Showing papers on "Coupled mode theory published in 2012"
TL;DR: It is found that not only phase matching but also loss matching plays a key role in the coupling process between the fundamental mode and plasmonic mode, which transforms from incomplete coupling to complete coupling with increasing analyte RI.
Abstract: We present and numerically characterize a closed-form multi-core holey fiber based plasmonic sensor. The coupling properties of the specific modes are investigated comprehensively by the finite element method. It is found that not only phase matching but also loss matching plays a key role in the coupling process between the fundamental mode and plasmonic mode. The coupling transforms from incomplete coupling to complete coupling with increasing analyte RI. An average sensitivity of 2929.39nm/RIU in the sensing range 1.33-1.42, and 9231.27nm/RIU in 1.43-1.53 with high linearity is obtained. The dynamic sensing range is the largest among the reported holey fiber based plasmonic sensors, to the best of our knowledge.
214 citations
TL;DR: In this article, a doubly resonant structure can exhibit spectral behavior analogous to electromagnetically induced transparency, as well as superscattering, depending on the excitation.
Abstract: We observe from simulations that a doubly resonant structure can exhibit spectral behavior analogous to electromagnetically induced transparency, as well as superscattering, depending on the excitation. We develop a coupled-mode theory that explains this behavior in terms of the orthogonality of the radiation patterns of the eigenmodes. These results provide insight in the general electromagnetic properties of photonic nanostructures and metamaterials.
185 citations
TL;DR: A governing equation for spectral asymmetry in electromagnetically induced transparency (EIT) is derived from the key parameters of asymmetry factor - namely dark mode quality factor Q(d), and frequency separation between bright and dark mode Δω(bd) = (ω(b) - ω(d)).
Abstract: In this paper, we derive a governing equation for spectral asymmetry in electromagnetically induced transparency (EIT). From the key parameters of asymmetry factor - namely dark mode quality factor Qd, and frequency separation between bright and dark mode Δωbd = (ωb - ωd) -, a logical pathway for the maximization of EIT asymmetry is identified. By taking the plasmonic metal-insulator-metal (MIM) waveguide as a platform, a plasmon-induced transparency (PIT) structure of tunable frequency separation Δωbd and dark mode quality factor Qd is suggested and analyzed. Compared to previous works on MIM-based plasmon modulators, an order of increase in the performance Fig. (12dB contrast at ~60% throughput) was achieved from the highly asymmetric, narrowband PIT spectra.
168 citations
TL;DR: A novel hybrid plasmonic waveguide consisting of two identical dielectric nanowires symmetrically placed on each side of a thin metal film is presented, which could enable various applications such as nanophotonic waveguides, high-quality nanolasers, and optical trapping and transportation of nanoparticles and biomolecules.
Abstract: It is well-known that, a dielectric cylinder on a metal surface offers the advantage of not yielding singular field, which would effectively reduce the propagation loss as opposed to a rectangle-shaped waveguide on a metal surface. In this article, a novel hybrid plasmonic waveguide consisting of two identical dielectric nanowires symmetrically placed on each side of a thin metal film is presented. With the strong interaction between the dielectric cylindrical waveguide mode and long-range surface plasmon polaritons (LRSPP) mode of a thin metal film, deep-subwavelength mode confinement can be achieved. Compared with the hybrid plasmonic mode guided in only one dielectric nanowire above a metal film, a much larger propagation length as well as improved figure of merit (FoM) can be simultaneously realized. A typical propagation length is 434 μm, and optical field is confined into an ultra-small area of approximately 0.0096 μm at 1.55 μm. This structure could enable various applications such as nanophotonic waveguides, high-quality nanolasers, and optical trapping and transportation of nanoparticles and biomolecules.
97 citations
TL;DR: An all-optical analog to electromagnetically induced transparency (EIT) on chip is experimentally demonstrated using coupled high-Q silica microtoroid cavities with Q-factors above 10(6) to control the transmission spectrum.
