Neil Na

Demonstration of a High Speed 4-Channel Integrated Silicon Photonics WDM Link with Hybrid Silicon Lasers

The demonstration of a 4λ×10Gbps Silicon Photonics CWDM link integrating all optical components, electronics and packaging technologies required for system integration is reported. Further demonstration of the link operating at 50Gbps, 4λ×12.5Gbps, is also shown.

Efficient broadband silicon-on-insulator grating coupler with low backreflection

We design and fabricate an efficient broadband grating coupler on a 400 nm thick silicon-on-insulator wafer. The measured coupling loss is 3 dB when coupling to a single-mode fiber at 1310 nm wavelength with TE polarization. The spectral FWHM and backreflection are determined to be 58 nm and -27 dB, respectively.

A self-assembled microbonded germanium/silicon heterojunction photodiode for 25 Gb/s high-speed optical interconnects

A novel technique using surface tension to locally bond germanium (Ge) on silicon (Si) is presented for fabricating high performance Ge/Si photodiodes. Surface tension is a cohesive force among liquid molecules that tends to bring contiguous objects in contact to maintain a minimum surface energy. We take advantage of this phenomenon to fabricate a heterojunction optoelectronic device where the lattice constants of joined semiconductors are different. A high-speed Ge/Si heterojunction waveguide photodiode is presented by microbonding a beam-shaped Ge, first grown by rapid-melt-growth (RMG) method, on top of a Si waveguide via surface tension. Excellent device performances such as an operating bandwidth of 17 GHz and a responsivity of 0.66 and 0.70 A/W at the reverse bias of −4 and −6 V, respectively, are demonstrated. This technique can be simply implemented via modern complementary metal-oxide-semiconductor (CMOS) fabrication technologies for integrating Ge on Si devices.

Massive parallel generation of indistinguishable single photons via the polaritonic superfluid to Mott-insulator quantum phase transition

We study the possibility of utilizing the superfluid to Mott-insulator quantum phase transition in an array of quantum well exciton–polariton traps to generate indistinguishable single photons in a massive parallel fashion. By means of analytical and numerical methods, the device operations and system properties are examined using realistic experimental parameters. Such a deterministic, massive parallel generation may find new applications in photonic quantum information processing.

A critically coupled Germanium photodetector under vertical illumination

We propose and study a practical design of a Germanium photodetector implemented on a Silicon-on-insulator substrate to reach the critical coupling regime under vertical illumination at 1310 nm wavelength. With appropriate optimization procedures, a high efficiency bandwidth product larger than 50 GHz and a large 3dB spectral full width around 30 nm can be obtained given realistic material parameters and fabrication constraints. Our device is fully compatible to the state-of-art CMOS process technology, and may serve as a high performance, low cost solution for the optical receiver in Silicon photonics based optical interconnects.

A High-Speed and Low-Breakdown-Voltage Silicon Avalanche Photodetector

A silicon avalanche photodetector with a low breakdown voltage of -6.78 V is demonstrated by narrowing down the intrinsic layer width of interdigitated p-i-n junctions to ~ 150 nm. It reaches the physical limit of avalanche breakdown in which the performance degradation caused by the Zener tunneling process is negligible. Dark current at -4 V is measured, and a responsivity (gain) exceeding 1.424 A/W (110) at -6.75 V is obtained with an 850-nm laser illumination. The intrinsic bandwidth is determined to be 10 GHz, suggesting our device is applicable for a 10-Gb/s high-speed optical receiver application and beyond.

Self-Aligned Microbonded Germanium Metal–Semiconductor–Metal Photodetectors Butt-Coupled to Si Waveguides

We present a butt-coupled Germanium (Ge) metal-semiconductor-metal photodetectors on silicon (Si) waveguides. This device is implemented by a novel process using self-aligned microbonding technique and rapid-melt-growth method for monolithically integrating single-crystal Ge and Si devices on the same plane. Through inserting a thin amorphous Si (a-Si) layer between the Ge and metal contact, the Schottky barrier height is modulated, which effectively reduces the dark current and increases the operation speed. The fabricated device shows a low dark current of 0.24 μA, a 3 dB bandwidth of 15 GHz and a responsivity of 0.25 A/W, at a bias voltage of -2.6 V for wavelength 1310 nm.

High-performance silicon-on-insulator grating coupler with completely vertical emission.

We study the physical concept of utilizing a critical coupling to obtain a high-performance grating coupler with completely vertical emission on a silicon-on-insulator substrate. Following our design strategy, we numerically show that when our grating coupler is coupled to a standard single-mode fiber operating at 1310 nm wavelength, a -1.46 dB coupling loss, a 20 nm spectral full-width-half-maximum, and a -24 dB back reflection can be achieved at the same time without full optimization. A practical design that largely relaxes the stringent lithography requirement is also proposed and presented.

Very strong coupling in GaAs-based optical microcavities

We show that when following a simple cavity design metric, a quantum well exciton-microcavity photon coupling constant can be made substantially larger than the exciton binding energy in GaAs-based optical microcavities. Consequently the very strong coupling regime becomes accessible in which a strong asymmetry between upper and lower polariton branches may be observed experimentally. We further show that the corresponding polariton dissociation and saturation boundaries on the phase diagram are much extended, which suggests the possibility of constructing a room temperature, high power exciton-polariton laser without resorting to wide band-gap semiconductors.

Self-aligned microbonded Ge/Si PIN waveguide photodetectors

A cost-effective process using self-aligned microbonded Ge-beams on silicon waveguides is presented. Heterojunction photodetectors featuring low dark-current of 0.7uA (-2V) and high turn-on current of 10.8 mA (+3V) are demonstrated. The operation bandwidth is 11-16GHz.