Fig. 3: Experimental verification of the actively phase-stabilizing signal-combining tree (SCT) based on 90∘ optical hybrids as passive combiners, see Fig. 2(b).
From: Optical arbitrary waveform generation (OAWG) using actively phase-stabilized spectral stitching
a Exemplary error signal \(U_{\rm{err}}(t)\) measured for a signal-combining element (SCE) with deactivated control loop. Random variations of the error signal are observed as the phase of the different spectral slices drifts randomly. b Overlay of 50 optical spectra recorded with deactivated control loop. The random drift of the relative phase \(\Delta \varphi(t)\) between adjacent spectral slices leads to randomly occurring spectral dips due to constructive and destructive interference in the overlap regions (ORs, marked in gray). Note that the depth of the measured dips is limited due to the non-zero resolution bandwidth (RBW = 2.48 GHz) of the optical spectrum analyzer (AQ6317B, Ando Electric Co., Ltd, now Yokogawa Electric Crop, Tokyo, Japan). c Residual error signal \(U_{\rm{err}}(t)\) measured when the phase control is activated. d Overlay of 50 optical spectra recorded with activated control loop. The relative phases of all spectral slices are aligned and stabilized, and no spectral dips can be found in the ORs (marked in gray)
