Abstract: A fiber optical system (1) for transmitting an optical signal comprises an optical fiber line (2) with a plurality of optical fiber spans (3) interconnected by a plurality of optical amplifiers (4). Each optical amplifier (4) comprises: At least one variable optical attenuator (5) generating a gain tilt of the amplification of the optical signal, a Raman tilt determining device (6) for determining a Raman tilt induced in the fiber span (3) following the optical amplifier (4), and a dynamic controller (7) connected to the variable optical attenuator (5) and to the Raman tilt determining device (6) adjusting the gain tilt such that the Raman tilt is compensated for.

Abstract: A method for modulating an optical signal includes the following steps: modulating the intensity of the optical signal with a nonreturn-to-zero bit signal, and modulating the phase of the optical signal with a periodic phase-shift signal creating an alternating ?-phase shift every second, third or more consecutive bit. An optical transmitter for performing the above method comprises a first modulator (2) modulating the intensity of the optical signal with a nonreturn-to-zero bit signal, and a second modulator (3) modulating the phase of the optical signal with a periodic phase-shift signal creating an alternating ?-phase shift every second, third or more consecutive bit.

Abstract: The invention discloses an optical amplifier (18) that amplifies signal light in a signal band in a fiber optic transmission system (10) having at least first and second optically pumped signal light gain amplifying stages (30), a tilt controller (40) linked to a control unit, a optical monitor (34) analyzing signal powers, characterized in that the amplified spontaneous emission of the optical amplifier (18) is measured at two extreme wavelengths of the signal band to derive control signals (44) for at least the tilt controller (40).

Abstract: It is proposed a method for processing optical signals to be transmitted through a succession of transmission lines spans made out of DSF and a system architecture allowing the implementation of such a method for compensating dispersion occurring at the transmission path without suffering too much from any cross-phase modulation. This is achieved by the use of a system architecture comprising a succession of transmission lines spans made out of dispersion shifted fibers DSF with in-between a stage made alternately by a single mode fiber SMF or a dispersion compensating fiber DCF. Both DSF and SMF have dispersion of same sign. In another embodiment of the system architecture, the used DSF and SMF have also both dispersion slope of same sign. In such a way, it is possible to limit the impact of the XPM by not compensating the dispersion and possibly the dispersion slope at each span.

Abstract: An Optical transmission system (10) is presented that comprises at least one transmitter (12), at least one transmission line (14), at least one optical fiber amplifier (18), and at least one receiver (21), the optical fiber amplifier (18) being designed to show a flat characteristic of output power versus wavelength. The optical fiber amplifier (18) is designed to show the flat output characteristic in response to a flat characteristic of a first input power level versus wavelength. At least one coupler (28) for coupling at least one Raman amplifier (30) to the optical transmission system (10) is provided, the Raman amplifier (30) having a Raman gain that is tilted in a direction opposite to a tilt of the optical fiber amplifier (18) that would occur in response to a flat characteristic of a second input power level versus wavelength. Thereby, an optical transmission system (10) is presented that can be upgraded to improve OSNR while maintaining a flat output characteristic.

Abstract: A device for processing a digital signal of an optical transmission system is described. The device comprises: a polarization beam splitter for receiving the signal, a phase shifter for shifting the phase of the signal at the orthogonal output of the polarization beam splitter, and means for combining the signal at the parallel output of the polarization beam splitter and the shifted signal.

Abstract: The present invention relates to a method of operating an optical amplifier (1a), in particular an erbium doped fiber amplifier (EDFA) or a Raman amplifier, an output signal of which is supplied to an optical fiber (2), characterized by determining a span loss of said optical fiber (2) and by controlling an output power (P_out) of said optical amplifier (1a) depending on said span loss. The present invention further refers to an optical amplifier (1a), in particular an erbium doped fiber amplifier (EDFA) or a Raman amplifier.

Abstract: A method of operating an optical transmission system is described. The transmission system is provided with a bit-to-bit polarization interleaved bitstream having a given bitrate. The transmission system comprises a birefringent element and/or a decision circuit. The birefringent element and/or the decision circuit are triggered by a trigger signal having a frequency of half of the bitrate.

