Showing papers in "Journal of The Optical Society of America B-optical Physics in 2009"
TL;DR: In this paper, an ultracompact all-optical photonic crystal AND gate based on nonlinear ring resonators was proposed, which can operate with a bit rate of about 120 Gbits/s.
Abstract: We have proposed an ultracompact all-optical photonic crystal AND gate based on nonlinear ring resonators, consisting of two Kerr nonlinear photonic crystal ring resonators inserted between three parallel line defects. We have employed a Si nanocrystal as the nonlinear material for its appropriate nonlinear properties. The gate has been simulated and analyzed by finite difference time domain and plane wave expansion methods. The proposed logic gate can operate with a bit rate of about 120 Gbits/s.
193 citations
TL;DR: In this paper, the authors proposed a design tool for dielectric optical resonator-based biochemical refractometry sensors to evaluate the functional dependence of S* on device parameters, such as resonant cavity quality factor (Q), extinction ratio, system noise, and light source spectral bandwidth, using a Lorentzian peak fitting algorithm and Monte Carlo simulations.
Abstract: We propose a design tool for dielectric optical resonator-based biochemical refractometry sensors. Analogous to the widely accepted photodetector figure of merit, the detectivity D*, we introduce a new sensor system figure of merit, the time-normalized sensitivity S*, to permit quantitative, cross-technology-platform comparison between resonator sensors with distinctive device designs and interrogation configurations. The functional dependence of S* on device parameters, such as resonant cavity quality factor (Q), extinction ratio, system noise, and light source spectral bandwidth, is evaluated by using a Lorentzian peak fitting algorithm and Monte Carlo simulations to provide theoretical insights and useful design guidelines for optical resonator sensors. Importantly, we find that S* critically depends on the cavity Q factor, and we develop a method of optimizing sensor resolution and sensitivity to noise as a function of cavity Q factor. Finally, we compare the simulation predictions of sensor wavelength resolution with experimental results obtained in Ge17Sb12S71 resonators, and good agreement is confirmed.
187 citations
TL;DR: In this paper, a compact analytical formula up to the order of k3, where k is a wave vector, is derived for the depolarization field Ed of a spheroidal particle by performing explicitly the steps of the recipe outlined by Meier and Wokaun.
Abstract: A compact analytical formula up to the order of k3, where k is a wave vector, is derived for the depolarization field Ed of a spheroidal particle by performing explicitly the steps of the recipe outlined by Meier and Wokaun [Opt. Lett.8, 581 (1983)]. For the static component of Ed a general electrostatic formula valid for a particle of a general shape is rederived within the Meier and Wokaun framework. The dynamic k2-dependent depolarization component of Ed is shown to depend on dynamic geometrical factors, which can be expressed in terms of the standard geometrical factors of electrostatics. The Meier and Wokaun recipe itself is shown to be equivalent to a long-wavelength limit of the Green's function technique. The resulting Meier and Wokaun long-wavelength approximation is found to exhibit a redshift compared against exact T-matrix results. At least for a sphere, it is possible to get rid of the redshift by assuming a weak nonuniformity of the field Eint inside a particle, which can be fully accounted for by a renormalization of the dynamic geometrical factors. My results may be relevant for various plasmonic, or nanoantenna, applications of spheroidal particles with a dominant electric dipole scattering, whenever it is necessary to go beyond the Rayleigh approximation and to capture the essential size-dependent features of scattering, local fields, SERS, hyper-Raman and second-harmonic-generation enhancements, decay rates, and photophysics of dipolar arrays.
163 citations
TL;DR: In this paper, the authors demonstrate undistorted THz pulse propagation via the single TE1 mode, solving the group-velocity dispersion and spectral-filtering problems caused by the mode's low-frequency cutoff.
