiency of the OSSG increases sharply not only for the blue probepump detuning resonant case but also for the red one. Using experimentally achievable parameters, we study the effect of the atomic ensemble on the efficiency of the OSSG in the PT-symmetric system. The numerical results show that the efficiency of the OSSG is 30% higher than that of the first-order sideband, which is realized easily by simultaneously modulating the atom-cavity coupling strength and detuning. Moreover, the efficiency of the OSSG can also be tuned effectively by the pump power, and the efficiency is robust when the pump power is strong enough. This study may have some guidance for modulating the nonlinear optical properties and controlling light propagation, which may stimulate further applications in optical communications.

Magneto-optical phase shift is effective to realize on-chip optical isolators. Optical isolators are fabricated on SOI platforms with isolation ratios of 30 and 16 dB for TM and TE mode input, respectively.

We demonstrate robust and low loss coupling into photonic crystal waveguide by using a one-dimensional dielectric metalens.

We developed a 2-dimensional fiber array (2D-FA) as an optical interconnection device for co-packaged optics. The 2D-FA was capable of maintaining a low connection loss of < 1.0 dB after reflow process at 260°C.

We investigate the nonlinear response of waveguides doped with dimers of noble-metal nanoparticles using a simple effective model. Our results show a markedly distinctive response depending on the dimer gap.

Topological photonics has attracted increasing interest, due to its robust light propagation. Here, we present two valley-Hall topological graphene plasmonic crystal waveguides, namely single- and bi-layer graphene plasmonic crystal waveguides.

A comprehensive study on structural and optical engineering of high-quality nanoporous anodic alumina gradient-index filters (NAA-GIFs) by selective addition of alcohols to the anodizing acid electrolyte is presented. Analysis of the combined effect of type (methanol, ethanol, isopropanol, and ethylene glycol) and concentration (from 10 to 70 vol %) of alcohol additives in sulfuric acid electrolytes on the optical features of the characteristic photonic stopband of NAA-GIFs - central wavelength, full width at half maximum, intensity, and quality factor - allows us to elucidate the most optimal fabrication conditions to produce high-quality NAA-GIFs by sinusoidal pulse anodization under mild conditions. Comprehensive electrochemical, structural, optical, and chemical analyses demonstrate that a suitable selection of type and concentration of the alcohol additive is critical in controlling the quality of forbidden light propagation within these photonic crystal (PC) structures. Particularly, NAA-GIFs produced by sinusoidal pulse anodization in the sulfuric acid electrolyte modified with 40 vol % methanol achieve an outstanding quality factor of ∼58 (32-54% superior than that of other alcohol additives). Our findings indicate that a combination of anodic oxide growth rate and suppressing dissolution efficiencies, mildly branched nanoporous structure, and incorporation of carbon-containing impurities into the structure of NAA-GIFs are critical factors in enhancing light-forbidding quality of these NAA-based PCs. Our results advance the understanding of structural engineering of NAA-PCs by dynamic modification of the input anodization profile under optimal electrolyte conditions Refereed/Peer-reviewed

We present an inverse design method making waveguides with high performance and high robustness to fabrication errors. As an example, we show a 1-to-4 mode converter with > -1.5 dB conversion efficiency under geometric variations within fabrication tolerances.

Magneto-optical isolators exhibit performance characteristics of a 30 dB isolation, a 20-dB isolation bandwidth of 8 nm, and a temperature-insensitive isolation. The magneto-optical switch is successfully demonstrated with a latching function. © 2020 The Author(s)

Light in the near infrared has advantageous properties such as reduced scattering and higher depth of penetration that make it ideal for optical imaging either in transmission or in fluorescence. This chapter gives an overview of the physics behind light propagation, the optical properties of biological tissues and finally presents the potential benefits that this part of the spectrum can offer to imaging.

