Shimao Li

Orbital Angular Momentum Divider of Light

Manipulation of orbital angular momentum (OAM) of light is essential in OAM-based optical systems. In particular, the OAM divider, which can convert the incoming OAM mode into one or several new smaller modes in proportion at different spatial paths, is very useful in OAM-based optical networks. However, this useful tool has rarely been reported. Here, we put forward a passive OAM divider based on coordinate transformation. The device consists of a Cartesian to log-polar coordinate converter and an inverse converter. The first converter converts the OAM light into a rectangular-shaped plane light with a transverse phase gradient, and the second converter converts the plane light into multiple diffracted light. The OAM of zeroth-order diffracted light is the product of the input OAM and the scaling parameter. The residual light is the output from other diffracted orders. Furthermore, we extend the scheme to realize equal N-division of OAM and arbitrary division of OAM. The ability of dividing OAM shows huge potential for OAM-based classical and quantum information processing.

Generation of photonic orbital angular momentum superposition states using vortex beam emitters with superimposed gratings

An integrated approach to produce orbital angular momentum (OAM) superposition states has been demonstrated. Superposition states between two vector OAM modes have been achieved by integrating a superimposed angular grating in one silicon micro-ring resonator.

Anatomical versus non-anatomical liver resection for hepatocellular carcinoma exceeding Milan criteria.

Liver resection is effective for hepatocellular carcinoma (HCC) exceeding the Milan criteria in selected patients. However, the benefit of anatomical resection (AR) versus non‐anatomical resection (NAR) has not been clarified in this patient subgroup. This study aimed to compare outcomes between AR and NAR for HCC exceeding the Milan criteria.

Direct fiber vector eigenmode multiplexing transmission seeded by integrated optical vortex emitters

Spatial modes have received substantial attention over the last decades and are used in optical communication applications. In fiber-optic communications, the employed linearly polarized modes and phase vortex modes carrying orbital angular momentum can be synthesized by fiber vector eigenmodes. To improve the transmission capacity and miniaturize the communication system, straightforward fiber vector eigenmode multiplexing and generation of fiber-eigenmode-like polarization vortices (vector vortex modes) using photonic integrated devices are of substantial interest. Here, we propose and demonstrate direct fiber vector eigenmode multiplexing transmission seeded by integrated optical vortex emitters. By exploiting vector vortex modes (radially and azimuthally polarized beams) generated from silicon microring resonators etched with angular gratings, we report data-carrying fiber vector eigenmode multiplexing transmission through a 2-km large-core fiber, showing low-level mode crosstalk and favorable link performance. These demonstrations may open up added capacity scaling opportunities by directly accessing multiple vector eigenmodes in the fiber and provide compact solutions to replace bulky diffractive optical elements for generating various optical vector beams.

Performance evaluation of analog signal transmission in an integrated optical vortex emitter to 3.6-km few-mode fiber system.

We experimentally demonstrate and evaluate the performance of an analog signal transmission system with photonic integrated optical vortex emitter and 3.6-km few-mode fiber (FMF) link using orbital angular momentum (OAM) modes. The fabricated photonic integrated device is capable of emitting vector optical vortices carrying well-defined and quantized OAM modes with topological charge l=-2 and 2. After propagating through 3.6-km FMF, we measure and assess the spurious free dynamic range of the second-order harmonic distortion. Moreover, we study the impact of nonlinearity-induced resonance wavelength shift of the optical vortex emitter on the analog link performance as increasing the input optical power.

Compact tunable electromagnetically induced transparency and Fano resonance on silicon platform

We propose and demonstrate an on-chip coupling resonant system to generate electromagnetically induced transparency (EIT)-like effect and Fano resonance on silicon platform. It is composed of a microring resonator (MRR) and two cascaded Sagnac-loop mirrors (SLMs) assisted Fabry-Perot (FP) cavity on silicon-on-insulator. According to the coupling conditions of the MRR, two cases are studied theoretically. When the MRR is over coupling, EIT-like transmission can be observed. In contrast, Fano resonances can be generated by the condition of under coupling. In the experiment, the add-drop MRR is under coupling, leading to a sharp asymmetric line shape for Fano resonance. The resonance wavelength of the MRR can be dynamically tuned based on thermal-optic effects by tuning the micro-heater. The experiment results show Fano resonances with maximum extinction ratio (ER) of 23.22 dB and maximum slope rate (SR) of 252 dB/nm. Moreover, the wavelength of Fano resonance can be shifted widely with a tuning efficiency of 0.2335 nm/mW.

Integrated optical vortex beam receivers

A simple and ultra-compact integrated optical vortex beam receiver device is presented. The device is based on the coupling between the optical vortex modes and whispering gallery modes in a micro-ring resonator via embedded angular gratings, which provides the selective reception of optical vortex modes with definitive total angular momentum (summation of spin and orbital angular momentum) through the phase matching condition in the coupling process. Experimental characterization confirms the correct detection of the total angular momentum carried by the vortex beams incident on the device. In addition, photonic spin-controlled unidirectional excitation of whispering-gallery modes in the ring receiver is also observed, and utilized to differentiate between left- and right-circular polarizations and therefore unambiguously identify the orbital angular momentum of incident light. Such characteristics provide an effective mode-selective receiver for the eigen-modes in orbital angular momentum fiber transmission where the circularly polarized OAM modes can be used as data communications channels in multiplexed communications or as photonic states in quantum information applications.

Orbital angular momentum modes emission from a silicon photonic integrated device for km-scale data-carrying fiber transmission

We experimentally demonstrate orbital angular momentum (OAM) modes emission from a high emission efficiency OAM emitter for 20-Gbit/s quadrature phase-shift keying (QPSK) carrying data transmission in few-mode fiber (FMF). The device is capable of emitting vector optical vortices carrying well-defined OAM efficiently with the efficiency of the device >37%. Seven modes propagate through a 2-km two-mode and a 3.6-km three-mode FMF with measured optical signal-to-noise ratio (OSNR) penalties less than 4 dB at a bit-error rate (BER) of 2 × 10-3. The demonstrations with favorable performance pave the way to incorporate silicon photonic integrated devices as transceivers in an OAM-enabled optical fiber communication link.

High-directional vortex beam emitter based on Archimedean spiral adiabatic waveguides

We demonstrate a highly directional integrated silicon photonic vortex beam emitter based on an Archimedean spiral adiabatic waveguide with angular grating. Various order orbital angular momentum modes can be selectively generated by the emitter at different wavelength and the side-mode superposition ratio is as large as 13.6 dB.

Measuring the Orbital Angular Momentum State of Light by Coordinate Transformation

We present a method to measure the orbital angular momentum (OAM) state of light by coordinate transformation. The input OAM mode with annular shape is uniaxially compressed into a linear-shaped light, so that the upper and lower portions of OAM mode overlap to produce an interference pattern, showing easily recognizable fringes both in the near field and far field. The far-field measurement is more suitable for detecting large OAM but with the cost of additional diffractive element. The incident light can illuminate any position of the device, showing good tolerance to adjust the optical path. In a practical application, the proposed scheme can be realized only by one or two elliptical lenses, which provides a convenient and economic method for measurement of OAM state.