Abstract: We experimentally and theoretically investigate the lowest-order transverse-electric (TE1) mode of the parallel-plate waveguide (PPWG) for the propagation of broadband THz pulses. We demonstrate undistorted THz pulse propagation via the single TE1 mode, solving the group-velocity-dispersion and spectral-filtering problems caused by the mode's low-frequency cutoff. We observe a remarkable counterintuitive property of the TE1 mode: its attenuation decreases with increasing frequency for all frequencies above cutoff. This phenomenon has not been observed with any other THz waveguide to date, and it can enable extremely low-loss propagation. We present a physical interpretation of this frequency-dependent behavior using a simple plane-wave description of the TE1 mode propagation. We also find that it is possible to achieve almost 100% coupling to the TE1 mode from a focused free-space Gaussian beam. In addition, using the above plane-wave analysis, we show how to mitigate the diffraction losses inherent to long path-length PPWGs via the use of transverse-concave plates.
155 citations
TL;DR: In this article, the sizeable crystals of RbBe2(BO3)F2 (RBBF) were obtained by the flux method and the crystal structure was determined by x-ray data and the space group was proven to be R32.
Abstract: Sizeable crystals of RbBe2(BO3)F2 (RBBF) were obtained by the flux method. The crystal structure was determined by x-ray data and the space group was proven to be R32, belonging to the uniaxial class. The linear and nonlinear optical parameters, including the cutoff wavelength, refractive indices, phase-matching angles, and effective nonlinear optical coefficients were determined for the first time to our knowledge, and then the Sellmeier equations were also constructed. By using an RBBF prism coupling device (PCD), tunable fourth-harmonic output from a Ti:sapphire laser and the sixth harmonic of an Nd-based laser were also obtained with relatively high power.
151 citations
TL;DR: In this paper, a review of the applicability of THz reflection spectroscopy in the identification of dangerous liquids is presented, and the knowledge of the dielectric function of aqueous mixtures can be used for inspection of liquids inside bottles.
Abstract: Terahertz (THz) radiation interacts strongly with the intermolecular hydrogen-bond network in aqueous liquids. The dielectric properties of liquid water and aqueous solutions in the THz spectral region are closely linked to the microscopic dynamics of the liquid solution, and hence THz spectroscopy offers an important insight into fundamental intermolecular interactions in polar liquids. At the same time, the strong and characteristic interaction between THz radiation and liquids offers a methodology for the classification of liquids inside containers, and hence the THz region is suitable for remote detection of some of the properties of bottled liquids. Here we present a review of THz spectroscopy and modeling of water-ethanol mixtures, and establish a link between the dielectric function of water-ethanol mixtures and some of their thermodynamic properties. We then review how the knowledge of the dielectric function of aqueous mixtures can be used for inspection of liquids inside bottles. Finally we draw up some of the limits to the applicability of THz reflection spectroscopy in the identification of dangerous liquids.
139 citations
TL;DR: In this article, the upconversion (UC) luminescence excited with 1.53 μm cw Er fiber laser is investigated in a wide spectral domain [from the near-infrared (NIR) to UV].
Abstract: Optical spectra of Er-doped modified ZBLAN glasses are studied at room temperature. Radiative quantum yields of the 4I11/2 and 4I13/2 levels are estimated from the experimentally measured lifetimes and from the spontaneous emission probabilities calculated from the Judd-Ofelt theory. The spectra of upconversion (UC) luminescence excited with 1.53 μm cw Er fiber laser are investigated in a wide spectral domain [from the near-infrared (NIR) to UV]. Absolute UC efficiency (i.e., the ratio of UC luminescence power to the absorbed pump power) is experimentally measured; efficiency of up to 12.7% is obtained. A conclusion is made about perspectives of use of the studied glasses as upconverter material for solar cells of enhanced efficiency.
138 citations
TL;DR: In this paper, a systematic study of Bloch surface wave (BSW) properties and applications in diffraction-based biosensors is presented, in which polarization and 1DPC termination effects are simply described.
Abstract: A systematic study of Bloch surface wave (BSW) properties and applications in diffraction-based biosensors is presented. The design of such devices starts with the calculation of the BSW dispersion relation for a semi-infinite one-dimensional photonic crystal. We propose an approach in which polarization and 1DPC termination effects are simply described. Since in a realistic device the number of periods is limited, we investigate the issues arising from finite size effects and the choice of a structure substrate. Diffraction efficiency is studied as a function index contrast, multilayer termination, grating thickness, and number of periods. Numerical examples for Si/SiO2 and a-Si1−xNx:H periodic dielectric stacks are presented, showing that BSW can be exploited for the realization of efficient diffraction-based biosensors from the infrared to the visible range.
