We experimentally investigate the performance of an active and passive optical fronthaul to be employed in a cloud/centralized radio access network (C-RAN) architecture based on software-defined radio (SDR) for 4G systems, and we discuss the viability to integrate these fronthaul configurations in coexisting 4G/5G systems based on SDR by considering the reconfigurable characteristics of SDRs and the capacity and latency characteristics of the optical fronthaul. The active optical fronthaul consists of two transponders employing dense wavelength division multiplexing (DWDM), whereas the passive optical fronthaul consists of a point-to-point scheme based on DWDM only. To perform a comparative study between the active and passive optical fronthaul in the C-RAN architecture, we have measured the throughput (bit rate) generated via iPerf® for uplink and downlink transmissions at different DWDM channels, and we analyze the losses and latency presented in both optical fronthaul schemes. We found that for different optical fronthaul lengths up to 21.76 km, the bit rate is practically the same for the passive and active fronthaul despite the higher optical losses present in the passive fronthaul in comparison to the active fronthaul. In addition, the latency among active and passive fronthaul are almost similar with an estimated increment of 20 μs in the active fronthaul. These results are independently of the number of remote radio heads (RRHs) and user equipment (UEs) considered in the C-RAN architecture. Our findings put forward the proposed DWDM passive fronthaul as a viable, less complex, and cost-sensitive solution for C-RAN systems with fronthaul lengths up to 21.76 km. These results and all the experiences reported on the C-RAN implementation provide valuable information to design and develop 4G and 5G C-RAN architectures based on SDR with the capability to operate in a DWDM optical fronthaul infrastructure.
We present a numerical analysis of the average intercore crosstalk (IC-XT) of wavelength-division multiplexed (WDM) optical channels in a homogeneous two-core fiber system. This analysis is performed considering cores with zero-dispersion wavelengths at 1550 nm. In the analysis, we consider 11 WDM channels spaced 100 GHz apart transmitted in three different schemes, one centered at 1510 nm with negative dispersion D = − 3.5 ps / nm · km, one centered at 1550 nm with D = 0, and one centered at 1590 nm with D = + 3.5 ps / nm · km. This selection allows for the observation of how the IC-XT of WDM channels is modified using positive, zero, and negative dispersion parameters. To analyze more realistic scenarios of IC-XT in multicore fibers, we considered random bending and twisting perturbations along the fiber. In addition, we considered fiber nonlinearities such as four-wave mixing (FWM) among WDM channels. The results show that FWM produces a power transfer among the transmitted WDM channels that depends on the dispersion parameter D at core 1, and this effect is transferred to the average crosstalk of the WDM channels at core 2. Therefore, the average IC-XT of WDM channels can be modified in a controlled way by selecting an adequate dispersion parameter D in combination with FWM nonlinearity. These results provide valuable information for understanding the wavelength dependence of the average IC-XT of homogeneous multichannel MCF systems working around a zero-dispersion wavelength.
An analytical and numerical analysis of light extraction from light pipes using total internal reflection grooves with linear and elliptical profiles is presented. We performed the study considering light sources with different aperture angles, such as sunlight delivered by optical fibers and LEDs. With this analysis, we propose an analytical model based on the edge ray concept that allows selecting the most convenient profile, size, and orientation of the groove to extract light with a desired illumination area according to the source aperture angle employed in the light pipe system. We also have numerically found that for sources with high aperture angles, the light extracted by the linear and elliptical grooves produces similar irradiance and angular distributions, whereas for sources with low aperture angles, the elliptical groove focuses the extracted light and produces a higher angular distribution in comparison to this obtained with the linear groove. Our results are scalable to different light pipe dimensions and provide a systematic way to obtain preliminary designs of grooves for lighting systems that employ optical sources with different aperture angles.
