Abstract: A laser apparatus includes an external cavity laser (ECL) where the optical signal is modulated by an electrical modulation signal for modulating in frequency the laser output signal. The modulation in frequency produces a modulation of intensity (power) of the laser output signal, also denoted amplitude modulation (AM). A method of controlling the AM amplitude of a signal emitted by an ECL includes a gain medium, a phase element with variable transmissivity induced by the modulation, and a spectrally selective optical filter that selects and keeps the AM amplitude below a certain desired value or minimizes such value. A control method and a laser apparatus are also described in which the reduction of the AM component of the output power is achieved by acting on the gain of the gain medium of the ECL.

Abstract: An external-cavity laser module includes a package defining an enclosure, the package including a base having a surface internal to the enclosure, a thermoelectric cooler within the enclosure, the thermoelectric cooler including an upper carrier plate and a lower carrier plate, the lower carrier plate being placed on the internal surface of the base and the thermoelectric cooler (TEC) being configured to stabilize the temperature of the upper carrier plate at a substantially constant temperature. The laser module further includes a laser assembly housed within the enclosure, including a gain medium for emitting an optical beam into the external cavity and an end mirror. Variations of the environmental temperature with respect to the thermally stabilized temperature cause mechanical deformations of the TEC upper carrier plate that is in thermal coupling with the laser assembly. The mechanical deformations in turn induce variations in the optical path length of the laser cavity.

Abstract: The present invention concerns a laser apparatus (200) comprising an external cavity laser (ECL) in which the optical signal is modulated by an electrical modulation signal with the purpose of modulating in frequency the laser output signal. The modulation in frequency produces in turn a modulation of intensity (power) of the laser output signal, also denoted amplitude modulation (AM). A method is described of control of the AM amplitude of a signal emitted by an ECL that comprises a gain medium (205), a phase element (206) with variable transmissivity induced by the modulation and a spectrally selective optical filter (209) and that selects and keeps the AM amplitude below a certain desired value or minimizes such value.

Abstract: An external-cavity laser module includes a package defining an enclosure, the package including a base having a surface internal to the enclosure, a thermoelectric cooler within the enclosure, the thermoelectric cooler including an upper carrier plate and a lower carrier plate, the lower carrier plate being placed on the internal surface of the base and the thermoelectric cooler (TEC) being configured to stabilise the temperature of the upper carrier plate at a substantially constant temperature. The laser module further includes a laser assembly housed within the enclosure, including a gain medium for emitting an optical beam into the external cavity and an end mirror. Variations of the environmental temperature with respect to the thermally stabilised temperature cause mechanical deformations of the TEC upper carrier plate that is in thermal coupling with the laser assembly. The mechanical deformations in turn induce variations in the optical path length of the laser cavity.

Abstract: A method of controlling an external-cavity tuneable laser which has a wavelength-elective tuneable mirror, in which wavelength selectivity is achieved by an electrical signal provided by an alternating voltage. The tuneable mirror has a liquid crystal material, a diffraction grating and a planar waveguide optically interacting with the grating. The diffraction grating and the waveguide form a resonant structure that reflects only a selected resonance wavelength from among all the other wavelengths impinging thereon. Depending on the amplitude of the voltage applied to the tunable mirror, the tuneable mirror reflects radiation only at a given wavelength. The lasing output wavelength of the laser is selected to correspond to the resonance wavelength of the tuneable mirror. Accurate selection of the emission wavelength (frequency) of the tuneable laser by the tuneable mirror can be derived from the analysis of the signal modulation induced by the AC voltage applied to the tuneable mirror.

Abstract: A single-mode external-cavity tuneable laser includes a gain medium, a tuneable element and a channel allocation grid element. The channel allocation grid element is preferably an FP etalon which is structured and configured to define a plurality of equally spaced transmission peaks corresponding to the ITU channel grid, e.g., 200, 100, 50 or 25 GHz. The tuneable element, preferably a tuneable mirror, serves as the coarse tuning element that discriminates between the peaks of the grid etalon. The tuneable laser of the invention has a relatively short cavity length of not more than 15 mm, preferably not larger than 12 mm. It has been found that the FP etalon introduces a phase non-linearity in the external cavity, which induces a compression of the cavity modes, i.e., a reduction in the cavity mode spacing, in correspondence to the etalon transmission peaks. Mode compression increases with the decrease of the FWHM bandwidth of the grid FP etalon, hereafter referred to as (FWHM)FP.

