Abstract:
A method for connecting a number of users with at least one signal bearing optical fiber contained in an optical cable. The method includes: a) interrupting the signal bearing optical fiber at a first branch point, obtaining a first optical fiber segment upstream of the branch point and a second optical fiber segment downstream of the branch point; b) providing an optical splitter at the branch point, the optical splitter including an input and two outputs; c) coupling the first optical fiber segment with the input of the optical splitter; d) coupling a first output of the optical splitter with a first user; e) coupling a second output of the optical splitter with a downstream optical fiber segment of an interrupted optical fiber contained in the optical cable; and f) coupling the downstream optical fiber segment with at least one further user at a further branch point downstream the first branch point.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Field of the Invention 
         [0002]    The present invention relates to an optical network arrangement for connecting a plurality of users, even in relatively high number, with a reduced number of optical fibers, and particularly to the deployment of cables for the connection of users to optical networks. 
         [0003]    Overview of the Related Art 
         [0004]    The deployment of broadband telecommunications networks calls for using optical fibers for the so-called “last mile”, i.e. the last trunk of the telecommunications network to which network termination devices, like for instance modems, network termination units (NTU) or, set-top boxes for receiving cable television services are directly connected. User devices such as computers, IP (Internet Protocol) phones and similar devices connect to the broadband telecommunications network via the network termination device. 
         [0005]    Typically, the deployment of the last mile of an optical telecommunication network provides for the lay in the field of optical cables containing a plurality of optical fibers, for instance in a number variable from 6 to 48. The cables are routed through conduits that can for example develop through or along the walls of a multi-floor building, often for more or less vertical segments, or, in the case of separate buildings set in succession along a city street, the optical cables extend horizontally through conduits preferably located under of the ground level. 
         [0006]    Typically, an optical cable of the type adapted for this use includes a tubular element, or sheath, inside which several optical fibers are placed. Depending on the specific type of application, the optical fibers can be accommodated within the sheath without protections, or they may be covered by a protective coating, or they may also be gathered in independent groups (also referred to as microcables or micromodules) contained in a thin tubular coating. 
         [0007]    In order to make the connection of the different users to the optical network, it is necessary to lead one or more optical fibers to the sites (apartments, houses, offices) of the users. To this end, openings need to be made in the sheath of the optical cables, so as to be able to access the optical fibers accommodated within each cable. Through such openings, the optical fibers can be at least partially drawn out, extracted from the cable and routed where needed, for example to sockets provided for in the premises of the users, to which the respective users can be connected. 
         [0008]    An example of such deployment is provided by WO 2009/113112 in the name of the same present Applicant, wherein optical fiber units contained in an optical cable are connected to users by means of the phases of: providing an opening in a sheath of the optical cable to access the optical fiber units contained in the optical cable; extracting a segment of at least one optical fiber unit from the optical cable through the opening; inserting a free end of the extracted segment of optical fiber unit into a protection tube; making the protection tube slide on the extracted segment of optical fiber unit to insert an end portion of the protection tube, distal from the free end of the extract segment of the optical fiber unit, into the optical cable through the opening; positioning a closure element on the optical cable in correspondence of the opening so as to substantially realize a closure thereof; securing in removable way the closure element to the optical cable and bringing the free end of the extracted segment of optical fiber unit in correspondence of a connection point of a user device. 
         [0009]    Another type of deployment for connecting different users is disclosed, for example, in WO 2006/13655, wherein an optical cable is disclosed containing several optical microcables where two openings in the external sheath are made: a first opening in correspondence of the point at which the cabling for the connection of a subscriber has to be realized, and a second opening downstream thereof, at a distance of the order of about some meters or tens of meters from the first opening. One of the optical microcables contained in the optical cable is selected (for example based on its color) and cut in correspondence of the second opening, and the segment of microcable between the first opening and the point of cut is then extracted from the optical cable through the first opening. The extracted microcable segment is then inserted into a pre-installed microconduit that extends to the connection point of the subscriber, or, depending on the circumstance, to a branch box. 