This work demonstrates optical trapping and transportation of nanoparticles along a nanofiber microring. The optical fiber, 800 nm in diameter, was formed to be a microring with a bending radius of about 42 μm. A microparticle, stuck to the junction of the ring, plays a critical role for confining nanoparticles on the microring. The experimental results show that, when a 650 nm laser light was launched into the ring, nanoparticles dispersed in the solution were trapped to the ring surface and delivered along the direction of the light propagation. Because the stuck microparticle on the junction for perturbation, nanoparticles can be confined over entire microring circumference. This technology offers a new degree of control for particles and lead to various nanomanipulation applictions.

We report our study on the effect of optical absorption in nanowire ultraviolet light-emitting diodes (LEDs) using three-dimensional finite difference time domain simulation. Utilizing nanowire structures can avoid the emission of guided modes inside LED structure and redirect the trapped light into radiated modes. The optical loss due to material absorption can be decreased by reducing light propagation path inside the LED structure, and consequently enhance the light extraction efficiency (LEE). Nanowire form factors including size, and density play important roles on the LEE of ultraviolet (UV) nanowire LEDs. In this paper, the nanowire spacing and diameter are considered in simulation to reach maximum LEE. Our results show an unprecedentedly high LEE of ∼34% can be achieved for deep UV emission at 240 nm. Moreover, UV nanowire LEDs with random structure can exhibit LEE of ∼19% which is comparable or higher than that of high efficiency UV thin-film LEDs.

In this paper, we report numerical studies of unidirectional light propagation in a heterojunction photonic crystal waveguide (PCW). The proposed structure consists of two square- lattice photonic crystals and a coupling region. By careful design of this region placed at the interface of the PCs, the light wave propagation in one direction can be significantly enhanced and improved. Two line defects of different shapes are introduced along the interface to control and modify the propagation of the light. The findings may be implemented in integrated optical systems.

We investigate the propagation of light in an ultra-thin gap in stacked-stripe three-dimensional (3D) photonic crystals operating in the near-infrared wavelength range. We fabricate 3D photonic crystals composed of 32 stacked layers with an artificially introduced gap (∼200 nm) in the center of the structure by using a wafer bonding method. In order to study the characteristics of the gap, we introduce oblique waveguides to connect the gap with the upper and lower sides of the photonic crystal. The observation of light output from waveguides that are distant from the waveguide used for incident light demonstrates for the first time that light propagates along the air gap and is distributed to multiple output waveguides. Moreover, we perform calculations that reveal the formation of a propagation mode resulting from introduction of the ultra-thin gap. We analyze the coupling between the propagation mode and the oblique waveguide mode and discuss the characteristics of light distribution via the gap.

In this work the theoretical model of holographic formation of controllable waveguide channels system in photopolymer-liquid crystalline composition is developed. The ability to control the light propagation conditions in waveguides by external electric field impact is demonstrated.

Naphthalenediimide-based n-type polymeric semiconductors are extensively used for constructing high-performance all-polymer solar cells (all-PSCs). For such all-polymer systems, charge recombination can be reduced by using thinner active layers, yet suffering insufficient near-infrared light harvesting from the polymeric acceptor. Conversely, increasing the layer thickness overcomes the light harvesting issue, but at the cost of severe charge recombination effects. Here we demonstrate that to manage light propagation within all-PSCs, a thick bulk-heterojunction film of approximately 350 nm is needed to effectively enhance photo-harvesting in the near-infrared region. To overcome the severe charge recombination in such a thick film, a non-halogenic additive is used to induce a well-ordered micro-structure that inherently suppresses recombination loss. The combined strategies of light management and delicate morphology optimization lead to a promising efficiency over 10% for thick-film all-PSCs with active area of 1 cm2, showing great promise for future large-scale production and application of all-PSCs., Thick film is preferred for sufficient light absorption and tolerant processing but it easily spoils the charge transport in the all-polymer solar cells. Here Fan et al. reconcile by tuning the film morphology and deliver high efficiency of 10% in 1 cm2 area devices.

