Optical microresonators

We report on the experimental demonstration of a chip-scale microresonator comb enabled optical frequency synthesizer using an agile and highly-integrated heterodyne optical phase-locked loop with InP-based photonic integrated circuit and commercial-off-the-shelf electronic components.

We report on the coherent coupling of whispering gallery modes (WGMs) in a photonic molecule formed from two melamine-formaldehyde spherical microcavities coated with a thin shell of light-emitting CdTe nanocrystals (NCs). Utilizing different excitation conditions, the splitting of the WGM resonances originating from bonding and antibonding branches of the photonic states is observed, and fine structure consisting of very sharp peaks resulting from lifting of the WGM degeneracy has been detected. Time-resolved measurements showed a slight increase in the spontaneous emission rate of NCs in a photonic molecule when compared to the spontaneous emission rate for NCs coating a single microsphere.

The authors demonstrate a new route to the fabrication of individual aluminosilicate microtubes that can act as micron-scale optical cylindrical resonators. The microtubes were prepared using a simple vacuum assisted wetting and filtration through a microchannel glass matrix. Microphotoluminescence spectra of the microtube cavity show sharp resonant modes with quality factors up to 3200. A strong reduction of the emission decay time at high excitation power confirms the occurrence of amplified spontaneous emission from a single microtube.

Reflective Semiconductor Optical Amplifiers (RSOAs) are essential devices for the development of new generation networks that rely on the convergence of optical and RF communications. Despite their proven potential for direct modulation, RSOAs’ electro-optic response is limited by their finite bandwidth, which hinders their employment both for signal amplification and modulation at the data rates envisioned by the target applications. In this paper, we elaborate on exploiting a Birefringent Fiber Loop (BFL) to enhance the operation of RSOAs as intensity modulators. We apply a mathematically and computationally reduced model to simulate the RSOA response in the time domain, and correlate it with that of the BFL in the frequency domain. We validate the model’s predictions by an extensive comparison of the simulation against experimental results. The reasonable theoretical findings allow us to establish the employed model as an efficient tool for describing electrically driven RSOA ope...

A silica resonator was demonstrated for random laser generation. The resonator consisted of a conventional microsphere fabricated in an optical fiber tip through electric arc discharge, and modifications to its geometry were carried out to create asymmetry inside the silica structure. The resulting Bunimovich stadium-like microsphere promotes multiple reflections with the boundaries, following the stochastic properties of dynamic billiards. The interference of the multiple scattered beams generates a random signal whose intensity was increased by sputter-coating the microstadium with a gold thin film. The random signal is amplified using an erbium-doped fiber amplifier (EDFA) in a ring cavity configuration with feedback, and lasing is identified as temporal and spectral random variations of the signal between consecutive measurements.

A silica resonator was demonstrated for random laser generation. The resonator consisted of a conventional microsphere fabricated in an optical fiber tip through electric arc discharge, and modifications to its geometry were carried out to create asymmetry inside the silica structure. The resulting Bunimovich stadium-like microsphere promotes multiple reflections with the boundaries, following the stochastic properties of dynamic billiards. The interference of the multiple scattered beams generates a random signal whose intensity was increased by sputter-coating the microstadium with a gold thin film. The random signal is amplified using an erbium-doped fiber amplifier (EDFA) in a ring cavity configuration with feedback, and lasing is identified as temporal and spectral random variations of the signal between consecutive measurements.

