Three-Dimensional Light Bullets in Arrays of Waveguides

We report the first experimental observation of 3D-LBs, excited by femtosecond pulses in a system featuring quasi-instantaneous cubic nonlinearity and a periodic, transversally-modulated refractive index. Stringent evidence of the excitation of LBs is based on time-gated images and spectra which perfectly match our numerical simulations. Furthermore, we reveal a novel evolution mechanism forcing the LBs to follow varying dispersion/diffraction conditions, until they leave their existence range and decay.Comment: 4 pages, 5 figures - Published by the American Physical Societ

Giant refractometric sensitivity by combining extreme optical Vernier effect and modal interference

The optical Vernier effect consists of overlapping responses of a sensing and a reference interferometer with slightly shifted interferometric frequencies. The beating modulation thus generated presents high magnified sensitivity and resolution compared to the sensing interferometer, if the two interferometers are slightly out of tune with each other. However, the outcome of such a condition is a large beating modulation, immeasurable by conventional detection systems due to practical limitations of the usable spectral range. We propose a method to surpass this limitation by using a few-mode sensing interferometer instead of a single-mode one. The overlap response of the different modes produces a measurable envelope, whilst preserving an extremely high magnification factor, an order of magnification higher than current state-of-the-art performances. Furthermore, we demonstrate the application of that method in the development of a giant sensitivity fibre refractometer with a sensitivity of around 500 µm/RIU (refractive index unit) and with a magnification factor over 850

Optical Harmonic Vernier Effect: A New Tool for High Performance Interferometric Fiber Sensors

The optical Vernier effect magnifies the sensing capabilities of an interferometer, allowing for unprecedented sensitivities and resolutions to be achieved. Just like a caliper uses two different scales to achieve higher resolution measurements, the optical Vernier effect is based on the overlap in the responses of two interferometers with slightly detuned interference signals. Here, we present a novel approach in detail, which introduces optical harmonics to the Vernier effect through Fabry–Perot interferometers, where the two interferometers can have very different frequencies in the interferometric pattern. We demonstrate not only a considerable enhancement compared to current methods, but also better control of the sensitivity magnification factor, which scales up with the order of the harmonics, allowing us to surpass the limits of the conventional Vernier effect as used today. In addition, this novel concept opens also new ways of dimensioning the sensing structures, together with improved fabrication tolerances

Yb-doped large mode area fiber for beam quality improvement using local adiabatic tapers with reduced dopant diffusion

A newly designed all-solid step-index Yb-doped aluminosilicate large mode area fiber for achieving high peak power at near diffraction limited beam quality with local adiabatic tapering is presented. The 45µm diameter fiber core and pump cladding consist of active/passively doped aluminosilicate glass produced by powder sinter technology (REPUSIL). A deliberate combination of innovative cladding and core materials was aspired to achieve low processing temperature reducing dopant diffusion during fiber fabrication, tapering and splicing. By developing a short adiabatic taper, robust seed coupling is achieved by using this Yb-doped LMA fiber as final stage of a nanosecond fiber Master Oscillator Power Amplifier (MOPA) system while maintaining near diffraction limited beam quality by preferential excitation of the fundamental mode. After application of a fiber-based endcap, the peak power could be scaled up to 375 kW with high beam quality and a measured M2 value of 1.3~1.7.A newly designed all-solid step-index Yb-doped aluminosilicate large mode area fiber for achieving high peak power at near diffraction limited beam quality with local adiabatic tapering is presented. The 45µm diameter fiber core and pump cladding consist of active/passively doped aluminosilicate glass produced by powder sinter technology (REPUSIL). A deliberate combination of innovative cladding and core materials was aspired to achieve low processing temperature reducing dopant diffusion during fiber fabrication, tapering and splicing. By developing a short adiabatic taper, robust seed coupling is achieved by using this Yb-doped LMA fiber as final stage of a nanosecond fiber Master Oscillator Power Amplifier (MOPA) system while maintaining near diffraction limited beam quality by preferential excitation of the fundamental mode. After application of a fiber-based endcap, the peak power could be scaled up to 375 kW with high beam quality and a measured M2 value of 1.3~1.7

