Thomas Y. L. Ang

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.

Numerical Modeling and Analysis for High-Efficiency Carrier-Depletion Silicon Rib-Waveguide Phase Shifters

In this paper, we report the efficiency and loss performance of a depletion silicon rib phase shifter with an overlayer of 220 nm and doping concentrationof 5 × 10¹⁷ cm^-3 for both p and n regions. A V_pi of 3.6 V and a loss of 5.2 dB, 4-mm device is reported. We identified a range of doping concentrations that allow the phase shifter to operate at <;6 V and <;5-dB loss. Junction placement variances suggested that with the reduced p dopant concentration (2 × 10¹⁷ cm^-3), better loss and phase performance can be achieved with a larger p-type region and smaller n-type region.

Optimized optical devices for edge-coupling-enabled silicon photonics platform

We present a library of high-performance passive and active silicon photonic devices at the C-band that is specifically designed and optimized for edge-coupling-enabled silicon photonics platform. These devices meet the broadband (100 nm), low-loss (< 2dB per device), high speed (≥ 25 Gb/s), and polarization diversity requirements (TE and TM polarization extinction ratio ≤ 25 dB) for optical communication applications. Ultra-low loss edge couplers, broadband directional couplers, high-extinction ratio polarization beam splitters (PBSs), and high-speed modulators are some of the devices within our library. In particular, we have designed and fabricated inverse taper fiber-to-waveguide edge couplers of tip widths ranging from 120 nm to 200 nm, and we obtained a low coupling loss of 1.80±0.28 dB for 160 nm tip width. To achieve polarization diversity operation for inverse tapers, we have experimentally realized different designs of polarization beam splitters (PBS). Our optimized PBS has a measured extinction ratio of ≤ 25 dB for both the quasiTE modes, and quasi-TM modes. Additionally, a broadband (100 nm) directional coupler with a 50/50 power splitting ratio was experimentally realized on a small footprint of 20×3 μm2 . Last but not least, high-speed silicon modulators with a range of carrier doping concentrations and offset of the PN junction can be used to optimise the modulation efficiency, and insertion losses for operation at 25 GHz.

Silicon modulators with optimized vertical PN junctions for high-modulation-efficiency in the O-band

Silicon modulators based on the carrier depletion mechanism are extensively used in recent years for high-speed data transmission. Lateral PN junctions are the most common electro-optical phase shifters for silicon Mach-Zehnder modulators (MZMs) due to its ease of fabrication. They have a relatively high DC VπLπ of around 2.5 V.cm in the Oband. An alternative approach is to design and optimize vertical PN junctions for lower DC VπLπ, which is currently lacking in the literature for silicon MZMs that operates using carrier depletion mechanism in the O-band. In this work, we look into the design and optimization of silicon phase shifters based on vertical PN junctions for high-modulationefficiency with VπLπ ≤ 1 V.cm, while meeting the stringent low loss budget of ≤ ∼1 dB/mm for data communication in the O-band. This is achieved by varying the offsets of the vertical PN junction with respect to different doping concentrations (2e17/cm3 – 3e18/cm3 ) near the depletion region. Different types of doping schemes are explored and optimized. Our optimized vertical PN junction designs are predicted to give low DC VπLπ of 0.26–0.5 V.cm for low DC reverse bias of ≥ –2V and low propagation loss of ≤ ∼1dB/mm, resulting in α.VπLπ = 1.7 for the best designs, which to the best of our knowledge, is the lowest α.VπLπ at the O-band to date. Electrical and optical modeling are based on our in-house proprietary software that is able to perform both optical and electrical simulations without loss of data fidelity.

Silicon-nitride/oxynitride wavelength demultiplexer and resonators for quantum photonics

SiOxNy shows promises for bright emitters of single photons. We successfully fabricated ultra-low-loss SiOxNy waveguide and AWG with low insertion loss <1dB and <3dB total loss (<2dB on-chip loss and <1dB coupling loss) at 1310nm.

Silicon modulators for 25 Gb/s photonics platform

We report on the design and simulation of silicon modulators based on the carrier-depletion mechanism for the communication wavelength of 1550 nm. The carrier-depletion silicon modulator is optimized for low loss, low power, and high modulation efficiency for the 25 Gb/s silicon photonics platform.

Versatile Bezier bends for silicon photonics

We report on the design and fabrication of silicon Bezier bends for the communication wavelength of 1550 nm. By varying the Bezier parameter B, the bend losses can be controlled for different bend radius. At a bend radius of 2 μm, bend losses of 0.0652 to 0.269 dB per 180o bend is experimentally demonstrated for the TE polarization using silicon channel waveguide with width 500nm, and height 220nm for B = 0.2–0.45.

Silicon nitride double-tip fiber-to-waveguide edge couplers at visible wavelengths

Silicon nitride fiber-to-waveguide inverse taper edge couplers with double tips are designed and simulated. Double tip edge couplers show a coupling efficiency improvement over single tip couplers at visible wavelengths, which is crucial for loss sensitive quantum optics applications. A loss optimized 2×1 MMI coupler is designed for use as a mode converter in double tip edge couplers.

Broadband silicon bridge waveguide polarization beam splitter

We have successfully fabricated and measured our silicon bridge waveguide polarization beam splitter (PBS). Our proposed PBS is based on a bend directional coupler with a bend bridge waveguide and is experimentally realized using silicon waveguide thickness of 220 nm and 250 nm, which are the commonly used silicon thickness for silicon photonics manufacturing. Our experimental results demonstrated high extinction ratio of > 20 dB for the TE-like mode, and > 15 dB for the TM-like mode across a broad bandwidth of 90 nm that covers the entire C-band with a small footprint of ~18×9 μm2. On-chip high performance PBS is important for polarization diversity in integrated photonics, and for communication applications such as dual-polarization quadrature phase-shift keying (DP-QPSK) modulation.

Numerical analysis and optimization of high-speed silicon microring resonator modulators using high-performance carrier-depletion phase shifters

Silicon microring resonator modulators are versatile active on-chip devices capable of high-speed modulation with low energy consumption. However, the effects of PN junction alignment variance for different doping concentrations during fabrication have not been looked into. In this work, we numerically demonstrate and analyse the optimisation of the silicon microring resonator modulator based on the carrier depletion mechanism for high extinction ratio and low energy consumption at the communication wavelength of 1550 nm. A range of carrier doping concentrations and offset of the PN junction to the waveguide centre can be used to optimise the modulation efficiency, energy consumption and insertion losses of the microring modulator. In particular, the effects of the offset of the PN junction are analysed for three cases in the carrier-depletion silicon phase shifter: (i) p-type doping < n-type doping, (ii) p-type doping = n-type doping, and (iii) p-type doping > n-type doping. Subsequently, three types of microring ring modulator architecture – the all-pass microring resonator, the add-drop microring resonator, and the all-pass dual uncoupled microring resonator – are realised and analysed. Our results suggests that doping concentration between 2 × 1017 cm-3 to 5 × 1017 cm-3, with the p-doping concentration lower than the n-doping concentration, should be employed in order to achieve a tunability of > 16 pm/V and extinction ratio of > 8 dB.