The transition from electronic integrated circuits to faster, more energy-efficient and interference-free optical circuits is one of the most important goals in the development of photon technologies. [26] With novel optoelectronic chips and a new partnership with a top silicon-chip manufacturer, MIT spinout Ayar Labs aims to increase speed and reduce energy consumption in computing, starting with data centers. [25] Following three years of extensive research, Hebrew University of Jerusalem (HU) physicist Dr. Uriel Levy and his team have created technology that will enable computers and all optic communication devices to run 100 times faster through terahertz microchips. [24] When the energy efficiency of electronics poses a challenge, magnetic materials may have a solution. [23] An exotic state of matter that is dazzling scientists with its electrical properties, can also exhibit unusual optical properties, as shown in a theoretical study by researchers at A*STAR. [22] measurements in nanoscale devices and the kilometer-scale gravitational wave detector at LIGO. Because of this troublesome background noise, we can never know an object's exact location, but a recent study provides a solution for rerouting some of that noise away from the measurement. [8] The accelerating electrons explain not only the Maxwell Equations and the Special Relativity, but the Heisenberg Uncertainty Relation, the Wave-Particle Duality and the electron's spin also, building the Bridge between the Classical and Quantum Theories. The Planck Distribution Law of the electromagnetic oscillators explains the electron/proton mass rate and the Weak and Strong Interactions by the diffraction patterns. The Weak Interaction changes the diffraction patterns by moving the electric charge from one side to the other side of the diffraction pattern, which violates the CP and Time reversal symmetry. The diffraction patterns and the locality of the self-maintaining electromagnetic potential explains also the Quantum Entanglement, giving it as a natural part of the relativistic quantum theory.

Excitation migration and upconversion process in the Erbium-doped silica-alumina glass microsphere lasers with concentrations of 2500-4000~ppm were investigated in detail. The experiment shows that under 976~nm excitation, the intense of up-conversion emission at 523, 546 and 657~nm, corresponding to the transitions $^{2}$H$_{11 / 2 } \to ^{4}$I$_{15 / }$, $^{4}$S$_{3 / 2} \to ^{4}$I$_{15 / 2}$, and $^{4}$F$_{9 / 2} \to ^{4}$I$_{15 / 2}$, respectively, $^{ }$depends on the erbium content, migration of excitation and pump power. The excitation migration has strongly influenced on the threshold and Red shift of lasing wavelength and migration-assisted up-conversion process leads to degraded amplification performance of microsphere lasers made by silica-alumina glasses with different contents of Er-ions.

In submerged microcavities there is a tradeoff between resonant enhancement for spatial water and light overlap. Why not transform the continuously resonating optical mode to be fully contained in a water microdroplet per se? Here we demonstrate a sustainable 30-mm-pure water device, bounded almost completely by free surfaces, enabling 41,000,000 re-circulations of light. The droplets survive for 416 h using a technique that is based on a nano-water bridge from the droplet to a distant reservoir to compensate for evaporation. More than enabling a nearly-perfect optical overlap with water, atomic-level surface smoothness that minimizes scattering loss, and B99% coupling efficiency from a standard fibre. Surface tension in our droplet is 8,000 times stronger than gravity, suggesting a new class of devices with water-made walls, for new fields of study including opto-capillaries.

Single-crystal nanotubes of precisely controlled length were produced on a (110) cleaved facet of heterostructure. The selective MBE growth of a strained InGaAs/GaAs strip and its subsequent self-rolling were used. The proposed technique is capable of ensuring good reproducibility of all sizes and exact positioning of nanotubes.

Optical microcavities and microlasers were recently introduced as probes inside living cells and tissues. Their main advantages are spectrally narrow emission lines and high sensitivity to the environment. Despite numerous novel methods for optical imaging in strongly scattering biological tissues, imaging at single-cell resolution beyond the ballistic light transport regime remains very challenging. Here, we show that optical microcavity probes embedded inside cells enable three-dimensional localization and tracking of individual cells over extended time periods, as well as sensing of their environment, at depths well beyond the light transport length. This is achieved by utilizing unique spectral features of the whisperinggallery modes, which are unaffected by tissue scattering, absorption, and autofluorescence. In addition, microcavities can be functionalized for simultaneous sensing of various parameters, such as temperature or pH value, which extends their versatility beyond the capabilities of standard fluorescent labels.

The motivation of the present work was to observe experimentally the unidirectional emission from a circular annular billiard. Such a billiard has been recently proposed by J. Wiersig and M. Hentschel, where the formation of long-lived modes with unidirectional emission was ...

