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Abstract In this paper, we numerically investigate the impact of shape factor (k) on the mode properties of graded-index ring-core fiber (GIRCF). A 50 mol% Ge-doped GIRCF with shape factor of 2 is devised to generate supercontinuum (SC) carrying orbital angular momentum (OAM) modes, which possesses flat dispersion with a minor variation of

Abstract D-amino acids, found in excess in a minority of organisms and crucial for marine invertebrates, contrast with the more common L-amino acids in most life forms. The local prebiotic origin of D-amino acid enantiomeric excess in natural systems remains an unsolved conundrum. Herein, we demonstrate the formation of enantiomeric excess (ee) D-amino acids through photocatalytic reductive amination of α-keto acids on natural pyrite. Various amino acids with ee values in the range of 14.5–42.4%, are formed. The wavy arrangement of atoms on the surface of pyrite is speculated to lead to the preferential formation of D-amino acids. This work reveals the intrinsic asymmetric photocatalytic activity of pyrite, which could expand understandings on mechanism of asymmetric catalysis and chirality of inorganic crystals. Furthermore, it provides a plausible pathway for the prebiotic formation of D-amino acids, adding further evidence to the origin of D-amino acids enantiomeric excess in natural systems.

Abstract Beams carrying orbital angular momentum (OAM) have exhibited significant potential across various fields, such as metrology, image coding, and optical communications. High-performance broadband coherent OAM sources are critical to the operation of optical systems. The emission of dispersive waves facilitates the efficient transfer of energy to distant spectral domains while preserving the coherence among the generated frequency components. Light sources that maintain consistency over a wide range can increase the efficiency of optical communication systems and improve the measurement accuracy in imaging and metrology. In this work, we propose a germanium-doped double ring-core fiber for five OAM dispersive waves (DWs) generation. The OAM1,1 mode supported in the fiber exhibits three zero-dispersion wavelengths (ZDWs) located at 1275, 1720 and 2325 nm. When pumped under normal dispersion, the output spectrum undergoes broadening and exhibits five DWs, situated around 955, 1120, 1450, 2795 and 2965 nm, respectively. Concomitant with blue-shifted and red-shifted dispersive waves, the spectrum spans from 895 to 3050 nm with high coherence. The effect of the fiber and input pulse parameters on DWs generation, as well as the underlying dynamics of the dispersive wave generation process, are discussed. As expected, the number and location of DWs generated in the output spectrum have agreement with the prediction of the phase-matching condition. Overall, this multiple DWs generation method in the proposed fiber paves the way for developing efficient and coherent OAM light sources in fiber-based optical systems.

Coarse wavelength division multiplexing (CWDM) technology has been widely used in short-reach optical communication systems. By using the same technology in a solid-state photonics-based Lidar, one can achieve significant cost reduction. Beam steering is realized through diffraction of light wave upon grating couplers. However, current design has a small viewing angle and a low angular resolution. We propose a configuration based on Silicon-on-Insulator (SOI) waveguide grating coupler. The viewing angle is increased by 2.5 times with light signals propagating bidirectionally. The angular resolution is doubled through interleaving beams with trans-electrical (TE) polarization and beams with trans-magnetic (TM) polarization. By optimizing the design of a single grating coupler, the output beams are evenly distributed and the transmittance is improved. With 4 CWDM lasers being the source, a 34° beam angle of view and an angular resolution of 1.9° are demonstrated.

Abstract In a solid-state photonics-based Lidar, all essential components can be integrated into a silicon chip. It is simple and effective to use a tunable laser source to implement Lidar’s beam steering. However, how to effectively increase the steering angle in a small wavelength tuning range is usually a key challenge due to the limited material and waveguide dispersion. In Silicon-on-insulator waveguide, we design a novel solid-state Lidar using two trans-electrical (TE) polarized beams counter-propagating towards each other. Two corresponding output beams from just a single grating coupler (GC) can be seamlessly combined to double the beam steering angle. Furthermore, a low-priced solid-state Lidar is designed for TE polarized beams counter-propagating towards each other by using wavelength division multiplexed laser array.

The bamboo shoot shell fibers were extracted by using environmental protection oxidant sodium percarbonate combined with alkali oxygen bath method. To explore the influence of various factors on its degumming, the efficiency of degumming through single-factor and orthogonal experiments was assessed. The results showed that the used method had a good effect on the degumming of bamboo shoot shell fiber, and most of the non-cellulose components such as hemicellulose, lignin, and pectin had been removed. After the treatment, the cellulose content and crystallinity were 73.19% and 61.40%, respectively. Taking the degumming rate as the index, the factors such as dosage of sodium percarbonate and hydrogen peroxide, soaking temperature, and time in alkali boiling treatment were optimized. The results showed that the degumming rate was 69.17% when the scouring temperature was 90°C, the alkali boiling time was 120 min, the dosage of sodium percarbonate was 24 g/L, and the dosage of hydrogen peroxide was 40 mL/L. The structure and properties of bamboo shoot shell fiber were analyzed by scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analyzer (TGA). The prepared bamboo shoot shell fibers would be considered as a promising and sustainable raw material for the textile industry and other prospects in the future.