Abstract: A method of controlling an external-cavity tuneable laser which has a wavelength-elective tuneable mirror, in which wavelength selectivity is achieved by an electrical signal provided by an alternating voltage. The tuneable mirror has a liquid crystal material, a diffraction grating and a planar waveguide optically interacting with the grating. The diffraction grating and the waveguide form a resonant structure that reflects only a selected resonance wavelength from among all the other wavelengths impinging thereon. Depending on the amplitude of the voltage applied to the tunable mirror, the tuneable mirror reflects radiation only at a given wavelength. The lasing output wavelength of the laser is selected to correspond to the resonance wavelength of the tuneable mirror. Accurate selection of the emission wavelength (frequency) of the tuneable laser by the tuneable mirror can be derived from the analysis of the signal modulation induced by the AC voltage applied to the tuneable mirror.

Abstract: A single-mode external-cavity tuneable laser includes a gain medium, a tuneable element and a channel allocation grid element. The channel allocation grid element is preferably an FP etalon which is structured and configured to define a plurality of equally spaced transmission peaks corresponding to the ITU channel grid, e.g., 200, 100, 50 or 25 GHz. The tuneable element, preferably a tuneable mirror, serves as the coarse tuning element that discriminates between the peaks of the grid etalon. The tuneable laser of the invention has a relatively short cavity length of not more than 15 mm, preferably not larger than 12 mm. It has been found that the FP etalon introduces a phase non-linearity in the external cavity, which induces a compression of the cavity modes, i.e., a reduction in the cavity mode spacing, in correspondence to the etalon transmission peaks. Mode compression increases with the decrease of the FWHM bandwidth of the grid FP etalon, hereafter referred to as (FWHM)FP.

Abstract: A multiple stage Raman amplifier includes an interstage wavelength-selective pump combiner. Wavelength-selection characteristics are such that the pump combiner substantially blocks the passage of the pump signal of the first stage to the second stage and/or vice versa while allowing the passage of the transmission signal from the first stage to the second stage. The pump combiner substantially blocks different portions of the wavelength spectrum of the pump radiation which is fed into the pump combiner from different ports. The pump combiner preferably includes thin-film filters. The pump combiner has the multiple function of coupling the pump signal of the first (or second) pump source and of isolating from one another the pump signals of the two amplification stages. This allows the reduction of the number of passive components present in a multistage optical amplifier, which in turn leads to a decrease of the overall insertion loss in the amplifier and to shorter assembly processing.

Abstract: Optical pumping unit comprising a first pump source adapted to emit a first pump radiation at wavelength ?p1; a second pump source adapted to emit a second pump radiation at wavelength ?p2, with wavelength ?p2 different from wavelength ?p1; and a common coupling section comprising a first and a second port connected to the first and second pump source for respectively receiving the first and the second pump radiation; a third port for a signal radiation at wavelength ?s; a fourth port, wherein the coupling section is adapted to combine, in the fourth port, the signal radiation and the first and second pump radiation through a reversal of the direction of propagation of the first pump radiation from the first port to the fourth port.

Abstract: A multiple stage Raman amplifier includes an interstage wavelength-selective pump combiner. Wavelength-selection characteristics are such that the pump combiner substantially blocks the passage of the pump signal of the first stage to the second stage and/or vice versa while allowing the passage of the transmission signal from the first stage to the second stage. The pump combiner substantially blocks different portions of the wavelength spectrum of the pump radiation which is fed into the pump combiner from different ports. The pump combiner preferably includes thin-film filters. The pump combiner has the multiple function of coupling the pump signal of the first (or second) pump source and of isolating from one another the pump signals of the two amplification stages. This allows the reduction of the number of passive components present in a multistage optical amplifier, which in turn leads to a decrease of the overall insertion loss in the amplifier and to shorter assembly processing.

