A new type of power-exponent-phase vortex-like beams with both quadratic and cubic azimuthal phase gradients is investigated in this work. The intensity and orbital angular momentum (OAM) density distributions are noticeably different when the phase gradient increases or decreases along the azimuth angle, while the orthogonality and total OAM remain constant. The characteristics of the optical field undergo a significant change when the phase shifts from linear to nonlinear, with the variation of the power index having little impact on the beam characteristics under nonlinear phase conditions. These characteristics provide new ideas for applications such as particle manipulation, optical communications, and OAM encryption.optical vortex orbital angular momentum optical spiral azimuthally varying phase gradient
Chinese Optics Letters
2023, 21(11): 112601
2023, 50(18): 1813015
The article comments on an important step towards understanding the nondiffractive nature of optical vortex polarization features and investigating the intrinsic nature of spin-orbital interaction.
2023, 5(3): 030503
Space-division multiplexing based on few-mode multi-core fiber (FM-MCF) technology is expected to break the Shannon limit of a single-mode fiber. However, an FM-MCF is compact, and it is difficult to couple the beam to each fiber core. 3D waveguide devices have the advantages of low insertion loss and low cross talk in separating various spatial paths of multi-core fibers. Designing a 3D waveguide device for an FM-MCF requires considering not only higher-order modes transmission, but also waveguide bending. We propose and demonstrate a 3D waveguide device fabricated by femtosecond laser direct writing for various spatial path separations in an FM-MCF. The 3D waveguide device couples the LP01 and LP11a modes to the FM-MCF with an insertion loss below 3 dB and cross talk between waveguides below . To test the performance of the 3D waveguide device, we demonstrate four-channel multiplexing communication with two LP modes and two cores in a 1-km few-mode seven-core fiber. The bit error rate curves show that the different degrees of bending of the waveguides result in a difference of approximately 1 dB in the power penalty. Femtosecond laser direct writing fabrication enables 3D waveguide devices to support high-order LP modes transmission and further improves FM-MCF communication.
2022, 10(12): 2677
Multiplexing and demultiplexing of optical orbital angular momentum (OAM) are critical operations in mode-division multiplexing communications. Traditional Dammann gratings, spiral phase planes, and optical geometric transformations are regarded as convenient methods for OAM mode (de)multiplexing. However, crosstalk between the different modes and the difficulty of mode multiplexing greatly limit their application to mode-division multiplexing communications. Here, using a set of inversely-designed phase planes, we demonstrate an OAM (de)multiplexer based on multiphase plane light conversion that can enable perfect OAM multiplexing communication. The sorted patterns are Gaussian-like and can be coupled easily into single-mode fiber arrays. Inputs from the fiber array are turned into coaxial OAM modes after the phase planes. OAM mode crosstalk generated by the multiplexer is less than , with insertion loss of less than 2.6 dB. OAM modes are sorted by the demultiplexer with mode crosstalk below , and the sorting results are coupled to the fiber array. OAM modes carrying 10 Gbit/s on–off keying signals were transmitted in a 5 km few-mode fiber. The measured bit-error-rate curves have power penalties of less than 10 dB. The proposed configuration is highly efficient and convenient and will be beneficial for potential applications in quantum information, information processing, and optical communications.