The temperature response of a tapered holmium-doped fiber amplifier and its impact in the performance of fiber lasers and temperature fiber sensors has numerically been analyzed. Different pump schemes and different longitudinal shapes of the tapered-doped fiber were investigated, and it was found that a parabolic shape of the tapered fiber amplifier in a co-propagating pump scheme shows the highest sensitivity to temperature changes. In particular, the temperature sensitivity of the amplified signal was 2.5 × 10 − 4 ° C for 1 W of pump power and 1 m of doped fiber length. In addition, this sensitivity can be increased up to 10 times for fiber lengths shorter than 1 m and pump powers lower than 300 mW. Our results can be used to describe the temperature response of tapered fiber amplifiers in the mid-infrared spectral region and contribute with new information for the development of fiber lasers and fiber temperature sensors.
Lightpipes are used for illumination in applications such as back-lighting or solar cell concentrators due to the high irradiance uniformity, but its optimal design requires several parameters. This work presents a procedure to design a square lightpipe to control the light-extraction on its lateral face using commercial LEDs placed symmetrically in the lightpipe frontal face. We propose the use of grooves using total internal reflection placed successively in the same face of extraction to control the area of emission. The LED area of emission is small compared with the illuminated area, and, as expected, the lateral face total power is attenuated. These grooves reduce the optical elements in the system and can control areas of illumination. A mathematical and numerical analysis are presented to determine the dependencies on the light-extraction.
The efficiency in Fresnel lenses is affected by three principal sources: energy loss by absorption, chromatic dispersion and reflectance losses at refracting surfaces. On this subject, the design of nonimaging Fresnel lenses integrated by refractive and total internal reflection prisms is presented. This design method uses iterative calculations for design every prism and it selects the best option for avoid reflectance losses. A design and characterization of a Fresnel lens that takes chromatic aberration into account is shown, including a comparison with a nonimaging Fresnel lens composed only by refraction prisms is performed and with other integrated by only total internal reflection prisms. In addition, the study about how acceptance angle and the number of prisms affects the final transmittance of the lens is included.
The efficiency of sunlight collection systems is related to the optical element used as a collector. On this subject, the design of a nontracking solar collector that consists of a segmented nonimaging Fresnel dome is presented. It is formed by the conjunction of different zones for solar collection, where each one is a nonimaging Fresnel lens that collects a specific angular range (θin) of sunlight received in the northeast of Mexico, but the methodology presented can be easily extended to other geographic locations. The final design is a semistationary segmented collector with a 100-cm diameter and 50-cm focal length that needs a 180-deg rotation over the XY-plane in each equinox. The numerical simulations show that the nontracking segmented collector has a combined acceptance semiangle of θin=±105 deg with an average efficiency of over 67% from 9:00 to 18:00 h. The spatial and angular distributions of the sunlight collected are also included. This design has a collection area equal to that of a single nonimaging Fresnel lens with an acceptance semiangle of θin=±45 deg. These results are reproducible and provide valuable data for designing nontracking solar collectors based on nonimaging Fresnel lens.
Extraction light in light-pipes with different specular surfaces was analyzed. In the analysis, the impact of the surface shape in all properties of the extracted light in order to obtain an efficient extraction and a uniform illumination using a LED as light source. Also, several parameters of the specular surface to obtain spatial uniformity inside the light-pipe are considered. In this case, the simulation was made for a rectangular lightpipe. One objective of this work is to compare how the front face shape of the specular surface can affect the extraction of light in the lateral face of the light-pipe, only straight and elliptical front faces were used in this work and the comparison between them at different tilts and lengths were made. The main purpose of the front face was extract the light uniformly at the lateral face and this was done by studying simulations on OpticStudio Zemax. The results show how the extraction length is lower in the elliptical front but its total power performs better than the line front.
The success of solar systems, such as photovoltaic and sunlight illumination systems, is principally determined
by the primary optical element used as collector. On this subject, the design of a segmented nonimaging Fresnel
lens is presented; this collector is formed by the conjunction of different zones for solar collection, where every
zone is made of a nonimaging Fresnel lens that collects a specific angular range of sunlight, according to the solar
radiation of the northeast received in Mexico. Every collector section focus in a common area. The different
zones are designed considering the apparent solar movement due to the daytime and the seasonal displacement
over the year. The collector total performance is presented, including spatial and angular distribution. The
collector presents an average performance over 80%, with an acceptance half-angle of 120°, and a collection area
similar to that in a collector with 45° of acceptance half-angle.
