Potential In Optical Communication Research Articles

High-crosstalk polarization filter based on double-D photonic crystal fiber with amethyst and gold

Polarization filters based on surface plasmon resonance (SPR) have undergone rapid development in recent years. In this work, a dual D-type PCF polarization filter based on SPR is designed and analyzed. The filter improves the limiting loss of the core mode by gilding the semi-circular split ring and inlaying amethyst. The influence of the structural parameters of the filter on the filtering characteristics is analyzed by the finite element method. The results show that the core mode losses of the x and y polarized light are 32[Formula: see text]dB/cm and 910.56[Formula: see text]dB/cm at 1.55[Formula: see text][Formula: see text]m, respectively. For a fiber length of 1000[Formula: see text][Formula: see text]m, the crosstalk and bandwidth are 763.11[Formula: see text]dB and 700[Formula: see text]nm, respectively. In addition, the impact of manufacturing errors in the structural parameters on the filter performance is discussed. The filter has excellent filtering characteristics and large potential in optical communication and optical sensing.

Ultra-sensitive all-optical phase modulation based on a fiber optic interferometer combined with Ti3C2Tx MXene-incorporated PDMS.

This study proposes an all-optical phase modulator based on a compact fiber optic interferometer combined with Ti3C2Tx MXene-incorporated PDMS. Due to the high photothermal conversion efficiency of MXene and the high thermo-optic coefficient of PDMS, changes in pump power can be effectively converted into refractive index (RI) variations in the PDMS. Then, by employing a fiber optic interferometer with a high RI response, ultra-sensitive all-optical phase modulation can be realized. The experimental results demonstrate that the resonant wavelength shift of the modulator with MXene-incorporated PDMS is 126 times higher than that of a modulator with single MXene deposition. Also, a maximum wavelength sensitivity of 14.57 nm/mW is achieved (equivalent to a phase sensitivity of 0.33π/mW); this excellent modulation performance is a great improvement on that of a previously reported fiber-based all-optical phase modulator. Furthermore, PDMS is also employed as a packaging layer to strengthen the device structure and restrict the heat in an enclosed space, which improves the heat utilization efficiency. The proposed device shows great potential in optical communication, optical filtering, sensing, and modulation applications.

Centralized Excited States and Fast Radiation Transitions Reduce Laser Threshold in Carbon Dots.

As a new type of solution-processed nano-laser material, carbon dots (CDs) have shown considerable potential in optical communication, laser displays, micro/nano processing, and biomedicine. Reducing the laser threshold of the gain material is of considerable significance for further development of CDs' applications in the field of micro/nano lasers. A series of blue-emissive CDs (B-CDs) are synthesized by changing the molar ratios of the precursors (citric acid (CA): L-Cysteine (L-Cys)). B-CDs have a structure of carbon nanoparticles with their surface being modified with 5-oxo-3,5-dihydro-2Hthiazolo [3,2-a]pyridine-7-carboxylic acid (TPCA). The laser can only be generated when the molar ratio of the precursors is between 1:1 and 2:1. With an increase in this ratio, the laser threshold decreases from 341.6 to 165.5 mJ cm-2 . The decrease in the laser threshold is attributed to the increase in the radiation transition rate and centralized sp3 -related excited state levels, which are favorable for light amplification and population inversion. These results will be instructional for the reasonably design of CDs-based laser materials and prompt their potential use in practical photonics.

The coupling of multi-channel optical vortices based on angular momentum conservation using a single-layer metal metasurface

Optical vortices (OVs) carry the orbital angular momentum with arbitrary topological charges, which has excellent potential in optical communication, photonic integrated circuits, optical trapping, and so on. However, generating arbitrary orders of adjustable optical vortices remains to be solved. Here, we propose a single-layer metal porous metasurface operating in infrared band for generating vortex beams from first to fourth order based on the spin-orbit interactions (SOI). The optical vortices with integral 2π phase are obtained through generating double geometric phase induced by structural element spin rotation. Furthermore, the new phenomenon of optical vortices emerging on the center has also been observed in our system, which is caused by the coupling of multi-channel same-order OVs. Our work possesses wide applications in optical communication, multiplex and demultiplex systems, optical capture devices, and communication coding.

