Patent ID: 7877010

Claim:
An optical signal quality monitor device, comprising: a local oscillator that generates a local oscillation signal; a mixer that mixes an input optical signal with the local oscillation signal, said mixer comprising an electro-absorption modulator; a first filter interconnected to said mixer for extracting at least one beat component of a signal output from said mixer; a first intensity detector interconnected to said first filter for detecting intensity of the extracted beat component, wherein the input optical signal is of one bit rate, and said first filter and said first intensity detector are provided for the one bit rate of the input optical signal; a second filter interconnected to said mixer for extracting another beat component of the signal output from said mixer, the other beat component being different from the one beat component; a second intensity detector interconnected to said second filter for detecting intensity of the extracted other beat component, wherein the input optical signal is of a short pulse, whereby it is determined from output signals from said first and second intensity detectors whether the input optical signal has been transmitted over a transmission line with a spread in its pulse width or with an increased loss thereof; and a pulse width compression circuit interconnected to an input of said mixer for compressing the pulse width of the pulse of the input optical signal to deliver the input optical signal with the pulse width thus compressed.