The flexibility of producing two dispersive waves (DWs) in silicon nitride (Si3N4) slot waveguide is demonstrated, by tailoring the slot features and the corresponding phase-matching condition. DWs are generated at visible and mid-infrared (mid-IR) wavelength regions, respectively. We obtain a broadband low normal dispersion region from 2 to $5.25~\mu \text{m}$ , which offers particular advantages for DW generation at mid-IR wavelength region. The long-wave dispersive wave (LWDW) can cover beyond $4~\mu \text{m}$ . This is the first time to illustrate the freedom of Si3N4 slot waveguide for DWs generation ever reported. A broadband spectrum can be extended from 0.5 to $4.5~\mu \text{m}$ at −30 dB level by launching a 1-kW 1550-nm hyperbolic secant input pump pulse to a 1-cm proposed waveguide. The newly formed spectrum has a high degree of coherence. This approach provides more flexibility for frequency conversion, and has the advantages for biophotonics, optical sensing, chip-integrated spectroscopy, health and environmental monitoring.

In this work, we design and numerically investigate a silica-cladded Germania-doped ring-core fiber (RCF) that supports orbital angular momentum (OAM) modes with all-normal dispersion. By optimizing the structure parameters of the designed RCF, an all-normal and flat dispersion with a total variation of 1,1 mode. A 1.3-octave supercontinuum spectrum of the OAM1,1 mode is generated numerically after launching a 40-fs 200-kW chirp-free hyperbolic secant pulse train centered at 1700 nm into a 2-cm long designed fiber with 50 mol% Ge-doped ring-core, covering 1290-nm bandwidth from 885 nm to 2175 nm at −40 dB power level. The coherence of the generated supercontinuum of the OAM1,1 mode depicts nearly perfect property over the whole spectral range. This design can serve as an efficient way to extend the spectral coverage of beams carrying OAM modes in various applications.

Orbital angular momentum (OAM) beams, featured by the helical phase front and doughnut intensity profile, have been demonstrating great potential for various applications. Ring‐core optical fiber is also experimentally proven to be an effective waveguide for OAM mode. In general, managing the chromatic dispersion in the optical fiber is important for a wide range of applications. In this article, a highly dispersive germanium‐doped ring‐core fiber with dual selectable operating windows for OAM mode is proposed. The proposed fiber consists of three concentric high‐refractive‐index germanium‐doped rings with different mole fractions. The chromatic dispersion of the OAM1,1 mode in the ring fiber can be as low as −129 964 ps/(nm·km) at 1644.4 nm as the light launches into the fiber from the innermost ring and −270 017 ps/(nm·km) at 1651 nm as the light enters from the outermost ring. Furthermore, the effect of the geometrical and material parameters on chromatic dispersion for OAM1,1 mode is investigated. When the parameters of the innermost and outermost rings are varied separately, the corresponding operation windows are changed independently. An extremely negative dispersion for the OAM1,1 mode of −817 576 ps/(nm·km) can be achieved. This design can serve as a dispersive element in various OAM‐based optical fiber systems.

We propose and design a hollow As2S3 ring-core photonic crystal fiber (PCF) with 514 radially fundamental orbital angular momentum (OAM) modes over 360 nm communications bandwidth across all the O, E, S, C, and L bands. The designed PCF with 40 $\mu \text{m}$ -radius air core and 150 nm-width As2S3 ring can support eigenmodes up to HE130,1 and EH128,1. The numerical analysis shows that the designed ring PCF has large effective refractive index contrast, and can transmit up to 874 OAM modes near 1.55 $\mu \text{m}$ . Simulation results show that in the C and L bands, the PCF with a hollow-core radius of 40 $\mu \text{m}$ and a ring width of 0.15 $\mu \text{m}$ can retain an $2.5\times 10 ^{-3}$ effective refractive index difference between the two highest order OAM modes, which achieves effective mode separation, thereby achieving stable OAM mode transmission. The $n_{eff}$ difference between the even and odd fiber eigenmodes and the intra-mode walk-off are also carefully studied under different bending radii. The results show that higher-order OAM modes has better tolerance to the fiber bending, compared with the lower-order modes. The fiber has the potential to support ultra-high capacity OAM mode division multiplexing in the optical fiber communication systems.

