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We demonstrate a new, to the best of our knowledge, dimensional “horizontal optimization” scheme, which can improve the high-speed characteristics of a PIN photodetector by designing the incident optical field distribution. First, coaxially incident faculae with the same peak and same power are studied and simulated, revealing that the bandwidth of the photodetector illuminated by uniform light is higher than that of the device illuminated by nonuniform light. Next, an annular optical field is designed incident to the photodetector, and the bandwidth is further improved. For a PIN photodetector, by carefully optimizing the incident optical field distribution, the photodetector bandwidth under an annular optical field can be increased significantly compared with that under conventional coaxial illumination.

A synchronous-traveling carrier photodetector (STC-PD) with a thick absorption region and large diameter is presented and investigated for 100 Gbps PAM4 applications. In the STC structure, a suitable electric field is introduced to synchronize the traveling of electrons and holes, which achieves high bandwidth while maintaining large responsivity. The characteristics of STC-PD, including electric field distribution, energy band diagram, responsivity, junction capacitance, and frequency response, have been studied carefully.

SUMMARYStructural variants (SVs) rearrange large segments of the genome and can have profound consequences for evolution and human diseases. As national biobanks, disease association studies, and clinical genetic testing grow increasingly reliant on genome sequencing, population references such as the Genome Aggregation Database (gnomAD) have become integral for interpreting genetic variation. To date, no large-scale reference maps of SVs exist from high-coverage sequencing comparable to those available for point mutations in protein-coding genes. Here, we constructed a reference atlas of SVs across 14,891 genomes from diverse global populations (54% non-European) as a component of gnomAD. We discovered a rich landscape of 433,371 distinct SVs, including 5,295 multi-breakpoint complex SVs across 11 mutational subclasses, and examples of localized chromosome shattering, as in chromothripsis. The average individual harbored 7,439 SVs, which accounted for 25-29% of all rare protein-truncating events per genome. We found strong correlations between constraint against damaging point mutations and rare SVs that both disrupt and duplicate protein-coding sequence, suggesting intolerance to reciprocal dosage alterations for a subset of tightly regulated genes. We also uncovered modest selection against noncoding SVs in cis-regulatory elements, although selection against protein-truncating SVs was stronger than any effect on noncoding SVs. Finally, we benchmarked carrier rates for medically relevant SVs, finding very large (≥1Mb) rare SVs in 3.8% of genomes (~1:26 individuals) and clinically reportable incidental SVs in 0.18% of genomes (~1:556 individuals). These data have been integrated directly into the gnomAD browser (https://gnomad.broadinstitute.org) and will have broad utility for population genetics, disease association, and diagnostic screening.

In this paper we propose a prototype of the visible light communications system for long distance applications. Channel impairments are analyzed, and the design of the transmitter and the receiver is described. Experiments show the system works well at a distance of 10.7 Km at a data rate of 28.8 Kbps.

A novel slanted grating coupler is proposed and demonstrated for perfectly-vertical coupling between optical fibers and waveguides. It offers a coupling efficiency as high as 88.6% for TE polarizations at the wavelength of $1.55\ \mu\mathrm{m}$ .

A 1.55 µm nanoscale laser array is proposed and designed on v-groove patterned Si (0 0 1) substrates. The laser array is designed by taking full advantage of the periodic groove structures of the patterned substrates. The periodic groove structures separated by a SiO2 mask can effectively reduce threading dislocation density in the active region and provide a strong lateral optical confinement for the laser array structure. The optical mode distributions of the single laser are investigated in detail, and the optical confinement factor is calculated to optimize the structure parameters of the laser array. An optimal value of 9.3% for the optical confinement factor is obtained. The analysis of threshold conditions shows that the laser array can achieve lasing with a cavity length of about 1 mm for an internal loss of 40 cm−1.

Optical microcavity can confine light into a small volume by resonant recirculation. Devices based on optical microcavities are already indispensable for a wide range of applications and studies. They not only apply to traditional optics, but also have broad application prospects in quantum information and integrated optoelectronic chips. In quantum optical devices, microcavity can cause atoms or quantum dots to emit spontaneous photons in a desired direction or can provide an environment where dissipative mechanisms such as spontaneous emission are overcome so that quantum entanglement of radiation and matter is possible. For better application in quantum communication, optical microcavity needs to have a high quality factor and a low mode volume. Considering the beam coupling, spot shape and experimental production and others, the Fabry-Perot (F-P) microcavity has been widely applied to the field of optoelectronics. However, the Q-factor of the F-P microcavity is generally low, and the mode volume is large, so it needs to be improved.In addition, high Q-factor microcavity can also play a large role in detecting particles and biological macromolecules.In this paper, through the theory of wave optics, the eigenmodes of a new type of cone-top cylindrical optical micro-cavity are analyzed, and the resonant wavelength expression of the resonant cavity is obtained. We discuss the effects of the top mirror angle on the resonator performance and application of COMSOL simulation software to verify the proposed cone-top cylindrical microcavity. The optimized design and simulation results show that the quality factor of the new resonator can be increased by 22.4% to 49928.5 and the effective mode volume of the resonator can be reduced by 47.8% compared with the traditional parallel resonator. In this case, the corresponding new cavity length is 4.51 μm and the diameter is 3.13 μm. In this article its fabrications are also discussed.

