NL2001948C - DEVICE FOR OPTICAL COMMUNICATION INCLUDING AN INTEGRATED OPTICAL COMBINING MODULE AND OPTICAL COMMUNICATION SYSTEM PROVIDED WITH SUCH DEVICE. - Google Patents

Abstract

A device for optical communication comprising an integrated optical combining module which comprises connection means (54) for exchanging information signals (59) with several end station connections (55, 56, 57, 58) in a bidirectional manner, receiving means (23) for receiving and passing on one or several broadcast/multicast signals, splitting means (22) for distributing said one or several broadcast/multicast signals over said end station connections, and combining means (50, 51, 52, 53) for combining said information signals and said one or several broadcast/multicast signals for each end station connection. In particular, switching means (60, 61, 62, 63) are provided which are connected to the splitting means (22) downstream thereof for selectively passing on said one or several broadcast/multicast signals under the control of externally supplied control signals (64).

Description

Device for optical communication comprising an integrated optical combining module and an optical communication system provided with such a device

BACKGROUND OF THE INVENTION

The invention relates to an optical communication device comprising an integrated optical combining module which comprises connecting means for bi-directionally communicating information signals with a plurality of terminal terminals, receiving means for receiving and transmitting one or more broadcasting / multicast signals, splitting means for distributing said one or more omrocp / multicast signals to said cindstation connection and combining means for combining said information signals and said one or more broadcast / multicast signals per terminal station, all as recited in the preamble of Claim 1.

In particular, such a device is used as a module in a point-to-point fiber-based architecture to connect individual houses, subscribers and the like to sources of TV signals, other broadcast signals, other multicast and even point-to-point signals. The end stations are then connected therewith to information networks with individual communication paths such as Ethernet, the latter then being logically separated from the previously recited categories of signals such as TV. For reasons of cost saving, the organization of this separation is preferably carried out centrally with regard to the decentralized terminal equipment of the users / subscribers, while the cabling to the latter must be as simple as possible. The general idea of combining individual or integrated WDM (Wavelength Division Multiplexing) filters with a splitter for cable television and similar signals in a single module or chip is known from European Patent Application EP 1,233,552 which was published on August 21, 2002. A An important aspect of the invention is the integration of hardware related to multiple terminals 30 on a small number or only one integrated carrier, such as one that works with optical and / or semiconductor chip technology.

The inventors have realized that in such a module device the admission of, for example, several cable television (CATV) signals would have many advantages, inter alia in the sense that it would then become feasible to have several television sources (providers) and / or several signals enable selections per source for a single end station. For a single user, each CATV package can have its own specific code or band on which the package and the like is superimposed. A simple realization would be with an on / off switch.

The tuning and filtering is preferably realized with a compact (dense) tunable filter (DWDM) according to distribution according to the wavelength. An advantageous idea is to introduce the multiple provider information streams into the optical combining module according to a compact wavelength grid, for example an International 10 Telecom Union (ITU) grid with 50,100 or 200 GHz gaps between the respective wavelength channels. Then one or more customer-specific wavelengths are filtered out to proceed to a triple WDM (see Figure 6) stage on the (integrated) chip and on to the customer. The filtering is controlled by means of an electrical voltage supply to the building block. The DWDM filter can be an interferometer with one or more stages that is based on a Mach-Zehnder interferometer or other switching element or on a micro-ring resonator.

Now switching between different CATV and such packages such as different transmitters is generally not time-critical with regard to the time scales at which the electronic processing takes place. A relatively slow process such as thermo-optical switching can therefore be used for switching. The latter is based on changing a refractive index in a material by changing an ambient temperature step by step. The heat is supplied, for example, by a film heater which converts an applied electric current to a temperature change.

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SUMMARY OF THE INVENTION

As a result, it is, inter alia, an object of the present invention to considerably increase the freedom in the selection of the television signals to be received 30 without the need for a substantial expansion of the necessary provisions, while changing the signal configuration substantially or entirely can take place in a central station.

Therefore, according to one of its aspects, the device according to the invention is characterized in that switching means are provided which are connected downstream to the 3 splitting means for selectively transmitting said one or more broadcast / multicast signals under the control of externally supplied control signals, as recited in the characteristic of Claim 1.

Preferably, the combining means annex switching means is operable to pass said one or more broadcast / multicast signals as superimposed on respective frequency-specific carrier color signals. The switching means can therefore also contain filters, while each respective carrier frequency represents a respective color.

