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Abstract The authors examine the state of submarine cable systems and conditions affecting potential widespread deployment of new spatial division multiplexing technologies, such as multicore optical fibre. The authors address areas such as cable capacity requirements, techno‐economic constraints, multicore fibre characteristics, and performance and other necessary technology advances.

Abstract In an experimental exploration, we successfully implemented a self-assembling methodology to construct a periodic liquid-air structure inside a hollow optical fiber (HOF). This fiber comprises a central air hole, a germanosilica ring core, and a silica cladding. A periodic structure of liquid droplets and air was obtained by the application of a microscopic heat source (MHS) traversing along the axial direction of the liquid-filled HOF. In the course of this study, we discerned three distinct zones within the structure. The first zone, referred to as Zone 1, demonstrated near-constant periodicity. The second zone, Zone 2, exhibited adaptable properties with regard to its periodicity, allowing it to be flexibly controlled. In the third zone, Zone 3, we noticed a chaotic response to external parameters, including temperature and the speed at which MHS was traversed. To regulate the liquid-air periodic structures, two different types of MHSs were utilized - a micro hydro-oxygen torch and a metal ring heater, each mounted on a translation stage. The study provides a detailed account of the parameters employed in utilizing these MHSs. Additionally, the optical properties of these liquid-air periodic structures were meticulously analyzed to explore the potential for developing new optofluidic applications.

Label-free and multiphoton micro-endoscopy can transform clinical histopathology by providing an in situ tool for diagnostic imaging and surgical treatment in diseases such as cancer. Key to a multiphoton imaging-based micro-endoscopic device is the optical fiber, for distortion-free and efficient delivery of ultra-short laser pulses to the sample and effective signal collection. In this work, we study a new hollow-core (air-filled) double-clad anti-resonant fiber (DC-ARF) as a high-performance candidate for multiphoton micro-endoscopy. We compare the fiber characteristics of the DC-ARF with a single-clad anti-resonant fiber (SC-ARF) and a solid core fiber (SCF). In this work, while the DC-ARF and the SC-ARF enable low-loss (−1), close to dispersion-free excitation pulse delivery (2000% of pulse width increase at 900 nm per 1 m fiber). An ideal optical fiber endoscope needs to be several meters long and should enable both excitation and collection through the fiber. Therefore, we performed multiphoton imaging on endoscopy-compatible 1 m and 3 m lengths of fiber in the back-scattered geometry, wherein the signals were collected either directly (non-descanned detection) or through the fiber (descanned detection). Second harmonic images were collected from barium titanate crystals as well as from biological samples (mouse tail tendon). In non-descanned detection conditions, the ARFs outperformed the SCF by up to 10 times in terms of signal-to-noise ratio of images. Significantly, only the DC-ARF, due to its high numerical aperture (NA) of 0.45 and wide-collection bandwidth (>1 µm), could provide images in the de-scanned detection configuration desirable for endoscopy. Thus, our systematic characterization and comparison of different optical fibers under different image collection configurations, confirms and establishes the utility of DC-ARFs for high-performing label-free multiphoton imaging-based micro-endoscopy.

Continuous spectral translation could allow expansion of the bandwidth available for communication without having to develop transceivers for the new bands. Here, the authors demonstrate this using AlGaAsOI nanowaveguides as spectral translators between the mature telecom C band and the 2-μm wavelength band.

We propose a new type of all-fiber mode scrambler for mode division multiplexed data transmission based on few mode fibers. By randomly placing multiple point-loads along the fiber length, low loss and wideband mode coupling is obtained amongst all the guided modes. The effect of mode coupling is simulated from a single point-load to multiple point-loads with a specific focus on the insertion loss and wavelength dependence. In an exemplar experimental demonstration we present a mode scrambler for step-index two mode fibers incorporating 150 randomly located point-loads. Uniform mode coupling is achieved over the C band with an insertion loss of less than 1 dB.

Structured light is a valuable addition to many optical applications. Here, the authors introduce a method for producing tailorable structured light beams at the output of a multicore fiber amplifier by controlling the input to each fiber core.

