Micro-resonator modulators working in the critical coupling mode is usually sensitive to fabrication variation. We employ two modulated racetrack-resonators symmetrically coupled to a waveguide on two sides on a silicon-on-insulator wafer. The structure in the strong-coupling regime can perform modulation function stably through the interference of two racetracks. Fabrication variation (30~50%) of coupling constant or quality factor can be compensated by static voltage bias applied on the diode-embedded resonators. Detailed working principle and fabrication-variation compensation will be presented. Experimentally, we demonstrate 50 ~ 56 Gb/s modulation with high extinction ratio of 7.9 ~ 9.4 dB and high signal-to-noise ratio of 6~7, while maintaining low driving voltage (<2.5 Vpp) and small size (tens of microns).
In a silicon Mach-Zehnder modulator with on-chip termination, the reflection of the driving signal in the traveling wave electrode often occurs due to non-ideal factors. This may influence the modulating signal characteristics. To study such influence, the S11 response of the electrode is averaged over different frequency ranges to characterize the reflection of the driving signal in the electrode. We find that the signal-to-noise ratio and the jitter can be substantially affected by the reflection. In addition, for the same characteristic, when the averaging frequency range for S11 varies, the relations between mean S11 and the output signal characteristics may also vary to some extent. Understanding of these phenomena are potentially useful to the applications of the modulators in the optical communication systems.
This work introduces a 2×2 silicon thermo-optical switch based on photonic crystal waveguides. Photonic crystal waveguides (PCWs) were used to replace conventional channel waveguides in the phase shifters of a Mach-Zehnder interferometer (MZI). This device was fabricated on silicon-on-insulator (SOI) platform. The active length of the PCWs-based phase shifter was only 50μm. Because of the slow light effect of PCWs, the heat needed to generate a phase shift of π reduced dramatically. The experiment results showed that the power needed for phase shifter of π is 6 times less than that of conventional MZI based optical switches.
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