Waveguide Dispersion Research Articles

Discretized Conical Waves in Multimode Optical Fibers.

Multimode optical fibers are essential in bridging the gap between nonlinear optics in bulk media and single-mode fibers. The understanding of the transition between the two fields remains complex due to intermodal nonlinear processes and spatiotemporal couplings, e.g., some striking phenomena observed in bulk media with ultrashort pulses have not yet been unveiled in such waveguides. Here we generalize the concept of conical waves described in bulk media towards structured media, such as multimode optical fibers, in which only a discrete and finite number of modes can propagate. Such propagation-invariant optical wave packets can be linearly generated, in the limit of superposed monochromatic fields, by shaping their spatiotemporal spectrum, whatever the dispersion regime and waveguide geometry. Moreover, they can also spontaneously emerge when a rather intense short pulse propagates nonlinearly in a multimode waveguide, their finite energy is also associated with temporal dispersion. The modal distribution of optical fibers then provides a discretization of conical emission (e.g., discretized X waves). Future experiments in multimode fibers could reveal different forms of dispersion-engineered conical emission and supercontinuum light bullets.

Analysis of Silica Based Single-Mode Fiber Doped with Germanium at Different Transmission Window

In this paper, a germanium doped silica-based single-mode fiber for high speed optical communication link has been proposed. It is found that the proposed fiber is suitable for three transmission widows an excellent result at the third transmission window. Here, attenuation loss, dispersion, mode field diameter, bending loss, and material loss of the proposed fiber has been analyzed. It is found that dispersion such as material dispersion and waveguide dispersion is very low at the third transmission window (1550 nm), which is used for high speed optical fiber communication link. In addition to this, at the third transmission window, micro bending loss is almost disappeared and macro bending loss is also very low (0.00101 dB/km). All these analysis has been done using FDTD technique.

The (2+1)-dimensional hyperbolic nonlinear Schrödinger equation and its optical solitons

<abstract> <p>A comprehensive study on the (2+1)-dimensional hyperbolic nonlinear Schrödinger (2D-HNLS) equation describing the propagation of electromagnetic fields in self-focusing and normally dispersive planar wave guides in optics is conducted in the current paper. To this end, after reducing the 2D-HNLS equation to a one-dimensional nonlinear ordinary differential (1D-NLOD) equation in the real regime using a traveling wave transformation, its optical solitons are formally obtained through a group of well-established methods such as the exponential and Kudryashov methods. Some graphical representations regarding optical solitons that are categorized as bright and dark solitons are considered to clarify the dynamics of the obtained solutions. It is noted that some of optical solitons retrieved in the current study are new and have been not retrieved previously.</p> </abstract>

Модулятор Маха–Цендера, использующий дисперсию в плазме носителей заряда в суженном фотонно-кристаллическом волноводе

Модулятор Маха–Цендера, использующий дисперсию в плазме носителей заряда в суженном фотонно-кристаллическом волноводе

Experimental Analysis and Study of Various Dispersions in Optical Fiber

Dispersion is a significant parameter in systems based on optical fiber. The numbers of channels that can be transmitted simultaneously are reduced by dispersion. The principal objective of this paper is to compute the waveguide dispersion and study the nature of the graph. Different values of wavelength and refractive index are used. In this paper Scilab, open-source programming is utilized. Some other sorts of dispersion and furthermore different parameters can be assessed utilizing Scilab. The intended evaluation of material dispersion in an optical fiber. Material dispersion occurs due to different optical wavelengths propagate at different velocities inside the fibers and it depends on the refractive index of the material used in the fiber core. In this paper, the material dispersion of an optical fiber is calculated and studied.

