Xinwan Li

Tunable magneto-optical wavelength filter of long-period fiber grating with magnetic fluids

In this paper, the authors propose a magneto-optical tunable filter based on a long-period fiber grating (LPG) coated with magnetic fluids (MFs) as the ambient media. By applying a tunable magnetic field, the center wavelength shift of the attenuation band of LPG is found as large as 7.4nm. The refractive index dependence of MF on the external magnetic intensity is measured and the simulation results show that it is well agreeable with the experimental observations.

Design and Analysis of a Miniature Intensity Modulator Based on a Silicon-Polymer-Metal Hybrid Plasmonic Waveguide

We propose a miniature optical intensity modulator based on a silicon-polymer-metal hybrid plasmonic waveguide. Benefiting from the high mode confinement of hybrid plasmonic waveguide and the high linear electro-optic effect of polymer material, the intensity modulator is ultra-compact with a length of only ~ 13 μm. The device is optimized using numerical simulations based on the finite element method (FEM). The modulator exhibits a large modulation bandwidth of 90 GHz, a modulation depth of 12 dB at 6 V, and low power consumption of 24.3 fJ/bit.

Design and analysis of a phase modulator based on a metal–polymer–silicon hybrid plasmonic waveguide

A plasmonic-hybrid-waveguide-based optical phase modulator is proposed and analyzed. The field enhancement in the low-index high-nonlinear polymer layer provides nanoscale optical confinement and a fast optical modulation speed. At 2.5 V drive voltage, a π phase shift can be obtained for a 13-μm-long plasmonic waveguide. Because of its small capacitance and parasitic resistance, the modulation bandwidth can reach up to 100 GHz with a low power consumption of ∼9 fJ/bit. The plasmonic waveguide is connected to a silicon wire waveguide via an adiabatic taper with a coupling efficiency of ∼91%. The phase modulator can find potential applications in optical telecommunication and interconnects.

Miniature microring resonator sensor based on a hybrid plasmonic waveguide.

We propose a compact 1-μm-radius microring resonator sensor based on a hybrid plasmonic waveguide on a silicon-on-insulator substrate. The hybrid waveguide is composed of a metal-gap-silicon structure, where the optical energy is greatly enhanced in the narrow gap. We use the finite element method to numerically analyze the device optical characteristics as a biochemical sensor. As the optical field in the hybrid micoring resonator has a large overlap with the upper-cladding sensing medium, the sensitivity is very high compared to other dielectric microring resonator sensors. The compactness of the hybrid microring resonator is resulted from the balance between bending radiation loss and metal absorption loss. The proposed hybrid microring resonator sensors have the main advantages of small footprint and high sensitivity and can be potentially integrated in an array form on a chip for highly-efficient lab-on-chip biochemical sensing applications.

Tunable two-stage self-coupled optical waveguide resonators.

We report tunable two-stage self-coupled optical waveguide (SCOW) resonators composed of a pair of mirror-imaged single SCOW resonators connected by a phase shifter in between. Experimental results show that the coupled-resonator-induced-transparency and high-order bandstop filtering characteristics can be obtained in the transmission spectra of the devices with two different configurations. The resonance spectrum can be tuned by using either a p-i-p microheater or a p-i-n diode in the phase shifter. Our theoretical modeling based on the transfer matrix method has a good agreement with the experimental results.

Stable dynamic detection scheme for magnetostrictive fiber-optic interferometric sensors

A stable dynamic detection scheme for magnetostrictive fiber-optic interferometric sensors is studied. The working principle is presented and the experimental verification is performed. The results show that the system employing the dynamic detection scheme has better stability and sensitivity in comparison with the system employing quadrature control technique.

18 wavelengths 83.9Gs/s optical sampling clock for photonic A/D converters

In this paper, a simple approach to generate the time-wavelength interleaved sampling clock for photonic A/D converters is proposed using commercially available mode-locked femtosecond fiber laser and optical wavelength/time division multiplexing (WDM/OTDM) techniques with low cost passive optical components. A time and wavelength mapping module is configured using specially designed wavelength division multiplexer and mechanical tunable fiber stretchers. OTDM modules with low optical insertion loss and flexibly configurable multiple factor are implemented with the fused-biconical optical fiber couplers. Experiment is carried out using 18 WDM channels and 128 times OTDM to demonstrate the generation of 83.9Gs/s time-wavelength interleaved sampling clock.

Temperature-Insensitive Microdisplacement Sensor Based on Locally Bent Microfiber Taper Modal Interferometer

We report a temperature-insensitive microdisplacement sensor with a locally bent microfiber taper interferometer. The microfiber taper waist diameter can be optimized to minimize the spectral shift of the sensor owing to the environmental temperature change. With a ~ 1.92-μm-diameter microfiber taper, a bimodal fiber interferometer is proposed and experimentally fabricated. The transmission spectrum shows substantially small temperature dependence matching well with the theoretical estimation. The transmission spectrum is red-shifted in response to microdisplacement with a high sensitivity of 102 pm/μm but without requirement for temperature compensation.

Continuously tunable reflective-type optical delay lines using microring resonators.

We present a reflective-type optical delay line using waveguide side-coupled 13 microring resonators terminated with a sagnac loop reflector. Light passes through the microring resonator sequence twice, doubling the delay-bandwidth product. Group delay is tuned by p-i-p type microheaters integrated directly in the microring waveguides. Experiment demonstrates that the delay line can potentially buffer 18 bits and the delay can be continuously tuned for 100 ps with a power tuning efficiency of 0.34 ps/mW. Eye diagrams of a 20-Gbps PRBS signal after 10 and 110 ps delays are also examined.

Efficient silicon polarization rotator based on mode-hybridization in a double-stair waveguide

We present a compact silicon polarization rotator (PR) based on mode-hybridization by breaking the cross-sectional symmetry of a double-stair waveguide. The device fabrication is fully compatible with the commonly used silicon photonics processes with no extra masks required. The dependence of device performance on the double-stair waveguide dimensions is investigated using FDTD simulations. Characterizations of the fabricated devices reveal that the 23-μm-long PR exhibits a polarization extinction ratio (PER) of >17 dB in the wavelength range of 1500-1540 nm. The maximum PER exceeds 30 dB at 1518 nm.