Amplified telecommunication system for wavelength-division multiplexing transmissions capable of limiting variations in the output power

Claim 2

An optical telecommunication system according to claim 1, characterized in that said wavelength band contiguous to the predetermined signal band contains a relative maximum of the spontaneous emission of said optical waveguide doped with a rare earth material being part of said pre-amplifier.

Claim 3

An optical telecommunication system according to claim 1, characterized in that said wavelength band contiguous to said predetermined signal band contains a relative maximum of the spontaneous emission of said active waveguide being part of the amplifying means.

Claim 4

An optical telecommunication system according to claim 1, characterized in that power variations of one of the input signals to the pre-amplifier within a range of 20 dB involve variations of the input power to the receiving means in a range not greater than 9 dB.

Claim 5

An optical telecommunication system according to claim 4, characterized in that power variations of one of the input signals to the pre-amplifier within a range of 20 dB involve variations of the input power to the receiving means in a range not greater than 6 dB.

Claim 6

An optical telecommunication system according to claim 1, characterized in that said second predetermined position of said filtering means is located along said doped waveguide between 15% and 50% of the overall length of the waveguide.

Claim 7

An optical telecommunication system according to claim 6, characterized in that said second predetermined position of said filtering means is located along said doped waveguide between 20% and 30% of the overall length of the waveguide.

Claim 8

An optical telecommunication system according to claim 1, characterized in that said first predetermined position of said differential-attenuation means is located along said doped waveguide between 50% and 75% of the overall length of the waveguide.

Claim 9

An optical telecommunication system according to claim 1, characterized by the presence of second filtering means disposed along said doped waveguide and adapted to transmit the signals in said predetermined band without attenuating them to an important degree and to attenuate the spontaneous emission at least at one wavelength band contiguous to said predetermined signal band.

Claim 10

An optical telecommunication system according to claim 9, characterized in that said second filtering means is located along said doped waveguide between 50% and 75% of the overall length of the waveguide.

Claim 11

An optical telecommunication system according to claim 1, characterized in that said doped waveguide is a silica-based doped optical fibre.

Claim 12

An optical telecommunication system according to claim 11, characterized in that said rare earth material is erbium.

Claim 13

An optical telecommunication system according to claim 12, characterized in that said optical fibre is further doped with aluminium, germanium and lanthanum.

Claim 14

An optical telecommunication system according to claim 12, characterized in that said optical fibre is further doped with aluminium and germanium.

Claim 15

An optical telecommunication system according to claim 12, characterized in that said filtering means have a cut-off wavelength at -3dB included between 1532 and 1534 nm.

Claim 16

An optical telecommunication system according to claim 12, characterized in that said predetermined wavelength band comprises the wavelength band between 1535 and 1560 nm.

Claim 17

An optical telecommunication system according to claim 1, characterized in that said filtering means consists of a portion of optical fibre having two cores optically coupled to each other for wavelengths in said band contiguous to said predetermined band, with one of the two cores which is coaxial with the fibre and connected at the two ends to the doped waveguide and with the other core which is off-centre and cut off at the ends.

Claim 18

An optical telecommunication system according to claim 1, characterized in that said filtering means consists of an interferential filter used in reflection.

Claim 19

An optical telecommunication system according to claim 1, characterized in that said filtering means comprises: - a first dichroic coupler separating the radiation in said predetermined band and said contiguous band to a first terminal and the radiation at said pumping wavelength to a second terminal; - a filter connected to said first terminal and capable of transmitting the signals in said predetermined band without attenuating them to an important degree and of attenuating the spontaneous emission in at least one wavelength band contiguous to said predetermined signal band; - a second dichroic coupler combining the radiation from said filter with the radiation at said pumping wavelength from said second terminal.

Claim 20

An optical telecommunication system according to claim 1, characterized in that the attenuation of said filtering means in said wavelength band contiguous to the predetermined signal band is at least 6 dB.