Homogenize light is the principal purpose of mixing rods. Light extraction from mixing rods is proposed by changing the shape of the face, the rod or a combination of both for many applications. Light extraction also can be done by its lateral face by cutting the Mixing rod. In this work a simulation of square and hexagonal poly(methyl methacrylate) (PMMA) mixing rods were made in Radiant Zemax ® 12 release 2 designed with an elliptical transversal cut to extract light from a lateral face. The cut is specular for rays that fulfill the total internal reflection condition, the reflected rays are deviated and the Total Internal Reflection (TIR) condition broken, then, extracted. An advantage of this cut is that it can be controlled in depth to extract the amount of light required and the remaining light used for other purposes. Also it can reduce the size of the mixing rods and optical components. For the simulation, an LED light were used as source, the light were homogenized by the mixing rod and due to it, the light extracted is also homogenous. The polar power map, radiant intensity and color of the light extracted are presented and compared in both mixing rods.
Among the main challenges for systems based in solar concentrators and plastic optical fibers (POF) the accuracy needed for the solar tracking is founded. One approach to overcome these requirements is increasing acceptance angle of the components, usually by secondary optical elements (SOE), however this technique is effective for photovoltaic applications but it has not been analyzed for systems coupled to POFs for indoor illumination. On this subject, it is presented a numerical analysis of a solar collector assembled by a Fresnel lens as primary optical element (POE) combined with a compound elliptical concentrator (CEC) coupled to POF in order to compare its performance under incidence angle direction and also to show a trade-off analysis for two different Fresnel lens shapes, imaging and nonimaging, used in the collector system. The description of the Fresnel lenses and its designs are included, in addition to the focal areas with space and angular distribution profiles considering the optimal alignment with the source and maximum permissible incident angle for each case. For both systems the coupling between the optical components is analyzed and the total performance is calculated, having as result its comparison for indoor illumination. In both cases, the systems have better performance increasing the final output power, but the angular tolerance only was improved for the system with nonimaging concentrator that had an efficiency over 80% with acceptance angles 𝜃𝑖 ≤ 2° and, the system integrated by the imaging lens, presented an efficiency ratio over 75% for acceptance angles 𝜃𝑖 ≤ 0.7°.
This work shows the results obtained from the “O4K” Project supported by International Society for Optics and Photonis (SPIE) and the Universidad Autonoma de Nuevo Leon (UANL) through its SPIE Student Chapter and the Dr. Juan Carlos Ruiz-Mendoza, outreach coordinator of the Facultad de Ciencias Fisico Matematicas of the UANL. Undergraduate and graduate students designed Optics representative activities using easy-access materials that allow the interaction of children with optics over the exploration, observation and experimentation, taking as premise that the best way to learn Science is the interaction with it. Several activities were realized through the 2011-2013 events with 1,600 kids with ages from 10 to 12; the results were analyzed using surveys. One of the principal conclusions is that in most of the cases the children changed their opinions about Sciences in a positive way.
This work presents preliminary results on wavelength sensitivity due to mechanically induced long period fiber grating (LPFG) on both standard single-mode and Er-doped fibers. The work presents and compares results for both types of fibers under different torsion conditions. In order to apply the torsion one of the fiber ends is fixed while torsion is applied on the other end. A LPFG whose period is 503μm is used to press on the fiber after the torsion, this will allow for micro curvatures to be formed on the fiber, which will in turn generate a periodical index perturbation on it. Here, it was noted that the rejection band shifts to shorter wavelengths for Er-doped fibers. It was detected that for torsion of 6 turns applied to 10cm doped fiber the wavelength peaks can shift up to 25nm, which is longer than similar results reported on standard fibers. Therefore, by using Er-doped fibers this technique will give more sensitive and accurate results on the real conditions of the structure under study. These results can be employed for sensing applications, especially for small to medium size structures, being these structures mechanical, civil or aeronautical. Theoretical calculations and simulations are employed for experimental results validation.
