Monitoring of WDM PONs by means of a single wavelength OTDR and a tuneable laser

Here, we present a WDM PON monitoring technique that uses a single wavelength OTDR and a standard telecommunication laser, tuneable over the ITU WDM grid. The coherent Rayleigh noise (CRN) is actually reduced by avoiding to regenerate the pulse by directly modulating the laser, like in ref. [2], or by using high speed semiconductor optical modulators like in Ref. [4], solutions which maintain a high coherence of the output pulse. Instead here we used a simpler external modulator realized by an acousto-optic device. Being based on standard and easily replaceable devices this instrument conjugates a moderate cost with a broad flexibility and shows a very good potential for the packaging of the external unit that regenerates the optical pulse.