Large-scale space division multiplexed transmission through multi-core fiber

Multicore fiber (MCF) sensors is an emerging research field. MCFs provide new alternatives for the development of innovative sensing devices whose performance cannot be achieved with conventional optical fibers. In general, MCFs have diameters similar to that of a standard single mode fiber (SMF) and have multiple individual cores sharing a common cladding. So far, a number of sensors based on MCF have been reported. Our group, for example, has reported different sensors based on single MCF interferometers that consist of a piece of MCF spliced to SMF [1,2]. One key issue of such sensors is the difficulty of discriminating the target parameter (measurand) from unwanted external perturbations that may be present during the use of the sensor. To address this issue, here, we introduce an innovative architecture that consists of two identical (twin) MCF interferometers in series that are interrogated in reflection mode, see Fig. 1. Our architecture has important advantages. As there are two MCF interferometers, one can be used as a reference or filter and the other as a sensor [3]. The signal of our twin MCF interferometers is the multiplication of individual reflection spectra. Consequently, their reflection exhibits a single narrow peak whose position in wavelength is easy to track. We have observed that periodic bending (vibrations) in one them resulted in prominent shifts in the reflection spectrum.

Design and analysis of ultra-large capacity heterogeneous nineteen-core seven-mode fiber

In this letter, we report on coupling optics for connecting single-core single-mode fibers with multicore single-mode fibers. After a brief discussion of the options for such coupling systems, we describe our approach of using bulk optics to fabricate low-loss and low-crosstalk devices for both 7- and 19-core multicore fibers with the free-space design approach. This enables the use of the same coupling device with a variety of multicore fibers whose structural parameters differ from one sample to another. We present the results of experimental evaluations of these devices, discuss various causes of insertion loss, and analyze the coupling loss in detail.

We experience Internet traffic growth of 100 times every 10 years. However, the capacity of existing standard single-mode fiber is approaching its fundamental limit regardless of significant realization of transmission technologies which allow for high spectral efficiencies. Space division multiplexing (SDM) based on multicore fibers (MCFs) has emerged as a solution to the problem of saturation of the capacity of optical transmission systems. This article presents the recent progress on the MCFs for future large capacity long-distance transmission systems. In MCFs, there is a tradeoff relationship between low crosstalk and high multiplicity, therefore the maximum number of cores and the core arrangement have to be carefully determined based on the required crosstalk level and core size. The state-of-the-art of fabricated MCFs and the transmission experiments using MCFs are reviewed. The current maximum capacity-distance product in MCF transmission is 368.2 (184.1+184.1) Pb/s/fiber km with the relative spatial efficiency of 4.7 compared with a standard single-mode fiber. In order to increase the spatial efficiency as well as the capacity-distance product further in MCFs, the possibility of heterogeneous MCFs and few-mode MCFs is also presented.

We assess the influence of fibre end termination on connector loss for single-core and multi-core plastic optical fibres (POF) using different finishing procedures. Insertion loss for standard ST connectors was measured for fibres from different manufacturers but all with poly-methyl-methacrylate (PMMA) cores, high numerical apertures (NAs) and claddings of 1 mm diameter. We tested single-core fibres with step-index (SI) profiles and a multi-core fibre with 19 cores. We found that the most suitable tool is different depending on the fibre characteristics and that connector insertion loss can be as low as 0.5 dB confirming the high impact of the finishing procedure.

We measure the dynamic skew fluctuations between cores in a multicore fiber and show that they are more than one order of magnitude smaller than those of parallel single-core fibers over a 24 hour period.

We investigate lensless endoscopy using coherent beam combining and aperiodic multicore fibers (MCF). We show that diffracted orders, inherent to MCF with periodically arranged cores, dramatically reduce the field-of-view (FoV), and that randomness in MCF core positions can increase the FoV up to the diffraction limit set by a single fiber core, while maintaining a MCF experimental feasibility. We demonstrate experimentally pixelation-free lensless endoscopy imaging over a 120 μm FoV with an aperiodic MCF designed with widely spaced cores. We show that this system is suitable to perform beam scanning imaging by simply applying a tilt to the proximal wavefront.

In this Letter, a long-range optical fiber displacement sensor based on an extrinsic Fabry-Perot interferometer (EFPI) built with a strongly coupled multicore fiber (SCMCF) is proposed and demonstrated. To fabricate the device, 9.2 mm of SCMCF was spliced to a conventional single-mode fiber (SMF). The sensor reflection spectrum is affected by super-mode interference in the SCMCF and the interference produced by the EFPI. Displacement of the SMF-SCMCF tip with respect to a reflecting surface produces quantifiable changes in the amplitude and period of the interference pattern in the reflection spectrum. Since the multicore fiber is an efficient light collecting area, sufficient signal intensity can be obtained for displacements of several centimeters. By analyzing the interference pattern in the Fourier domain, it was possible to measure displacements up to 50 mm with a resolution of approximately 500 nm. To our knowledge, this is the first time that a multicore fiber has been used to build a displacement sensor. The dynamic measurement range is at least seven times larger than that achieved with an EFPI built with a conventional SMF. Moreover, the SMF-SCMCF tip is robust and easy to fabricate and replicate.

