Kaixuan Chen

Experimental demonstration of simultaneous mode and polarization-division multiplexing based on silicon densely packed waveguide array.

A silicon mode and polarization-division multiplexing scheme based on a densely packed waveguide array structured as a bus waveguide is introduced. A short adiabatic taper is adopted for (de)multiplexing. Such a structure shows theoretical insertion losses that are <0.05  dB and crosstalk that is <-20  dB over a wide wavelength band for all five supported modes. The structures for (de)multiplexing are fabricated and characterized experimentally. A device, which consists of a multiplexer, a 50-μm-long straight-bus waveguide, and a demultiplexer, exhibits insertion losses that are <0.6  dB and crosstalk that is <-15  dB over an 80 nm wavelength band. The demonstrated (de)multiplexer has a total length of 60 μm, and the bus waveguide has an effective width of 1.58 μm.

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.

Silicon waveguide grating coupler for perfectly vertical fiber based on a tilted membrane structure

A grating coupler for interfacing between a silicon-on-insulator waveguide and a single-mode fiber located at a perfectly vertical direction is demonstrated based on a tilted membrane structure. The proposed design is compatible with that of conventional grating couplers for oblique fibers and facilitates mass production. A peak coupling efficiency of 28.5% and 1 dB bandwidth of 38 nm are obtained experimentally for transverse-electrics polarized light. Back reflection in the SOI waveguide is also estimated to be 1.4%. The present grating coupler for perfectly vertical fiber exhibits similar performances to the conventional grating coupler for oblique fiber concerning coupling efficiency, bandwidth, and back reflections.

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.

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.

Multimode 3 dB Coupler Based on Symmetrically Coupled Waveguides for On-Chipbrk Mode Division Multiplexing

Mode division multiplexing on chips can enhance optical interconnect capacity tremendously, avoiding expensive wavelength division multiplexing technology. It is a critical functionality to switch or process different mode channels together for future optical network-on-chip based on mode division multiplexing. However, controlling different modes simultaneously in the traditional wide multimode waveguide is very difficult due to very different optical properties of the modes. Here, we introduce a novel concept to realize compact multimode 3 dB couplers, which can process multiple modes of a densely-packed waveguide array bus waveguide simultaneously. A dual-mode 3 dB coupler with two input and two output bus waveguides, each of which supports two transverse electrical modes, is designed with simulated insertion losses of less than 0.23 dB and crosstalks of ∼–18.1 dB for both modes at the central wavelength. The relative phases at the two outputs are 90° for both modes theoretically. The designed device has a short coupling length of 21 μm with SiO2 cladding. The fabricated one demonstrates insertion losses of ∼0.3 dB and ∼0.5 dB and crosstalks of –19.6 dB and –14.1 dB for the two modes, respectively. A triple-mode

IIIV/Si hybrid integrated devices for optical interconnect

2\,\times \,2

Silicon mode (de)multiplexer based on densely packed waveguide array (DPWA)

3 dB coupler, consisting of six coupled waveguides in the coupling region of 87 μm length, shows average insertion losses and crosstalks for all three modes of ∼0.25 dB and ∼–14 dB, respectively. The present design method is also extended to 3 dB couplers for more modes theoretically.

Compact Multimode 3dB Coupler for On-chip Mode Division Multiplexing

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.

5 × 20 Gb/s III-V on silicon electroabsorption modulator array heterogeneously integrated with a 1.6nm channel-spacing silicon AWG

A five-mode densely packed waveguide array and (de)multiplexer on Si are demonstrated for mode division multiplexing. Insertion losses of -0.8dB and cross-talks of -22dB have been obtained experimentally for a device with multiplexing and de-multiplexing structures.