Abstract: An in-fiber mode converter comprises fiber portions (10) constituting an input microlens, a fiber portion (20) constituting a phase shifting region adapted to convert a propagation mode of an optical signal into another propagation mode, and fiber portions (30) constituting an output microlens. The fiber portions are spliced, the converter is compact and losses are minimized relative to mode conversion in free space.

Abstract: An optical device (D) is dedicated to the transformation of the propagation mode of optical signals. This device comprises at least a first mode converter (3) that is supplied with signals that are propagated in a first guided mode and that delivers the signals in a multimode fibre (4) partly in the first guided mode and partly in a second guided more of a higher order that the first. The multimode fibre (4) comprises at least first passive filtering means (R) which have the task of converting the first guided mode into at least one dissipative cladding mode in order to prevent or limit the propagation of the signals in this first guided mode while at the same time authorising the propagation of the signals having the second guided mode in the multimode fibre (4).

Abstract: An optical device (D) is dedicated to the transformation of the propagation mode of optical signals. This device comprises at least a first mode converter (3) that is supplied with signals that are propagated in a first guided mode and that delivers the signals in a multimode fibre (4) partly in the first guided mode and partly in a second guided more of a higher order that the first. The multimode fibre (4) comprises at least first passive filtering means (R) which have the task of converting the first guided mode into at least one dissipative cladding mode in order to prevent or limit the propagation of the signals in this first guided mode while at the same time authorising the propagation of the signals having the second guided mode in the multimode fibre (4).

Abstract: An in-fiber mode converter comprises fiber portions (10) constituting an input microlens, a fiber portion (20) constituting a phase shifting region adapted to convert a propagation mode of an optical signal into another propagation mode, and fiber portions (30) constituting an output microlens. The fiber portions are spliced, the converter is compact and losses are minimized relative to mode conversion in free space.

Abstract: An optical waveguide suitable for a slanted Bragg grating (SBG) to be written thereinto has a refractive index profile defining a core and a cladding and a specific photosensitivity profile. This photosensitivity profile W(r) is such that, for a given SBG writing angle ?, the coupling of the fundamental mode into itself as counterpropagation in the waveguide, K(?), is substantially zero and such that its derivative K?(?) with respect to the angle ? is also substantially equal to zero. The zero derivative, and also the zero coupling of the fundamental mode as a function of the angle, means that a widened reflection pocket about the grating write angle is guaranteed.

Abstract: The invention relates to the field of dispersion managed optical fibres for use in wavelength division multiplex transmission networks. A multimode optical fibre in which at least one higher-order mode can be propagated, is constituted radially by a single central core surrounded by an optical cladding (13), and comprises, for said higher mode or for at least one of said higher-order modes, positive chromatic dispersion optical fibre portions (D+) alternating longitudinally with negative chromatic dispersion optical fibre portions (D?).

Abstract: Disclosed is a Raman laser device (10) having a first cavity in which lasing occurs at a first frequency, and at least one second cavity in which lasing occurs at a second frequency. Thereby respective first and second waves inside the respective cavities are generated having a first power and a second power, respectively. Further, beams propagating outside the cavities are generated by coupling out a part of the first power and a part of the second power utilizing respective output mirrors. The part of the second power that is coupled out is attenuated without attenuating the complementary part of the second power remaining in the second cavity. The Raman laser device is characterized in that the part of the second power that is coupled out is attenuated utilizing at least one Fiber Bragg Grating (46, 62).

Abstract: An optical filter comprises a first mode converter converting an incident light signal propagating in an incident mode into a signal propagating in a propagation mode LPnm of order higher than that of said incident mode; a second mode converter converting the light signal of higher propagation order LPnm into a signal propagating in the incident propagation mode; and a slanted Bragg grating disposed between said first and second mode converters and adapted to couple the higher propagation order light signal LPnm in back-propagation into said incident mode. The filter is applicable to flattening gain and to multiplexing DWDM signals.

Abstract: The invention is related to an optical waveguide device comprising a length of fiber including a monomode core having a refraction index of nco, a photosensitivity of Sco and a radius Rco and an internal cladding with an refractive index of ncl, a photosensitivity of Scl and a radius of Rcl, and a outer cladding surrounding the internal cladding with an refractive index that allows the existence of multiple cladding modes, and a slanted Bragg grating with an effective tilt angle of ? written in core and inner cladding of the optical waveguide, coupling the fundamental mode into several cladding modes where Rcl?2.5 Rco and the Sco?Scl.

Abstract: The invention relates to an optical fiber presenting a core, cladding, and a grating written by irradiation and coupling at least one light mode into the cladding so that it is dissipated therein. The invention proposes causing the mean index to vary progressively along the grating, at least at the ends of the grating. The progressive variation in mean index or in the amplitude of index modulation for writing the grating serves to limit insertion losses to the filter formed by the grating. Analogously, in a written-in grating, the invention provides the equivalent of progressively varying the core size of the fiber for interconnecting two optical fibers presenting different core diameters. The invention is applicable in particular to gain-equalizing filters in WDM transmission systems.

