Embodiments of this disclosure provide a method and apparatus for establishing a transmission impairment decomposition model for a Raman amplified system and a system. The method includes: converting a Jones vector of a test signal after passing through a Raman amplified system into a Stokes vector; calculating transmission impairments to which the test signal is subjected by using the Stokes vector according to a pre-established transmission impairment decomposition model; and substituting values of the transmission impairments into the pre-established transmission impairment decomposition model to obtain a complete transmission impairment decomposition model used for estimating transmission impairments.

Embodiments of this disclosure provide a method and apparatus for establishing a transmission impairment decomposition model for a Raman amplified system and a system. The method includes: converting a Jones vector of a test signal after passing through a Raman amplified system into a Stokes vector; calculating transmission impairments to which the test signal is subjected by using the Stokes vector according to a pre-established transmission impairment decomposition model; and substituting values of the transmission impairments into the pre-established transmission impairment decomposition model to obtain a complete transmission impairment decomposition model used for estimating transmission impairments.

An optical system, comprising a first wavelength conversion module to: adjust a power of a first pump wavelength; couple an input signal with the first pump wavelength to generate a first coupled signal; perform a first wavelength conversion of the first coupled signal to generate a first wavelength converted signal, the power of the first pump wavelength is adjusted such that the first wavelength conversion is performed with 0 dB conversion efficiency; the optical amplifier to amplify the first wavelength converted signal; a second wavelength conversion module to: adjust a power of a second pump wavelength; couple the amplified first wavelength converted signal with the second pump wavelength to generate a second coupled signal; perform a second wavelength conversion of the second coupled signal to generate a second wavelength converted signal with 0 dB conversion efficiency.

Disclosed herein is a method of encoding and/or decoding data for optical data transmission along a transmission link, as well as corresponding transmitters and receivers. The data is encoded based on an adaptive constellation diagram in a 2-D plane, said constellation diagram including a first and a second pair of symbols, wherein the symbols of the first pair of symbols are located at opposite sides of the origin of the 2-D plane at a first distance di from each other, and wherein the symbols of the second pair of symbols are located at opposite sides of the origin of the 2-D plane at a second distance d2 from each other. The method comprises a step of adapting the constellation diagram by varying the ratio of the first and second distances d.sub.1, d.sub.2 such as to minimize or nearly minimize a bit error rate in the transmitted data.

Disclosed herein is a method of encoding and/or decoding data for optical data transmission along a transmission link, as well as corresponding transmitters and receivers. The data is encoded based on an adaptive constellation diagram in a 2-D plane, said constellation diagram including a first and a second pair of symbols, wherein the symbols of the first pair of symbols are located at opposite sides of the origin of the 2-D plane at a first distance di from each other, and wherein the symbols of the second pair of symbols are located at opposite sides of the origin of the 2-D plane at a second distance d2 from each other. The method comprises a step of adapting the constellation diagram by varying the ratio of the first and second distances d.sub.1, d.sub.2 such as to minimize or nearly minimize a bit error rate in the transmitted data.

Embodiments of this disclosure provide a method and apparatus for establishing a transmission impairment decomposition model for a Raman amplified system and a system. The method includes: converting a Jones vector of a test signal after passing through a Raman amplified system into a Stokes vector; calculating transmission impairments to which the test signal is subjected by using the Stokes vector according to a pre-established transmission impairment decomposition model; and substituting values of the transmission impairments into the pre-established transmission impairment decomposition model to obtain a complete transmission impairment decomposition model used for estimating transmission impairments.

Embodiments of this disclosure provide a method and apparatus for establishing a transmission impairment decomposition model for a Raman amplified system and a system. The method includes: converting a Jones vector of a test signal after passing through a Raman amplified system into a Stokes vector; calculating transmission impairments to which the test signal is subjected by using the Stokes vector according to a pre-established transmission impairment decomposition model; and substituting values of the transmission impairments into the pre-established transmission impairment decomposition model to obtain a complete transmission impairment decomposition model used for estimating transmission impairments.

Techniques for transmitting an optical signal through optical fiber with an improved cost effective stimulated Brillouin scattering (SBS) suppression include externally modulating a light beam emitted from a light source with a high frequency signal. The light beam is also modulated externally with an RF information-carrying signal. The high frequency signals are at least twice a highest frequency of the RF signal. The high frequency signals modulating the light source can be gain and phase adjusted by the first set of gain and phase control circuit to achieve a targeted spectrum shape. The adjusted high frequency signals then are split, providing a portion of the split signals to modulate the light source and another portion of the split signals to the second set of phase and gain control circuit for adjusting a phase/gain. The output of second set of phase and gain control circuits can be applied to the external modulator to eliminate intensity modulation caused by the corresponding high frequency signals that modulate the light source. The spread spectrum for SBS suppression or the optical transmitter's SNR is further improved by cancelling a beat between SBS suppression modulation tones and out of band distortion spectrum of information bearing RF signal.

Techniques for transmitting an optical signal through optical fiber with an improved cost effective stimulated Brillouin scattering (SBS) suppression include externally modulating a light beam emitted from a light source with a high frequency signal. The light beam is also modulated externally with an RF information-carrying signal. The high frequency signals are at least twice a highest frequency of the RF signal. The high frequency signals modulating the light source can be gain and phase adjusted by the first set of gain and phase control circuit to achieve a targeted spectrum shape. The adjusted high frequency signals then are split, providing a portion of the split signals to modulate the light source and another portion of the split signals to the second set of phase and gain control circuit for adjusting a phase/gain. The output of second set of phase and gain control circuits can be applied to the external modulator to eliminate intensity modulation caused by the corresponding high frequency signals that modulate the light source. The spread spectrum for SBS suppression or the optical transmitter's SNR is further improved by cancelling a beat between SBS suppression modulation tones and out of band distortion spectrum of information bearing RF signal.

An optical transmission system includes an optical transmitter, an optical receiver, and a control apparatus. The control apparatus repeatedly performs an adjustment process for adjusting power of an optical signal of a frequency band to be adjusted while switching the frequency band to be adjusted between at least two frequency bands including at least a frequency band where stimulated Raman scattering occurs among frequency bands that are multiplexed in a multiplexed optical signal transmitted by the optical transmission system. In the adjustment process, when power of an optical signal of the frequency band to be adjusted transmitted from the optical transmitter has been changed, the control apparatus determines the power of the optical signal of the frequency band to be adjusted on the basis of a signal quality measured by the optical receiver that has received the optical signal.