Periodic Cladding Research Articles

Propagation properties of Bragg fiber analyzed by a Hankel function formalism

This article describes the propagation characteristics of a Bragg fiber whose guiding principle is based on Bragg diffraction due to the periodic cladding. An asymptotic expansion for Hankel function at large arguments is used to express cladding fields with a simple form. A division in matrix calculation enables us to understand the cladding field physically. Condition for getting an asymptotically decaying wave in the cladding is revealed on the basis of property of Bloch wavenumber. It is shown that cutoff effective index giving the cutoff condition determines the lower limit for the cladding index difference.

Waveguide modes of electromagnetic radiation in hollow-core microstructure and photonic-crystal fibers

The properties of waveguide modes in hollow-core microstructure fibers with two-dimensionally periodic and aperiodic claddings are studied. Hollow fibers with a two-dimensionally periodic cladding support air-guided modes of electromagnetic radiation due to the high reflectivity of the cladding within photonic band gaps. Transmission spectra measured for such modes display isolated maxima, visualizing photonic band gaps of the cladding. The spectrum of modes guided by the fibers of this type can be tuned by changing cladding parameters. The possibility of designing hollow photonic-crystal fibers providing maximum transmission for radiation with a desirable wavelength is demonstrated. Fibers designed to transmit 532-, 633-, and 800-nm radiation have been fabricated and tested. The effect of cladding aperiodicity on the properties of modes guided in the hollow core of a microstructure fiber is examined. Hollow fibers with disordered photonic-crystal claddings are shown to guide localized modes of electromagnetic radiation. Hollow-core photonic-crystal fibers created and investigated in this paper offer new solutions for the transmission of ultrashort pulses of high-power laser radiation, improving the efficiency of nonlinear-optical processes, and fiber-optic delivery of high-fluence laser pulses in technological laser systems.

Waveguiding properties and the spectrum of modes of hollow-core photonic-crystal fibres

Glass fibres with a hollow core and a two-dimensionally periodic cladding are studied experimentally and theoretically. The spectrum of modes guided in the hollow core of these fibres displays isolated maxima, indicating that waveguiding is supported due to the high reflectivity of the fibre cladding within photonic band gaps. The main properties of the spectrum of modes guided in a hollow core of a photonic-crystal fibre and radiation intensity distribution in these modes are qualitatively explained in terms of the model of a periodic coaxial waveguide.

Transverse Bragg resonance laser amplifier.

We propose and analyze a new type of optical amplifier that is formed by addition of gain in the periodic cladding of a transverse Bragg resonance waveguide [Opt. Lett. 27, 936 (2002)]. Using the coupled-wave formalism, we calculate the mode profiles, the exponential gain constant, and, for comparison, the gain enhancement compared with those of conventional semiconductor optical amplifiers. In contrast with coupled-mode theory, in one-dimensional structures (e.g., the distributed-feedback laser) the exponential gain constant in the longitudinal direction is involved in both longitudinal and transverse confinement, and its solution has to be achieved self-consistently, together with the quantized guiding channel width.

Very large effective area singlemode photonic bandgap fibre

A photonic bandgap fibre consisting of a 34 µm diameter pure silica core surrounded by a periodic cladding has been modelled and characterised. It guides a robust HE11 mode at 1.55 µm with a 517 µm2 effective area and 0.4 dB/m propagation losses.

Cylinder gratings in conical incidence with applications to modes of air-cored photonic crystal fibers.

We develop a formulation for cylinder gratings in conical incidence, using a multipole method. The theory, and its numerical implementation, is applied to two-dimensional photonic crystals consisting of a stack of one-dimensional gratings, each characterized by its plane wave scattering matrix. These matrices are used in combination with Bloch's theorem to determine the band structure of the photonic crystal from the solution of an eigenvalue problem. We show that the theory is well adapted to the difficult task of locating the complete band gaps needed to support air-guided modes in microstructured optical fibers, that is, optical fibers in which the confinement of light in a central air hole is achieved by photonic band-gap effects in a periodic cladding comprising a lattice of air holes in a glass matrix.

Waveguide modes of hollow photonic-crystal fibers

Waveguide modes of microstructure fibers with a hollow core and a two-dimensionally periodic cladding are studied experimentally and theoretically. The spectrum of modes guided in the hollow core of these fibers displays isolated maxima, indicating that waveguiding is supported due to the high reflectivity of the fiber cladding within photonic band gaps. The main properties of the spectrum of modes guided in a hollow core of a photonic-crystal fiber and radiation intensity distribution in these modes are qualitatively explained in terms of the model of a periodic coaxial waveguide.

Design of weakly guiding Bragg fibres for chromatic dispersion shifting towards short wavelengths

The waveguiding in Bragg optical fibres is based on a radial photonic bandgap effect due to their periodic cladding. Even with a weak index contrast, these fibres can be used to strongly bind the electromagnetic field in the core. With an adequate index profile, the resulting field localization allows us to shift the zero-chromatic-dispersion wavelength of the unique mode below 1.3 µm, i.e. into a spectral range where nonlinear phenomena such as solitons or continuum generation become possible, in contrast to standard monomode fibres. A preliminary analysis, performed with the planar Bragg waveguide for simplicity, gives conditions to obtain a fast decrease of the field distribution in the periodic area. These conditions are then used to develop a simple method for determining an adequate geometry of weak-guiding fibres to achieve dispersion shifting. An approximate formula is given for index transition positions in the case of step index profiles. Examples of such profile determinations are presented. The possibility of reducing the zero-dispersion wavelength to 0.8 µm by means of a realistic index profile is proven. The validity of the method is confirmed by first measurements on an experimental Bragg fibre.

Traverse electric mode characteristics in a cylinder waveguide with a periodic dielectric cladding

The transverse electric mode characteristics in a cylinder waveguide with a periodic dielectric cladding have been analytically studied. The periodic dielectric cladding induces band structures in the characteristics and enhances the confinement of the electromagnetic energy in the core compared to a cylinder waveguide with a uniform cladding. Potential applications based on the characteristics are discussed in optical communications and photonics.

Periodic cladding surface structures induced when recording fiber Bragg reflectors with a single pulse from a KrF excimer laser

Observations are presented of ∼1 μm deep periodic structures on the cladding surface of optical fibers which are simultaneously induced when recording first-order fiber Bragg reflectors by single pulse KrF excimer laser holographic exposure.