In this paper, we propose and design a Ge-doped air-core ring fiber, which can support a large amount of OAM modes for mode-division multiplexing (MDM) in optical fiber communications. By varying the mole fraction of GeO2 and adjusting the structure parameter, including the air-core radius and the GeO2-doped ring width, we investigate the influence of different fiber parameters on the total supported OAM mode number. The hollow silica fiber with a 50- $\mu \text{m}$ air core and a 1.5- $\mu \text{m}$ thickness of Ge-doped ring is designed in simulation to support fiber eigenmodes up to HE112,1 and EH107,1. This provides 436 OAM modes at 1550 nm while maintaining radially single mode condition. Moreover, it can support more than 400 radially fundamental OAM modes for the wavelength from 1460 nm to 1625 nm, covering entire S, C and L bands. The optical parameters of the guided OAM modes in the fiber are also numerically analyzed, including effect of material loss, optical field distribution, effective refractive index profile and chromatic dispersion, etc. The simulation results show that the higher-order OAM modes have longer $2\pi $ and 10-ps walk-off length in the air-core ring fiber with ellipticity or bending compared with low-order modes.

It is well-known now that orbital angular momentum (OAM) modes can be a potential technology to take full advantages of the space resources in the fiber-based optical communication system because of its infinite states. However, the corresponding fiber design for OAM modes to meet various requirements in the fiber-based communication system is still not enough. For the dispersion property, there are various attributes given in the standard of ITU-T series, which has not yet been proposed for the OAM modes. In this paper, we propose and design a non-zero dispersion-shifted air-core ring fiber for OAM mode, which can offer more options on dispersion values. A negative dispersion of −1.246 ps/(nm $\cdot $ km) or a positive dispersion of 1.541 ps/(nm $\cdot $ km) at 1550 nm with < 1.5 ps/(nm $\cdot $ km) dispersion variation across the C band or < 4 ps/(nm $\cdot $ km) dispersion variation across the C and L bands for OAM $_{1,1}$ mode is achieved in the numerical simulation.

In this work, an air-core ring fiber is designed with a record high 1322 orbital angular momentum (OAM) modes at 1550 nm while maintaining radially single-mode condition. Moreover, it can support over 1004 OAM modes across all O, E, S, C, and L bands, exploiting to our knowledge the highest number of OAM modes ever supported in the optical fiber within a wide wavelength range. Simulations show that, across the C and L bands, the fiber with 55-μm air-core radius and 0.45-μm ring width can preserve 3.3 × 10-3 effective refraction index difference between the two highest-order OAM modes HE340,1 and EH271,1. This enables efficient mode separation, and thus achieving stable OAM modes transmission. The effective refractive index differences between the even and odd fiber eigenmodes are also analyzed in the elliptical and bent fibers. We note that higher-order OAM modes are more tolerant to the fiber ellipticity and bending. This ring fiber design has the potential to increase the spectral efficiency and the overall capacity in fiber-based communications system.

We design and simulate an all-normal dispersion arsenic trisulfide (As2S3) photonic crystal fiber (PCF) with high nonlinearity to enable a flat and coherent orbital angular momentum (OAM) supercontinuum (SC) generation. The photonic crystal fiber features a near-zero and flat negative dispersion with variation between -96.5 and -36.5 ps/(nm·km) over a 940-nm wavelength range from 1740 to 2680 nm. A 1946-nm supercontinuum forms from 959 to 2905 nm at -20 dB level which covers a 1.6-octave bandwidth, by launching a 100-fs 5-kW chirp-free hyperbolic secant pulse with wavelength at 2000 nm into a 1.0-cm designed fiber. The generated supercontinuum of the other two vortex modes (TE01 and TM01) can cover more than two octaves by optimizing the proposed fiber structures. The coherence of the generated supercontinuum of the three modes all shows nearly perfect property over the whole bandwidth. In general, we found that the designed ring-core As2S3 PCF with all-normal dispersion could be used for broadband coherent supercontinuum generation of various vortex modes.

In this work, we design and simulate an air-core As2S3 ring fiber for high-order orbital angular momentum (OAM) supercontinuum generation. We show that the chromatic dispersion of the ring fiber can be substantially tailored by proper optimization of the air-core radius. Two-octave supercontinuum carrying OAM17,1 mode, spanning from 1560 to 6250 nm, is obtained by pumping a 50-fs 100-kW secant hyperbolic pulse centered at the wavelength of 3800 nm into the designed fiber with 50-μm air-core radius and 1-μm ring width. We further engineer the chromatic dispersion of some other OAM modes and perform simulations of supercontinuum spectra using different kilowatt-level peak power, which indicates that the fiber we design represents a promising avenue for supercontinuum generation of all the OAMl,1 modes (|l| ≤17). The proposed fiber is suitable for the transmission of OAM beams in infrared wavelength range and it could promote the development and application of high-order OAM beams.