Broadband, Polarization-Sensitive, and Self-Powered High-Performance Photodetection of Hetero-Integrated MoS2 on Lithium Niobate.

High-performance photodetectors hold promising potential in optical communication and imaging systems. However, conventional counterparts are suffering narrow detection range, high power consumption, and poor polarization sensitivity. Characteristics originating from switchable polarization in ferroelectrics can be used to optimize the photo-to-electric procedure and improve the photodetection performance. In this regard, we constructed a configuration by integrating 2-dimensional molybdenum disulfide (MoS2) with ferroelectric lithium niobate (LiNbO3), resulting in the MoS2/LiNbO3 heterostructured photodetector. Benefiting from the pyroelectric effect of LiNbO3, the limitation of bandgap on the detection range can be broken, thus broadening the response band of the detector to 365 to 1,064 nm, as well as enabling the self-powered characteristic. Meanwhile, high carrier mobility and decent light absorbance of MoS2 introduce robust light-matter interactions with the underlying LiNbO3, leading to ultrafast rise/fall times of ≈150 μs/250 μs and switching ratios of up to ≈190. Moreover, the highest responsivity, specific detectivity, and external quantum efficiency achieved were 17.3 A·W-1, 4.3 × 1011 Jones, and 4,645.78%, respectively. Furthermore, because of the anisotropy of the spontaneous-polarized LiNbO3 substrate, the photocurrent of the device achieved a dichroic ratio of 7.42, comparing favorably to most MoS2-based photodetectors. This work demonstrates the integration potential between ferroelectric LiNbO3 and 2-dimensional materials for high-performance photodetection.

Theoretical solution of second-harmonic generation in periodically poled lithium niobate and chirped periodically poled lithium niobate thin film via quasi-phase-matching

We present an effective nonlinear coupled mode coefficient model to evaluate and analyze the second harmonic generation (SHG) process under the quasi-phase-matching (QPM) scheme in periodically poled lithium niobate (PPLN) thin film. The theoretical model derives directly from the nonlinear coupled mode equations and simplifies the QPM process in PPLN thin film. The simulated results agree excellently with the rigorous numerical calculations in a variety of situations. We also propose using the chirped PPLN (CPPLN) thin film to achieve the SHG of ultrashort laser pulse and develop a broadband nonlinear coupled mode theory to evaluate this complex nonlinear coupling interaction process. All the frequency components in fundamental wave (FW) and second harmonic wave (SHW) have been considered in the theory, and the spectral evolution of FW and SHW can be obtained by solving a series of nonlinear coupled mode equations. CPPLN thin film supports broadband up-conversion in telecommunications bands and can generate broadband entangled photons in infrared region, which shows great potential in optical communication and quantum optics. The developed theories provide an efficient tool to design and optimize the PPLN and CPPLN thin film for various applications based on nonlinear frequency conversion and help to achieve high-efficiency on-chip SHG of the ultrashort laser pulse.

Dual-core photonic crystal fiber polarization beam splitter filled with salt water

A dual-core photonic crystal fiber polarization beam splitter filled with salt water in the central ellipse is designed and optimized by the full-vector finite element method. For a polarization beam splitter length of 31.1245 μm, the orthogonally polarized light with a bandwidth of 180 nm around 1.55 μm can be separated effectively and the extinction ratio (ER) is 139.88 dB. The photonic crystal fiber polarization beam splitter offers advantages such as the short length, high ER, and broadband characteristics and have large potential in optical communication.

Circular anti-resonance fibre supporting orbital angular momentum modes with flat dispersion, high purity and low confinement loss

A novel ring anti-resonance fibre (ARF) is designed and demonstrated for the transmission of orbital angular momentum (OAM) modes. The fibre consists of two layers of negative curvature tubes arranged orderly inside and outside the ring region and OAM modes can be transmitted in the ring region. The properties of the fibre are investigated by the finite element method based on the COMSOL multiphysics software and a manufacturing method is proposed. The fibre shows stable transmission of 30 OAMs in the 1.5–1.6 μm band, low and flat dispersion (5.98 ps/(km nm)), extremely small nonlinear coefficient (0.539 km−1 W−1 at 1.55 μm) and confinement loss (10−9–10−11 dB/m), as well as high OAM purity (larger than 98.295%). Therefore, the structure has immense potential in optical communication.

