Experimental optical computing of complex vector convolution with twisted light

Orbital angular momentum(OAM),emerging as an inherently high-dimensional property of photons,has boosted information capacity in optical communications.However,the potential of OAM in optical computing remains almost unexplored.Here,we present a highly efficient optical computing protocol for complex vector convolution with the superposition of high-dimensional OAM eigenmodes.We used two cascaded spatial light modulators to prepare suitable OAM superpositions to encode two complex vectors.Then,a deep-learning strategy is devised to decode the complex OAM spectrum,thus accomplishing the optical convolution task.In our experiment,we succeed in demonstrating 7-,9-,and 11-dimensional complex vector convolutions,in which an average proximity better than 95%and a mean relative error<6%are achieved.Our present scheme can be extended to incorporate other degrees of freedom for a more versatile optical computing in the high-dimensional Hilbert space.

Frequency upconversion detection of rotational Doppler effect

We demonstrated an efficient scheme of measuring the angular velocity of a rotating object with the detection light working at the infrared regime.Our method benefits from the combination of second-harmonic generation(SHG)and rotational Doppler effect,i.e.,frequency upconversion detection of rotational Doppler effect.In our experiment,we use one infrared light as the fundamental wave(FW)to probe the rotating objects while preparing the other FW to carry the desired superpositions of orbital angular momentum.Then these two FWs are mixed collinearly in a potassium titanyl phosphate crystal via typeⅡphase matching,which produces the visible secondharmonic light wave.The experimental results show that both the angular velocity and geometric symmetry of rotating objects can be identified from the detected frequency-shift signals at the photon-count level.Our scheme will find potential applications in infrared monitoring.