Modal Power Distribution Research Articles

Performance of Cladding Modified PANI‐ZnO Nanocomposite Glucose Oxidase Immobilized Fiber Optic Intrinsic Glucose Biosensor

SummaryThe cheapness, easy availability of raw materials, easy synthesis, good environmental stability, good electrical and optical properties, simple doping and de‐doping chemistry makes the place of polymers very important in sensing applications. Besides all the conducting polymers, polyaniline (PANI) has found comfortable and suitable for the immobilization of biomolecules. In the present study, we have fabricated PANI‐ZnO nanocomposite by chemical polymerization route and used to modify cladding of an optical fiber for immobilization of enzyme glucose oxidase (GOx) on it with the help of cross‐linking technique for the development of cladding modified fiber optic intrinsic glucose biosensor (FOIGB). The properties of deposited PANI‐ZnO nanocomposite have been studied. The sensitivity of prepared sensor in the form of power and modal power distribution (MPD) has also been reported.

A sound power measurement technique optimised for low-speed fan tones

Air-moving devices such as fans are routinely characterised experimentally in terms of their sound power, and sound quality which depends on both broadband and tonal noise levels. The International Organization for Standardization method 5136, widely used in industry and academia, estimates sound power in third-octave bands radiated into a duct. Since the International Organization for Standardization method is not designed for tone measurements and overlooks the unevenness of the modal power distribution, an extended method has been developed and implemented based on mode decomposition. The ‘two-port’ source model is formulated to include higher-order modes and applied for the first three modes which require six independent stationary measurements on each side or ‘port’. The resulting experimental rig is much shorter than the International Organization for Standardization rig and does not require anechoic terminations. Both methods have been used to characterise the same fan, and the results compared to understand tone measurement shortfall of the International Organization for Standardization rig.

Numerical simulation and optimization of beam quality of 2.1 μm Cr, Tm, Ho: YAG laser with symmetric spherical resonator based on gradient-reflectivity mirror

The thermal lens effect of 2.1μm Cr, Tm, Ho: YAG (CTH:YAG) solid-state laser under high pumping power condition is analyzed, and a symmetric spherical resonator which is insensitive to thermal focal length change is proposed to improve the beam quality of Fabry–Perot (F–P) resonator. Then the gradient-reflectivity mirror is introduced as output mirror to optimize the resonator mode and beam quality. Based on the scalar diffraction theory, the Fox-Li numerical iteration method and fast Fourier transform (FFT) algorithm are used to calculate the resonator mode and output power distribution of resonators with Gaussian, super-Gaussian and parabolic gradient mirror, respectively. By comparing the cavity loss and beam quality, one can find that the symmetric spherical resonator with a super-Gaussian mirror can provide the best output beam quality, it has the minimum cavity loss of 0.1907, the minimum far-field divergence angle of 1 mrad and the maximum power in the bucket (PIB) of 89.42%.

Encircled Angular Flux Representation of the Modal Power Distribution and Its Behavior in a Step Index Multimode Fiber

The optical properties of inline optical components inserted at the input to a multimode optical fiber (MMF) strongly affect the propagating modal power distribution (MPD). To realize stable systems with predictable reproducible performance and to encourage widespread use of MMF systems, improvements to the system design process and to the characterization process need to be made and new interface standards need to be defined. To this end, we have developed a new reproducible MPD measurement and representation together with its theoretical definition. By modifying the encircled flux (EF) representation, which is based on the near-field pattern of a graded-index multimode optical fiber (GI-MMF), we define the encircled angular flux (EAF) for step-index multimode optical fibers (SI-MMFs) based on their far-field patterns (FFPs). Using a SI-MMF, which is used for low cost short distance interconnects, as an example, we show the changes in the MPD along the fiber, reveal an unusual insertion loss-increasing phenomenon due to the evanescent tails of the core modes extending into the cladding, and characterize the equilibrium mode distribution (EMD) in the fiber. The EAF representation enables these phenomena to be quantified. We also propose an EAF template that consists of the target EMD and its tolerance. If device system designers use the EAF template to set the launch conditions, they can perform a fair assessment of the components, and they can design the system performance even if some components are replaced with others from a different supplier manufactured by a different method. We call this concept “Total MPD Management.”