The splitting means are preferably connected to a measuring device for determining / detecting a functionality in a connection and / or terminal as being selected under the cooperation of said switching means. As a result of the selectivity brought about by the switching means, the determination can be carried out selectively and automatically and optionally with a selectable repeat frequency, whereby simplicity, speed and effectiveness are increased.

The measuring device is preferably based on the principle of an Optical

Reflectometer in the Time Domain (OTDR) to selectively determine / detect a state and / or quality of the connection by detecting the dynamic reflection behavior in time per terminal connection. By the controllable switching means detection and localization of errors and the like can now be carried out quickly without mechanical intervention for a large number of end stations.

In the network infrastructure, the respective provider streams are then multiplexed with each other, for example, before they reach an optical amplifier; the other way round is also feasible. Preferably, for reasons of low costs, the per se expensive optical amplifier is integrated together with the rest of the circuit on a single carrier which can then serve several terminals. The realization can be, for example, by means of a separate multi-channel compact multiplexer based on distribution by wavelength or by a multi-channel combiner. Then all provider streams are amplified by the same optical amplifier. This is particularly advantageous because this amplifier is a very expensive building block. The multiplcxtc and amplified information stream is then supplied to the integrated combining module which includes, for example, tunable filter elements.

The invention also relates to an optical communication system comprising a device with an integrated optical combining module which is connected to receive a plurality of broadcasts and / or multicast signals and to communicate bidirectionally 4 information signals with a plurality of terminals as previously recited. In many cases this will only require a considerably smaller space than according to solutions realized in older technology. In particular, control is simplified in that the switching means are centrally controlled by a management platform.

Preferably, optical amplifier means are present in a path for the one or more broadcast / multicast signals. In particular, a unity gain amplifier can greatly reduce the sensitivity to disturbances and the like.

Such a system is preferably placed in a Central Office to connect from there to underground terminating terminal connections, in particular when placed in the limited space of an Optical Distribution Frame. The integration brings the possibility of arranging many elements close to each other, whereby among other things the number of splices is drastically reduced.

Further advantageous aspects of the invention are recited in further dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

These and further elements, aspects and advantages of the invention will be discussed in more detail below with reference to preferred embodiments of the invention, and in particular with reference to the accompanying figures, which illustrate:

Figure 1, an overview of a known network structure for Ethernet / CATV; Figure 2, a variation on Figure 1 with a single fiber per subscriber; Figure 3, a known distribution mechanism for CATV with combined WDM (Wavelength Division Multiplexing) filters;

Figure 4, an improved distribution mechanism with controlled DWDM (Dense Wavelength Division Multiplexing) filters;

Figure 5, another improved distribution mechanism with controlled switches 30 for C ATV;

Figure 6, a detailed design for a WDM filter;

Figure 7, the use of the invention with an OTDR (Optical Time Domain Reflectometer) or other measuring device.

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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 provides an overview of a known network structure for Ethemet / CATV. Instead of CATV, other broadcasting / broadcast, multicast, and similar signals may also be present, possibly even with a return path associated with the broadcasting / multicast. In addition, each 'customer' or terminal connection 26 is connected via a two-wire system 24 to an access switch 20 for cable television and a splitter 22 for the information network. If applicable, there is also a management module 28, a conductor 30, a firewall module 32, a PSTN port (gateway) 34, a SIP proxy 36, a 1550 nm band transceiver 38 and an optical EDFA or other type of amplifier module 40. All these elements are known per se in the prior art.

The customer 26 can be one of several connected together via the pair 24, access switch 20 and splitter 22 can be connected to several of such pairs, and conductor 30 and EDFA 40 can be connected to multiple access switches 20 and EDFAs 40 respectively plugged in. Further unnumbered elements are in each case corresponding with similar and correspondingly represented elements. The outgoing frequencies are in the 1550 nm band, incoming frequencies in the 1310 nm band as indicated. As can be seen, the control is incorporated in the central office 18.

Figure 2 illustrates a variation on Figure 1 with a single fiber 44 per subscriber. Then the outgoing data frequency goes to the 1490 nm band, while the splitters are replaced by splitters / combiners 42 which are connected to the respective access switches 20. The invention provides solutions that enable combining on a single cable, while furthermore the facilities at the location of the subscribers can remain minimal.