3D nanoprinted kinoform spiral zone plates on fiber facets for high-efficiency focused vortex beam generation.

In this paper, we propose and demonstrate an all-fiber high-efficiency focused vortex beam generator. The generator is fabricated by integrating a kinoform spiral zone plate (KSZP) on the top of the composite fiber structure using fs-laser two-photon polymerization 3D nanoprinting. The KSZP with spiral continuous-surface relief feature is designed by superimposing a spiral phase into a kinoform lens, which can efficiently concentrate and transform an all incident beam to a single-focus vortex beam, without the undesired zero-order diffracted light and extra high-order focus. Under arbitrary polarized light incident conditions, experiment results show that the focusing efficiency and vortex purity of the all-fiber generators are over 60% and 86%, respectively, which is much higher than that of a traditional binary SZP integrated on an optical fiber facet. In addition, characteristics of the generated vortex beam, such as focal spot, focal length and vortex topological charge are numerically designed and experimentally investigated. The experimental results agree well with the numerical simulation model using the FDTD algorithm. Due to the compact size, flexible design, polarization insensitivity, high focusing efficiency and high vortex purity, the proposed all-fiber photonic devices have promising potential in optical communication, particle manipulation and quantum computation applications.

High Output Power GaN-Based Green Resonant-Cavity Light-Emitting Diodes With Trapezoidal Quantum Wells

Green resonant-cavity light-emitting diode (RCLED) has great potential in optical communication but suffers low efficiency. In this study, GaN-based flip-chip green RCLED incorporated with nitrogen face-oriented inclination asymmetric trapezoidal quantum wells (NOAT-QWs) is proposed to enhance the light-output power (LOP). Samples with NOAT-QWs and normal symmetric square quantum wells (SS-QWs) were fabricated and characterized. Although their electrical characteristics and emission spectra are similar, the LOP and emission efficiency are significantly improved. At a driving current of 450 mA, the improvement of LOP for RCLED with NOAT-QWs can be as high as 1.44 times in comparison to the sample with SS-QWs. The unprecedented high output power of 115 mW and the narrow full-width-at-half-maximum (FWHM) of 6.4 nm in the emission spectrum give great potential in optical communication. The inherent mechanism was investigated by the finite element analysis, from which the simulation results match well with the experimental measurements. The simulation results reveal that the NOAT-QWs are beneficial in alleviating the quantum confined stark effect and facilitating easier hole carriers’ flow across the barriers, leading to more electron–hole wave function overlaps and higher radiative recombination rate.

Hot-Electron Photodetection Based on Graphene Transparent Conductive Electrode

Excited in metal nanoantennas by surface plasmons, the hot electrons with high energy can pass through the Schottky barrier between metal and semiconductor to form photocurrent. Because the energy required to excite hot-electrons is lower than the bandgap of the semiconductor of silicon, the photodetectors can obtain a wider detection spectrum, including the communication wavelengths. In recent years, the two-dimensional material of graphene has attracted wide attention due to its excellent optical transmissivity and electrical conductivity. In this paper, hot-electron photodetectors based on graphene transparent conductive electrode are proposed. Compared with the device utilizing Indium Tin Oxide (ITO) as transparent conductive electrode, the responsivity of the proposed device is greatly enhanced, which achieves 27.5 nA/mW and 17.4 nA/mW for wavelength of 1520 nm and 1550 nm respectively. This study shows that the proposed hot-electron photodetector with graphene transparent conductive electrode possesses great potential in optical communication.

Encoding orbital angular momentum onto multiple spin states based on a Huffman tree

Based on single-photon spin–orbit entanglement, we propose in this paper an experimental scheme to sort orbital angular momentum (OAM) by cascading conventional polarizing beam splitters. An economical algorithm, taking advantage of the pair's complementary notation of OAM numbers, is designed to separate a mixture of definite OAM. Our scheme provides an alternative technique to encode OAM onto multiple spin states based on a Huffman tree and its potential in optical communication is demonstrated.