A high-index polymer coated no-core fiber (PC-NCF) is effectively a depressed core fiber, where the light is guided by the anti-resonant, inhibited coupling and total internal reflection effects, and ...the dispersion diagram shows periodic resonant and anti-resonant bands. In this article, the transmission spectra of the straight and bent PC-NCFs (length > 5 cm) are measured and analyzed from a modal dispersion perspective. For the purpose of the study, the PC-NCFs are contained within a fiber hetero-structure using two single-mode fiber (SMF) pigtails forming a SMF-PC-NCF-SMF structure. The anti-resonant spectral characteristics are suppressed by the multimode interference in the PC-NCF with a short fiber length. The increase of the length or fiber bending (bend radius > 28 cm) can make the anti-resonance dominate and result in the periodic transmission loss dips and variations in the depth of these loss dips, due to the different modal intensity distributions in different bands and the material absorption of the polymer. The PC-NCFs are expected to be used in many devices including curvature sensors and tunable loss filters, as the experiments show that the change of loss dip around 1550 nm is over 31 dB and the average sensitivity is up to 14.77 dB/m -1 in the bend radius range from ∞ to 47.48 cm. Our study details the general principles of the effect of high-index layers in the formation of the transmission loss dips in fiber optics.
We present a novel design approach to reduce the overall microstructure diameter (MSD) of multi-layered anti-resonant hollow-core fiber (AR-HCF) while maintaining their exceptional optical ...performance. By strategically truncating the outermost layer of the large tubular element in the AR-HCF structure by a central angle of 130o, the MSD is reduced by 16% compared to its intact tube design counterpart. The fabricated truncated AR-HCF demonstrates a minimum loss of 0.28 ± 0.1 dB/km at 1290 nm and below 0.5 dB/km in the O-band from 1220-1340 nm. A similar truncated AR-HCF designed for C-band operation achieves 0.23 ± 0.1 dB/km around 1550 nm. Furthermore, the fiber exhibits low dispersion, negligible bending loss, and satisfactory higher-order mode extinction capability. This truncated AR-HCF design with reduced MSD strikes an optimal balance between exceptional optical performance and ease of integration, expanding the versatility of AR-HCFs across diverse applications like communications, sensing, and laser technologies.
Space division multiplexing (SDM) is mainly seen as a means to increase data throughput and handle exponential traffic growth in future optical networks. But its role is certainly more diverse. ...Research on SDM encourages device integration, brings newfunctionality to network elements, and helps optical networks to evolve. As a result, the number of individual components in future networks will decrease, which in turn will improve overall network reliability and reduce power consumption as well as operational expenditure. After reviewing the state-of-the-art in SDMfiber research and development with a particular focus on weakly coupled single-mode multi-core fibers, we take a look beyond the capabilities of SDM as a means of boosting transmission capacity and discuss ideas and concepts on howto exploit the spatial dimension for improved efficiency and resource sharing in optical networks.
In this paper, we review recent progress on space division multiplexed (SDM) transmission and our proposal of dense SDM (DSDM) with more than 30 spatial channels toward capacities beyond petabit/s. ...Furthermore, we discuss the requirements for realizing long-haul DSDM transport systems using multicore and/or multimode fiber, including power and space efficient amplification schemes, the use of fibers with large effective areas and transmission lines with low intercore crosstalk, low differential mode delay (DMD), and low mode dependent loss (MDL). Graded index heterogeneous 12-core × 3-mode fiber with low crosstalk, low DMD, and low MDL, parallel multiple-input and multiple-output signal processing, low mode dependent gain Erbium-doped fiber amplifiers, and MDL equalization technologies are significant as regards extending the reach of multicore and multimode transmission. We review our long-distance transmission experiment on polarization-division multiplexed 16-quadrature amplitude modulation signaling over 12-core × 3-mode fiber.
Dual-wavelength mode-locked fiber lasers are considered as ideal solutions for fast, precise, and sensitive dual-comb spectroscopy. In this study, we present a self-started dual-wavelength fiber ...laser by combining a nonlinear amplifying loop mirror and a Lyot filter. Nonlinear phase accumulation, dual-wavelength competition, and crosstalk between the mode-locking mechanism and filtering effect are well addressed to realize the self-started dual-wavelength mode-locking. Furthermore, by temperature controlling the specific polarization-maintaining fiber, our dual-wavelength laser can be continuously tuned in a wavelength range of ∼6 nm, corresponding to a well-controlled repetition rates change of 80 Hz and their difference change of 30 Hz. Mutual coherence of the dual-wavelength pulses is demonstrated by detecting the multi-heterodyne beat notes and measuring the fluctuation of the repetition rate difference. Within 10 hours of measurement, the dual-wavelength repetition rates difference remains stable at 1180 Hz with an Allan deviation of ∼9 × 10 −3 Hz @ 1s. By virtue of the all polarization-maintaining structure, our dual-wavelength laser shows improved long-term stability and repeatability, which will facilitate the turn-key, robust, and reproducible dual-comb spectroscopy for high-power or field applications.
