Enhanced Coexistence of Quantum Key Distribution and Classical Communication over Hollow-Core and Multi-Core Fibers.

In this paper, we investigate the impact of classical optical communications in quantum key distribution (QKD) over hollow-core fiber (HCF), multi-core fiber (MCF) and single-core fiber (SCF) and propose wavelength allocation schemes to enhance QKD performance. Firstly, we theoretically analyze noise interference in QKD over HCF, MCF and SCF, such as spontaneous Raman scattering (SpRS) and four-wave mixing (FWM). To mitigate these noise types and optimize QKD performance, we propose a joint noise suppression wavelength allocation (JSWA) scheme. FWM noise suppression wavelength allocation and Raman noise suppression wavelength allocation are also proposed for comparison. The JSWA scheme indicates a significant enhancement in extending the simultaneous transmission distance of classical signals and QKD, reaching approximately 100 km in HCF and 165 km in MCF under a classical power per channel of 10 dBm. Therefore, MCF offers a longer secure transmission distance compared with HCF when classical signals and QKD coexist in the C-band. However, when classical signals are in the C-band and QKD operates in the O-band, the performance of QKD in HCF surpasses that in MCF. This research establishes technical foundations for the design and deployment of QKD optical networks.

Semen promotes oocyte development in Sebastesschlegelii elucidating ovarian development dynamics in live-bearing fish.

In some vertebrates and invertebrates, semen release factors affecting female physiology and behavior. Here, we report that semen delivered to females is potentially beneficial for promoting oocyte development in a viviparous teleost, Sebastes schlegelii. 88% of mated ovaries develop normally and give birth to larval fish, whereas 61% of non-mated ovaries are arrested in the previtellogenic stage. Semen's significant role (p < 0.0001) in promoting oocyte development may involve remodeling follicular cells and regulating the expression of the extracellular matrix, which facilitates cell communication. Furthermore, the ovarian response to semen may influence the brain, affecting hormone release, follicular cell development and steroid production, and crucial for oocyte growth. This mechanism, which could potentially delay maternal investment in offspring until male genetic input occurs to avoid energy wastage, has not been previously described in teleosts. These findings enhance our understanding of ovarian development in viviparous fish, with broader implications for reproductive biology.

Few-mode erbium-doped fiber with trench and weak coupling for mode gain equalization based on layered-doping technology.

A few-mode erbium-doped fiber (FM-EDF) with a step refractive index and trench structure is designed and proposed to realize the modal gain equalization of a few-mode erbium-doped fiber amplifier (FM-EDFA). The layered-doping technology is used to reduce the mode gain difference (DMG). The doping radius and doping concentration are adjusted to obtain the optimum FM-EDF structure. When the designed FM-EDF is applied to the FM-EDFA, the DMG of the whole C-band is less than 0.15 dB and the DMG is less than 0.12 dB at 1550 nm. The minimum refractive index difference (Δ n eff) between modes can be calculated according to the refractive index and radius of the fiber core; i.e., 1.35×10-3, which will greatly reduce the coupling between modes in a practical application. Tolerances in the fiber manufacturing process are also considered for reliable FM-EDFA performance. When the doping radius and concentration of each doping layer fluctuate by ±15% based on the precise value, the maximum DMG increases to 1.8 dB. In general, DMG can maintain a small value, which is beneficial for application in optical communications systems.

Flexible Pressure Sensors Based on Microcrack Structure and Composite Conductive Mechanism for Medical Robotic Applications.

With the advancement of intelligent medical robot technology, machine touch utilizing flexible sensors has emerged as a prominent research area. In this study, a flexible resistive pressure sensor was designed incorporating a microcrack structure with air pores and a composite conductive mechanism of silver/carbon. The aim was to achieve enhanced stability and sensitivity with the inclusion of macro through-holes (1-3 mm) to expand the sensitive range. This technology solution was specifically applied to the machine touch system of the B-ultrasound robot. Through meticulous experimentation, it was determined that the optimal approach involved uniformly blending ecoflex and nano carbon powder at a mass ratio of 5:1, and subsequently combining the mixture with an ethanol solution of silver nanowires (AgNWs) at a mass ratio of 6:1. This combination of components resulted in the fabrication of a pressure sensor with optimal performance. Under the pressure testing condition of 5 kPa, a comparison of the resistance change rate was conducted among samples using the optimal formulation from the three processes. It was evident that the sample of ecoflex-C-AgNWs/ethanol solution exhibited the highest sensitivity. Its sensitivity was increased by 19.5% compared to the sample (ecoflex-C) and by 11.3% compared to the sample (ecoflex-C-ethanol). The sample (ecoflex-C-AgNWs/ethanol solution), which only incorporated internal air pore microcracks without through-holes, exhibited sensitive response to pressures below 5 N. However, with the addition of through-holes, the measurement range of its sensitive response increased to 20 N, representing a 400% increase in the measurement range.