Abstract: We experimentally demonstrate an all-optical analog to electromagnetically induced transparency (EIT) on chip using coupled high-Q silica microtoroid cavities with Q-factors above 106. The transmission spectrum of the all-optical analog to EIT is precisely controlled by tuning the distance between the two microtoroids, as well as the detunings of the resonance frequencies of the two cavities.
75 citations
TL;DR: The threshold optical intensity of BS and SP is derived from the coupled mode theory and a linear stability analysis method and it is shown that, SP occurs only if the carrier lifetime ranges from several ps to several-hundred ps and the input light intensity is higher than 10⁶W/cm².
Abstract: Bistability (BS) and self-pulsation (SP) phenomena in silicon microring resonators (MRR) with intense CW light injection are studied. Several nonlinear optical effects including Kerr effect, two-photon absorption, free carrier absorption and free carrier dispersion are taken into account. The threshold optical intensity of BS and SP is derived from the coupled mode theory and a linear stability analysis method. The influences of MRR's parameters (carrier lifetime, linear loss and radius) and light injection conditions (input power, wavelength detuning) on the characteristics of SP (modulation depth and oscillating frequency) are analyzed and discussed. It is shown that, SP occurs only if the carrier lifetime ranges from several ps to several-hundred ps and the input light intensity is higher than 10⁶W/cm². The modulation depth of SP can be as large as 8dB and the associated oscillating frequency is in the range from several GHz to beyond 10 GHz.
68 citations
TL;DR: In this paper, a temporal coupled-mode theory was developed to describe the interaction of plane wave with an individual scatterer having an arbitrary shape, which involves the expansion of the fields on cylindrical or spherical wave basis for the two-dimensional and three-dimensional cases, respectively.
Abstract: We develop a temporal coupled-mode theory to describe the interaction of plane wave with an individual scatterer having an arbitrary shape. The theory involves the expansion of the fields on cylindrical or spherical wave basis for the two-dimensional and three-dimensional cases, respectively, and describes the scattering process in terms of a background scattering matrix and the resonant radiation coefficients into different cylindrical or spherical wave channels. This theory provides a general formula for the scattering and absorption cross sections. We show that for a subwavelength asymmetric scatterer with a single resonance, the scattering and absorption cross sections can exceed the single-resonance limit for some specific incident angles of illumination, but the sum of these cross sections over all angles has an upper limit. We validate the theory with numerical simulations of a metallic scatterer that does not have any rotation symmetry.
62 citations
TL;DR: By directly simulating Maxwell's equations via the finite-difference time-domain (FDTD) method, the possibility of achieving high-efficiency second harmonic generation in a structure consisting of a microscale doubly-resonant ring resonator side-coupled to two adjacent waveguides is demonstrated.
Abstract: By directly simulating Maxwell’s equations via the finite-difference time-domain (FDTD) method, we numerically demonstrate the possibility of achieving high-efficiency second harmonic generation (SHG) in a structure consisting of a microscale doubly-resonant ring resonator side-coupled to two adjacent waveguides. We find that ≳ 94% conversion efficiency can be attained at telecom wavelengths, for incident powers in the milliwatts, and for reasonably large bandwidths (Q ∼ 1000s). We demonstrate that in this high efficiency regime, the system also exhibits limit-cycle or bistable behavior for light incident above a threshold power. Our numerical results agree to within a few percent with the predictions of a simple but rigorous coupled-mode theory framework.
62 citations
TL;DR: A dedicated 3D numerical model based on coupled mode theory and solving the rate equations has been developed to analyse, design and optimize an optical amplifier obtained by using a tapered fiber and a Er³⁺-doped chalcogenide microsphere.