In this work, we designed and simulated a novel air-core As2S3 ring fiber that supports orbital angular momentum (OAM) modes. By optimizing the structure parameters of the designed fiber to effectively tailor its chromatic dispersion, a near-zero flat dispersion profile with a total of 1,1 mode. After launching a 100-fs 70-kW hyperbolic secant pulse into an 8-mm air-core As2S3 ring fiber, a light-carrying OAM supercontinuum is numerically formed beyond two-octave range, covering 5717nm bandwidth from 1182 nm to 6897 nm at -30dB. Furthermore, the generated supercontinuum is highly coherent across the whole spectral range. This can serve as an effective manner to expand the spectral coverage of the OAM beams for various applications.

High-baud-rate coherent optical system is essential to support the ever-increasing demand for high-speed applications. Owing to the recent progress in advanced modulation formats, over 1 Tb/s single-carrier data transmission has been achieved in the laboratory, and its commercial application is envisioned in the near future. This paper presented the trend of increasing baud rate and utilizing high-order quadrature-amplitude modulation (QAM), and several enabling technologies in the coherent optical communication systems. We first discussed recent progress of high-order QAM system and digital signal processing technology. Furthermore, we compared the transmission performance of three different ultrahigh-order QAM formats. The paper then reviewed the commonly used methods of achieving over 100 GBaud optically modulated signals. Besides, five attractive modulators and their corresponding modulation structures are illustrated. Key performance parameters including electrode length, 3-dB bandwidth, half-wave voltage, extinction ratio and optical loss are also compared. Finally, the trade-off between the baud rate and QAM orders in implementing high-speed systems are investigated in simulations. The results show that for the coming 800 GbE or 1.6 TbE, PDM-64-QAM might be an idea choice by considering the trade-off between the link reach and required system bandwidth. By adopting the latest probabilistic shaping technology, higher-order QAM signals, such as PS PDM-256-QAM, could be favorable for long reach applications while using extra system bandwidth.

A silicon nitride horizontal slot waveguide with silicon dioxide cladding is designed to achieve flat negative dispersion (-3 W. After passing through another ideal positive dispersion element, we find that the output pulse peak power can be recompressed close to 1 W in the case of different input pulse widths. Moreover, for the input pulse with a much higher peak power, the pulse width of the output pulse can be compressed to a much narrower level because of the spectral broadening introduced by optical nonlinearity. A 100-fs input pulse with 10-kW peak power can be compressed to 12.5 fs with a peak power of 63 kW. Considering the time-domain broadening and the peak power reduction, such a slot waveguide with a flat negative dispersion could be used as a time stretcher for 10-fs level pulse in on-chip chirped pulse amplification (CPA) system.

In this paper, we design a silica-cladded Germania-doped ring-core fiber (RCF) that supports orbital angular momentum (OAM) modes. By optimizing the fiber structure parameters, the RCF possesses a near-zero flat dispersion with a total variation of 1,1 mode. A beyond-two-octave supercontinuum spectrum of the OAM1,1 mode is generated numerically by launching a 40 fs 120 kW pulse train centered at 1400 nm into a 12 cm long designed 50 mol% Ge-doped fiber, which covers 2130 nm bandwidth from 630 nm to 2760 nm at −40 dB of power level. This design can serve as an efficient way to extend the spectral coverage of beams carrying OAM modes for various applications.

In this paper, we propose an Si3N4/SiO2 horizontal-slot-waveguide-based polarization beam splitter (PBS) with low nonlinearity for on-chip high-power systems. The coupling length ratio between the quasi-TE and quasi-TM modes (LTE/LTM) was optimized to 2 for an efficient polarization splitting. For the single-slot design, the coupling length of the PBS was 281.5 μm, while the extinction ratios (ER) of the quasi-TM and quasi-TE modes were 23.9 dB and 20.8 dB, respectively. Compared to PBS based on the Si3N4 strip waveguide, the coupling length became 22.6% shorter. The proposed PBSs also had a relatively good fabrication tolerance for an ER of >20 dB. For the multi-slot design, the coupling length of the PBS was 290.3 μm, while the corresponding ER of the two polarizations were 24.0 dB and 21.0 dB, respectively. Furthermore, we investigated the tradeoff between the ER and coupling length for the optimized PBSs with single slot or multiple slots.