Dispersion Measurement Technique Research Articles

Dispersion measurement assisted by a stimulated parametric process.

Dispersion plays a major role in the behavior of light inside photonic devices. Current state-of-the-art dispersion measurement techniques utilize linear interferometers that can be applied to devices with small dispersion-length products. However, linear interferometry often requires beam alignment and phase stabilization. Recently, common-path nonlinear interferometers in the spontaneous regime have been used to demonstrate alignment-free and phase-stable dispersion measurements. However, they require single-photon detectors, resulting in high system cost and long integration times. We overcome these issues by utilizing a nonlinear interferometer in the stimulated regime and demonstrate the ability to measure the dispersion of a device with a dispersion-length product as small as 0.009 ps/nm at a precision of 0.0002 ps/nm. Moreover, this regime allows us to measure dispersion with shorter integration times (in comparison to the spontaneous regime) and conventional optical components and detectors.

Investigation of continuum generation in the non-zero dispersion-shifted fiber pumped by femtosecond nanojoule pulses in 1450–1800 nm spectral range

A synchronously pumped optical parametric oscillator based on periodically poled potassium titanyl phosphate (PPKTP) crystal delivering femtosecond nanojoule energy pulses in the 1.45 μm–1.8 μm spectral range is used as pump source for continuum generation in conventional non-zero dispersion shifted optical fiber. Detailed numerical simulations and experiments employing cross-correlation frequency-resolved optical gating (XFROG) reveal soliton and dispersive wave generation dynamics and can help to estimate limits of how far the pump wavelength can be shifted from zero-dispersion wavelength (ZDW) to still obtain sufficient spectrum broadening. We also demonstrate the applicability of recently introduced fiber dispersion measurement technique based on XFROG trace analysis to conventional optical fibers. Combination of this efficient parametric device with standard non-zero dispersion shifted low cost and low loss optical fiber results in efficient continuum generation with output/input average power ratio greater than 50%.

Surface waves at metal-dielectric interfaces: Material science perspective

Abstract Surface modes at interfaces, especially, the surface plasmon polaritons at metal-dielectric interfaces localize field. Associated applications are well pursued in addition to their basic properties which themselves are interesting. There are several metal-dielectric geometries that support surface modes like the gap, Tamm, spoof, and magneto-plasmons. After a brief pedagogical overview of these surface modes and the often-used dispersion measurement techniques, material science aspects like the quest for lossless plasmonic metal, dispersionless plasmonic structures, and plasmon dynamics are discussed. Some of the open problems are presented.

Neurite dispersion: a new marker of multiple sclerosis spinal cord pathology?

ObjectiveConventional magnetic resonance imaging (MRI) of the multiple sclerosis spinal cord is limited by low specificity regarding the underlying pathological processes, and new MRI metrics assessing microscopic damage are required. We aim to show for the first time that neurite orientation dispersion (i.e., variability in axon/dendrite orientations) is a new biomarker that uncovers previously undetected layers of complexity of multiple sclerosis spinal cord pathology. Also, we validate against histology a clinically viable MRI technique for dispersion measurement (neurite orientation dispersion and density imaging, NODDI), to demonstrate the strong potential of the new marker.MethodsWe related quantitative metrics from histology and MRI in four post mortem spinal cord specimens (two controls; two progressive multiple sclerosis cases). The samples were scanned at high field, obtaining maps of neurite density and orientation dispersion from NODDI and routine diffusion tensor imaging (DTI) indices. Histological procedures provided markers of astrocyte, microglia, myelin and neurofilament density, as well as neurite dispersion.ResultsWe report from both NODDI and histology a trend toward lower neurite dispersion in demyelinated lesions, indicative of reduced neurite architecture complexity. Also, we provide unequivocal evidence that NODDI‐derived dispersion matches its histological counterpart (P < 0.001), while DTI metrics are less specific and influenced by several biophysical substrates.InterpretationNeurite orientation dispersion detects a previously undescribed and potentially relevant layer of microstructural complexity of multiple sclerosis spinal cord pathology. Clinically feasible techniques such as NODDI may play a key role in clinical trial and practice settings, as they provide histologically meaningful dispersion indices.