         [0010]    Finally, US 2008/0240662 discloses a duplicated use of optical fibers in an optical cable. The optical cable comprises a main optical fiber module and a secondary optical fiber module. Optical fibers of the main optical fiber module are sectioned, at one end, and connected to optical fibers of the secondary optical fiber module in order to form a connection loop. 
       SUMMARY OF THE INVENTION 
       [0011]    It often happens that the optical cable has to be passed through conduits already existing in buildings or other infrastructures, originally intended to contain other types of cables, for instance for the distribution of electric energy and/or of television and/or telephone signals and/or other optical fiber cables. This is for example the case where optical fibers have to be deployed in buildings or beneath infrastructures built in relatively remote past times. It also often happens that the optical cable has to be passed through conduits located under ground level along streets and roads, and these conduits may already be occupied with existing other cables. Therefore, a very limited space may be available for the lay of optical cables to the extent that the number of optical fibers comprised in the optical cable which can be laid could not suffice for coupling of all the users to be connected with the optical network. 
         [0012]    In view of the above, the Applicant has observed that known prior art deployment systems and methods do not provide a satisfying solution adapted to allow utilization of congested ducts, that would otherwise not support conventional realizations for maximizing the fiber efficiency of an optical network. 
         [0013]    The Applicant has found that it is possible, in the same cable, taking out an optical fiber through which an optical signal propagates, interrupting said optical fiber in a point of the cable, splitting the optical signal of such interrupted optical fiber into split optical signals at said point, as required to connect a user, and, downstream of the interruption, continuing to propagate at least some of the split optical signals to further users, by injecting such some split optical signals into the same optical fiber after the interruption thereof, or/and, if available, into further interrupted optical fibers of the cable, thereby achieving the result of connecting a high number of users with a reduced number of optical fibers. 
         [0014]    The present invention relates to a method for connecting users, even in relatively high number, with an optical fiber contained in an optical cable, comprising the steps of interrupting the optical fiber at a branch point obtaining a first corresponding optical fiber segment upstream of said branch point and a second corresponding optical fiber segment downstream of said branch point; providing an optical splitter at the branch point which comprises an input and at least two outputs; coupling the first corresponding optical fiber segment to the input of the optical splitter provided at the branch point; coupling a first output of the optical splitter with at least one user; coupling the second output of the optical splitter at the branch point to the second corresponding optical fiber segment or to a further optical fiber segment of a further interrupted optical fiber. 
         [0015]    In one embodiment of the invention, said downstream optical fiber segment of an interrupted optical fiber is said second optical fiber segment. 
         [0016]    In one embodiment of the invention, in which said downstream optical fiber segment of an interrupted optical fiber is an idle optical fiber segment of a further optical fiber. 
         [0017]    In one embodiment of the invention, the method further comprises the step of coupling the first optical fiber segment at one end thereof with a network element for propagating one or more optical signals from/to the network element to/from the user and/or the further user. 
         [0018]    In one embodiment of the invention, the method further comprises the following steps: interrupting the second optical fiber segment at the further branch point, and providing a further optical splitter at the further branch point, the further optical splitter comprising an input and at least two outputs; coupling the second optical fiber segment with the input of the further optical splitter provided at the further branch point, and coupling one of the at least two outputs of the further optical splitter with the at least one further user. 
         [0019]    In one embodiment of the invention, the method further comprises repeating the following steps: coupling said downstream optical fiber segment with at least one further user at a further branch point downstream the first branch point; interrupting the second optical fiber segment at the further branch point, and providing a further optical splitter at the further branch point, the further optical splitter comprising an input and at least two outputs; coupling the second optical fiber segment with the input of the further optical splitter provided at the further branch point, and coupling one of the at least two outputs of the further optical splitter with the at least one further user in correspondence of at least one subsequent branch point downstream said further branch point. 
         [0020]    In one embodiment of the invention, the step of coupling a first output of the optical splitter with a first user comprises coupling the first output of the optical splitter with a further idle optical fiber segment of an another further optical fiber contained in the optical cable. 
         [0021]    In one embodiment of the invention, the step of coupling a second output of the optical splitter with a downstream optical fiber segment of an interrupted optical fiber contained in the optical cable comprises segregating the downstream optical fiber segment at the further branch point, obtaining the idle optical fiber segment upstream the further branch point. 
