Guoxuan Zhu

Scalable mode division multiplexed transmission over a 10-km ring-core fiber using high-order orbital angular momentum modes

We propose and demonstrate a scalable mode division multiplexing scheme based on orbital angular momentum modes in ring core fibers. In this scheme, the high-order mode groups of a ring core fiber are sufficiently de-coupled by the large differential effective refractive index so that multiple-input multiple-output (MIMO) equalization is only used for crosstalk equalization within each mode group. We design and fabricate a graded-index ring core fiber that supports 5 mode groups with low inter-mode-group coupling, small intra-mode-group differential group delay, and small group velocity dispersion slope over the C-band for the high-order mode groups. We implement a two-dimensional wavelength- and mode-division multiplexed transmission experiment involving 10 wavelengths and 2 mode groups each with 4 OAM modes, transmitting 32 GBaud Nyquist QPSK signals over all 80 channels. An aggregate capacity of 5.12 Tb/s and an overall spectral efficiency of 9 bit/s/Hz over 10 km are realized, only using modular 4x4 MIMO processing with 15 taps to recover signals from the intra-mode-group mode coupling. Given the fixed number of modes in each mode group and the low inter-mode-group coupling in ring core fibres, our scheme strikes a balance in the trade-off between system capacity and digital signal processing complexity, and therefore has good potential for capacity upscaling at an expense of only modularly increasing the number of mode-groups with fixed-size (4x4) MIMO blocks.

Characterizing a 14 × 14 OAM mode transfer matrix of a ring-core fiber based on quadrature phase-shift interference

The transfer matrix of light propagating in fibers can quantitatively elucidate the mechanisms of mode coupling, thus having important implications for the knowledge such as the mode division multiplexing communication link characteristics in fibers. However, most methods for measuring the transfer matrix require a prior knowledge of the launched modes at the input and a complex optical system for the characterization at the output of the fiber. In this Letter, we use an interferometric approach for decomposing orbital angular momentum (OAM) modes of the output beams from a ring-core fiber, thereby processing a 14×14 OAM mode transfer matrix of the fiber with merely a camera imaging the mode field at the output of the fiber. The suitability of such a method is validated by the beam reconstruction. Thus, this method is crucial for characterizing the fiber transfer matrix with promising features of fast response and simple operation.

A graded index ring-core fiber supporting 22 OAM states

We present a graded index ring-core fiber for long-distance OAM mode transmission. Due to the graded index profile of the ring-shaped fiber core, the supported OAM modes are more pure and degenerate than those in the step-index ring-core fibers. A simple ring-core fiber design scheme is introduced. This scheme illustrates the relationship between the mode effective refractive indices and the designed ring-core structure parameters. 5 orders of OAM modes are excited in the fiber. The purity of OAM states after 1 km transmission is verified by spiral phase demodulation.

Orbital angular momentum assisted spin-directional coupling

Spin-directional coupling is associated with the quantum spin-Hall effect of photons, which has attracted much attention over the past few years. Here, we report orbital angular momentum (OAM) assisted spin-directional coupling and its reversal in a silicon nitride (SiNx) photonic integrated circuit. SiNx microring resonators with angular grating have been designed and realized to emit high purity circularly polarized OAM beam. In addition, utilized as an OAM receiver, photonic spin-controlled unidirectional excitation of whispering-gallery modes in ring resonator is also observed, coupling the left-hand and right-hand circularly polarized OAM beam to different channel waveguide, respectively. Our results exemplify a very promising waveguide-based OAM device such as a robust OAM assisted spin-directional coupler and may open up many new capabilities in emerging applications of on-chip chiral photonics and quantum optics.

Generation of Accelerating Light Beams Based on Integrated Photonic Approaches

Previous methods for the generation of accelerating beams are mostly based on bulky phase-only spatial light modulator. Here we propose an experimental scheme for the generation of accelerating beams by fabricating a quartz plate capable of realizing both phase and amplitude modulation. The phase modulation is implemented by aligned 16-level etching into the quartz plate, while the amplitude modulation is realized by controlling the duty ratio of the partial metal coverage locally. Based on this approach, a sinusoidal accelerating beam with multiple bending is generated for demonstration and propagates along a sinusoidal trajectory as expected.

Microstructured Optical Fibers for Transmitting Orbital Angular Momentum (OAM) Modes

We present the design of a microstructured fiber for optical communications with orbital angular momentum (OAM) modes, which can effectively avoid the excitation of linearly polarized (LP) modes with its unique air-core and air-coated structure.

A numerical study of UTC-PD structures with berylium as the p-dopant

We numerically investigate UTC PD structures that use highly diffusible beryllium (Be) as the p-type impurity in absorption layer An intrinsic InGaAs layer is added between the absorption layer and collection layer as a diffusion buffer. The influence of this buffer layer is analyzed, and the results obtain shows that high responsivity and high speed can be achieved.