Generalization of an Optical ASA Switch

An arrayed waveguide grating (AWG) is a kind of passive wavelength router, and it is the most promising technology for developing large optical switches. However, AWGs have poor scalability, and using small AWGs to construct a large switch has been done in many prior works. A novel AWG-based switch called ASA (AWG, Space switching, AWG) that does not use wavelength converters has been proposed. It can expand the switch size from N to N2 by using N × N AWGs. In this paper, we generalize the ASA switch by using only N × N AWGs, N × N space switches, and N wavelengths such that the switch size is expanded to Nt for any positive integer t. Since each port of an N × N AWG can transmit up to N wavelengths simultaneously, the total capacity of the generalized ASA switch is extended to be close to Nt+1 × the bandwidth of a wavelength channel, provided that the inputs which are located in the same port position of each input AWG are destined to distinct outputs.

Reduction in Earth Reflected Radiance during the Eclipse of 21 August 2017

Ten wavelength channels of calibrated radiance image data from the Sunlit Earth are obtained every 65 minutes during Northern Hemisphere summer from the DSCOVR/EPIC instrument located near the Earth-Sun Lagrange-1 point (L1), 1.5 million km from the Earth. The L1 location permitted seven observations of the Moon’s shadow on the Earth for about 3 hours during the 21 August 2017 eclipse. Two of the observations were timed to be over Casper, Wyoming and Columbia, Missouri. Since, the solar irradiances within 5 channels (λi = 388, 443, 551, 680, and 780 nm) are not strongly absorbed in the atmosphere, they can be used for characterizing eclipse reduction in reflected radiances for the sunlit face of the Earth containing the eclipse shadow. Five channels (λi = 317.5, 325, 340, 688, and 764 nm) that are partially absorbed in the atmosphere give consistent reductions compared to the non-absorbed channels. This indicates that cloud reflectivities dominate the 317.5 to 780 nm radiances reflected back to space from the sunlit Earth’s disk with a strong contribution from Rayleigh scattering for the shorter wavelengths. A reduction of 9.7 ± 1.7 % in the radiance (387 to 781 nm) reflected from the Earth towards L1 was obtained for the set of observations on 21 August 2017, while the shadow was in the vicinity of Casper, Wyoming (42.8666° N, 106.3131° W, centered on 17:44:50 UTC). In contrast, when successive non-eclipse days are compared for each wavelength channel, the change in reflected light is much smaller (less than 1 % for 443 nm compared to 9 % during the eclipse). Also measured was the spatially averaged ratio of reflected radiance within the eclipse totality region to radiances for the same geometry on adjacent non-eclipse days for all 10 wavelength channels. The measured was smaller for Columbia (35) than for Casper (122), because Columbia had more cloud cover than Casper. REN(λi) forms a useful test of 3-D radiative transfer models for an eclipse in the presence of optically thin clouds. A previously published clear-sky model (Emde and Mayer, 2007) shows results for a nearly overhead eclipse had REN(340 nm)=1.7 x 104 compared to the maximum measured non-averaged REN(340) at Casper of 515 ± 27 with optically thin clouds under similar geometrical conditions.

Mathematical Verification for Transmission Performance of Centralized Lightwave WDM-RoF-PON with Quintuple Services Integrated in Each Wavelength Channel

Wavelength-division-multiplexing passive-optical-network (WDM-PON) has been recognized as a promising solution of the “last mile” access as well as multibroadband data services access for end users, and WDM-RoF-PON, which employs radio-over-fiber (RoF) technique in WDM-PON, is even a more attractive approach for future broadband fiber and wireless access for its strong availability of centralized multiservices transmission operation and its transparency for bandwidth and signal modulation formats. As for multiservices development in WDM-RoF-PON, various system designs have been reported and verified via simulation or experiment till now, and the scheme with multiservices transmitted in each single wavelength channel is believed as the one that has the highest bandwidth efficiency; however, the corresponding mathematical verification is still hard to be found in state-of-the-art literature. In this paper, system design and data transmission performance of a quintuple services integrated WDM-RoF-PON which jointly employs carrier multiplexing and orthogonal modulation techniques, have been theoretically analyzed and verified in detail; moreover, the system design has been duplicated and verified experimentally and the theory system of such WDM-RoF-PON scheme has thus been formed.