         [0022]    In one embodiment of the invention, the at least one signal bearing optical fiber comprises a plurality of signal bearing optical fiber grouped in optical fiber modules and wherein the step of interrupting said signal bearing optical fiber at a first branch point, obtaining a first optical fiber segment upstream of said branch point and a second optical fiber segment downstream of said branch point comprises segregating all the optical fibers of a same optical fiber modules at the same branch point, and wherein the steps and of providing an optical splitter at the branch point and coupling the first optical fiber segment with the input of the optical splitter comprises providing a respective optical splitter for each optical fiber of the same optical fiber module, and coupling the first optical fiber segment of each optical fiber of the same module with the input of the respective optical splitter. 
         [0023]    In one embodiment of the invention, the downstream optical fiber segment of an interrupted optical fiber comprises a plurality of downstream optical fiber segments grouped in idle optical fiber modules contained in the optical cable, wherein the further branch point comprises a respective further branch point for each one of the idle optical fiber modules, and wherein the step of coupling said downstream optical fiber segment with at least one further user at a further branch point downstream the first branch point comprises coupling each of said downstream optical fiber segments grouped in idle optical fiber modules with at least one further user at the respective further branch point of the idle optical fiber modules downstream the first branch point. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    These and others features and advantages of the solution according to the present invention will be better understood by reading the following detailed description of an embodiment thereof, provided merely by way of non-limitative example, to be read in conjunction with the attached drawings, wherein: 
           [0025]      FIG. 1  is a schematic diagram of optical fibers deployment according to an embodiment of the present invention, and 
           [0026]      FIG. 2  is a schematic diagram of optical fibers deployment according to another embodiment of the present invention, in the exemplary case of a multi-tube optical cable. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    For the purposes of the present description and claims an optical cable is deemed to be an optical cable comprising one or more optical fibers, possibly arranged inside one or more buffer tubes, an outer sheath and, optionally, one or more strength members. 
         [0028]    An optical fiber is typically constituted by an optical waveguide, constituted by an optically transmissive core, surrounded by a cladding; core and cladding are preferably constituted by silica-based material, and the material of the cladding has a refraction index lower than the refraction index of the material of the core, for substantially confining the optical radiation within the core. The optical waveguide is preferably covered by at least one protective coating layer (“coating”); typically two protective coating layers are present: the first coating layer (“primary coating”) is in direct contact with the optical waveguide, while the second coating layer (“secondary coating”) covers the primary coating. In addition, a buffer layer may cover each optical fiber, the buffer layer may be substantially in contact with the secondary coating (“tight buffer”) or it may consist of a small tube of inner diameter somehow larger than the outer diameter of the secondary coating (“loose buffer”). The coating layers may be colored by means of suitable inks for an easier identification of the different optical fibers accommodated within the optical cable. 
         [0029]    The optical fibers may be arranged in various ways in the cable. 
         [0030]    In the so-called “central loose tube cables” (briefly, CLT cables), the optical fibers are loosely arranged within a single buffer tube, which is in turn enclosed by the external sheath. 
         [0031]    In the so-called “multi loose tube cables” (briefly, MLT cables), the optical fibers are grouped in multiple bundles, the optical fibers of each bundle being loosely arranged within a respective buffer tube. Typically, the buffer tubes may be arranged around a central strength member and stranded according to a closed or open helix (S-Z arrangement). 
         [0032]    Further, a so-called “blown fiber tube cables” (briefly, BLT cables), similarly to the MLT cables, comprises a plurality of buffer tubes stranded together (or arranged around a central strength member) according to a closed or open helix (S-Z arrangement). The buffer tubes are designed to receive single optical fibers (or bundles of optical fibers) blown inside the buffer tubes. 
         [0033]    Both in CLT cables and in MLT cables, the external sheath may comprise strength members (typically made of steel or fiber reinforced resin) embedded within the sheath&#39;s thickness and placed at diametrically opposed positions. Moreover, or alternatively, the optical fibers or buffer tubes may be surrounded by flexible strength members arranged radially externally of the optical fibers. Flexible strength members may comprise aramid yarns or the like. 
