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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.

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 $1.55\ \mu\mathrm{m}$ .

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.

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.

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.

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.