WO1998004942A1 - Insertion and extraction of a third channel or band on a fibre optics carrying two channels or optical bands through one single mach-zehnder interferometer - Google Patents
Insertion and extraction of a third channel or band on a fibre optics carrying two channels or optical bands through one single mach-zehnder interferometer Download PDFInfo
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- 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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- 239000000835 fiber Substances 0.000 title claims abstract description 48
- 238000000605 extraction Methods 0.000 title claims abstract description 18
- 238000003780 insertion Methods 0.000 title claims abstract description 15
- 230000037431 insertion Effects 0.000 title claims abstract description 15
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Classifications
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- 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
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- 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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Abstract
The present invention finds its application in an on-line control system of an optic fibre transmission network, supporting or destined to support optic signals in a second (μ1) and/or third (μ2) window and including the transmission by means of said fiber of a control signal having a band or wavelength (μ3) out of said second and third window. The system employs a single Mach-Zehnder interferometer as insertion and extraction device of said third service optic channel or optic band (μ3), consisting of: a first and a second directional coupler having a first L1 and a second L2 coupling length, respectively; a phase shifting stage suitable to introduce an optic path ΔL difference. Parameters L1, L2 and Δ are dimensioned in such a way to satisfy some pre-set relations.
Description
INSERTION AND EXTRACTION OF A THIRD CHANNEL OR BAND ON A FIBRE OPTICS CARRYING TWO CHANNELS OR OPTICAL BANDS THROUGH ONE SINGLE MACH-ZEHNDER INTERFEROMETER
Application field
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.
Therefore, the term "channel" means herein a given band of the optic spectrum or "window", used for the transmission of wavelength division multiplexed (WDM) optic signals.
In other words, by the term 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.
In this logic, 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.
Consequently, 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 λ, (for instance 1310 nm) can also support transmissions made in a second channel or windows, whose central or main wavelength is λ2 (e.g. 1550 nm.). As an alternative, 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 Λ_ operating in another channel or window λ2.
Finally, it is a recurring situation the one for which on the same fibre optics transmission network and therefore on each single fibre optics, two different channels or optic bands are used for the simultaneous transmission of signals of different type, that is each fibre is crossed at the same time by two separate carrier signals, each of them belonging to a different window or channel or optic band. In other words there is a given separation between the wavelength of the two carrier signals.
Nevertheless, as any other type of network, also 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. Background Art In the conference paper under the title "Control system design for the preventive maintenance of fibre optics plants", presented by E. Cottino, D. Dellera, S. de Paoli, C. Colle, L Bozzolan, "Proceedings of 11th Annual Conference on European Fibre Optics Communication and Networks, Hague June 30 - July 2, 1993" it was described the use of an optic signal having a wavelength of 1625 nm useful to
implement a monitoring system of fibre optics integrity of a given net section of the transmission network.
In particular 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.
An optic communication system suitable to determine the location of malfunctions along the optic carrier employing reflectometry techniques is also described in WO 9605665.
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.
When one intends to implement an auxiliary system of said nature in a flexible manner and therefore completely compatible with the simultaneous use of two separate optic channels {λ-, λ-*-) used for transmissions, the known solutions foresee the use of optic multiplexers realized with directional couplers, optic switching devices of the opto-mechanical type as well as suitable filters to avoid interference between transmission signals and the control or service signal or signals.
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. These devices are well described in literature, such as for instance in the volume "Fundamentals of Fotonics - B.E.A. Seteh.M.M. Teich - John Wiley & Sons".
Generally 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).
Of course, a Mach-Zehnder interferometer (MZI) gives the functionality requested by a service auxiliary system to insert and extract service signals from an optic fibre supporting a different communication channel. However, 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.
To equip the system including said separate service channel of said flexibility or compatibility in changed operation conditions of the network, it is necessary to foresee the use of multiplexers and switches or similar expensive equipment.
On the other side, 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.