We show that application of the double clad hollow core fiber (DCHCF) significantly affects efficiency of collecting a two photon fluorescence signal. In our approach we propose a new construction of the hollow core double clad fiber which can be used to send simultaneously an ultrafast signal through the single-mode air core and collect the florescence signal through a multimodal clad. The presented fiber has a dispersion equal to 5.13 ps/nm km and losses 0.5 dB/m in the range of 800 nm. In the wavelengths range between 770 to 850 nm the fiber is endlessly single mode with higher order modes HOM's losses above 17 dB/m. The use of such a fiber allows elimination of prevalent precompensation dispersion systems and considerably simplifies the two photon fluorescence endoscopy setup.

Distributed Feedback Laser plays a key role as a light source component in optical fiber communication systems ranging from metro, long-haul to submarine one thanks to its competitive features of superior narrow spectral width and wavelength cohesion. Characterizing such lasers via obtaining their electrical and spectral data and extracting their internal parameters therefore remains a critical task in designing and troubleshooting optical fiber systems. This paper presents first an agile framework for a rapid collection of laser data via automatic measurement and second an efficient approach for extracting laser internal parameters.

In this paper we propose a new optical ring resonator with a very high Q-factor, to be used as a basic element in a wide range of physics and engineering applications. We theoretically demonstrate that in large size conventional ring resonators, a value of the Q-factor higher than 109 is achievable by exploiting the band-edge resonances in a waveguiding long period Bragg grating closed loop, excited through a bus waveguide. The dispersion introduced by the Bragg grating is responsible for a reduction in the band edge resonance linewidth, which is inversely proportional to the square of the number of periods of the grating, thus allowing the overall Q-factor to be enhanced. Numerical results show a substantial improvement in the Q-factor, giving a number of order of magnitude higher than that of a conventional large size ring resonator.

The decay dynamics of perylene dye molecules encapsulated in polymer nanofibers produced by electrospinning of polymethyl methacrylate are investigated using a confocal fluorescence lifetime imaging microscopy technique. Time-resolved experiments show that the fluorescence lifetime of perylene dye molecules is enhanced when the dye molecules are encapsulated in a threedimensional photonic environment. It is hard to produce a sustainable host with exactly the same dimensions all the time during fabrication to accommodate dye molecules for enhancement of spontaneous emission rate. The electrospinning method allows us to have a control over fiber diameter. It is observed that the wavelength of monomer excitation of perylene dye molecules is too short to cause enhancement within nanofiber photonic environment of 330 nm diameters. However, when these nanofibers are doped with more concentrated perylene, in addition to monomer excitation, an excimer excitation is generated. This causes observation of the Purcell effect in the threedimensional nanocylindrical photonic fiber geometry.

The advent of controlled experimental accessibility of Bose-Einstein condensates, as realized with e.g. cold atomic gases, exciton-polaritons, and more recently photons in a dye-filled optical microcavity, has paved the way for new studies and tests of a plethora of fundamental concepts in quantum physics. We here describe recent experiments studying a transition between laser-like dynamics and Bose-Einstein condensation of photons in the dye microcavity system. Further, measurements of the second-order coherence of the photon condensate are presented. In the condensed state we observe photon number fluctuations of order of the total particle number, as understood from effective particle exchange with the photo-excitable dye molecules. The observed intensity fluctuation properties give evidence for Bose-Einstein condensation occurring in the grand-canonical statistical ensemble regime.

We report a time-resolved study of the thermalization dynamics and the lasing to photon Bose-Einstein condensation crossover by in-situ monitoring the photon kinetics in a dye microcavity. When the equilibration of the light to the dye temperature by absorption and re-emission is faster than photon loss in the cavity, the optical spectrum becomes Bose-Einstein distributed and photons accumulate at low-energy states, forming a Bose-Einstein condensate. The thermalization of the photon gas and its evolution from nonequilibrium initial distributions to condensation is monitored in real-time. In contrast, if photons leave the cavity before they thermalize, the system operates as a laser.

