Tunable Dispersion Research Articles

True time-delay line with high resolution and wide range employing dispersion and optical spectrum processing

True time-delay line with a high resolution and wide range is proposed and demonstrated. Tunable lasers and dispersion fibers are employed to control the time delay coarsely. An optical spectrum processor is utilized to realize high-resolution time-delay control by adding a quadratic optical phase shift, which compensates the group velocity dispersion of the fiber simultaneously. A coarse tuning range of 1717 ps is realized by changing the wavelength of the optical carrier, and a high resolution of 0.67 ps is achieved by translating the symmetry axis of the quadratic phase shift.

Core–Shell Tin Oxide, Indium Oxide, and Indium Tin Oxide Nanoparticles on Silicon with Tunable Dispersion: Electrochemical and Structural Characteristics as a Hybrid Li-Ion Battery Anode

Tin oxide (SnO2) is considered a very promising material as a high capacity Li-ion battery anode. Its adoption depends on a solid understanding of factors that affect electrochemical behavior and performance such as size and composition. We demonstrate here, that defined dispersions and structures can improve our understanding of Li-ion battery anode material architecture on alloying and co-intercalation processes of Lithium with Sn from SnO2 on Si. Two different types of well-defined hierarchical Sn@SnO2 core-shell nanoparticle (NP) dispersions were prepared by molecular beam epitaxy (MBE) on silicon, composed of either amorphous or polycrystalline SnO2 shells. In2O3 and Sn doped In2O3 (ITO) NP dispersions are also demonstrated from MBE NP growth. Lithium alloying with the reduced form of the NPs and co-insertion into the silicon substrate showed reversible charge storage. Through correlation of electrochemical and structural characteristics of the anodes, we detail the link between the composition, areal and volumetric densities, and the effect of electrochemical alloying of Lithium with Sn@SnO2 and related NPs on their structure and, importantly, their dispersion on the electrode. The dispersion also dictates the degree of co-insertion into the Si current collector, which can act as a buffer. The compositional and structural engineering of SnO2 and related materials using highly defined MBE growth as model system allows a detailed examination of the influence of material dispersion or nanoarchitecture on the electrochemical performance of active electrodes and materials.

Format transparent, wide range and independent dispersion monitoring method based on four-wave mixing

In this paper we propose an improved all optical chromatic dispersion (CD) monitoring method based on highly nonlinear power transfer function (PTF) provided by four-wave mixing (FWM) in highly nonlinear fibers (HNLFs). This method can be applied for various modulation formats, including on–off keying and advanced multi-level modulation formats, without necessitating any changes of the hardware or software. Furthermore, it can expand the CD monitoring range beyond the limitation of Talbot effects and is insensitive to optical signal-to-noise ratio (OSNR) and polarization mode dispersion (PMD). These improvements are achieved by optimizing the profile of the PTF curve and utilizing a sweeping tunable dispersion compensator (TDC) in combination with an extremely simple digital signal processing (DSP) to find the zero residual dispersion point. Numerical simulations are then used to demonstrate the effectiveness of this method.

In-situ encapsulating MMT intermediate particles by suspension polymerization of poly (methyl methacrylate-co-styrene): preparation, tunable dispersion and properties

Effectively encapsulating large size inorganic particles by polymeric materials is of great significance in making functional materials. In this paper, poly (methyl methacrylate-co-styrene)/montmorillonite (MMT) intermediate particles (PMMAS/I-MMT) were prepared by the suspension polymerization method. The chemical composition, dispersion behavior, particle size distribution and properties of PMMAS/I-MMT composite particles were characterized by energy dispersive spectrometer (EDS), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), transmission electron microscopy (TEM), thermo-gravimetric analysis (TGA) and a laser particle analyzer. By using a step-by-step intercalation process of MMT clay and a careful separation process, the interlayer spacing of pristine Na-MMT was well tuned from 1.2 nm to 1.9 nm to provide I-MMT phase. MMT layers encapsulated in PMMAS copolymer were characterized by FTIR. XRD indicated that I-MMT interlayer spacing was further enlarged to 3.3 nm in the PMMAS composite with 3.0 wt% I-MMT loading and these composite films showed tunable and gradual exfoliation behavior, which was consistent with TEM analysis. The obtained volume average size of PMMAS/I-MMT composite particles had a narrow size distribution from 52.0 μm to 79.0 μm. The active layer exfoliations had greatly enhanced PMMAS thermal stability up to 453 °C by TGA, and the properties of its surface wetting and barrier against water were stably improved. Such encapsulated MMT composite particles may provide candidate materials for modifying fluid channels of petroleum engineering.

