Yong Qing Huang

Design Net-Grid Subwavelength Gratings for High Quantum Efficiency Photodetectors

Subwavelength gratings (SWGs) that consist of net-grid structure are designed as infrared reflectors in this paper. By rigorous coupled wave approach (RCWA) and finite difference time domain (FDTD) method, we simulate its reflectivity which can reach 99.98% at 1.55μm while maintaining reflectivity higher than 99% across the 1.47-1.59μm wavelength range. We introduce SWG reflectors as the bottom mirrors in resonant cavity enhanced photodetectors (RCE PDs). RCE PDs quantum efficiency is increased to 95.7% at 1.55μm and the device has a significant size reduction compared with only using DBR bottom mirror.

Growth and Characterization of Radial pn Junction Gaas Nanowire by MOCVD

Radial pn-junction GaAs nanowires were fabricated and investigated in detail. These nanowires were grown on GaAs (111)B substrate by metal-organic chemical vapor deposition via Au-catalyzed vapor-liquid-solid mechanism. Two types of nanowire p-n junctions were fabricated by growing a n(p)-doped GaAs shell outside a p(n) GaAs core. P-type doping was provided by diethyl zinc, while silane was introduced for n-type doping. The morphology, crystal structure and doping characteristics were investigated by FESEM, TEM and EDS. The results showed that both the two structures were of good morphology and both dopants were successfully incorporated into the nanowires.

Theoretical Analysis of Electrical Properties of GaAs Substrate-Nanowire P-N Junction

We theoretically analyze the electrical properties of GaAs substrate-nanowire p-n junction using Technology Computer Aided Design (TCAD). The results show that GaAs nanowire-substrate p-n junction exhibits clear diode behavior which has been confirmed in some experiments. Increasing NWs doping concentration and diameter or shortening NWs length can enlarge the total current after the diode is conducted. Total current through p-n junction is approximately linearly proportional to NWs growth density. The substrate-nanowires p-n junction has smaller current than that of substrate-layer p-n junction, which implies the superiority of NW structure. These results constitute an important progress for experimental researches on nanowire-integrated devices.

Performance Analysis of Coherent Atmospheric Optical Communications with Soft-decision Forward Error Correction

Performance of coherent atmospheric optical communication system with heterodyne detection and LDPC codes was evaluated over atmospheric channel attenuations of which are about 20-30 dB/km. To reduce bit error and enhance the system performance LDPC code was implemented in system. Combining coherent detection and LDPC codes could reduce the received power requirement ~4 dBm at the BER of 10-9.

Design and Analysis of Hybrid Integrated High-Speed Mushroom Vertical PIN Photodetector

We present a new high-speed drift-enhanced InGaAs/InP mushroom vertical PIN photodetector which is integrated on a GaAs/AlGaAs F-P filter cavity using an undercut mushroom mesa structure to significantly reduce both the detector RC constant and the parasitic capacitance. A 3dB bandwidth of 110 GHz and a quantum efficiency of 68% are simultaneously obtained at 1.55 μm wavelength.

High-Speed Drift-Enhanced Multiple-Junction Photodetector with Si-Based Subwavelength Gratings

We demonstrate a new multiple-junction photodetector incorporating concentric circular subwavelength gratings as a broadband reflector. A quantum efficiency of 81% and a 3dB bandwidth of 121 GHz are simultaneously obtained due to the suitable design of junction number and absorption layer thickness.

Design and Analysis of Optical-Communication-Band Sub-Wavelength Grating Polarizer

According to the requirement of the optical communication devices, sub-wavelength grating polarizer was studied based on rigorous coupled-wave analysis (RCWA) and designed with SOI materials. The paper analyzes the grating parameters such as the period, depth, fill groove that influence the diffraction efficiency of the grating. The TM mode diffraction efficiency is more than 95%, and the TE mode diffraction efficiency is less than 5%, the pyramidal sub-wavelength polarizer grating has good polarizer performance than others shapes in the optical communication band of 1550nm. In this paper, we designed this kind of sub-wavelength grating polarizer has great potential applying in optical switching, optical memory, optical detectors and other photo-electronic devices.

Design and Analysis of a Novel Wavelength-Selelctive Waveguide Photodetector

A novel wavelength-selective waveguide photodetector is designed in this paper , which consists of a waveguide photodetector (WGPD) and a Fabry-Pérot (F-P) cavity filter . The peak wavelength of the integrated device is at 1538nm . The 3-dB line-width of 0.3nm , quantum efficiency of 25% and responsivity of 0.2A/W are theoretically obtained . The analysis method can be applied to other integrated devices that have more components . The epitaxial growth and fabrication of the photodetector is discussed, exhibiting the experimental character .

A Novel Demultiplexing Photodetector with Integrated Vertical Conical Structure

A novel demultiplexing photodetector which consists of a filtering cavity and a conical absorption cavity is proposed. The filtering cavity is formed by four coupled （Fabry-Pérot）F-P cavities, which can realize flat-top and steep-edge spectral response. The top mirror of the absorption cavity is designed to be conical, which can increase the times of light reflection. Then the quantum efficiency is improved. Through the theoretical analysis and simulation, the peak quantum efficiency of the photodetector is 88.87% around 1550nm. In addition, this photodetector has good performance in the flat-top and steep-edge spectral response: the 0.5dB bandwidth is 0.4nm , the 3dB bandwidth is 0.56nm and the 20dB bandwidth is 0.98nm.

Performance Enhancement of Atmospheric Coherent Optical Communication Systems Using DPSK

A coherent DPSK transmission system is presented to improve the receiver sensitivity for free space optical (FSO) communication. The coherent DPSK is an effective way to overcome the atmospheric turbulence. The eye diagram and bit error rate (BER) of the system are got by the simulation. Results show that with the coherent reception method, coherent DPSK offers improved signal-to-noise ratio (SNR) performance compared to the DPSK without coherent and OOK format. And hence it can be effective to overcome the signal impairment caused by atmospheric turbulence. It is shown that the sensitivity of the system employing coherent DPSK is 3dB better than a comparable system using DPSK without coherent and 9dB better than a system using OOK.