We analyze the potential suitability or strength of arguments for the application of multicore optical fibers in high capacity submarine cable systems via transmission and techno-economic modeling. ...We consider hypothetical multicore fibers (MCFs) with 2-4 weakly coupled cores and compare capacity and cost/bit against conventional single-core fibers (SCFs). The analysis is performed in the context of a trans-Atlantic link length system and we evaluate the relative fiber performance with three different, but related, system design approaches. Two SCF coating diameters are assessed in terms of how this parameter affects the cost/bit through fiber density in submarine cables and resulting cable cost. We find that MCFs may enable higher cable capacity when fiber pair limits are imposed, but likely not at lower cost/bit unless optimistic and best case assumptions are made with respect to MCF relative fiber cost. We also find that reduced diameter SCFs can deliver much of the density and cable cost savings that motivates interest in MCF without the challenges of a new eco-system as required by MCF. However, MCF may enable the design of the largest cable capacities such as 1 Pb/s or more that might not be attainable with SCFs without significant cable changes.
In this paper we experimentally show parametric amplification and wavelength conversion in a custom manufactured dual-core highly nonlinear fiber. On-off gain <inline-formula><tex-math ...notation="LaTeX">></tex-math></inline-formula>10 dB and conversion efficiencies between <inline-formula><tex-math notation="LaTeX">-1</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">-8.5</tex-math></inline-formula> dB were measured for both cores. The estimated effective nonlinear parameter for the cores of the fiber are 6.6 W<inline-formula><tex-math notation="LaTeX">^{-1}\mathrm{km}^{-1}</tex-math></inline-formula> and 6.3 W<inline-formula><tex-math notation="LaTeX">^{-1}\mathrm{km}^{-1}</tex-math></inline-formula>, while the zero-dispersion wavelength for the individual cores is shown to be relatively close from each other. Furthermore, complementary analytical and numerical results show that coupled cores fiber optical parametric amplifier offer the potential of wide-band gain even when they have significantly distinct zero-dispersion wavelengths.
In the research field of hollow-core optical fiber (HCF), one type of fiber geometry with a leaky mode nature has unexpectedly taken center stage over the last couple of years: the so-called ...hollow-core anti-resonant fiber (ARF). The guidance mechanism of this ARF has been elucidated explicitly, the optical performance of the fiber has improved significantly, and the range of potential fiber application areas has expanded steadily. This paper will review our continuous efforts to understand, design, and fabricate this hollow-core ARF with the aim of lower loss and wider bandwidth. We also explore the possibility of using an advanced form of ARF in communications applications. In the long journey of looking for optical fibers that provide better performance than conventional solid-core glass fibers, exploitation of the hidden potential of artificial photonic micro-structures will continue to advance.
As traffic volumes carried by optical networks continue to grow by tens of percent year over year, we are rapidly approaching the capacity limit of the conventional communication band within a ...single-mode fiber. New measures such as elastic optical networking, spectral extension to multi-bands, and spatial expansion to additional fiber overlays or new fiber types are all being considered as potential solutions, whether near term or far. In this tutorial paper, we survey the photonic switching hardware solutions in support of evolving optical networking solutions enabling capacity expansion based on the proposed approaches. We also suggest how reconfigurable add/drop multiplexing nodes will evolve under these scenarios and gauge their properties and relative cost scalings. We identify that the switching technologies continue to evolve and offer network operators the required flexibility in routing information channels in both the spectral and spatial domains. New wavelength-selective switch designs can now support greater resolution, increased functionality and packing density, as well as operation with multiple input and output ports. Various switching constraints can be applied, such as routing of complete spatial superchannels, in an effort to reduce the network cost and simplify the routing protocols and managed pathway count. However, such constraints also reduce the transport efficiency when the network is only partially loaded, and may incur fragmentation. System tradeoffs between switching granularity and implementation complexity and cost will have to be carefully considered for future high-capacity SDM–WDM optical networks. In this work, we present the first cost comparisons, to our knowledge, of the different approaches in an effort to quantify such tradeoffs.
This paper presents analytical results on longitudinal power profile estimation (PPE) methods, which visualize signal power evolution in optical fibers at a coherent receiver. The PPE can be ...formulated as an inverse problem of the nonlinear Schrödinger equation, where the nonlinear coefficient (and thus signal power) is reconstructed from boundary conditions, i.e., transmitted and received signals. Two types of PPE methods are reviewed and analyzed, including correlation-based methods (CMs) and minimum-mean-square-error-based methods (MMSEs). The analytical expressions for their output power profiles and spatial resolution are provided, and thus the theoretical performance limits of the two PPE methods and their differences are clarified. The derived equations indicate that the estimated power profiles of CMs can be understood as the convolution of a true power profile and a smoothing function. Consequently, the spatial resolution and measurement accuracy of CMs are limited, even under noiseless and distortionless conditions. Closed-form formulas for the spatial resolution of CMs are shown to be inversely proportional to the product of a chromatic dispersion coefficient and the square of signal bandwidth. With MMSEs, such a convolution effect is canceled out and the estimated power profiles approach a true power profile under a fine spatial step size.
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