Abstract: Optical pumping unit comprising a first pump source adapted to emit a first pump radiation at wavelength ?p1; a second pump source adapted to emit a second pump radiation at wavelength ?p2, with wavelength ?p2 different from wavelength ?p1; and a common coupling section comprising a first and a second port connected to the first and second pump source for respectively receiving the first and the second pump radiation; a third port for a signal radiation at wavelength ?s; a fourth port, wherein the coupling section is adapted to combine, in the fourth port, the signal radiation and the first and second pump radiation through a reversal of the direction of propagation of the first pump radiation from the first port to the fourth port.

Abstract: An optical device is described comprising at least one fiber-optic component arrange inside said device and a particular polymer composition capable of holding said optical component(s) in a predetermined position and protecting them inside said device. The polymer composition is a silicone elastomer obtained by crosslinking a mixture comprising at least one polysiloxane containing two or more hydrogen-siloxane functional groups of formula >SiH—O—, and at least one polysiloxane containing at least two vinyl groups of formula —CH═H2, where said polysiloxane are reacted in an amount such that the molar ratio between the hydrogen-siloxane groups and the vinyl groups is less than or equal to 1:1. The polymer composition has extremely low emission of hydrogen, less than 1 cm3 per kg of composition.

Abstract: Optical pumping unit comprising a first pump source adapted to emit a first pump radiation at wavelength &lgr;p1; a second pump source adapted to emit a second pump radiation at wavelength &lgr;p2, with wavelength &lgr;p2 different from wavelength &lgr;p1; and a common coupling section comprising a first and a second port connected to the first and second pump source for respectively receiving the first and the second pump radiation; a third port for a signal radiation at wavelength &lgr;s; a fourth port, wherein the coupling section is adapted to combine, in the fourth port, the signal radiation and the first and second pump radiation through a reversal of the direction of propagation of the first pump radiation from the first port to the fourth port.

Abstract: An optical device is described comprising at least one fibre-optic component arranged inside the said device and a particular polymer composition capable of holding the said optical components in a predetermined position and protecting them inside the said device. The polymer composition is a silicone elastomer obtained by crosslinking a mixture comprising at least one polysiloxane containing two or more hydrogen-siloxane functional groups of formula >SiH—O— at least one polysiloxane containing at least two vinyl groups of formula —CH═CH2, where the said polysiloxanes are reacted in an amount such that the molar ratio between the hydrogen-siloxane groups and the vinyl groups is less than or equal to 1:1. The said polymer composition has extremely low emission of hydrogen, less than 1 cm3 per kg of composition.

Abstract: Optical pumping unit comprising a first pump source adapted to emit a first pump radiation at wavelength &lgr;p1; a second pump source adapted to emit a second pump radiation at wavelength &lgr;p2, with wavelength &lgr;p2 different from wavelength &lgr;p1; and a common coupling section comprising a first and a second port connected to the first and second pump source for respectively receiving the first and the second pump radiation; a third port for a signal radiation at wavelength &lgr;s; a fourth port, wherein the coupling section is adapted to combine, in the fourth port, the signal radiation and the first and second pump radiation through a reversal of the direction of propagation of the first pump radiation from the first port to the fourth port.

Abstract: Splice between a first optical fiber, having a first propagation constant, and a second optical fiber, having a second propagation constant which is different from the first. The said splice comprises a coupling region between an end portion of the said first optical fiber and an end portion of the said second fiber, such that a coupling of at least 90% of the optical power in a waveband of at least 100 nm is obtained between the said first fiber and the said second fiber.

Abstract: Coupling system between an optical waveguide (1) and an optical device (8) suitable for receiving and/or transmitting an optical beam having a first maximum MFR, comprising a single-mode optical fiber (1) having at one end a portion (10) of its core (2) expanded with a second MFR. An aspherical lens (6) is formed on said end of the fiber (1). Said aspherical lens comprises a pair of inclined surfaces (41, 42) which intersect on a line, generating an edge, in a position substantially corresponding to the center of said core (2), said edge is rounded to form an aspherical profile.