An optically tunable wideband optoelectronic oscillator based on a bandpass microwave photonic filter

An optoelectronic oscillator (OEO) with wideband frequency tunability and stable output based on a bandpass microwave photonic filter (MPF) has been proposed and experimentally demonstrated. Realized by cascading a finite impulse response (FIR) filter and an infinite impulse response (IIR) filter together, the tunable bandpass MPF successfully replaces the narrowband electrical bandpass filter in a conventional single-loop OEO and serves as the oscillating frequency selector. The FIR filter is based on a tunable multi-wavelength laser and dispersion compensation fiber (DCF) while the IIR filter is simply based on an optical loop. Utilizing a long length of DCF as the dispersion medium for the FIR filter also provides a long delay line for the OEO feedback cavity and as a result, optical tuning over a wide frequency range can be achieved without sacrificing the quality of the generated signal. By tuning the wavelength spacing of the multi-wavelength laser, the oscillation frequency can be tuned from 6.88 GHz to 12.79 GHz with an average step-size of 0.128 GHz. The maximum frequency drift of the generated 10 GHz signal is observed to be 1.923 kHz over 1 hour and its phase noise reaches the -112 dBc/Hz limit of our measuring equipment at 10 kHz offset frequency.

Quantum dynamics of an atom orbiting around an optical nanofiber

We propose a novel platform for the investigation of quantum wave packet dynamics, offering a complementary approach to existing theoretical models and experimental systems. It relies on laser-cooled neutral atoms which orbit around an optical nanofiber in an optical potential produced by a red-detuned guided light field. We show that the atomic center-of-mass motion exhibits genuine quantum effects like collapse and revival of the atomic wave packet. As distinctive advantages, our approach features a tunable dispersion relation as well as straightforward readout for the wave packet dynamics and can be implemented using existing quantum optics techniques.

Generation of Time- and Wavelength-Interleaved Optical Pulse-Train With Tunable Pulsewidth Based on Dispersion and Sectional Compression

We show analytically as well as experimentally a technique to generate a time- and wavelength interleaved optical pulse-train (TWIPT) with tunable pulsewidth. The technique involves dispersing an initial pulse-train using a standard single-mode-fiber (SMF) followed by sectional dispersion compensation using a tunable multi-channel dispersion compensation module. Using an initial pulse-train with a fixed repetition frequency frep and a tunable multi-channel dispersion compensation module with a fixed frequency spacing between the adjacent channels, our scheme shows that by choosing appropriate value for the length of the SMF, we can generate a N×frep TWIPT in the case when there are N channels within the bandwidth of the initial pulses. By tuning the channel dispersion to be the opposite of the dispersion introduced by the SMF, one is able to generate transform-limited pulsewidths for the TWIPT. Furthermore, tuning the channel dispersion to other values permits pulsewidth tunability. Based on the proposed scheme, using a 2 GHz supercontinuum source as an initial pulse-train, we demonstrate the generation of a 10 × 2 GHz TWIPT with pulsewidth tunability.

Reversible Fano resonance by transition from fast light to slow light in a coupled-resonator-induced transparency structure

We theoretically propose and experimentally perform a novel dispersion tuning scheme to realize a tunable Fano resonance in a coupled-resonator-induced transparency (CRIT) structure coupled Mach-Zehnder interferometer. We reveal that the profile of the Fano resonance in the resonator coupled Mach-Zehnder interferometers (RCMZI) is determined not only by the phase shift difference between the two arms of the RCMZI but also by the dispersion (group delay) of the CRIT structure. Furthermore, it is theoretically predicted and experimentally demonstrated that the slope and the asymmetry parameter (q) describing the Fano resonance spectral line shape of the RCMZI experience a sign reversal when the dispersion of the CRIT structure is tuned from abnormal dispersion (fast light) to normal dispersion (slow light). These theoretical and experimental results indicate that the reversible Fano resonance which holds significant implications for some attractive device applications such as highly sensitive biochemical sensors, ultrafast optical switches and routers can be realized by the dispersion tuning scheme in the RCMZI.

