ES2530888B2 - PASSIVE OPTICAL MULTIPLEXOR - Google Patents

Abstract

Passive optical multiplexer of type “add-drop” for telecommunication systems based on the transmission of multiple optical signals by means of its wavelength division multiplexing (WDM). The device distinguishes between signals transmitted in sets of one or more optical channels located in bands separated from the optical spectrum. It incorporates at least two optical filters (20, 30, 120, 130), a first WDM multiplexer (50, 150) and a combiner (40, 140). The first filter (20, 120) and the second filter (30, 130) are optically connected to each other and also to the first WDM multiplexer (50, 150). The combiner (40, 140) combines in one optical output signal, a channel to be inserted with the reflected optical signal without the at least two different optical channels deflected by the filters.

Description

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PASSIVE OPTICAL MULTIPLEXOR

DESCRIPTION

5

Technical sector

The present invention is related to telecommunication systems based on signal multiplexing

10 optics per wavelength division and, in particular, with telecommunication systems based on the multiplexing of optical signals per wavelength division over passive optical networks.

15 State of the art

The growing demand for bandwidth in telecommunication systems has propelled the usual use of fiber optics as a means for signal transmission [Ref. one]. 20 In this medium, Wavelength Division Multiplexing (WDM) allows the simultaneous transmission of several optical signals through a single optical fiber using different wavelengths (i.e., optical channels). Some

25 examples of telecommunication systems with high demand for bandwidth that use WDM optical technology are backbone networks, and metropolitan area networks, among others. A fundamental device or component in a system of

30 optical telecommunication WDM is the Optical Add-Drop Multiplexer (OADM). The OADM allows to insert and extract optical channels to a WDM optical signal. Since its inception, OADM has been designed to meet the requirements imposed by the systems of

35 telecommunication with high demand for bandwidth, usually used in long-range optical networks. These requirements have promoted, for example: (i) the use of division multiplexing schemes in dense wavelengths (DWDM), which allow

40 incorporate a greater number of channels per optical fiber, and

(ii) the use of active components that modify the transmitted signal (e.g., amplifiers, which retransmit a signal at a greater distance). Both examples, the use of amplifiers and DWDM schemes, limit the usefulness of

45 telecommunication systems to a specific type of optical communications, and the use of a small portion of the optical spectrum. Examples are EP0730172A, EP1009120A, EP1079248A and US5982518A.

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On the other hand, in quantum key distribution systems (QKD), the use of weak optical signals is known [Ref. 3]. In the case of the QKD, the transmission of optical signals also

5 requires the use of passive optical technology to avoid disturbance of the same optical nature of the signal and the introduction of noise to the signal [Ref. 2].

Bibliographic references:

10 [Ref. 1] R. Ramaswami et al, "Optical Networks: A Practical Perspective," 3rd ed., Morgan Kaufmann, ISBN 0080920721, p. 928, 2009. [Ref. 2] T. E. Chapuran et al., “Optical networking for quantum key distribution and quantum communications,” New

15 Journal of Physics, vol. 11, p. 105001, 2009. [Ref. 3] N. Gisin, G. Ribordy, W. Tittel and H. Zbinden, "Quantum cryptography," Reviews of Modern Physics, vol. 74, pp. 145-195, 2002.

Brief Description of the Invention

WDM optical technology has also been extended to the rest of the telecommunication systems. Modern access networks that connect end users with a provider

25 services (i.e., point-to-multipoint networks) also use WDM optical technology. These types of networks are also known as last kilometer networks, and usually short range. The use of the Passive Optical Network (PON) paradigm predominates in these networks

30 Optical Network), where the transmitted optical signals are not modified by the network components. We refer to them as passive optical networks WDM or WDM-PON.

The proposed passive optical add-drop multiplexer device

35 in the present invention it allows to connect different telecommunication systems using the passive optical paradigm. This allows you to connect, for example, a backbone network

or WDM optical metropolitan network with a WDM-PON access network maintaining the passive optical paradigm. The multiplexer 40 distinguishes between different bands of the optical spectrum (e.g., O and C bands), thus allowing to use a particular band for the transmission of optical signals other than conventional ones. For example, the multiplexer allows two different bands to be used than

45 spectrum to simultaneously transmit conventional optical signals and optical signals with a reduced number of photons per pulse of transmitted light, or individual photons (i.e., weak optical signals). This type of

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Weak optical signals are common, as indicated, for example, in QKD systems.

