Bundles Of Single-mode Fibers Research Articles

Light-field micro-endoscopy using a fiber bundle: a snapshot 3D epi-fluorescence endoscope

Micro-endoscopes are widely used for detecting and visualizing hard-to-reach areas of the human body and for in vivo observation of animals. A micro-endoscope that can realize 3D imaging at the camera framerate could benefit various clinical and biological applications. In this work, we report the development of a compact light-field micro-endoscope (LFME) that can obtain snapshot 3D fluorescence imaging, by jointly using a single-mode fiber bundle and a small-size light-field configuration. To demonstrate the real imaging performance of our method, we put a resolution chart in different z positions and capture the z-stack images successively for reconstruction, achieving 333-μm-diameter field of view, 24 μm optimal depth of field, and up to 3.91 μm spatial resolution near the focal plane. We also test our method on a human skin tissue section and HeLa cells. Our LFME prototype provides epi-fluorescence imaging ability with a relatively small (2-mm-diameter) imaging probe, making it suitable for in vivo detection of brain activity and gastrointestinal diseases of animals.

On the Efficient Flow Restoration in Spectrally-Spatially Flexible Optical Networks

We focus on the efficient modeling and optimization of the flow restoration in the spectrally-spatially flexible optical networks (SS-FONs) realized using a single mode fiber bundle. To this end, we study a two-phase optimization problem, which consists of: (i) the network planning with respect to the spectrum usage and (ii) the flow restoration after a failure aiming at maximizing the restored bit-rate. Both subproblems we formulate using the integer linear programming with two modeling approaches—the node-link and the link-path. We perform simulations divided into: (i) a comparison of the proposed approaches, (ii) an efficient flow restoration in SS-FONs—case study. The case study focuses on the verification whether the spectral-spatial allocation may improve the restoration process (compared to the spectral allocation) and on the determination of the full restoration cost (the amount of additional resources required to restore whole traffic) in two network topologies. The results show that the spectral-spatial allocation allows us to restore up to 4% more traffic compared to the restoration with only the spectral channels. They also reveal that the cost of the full traffic restoration depends on plenty of factors, including the overall traffic volume and the network size, while the spectral-spatial allocation allows us to reduce its value about 30%.

An Efficient Optimization Framework for Solving RSSA Problems in Spectrally and Spatially Flexible Optical Networks

We focus on the routing, spatial mode, and spectrum allocation (RSSA) problem-a basic optimization problem in spectrally and spatially flexible optical networks (SS-FON). RSSA is a very challenging problem since it introduces a new dimension, related to the selection of spatial resources, to the already complex (NP-hard) routing and spectrum allocation (RSA) problem. To allow solving large RSSA problem instances, in particular, in optical backbone networks with tens of nodes and hundreds of demands as well as with optical fibers supporting a numerous number of spatial modes, specialized optimization algorithms are required. In this paper, we propose and study several dedicated optimization procedures and some enhancements in algorithm processing, including parallel processing, which aim at both speeding up and increasing the effectiveness of the RSSA process and at estimating the quality of generated solutions. We combine the proposed procedures into an efficient optimization framework which, as presented numerical results show, is capable of providing high-quality solutions to large instances of the RSSA optimization problem in reasonable computation times. As a case study scenario, we consider an SS-FON with spectral super-channels (SChs) transmitted over bundles of single-mode fibers (SMFB) without spatial mode conversion. Nonetheless, the proposed optimization framework is generic and can be straightforwardly adapted to other SS-FON scenarios.

Robust compressive multimode fiber imaging against bending with enhanced depth of field.

Imaging through single multimode fiber prevails its counterpart using single mode fiber bundle on spatial resolution limit and minimum radius. Current multimode fiber imaging suffers from fussy calibration, which can be reduced by recent developed compressive sensing scheme [ [L. V. Amitonova, Opt. Lett. 43, 5427 (2018)]. Experiments demonstrate improvement on depth of field by more than three orders of magnitude, together with robustness against macro fiber bending, which is vital to endoscopic applications.