Experimental study on parametric tunable dispersion compensation for WDM channels with mixed OOK and QPSK formats

Presented is a parametric tunable dispersion compensation (PTDC) for 43 Gbit/s WDM channels with mixed modulation formats of OOK and QPSK. The residual dispersion for the OOK channels is successfully compensated for, while the QPSK channels with digital coherent detection maintain a good signal quality regardless of various settings of PTDC that involve nonlinear processes of wavelength conversion based on four-wave mixing. Specific design issues on PTDC are discussed, considering the characteristics of the modulation formats of the received channels.

Tunable narrow dispersion compensation for independent CWDM channels using the acousto-optic modulation

A new method for dynamic control of the group delay of a fiber Bragg grating (FBG) is presented. It is based on an acoustic wave applied to the fiber. Tunability is obtained through adjustment of the intensity and/or frequency of the acoustic wave. The experimental results were verified by theoretical simulation. Application as a tunable narrow dispersion compensator for independent coarse wavelength division multiplexing (CWDM) channels is discussed. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:929–932, 2013; View this article online at wileyonlinelibrary.com. DOI: 10.1002/mop.27463

High-speed dispersion-tuned wavelength-swept fiber laser using a reflective SOA and a chirped FBG

We present a high-speed wavelength-swept fiber laser based on a dispersion tuning method using a reflective semiconductor optical amplifier (RSOA) and a chirped fiber Bragg grating (CFBG). By using these devices, the cavity length can be shortened drastically. The short cavity improves the laser performance at high sweep rates over 200 kHz. We achieve a sweep range of 60 nm and an output power of 8.4 mW at 100 kHz sweep. We applied the dispersion-tuned fiber laser to the swept-source OCT system and successfully obtained OCT images of an adhesive tape at up to 250 kHz sweep rate.

Dispersion characteristics of all-glass photonic crystal fibers

In this paper, we numerically investigate all-glass photonic crystal fiber (AGPCF) structure using finite difference time domain method. The proposed PCF structure exhibit improved endlessly single-mode behavior and tunable dispersion properties. The proposed structure consists of fluorine-doped rods in the cladding region which might reduce the deformation of air-holes as in air-hole cladding PCF structures. By varying the doping concentration, the optical characteristics can be varied and makes it possible to achieve several improved PCF designs.

Plasmon transport in graphene investigated by time-resolved electrical measurements.

Plasmons, which are collective charge oscillations, could provide a means of confining electromagnetic field to nanoscale structures. Recently, plasmonics using graphene have attracted interest, particularly because of the tunable plasmon dispersion, which will be useful for tunable frequency in cavity applications. However, the carrier density dependence of the dispersion is weak (proportional to n1/4) and it is difficult to tune the frequency over orders of magnitude. Here, by exploiting electronic excitation and detection, we carry out time-resolved measurements of a charge pulse travelling in a plasmon mode in graphene corresponding to the gigahertz range. We demonstrate that the plasmon velocity can be changed over two orders of magnitude by applying a magnetic field B and by screening the plasmon electric field with a gate metal; at high B, edge magnetoplasmons, which are plasmons localized at the sample edge, are formed and their velocity depends on B, n and the gate screening effect.

Tunability of the FBG group delay through acousto-optic modulation

A new method for fine control of the group delay of a fiber Bragg grating (FBG) is presented. It is based on an acoustic wave applied to the fiber. The standing acoustic wave imposes a periodic chirp to the uniform FBG. Tunability is obtained through adjustment of the intensity and/or frequency of the acoustic wave. A fast switching time of ∼17μs was achieved. The experimental results were verified by theoretical simulation showing a good agreement between them. It can be used for different applications such as tunable narrow dispersion compensator for independent coarse wavelength division multiplexing (CWDM) channels or optical delay lines.

