A silicon hybrid photodetector was demonstrated based on die-to-die bonding technology. The vertically incident InGaAs/InP photodetector die was integrated on silicon-on-insulator (SOI) die by using divinyldisiloxane benzocyclobutene (DVS-BCB) as adhesive layer. A grating coupler was fabricated on SOI substrate to diffract the light out of the SOI waveguide into the detector. The measured coupling efficiency output at 1550 nm for the TE mode reached to 39.8%, which is equal to 8.2 dB fiber-to-fiber loss. After integrating, when the thickness of the BCB bonding layer was 380 nm, the optical loss reached to 13.8 dB with 30×30 μm2 device. The measured dark current, bandwidth and responsivity of the hybrid InGaAs/InP photodetector with light absorbing mesa of 10×10 μm2 were 37.7 nA, 30.9 GHz and 0.48 A/W respectively at -3 V DC bias.
Nanjing, a typical megacity in eastern China, has undergone dramatic expansion during the past decade. The surface urban heat island (SUHI) effect is an important indicator of the environmental consequences of urbanization and has rapidly changed the dynamics of Nanjing. Accurate measurements of the effects and changes resulting from the SUHI effect may provide useful information for urban planning. Index, centroid transfer, and correlation analyses were conducted to measure the dynamics of the SUHI and elucidate the relationship between the SUHI and urban expansion in Nanjing over the past decade. Overall, the results indicated that (1) the region affected by the SUHI effect gradually expanded southward and eastward from 2000 to 2012; (2) the centroid of the SUHI moved gradually southeastward and then southward and southwestward, which is consistent with the movement of the urban centroid; (3) the trajectory of the level-3 SUHI centroid did not correspond with the urban mass or SUHI centroids during the study period and (4) the SUHI intensity and urban fractal characteristics were negatively correlated. In addition, we presented insights regarding the minimization of the SUHI effect in cities such as Nanjing, China.
Passive microwave remote sensing was firstly applied to detect the moon by Chang'E-1 satellite with a four channel
microwave radiometer. Its primary goal is to detect the thickness of lunar regolith and to assess the content of 3He. There
are remained theoretical problems to be systematically solved, which include to research the microwave radiation
transfer properties and to establish the suitable model to inverse lunar regolith depth. Considering the variation of these
factors influencing on the brightness temperature, a new multi-layer microwave transfer model to inverse the depth of
lunar regolith is presented. The physical factors among top lunar regolith influencing the brightness temperature change
sharply with the thickness, so the top lunar regolith is divided subtly. On the contrary, the deep lunar regolith where the
factors vary slowly with the thickness is divided roughly. Then, by applying the fluctuation dissipation theorem, the
brightness temperatures obtained from four frequency channels (3.0GHz, 7.8GHz, 19.35GHz, 37GHz) are simulated
based on the multi-layer model at different locations on the moon and at different times of a lunar day. In comparison the
calculated results with other models, it indicates that the proposed model has better stability and less calculation.
Instead of real phase shifts, equivalent phase shifts (EPS) are adopted to construct ultra narrow phase-shifted band-pass
filer in sampled Bragg gratings (SBG). Two optimized distributions of multiple equivalent phase shifts, using 2 and 5
EPSs respectively, are given in this paper to realize flat-top and ripple-free transmission characteristics simultaneously.
Also two demonstrations with 5 EPSs both on hydrogen-loaded and photosensitive fibers are presented and their
spectrums are examined by an optical vector analyzer (OVA). Given only ordinary phase mask and sub-micrometer
precision control, ultra-narrowband flat-top filters with expected performance can be achieved flexibly and cost-effectively.