Multimode Fiber Waveguides Research Articles

Method for stabilization of the maximum sensitivity of a two-arm interferometer using a multimode waveguide

The feasibility of stabilization of the maximum sensitivity of a two-arm Mach–Zehnder interferometer by varying the length of a multimode fiber waveguide in one of the arms (with the aid of a piezoelectric ceramic device) was confirmed experimentally. A quasiperiodic dependence of the interference signal on the waveguide length was obtained and it was found that the period of this dependence agreed well with the cophasal length of the waveguide. The interferometer was tuned to the optimal operation by bending a section of the waveguide to a specific radius.

Speckle structure of an optical field in multimode fiber waveguides

An investigation is made of the statistical properties of an optical field with a speckle structure in multimode fiber waveguides. Asymptotic formulas are obtained for the spatial correlation function of the field. This function is used to obtain expressions for the statistical average density of dislocations in the wavefront of the field distributed over a transverse cross section of a waveguide with an arbitrary refractive index profile. It is shown that the dislocation density is an oscillatory function of the transverse coordinate. A study is also reported of the dependence of the dislocation density on the refractive index profile and on the conditions of excitation of a waveguide.

Cross-correlation reduction in the divergence of light beams at the exits from multimode waveguides

It was demonstrated for the first time that an optical signal with specific spatial and angular characteristics can be obtained by holographic correction of wavefronts of transient fields at the exits of long sections of multimode fiber waveguides.

Experimental investigation of cross talk in two-channel fiber waveguides

An experimental investigation was made of the dependences of the cross-talk level on the parameters of a two-channel multimode fiber waveguide. The existence of a steady-state cross-talk level was established. The dependence of this level on the normalized distance between the channels was readily approximated by an exponential law. The possibility of selection of parameters of a two-channel waveguide to achieve a given cross-talk level was established.

Temporal coherence of laser radiation transmitted by a multimode waveguide

The results are given of a theoretical calculation and of experimental investigations of the temporal correlation function of multifrequency laser radiation transmitted by multimode fiber waveguides of up to 550 m in length. The results indicate that the periodic dependence of the correlation function γ(τ) on the delay time τ is retained under multimode conditions. An increase in the fiber length broadens the dependence γ(τ) .

Effect of low dose rate irradiation on doped silica core optical fibers

The optical attenuation induced in multimode doped silica core optical fiber waveguides by a year's exposure to low dose rate (1 rad/day) ionizing radiation was studied, allowing a characterization of fibers deployed in these environments and a determination of the permanent induced loss in the waveguides. Variations in the induced attenuation at 0.85 microm have been observed with changes in the dose rate between 1 rad/day and 9000 rads/min. These dose rate dependences have been found to derive directly from the recovery that occurs during the exposure; the recovery data predict little or no dose rate dependence of the damage at 1.3 microm. The low dose rate exposure has been found to induce significant permanent attenuation in the 0.7-1.7-microm spectral region in all fibers containing P in the core, whether doped uniformly across the diameter or constrained to a narrow spike on the centerline. Whereas permanent loss was induced at 0.85 microm in a P-free binary Ge-doped silica core fiber by the year's exposure, virtually no damage was observed at 1.3 microm.

Ring interferometer with a multimode fiber waveguide

An expression is obtained for the output signal of a fiber ring interferometer with a multimode waveguide. It is shown that the precision of such an interferometer can be improved by the use of a light source characterized by a low spatial coherence. An analysis is made of the possibility of increasing the stability of the output signal by effective mode mixing at the input or in the multimode interferometer loop. The results are given of an experimental investigation of a prototype ring interferometer consisting entirely of a multimode fiber waveguide.

Influence of temperature on the transmission of light by bent multimode fiber waveguides

The temperature dependences of the transmission of light by bent multimode fiber waveguides were determined experimentally and analyzed. A study was made of the influence of the directionality of the radiation from a source exciting a waveguide, of the bending of a waveguide, and of the parameters of quartz-polymer and quartz-quartz fibers on the sensitivity of waveguides to temperature. The information on the sensitivity should be useful in the design of displacement and temperature sensors constructed from bent multimode waveguides.

Methods for the determination and calculation of dispersion properties of multimode fiber waveguides (review)

An analysis was made of the published information on the data-carrying capacity of multimode fiber waveguides. The main mechanisms which influence the dispersion of a pulse in a fiber are discussed and methods for calculating the dispersion are reviewed. The problems encountered in experimental investigations of dispersion properties of fiber waveguides and in quantitative description of these properties are considered. The apparatus needed in various methods for the determination of the dispersion of a pulse and future trends in such methods are discussed. An analysis is made of the relationship between the conditions during measurement of dispersion properties of fiber waveguides and the results obtained. The problem of standardization of the description of fiber waveguides is considered. Much attention is given to the influence on the bandwidth of fiber waveguides of defects of the real refractive index of fiber waveguides due to the characteristic features of the technological processes and methods for compensating this influence are discussed.