Novel methods in the Particle-In-Cell accelerator Code-Framework Warp

The Particle-In-Cell (PIC) Code-Framework Warp is being developed by the Heavy Ion Fusion Science Virtual National Laboratory (HIFS-VNL) to guide the development of accelerators that can deliver beams suitable for high-energy density experiments and implosion of inertial fusion capsules. It is also applied in various areas outside the Heavy Ion Fusion program to the study and design of existing and next-generation high-energy accelerators, including the study of electron cloud effects and laser wakefield acceleration for example. This paper presents an overview of Warp's capabilities, summarizing recent original numerical methods that were developed by the HIFS-VNL (including PIC with adaptive mesh refinement, a large-timestep ?drift-Lorentz? mover for arbitrarily magnetized species, a relativistic Lorentz invariant leapfrog particle pusher, simulations in Lorentz-boosted frames, an electromagnetic solver with tunable numerical dispersion and efficient stride-based digital filtering), with special emphasis on the description of the mesh refinement capability. Selected examples of the applications of the methods to the abovementioned fields are given.

A Switchable and Tunable Dual-Wavelength Actively Mode-Locked Fiber Laser Based on Dispersion Tuning

A switchable and tunable dual-wavelength actively mode-locked fiber laser based on a dispersion tuning technique is proposed and demonstrated. Synchronous wavelength tuning of dual-wavelength operation with wavelength spacing of 22.9 nm can be achieved up to 23.2 nm by changing the modulation frequency. The proposed laser can operate in dual-wavelength or single-wavelength by simple adjustment of the polarization controller. Moreover, wavelength spacing can also be varied from 22 to 45 nm at the cost of a reduced tuning range by changing the harmonic order, which is determined by the modulation frequency. These experimental observations agree well with the theoretical analysis.

Efficient low-temperature selective hydrogenation of esters on bimetallic Au–Ag/SBA-15 catalyst

Gold (Au)–silver (Ag) bimetallic catalyst supported on ordered mesoporous silica SBA-15 exhibits unprecedentedly high activity and superior stability for the selective hydrogenation of dimethyl oxalate to methyl glycolate at a low temperature of 418K. By contrast, monometallic Au/SBA-15 and Ag/SBA-15 catalysts are almost inactive under identical conditions. A combined tuning of particle dispersion and its surface electronic structure is shown as a consequence of the changes in the size and valence band structure of Au and Ag, which leads to significantly enhanced synergy. Considerably reduced apparent activation energies indicate that special active sites with the ability to activate substrate molecules more efficiently are generated in Au–Ag alloy nanoparticles. The Au–Ag bimetallic catalyst also displays excellent activity for the selective hydrogenation of some other unsaturated or saturated esters and acetic acid.

Spatial and Spectral Light Shaping with Metamaterials

Plasmonic metamaterials exhibit strong and tunable dispersion, as a result of their pronounced resonances. This dispersion is used to construct an ultrathin light-shaping element that produces different waves at two distinct wavelengths in the near IR range. The optical response of the pixelated element is adjusted by variations in the geometry of the metamaterial's unit cell. Applications requiring spatial and spectral control of light become feasible.

Generation of WDM adaptive-rate pulse bursts by cascading narrow/wideband tunable optical dispersion compensators

We demonstrate passive generation of optical pulse trains with each pulse having distinct center carrier and spectra using tunable group delay (GD) staircase transfer functions. The GD steps result from opposite and equal magnitude GD slopes from narrowband and wideband tunable optical dispersion compensators. We use this technique to split the spectrum of a femtosecond pulse to a pulse burst with precise control of pulse time separation.

Piezoelectric resonator arrays for tunable acoustic waveguides and metamaterials

One of the outstanding challenges in phononic crystals and acoustic metamaterials development is the ability to tune their performance without requiring structural modifications. We report on the experimental demonstration of a tunable acoustic waveguide implemented within a two-dimensional phononic plate. The waveguide is equipped with a periodic array of piezoelectric transducers which are shunted through passive inductive circuits. The resonance characteristics of the shunts lead to strong attenuation and to negative group velocities at frequencies defined by the circuits' inductance. The proposed waveguide illustrates the concept of a controllable acoustic logic port or of an acoustic metamaterial with tunable dispersion characteristics.