Distortion measurement in optical communication systems

An optical transmission system comprising measuring means to measure the amplitude distortion component in an optical transmission signal subject to noise and amplitude distortion components, the measuring means adapted to measure the amplitude distortion component by analyzing the bit error ratio (BER) of the signal as a function of a movable decision threshold, wherein said measuring means is adapted to perform said analysis in a high bit error ratio area of the function, away from a center of an eye, and in a low bit error ratio area closer to the centre of the eye;

• and further comprising comparing means to provide said BER values by comparing the signal with a variable decision threshold.

An optical transmission system, comprising optical receiver means to detect optical transmission signals and convert them into their electrical equivalent, clock extraction means to extract clock timing signals from the received optical signals, first and second digital-to-analogue converters providing first inputs to first and second analogue amplifiers, said optical receiver means providing second inputs to said first and second analogue amplifiers, first and second bi-stable circuit means connected respectively to outputs of said first and second analogue amplifiers and synchronised by said extracted clock signals, outputs of said bi-stable circuit means connected to inputs of an exclusive-OR gate, an output of said exclusive-OR gate providing error signals input to a counter, whereby said counter accumulates a count representing the bit error ratio in said received optical signals, and said digital-to-analogue converters being controlled by processor means to determine decision threshold separations V1 and V2 in the eye that represent amplitude distortion components in said received optical signals.

An optical receiver comprising detector means to detect optical signals from an optical transmission system and convert them into their electrical equivalent, the receiver comprising measuring means to measure the amplitude distortion component in a said optical signal subject to noise and amplitude distortion components, the measuring means adapted to measure the amplitude distortion component by analysis of the bit error ratio (BER) of the signal as a function of a movable decision threshold, wherein said measuring means is adapted to perform said analysis in a high bit error ratio area of the function, away from a center of an eye, and in a low bit error ratio area closer to the centre of the eye.

An optical receiver comprising detector means to detect optical signals from an optical transmission system and convert them into their electrical equivalent, clock extraction means to extract clock timing signals from the received optical signals, first and second digital-to-analogue converters providing first inputs to first and second analogue amplifiers, said optical receiver means providing second inputs to said first and second analogue amplifiers, first and second bi-stable circuit means connected respectively to outputs of said first and second analogue amplifiers and synchronised by said extracted clock signals, outputs of said bi-stable circuit means connected to inputs of an exclusive-OR gate, an output of said exclusive-OR gate providing error signals input to a counter, whereby said counter accumulates a count representing the bit error ratio in said received optical signals, and said digital-to-analogue converters being controlled by processor means to determine decision threshold separations V1 and V2 in the eye that represent amplitude distortion components in said received optical signals.