Claim 21

An optical telecommunication system according to claim 20, characterized in that the attenuation of said filtering means in said wavelength band contiguous to the predetermined signal band is at least 10 dB.

Claim 22

An optical telecommunication system according to claim 1, characterized in that said differential-attenuation means consists of: - a first dichroic coupler separating the radiation in said predetermined band and the radiation at said pumping wavelength respectively towards a first terminal and a second terminal; - an attenuating component connected to said first terminal, capable of attenuating said signals in said predetermined band; - a second dichroic coupler combining the radiation from said attenuating component with the radiation at said pumping wavelength from said second terminal.

Claim 23

An optical telecommunication system according to claim 22, characterized in that said attenuating component is an optical fibre.

Claim 24

An optical telecommunication system according to claim 22, characterized in that an optical isolator is inserted between said attenuating component and second dichroic coupler.

Claim 25

An optical telecommunication system according to claim 1, characterized in that said differential-attenuation means consists of a winding having a predetermined bending radius and consisting of one or more turns of optical fibre.

Claim 26

An optical telecommunication system according to claim 11 and 25, characterized in that said winding is made up of a portion of said doped optical fibre.

Claim 27

An optical telecommunication system according to claim 1, characterized in that the attenuation of said differential-attenuation means in said predetermined wavelength band is greater than the attenuation at said pumping wavelength by an amount of 5 ± 1 dB.

Claim 28

An optical telecommunication system according to claim 1, characterized in that said optical amplifying means consists of at least three active-fibre optical amplifiers disposed in cascade along the optical-fibre connecting line.

Claim 29

An optical telecommunication system according to claim 28, characterized in that said optical amplifying means comprises a silica-based active fibre, having a core doped with at least one fluorescent main dopant and at least one secondary dopant, in such a functional relation with respect to each other that they provide an optical signal/noise ratio at the reception, measured with a filter amplitude of 0.5 nm, which is not lower than 15 dB for signals of a wavelength included in said predetermined band when the input signal power at each of said active-fibre optical amplifiers is not lower than -16dBm.

Claim 30

An optical telecommunication system according to claim 29, characterized in that said main dopant is erbium and said secondary dopants are aluminium, germanium and lanthanum.

Claim 31

An optical amplifier comprising: - a rare-earth-doped optical waveguide (5, 7, 9), - input means (1) for one or more signals included in a predetermined wavelength band and a predetermined range of input powers, - pumping means (3) for said doped waveguide, adapted to provide optical pumping power at a pumping wavelength, - coupling means (4) within said doped waveguide of said optical pumping power and said input signal or signals, - output means (11) emitting at a given output level, one or more output signals amplified by the stimulated emission of said rare earth material submitted to pumping in said doped waveguide, - differential-attenuation means (8) located in a first predetermined position along the active waveguide, capable of supplying a predetermined attenuation having a value at said predetermined wavelength band which is different from the attenuation supplied at said pumping wavelength, characterized by filtering means (6) located at a second predetermined position along said doped waveguide and provided with a spectral attenuation curve adapted to transmit the signals at said predetermined wavelength band without attenuating them to an important degree and to attenuate by a value higher than a predetermined minimum the spontaneous emission at a wavelength band contiguous to said predetermined band, wherein said first and second predetermined positions, said predetermined attenuation values of the differential-attenuation means, said predetermined attenuation minimum of the filtering means and said wavelength band contiguous to said predetermined band are selected in such a functional relation with respect to each other that power variations in one of the input signals within a range of 20 dB involve power variations in the output power from the amplifier included in a range not greater than 12 dB.

Claim 32

An optical amplifier according to claim 31, characterized in that said wavelength band contiguous to said predetermined signal band contains a relative maximum of the spontaneous emission of said optical waveguide doped with a rare earth material.

Claim 33

An optical amplifier according to claim 31, characterized in that power variations of one of the input signals to the pre-amplifier within a range of 20 dB involve variations of the output power from the amplifier in a range not greater than 9 dB.