In this connection, Figure 3 illustrates a distribution mechanism for CATV and the like known from the previously cited Patent Application with combined WDM (Wavelength Division Multiplexing) filters 50, 51,52, 53 which act as combination means 30. Referring to Figures 1 and 2, Figure 3 shows a terminal 23 for the CATV signal at 1550 nm with optical matching unit (interface) 23a, all to be connected to the optical amplifier 40 of Figure 1, and a splitter 22 as previously shown . Further shown for each terminal are respective Ethemel connections 59 which are connected via a distributor 54 to the filters 50, 51,52,53. The corresponding connection 55, 56, 57, 58 is then indicated for each 6 end station. Here, the single chip performs the same functionality as combining a separate 1: N split crNN separate triple (triplex) WDM filters on each respective branch, see Figure 6 below.

Figure 4 illustrates, according to an aspect of the invention, selective passage through DWDM (Dense Wavelength Division Multiplexing) filters 60, 61, 62, 63, which are controlled by control signals 64 supplied from outside, for example from a central management platform, and which co-operate as switching means. The permeability of these switching means can be adjustable to many desired pass patterns, so that the terminals can receive corresponding selections of the broadcast / multicast signals. The selection does not have to be unique for a particular terminal; on the other hand, the selection for a particular terminal can be completely independent of that for other terminals. The connection to the Ethernet connections 75, 76, 77, 78 is done separately for each terminal station connection 15 via the Alters 50, 51, 52, 53. For example, since switching can take place at low speeds, a relatively slow-acting thermal optical effect: the refractive index of an optically active substance is changed by increasing the temperature. To this end, a thin-film heating element can be arranged on the switching element, for example an interferometer or a resonator. In this case, filters 60, 61, 62.63 selectively control a block for the CATV signals. In contrast to Figure 3, it is indicated here that, in addition to a single, multiple signal sources 80 for the broadcast / multicast signals may be present. As a result, the control 64 thereof can now have a larger number of individual states.

Figure 5 illustrates another improved distribution mechanism with controlled switches 65.66, 67.68 for CATV and the like. The switches again receive an excitation signal 64 to make them impermeable (65), and are further transmissive (66, 67, 68) in the absence of a received excitation signal. In the event of a malfunction, the subscriber will in any case receive a CATV signal, which reduces the occurrence of subjectively annoying disturbances: in general, the subscriber will immediately experience the absence of a TV signal as a nuisance, which would be less rapid with regard to the information connection performance. This applies in particular to customers who pay for TV. In a subsequent implementation, the switch can be designed as a bistable element that only switches with a received energizing current (- 7 pulse) and otherwise remains unchanged. The splitter 22 can be embodied as a cascade of 1: 2 splitting elements, which for the sake of simplicity is not specifically shown. Furthermore, Figure 5 also contains an optical amplifier 90 which in turn can be present for several sources 80 (Figure 4). This can be an Erbium-contaminated (doped) fiber amplifier (EDFA) or semiconductor optical amplifier (SOA) but also an optical amplifier of a different type. Due to the presence of the splitter, switching elements and WDM filters, the building block shown generally has a significant loss in signal amplitude. The optical amplifier compensates for this loss and can for example be a unit amplifier (with “unity gaiii”). Of course, the location of the optical amplifier in the signal path can also be elsewhere.

Figure 6 illustrates a detailed design for a WDM filter. The black lines represent light signals applied to a substrate / substrate. For a first design, the size of the arrangement shown was of the order of 2 x 6 centimeters. The terminal 90 was operative for receiving 1310 nm and delivering 1490 nm. The double filter 92 according to the Mach-Zehnder principle allows 1490 nm (in fact from 1480 to 1500 nm) and 1550 nm to the right and 1310 nm to the left. A relatively large bandwidth is possible due to the double version. The wavelength of 1310 nm is actually a central wavelength of the region of 1260 to 1360 nm. A further filter 94 blocks the wavelength of 1310 nm to the left, but transmits well the wavelength of 1550 nm to the right. In particular, the latter lets only have little loss. The loss is less critical for the other wavelengths (data traffic). The light guides are connected by fibers (not shown) to fibers running outside the module. As indicated by blocks 95, a single carrier (semiconductor substrate or other) with dimensions such as in the area of 2 x 6 cm for a larger number such as 16 filters according to the principle of Figure 6 can be provided. Because the dimensions are small, the elements shown can be arranged directly in front of the point where the fiber cables go “underground.

Figure 7 illustrates the use of the invention with a measuring device such as, for example, OTDR (Optical Time Domain Protocol). The circuit comprises an Optical Reflectometer in the Time Domain OTDR 110, a splitter 112 as already described with reference to Figure 4, a (large) number of subscriber arrangements 114, and an interruption 116 or other cause for excessive signal reflection in the fiber wiring, splices, and the like to one of the subscribers. The tunable or switchable filter elements as described above are not further specified for the sake of simplicity. The elements such as 110 are known per se and are used to determine the condition and quality of the fiber connections and the connectors, splits, and clearances included therein. To that end, a very short light pulse is sent into the fiber and the time-dependent behavior of the reflections occurring is determined.