118 citations
TL;DR: In this paper, the dynamics of carrier cooling in GaAs and impact ionization in InSb were monitored using THz-pump/THz probe spectroscopy, which provided both sub-bandgap excitation and probing, eliminating any direct optical electron-hole generation that complicates the evaluation of results in optical pump/thz probe experiments.
Abstract: Pumping n-type GaAs and InSb with ultrafast THz pulses having intensities higher than 150 MW/cm2 shows strong free-carrier absorption saturation at temperatures of 300 K and 200 K, respectively. If the energy imparted to the carriers exceeds the bandgap, impact ionization processes can occur. The dynamics of carrier cooling in GaAs and impact ionization in InSb were monitored using THz-pump/THz probe spectroscopy, which provides both sub-bandgap excitation and probing, eliminating any direct optical electron-hole generation that complicates the evaluation of results in optical pump/THz probe experiments.
111 citations
TL;DR: In this paper, a model of an infrared metamaterial absorber composed of metal dendritic resonators, dielectric substrate, and continuous metal film is presented, and numerical simulation confirms an absorptivity of 98.6% at the infrared wavelength of 2.79 μm.
Abstract: We present a model of an infrared metamaterial absorber composed of metal dendritic resonators, dielectric substrate, and continuous metal film. Numerical simulation confirms an absorptivity of 98.6% at the infrared wavelength of 2.79 μm. The proposed metamaterial absorber has an excellence of two-dimensional isotropy, and it could be fabricated with a chemical double-template technique. Our simulation shows it could be operated for a wide range of incident angles. The optical metamaterial absorber proposed in this paper has potential applications such as in infrared imaging devices, thermal bolometers, and wavelength-selective radiators.
105 citations
TL;DR: In this article, the photochemical processes present during free-radical-based holographic grating formation are examined and a kinetic model is presented, which includes, in a more nearly complete and physically realistic way, most of the major photochemical and non-local photopolymerization-driven diffusion effects.
Abstract: The photochemical processes present during free-radical-based holographic grating formation are examined. A kinetic model is presented, which includes, in a more nearly complete and physically realistic way, most of the major photochemical and nonlocal photopolymerization-driven diffusion effects. These effects include: (i) non-steady-state kinetics (ii) spatially and temporally nonlocal polymer chain growth (iii) time varying photon absorption (iv) diffusion controlled viscosity effects (v) multiple termination mechanisms, and (vi) inhibition. The convergence of the predictions of the resulting model is then examined. Comparisons with experimental results are carried out in Part II of this series of papers [J. Opt. Soc. Am. B26, 1746 (2009)].
TL;DR: In this article, a novel generation process of a terahertz (THz) electromagnetic wave via a noncollinear χ(2) process in LiNbO3 with a phase-front-controlled femtosecond Ti:sapphire laser pulse was demonstrated.
Abstract: We demonstrate, to the best of our knowledge, a novel generation process of a terahertz (THz) electromagnetic wave via a noncollinear χ(2) process in LiNbO3 with a phase-front-controlled femtosecond Ti:sapphire laser pulse. Systematic measurements of both the THz electric field and the excitation transmitted through an LiNbO3 crystal at different excitation powers show that the maximum amplitude of the THz electric field increases nonlinearly above the critical input powers. This enhancement of optical rectification efficiency is attributed to the distortion of the excitation pulse shape via electro-optic (EO) phase modulation by the emitted THz wave. Actually, spectral line shapes of both the THz wave and the excitation pulse become broadened above the threshold, and they are well reproduced by numerical simulations with equivalent one-dimensionally mapped coupled equations in the frequency domain. This generation scheme shows potential optimization of further generation efficiency.
