Multi-core fibers (MCFs) are promising solutions for high power fiber based devices as they reduce nonlinearity and other unwanted detrimental effects, like transverse mode instability, by transporting, instead of a single high power beam, several low-powered ones to be coherently combined at the fiber output. This method relies on accurate evaluation of the phase differences between signals in different cores, which are significantly impacted by changes in the effective index of the propagating modes. For this to be effective, spatial heat generation must be accounted for. In particular, the heat flux from the doped cores to the external boundary causes a temperature gradient across the fiber, which affects the refractive index distribution, creating the chance for effective index change and thus dephasing of the output beams, which is harmful for beam combining. The results of in-depth numerical analysis on the performance of 9-core and 16-core MCFs under thermal effects are presented by studying the mode phase sensitivity to heat load and by introducing a coupled-mode theory model to study possible optical coupling effects. The effectively single-mode condition is also investigated by calculating the core modal overlap differences between fundamental and higher-order modes.
Multi-core fiber capability to deliver several independent beams in a single structure has been deeply investigated to obtain spatial multiplexing in optical communication. Recently, the coherent beam multiplexing idea has been extended to high power fiber laser field, where multi-core fiber amplifiers, combining low power beams, promise to overcome thermal mode instability, which characterizes single-core fiber amplifiers. Although coherent output beam combination is advantaged in multi-core fiber, the understanding of core phase shifts is necessary to implement efficient beam combination. In presence of thermal load, induced by pump-to-signal conversion quantum defect, a refractive index gradient is formed on the multi-core fiber amplifier cross-section, thus changing core propagation properties and possibly creating unwanted core couplings. In this work a 9-core double-cladding fiber amplifier is numerically investigated by varying the core thermal load, from 2 to 15 W/m, in order to understand the structure propagation mismatch. The 9 cores are organized in a 3×3 regular grid, each core has a diameter of 19 μm and a spacing of 55 μm. Cores numerical aperture is 0.06. The outer cladding has a diameter of 340 μm. A comparison between a rod-type fiber amplifier configuration and a flexible fiber amplifier has been performed. Results show that the cores can be divided in three groups according to their propagation properties: central core, side cores, and corner ones. The phase shift between these groups, or equivalently the effective index difference, becomes higher with the increase of thermal load. These observations are fundamental to implement a model for beam propagation in presence of thermal effect, to investigate the amplification dynamics along z-direction.
Photonic Crystal Fibers represent a good platform for the development of sensitive and cheap sensors for the detection of protein and DNA sequence. The holes running along the fiber allows the infiltration of biological substances and for biological layers to attach on the air-dielectric interfaces. In addition, the presence of a hollow core can further increase the infiltration feasibility and the sensor sensitivity.
Recently, the possibility in using hollow core tube lattice fibers (HC-TLFs) for label-free DNA detection have been numerically investigated. The sensing is based on the waveguiding mechanism, that is inhibited-coupling which makes the HC-TLF transmission properties particularly sensitive to the thickness of the glass struts composing the microstructured cladding of those fibers. The molecular interactions between the surface of the glass and the target to be detected results in a generation of a biological layer which modifies the strut thickness and thus the fiber transmission properties.
The aim of the present work is to experimentally demonstrate that HC-TLF can be successfully used as bio sensor for proteins. After a functionalization of the silica surface through a solution of aptes, a layer of biotin was deposited on inner surfaces of the fiber. The fiber was than infiltrated with a solution containing streptavidin and an additional bio-layer is deposited on the surfaces. The experimental results demonstrated a red shift of the entire fiber transmission spectrum of about 7 nm corresponding to an additional bio-layer with thickness of 6.45 nm which is fully compatible with the size of streptavidin molecules of about 6nm.
The dramatic progress in power-scaling of ultra-short pulse (USP) lasers and their growing use in industrial applications call for flexible and robust beam delivery systems (BDS) over several meters with no temporal or modal distortions. Inhibited coupling (IC) hypocycloid Kagome hollow-core photonic crystal fiber (HC-PCF) has recently proved to be an excellent solution for guiding these USP. In order to reduce further the attenuation of such fiber and then to increase the BDS capabilities, we report on an optimized IC Kagome HC-PCF exhibiting record loss level (8.5dB/km at 1030nm) associated with a 225nm wide 3-dB bandwidth and low bend sensitivity.
The development of low loss, small size and flexible waveguides is one of the most challenging issues of THz research due to the poor characteristics of both metal and dielectrics in this frequency range. Hollow core tube lattice fibers (HCTLFs) have been recently proposed and experimentally demonstrated to overcome this problem. However, they require very large hollow core size leading to big and hardly flexible fibers. Scaling law analysis plays an important role in determining the best trade-off between low loss and small fiber diameter. The dependence of the confinement on frequency and core radius are here numerically investigated. Results show that confinement loss exhibits a stronger dependence on core size and frequency with respect to other hollow core fibers proposed for THz waveguiding, such as Bragg, Tube, and Kagome fibers.
Confinement Loss of microstructured fibers whose cladding is composed by a triangular arrangement of tubes of various
shapes is theoretically and numerically investigated. Kagome Fibers belong from this family of fibers with cladding
tubes with hexagonal shape. The shape of the cladding tubes is proved to strongly affect the performance of the
microstructured fiber. In order to understand the reasons for this behavior, the spectral properties of the tubes that
constitute the cladding are investigated first. It is proved that also these tubes suffer from additional Fano Resonances
when they are given a polygonal shape. It is proved that, by using the analytical model developed for the stand alone
polygonal tubes, it is possible to predict the spectral position of Fano Resonances also in microstructured fibers. This is
extremely important since it suggest new ways to reduce confinement loss in kagome fibers and microstructured fibers in
general.
Dispersion and loss properties of hollow core tube fibers with elliptical cross section are numerically investigated.
Results show unusual characteristics. For example, the birefringence always goes to zero in the middle of the low loss
region irrespectively of the ellipticity and it always assume opposite sign approaching the two edges of the low loss
region.
Three different first order polarization mode dispersion compensation techniques are compared in terms of outage probability, calculated for a fixed value of sensitivity penalty at the receiver, with the purpose of evaluating their impact on 10 Gbit/s communication system performance. A numerical approach is followed for different conditions of polarization mode dispersion and for varying compensation parameters, looking for the best operating point of compensation.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.