         [0034]    The term “user” is to be herein construed as meaning any generic user (or device of a user) connectable to the telecommunication network. User devices may comprise for example modems, set-top boxes for cable TV (for instance IPTV—Internet Protocol TeleVision), IP phones and similar devices. 
         [0035]    The term “signal bearing optical fiber” or “signal bearing optical fiber segment” is to be herein construed as meaning the optical fiber or the optical fiber portion of an optical fiber contained in the optical cable and coupled, either directly or indirectly, with a network element, e.g. an Optical Line Terminal or OLT able to bear the optical signal from the Optical Line Terminal to a user. 
         [0036]    The term “idle optical fiber” or “idle optical fiber segment” is to be herein construed as meaning the optical fiber or the optical fiber portion of an optical fiber, contained in the optical cable, and not directly coupled to the Optical Line Terminal. 
         [0037]    With reference to the embodiment shown in the example of  FIG. 1  of the present invention, a single optical cable  105  (even though embodiments of the present invention many be applied to microcables or micromodules included in an optical cable) comprising at least one optical fibers  110   1 , preferably a plurality of optical fibers  110   1  to  110   z  (where z≧1, for example z=8), is used for propagating one or more optical signals along a “last mile” of a telecommunication network (i.e., a so-called “Fiber To The x”, FTTx, architecture, such as for example a “Fiber To The Premises”, FTTP, architecture) to a certain number of users (e.g., users in a same building and/or in buildings facing a same street and/or in buildings standing in a same block etc.). 
         [0038]    As known, a size of the optical cable  105  depends on the number of optical fibers  110   1  to  110   z  which are accommodated therein. 
         [0039]    In the optical fibers network (for example a Gigabit Passive Optical Network, or GPON) of the embodiment depicted in the example of  FIG. 1 , at least one optical fiber  110   x  (which has to be considered the signal bearing optical fiber coupled, either directly or indirectly, with a network element) in the optical cable  105  is interrupted, or segregated in the jargon, at a first (primary) branch point  115   x|1  along the cable (the first branch point  115   x|1  is schematized by a loosely circular closed line in  FIG. 1 ), wherein the first branch point  115   x|1  is provided for connecting a certain number of respective user (not shown) located in a same area (e.g., a floor of a building or a whole building) to the telecommunication network. 
         [0040]    Preferably, the optical cable  105  sheath is cut, for example by making a window or opening therein, in order to expose the optical fibers  110   1  to  110   z  contained therein. 
         [0041]    The segregation of the optical fiber  110   x  at the first branch point  115   x|1  allows obtaining an optical fiber portion (hereinafter referred to as first optical fiber segment)  110   x|1  upstream the first branch point  115   x|1  and a remaining optical fiber portion (from which at least a second optical fiber segment  110   x|2  may be obtained, as described in the following) downstream the first branch point  115   x|1  (possible uses of the remaining optical fiber portion downstream the first branch point  115   x|1  will be described shortly hereafter). 
         [0042]    At the first branch point  115   x|1 , a first main optical splitter  120   x|1  is provided (being a 1:2 optical splitter in the example of  FIG. 1 ). The first main optical splitter  120   x|1  comprises one input and two outputs (other examples may be 1:4, 1:8, 1:16, 1:32 etc. optical splitters). 
         [0043]    The input of the first main optical splitter  120   x|1  is coupled with the first optical fiber segment  110   x|1 . 
         [0044]    Preferably, said one output of the first main optical splitter  120   x  may be (directly) coupled to a respective user which receives the first split optical signal outputted by the first main optical splitter  120   x|1 . 
         [0045]    In this way, optical signals transmitted (e.g., by the OLT) into the first optical fiber segment  110   x|1  and propagating through it towards the first main optical splitter  120   x|1  at the first branch point  115   x|1  are split (e.g., replicated in a passive optical network) at each of the (two, in the considered example) outputs of the first main optical splitter  120   x|1  into (two) corresponding split optical signals. Each one of the split optical signals is provided to a respective user. 