Generalized modulational instability in multimode fibers: Wideband multimode parametric amplification

In this paper intermodal modulational instability (IM-MI) is analyzed in a multimode fiber where several spatial and polarization modes propagate. The coupled nonlinear Schr\"odinger equations describing the modal evolution in the fiber are linearized and reduced to an eigenvalue problem. As a result, the amplification of each mode can be described by means of the eigenvalues and eigenvectors of a matrix that stores the information about the dispersion properties of the modes and the modal power distribution of the pump. Some useful analytical formulas are also provided that estimate the modal amplification as function of the system parameters. Finally, the impact of third-order dispersion and of absorbtion losses is evaluated, which reveals some surprising phenomena into the IM-MI dynamics. These outcomes generalize previous studies on bimodal MI, related to the interaction between two spatial or polarization modes, to the most general case of $N>2$ interacting modes. Moreover, they pave the way towards the realization of wideband multimode parametric amplifiers.

Wavelength dependence of stress-induced time of flight variations in graded-index multimode fibers

We investigate the wavelength dependence of stress-induced time of flight variations in graded-index multimode fibers (GI-MMFs) for wavelength λ=1.26μm ∼1.58μm, theoretically and experimentally. Calculations were made based on simple equations using the refractive index of silica fibers. We measured the wavelength dependence of stress-induced time of flight variations by a newly proposed measurement method. We confirmed the similar wavelength dependence of GI-MMFs to that for standard single mode fibers (SSMF). However, the value of them is different. We compare the experimental and theoretical results for two types of fibers. The comparison indicates that the difference of stress-induced time of flight variations between two types of fibers is mainly due to the group velocity difference. We conclude that there is no significant difference of the photo-elastic constant between the measured SSMFs and GI-MMFs. Although many properties of GI-MMFs depended on the mode power distribution in general, we conclude the dependence of stress-induced time of flight variations on mode power distribution is small for the measured fibers.

Quasi-periodic oscillations in accreting magnetic white dwarfs

Magnetic cataclysmic variables are close binary systems containing a strongly magnetized white dwarf that accretes matter coming from an M-dwarf companion. High-energy radiation coming from those objects is emitted from the accretion column close to the white dwarf photosphere at the impact region. Its properties depend on the characteristics of the white dwarf and an accurate accretion column model allows the properties of the binary system to be inferred, such as the white dwarf mass, its magnetic field, and the accretion rate. We study the temporal and spectral behaviour of the accretion region and use the tools we developed to accurately connect the simulation results to the X-ray and optical astronomical observations. The radiation hydrodynamics code Hades was adapted to simulate this specific accretion phenomena. Classical approaches were used to model the radiative losses of the two main radiative processes: bremsstrahlung and cyclotron. The oscillation frequencies and amplitudes in the X-ray and optical domains are studied to compare those numerical results to observational ones. Different dimensional formulae were developed to complete the numerical evaluations. The complete characterization of the emitting region is described for the two main radiative regimes: when only the bremsstrahlung losses and when both cyclotron and bremsstrahlung losses are considered. The effect of the non-linear cooling in- stability regime on the accretion column behaviour is analysed. Variation in luminosity on short timescales (~ 1 s quasi-periodic oscillations) is an expected consequence of this specific dynamic. The importance of secondary shock instability on the quasi-periodic oscillation phenomenon is discussed. The stabilization effect of the cyclotron process is confirmed by our numerical simulations, as well as the power distribution in the various modes of oscillation.

Mode-dependent characteristics of Rayleigh backscattering in weakly-coupled few-mode fiber

We theoretically investigate the mode-dependent characteristics of Rayleigh backscattering arising in weakly-coupled few-mode fibers (FMFs). Based on the theory of Lorentz reciprocity and surface wave excitation, we derive a general analytical equation of excitation efficiency and power distribution of Rayleigh backscattering light among backward propagation modes under the condition of impulse response. Thus, we are able to characterize the Rayleigh backscattering of weakly-coupled FMF with arbitrary refractive index profile. As for the weakly-coupled FMF with a step-index profile, the power distribution ratio of individual modes in the Rayleigh backscattering light is mainly determined by the forward propagation mode. In particular, the backscattering mode with the same profile as the forward propagation one has the highest excitation efficiency. The FMF parameters have influence on the total backscattering power, but little effect on the mode power distribution ratio.

A novel multimode hybrid energy storage system and its energy management strategy for electric vehicles

This paper proposes a novel topology of multimode hybrid energy storage system (HESS) and its energy management strategy for electric vehicles (EVs). Compared to the conventional HESS, the proposed multimode HESS has more operating modes and thus it could in further enhance the efficiency of the system. The rule-based control strategy and the power-balancing strategy are developed for the energy management strategy to realize mode selection and power distribution. Generally, the DC–DC converter will operate at peak efficiency to convey the energy from the batteries to the UCs. Otherwise, the pure battery mode or the pure ultracapacitors (UCs) mode will be utilized without the DC–DC converter. To extend the battery life, the UCs have the highest priority to recycle the energy and the batteries are isolated from being recharged directly during regenerative braking. Simulations and experiments are established to validate the proposed multimode HESS and its energy management strategy. The results reveal that the energy losses in the DC–DC converter, the total energy consumption and the overall system efficiency of the proposed multimode HESS are improved compared to the conventional HESS.