We present a numerical analysis of different fiber termination shapes in order to study the maximum numerical aperture that can be obtained in end emitting plastic optical fibers with diameters around 10 mm. Our analysis includes the modeling of polished fibers with parabolic shape, conical lensed fibers, and wedged fibers with different lengths, angles and curvatures respectively. The optimization of these parameters allows us to obtain a maximum possible angle which the light can be emitted at the plastic fiber end. These results contribute to minimize the use of fiber components in luminaire systems which can be based in solar concentrators coupled to plastic optical fibers, and consequently it allows us to reduce their installation cost. We also analyze the light distribution of the emitted light and the optical tolerances of the parameters above mentioned to evaluate the performance of the optimized fiber lens. These results are of great interest for the improvement and design of compact luminaire systems based in optimized plastic fiber lens for indoor illumination.
We present an experimental characterization of a fiber laser composed by an Yb-doped fiber spliced with a birrefringent
photonic crystal fiber and a mechanically-induced long-period grating (LPG) into the laser cavity. According to the
torsion properties of the LPG induced in the photonic crystal fiber, the Yb-doped fiber laser can be highly sensitive to
twist and it can shown novel properties in its laser emission. Also, we show the splitting of attenuation bands of a longperiod
fiber grating induced mechanically in different twisted photonic crystal fibers with high birefringence and their
applications on the performance of tunable and switchable multiwavelength double-clad Ytterbium-doped fiber lasers.
The thermal effect of an Yb-doped fiber laser with fattening is numerically investigated. We have identified two principal sources of thermal sensitivity: The temperature dependence of the cross-section of the pump and signal radiations, and modifications of the numerical aperture (NA) due to changes in temperature. We have found that the first factor affects principally the thermal response of the fiber laser with fattening and this sensitivity can be modulated according to the fattening ratio. Additionally this thermal response is higher than that found in doped fibers without fattening. Our results are reproducible and contribute with new information for the development of novel temperature fiber laser sensors
We report the numerical investigation of an Yb-doped fiber amplifier with a taper end in order to be used as a thermal sensor. The spectral fluorescence intensity of the Yb-doped fiber is highly modified when the tapered end is subject to different temperatures from 20 to 150°C, and these changes are more sensitive than that presented in untapered doped fibers. This enhanced temperature response is attributed to the taper effects on the temperature dependence of the crosssections of the pump and signal radiations and additional changes of the numerical aperture of the doped tapered core due to temperature. These results can be extrapolated to other doped fibers and contribute with new information for the development of temperature fiber laser sensors.
The temperature sensitivity of a tapered Yb-doped fiber laser is numerically investigated. The laser rate equations are modified to analyze the output characteristics of the tapered fiber laser in the continuous wave regime under different temperature conditions. Numerical analysis shows that for different pump schemes, high sensitivity can be achieved when the pump power is reduced to close to the threshold value. Our results are reproducible and contribute new information to the development and optimization of tapered Yb-doped fiber lasers and temperature fiber laser sensors.
Metallo Dielectric Photonic Crystals formed by same periodicity metallic inserts in a Dielectric Photonic Crystal show
three kind of band gaps, those at the well know dielectric band gap, the ones attributed to the absorption of metal to low
frequencies and a new class of metallic bandgaps. Numerical studies have confirmed that while the dielectric band gap
width is basically described by the refraction index contrast, the width of the metallic band is described by the thickness
of the metal inserts. In this work we carry on the corresponding analytical analysis of both band gaps for this one
dimensional ternary dielectric-dielectric-metal structure. The stack that we are proposing is a quarter-wave for the
dielectrics and the thickness of the metallic layers is changed as a free parameter. Using standard transfer matrix
formalism, we find a closed form of the dispersion relation and from it; we have analytically demonstrated the formation
and width of the dielectric band gap and its metallic perturbation, as well as those of the additional metallic band gap.
We present the numerical modeling of the interaction between a spatial soliton and a surface plasmon polariton under
leak and strong coupling in the following two cases: at metal/dielectric/Kerr structures and metal/Kerr structures in 1D.
