Showing papers on "Equilibrium mode distribution published in 2003"

Improved large-mode-area endlessly single-mode photonic crystal fibers

Abstract: We numerically study the possibilities for improved large-mode-area endlessly single-mode photonic crystal fibers for use in high-power delivery applications. By carefully choosing the optimal hole diameter, we find that a triangular core formed by three missing neighboring air holes considerably improves the mode area and loss properties compared with the case with a core formed by one missing air hole. In a realized fiber we demonstrate an enhancement of the mode area by ∼30% without a corresponding increase in the attenuation.

Photonic crystal fiber design based on the V-parameter.

Abstract: Based on a recent formulation of the V–parameter of a photonic crystal fiber we provide numerically based empirical expressions for this quantity only dependent on the two structural parameters—the air hole diameter and the hole-to-hole center spacing. Based on the unique relation between the V–parameter and the equivalent mode field radius we identify how the parameter space for these fibers is restricted in order for the fibers to remain single mode while still having a guided mode confined to the core region.

Quantitative estimates of mode coupling and differential modal attenuation in perfluorinated graded-index plastic optical fiber

Abstract: The performance of plastic optical fiber is greatly influenced by the related but distinct effects of mode coupling and differential modal attenuation (DMA). We establish a method for estimating the matrix that governs both of these effects and allows us to distinguish the two. We obtain partial quantitative estimates of this matrix for a particular graded-index plastic optical fiber (GI-POF). The sample we studied exhibited strong but incomplete mode coupling over 100-m lengths, while DMA was largely limited to a centerline defect. We show that much of the loss of the fiber can be attributed to mode coupling between mode groups with similar effective indexes.

Mode field patterns and preferential mode coupling in planar waveguide-coupled square microcavities.

Abstract: We report a numerical and analytical study of mode field patterns and mode coupling in planar waveguide-coupled square microcavities, using two-dimensional (2-D) finite-difference time-domain (FDTD) method and k-space representation. Simulated mode field patterns can be identified by k-space modes. We observe that different mode number parities permit distinctly different mode field patterns and spectral characteristics. Simulation results suggest that k-space modes that nearly match the waveguide propagation mode have a relatively high coupling efficiency. Such preferential mode coupling can be modified by the mode number parity.

Quantitative characterization of higher-order mode converters in weakly multimoded fibers.

Abstract: We present a rigorous analysis methodology of fundamental to higher order mode converters in step index few mode optical fibers. We demonstrate experimental conversion from a fundamental LP01 mode to the higher order LP11 mode utilizing a multiple mechanical bend mode converter.We perform a quantitative analysis of the measured light intensity, and demonstrate a modal decomposition algorithm to characterize the modal content excited in the fiber. Theoretical modelling of the current mode converter is then performed and compared with experimental findings.

Electrical spectrum measurements of dispersion in higher order mode fibers

Abstract: We present a novel technique for measuring the chromatic dispersion of the higher order mode of an optical fiber. The measurement technique is simple, accurate, and capable of measuring the dispersion of kilometer lengths of fiber without the need for mode converters. The dispersion of the LP/sub 02/ mode is measured for several different fibers, and accuracies of better than 1%, compared with a measurement with the modulation phase shift method, are achieved.

Optical fiber polarization mode dispersion measurement method and measurement device

Abstract: An optical fiber polarization mode dispersion measurement method includes a step of inputting a pulse light subjected to a single rectilinear polarization to an optical fiber to be measured, a step of isolating the single rectilinear polarization from the backward scattering light by the input pulse light, a step of detecting the light intensity as time series data from pulse light generation, a step of calculating irregularities of the light intensity in the time series data, and a step of evaluating the polarized mode dispersion of the optical fiber to be measured.

Polarization mode dispersion of spun fibers with randomly varying birefringence.

Abstract: We show analytically how periodic spinning affects the polarization mode dispersion of a fiber in three different practical regimes that are determined by the values of three length scales: the beat length, the birefringence correlation length, and the spin period. We determine in which limits the spin is effective in reducing the mean differential group delay.

Optical signal processing using a vertical-cavity surface-emitting laser with external optical injection

Abstract: A novel optical signal processing using an optically pumped vertical-cavity surface-emitting laser (VCSEL) with an external optical input is proposed. The mode transition between a fundamental and a high-order transverse mode is induced by an external optical injection. When we select a fundamental transverse mode through a single-mode fiber as an output signal, we are able to realize non-linear transfer functions, which may be useful for re-amplification and re-shaping in high speed photonic networks. The switching characteristic of a 1.55 μm optically pumped two-mode VCSEL has been simulated by using a two-mode rate equation, including the effects of spatial hole burning and spectral hole burning as gain saturation coefficients. Also, the detuning effect in the injection locking is investigated. When the wavelength of an input light with a fundamental mode is slightly longer than that of a VCSEL operating in a 1st-order transverse mode, the transverse mode of the VCSEL is switched to a fundamental mode at a critical input power level. This gives us an ideal 2R function with amplification and nonlinear transfer functions.

