Abstract: The amplifying optical fiber comprises a single-mode core and a multimode core surrounding the single-mode core, the multimode core containing a doped layer referred to as a “doped ring” and having a certain concentration of active rare earth ions to perform amplification by active rare earth ions on at least one optical signal for injection into the amplifying fiber. The fiber is dimensioned so that the product of its length multiplied by its Raman efficiency is greater than or equal to 0.5 W?1. In addition, the fiber presents absorption defined by an absorption coefficient expressed in dB/m, which absorption presents, at a certain wavelength, a maximum value referred to as the “absorption maximum”, the fiber presents accumulated absorption, corresponding to the product of its length multiplied by the absorption maximum, that is greater than or equal to 100 dB. The invention also provides an amplifier including such a fiber, a single-mode pump, and a multimode pump.

Abstract: The amplifying optical fiber comprises a single-mode core and a multimode core surrounding the single-mode core, the multimode core containing a doped layer referred to as a “doped ring” and having a certain concentration of active rare earth ions to perform amplification by active rare earth ions on at least one optical signal for injection into the amplifying fiber. The fiber is dimensioned so that the product of its length multiplied by its Raman efficiency is greater than or equal to 0.5 W?1. In addition, the fiber presents absorption defined by an absorption coefficient expressed in dB/m, which absorption presents, at a certain wavelength, a maximum value referred to as the “absorption maximum”, the fiber presents accumulated absorption, corresponding to the product of its length multiplied by the absorption maximum, that is greater than or equal to 100 dB. The invention also provides an amplifier including such a fiber, a single-mode pump, and a multimode pump.

Abstract: The amplifying optical fiber (1) comprises a single-mode core (10) and a multimode core (20) surrounding the single-mode core, the multimode core containing a doped layer referred to as a “doped ring” (21) and having a certain concentration of active rare earth ions (6) to perform amplification by active rare earth ions on at least one optical signal for injection into the amplifying fiber. The fiber is dimensioned so that the product of its length multiplied by its Raman efficiency is greater than or equal to 0.5 W?1. In addition, the fiber presents absorption defined by an absorption coefficient expressed in dB/m, which absorption presents, at a certain wavelength, a maximum value referred to as the “absorption maximum”, the fiber presents accumulated absorption, corresponding to the product of its length multiplied by the absorption maximum, that is greater than or equal to 100 dB. The invention also provides an amplifier including such a fiber, a single-mode pump, and a multimode pump.

Abstract: A method for remodulation of a modulated optical signal is disclosed which uses a disturbed line signal and an optical clock signal derived from the undisturbed original line signal modulated with the bitrate frequency feeding both signals in a Raman amplifying fiber connected to at least one Raman pump running the clock signal as Raman pump wavelength for the line signal.

Abstract: A Raman amplifier for a use in optical transmission systems. The Raman amplifier comprises a Raman active optical fiber and a Raman pump in operative connection with said optical fiber. The Raman pump further comprises a plurality of pairs of pump light sources which emit polarized pump light. Each pair of pump light sources generates a pair of mutually orthogonal pump fields with respective central frequencies (?1a-c, ?2a-c). The Raman pump also comprises a pump field combiner in operative connection with the pump light sources. The pump field combiner is adapted to couple each of the plurality of pairs of pump fields at mutually orthogonal directions of polarization into said optical fiber. It is proposed that the respective central frequencies (?1a-c, ?2a-c) of the pump fields of at least one, preferably each pair of mutually orthogonal pump fields are different from each other and exhibit a frequency shift (??) below 1.8 THz.