2022, 10(9): 2015
We introduce a simple one-dimensional (1D) structure in the design of 1D color splitters (1D-CSs) with RGB unit cells for color imaging and propose a single-to-double-layer design in 1D-CSs. Based on inverse design metasurfaces, we demonstrate numerically a single-layer 1D-CS with a full-color efficiency of 46.2% and a double-layer 1D-CS with a full-color efficiency of 48.2%; both of them are significantly higher than that of traditional color filters. Moreover, we demonstrate a 1D-CS that has application value by evaluating the double-layer 1D-CS’s performances in terms of incident angle sensitivity, polarization angle sensitivity, and assembly tolerance.color splitter color imaging inverse design metasurfaces
Chinese Optics Letters
2022, 20(7): 073601
Optical skyrmions, quasiparticles that are characterized by the topologically nontrivial vectorial textures of optical parameters such as the electromagnetic field, Stokes parameters, and spin angular momentum, have aroused great attention recently. New dimensions for optical information processing, transfer, and storage have become possible, and developing multiple schemes for manipulating the topological states of skyrmions, thus, is urgent. Here we propose an approach toward achieving dynamic modulation of skyrmions via changing the field symmetry and adding chirality. We demonstrate that field symmetry governs the skyrmionic transformation between skyrmions and merons, whereas material chirality modulates the twist degree of fields and spins and takes control of the Néel-type–Bloch-type skyrmionic transition. Remarkably, the enantioselective twist of skyrmions and merons results from the longitudinal spin arising from the chirality-induced splitting of the hyperboloid in the momentum space. Our investigation, therefore, acts to enrich the portfolio of optical quasiparticles. The chiral route to topological state transitions will deepen our understanding of light–matter interaction and pave the way for chiral sensing, optical tweezers, and topological phase transitions in quantum matter.
2022, 10(4): 04000947
Characterizing the amplitude, phase profile, and polarization of optical beams is critical in modern optics. With a series of cascaded optical components, one can accurately resolve the optical singularity and polarization state in traditional polarimetry systems. However, complicated optical setups and bulky configurations inevitably hinder future applications for integration. Here, we demonstrate a metadevice that fully resolves arbitrary beams on a higher-order Poincaré sphere (HOPS) via a single-layer all-silicon metasurface. The device is compact and capable of detecting optical singularities and higher-order Stokes parameters simultaneously through a single intensity measurement. To verify the validity of the proposed metadevice, different beams on and are illuminated on the metadevices. The beams are fully resolved, and the reconstructed higher-order Stokes parameters show good agreement with the original ones. Taking the signal-to-noise ratio into account, the numerical simulations indicate that the design strategy can be extended to fully resolve arbitrary beams on HOPS with order up to 4. Because of the advantages of compact configuration and compatibility with current semiconductor technology, the metadevice will facilitate potential applications in information processing and optical communications.
2021, 9(3): 03000331
Metasurfaces have found broad applicability in free-space optics, while its potential to tailor guided waves remains barely explored. By synergizing the Jones matrix model with generalized Snell’s law under the phase-matching condition, we propose a universal design strategy for versatile on-chip mode-selective coupling with polarization sensitivity, multiple working wavelengths, and high efficiency concurrently. The coupling direction, operation frequency, and excited mode type can be designed at will for arbitrary incident polarizations, outperforming previous technology that only works for specific polarizations and lacks versatile mode controllability. Here, using silicon-nanoantenna-patterned silicon-nitride photonic waveguides, we numerically demonstrate a set of chip-scale optical couplers around 1.55 μm, including mode-selective directional couplers with high coupling efficiency over 57% and directivity about 23 dB. Polarization and wavelength demultiplexer scenarios are also proposed with 67% maximum efficiency and an extinction ratio of 20 dB. Moreover, a chip-integrated twisted light generator, coupling free-space linear polarization into an optical vortex carrying orbital angular momentum (OAM), is also reported to validate the mode-control flexibility. This comprehensive method may motivate compact wavelength/polarization (de)multiplexers, multifunctional mode converters, on-chip OAM generators for photonic integrated circuits, and high-speed optical telecommunications.
2020, 8(4): 04000564
The photonic spin Hall effect plays an important role in photonic information technologies, especially in on-chip spin Hall devices. However, conventional devices suffer from low efficiency or narrow bandwidth, which prevents their practical application. Here, we introduce a spin Hall device using inverse design to achieve both high efficiency and broadband. Spin-dependent light separation is enabled by a 2.4 μm circular device with 100 nm pixels. The photonic spin Hall element is fabricated on a silicon-on-insulator wafer compatible with a standard integrated photonic circuit. The spin light is detected and emitted with an efficiency of up to 22% and 35%, respectively, over a 200 nm bandwidth at optical wavelength.
2020, 8(2): 02000121