New field measurement system for single-mode fibre dispersion utilising wavelength division multiplexing technique

A new system designed to measure the chromatic dispersion of installed single-mode fibres is presented. This system utilises the modulation phase technique but eliminates the reference laser and fibre. A large dynamic range was demonstrated by the measurement of an 81.1 km length of fibre.     

Refracted power technique for cutoff wavelength measurement in single-mode waveguides

A technique to measure the local (2?3 mm) values of cutoff wavelength ?c in single-mode waveguides is described. The technique, insensitive to the length of waveguide used, involves the spectral measurement of refracted power. The feasibility of using the cutoff wavelength determined by this technique to predict the zero dispersion wavelength is also studied.     

Polarization mode dispersion measurement in elliptical core single-mode fibers by a spatial technique

Polarization mode dispersion in elliptical core single-mode fibers has been measured by a spatial technique based on a visibility maximum position measurement in an interferometer. Using the technique, wavelength dependence of the modal dispersion has been measured by varying optical source wavelength between 821 and 904 nm. As a result, contribution of geometrical and strain birefringences on the modal dispersion has been evaluated, and normalized frequency dependence of the modal dispersion has been clarified. Moreover, the dispersion compensation effect has been observed by interchanging the fast and slow modes of two fibers at a splice point. The experimental results reveal that the spatial technique is very useful for polarization mode dispersion measurement.     

Wavelength dependence of polarisation mode dispersion in elliptical-core single-mode fibres

Polarisation mode dispersion in elliptical-core single-mode fibres has been measured by a spatial technique based on a visibility maximum position measurement in an interferometer. Using the technique, wavelength dependence of the modal dispersion has been measured by varying optical source wavelengths between 821 and 904 nm. As a result, contribution of geometrical and strain birefringences on the modal dispersion has been evaluated, and normalised frequency dependence of the modal dispersion has been clarified.     

Characterization of single-mode fibers from wavelength dependence of modal field and far field

We present direct methods for determination of equivalent-step-index (ESI) parameters and file modal field by measurement of the wavelength dependence of the far-field intensity in single-mode fibers. A comparison is made with the spot-size method commonly used for characterization of such fibers. A new technique for measuring the LP11mode cutoff wavelength is also presented.     

Analysis of mode field radius calculated from single-mode fiber far-field radiation patterns

We have investigated the angular range and mesh size required to calculate accurate mode field radii (MFR) from single-mode fiber far-field radiation patterns using the inverse Hankel transform. A computer aided fiber modeling program was used to calculate near-field mode distributions for both step-index and triangular index fibers at 1.55 μm. These distributions were then transformed to the far-field and used as input "data" for the inverse transform studies. Experimental far-field data measured on fibers similar to those modeled were also used. We find that the MFR is insensitive to mesh sizes less than 0.6° but the range of far-field data required depends upon the fiber design and the criteria used to determine the MFR. This study provides guidelines for calculating accurate MFR from experimental data when using the Hankel transform.     

Polarization dispersion measurement in long single-mode fibers with zero dispersion wavelength at 1.5 µm

Polarization dispersion in 1 km long single-mode fibers is measured by observing the wavelength dependence of fiber birefringence. A typical measured value is 0.24 ps/km at the 1.2 μm wavelength. The measured wavelength dependence of polarization dispersion is explained well by a theory taking into account elliptical core deformation. Fitted core ellipticity values for the two test fibers are 0.012 and 0.003.     

Distributed beat length measurement in single-mode optical fibersusing stimulated Brillouin-scattering and frequency-domain analysis

We present a method for distributed measurement of beat length, differential group delay, strain, and temperature in long length single-mode optical fibers. Toward this aim, we employ the polarization state sensitive effect of stimulated Brillouin scattering (SBS). The distributed measurement is realized by applying frequency-domain analysis. We present the analytical relationships between the Brillouin interaction of two counterpropagating waves in the fiber and the polarization states. Experimental results confirm the ability of the method to measure distributed beat length     

Measurement of wavelength variation of mode field radius using far-field pattern method

The far-field pattern measuring technique is used to measure the wavelength dependence of the mode field radius in standard single-mode fibres. Chromatic dispersion calculated from these results is shown to be accurate using as few as three lasers. Both theoretical and experimental results are presented.     

Phase-shift technique for the measurement of chromatic dispersion in single-mode optical fibres using LEDs

The phase-shift technique has been successfully extended to chromatic dispersion measurements in single-mode optical fibres. Using only two sinusoidally modulated LEDs operating at 1.33 and 1.47 ?m, accurate results have been achieved in the spectral region of interest, in good agreement with those obtained with the Nd-Yag laser and Raman fibre technique.     