The surface mode of a dielectric waveguide with metal substrate

Abstract: The conditions of excitation and the waveguide characteristics are determined in an analytical form for the TM0 mode of a planar waveguide with metal substrate. This mode has a surface character, in contrast to other (bulk) modes excited in the system. The propagation and damping constants and the energy flux density distributions are compared for the TM0 and TE0 modes.

Design of mode converters for generating the TE11 mode from TM01 vircator at 4GHz

Abstract: This work reports on measurements and calculations (coupled mode equations) on the conversion of transverse magnetic TM01 vircator mode at 4 GHz to the linearly polarized TE11 mode by means of mode converter systems using a circular waveguide with curvature. The mode converter is composed of a 38.78° bend with 39.07 cm curvature and a 50.78° inverse bend with 25.24 cm curvature in 9 cm internal diameter (ID) circular waveguide. The efficiency of conversion from TM01 to TE11 at 4 GHz exceeds 99%, and the overall efficiency from TM01 to TE11 exceeds 90% over a calculated range of 3.72–4.8 GHz.

Method and apparatus for optical mode conversion

Abstract: A mode conversion apparatus including a dynamic waveguide section associated with a plurality of control elements that, when activated, are able to produce a periodic refractive-index perturbation pattern in the dynamic waveguide section, wherein the periodic refractive-index perturbation pattern is able to convert at least a fraction of an input signal from a first guided mode of the dynamic waveguide section into a second guided mode of the dynamic waveguide section.

Systems and methods for accurately measuring low values of polarization mode dispersion in an optical fiber using localized external perturbation induced low mode coupling

Abstract: Systems and methods are disclosed for measuring Polarization Mode Dispersion (PMD) of single-mode optical fiber. The method allows for a faster and easier method of accurately measuring intrinsic ultra low PMD optical fiber in a low mode coupling state. The method involves the introduction of a plurality of localized external perturbations on the optical fiber, after which the optical fiber is allowed to reach a steady state, and then measurement of the differential group delay occurs using standard measurement techniques. The plurality of localized external perturbations is altered followed by another measurement of the differential group delay. After obtaining a sufficient number of measurements to provide a Maxwellian distribution, the Polarization Mode Dispersion value can be calculated as the average of the distribution.

Development of an Adaptive Polarization-Mode Dispersion Compensation System

Abstract: Polarization-mode dispersion (PMD), in single-mode optical fibers, is a phenomenon that can limit the bit-rate-distance product of amplified, lightwave communication systems. PMD compensation is a solution to overcome the limitations posed by PMD. However, compensation is complicated due to the random nature of PMD. Therefore, adaptive compensation techniques are required. We modified an adaptive PMD compensation system that was earlier developed and made it robust and bit-rate independent. The new setup uses the degree of polarization (DOP) of the received optical signal for monitoring the fiber-link's PMD. An analog voltage equivalent of the DOP, commonly referred to as the PMD monitor signal, is used for the PMD compensation. We performed experiments to identify the effect of polarization scrambling on the PMD monitor signal and to find the appropriate range of scrambling frequencies. The appropriate polarization scrambling frequency range for the present setup was determined to be between 80 Hz and 100 Hz. Next, we performed different tests on the adaptive PMD compensation system. The time taken by the compensator to complete a compensation cycle was determined to be 100 s. OSNR (optical signal to noise ratio) tests were conducted from which it was determined that the PMD compensator could perform satisfactory compensation at 10 dB of OSNR and above. We then successfully performed a field trial of the adaptive PMD compensation system on an underground fiber-optic link spanning about 95 km.

Characteristics of the transmission spectrum of the long period fiber gratings based on the coupling of core mode to the higher order cladding modes

Abstract: The characteristics of the transmission spectrum of the Long-period fiber gratings (LPFGs) based on the coupling of core mode to a higher order cladding mode (HE mode) are investigated using the coupled mode theory. This kind of LPFGs is different from that based on the coupling of core mode to a lower order cladding mode because of the effect of the coupling of core mode to EH cladding mode. When the cladding mode order is higher, the coupling coefficients of core mode to HE and EH cladding modes are comparable and both of the propagation constants of HE and EH cladding modes approach, so the spectrum has an additional loss peak. The bandwidth of LPFG based on the coupling of core mode to different cladding mode differs greatly. With the change of the mode orders from lower to higher, the transmission spectrum changes from narrow to wide and more narrow.