Probing into the mesoporous structure of carbon xerogels via the low-field NMR relaxometry of water and cyclohexane molecules

The liquid morphology of water and cyclohexane molecules, under partially saturated conditions inside the porous structure of two mesoporous carbon xerogels, was investigated using low-field nuclear magnetic resonance (NMR) relaxometry. The two xerogels were prepared under the same conditions, but with a different resorcinol-to-catalyst ratio. Two techniques were used in our investigations: the well-known Carr–Purcell–Meiboom–Gill (CPMG) pulse sequence for transverse relaxation measurements and the Fast Field-Cycling (FFC) relaxometry technique for longitudinal relaxation dispersion measurements. It was found a stronger interaction of cyclohexane molecules with the pore surface as compared with water molecules. This leads to a uniform coverage of cyclohexane molecules on the pore surface for lower filling degrees while, in the case of water filled carbon xerogels, the distribution was non-uniform. Due to the stronger adsorption of cyclohexane molecules on the pore surface, it was possible to identify the micropores of the carbon xerogels predicted by nitrogen adsorption data. The NMR relaxation data have clearly demonstrated that, by increasing the resorcinol-to-catalyst ratio, the size of mesopores increases. Moreover, the enhanced adsorption affinity of carbon xerogels for cyclohexane shows that this type of materials can be employed as adsorbents for the removal of similar organic contaminants from water.

Estimation of photonic crystal fiber dispersion by means of supercontinuum generation.

We present a technique for photonic crystal fiber dispersion measurement. We demonstrate that investigating supercontinuum using cross-correlation frequency resolved optical gating (XFROG) technique can be used for quantitatively characterizing dispersion and observing orthogonal polarization modes in polarization maintaining photonic crystal fibers. In addition, an XFROG trace of supercontinuum generated in a polarization maintaining photonic crystal fiber reveals complex behavior of orthogonal polarization modes that is different in normal and anomalous dispersion regions of the photonic crystal fiber.

Explicit calculation of nuclear-magnetic-resonance relaxation rates in small pores to elucidate molecular-scale fluid dynamics.

Nuclear-magnetic-resonance (NMR) spin-lattice (T_{1}^{-1}) and spin-spin (T_{2}^{-1}) relaxation rate measurements can act as effective nondestructive probes of the nanoscale dynamics of ^{1}H spins in porous media. In particular, fast-field-cycling T_{1}^{-1} dispersion measurements contain information on the dynamics of diffusing spins over time scales spanning many orders of magnitude. Previously published experimental T_{1}^{-1} dispersions from a plaster paste, synthetic saponite, mortar, and oil-bearing shale are reanalyzed using a model and associated theory which describe the relaxation rate contributions due to the interaction between spin ensembles in quasi-two-dimensional pores. Application of the model yields physically meaningful diffusion correlation times for all systems. In particular, the surface diffusion correlation time and the surface desorption time take similar values for each system, suggesting that surface mobility and desorption are linked processes. The bulk fluid diffusion correlation time is found to be two to five times the value for the pure liquid at room temperature for each system. Reanalysis of the oil-bearing shale yields diffusion time constants for both the oil and water constituents. The shale is found to be oil wetting and the water T_{1}^{-1} dispersion is found to be associated with aqueous Mn^{2+} paramagnetic impurities in the bulk water. These results escalate the NMR T_{1}^{-1} dispersion measurement technique as the primary probe of molecular-scale dynamics in porous media yielding diffusion parameters and a wealth of information on pore morphology.

Novel time-of-flight fiber dispersion measurement technique using supercontinuum light sources and acousto-optical tunable filters.

Long-distance fiber links require precise knowledge of fiber dispersion characteristics. Similar dispersion characteristics are necessary for supercontinuum broadband laser absorption spectroscopy (SCLAS) to allow proper data evaluation and species concentration determination, as well as numerous other applications. In this work, a time-of-flight approach to measuring the dispersion characteristic of fibers with supercontinuum laser light sources (SCLs) and acousto-optical tunable filters (AOTFs) is presented. Broadband emission of the SCL is filtered with a narrowband AOTF and dispersed in time by the fiber under test. By using the wavelength-specific delay, the dispersion characteristic can be calculated. The technique is especially suited for longer fibers and was verified against a state-of-the-art phase-shift-based dispersion measurement system. Advantages of the new approach include solely utilizing SCLAS system components, as well as a high level of automation and wide spectral coverage, ranging from 1100 to 1700nm in a single measurement setup.