Wideband large dispersion group delay chip based on silicon photonics integration (Invited)

Content integrated, broadband, large group delay devices have important applications in microwave photonic filtering, true delay phased array antenna and other fields, which can effectively reduce the system size and power consumption. In this paper, a broadband large dispersion delay chip based on silicon-based photonic integration was proposed and implemented. By using ultra-low loss waveguide structure and side wall normal vector modulation structure, on-chip integration of large dispersion waveguide grating was realized. The dispersion was about 250 ps/nm, maximum group delay was 2440 ps and the bandwidth was more than 9.4 nm. The chip is expected to be used in microwave photonics, high-speed fiber communication system and other fields.

Nonlinear Optical Fibers, Their Properties, and Applications

Nonlinear optical properties and preparation of nonlinear optical fiber based on Bismuth oxide were described. Wavelength dependence of refractive index of ABH160 and B027 was studied and analyzed. Working and construction of optical ON-OFF switches, based on Bi-HNLF was reported. It was investigated that refractive index of ABH160 and Bo27 were found to be exponentially decaying as a function of wavelength. Absorption coefficient of ABH160 as a function of wavelength was found to be decaying exponentially. In optical fiber the total group velocity dispersion is divided into the material dispersion DM and waveguide dispersion DW. Material dispersion and waveguide dispersion were calculated theoretically and a good agreement with the experimental result. The process of four wave mixing and consequences was reviewed.

High-resolution wavemeter based on polarization modulation of fiber speckles

For speckle pattern-based wavemeters or spectrometers, the intermodal and the chromatic dispersion of the diffusion waveguide are key factors in determining the wavelength resolution. In this study, we propose a new mechanism to modulate the fiber speckles aside from the dispersion related effect. The polarization modulation is introduced in a rectangular core fiber (RCF) by using an in-line polarization rotator (IPR). The IPR can rotate the polarization angle at different wavelengths. Interestingly, it is observed that the modulated speckle patterns appear periodically similar, and they present more variations when compared to unmodulated ones. The theoretical simulation indicates that the polarization exerts an influence on the fiber speckles by modulating the mode coupling coefficients when light is coupled into the RCF. In the demonstration experiment, we first built a precise laser frequency tuning system based on an electro-optic modulator and a microwave source. By comparing the recorded speckles with and without polarization modulation, the former speckles have lower correlations, which are evaluated using the Arc Cosine Similarity algorithm. Reconstructing the spectrum of speckles, the smallest detectable wavelength that can be detected with polarization modulation is 0.2 fm. The experimental results prove that the polarization modulation is a convenient and effective method to enhance the speckle’s wavelength sensitivity. In addition, this study paves a new way to design high-resolution wavemeters with shorter, more compact optical waveguides.

Slow propagation of 2 GHz acoustical waves in a suspended GaAs phononic waveguide on insulator

Optoelectronic oscillators have dominated the scene of microwave oscillators in the last few years thanks to their great performances regarding frequency stability and phase noise. However, miniaturization of such devices is an up-to-date challenge. Recently, devices based on a phonon–photon interaction have gathered a lot of interest thanks to their extreme compactness and working frequency directly in the GHz. In this frame, a still-missing element to obtain long-term frequency stability performances is an on-chip delay within the feedback loop. Here, we experimentally show filtering and slow propagation of 2 GHz acoustic waves on a Gallium Arsenide membrane heterogeneously integrated on a silicon wafer. By engineering the dispersion of an acoustical waveguide, we evidence a group velocity below 1000 m/s for the mode able to propagate. Thus, an integrated delay implementation is at reach for potential improvement of opto-acoustic devices such as optomechanical oscillators or wireless applications.