The generation of a flat supercontinuum of over 80 nm in the 1550 nm region by injecting 1.6 ps 10 GHz repetition rate optical pulses into an 80-m-long dispersion-flattened microstructure fibre is demonstrated. The fibre has small normal dispersion with a variation smaller than 1.5 (ps.nm−1.km−1) between 1500 and 1650 nm. The generated supercontinuum ranging from 1513 to 1591 nm has the flatness of ±1.5 dB and it is not so flat in the range of several nanometres around the pump wavelength 1552 nm. Numerical simulation is also used to study the effect of optical loss, fibre parameters and pumping conditions on supercontinuum generation in the dispersion-flattened microstructure fibre, and can be used for further optimization to generate flat broad spectra.

A fully vectorial effective index method is developed for accurate dispersion calculation of photonic crystal fibres (PCFs). In order to improve the accuracy of the model, different values for the effective core radius are used when PCFs have different fibre parameters. The accuracy of our approach is demonstrated by comparing our results with other numerical and experimental results reported in literature. It is found that the accuracy of the fully vectorial effective index method is improved and our results agree well with accurate numerical results obtained by other methods as well as the previously reported experimental data.

A reflection-enhanced dual-absorption InP-PIN/GaAs-DBR photodetector was fabricated and characterized. The photodetector is monolithically integrated using a heteroepitaxy growth of an InGaAs/InP dual-absorption “PINIP” structure on the GaAs/AlGaAs Bragg reflectors. These features lead to an increase in quantum efficiency over a wide wavelength range while maintaining a high speed. The measured quantum efficiency was increased by 48.8% in comparison with that without reflectors. A quantum efficiency of 64% at a wavelength of 1522 nm and a 3 dB bandwidth of 26 GHz at a reverse bias of 3 V were simultaneously obtained in the device.

High-contrast-gratings reflector providing phase front control of transmitted light as well as high reflectivity is presented. The properties of the beam steering and transmission are numerically studied with the Finite Element Method (FEM). The results show that the reflectivity is 90.4% and the steering angle is 36.2510 degree which is very consistent with the theoretical 40 degree.

A dispersion-flattened photonic crystal fiber with normal dispersion is designed for generating flat wideband supercontinuum, and the supercontinuum generation in this fiber is numerically analyzed. The results show that by appropriately designing the photonic crystal fiber, it can achieve flattened dispersion in the normal dispersion region. It is found that a fiber characterized by a flattened dispersion with a small normal dispersion is suitable for a flat wideband supercontinuum generation. In the process of spectral broadening, self-phase modulation effect plays a dominant role. By filtering the supercontinuum, pulses with different central wavelength over a wide spectral range can be obtained. The pulse width is determined by the bandwidth of the filter.

Non-degenerate four wave mixing based on third-order susceptibility χ3 in high nonlinearity microstructure fibres is experimentally demonstrated. The Stokes and anti-Stokes peaks are observed simultaneously by launching 10-fs pulses from an 800 nm Ti:sapphire laser into the fibre.

Two-dimensional subwavelength gratings (2D-SWGs) that consist of net-grid structure are studied by rigorous coupled-wave approach (RCWA) and finite-difference-time-domain (FDTD) method. 2D-SWGs can be designed as infrared reflectors whose reflectivity can reach 99.98% at 1.55µm while maintaining reflectivity higher than 99% across the 1.47–1.59µm wavelength range. We design these SWGs as the bottom mirrors in resonant cavity enhanced photodetectors (RCE-PDs) for optical communication system. Because SWGs can achieve high reflectivity as well as wide bandwidth, RCE PD's quantum efficiency is increased to 95.7% at 1.55µm and the device has a significant size reduction compared with using DBR bottom mirror.