Abstract: An optical filter comprises a waveguide and a plurality of Slanted Bragg Gratings written in the waveguide, wherein at least two of the Slanted Bragg Gratings overlap one another. A method of producing an optical filter comprises the steps of passing an ultraviolet light through a first portion of a chirped phase mask onto a first portion of a photosensitive waveguide so as to form a first Slanted Bragg Grating in the first portion of the waveguide and passing the ultraviolet light through a second portion of the chirped phase mask onto a second portion of the photosensitive waveguide so as to form a second Slanted Bragg Grating in the second portion of the waveguide, wherein the first and second Slanted Bragg Gratings overlap one another. A further annealing step may cause a spectrum of the filter to match a target spectrum.

Abstract: An optical device (D) is dedicated to transforming the propagation mode of optical signals. The device comprises mode transformation means (3–5) associated with a multimode fiber (2) and comprising first and second mode converters (3and 5) coupled to each other by a multimode fiber portion (4) of selected length (L). The first converter (3) is fed with signals propagating in a first mode and it delivers the signals to the fiber portion (4) in part in the first mode and in part in a second mode of order higher than the first, and the second converter (5) is arranged to cause the signals in the first and second modes to interfere so that on outlet therefrom they present a selected spectral spacing.

Abstract: The invention relates to the field of dispersion managed optical fibres for use in wavelength division multiplex transmission networks. A multimode optical fibre in which at least one higher-order mode can be propagated, is constituted radially by a single central core surrounded by an optical cladding (13), and comprises, for said higher mode or for at least one of said higher-order modes, positive chromatic dispersion optical fibre portions (D+) alternating longitudinally with negative chromatic dispersion optical fibre portions (D?).

Abstract: An optical filter composed of a concatenation of elementary filters consisting of chirped slanted Bragg gratings written on a continuous portion of an optical waveguide, characterized in that the various gratings in the concatenation have the same angle, identical lengths and a linear chirp.

Abstract: An optical mode converter comprising an optical guide able to transmit an optical signal in at least one guided mode, characterised in that the optical guide comprises a photosensitive zone inducing a specific index profile along a section of the guide, the said index profile simultaneously defining a longitudinal adiabatic transition and a transverse distribution of the guided mode or modes so as to deconfine the fundamental mode and to maximise the overlap with a higher-order mode.

Abstract: The present invention relates to the field of optical fiber telecommunications. More specifically, the subject of the invention is a slanted Bragg grating optical fiber and a process for manufacturing such a fiber. The slanted Bragg grating optical fiber of longitudinal axis Z has slanted Bragg gratings photowritten in said fiber and having refractive index modulations along said axis Z, inclined at a same writing angle with respect to a normal plane to said axis Z and defining planes called writing planes forming the same angle than the writing angle with said normal plane, each writing plane forming with others writing planes specific angles called angles of rotation about said axis Z.

Abstract: The present invention relates to a Raman laser comprising a Raman fiber (10), wherein said Raman fiber (10) comprises a plurality of wavelength selectors (16, 18, 20, 22, 24, 26, 28, 30) for closing a plurality of laser cavities (32, 34, 36, 38, 40). Some laser cavities (38, 40) have a single common first wavelength selector (44) so as to reduce the number of wavelength selectors. The present invention further relates to a method of manufacturing a Raman laser.

Abstract: A tuneable optical fibre comprising a long-period Bragg grating (5) written in a portion of an optical waveguide (10) comprising a core and an optical cladding (11), characterised in that the portion of the waveguide comprising the grating (5) is at least partially immersed in an external environment consisting of two distinct sections, a first section (1) whose refractive index is higher than that of the optical cladding (11) and a second section (2) whose refractive index is lower than that of the optical cladding (11), the long-period grating being at least partially immersed in one of the said sections so as to almost independently tune the wavelength and/or the contrast of the spectral response of the filter.

Abstract: An optical filter comprising a slanted Bragg grating inscribed in an optical fiber portion comprising a core having a refractive index n1 and a radius Rcore and a cladding having an average refractive index n2 lower than n1 and a radius Rcladding, the core and the cladding of the fiber being doped with a photosensitive dopant in the fiber portion comprising the Bragg grating, which filter is characterized in that, in the fiber portion comprising the Bragg grating, the photosensitivity of the cladding is greater than the photosensitivity of the core and the cladding includes an index step area having a refractive index n3 greater than n2 and less than n1, said index step area having a width L defined by an inside radius Rs1 greater than or equal to the radius Rcore of the core and an outside radius Rs2 less than or equal to the radius Rcladding of the cladding.

Abstract: The present invention relates to a cascaded multi-wavelength Raman fiber laser adapted for emitting radiation of at least one wavelength &lgr;s1, with a length of optical fiber (13) having input (15) and output (16) sections, means (11) for introducing pump radiation of wavelength &lgr;p into said length of optical fiber (13), at least one pair of spaced-apart reflector means (151,161; . . .