The proposed multiplexer is a passive optical component

5 (i.e., no external power is required), and therefore, the transmitted signals are not converted to other domains (e.g., electrical); The nature of the input signal does not change: the photons or pulses of photons that make up the input signal are routed to the output

10 appropriate. This is of vital importance for the transmission of quantum level signals, in which the information is transported in the physical state of the photon itself (e.g., polarization). On the other hand, none of the components that make up the add-drop multiplexer is aimed at

15 generate new photons (e.g., conventionally amplifying existing signals), since these procedures introduce errors in the transmission of signals with quantum information.

20 This and other objectives are achieved by means of a passive optical multiplexer with functionality to insert into and / or extract from an optical input signal, at least one channel, with said passive optical multiplexer comprising at least two optical filters to deflect, in the signal optics

25 minus a different optical channel and reflect the rest of the channels; a first WDM multiplexer; and a combiner. In the multiplexer the first filter and the second filter are optically connected to each other and also to the first WDM multiplexer, with said first WDM multiplexer

30 configured to multiplex the optical channels diverted from the optical input signal by the filters. The combiner is configured to combine into an optical output signal, an insertion channel with the reflected optical signal without the at least two different optical channels

35 deflected.

Optionally, the passive optical multiplexer further comprises: a second WDM multiplexer optically connected to the combiner; a first and a second circulator; where

The first optical filter and the second optical filter are optically communicated with the first WDM multiplexer through two circulators, so that an optical path is established from the first WDM multiplexer to the second WDM multiplexer.

Optionally, the passive optical multiplexer comprises at least four separate ports. A first input port optically communicated with the common port of the first filter, a second release port communicated

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optically with the common multiplexed port of the first WDM multiplexer, a third insertion port optically communicated with one of the combiner's input ports and a fourth communicated output port

5 optically with the output port of said combiner.

Optionally, the passive optical multiplexer comprises at least four ports, a first input port optically communicated with the common port of the first

10 filter, a second extraction port and a third insertion port both shared and optically communicated with the common multiplexed port of the first WDM multiplexer and a fourth output port optically communicated with the output port of said combiner.

15 Optionally, the optical filter is of the Bragg grid type.

Optionally, the optical filter is thin-film type.

twenty

Optionally, the optical filter is a WDM multiplexer.

Optionally, the optical filter is an optical splitter.

25 Optionally, the optical filter is of the type is a combiner.

Brief description of the drawings

30 FIG. 1 schematically shows an optical add-drop multiplexer according to an embodiment of the present invention with separate ports for "add" and "drop".

35 FIG. 2 schematically shows an optical add-drop multiplexer according to another embodiment of the present invention with a single port for "add" and "drop".

40

Detailed description of the invention

The present invention is further described by embodiments with reference to the figures

Previous 45. These embodiments should not be construed as limiting, refer to a passive optical add-drop multiplexer device (hereinafter add-drop multiplexer) for telecommunication systems based on the multiplexing of optical signals by length division

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cool. The proposed add-drop multiplexer allows different telecommunication systems to be connected while maintaining the passive optical paradigm. In particular, the proposed device allows to passively connect optical networks

5 WDM, trunk or metropolitan area networks, with WMD-PON access networks. The proposed device distinguishes between sets of one or more optical channels located in bands separated from the optical spectrum.

10 The add-drop multiplexer proposed in this first embodiment incorporates four ports: input, insert (add), extraction (drop) and output. The input port of the multiplexer is connected to two optical filters that allow a set of optical channels to be diverted to the port of

15 extraction, drop port. Each filter diverts a set of channels corresponding to a band other than the optical spectrum. An optical combiner connects the insertion port, “add” port, and the output port, so that the proposed device allows to add optical channels

20 of any set of channels. The combiner is also connected to the signal that has not been diverted by the filters. The proposed add-drop multiplexer performs three functions on an input WDM optical signal: (i) add optical channels, (ii) extract optical channels, and (iii) leave

25 pass the rest of the optical channels.

The optical filters used are selected from any three-port optical device (common, filtered and reflected) capable of filtering optical signals from a common port to a filtered port, and allowing the rest of the optical signal to pass to a reflected port. . Any component capable of performing this action can be used in the present invention. For example, optical filters based on thin-film technology can be used,

35 Fabry-Perot or Bragg gratings; WDM multiplexers or optical dividers.

Next, one of the embodiments of the present invention, shown in FIG. 1 (where

40 numbers indicate similar or related elements).

A first optical transmission path (11) optically communicates the input port with the common port (21) of the first optical filter (20), and carries a signal

WDM optics that includes sets of one or more optical channels located in bands separated from the optical spectrum, and from which some of said sets (frequencies from λn to λm) are to be filtered.

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The term "optically communicates" refers to any connection, junction, link or the like, whereby optical signals carried by an element of an optical system are carried to another element of an optical system.