Consistency of measurement methods for the mode field results in a single-mode fiber

The fields in the core, the far-field radiation pattern, and the transmission through an offset splice for single-mode fibers all are well approximated by Gaussian functions. However, the method used to fit the Gaussian function to measured data influences the resulting width of the Gaussian, which is called the mode field radius. Of the fitting methods studied, only maximization of the launch efficiency integral gives values of mode field radii which are consistent between near-field and far-field measurement methods. The transverse offset measurement method is consistent with these two if an unweighted truncated fit is used. Also. two published analytical formulas for the mode field radius are studied, and only one of the two gives accurate values. A third analytical formula, which is simpler and more accurate over a smaller range of wavelengths, is presented.     

Technique for direct measurement of single-mode fiber chromatic dispersion

A technique for the direct measurement of single-mode fiber chromatic dispersion is presented. The technique uses wavelength modulation to provide a differential fiber chromatic delay signal from which chromatic dispersion is obtained directly. The system is described in detail and practical measurement results shown to illustrate the high accuracy of the technique and its versatility in use with all fiber types.     

Length dependence of effective cutoff wavelength in single-mode fibers

Transmission characteristics of single-mode fiber operated in the two-mode (LP01and LP11) propagation region is investigated experimentally and theoretically. The effective cutoff wavelength of the LP11mode λceis commonly used to assure practically the single-mode operation of the LP01mode above λceup to certain fiber length. The experimental λcedecreases linearly in a logarithmic scale of fiber length as increasing fiber length, and eventually becomes constant after a few kilometers' propagation. Theoretical λceis obtained from a coupled power equation by taking into account the mode coupling as well as the losses of the two modes. To calculate λce, the losses of the two modes are individually measured by a new measurement technique. It is clarified from the theory that the nonlinear property of the length dependence of λcein the logarithmic scale is due to a relatively small mode coupling between the LP01and LP11modes.     

Prediction of mode dispersion in graded-index single-mode fibres

A Cheby?shev power series method is presented for the calculation of the propagation constant of graded-index fibres. Accurate predictions of the dispersion parameters can be obtained as shown by examples of step and parabolic profiles. Measured index profiles can also be used with local index values found by linear interpolation from nearest reading points. Examples are given to demonstrate the effectiveness of this approach.     

Cutoff wavelength determination in single-mode optical fibres by measurement of equalisation wavelength

A simple interferometric method for indirectly determining a value for the cutoff wavelength of single-mode optical fibres is described. The technique is accurate and no stringent requirements are placed on the experimental equipment.     

Curvature dependence of the effective cutoff wavelength in single-mode fibers

The curvature dependence of the effective cutoff wavelength is investigated for both matched-cladding and depressed-cladding fibers. Contrary to the depressed-cladding fiber, the cutoff wavelength of the matched-cladding fiber is strongly curvature dependent. A formula is developed for the bending loss of the first higher-order mode group in a depressed-cladding fiber. By taking into account the effect of the stress-induced changes in the refractive index on the loss the first higher-order mode group, the effective cutoff wavelength as a function of curvature is calculated. The theoretical results show good agreement with measured values, which verify the curvature insensitivity of the effective cutoff wavelength of depressed cladding fibers.     

Soliton technique to characterize single-mode fiber dispersion

Transmitting subpicosecond pulses at moderate powers over a few meters of fiber creates a notch in the pulses' power spectra in the vicinity of the fiber's zero-dispersion wavelength. This is caused by the interaction of nonlinear self-phase modulation and third-order dispersion. This phenomenon can be used to determine the zero-dispersion wavelength of single-mode fibers     

Length dependence of the effective cutoff wavelength in single-mode fibers

The effective cutoff wavelength of a depressed cladding single-mode fiber in either a cabled or a loose state depends upon the length of the fiber. This dependence can be accurately represented by a linear function of the logarithm of the fiber length for lengths between 1 m and 1 km. Cutoff will shift 55-66 nm per decade length for slightly and moderately depressed cladding designs, respectively. Neglecting all sources of differential mode attenuation except leaky-mode loss, the computed behavior of cutoff as a function of fiber length agrees reasonably well with the observed behavior for a moderately depressed cladding design. On the other hand, agreement is poor for a slightly depressed cladding design. A knowledge of the length dependence of cutoff is essential for establishing a production requirement for cutoff based upon the needs of the system.     

Determination of modal dispersion in monomode fibres from wavelength dependence of the mode spot size

It is demonstrated in this letter that the spectral mode spot size measurement is a useful means of determining the modal dispersion of monomode fibres used in the 1.3 ?m wavelength region.     

Chromatic dispersion measurement over a 120 km dispersion-shifted single-mode fibre in the 1.5 ?m wavelength region

Chromatic dispersion in the 1.47?1.60 ?m wavelength region is measured successfully for a dispersion-shifted fibre over 120 km by the LD phase-shift method. The measured value of a 123 km spliced fibre agrees well with the sum of chromatic dispersion values of its constituent fibres. This confirms the additive rule of chromatic dispersion for long dispersion shifted fibre in the 1.5 ?m wavelength region.