TL;DR: In this article, a smooth magnetic dielectric film is covered with a thin noble metal layer perforated with subwavelength slit arrays, which can be used as an efficient tool for surface plasmons detection.
Abstract: We predict a significant enhancement of the magneto-optical transverse Kerr effect when a smooth magnetic dielectric film is covered with a thin noble metal layer perforated with subwavelength slit arrays. The relative intensity change can be as large as 50%. The Kerr effect increase is due to the magnetization-induced change of the phase velocity of the resonantly excited surface plasmons. It can be used as an efficient tool for surface plasmons detection.
TL;DR: In this paper, the authors proposed a technique of doubling optical pulses in both frequency and time domains based on a combination of cross-phase modulation induced by a triangular pump pulse in a nonlinear Kerr medium and subsequent propagation in a dispersive medium.
Abstract: We propose a novel technique of doubling optical pulses in both frequency and time domains based on a combination of cross-phase modulation induced by a triangular pump pulse in a nonlinear Kerr medium and subsequent propagation in a dispersive medium.
TL;DR: In this paper, the effects of magnetic birefringence of liquid crystal E7 on the photonic bandgaps and the transmitting properties in two-dimensional photonic crystal waveguides were investigated by using the plane wave expansion and finite-difference time domain methods.
Abstract: The effects of magnetic birefringence of liquid crystal E7 on the photonic bandgaps and the transmitting properties in two-dimensional photonic crystal waveguides are investigated by using the plane wave expansion and finite-difference time domain methods. Detailed calculations on the shifts and variations in the frequency width of bandgaps reveal that under the control of an external magnetic field the two-dimensional liquid-crystal-filled photonic crystal waveguide can serve as a switch and continuously tunable bandpass filter at the terahertz wave band.
TL;DR: In this article, a simple analytical model for the modification of optical properties of active molecules and other objects when they are placed in the vicinity of metal nanoparticles of subwavelength dimensions is provided.
Abstract: We provide a simple analytical model for the modification of optical properties of active molecules and other objects when they are placed in the vicinity of metal nanoparticles of subwavelength dimensions. Specifically, we study the enhancement of optical radiation, electroluminescence, and photoluminescence absorbed or emitted by these objects. The theory takes into account the radiative decay of the surface plasmon mode supported by the metal nanospheres--a basic phenomenon that has been ignored in electrostatic treatment. Using the example of Ag nanospheres embedded in a GaN dielectric, we show that enhancement for each case depends strongly on the nanoparticle size-enabling optimization for each combination of absorption cross section, original radiative efficiency, and separation between the object and metal sphere. The enhancement effect is most significant for relatively weak and diluted absorbers and rather inefficient emitters that are placed in close proximity to the metal nanoparticles.
TL;DR: In this paper, the application of metallized photonic crystal fibers in surface plasmon resonance sensors of biolayer thickness is demonstrated, where the effective refractive index of the fundamental core mode can be tuned to enable efficient phase matching with a plasmor anywhere from the visible to near IR.
Abstract: The application of metallized photonic crystal fibers in surface plasmon resonance sensors of biolayer thickness is demonstrated. By the judicious design of photonic crystal fibers, the effective refractive index of the fundamental core mode can be tuned to enable efficient phase matching with a plasmon anywhere from the visible to near IR. Among other advantages of the presented sensors we find high sensitivity in the visible and near-IR spectral regions, as well as high coupling efficiency from an external Gaussian beam. Based on the numerical simulations, we present designs using various types of photonic crystal fibers, including holey fibers with and without defect, as well as honeycomb photonic crystal fibers. We find that in addition to the fundamental plasmonic excitation, higher order plasmonic modes can also be excited. In principle, using several plasmonic excitations at the same time can enhance sensor detection limit. Both amplitude and spectral-based methodologies for the detection of changes in the biolayer thickness are discussed. Sensor resolutions of the biolayer thickness as high as 0.039-0.044 nm are demonstrated in the whole 600-920 nm region. Finally, we perform analysis of the effect of imperfections in the metal layer geometry on the sensor sensitivity.
