In this paper, we propose a method to remove the imaging ambiguity caused by scattering in foggy days based on the utilization of generalized Gaussian function. We use the generalized Gaussian function to simulate the light transmission performance in foggy weather and then obtain its attenuation charateristics for further achieving image defogging results. We also propose a zonal dehazing method according to the distribution of fog in hazed image, thereby further improving the quality of the dehazing image. We use real fog data sets to quantitatively analyze and visualize the results. The simulation results show that the image information entropy and visible edge ratio obtained by the algorithm are improved, which verifies the effectiveness and superiority of the proposed algorithm.
We report a maskless reactive ion etching (RIE) method that employs O2, CHF3 and SF6&O2 gas plasma sequentially to generate nano-cones structures on silicon substrates with good uniformity. In this method, nano-cones are made under carefully-controlled conditions that restrict their width and height to 60 nm and 82 nm, respectively. According to the formation trend of nano-cones under different plasma conditions, the contributing mechanism is discussed. With the multiple effects of etching time, chamber pressure and self-bias voltage, the height, angle and density of nano-cones will be varied within a certain range. Given these variations, a nano-cone structure with good uniformity was generated using the following parameters: etching time of 300 s, chamber pressure of 40 mtorr, self-bias voltage of 75 W, and a SF6&O2 flow ratio of 75 sccm: 75 sccm. The experiment in this report demonstrates a promising way to fabricate silicon-based nano-cone structures for photonic and optoelectronic applications, with advantages of the controllability and compatibility of its dry-etching process.
A modified uni-traveling carrier photodiode (MUTC-PD) with an electric field control layer is proposed. The novel MUTC-PD can achieve high-speed and high-power performance at a lower bias voltage. The insertion of the electric field control layer can change the electric field distribution in the depletion region at a fixed bias voltage. It is beneficial for reducing power consumption, relieving the limitation of heat dissipation on the high-power performance, and suppressing the space-charge effect. In the simulation, the 20-μm-diameter device reaches an RF output power of 23.9 dBm at 20 GHz. Compared with the original structure without the electric field control layer, the junction capacitance of the novel device is decreased from 73.7 fF to 54.7 fF, and the 3-dB bandwidth is increased from 29.5 GHz to 37.5 GHz at a reverse bias of 2 V.
The influence of a multi-mesa structure on a pin photodiode (pin-PD) was carefully studied. It was found that PDs with multi-mesa structures form an uneven electric field in the device under the working voltage, and the electron obtains the overshoot velocity in the uneven electric field. The device that adopts the multi-mesa structure can also reduce the capacitance. The introduction of multi-mesa structures provides another way to improve the performance of the pin-PD. Compared with the one-mesa structure, the multi-mesa structure improved the bandwidth of 5.5 GHz and reduced the capacitance from 26 to 19 fF. The modified pin-PD with a multi-mesa structure can be used in 100-Gbits optical communication systems.
Two planar dielectric reflectors with polarization-independent focusing ability have been designed. They are designed and compared on the base of the square lattice of circular two-dimensional (2-D) subwavelength gratings (SWGs) and the hexagonal lattice of circular 2-D SWGs on a silicon-on-insulator wafer.
We report a novel optical microcavity with micro-nano size based on the Fabry-Perot microcavity, which is a roof structure with two top reflectors that are symmetrical structure and proper inclined angle. The special design of the top reflectors increases the one-period-length for the mode light ray inside the microcavity and confines light in a smaller area effectively. The resonance principle of the microcavity is analyzed and the properties are numerically studied by the finite element method (FEM). Compared with the Fabry-Perot microcavity, the result show that the proposed microcavity has outstanding advantages such as high quality factor, narrow spectrum, and small effective module volume, which has a great potential in photonic devices and optoelectronic devices.
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