Thus, the pulse propagation in a nonlinear periodic structure (FBG) exhibits different kinds of fundamentally unique and technologically interesting regimes. The observation of solitons in FBG also paves the way for many potential applications, such as all optical-logic gates, pulse compression, all-optical switching, and limiting. Recent developments in theory as well as experimental investigations of these solitons provide a wide scope for realizing many devices such as optical add/drop multiplexers, optical filters, and sensors that ultimately could improve the OFC and sensor technology. Thus, based on the pulse frequency spectrum with respect to PBG, solitons in FBG can be classified into two categories, namely Bragg grating solitons and gap solitons. They are referred to in this way because the frequency of the incident pulse exactly matches the Bragg frequency. They are often referred to as gap solitons if their spectra lie well within the frequency (photonic) bandgap. As a result, there is a formation of slowly traveling localized envelope in FBG structures known as, in general, Bragg grating solitions. We can also expect a similar soliton-type pulse formation in FBG where the strong grating-induced dispersion is exactly counterbalanced by the Kerr nonlinearity through the SPM and cross-phase modulation effects. It is obvious that the soliton in fibers is formed after the exact balancing of GVD arising as a combination of material and waveguide dispersion with that of the SPM due to Kerr nonlinearity. Porsezian, Krishnan Senthilnathan, in Guided Wave Optical Components and Devices, 2006 6 SOLITONS IN FBG The units of chromatic dispersion are picoseconds per nanometer-kilometer that is, for a 1-nm, free-space wavelength change, this gives the number of picoseconds of delay change per kilometer of fiber length. The ratio of velocity change to wavelength change due to this effect is known as waveguide dispersion.Īs with modal dispersion, chromatic dispersion is a linear function of transmission system length. Since the refractive index is different in the core than in the cladding, a change in mode field diameter also results in a change in average dispersion index and, therefore, signal velocity. In optical fibers, the signal travels partially in the core and partially in the cladding, and the total mode field diameter changes with wavelength. It is the sum of two factors: material dispersion-a measure of the change in refractive index of the glass with wavelength-and waveguide dispersion. Chromatic dispersion is a measure of the degree to which the effective propagation velocity changes as a function of wavelength. With the large modal dispersion eliminated, more subtle dispersion mechanisms become the limiting factors. We report here our recent advances on the fabrication of single-mode highly nonlinear lead-silicate MOFs with low dispersion and dispersion slope values at 1.55 micron.David Large, James Farmer, in Broadband Cable Access Networks, 2009 4.4.3 Chromatic (Wavelength) Dispersion However, for such applications as wavelength-conversion, optical parametric amplification, supercontinuum generation etc, apart from a high gamma value, it is equally desirable that the nonlinear fiber also exhibits near-zero dispersion and dispersion slope at the operating wavelengths. Due to the higher linear (n) and nonlinear refractive index (n2 > 2) of non-silica glasses as compared to silica, it has been demonstrated that the effective nonlinearity (gamma) of a non-silica glass MOF can be between 2-4 orders of magnitudes higher than that of the conventional silica fiber (gamma ~ 1 /W /km), thus enabling the realisation of compact nonlinear devices operating at practical power levels. The novel optical properties of MOFs arise from the combination of wavelength-scale features in the fiber cross-section with the large index-contrast of the materials comprising the microstructured cladding. Microstructured optical fiber (MOF) technology has generated several new opportunities for the implementation of optical fibers with novel properties and functions.
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