Here, we solved the vectorial and nonlinear wave equation using a novel iterative method based in self-autoconsistency,
and we found two kinds of nonlinear stationary solutions called odd and even modes. On the other hand, the propagation
of the stationary solutions is performed for the metal/Kerr system, and quantitatively it shows that odd modes are more
stable than even modes when the spatial soliton and surface plasmon are strongly coupled. Also, we analyzed the
influence of the dielectric layer between the metal and Kerr media, and we discuss their implication and feasibility for
applications in photonic nanodevices. Additionally, the advantages and disadvantages of the numeric method used to
obtain the stationary solutions are discussed. The results obtained in this work are reproducible and contributes with new
information for the development of power-tunable photonic nanocircuits based in nonlinear plasmonic waveguides.
We investigated numerically the TM electric field solutions of a dielectric slab formed by a photorefractive crystal with
diffusion-type nonlinearity and limited by two metallic films. This study allows us the analysis of nonlinear surface
optical waves as nonlinear solutions of the photorefractive crystal slab. Additionally, we analyzed the influence of these
nonlinear solutions to excite surface plasmon-polariton waves at the metallic interfaces. In this case, the coupling
between plasmons and nonlinear solutions it is possible because only TM electromagnetic waves are supported by a
metal-dielectric planar waveguide. Here, we solved the vectorial and nonlinear wave equation using an iterative method
based in self-autoconsistency. With this algorithm, the coupling between the waveguide modes and the surface plasmon-polariton
waves are systematically investigated. The results obtained in this work are reproducible and contributes with
new information for the design of tunable plasmonic devices based in nonlinear photorefractive crystals.
We present the calculations of the higher order dispersion coefficients in a photonic crystal fiber. The dispersion
coefficient is obtained from the calculated effective index of the fiber structure by double differentiation with respect to
the wavelength (or frequency), or from the integral formula used to calculate the group index. Although both approaches
are equivalent we show that they lead to totally dissimilar results, like different zero dispersion wavelength and hence the
higher-order dispersion coefficients are different. In fact, the way in which the higher-order dispersion coefficients are
calculated will affect the prediction of the dynamics of the supercontinuum generation. This effect will be discussed in
this work.
A numerical study of the effects of tapering a hollow-core photonic bandgap fiber (HC-PBGF) on the spatial
parameters: effective area, nonlinear parameter and dispersion parameter is presented. The taper on the fiber is
modeled by scaling the cross section of the original fiber geometry. Both the air and the silica contribution to the
effective area and the nonlinear parameter are shown. The obtained results show a blueshift of the transmission
band and of the zero-dispersion wavelength. By tapering the fiber 30%, the transmission band and the zerodispersion
wavelength blueshift around 300 nm and 320 nm, respectively. HC-PBGFs have made possible the
study of nonlinear optical effects and by tapering the fiber, such nonlinear phenomena can be made stronger.
A three-wavelength ytterbium-doped fiber laser based on a long period grating induced mechanically in a twisted holey
fiber is proposed and demonstrated. The long period grating is inserted into the laser cavity to introduce inhomogeneous
loss in order to obtain up to three output laser wavelengths at room temperature. The lasing wavelengths are localized at
1081.5 nm, 1090.5 nm, and 1100.7 nm with an average wavelength separation of 9.6 nm which can be slightly modified
by changing the twist rate of the holey fiber into the laser cavity.
A birefringence compensation method for a mechanically induced tunable long period holey fiber grating is proposed.
With this method the tunable long period holey fiber grating becomes polarization-insensitive. A device with such
characteristics is desirable in applications where filter tunability is used to reject (or simply attenuate) non desired optical
bands. Characterizations with polarized and nonpolarized light are presented and the potential applications are discussed
as well.
In this work we demonstrate direct writing of a computer generated hologram using optical damage in glass as a possible recording process. The recording was performed by ablation in BK7 optical glass. We used a 10 Hz, 35 picoseconds, 5 mJ Nd:YAG pulse focused using a lens to create 50 μm spots. It was observed that the material surrounding the damage spot was altered producing a 70 μm minimum pixel resolvable separation by induced birrefringence.
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