Abstract: A dedicated 3D numerical model based on coupled mode theory and solving the rate equations has been developed to analyse, design and optimize an optical amplifier obtained by using a tapered fiber and a Er³⁺-doped chalcogenide microsphere. The simulation model takes into account the main transitions among the erbium energy levels, the amplified spontaneous emission and the most important secondary transitions pertaining to the ion-ion interactions. The taper angle of the optical fiber and the fiber-microsphere gap have been designed to efficiently inject into the microsphere both the pump and the signal beams and to improve their spatial overlapping with the rare earth doped region. In order to reduce the computational time, a detailed investigation of the amplifier performance has been carried out by changing the number of sectors in which the doped area is partitioned. The simulation results highlight that this scheme could be useful to develop high efficiency and compact mid-infrared amplifiers.
46 citations
TL;DR: In this paper, the even and odd modes in a line-defect photonic crystal waveguide are coupled using group theory analysis, rather than by trial-error optimisation of the design parameters.
Abstract: We demonstrate dispersion tailoring by coupling the even and the odd modes in a line-defect photonic crystal waveguide. Coupling is determined ab-initio using group theory analysis, rather than by trial-error optimisation of the design parameters. A family of dispersion curves is generated by controlling a single geometrical parameter. This concept is demonstrated experimentally with very good agreement with theory.
46 citations
TL;DR: In this paper, the authors present analytical descriptions of the behavior of weakly-guiding/weakly-coupled mode-selective fiber couplers, based on coupled-mode theory.
Abstract: This paper presents analytical descriptions of the behavior of weakly-guiding/weakly-coupled mode-selective fiber couplers, based on coupled-mode theory. Mode-selective couplers rely on the phase-matching of a higher-order mode in one fiber with the fundamental mode of a second, closely-positioned fiber. Their behavior is shown to be highly-dependent on the principle and azimuthal mode numbers of the higher-order mode, as well as its spatial-orientation. Zero coupling is shown to be possible for an asymmetric higher-order mode even when there is perfect phase-matching. The theory is also numerically simulated, and could assist in the future design of efficient mode-selective couplers for a wide range of optical communications and sensor systems.
TL;DR: The calculation on realistic metal-dielectric multilayer structures indicates that the predicted giant optical forces are achievable in experiments, which will open the door for various optomechanical applications in nanoscale, such as optical nanoelectromechanical systems, optical sensors and actuators.
Abstract: Here we demonstrate that giant transverse optical forces can be generated in nanoscale slot waveguides of hyperbolic metamaterials, with more than two orders of magnitude stronger compared to the force created in conventional silicon slot waveguides, due to the nanoscale optical field enhancement and the extreme optical energy compression within the air slot region. Both numerical simulation and analytical treatment are carried out to study the dependence of the optical forces on the waveguide geometries and the metamaterial permittivity tensors, including the attractive optical forces for the symmetric modes and the repulsive optical forces for the anti-symmetric modes. The significantly enhanced transverse optical forces result from the strong optical mode coupling strength between two metamaterial waveguides, which can be explained with an explicit relation derived from the coupled mode theory. Moreover, the calculation on realistic metal-dielectric multilayer structures indicates that the predicted giant optical forces are achievable in experiments, which will open the door for various optomechanical applications in nanoscale, such as optical nanoelectromechanical systems, optical sensors and actuators.
TL;DR: In this article, a broadband silicon Mach-Zehnder switch (MZS) is proposed for wavelength division multiplexing applications on photonic networks on chip. But the phase shift is achieved via a p-i-n diode.
Abstract: In this paper, we propose a broadband silicon Mach-Zehnder switch (MZS) for wavelength division multiplexing applications on photonic networks on chip. The proposed reconfigurable switch is based on a single-stage three-waveguide interferometric configuration in which the phase shift is achieved via a p-i-n diode. The device is analyzed by the coupled-mode theory and by the finite-difference beam propagation method. The proposed configuration leads to a considerable increase in the bandwidth with respect to the conventional MZS. For example, the two-waveguide MZS with a gap g=0.30 μm between the two coupled waveguides exhibits bandwidth Δλ = 60 nm, crosstalk CT = - 15 dB, and insertion loss IL = 1.1 dB. Conversely, a bandwidth Δλ = 115 nm is achieved for the three-waveguide configuration to parity of the other parameters.