We design and fabricate ultrasmall silicon waveguide lenses designed by a wavefront-matching (WFM) method by a standard CMOS process. It is experimentally demonstrated that a low-loss several micron free-space light propagation is possible by using the waveguide lens designed by the WFM method.

A Tm:LiYF4/LiYF4 channel waveguide laser was passively Q-switched by Cr2+:ZnSe and Co2+:ZnSe saturable absorbers. For Cr2+:ZnSe, the laser operated at 1876.5 nm generating 9 ns/2.1 μJ pulses at a repetition rate of 0.29 MHz.

We propose and theoretically demonstrate a high-speed and high-power silicon-germanium photodiode assisted by doping region regulation. The simulations imply a large 3 dB bandwidth of 14 GHz at 30 mW input optical power.

The modified Ambartsumyan method of addition of layers is used for solving the problem of oblique light propagation through a layer of gyrotropic metamaterial in the field of two counterpropagating ultrasonic waves. It is shown that the studied system can operate as a tunable optical diode. The possibility of controlling the system parameters by changing the parameters of ultrasonic waves is studied.

Single-atomic-layered materials are important for future electronics. They allow optoelectronic devices to be fabricated at the single-atomic layer level. A single-atomic-layered two-dimensional (2D) transition metal dichalcogenide (TMD) film is usually composed of randomly orientated single-crystalline domains, and the size distribution of the domains on a large-area film has a significant impact on the applications of the film, but the impact is difficult to characterize. We report an approach to evaluate the size of the single-crystalline domains by measuring the second-harmonic generation divergence caused by the domains of different orientations. Using this method, domain size mapping on an 8 × 8 m m 2 region of a continuous M o S 2 film is achieved. This method provides a fast and efficient way of domain size characterization across a large area in a non-destructive and transfer-free manner for single-atomic-layered TMD films.

Plasmonic devices enable extreme photonic miniaturization and extreme light–matter interactions, but their integration with conventional photonic circuits has proved challenging. In work that was published this year, we offered an approach for hybrid silicon–plasmonic devices that enables modular design of the plasmonic elements.

In recent work, we showed that one-way light propagation, with respect to the incidence angle, can occur in simple, natural crystalline materials, such as crystal quartz, at far-infrared frequencies. Our results support the idea that natural crystals can serve as efficient and functional oriented asymmetric absorbers, features that have led to the use of materials such as the quartz we have studied in developing on-chip devices.

One-way edge states at the surface of photonic topological insulators are of significant interest for communications, nonlinear and quantum optics. Moreover, when reciprocity is broken in a photonic topological insulator, these states provide protection against disorder, which is of particular importance for slow light applications. Achieving such a one-way edge state, however, requires the construction of a two-dimensional structure. Here, we show how unidiriectional Floquet bands can arise in purely one-dimensional, adiabatically-modulated dynamic systems, in contrasts with the higher dimensionality needed in topological insulators. We also show that, using realistic experimental parameters, the concept can be implemented using both a coupled-resonator optical waveguide and a photonic crystal waveguide. Furthermore, we illustrate the associated protection against disorder, and find it to be of a novel nature when compared to Floquet topological insulators.

The objective of this study was to control the transmission, dispersion and, eventually, the nonlinearity of an optical fiber by intercepting and manipulating the evanescent field extending from the core to the cladding with a variety of plasmonic and metamaterial nanostructures. The access to evanescent waves is enabled by placing the core close to the flat surface of the cladding in the so-called D-shaped fiber design. In the first phase of the project, reported here, the numerical simulations of D-shaped fibers with deposited metal (Au) have been performed. We, furthermore, demonstrated that the fiber transmission can be controlled by highly concentrated rhodamine 6G molecules deposited onto the fiber’s flat surface.

We employed an automated dual-probe scanning near-field optical microscope to study the light propagation and localization in ordered and disordered nanodisc arrays.