Efficient stochastic parallel gradient descent training for on-chip optical processor

In recent years,space-division multiplexing(SDM)technology,which involves transmitting data information on multiple parallel channels for efficient capacity scaling,has been widely used in fiber and free-space optical communication sys-tems.To enable flexible data management and cope with the mixing between different channels,the integrated reconfig-urable optical processor is used for optical switching and mitigating the channel crosstalk.However,efficient online train-ing becomes intricate and challenging,particularly when dealing with a significant number of channels.Here we use the stochastic parallel gradient descent(SPGD)algorithm to configure the integrated optical processor,which has less com-putation than the traditional gradient descent(GD)algorithm.We design and fabricate a 6×6 on-chip optical processor on silicon platform to implement optical switching and descrambling assisted by the online training with the SPDG algorithm.Moreover,we apply the on-chip processor configured by the SPGD algorithm to optical communications for optical switching and efficiently mitigating the channel crosstalk in SDM systems.In comparison with the traditional GD al-gorithm,it is found that the SPGD algorithm features better performance especially when the scale of matrix is large,which means it has the potential to optimize large-scale optical matrix computation acceleration chips.

Contactless integrated photonic probes:fundamentals,characteristics,and applications

On-chip optical power monitors are indispensable for functional implementation and stabilization of large-scale and complex photonic integrated circuits(PICs).Traditional on-chip optical monitoring is implemented by tapping a small portion of optical power from the waveguide,which leads to signifcant loss.Due to its advantages like non-invasive nature,miniaturization,and complementary metal-oxide-semiconductor(CMOS)process compatibility,a transparent monitor named the contactless integrated photonic probe(CLIPP),has been attracting great attention in recent years.The CLIPP indirectly monitors the optical power in the waveguide by detecting the conductance variation of the local optical waveguide caused by the surface state absorption(SSA)efect.In this review,we frst introduce the fundamentals of the CLIPP including the concept,the equivalent electric model and the impedance read-out method,and then summarize some characteristics of the CLIPP.Finally,the functional applications of the CLIPP on the identifcation and feedback control of optical signal are discussed,followed by a brief outlook on the prospects of the CLIPP.