         [0046]    In another embodiment of the invention (not shown), one output of the first main optical splitter  120   x|1  (in the exemplary case the first main optical splitter  120   x|1  is a 1:2; at least one output of the first main optical splitter in case the latter has more than two outputs, being e.g. a 1:4, or a 1:8, etc., optical splitter) is coupled to an input of a first cascaded optical splitter (for example a 1:8 optical splitter, which has one input and eight outputs (other examples are 1:2, 1:4, 1:16, 1:32 etc. optical splitters). The outputs of the first cascaded optical splitter are then coupled to the (eight) users located in the same area mentioned above. 
         [0047]    By “cascaded optical splitter” it is meant an optical splitter arranged downstream an optical splitter (such as the main optical splitter  120   x|1 ), i.e. having its input fiber connected to an output fiber of a preceding optical splitter. 
         [0048]    In this way, optical signals transmitted (e.g., by the OLT) into the first optical fiber segment  110   x|1  and propagating through it towards the first main optical splitter  120   x|1  at the first branch point  115   x|1  are split (e.g., replicated in a passive optical network) at each of the (two, in the considered example) outputs of the first main optical splitter  120   x|1  into (two) corresponding split optical signals. One of the (two) split optical signals outputted by the first main optical splitter  120   x|1  (first split optical signal) is further split into corresponding (eight in the considered example) optical signals by the first cascaded optical splitter. Each one of the further split optical signals is provided to a respective user device. 
         [0049]    Advantageously, the remaining output of the first main optical splitter  120   x|1  (at which a second split optical signal is made available) is expediently connected to the remaining optical fiber portion of the optical fiber  110   x  downstream the first branch point  115   x|1 , thereby the remaining optical fiber portion of the optical fiber  110   x  downstream the first branch point  115   x|1  is not left unused, being instead advantageously re-used to distribute optical signals to further users. The remaining optical fiber portion of the optical fiber  110   x  can be either the signal bearing optical fiber or the idle optical fiber. 
         [0050]    In a further embodiment of the present invention, the remaining output of the first main optical splitter  120   x|1  is connected to an optical fiber segment of another interrupted optical fiber (for example, a segment of a further idle optical fiber). 
         [0051]    Preferably, in order to increase the number of users that can be served by means of one of the optical fibers of the optical cable, one or more further branch points (not shown at a certain distance from the branch point  115   x|1 ) similar to the branch point  115   x|1  are provided along the optical cable  105 , wherein at each of said further branch points the remaining optical fiber portion of the optical fiber  110   x  downstream the first branch point  115   x|1  is further segregated and coupled to users. 
         [0052]    Other optical fibers  110   1  to  110   z  contained in the cable  105 , such as the optical fibers  110   x+i ,  110   x+2 , in the example of  FIG. 1 , can be treated like the optical fiber  110   x , at respective branch points  115   x|2  and  115   x|3 , with respective optical splitters  120   x|2  and  120   x|3 . 
         [0053]    Advantageously, the structure just described may be iterated for a number of optical splitters comprising m outputs and wherein the optical cable  105  comprises at least m−2 idle fibers (or idle fiber segments). 
         [0054]    Preferably, a generic n-th optical fiber segment is coupled, at one end thereof, with a second output of a (n−1)-th main optical splitter of a previous (n−1)-th branch point and the other end of the n-th optical fiber segment is coupled to an input of a n-th main optical splitter of a n-th branch point. 
         [0055]    Therefore, any optical signals transmitted (e.g., by the OLT) through the first optical fiber segment  110   x|1  and propagating through it is split at the branch point  115   x|1  (by a corresponding main optical splitter  120   x|1 ) into respective first and second split optical signals at the outputs of the respective main optical splitter  120   x|1 . The first split optical signal is provided to the users coupled with a first output of the respective main optical splitter  120   x|1 . The second split optical signal is propagated to a respective next branch point through a respective segment obtained by segregating the remaining optical fiber portion of the generic optical fiber  110   x . The same applies for the optical fibers  110   1  to  110   z  contained in the cable  105 , such as the optical fibers  110   x+1 ,  110   x+2 , in the example of  FIG. 1 . 
