70 Gbps PAM-4850-nm oxide-confined VCSEL without equalization and pre-emphasis

Directly modulated 850-nm vertical-cavity surface-emitting lasers(VCSELs)with the advantages of low cost,high modulation speed,good reliability,and low power consumption,are the key sources in the optical interconnects with multimode fibers for the supercomputers,data centers,and machine learning applications[1−3].Typically,non-return-tozero(NRZ)modulation format is used.

Single-fundamental-mode cryogenic(3.6 K)850-nm oxideconfined VCSEL

Cryogenic oxide-confined vertical-cavity surface-emitting laser(VCSEL)has promising application in cryogenic optical interconnect for cryogenic computing.In this paper,we demonstrate a cryogenic 850-nm oxide-confined VCSEL at around 4 K.The cryogenic VCSEL with an optical oxide aperture of 6.5μm in diameter can operate in single fundamental mode with a side-mode suppression-ratio of 36 dB at 3.6 K,and the fiber-coupled output power reaches 1 mW at 5 mA.The small signal modulation measurements at 298 and 292 K show the fabricated VCSEL has the potential to achieve a high modulation bandwidth at cryogenic temperature.

Photonic integrated neuro-synaptic core for convolutional spiking neural network

Neuromorphic photonic computing has emerged as a competitive computing paradigm to overcome the bottlenecks of the von-Neumann architecture.Linear weighting and nonlinear spike activation are two fundamental functions of a photonic spiking neural network(PSNN).However,they are separately implemented with different photonic materials and devices,hindering the large-scale integration of PSNN.Here,we propose,fabricate and experimentally demonstrate a photonic neuro-synaptic chip enabling the simultaneous implementation of linear weighting and nonlinear spike activation based on a distributed feedback(DFB)laser with a saturable absorber(DFB-SA).A prototypical system is experimentally constructed to demonstrate the parallel weighted function and nonlinear spike activation.Furthermore,a fourchannel DFB-SA laser array is fabricated for realizing matrix convolution of a spiking convolutional neural network,achieving a recognition accuracy of 87%for the MNIST dataset.The fabricated neuro-synaptic chip offers a fundamental building block to construct the large-scale integrated PSNN chip.

Semiconductor photonic crystal laser

By combing artificial micro–nano structures,photonic crystals(PCs),with traditional semiconductor laser material to realize the dynamic collaborative control of photonic states and confined electrons,the band engineering of the PC has been confirmed.This brings new development space for the semiconductor laser,such as for low threshold and high efficiency.Based on a series of works by Zheng's group,this paper has reviewed kinds of PC lasers including electrical injection PC vertical cavity and lateral cavity surface-emitting lasers,and PC high beam quality lasers,to show that the PC is vital for promoting the continuous improvement of semiconductor laser performance at present and in the future.

Low-Spatial Coherence High-Power Electrically Injected 6xx nm Dual-Emitter Laser

Laser-based displays have attracted much attention owing to large-size screen and full-color gamut compared with other displays such as liquid crystal display and light emitting diode. However, there exists a phenomenon, speckle, limits the applications of laser display because of the high coherence of laser. In this work, we developed an electrically injected 6xx nm dual-emitter laser which combines the low-spatial coherence with the high-power. The output power of the dual-emitter laser exceeds 500 mW under 20?C pulse operation. The single emitter consists of D-shaped section used to obtain more independent spatial modes thus reduces coherence and a stripe area to obtain the high power. The radius of the D-shaped cavity is 500 μm and the length of stripe is 1000 μm. We used the standard photolithography and inductively coupled plasma (ICP) process to fabricate the device. The speckle contrast was measured to be 5%. It exhibits a great potential of reducing speckle from the source directly for laser display.

Silicon cross-coupled gated tunneling diodes

Tunneling-based static random-access memory(SRAM)devices have been developed to fulfill the demands of high density and low power,and the performance of SRAMs has also been greatly promoted.However,for a long time,there has not been a silicon based tunneling device with both high peak valley current ratio(PVCR)and practicality,which remains a gap to be filled.Based on the existing work,the current manuscript proposed the concept of a new silicon-based tunneling device,i.e.,the silicon crosscoupled gated tunneling diode(Si XTD),which is quite simple in structure and almost completely compatible with mainstream technology.With technology computer aided design(TCAD)simulations,it has been validated that this type of device not only exhibits significant negative-differential-resistance(NDR)behavior with PVCRs up to 10^(6),but also possesses reasonable process margins.Moreover,SPICE simulation showed the great potential of such devices to achieve ultralow-power tunneling-based SRAMs with standby power down to 10^(−12)W.

