ABSTRACT
Optical switches are important in signal routing and switching. In this paper, a thermal optical switch with trapezoidal air trenches is proposed. The proposed structure consists of two cascaded 4×4 multimode interference (MMI) couplers. The beam propagation method is used to optimize the dimension and analyze the characteristics. Simulation results show excess loss (EL) and insertion loss (IL) are less than 0.14 dB and 0.22 dB at the wavelength of 1550 nm, respectively. Besides, the extinction ratio (ER) is higher than 21 dB. This design has the advantages of small size, low loss, and high flexibility, which is promising for application to all-optical network routing.
ABSTRACT
A three-dimensional polymer mode (de)multiplexer based on mode evolution is proposed. The proposed configuration is mainly composed of cascaded two tapered couplers where waveguides with different heights are inversely tapered to achieve mode conversions of the E11,E21, and E31 modes. The dimensional parameters and characteristics are analyzed by the beam propagation method. This mode (de)multiplexer exhibits the coupling ratio greater than 0.97, excess loss lower than 0.15 dB and extinction ratio higher than 20 dB for TE and TM polarizations over the wavelength range 1530â¼1625nm (the C+L band). This design has weak wavelength dependence and polarization dependence, which is promising to be applied to broadband on-board mode multiplexing.
ABSTRACT
In low-duty-cycle wireless networks with unreliable and correlated links, Opportunistic Routing (OR) is extremely costly because of the unaligned working schedules of nodes within a common candidate forwarder set. In this work, we propose a novel polynomial-time node scheduling scheme considering link correlation for OR in low-duty-cycle wireless networks (LDC-COR), which significantly improves the performance by assigning nodes with low correlation to a common group and scheduling the nodes within this group to wake up simultaneously for forwarding packets in a common cycle. By taking account of both link correlation and link quality, the performance of the expected transmission count (ETX) is improved by adopting the LDC-COR protocol. As a result, the energy consumption of low-duty-cycle OR is significantly reduced. LDC-COR only requires the information of one-hop neighboring nodes which introduces minimal communication overhead. The proposed LDC-COR bridges the gap between the nodes' limited energy resource and the application lifetime requirements. We evaluate the performance of LDC-COR with extensive simulations and a physical wireless testbed consisting of 20 TelosB nodes. The evaluation results show that both transmission efficiency and energy consumption of low-duty-cycle OR are significantly improved with only a slight increase of end-to-end delay.