         [0056]    Preferably, in correspondence of each branch point, a branch box, or tapping box, is provided. The tapping box (not shown in detail) substantially comprises a box-shaped enclosure, e.g. of generically rectangular or square shape, comprising an opening provided with a closure cover, attachable or hinged to the box-shaped enclosure. The tapping box contains the main optical splitter and the cascaded optical splitter provided at each branch point, as well as optical fiber connector(s). 
         [0057]    The invention embodiment described up to now allows connecting a relatively high number of users by exploiting even just one of the optical fibers of an optical cable. 
         [0058]    Turning now to  FIG. 2 , it is a schematic diagram of an optical fibers deployment according to another embodiment of the present invention, in the exemplary case of a multi-tube optical cable. 
         [0059]    The optical fibers deployment of  FIG. 2  differs from the optical fibers deployment previously described essentially in what follows (wherein similar elements are denoted by similar numeral references). 
         [0060]    An optical cable  205  comprises one or more optical fiber modules (microcables or micromodules)  210   1÷z  (wherein z indicates the overall number of optical fiber modules contained in the optical cable  205 ; z=10 in the example of  FIG. 2 ). Each optical fiber module  210   1÷z  comprises a tube containing a number a optical fibers, for example each optical fiber module  210   1÷z  contains a=32 optical fibers (other examples of the optical fiber module may comprise 2, 4, 8, 12, 16, 24 etc. optical fibers). 
         [0061]    In one exemplary implementation, at a branch point along the optical cable  205  an optical fiber module  210   1÷x  is accessed, generally extracted from the cable, and the relevant optical fibers of the first subset  210   1÷x  are segregated, so as to distribute optical signals (injected by the OLT with which the optical fibers are coupled) to user devices located substantially at same positions corresponding to the branch points (e.g., a same floor of a building or a same building in a street). 
         [0062]    In particular, the example of  FIG. 2  shows a first subset  210   1÷x  of optical fiber modules comprising eight optical modules, i.e. the optical modules  210   1  to  210   8 . 
         [0063]    Considering the generic optical fiber module of the first subset  210   1÷x , downstream the respective branch point (where the optical fibers contained in the considered module are segregated) there remain idle optical fiber portions, namely those portions of the optical fibers of the module after the cut which do not carry an optical signal (downstream a branch point there remains an idle module portion). 
         [0064]    Expediently, the idle optical fiber portions of one or more of the modules of the cable  205  are not left unused, being instead exploited for distributing optical signals to further user devices, as described in the following. 
         [0065]    The optical fibers of a second subset  210   (x+1)÷z  of optical fiber modules contained in the optical cable  205  are coupled (either directly or indirectly) at one of their ends to the OLT (or other equivalent network element) in order to bear optical signals to be distributed to a plurality of user devices located at different positions from each other (e.g., different floor of a building or different buildings in a street). 
         [0066]    In the example of  FIG. 2  the second subset of optical fiber modules comprises the optical fibers  210   9  and  210   10 . 
         [0067]    The optical fibers of each optical fiber module  210   1  to  210   x  of the first subset  210   1÷x  of modules have been interrupted, at a respective primary branch point  215   p   1  to  215   p   x , provided for connecting a certain number of respective user devices (not shown) located in same areas corresponding to the branch point  215   p   1  to  215   p   x  (e.g., a floor of a building or a whole building) to the telecommunication network. The interruption of the fibers of the optical fiber modules  210   1  to  210   x  at the respective primary branch points  215   p   1  to  215   p   x  allows obtaining, for each of the optical fiber modules  210   1  to  210   x , a respective first optical fiber module segment  210   i   1  to  210   i   x , respectively, upstream the respective primary branch point  215   p   1  to  215   p   x , which respective first optical module segment  210   i   1  to  210   i   x  is connected with the OLT, and a respective (idle) remaining optical module portion downstream the respective primary branch point  215   p   1  to  215   p   x . 
         [0068]    At each primary branch point  215   p   1÷x  the optical fibers of the respective first optical fiber module segment  210   i   1÷x  are coupled (either directly or indirectly, e.g. through relevant optical splitters) with one or more respective user devices. 
