Optical beamforming networks (OBFNs) based on optical true time delay lines (OTTDLs) are well-known as the promising candidate to solve the bandwidth limitation of traditional electronic phased array antennas (PAAs) due to beam squinting. Here we report the first monolithic 1×8 microwave photonic beamformer based on switchable OTTDLs on the silicon-on-insulator platform. The chip consists of a modulator, an eight-channel OBFN, and 8 photodetectors, which includes hundreds of active and passive components in total. It has a wide operating bandwidth from 8 to 18 GHz, which is almost two orders larger than that of electronic PAAs. The beam can be steered to 31 distinguishable angles in the range of -75.51° to 75.64° based on the beam pattern calculation with the measured RF response. The response time for beam steering is 56 μs. These results represent a significant step towards the realization of integrated microwave photonic beamformers that can satisfy compact size and low power consumption requirements for the future radar and wireless communication systems.

I. ABSTRACTIn heterogeneous cellular network, task scheduling for computation offloading is one of the biggest challenges. Most works focus on alleviating heavy burden of macro base stations by moving the computation tasks on macro-cell user equipment (MUE) to remote cloud or small-cell base stations. But the selfishness of network users is seldom considered. Motivated by the cloud edge computing, this paper provides incentive for task transfer from macro cell users to small cell base stations. The proposed incentive scheme utilizes small cell user equipment to provide relay service. The problem of computation offloading is modelled as a two-stage auction, in which the remote MUEs with common social character can form a group and then buy the computation resource of small-cell base stations with the relay of small cell user equipment. A two-stage auction scheme named TARCO is contributed to maximize utilities for both sellers and buyers in the network. The truthful, individual rationality and budget balance of the TARCO are also proved in this paper. In addition, two algorithms are proposed to further refine TARCO on the social welfare of the network. Extensive simulation results demonstrate that, TARCO is better than random algorithm by about 104.90% in terms of average utility of MUEs, while the performance of TARCO is further improved up to 28.75% and 17.06% by the proposed two algorithms, respectively.

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Silicon nitride (Si 3 N 4) has a higher nonlinear threshold compared to silicon, which reduces the effect of two-photon absorption. However, the low thermo-optic coefficient and the reduced refractive index contrast of thin Si 3 N 4 waveguides lead to a low thermal tuning speed and low thermal efficiency. This paper demonstrates a widely tunable III-V/Si 3 N 4 hybrid-integrated external cavity laser with a relatively faster switching time. The Si 3 N 4 external feedback circuit is based on 800-nm-thick Si 3 N 4 waveguides with an optical confinement factor of 87%. It allows the reduction of the oxide under-cladding layer thickness to 4 μm and the oxide upper-cladding layer to 1.7 μm without additional loss. The switching time between two non-adjacent lasing wavelengths is 60.7 μs. The maximum output power is 34 mW under 500 mA injection current. The side mode suppression ratio is more than 70 dB over the tuning range of 58.5 nm. The laser intrinsic linewidth is 2.5 kHz.

We report a reconfigurable optical filter chip based on the Si 3 N 4 waveguide platform. Microwave filtering is realized using a device with optical-to-electrical mapping. The filter chip is based on a lattice structure with the dual-ring-coupled Mach-Zehnder interferometers (DR-MZIs) as the basic elements. Both the lattice and ring couplers are tunable, making the chip reconfigurable to various filter functions. A theoretical model is developed to analyze its optical filtering performance. Measurement reveals that the filter passband can reach hundreds of megahertz in the lower limit and several gigahertz in the upper limit. Various orders of infinite impulse response filters are implemented with a tailorable passband. The flexibility in tuning filter center frequency and passband makes it suitable in high-resolution adaptable microwave signal front-end processing.