Abstract: A Raman-amplified optical transmission system (1) comprises at least one transmission fiber (4) for Raman amplifying of an optical signal (S), at least one corresponding pump (5, 5.1, 5.2, 5.3) for pumping the transmission fiber (4) at a plurality of pumping wavelengths (?P1, ?P2, ?P3), at least one Lumped Raman Amplifier LRA (9, 10, 11) for imparting an additional gain on the optical signal (S), and at least one corresponding LRA pump (10, 10.1) for pumping the lumped Raman amplifier LRA. According to the present invention the LRA pump (10, 10.1) is adapted to operate at a single LRA pumping wavelength (?P3), which is essentially equal to one of the pumping wavelengths (?P3) of the pump (5, 5.3) for pumping the transmission fiber (4).

Abstract: It is disclosed a pump energy source (20) for providing pump energy (E_p) to an optical transmission system (100) transmitting an optical signal along an optical fiber, in particular an optical transmission system (100) in which a beam of said pump energy (E_p) is introduced to said optical fiber so that said beam of said pump energy (E_p) copropagates with said optical signal.

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: The invention is dealing with a Raman amplifying device comprising an optical path, pump sources for generating a plurality of Raman pump signals and means for coupling the plurality of Raman pump signals into the optical path for backward pumping. The plurality of optical Raman pump signals are time-division multiplexed by multiplexing controlling means and the controlling means apply a modulation frequency beyond the corner frequency of the co-propagating modulation transfer function. The method to modulate the time division multiplexed Raman signal gives a condition to avoid the increase of double Rayleigh scattering noise.

Abstract: The gain characteristic of a distributed Raman amplifier (RA) is controlled by estimating its gain curve in a simulation, selecting NP data channels (?1, ?2, ?3) for an online measurement and determining target gain values for the selected channels from the simulated gain curve (24). The number of selected channels corresponds to the number of pump wavelengths (?P1, ?P2, ?P3). A controller (CTR) varies the power of at least one of the pump light signals (?1, ?2, ?3) to minimize a power difference between the measured power value of any of the NP signal channels and its estimated target gain value.

Abstract: A Raman amplifier (10) including at least one amplifying fiber (12) and a coupler (14) for coupling at least first (16) and second (18) pump laser modules to the amplifying fiber (12), the first pump laser module (16) including a frequency discriminator (24) for selecting an optical frequency to be emitted with an optical power exceeding an optical power of remaining optical frequencies that are also emitted by the first pump laser module (16). The first optical frequency is spaced apart from a local maximum (28; 36; 48) in optical power of the remaining optical frequencies, and the second pump laser module (18) emits at an optical frequency one Stokes-frequency above the frequency of the local maximum (28; 36; 48). The first optical frequency and the frequency of the local maximum are chosen on Stokes-frequency above the signal frequency range. As a consequence, the Raman gain provided in the Raman amplifying fiber 12 is broadened.

Abstract: A cascaded Raman laser (10) has a pump radiation source (12) emitting at a pump wavelength ?p, an input section (14) and an output section (16) made of an optical medium. Each section (14, 16) comprises wavelength selectors (141, 142, . . . , 145 and 161, 162, . . . , 165) for wavelengths ?1, ?2, . . . , ?n?k, where n?3, ?p<?1<?2< . . . <?n?1<?n and ?n?k+1, ?n?k+2, . . . , ?n being k?1 emitting wavelengths of the laser (10). The laser further comprises an intracavity section (18) that is made of a non-linear optical medium, has a zero-dispersion wavelength ?0 and is disposed between the input (14) and the output (16) section. The wavelengths ?1, ?2, . . . , ?n?k of the wavelength selectors (141, 142, . . . , 145 and 161, 162, . . . , 165) and the zero-dispersion wavelength ?0 of the intracavity section (18) are chosen such that energy is transferred between different wavelengths by multi-wave mixing.

Abstract: A method of determining the gain characteristic of a Raman amplifier includes the steps of launching a pump light signal into a fiber; preliminary adjusting the power of the pump light signal to a value that lies in a range where the amplified spontaneous emission noise originating from the pump light signal is substantially proportional to the on/off gain provided by the power of the pump light signal; monitoring the power of the amplified spontaneous emission noise signal; varying the power of the pump light signal; measuring a variation in the power of the amplified spontaneous emission noise signal corresponding to the pump power variation; and determining the gain characteristic of the amplifier from the relative variation in pump power and the measured variation in noise power.