The advent of controlled experimental accessibility of Bose-Einstein condensates, as realized with e.g. cold atomic gases, exciton-polaritons, and more recently photons in a dye-filled optical microcavity, has paved the way for new studies and tests of a plethora of fundamental concepts in quantum physics. We here describe recent experiments studying a transition between laser-like dynamics and Bose-Einstein condensation of photons in the dye microcavity system. Further, measurements of the second-order coherence of the photon condensate are presented. In the condensed state we observe photon number fluctuations of order of the total particle number, as understood from effective particle exchange with the photo-excitable dye molecules. The observed intensity fluctuation properties give evidence for Bose-Einstein condensation occurring in the grand-canonical statistical ensemble regime.

We report a time-resolved study of the thermalization dynamics and the lasing to photon Bose-Einstein condensation crossover by in-situ monitoring the photon kinetics in a dye microcavity. When the equilibration of the light to the dye temperature by absorption and re-emission is faster than photon loss in the cavity, the optical spectrum becomes Bose-Einstein distributed and photons accumulate at low-energy states, forming a Bose-Einstein condensate. The thermalization of the photon gas and its evolution from nonequilibrium initial distributions to condensation is monitored in real-time. In contrast, if photons leave the cavity before they thermalize, the system operates as a laser.

Bose-Einstein condensation has in the last two decades been observed in cold atomic gases and in solid-state physics quasiparticles, exciton-polaritons and magnons, respectively. The perhaps most widely known example of a bosonic gas, photons in blackbody radiation, however exhibits no Bose-Einstein condensation, because the particle number is not conserved and at low temperatures the photons disappear in the system's walls instead of massively occupying the cavity ground mode. This is not the case in a small optical cavity, with a low-frequency cutoff imprinting a spectrum of photon energies restricted to values well above the thermal energy. The here reported experiments are based on a microscopic optical cavity filled with dye solution at room temperature. Recent experiments of our group observing Bose-Einstein condensation of photons in such a setup are described. Moreover, we discuss some possible applications of photon condensates to realize quantum manybody states in periodic photonic lattices and photonic Josephson devices.

We report measurements of particle number correlations and fluctuations of a photon Bose-Einstein condensate in a dye microcavity using a Hanbury Brown-Twiss experiment. The photon gas is coupled to a reservoir of molecular excitations, which serve as both heat bath and particle reservoir to realize grand-canonical conditions. For large reservoirs, we observe strong number fluctuations of the order of the total particle number extending deep into the condensed phase. Our results demonstrate that Bose-Einstein condensation under grand-canonical ensemble conditions does not imply second-order coherence.

On-chip high-Q microcavities possess significant potential in terms of integration of optical microresonators into functional optoelectronic devices that could be used in various applications, including biosensors, photonicintegrated circuits, or quantum optics experiments. Yet, despite the convenience of fabricating wafer-scale integrated microresonators with moderate Q values using standard microfabrication techniques, surfacetension-induced microcavities (STIMs), which have atomic-level surface roughness enabling the observation of Q values larger than 10 6 , could only be produced using individual thermal treatment of every single microresonator within the devised area. Here, we demonstrate a facile method for large-scale fabrication of silica STIMs of various morphologies. Q values exceeding 10 6 are readily obtained using this technique. This study represents a significant advancement toward fabrication of wafer-scale optoelectronic circuitries.

This study considers the mathematical analysis framework aimed at the adequate description of the modes of lasers on the threshold of non-attenuated in time light emission. The lasers are viewed as open dielectric resonators equipped with active regions, filled in with gain material. We introduce a generalized complex-frequency eigenvalue problem for such cavities and prove important properties of the spectrum of its eigensolutions. This involves reduction of the problem to the set of the Muller boundary integral equations and their discretization with the Nystrom technique. Embedded into this general framework is the application-oriented lasing eigenvalue problem, where the real emission frequencies and the threshold gain values together form two-component eigenvalues. As an example of on-threshold mode study, we present numerical results related to the two-dimensional laser shaped as an active equilateral triangle with a round piercing hole. It is demonstrated that the threshold of lasing and the directivity of light emission, for each mode, can be efficiently manipulated with the aid of the size and, especially, the placement of the piercing hole, while the frequency of emission remains largely intact.

