Fig. 2: Characterization of the Si3N4 photonic chip based pulse interleaver.
From: Large-scale photonic chip based pulse interleaver for low-noise microwave generation
a Schematic of the balanced MZI tunable coupler implemented with two 50:50 waveguide directional couplers. DC: direct current. b Optical transmission through the bar port as a function of the heating power applied to either arm at 1550 nm. The shaded area shows the minimum to maximum range of the transmission within 1550 ± 10 nm. c Normalized transmission spectrum of the tunable coupler when cold and having 187 mW heating applied to one arm. d Optical micrograph of a single interleaver stage, highlighting the tunable coupler in (a). e Waveguide propagation loss of the delay line section, characterized by the Lorentzian fit of ring resonator resonances, which gives the intrinsic loss rate. Circles represent individual resonances, and the red line is the moving median. f Simulated and characterized waveguide dispersion of the long delay line, described as D = −2πcβ2/λ2, where c is the speed of light and β2 is the group velocity dispersion parameter. g Normalized transmission spectrum through the 6-stage interleaver near 193 THz, showing a part of the interference fringes used in the delay length characterization. h Time delay error characterized by the Fourier transformation of the optical transmission spectrum, zoomed in to the relevant frequency component indicating the time delay errors of each delay line.