Use of a modified Drude's equation to investigate the optical rotation property of sugars

Sugar compounds (glucose, xylose, arabinose, and galactose) and their mixed solutions were examined using the optical rotatory dispersion (ORD) measurement technique with a modified Drude's equation. Commonly, spectroscopic methods utilize the observation of absorption bands which are, in the case of sugars, located in the UV-spectral range. However, the polarization method used in this study allows us to investigate sugar samples in a convenient visible spectral range where sugar solutions are relatively transparent. The ORD set-up can be simple and robust as we will demonstrate: the self-constructed apparatus consists of only two linear polarizers, placed one after the other, with the angle between their transmission axes adjusted to 45°. The sugar solution sample in a cuvette was put between the polarizers. The set-up was connected to a sample compartment of a commercial UV–vis spectrophotometer. The method provided us the specific optical rotation and concentration of sugar solutions with a reasonable accuracy. In addition, the optical rotation value for mixed sugars has been found to be the average optical rotation value of individual sugar content. Beside use in the laboratory environment, the method could also have industrial on-site monitoring applications, for example in bio fuel production.

Frequency-Derivative Measurement Technique for Dispersive Effects in Single-Mode Fiber Systems

An optical dispersion analysis and measurement technique based on frequency derivatives of the Jones matrix is presented. This approach enables measurement of all scalar and polarization-dependent phase and amplitude dispersion effects over a broad wavelength range in a single sweep. Owing to its differential nature, it can be more accurate than techniques that calculate dispersion by comparing phase and amplitude measurements from adjacent wavelengths in a sweep. The method involves measuring eight elementary parameters related to the frequency derivative of the Jones matrix. An experimental setup and data analysis methods for measuring the elementary parameters are presented. Three optical devices exhibiting various dispersive effects are tested, and the ability to measure all the elementary parameters is demonstrated. Elementary parameter estimation error is 1-2 ps in this proof-of-concept experiment.

Development of an Improved Acoustic Dispersion Measurement Technique in Liquids

The present paper is an extension of our earlier series of studies carried out on technique of ultrasonic phase velocity measurement in liquid/mixtures (Joshi et al. MAPAN J Metrol Soc India 29:9–17, 2014) with modified/improved designs related to jigs and fixtures, temperature stability arrangement, improved data acquisition for digitization by using 2.5 GS/s sampling frequency. An improved dispersion measurement technique in liquids is described herein this paper. We have also described a method of estimation of measurement uncertainty in the ultrasonic phase velocity measurements. The parametric uncertainty components are evaluated using Type A and Type B approaches. Several design and developmental aspects are also introduced to enable the technique with improved measurement uncertainty. The technique thus developed has been tested on water sample with repetitive measurements, achieving measurement uncertainty of ±0.5 ms−1 in phase velocity. The repetitive experiments have been performed in water as a function of temperature ranging from 15 to 35 °C and frequency range from 3–7 MHz. The results are discussed in the light of improvements in the technique.

Two-dimensional single-shot measurement of angular dispersion for compressor alignment

Misalignment of the stretcher-compressor stages of chirped pulse amplification (CPA) lasers can aggravate the spatiotemporal shape of ultrashort pulses. We demonstrate a simple technique for angular dispersion measurement, which offers real-time single-shot two-dimensional characterization across the entire beam profile. The accuracy of our pilot experiment approaches its current theoretical limit of 0.1 μrad/nm. Unlike the current one-dimensional techniques working in the near field, the method works in the far field; hence, it is especially appropriate for assisting the most accurate alignment of a CPA laser compressor ensuring the maximum intensity on the target.

Time-domain multimode dispersion measurement in a higher-order-mode fiber

We present a new multimode dispersion measurement technique based on the time-of-flight method. The modal delay and group velocity dispersion of all excited modes in a few-mode fiber can be measured simultaneously by a tunable pulsed laser and a high speed sampling oscilloscope. A newly designed higher-order-mode fiber with large anomalous dispersion in the LP(02) mode has been characterized using this method, and experimental results are in good agreement with the designed dispersion values. The demonstrated technique is significantly simpler to implement than the existing frequency-domain or interferometry-based methods.

