The introduction of reconfigurable optical add-drop multiplexers (ROADMs) is driving the requirement for optical performance monitoring of channels in optical communication networks. A key monitoring parameter is optical signal-to-noise ratio (OSNR), which is traditionally estimated by linear interpolation of the amplified spontaneous emission (ASE) noise measured between WDM channels. This “out of band” technique is no longer valid in reconfigurable networks, since the optical filtering in the ROADMs removes the noise between the channels. Instead, in-band monitoring techniques are essential to measure the actual OSNR. 

Requirements for a practical OSNR monitor include low cost, low power requirements, insensitivity to other impairments and format/bit rate independence.  We have developed a simple, robust solution to directly monitor the OSNR within the optical channel bandwidth, where it really matters.

How we do it

Our technique directly measures the fluctuations induced by amplified spontaneous emission (ASE).  Unlike other methods, we measure both the signal-spontaneous beat noise, and the spontaneous-spontaneous beat noise.  By splitting the signal into two polarization states, and applying some funky analysis techniques, we can determine the OSNR. 

There is no time-consuming polarisation state search.  We work with megahertz electrical bandwidths, to get a result fast.

Download 1 page summary of in-band OSNR technology