From the time-dependent behavior the location and the severity of discontinuities and the like can be determined. However, in order to also identify the connection at which discontinuity occurs, the reflectometer must be successively connected to all fibers separately. This is of course time-consuming.

According to the invention, an integrated optical combiner module is used for this purpose. This can be done by tuning the specific wavelength of the OTDR to a channel or by successively turning on / off the WDM filters and selectively following a connection each time without the need for manual or similar mechanical on / off switching operation. In fact, a total broadcast (or broadcast) or multi-broadcast (multicast) system can be temporarily converted to a 15-point connection. Furthermore, the signals are combined with the lole owl system, and therefore the status of the entire network can be measured from a central location.

The building block can be realized 110 as a permanent building block in the network, and if desired can be connected to a plurality of optical combiner modules, such as by a switching matrix. This is combined with the normal CATV signals by using the optical combiner with tunable elements, because in this case the OTDR is realized with its own very specific wavelength band.

If, on the other hand, the optical combining module with on / a (switching possibility 25) is used, then it can replace the CATV total broadcast signal by means of the switching matrix. In itself, realization thereof can take place in the usual way. last Figure (hours) shows that the static WDM filters for combining CATV / OTDR signals for this application of a computer device do not constitute a necessary condition here.

The invention has been described above with reference to preferred embodiments thereof. Those skilled in the art will realize that many changes and changes can be made thereto without going beyond the scope of the appended claims. Therefore, such preferred embodiments are to be regarded as illustrative rather than limiting, and 9 should not be construed as limitations other than those expressly stated in the appended claims.

Claims (15)

An optical communication device comprising an integrated optical combining module which comprises connection means (54) for bi-directional communication of information signals (59) with a plurality of terminal connections (55, 56, 57, 58), receiving means (23) for receiving and transmitting one or more broadcast / multicast signals, splitting means (22) for distributing said one or more broadcast / multicast signals to said terminal connections and combining means (50, 51, 52, 53) for per terminal connection combining said information signals and said one or more broadcast / multicast signals, characterized in that switching means (60, 61, 62, 63) are provided which are connected downstream to the splitting means (22) for selectively passing on said one or more more broadcast / multicast signals under the control of externally supplied (64) control signals. 15 Device as claimed in claim 1, characterized in that said switching means are designed as switches for receiving an excitation signal which continuously transmit a received broadcast / multicast signal in the non-energized state. 20 Device as claimed in claim 1, characterized in that said switching means are designed as energized switches that use an energizing signal for switching only. Device as claimed in claim 2 or 3, characterized in that said excitation signal is active by means of a thermo-optical effect. 5. Device as claimed in claim 1, characterized in that the combining means (50, 51, 52, 53) and switching means (60, 61, 62, 63) are operable around said one or more broadcast / multicast signals as superimposed on respective frequency-specific to transmit optical signals. Device as claimed in claim 1, characterized in that it is formed integrally on a single substrate to be connected to a plurality of end stations. Device according to claim 1, characterized in that the splitting means (22) are designed as a binary cascade of 1: 2 splitting cycles. Device according to claim 1, characterized in that the splitting means (22) are connected to a measuring device (110) for determining a functionality in a connection and / or terminal selected as selected with the cooperation of said switching means. Device as claimed in claim 8, characterized in that the measuring device (110) comprises an Optical Reflectometer in the Time Domain (OTDR) for selectively determining a state and / or quality of the connection per terminal terminal connection by detecting the dynamic rcflccticgcdrag in time . Device according to claim 1, characterized in that the switching means of an interface (64) are centrally controlled by a management platform. 11. Device as claimed in claim 1, characterized in that optical amplifier means (90) are present in a path for the one or more broadcasting / multicast signals. 12. Device as claimed in claim 1, characterized in that said combining means (50, 51, 52, 53) are provided with a backward suppression filter (94) for said bidirectional information signals and a multi-stage filter (92) for transmitting the broadcasting / multicast signals and the bidirectional information signals. 13. Optical communication system provided with a device according to claim 1, comprising an integrated optical combination module which is connected to receive a plurality of broadcasts and / or multicast signals and to communicate bi-directional information signals with a plurality of terminals. 14. Optical communication system according to claim 13 and placed in a Central Office to connect from there to underground terminating terminal connections. An optical communication system according to claim 13 and placed in the limited space of an Optical distribution frame.