We demonstrate ultrasmall demultiplexers based on photolithographic photonic crystals. The footprint of the demultiplexers is 110 μm² per channel. Our in-plane demultiplexers are clad with silica, which makes them stable and easy to integrate with other silicon photonic devices. We describe two types of demultiplexers with spacings of 136 and 267 GHz between channels for application to dense wavelength division multiplexing. Integrated titanium nitride heaters allow us to precisely control the channel wavelength. We report a 2.5 Gbps transmittance experiment with sufficiently small crosstalk and discuss ways of achieving even lower crosstalk between channels.

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We demonstrate the efficient coupling (99.5%) of a silica whispering gallery mode microresonator directly with a silicon chip by using a silicon photonic crystal waveguide as a coupler. The efficient coupling is attributed to the small effective refractive index difference between the two devices. The large group index of the photonic crystal waveguide mode also contributes to the efficient coupling. A coupling Q of 2.68×10 6 is obtained, which allows us to achieve the critical coupling of a silica whispering gallery mode with an intrinsic Q of close to 10 7 with a Si chip.

This document Designing system with Free-space optical (FSO) communication can supply high-speed digital data linkages to rural regions where geography, setup costs, and groundwork safety are major obstacles. Transmission impairments and space loss could be considered major challenges for handling the FSO system. This work has been designed and analyzed a system based on the combination of Dual Polarization Differential Quadrature Phase Shift Keying (DP-DQPSK) and Dense Wavelength Division Multiplexing (DWDM) using the Direct Detection (DD) technique. The proposed system has been utilized with a hybrid transmission medium of Single-Mode Fiber (SMF) with a fixed length of 60 km and FSO with varied lengths of (5, 7, and 9) km. The system was designed with Optisystem software 18 and consist of 64 channels and 14 Gbps of data rate per channel to make the system 5G communication compatible, 3.5 GHz RF electrical signals have been used to modulate the optical carrier. The channels 1,6,12, …,64 were selected as samples among all channels to be investigated and analyzed along with four different atmospheric weather conditions. Additionally, the proposed system is designed to investigate based on different weather attenuation that affected the parameters of Quality Factor (QF) and Bit Error Rate (BER). The significant advantage of the proposed system by using the DD technique, is no reference wave required. Hence, make the system become less complex and possible to be implemented and tested via different weather conditions. Results obtained indicate reverse relation between the QF and both the FSO distance and attenuation. While, BER based parameters showed a direct relation. For light air and haze, the results showed that the system have higher reliability for all the three investigated FSO distances.  For the medium haze, the system has shown capability to transfer as far as 7 km. And for the rain condition, the system capability was set to 5 km.

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