TL;DR: Computer-generated planar holograms are used to mimic the shaped pulses used to speed up adiabatic passage in quantum systems based on the transitionless quantum driving algorithm and show reduced device length using the shortcut scheme as compared to the common adiABatic scheme.
Abstract: A shortcut to adiabatic mode conversion in multimode waveguides using optical analogy of stimulated Raman adiabatic passage is investigated. The design of mode converters using the shortcut scheme is discussed. Computer-generated planar holograms are used to mimic the shaped pulses used to speed up adiabatic passage in quantum systems based on the transitionless quantum driving algorithm. The mode coupling properties are analyzed using the coupled mode theory and beam propagation simulations. We show reduced device length using the shortcut scheme as compared to the common adiabatic scheme. Modal evolution in the shortened device indeed follows the adiabatic eigenmode exactly amid the violation of adiabatic criterion.
TL;DR: In this paper, the feasibility of using ring resonators as solid-state angular rate sensors (gyroscopes) based on the Sagnac effect is assessed, and an extensive analysis of the optimal values of resonator length, coupling, and detuning is carried out, for the drop port of a double-bus ring, and for an all-pass, single bus ring, for different values of propagation losses, consistent with different available technologies.
Abstract: Semiconductor ring resonators as the core components of instruments and devices have found applications in the areas of telecommunications and sensors. In this study, the feasibility of using ring resonators as solid-state angular rate sensors (gyroscopes) based on the Sagnac effect is assessed, and an extensive analysis of the optimal values of resonator length, coupling, and detuning is carried out, for the drop port of a double-bus ring, and for an all-pass, single-bus ring, for different values of propagation losses, consistent with different available technologies. We show that for both the all-pass and the drop-port configurations, optimally undercoupled rings show larger extinction ratios and, thus, better resolutions than critically coupled rings of the same length, contrary to our initial intuitive assumption that critically coupled rings should offer the best resolutions. Our analysis also shows that the ring resonator gyroscopes require a technology-constrained optimization, with the propagation loss as the main factor that hinders the resolution, and that determines the optimum values of all other parameters, namely length, coupling, and resonance detuning. According to our model, standard-chip-sized racetrack gyroscopes are suitable for rate- and tactical-grade applications for selected, currently feasible low propagation loss waveguides.
TL;DR: In this paper, the authors proposed an approach for enhancing the absorption of thin-film amorphous silicon solar cells using periodic arrangements of resonant dielectric nanospheres deposited as a continuous film on top of a thin planar cell.
Abstract: We propose an approach for enhancing the absorption of thin-film amorphous silicon solar cells using periodic arrangements of resonant dielectric nanospheres deposited as a continuous film on top of a thin planar cell. We numerically demonstrate this enhancement using three dimensional (3D) full field, finite difference time domain simulations and 3D finite element device physics simulations of a nanosphere array above a thin-film amorphous silicon solar cell structure featuring back reflector and anti-reflection coating. In addition, we use the full field finite difference time domain results as input to finite element device physics simulations to demonstrate that the enhanced absorption contributes to the current extracted from the device. We study the influence of a multi-sized array of spheres, compare spheres and domes, and propose an analytical model based on the temporal coupled mode theory.
TL;DR: The analyses of surface plasmon polaritons (SPPs) coupling induced interference in metal/dielectric (M/D) multilayer metamaterials and techniques to improve the performance of sub-wavelength Plasmonic lithography are presented.
