Monomode Optical Fiber Research Articles

Scanning second harmonic microscopy techniques with monomode and near field optical fibers

Extending our scanning second harmonic microscopy (SSHM) technique for the detection of lateral orientational inhomogeneities in high field poled polymer films, we present results with considerably improved lateral resolution by using optical fiber technology. Two experimental setups for measuring the χ(2) susceptibility of thin films are introduced. The first setup uses a standard monomode infrared-fiber with 10 μm core that carries the coherent fundamental infrared wave to the surface of a poled polymer film (illumination mode). The generated doubled frequency wave behind the nonlinear optical sample is detected by a photomultiplier tube. In the second setup a lens focuses the fundamental wave into the poled film. The resulting second harmonic wave is coupled into a 2.5 μm single mode fiber. SSHM micrographs of high field poled nonlinear optical polymer films were obtained with lateral resolutions of <3.5 μm. SSHM was also realized with a scanning near field optical microscopy fiber in pick up mode.

Perturbation Theory for Optical Soliton

Based on the main idea of the derivative expansion method, a perturbation approach is proposed for the investigation of single soliton propagating down a nonideal monomode optical fiber. This approach is totally independent of inverse scattering theory, which has substantial difference from the past methods. In this scheme, the first-order correction is derived by the method of eigenfunction expansion, and the parameters change is directly obtained from the secularity conditions for some cases.

Photoviscous flow and glass macroproperties

The interest in glass photosensitivity has been renewed due to the importance of photosensitivity phenomena in potical fibers devices which promise a host of novel applications. Among these developments, one is the ability to imprint periodic and permanent refractive-index changes (Bragg gratings) on monomode germanosilicate optical fibers using excimer lasers. Defect formation in the structure of the glass core mainly germanium GODC (germanium-related oxygen-deficient centers) defects are supposed to be responsible for the grating formation. Here the phenomena are analyzed under another perspective that is related with high temperature gradient inside monomode optical fibers and its consequences. Because temperatures much higher than the germanium silicate glass softening point could be achieved during exposure to excimer lasers, the formation of Bragg gratings is a two step process to modify vitreous media. First, UV energy should be absorbed at the fiber core - by defects, dopants and glass components - and a second step where this energy is thermalised. There is no ablation in the glass core and energy transfer is governed by viscous flow or photoviscous flow and internal structural rearrangements. Alternatives to enhance optical fiber glass photosensitivity via glass composition and viscous behaviour are discussed.

Modeling the interaction among solitons in optical fibers using wavelets

A new numerical method for the interactions among the multisolitons propagating along monomode optical fibers is presented. On the basis of the derivative function belonging to the Sobolev space and under the norm of L(2)(I), the base in the Sobolev space S2(I) is the one in space L(2)(I), by which the derivative operator can be approximately expressed by a wavelet matrix. We use the operator to act on the time variable in the nonlinear Schrödinger equation governing the propagating soliton, and obtain a new, simple iterative equation for solitons propagating in optical fiber. The results obtained are similar to those reported in the references, so this method is effective. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 17: 250–253, 1998.

Large mode area photonic crystal fibre

The authors report the realisation of a new design for a large mode area monomode optical fibre. This photonic crystal fibre will guide only a single mode, no matter how large the fibre diameter, provided the shape is kept constant. This is demonstrated with a fibre which has a core diameter equal to approximately 50 free-space wavelengths.

A new type of spatial light modulator at 1.3 µm on silicon-on-insulator substrate

The excellent thickness uniformity of the silicon film of standard silicon-on-insulator Simox substrates and the maturity of microelectronics processes allow to design optical modulator arrays using original waveguide ring resonators combined with two grating couplers. A first grating couples light from a monomode optical fiber into the resonator, part of the stored light is outcoupled by a second grating towards the output fiber. The output power is modulated by free-carrier injection in the waveguide core. Optical and electrical simulations show that for the modulator with a size compatible with fiber bundles, 10 ns switching times are achievable. Optimizations of the integrated optical elements and electrical control simulations are presented. A brief description of the fabrication process of the devices is also given.

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.

Phase-matched excitation of whispering-gallery-mode resonances by a fiber taper

We show that high-Q whispering-gallery modes in fused-silica microspheres can be efficiently excited by an optical fiber taper. By adjusting the taper diameter to match the ropagation constant of the mode in the taper with that of the resonant mode of interest, one can couple more than 90% of the light into the sphere. This represents a significant improvement in excitation efficiency compared with other methods and is, we believe, the most efficient excitation of a high- Q microcavity resonance by a monomode optical fiber yet demonstrated.

Painlevé analysis and bright solitary waves of the higher-order nonlinear Schrödinger equation containing third-order dispersion and self-steepening term

A general form of the higher-order nonlinear Schr\odinger equation that includes terms accounting for the third-order dispersion and the self-steepening effect has been investigated using the Painlev\'e singularity structure analysis in order to identify the underlying integrable models. This equation fails to pass the Painlev\'e test for the entire parameter space except for two specific choices of the parameters. As a consequence, it was found that two recently introduced higher-order nonlinear Schr\odinger equations fail to pass the Painlev\'e integrability test. Moreover, one of those equations describes optical pulses with large frequency shifts as compared to the chosen carrier frequency that renders that equation inappropriate for describing femtosecond soliton propagation in monomode optical fibers. Another equation is introduced and bright solitary waves are provided. These solitary waves describe pulses with either very small or even zero-frequency shifts. The conditions on fiber parameters for the existence of those solitary waves are also discussed.

