Apparatus for monitoring optical signal-to-noise ratio

An apparatus for monitoring an optical signal-to-noise ratio, comprising:

• an orthogonal polarization component module for receiving an optical signal and outputting it after removing a signal component thereof at a specific frequency band;
• and
• calculation means for measuring both average optical intensity and electrical noise component intensity of the optical signal outputted from the orthogonal polarization component module, wherein the orthogonal polarization component module includes:
• a polarization controller for receiving the optical signal and outputting it while controlling first and second polarization components of the optical signal perpendicular to each other to have the same intensity;
• a polarization divider for receiving the optical signal outputted from the polarization controller, and dividing it into the first and second polarization components, and then outputting them;
• an optical delay element for receiving one of the first and second polarization components outputted from the polarization divider, and delaying and outputting the received polarization component;
• and
• a polarization combiner for receiving the two polarization components outputted from the polarization divider, one being delayed by the optical delay element and the other not delayed, and combining them into an optical signal and outputting the optical signal.