Determination of the refractive index profile of fiber waveguides by a modified near-field refraction method

A modification of the near-field refraction method was developed for determination of the refractive index profile of fiber waveguides. Side illumination of a fiber and determination of the distribution of the illumination over the fiber end make it possible to eliminate precision alignments and use visual displays. A description is given of the apparatus which can be used to determine the refractive index profiles of multimode and single-mode fiber waveguides both rapidly and easily.

Nonreciprocal effects in a ring interferometer with a multimode fiber waveguide

An analysis is made of parasitic nonreciprocal effects in a ring interferometer utilizing a multimode fiber waveguide. These effects are associated with intermode exchange, which is a specific property of multimode waveguides. It is shown that these effects can be reduced significantly by utilizing a light source with a low spatial coherence. The results of the analysis yield dependences which are in order-of-magnitude agreement with those found experimentally.

Characteristics of backscattering in fiber waveguides

A rigorous ray approach is used to obtain analytic relationships between the characteristics of the forward and backward Rayleigh-scattered radiation in multimode fiber waveguides with an arbitrary refractive index profile. Experimental results obtained for step and graded index fiber waveguides are shown to be in agreement with the calculated dependences.

Optical fiber coupling of 1.2–1.6 μ radiation emitted from buried mesastripe injection lasers

An investigation was made of the efficiency of coupling—into fiber waveguides—of 1.2–1.6 μ radiation emitted by a buried mesastripe InGaPAs–InP heterojunction laser. The maximum power of the radiation coupled into a fiber waveguide was 16 mW in the cw regime at room temperature. The coupling efficiency was 90% in the case of a multimode fiber waveguide and 36% in the case of a single-mode waveguide when matching was provided by a microlens with a radius of ~10 μ

Determination of the amplitude-frequency characteristics ofW-type fiber waveguides

The results are given of theoretical and experimental investigations of the amplitude-frequency characteristics of fiber waveguides obtained using continuous optical radiation modulated by a microwave signal. A simple analytic expression is derived for the transfer function of an ideal fiber waveguide when a Gaussian light beam is coupled in and the numerical aperture of the fiber is considerably less than unity. The results are given of experimental determinations of the amplitude-frequency characteristics of quartz multimode fiber waveguides with a W-like profile of the refractive index, obtained in the modulation frequency range 800–1250 MHz. The amplitude-frequency characteristics determined in this way are compared with calculated results.

Generation of wide-band optical continuum in fiber waveguides

Excitation of multimode phosphosilicate fiber waveguides with pulses of 0.53 and 1.06 ? wavelengths gave rise to the Stokes components of the stimulated Raman scattering as well as to an anomalously wide continuous emission spectrum extending from ultraviolet to near infrared. The observed effects were explained by four-photon parametric processes. Absorption lines attributed to inverse Raman scattering were observed in the anti-Stokes part of the spectrum.

Use of a fiber Raman converter for the study of backscattering in multimode fiber waveguides

Stimulated Raman scattering in a fiber converter pumped by a pulsed YAG:Nd laser made it possible to investigate backscattering in fiber waveguides over a wide range of wavelengths. The attenuation of light found by the backscattering method in a multimode fiber waveguide at wavelengths 0.53–0.8μ and 1.06–1.37 μ was in good agreement with the results obtained by the usual break-off method.

Mode selection and frequency tuning of a laser with a waveguide resonator

It was found experimentally that a laser with a resonator containing a section of a multimode fiber waveguide exhibited a characteristic frequency selection, which made it possible to control the emission spectrum. The effects observed were explained qualitatively.

Calculation of the optical characteristics of a bent waveguide

A multimode fiber waveguide bent along the circumference of a circle is considered. It is assumed that initially the refractive index profile is rectangular. A study is made of the geometry of meridional rays making allowance for the refractive index gradient resulting from bending. A calculation is made of the change in the entry aperture of the waveguide and in the mean free path of a ray between reflections, and of the relative increase in the optical path and number of reflections of a ray during its passage along the whole of the fiber.

Spectral channel demultiplexer utilizing a planar multimode waveguide

The technology of fabrication of glass planar multimode waveguides with a guiding layer a few tens of microns thick was mastered. Such waveguides should find use in various integrated-optics components of fiber-optical communication lines employing multimode fibers. A waveguide of this type was used to construct a channel demultiplexer with a holographic concave diffraction grating designed for lines with spectral channel multiplexing in multimode or single-mode fiber waveguides. The reciprocal linear dispersion of this demultiplexer was 43 nm/mm and the crosstalk level was less than 15 dB (measured in terms of the optical power) after demultiplexing of channels for monochromatic carriers separated by spectral intervals of 43 nm.

Low-loss fiber-optical directional couplers

A method was developed for the fabrication of directional couplers for multimode quartz glass fiber waveguides. These couplers were made by electric-arc welding without preliminary etching away of the cladding. Couplers with branching into two or three channels were characterized by average additional losses of 1.4 and 2.5 dB, respectively. The return-channel isolation of 50–60 dB was evidence of a high directionality of these couplers. The mode composition of the radiation was also determined.