DISTRIBUTION POINT UNIT FOR COUPLING EXTERNAL ELECTRICAL AND OPTICAL CABLES

A distribution point unit for coupling an external electrical and optical cable comprises a casing comprising a first port to receive the external optical cable and a second port to receive the external electrical cable. The distribution point unit comprises an electronic board comprising electronic components and at least one heat transferring device. A tray comprises at least one hole to receive a section of the at least one heat transferring device. The at least one heat transferring device is thermally coupled to at least one of the electronic components to thermally couple the at least one electronic component to the casing.

BACKGROUND

Optical access networks connect subscribers of high bandwidth telecommunication services to their providers. Because of its high dependency on building access and infrastructure, the best performing, all optical, fiber to the home (FTTH) model has problems being accepted by the market, in particular since a possible bandwidth of up to 100 Gb/s is often not needed. Fiber to the cabinet (FTTC) is a much more cost-efficient model. It connects the existing street cabinet of the legacy copper cable infrastructure with optical fibers to a central office. The cabinets are equipped with optical network units (ONU) that perform the opto-electrical conversion and VDSL modems. The subscriber's VDSL modems are connected to the cabinets using the legacy copper infrastructure. In this model, the distance of the cabinets to the subscribers which is usually lower than 400 m limits the possible bandwidth to 50-100 Mb/s.

Another technology is based on the fiber to the distribution point (FTTdp) architecture and brings the fiber optic cable closer to the subscriber than the technology based on fiber to the cabinet (FTTC) architecture, but still uses the existing copper cable infrastructure for the last 100 m from a fiber distribution point to a subscriber. It is assumed that in the future the FTTdp architecture will be the favoured technology for optical access networks, since it allows increased bandwidth but still no optical fiber has to be employed in the building infrastructure.

However, the FTTdp architecture also brings challenges for the active distribution point equipment (DPE). The distribution point is the place in the optical network at which a subsequent fiber optic cable usually coming from an optical splitter at which a main fiber optic cable coming from the provider/central office is split to different ones of the subsequent fiber optic cable is coupled to an electrical cable of the legacy copper cable infrastructure. The electrical cable is connected to the home of the subscriber. The distribution point equipment is provided in a distribution point unit.

Instead of using large scale environmentally protected cabinets as usually utilized for housing the Distribution Point Equipment (DPE) in the fiber to the cabinet (FTTC) architecture, in case of the fiber to the distribution point (FTTdp) model, the equipment is deployed in much rougher and size-constrained environmental conditions like handholds. The usage of hardened fiber optical connectors (HFOC) providing sufficient water—and thus protection—is mandatory for every outside plant (OSP) environment. However, some of the active electronic devices, for example microchips, incorporated in a distribution point unit also require proper thermal management which is a major challenge because of size constraints.

Heat removal from electronic components that are deployed in protected environments mostly relies on natural or forced convection of air through a finned heat exchange body. The input air gets heated in a heat-exchanger and is removed away from the heat source. However, in a buried underground deployment scenario with sealed enclosures as the distribution point unit in a fiber to the distribution point network, air exchange is not possible so that convective heat dissipation is not very efficient.

It is desired to provide a distribution point unit for coupling an external electrical and optical cable that allows the processing of opto-electrical signals as well as cable routing and fiber splice protection functionality in a small constructed space and provides an efficient heat dissipation.

SUMMARY

Embodiments of a distribution point unit for coupling an external electrical and optical cable are described herein. The distribution point unit may provide processing of optical/electrical signals as well as efficient heat dissipation. For example, the distribution point unit may include a casing having a first port to receive the external optical cable and a second port to receive the external electrical cable; an electronic board including at least an electronic component for processing optical and/or electrical signals, wherein the electronic board is housed within the casing; at least one heat transferring device having a first section with a first end and an adjacent second section with a second end, wherein the at least one heat transferring device is housed by the casing; a tray arranged above the electronic board, wherein the tray comprises at least one hole completely penetrating the tray from an upper surface of the tray to an opposite lower surface of the tray directed to the electronic board to receive the second section of the at least one heat transferring device, wherein the tray is housed by the casing. In some embodiments, the first end of the at least one heat transferring device is thermally coupled to the at least one electronic component. In some embodiments, the second end of the at least one heat transferring device is thermally coupled to the casing.

The distribution point unit for coupling an external electrical and optical cable may include a casing comprising a first port to receive the external optical cable and a second port to receive the external electrical cable. The distribution point unit may further include an electronic board comprising at least an electronic component for processing optical and/or electrical signals. The electronic board is housed within the casing. The distribution point unit may also include at least one heat transferring device having a first section with a first end and an adjacent second section with a second end. The at least one heat transferring device may be housed by the casing.