5 using an optical transmission path. At no time does the optical nature of the signal change. For example, an optical transmission path may be a single mode optical fiber (typical means for the transmission of WDM optical signals).

10 A second optical transmission path (12) optically communicates the reflected port (23) of the first optical filter (20) with the common port (31) of the second optical filter (30), and carries a composite WDM optical signal

15 by the sets of optical channels not filtered by the first optical filter, some of which will now be filtered (frequencies from λk to λh). Since the frequency ranges λn-λm and λk-λh may not belong to the same band, it is necessary to use two optical filters.

20 A third and fourth optical transmission path (13 and 14) optically communicate the filtered ports (22 and 32) of the optical filters (20 and 30) with the demultiplexed ports (51 and 52) of the WDM multiplexer (50), and

25 carry two optical signals, each consisting of the sets of optical channels filtered by the corresponding optical filter. The WDM multiplexer combines both optical signals into a single WDM optical signal that exits through the common multiplexed port (53).

30 The WDM multiplexer must have at least 3 ports: two demultiplexed and one multiplexed. In addition, it must function properly in the bands of the optical spectrum to which the filtered optical channel assemblies belong. In

In particular, the first port must be able to multiplex

or demultiplex optical signals in the band of the optical spectrum for which the first optical filter works, and the second port must do the same with the second optical filter. For example, if the first optical filter filters 40 sets of optical channels of the O band (ie, 1260-1360 nm) and the second optical filter filters sets of optical channels of the C band (ie, 1530-1565 nm), the WDM multiplexer should be a multiplexer of the O and C bands, where the first port works with the O band and the second port

45 with the C band. Although in this case we describe a WDM multiplexer, any optical component capable of combining optical signals from different bands of the optical spectrum into a single one can be used in the present invention (e.g., optical combiners).

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A fifth optical transmission path (16) optically communicates the multiplexed common port (53) of the WDM multiplexer (50) with the extraction port, port

5 "drop" of the add-drop multiplexer, and carries a WDM optical signal composed of the sets of optical channels extracted from the WDM optical signal that entered the add-drop multiplexer.

10 The add-drop multiplexer also includes an optical combiner with two input ports and one output port. A sixth optical transmission path (15) optically communicates the reflected port (33) of the second optical filter (30) with the first input port (41) of the optical combiner (40), and

15 carries a WDM optical signal composed of the sets of optical channels that have not been extracted by any of the optical filters.

A seventh optical transmission path (17) communicates

20 optically the second input port (42) of the optical combiner (40) with the insertion port, "add" port of the add-drop multiplexer, whereby a WDM optical signal composed of optical channels arrives to be added to the WDM optical signal that entered the multiplexer

25 add-drop The optical combiner combines both WDM optical signals from the input ports into a single WDM optical signal. The new WDM optical signal is output through the output port (43) of the optical combiner (40).

30 It should be borne in mind that the optical channels to be added can belong to any set of channels within any band of the optical spectrum for which the add-drop multiplexer works, not just the sets that were extracted. Therefore, each port of the optical combiner

35 must operate in all these bands of the optical spectrum (unlike the WDM multiplexer). Typically, the optical signals are combined in the same proportion (i.e., 50:50), but other ratios (e.g., 70:30, 80:20, etc.) can be used to prioritize any of the signals

40 input optics.

An eighth optical transmission path (18) optically communicates the output port of the optical combiner with the output port of the add-drop multiplexer, and transports

45 the WDM optical signal that entered less the sets of extracted optical channels and more the added optical channels.

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In a second embodiment of the present invention, represented in FIG. 2, the addition of a second WDM multiplexer identical to the first and two optical circulators allows to reduce the number of 5 ports used to three, joining the extraction and insertion ports, "drop" and "add" ports, respectively, in a single Extraction and insertion port, "drop & add" port. The proposed change does not change the described operation of the device. The optical circulators have three 10 input-output ports, and their operation is to redirect the optical signals from one port to the next (ie, the first to the second, 1-> 2, and from the second to the third, 2-> 3 ). That is, an optical signal entering through port 1 will exit through port 2. This embodiment of three ports is detailed below. Based on the first embodiment of the present invention, the main difference is the use of two optical circulators (160 and 180) each connected to the filtered port (122 and 132) of the two optical filters (120 20 and 130) . In this embodiment, the first ports of the circulators (161 and 181) are optically connected to the filtered ports of the optical filters, and the second ports (162 and 182) with the demultiplexed ports (151 and 152) of the WDM multiplexer (150). Thus, it is observed that the introduction of the two optical circulators does not modify the operation of the extraction of the optical channel assemblies by the optical filters and the WDM multiplexer up to the "drop & add" port. For this to happen, the optical circulators must work correctly in the bands of the spectrum in which the optical filters work and the demultiplexed output of the WDM multiplexer to which they are connected. Following the example offered for the WDM multiplexer, one optical circulator should work in the C band and the other in the band

