Zengzhi Huang

High-quality-factor photonic crystal ring resonator

A design for enhancing the quality (Q) factor of a photonic crystal ring resonator (PCRR) is introduced. The highest Q factor based on simulations is 121,000. The analysis of momentum space distributions of the electric field profile for PCRR resonance shows that a high Q factor of a PCRR is attributed to the reduction of tangential k-vector component inside the leaky region. A high Q factor of 75,200 is experimentally demonstrated for a modified PCRR on a silicon-on-insulator wafer. The high-Q-factor PCRR demonstrated here will be beneficial for channel drop filters, lasers, sensors, and other applications.

Ultralow Power Nonlinear Response in an Si Photonic Crystal Nanocavity

Optical nonlinear response and bistability behavior are observed in a fabricated silicon photonic crystal three defect-long (L3) nanocavity. The L3 cavity, which is coupled with a photonic crystal waveguide, has a quality factor of 60 000. Optical nonlinear response of the L3 cavity is observed at 4.65- μW input power, and the threshold power for optical bistability in the L3 cavity is 26.1 μW, which are the lowest values for silicon L3 cavities. A nonlinear coupled mode model is established to analyze nanocavity characteristics systematically. Numerical simulation results indicate that the ultralow power nonlinearity is due to the high Q factor and large thermal resistance of the nanocavity.

Enhanced 1524-nm Emission From Ge Quantum Dots in a Modified Photonic Crystal L3 Cavity

Light emitters based on Ge quantum dots embedded in modified photonic crystal three defect-long (L3) cavities are fabricated and characterized. Several sharp resonant luminescence peaks dominate the photoluminescence (PL) spectrum at room temperature. The strongest resonant luminescence peak is obtained at 1524 nm. The enhancement factor is 110, and the corresponding Purcell factor is estimated to be 6.7. The large enhancement is due to high Purcell factor and high collection efficiency of modified L3 cavity verified by far-field patterns. The intrinsic Q factor measured from crossed-polarized resonant scattering is much higher than the Q factor measured from PL, indicating that the Q factors measured from PL are inaccurate due to free-carrier absorption of the photogenerated carriers.

Compact Grating Coupler for 700-nm Silicon Nitride Strip Waveguides

700-nm-thick silicon nitride-on-insulator (SNOI) is widely used for nonlinear applications due to its broadband nearly zero flattened dispersion. In this paper, we present a grating coupler for the TE mode of strip waveguides on 700-nm-thick SNOI. Focusing grating structure and inverse taper are combined to reduce the footprint to 70.2 μm × 19.7 μm. The peak coupling efficiency is -3.7 dB and the 1-dB bandwidth is 54 nm. The fabrication process is CMOS-compatible with only one additional etching step required.

Single germanium quantum dot embedded in photonic crystal nanocavity for light emitter on silicon chip.

A silicon light emitter in telecom-band based on a single germanium quantum dot precisely embedded in a silicon photonic crystal nanocavity is fabricated by a scalable method. A sharp resonant luminescence peak is observed at 1498.8 nm, which is enhanced by more than three orders of magnitude. The Purcell factor for the fundamental resonant mode is estimated from enhancement factor and increased collection efficiency. The cavity modes coupled to the ground state and excited state emission of germanium quantum dot are identified in the luminescence spectrum. Our devices provide a CMOS-compatible way of developing silicon-based low-power consuming light emitters, and are promising for realizing on-chip single photon sources.

Compact grating coupler for thick silicon nitride

Thick Silicon nitride-on-insolater (SNOI) is widely used for nonlinear applications due to its broadband nearly-zero flattened dispersion. In this paper, we present a grating coupler for strip waveguides on 700-nm-thick SNOI. Focusing grating structure and inverse taper are combined to minify the footprint to 70μm × 19μm. The peak couplin g efficiency is -3.7dB and the 1-dB bandwidth is 54nm.

Design the Structure of Vertical Multilayer Hybrid Silicon Waveguide to Work in Anomalous Dispersion Region

In order to decrease the dispersion of the silicon vertical slot waveguide, we propose a vertical multilayer hybrid silicon waveguide. The optical mode distribution of the multilayer waveguide is simulated by a finite element method. By a proper design of the waveguide parameters, the dispersion of waveguide can in the range of ±300 ps/nm/km in 1510-1590 nm, with one zero-group-dispersion point in the C band. This waveguide can be an alternative in on-chip nonlinear application, such as all optical signal processing.