The distribution point unit may include a tray arranged above the electronic board. The tray may include at least one hole completely penetrating the tray from an upper surface of the tray to an opposite lower surface of the tray directed to the electronic board to receive the second section of the at least one heat transferring device. The tray is housed by the casing.

The first end of the at least one heat transferring device is thermally coupled to the at least one electronic component. The second end of the at least one heat transferring device is thermally coupled to the casing.

DETAILED DESCRIPTION

The distribution point unit for coupling an external electrical and optical cable will now be described in more detail hereinafter with reference to the accompanying drawings showing different embodiments of the distribution point unit. The distribution point unit may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that the disclosure will fully convey the scope of the distribution point unit to those skilled in the art. The drawings are not necessarily drawn to scale but are configured to clearly illustrate the distribution point unit.

FIG. 1shows an architecture of an optical access network according to the fiber to the distribution point (FTTdp) deployment scheme. A central office/provider10, for example, configured as a backbone to provide internet access to different subscribers20is coupled via a fiber optic cable40to an optical splitter30. The optical splitter30is connected to distribution point units50by fiber optic cables70. The distribution point units50are electrically coupled by an existing copper cable infrastructure80to the subscribers20. Another output side of the optical splitter30is coupled by a fiber optic cable80to an antenna60to provide wireless access for a subscriber to the telecommunications network.

The distribution point units50are respectively configured as an interface for coupling the optical cables70to the electrical cables80. The distribution point units50respectively comprise an electronic board within their casings. The electronic board comprises microchips, for example electronic components for processing optical and/or electrical signals. Furthermore, the distribution point units respectively have to provide a cable routing functionality and a splice protection functionality. The electronic components, for example the incorporated microchips, require proper thermal management to prevent damage to the electronic devices due to overheating.

FIG. 2shows an embodiment of an enclosure of a distribution point unit for buried deployment.FIG. 3shows an opened casing of a distribution point unit with a front panel removed and an electronic board200to be placed inside the casing100of the distribution point unit.FIG. 4shows a possible embodiment of an electronic board200and a tray400with cable routing and splice protection functionality as well as heat dissipation functionality to thermally couple the electronic components of the electronic board200to the casing100of the distribution point unit to prevent any damage to the electronic components by overheating.

As shown inFIGS. 2 to 4the distribution point unit for coupling an external electrical cable2to an external optical cable1comprises a casing100. The casing100comprises a first port101to receive the external optical cable1and a second port102to receive the external electrical cable2. The external optical cable1may be coupled by an external optical connector to the fiber optic cable40shown inFIG. 1. The external electrical cable2may correspond to the electrical cable80shown inFIG. 1. The distribution point unit further comprises the electronic board200. The electronic board200comprises electronic components210for processing optical and/or electrical signals. The electronic board200is housed within the casing100.

The distribution point unit further comprises at least a heat transferring device300having a first section310with a first end311and an adjacent second section320with a second end321. The at least one heat transferring device300is housed by the casing100. The distribution point unit further comprises a tray400arranged above the electronic board200. The tray400comprises at least a hole420completely penetrating the tray400from an upper surface401of the tray to an opposite lower surface402of the tray directed to the electronic board200to receive the second section320of the at least one heat transferring device300. The second end321of the at least one heat transferring device300protrudes out of the at least one hole420of the tray400. The tray400is housed by the casing100.

The distribution point unit further comprises an internal optical cable3arranged within the casing100. The internal optical cable3shown inFIG. 3is coupled to the external optical cable1at a splicing area of the external and internal optical cables. The splicing area is held at the tray400by the splice protection device410. The internal optical cable3is coupled to the electronic board200by means of an optical transceiver220. The electrical cable2is coupled to one of the electronic components210being configured as an electrical transceiver.

The first end311of the at least one heat transferring device300is thermally coupled to at least one of the electronic components210. To this purpose, the first end311of the at least one heat transferring device300touches the outer surface of the respective housing of the at least one electronic component210. The second end321of the at least one heat transferring device300is thermally coupled to the casing100.

The electronic board200and the tray400are housed by the casing100and are hermetically sealed in the casing100. The microchips, for example the at least one electronic component210for processing optical and/or electrical signals, require proper thermal management. Because of the limited efficiency of convective cooling, due to the sealed closure, heat transferring devices300are used to provide a conductive heat transfer to the surface of the enclosure/casing100. The conductive heatsink bodies of the heat transferring devices300are placed in openings/holes420of the tray400at projected positions of the electronic components210that require heat removal. The at least one heat transferring device300is configured as a block of a thermally conductive material, for example as a block of aluminum.

According to a further embodiment of the distribution point unit, the distribution point unit may comprise a thermal bridging material500being arranged within the casing100between the second end321of the at least one heat transferring device300and the casing100to thermally couple the at least one heat transferring device300to the casing100. The thermal bridging material500may be configured as a compressible thermally conductive pad510arranged in a gap between the second end321of the at least one heat transferring device300and the casing100.

