Mode Field Radius Research Articles

Cut-off wavelength and mode field radius determinations in monomode fibres by means of a new single measurement device

We present a new experimental set-up capable of providing measurements of both the cut-off wavelength and the mode field radius of monomode optical fibres. The work consists in an original implementation, by means of a single experimental device, of two efficient methods conceived previously in our laboratory: the azimuthal far-field analysis technique for and the analysis of the autocorrelation function of the far field for . Two components (a mirror and a small screen pierced by a narrow slit) are fixed or rotated at the output of the fibre tested, to suitably filter the far field, according to the required parameter. This parameter is finally computed from the temporal variations of the power detected after the slit. The results obtained for both and are demonstrated to be precise and reliable. The measurements are self-referenced and can be achieved for any length of fibre as well as for fibres in cables or installed optical links.

Precise and repeatable determination of the mode field radius by means of a simple measurement device

The measurement of the mode field radius is provided by a quick, accurate and repeatable method based on the analysis of the autocorrelation function of the far-field. The principle is described and the experimental results are successfully compared to those given by the method recommended by the CCITT.

Coupling of single-mode fibers to single-mode GRIN waveguides by butt-joining

We present an analytical expression for the mode field radius of the fundamental mode of a planar surface GRIN waveguide for the optimum coupling of radiation from a given single-mode fiber with a Gaussian mode field distribution. It is shown that the fundamental mode of a single-mode ion-exchanged waveguide can be represented by a Hermite-Gaussian profile. The method presented here allows the determination of suitable waveguide parameters for optimum coupling. Theoretical predictions are in good agreement with the experimentally measured efficiency when other losses are accurately accounted for.

Mode‐field‐diameter measurement method using a field mask

AbstractIn the mask method, which is one of the measurement procedures of estimation of the mode field size of single mode optical fibers, measurement setup can easily be devised. the advantage is that the overall system is small in size. However, there are few investigations with only a few reports on the physical properties of the field mask required in realization of the measurement method or the details of applications to the dispersion shifted optical fibers used in trunk lines. the present paper investigates the required physical characteristics of the mask and it is found that in order to keep the error in the measurement of the mode field radius below, the mask attenuation must be larger than 45 dB. Further, when the required attenuation is not satisfied by the mask, the equation under which there is still the possibility of field measurement is derived. Using the derived equation, it became clear that it is possible to measure the mode field radius of the 1.3 μm band and the dispersion shifted fibers by the far field method with deviations below 1 percent. Further, when such a method is devised to fit into the far end of the fiber cables, their mode field radius can be measured when the maximum cable loss is 45 dB.

Influence of the drawing ratio and the relative index difference on propagation characteristics in single-mode fibers with arbitrary refractive index profile

Simple formulas are derived for the sensitivity of dispersion, mode field radii, and cutoff wavelengths in single-mode fibers due to arbitrary variations of the drawing ratio and the relative index difference simultaneously. For calculations only the propagation characteristic spectrum of the ideal fiber is required. Some applications are given.

The effect of pump and signal field overlap with the ion distribution on the efficiency of an Er 3+-doped fibre amplifier

We report the use of a far-field scanning system to measure the pump and signal fields within erbium doped fibre amplifiers. Measurements were carried out on fibres with both uniform dopant throughout the core and dopant confined to the central region of the core. We have demonstrated that the improvement in amplifier performance associated with ion confinement is consistent with the change in overlap between pump and signal fields and the radial ion distribution. It is shown that most of the improvement available through the process of confinement can be obtained through restricting the dopant to the inner 40% of the pump mode field radius. The effects of radial ion confinement on the small-signal gain performance of amplifiers exhibiting pump excited states absorption are discussed and compared to the effects on amplifiers free from pump ESA. We conclude that the process of confinement is only of benefit in amplifiers free from the parasitic effects of pump excited state absorption.

Waveguide dispersion measurement technique for single-mode fibers using wavelength dependence of mode field radius

A waveguide dispersion measurement technique using a simple fitting function for wavelength dependence of the root-mean-square width in the far field and its theoretical measurement error are discussed. Results indicate that waveguide dispersion can be evaluated with theoretical accuracy of 0.5 ps/km/nm using this technique. The waveguide dispersions for conventional and dispersion-shifted fibers have been measured using the far-field pattern method. Good agreement between measured and theoretical values of waveguide dispersion was obtained. Material dispersion and dispersion sensitivity evaluation methods that are applications of this technique are also described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Propagation constant of single-mode fibers measured from the mode-field radius and from the bending loss

The propagation constant was measured directly using the fiber bending losses (FBI) at different wavelengths, the outcome was compared with the more indirect results of the mode-field radius (MFR) method, and the integration constant determined for the measured wavelengths. This constant was found to be reasonably wavelength-independent. The absolute value rests strongly on the propagation constant model, i.e. on the structure of its empirical formula. As a result it is proposed to use the simple MFR method to determine the relative wavelength dependence of the propagation constant, and to fix its absolute values with only one more complicated FBL measurement at a convenient wavelength. >

Mode-field radius of noncircular field single-mode fibre: new definition and application to calculation of splice loss and waveguide dispersion

A new definition of the mode-field radius (MFR) of a non-circular field single-mode fibre (NCSMF) is proposed, based on the quadratic moment of far-field distribution. Relations between MFR and splice loss, propagation constant and waveguide dispersion of the NCSMF are derived, which reduce to known results under cases of circular and Gaussian-elliptic field distribution.

