Microwave photonic systems have huge potential for both existing and future applications, including radar, radiofrequency sensing and modern wireless communications due to their distinct advantages in terms of ultra-wide bandwidth, flexible tunability, and immunity to electromagnetic interference. There is a strong research trend in microwave photonic systems towards integration and miniaturization, resulting in multiple radio frequency functions on a single chip which is both compact and light weight. Thus integrated microwave photonics has attracted a lot of attentions and achieves significant improvements in last ten years. In this paper, we will review some research progresses on silicon-based integrated microwave photonics in our group, including highly efficient micro heater on silicon photonic chip, chip-scale microwave waveform generation, on-chip true time delay, and microwave photonic processing and measurement. Our schemes are all fabricated on silicon-on-insulator chips and have advantages of compactness and capability to integrate with electronic units. These chips may motivate the great application potentials in silicon-based integrated microwave photonics.
We present our work on photonic crystal membrane devices exploiting Fano resonance between a line-defect waveguide and a side coupled nanocavity. Experimental demonstration of fast and compact all-optical switches for wavelength-conversion is reported. It is shown how the use of an asymmetric structure in combination with cavity-enhanced nonlinearity can be used to realize non-reciprocal transmission at ultra-low power and with large bandwidth. A novel type of laser structure, denoted a Fano laser, is discussed in which one of the mirrors is based on a Fano resonance. Finally, the design, fabrication and characterization of grating couplers for efficient light coupling in and out of the indium phosphide photonic crystal platform is discussed.
Space division multiplexing (SDM) is currently widely investigated in order to provide enhanced capacity thanks to the utilization of space as a new degree of multiplexing freedom in both optical fiber communication and on-chip interconnects. Basic components allowing the processing of spatial modes are critical for SDM applications. Here we present such building blocks implemented on the silicon-on-insulator (SOI) platform. These include fabrication tolerant wideband (de)multiplexers, ultra-compact mode converters and (de)multiplexers designed by topology optimization, and mode filters using one-dimensional (1D) photonic crystal silicon waveguides. We furthermore use the fabricated devices to demonstrate on-chip point-to-point mode division multiplexing transmission, and all-optical signal processing by mode-selective wavelength conversion. Finally, we report an efficient silicon photonic integrated circuit mode (de)multiplexer for few-mode fibers (FMFs).
We have designed and for the first time experimentally verified a topology optimized mode (de)multiplexer, which
demultiplexes the fundamental and the first order mode of a double mode photonic wire to two separate single mode
waveguides (and multiplexes vice versa). The device has a footprint of ~4.4 μm x ~2.8 μm and was fabricated for
different design resolutions and design threshold values to verify the robustness of the structure to fabrication tolerances.
The multiplexing functionality was confirmed by recording mode profiles using an infrared camera and vertical grating
couplers. All structures were experimentally found to maintain functionality throughout a 100 nm wavelength range
limited by available laser sources and insertion losses were generally lower than 1.3 dB. The cross talk was around -12
dB and the extinction ratio was measured to be better than 8 dB.
The microring resonator is a high-performance and low-cost optical waveguide device, suitable for integration with large
dimensions. This paper presents the design of laterally coupled racetrack microring resonators working around 1.55μm,
using combinations of the 3D full vectorial film mode matching method, the coupled mode theory and the parameter
model. This combined simulation technique shows convenience to perform the design process.
The electrically pumped InGaAsP/InP active microring has been theoretically analyzed and numerically simulated
based on subsection model, with carrier rate equation and amplified spontaneous emission taken into account. After the
subsection model is introduced in detail, the spectrum characteristics are numerically investigated. The simulation
results show that spectrum characteristics will shift under different pump current and injected light power. The
performances of an optical on/off switching utilizing pump-probe method based on InGaAsP/InP active microring are
investigated. The results show that if we choose probe light off resonation initially, and pump light on resonation, only
several hundred of microwatt power of pump light can realize the probe light on/off conversion. Such a potential will be
applied in many other optical applications with ultra low power consumption. However, carrier lifetime will be the main
factor restricting the characteristics of electrically pumped active microring due to the fact that the refractive index
change is induced by carrier density change.
In this paper, a novel approach for loadable and erasable optical memory unit based on dual microring optical integrators
coupled via 3×3 couplers is proposed and studied. The optical integrator, which can generate an optical step function for
data storing, is synthesized using active media for loss compensation and a tunable phase shifter for data reading at any
time. The input data into the memory is return-to-zero (RZ) signal, and the output data read out from the memory is also
RZ format with a narrower pulse width, which is determined by the phase shift pulse. A great number of such memory
units is promised to be densely integrated on a photonic circuit for future large scale data storage and buffer.
Dual microring resonator array coupled via 3×3 couplers are studied using matrix formalisms. Transmission spectra are
investigated as functions of column numbers and coupling coefficients in detail. Multiple transparent peaks appear when
the column number increases for arrays of the first two types. The spectra for arrays of the other two types show
complicated characteristics as functions of coupling coefficients.