A formulation for the bilateral distributed amplifier network using a normalized transmission matrix approach is proposed in this letter. The analysis takes into consideration the effect of Cgd in the active device. Our approach is compared to the theoretical predictions for the unilateral case and measured results. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 120–122, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10693

Emission spectra from microdroplets doped with CdSe/ZnS quantum dots (QDs) have been recorded on superhydrophobic coatings (water contact angle > 170). Whispering gallery modes (WGMs) with Q-factors as high as 4.0 Â 10 3 were discernible. Excitation parameters for optimal microdroplet WGM response illumination and acquisition are also presented. Fluorescent QDs provide a robust WGM reporting mechanism under extreme continuous wave microdroplet excitation (465.5 mW) for periods greater than 15 minutes. In this format droplets could be optically tuned on demand using combinations of QDs. Ionic liquid QD-doped droplet emission was found to be spectrally stable: a >75% improvement in WGM blue-shift was recorded (due to droplet evaporation) compared to QD-doped glycerol/water droplet emission. Theoretical analysis of emission spectra confirmed the observed emission response curves correspond to Mie theory suggesting the droplets are extremely close to spherical on the surface. This versatile liquid resonator system has direct implications in high performance room-temperature laser development, telecommunications research and lab-on-a-chip based diagnostics.

Liquid droplets offer a great number of opportunities in biochemical and physical research studies in which droplet-based microlasers have come into play over the past decade. While the recent emergence of droplet lasers has demonstrated their powerful capabilities in amplifying subtle molecular changes inside the cavity, the optical interactions between droplet resonators and an interface remain unclear. We revealed the underlying mechanism of droplet lasers when interacting with a droplet-solid interface and explored its correlation with intermolecular forces. A vertically oriented oscillation mode-arc-like mode-was discovered, where the number of lasing modes and their Q-factors increase with the strength of interfacial hydrophobicity. Both experimental and theoretical results demonstrated that hydrophobicity characterized by contact angle and interfacial tension plays a significant role in the geometry of droplet cavity and laser mode characteristics. Finally, we demonstrated how tiny forces induced by proteins and peptides could strongly modulate the lasing output in droplet resonators. Our findings illustrate the potential of exploiting optical resonators to amplify intermolecular force changes, providing comprehensive insights into lasing actions modulated by interfaces and applications in biophysics.

We demonstrate pulsed, photopumped multimode laser emission in the visible spectral range from cylindrical microcavities formed by conducting polymer thin films deposited around optical fibers. The laser is characterized by narrow emission lines (ϳ1.5 cm Ϫ1), a well-defined excitation threshold, anisotropic emission in both polarization and azimuthal intensity distribution, and high Q(у3000), which leads to a low excitation threshold of order 1 nJ/pulse. We observed two different sets of laser modes; these are waveguided ring modes in the polymer film and whispering gallery modes close to the optical fiber surface. ͓S0163-1829͑97͒53032-3͔ RAPID COMMUNICATIONS

Substantially improved, photopumped polymer lasers are demonstrated using microrings and microdisks of various diameters D ranging from 5 to 200 μm. Various cavity-dependent laser modes were observed, which for D<10 μm were dominated by a single longitudinal mode with linewidth of less than 1 Å. These microlasers were also characterized by Q of order 5000, low threshold excitation energy of order 100 pJ/pulse for pulse duration ranging from 100 ps to sub-μs, and an abrupt increase in the emission directionality and polarization degree. Light emitting diodes with cylindrical geometry, fully compatible with these microlasers are also demonstrated.

