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We propose a photonic spiking neural network (SNN) based on excitable vertical-cavity surface-emitting lasers with an embedded saturable absorber (VCSELs-SA) for emulating the sound azimuth detection function of the brain for the first time. Here, the spike encoding and response properties based on the excitability of VCSELs-SA are employed, and the difference between spike timings of two postsynaptic neurons serves as an indication of sound azimuth. Furthermore, the weight matrix contributing to the successful sound azimuth detection is carefully identified, and the effect of the time interval between two presynaptic spikes is considered. It is found that the weight range that can achieve sound azimuth detection decreases gradually with the increase of the time interval between the sound arriving at the left and right ears. Besides, the effective detection range of the time interval between two presynaptic spikes is also identified, which is similar to that of the biological auditory system, but with a much higher resolution which is at the nanosecond time scale. We further discuss the effect of device variations on the photonic sound azimuth detection. Hence, this photonic SNN is biologically plausible, which has comparable low energy consumption and higher resolution compared with the biological system. This work is valuable for brain-inspired information processing and a promising foundation for more complex spiking information processing implemented by photonic neuromorphic computing systems.

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Abstract-A new frequency reconfigurable unequal U-slot antenna is presented in this paper. The U-slot antenna loaded with two lumped variable varactors is capable of 6 different frequencies switching between 2.3 GHz and 3.6 GHz. The small slots in the ground plane are employed for the biasing circuit to minimize the parasitic effects towards the performance of the antenna. It is found that the unequal U-slot fed by an L-shaped feed line can reduce 30% of the size of the conventional U-slot antenna. Moreover, the proposed antenna offers stable radiation characteristics for each operating frequency in the tunable range. The antenna offers a gain of 4.5 dB in average. The designs are verified through both numerical simulations and measurements of an experimental prototype. Details of the antenna designs and measured results are presented and discussed.