Increasing energy transfer over Eurasia and the North Atlantic enhancing the Eurasian low‐frequency wave and boreal summer droughts in China

AbstractThe prolonged droughts that frequently occur in northern China are related to persistent anomalies of circulation and the low‐frequency waves. To explore the formation of the low‐frequency waves and the related internal variability and external forcing, the intra‐seasonal kinetic energy (KE) and the corresponding energy transfer terms are investigated algorithmically with multiscale energy and vorticity analysis. The results show two major energy sources located over the central North Atlantic (NA) and Europe, with increasing baroclinicity and energy conversion. The major energy conversion is from basic flow to intra‐seasonal KE, which corresponds to a southeastern extension of NA jet stream (JS) exit and the northward shift in the entrance of Afro Asian JS. JS shifts are helpful to the conjunction of both JS, and thereby enhance JS waveguide and wave energy dispersion. In addition, with increasing surface temperature and diabatic heating over Europe and the Mediterranean Sea, there are increase baroclinicity that facilitates the buoyancy energy conversion, ascending KE flux and positive pressure flux in the lower troposphere, those result in higher mid‐upper‐troposphere KE. The divergent energy contributes to the development and enhancement of the low‐frequency waves, favouring the extratropical eddy, wave structure, and quasi‐stationary waves amplitude, which is thereby conducive to magnified wave amplitude and extreme droughts in northern China. The results emphasize the internal dynamics and local forcing and provide prediction reference for extratropical extremes.

Solid-State Photonics-Based Lidar With Large Beam-Steering Angle by Seamlessly Merging Two Orthogonally Polarized Beams

In a solid-stage photonics-based Lidar, all essential components are integrated into a silicon chip using silicon photonic technique. It is preferable to implement Lidar's beam steering through wavelength tuning due to its simplicity. However, a large wavelength tuning range is usually required to generate a satisfactory beam-steering angle, which usually is constrained by the limited material and waveguide dispersion. In silicon-on-insulator (SOI) waveguide, the effective index of the transverse-electric (TE) mode is significantly different from that of the transverse-magnetic (TM) mode. This allows us to design a novel device that is composed of two grating couplers optimized for two orthogonal polarizations. Two beams diffracted from two grating couplers with the orthogonal polarization can be seamlessly merged together. Combining these two orthogonally-polarized output beams significantly increases the beam-steering angle and dramatically reduces the required wavelength-tuning range.

Quartic and dipole solitons in a highly dispersive optical waveguide with self-steepening nonlinearity and varying parameters

We show theoretically that highly dispersive optical media characterized by a Kerr nonlinear response may support the existence of quartic and dipole solitons in the presence of the self-steepening effect. The existence and stability properties of these localized pulses are examined in the presence of all the material parameters. Regimes for the modulation instability of a continuous-wave signal propagating inside the nonlinear medium are investigated and an analytic expression for the gain spectrum is obtained and shown to be dependent on the self-steepening parameter in addition to second- and fourth-order group velocity dispersion parameters. Self-similar soliton solutions are constructed for a generalized nonlinear Schr\odinger equation with distributed second-, third-, and fourth-order dispersions, self-steepening nonlinearity, and gain or loss describing ultrashort pulse propagation in the inhomogeneous nonlinear media via the similarity transformation method. The evolutional dynamics of the self-similar structures are investigated in a periodic distributed waveguide system and an exponential dispersion decreasing waveguide.

Few-mode fiber-embedded long-period fiber grating for simultaneous measurement of refractive index and temperature.

A few-mode fiber (FMF)-embedded long-period fiber grating is proposed as a sensor for simultaneous measurement of refractive index and temperature. Periodically embedding the FMFs induces the local refractive index modulation to achieve a compact sensor size and obtains a low insertion loss. The simulated results show that the two resonance dips have opposite waveguide dispersion coefficients. Therefore, they show different refractive indices and temperature sensitivities in the experiment. At the same time, the spectral characteristics of double-resonance dips provides a condition for simultaneous measurement of two parameters. By monitoring wavelength shift of the two dips, the simultaneous measurement of refractive index and temperature is easily realized.