Optical Harmonic Vernier Effect: A New Tool for High Performance Interferometric Fibre Sensors

The optical Vernier effect magnifies the sensing capabilities of an interferometer, allowing for unprecedented sensitivities and resolutions to be achieved. Just like a caliper uses two different scales to achieve higher resolution measurements, the optical Vernier effect is based on the overlap in the responses of two interferometers with slightly detuned interference signals. Here, we present a novel approach in detail, which introduces optical harmonics to the Vernier effect through Fabry-Perot interferometers, where the two interferometers can have very different frequencies in the interferometric pattern. We demonstrate not only a considerable enhancement compared to current methods, but also better control of the sensitivity magnification factor, which scales up with the order of the harmonics, allowing us to surpass the limits of the conventional Vernier effect as used today. In addition, this novel concept opens also new ways of dimensioning the sensing structures, together with improved fabrication tolerances.Comment: 19 pages, 8 figures, Published in MDPI Sensor

Germania and alumina dopant diffusion and viscous flow effects at preparation of doped optical fibers

We report on germania and alumina dopant profile shift effects at preparation of compact optical fibers using packaging methods (Stack-and-Draw method, Rod-in-Tube (RiT) technique). The sintering of package hollow volume by viscous flow results in a shift of the core-pitch ratio in all-solid microstructured fibers. The ratio is increased by about 5% in the case of a hexagonal package. The shift by diffusion effects of both dopants is simulated for typical slow speed drawing parameters. Thermodynamic approximations of surface dissociation of germania doped silica suggest the need of an adequate undoped silica barrier layer to prevent an undesired bubble formation at fiber drawing. In contrast, alumina doping does not estimate critical dissociation effects with vaporous aluminium oxide components. We report guide values of diffusion length of germania and alumina for the drawing process by kinetic approximation. The germania diffusion involves a small core enlargement, typically in the sub-micrometer scale. Though, the alumina diffusion enlarges it by a few micrometers. A drawn pure alumina preform core rod transforms to an amorphous aluminosilicate core with a molar alumina concentration of only about 50% and a non-gaussian concentration profile

5G transport network requirements for the next generation fronthaul interface

To meet the requirements of 5G mobile networks, several radio access technologies, such as millimeter wave communications and massive MIMO, are being proposed. In addition, cloud radio access network (C-RAN) architectures are considered instrumental to fully exploit the capabilities of future 5G RANs. However, RAN centralization imposes stringent requirements on the transport network, which today are addressed with purpose-specific and expensive fronthaul links. As the demands on future access networks rise, so will the challenges in the fronthaul and backhaul segments. It is hence of fundamental importance to consider the design of transport networks alongside the definition of future access technologies to avoid the transport becoming a bottleneck. Therefore, we analyze in this work the impact that future RAN technologies will have on the transport network and on the design of the next generation fronthaul interface. To understand the especially important impact of varying user traffic, we utilize measurements from a real-world 4G network and, taking target 5G performance figures into account, extrapolate its statistics to a 5G scenario. With this, we derive both per-cell and aggregated data rate requirements for 5G transport networks. In addition, we show that the effect of statistical multiplexing is an important factor to reduce transport network capacity requirements and costs. Based on our investigations, we provide guidelines for the development of the 5G transport network architecture.Peer ReviewedPostprint (published version

5G infrastructures supporting end-user and operational services:The 5G-XHaul architectural perspective

We propose an optical-wireless 5G infrastructure offering converged fronthauling/backhauling functions to support both operational and end-user cloud services. A layered architectural structure required to efficiently support these services is shown. The data plane performance of the proposed infrastructure is evaluated in terms of energy consumption and service delay through a novel modelling framework. Our modelling results show that the proposed architecture can offer significant energy savings but there is a clear trade-off between overall energy consumption and service delay.Peer ReviewedPostprint (author's final draft