We have produced high transmission sub-wavelength tapered optical fibers for the purpose of whispering gallery mode coupling in fused silica microcavities at 780 nm. A detailed analysis of the fiber transmittance evolution during tapering is demonstrated to reflect precisely the mode coupling and cutoff in the fiber. This allows to control the final size, the number of guided modes and their effective index. These results are checked by evanescent wave mapping measurements on the resulting taper.

To introduce a positive Gaussian curvature into a planar sheet of graphene, one cuts a segment with opening angle π/3 from the hexagonal lattice and attaches the open ends to one another. This amounts to introducing a single pentagon into the lattice which acts as a topological defect. To obtain a fullerene C60 molecule, one needs to introduce 12 pentagons. Mathematically, the curvature can be described by two gauge fields: One gauge field is used to describe the curved topology, which can be represented by magnetic monopoles, and the other gauge field is used to describe the mixing of the two sublattices. The topological index of the Dirac operator on the curved manifold can then be calculated using the Euler characteristic of the manifold. The analytical index of the Dirac operator is the difference of the number of its zero energy states at the two Fermi points. The Atiyah-Singer index theorem gives a connection between the topological index and the analytical index: It states th...

have been proposed and demonstrated. Among these alternatives, the WGM microcavities have attracted increasing research attention in recent years due to their low optical losses and tight mode confinement. In such resonators, light wave is guided by continuous total internal reflection (TIR) at the cavity boundary. When the round trip optical path length is equal to an integer number of the light wavelength, constructive interference of light takes place inside the WGM microcavity. WGM lasing from various geometries, including microspheres [13, 14], microrings [15, 16], and microcylinders [17, 18], have been reported. For spherical resonators such as microdroplets, laser emission can be generated by embedding gain materials into such cavity [13], while for the microring cavities, the WGM lasing is obtained by coating a polymer gain layer around the optical fiber [16]. However, the difficulty in manipulation and mechanical fragility largely hinder their practical applications. Obviously, the layered cylindrical microcavity consisting of a fused-silica capillary filled with a high refractive index (RI) liquid might be favorable for WGM lasing in terms of both simpler fabrication and better mechanical stability. Moreover, capillary cavities are easier to be aligned into arrays and readily compatible with microfluidic systems [19]. Besides the high quality performance, laser modulation capability is also required in the application of modern technologies such as tunable optical sources and optical communication. Generally, laser modulation has been realized by adjusting optical cavity size and shape [20, 21], but mechanical control is inaccurate and impractical for real applications. Another possible scheme indicated by the previous studies [22-24] is using coupled asymmetric microcavity via the Vernier effect. Compared with traditional approaches, the capillary cavities can easily integrate Abstract Optically pumped lasing behaviors modulation was realized in a layered cylindrical microcavity dye laser formed by rhodamine 6G-doped quinoline in a capillary. By inserting an optical fiber into the cylindrical microcavity, whispering gallery modes were successfully suppressed and a new kind of waveguide mode lasing was obtained. The lasing characteristics and resonance mechanism of the two configurations were systematically discussed in both experiment and theoretical calculation. Moreover, the time domain and frequency domain finite element methods were performed and found that with the adjustment of the central fiber, the transition of resonant mode from WGMs to waveguide modes can be achieved.

A silica resonator was demonstrated for random laser generation. The resonator consisted of a conventional microsphere fabricated in an optical fiber tip through electric arc discharge, and modifications to its geometry were carried out to create asymmetry inside the silica structure. The resulting Bunimovich stadium-like microsphere promotes multiple reflections with the boundaries, following the stochastic properties of dynamic billiards. The interference of the multiple scattered beams generates a random signal whose intensity was increased by sputter-coating the microstadium with a gold thin film. The random signal is amplified using an erbium-doped fiber amplifier (EDFA) in a ring cavity configuration with feedback, and lasing is identified as temporal and spectral random variations of the signal between consecutive measurements.