Deeper Confinement of Electromagnetic Waves Beyond Spoof Surface Plasmon Polaritons

The physics of spoof surface plasmon polaritons (SSPPs) is widely studied for their intrinsic confinement of electromagnetic wave, leading to the useful applications of device miniaturization and signal integrity. As another imitation of surface plasmon polaritons (SPPs) in microwave, effective SPPs (ESPPs) are excited inside the waveguide based on structural dispersion. Without using lossy plasmonic materials, slow wave property is achieved inside the waveguide for the interface confinement. In this work, for further enhancing the field confinement of SSPPs, the waveguide dispersion method is utilized on the structure of SSPPs. In this way, the techniques of ESPPs and SSPPs are feasibly combined for the first time, coining the name of “effective SSPPs (ESSPPs).” The dispersion relation of the ESSPPs is analyzed theoretically and numerically with the obvious field confinement. The structural dispersion makes the wavelength of ESSPPs reach 1/18 of the wavelength of SSPPs, which has potential applications for device miniaturization and signal integrity. Finally, two prototypes of the ESSPPs waveguide are fabricated on the substrate integrated waveguide (SIW) platform. The experimental results of the prototypes verify the stronger field confinement, indicating new possibilities to slow down the wave propagation with controllable confinement.

The Development of broadband millimeter-wave and terahertz gyro-TWAs

The gyrotron travelling wave tube amplifiers (gyro-TWAs) presented in this paper can operate with high efficiency (30%), huge powers and wide bandwidths at high frequencies that no other amplifier can provide. In principle, this is a technology that can be scaled to >1 THz and operate with 20% bandwidths. Resonant coupling of two dispersive waveguide modes in a helically corrugated interaction region (HCIR) can give rise to a non-dispersive eigenwave over a wide frequency band. The synchronism between the ideal wave and an electron cyclotron mode, either fundamental or harmonic, of a large orbit electron beam contributes to the broadband amplification. An electron beam of 55 keV, 1.5 A with a velocity pitch angle of ~1 generated by a thermionic cusp gun is used in our 100 GHz gyro-TWA experiment, which achieves an unsaturated output power of 3.4 kW and gain of 36–38 dB. The design and experimental results of the many components making the gyro-TWA will be presented individually and then the whole system will be introduced. The amplification of a swept signal by the W-band gyro-TWA is demonstrated showing its capabilities in the field of telecommunications. Furthermore, the design studies of a cusp electron gun in the triode configuration and the realization of a 3-fold HCIR operating at 372 GHz will also be displayed.

Broadband quasi-phase-matching in dispersion-engineered all-optically poled silicon nitride waveguides

Quasi-phase-matching (QPM) has become one of the most common approaches for increasing the efficiency of nonlinear three-wave mixing processes in integrated photonic circuits. Here, we provide a study of dispersion engineering of QPM second-harmonic (SH) generation in stoichiometric silicon nitride ( Si 3 N 4 ) waveguides. We apply waveguide design and lithographic control in combination with the all-optical poling technique to study the QPM properties and shape the waveguide dispersion for broadband spectral conversion efficiency inside Si 3 N 4 waveguides. By meeting the requirements for maximal bandwidth of the conversion efficiency spectrum, we demonstrate that group-velocity matching of the pump and SH is simultaneously satisfied, resulting in efficient SH generation from ultrashort optical pulses. The latter is employed for retrieving a carrier-envelope-offset frequency of a frequency comb by using an f − 2 f interferometric technique, where supercontinuum and SH of a femtosecond pulse are generated in Si 3 N 4 waveguides. Finally, we show that the waveguide dispersion determines the QPM wavelength variation magnitude and sign due to the thermo-optic effect.

