Spiking neural networks are a class of artificial neural networks maintaining a strict analogy to brain-like processing. I’ll show a new hardware approach in which semiconductor microcavities in strong light-matter coupling regime can operate as optical spiking neurons. We demonstrated the intrinsic property of exciton-polaritons to resemble the Leaky Integrate-and-Fire spiking mechanism. Polaritons when pumped with a pulsed laser exhibit leaky-integration due to relaxation of the excitonic reservoir, threshold-and-fire mechanism due to transition to polariton condensate, and resetting due to stimulated emission of photons. Our approach provides means for energy-efficient ultrafast processing of spike-like laser pulses at the level below 1 pJ/spike.
We show that time-delayed nonlinear effects observed between exciton-polariton condensates can be used to create neural networks in which information is encoded in time. We form condensates on semiconductor microcavity using optical pulses that reach the sample at different times. Strongly nonlinear effects are induced by time-dependent interactions with a long-lived excitonic reservoir. Such nonlinearities make it possible to create a nonlinear XOR logic gate that performs operations with a picosecond time scale. A neural network based on such a logic gate performs a speech recognition tasks with high accuracy.
The concept of Neuromorphic Photonics introduces advantages of optical information processing into the neuromorphic engineering domain. Most of the current efforts in the field are focused on identifying the potential mechanisms for useful and flexible spiking neuron implementation. We propose a new approach in which microcavities exhibiting strong exciton-photon interaction may serve as building blocks of optical spiking neurons. Our experiments prove similarities between polariton in-out pulse characteristics and the fundamental spiking behavior of a biological neuron. These effects, evidenced in photoluminescence characteristics, arise within sub-ns timescales. The presented approach provides means for energy-efficient ultrafast processing of spike-like laser pulses.
We realize a tunable laser based on a liquid crystal optical microcavity doped with the pyrromethene 580 organic dye. The tunable range reaches 40 nm. By transforming the system into the Rashba-Dresselhaus coupling regime, the laser action takes place from the bottoms of two oppositely polarized valleys shifted apart in reciprocal space. Measurements of emissions in real space show the persistent spin-helix lasing, which is a consequence of the spin coherence of the system. The platform that we propose can be used in quantum communication, in which information is encoded through light polarization.
In this work we realize an optical resonator incorporating nematic liquid crystal in which photonic cavity modes are in strong light-matter coupling regime with excitons in a 2D organic-inorganic perovskite layer. Using electric field tunability provided by the liquid crystal we can bring our structure to the regime of Rashba-Dresselhaus spin orbit coupling. By a preparation of the orienting polymer layers within the cavity to break inversion symmetry of the liquid crystal layer we were able to engineer polariton energy band structure exhibiting locally non-zero photonic Berry curvature, which can be tuned by an external electric field.
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