Detector-integrated vertical-cavity surfaceemitting laser with a movable high-contrast grating mirror

In this paper, we present a detector-integrated vertical-cavity surface-emitting laser(VCSEL) with a movable high-contrast grating(HCG) mirror in an n-i-p-i-n manner. The detector-integrated VCSEL with a movable HCG can achieve three functions, including wavelength tuning, power monitoring, and resonant-cavity-enhanced(RCE)photon detection. Currently, the device can achieve a wavelength tuning range of 27 nm at room temperature when the suspended HCG is driven by the reverse-bias voltage. The n-i-p structure located at the upper part of the device can serve as an intra-cavity photodiode to monitor the output power due to the defect absorption. The RCE photon detection function of the detector-integrated VCSEL with a movable HCG is measured, and it has a peak responsivity at about 926 nm. This detector-integrated VCSEL with a movable HCG will be useful for sensing and imaging.

Observation of maximal intrinsic chirality empowered by dual quasi-bound states in the continuum in a planar metasurface

Metasurfaces with spin-selective transmission play an increasingly critical role in realizing optical chiral responses,especially for strong intrinsic chirality,which is limited to complex three-dimensional geometry.In this paper,we propose a planar metasurface capable of generating maximal intrinsic chirality and achieving dual-band spinselective transmission utilizing dual quasi-bound states in the continuum(quasi-BICs)caused by the structural symmetry breaking.Interestingly,the value of circular dichroism(CD)and the transmittance of two kinds of circular polarization states can be arbitrarily controlled by tuning the asymmetry parameter.Remarkable CD approaching unity with the maximum transmittance up to 0.95 is experimentally achieved in the dual band.Furthermore,assisted by chiral BICs,the application in polarization multiplexed near-field image display is also exhibited.Our work provides a new avenue to flexibly control intrinsic chirality in planar structure and offers an alternative strategy to develop chiral sensing,multiband spin-selective transmission,and high-performance circularly polarized wave detection.The basic principle and design method of our experiments in the microwave regime can be extended to other bands,such as the terahertz and infrared wavelengths.

Steerable merging bound states in the continuum on a quasi-flatband of photonic crystal slabs without breaking symmetry

Optical resonators with high quality(Q)factors are paramount for the enhancement of light–matter interactions in engineered photonic structures,but their performance always suffers from the scattering loss caused by fabrication imperfections.Merging bound states in the continuum(BICs)provide us with a nontrivial physical mechanism to overcome this challenge,as they can significantly improve the Q factors of quasi-BICs.However,most of the reported merging BICs are found atΓpoint(the center of the Brillouin zone),which intensively limits many potential applications based on angular selectivity.To date,studies on manipulating merging BICs at off-Γpoint are always accompanied by the breaking of structural symmetry that inevitably increases process difficulty and structural defects to a certain extent.Here,we propose a scheme to construct merging BICs at almost an arbitrary point in momentum space without breaking symmetry.Enabled by the topological features of BICs,we merge four accidental BICs with one symmetry-protected BIC at theΓpoint and merge two accidental BICs with opposite topological charges at the off-Γpoint only by changing the periodic constant of a photonic crystal slab.Furthermore,the position of off-Γmerging BICs can be flexibly tuned by the periodic constant and height of the structure simultaneously.Interestingly,it is observed that the movement of BICs occurs in a quasi-flatband with ultra-narrow bandwidth.Therefore,merging BICs in a tiny band provide a mechanism to realize more robust ultrahigh-Q resonances that further improve the optical performance,which is limited by wide-angle illuminations.Finally,as an example of application,effective angle-insensitive second-harmonic generation assisted by different quasi-BICs is numerically demonstrated.Our findings demonstrate momentum-steerable merging BICs in a quasi-flatband,which may expand the application of BICs to the enhancement of frequency-sensitive light–matter interaction with angular selectivity.

Improvement on the topological localized interface enabled by chiral symmetry

Zero-energy topological states,which are protected by chiral symmetry against certain perturbations topologically,localize at interfaces between trivial and non-trivial phases in the Su–Schrieffer–Heeger(SSH)chain model.Here,we propose and demonstrate a method to manipulate chiral symmetry itself to improve the localized interfaces and enlarge the mode volume of topological states in the SSH model,thus optimizing the lasing performance of localized interfaces.As multiple defects corresponding to off-diagonal perturbations in an eigenmatrix are introduced,the topological state expands and extends to extra defects at the topological interface without breaking chiral symmetry.We apply the proposed method in electrical pumping semiconductor laser arrays to verify our theoretical prediction and optimize the output characteristics of the devices.The measured results of the proposed multi-defect SSH laser array show that the output power has been increased by 27%,and the series resistance and far-field divergence have been reduced by half compared to the traditional SSH laser array,establishing a high-performance light source for integrated silicon photonics,infrared light detection and ranging,and so on.Our work demonstrates that the proposed method is capable of improving topological localized interfaces and redistributing zero-energy topological states.Furthermore,our method can be applied to other platforms and inspire optimizations of more devices in broader areas.