Glucose oxidase immobilized PANI cladding modified fiber optic intrinsic biosensor for detection of glucose

In the present study, we report design, development and study of polyaniline (PANI) cladding modified fiber optic intrinsic glucose biosensor (FOIGB) for glucose sensing applications. Chemically and biologically sensitive material PANI has been exploited for the preparation of sensing element by cladding modification technique. Enzyme-glucose oxidase (GOx) was immobilized on porous supportive matrix of PANI using glutaraldehyde as a cross-linking agent. As-synthesized and deposited PANI film on fiber optic core was characterized by ultraviolet–visible and Fourier transform infra-red spectroscopies. X-ray diffraction and field emission scanning electron microscopy were employed to study structure and morphology of modified cladding. Sensing parameters, such as modal power distribution (MPD), sensing response, selectivity and stability were analyzed in order to study the performance of sensor. These parameters were determined by measuring change in optical power and MPD. The sensor, stored at a temperature 4°C, showed lowest detection limit of 10nM and found stable up to 36 days. It also showed good selectivity toward glucose and stability with high result reproducibility.

Sensitivity and design of grating-assisted bimodal interferometers for integrated optical biosensing.

The sensitivity of bimodal waveguides for integrated optical biosensors is compared to single mode waveguides and grating-assisted bimodal interferometers are proposed as improved sensor concept. Grating-assisted bimodal interferometers are an elegant and compact sensor concept, which features easy fabrication and overcomes typical weaknesses of classical Mach-Zehnder interferometers. Long period gratings for mode conversion in the proposed sensor concept have been simulated employing the FDTD method. Such gratings give full control over the power distribution in the waveguides modes, which is not possible with other methods. Designs for three typical material systems are given and fabrication tolerances were investigated.

Transverse mode propagation studies in a thulium-doped fiber laser

In this paper, we apply a transverse mode propagation model of thulium-doped fiber laser based on propagation equations. Based on this model the behaviors of transverse mode propagation are demonstrated and individual transverse mode power distributions of output are simulated numerically under various conditions including bending radius, fiber length, and pump power. Furthermore, the output power and beam quality characteristic for the thulium-doped fiber laser are investigated experimentally, and the experimental results agree well with the numerical results.

Dependence of the signal of a multimode fiber-optic interferometer on the mode power distribution

Multimode fiber-optic interferometer (MFI) signals formed under conditions of external actions and a change in the optical power distribution between modes along the fiber have been studied. It is experimentally established that parameters of the MFI signal significantly depend on the number of propagating modes in the region of external action upon the fiber.

Terahertz plasmonic waveguide based on metal rod arrays for nanofilm sensing.

A high-aspect-ratio metallic rod array is demonstrated to generate and propagate highly confined terahertz (THz) surface plasmonic waves under end-fire excitation. The transverse modal power distribution and spectral properties of the bound THz plasmonic wave are characterized in two metallic rod arrays with different periods and in two configurations with and without attaching a subwavelength superstrate. The integrated metallic rod array-based waveguide can be used to sense the various thin films deposited on the polypropylene superstrate based on the phase-sensitive mechanism. The sensor exhibits different phase detection sensitivities depending on the modal power immersed in the air gaps between the metallic rods. Deep-subwavelength SiO(2) and ZnO nanofilms with an optical path difference of 252 nm, which is equivalent to λ/3968 at 0.300 THz, are used as analytes to test the integrated plasmonic waveguide. Analysis of the refractive index and thickness of molecular membranes indicates that the metallic rod array-based THz waveguide can integrate various biochip platforms for minute molecular detection, which is extremely less than the coherent length of THz waves.

Modal characteristics analysis of a doubly clad optical fiber with semi-weakly guiding approximation

Modified characteristic equations for doubly clad multimode fibers were rigorously derived under semi-weakly guiding approximation in this article. The analytical expressions of the power flows distributed in the three regions of fiber cross section are also given. Different from previous works, results in this paper elucidate that, other than the inner cladding, the refractive indices also hold a non-ignorable influence on the modal power distribution and mode behaviors. By comparing the results of two models, this article demonstrates that the singly clad fiber model may not be suitable for analyses of common doubly clad fibers.

