Linjie Zhou

Silicon electro-optic modulators using p-i-n diodes embedded 10-micron-diameter microdisk resonators

We demonstrate a silicon electro-optic modulator using a 10-micron-diameter microdisk resonator with a laterally integrated p-i-n diode surrounding essentially the entire microdisk. Our experiments reveal a modulation bandwidth of 510 MHz using a Q ~ 16,900 resonance mode under a square-wave drive voltage of ~0.9 V forward bias and ~-6 V reverse bias.

Silicon microring carrier-injection-based modulators/switches with tunable extinction ratios and OR-logic switching by using waveguide cross-coupling.

We demonstrate silicon microring carrier-injection-based modulators/switches with waveguide cross-coupling. We tune the modulator extinction ratio by forward-biasing either the microring or cross-coupled waveguide p-i-n diode, while modulating the other. We also demonstrate OR-logic switching functionality by simultaneously applying two different electrical data streams across the microring and cross-coupled waveguide diodes. For both the modulator and the switch, we observe NRZ pattern-dependent optical waveform distortions.

Electrically reconfigurable silicon microring resonator-based filter with waveguide-coupled feedback

We demonstrate an electrically reconfigurable silicon microring resonator-based filter with waveguide-coupled feedback. Our experiments and scattering-matrix-based modeling show that the resonance wavelengths, extinction ratios, and line shapes depend on the feedback coupling and can be controllably tuned by means of carrier injection to the feedback- waveguide. We also demonstrate nearly uniform resonance line shapes over multiple free-spectral ranges by nearly phase-matching the feedback and the microring.

Athermalizing and Trimming of Slotted Silicon Microring Resonators With UV-Sensitive PMMA Upper-Cladding

This letter experimentally demonstrates significant reduction in the resonance thermal sensitivity of the slotted silicon microring resonators by exploiting polymethyl methacrylate (PMMA) as upper-cladding. We investigate the resonance temperature dependence on the slot width with and without PMMA upper-cladding. The experimental results show that the temperature dependence is reduced from 91 pm/degC for a regular microring resonator to 27 pm/degC for the PMMA-clad slotted microring resonator. The ultraviolet (UV) sensitive PMMA upper-cladding also allows the resonance wavelengths of slotted microring resonators shift by 0.5 nm under UV light trimming. With the demonstrated schemes, each individual optical component can be athermalized and precisely registered to standard wavelengths for a future multiwavelength optically interconnected computing system-on-a-chip.

Fano resonance-based electrically reconfigurable add-drop filters in silicon microring resonator-coupled Mach-Zehnder interferometers

We report a Fano resonance-based electrically reconfigurable add-drop filter using a microring resonator-coupled Mach-Zehnder interferometer (MZI) on a silicon substrate. Our experiments reveal a pair of complementary Fano resonance line shapes that can be electrically tuned and output coupled from the MZI output ports. A near symmetrical resonance peak can be flipped to a near symmetrical resonance dip by applying a forward-bias voltage of less than 1V across a laterally integrated p-i-n diode in the MZI non-resonator-coupled arm. Our scattering-matrix-based modeling shows good agreement with the experiments and indicates ways to enhance the resonance routing functionality. Our work demonstrates the feasibility of an integrated reconfigurable add-drop filter with actively interchangeable throughput and drop ports.

Design and Analysis of a Miniature Intensity Modulator Based on a Silicon-Polymer-Metal Hybrid Plasmonic Waveguide

We propose a miniature optical intensity modulator based on a silicon-polymer-metal hybrid plasmonic waveguide. Benefiting from the high mode confinement of hybrid plasmonic waveguide and the high linear electro-optic effect of polymer material, the intensity modulator is ultra-compact with a length of only ~ 13 μm. The device is optimized using numerical simulations based on the finite element method (FEM). The modulator exhibits a large modulation bandwidth of 90 GHz, a modulation depth of 12 dB at 6 V, and low power consumption of 24.3 fJ/bit.

Coherent interference induced transparency in self-coupled optical waveguide-based resonators

We propose a self-coupled optical waveguide (SCOW)-based resonator to generate an optical resonance analogous to electromagnetically induced transparency (EIT). The EIT-like effect is formed by the coherent interference between two resonance paths inherent to the SCOW resonator. For cascaded SCOW resonators, the spectrum they produce is significantly affected by the phase shift between them, with the EIT-like peak flattened or split as the two extreme cases. We also investigate the dispersion characteristics of an infinite array of SCOW resonators and show that the dispersion relation and group index in the EIT subband can be greatly changed by a small phase shift between the SCOW resonators.

Design and analysis of a phase modulator based on a metal–polymer–silicon hybrid plasmonic waveguide

A plasmonic-hybrid-waveguide-based optical phase modulator is proposed and analyzed. The field enhancement in the low-index high-nonlinear polymer layer provides nanoscale optical confinement and a fast optical modulation speed. At 2.5 V drive voltage, a π phase shift can be obtained for a 13-μm-long plasmonic waveguide. Because of its small capacitance and parasitic resistance, the modulation bandwidth can reach up to 100 GHz with a low power consumption of ∼9 fJ/bit. The plasmonic waveguide is connected to a silicon wire waveguide via an adiabatic taper with a coupling efficiency of ∼91%. The phase modulator can find potential applications in optical telecommunication and interconnects.

Miniature microring resonator sensor based on a hybrid plasmonic waveguide.

We propose a compact 1-μm-radius microring resonator sensor based on a hybrid plasmonic waveguide on a silicon-on-insulator substrate. The hybrid waveguide is composed of a metal-gap-silicon structure, where the optical energy is greatly enhanced in the narrow gap. We use the finite element method to numerically analyze the device optical characteristics as a biochemical sensor. As the optical field in the hybrid micoring resonator has a large overlap with the upper-cladding sensing medium, the sensitivity is very high compared to other dielectric microring resonator sensors. The compactness of the hybrid microring resonator is resulted from the balance between bending radiation loss and metal absorption loss. The proposed hybrid microring resonator sensors have the main advantages of small footprint and high sensitivity and can be potentially integrated in an array form on a chip for highly-efficient lab-on-chip biochemical sensing applications.

Design of an Electro-Optic Modulator Based on a Silicon-Plasmonic Hybrid Phase Shifter

We propose a silicon-compatible plasmonic electro-optic modulator employing a silicon racetrack ring resonator coupled to a bus waveguide. A silicon-plasmonic hybrid phase shifter clad with electro-optic polymer is introduced to achieve high-speed performance and low energy consumption. Simulations show that the proposed modulator can achieve an extinction ratio of more than 15 dB at 1550-nm wavelength under a 1.2-V bias voltage. The misalignment tolerance and fabrication feasibility of the modulator are also discussed.