Abstract: We present the analyses of surface plasmon polaritons (SPPs) coupling induced interference in metal/dielectric (M/D) multilayer metamaterials and techniques to improve the performance of sub-wavelength plasmonic lithography. Expressions of beam spreading angles and interference patterns are derived from analyses of numerical simulations and the coupled mode theory. The new understandings provide useful guidelines and design criteria for plasmonic lithography. With proper layer structure design, sub-wavelength uniform periodic patterns with feature size of 1/12 of the mask's period can be realized. High pattern contrast of 0.8 and large field depth of 80 nm are also demonstrated numerically by considering the SPPs coupling in the photoresist. Both high contrast and large image depth are crucial for practical application of plasmonic lithography.
TL;DR: A coupled-mode theory is developed that explains how a doubly resonant structure can exhibit spectral behavior analogous to electromagnetically induced transparency, as well as superscattering, depending on the excitation, which provides insight in the general electromagnetic properties of photonic nanostructures and metamaterials.
Abstract: We observe from simulations that a doubly resonant structure can exhibit spectral behavior analogous to
electromagnetically induced transparency, as well as superscattering, depending on the excitation. We develop a
coupled-mode theory that explains this behavior in terms of the orthogonality of the radiation patterns of the
eigenmodes. These results provide insight in the general electromagnetic properties of photonic nanostructures and
metamaterials.
TL;DR: Three-dimensional finite-difference time-domain (FDTD) simulations reveal that up to 60% vertical emission efficiency is possible in a structure only four wavelengths long with a 3 dB bandwidth of over 300 nm.
Abstract: Herein we propose, theoretically investigate, and numerically demonstrate a compact design for a vertical emitter at a wavelength of 1.5 μm based on nanophotonic aperture antennas coupled to a dielectric waveguide. The structure utilizes a plasmonic antenna placed above a Si3N4 waveguide with a ground plane for breaking the up—down symmetry and increasing the emission efficiency. Three-dimensional (3-D) finite-difference time-domain (FDTD) simulations reveal that up to 60% vertical emission efficiency is possible in a structure only four wavelengths long with a 3 dB bandwidth of over 300 nm.
TL;DR: In this paper, a set of coupled-mode equations for describing three-wave mixing in a metamaterial, using Bloch modes as the basis, were developed, and closed-form expressions for the macroscopic nonlinear susceptibilities were derived.
Abstract: Artificially structured metamaterials hybridized with elements that respond nonlinearly to incident electromagnetic fields can, from a macroscopic perspective, support nonlinear responses that cannot be described by purely electric or magnetic interactions. To investigate the mechanisms and behaviors of such interactions, termed nonlinear magnetoelectric coupling, we develop a set of coupled-mode equations for describing three-wave mixing in a metamaterial, using Bloch modes as the basis. By equating these coupled-mode equations to those of a homogenized system, we derive closed-form expressions for the macroscopic nonlinear susceptibilities. From these expressions, a great deal can be inferred about the nature and construction of magnetoelectric nonlinearities in metamaterials. As an example, we apply this method in the analysis of a prototypical nonlinear magnetoelectric metamaterial. In particular, we show that independent control of the eight second-order susceptibility tensors encompasses a massive parameter space from which new realms of nonlinear interference and wave manipulation can be accessed.
TL;DR: The demonstrated planar-type achromatic beam splitter opens new opportunities for the realization of ultra-high bandwidth on-chip photonic devices.
Abstract: We introduce a novel achromatic and robust scheme for n-fold multiple beam splitting based on adiabatic light transfer in a planar geometry of coupled waveguides (WGs). The concept is experimentally verified for a one-to-three beam splitter by using a reconfigurable light-induced WG structure at two operating wavelengths. The demonstrated planar-type achromatic beam splitter opens new opportunities for the realization of ultra-high bandwidth on-chip photonic devices.
TL;DR: In this paper, the authors demonstrate far-field optimized H1 photonic crystal membrane cavities combined with an additional back reflection mirror below the membrane that meet the optical requirements for implementing hybrid quantum information protocols.