SFP optical modules are widely used in the practical network, this paper proposes an application and realization of a monitoring system for SFP optical transceiver module. It analyses the basic principles of digital diagnosis monitoring function of the intelligent SFP optical modules first. Then it introduces the SFF-8472 protocol architecture and the basic principles of I2C bus. With the adoption of this system, the key parameters of optical transceiver module's monitoring can be realized. Moreover the testing results of the optical transceiver module base on this system are according to the requirements.

A new management framework of GMPLS protocol stack is proposed. On the basis of the requirement of intelligent optical network, we explore design scheme for the management model. Specially, the management model focuses on global topology discovery, point-to-point link management, fault management and link provision. Then the performance of the framework will be analyzed in the test-bed setup in our lab.

In this paper, polarization dependent characteristics of resonant cavity enhanced (RCE) photodetector (PD) with respect to the incident light angle were analyzed in detail. The simulations carry out on a 1.3μm GaInNAs quantum wells RCE PD, which is fabricated in our group. Analysis results show that the influence of polarization can only be neglected at small angle of incidence.

This paper discussed a novel resonant cavity enhanced (RCE) photodetector with a flat-top response, which is promising for WDM application. We analyzed and compared the response curves and crosstalks of the novel RCE and conventional RCE photodetectors, and the influences of the layer-thickness errors on the response curves of the flat-top response RCE photodetectors, and the dependencies of the flat-top RCE photodetector's response on incident angle and polarization were also given.

In this paper, an InP-based mesa-structure uni-traveling-carrier photodetector is designed. By adopting Gaussian doping scheme in the absorption layer and incorporating an appropriate cliff layer, high speed and high saturation current characteristics are both achieved simultaneously. For the device with a 14 μm2 active area, the simulated results indicate that the bandwidth reaches 58 GHz and DC saturation current increases up to 158 mA at a reverse bias of 2 V. Under high optical injection, the bandwidth degradation and current saturation are studied, which are caused by energy band shift and electric field collapse.

A new approach to designing planar, high numerical aperture, low loss, focusing reflectors using circular subwavelength high contrast gratings is presented. Through analyzing particular physical scene, a mathematical transformation from existing “focus line” convergent beam, which can be achieved by bar grating reflector, to the convergent beam with a “focus point”, is obtained. By changing the shape of the bar grating reflector with the mathematical transformation obtained, a circular grating reflector, which can achieve “focus point” convergent beam, is obtained. The focusing properties and reflection characteristic of the circular grating reflector are numerically studied with the finite element method. After the radially polarized light reflected from circular grating reflector with a diameter of 29.788 μm, the beam will focus at 10 μm away from the reflector, resulting in a numerical aperture of 0.8302 and a reflectivity of 0.9163. In the focal plane, the numerical simulation results present a field distribution with a full width half maximum value of 1.5548μm, which is extremely close to diffraction limit.

To explain different doping effects in a buffer layer, thermally annealed interface, and upper epilayers of GaAs/Si films grown by Metalorganic Chemical Vapor Deposition (MOCVD), the behaviors of unintentional doping in GaAs/Si films are investigated in detail. A third doping mechanism of arsine impurity incorporation during the growth process of GaAs/Si films, apart from conventional mechanisms of gas phase reaction and diffusion from the silicon substrate, is proposed. The experimental results reveal that the doping behavior in the buffer layer studied is determined by the three types of doping mechanisms together. However in the thermally annealed interface and upper epilayers, the third doping mechanism is dominant. According to the third mechanism, the background carrier concentration in GaAs/Si films grown by MOCVD could be properly controlled through the arsine flow rate.

InAs/GaAs and InAs/In xGa1-xAs/GaAs nanowire heterostructures are grown by metal organic chemical vapor deposition via Au-assistant vapor-liquid-solid mechanism. We find that the InAs nanowires grow directly on GaAs nanowires in a random way, or they grow along the sidewall of the GaAs nanowires, and thet InAs nanowires grow vertically on GaAs nanowires by using an In x Ga1-xAs (0≤x≤1) buffer segment. It can be concluded that the influences of crystal lattice mismatch and difference in interfacial energy can be eliminated by inserting a ternary compound semiconductor buffer segment, thereby improving the crystal quality and the capability to control the growth of nanowire heterostructure.

Theoretical expressions of the epitaxial lateral overgrowth rate in the metalorganic chemical vapor deposition (MOCVD) have been formulated in this paper, with respect to two separate processes: vapor phase diffusion and mask surface diffusion. In the case of InP deposition on GaAs substrate, a parametric study was accomplished in order to determine the impact of the mask/window width to the growth rate. The model, which uses a new parameter “effective mask length” Lmask, reveals that the key factors determining the growth rate are mask/window width and mask width/effective mask length. This model can be used as a tool for predict the growth conditions leading to expected growth rate.