Knowledge of temperatures at the nanoscale is essential for studying and controlling the heat-induced local thermal responses. The temperature rise of a heated nanoparticle (NP) near the interface of two kinds of media with different thermal conductivities is numerically investigated. We find that the temperature rise becomes size independent if it is scaled by the temperature rise in the case where the particle-interface distance is zero and the distance is scaled by the equivalent radius of the NP. This universal scaling behavior can be understood with the principle of dimensional homogeneity. An empirical equation is retrieved to predict the actual particle temperature at a given position. Our results may benefit precise control of heat at the nanoscale with applications in plasmonic absorbers, immunotargeted photothermal cancer cell killing, etc.
We propose a tunable unidirectional long-range surface plasmon polaritons (LRSPP) launcher based on subwavelength metallic nanoslits in the visible range. The direction of the generated LRSPPs could be tuned simply by varying the incident angles. The extinction ratio reaches up to 28 dB with a wide angular width of 30º. The influences of the launcher geometry on its performance are investigated in this study as well. The broadband property of the launcher is also demonstrated.
Absorption properties of film-coupled log-periodic optical antennas in the near-infrared region are numerically investigated. The maximum absorption for TE and TM polarizations at normal incidence reach to 95% and 93%, respectively, and the optimal absorption of around 90% can be simultaneously obtained for both cases. It is shown that the main absorption peak is independent to light polarizations at normal incidence. Moreover, the log-periodic antenna-assisted absorption represents district polarization selectivity at high-order resonances. For oblique incidence, only the incident light of specific wavelengths within a narrow incidence angle can be almost entirely trapped inside the absorber, indicating special direction and wavelength selectivity of the absorber. All these features would lead to potential applications in photovoltaic technology, sensing, etc.
Our recent theoretical and experimental investigation of the photothermal effect in a planar metamaterial absorber is
reviewed in the present paper. The observed ultrasensitive photothermal heating in such an absorber nanostructure
irradiated by a pulsed white-light source is elaborated with a simple yet compelling heat transfer model, which is
subsequently solved with a finite-element method. The simulation results not only agree with the experimental finding,
but also provide more detailed understanding of the temperature transition in the complex system.
Metal nanoparticle arrays offer the possibility to considerably surpass the optical field confinement of silicon
waveguides. The properties of directional couplers composed of such plasmonic nanoarrays are analyzed theoretically,
while neglecting material losses. It is found that it is possible to generate very compact, submicron length, high fieldconfinement
and functionality devices with very low switch energies. We further perform a study of spatial losses in Ag
nanoparticle arrays by obtaining the group velocity and the lifetime of the surface plasmon polaritons. The losses are
determined for different host permittivities, polarizations, and for spherical and spheroidal particles, with a minimum
loss of 12 dB/μm. The possibilities to compensate the losses using gain materials, and the added noise associated with
that, is briefly discussed.
We experimentally demonstrate silver nanowire based plasmonic devices at optical communication wavelength 1.55 μm.
The plasmon propagation loss in a 300 nm diameter silver nanowire is measured to be 0.3 dB/μm. Two types of
plasmonic functional devices based on the coupling between two silver nanowires, nano-couplers and nano-splitters, are
realized.
We experimentally demonstrate an efficient coupler between a silicon waveguide and a hybrid
plasmonic waveguide for the wavelength range 1460-1540 nm. The coupling efficiency for a single
coupler is ~70% in the whole spectrum range which is consisted with the theoretical prediction. Such
compact, efficient plasmonic couplers provide a promising platform for integrated photonic circuits.
We experimentally demonstrate all-optical signal processing functions using silicon microring resonators with a
450×250-nm cross section. These results include slow-light delay of phase-modulated data and microwave
photonic signal, wavelength conversion/multicasting, format conversions, optical differentiation, and concentric
micro-ring resonators with deeper notches for label-free bio-sensing applications.
KEYWORDS: Resonators, Silicon, Microrings, Signal generators, Extremely high frequency, Waveguides, Integrated optics, Radio over Fiber, System integration, Modulators
We propose a prototype of a silicon-chip-based frequency quadrupling system integrating a single-drive silicon Mach-
Zehnder modulator and a race-track resonator as an optical differentiator. A proof-of-concept demonstration of 40-GHz
millimeter-wave signal generation using 10-GHz driving signal is experimentally provided. The factors that impacting
the purity of the RF spectrum are discussed through simulation.
In the present paper, the properties of an antenna centred at a metamaterial slab with zero permittivity are investigated. It
is analyzed that the antenna can achieve high directive performance. Its half power beam width (HPBW) decreases
monotonically with the increase of the width of the slab. While the gain of such antenna can only be 0dB independent of
the slab's width. When the permittivity deviates form zero to a little positive number, antenna can achieve high gain by
choosing appropriate slab's width due to the transmission resonance. The effect of loss is also analyzed.