Said devices, though being able to perform also the above mentioned function to enable the insertion and extraction of a third channel or optic service band on an optic fibre supporting two separate transmission optic channels, are comparatively complex and expensive for the type of auxiliary application or service considered, such as for instance the monitoring of the integrity of the fibres of a given net section. Object of the Invention 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. Summary of the Invention
In presence of this state of technique, of these difficulties and incompatibilities as for implementation costs of such a flexible service system, a device, a method and a system have now been found and form the object of the present invention, implemented in accordance with what described in claims 1 , 6 and 7, capable to enable the insertion and extraction of a third optical channel on fibre optics, supporting two separate transmission optic channels, with a negligible and perfectly compatible attenuation through an exceptionally simple and cost-saving device.
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.
It has been found that modifying some structural parameters of a Mach- Zehnder interferometer, it is possible to produce a transfer characteristic whose typical periodical trend can be almost completely "compressed" in a wide interval of wavelengths up to obtain a wavelength field in which the response results essentially flat and with a negligible attenuation. Said wavelength field can assume an extension such to include two windows or transmission bands (for instance the 2nd and 3rd windows) and at the same time assure a highly forced rejection of a third channel or optic band in one transmission direction and vice versa in the opposite direction. These exceptional and completely unusual performances are obtained, according to the invention, with a device which can be implemented in an integrated form according to the technique known as "glass on silicon" having a conventional structure of a Mach-Zehnder interferometer and therefore a production cost similar to that of a common Mach-Zehnder interferometer.
According to an important aspect of the invention, 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 ΔL, satisfy the relations identified following studies conducted by the applicant and forming the scope of the present invention.
Additional advantageous characteristics of the present invention, considered to have an innovative character, are object of the appended claims.
Brief Description of the Drawings
The invention, together with further objects and advantages thereof, may be understood with reference to the following description taken in conjunction with the accompanying drawings, and the several figures of which like referenced numerals identify like elements, and in which:
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.
Detailed description of a preferred embodiment of the invention
Making reference to the diagram in Fig. 1 , 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. Differently from the case of a "melt fibre" manufacturing technique, in an integrated embodiment the 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 ΔL 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.
As it can be noticed, 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.
In the following description, reference shall be made for instance to an application example of the invention, the requirements of which were to enable the insertion and extraction of a third optic channel and in particular a main 1625 nm wavelength (λ3) on a fibre optics supporting two separate optic channels and particularly the so-called second window or a main 1320 nm (λi) wavelength and the so called third window or more particularly a main 1550 nm (λ2) wavelength.
The process of the invention to modify and adapt the parameters of the integrated structure of a Mach-Zehnder interferometer, conducted for three wavelengths λi, λ2l and λ3 as those indicated above as well as for different wavelength triplets, confirmed the possibility to modify the response characteristic of the device in order to enable to multiplex and/or demultiplex with a very high performance a "multichannel" represented for instance by the pair of transmission channels (that is of the main 1550 nm and 1310 nm wavelengths) and by a third monitoring channel or wavelength, for instance 1625 nm. In particular said device consists of a single Mach-Zehnder interferometer consisting of:
- a 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;
- a phase shifting stage having an optic path difference ΔL, and.
- a second directional coupler having a second coupling length L2 generally different from said first coupling length Li, where the other end of said fibre optics is coupled to one port of the same, and to the other port it can be possible to couple, with methods completely symmetrical to what specified above, said launch and/or reception device of said third optic channel on/from said fibre optics.
Parameters L→, L2 and ΔL are dimensioned according to the invention in order to meet the following conditions:
Lι +L2-=(2km+1)*Lc(λ3; d)-2Lo(λ3; d)
ΔL neff &*\)
- k and m are integer numbers;
- nβff represents the effective refraction index of the optic guide forming said phase shifting stage;
- 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 λ 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. As it is well known to a skilled in the art, the neff 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.
