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).
We demonstrate a photonic crystal (PhC) waveguide modulator based on a Mach-Zehnder Interferometer (MZI) configuration on a silicon-on-insulator (SOI) substrate. A p-n junction is embedded in the PhC waveguide such that the carrier concentrations in the waveguide can be changed with applied voltage, which changes the refractive index of the silicon material forming the waveguide. Our PhC waveguide is designed to work at 1550 nm. The slow light effect in the photonic crystal waveguide can enhance light-matter interaction, which helps to achieve sufficient modulation in a short interaction length around 100 micron, which may also help reduce the power consumption. Modulation speed of 8.5Gb/s has been measured.
We propose a compact ultra-broadband silicon-on-insulator polarization rotator. The conversion area of the polarizer rotator is a stair-shaped waveguide, where the middle step is partially replaced by a sub-wavelength grating. The length of the conversion region of the polarization rotator is only 3.36 µm. For TM-TE and TE-TM working cases, the insertion loss is less than 0.9 dB, the polarization conversion efficiency reached 99%, and the polarization extinction ratio is greater than 20 dB, in an ultra-broad wavelength range of 1260 nm to 1740 nm, which covers O-, E-, S-, C-, L-, and Ubands.
We investigate the response time of silicon-based thermo-optic switches under different device configurations. We design two tunable thermo-optic switches on a silicon-on-insulator (SOI) chip. One uses a waveguide embedded phase shifter based on direct heating due to electric current flow through waveguide. The other traditional switch structure has a metallic heater on top of the waveguide. Owing to direct current injection to heat the waveguide, which avoids the heat conduction from heater to waveguide, the switching time would reduce significantly. The experimental result shows that the direct heating device realizes a fast response time close to 1.5μs. As a comparison, the traditional heater-on-top device’s response time is over 10μs. That is to say, switching time of the direct-current-injection device is over ten times less. The insertion loss of both devices are reasonable. The fast heating device shows a potential for applications in the future optica interconnects.
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