Abstract: Hybrid quantum information protocols are based on local qubits, such as trapped atoms, NV centers, and quantum dots, coupled to photons. The coupling is achieved through optical cavities. Here we demonstrate far-field optimized H1 photonic crystal membrane cavities combined with an additional back reflection mirror below the membrane that meet the optical requirements for implementing hybrid quantum information protocols. Using numerical optimization we find that 80% of the light can be radiated within an objective numerical aperture of 0.8, and the coupling to a single-mode fiber can be as high as 92%. We experimentally prove the unique external mode matching properties by resonant reflection spectroscopy with a cavity mode visibility above 50%.
TL;DR: The numerical characterization of strong gratings, the design of high-Q tapered grating-defect resonators, and the control of inter-resonator coupling for CROWs are demonstrated.
Abstract: We present a systematic design of coupled-resonator optical waveguides (CROWs) based on high-Q tapered grating-defect resonators. The formalism is based on coupled-mode theory where forward and backward waveguide modes are coupled by the grating. Although applied to strong gratings (periodic air holes in single-mode silicon-on-insulator waveguides), coupled-mode theory is shown to be valid, since the spatial Fourier transform of the resonant mode is engineered to minimize the coupling to radiation modes and thus the propagation loss. We demonstrate the numerical characterization of strong gratings, the design of high-Q tapered grating-defect resonators (Q>2 × 10^6, modal volume = 0.38•(λ/n)^3), and the control of inter-resonator coupling for CROWs. Furthermore, we design Butterworth and Bessel filters by tailoring the numbers of holes between adjacent defects. We show with numerical simulation that Butterworth CROWs are more tolerant against fabrication disorder than CROWs with uniform coupling coefficient.
TL;DR: A novel fiber-optic bending sensor based upon the propagation of LP21 mode, which incorporates inexpensive single-mode fiber at 650 nm for few-mode operation, enabling low-loss transmission and compatibility with existing interfaces is demonstrated.
Abstract: A novel fiber-optic bending sensor based upon the propagation of LP21 mode is demonstrated. The sensor, comprised of an S-bend fiber on an elastic film, measures LP21 mode specklegram rotation, which increments linearly with bending angle by the stress-optic effect. The sensor is capable of experimentally achieving a sensitivity as high as 4.13 rad/m(-1). The theoretical analysis of the sensor, which is a combination of fiber coupled-mode theory and elastic-optic theory, validates the accuracy of the sensor. The sensor is also shown to be temperature-immune, and can detect both bending direction and bending angle with a large dynamic range. Furthermore, the sensor implementation incorporates inexpensive single-mode fiber at 650 nm for few-mode operation, enabling low-loss transmission and compatibility with existing interfaces.
TL;DR: A general method is presented to determine the coupling coefficients of lateral gratings in terms of the coupled-mode theory, which demonstrates that large coupling strengths are obtained in the presence of corrugated metal layers.
Abstract: We report on terahertz quantum-cascade lasers (THz QCLs) based on first-order lateral distributed-feedback (lDFB) gratings, which exhibit continuous-wave operation, high output powers (>8 mW), and single-mode emission at 3.3–3.4 THz. A general method is presented to determine the coupling coefficients of lateral gratings in terms of the coupled-mode theory, which demonstrates that large coupling strengths are obtained in the presence of corrugated metal layers. The experimental spectra are in agreement with simulations of the lDFB cavities, which take into account the reflective end facets.
TL;DR: Ultraviolet single-frequency lasing is realized in a coupled optofluidic ring resonator (COFRR) dye laser that consists of a thin-walled capillary microfluidicRing resonator and a cylindrical resonator.
Abstract: Ultraviolet single-frequency lasing is realized in a coupled optofluidic ring resonator (COFRR) dye laser that consists of a thin-walled capillary microfluidic ring resonator and a cylindrical resonator. The whispering gallery modes (WGMs) in each resonator couple to each other and generate single-frequency laser emission. Single-frequency lasing occurs at 386.75 nm with a pump threshold of 5.9 μJ/mm2. The side-mode-suppression ratio (SMSR) is about 20 dB. Moreover, the laser emits mainly in two directions, and each of them has a divergence of only 10.5°.