Magnetohydrodynamic Waves in the Solar Corona

The corona of the Sun is a unique environment in which magnetohydrodynamic (MHD) waves, one of the fundamental processes of plasma astrophysics, are open to a direct study. There is striking progress in both observational and theoretical research of MHD wave processes in the corona, with the main recent achievements summarized as follows: ▪ Both periods and wavelengths of the principal MHD modes of coronal plasma structures, such as kink, slow and sausage modes, are confidently resolved. ▪ Scalings of various parameters of detected waves and waveguiding plasma structures allow for the validation of theoretical models. In particular, kink oscillation period scales linearly with the length of the oscillating coronal loop, clearly indicating that they are eigenmodes of the loop. Damping of decaying kink and standing slow oscillations depends on the oscillation amplitudes, demonstrating the importance of nonlinear damping. ▪ The dominant excitation mechanism for decaying kink oscillations is associated with magnetized plasma eruptions. Propagating slow waves are caused by the leakage of chromospheric oscillations. Fast wave trains could be formed by waveguide dispersion. ▪ The knowledge gained in the study of coronal MHD waves provides ground for seismological probing of coronal plasma parameters, such as the Alfvén speed, the magnetic field and its topology, stratification, temperature, fine structuring, polytropic index, and transport coefficients.

Pulse time reversal and stopping by a refractive index front

We discuss how dynamic light stopping and pulse time reversal can be implemented in dispersive waveguides via indirect photonic transitions induced by moving refractive index fronts. The previous concepts of light stopping/time reversal either require complex local variation of the device’s refractive index or rely on the strict phase matching condition, which imposes limitations on the amount of manipulated information. Until now, only single pulses or continuous waves were manipulated experimentally. Our scheme is not limited by a strict phase matching condition and does not require local index variations, thus it can manipulate broadband signals in a single step process. Here, we present several numerically integrated results for pulse time reversal and stopping/storage via indirect front-induced transitions. The presented results are experimentally feasible using existing photonic waveguide technologies.

Dual-Mode GVD Tailoring in a Convex Waveguide

Mode division multiplexing (MDM) silicon photonic integrated circuits (PICs) have been widely developed for achieving high-speed optical interconnects and communications. As an excellent nonlinear optical platform, silicon PICs also receive great attention in applications of optical parametric devices and nonlinear optical signal processing. However, it is still challenging to develop MDM optical parametric devices due to the strong mode dependence of the group velocity dispersion (GVD) in a silicon waveguide. Here, we theoretically design a convex waveguide exhibiting almost the same GVD profiles for quasi-TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> and quasi-TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> modes based on the standard fabrication flow of silicon photonic foundries. Specifically, flat GVD curves varying from -1500 ps/nm/km to -1000 ps/nm/km are obtained for the two modes in a convex waveguide within a spectral region of 1.37 μm to 1.75 μm covering from E-band to U-band. The study is expected to open an avenue for exploring unprecedented MDM nonlinear applications.

Tailoring the waveguide dispersion of nonlinear fibers for supercontinuum generation with superior intrapulse coherence

Spectral coherence is an important prerequisite for many applications of femtosecond supercontinua, including precision frequency metrology, attosecond science, and high-field physics. These applications often critically depend on measurement of the carrier-envelope phase via f − 2 f interferometry. As mode-locked laser sources cannot directly provide octave-spanning spectra, one typically resorts to spectral broadening in highly nonlinear optical fibers to generate the necessary spectral coverage. This process comes with a caveat, as coherence can be severely degraded in the broadening process. This degradation can be mitigated by suitable choice of a fiber dispersion profile. Here we numerically investigate prototypical fiber designs and analyze their susceptibility to coherence degradation. It is found that the generally favored soliton fission process provides the best broadening efficiency at the expense of rather scarce coherence conditions. Sufficient pulse energy provided, all-normally dispersive fiber designs fare far better in terms of spectral coherence. Finally, fiber designs with flattened normal dispersion provide the best compromise between efficiency and resulting spectral coherence. Our study indicates that the spectral width of a supercontinuum may be deceiving. Even when compressible into a short pulse, this does not automatically qualify for sufficient spectral coherence to conduct carrier-envelope-phase-sensitive experiments. The numerical simulations in this study provide a guideline for coherent spectral broadening. In turn, these guidelines may help to improve carrier-envelope phase stabilization and, in particular, to enable stabilization of laser oscillators that have previously proven difficult to stabilize.