According to another possible embodiment, instead of using a compressible thermally conductive pad, a gel-like gap-filling material could be used in the gap between the second end321of the at least one heat transferring device300and the casing100to thermally couple the at least one heat transferring device300to the enclosure/casing100.

As shown inFIG. 4, the tray400comprises a cable routing device440arranged on the upper surface401of the tray400. The cable routing device440may be configured as a circular ring of the material of the tray400.

The internal optical cable3is arranged within the casing100and coupled to the external optical cable1at a splicing area of the external and internal optical cable. The tray400comprises a splice protection device410. The splicing area is held at the tray400by the splice protection device410. As shown inFIG. 4, the splice protection device410may be configured as a structure with grooves411to insert a spliced area of the external optical cable1and the internal optical cable3. The external optical cable1and the internal optical cable3are spliced together at the spliced area. The splice protection device410protects the spliced area of the external and internal optical cables1and3and additionally provides a strain-relief element for the optical cables to prevent any damage at the coupling zone of the internal optical cable3to the optical transmitter220.

The tray400may be formed as a monolithic component including the splice protection device410and the cable routing device430. The splice protection device410and the cable routing device430may be arranged on the top surface401of the tray. The tray400may be made of a thermoplastic material which comprises the structures of the splice protection device410and the cable routing device430as molded components.

The distribution point unit further comprises at least one spacer600being arranged between the tray400and the electronic board200to arrange the tray400in a distance defined by the spacer600far away from the electronic board200. According to the embodiment of the sub-assembly shown inFIG. 4, four spacers600are provided which keep the tray400in a defined distance far away from the electronic board200.

FIGS. 5A and 5Bshow an embodiment of a self-locking mechanism of the spacers600to fix the tray400to the electronic board200and to provide a distance between the tray400and the electronic board200defined by the respective length of the spacers. The at least one spacer600may be configured as a post having a first end section610penetrating the tray400and a second end section620penetrating the electronic board200. The first end section610of the post comprises an expanded head611arranged above the upper surface401of the tray to fix the post to the tray400. The second end section620comprises a self-locking means621to fix the post to the electronic board200.

According to an embodiment of the distribution point unit, the tray400provides a defined contact pressure between the heatsink of the heat transferring devices300and the electronic components210of the electronic board200that is required for sufficient thermal contact. The tray400and the at least one heat transferring device300are configured such that the at least one heat transferring device300is pressed against the at least one electronic component210by the defined contact pressure. This is done by a mechanical stop for the heatsinks in vertical direction at the tray400in combination with a mechanical snatch for a self-locking of the tray400on the electronic board200.

FIGS. 6 and 7show two different embodiments for the heatsink stop.FIG. 6shows an embodiment of the heat transferring devices300with a change in the geometry of the heatsink. The circuit-board sided part/first section310of the heat transferring device300shown inFIG. 6is wider than the enclosure-sided part/second section320of the heat transferring device300. According to a possible embodiment of the distribution point unit, a cross-section of the first section (circuit-board sided part)310of the at least one heat transferring device300being perpendicularly oriented to the longitudinal direction of the at least one heat transferring device300has a larger area than a cross-section of the second section (enclosure-sided part)320of the at least one heat transferring device300being perpendicularly oriented to the longitudinal direction of the heat transferring device300.

The cross-section of the hole420of the tray400being perpendicularly oriented to the longitudinal direction of the second section320of the at least one heat transferring device300has a smaller area than the area of the cross-section of the first section310of the at least one heat transferring device300. The configuration of the at least one heat transferring device300having different diameters D1and D2in combination with the holes420of the tray allows that the at least one heat transferring device300is pressed with its lower end321against the top surface of the electronic components210by a defined contact pressure, when the tray400is fixed to the electronic circuit board200by means of the at least one spacer600.

According to the embodiment of the distribution point unit shown inFIG. 7, the distribution point unit comprises a clamping device430being arranged on the upper surface401of the tray400. The clamping device430is configured to prevent a movement of the at least one heat transferring device300out of the at least one hole420of the tray400and to press the at least one heat transferring device300against the at least one electronic component210by a defined contact pressure.

The tray400is configured as a monolithic subassembly for the FTTdp distribution point equipment and incorporates heatsink fixation, cable routing and splice protection functionality in a single, injection-molded part. The monolithic integration of heatsink fixation, cable routing and splice protection functionality compared to individual parts for each functionality provides a reduction of required enclosure volume, and thus increases acceptance from the customers who have to deal with limited sizes of legacy handholds for the deployment of the FTTdp equipment. It further reduces the complexity of the assembly and thus reduces the device costs.