Sang-Hun Kim

Ultra-compact 8 × 8 strictly-non-blocking Si-wire PILOSS switch

We report on a path-independent insertion-loss (PILOSS) 8 × 8 matrix switch based on Si-wire waveguides, which has a record-small footprint of 3.5 × 2.4 mm2. The PILOSS switch consists of 64 thermooptic Mach-Zehnder (MZ) switches and 49 low-crosstalk intersections. Each of the MZ switches and intersections employs directional couplers, which enable the composition of a low loss PILOSS switch. We demonstrate successful switching of digital-coherent 43-Gbps QPSK signal.

Ultra-high-extinction-ratio 2 × 2 silicon optical switch with variable splitter.

We demonstrate a record-high extinction-ratio of 50.4 dB in a 2 × 2 silicon Mach-Zehnder switch equipped with a variable splitter as the front 3-dB splitter. The variable splitter is adjusted to compensate for the splitting-ratio mismatch between the front and rear 3-dB splitters. The high extinction ratio does not rely on waveguide crossings and meets a strong demand in applications to multiport circuit switches. Large fabrication tolerance will make the high extinction ratio compatible with a volume production with standard complementary metal-oxide semiconductor fabrication facilities.

Demonstration of a 3-dB directional coupler with enhanced robustness to gap variations for silicon wire waveguides

We demonstrate a robust 3-dB directional coupler which has a narrow silicon wire core and a wide gap. Sensitivity to the gap variation is decreased to one tenth that of a conventional directional coupler. Better spectral stability due to the enhanced robustness to waveguide geometrical fluctuations was experimentally verified.

Tilted MMI crossings based on silicon wire waveguide.

Waveguide crossings employing tilted MMI structures on silicon wire waveguide are proposed and demonstrated. Intersecting angle of the two MMI waveguides is optimized for low crosstalk. The optimization is carried out with input polarizations specified. On the fabricated MMI crossings, crosstalk lower than -38 dB in the C-band was experimentally confirmed. A novel polarization-insensitive crossing based on a diversity circuit was fabricated. Crosstalk lower than -30 dB in the C-band is demonstrated.

Compact 2 × 2 polarization-diversity Si-wire switch.

A polarization-independent 2 × 2 switch based on silicon-wire waveguides has been realized with a compact size of 600 × 500 μm². Polarization-independent operation was achieved with a polarization-diversity technique which implements polarization splitters, TE-TM intersections, and Mach-Zehnder switches. The extinction ratios of the 2 × 2 switch for TE, TM, and a mixed polarization at a wavelength of 1550 nm were measured to be larger than 30 dB, 25 dB, and 30 dB, respectively. The measured switching powers for the TE and TM polarizations were 25 and 55 mW, respectively. The measured polarization-dependent loss was lower than 1 dB. The differential group delay (DGD) between the TE and TM modes was also evaluated using the Mueller matrix method, which was in good agreement with the values estimated from the path lengths for each mode. A path-length-compensated switch was fabricated, whose DGDs for all paths were indeed as small as ~2 ps, mainly from the access waveguides. The switch could provide an important route to develop ultra-compact polarization-independent integrated circuits based on silicon-wire waveguides.

Polarization-Rotator-Free Polarization-Diversity 4

We present a polarization-diversity 4×4 optical switch composed of silicon-wire waveguides. The proposed 4×4 switch does not require a polarization rotator, which enforces a modification in a standard complementary metal-oxide-semiconductor (CMOS) process to achieve vertical asymmetry. The switch is fabricated on a 300-mm silicon-on-insulator (SOI) wafer with argon fluoride (ArF) immersion lithography, and its footprint is 2.1 mm × 1.1 mm. The switch exhibited a 12.5-dB on-chip loss, a 1.9-dB polarization-dependent loss, and an approximately 5-ps differential group delay.

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We first-time demonstrate gray-scale control by pulse-width modulation for silicon thermo-optic (TO) phase shifters using monolithic MOSFET. This work enables simple and power efficient control of TO modules without using DAC and analog current drivers.

4 Si-Wire Optical Switch

An 8×8 path-independent insertion-loss (PILOSS) switch based on Si-wire waveguides, which has a record-small footprint of 3.5×2.4 mm^2, is reported. The PILOSS switch exhibits successful switching of digital-coherent 43-Gbps QPSK signal.

Power-efficient gray-scale control of silicon thermo-optic phase shifters by pulse width modulation using monolithically integrated MOSFET

We demonstrate that record-high extinction-ratio of 50 dB is achievable in a 2×2 Si optical switch by making use of a variable splitter. The proposed switch will enable such high extinction-ratio even in volume production using standard CMOS fabrication facilities.

Ultra-Compact 8 x 8 Strictly Non-Blocking PILOSS Switch Based on Si-Wire

Waveguide crossing based on a tilted multimode-interference (MMI) structure in high-index-contrast silicon wire is reported. For low crosstalk and low loss, crossing angle of MMIs is optimized. The measured crosstalk with the optimal crossing angle of 110° is -44 dB at wavelength of 1550 nm. This corresponds to improvement by more than 14 dB from previously reported crosstalk with 90°-crossings of MMIs.