Claim 34

An optical amplifier according to claim 33, characterized in that power variations of one of the input signals to the pre-amplifier within a range of 20 dB involve variations of the output power from the amplifier in a range not greater than 6 dB.

Claim 35

An optical amplifier according to claim 31, characterized in that said second predetermined position of said filtering means is located along said doped waveguide between 15% and 50% of the waveguide length.

Claim 36

An optical amplifier according to claim 35, characterized in that said second predetermined position of said filtering means is located along said doped waveguide between 20% and 30% of the waveguide length.

Claim 37

An optical amplifier according to claim 31, characterized in that said first predetermined position of said differential-attenuation means is located along said doped waveguide between 50% and 75% of the waveguide length.

Claim 38

An optical amplifier according to claim 31, characterized by the presence of second filtering means disposed along said doped waveguide and adapted to transmit the signals in said predetermined band without attenuating them to an important degree and to attenuate the spontaneous emission at least at one wavelength band contiguous to said predetermined signal band.

Claim 39

An optical amplifier according to claim 38, characterized in that said second filtering means is located along said doped waveguide between 50% and 75% of the overall length of the waveguide.

Claim 40

An optical amplifier according to claim 31, characterized in that said doped waveguide is a silica-based doped optical fibre.

Claim 41

An optical amplifier according to claim 41, characterized in that said rare earth material is erbium.

Claim 42

An optical amplifier according to claim 41, characterized in that said optical fibre is further doped with aluminium, germanium and lanthanum.

Claim 43

An optical amplifier according to claim 41, characterized in that said optical fibre is further doped with aluminium and germanium.

Claim 44

An optical amplifier according to claim 41, characterized in that said filtering means have a cut-off wavelength at -3dB included between 1532 and 1534 nm.

Claim 45

An optical amplifier according to claim 41, characterized in that said predetermined wavelength band comprises the wavelength band between 1535 and 1560 nm.

Claim 46

An optical amplifier according to claim 31, characterized in that said filtering means consists of a portion of optical fibre having two cores optically coupled to each other for wavelengths in said band contiguous to said predetermined band, with one of the two cores which is coaxial with the fibre and connected at the two ends to the doped waveguide and with the other core which is off-centre and cut off at the ends.

Claim 47

An optical amplifier according to claim 31, characterized in that said filtering means consists of an interferential filter used in reflection.

Claim 48

An optical amplifier according to claim 31, characterized in that said filtering means comprises: - a first dichroic coupler separating the radiation in said predetermined band and said contiguous band to a first terminal and the radiation at said pumping wavelength to a second terminal; - a filter connected to said first terminal and capable of transmitting the signals in said predetermined band without attenuating them to an important degree and of attenuating the spontaneous emission in at least one wavelength band contiguous to said predetermined signal band; - a second dichroic coupler combining the radiation from said filter with the radiation at said pumping wavelength from said second terminal.

Claim 49

An optical amplifier according to claim 31, characterized in that the attenuation of said filtering means in said wavelength band contiguous to the predetermined signal band is at least 6 dB.

Claim 50

An optical amplifier according to claim 49, characterized in that the attenuation of said filtering means in said wavelength band contiguous to the predetermined signal band is at least 10 dB.

Claim 51

An optical amplifier according to claim 31, characterized in that said differential-attenuation means consists of: - a first dichroic coupler separating the radiation in said predetermined band and the radiation at said pumping wavelength respectively towards a first terminal and a second terminal; - an attenuating component connected to said first terminal, capable of attenuating said signals in said predetermined band; - a second dichroic coupler combining the radiation from said attenuating component with the radiation at said pumping wavelength from said second terminal.

Claim 52

An optical amplifier according to claim 51, characterized in that said attenuating component is an optical fibre.

Claim 53

An optical amplifier according to claim 51, characterized in that an optical isolator is inserted between said attenuating component and second dichroic coupler.