In a preferred integrated embodiment of the device, 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 L2 of the two input and output couplers of the device.
This function, whose form can depend even on other factors of the integration process, applied in the example the following formula: Lc = 6.89E3*λ2 + 2.35E4*λ + 2.15E4
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.
According to the invention, such a system advantageously employs an insertion and extraction device of the 1625 nm signal as the one in the example above.
While a particular embodiment of the present invention has been shown and described, it should be understood that the present invention is not limited thereto since other embodiments may be made by those skilled in the art without departing from the scope thereof.
It is thus contemplated that the present invention encompasses any and all such embodiments covered by the following claims.
Claims
1. Device for the insertion and extraction of a third channel or optic band (λ3< with
K = 1 1 and defined hereafter in short λ3) on a fibre optics supporting one or the other one of two separate channels or optic bands, or (λ1- with i = 1 ,...n, or λ2 j : with j = 1 , ...m and defined hereafter in short λ→ or λ-j), or both at the same time, characterized in that it consists of a single Mach-Zehnder interferometer consisting of:
- a first directional coupler having a first coupling length Li, where at one input port can be connected one end of said fibre and at the other port a launch and/or reception device of said third optic channel on/from said fibre optics is connected; - a phase shifting stage having an optic path difference ΔL, and.
- a second directional coupler having a second coupling length L2 generally different from said first coupling length Li, where the other end of said fibre optics is coupled to one port, and to the other port it can be possible to couple, with methods completely symmetrical to what specified above, said launch and/or reception device of said third optic channel on/from said fibre optics, and where said parameters satisfy the following conditions:
L1 +L2=(2km+1)*l_c(λ3; d)-2Lo(λ3; d)
/B* λ
ΔL neff " 2 )
2. Device according to claim 1 , characterized in that said first coupler, said phase shifting stage and said second coupler are implemented in integrated technology.
3. Device according to claim 1 , characterized in that said optic channels have an uneven separation one from the other, in terms of the relevant wavelengths.
4. Device according to claim 3, in which said two optic channels have main wavelengths of 1310 and 1550 nm respectively and said third optic channel has a wavelength of 1625 nm approx.
5. Device according to claim 2, characterized in that said technology is the so-called "glass on silicon" one (SiOB).
6. Method for the insertion and extraction of a third optic channel (λ3) on a fibre optics supporting one or the other of two separate optic channels (λ1( λ-**) or both at the same time, characterized in that it consists in employing a single Mach-Zehnder 4-port ' interferometer, consisting of a first coupler, a phase shifter and a second coupler connecting to a first port of said couplers one end of said fibres, connecting to the corresponding port of the other coupler the other end of said fibre and connecting to the second port of any one of the two couplers, a launch and/or extraction equipment of said third optic channel (λ3) and eventually and at the same time connecting to the fourth port an extraction and/or launch equipment of the same optic channel.
7. On-line control system of a fibre optics transmission network supporting or adapted to support optic signals in a second (λi) and/or third (λ->) window including the transmission in fiber of a service signal with a wavelength or band (λ3) outside said second and said third window and such not to interfere with communications established at the same time through the fibre optics with second and/or third window signals (λi, λ2), characterized in that it employs as insertion and extraction device of said third service optic channel on any fibre optics of the network a single Mach- Zehnder interferometer consisting of:
- a first directional coupler having a first coupling length L , where one end of said fibre can be connected to an input port, and at the other port a launch and/or reception device of said third optic channel on/from said fibre optics is connected;
- a phase shifting stage having an optic path difference ΔL, and.
