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WO1998004942A1 - Interferometre de mach-zehnder unique inserant et extrayant un 3eme canal ou une 3eme bande dans une fibre optique 2 canaux ou 2 bandes optiques - Google Patents

Interferometre de mach-zehnder unique inserant et extrayant un 3eme canal ou une 3eme bande dans une fibre optique 2 canaux ou 2 bandes optiques Download PDF

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Publication number
WO1998004942A1
WO1998004942A1 PCT/EP1997/003969 EP9703969W WO9804942A1 WO 1998004942 A1 WO1998004942 A1 WO 1998004942A1 EP 9703969 W EP9703969 W EP 9703969W WO 9804942 A1 WO9804942 A1 WO 9804942A1
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WO
WIPO (PCT)
Prior art keywords
optic
port
channel
fibre optics
fibre
Prior art date
Application number
PCT/EP1997/003969
Other languages
English (en)
Inventor
Antonio Fincato
Maurizio Lenzi
Original Assignee
Italtel S.P.A.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Italtel S.P.A. filed Critical Italtel S.P.A.
Publication of WO1998004942A1 publication Critical patent/WO1998004942A1/fr

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
    • G02B6/2938—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device for multiplexing or demultiplexing, i.e. combining or separating wavelengths, e.g. 1xN, NxM
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29346—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by wave or beam interference
    • G02B6/2935—Mach-Zehnder configuration, i.e. comprising separate splitting and combining means
    • G02B6/29352—Mach-Zehnder configuration, i.e. comprising separate splitting and combining means in a light guide