Mode field radius definitions for arbitrary planar single-mode optical waveguides and their relations to splice loss and propagation constant

Root-mean-square and Laplacian mode field radius (MFR) definitions for planar single-mode optical waveguides (PSMOW) with arbitrary index profile are proposed based on the second moment of the near-field (NF) and far-field (FF) distributions. Expressions of these definitions in both NF and FF, as well as their simple relations to the propagation constant and splice loss between two identical waveguides, are derived.

Propagation constant and waveguide dispersion of single-mode fibers measured from far-field

Wavelength-dependent measurements of the far-field pattern can be evaluated to yield a mode-field radius. It was recently proposed to fit these data to a formula that contained all the parameters necessary to construct an empirical relation for the wavelength dependence of the propagation constant. The authors report on the feasibility of this technique, using actual measurement data. They discuss the calculation of the waveguide dispersion from the measured mode-field radius. In both cases the choice of the empirical fitting function proves to be of great importance. >

Experience with mode-field radius measurements

The transverse offset, and variable-aperture far-field methods have been applied to the measurements of the mode-field radii of two types of single mode optical fibre. Comparison with the results of calculations based on the measured refractive index profiles shows that discrepancies between the experimental results by the two methods may be confidently attributed to the deviation of the electromagnetic field in the fibre from a Gaussian form. A possible alternative test method for measuring the numerical aperture of a parabolic-index multimode fibre is described. The paper includes a number of comments on the technical problems associated with the measurement methods.

Measurement of mode field radius in axially nonsymmetrical single-mode fibers with arbitrary power distribution

A new method for the measurement of mode field radius in axially symmetrical and nonsymmetrical single-mode fibers with non-Gaussian power distribution is proposed. It is based on monitoring the power passed through a variable-width slit in the far field. A few results for different types of single-mode optical fiber are presented.

Waveguide-dispersion characteristics of dual-shape-core dispersion-shifted fibers

Waveguide-dispersion characteristics are discussed experimentally and numerically. The waveguide dispersions of both dual-shape-core (DSC) and graded-index types of dispersion-shifted fibers are evaluated from the measured wavelength dependence of the mode field radius. It is shown that the dispersion sensitivity to core-radius change of a bend-optimized DSC fiber is smaller than that of the graded-index dispersion-shifted fiber.

Mode field radius of dispersion flattened single mode fibers

We report a comparison between the main definitions of the mode field radius (MFR) in various dispersion flattened single mode fibers. The study shows that the Petermann and gaussian spot sizes for triangular core W-type fiber are larger compared to the fibers with other profiles and similar dispersion properties so as to give minimum splice loss.

Preferred approaches to the determination of optical fibre mode field diameter

The letter describes the properties of the two most useful definitions of the mode field radius of a single-mode optical fibre when they are evaluated in the presence of noise for both near-field and far-field measurements.

New method for mode-field radius measurements in single-mode fibres based on harmonics detection

A new, easily implementable technique for mode-field radius measurement is described. It is based on a dynamical filtering and the detection of two harmonics of the fibre output radiation. The results are presented and discussed.

Mode field radius measurements in single‐mode fibers by nfp technique

AbstractThere are various methods for measuring the mode field radius in single‐mode fibers. However, measurement accuracy of the methods has not been reported yet. This paper describes the error factors for the mode field radius measurement by NFP technique to improve the accuracy of this technique. The input optical (10) sensitivity of the infrared (IR) vidicon camera is investigated which affects the precision of the NFP technique. As a result, the nonlinearity and shading distribution of the IR vidicon camera are clarified. Moreover, error factors for the technique are investigated. On the basis of investigation, the measurement conditions for this technique to obtain high accuracy are specified. The mode field radius of various types of fibers is increased under these conditions. As a result, measurement of the mode field radius became possible with reproduction error of less than 0.1 μm.

Non-Gaussian model for fundamental-mode field in single-mode optical fibres

The model fits the fundamental-mode field better than the Gaussian distribution. It reduces the differences, caused by non-Gaussian field shapes, among methods for measuring mode field radius. Formulas are provided for calculating Petermann's mode field radius from lateral offset, pinhole scan and VAMFF data.

Application of harmonics detection to the measurement of mode field radius in single-mode optical fibers

In this paper, new techniques for the easy implementation of the measurement of the mode field radius in single-mode optical fibers are discussed. All of them are based on a dynamical filtering of the fiber output radiation and on a subsequent detection of suitable harmonic components. The capabilities of these procedures are considered, showing typical experimental results.