Scaling SDM Optical Networks Using Full-Spectrum Spatial Switching

In today's optical networks, the capacity supported by a single optical fiber is far higher than the demand between source–destination pairs. Thus, to take advantage of the installed capacity, lightpaths allocated between distinct source–destination pairs share the capacity provided by an optical fiber. This sharing is only possible if these lightpaths have different wavelengths. With the exponential evolution of traffic, the demand between source– destination pairs in a network can approach or exceed the capacity of a single fiber. In this scenario, spacedivision multiplexing (SDM) networks appear as a viable option, and new network-sharing technologies become relevant. In this paper, we study different switching approaches for SDM networks with uncoupled spatial superchannels—such as networks with multicore fibers or bundles of single-mode fibers—which result in different network-sharing strategies. We start by comparing three switching architectures considering the evolution of traffic over time: (1) full-spectrum spatial switching (full-spectrum SS); (2) wavelength switching (WS) of uncoupled spatial superchannels; and (3) independent switching (IS) of spatial and wavelength channels. IS provides high network flexibility at the cost of complex switching nodes. On the other hand, full-spectrum SS and WS simplify network nodes but reduce flexibility by switching superchannels. Simulation results indicate that WS offers poor utilization in the long term. Full-spectrum SS, in contrast, exhibits low utilization in the short term, but outperforms IS in the long term. We also propose alternative hybrid switching strategies that start with IS and change to full-spectrum SS after a certain number of spatial channels are activated. The simulations suggest that well-designed strategies for migration from IS to full-spectrum SS delay premature activation investments while saving on switching costs.

Physical-Layer-Aware Performance Evaluation of SDM Networks Based on SMF Bundles, MCFs, and FMFs

In this work, we compare the performance of several space division multiplexing (SDM) network realizations utilizing different types of transmission media. In this regard, we first present a tool developed for the estimation of signal quality degradation in SDM-based optical networks. The tool supports SDM networks utilizing few-mode fibers (FMFs) and multicore fibers (MCFs), as well as bundles of single-mode fibers (BuSMFs), and provides an accurate quality of transmission (QoT) estimation allowing the network operators and designers to take into account physical layer impairments while performing network planning analysis. Considering the proposed QoT tool, we present extensive simulation results comparing the performance of FMFs, MCFs, and BuSMFs in terms of maximum achievable optical transparent reach in a multispan point-to-point scenario, where the impact of amplifier span length, channel spacing, and number of co-propagating spectral channels is studied. These results are used to perform physical-layer-aware SDM network planning analysis following the LOGON approach, which allows us to evaluate the impact of reach-limited transmission along different types of fibers in a networking scenario for different sizes of an optical network topology. The results of this study compare different SDM network realizations in terms of average spectrum utilization and the number of in-operation transceivers operating over different modulation formats showcasing the benefits and drawbacks of SDM networks relying on different transmission media.

Impact of Spatial and Spectral Granularity on the Performance of SDM Networks Based on Spatial Superchannel Switching

Spatially integrated switching architectures have been recently investigated in an attempt to provide switching capability for networks based on spatial division multiplexing (SDM) fibers, as well as to reduce the implementation cost. These architectures rely on the following switching paradigms, furnishing different degrees of spectral and spatial switching granularity: independent switching, which offers full spatial-spectral flexibility; joint-switching, which treats all spatial modes as a single entity; and fractional-joint switching, whereby subgroups of spatial modes are switched together as independent units. The last two paradigms are categorized as spatial group switching solutions since the spatial resources (modes, cores, or single-mode fibers) are switched in groups. In this paper, we compare the performance (in terms of spectral utilization, data occupancy, and network switching infrastructure cost) of the SDM switching paradigms listed above for varying spatial and spectral switching granularities in a network planning scenario. The spatial granularity is related to the grouping of the spatial resources, whereas the spectral granularity depends on the channel baud rate and the spectral resolution supported by wavelength selective switches (WSS). We consider two WSS technologies for handling of the SDM switching paradigms: 1) the current WSS realization, 2) WSS technology with a factor-two resolution improvement. Bundles of single-mode fibers are assumed across all links as a near-term SDM solution. Results show that the performance of all switching paradigms converge as the size of the traffic demands increases, but finer spatial and spectral granularity can lead to significant performance improvement for small traffic demands. Additionally, we demonstrate that spectral switching granularity must be adaptable with respect to the size of the traffic in order to have a globally optimum spectrum utilization in an SDM network. Finally, we calculate the number of required WSSs and their port count for each of the switching architectures under evaluation, and estimate the switching-related cost of an SDM network, assuming the current WSS realization as well as the improved resolution WSS technology.

Efficient Pump Beam Multiplexer Based on Single-Mode Fibers

An efficient pump beam combining technique using single-mode fibers was introduced. Well-defined modes formed from a single-mode fiber bundle were efficiently coupled into an output multimode fiber. The coupling rate can be maintained up to an input fiber number of 331. The total power of a multimode output fiber combined with single-mode fibers can greatly exceed the output power of a multimode laser diode pigtailed with the same multimode fiber.