Abstract: A method of transmitting digital signals over an optical transmission system is described. The method comprises the following steps: generating a signal according to the differential phased shift keying (DPSK) format, forwarding the DPSK signal to an optical delay filter, and using an output signal of the optical delay filter as a signal according to the phase shaped binary transmission (PSBT) format.

Abstract: The invention relates to an interleaver circuit (10, 10?) for interleaving optical signals, comprising a first and a second input port (12, 14), an output port (16), a first optical filter (18; 18?) that has a first filter function with periodic passbands (32, 34, 36) and is connected to the first input port (12), a second optical filter (20; 20?) that has a second filter function with periodic passbands (38, 40) and is connected to the second input port (14), and an optical interleaver (22). The latter comprises a multiplexing port (23) connected to the output port (16) and two de-multiplexing ports (24, 26) connected to the first input port (12) via the first optical filter (18; 18?) and the second optical filter (20; 20?), respectively. At least one optical filter (18, 20; 18?, 20?) is tunable such that the passband frequencies are collectively shiftable without altering the periodicity of the filter function.

Abstract: A Raman amplifier for use in an optical fiber communication system with dispersion compensation has a first order Raman pump source and a second order Raman pump source both coupled to the input ports of a four-port optical coupler having two input ports and two output ports. One output port is connected to an optical fiber length to inject a pump light signal into the fiber length for second-order Raman amplification and the other output port is connected to a dispersion compensating fiber.

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 discloses an optical amplifier (18) that amplifies signal light in a signal band in a fiber optic transmission system (10) having at least first and second optically pumped signal light gain amplifying stages (30),

Abstract: The invention is related to a Raman pump source with a first laser diode (40) and a second laser diode (41), a coupler (43) and a polarization beam combiner (46). The signals of the two laser diodes are combined in a polarization maintaining coupler (43) with two in- and two outputs, and the outputs of the coupler (43) are linked to the polarization beam combiner.

Abstract: To optimize the resources of an optical transmission network using wavelength division multiplexing, assigning carrier frequencies to signals to be transmitted consists in associating N sets of optical frequencies of the comb with N respective ranges of consecutive error rate values, each of the sets comprising frequencies generating a mean error rate in the associated range, defining a measured signal transmission constraint level that is a function of the transmission constraint parameter(s) and may take N distinct values referred to as constraint values, associating the N constraint values in increasing order respectively with the N sets of frequencies in decreasing order of the error rate values of the associated N ranges, assigning any signal to be transmitted a constraint value obtained by applying the measurement, and assigning the signal to be transmitted a carrier frequency belonging to one of the sets of frequencies that is associated with a constraint value at least equal to the constraint value as

Abstract: An Optical transmission system (10) is presented that comprises at least one transmitter (12), at least one transmission line (14), at least one optical fiber amplifier (18), and at least one receiver (21), the optical fiber amplifier (18) being designed to show a flat characteristic of output power versus wavelength. The optical fiber amplifier (18) is designed to show the flat output characteristic in response to a flat characteristic of a first input power level versus wavelength. At least one coupler (28) for coupling at least one Raman amplifier (30) to the optical transmission system (10) is provided, the Raman amplifier (30) having a Raman gain that is tilted in a direction opposite to a tilt of the optical fiber amplifier (18) that would occur in response to a flat characteristic of a second input power level versus wavelength. Thereby, an optical transmission system (10) is presented that can be upgraded to improve OSNR while maintaining a flat output characteristic.

Abstract: The invention relates to an interleaver circuit (10, 10′) for interleaving optical signals, comprising a first and a second input port (12, 14), an output port (16), a first optical filter (18; 18′) that has a first filter function with periodic passbands (32, 34, 36) and is connected to the first input port (12), a second optical filter (20; 20′) that has a second filter function with periodic passbands (38, 40) and is connected to the second input port (14), and an optical interleaver (22). The latter comprises a multiplexing port (23) connected to the output port (16) and two de-multiplexing ports (24, 26) connected to the first input port (12) via the first optical filter (18; 18′) and the second optical filter (20; 20′), respectively. At least one optical filter (18, 20; 18′, 20′) is tunable such that the passband frequencies are collectively shiftable without altering the periodicity of the filter function.