example the optical signal 112 consists of a 40 gbit s optical clock signal of linear polarization the optical signal 112 from the optical signal input port 110 enters a rutile crystal 118 at an angle of 45 u00b0 of the polarization plane relative to the birefringent axis of the rutile crystal the rutile crystal 118 divides the input optical signal into two polarization components and output them after separating them in the time base by 12 5 ps a wdm optical coupler 120 combines the output light fromthe rutile crystal 118 with the assist light fromthe assist light input port 114 a pulse 122 illustrated at the output stage of the wdm optical coupler 120 is an optical signal pulse preceded by the birefringent medium 118 in the time base and a pulse 124 is a following signal pulse which is delayed in the time base the preceding optical signal pulse 122 following optical signal pulse 124 and assist light enter a semiconductor optical amplifier soa 128 the soa 128 is forward biased by a direct power source 130 for example similarly to the soas 28 and 228 the soa 128 consists of a buried waveguide using the ingaasp inp system as an active layer material and both ends are applied with antireflection coating the optical signal output side of the soa 128 connects to a port b of the optical circulator 132 and a control light 134 enters a port a of the optical circulator 132 the wavelength of the control.