The effect of the polarization rotation in bent waveguide on the frequency response of optical ring resonators is theoretically and experimentally investigated. A simple model that fairly well agrees with measured spectral responses is proposed.

Optical technologies are increasingly considered for use in high-performance electronic systems to overcome the performance bottleneck of electrical interconnects when operating at high frequencies and provide high-speed communication between electronic chips and modules. Polymer waveguides are leading candidates for implementing board-level optical interconnections as they exhibit favourable mechanical, thermal and optical properties for direct integration onto conventional printed circuit boards (PCBs). Numerous system demonstrators have been reported in recent years featuring different types of polymer materials and opto-electronic (OE) PCB designs. However, all demonstrated polymer-based interconnection technologies are currently passive, which limits the length of the on-board links and the number of components that can be connected in optical bus architectures. In this paper therefore, we present work towards the formation of low-cost optical waveguide amplifiers that can be readily integrated onto standard PCBs by combining two promising optical technologies: siloxane-based polymers and ultra-fast laser plasma implantation (ULPI). Siloxane-based waveguides exhibit high-temperature resistance in excess of 300°C and low loss at different wavelength ranges, while ULPI has been demonstrated to produce very high dopant concentrations in glass thin films with values of 1.63×10 21 cm −3 recently reported in Er-doped silica layers. Here we present detailed simulation studies that demonstrate the potential to achieve an internal gain of up to 8 dB/cm from such structures and report on initial experimental work on Er-doped films and waveguides demonstrating photoluminescence and good lifetimes.

The results of this study facilitate the selection of the morphology of an optically active material and the corresponding sensing method to be employed in the development of an optical temperature sensor. Sensor Parameter Microsphere Optical Fiber Bulk Glass Relative sensitivity (K-1) 9.

We report experimental results on the characterization of microspherical cavities fabricated in Er3+-doped modified-silica and phos- phate glasses. The spectroscopic properties of the bulk precursor glasses as compared to the obtained microspheres were investigated by photoluminescence spectroscopy and lifetime measurement for the 4I13/2 ! 4 I15/2 transition of Er 3+ ions. In both types of glasses we dem- onstrate whispering gallery mode laser action at various wavelengths around 1550 nm by using a 1480 nm pump laser coupled through a tapered fiber.

We investigated the possibility of using charged luminescent nanoparticles as nanoprobes for studying the evolution scenarios of surface and internal structure of slowly evaporating free (light-absorbing) microdroplets of suspension. Three concentrations (1, 10 and 50 mg/ml) of luminescent nanoparticles were used. Single microdroplets were kept in a linear electrodynamic quadrupole trap and the luminescence was excited with a CW IR laser with an irradiance of ~50 W/mm 2. Since the microdroplet acted as an optical spherical resonance cavity, the interaction of nanoparticles with light both reflected and modified the internal light field mode structure. Depending on the nanoparticle concentration used, it led, among others, to a very significant increase in modulation depth and narrowing of spherical cavity resonance maxima (morphology dependent resonances-MDRs) observed both in luminescence and scattering, the abrupt changes in the ratio between the luminescence and the scattering and the bi-stability in luminescence signal. The observed phenomena could be attributed to the interaction of optical MDRs with nanoparticle lattice shells forming and changing their structure at the microdroplet surface. In this way, the formation and collapse of such lattices could be detected.

A detailed study of the photonic modes in microtube cavity of ~ 7-8 µm outer diameter is presented. We demonstrate a new route to the fabrication of individual microtubes with the maximum length of 200 µm, using a vacuum assisted wetting and filtration through a microchannel glass matrix. The microtubes were studied using micro-photoluminescence spectroscopy and luminescence lifetime imaging confocal microscopy. In the emission spectra of the microresonators we find periodic very narrow peaks corresponding to the whispering gallery modes of two orthogonal polarizations with quality factors upto 3200 at room temperature. In order to identify the peaks in the observed mode structure, we have adopted the boundary-value solution to the problem of scattering of electromagnetic waves by a dielectric microcylinder. A strong enhancement in photoluminescence decay rates at high excitation power suggest the occurrence of amplified spontaneous emission from a single microtube. The evanescent field in these photonic structures extends a couple of micrometers into the surroundings providing the possibility for efficient coupling to an external photonic device.