Spectral interferometry-based chromatic dispersion measurement of fibre including the zero-dispersion wavelength

We report on a simple spectral interferometric technique for chromatic dispersion measurement of a short length optical fibre including the zero-dispersion wavelength. The method utilizes a supercontinuum source, a dispersion balanced Mach-Zehnder interferometer and a fibre under test of known length inserted in one of the interferometer arms and the other arm with adjustable path length. The method is based on resolving one spectral interferogram (spectral fringes) by a low-resolution NIR spectrometer. The fringe order versus the precise wavelength position of the interference extreme in the recorded spectral signal is fitted to the approximate function from which the chromatic dispersion is obtained. We verify the applicability of the method by measuring the chromatic dispersion of two polarization modes in a birefringent holey fibre. The measurement results are compared with those obtained by a broad spectral range (500–1600 nm) measurement method, and good agreement is confirmed.

Spatially Resolved Measurement in Waveguides With Arbitrary Chromatic Dispersion

A high-resolution technique for dispersion measurement in waveguides with arbitrary chromatic dispersion is reported. The technique is based on localization of four-photon mixing achieved by abrupt increase in signal-probe interaction along the measured waveguide. Arbitrary increase in optical power is achieved by counter colliding power transfer between signal and counterpropagating pump wave. The new technique was used to demonstrate meter-scale dispersion retrieval from highly nonlinear fiber for the first time. The measurement sensitivity exceeds that of the existing methods by two orders of magnitude.

Dispersion measurement technique based on the self-seeding laser oscillation of a Fabry–Perot laser diode

A simple dispersion measurement technique has been proposed and demonstrated by using the self-seeding laser oscillation of a Fabry–Perot laser diode through an optical closed-loop path. When the multi-mode optical pulses emitted from the laser are re-injected into the laser after traversing a fiber-under-test, a single mode laser oscillation occurs through the closed-loop path due to the group velocity difference between the pulses of different wavelengths. We measured the dispersion parameter of the fiber-under-test from the modulation frequency changes required to induce single-mode laser oscillations through the optical closed-loop path. The maximum measurement error was less than 1.5% for the optical fibers as compared with a commercial instrument.

Single-end Measurement of Polarization Mode Dispersion in Optical Fibers with Polarization-dependent Loss

A new re∞ectometric technique is proposed to measure the polarization mode dispersion (PMD) in optical flber links with polarization-dependent loss. Based on the PMD dynamical equation, some important relations can be obtained to make the backre∞ection mea- surement of PMD possible. Thus we can perform the single-end spectral resolved measurement of the difierential group delay and the difierential attenuation slope in both frequency and time do- mains simultaneously. In principle, this technique can be realized using continue-wave or pulsed probe lights and based on far-end Fresnel re∞ection or distributed Rayleigh backscattering. Some experimental results conflrm the validity of the proposed method. DOI: 10.2529/PIERS061005224120 Most of the polarization mode dispersion (PMD) measurement techniques require both flber ends to implement the tests, consequently, fleld tests on installed cables are time consuming and not simple (1). Thus the backscattering technique has been proposed to perform the single-end PMD measurement (1{3). In an optical flber link with polarization-dependent loss (PDL), due to the round-trip efiect, the round-trip complex PMD vector ~ WB = ~B+i ~B, which can be measured directly in the test, is only explicitly related with the flrst two elements of the complex PMD vector ~ W = ~ › + i~ ⁄ as (4) › 2 i ⁄ 2 = 4 i › 2 i ⁄ 2 ¢ ; ~B ¢ ~B = 4 ~L ¢ ~ ⁄L:

Optimization of chromatic dispersion measurement technique using relative power of two beating frequencies

AbstractOptimization study of the Chromatic Dispersion measurement technique using relative power of two beating frequencies is presented in this paper. The performance of the CD measurement technique is studied in terms of the measurement range and sensitivity as the wavelength separation is varied. Based on the mathematical model and experimental results the technique sensitivity increases with wavelength separation. However, this increase in sensitivity is traded off with narrower measurement range. The measurement technique is optimized at 5.0 GHz wavelength separation with sensitivity of 0.009 (dB/ps/nm) and measurement range of 2500 (ps/nm). © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2154–2156, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21893

Fabry-Perot 레이저의 자기궤환 레이저 발진을 이용한 색분산 측정법

Fabry-Perot 레이저의 자기궤환 레이저 발진을 이용한 색분산 측정법

In-service measurements of polarization-mode dispersion and correlation to bit-error rate

We introduce a nondisruptive in situ polarization-mode dispersion measurement technique using the sidebands of working channels and show that it compares favorably with the standard Mueller matrix method. Using this technique, we observed time correlations between the instantaneous differential group delay and bit-error rate on a 1000-km field-installed 43-Gb/s transmission system.