A duplicated amh is the master sex-determining gene for Sebastes rockfish in the Northwest Pacific.

Teleost fish are the most diverse group of vertebrates and provide opportunities to study the evolution of sex determination (SD) systems. Using genomic and functional analyses, we identified a male-specific duplication of anti-Müllerian hormone (amh) gene as the male master sex-determining (MSD) gene in Sebastes schlegelii. By resequencing 10 males and 10 females, we characterized a 5 kb-long fragment in HiC_Scaffold_12 as a male-specific region, which contained an amh gene (named amhy). We then demonstrated that amhy is a duplication of autosomal amh that was later translocated to the ancestral Y chromosome. amha and amhy shared high-nucleotide identity with the most significant difference being two insertions in intron 4 of amhy. Furthermore, amhy overexpression triggered female-to-male sex reversal in S. schlegelii, displaying its fundamental role in driving testis differentiation. We developed a PCR assay which successfully identified sexes in two species of northwest Pacific rockfish related to S. schlegelii. However, the PCR assay failed to distinguish the sexes in a separate clade of northeast Pacific rockfish. Our study provides new examples of amh as the MSD in fish and sheds light on the convergent evolution of amh duplication as the driving force of sex determination in different fish taxa.

Design of steering wheel-type ring depressed-core 10-mode fiber with fully improved mode spacing.

We present a steering wheel-type ring depressed-core few-mode fiber (SWTR-DC-FMF) that features a central depressed step-index core and a novel SWTR structure consisted of two symmetrical high-index parts and low-index parts, respectively. The DC and SWTR make great contribution to separate the non-degenerated LP modes and spatial modes in the circular symmetry core, resulting in fully improved mode spacing. The designed fiber is able to support 10 spatial modes with the minimum effective index difference (Min Δneff) between adjacent spatial modes larger than 1.93 × 10-4 and the Min Δneff between adjacent LP modes above 1.51 × 10-3 at the same time, facilitating potential fiber spatial mode multiplexing transmission with less multiple-input multiple-output (MIMO-less) digital signal processing technique. The broadband performance including neff, Δneff, effective mode area (Aeff) and differential mode delay (DMD) is comprehensively investigated over the whole C and L band. Moreover, the birefringence and fabrication tolerance are discussed. The designed fiber targets emerging applications in short-reach weakly coupled space-division multiplexing (SDM) optical networking to increase transmission capacity and spectral efficiency and further reduce the system complexity effectively.

Impact analysis of a dense hole-assisted structure on crosstalk and bending loss in homogeneous few-mode multi-core fibers.

We present a novel dense hole-assisted structure (DHAS) in homogeneous few-mode multi-core fibers (FM-MCFs) for significantly suppressing inter-core crosstalk (XT) and bending loss while realizing a high spatial density in limited cladding diameter. The fabrication methods of DHAS FM-MCFs are illustrated and the equivalent model of DHAS is proposed. To point out the superiority, the XT of a DHAS 7-core 4-LP-mode fiber is investigated by an average power-coupling coefficients analytical expression in DHAS model and the equivalent model, respectively. A simple derived analytical expression for XT estimation in the trench-assisted homogeneous MCFs is introduced to verify the change of XT with fiber parameters in the equivalent model. The results imply that the XT obtained by the equivalent model is in good agreement with the one through DHAS model. Furthermore, the bending loss and chromatic dispersion dependences on DHAS are calculated by the finite element method (FEM). Through numerical simulations, we show that the DHAS has great contribution to meet the XT value requirement of lower than -30 dB/100km and make the bending loss values satisfy the ITU-T recommendations of G. 654 in a 7-core 4-LP-mode fiber with a 125-µm cladding diameter. The designed structure targets applications in space division multiplexing (SDM) fibers with independent transmission channels.

Design and analysis of a combined-ring core weakly coupled few-mode fiber with six linearly polarized modes and an ultra-large effective index difference.

The theory and properties of weakly coupled few-mode fiber (FMF) have been investigated by means of mode power distribution. According to that, a novel weakly coupled FMF with a combined-ring core structure has been proposed. To the best of our knowledge, it is the first time a weakly coupled FMF has realized the goal of supporting six modes and ultra-large minimum effective index difference (min Δneff) of 1.83*10-3 between all neighboring modes. The combined-ring core structure evidently relieves the pressure of modifying neff via inserting a single low-index area and a single high-index ring in step-index FMFs. Due to this structure, a weakly coupled FMF design can be realized by the smaller low-index central area (central area radius d=0.82 µm) and lightly doped high-index ring (the refractive index difference between the ring and the core Δn2=0.11%) compared with former designs. The effective area (Aeff) and differential mode delay characteristics of the designed FMF have been optimized. Furthermore, we calculated the bending loss and fiber properties at the C and L bands to prove that our proposed FMF satisfies the requirement of large-capacity mode-division multiplexing optical networking.