Abstract: The invention is dealing with a Raman amplifying device comprising an optical path, pump sources for generating a plurality of Raman pump signals and means for coupling the plurality of Raman pump signals into the optical path for backward pumping. The plurality of optical Raman pump signals are time-division multiplexed by multiplexing controlling means and the controlling means apply a modulation frequency beyond the corner frequency of the co-propagating modulation transfer function. The method to modulate the time division multiplexed Raman signal gives a condition to avoid the increase of double Rayleigh scattering noise.

Abstract: The amplifying optical fiber (1) comprises a single-mode core (10) and a multimode core (20) surrounding the single-mode core, the multimode core containing a doped layer referred to as a “doped ring” (21) and having a certain concentration of active rare earth ions (6) to perform amplification by active rare earth ions on at least one optical signal for injection into the amplifying fiber. The fiber is dimensioned so that the product of its length multiplied by its Raman efficiency is greater than or equal to 0.5 W−1. In addition, the fiber presents absorption defined by an absorption coefficient expressed in dB/m, which absorption presents, at a certain wavelength, a maximum value referred to as the “absorption maximum”, the fiber presents accumulated absorption, corresponding to the product of its length multiplied by the absorption maximum, that is greater than or equal to 100 dB.

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: It is disclosed a pump energy source (20) for providing pump energy (E_p) to an optical transmission system (100) transmitting an optical signal along an optical fiber, in particular an optical transmission system (100) in which a beam of said pump energy (E_p) is introduced to said optical fiber so that said beam of said pump energy (E_p) copropagates with said optical signal.

Abstract: Disclosed is a Raman amplifier (10) comprising at least one length of fiber (12) and at least a coupler (14) for coupling at least a first pump laser module (16) and a second pump laser module (18) to said Raman amplifying fiber (12), the first pump laser module (16) comprising a frequency discriminator (24) for selecting an optical frequency to be emitted with an optical power exceeding an optical power of remaining optical frequencies that are also emitted by said first pump laser module (16). The first optical frequency is selected to be spaced apart from a local maximum (28; 36; 48) in optical power of said remaining optical frequencies, and the second pump laser module (18) emits at an optical frequency one Stokes-frequency above the frequency of said local maximum (28; 36; 48). The firts optical frequency and the frequency of said local maximum are chosen on Stokes-frquency above the signal frequency range. As a consequence, the Raman gain provided in Raman amplifying fiber 12 is broadened.

Abstract: A cascaded Raman laser (10) has a pump radiation source (12) emitting at a pump wavelength &lgr;p, an input section (14) and an output section (16) made of an optical medium. Each section (14, 16) comprises wavelength selectors (141, 142, . . . , 145 and 161, 162, . . . , 165) for wavelengths &lgr;1, &lgr;2, . . . , &lgr;n−k, where n≧3, &lgr;p<&lgr;1<&lgr;2< . . . <&lgr;n−1<&lgr;n and &lgr;n−k+1, &lgr;n−k+2, . . . , &lgr;n being k≧1 emitting wavelengths of the laser (10). The laser further comprises an intracavity section (18) that is made of a non-linear optical medium, has a zero-dispersion wavelength &lgr;0 and is disposed between the input (14) and the output (16) section. The wavelengths &lgr;1, &lgr;2, . . . , &lgr;n−k of the wavelength selectors (141, 142, . . . , 145 and 161, 162, . . .

Abstract: A method for remodulation of a modulated optical signal is disclosed which uses a disturbed line signal and an optical clock signal derived from the undisturbed original line signal modulated with the bitrate frequency feeding both signals in a Raman amplifying fiber connected to at least one Raman pump running the clock signal as Raman pump wavelength for the line signal.