Pengxin Chen

Improved 8-channel silicon mode demultiplexer with grating polarizers

An improved 8-channel silicon mode demultiplexer is realized with TE-type and TM-type grating polarizers at the output ends, and these gratings serve as fiber-chip couplers simultaneously. The present 8-channel silicon mode demultiplexer includes a three-waveguide PBS (for separating the TE0 and TM0 modes) and six cascaded ADCs (for demultiplexing the high-order modes of both polarizations). The grating polarizers with high extinction ratios are used to filter out the polarization crosstalk in the 8-channel hybrid multiplexer efficiently and the measured crosstalk for all the mode-channels of the improved 8-channel mode multiplexer is reduced greatly to ~-20dB in a ~100nm bandwidth.

High-order microring resonators with bent couplers for a box-like filter response

High-order microring resonator (MRR) filters with bent directional couplers are proposed and demonstrated to achieve a box-like filter response. When using bent couplers, the coupling ratio can be adjusted easily by choosing the length of the coupling region, and the excess loss is almost zero while the perimeter of the microring length is unchanged. For the present fabricated five-microring filters with bent directional couplers, the excess loss is less than 1.0 dB, the out-of-band extinction ratio is ∼36  dB, and the response has rising and falling edges as sharp as 48  dB/nm. The thermal tunability of the high-order MRR filter with a Ti-microheater is also demonstrated and the thermally tuning efficiency is about 0.10  nm/mW.

An efficiently tunable microring resonator using a liquid crystal-cladded polymer waveguide

An electrically tunable polymer microring resonator of large tunability and low applied voltage is demonstrated using active liquid crystal (LC) cladding. A large tuning range of 0.73 nm is achieved due to more homogenous LC molecular alignment and enhanced interaction of the light with the LC cladding in the simplified polymer waveguide structure. The operating voltage decreases to 10 V with a threshold of only 3 V by the utilization of interdigital electrodes.

Large-area bulk self-assembly of plasmonic nanorods in nematic liquid crystal via surface-mediated alignment

In this paper, we introduce a novel method to organize gold nanorods (GNRs) on a large scale by means of nematic lyotropic liquid crystal (LC) and surface-induced bulk alignment. LC is unidirectionally aligned via surface-treatment, and then gets GNRs organized with a negative order parameter in bulk through elastic force. The self-assembled GNRs (with a considerable high concentration of about 6 wt%) in LC exhibit a strong polarization-dependent localized surface plasmon resonance (LSPR). Polarized optical microscopic imaging, polarization-dependent extinction and scattering spectra of LSPR are utilized to characterize the spatial orientation of GNRs. This method is compatible with the state-of-the-art LC display technique and allows for large-scale fabrication of optical metamaterials, plasmonic polarizers comprised of self-aligned anisometric nanoparticles with extremely low cost.

Fabrication and characterization of suspended SiO 2 ridge optical waveguides and the devices

Novel suspended SiO(2) ridge optical waveguides on silicon are fabricated and characterized. The present suspended SiO(2) ridge optical waveguide has a SiO(2) ridge core surrounded by air. The propagation loss and the bend loss measured are about 0.385dB/cm and 0.037dB/90° respectively for the fabricated 1 μm-wide waveguides with a bending radius of 100 μm when operating at the wavelength of 1550 nm. With the present suspended SiO(2) optical waveguides, a small racetrack resonator with a radius of 100 μm is also demonstrated and the measured Q-factor is about 3160.

Fabrication of High Precision Self-Aligned V-Grooves Integrated on Silica-on-Silicon Chips

In this letter, we propose a simple method to fabricate V-grooves integrated on silica-on-silicon chips. We have utilized the photolithographic self-alignment principle to form the etching mask for V-grooves during waveguide core etching. With such designed processes, the waveguides and V-grooves can be fabricated without any lateral displacement.

Novel Optical Filter Based on High-order Microring Resonators with Bent Couplers

A five-order microring resonator filter using bent directional couplers is proposed and demonstrated and a box-like filter response is achieved with low excess loss (∼1.0dB) and high out-of-band extinction ratio (∼35dB). The thermal tunability is also demonstrated.

Surface-induced self-organization of gold nanorods into predesigned patterns in liquid crystals

We introduce a method to organize gold nanorods (GNRs) into predesigned patterns (radical and periodical) in liquid crystals by surface-mediated alignment. Optical polarized microscopic and scattering imaging are utilized to characterize spatial orientation of GNRs.