Cselt-centro Studi E Laboratori Telecomunicazioni S.p.a.

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Cselt- Centro Studi E Laboratori Telecommunicazioni Spa

Pietro Di Vita

Gianni Coppa

Renato Caponi

Marcello Potenza

Massimo Calzavara

Umberto Rossi

The value of a transverse moment of any order of the electromagnetic field associated with an optical beam (and in particular the spot-size of such a beam) is determined by two successive measurements of the optical power of the beam: one measurement is a direct measurement, the other is effected after spatially modulating the transverse distribution of the electromagnetic field by a factor proportional to the n-th power of the transverse coordinate of the beam, n being the moment order. The moment can be obtained from the ratio between the two measurements. The invention includes also the apparatus for carrying out the method.

Apparatus for measuring transverse moment of an electromagnetic field

A silica glass optical fiber is subjected to an external strain which causes vitreous matrix atoms to stabilize in a lower energy condition. In this way inhomogeneity domain sizes and as a consequence the attenuation due to Rayleigh scattering, depending on such inhomogeneity, are reduced.

Apparatus for reducing optical-fiber attenuation

Method of reducing optical-fiber attenuation

Mode field radius in single-mode optical fibers is measured by the modulation of an optical beam by means of a spatial filter with radial-distribution of transmittivity of Gaussian type. Modulated beam intensity is measured in correspondence with the beam axis for different widths of the Gaussian curve, and the mode field radius is derived from both such intensity values and a parameter dependent on the Gaussian width.

Method of and apparatus for the measurement of mode field radius in

An optical beam is injected into a single-mode fiber of a given length and outgoes from an end face of the fiber, is reflected by a reflecting optical system into the fiber; the optical power of the reflected beam guided backward by the fiber is measured. The end face of the fiber is placed in the optical center of the reflecting system to obtain the maximum reflected power, and is then deviated from the position detecting the occurring reductions of the reflected optical power.

Method and device for measuring coupling losses in single mode optical

These improvements to semiconductor lasers allow the fabrication of high-efficiency photoemitting devices thanks to a decrease in the threshold current necessary to optical emission stimulation. They consist in the application of a suitable magnetic field apt to confine carrier current within a limited zone of the active layer.

Semiconductor lasers

The refractive-index value is obtained by radially scanning a near-field image of the fiber output face and by computing, for each image point, the ratio between a first intensity value, obtained in the presence of a mask, having a transmissivity proportional to the fourth power of the transversal beam coordinate and located in a far-field plane, and a second intensity value, obtained in the absence of such a mask. An automated measurement apparatus for implementing the method is also provided.

Method of and apparatus for the measurement of the refractive-index

A method and an apparatus wherein a light beam is passed through a slit oscillating with respect to the beam, and a periodic signal is obtained from the beam portion traversing the slit. The periodic signal is split into its spectral components. Moment values are derived from the values of the amplitudes of such components.

Method of and apparatus for measuring transverse moments of an

The cut-off wavelength of the first higher order mode in optical fibers for telecommunication is measured based on the fact that the introduction of perturbations in an optical fiber can generate greater losses on higher order modes than on the lower order modes. A spectral scanning of the fiber output power is effected under a certain number of different perturbations conditions and the values obtained are combined so as to determine the fraction of power guided in the fundamental mode. The cut-off wavelength is that where this fraction exceeds a certain value.

Method of and apparatus for measuring the cut-off wavelength of the

To facilitate determination of the refractive-index profile of an optical fiber by the near-field technique, the fiber to be examined is inserted into a body of transparent liquid held by surface tension in a surrounding capillary tube also made of light-transmissive material. The tube, which is axially coextensive with the inserted fiber, has a refractive index less than the minimum index of the fiber core and cladding whereas the liquid has a refractive index exceeding the maximum index of the fiber core.

Method of and system for determining refractive-index profiles of

For the splicing of trunks of optical fibers, confronting trunk ends are closely juxtaposed in a surrounding enclosure which is subjected to vibrations transverse to its axis to generate an oscillating air column setting the trunk ends in vibration, the fiber trunks being clamped at points spaced from these ends by a distance sufficient to give rise to several standing-wave nodes at the applied frequency on the free fiber extremities. With these extremities vibrating in unison but at limited amplitudes compatible with the maximum permissible offset of the trunk axes, the confronting trunk ends are joined by the hardening of a blob of cement matching their refractive index, by electric fusion, or with the aid of a laser beam.

Method of and apparatus for splicing optical fibers

Signals, especially short pulses, are transmitted by way of a series of aligned light guides with internally reflecting boundaries (i.e. fibers or foils), with interposition of two identical transparent elements each refracting incident rays from the proximal guide end toward the remote guide end along paths which intersect the common guide axis at points near the center of the respective element for angles of incidence close to zero and at points near the center of the opposite element for angles of incidence close to a critical angle .THETA..sub.M &lt;&lt; 1 (in radians). The transparent elements could be planoconvex lenses, which may be divided into Fresnel zones, or holograms; they could also be replaced by an optically equivalent transparent body whose refractive index varies along a generally parabolic law with increasing distance from the axis.

Ray-path equalizer for signal-transmission system using multimode light

Signals, especially short pulses, are transmitted by way of cascaded light guides with internally reflecting boundaries (i.e. fibers or foils) between which a transparent body of graded refractive index is interposed. The refractive index of the body varies, on opposite sides of a centerline coinciding with the axes of the aligned guides, according to a parabolic law, increasing from the centerline outwardly over a radial distance r.sub.o and then decreasing in a symmetrical manner over a like radial distance, whereby light rays incident at various angles on an entrance face of the body are deflected onto a generally sinusoidal path which peaks at a radial distance 2r.sub.o. The axial length of the body equals three quarter-wavelengths of the sine curve whereby substantially axially incident rays emerge from an exit face of the body at a limiting angle .theta..sub.M, and vice versa, the radial distance r.sub.o being given by r.sub.o = s.multidot.tan .theta..sub.M where s is the axial distance between the confronting ends of the light guides and the adjoining body faces.

Optical path-length equalizer with graded refractive index

Signals, especially short pulses, are transmitted by way of a series of aligned light guides with internally reflecting boundaries (i.e., fibers or foils), with interposition of two identical transparent bodies of positive refractivity between confronting guide ends. The cross-section of each refractive body in a common longitudinal plane of symmetry of the guides consists of two symmetrical truncated lens profiles whose boundary lies on a common centerline of the adjoining guides, the optical axes of the two lens profiles lying on opposite sides of that boundary.

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Turin, Italy

Pietro Di Vita