Definitions

  • the present invention relates to a general optic communication systems and more in particular, a device to enable the insertion and extraction of the signals belonging to a third channel or optic band, on a fibre optics carrying signals belonging to one or to the other, or to both, separate channels or optic bands.
  • Fibre optics transmission systems mainly employ pre-set "windows" or bands of the optic spectrum for which the transmission of signals along the fibres takes place with a minimum attenuation.
  • Carrier signals or communication channels each one having its own and accurately defined wave length so as it is produced by a relevant laser generator, included in one of said windows or preference bands which can be modulated in intensity (generally in the digital or analogue way), can be transmitted along a fibre optics with very low losses.
  • the simultaneous transmission of more channels belonging to a given band or window, or channel on a same fibre is enabled operating in Wavelength Division Multiplexing (WDM) mode.
  • WDM Wavelength Division Multiplexing
  • channel means herein a given band of the optic spectrum or “window”, used for the transmission of wavelength division multiplexed (WDM) optic signals.
  • WDM wavelength division multiplexed
  • optic band it is meant a continuous interval of wave lengths which can house more optic channels, such as for instance one or more channels for data transmission, one or more, simple or high definition telephone type channels, etc.
  • a given carrier optic signal having wavelength belonging to one or to the other of said windows (or channels or optic bands) is selected by an operator of a fibre optics communication system, in accordance with economic considerations relevant to the type of laser source which can be employed, etc.. Therefore, communications of a given type, such as for instance telephone communications, both voice and data ones, can be destined to a given band or window, for instance the so-called 2nd window, defined between 1260 and 1350 nm, as it is already well known. According to the same logic, the so-called 3rd useful window, whose bandwidth lies in the range from about 1480 to 1580 nm, can be destined or reserved to cable video transmissions.
  • a given fibre optics transmission system operating with carrier signals having a wavelength included in the pass band of a first channel or window, whose central or main wavelength is ⁇ , (for instance 1310 nm) can also support transmissions made in a second channel or windows, whose central or main wavelength is ⁇ 2 (e.g. 1550 nm.).
  • this second utilization of the transmission optic network can be foreseen as future expansion of the services offered. For other reasons, it can also be considered the opportunity to change the transmission channel or window used, for instance ⁇ _ operating in another channel or window ⁇ 2 .
  • optic networks require systems for the protection, alarm of network equipment, monitoring of the physical integrity of the network and similar.
  • These systems can often take high advantage of the opportunity to introduce an actual channel or service band in the network, so to enable the use of carrier signals which can be modulated having a wavelength distant enough from the wavelength of the transmission carrier signal or from the wavelengths of two transmission carrier signals present in the network and included in said third window or transmission band. This enables to make the desired detections or to monitor in an almost continuos way the integrity of the different net sections of the network (for instance a length of subsea or underground cable) without interfering in any way with transmission signals present on the fibres.
  • the monitoring of the net section is made employing reflectometry techniques, that is employing an instrument called OTDR (Optical Time Demain Reflectometer).
  • Said instrument is adapted to send a 1625 nm signal on the optic carrier, that is a signal showing a wavelength different from the service wavelength, and performs also the correlation of the echoes of the pulse sequence reflected by the above mentioned carrier with a reference pulse sequence. In this way it is possible to determine the presence and location of malfunctions along said optic carrier on the echo time measurement basis.
  • Control systems mentioned above require insertion and extraction means of said auxiliary optic channel on a fibre optics adapted to support a first and/or a second transmission optic channel.
  • a common integrated optic device for the low optimization coupling device and having three ports, based on the Mach-Zehnder interferometer principle, is commonly formed of a first directional coupler (input), a phase shifting stage and a second directional coupler (output), coupled among them in said order.
  • the transfer characteristic of said well known passive optic device which can be manufactured in the integrated form according to the "glass on silicon” technology, is characterized by a definite periodicity.
  • the Mach-Zehnder interferometer (or MZI in short), is employed for the insertion and extraction of a signal or of a given optic channel having a given wavelength (or band) on a fibre optics carrying another optic signal or optic channel of different wavelength (or band).
  • MZI Mach-Zehnder interferometer
  • a Mach-Zehnder interferometer gives the functionality requested by a service auxiliary system to insert and extract service signals from an optic fibre supporting a different communication channel.
  • a common Mach- Zehnder interferometer does not enable expansion or compatibility of the system in case two separate transmission channels are already employed on the fibre optics, and the system cannot be adapted in case the transmission band or channel is changed in the future.
  • devices are known, generally defined ADD/DROP for WDM transmission optic systems, consisting of a cascade of Mach-Zehnder interferometers, suitable to realize a filter for the extraction of a given communication channel of a given window or transmission optic band from a fibre supporting a plurality of channels, as described in the essay "Cascaded Coupler Mach-Zehnder Channel Drop Filter for Wavelength-Division-Multiplexed Optical System * by M. Kuznetov, Journal of Lightwave Technology, Vol. 12 No. 2, February 1994.