TL;DR: In this article, a three-port waveguide splitter based on multiple-beam interference and the scattering matrix method is proposed to achieve ultra-high integration and relatively easy fabrication, and the transmittance spectra as a function of teeth width, depth, period, and period number are addressed.
Abstract: Tooth-shaped and multiple-teeth-shaped plasmonic filters in the metal-insulator-metal (MIM) waveguides are demonstrated numerically. By introducing a three-port waveguide splitter, a modified model based on multiple-beam interference and the scattering matrix method is given. The transmittance spectra as a function of teeth width, depth, period, and period number are addressed, respectively. The results show that the new structure not only performs the filtering function as well as MIM gratinglike structures, but that it is also of submicrometer size for ultrahigh integration and relatively easy fabrication.
TL;DR: In this article, a single-step melt-quench technique involving selective thermochemical reduction principle was used to synthesize a new reducing glass (dielectric) matrix (mol%) K2O-B2O3-Sb2O 3 (KBS) by using hexagonal Auo nanoparticles having major axes about 9-23 nm.
Abstract: Dichroic Er3+:Au-antimony glass nanocomposites are synthesized in a new reducing glass (dielectric) matrix (mol%) K2O-B2O3-Sb2O3 (KBS) by a single-step melt-quench technique involving selective thermochemical reduction principle. Transmission electron microscopic images reveal hexagonal Auo nanoparticles having major axes about 9-23 nm. Dichroic behavior arises due to hexagonal Auo nanoparticles of aspect ratio 1.2-1.3. Auo nanoparticles of concentration of 0.03 wt%(4.1×1018 atoms/cm3) drastically enhances the intensity (2-5 folds) of both 536 (S3/24-->I15/24, green) and 645 (F9/24-->I15/24, red) nm emission bands of Er3+. Local field enhancement induced by Auo surface plasmon resonance (SPR) and energy transfer from fluorescent Auo-->Er3+ ions are found to be responsible for enhancement while, at very high Au concentration, energy transfer from Er3+-->Auo and optical reabsorption due to Auo SPR result in quenching.
TL;DR: In this paper, a new kinetic model, which includes most of the major photochemical and nonlocal photopolymerization driven diffusion effects, was proposed, and the numerical convergence of these simulations were examined when retaining higher-concentration harmonics.
Abstract: In the first of this series of papers [J. Opt. Soc. Am. B26, 1736 (2009)], a new kinetic model, which includes most of the major photochemical and nonlocal photopolymerization driven diffusion effects, was proposed. Predictions made using the model were presented, and the numerical convergence of these simulations were examined when retaining higher-concentration harmonics. The validity and generality of the model is examined by applying it to fit experimental data for two different types of photopolymer material appearing in the literature. The first of these photopolymer materials involves an acrylamide monomer in a polyvinylalcohol matrix. The second is a more complex photopolymer in an epoxy resin matrix. Using the new model, key material parameters are extracted by numerically fitting experimentally obtained diffraction efficiency growth curves. The growth curves used include data captured both during exposure and post-exposure, allowing examination and analysis of “dark reactions.”
TL;DR: In this article, the authors reported the efficient compact deep-blue laser at 457 nm generation by intracavity frequency doubling of a continuous wave (cw) laser operation of a diode-pumped Nd:YVO4 laser on the 4F3/2→4I9/2 transition at 914 nm.
Abstract: We report the efficient compact deep-blue laser at 457 nm generation by intracavity frequency doubling of a continuous wave (cw) laser operation of a diode-pumped Nd:YVO4 laser on the 4F3/2→4I9/2 transition at 914 nm. An LBO crystal, cut for critical type I phase matching at room temperature is used for second-harmonic generation (SHG) of the laser. At an incident pump power of 38 W, as high as 13.2 W of cw output power at 457 nm is achieved with 15-mm-long LBO. The optical-to-optical conversion efficiency is up to 34.7%, and the power stability in 2 h is better than ±2.68%.
TL;DR: In this article, a detailed experimental and theoretical study of the interaction between a single fluorescent molecule and a dielectric microsphere illuminated by a tightly focused Gaussian beam is presented.
