Ultra-broadband on-chip twisted light emitter for optical communications

On-chip twisted light emitters are essential components of orbital angular momentum(OAM)communication devices1,2.These devices address the growing demand for high-capacity communication systems by providing an additional degree of freedom for wavelength/frequency division multiplexing(WDM/FDM).Although whispering-gallery-mode-enabled OAM emitters have been shown to possess some advantages3–5,such as compactness and phase accuracy,their inherent narrow bandwidths prevent them from being compatible with WDM/FDM techniques.Here,we demonstrate an ultra-broadband multiplexed OAM emitter that utilizes a novel joint path-resonance phase control concept.The emitter has a micron-sized radius and nanometer-sized features.Coaxial OAM beams are emitted across the entire telecommunication band from 1,450 to 1,650 nm.We applied the emitter to an OAM communication with a data rate of 1.2 Tbit/s assisted by 30-channel optical frequency combs(OFCs).The emitter provides a new solution to further increase capacity in the OFC communication scenario.

Bias-drift-free Mach–Zehnder modulators based on a heterogeneous silicon and lithium niobate platform

Optical modulators have been and will continue to be essential devices for energy-and cost-efficient optical communication networks.Heterogeneous silicon and lithium niobate modulators have demonstrated promising performances of low optical loss,low drive voltage,and large modulation bandwidth.However,DC bias drift is a major drawback of optical modulators using lithium niobate as the active electro-optic material.Here,we demonstrate high-speed and bias-drift-free Mach–Zehnder modulators based on the heterogeneous silicon and lithium niobate platform.The devices combine stable thermo-optic DC biases in silicon and ultra-fast electro-optic modulation in lithium niobate,and exhibit a low insertion loss of 1.8 d B,a low half-wave voltage of 3 V,an electro-optic modulation bandwidth of at least 70 GHz,and modulation data rates up to 128 Gb/s.

Progress in integrating Ⅲ–Ⅴ semiconductors on silicon could drive silicon photonics forward

Why integratingⅢ–Ⅴsemiconductor on silicon Photonics is an enabling technology and play a significant role in today’s information age.In the last few decades,starting from the fiber long haul optical communications,optical interconnects have gradually replaced copper interconnects due to its advantage of the bandwidth distance product.As photonics is moving closer and closer to the processor and memory of computers,and eventually,to on-chip level,silicon photonics becomes a viable solution for future optical interconnections due to the feasibility of high-bandwidth,high-density I/O capability and dense integration enabled by the high index contrast.

Laplace metasurfaces for optical analog computing based on quasi-bound states in the continuum

Laplace operation,the isotropic second-order differentiation,on spatial functions is an essential mathematical calculation in most physical equations and signal processing.Realizing the Laplace operation in a manner of optical analog computing has recently attracted attention,but a compact device with a high spatial resolution is still elusive.Here,we introduce a Laplace metasurface that can perform the Laplace operation for incident lightfield patterns.By exciting the quasi-bound state in the continuum,an optical transfer function for nearly perfect isotropic second-order differentiation has been obtained with a spatial resolution of wavelength scale.Such a Laplace metasurface has been numerically validated with both 1D and 2D spatial functions,and the results agree well with that of the ideal Laplace operation.In addition,the edge detection of a concerned object in an image has been demonstrated with the Laplace metasurface.Our results pave the way to the applications of metasurfaces in optical analog computing and image processing.

Integrated thin film lithium niobate Fabry–Perot modulator[Invited]

Integrated traveling-wave lithium niobate modulators need relatively large device lengths to achieve low drive voltage. To increase modulation efficiency within a compact footprint, we report an integrated Fabry–Perot-type electro-optic thin film lithium niobate on insulator modulator comprising a phase modulation region sandwiched between two distributed Bragg reflectors. The device exhibits low optical loss and a high tuning efficiency of 15.7 pm/V. We also confirm the modulator's high-speed modulation performance by non-return-to-zero modulation with a data rate up to 56 Gbit/s.

Vector mode based optical direct detection orthogonal frequency division multiplexing transmission in short-reach optical link

As one solution to implement the largecapacity space division multiplexing(SDM)transmission systems,the mode division multiplexing(MDM)has gained much attention recently.The vector mode(VM),which is the eigenmode of the optical fiber,has also been adopted to realize the optical communications including the transmission over free-space optical(FSO)and optical fiber links.Considering the concerns on the short-reach optical interconnects,the low cost and high integration technologies should be developed.Direct detection(DD)with higher-order modulation formats in combination of MDM technologies could offer an available trade-off in system performance and complexity.We review demonstrations of FSO and fiber high-speed data transmission based on the VM MDM(VMDM)technologies.The special VMs,cylindrical vector beams(CVB),have been generated by the q-plate(QP)and characterized accordingly.And then they were used to implement the VMDM transmission with direct-detection orthogonal frequency division multiplexing(DD-OFDM).These demonstrations show the potential of VMDM-DD-OFDM technology in the large-capacity short-reach transmission links.

High-speed Stokes vector receiver enabled by a spin-dependent optical grating

Stokes vector direct detection is a promising,cost-effective technology for short-distance communication applications.Here,we design and fabricate a spin-dependent liquid crystal grating to detect light polarization states.By separating the circular and linear components of incident light,the polarization states can be resolved with accuracy of up to 0.25°.We achieved Stokes vector direct detection of quadrature phase-shift keying(QPSK),8 PSK,and16-ary quadrature amplitude modulation signals with 32,16,and 16 GBd rates,respectively.We integrated the system,including the grating,photodetectors,and optical elements,on a miniaturized printed circuit board and demonstrated high-speed optical communications with 16 GBd rate QPSK signals.

Locally periodically poled LNOI ridge waveguide for second harmonic generation [Invited]

Periodically poled lithium niobate on insulator(LNOI) ridge waveguides are desirable for high-efficiency nonlinear frequency conversions, and the fabrication process of such waveguides is crucial for device performance. In this work, we report fabrication and characterization of locally periodically poled ridge waveguides. Ridge waveguides were fabricated by dry etching, and then the high-voltage pulses were applied to locally poled ridge waveguides. Second harmonic generation with normalized conversion efficiency of 435.5% W^(-1)·cm^(-2) was obtained in the periodically poled LNOI ridge waveguide,which was consistent with the triangular domain structure revealed by confocal microscopy.