In this work, we have analyzed, fabricated and demonstrated concentric micro-ring resonators in silicon-on-insulator (SOI) structure for enhanced transmission notches. The operation principles of the concentric ring resonators are studied by time-domain coupled-mode theory. Directional coupling between concentric rings offers another freedom in designing deep notch optical filters and ultra-sensitive biosensors. The finite-difference-time-domain (FDTD) simulations have shown the improvement of the notch depth, evenly distributed mode field and the effect of the resonance shift. The device is demonstrated in silicon-on-insulator structure. Transmission notch depth improvement of ~ 15dB is demonstrated for the 21-20.02-μm-radius double-ring structure comparing with the single 21-μm-radius ring.
In this paper, we briefly summarize the theory of transformation optics and introduce its application in achieving
perfect invisibility cloaking. In particular, we theoretically show how the task of realizing cylindrical invisibility
cloaks can be eased by using either structural approximation or material simplification. The corresponding
invisibility performances of the approximate or simplified cylindrical cloaks are presented in detail.
We propose and experimentally demonstrate all optical format conversion from non-return-to-zero (NRZ) format to
frequency-shift-keying (FSK) format based on free carrier dispersion effect in a silicon mode-split microring resonator.
The injection of the high-power NRZ signal generates free carriers leading to the blue shift of the spectrum when a '1'
comes. Therefore, there is a selective filtering for the two probes with certain separation located at different position of
the split mode according to the information carried by the NRZ signal. Then the NRZ signal is converted to the FSK
format. The microring resonator features ultra-compact size with a radius of 10 μm thus is suitable for integration with
silicon-on-insulator (SOI) based optical and electronic devices. The split mode can provide large and variable frequency
deviation for the FSK signal. 1 Gb/s NRZ signal is successfully converted to FSK format with a frequency deviation of
40 GHz, which can find application for interconnection between a metropolitan area networks (MAN) and a passive
optical network (PON) system.
We show that a ring resonator with mutual modes coupling can achieve pulse delay or advancement of tens nanoseconds,
which is similar as a ring resonator with single mode. Nevertheless, the pulse response can be sensitively
tunable either through mutual mode coupling or through waveguide-ring coupling in the vicinity of resonant frequency.
We present the fabrication of high Q factor micro-ring resonators on SOI substrate by directly focused-ion-beam (FIB)
milling. Micro-ring resonators with diameters of 10 μm and 80 μm are fabricated and their corresponding intrinsic Q
factors are 4,000 and 130,000, respectively.
Surface plasmon poalriton (SPP) waveguides have the potential to bring technology revolutions in fields like photonic
integration, optical sensing, and even deep sub-wavelength imaging. The peculiar guidance mechanism of such
waveguides however imposes great challenges on our existing theoretical modeling tools. In this paper, the superiority of
finite element method (FEM) is examined for deriving modes guided by realistic SPP waveguides. In consideration of
the anisotropic field profiles of most SPP waveguides, we propose the deployment of anisotropic finite element mesh.
The anisotropic finite mesh is found to be able to reduce the numerical problem size greatly. Among all SPP waveguides,
we emphasis the importance of the metal-corner waveguides, including both V-channel and Λ-wedge waveguides. Such
metal corners can be found in most SPP waveguides proposed or fabricated so far. The properties like dispersion and
propagation loss etc are studied by using FEM. Subwavelength light guidance can be achieved by such corner
waveguides when their angles are kept small enough. However their applicability in nanoscaled optical circuits is
affected by high propagation loss. Loss reduction or introduction of metamaterial with gain is desired in order to obtain
small mode field size as well as low loss.
We experimentally demonstrate optically tunable buffer in a
nano-scale silicon microring resonator with a 20-μm
radius. The delay-tuning mechanism is based on the red shift of the resonance induced by the thermal nonlinear
effect. We use a non-return-to-zero (NRZ) pseudo random bit sequence (PRBS) signal with different data rates as
the probe signal, and investigate its delay performance under different pump powers.
Enhanced slow light propagation is predicted in a coupled resonator optical waveguide structure possessing highly dispersive elements using the finite-difference time-domain method. The group velocity is shown to be below 0.01co.
Channel drop filters with ring/disk resonators in a plasmon-polaritons metal are studied. It shows that light can be efficiently dropped. Results obtained by the finite difference time domain method are consistent with those from the coupled mode theory. It also shows, without considering the loss of the metal, that the quality factor for the channel drop system can be very high. The quality factor decreases significantly if we take into account the loss, which also leads to a weak drop efficiency.
Optical microcavities based on zero-group-velocity surface modes
in photonic crystals are studied. It is shown that high quality
factors can be easily obtained for such microcavities in photonic
crystals. With increasing of the cavity length, the quality factor
is gradually enhanced and the resonant frequency converges to that
of the zero-group-velocity surface mode in the photonic crystals.
Different with other microcavities mentioned in the literature,
microcavities proposed in this paper can be considered as open
cavities in the sense that one of the in-plane boundaries is
exposed to air.
