Qiangsheng Huang

Nonlocal effects in a hybrid plasmonic waveguide for nanoscale confinement

The effect of nonlocal optical response is studied for a novel silicon hybrid plasmonic waveguide (HPW). Finite element method is used to implement the hydrodynamic model and the propagation mode is analyzed for a hybrid plasmonic waveguide of arbitrary cross section. The waveguide has an inverted metal nano-rib over a silicon-on-insulator (SOI) structure. An extremely small mode area of~10⁻⁶λ² is achieved together with several microns long propagation distance at the telecom wavelength of 1.55 μm. The figure of merit (FoM) is also improved in the same time, compared to the pervious hybrid plasmonic waveguide. We demonstrate the validity of our method by comparing our simulating results with some analytical results for a metal cylindrical waveguide and a metal slab waveguide in a wide wavelength range. For the HPW, we find that the nonlocal effects can give less loss and better confinement. In particular, we explore the influence of the radius of the ribs tip on the loss and the confinement. We show that the nonlocal effects give some new fundamental limitation on the confinement, leaving the mode area finite even for geometries with infinitely sharp tips.

5 x 20 Gb/s heterogeneously integrated III-V on silicon electro-absorption modulator array with arrayed waveguide grating multiplexer

We present a five-channel wavelength division multiplexed modulator module that heterogeneously integrates a 200 GHz channel-spacing silicon arrayed-waveguide grating multiplexer and a 20 Gbps electro-absorption modulator array, showing the potential for 100 Gbps transmission capacity on a 1.5x0.5 mm² footprint.

Ultracompact tapered coupler for the Si/III–V heterogeneous integration

An ultracompact tapered coupler, which is suitable for mode transformation between a 220 nm high silicon wire waveguide and a Si/III-V hybrid waveguide, is proposed for Si/III-V heterogeneous integration. The tapered coupler is composed of three sections. Since the tapered coupler avoids exciting the unwanted high-order modes in the III-V waveguide, the length of the tapered coupler can be dramatically shortened. In the proposed structure, the total length of the trisectional tapered coupler can be as short as 8 μm with a fundamental mode-coupling efficiency of over 95% in a bandwidth of over 100 nm. The alignment tolerance of the proposed structure is also analyzed.

Experimental Demonstration of Single Mode- Splitting in Microring With Bragg Gratings

We demonstrate single mode-splitting in two types of microring resonators with Bragg gratings. In the first device type, gratings are periodically embedded to the inner wall of the microring resonator. By adjusting the reflection coefficient of the grating and the self-coupling coefficient between the waveguide and microring, experimental results show that the distance between the splitting dips can vary from 0 to more than 1 nm. In the second device type, Bragg gratings break into two identical parts with a π phase shift between them. The center peak in the mode-splitting spectrum has a full-width at half-maximum of 0.1 nm. The spectra can also be a Fano-type transmission, when the phase shift deviates from π.

Low driving voltage band-filling-based III-V-on-silicon electroabsorption modulator

In this paper, a method for realizing a low driving voltage electroabsorption modulator based on the band-filling effect is demonstrated. The InP-based electroabsorption modulator is integrated using divinylsiloxane-bis-benzocyclobutene adhesive bonding on a silicon-on-insulator waveguide platform. When the electroabsorption modulator is forward biased, the band-filling effect occurs, which leads to a blue shift of the exciton absorption spectrum, while the absorption strength stays almost constant. In static operation, an extinction ratio of more than 20 dB with 100 mV bias variation is obtained in an 80 μm long device. In dynamic operation, 1.25 Gbps modulation with a 6.3 dB extinction ratio is obtained using only a 50 mV peak-to-peak driving voltage. The band-filling effect provides a method for realizing ultra-low-driving-voltage electroabsorption modulators.

All-optical NRZ wavelength conversion based on a single hybrid III-V/Si SOA and optical filtering.

We demonstrate all-optical wavelength conversion (AOWC) of non-return-to-zero (NRZ) signal based on cross-gain modulation in a single heterogeneously integrated III-V-on-silicon semiconductor optical amplifier (SOA) with an optical bandpass filter. The SOA is 500 μm long and consumes less than 250 mW electrical power. We experimentally demonstrate 12.5 Gb/s and 40 Gb/s AOWC for both wavelength up and down conversion.

Fabrication of all shallowly etched silicon reflection-type arrayed-waveguide gratings with one stigmatic point

We design, fabricate and measure an all shallowly etched reflection-type silicon arrayed waveguide gratings(R-AWG) with one stigmatic point, which contributes to reducing the crosstalk of R-AWG.

Resonantly enhanced silicon photonics Mach-Zehnder modulator

In this work we present the design, fabrication and characterization of a silicon photonics Mach-Zehnder modulator (MZM) with resonant electrode. The device shows an enhanced modulation response in the 20GHz frequency range compared to a standard traveling-wave MZM.

Design, optimization and fabrication of two-dimension high contrast subwavelength grating (HCG) mirror on Silicon-on-insulator

The high contrast grating (HCG) mirror has been illustrated and characterized. The investigated parameters including grating periods and filling factors were calculated by finite-difference time-domain method. The two-dimension HCG was fabricated by electron-beam lithography and inductively coupled plasma process. The reflectivity of the fabricated HCG mirror was measured, resulting in around 200 nm bandwidth. The measured result also showed a good agreement with calculated one. This achievement was promising in developing the novel light emitters in the telecommunication region.

IIIV/Si hybrid integrated devices for optical interconnect

As the increasing demand for information interconnect, the traditional electrical interconnect will encounter a bottleneck on speed and power consumption. As a comparison, optical interconnect can offer better performance considering the above aspects. Multifunctional, high-speed, highly-integrated photonic circuits are necessary for the next generation optical interconnect. Due to the compatible fabrication processes with CMOS electronics, silicon photonics has drawn much attention towards large scale integration of photonic devices. In this presentation, we discuss our view of the on-chip interconnect infrastructure for future multi-core processers based on wavelength-multiplexing and our recent results on some key devices of such structure. Cascading performances of various wavelength multiplexer and de-multiplexer including arrayed waveguide gratings and echelle gratings based on silicon-on-insulator platform are discussed and compared. Besides passive functions, active devices, including modulators, light sources, etc., are also important for interconnect applications. Due to the limitations of silicon, hybrid integration through combining active III-V components and passive silicon waveguide circuits by DVS-BCB adhesive bonding are employed to realize some active photonic functions. InP based electro-absorption (EA) modulators on silicon with sub 100mV driving voltage are realized. Ultra short adiabatic tapers for mode converters between passive silicon waveguides and InP active structures are designed. The integration of multi-channel EA modulators and wavelength (de)multiplexer are realized. In addition, we also demonstrate a novel doubled-side processed III-V nanowire waveguide. This waveguide contains asymmetric thin upper and lower InP layers for lateral current injection, which make the metal contacts away from optical field while keeping a high index contract in all directions.