Few-mode erbium-doped fiber amplifiers (FM-EDFAs) are one of the most important optical subsystems for successful space division multiplexed transmission systems. In this paper, we propose a new FM-EDFA designed to achieve significantly reduced differential modal gain (DMG) via strong mode coupling. Using a new numerical model based on a fiber transfer matrix, the DMGs of FM-EDFAs are systematically investigated and two different types of six-mode fiber amplifiers are analyzed, as exemplar demonstrations. In a uniformly doped step-index fiber, the DMG can be reduced from 9.3 to 1.1 dB (i.e., 8.2 dB reduction) and further reduced to 0.5 dB in a dual-layer doping structure.

Here, the authors show that integration of metamaterial and optical fibre technologies enables all-optical XOR, NOT and AND logical functions that are performed at up to 40 gigabits per second with few femtojoules per bit energy consumption within a coherent fully fiberized network.

All-optical data processing continues to attract significant interest as a way to overcome the electronic signal processing bottleneck of fiber telecommunication networks. Nonlinear optical devices such as limiters and saturable absorbers rely on intensity-dependent attenuation of light. However, making such devices using intensity-dependent multiphoton dissipation processes is an issue as these make complete absorption and transmission impossible. Here, we show that nonlinear phase retardation in an optical fiber can control the dissipation of coherent light waves interacting on a thin plasmonic absorber from total absorption to perfect transmission. The fiber’s instantaneous Kerr nonlinearity and the femtosecond coherent absorption time scale make this approach ultrafast. We report proof-of-principle demonstrations of all-optical intensity discrimination, power limiting, pulse restoration, pulse splitting, and signal transfer between carrier wavelengths within a fiber circuit. Our results indicate that nonlinear control of coherent absorption can imitate and outperform saturable and multiphoton absorption in terms of bandwidth and contrast.

All-optical encryption of information in fibre telecommunication networks offers lower complexity and far higher data rates than electronic encryption can deliver. However, existing optical layer encryption methods, which are compatible with keys of unlimited length, are based on nonlinear processes that require intense optical fields. Here, we introduce an optical layer secure communication protocol that does not rely on nonlinear optical processes but instead uses energy redistribution of coherent optical waves interacting on a plasmonic metamaterial absorber. We implement the protocol in a telecommunication optical fibre information network, where signal and key distribution lines use a common coherent information carrier. We investigate and demonstrate different encryption modes, including a scheme providing perfect secrecy. All-optical cryptography, as demonstrated here, exploits signal processing mechanisms that can satisfy optical telecom data rate requirements in any current or next-generation frequency band with bandwidth exceeding 100 THz and a switching energy of a few photons per bit. This is the first demonstration of an optical telecommunications application of metamaterial technology.

We report on the design, fabrication, and experimental characterization of germanium-doped graded-index multi-mode fibers that are tailored to achieve broadband operation for the inter-modal Bragg scattering four wave mixing process. First, we show that increasing the core diameter decreases the separation between the pumps and the signal/idler pair. Second, we demonstrate a conversion efficiency bandwidth (7 nm) of more than twice that achieved previously with half the fiber length (50 m).

A micro-optic collimator assembly represents an important platform for the realization of many commonly used fiber optic components and devices including optical isolators, circulators, gain flattening filters, and so on. In this paper, we investigate the incorporation of space division multiplexing (SDM) fibers (particularly, few mode fibers and multicore fibers) in a micro-optic collimator assembly and develop a technology base to provide fully integrated SDM components. A few exemplary SDM fiber isolators (e.g., 3 or 6-moded fiber isolator and a 32-core multicore fiber isolator) are successfully fabricated with low insertion loss and low mode (or core) dependent losses. Improved sharing of the functional optical element and significant device integration is efficiently achieved in these devices as will be required to ultimately realize the anticipated cost reduction benefits of SDM technology.

We demonstrate the design and fabrication of an in-line evanescent field gas sensor based on a novel suspended ring-core photonic crystal fiber (PCF) to further overcome limitations in sensing capability. The suspended ring-core PCF is made by the stack-and-draw technique with a large central capillary of ~60 μm and adapted small capillaries in a larger cladding tube. Sensing capabilities of two variations of the proposed suspended ring-core PCFs were investigated experimentally by detecting absorption lines of acetylene gas. The sensitivity of the two PCF structures was also numerically analyzed using a full-vectorial finite-element method. The dynamic response of the sensors was quantified in detail. The results demonstrated significant improvement in both sensitivity and response time of the suspended ring-core PCF as this special PCF can provide larger gas diffusion and higher overlap between the sensing species and the guided light than either a Ge-doped ring defect PCF or a conventional index-guided PCF.