  • the essay shows how through a cascade of N Mach-Zehnder interferometers, it is possible to exploit the periodicity of the transfer characteristics typical of these devices to enable the insertion -or extraction of a given carrier signal from a fibre carrying a number N of wavelength-division multiplexed signals.
  • a different device for the insertion and extraction of carrier signals is based on a tunable optic filter and described in the US patent No. 5,488,500.
  • One object of the present invention is to overcome the disadvantages and restrictions of the former technique and in particular to implement a system, a method and a device enabling the simultaneous utilization of two different optic channels or bands and the use of said monitoring signal at the same time, without employing optic switching devices or other devices suggested by the background art.
  • the device of the invention is essentially a Mach-Zehnder interferometer, having typical 1 *2 architecture but able, to multiplex-demultiplex three different wavelengths in both the directions with a negligible attenuation.
  • a suitable modification of response characteristics of a typical structure of Mach-Zehnder interferometer such to produce the desired compression of the periodical character of the response characteristic, inside a well defined wavelength band, is obtained operating in such a way that the coupling length of the first directional (input) coupler L1 , the coupling length of the second directional (output) coupler L2 and the difference of optical path of the phase shifting stage ⁇ L, satisfy the relations identified following studies conducted by the applicant and forming the scope of the present invention.
  • Figure 1 is a functional diagram of a Mach-Zehnder interferometer highlighting the main functional parameters scope of the peculiar embodiment according to the invention
  • Figure 2 shows a characteristic curve of attentuation of a common Mach- Zehnder interferometer
  • Figure 3 shows a characteristic curve of attentuation of a Mach-Zehnder interferometer modified according to the present invention
  • Figure 4 shows the same response curve as in Fig. 3, after optimization of the device structural parameters;
  • Figure 5 shows a system employing the device of the invention.
  • a Mach-Zehnder interferometer essentially consists of a first input directional coupler, whose structure is essentially that of two optical paths (e.g. two fibres) approached each other for a given coupling length L1 and of a second output directional coupler with coupling length L2.
  • two optical paths in the two input and output directional couplers are not melt together, but they are defined in order to develop one in parallel to the other at a given separation distance d (not represented in the figure for graphic requirements).
  • the intermediate stage of the device is essentially a phase shifting stage suitable to determine a given difference ⁇ L of the optical path on the two branches of the device.
  • the attenuation characteristic curve of a common Mach-Zehnder interferometer is shown in Fig. 2.
  • the response is essentially periodical and characterized by comparatively selective peaks which are used to insert and/or extract a given frequency (centered wavelength versus one of said peaks) into a fibre.
  • a third optic channel and in particular a main 1625 nm wavelength ( ⁇ 3 ) on a fibre optics supporting two separate optic channels and particularly the so-called second window or a main 1320 nm ( ⁇ i) wavelength and the so called third window or more particularly a main 1550 nm ( ⁇ 2 ) wavelength.
  • said device consists of a single Mach-Zehnder interferometer consisting of:
  • first directional coupler having a first coupling length - t where, at an input port, one end of said fibre can be connected, and to the other input port a launch and/or reception device of said third optic channel on from said fibre optics can be connected;
  • phase shifting stage having an optic path difference ⁇ L, and.
  • - Lc is the coupler length which is a function of the wavelength and of the separation distance (d) between the two parallel optic paths of said first and second directional coupler;
  • - Lo is a correction function depending on d and ⁇ and considers the coupling effects due to transition areas.
  • Figures 3 and 4 show the attenuation characteristic curves obtained from the device implemented according to the invention, in a pre-optimization phase and at the end of the optimization process to obtain an almost complete satisfaction of the above mentioned relations.
  • the n eff parameter represents the effective refraction index of the optic guide and as it is well known depends both on the intrinsic refraction index of the core material and on the difference between the relevant refraction indexes of the core material and of the cladding material.
  • the U parameter is function of the wavelength and of the separation distance d- (-) between the axis of the two integrated optic guides, along the coupling section of length L- and L 2 of the two input and output couplers of the device.
  • the application diagram considered for the example above is given in Fig. 5.
  • the diagram represents a fibre optics through which a transmitter Tx transmits signals on two channels, for instance second window signals and third window signals, received by a receiver Rx.
  • a monitoring system in co-propagating and counter-propagating configuration can be represented by an OTDR block (Optical Time Domain Reflectometer), which can insert on the fibre a monitoring signal which can be modulated and having 1625 nm wavelength, through a suitable launch device.
  • OTDR block Optical Time Domain Reflectometer
  • such a system advantageously employs an insertion and extraction device of the 1625 nm signal as the one in the example above.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Mechanical Coupling Of Light Guides (AREA)
  • Optical Communication System (AREA)

