Ao Shen

Ultracompact optical modulator based on graphene-silica metamaterial

We present an ultracompact electro-optic modulator with a length of 15 nm by utilizing a permittivity-tunable metamaterial channel, which is composed of alternative layers of graphene and silica. Optical waves can propagate through the metamaterial channel only if its permittivity is tuned to be near zero. The finite-difference time-domain (FDTD) simulations show the insertion loss is roughly -0.27  dB while the 3 dB extinction ratio is obtained with a 0.8 V gate voltage. The devices footprint is as small as 0.01 μm2. This modulator consumes low power and can potentially be ultrafast.

Proposal for a 2

We propose a new method to change the resonant status of the microring by modifying the light-absorption ability of the waveguide. A conception of a 2 × 2 microring switch based on the graphene-silicon-waveguide is presented by inserting a single graphene flake inside the lateral slot waveguide. The resonance procedure of the microring is thoroughly blocked when the graphene is tuned to be a zero-permittivity material, which significantly enhances the waveguides loss. Neither a high quality factor nor a large driving voltage of the microring is needed. According to the numerical analysis, an extinction ratio for is obtained in the drop port with a broad bandwidth. The extinction ratio in the through port is 34 dB. The radius of the microring is 5.1 μm and the driving voltage is 2.38 V.

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Controlling the light transmission in the epsilon-near-zero channel, which is covered by the perfect-electric-conductor (PEC) walls, has been demonstrated in [L. Yang, T. Hu, A. Shen, C. Pei, B. Yang, T. Dai, H. Yu, Y. Li, X. Jiang, and J. Yang, Opt. Lett. 39, 1909 (2014)]. In this work, we investigate the possibility of replacing the PEC by some practical metal materials. Based on it, an ultracompact plasmonic switch with the length of 15 nm is presented. Its highest extinction ratio is more than 13 dB, while the 3-dB extinction ratio is obtained with a 0.41 V gate voltage.

2 Optical Switch Based on Graphene-Silicon-Waveguide Microring

An ultra-compact silicon bandpass filter with wide bandwidth tunability is proposed and experimentally demonstrated. The filter architecture is based on a multiple micro-ring resonator-cascaded structure. A wide bandwidth tunability (from 75 to 300 GHz) can be achieved by controlling the resonant frequency of the microring resonators when a good shape factor (0.24-0.44) is held. The filter has a wide free spectral range (about 1.2 THz). The center wavelength can be tuned over several nanometers linearly. The footprint is only 0.053  mm2.

Ultracompact plasmonic switch based on graphene-silica metamaterial

We report a theoretical study showing that by utilizing the illumination of an external laser, the Surface Plasmon Polaritons (SPP) signals on the graphene sheet can be modulated in the sub-micron scale. The SPP wave can propagate along the graphene in the middle infrared range when the graphene is properly doped. Graphenes carrier density can be modified by a visible laser when the graphene sheet is exfoliated on the hydrophilic SiO2/Si substrate, which yields an all-optical way to control the graphenes doping level. Consequently, the external laser beam can control the propagation of the graphene SPP between the ON and OFF status. This all-optical modulation effect is still obvious when the spot size of the external laser is reduced to 400 nm while the modulation depth is as high as 114.7 dB/μm.

Bandwidth and wavelength tunable optical passband filter based on silicon multiple microring resonators

The measurable wavelength range and the resolution of the ratio-metric wavelength monitor are limited by each other in a conventional structure. To solve this problem we designed and fabricated a high-performance integrated double ratio-metric wavelength measurement device on glass by the method of ion-exchange. It consists of four unbalanced Mach–Zehnder interferometers (MZIs) to form a rough wavelength measurement with a wide range and a fine wavelength measurement with high resolution. The highest measured resolution can reach 10 pm in a 1.6 nm-wide wavelength range for the fine wavelength measurement together with a 45 nm-wide wavelength range for the rough measurement. By heating the unbalanced MZI, the performance of the fine wavelength monitor can be improved.

An all-optical modulation method in sub-micron scale

An integrated high-resolution ratio-metric wavelength monitor (RMWM) is demonstrated on SOI platform. The device consists of a reconfigurable demultiplexing filter based on cascaded thermally tunable microring resonators (MRRs) and Ge-Si photodetectors integrated with each drop port of the MRRs. The MRRs are supposed to achieve specific resonant wavelength spacing to form the “X-type” spectral response between adjacent channels. The ratio of the two drop power between adjacent channels varies linearly with the wavelength in the “X-type” spectral range, thus the wavelength can be monitored by investigating the drop power ratio between two pre-configured resonant channels. The functional wavelength range and monitor resolution can be adjusted flexibly by thermally tuning the resonant wavelength spacing between adjacent rings, and an ultra-high resolution of 5 pm or higher is achieved while the resonant spacing is tuned to 1.2nm. By tuning the resonant wavelength of the two MRRs synchronously, the monitor can cover the whole 9.6nm free spectral range (FSR) with only two ring channels. The power consumption is as small as 8 mW/nm. We also demonstrate the multi-channel monitor that can measure multi-wavelength-channel simultaneously and cover the whole FSR by presetting the resonant wavelengths of every MRR without any additional power consumption. The improvements to increase the resolution are also discussed.

An integrated high-performance ratio-metric wavelength measurement device on glass

A high sensitivity photonic temperature sensor based on silicon eye-like microring resonator system (EMRS) is reported. The results show great enhancement of the sensing performance by using the EMRS configuration.

Microring based ratio-metric wavelength monitor on silicon

An ultrahigh-resolution ratio-metric wavelength monitor based on microring resonators (MRRs) is demonstrated on silicon. The theoretical wavelength resolution is related to the functional wavelength range and the quality (Q)-factor of the microring. We analyze the relationship and experimentally demonstrate that the functional range and the resolution can be adjusted by thermally tuning the resonance spacing of the MRRs. The resolution is also limited by the noise introduced in the measurements. An ultrahigh experimental resolution of 1.5 pm is obtained within a 0.72 nm functional range and an ultrahigh theoretical extreme resolution of ~0.4

A temperature sensor based on silicon eye-like microring with sharp asymmetric fano resonance

pm can be expected considering of the intrinsic systems noise only. The causes of the difference between the experimental and theoretical resolution and the measures to reduce the difference are also discussed.