Abstract: Dielectric microspheres illuminated by a tightly focused Gaussian beam can focus light on a tiny spot with subwavelength dimensions along the three directions of space. We report here a detailed experimental and theoretical study of the interaction between a single fluorescent molecule and this peculiar electromagnetic distribution. The microsphere increases the excitation intensity sensed by the molecule up to a factor of 2.2, while at the same time it allows for a collection efficiency of up to 60% by redirecting the light emitted at large incidences toward the optical axis. By combining these two effects, the number of collected fluorescence photons can be increased up to a factor of 5. We quantify the evolution of the excitation and collection contributions with the microsphere dimensions and compare our experimental findings with numerical simulations.
TL;DR: In this article, the field distribution of the azimuthally polarized beam focused by a high-numerical-aperture (NA) objective lens is described by the vectorial diffraction integral, and then the radiation forces on spherical particles with different parameters such as radius and refractive index are calculated by the T-matrix method.
Abstract: Azimuthally polarized beams, focused by a high-numerical-aperture (NA) objective lens, form a hollow intensity distribution near the focus, which is appropriate for trapping low-refractive-index particles, in contrast to common linearly polarized or radially polarized beams. In this paper, the field distribution of the azimuthally polarized beam focused by a high-NA objective is described by the vectorial diffraction integral, and then the radiation forces on spherical particles with different parameters such as radius and refractive index are calculated by the T-matrix method. Numerical results show that the azimuthally polarized beam not only can steadily trap low-refractive-index particles at the focus center but also can trap multiple high-refractive-index particles around the focus center by virtue of the hollow-ring configuration. The range of the sizes of low-refractive-index particles that can be trapped steadily are presented, corresponding to different parameters such as the NA of the objective and the relative refractive index, based on which the NA of the objective can be selected to trap the appropriate size of particles. (C) 2009 Optical Society of America
TL;DR: An analytical model of the influence of the amplified spontaneous emission on the effective lifetime of the excited ions is developed and with this model optimized parameters for the minimization of the lifetime reduction are found.
Abstract: For the thin-disk laser the increased amplification of spontaneous emission for larger disks limits the scalability. An analytical model of the influence of the amplified spontaneous emission on the effective lifetime of the excited ions is developed and with this model optimized parameters for the minimization of the lifetime reduction are found. It is shown that output powers up to the megawatt level are achievable with a single disk, but with disk dimensions far beyond the actual technical limits. The model is also used to evaluate the limits of achievable energy.
TL;DR: In this article, the authors developed a comprehensive simulation model for accurately studying the dynamics in optoelectronic oscillators (OEOs), which includes all of the physical effects in the Yao-Maleki model as well as other physical effects that are needed to calculate important features of the OEO dynamics, such as the impact of the fast response time of the modulator on the phase noise power spectral density.
Abstract: We have developed a comprehensive simulation model for accurately studying the dynamics in optoelectronic oscillators (OEOs) Although the OEO is characterized by three widely separated time scales, our model requires neither long run times nor a large amount of memory storage The model generalizes the Yao-Maleki model and includes all of the physical effects in the Yao-Maleki model as well as other physical effects that are needed to calculate important features of the OEO dynamics, such as the impact of the fast response time of the modulator on the phase noise power spectral density, the fluctuations of the OEO output due to the input noise, the cavity mode competition during the OEO start-up, and temporal amplitude oscillations in steady state We show that the absolute value of the phase noise is 2-3 dB lower than predicted by the Yao-Maleki model The Yao-Maleki model does not take into account amplitude noise suppression due to the fast time response of the modulator, which accounts for this difference We show that a single cavity mode oscillates in the OEO at steady state, and this mode is determined by the noise that is present when the OEO is turned on When the small-signal open-loop gain is higher than 231, we show that the OEO amplitude oscillates in steady state This temporal amplitude oscillation can be suppressed by using a narrow filter Our simulation model, once extended to include flicker (1/f) noise and different amplifier and modulator designs, will enable its users to accurately design OEOs
TL;DR: In this article, the modal properties of hexagonal nanowires with a hexagonal cross-section were studied and compared with those of circular nano-nodes with a single point emitter and axial and radial nanowire heterostructures.