Experimental Measurements of Path Length Sensitivity in Coherent Beam Combining by Spatial Filtering

The supermode behavior of lasers coherently coupled by a passive spatially filtered cavity has been experimentally measured as a function of path length error between laser cavities. A custom laser-diode pumped Nd:YAG laser is constructed containing two laser channels coupled by a spatial filter. The supermodes are seen to exhibit two different types of behavior depending on the magnitude of the relative path length error. When the path length error is small, the two supermodes present different cavity loss values and can be differentiated by gain. However, when the error exceeds a specific value, the two supermodes have identical loss and different resonant frequencies. Experiments show the two distinct regions predicted by theory, and quantitatively verify the loss, oscillation frequency, and modal power distribution of the supermodes as a function of path length error.

Theoretical and simulation analysis of a novel multiple-input multiple-output scheme over multimode fiber links with dual restricted launch techniques

Different launching methods over multimode fiber (MMF) are reviewed and compared under various aspects such as coupling coefficient, mode power distribution, and bit error rate performance. Among these, center launch and ring launch are elaborated and chosen as the inputs of multiple-input multiple-output (MIMO) scheme for center launch exciting limited lower-order modes while ring launch exciting limited higher ones. Furthermore, we discuss the theoretical background and give a new wide-band MMF MIMO mathematical model. This paper also proposes a novel MMF MIMO system combining the dual restricted launches together with multi-segments receiving. The simulated results indicate that an aggregate data rate of 20 Gb/s over 800-m graded index-multimode fiber can be achieved by using this newly established MIMO scheme.

Structural and wavelength dependence of mode power distribution for a broadband dispersion compensating microstructured fiber

Approximate empirical analysis of mode power distribution (MPD) carried by the fundamental mode is newly investigated based on a broadband dispersion compensating microstructured fiber (MF). The fraction of modal power in the core region, η, is defined with the help of extending the applicability of well-established classical optical fiber theories to MFs. In doing so, the influences of structural parameters and wavelength on MPD characteristics of the fundamental mode are systematically analyzed in detail based on simple physically consistent concepts of conventional fibers. As a result, it is shown that for the optimum MF design in Ref. [11] as a multimode fiber, when the number of guiding modes increases, the mode power ratio of the fundamental mode constantly increases from 69.4%; in addition, we find that as wavelength increases within 1.2–1.6μm, mode power confinement ability of the fundamental mode is lessened for single-mode propagation, whereas for multimode propagation it becomes enhanced.

Optimal design of MPD based fiber optic strain sensors and comparison of power-meter and CCD camera measurements

In this paper, we consider optimal sensor design problem and compare power-meter and CCD camera based techniques for strain measurements using Modal Power Distribution (MPD). MPD is a sensitive and low-cost fiber optic sensing technique which uses spatial intensity modulation in two dimensional setting. In a power-meter based fiber optic sensor, light intensity is measured at one or more points, and selection of these points is usually very critical in sensor design. Single point based sensors are not usually very successful, because of the time varying feature of a laser source output intensity. To the best of authors’ knowledge, most of the power-meter based MPD sensors utilize a single photo-detector, and there is only one known work where two photo-detectors are used with no optimization on measurement locations. In this work, we both consider optimal measurement location selection problem, and compare of power-meter and CCD camera based sensor measurements. We also show that there is an almost one-to-one relationship between CCD based and power-meter based fiber optic sensor measurements, which allows estimation of power-meter based measurements using CCD camera images. In our experimental setup, power-meter measurements and CCD camera images were recorded for different strain values. Power-meter measurements were estimated from CCD camera images with an average error of less than 4% by utilizing image processing techniques and non-linear least squares techniques.

Near-Field Measurements and Mode Power Distribution of Multimode Optical Fibers

This paper analyzes the impact of some of the most common uncertainties arising in the computation of modal transfer function (MTF) and mode power distribution (MPD) in multimode fibers (MMFs). The evaluation of these parameters is carried out following a procedure that is currently being tested in the framework of an international round robin before becoming a recognized standard. MTF and MPD are key parameters for the determination of device excitation conditions and for the determination of whether a so called ¿equilibrium modal distribution¿ (EMD) has been achieved. The procedure evaluates these parameters by relying on near-field (NF) measurements, and this paper investigates the effects related to the nonlinearity of the camera used to grab the images, the image scale factor, and the defocus. In particular, the experimental assessment of these effects evidences the fault-tolerant properties of NF measurement provided some precautions are taken in the images' acquisition and elaboration. Then, given the importance of operating the devices under an EMD, some typical techniques to achieve such a condition are reviewed, and an experimental realization of an effective mode conditioner is presented.