Device and method for producing a defined mode distribution in an optical waveguide

Abstract: The invention relates to a method and device for producing a defined mode distribution in an optical wave guide. The inventive device comprises a light source (1) optically connected to the first butt end of the front part of a first optical fibre (7), the second butt end of the front part of the first optical fibre (7) is optically connected to the first butt end of the front part of the second optical fibre (4) with the aid of an air gap (3), and the second butt end of the front part of the second optical fibre (4) is connected to an interface (5) in such a way that the second optical fibre (4) is optically connected to an optical waveguide. Adequate configuration of coupling geometry makes it possible to adjust the air gap (3) between two optical fibres (4,7) in such a way that the mode distribution of an input power of the optical waveguide corresponds to an equilibrium mode distribution (EMD).

Fiber-optic interferometer and interfering method thereof

Abstract: A fiber-optic interferometer is provided. The interferometer includes a first dual-mode optical fiber for receiving a light input and exciting a first spatial mode and a second spatial mode, a first modal processor connected to the first dual-mode optical fiber for selecting the first spatial mode and the second spatial mode, a second dual-mode optical fiber connected to the first modal processor for propagating the first spatial mode and the second spatial mode and producing a phase shift (Δ φ) between the first spatial mode and the second spatial mode in response to an external perturbation effect, a second modal processor connected to the second dual-mode optical fiber for re-selecting the first spatial mode and the second spatial mode and producing a first light output interference pattern, and an analyzer having a polarization axis and connected to the second modal filter for adjusting the first light output interference pattern to produce a second light output interference pattern, so that the second light output interference pattern obtains an optimal contrast (C) through an adjustment of the polarization axis.

Measurement of second-order polarization mode dispersion in single mode fiber with Poincare sphere method

Abstract: We measured the second-order polarization mode dispersion (SOPMD) in a 75 km single mode fiber with the Poincare sphere method. The parallel component and perpendicular component (also called the depolarization component) of SOPMD were analyzed, and the statistical properties of them were also analyzed. According to these we found that the perpendicular component has a greater impact on pulse than that of the parallel component in mean.

Mode filtering and mode selection for multimode optical fibre with core and envelope, which has periodic index structure with rising reflection capacity of envelope only for specified transversal mode

Abstract: The multimode optical fibre has core and envelope, with latter containing periodic index structure, with increasing reflection capacity of envelope for specified transversal mode only. Thus only this transversal mode can propagate along optical fibre. For mode selection optical fibre cross-section has periodically variable refraction index structure, which permits only specified mode to propagate along optical fibre, with specified mode selected as desired mode only. An Independent claim is also included for optical fibre.

Dispersion-compensation fiber using higher order mode

Abstract: The fibre optic dispersion compensation has a profiled index from the fibre center to the outside, then a constant gain with profile providing mix fundamental/upper order mode propagation.

Electrical estimation of polarization mode dispersion parameters for compensation

Abstract: A method to estimate the parameters of polarization mode dispersion (PMD) from the received signal power is developed and used to mitigate pulse distortion due to PMD.

Metro Ring Node Module Based on Polymeric

Abstract: is? cm and its length 2.5 cm. Propagation losses of the s-bend channel waveguides. tvmicallv 5 to 6 cm lane. were meas~ied~usind iib'ber dad-coupling technique [SI. Typically, light at 1.55 pm is coupled via a single mode fiber into the channel waveguide and output is recorded via either a single mode fiber or an objective lens. Using this technique, knowing the transmission of the objective lens and the fibers. both propagation and coupling losses are simultaneously measured. The lowest measured propagation losses are 0.4 dB/cm and coupling losses are typically around 1.5 dB. The coupling losses are primarily due to the mode mismatch between the Gaussian mode of fiber and the single mode solgel waveguide. The FWHM of the current sol-gel waveguide is estimated to be 6 pm to 7 Vm, while that of single mode fiber is 9 pm to I1 pm. Typical power uniformities are

Second harmonic generation with a high-order mode laser beam

Abstract: Second harmonic generation can be highly efficient with a laser operating with a single high order mode. A 90% increase in output power was obtained with a Q-Switch Nd:YAG laser when it was operating with TEM01 rather than TEM00 mode.