- a second directional coupler having a second coupling length L2 generally different from said first coupling length Li. to one port of which the other end of said fibre optics is coupled, and to the other port it can be possible to couple, with methods completely symmetrical to what specified above, said launch and/or reception device of said third optic channel on/from said fibre optics, and where said parameters satisfy the following conditions: L1 +L2=(2km+1)*Lc(λ3; d)-2Lo(λ3; d)
ΔL « neff fal)
where m and k are integer numbers, nβfI represents the effective refraction index of the guide forming said phase shifting stage and U represents the coupling length and is a function of the wavelength (λ) and of the separation distance (d) between the two parallel optic paths of said first and second directional coupler.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| ITMI96A001587 | 1996-07-26 | ||
| IT96MI001587A IT1283522B1 (en) | 1996-07-26 | 1996-07-26 | INSERTION AND EXTRACTION OF A THIRD CHANNEL OR BAND ON AN OPTICAL FIBER CARRYING TWO OPTICAL CHANNELS OR BANDS USING A SINGLE |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| WO1998004942A1 true WO1998004942A1 (en) | 1998-02-05 |
Family
ID=11374677
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/EP1997/003969 WO1998004942A1 (en) | 1996-07-26 | 1997-07-22 | Insertion and extraction of a third channel or band on a fibre optics carrying two channels or optical bands through one single mach-zehnder interferometer |
Country Status (2)
| Country | Link |
|---|---|
| IT (1) | IT1283522B1 (en) |
| WO (1) | WO1998004942A1 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2001069292A3 (en) * | 2000-03-16 | 2002-02-07 | Itf Technologies Optiques Inc | All-fiber mach-zehnder interferometer and method of making the same |
| EP1249718A2 (en) * | 2001-04-11 | 2002-10-16 | The Furukawa Electric Co., Ltd. | Optical multiplexer based on interferometer with couplers |
| EP1293814A2 (en) * | 2001-09-14 | 2003-03-19 | Tsunami Optics, Inc. | Cascaded optical multiplexer |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US5488500A (en) * | 1994-08-31 | 1996-01-30 | At&T Corp. | Tunable add drop optical filtering method and apparatus |
| WO1996005665A1 (en) * | 1994-08-17 | 1996-02-22 | Northern Telecom Limited | Fault location in optical communication systems |
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- 1996-07-26 IT IT96MI001587A patent/IT1283522B1/en active IP Right Grant
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1997
- 1997-07-22 WO PCT/EP1997/003969 patent/WO1998004942A1/en active Application Filing
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| WO1996005665A1 (en) * | 1994-08-17 | 1996-02-22 | Northern Telecom Limited | Fault location in optical communication systems |
| US5488500A (en) * | 1994-08-31 | 1996-01-30 | At&T Corp. | Tunable add drop optical filtering method and apparatus |
Non-Patent Citations (1)
| 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)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2001069292A3 (en) * | 2000-03-16 | 2002-02-07 | Itf Technologies Optiques Inc | All-fiber mach-zehnder interferometer and method of making the same |
| US6836599B2 (en) | 2000-03-16 | 2004-12-28 | Itf Technologies Optiques Inc. | All-fiber Mach-Zehnder interferometer and method of making the same |
| EP1249718A2 (en) * | 2001-04-11 | 2002-10-16 | The Furukawa Electric Co., Ltd. | Optical multiplexer based on interferometer with couplers |
| EP1249718A3 (en) * | 2001-04-11 | 2004-12-01 | The Furukawa Electric Co., Ltd. | Optical multiplexer based on interferometer with couplers |
| EP1293814A2 (en) * | 2001-09-14 | 2003-03-19 | Tsunami Optics, Inc. | Cascaded optical multiplexer |
| EP1293814A3 (en) * | 2001-09-14 | 2004-09-15 | Tsunami Optics, Inc. | Cascaded optical multiplexer |
| US6871022B2 (en) | 2001-09-14 | 2005-03-22 | Stratos International, Inc. | Cascaded optical multiplexer |
Also Published As
| Publication number | Publication date |
|---|---|
| ITMI961587A1 (en) | 1998-01-26 |
| ITMI961587A0 (en) | 1996-07-26 |
| IT1283522B1 (en) | 1998-04-21 |
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