Relation between macrobending losses and cutoff wavelength in dispersion-shifted segmented-core fibres

Dispersion-shifted triangular-core designs with and without rings and equal values of the Laplace spot size at ? = 1.55 ?m are compared. Although increased cutoff wavelengths are obtained by the segmented-core designs, the bending properties are not necessarily improved, and when improvement is gained it is at the cost of higher Rayleigh loss.     

New simple method for measuring the mode spot size in monomode fibres

The equivalent step index (ESI) parameters associated with single-mode fibres can be evaluated by observing the changes in transmitted power on the far field when a Ronchi ruling is inserted between the end face of the fibre and a detector collecting the output intensity. Measurements as a function of wavelength allow one to determine the cutoff wavelength, ESI parameters for short lengths of fibre and effective cutoff wavelength for long lengths.     

Sinusoidal microbending loss of HE11-mode in step-index fibres

Sinusoidal microbending losses of the HE11-mode in step-index fibres are compared by using a perturbation solution of electromagnetic wave scattering theory. The HE11-mode in a multi-mode step-index fibre is found to suffer much higher bending loss than that in a single-mode step-index fibre, except that in nearly perpendicular directions and in the perpendicular direction with respect to the fibre axis the HE11-mode in the single-mode step-index fibre shows some higher bending loss than that in the multimode step-index fibre.     

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.     

Analysis of approximations for the mode dispersion in monomode fibres

A number of recent papers have discussed the mode dispersion in step-index, monomode fibres using formulae based on accurate approximations for the modal propagation constant. It is shown here that, since dispersion depends on the first and second derivatives of the propagation constant, the use of such formulae may often be invalid and that a different type of approximation may be more useful     

Effective cutoff wavelength of the LP11mode in single-mode fiber cables

The effective cutoff wavelength of the LP11mode is investigated for nylon-coated step-index type single-mode fibers stranded in a cable. It is found from the pulse propagation experiments that the single-mode operation is effectively attained in the two-mode region up to theV-value of 3.0. It is numerically estimated that splice loss, bending loss, and absorption loss due to the OH-ion in cladding are reduced by choosing the operatingV-value as large as 3.0.     

Novel method for measuring cutoff wavelength of HE21-, TE01-and TM01-modes

A new measurement method for the cutoff wavelength of HE21-, TE01-and TM01 modes using a polariser is described. The experimental results show that higher measurement accuracy and sensitivity are obtained compared with the previous method.     

Progress in monomode transmission techniques in the United Kingdom

The key results obtained from experimental systems studies over monomode fiber and cable links are given for both direct detection and coherent optical systems. Direct detection techniques have been studied at 1300 nm using conventional lasers and at 1500 nm with narrow line transmitters of the injection-locked and external cavity types. In the case of coherent optical systems, developments of the same transmitters have been used in conjunction with amplitude and phase shift key (PSK) modulation techniques to obtain improved performance. Increases in receiver sensitivity of up to 14 and 17 dB have been obtained using, respectively, heterodyne and homodyne detection techniques. These results approach theoretical predictions and offer the possibility of much greater transmission capacity and extended regenerator spacings for monomode systems.     

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.     

Comparison of novel coding techniques for a fixed wavelength hopping SAC-OCDMA

The optical code division multiple access (OCDMA), the most advanced multiple access technology in optical communication has become significant and gaining popularity because of its asynchronous access capability, faster speed, efficiency, security and unlimited bandwidth. Many codes are developed in spectral amplitude coding optical code division multiple access (SAC-OCDMA) with zero or minimum cross-correlation properties to reduce the multiple access interference (MAI) and Phase Induced Intensity Noise (PIIN). This paper compares two novel SAC-OCDMA codes in terms of their performances such as bit error rate (BER), number of active users that is accommodated with minimum cross-correlation property, high data rate that is achievable and the minimum power that the OCDMA system supports to achieve a minimum BER value. One of the proposed novel codes referred in this work as modified random diagonal code (MRDC) possesses cross-correlation between zero to one and the second novel code referred in this work as modified new zero cross-correlation code (MNZCC) possesses cross-correlation zero to further minimize the multiple access interference, which are found to be more scalable compared to the other existing SAC-OCDMA codes. In this work, the proposed MRDC and MNZCC codes are implemented in an optical system using the optisystem version-12 software for the SAC-OCDMA scheme. Simulation results depict that the OCDMA system based on the proposed novel MNZCC code exhibits better performance compared to the MRDC code and former existing SAC-OCDMA codes. The proposed MNZCC code accommodates maximum number of simultaneous users with higher data rate transmission, lower BER and longer traveling distance without any signal quality degradation as compared to the former existing SAC-OCDMA codes.     

Attenuation coefficient and effective cutoff wavelength of the LP11 modes in curved optical fibers

The measured attenuation coefficient of the LP₁₁ modes in curved optical fibers for various radii of curvature in the wavelength region below the cutoff wavelength for LP₁₁ modes is discussed. The experimental results indicate that the attenuation coefficient may be strongly enhanced at certain wavelengths due to phase-matched coupling between the LP₁₁ modes of the fiber core and whispering gallery modes of cladding. Implications for measurements of the effective cutoff wavelength in optical fibers are discussed     

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.     

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.     

New method for measuring the chromatic dispersion of installed single-mode fibers utilizing wavelength division multiplexing techniques

This paper describes a novel method designed to measure the chromatic dispersion of installed single-mode fiber cables. The systems developed utilize the modulation phase/multiple laser diode techniques; however, by the addition of wavelength division multiplexing, the reference laser and fiber was eliminated. Laboratory and field results for measured wavelength ranges of 1200-1330 and 1200-1550 nm are presented.     

Perturbation theory for the evaluation of the normalised cutoff frequencies in radially inhomogeneous fibres

A simple perturbation theory has been used to study the normalised cutoff frequencies of radially inhomogeneous fibres. The formalism has been developed with a truncated parabolic-index profile as zero-order solution. Numerical calculations have been carried out for ?-profiles and have been found to be in good agreement with more rigorous approaches reported by previous authors.     

Optimum operating wavelength for chromatic equalisation in multimode optical fibres

Complete chromatic equalisation is not possible in a graded-index fibre owing to the variation of material properties across the core. We show that it is still possible to choose an operating wavelength which effectively eliminates first-order material dispersion.     

Fast method for calculating cutoff frequencies in single-mode fibres with arbitrary index profiles

A Cheby?shev power-series approach is used for cutoff frequencies of the second mode in fibres with arbitrary refractive-index profiles. The method is fast because only a small number of terms is required to give high accuracy. A feature of this approach is that measured profiles can be used directly without being first converted to any specific forms. Examples are given as illustrations.     

Simple method for measuring material dispersion in optical fibres

A simple and accurate method, using a sinusoidally modulated l.e.d., is proposed to measure material dispersion of optical fibres. By this method, material dispersion was measured using a step and a graded index fibre. The results were in good agreement with those of other methods.     

DWDM全光网络中波长转换技术的比较

波长转换技术是 DWDM全光网络中一项重要的基础技术。介绍了波长转换技术的基本原理 ,并对现有主要的几种波长转换技术进行比较 ,最后指出基于四波混频技术的波长转换技术是未来的研究方向