Methods, systems and devices implement optical tapped delay lines. In one aspect, a device includes an optical tapped delay (TDL) including a wavelength conversion element, and a dispersive element, coupled with the wavelength conversion element, to impose a relative delay to an optical signal. The optical TDL can include a nonlinear element to combine signals in a phase coherent manner. The wavelength conversion element can include an optical nonlinear device such as a periodically poled lithium niobate (PPLN) or a highly nonlinear fiber (HNLF) with a high nonlinear coefficient and a low dispersion slope to effect four-wave mixing (FWM). The dispersive element can have a low dispersion slope, and the delays effected by the optical TDL can be tunable.