Ching Eng Png

Single mode, polarization-independent submicron silicon waveguides based on geometrical adjustments

In this work, we demonstrate via computer simulation the single mode and zero birefringence conditions for photonic wires with height and width less than 600 nm. We report on the simulation conditions for both single mode and zero birefringence in silicon-on-insulator photonic wires and sub-micron rib waveguides using a 3-dimensional imaginary beam propagation method. The results show that operation in both single mode and zero birefringence is possible under certain circumstances and that the conditions are restricted by fabrication processes where birefringence is strongly dependent upon waveguide dimensions. A matrix of waveguide parameters has been identified at both operating wavelengths of 1310 nm and 1550 nm, which can satisfy single mode and zero birefringence conditions simultaneously. This is to provide a general design rule for waveguides in small dimensions on the order of hundreds of nanometres.

Accurate high-speed eye diagram simulation of silicon-based modulators

Optical modulation is one of the key determinants to the operating speed of a network. In this work, we report an accurate methodology to study high-speed eye diagram from electrical and optical simulation data of individual modulators. The methodology constitutes electrical parameters such as capacitance, conductance and transitioning times to model time response and effective complex refractive index from optical simulations of phase shifter arms and in turn model the phase change and resultant loss induced by each arm. This methodology is suitable for interferometer-based optical devices and has been applied to silicon-based depletion mode modulators at 10-, 40-Gbps.

Low-loss high-speed silicon Mach-Zehnder modulator for optical-fiber telecommunications

Low-loss high-speed traveling-wave silicon Mach-Zehnder modulator with reduced series resistance is studied in microwave and optical measurements. Microwave impedance and propagation loss under reverse bias are characterized by S-parameter measurements. Resonant loss due to series inductance-resistance-capacitance coupling limits microwave performances of the traveling-wave modulator. High-speed optical performances are characterized, based on eyediagram measurements in on-off keying at 10-32 Gb/s and constellation and eye-diagram measurements in differential phase-shift keying at 20 Gb/s. Dispersion tolerance in error-free transmission in 10-Gb/s on-off keying and 20-Gb/s differential phase-shift keying is obtained as +/-950 ps/nm and +/-220 ps/nm, respectively by path-penalty measurements. Transmission performance in 10-Gbps on-off keying is comparable with lithium niobate Mach-Zehnder modulator.

Modeling and experimental investigations of Fano resonances in free-standing LiNbO 3 photonic crystal slabs

In this paper the Fano resonance in a free-standing LiNbO(3) photonic crystal slab is demonstrated. We present a numerical analysis and experimental measurements with free space illumination where the dependence of slab thickness, radius of air holes and lattice types are investigated. The unique property of polarization dependence for LiNbO(3) photonic crystal slabs is also analyzed, and we show that the transmission spectra exhibit significant sensitivity (~25nm) to polarization. A monolithic free-standing LiNbO(3) photonic crystal slab was fabricated using ion beam enhanced etching (IBEE) technology. Measurement results of the reflection spectra agree with the numerical analysis.

Deep anisotropic LiNbO3 etching with SF6/Ar inductively coupled plasmas

A SF6/Ar inductively coupled plasma (ICP) technique was investigated to improve etching of proton exchanged LiNbO3. The influences of He backside cooling, power, and gas flows on characteristics such as etching rate, sidewall slope angle, and surface roughness were investigated. Total gas flow is a key parameter that affects etching results, and an optimized gas flow (50 sccm) was used for lengthy etching processes (30 min). Deep (>3 μm) and highly anisotropic etching, as well as ultra smooth LiNbO3 surfaces were achieved in a single-step run. The authors’ proposed method has achieved the deepest, most vertical, minimal residue structure yet reported for single-step ICP etching.A SF6/Ar inductively coupled plasma (ICP) technique was investigated to improve etching of proton exchanged LiNbO3. The influences of He backside cooling, power, and gas flows on characteristics such as etching rate, sidewall slope angle, and surface roughness were investigated. Total gas flow is a key parameter that affects etching results, and an optimized gas flow (50 sccm) was used for lengthy etching processes (30 min). Deep (>3 μm) and highly anisotropic etching, as well as ultra smooth LiNbO3 surfaces were achieved in a single-step run. The authors’ proposed method has achieved the deepest, most vertical, minimal residue structure yet reported for single-step ICP etching.