Abstract

La présente invention concerne un système de commande en ligne d'un réseau de transmissions par fibres optiques assurant (ou devant assurer) la transmission de signaux optiques dans une 2ème (μ¿1?) et/ou une 3?ème¿ (μ¿2?) plage, tout en transmettant au moyen de la fibre optique considérée un signal de commande dont la bande ou la longueur d'onde (μ3) se situe en dehors des 2?ème et 3ème¿ plages. Comme dispositif d'insertion et d'extraction du 3ème canal ou de la 3ème bande optique (μ¿3?) de service, le système utilise un unique interféromètre de Mach-Zehnder constitué: d'un 1?er¿ et d'un 2ème coupleur directionnel caractérisés par une 1ère et une 2ème longueur de couplage L¿1? et L2; et d'un étage de déphasage capable d'introduire un différentiel de trajet optique ΔL. Les paramètres L1, L2 et Δ sont définis de façon à satisfaire certaines relations prédéfinies.
PCT/EP1997/003969 1996-07-26 1997-07-22 Interferometre de mach-zehnder unique inserant et extrayant un 3eme canal ou une 3eme bande dans une fibre optique 2 canaux ou 2 bandes optiques WO1998004942A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
ITMI96A001587 1996-07-26
IT96MI001587A IT1283522B1 (it) 1996-07-26 1996-07-26 Inserimento ed estrazione di un terzo canale o banda su una fibra ottica portante due canali o bande ottiche mediante un singolo

Publications (1)

Publication Number Publication Date
WO1998004942A1 true WO1998004942A1 (fr) 1998-02-05

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IT (1) IT1283522B1 (fr)
WO (1) WO1998004942A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001069292A3 (fr) * 2000-03-16 2002-02-07 Itf Technologies Optiques Inc Interferometre mach-zehnder tout en fibres et son procede de fabrication
EP1249718A2 (fr) * 2001-04-11 2002-10-16 The Furukawa Electric Co., Ltd. Multiplexeur optique basé sur un interféromètre avec des coupleurs
EP1293814A2 (fr) * 2001-09-14 2003-03-19 Tsunami Optics, Inc. Multiplexeur optique cascadé

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5488500A (en) * 1994-08-31 1996-01-30 At&T Corp. Tunable add drop optical filtering method and apparatus
WO1996005665A1 (fr) * 1994-08-17 1996-02-22 Northern Telecom Limited Localisation d'erreurs dans des systemes de communication optiques

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1996005665A1 (fr) * 1994-08-17 1996-02-22 Northern Telecom Limited Localisation d'erreurs dans des systemes de communication optiques
US5488500A (en) * 1994-08-31 1996-01-30 At&T Corp. Tunable add drop optical filtering method and apparatus

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
M.KUZNETSOV: "CASCADED COUPLER MACH-ZEHNDER CHANNEL DROPPING FILTERS FOR WAVELENGTH-DIVISION-MULTIPLEXED OPTICAL SYSTEMS", JOURNAL OF LIGHTWAVE TECHNOLOGY., vol. 12, no. 2, February 1994 (1994-02-01), NEW YORK US, pages 226 - 230, XP000676152 *

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001069292A3 (fr) * 2000-03-16 2002-02-07 Itf Technologies Optiques Inc Interferometre mach-zehnder tout en fibres et son procede de fabrication
US6836599B2 (en) 2000-03-16 2004-12-28 Itf Technologies Optiques Inc. All-fiber Mach-Zehnder interferometer and method of making the same
EP1249718A2 (fr) * 2001-04-11 2002-10-16 The Furukawa Electric Co., Ltd. Multiplexeur optique basé sur un interféromètre avec des coupleurs
EP1249718A3 (fr) * 2001-04-11 2004-12-01 The Furukawa Electric Co., Ltd. Multiplexeur optique basé sur un interféromètre avec des coupleurs
EP1293814A2 (fr) * 2001-09-14 2003-03-19 Tsunami Optics, Inc. Multiplexeur optique cascadé
EP1293814A3 (fr) * 2001-09-14 2004-09-15 Tsunami Optics, Inc. Multiplexeur optique cascadé
US6871022B2 (en) 2001-09-14 2005-03-22 Stratos International, Inc. Cascaded optical multiplexer

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Publication number Publication date
ITMI961587A1 (it) 1998-01-26
ITMI961587A0 (fr) 1996-07-26
IT1283522B1 (it) 1998-04-21

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