Graphene photodetector employing double slot structure with enhanced responsivity and large bandwidth

Silicon photonics integrated with graphene provides a promising solution to realize integrated photodetectors operating at the communication window thanks to graphene’s ultrafast response and compatibility with CMOS fabrication process.However, current hybrid graphene/silicon photodetectors suffer from low responsivity due to the weak light-graphene interaction. Plasmonic structures have been explored to enhance the responsivity, but the intrinsic metallic Ohmic absorption of the plasmonic mode limits its performance. In this work, by combining the silicon slot and the plasmonic slot waveguide, we demonstrate a novel double slot structure supporting high-performance photodetection, taking advantages of both silicon photonics and plasmonics. With the optimized structural parameters, the double slot structure significantly promotes graphene absorption while maintaining low metallic absorption within the double slot waveguide. Based on the double slot structure, the demonstrated photodetector holds a high responsivity of 603.92 m A/W and a large bandwidth of 78 GHz. The high-performance photodetector provides a competitive solution for the silicon photodetector. Moreover,the double slot structure could be beneficial to a broader range of hybrid two-dimensional material/silicon devices to achieve stronger light-matter interaction with lower metallic absorption.

Soft monolithic infrared neural interface for simultaneous neurostimulation and electrophysiology

Controlling neuronal activity using implantable neural interfaces constitutes an important tool to understand and develop novel strategies against brain diseases.Infrared neurostimulation is a promising alternative to optogenetics for controlling the neuronal circuitry with high spatial resolution.However,bi-directional interfaces capable of simultaneously delivering infrared light and recording electrical signals from the brain with minimal inflammation have not yet been reported.Here,we have developed a soft fibre-based device using high-performance polymers which are>100-fold softer than conventional silica glass used in standard optical fibres.The developed implant is capable of stimulating the brain activity in localized cortical domains by delivering laser pulses in the 2μm spectral region while recording electrophysiological signals.Action and local field potentials were recorded in vivo from the motor cortex and hippocampus in acute and chronic settings,respectively.Immunohistochemical analysis of the brain tissue indicated insignificant inflammatory response to the infrared pulses while the signal-to-noise ratio of recordings still remained high.Our neural interface constitutes a step forward in expanding infrared neurostimulation as a versatile approach for fundamental research and clinically translatable therapies.

Bidirectional high sidelobe suppression silicon optical phased array

An optical phased array(OPA),the most promising non-mechanical beam steering technique,has great potential for solid-state light detection and ranging systems,holographic imaging,and free-space optical communications.A high quality beam with low sidelobes is crucial for long-distance free-space transmission and detection.However,most previously reported OPAs suffer from high sidelobe levels,and few efforts are devoted to reducing sidelobe levels in both azimuthal(φ)and polar(θ)directions.To solve this issue,we propose a Y-splitter-assisted cascaded coupling scheme to realize Gaussian power distribution in the azimuthal direction,which overcomes the bottleneck in the conventional cascaded coupling scheme and significantly increases the sidelobe suppression ratio(SLSR)in theφdirection from 20 to 66 dB in theory for a 120-channel OPA.Moreover,we designed an apodized grating emitter to realize Gaussian power distribution in the polar direction to increase the SLSR.Based on both designs,we experimentally demonstrated a 120-channel OPA with dual-Gaussian power distribution in bothφandθdirections.The SLSRs inφandθdirections are measured to be 15.1 d B and 25 dB,respectively.Furthermore,we steer the beam to the maximum field of view of 25°×13.2°with a periodic 2λpitch(3.1μm).The maximum total power consumption is only 0.332 W with a thermo-optic efficiency of 2.7 m W∕π.

Energy‑efcient integrated silicon optical phased array

An optical phased array(OPA)is a promising non-mechanical technique for beam steering in solid-state light detection and ranging systems.The performance of the OPA largely depends on the phase shifter,which afects power consumption,insertion loss,modulation speed,and footprint.However,for a thermo-optic phase shifter,achieving good performance in all aspects is challenging due to trade-ofs among these aspects.In this work,we propose and demonstrate two types of energy-efcient optical phase shifters that overcome these trade-ofs and achieve a well-balanced performance in all aspects.Additionally,the proposed round-spiral phase shifter is robust in fabrication and fully compatible with deep ultraviolet(DUV)processes,making it an ideal building block for large-scale photonic integrated circuits(PICs).Using the high-performance phase shifter,we propose a periodic OPA with low power consumption,whose maximum electric power consumption within the feld of view is only 0.33 W.Moreover,we designed Gaussian power distribution in both the azimuthal(ψ)and polar(θ)directions and experimentally achieved a large sidelobe suppression ratio of 15.1 and 25 dB,respectively.

Reflection sensitivity of dual-state quantum dot lasers

This work experimentally and theoretically demonstrates the effect of excited state lasing on the reflection sensitivity of dual-state quantum dot lasers,showing that the laser exhibits higher sensitivity to external optical feedback when reaching the excited state lasing threshold.This sensitivity can be degraded by increasing the excited-to-ground-state energy separation,which results in a high excited-to-ground-state threshold ratio.In addition,the occurrence of excited state lasing decreases the damping factor and increases the linewidth enhancement factor,which leads to a low critical feedback level.These findings illuminate a path to fabricate reflectioninsensitive quantum dot lasers for isolator-free photonic integrated circuits.