TL;DR: In this paper, a two-dimensional circular photonic crystal ring resonator (PCRR)-based add-drop filter (ADF) is designed for ITU-T G.694 eight-channel coarse wavelength division multiplexing systems.
Abstract: A two-dimensional circular photonic crystal ring resonator (PCRR)-based add-drop filter (ADF) is designed for ITU-T G.694.2 eight-channel coarse wavelength division multiplexing systems. The resonant wavelength and pass-band width of the ADF are 1491 and 13 nm, respectively. Close to 100% of coupling and dropping efficiencies and a 114.69 quality factor are observed through simulation. Then the coupled mode theory (CMT) analysis of circular PCRR-based ADF is attempted to compare obtained CMT response into simulated finite difference time domain method response. The overall size of the device is much smaller; that is, 11.4×11.4 μm, which is highly suitable for photonic integrated circuits and all optical photonic network applications.
TL;DR: Far-field measurements of L3 photonic crystal (PhC) cavities with high quality beaming by means of the so-called "band folding" technique, which further validate the "folding" technique on L3 cavities for nanocavity realization with efficient free-space coupling and high Q factors.
Abstract: We report on far-field measurements of L3 photonic crystal (PhC) cavities with high quality beaming. This is achieved by means of the so-called “band folding” technique, in which a modulation of the radius of specific holes surrounding the cavity is introduced. Far-field patterns are measured from photoluminescence of quantum wells embedded in the PhC. A very good agreement between experimental results and simulated radiation patterns has been found. Laser effect is demonstrated in the beaming cavity with a threshold comparable to the regular one. In addition, free-space input coupling to this cavity has been achieved. In order to fully analyze the coupling efficiency, we generalize the approach developed in S. Fan, et al., [J. Opt. Soc. Am. A 20, 569 (2003)], relaxing the hypothesis of mirror symmetry. The obtained coupling efficiencies are about 15% with quality factors (Q) exceeding 104. These results further validate the “folding” technique on L3 cavities for nanocavity realization with efficient free-space coupling and high Q factors.
TL;DR: A wavelength converter composed of a metallic finite 2-dimensional particle grating on top of an optical waveguide that sustained plasmonic resonances will result in the near-field enhancement and therefore, high conversion efficiency.
Abstract: The paper introduces a wavelength converter composed of a metallic finite 2-dimensional particle grating on top of an optical waveguide. The particles sustain plasmonic resonances which will result in the near-field enhancement and therefore, high conversion efficiency. Due to near-field interaction of the grating field with the propagating modes of the waveguide, the generated third harmonic wave is phase-matched to a propagating mode of the waveguide, while the fundamental frequency component is not coupled into the output waveguide of the structure. The performance of this structure is numerically investigated using a full-wave transmission line method for the linear analysis and a three-dimensional finite-difference time-domain method for the nonlinear analysis.
TL;DR: Different strategies for designing optical couplers, optimized to enhance the pump absorption in the rare-earth-doped core of microstructured fiber lasers, are illustrated.
Abstract: Different strategies for designing optical couplers, optimized to enhance the pump absorption in the rare-earth-doped core of microstructured fiber lasers, are illustrated. Three kinds/configurations of optical couplers have been designed and compared as examples of the different design strategies which can be followed. Their effectiveness to enhance the performance of an ytterbium-doped, double cladding, microstructured optical fiber laser has been accurately simulated. They consist of a suitable cascade of multiple long-period gratings (MLPGs) inscribed in the fiber core region. The characteristics of the MLPG couplers have been simulated via a homemade computer code based on both rate equations and an extended coupled mode theory. The proposed MLPG couplers seem particularly useful in the case of low rare-earth concentration but, even for a middle-high ytterbium concentration, as NYb=5×1025 ions/m3, the slope efficiency S can be increased up to 20%, depending on the fiber length.