Soon Thor Lim

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.

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.

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.

Broadband Silicon-On-Insulator directional couplers using a combination of straight and curved waveguide sections

Broadband Silicon-On-Insulator (SOI) directional couplers are designed based on a combination of curved and straight coupled waveguide sections. A design methodology based on the transfer matrix method (TMM) is used to determine the required coupler section lengths, radii, and waveguide cross-sections. A 50/50 power splitter with a measured bandwidth of 88 nm is designed and fabricated, with a device footprint of 20 μm × 3 μm. In addition, a balanced Mach-Zehnder interferometer is fabricated showing an extinction ratio of >16 dB over 100 nm of bandwidth.

High-contrast and accurate high-speed simulation of silicon-based modulators

Silicon-based optical modulator devices have experienced dramatic improvements over the last decade with data rates up to 50Gbps for On-Off-Keying (OOK) consuming ultra low power in fJ/bit [1-3]. The ability to fully understand the performances of these plasma dispersion effect-based devices from a simulation standpoint could be further improved especially in the coupling of high-speed electrical and optical effects. Here, we report an accurate methodology to study high-speed eye diagrams from the electrical and optical simulation data of individual silicon modulators. In particular, we demonstrate the capacity of this simulation methodology by applying it to the current state-of-the-art experimental demonstrated silicon optical modulator using OOK at 50Gbps [3].

A high speed electro-optic phase shifter based on a polymer-infiltrated P-S-N diode capacitor

A polymer-infiltrated P-S-N diode capacitor configuration is proposed and a high speed electro-optic phase shifter based on a silicon organic hybrid platform is designed and modeled. The structure enables fast carrier depletion in addition to the second order nonlinearity so that a large electro-optic overlapped volume is achievable. Moreover, the device speed can be significantly improved with the introduction of free carriers due to a reduced experienced transient capacitance. The advantages of the diode capacitor structure are highly suitable for application to a class of low aspect ratio slot waveguides where the RC limitation of the radio frequency response is minimized. According to our numerical results, by optimizing both the waveguide geometry and polarization mode, at least 269 GHz 3-dB bandwidth with high efficiency of 5.5 V-cm is achievable. More importantly, the device does not rely on strong optical confinement within the nano-slot, a feature that gives considerable tolerance in the use of nano-fabrication techniques. Finally, the high overlap and energy efficiency of the device can be applied to slow light or optical resonance media for realizing photonic integrated circuits-based green photonics.

Two- and three-dimensional studies of a silicon-based chromatic dispersion compensator

In this work, we demonstrate two- and three-dimensional (3D) simulations of an active silicon-based photonic crystal chromatic dispersion compensator utilizing the free carrier dispersion effect. The device has a low power consumption of 114nW and its intrinsic device modulation speed is predicted to function at 40.5MHz. Due to the device architecture, simulation must be carried out in 3D so as to fully encapsulate the effects of the photonic crystal contributions in the active silicon. The novel device allows waveguiding and electrical transport to be individually tailored to a large extent.