Claim 54

An optical amplifier according to claim 31, characterized in that said differential-attenuation means consists of a winding having a predetermined bending radius and consisting of one or more turns of optical fibre.

Claim 55

An optical amplifier according to claims 40 and 54, characterized in that said winding is made up of a portion of said doped optical fibre.

Claim 56

An optical amplifier according to claim 31, characterized in that the attenuation of said differential-attenuation means in said predetermined wavelength band is greater than the attenuation at said pumping wavelength by an amount of 5 ± 1 dB.

Claim 57

An optical telecommunication system comprising: - transmitting means (37, 38, 39, 40) generating at least two optical signals with different wavelengths included in a predetermined wavelength band - receiving means (54, 55, 56, 57), - an optical fibre line for connection between said transmitting means and receiving means, - an active-waveguide optical amplifier (45, 47) disposed along said line operatively connected with each other to transmit said optical signals from said transmitting means to said receiving means, characterized in that said active-waveguide optical amplifier comprises: - a first optical rare-earth-doped waveguide (105, 118) fed, through coupling means (103, 106, 117, with pumping radiation at a pumping wavelength from a first pumping source (104) and with signals from said optical fibre line, - differential-attenuation means (106, 130, 117), located at a predetermined position along said first doped waveguide, capable of causing an attenuation, at each of said different signal wavelengths, greater by a given amount than the attenuation caused at said pumping wavelength, - filtering means (130) located at said predetermined position along said first doped waveguide and provided with a spectral attenuation curve adapted for transmitting, without attenuating it to an important degree, the radiation with wavelengths included in a series of non-overlapping intervals, each including only one of said optical signals and for attenuating by a value higher than a predetermined minimum the spontaneous emission at the wavelengths outside said intervals, - a second optical rare-earth-doped waveguide (120) fed, through coupling means (121), with pumping radiation at a pumping wavelength from a second pumping source (122) and with signals from said first optical rare-earth-doped waveguide, wherein said predetermined position, said given attenuation amount of the differential-attenuation means and said predetermined attenuation minimum of the filtering means are selected in such a functional relation with respect to each other that power variations in one of the signals input to the amplifier within a range of 20 dB involve variations of the output power included in a range not greater than 3 dB.

Claim 58

An optical telecommunication system according to claim 57, characterized in that power variations in one of the signals input to the amplifier within a range of 20 dB involve variations of the output power included in a range not greater than 2 dB.

Claim 59

An optical telecommunication system according to claim 57, characterized in that said given attenuation amount of the differential-attenuation means is higher than 5 dB ± 1 dB.

Claim 60

An optical telecommunication system according to claim 57, characterized in that said filtering means includes a distributed Bragg reflection filter.

Claim 61

Method for transmitting optical signals on an optical communication line including cascade active-fibre optical amplifiers (45, 45', 45'', 45'''), comprising - feeding at least two optical signals with different wavelengths in said optical communication line, - feeding pumping radiation in each of said active-fibre optical amplifiers, characterized in that it comprises: - filtering at least a portion of the spontaneous emission at a first predetermined position along the active fibre of at least one of said optical amplifiers, - attenuate said optical signals with respect to said pumping radiation, at a second predetermined position along the active fibre of said at least one optical amplifier, by a value greater than a given amount, wherein said first and second predetermined positions and said given attenuation amount are operatively selected in such a way that power variations in one of the signals input to said amplifier within a range of 20 dB involve variations of the power of said signal at the output of said amplifier included in a range not greater than 3 dB.

Claim 62

Method for transmitting optical signals according to claim 61, characterized in that said first predetermined position coincides with said second predetermined position.

Claim 63

Method for transmitting optical signals according to claim 61, characterized in that said operation of filtering at least a portion of the spontaneous emission includes removing the spontaneous emission in the bands comprised between each couple of contiguous wavelengths of said communication signals.