Mutual compensation of the higher-order nonlinearity and the third-order dispersion

We obtain the exact bright and dark solitary wave solutions of the nonlinear Schrödinger equation (NLSE) with the higher-order nonlinearity and the third-order dispersion without any specified conditions, and analyze the features of the solutions. The results show that the higher-order nonlinearity and the third-order dispersion can mutually compensate for a soliton just as the usual self-phase modulation (SPM) and the group-velocity dispersion (GVD) in the NLSE; whether a bright or dark soliton exists in a monomode optical fiber is determined by the sign of the third-order dispersion instead of the group velocity dispersion; the peak intensity of the soliton is proportional to the ratio of the third-order dispersion and the higher-order nonlinearity; the velocity of the soliton depends on the soliton width η, so no bound N-soliton states exist.

Determination of the optical properties of a monomode optical fibre by fringes of equal chromatic order

Determination of the optical properties of a monomode optical fibre by fringes of equal chromatic order

Determination of the optical properties of a monomode optical fibre by fringes of equal chromatic order

Multiple beam fringes of equal chromatic order are used to study the optical properties of a monomode optical fibre. The material dispersion of the core and that of the cladding of the fibre are measured. A modified single term Sellmeier dispersion formula is adopted and fitted to the experimental data. A new simple scheme of calculation is applied to reduce the interferogram. A single interferogram is sufficient to give the whole dispersion information needed across the visible spectrum.

Timing jitter of femtosecond solitons in monomode optical fibers

We study the propagation over long distances under the influence of the Raman effect of certain subpicosecond solitons, which are solutions of a perturbed nonlinear Schro¨dinger equation describing the propagation of light pulses in monomode optical fibers. We calculate the corresponding propagation distance limit due to the intrapulse Raman scattering soliton timing jitter. A formula that describes the soliton timing jitter effect due to the influence of amplified spontaneous emission noise on soliton group velocity induced by the coupling between amplitude and velocity is given and the propagation distance limit of soliton communication systems caused by this effect is evaluated.

An improved procedure to calculate the refractive index profile from the measured near-field intensity

Refractive index profile of optical waveguides is reconstructed from the measured transmitted near-field intensity. A Butterworth low-pass digital filter is employed in the frequency domain to remove impulsive and high frequency fluctuations which have severe effects on the procedure to calculate the index profile from the measured power intensity. The proposed method has been applied to measure the index profile of monomode optical fiber, Ti:LiNbO/sub 3/ and buried MgTi:LiNbO/sub 3/ channel waveguides.

Tapered optical-fiber temperature sensor

Optical power transmission changes of 10–20 dB have been experimentally demonstrated by varying the temperature of a tapered monomode optical fiber that is fixed to a glass plate by two drops of adhesive. The effect arises from different expansion coefficients of the glass substrate and the silica fiber. This induces microbendings in the tapered region. The temperature range of the sensor may be adjusted from 2 to 100°C, depending on the taper length and width. © 1996 John Wiley & Sons, Inc.

Tapered optical‐fiber temperature sensor

Optical power transmission changes of 10–20 dB have been experimentally demonstrated by varying the temperature of a tapered monomode optical fiber that is fixed to a glass plate by two drops of adhesive. The effect arises from different expansion coefficients of the glass substrate and the silica fiber. This induces microbendings in the tapered region. The temperature range of the sensor may be adjusted from 2 to 100°C, depending on the taper length and width. © 1996 John Wiley & Sons, Inc.

Fibre-optic sensor based on surface plasmon resonance

An optical fibre sensor based on resonant coupling between a mode of a monomode optical fibre and a surface plasmon is reported. It is demonstrated that, by measuring the optical power transmitted through the sensing element, very small changes in the refractive index of the sensed medium can be determined.

Dark-soliton timing jitter caused by fluctuations in initial pulse shape.

The dark-soliton timing jitters caused by fluctuations in either the soliton initial phase angle or the background amplitude when such a soliton propagates in a monomode optical fiber under the influence of the stimulated Raman scattering are investigated and compared with those that exist when the stimulated Raman scattering is not present. In addition, it is demonstrated that in the presence of the stimulated Raman scattering, there exists a distance at which, for the negative soliton initial phase angle, the dark-soliton timing jitter caused by fluctuations in the background amplitude becomes zero.

Enhancement of third-harmonic blue-violet light at 440 nm by erbium ions in Er^3+–GeO_2-doped silica monomode optical fibers pumped at 1319 μm

The efficient generation of third-harmonic blue-violet light at 440 nm in short lengths of Er3+-doped germanosilicate single-mode optical fibers pumped at 1.319 μm is reported. Measurement indicates that the third-harmonic generation process that is due to a GeO2–SiO2 core is resonantly enhanced through the amplification of the signal light at 440 nm by population inversion of the erbium ions in the fiber core. An average signal power at 440 nm of ~5 μW was observed.

Photoacoustic detection of trace gases with an optical microphone

An alternative to the electrical microphone for photoacoustic detection of trace gases is presented. This new microphone is made of standard monomode optical fibers wound and glued on a thin plate and is one of the arms of a Michelson interferometer. A detection scheme with a Sagnac interferometer has also been used and has given better results. Three cells working with different resonance modes and different microphone configurations have been tested.