         [0069]    Optical fibers of each optical fiber module  210   (x+1)  to  210   z  of the second subset  210   (x+1)÷z  of modules are interrupted at a respective primary branch point  215   p   (x+1)  to  215   p   z . The segregation of the fibers of the optical fiber modules  210   (x+1)  to  210   z  of the second subset  210   (x+1)÷z  of modules at the respective primary branch points  215   p   (x+1)  to  215   p , allows obtaining, for each of the optical fiber modules  210   (x+1)  to  210   z , a respective first optical fiber module segment  210   i   (x+1)  to  210   i   z  upstream the respective primary branch point  215   p   (x+1)  to  215   p   z , which respective first optical module segment  210   i   (x+1)  to  210   i   z  is connected with the OLT, and a respective (idle) remaining optical module portion downstream the respective primary branch point  215   p   (x+1)  to  215   p   z . 
         [0070]    In the example of  FIG. 2 , the optical fiber modules  210   9  and  210   10  are interrupted at the respective primary branch points  215   p   9  and  215   p   10  thus obtaining first optical fiber module segments  210   i   9  and  210   i   10 . 
         [0071]    The generic primary branch point  215   p   (x+1) , at which optical fibers of the optical fiber module  210   (x+1)  of the second subset  210   (x+1)÷z  are interrupted, is provided with a number a (i.e. equal to the number of optical fibers contained in each optical fiber module) of optical splitters  220   (x+1)|1÷a , being a 1:8 optical splitter in the example of  FIG. 2  each having one input and eight outputs (other examples are 1:2, 1:4, 1:16, 1:32 etc. optical splitters). The input of each one of the a optical splitters  220   (x+1)|1÷a  located at the generic primary branch point  215   p   (x+1)  is coupled with a respective one of the a optical fibers contained in the respective first optical module segment  210   i   (x+1)  of the optical fiber module  210   (x+1)  of the second subset  210   (x+1)÷z  of optical fibers modules. 
         [0072]    As visible in  FIG. 2 , the 32 optical fibers contained in the first optical fiber module segment  210   i   9  are each coupled with the input of a respective optical splitter  220   9|1÷32 . 
         [0073]    In this way, optical signals injected (e.g., by the OLT) into a generic one of the optical fibers contained in the first optical fiber module segment  210   i   (x+1)  of the second subset  210   (x+1)÷z  of optical fiber modules, like the first optical fiber module segment  210   i   9 , and propagating through it in downlink to the respective optical splitter  220   (x+1)|1÷a , like the optical splitter  220   9|1÷32 , are split at each of the (e.g. eight) outputs thereof into (eight) corresponding split optical signals. 
         [0074]    Each one of optical fiber segments contained in the remaining optical module portions of the optical fiber modules  210   i   1÷x  of the first subset  210   1÷x  of modules downstream the respective primary branch point  215   p   1  to  215   p   x  are expediently coupled with a respective one of the outputs of the a optical splitters  220   (x+1)|1÷a  provided at the primary branch point  215   p   (x+1) . 
         [0075]    As visible in  FIG. 2 , the 32 optical fiber segments contained in each one of the remaining (idle) optical module portions of the optical fiber modules  210   1÷8  of the first subset of modules are each coupled with a respective output of the a optical splitters  220   9|1÷32  provided at the primary branch points  215   p   9 . 
         [0076]    In order to propagate the split optical signals available at the output of the a optical splitters  220   (x+1)|1÷a  to a number of user devices through the optical fibers contained in the remaining optical module portions of the optical fiber modules  210   1÷x  of the first subset of modules, each one of the remaining optical module portions of the optical fiber modules  210   1÷x  is further interrupted at a respective secondary branch point  215   s   (x+1)|1÷x . In this way, second (idle) optical module segments  210   (x+1)|1÷x  are obtained downstream the respective primary branch points  215   p   (x+1) , and further (idle) remaining optical module portions are obtained at the secondary branch points  215   s   (x+1)|1÷x , respectively. 
