Jianyi Yang

Characteristics of electro-refractive modulating based on Graphene-Oxide-Silicon waveguide

Graphene has attracted a high level of research interest because of its outstanding electronic transport properties and optical properties. Based on the Kubo formalism and the Maxwell equations, its demonstrated that the optical conductivity of graphene can be controlled through the applied voltage. And we find that the graphene-oxide-silicon (GOS) based waveguide can be made into either the electro-absorptive or electron-refractive modulators. Using graphene as the active medium, we present a new electro-refractive Mach-Zender interferometer based on the GOS structure. This new GOS-based electron-refractive modulation mechanism can enable novel architectures for on-chip optical communications.

Silicon mode multi/demultiplexer based on multimode grating-assisted couplers

A simple and low-crosstalk 1 × 4 silicon mode (de)multiplexer based on multimode grating-assisted-couplers is proposed. Mode transitions can be flexibly controlled by designing the grating period at the phase-matching condition. Due to the contra-directional coupling, precise control of the coupling strength and the coupling length are not needed in the system. Calculation results show that the insertion loss and the 3 dB bandwidths of the device are 0.2 dB and 3.7 nm, 0.34 dB and 7.6 nm, and 0.21 dB and 11.8 nm for the channels which (de)multiplex to the 1st, 2nd, and 3rd modes of the bus waveguide, respectively.

Optical switch based on multimode interference coupler

An optical switch based on the multimode interference (MMI) coupler is demonstrated in this letter. The device is designed and fabricated in polymeric materials and the thermooptic (TO) effect of polymers, which has a negative TO coefficient, is employed to change the self-imaging effect of a side-heated MMI coupler and realize optical switching. The switching power is only 22 mW. The experimental results show that the crosstalk of the switch is about -20 dB at both the cross and bar states.

Mode multi/demultiplexer based on cascaded asymmetric Y-junctions.

A mode-(de)multiplexer with low loss and large spectral bandwidth is proposed. The device is designed by utilizing a structure with cascaded asymmetric Y-junctions. By carefully controlling the widths of the wide and narrow arms of the Y-junctions, the fundamental mode of a narrow arm excites the higher-order mode of its stem in the multiplexing case, and a high-order mode of the stem separated from other lower-order modes evolves into the fundamental mode of the narrow arm in the demultiplexing case. As an example, a 1 × 4 mode-(de)multiplexer is analyzed by using the beam propagation method. Simulation results show the demultiplexed crosstalk is lower than -21.8 dB, under a common spectral bandwidth of 140 nm. The insertion loss is negligible.

A Generic Optical Router Design for Photonic Network-on-Chips

Photonic network-on-chip (NoC) architectures are emerging as a new paradigm to interconnect a large number of processing cores at chip level, meeting the pressing demand for extremely high bandwidth and low power consumption. Optical routers, which are typically composed of silicon waveguides and optical switches, play a key role in an on-chip photonic interconnection network. In this paper, we propose a micro-ring-resonator (MRR)-based, scalable, and non-blocking passive optical router design, namely the generic wavelength-routed optical router (GWOR). We first introduce the four 4 × 4 GWOR router structures and then show how to construct GWORs of larger sizes by using the proposed 4 × 4 GWORs as the primitive building blocks. The number of MRRs used in the proposed GWOR is the least among the existing passive router designs for the same network size. In addition, we show that the power loss experienced on GWORs is lower than other comparative designs. Furthermore, to improve the bandwidth and fault tolerance capability of the GWORs, the redundant GWOR (RGWOR) structure is presented. RGWOR can provide multiple routing paths between each pair of input-output ports by cascading different types of GWORs.

Polyimide-waveguide-based thermal optical switch using total-internal-reflection effect

A total-internal-reflection waveguide switch with an X junction was designed and fabricated by using the thermo-optic effect of polyimide materials. Experimental results show that the crosstalk is below −28 dB at the wavelength of 1.55 μm. The switching power with the current electrode is 132 mW, which can be reduced to 20–30 mW with an optimized design together with electroplating to form a thick conducting path.

Low-chirp high-extinction-ratio modulator based on graphene–silicon waveguide

We present a hybrid graphene-silicon waveguide, which consists of a lateral slot waveguide with three layers of graphene flakes inside. Through a theoretical analysis, an effective index variation for about 0.05 is found in the waveguide by applying a voltage on the graphene. We designed a Mach-Zehnder modulator based on this waveguide and demonstrated it can process signals nearly chirp-free. The calculation shows that the driving voltage is only 1 V even if the length of the arm is shortened to be 43.54 μm. An extinction up to 34.7 dB and a minimum chirp parameter of -0.006 are obtained. Its insertion loss is roughly -1.37 dB. This modulator consumes low power and has a small footprint. It can potentially be ultrafast as well as CMOS compatible.

Tunable Fano resonances based on two-beam interference in microring resonator

In this paper, a resonant system is demonstrated on silicon-on-insulator wafer to achieve tunable Fano resonances. In this system, the Fano resonance originates from the interference of two beams resonant in the microring resonator. The shapes of the Fano resonances are tunable through controlling the phase difference of the two beams. Both large slope and high extinction ratio (ER) are obtained when the phase difference is 0.5π or 1.5π. Experimental results show that Fano resonances with steep slope and ER over 20 dB are achieved in the whole free spectral range by controlling the microheaters to meet the phase condition.

Wavelength-selective 4 × 4 nonblocking silicon optical router for networks-on-chip.

We design and fabricate a wavelength-selective nonblocking 4 × 4 silicon optical router based on microring resonator for use in future integrated photonic interconnection networks. We successfully demonstrate 12 possible I/O routing paths and present 13 nonblocking operating states, including four broadcasting states, with worst-case extinction ratio and cross talk of 21.05 and -21.56 dB, respectively. Thermal tuning is employed to compensate the resonance shift of microring resonators caused by fabrication errors and adjust the resonance to match the International Telecommunication Unit grid with the channel spacing of 100 GHz.

Ultracompact and wideband power splitter based on triple photonic crystal waveguides directional coupler

Three single-mode photonic crystal waveguides (PCWs) are put together closely to construct three PCWs directional coupler (3PCWDC). It is found that the coupling coefficient of two even modes excited by the input field symmetrically entering 3PCWDC may be increased dramatically by reducing the size scales of dielectric rods between the neighbouring PCWs. The coupling length in this structure can be much shorter than that in conventional PCWs within the frequency range of interest. The application of this feature to an ultracompact, wide bandwidth and high-transmission power splitter is addressed. The simulation results by using the finite-difference time-domain method show that the structure exhibits new interesting characteristics.