Special issue on "optimization and application in converged optical and data center networks" Cloud computing services and cloud-based data centers have become an essential part of any IT infrastructure. Network virtualization technology is a key enabler for cloud computing that facilitates the deployment of coexisting heterogeneous and customizable network architectures on the same underlying network, and overcoming the limitations of the existing networks. Optical networks are the prime candidates for interconnecting geographically distributed data centers and resources due to their high speed, huge bandwidth capacity, increased dynamicity and flexibility and control through Generalized Multi-Protocol Label Switching (GMPLS) based protocols. This special issue was well received, and the guest editors received 28 papers from different countries and regions. We are pleased to introduce a collection of eleven papers (acceptance ratio of 39%) covering a range of hot topics in converged optical and data center networks, such as anycast/multicast service oriented Virtual Infrastructure (VI) planning, intra-or inter-data-center VI planning, survivable VI planning, elastic VI planning, software-defined VI planning, and intra-domain or inter-domain VI planning. In terms of inter-data-center VI planning, the paper "Virtual infrastructures as a service enabling converged optical networks and data centres", by J.F. Rierra et al., brings the readers back to the popular topic of "a distributed Enterprise Information System", and achieves the dynamic re-planning of the service with the coordination of Cloud and optical network resource in an optimal way in terms of resource utilization. The paper "A novel dynamic virtual infrastructure planning for converged optical and data center networks under power outage and evolving recovery", by C. Yu et al., integrates traffic grooming with server consolidation to achieve anycast service oriented VI planning. On the other hand, the papers "Planning of survivable cloud-integrated wireless-optical broadband access network against distribution fiber failure" and "Deployment of survivable fiber-wireless access for converged optical and data center networks" focus on planning for survivable VI in cloud-integrated wireless-optical broadband access network.

We investigated the possibility of using charged luminescent nanoparticles as nanoprobes for studying the evolution scenarios of surface and internal structure of slowly evaporating free (light-absorbing) microdroplets of suspension. Three concentrations (1, 10 and 50 mg/ml) of luminescent nanoparticles were used. Single microdroplets were kept in a linear electrodynamic quadrupole trap and the luminescence was excited with a CW IR laser with an irradiance of ~50 W/mm 2. Since the microdroplet acted as an optical spherical resonance cavity, the interaction of nanoparticles with light both reflected and modified the internal light field mode structure. Depending on the nanoparticle concentration used, it led, among others, to a very significant increase in modulation depth and narrowing of spherical cavity resonance maxima (morphology dependent resonances-MDRs) observed both in luminescence and scattering, the abrupt changes in the ratio between the luminescence and the scattering and the bi-stability in luminescence signal. The observed phenomena could be attributed to the interaction of optical MDRs with nanoparticle lattice shells forming and changing their structure at the microdroplet surface. In this way, the formation and collapse of such lattices could be detected.

The ability to confine excitons within monolayers has led to fundamental investigations of nonradiative energy transfer, super-radiance, strong light-matter coupling, high-efficiency light-emitting diodes, and recently lasers in lateral resonator architectures. Vertical cavity surface emitting lasers (VCSELs), in which lasing occurs perpendicular to the device plane, are critical for telecommunications and large-scale photonics integration, however strong optical self-absorption and low fluorescence quantum yields have thus far prevented coherent emission from a monolayer microcavity device. Here we show lasing from a monolayer VCSEL using a single molecule thick film of amphiphilic fluorescent dye, assembled via Langmuir-Blodgett deposition, as the gain layer. Threshold was observed when 5% of the molecules were excited (4.4 μJ/cm(2)). At this level of excitation, the optical gain in the monolayer exceeds 1056 cm(-1). High localization of the excitons in the VCSEL gain layer can en...