35 O.

Now, the WDM optical signal with the optical channels to be added is introduced through the same "drop & add" port and reaches the multiplexed port (153) of the WDM multiplexer (150). 40 This signal is demultiplexed in the different bands of the spectrum for which the WDM multiplexer works and exits through the demultiplexed ports (151, 152). Following this direction, they enter through the second ports (162, 182) of the optical circulators (160, 180) and exit through the 45 third ports (163, 183) to two new optical transmission paths (191, 192). These optical transmission paths communicate optically with the demultiplexed ports (171, 172) of a second WDM multiplexer

(170) identical to the first. Therefore, through

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multiplexed port (173) will output a WDM optical signal identical to the one that entered through the “drop & add” port.

The multiplexed common port (173) of the second 5 WDM multiplexer (170) communicates optically using an optical transmission path (117) with the second input port

(142) of an optical combiner (140). In the same way as in the first embodiment, the optical combiner combines this WDM signal with the original WDM signal from which certain sets of optical channels were filtered. Thus, through the output port (143), an optical transmission path (118) transports a new WDM optical signal to the output port of the add-drop multiplexer. This WDM optical signal, as in the first mode of

In this embodiment, it is composed of the sets of unfiltered optical channels and the added optical channels.

Although the present invention has been described in terms of the embodiments represented in FIG. 1 and

20 FIG. 2, numerous variants are possible. In this way, modifications and changes such as those suggested here, although not limited only to them, are considered within the scope and scope of the present invention and its claims.

25

Industrial application

The proposed device is of special interest for telecommunication systems based on multiplexing of

30 optical wavelength signals that offer services based on the transmission of quantum information (e.g., quantum key distribution), and that in turn require compatibility with CWDM systems or that operate in more than one band of the optical spectrum.

35

Claims (6)

1. A passive optical multiplexer with functionality to insert into and / or extract from an optical input signal, when 5 minus one channel, with said passive optical multiplexer comprising: - at least two optical filters (20,30,120,130) configured to divert, in the optical signal, at least one different optical channel and reflect the rest of the channels; 10 - a first WDM multiplexer (50,150); -a combiner (40,140); - the first filter (20,120) and the second filter (30,130) are optically connected to each other and also to the first WDM multiplexer (50,150), with said first 15 WDM multiplexer (50,150) configured to multiplex the optical channels diverted from the optical input signal by the filters; -the combiner (40,140) is configured to combine into an optical output signal, an insertion channel with the 20 reflected optical signal without the at least two different optical channels diverted; characterized in that it also includes: - a second WDM multiplexer (170) optically connected to the combiner (140); 25 - a first and a second circulator (160,180); where the first optical filter (120) and the second optical filter (130) are optically communicated with the first WDM multiplexer (150) through two circulators (160,180) so that from the first multiplexer 30 WDM (150) to the second WDM multiplexer (170) an optical path is established. 2. The passive optical multiplexer according to claim 1, characterized in that it comprises at least four separate ports, a first input port (11) optically communicated with the common port of the first filter (20), a second extraction port (16 ) optically communicated with the common multiplexed port (53) of the first WDM multiplexer (50), a third insertion port (17) 40 communicated optically with one of the input ports (42) of the combiner (40) and a fourth output port (18) optically communicated with the output port (43) of said combiner (40). The passive optical multiplexer according to claim 2, characterized in that it comprises at least four ports, a first input port (11) optically communicated with the common port of the first filter (20), a second port of eleven extraction (16) and a third insertion port (17) both shared and communicated optically with the common multiplexed port (53) of the first WDM multiplexer (50) and a fourth output port (18) optically communicated with 5 the output port (43) of said combiner (40).

Four.

 The passive optical multiplexer according to any one of claims 1 to 3, characterized in that the optical filter (20,120,30,130) is of the Bragg grid type.

5.

 The passive optical multiplexer according to any one of claims 1 to 3, characterized in that the optical filter (20,120,30,130) is of thin film type.

10 The passive optical multiplexer according to any one of claims 1 to 3, characterized in that the optical filter (20,120,30,130) is a WDM multiplexer. 7. The passive optical multiplexer according to any one of the Claims 1 to 3, characterized in that the optical filter (20,120,30,130) is an optical splitter. 8. The passive optical multiplexer according to any one of the claims 1 to 3, characterized in that the optical filter (20,120,30,130) is a combiner. 12