To generate all-optical domain monocycle UWB and doublet signals

and reduce the cost of UWB over-fiber system

a methodbased on polarization modulationisproposed.Two Gaussian pulses with opposite polarity arephase-modulated to theorthogonal optical carrierswith the Polarization Modulator（PM）.Then an appropriate group delayis introduced by Polarization Maintaining Fiber（PMF）to generate monocycle UWB signal.By changing the angle between the signal polarization direction and PMF principal axis

two monocycles UWB with opposite polarity can be generated.Then by introducing appropriate time delay to one of them before the combination of the two monocycles UWB

a doublet UWB can be obtained.Monocycle and doublet UWB have a central frequency about 5.36 GHz and 5.83 GHz

a-10 dB bandwidth about 8.96 GHz and 7.36 GHz

and a fractional bandwidth about 167 % and 126%

which both meet the FCC standards.The performance effects of the delay are analyzed.The result shows that whenτ= TFWHM

the generated doublet UWB signal meets the FCC standards best.