Jun Rong Ong

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.

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.

Broadband silicon polarization beam splitter with a high extinction ratio using a triple-bent-waveguide directional coupler

We report on the design and experimental demonstration of a broadband silicon polarization beam splitter (PBS) with a high extinction ratio (ER)≥30  dB. This was achieved using triple-bent-waveguide directional coupling in a single PBS, and cascaded PBS topology. For the single PBS, the bandwidths for an ER≥30  dB are 20 nm for the quasi-TE mode, and 70 nm for the quasi-TM mode when a broadband light source (1520-1610 nm) was employed. The insertion loss (IL) varies from 0.2 to 1 dB for the quasi-TE mode and 0.2-2 dB for the quasi-TM mode. The cascaded PBS improved the bandwidth of the quasi-TE mode for an ER≥30  dB to 90 nm, with a low IL of 0.2-2 dB. To the best of our knowledge, our PBS system is one of the best broadband PBSs with an ER as high as ∼42  dB and a low IL below 1 dB around the central wavelength, and experimentally demonstrated using edge-coupling.

High-performance silicon-on-insulator polarization beam splitter using novel bend directional coupler

High performance silicon-on-insulator polarization beam splitter with a small footprint of ~18 × 9 μm2 is demonstrated using a bend directional coupler with a bridge waveguide. High extinction ratio of > ~20 dB over the entire C band is achieved for both TE-like and TM-like polarizations.