One of the most distinctive features of photonic crystals (PhCs) is their unique wavelength dispersion allowing novel device concepts for enhancement of photonic functionality and performance. Here, we present examples of our design and demonstrations utilizing dispersion properties of 1D and 2D photonic crystals. This includes the demonstration of negative refraction in 2D PhC at optical wavelengths, filters based on 1D and 2D PhC waveguides, and the design of a widely tunable filter involving 1D PhC.
Photonics is far behind electronics in maturity. The devices are orders of magnitude larger than their electronics counterparts and the functionality is low. But it appears that these issues are not fundamentally impossible to solve. In this paper some of the emerging possibilities to overcome the limitations mentioned above are briefly treated, and we discuss the utilization of these comparatively new phenomena to widen the application envelope of photonics technology to generate functions not normally associated with photonics. These developments could lead to quantum leaps in photonics devices, to complement the forceful engineering improvements. Examples of such potential candidate research fields for quantum leaps are: Coherent light matter interaction, plasmonics, quantum information and communications, photonic crystals, intersubband based devices. The list is by no means exhaustive. This paper will concentrate on coherent light matter interaction, plasmonics and photonic crystals.
A series of microcavities in 2D hexagonal lattice photonic crystal slabs (PCS’s) are studied. A combination of FDTD techniques and Pade approximation with Baker's algorithm is used to accurately determine the resonant frequencies and quality factors of the cavity modes simultaneously. Q factor larger than 106 is obtained for a one missing hole cavity. Another cavity with smaller and simpler design keeps Q factor larger than 105. Microcavities in silicon-on-insulator-type (SOI-type) PCS’s are also studied. Simulations show that Q factors of cavities in SOI-type PCS’s are much smaller than those in the membrane PCS’s. Deep etching of air holes is still required to obtain relatively high Q cavities in SOI-type PCS’s.
The coupling efficiency between external plane waves and the Bloch waves in photonic crystals are investigated. It is found that the coupling coefficient is highly angular dependent even for an interface between air n=1 and a photonic crystal with effective index -1. It is also shown that, for point imaging by a photonic crystal slab owing to the negative refraction, the influence of the surface termination to the transmission and the imaging quality is significant. Finally, we present results demonstrating experimentally negative refraction in a two-dimensional photonic crystal.
Practical realizations of 2D (planar) photonics crystal (PhC) are either on a membrane or etched through a conventional heterostructure. While fascinating objects can emerge from the first approach, only the latter approach lends itself to a progressive integration of more compact PhC's towards monolithic PICs based on InP. We describe in this talk the various aspects from technology to functions and devices, as emerged from the European collaboration "PCIC." The main technology tour de force is deep-etching with aspect ratio of about 10 and vertical sidewall, achieved by three techniques (CAIBE, ICP-RIE, ECR-RIE). The basic functions explored are bends, splitters/combiners, mirrors, tapers, and the devices are filters and lasers. At the end of the talk, I will emphasize some positive aspects of "broad" multimode PhC waveguides, in view of compact add-drop filtering action, notably.
Optical add/drop filters using two-dimensional photonic crystals (PC’s) are presented for different designs. In-plane channel add/drop filter composed of two waveguides and an optical resonator system is very compact, but sensitive to the losses. While add/drop filter based on a contra-directional PC waveguide coupler is much more robust to the losses, and reasonable compactness is possible with careful designs. The possibility to utilize the PC dispersion properties to design optical filters is also discussed briefly.
We report on the fabrication and characterization of 2D photonic crystals (PhCs) in InP/InGaAsP/InP heterostructures. It is demonstrated that Ar/Cl2 based chemically assisted ion beam etching (CAIBE) is a very promising method to obtain high aspect ratio etching of PhCs in the InP-based materials. With this process, it is possible to obtain PC-holes as deep as 3 microns even for feature (PhC-hole) sizes as small as 200-250 nm. The optical characteristic of the fabricated PhC-based elements/devices such as line-defect waveguides, in-plane resonant cavities and drop-filter based on contra-directional coupling will be reported. The devices were measured using end-fire coupling and the obtained results were simulated using the 2D finite difference time domain (FDTD) method including an effective loss-approximation. The etched PhC-waveguides show low transmission losses, less than 1 dB/100 μm. A quality factor of 400 for a 6 micron long cavity with 6-hole mirrors is obtained. Finally, drop-functionality in a PhC-based filter using contra-directional coupling is demonstrated.
Photonic crystal waveguides in InP-based heterostructures are studied experimentally and theoretically. The waveguides are fabricated in an InP/GaInAsP/InP low index contrast heterostructure using Ar/Cl2 Chemical Assisted Ion Beam Etching, and characterized using the end-fire method. The obtained experimental near-infrared transmission spectra are further analyzed by comparing with theoretical results calculated by the finite-difference time-domain method. A loss of 1 dB/100 μm in the photonic crystal waveguides is demonstrated. The mini-stop bands, positioned in agreement with our theory, are observed. In-plane cavities with photonic crystal boundaries inside the waveguide are also realized. A quality factor of 400 for a 6 mm long cavity is obtained.
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