Abstract: Nanowires as an active medium are promising for getting high brightness light emitting diodes. Semiconductors such as GaN and ZnO grow as nanowires with a hexagonal cross section and their optical properties have been little explored. We study important properties for nanowire LED optimization. In particular we review the modal properties of hexagonal nanowires and compare them with those of circular nanowires. We also study the modal reflectivity of guided modes at nanowire end facets and explore the relevance of a comparison with plane-wave reflectivity. Finally we analyze the distribution of the emitted power in three different cases: a single point emitter and an axial and a radial nanowire heterostructure.
TL;DR: In this paper, the authors report a wave turbulence regime that, starting with weakly nonlinear waves with randomized phases, shows an inverse cascade of photons toward the lowest wavenumbers.
Abstract: In an optical experiment, we report a wave turbulence regime that, starting with weakly nonlinear waves with randomized phases, shows an inverse cascade of photons toward the lowest wavenumbers. We show that the cascade is induced by a six-wave resonant interaction process and is characterized by increasing nonlinearity. At low wavenumbers the nonlinearity becomes strong and leads to modulational instability developing into solitons, whose number is decreasing farther along the beam.
TL;DR: In this article, a tapered photonic crystal fiber for various taper profiles with the purpose of optimizing the soliton self-frequency shift (SSFS) in such geometries is presented.
Abstract: Soliton propagation is modeled in a tapered photonic crystal fiber for various taper profiles with the purpose of optimizing the soliton self-frequency shift (SSFS) in such geometries. An optimal degree of tapering is found to exist for tapers with an axially uniform waist. In the case of axially nonuniform waists, an additional enhancement of the SSFS is achieved by varying the taper waist diameter along its length in a carefully designed fashion in order to present an optimal level of group-velocity dispersion to the soliton at each point, thus avoiding the spectral recoil due to the emission of dispersive waves. In doing so, the increased nonlinearity and dispersion engineering afforded by the reduction of the core size are exploited while circumventing the limitation imposed on the soliton redshift by the associated shortening of the red zero-dispersion wavelength.
TL;DR: In this paper, the ordinary and extraordinary refractive indices of an ǫ-GaSe crystal at terahertz (THz) frequencies were experimentally determined in the presence of a Fourier transform infrared spectrometer.
Abstract: Ordinary and extraordinary refractive indices of an ɛ-GaSe crystal at terahertz (THz) frequencies are experimentally determined in this study. Fitting experimental data by THz time-domain spectroscopy (THz-TDS) and a Fourier transform infrared spectrometer (FTIR), we proposed revised complex dielectric functions and Sellmeier equations of GaSe for both ordinary and extraordinary waves from 0.2 to 100 THz. Phonon vibrational modes and overtones in the THz frequency range are examined in detail. The high magnitude of the figure of merit (FOM~103 at 1 THz), the large birefringence (Δn~0.76 at 1 THz). and the low absorption coefficient (α~0.2 cm−1 at 1 THz) of GaSe are also identified. Potential applications to practical photonic devices such as phase shifters at THz frequencies are proposed.
TL;DR: In this article, the authors developed an iterative (averaging) method to characterize the mode-locking dynamics in a laser cavity mode locked with a combination of wave plates and a passive polarizer.
Abstract: We develop an iterative (averaging) method to characterize the mode-locking dynamics in a laser cavity mode locked with a combination of wave plates and a passive polarizer. The model explicitly accounts for the effects of self- and cross-phase modulation, an arbitrary alignment of the fast- and slow-axes of the fiber with the wave plates and polarizer, fiber birefringence, saturable gain, and chromatic dispersion. The general averaging scheme results in the cubic-quintic Ginzburg-Landau equation at the leading order and the Swift-Hohenberg equation at the next order. An extensive comparison between the full model and the averaged equations shows a quantitative agreement that allows for characterizing the stability and operating regimes of the laser cavity.