We describe a new multicore fiber (MCF) receptacle for space division multiplexing (SDM) based transceiver applications, in which we integrated a compact fiber-bundle type fan-in/fan-out device for directly connecting MCF to LDs and PDs. We design the length of the fan-out fibers taking their bending stress into account to achieve a configuration with a smaller footprint. With the proposed receptacle, we develop a 100 Gb/s SDM transmitter based on a four-channel, 1.3 μm membrane laser array on Si, in which spot-size convertor (SSC) using inverse taper InP and SiON waveguides is integrated. Since the core size of SiON waveguide is much smaller than that of MCF, we utilize different fibers with optimized modal fields at each connection point and introduce thermally-expanded-core (TEC) fusion splicing to realize a low-loss connection between them. We achieve a pluggable connection between the lasers and 125 μm-cladding 4-core MCF in an LC connector. The developed receptacle maintained satisfactory laser characteristics including sufficient output power and clear eye openings for directly modulated 28 Gb/s NRZ signals. We also achieve an error-free transmission at a bit-error rate of less than 10−12 with a 500-m MCF transmission link for all 4 channels with simultaneous 4-channel operation.

The capacity of the optical communication infrastructure in backbone networks has increased 1000-fold over the last 20 years. Despite this rapid progress, internet traffic is continuing to grow at an annual rate of 40%. This means that in 20 years, we will need petabit/s or even exabit/s optical communication. In this paper, we present recent challenges and efforts toward achieving a hardware paradigm shift to overcome the capacity limitation imposed by the current optical communication infrastructure. We will overview the latest advances on the three “multi” technologies, i.e., multi-level transmission with ultrahigh spectral efficiency, space division multiplexing in multi-core fibers, and mode division multiplexing with multiple-input multiple-output (MIMO).

Studying the temperature field of photovoltaic modules is important for improving their power generation efficiency. To solve the problem of traditional sensors being unsuitable for measuring the spatial temperature field, we designed a real-time detection scheme of the photovoltaic module temperature field based on a fiber Bragg grating (FBG) sensor array. In this scheme, wavelength division multiplexing and space division multiplexing technologies were applied. The multi-channel FBG sensor strings were arranged on the surface and in the near field of the photovoltaic module. Different FBG strings were selected through optical switches, and the wavelength of the FBG string was addressed and demodulated using the tunable laser method and a peak-seeking algorithm. A measurement experiment of the photovoltaic module temperature field was carried out in an outdoor environment. The experimental results showed that the fluctuation law of the photovoltaic module surface and near-field temperature is basically consistent with that of solar radiation power. The temperature of the photovoltaic module decayed from the surface to space. Within 6 mm of the photovoltaic module surface, the temperature sharply dropped, and then the downward trend became flat. The lower the solar radiation power and the higher the wind speed, the faster the temperature decay. This method provides technical support for measuring the temperature field of a photovoltaic module and other heat source equipment.

Fiber Bragg gratings in multicore fibers can be used as compact and robust filters in astronomical and other research and commercial applications. Strong suppression at a single wavelength requires that all cores have matching transmission profiles. These gratings cannot be inscribed using the same method as for single-core fibers because the curved surface of the cladding acts as a lens, focusing the incoming UV laser beam and causing variations in exposure between cores. Therefore we use an additional optical element to ensure that the beam shape does not change while passing through the cross-section of the multicore fiber. This consists of a glass capillary tube which has been polished flat on one side, which is then placed over the section of the fiber to be inscribed. The laser beam enters the fiber through the flat surface of the capillary tube and hence maintains its original dimensions. This paper demonstrates the improvements in core-to-core uniformity for a 7-core fiber using this method. The technique can be generalized to larger multicore fibers.

Multicore fibers possess the potential to develop dense-space-division multiplexing systems. Several dense-space-division multiplexing system transmission experiments concerning multicore fibers have been demonstrated. Multicore fibers, including recent results by our group, are reviewed in this study.

We investigate the application of space division multiplexing (SDM) technology to a long haul undersea transmission using multi-core fiber (MCF). We discuss two experimental demonstrations conducted with a 12-core fiber. The first study shows that SDM can help to achieve simultaneous improvement of power efficiency and capacity of long-haul transmission. Using SDM, power efficient optical system design and modulation format with high receiver sensitivity we demonstrate 105.1 Tb/s transmission over 14,350 km with pump power per 12 EDFAs equivalent to a single 800 mW 980 nm pump laser. In the second study, we investigated capacity limits of transoceanic transmission achievable with MCF and extended C and L bandwidth of optical amplification. The study shows 520 Tb/s potential transmission capacity over 8,830 km using 9 THz of optical bandwidth. To achieve this capacity, we also used new coded modulation with 1.0 dB sensitivity improvement compared to 8QAM with the same SE of 4.86 b/s/Hz.

A RMSCA algorithm for space division multiplexing elastic optical networks with core switching