Perfect light absorber with a PT phase transition via coupled topological interface states

Recently,the concepts of parity–time(PT)symmetry and band topology have inspired many novel ideas for light manipulation in their respective directions.Here we propose and demonstrate a perfect light absorber with a PT phase transition via coupled topological interface states(TISs),which combines the two concepts in a onedimensional photonic crystal heterostructure.By fine tuning the coupling between TISs,the PT phase transition is revealed by the evolution of absorption spectra in both ideal and non-ideal PT symmetry cases.Especially,in the ideal case,a perfect light absorber at an exceptional point with unidirectional invisibility is numerically obtained.In the non-ideal case,a perfect light absorber in a broken phase is experimentally realized,which verifies the possibility of tailoring non-Hermiticity by engineering the coupling.Our work paves the way for novel effects and functional devices from the exceptional point of coupled TISs,such as a unidirectional light absorber and exceptional-point sensor.

Demonstration of electrically injected vertical-cavity surface-emitting lasers with post-supported high-contrast gratings

We experimentally demonstrate for the first time to our knowledge electrically injected vertical-cavity surfaceemitting lasers(VCSELs) with post-supported high-contrast gratings(HCGs) at 940 nm. The HCG-VCSELs have two posts to support the air-suspended HCGs, which are realized by simple fabrication without critical point drying. The HCG-VCSEL achieves a threshold current of about 0.65 m A and a side-mode suppression ratio of 43.6 d B under continuous-wave operation at 25℃. Theoretically the HCG-VCSEL with a λ∕2-cavity for the transverse magnetic polarization has a smaller effective mode length of 1.38 ·(λ∕n). Thus, the relaxation resonance frequency can be increased by 16% compared with that of the conventional VCSEL. The modulation speed of 100 Gbit/s for the HCG-VCSEL is expected in the on–off keying modulation format. Our easy design of HCGVCSELs has great potential for applications in optical interconnects, sensing, illumination, and so on.

Narrow vertical beam divergence angle for display applications of 645 nm lasers

We design a 645 nm laser diode(LD)with a narrow vertical beam divergence angle based on the mode expansion layer.The vertical beam divergence of 10.94°at full width at half-maximum is realized under 1.5 A continuous-wave operation,which is the smallest vertical beam divergence for such an LD based on the mode expansion layer,to the best of our knowledge.The threshold current and output power are 1.07 A and 0.94 W,limited by the thermal rollover for the 100μm wide and 1500μm long broad area laser,and the slope efficiency is 0.71 W/A.The low coherence device is fabricated with the speckle contrast of 3.6%and good directional emission.Such 645 nm LDs have promising applications in laser display.

High efficiency of spectral beam combining by using large optical cavity lasers

We studied the spectral beam combining[SBC]of a large optical cavity[LOC]laser array to achieve high-power and highbrightness laser output.We discussed the characteristics of the external cavity feedback efficiency and the focal length of the transform lens for lasers with different waveguide thicknesses.We have found that using LOC laser diodes can increase the proportion of external cavity feedback,thereby improving the SBC efficiency.At a current of 90 A,the CW output power of the SBC system is 59.2 W,and the SBC efficiency reaches up to 102.8%.All emitters of the laser array have achieved spectral locking with a spectral width of 11.67 nm,and the beam parameter product is 4.38 mm·mrad.

Design of the low-loss waveguide coil for interferometric integrated optic gyroscopes

With the development of manufacturing technology,the propagation loss of the planar waveguide is getting lower and lower,and the shot-noise-limited sensitivity of an HOG will be greatly improved.When the propagation loss is getting lower,improper coupling-out waveguide in the waveguide coil may lead to non-ignorable bending loss and crosstalk because of the small radius of curvature and X-junction.In this paper,different couplingout waveguides have been designed.After calculation and optimization by the beam propagation method,we found the proper coupling-out waveguide having relatively low propagation loss,which can improve the sensitivity of the HOG.

High peak power density and low mechanical stress photonic-band-crystal diode laser array based on non-soldered packaging technology

A high peak power density and low mechanical stress photonic-band-crystal(PBC)diode laser array based on non-soldered packaging technology is demonstrated.The array consists of the PBC diode laser bars with small fast axis divergence angles.Meanwhile,we design the non-soldered array structure that realizes mechanical stacking of 10 bars in the vertical direction.In the experiment,the peak power density of the PBC array is about 1.75 times that of the conventional array when the same total power is obtained.The peak power of the non-soldered array is 292.2 W,and the“smile”effect is improved by adjusting the mechanical fixing force of the array.