Installed Radiation Pattern of Patch Antennas: Prediction based on a novel equivalent model.

A simple but efficient equivalent model of patch antennas is proposed for predicting the radiation pattern of patch antennas on large platforms. The equivalent model is constructed based on the radiation mechanism of a patch antenna. Only three design parameters need to be optimized, making the model more computationally efficient than those equivalent dipole models for general problems. After the equivalent model is optimized with a differential evolution (DE) algorithm, it is further installed on a platform to compute installed radiation patterns. Simulation results show that the installed radiation patterns of both a single element and an array can be accurately predicted using the equivalent model, where the root-mean-square errors (RMSEs) are less than 0.94%. The proposed equivalent model method does not require detailed geometry information of the patch antennas. Furthermore, it avoids direct modeling of antenna structures, leading to a drastic reduction in computation and storage costs.

Fundamental characteristics and high-speed applications of carrier-depletion silicon Mach-Zehnder modulators

Carrier-depletion Si Mach-Zehnder modulators incorporating lateral PN-junction phase shifters are reviewed in the lights of fundamental characteristics and applications to high-speed optical fiber transmission. Experimental reverse-bias characteristics are supported by numerical analysis with good agreement, implying that the Si modulators are fabricated precisely as designed. Numerical high-speed response proves that the phase shifter operates beyond 100-Gbaud symbol rate. Traveling-wave electrodes are characterized in S-parameter measurements to reveal LRC resonance as a limiting factor in high-speed modulation. High-speed optical-fiber transmission in on-off and phase-shift keying formats is demonstrated using the Si Mach-Zehnder modulators assembled in ceramic-based metal packages.

Electrically controlled silicon-based photonic crystal chromatic dispersion compensator with ultralow power consumption

We show full 3-Dimensional (3D) electrical and optical simulation of a tunable silicon-based Photonic Crystal (PhC) Chromatic Dispersion Compensator (CDC) with high power efficiency and ultra-low power consumption (114nW), operating at a speed of 40.5MHz. The device exploits a structure where the optical field maximum is not in a PhC waveguide, but rather in a hybrid Si3N4/Si/SiO2 structure that will allow greater ease of fiber coupling due to larger mode size and reduced loss. The CDC is broadband, and produces constant 2 nd order chromatic dispersion over an optical communication band such as C-band.

Electromagnetic wave propagation in a Ag nanoparticle-based plasmonic power divider

In this paper a new silver (Ag) nanoparticle-based structure is presented which shows potential as a device for front end applications, in nano-interconnects or power dividers. A novel oxide bar ensures waveguiding and control of the signal strength with promising results. The structure is simulated by the two dimensional finite difference time domain (FDTD) method considering TM polarization and the Drude model. The effect of different wavelengths, material loss, gaps and particle sizes on the overall performance is discussed. It is found that the maximum signal strength remains along the Ag metallic nanoparticles and can be guided to targeted end points.

How small can a microring resonator be and yet be polarization independent

There has been a recent trend to reduce the size of photonic waveguide devices to enable high-density integration in silicon photonic integrated circuits. However, this miniaturization tends to result in increased polarization dependency. Particularly challenging is designing devices based on ring waveguides with small radii, which exacerbates the polarization sensitivity. For these microring resonators, a legitimate question is then: Is it possible to simultaneously maintain the conditions of single-mode and structural polarization independence while shrinking the size of both the bend radius and the waveguide cross section, and, if so, how small can the ring resonator be? We demonstrate theoretically the feasibility of achieving this via deeply etched submicrometer silicon-on-insulator rib waveguides, and we show that, for a given cladding and core thickness, the radius of a polarization independent microring resonator can be as small as 3 microm, being limited chiefly by the residual birefringence of the resonator cavity and the bend losses.