In this invited paper, we discuss how optical fibers, the de-facto choice for last-mile connectivity of radio access network equipment, can rise to the challenges of 5G. We start by addressing technologies and trends for point- to-point connectivity, from fully passive to auto-tunable wavelength division multiplexing. Then, we assess niche solutions based on point-to-multipoint optical connectivity and possible scenarios allowing fixed-mobile convergent topologies. Finally, we brie y exploit the potential of abstraction of optical and radio access equipment through software defined networking for intelligent and multi-tenancy ready traffic management compliant with the constraints of mobile interfaces and hosting locations of cloud infrastructures.
Dense wavelength division multiplexing (DWDM) metropolitan networks are currently being extensively deployed with distances ranging from a couple of ten’s kilometers to several hundred kilometers. 40 DWDM channels are commonly used; each of them is carrying today Ethernet or Fiber Channel traffics ranging from 1 to 10 Gb/s. This type of network requires achromatic components, for which the provider can fix the operating wavelength in order to have the same type of components in the consumer’s home. The DWDM sources could be based on a tunable laser source or on a selfseeded- reflective semiconductor optical amplifier (RSOA) as recently proposed. In this last case, the RSOA is coupled to a mirror, located at a few kilometers in a central office. A frequency filter fixes the wavelength. The RSOA is then directly modulated at a few GHz. However even if a 100 GHz-wide filter is used, a much narrower slot of wavelengths is selected on the “red” side of the transmission window of the filter. This communication gives from a Green function approach the modal structure of an RSOA coupled to a long cavity with strong optical feedback and explains how such coupled structure is operating.
In this paper we review our recent works on low cost lasers and remote modulators for Optical Network Unit in access
network. Our work is carried out in the context of an FTTH PON migration scenario towards 10Gbit/s base rate as well
as towards more capacity and flexibility using WDM technology. All components are based on the attractive thermal,
gain and absorption properties of AlGaInAs/InP material system. As a first step to the speed increase we propose a new
uncooled 10Gb/s laser based on a self thermal compensation principle. As a next step, new WDM PON architectures will
require wavelength agnostic component for ONU. For this purpose, we demonstrate new colorless concepts on 10Gb/s
remote amplified electro-absorption modulators. We show low-cost FTTH components may also be attractive for
emerging access-metro WDM technology introducing colorless principle in reconfigurable add and drop multiplexers
We present a 1:2 variable optical splitter (VOS) with a self-latching property. This new generation of optical coupler presents two coupling ratio states (50%–50% and 100%–0%) and is based on magneto-optical technology. Fabricated VOS has an intrinsic loss of about 1 dB with a polarization-dependent loss (PDL) less than 0.1 dB. The flatness of the optical characteristics has also been measured in the C+L band at various temperatures. The active optical component needs an electrical pulse (with =1 ms) of around 2 V and 60 mA to be activated. Various passive optical network (PON) architectures using active 1:2 VOSs with self latching are investigated here. These components are cascaded to make a splitter with a tunable number of branches. The use of this splitter allows the achievement of adaptive, flexible, and scalable optical network architectures. The devices can be implemented in the central office (CO) or in the middle of the network. Last, we propose a remote powering and/or monitoring technology using a fiber-optic link in order to activate the dynamic optical power splitter. The key element of this technology is a pigtailed power converter module. The powering system avoids use of a local power supply via a power line and/or battery, maintains the passive and reliable properties of the network, and significantly limits its cost.
We have developed a simple and low-cost microlens for optical communication systems involving the coupling of laser diodes or integrated waveguides to single-mode fibers (SMFs), and fiber-to-fiber interconnection. More generally, the applications concern coupling active or passive components to SMFs. The novelty consists in using a graded-index section of 125-µm core diameter without cladding and taking into account the diffraction effects. This new microlens offers a wider range of mode field diameters (from around 5 to 90 µm) and working distances (up to 2000 µm) than previously demonstrated. This paper investigates the influence of the Fresnel diffraction of a Gaussian beam, during its propagation through the microlens, on the mode field intensity profile, the working distance, and the coupling efficiency of this kind of microlens in front of a SMF. It shows that while truncation causes multiple maxima of the coupling efficiency as a function of z displacement, it does not decrease the maximum coupling efficiency.
For high speed remote colorless modulation in FTTH technology, a new 10Gbit/s monolithically integrated amplified
reflective electroabsorption modulator (R-EAM-SOA) is demonstrated over 50nm spectral range and over 20°C-60°C,
with excellent eye diagrams.
A compact large Gaussian mode field diameter single-mode fiber is developed. This expanded single-mode fiber consists of splicing fibers with various lengths and characteristics. The principle of this optical arrangement is to excite the first mode of propagation of the multimode graded index to preserve a Gaussian field. The coupling properties are numerically analyzed, considering the effects of gap, radial offset, and tilt. The fiber connections loss between the same kinds of expanded single-mode fibers with a Gaussian mode field diameter of 18 µm is measured with an average of 0.55 dB. This large mode field diameter is preserved on a long length of fiber >20 cm.
To improve variable optical attenuator (VOA) performance, the object of this study is to know the most appropriate structure of a polymer-dispersed liquid crystal (PDLC) composite. In fact, using its electro-optical properties, PDLC can be inserted between two optical fibers for adjusting the coupling efficiency. We utilize here the photopolymerization-induced phase separation (PIPS) method as a fabrication process. Furthermore, we present a theoretical analysis of light scattering by anisotropic spheres based on the anomalous diffraction approach (ADA) and compare this model with some experimental results. The optical attenuation (OA) range is optimized in the case where LC, the droplets nematic directors, are randomly oriented. If the nematic directors have a quasiprivileged direction, we demonstrate that PDLC transmission depends on the incident light polarization. Polarization-dependent loss (PDL) and OA behaviors are then studied at the 1.55-µm wavelength according to several parameters such as PDLC thickness, LC droplet size, and the device driving voltage.
A new concept is proposed for lenses fibers fabricated according to a collective and low cost process is based on the cleaving and splicing of optical fiber ribbons and is suitable for the coupling of laser diode arrays and fiber ribbons.
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