         [0077]    As visible in  FIG. 2 , each one of the remaining optical module portions of the optical fiber modules  210   1÷8  is further interrupted at a respective secondary branch point  215   s   9|1÷8  obtaining a respective second optical module segment  210   9|1÷8 . 
         [0078]    At each secondary branch point  215   s   (x+1)|1÷x  the optical fibers contained in the respective second optical module segment  210   1÷x|(x+1)  are coupled (either directly or indirectly, e.g. through relevant optical splitters) with one or more respective user devices. 
         [0079]    The procedure just described with reference to the optical fiber module  210   (x+1)  (optical fiber module  210   9  referring to  FIG. 2 ) of the second subset of optical fibers modules may be iterated for any other optical fiber module  210   (x+2)÷z  (such as for example the optical fiber module  210   10  of the  FIG. 2 ) of the second subset of optical fibers modules by exploiting the further remaining optical module portions obtained at the secondary branch points  215   s   (x+1)|1÷x , respectively. 
         [0080]    The embodiment of  FIG. 2  allows deploying a local loop adapted to serving a relatively high number of user devices with a very limited number of optical fibers  210   1÷z  (instead of e.g. using respective optical fibers for connecting the OLT not only with each one of the respective primary branch points  215   p   x+1  to  215   p   x , but also with and respective optical fibers for connecting the OLT with each one of secondary branch points  215   s   (x+1):z|1÷x ) of the optical cable  105 , thus enabling the use of an optical cable with less fibers requiring a very limited physical space for the deployment of the optical cable  105 . 
         [0081]    Indeed, any optical signals injected (e.g., by the OLT) into optical fibers of the first optical fiber modules segments  210   i   (x+1)  to  210   i   z  of the second subset  210   (x+1)÷z  of optical fiber modules may be propagated to a number of secondary branch points  215   s   (x+1)÷z|1÷x  equal to a number x of the optical fiber modules  210   1÷x  of the first subset  210   1÷x  of optical fiber modules—eight in the example of  FIG. 2 . Therefore, any optical signals injected (e.g., by the OLT) into optical fibers of the first optical fiber modules segments  210   i   (x+1)  to  210   i   z  may be propagated to a number of user devices equal to the number x of the optical fiber modules  210   1÷x  of the first subset  210   1÷x  multiplied by the number a of optical fibers contained in each optical fibers module. 
         [0082]    Obviously, the optical cable  205  comprising ten optical fiber modules  210   1÷10  shown in  FIG. 2  has to be construed as a mere, non-limitative, example of implementation of an embodiment of the present invention. Indeed, in other embodiments according to the present invention (not shown) optical cables comprising a different number of optical fiber modules or modules having containing different number of optical fibers may be used. The optical splitters may have different number of outputs one from the other in order to be connected to a different number of secondary branch points and/or of user device to be served (according to implementation requirements, e.g. a different number of user devices have to be served each branch point). 
         [0083]    It should be noted that, thanks to the subdivision of the optical fiber modules  210   1÷z  in the first subset  210   1÷x  of optical fiber modules and in the second subset  210   (x+1)÷z  of optical fiber modules  210   (x+1)÷z  together with the different coloration of the optical fibers  210   1÷z , the deployment of the optical cable  105  results faster and less prone to errors. 
         [0084]    It should further be noted that, the optical fiber modules of the first subset  210   1÷x  of optical fiber modules and the optical fiber modules of the second subset  210   (x+1)÷z  of optical fiber modules  210   (x+1)÷z  of the optical fiber modules  210   1÷z  are not necessarily consecutive fiber modules but any fiber module  210   1÷z  may be used as optical fiber modules of the first subset  210   1÷x  of optical fiber modules or as optical fiber modules of the second subset  210   (x+1)÷z    
         [0085]    As for the embodiment of  FIG. 1 , preferably, in correspondence of each branch point, a branch box, or tapping box, is provided. The tapping box (not shown in detail) substantially comprises a box-shaped enclosure, e.g. of generically cylindrical, rectangular or square shape, comprising an opening provided with a closure cover, attachable or hinged to the box-shaped enclosure. The tapping box contains the main optical splitter and can contain also the cascaded optical splitter provided at said branch point, as well as optical fiber connector.