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This paper gives a review for recent progresses on silicon photonic waveguides and devices with structural asymmetry, including special power splitters/couplers, high-performance polarization-handling devices, and efficient mode converters/(de)multiplexers.

A 10-channel mode (de)multiplexer with low crosstalks and low loss over a broad wavelength band is proposed and realized with cascaded dual-core adiabatic tapers on a silicon-on-insulator (SOI) platform for the first time.

A novel silicon-based hybrid multiplexer consisting of a mode (de)multiplexer and a microring-resonator (MRR) array is proposed and demonstrated for mode-division-multiplexing and wavelength-division-multiplexing system. The demonstrated hybrid multiplexer enables 32 channels by combining 4 mode-channels (TE0, TEi, TE2, TE3) and 8 wavelength-channel with a channel spacing of 3.2nm. For the hybrid multiplexer, the excess loss is ∼5dB, the mode-channel crosstalk and the wavelength-channel crosstalk are —20dB and ∼-30dB, respectively.

We demonstrate optical bistability on a small SU-8 race-track-resonator with a Q-value as high as 30000, which helps to achieve nonlinear optical responses even at low operation power due to an enhancement of optical power density in the resonator. Significant thermal nonlinear optical effect in the fabricated SU-8 race-track-resonator is demonstrated experimentally, which is attributed to the high Q-value and the large negative thermo-optical coefficient.

Novel suspended SiO2 ridge optical waveguides on silicon are fabricated and characterized. The propagation loss and the bend loss measured are about 0.385dB/cm and 0.037dB/90° respectively for the fabricated 1μm-wide waveguides with a bending radius of 100μm when operating at 1550 nm.

We presented a set of fabricated devices based on silicon nanowire waveguides in application to telecom and optical interconnects. New developments in form of hybrid plasmonic waveguides allowing for sub-wavelength light confinement are also included.

Silicon-on-insulator (SOI) optical waveguides are fabricated via selective oxidation process without any silicon etching step so that the waveguide surface becomes very smooth to achieve low-loss light propagation potentially. A high-Q ring-resonator is also demonstrated.

A 170 nm wide hybrid plasmonic waveguide with a loss of 0.08 dB/µm is demonstrated experimentally. Directional couplers with different gaps and microdisks with 0.5 µm radius based on such waveguides are also presented.

Nanophotonic integrated devices based on nano-scale silicon hybrid plasmonic waveguides have been demonstrated experimentally, including directional couplers and disk-resonators. The temperature-dependence of the hybrid plasmonic disk-resonators is also characterized.

Hybrid multiplexing technology combining polarization multiplexing and mode multiplexing is presented to expand the capacity of photonic networks-on-chip by 2N times with a multimode optical waveguide which supports 2N guided-modes. Only one laser diode is needed for such a multiplexing system. A novel mode-(de)multiplexer with low excess-loss and low crosstalk is proposed by utilizing a structure with cascaded asymmetrical directional couplers. A 1×4 mode-(de)multiplexer is designed as an example. It is possible to achieve more channels (e.g., 2N=16) with two orthogonal polarizations. When an array of high-speed optical modulators (e.g., 70Gbps) is integrated, the total capacity of an on-chip photonic link can be over 1Tbps with a single-wavelength-carrier light.

An ultra-short (L=9.5µm) polarization beam splitter (PBS) based on an asymmetrical bent directional coupler is demonstrated experimentally. The measured extinction ratios are about 15dB and 10dB for the TE and TM polarized lights around 1550nm.