System and method for identifying and verifying a fiber optic link

Abstract

System and method for identifying and verifying a fiber optic link The system comprises at a first end (12) of the fiber (10) a light source (32) generating coherent light radiation injected into the fiber and, at the opposite end (16), a light sensor sensitive to radiation diffused by the fiber. The light source (32) is a Class 1 or 1M source according to IEC 60825-1, which generates the incident radiation in the near infrared. The light sensor (34, 48) is devoid of an IR optical filter and is sensitive to the wavelength located in the near infrared. It further comprises a display interface (48) capable of transforming an image formed in the near infrared into an image in the visible range (44), directly observable by an operator using the sensor. (Figure to be published with the abstract: Figure 3)

Description

Description Title of the invention: System and method for identification and verification- installation of a fiber optic connection

[0001] — The invention relates to the identification and verification of optical fiber links in communication networks, in particular for the interconnection of devices optical indoor termination (DTIO) with mutualization points (PM) of a fiber optic distribution network of a communications operator. Technical field of the invention

[0002] In such an application, when connecting a subscriber or any other in- intervention on the network, it is necessary to identify on the table of the mutual point- lization, which brings together a very large number of fiber terminations, the termination particular which leads to the DTIO of the subscriber concerned by the intervention.

[0003] Once this fiber termination has been identified, it will be possible, for example, to connect the subscriber to the operator's network by connecting a patch cord ensuring the interface between the distribution network and the operator's network. State of the prior art

[0004] — The technique usually used for this purpose consists of using a device called "VFL" (Visual Fault Locator), which is a pen-shaped device with a light source such as a laser diode producing coherent light in the visible wavelength range. The output lens of the light source is coupled to the fiber termination at one end of the latter (for example at the DTIO level), so that visible radiation can propagate over the entire length of the fiber to the opposite end of the fiber, located at the level of the PM mixing grid.

[0005] It is then sufficient for an operator located in front of this mixing grid to observe all the fiber terminations until you find the one that emits visible light, which will be made the one illuminated at the other end by the VFL laser source.

[0006] — This manipulation not only allows you to identify this or that fiber, but also to check its integrity since the presence of a visible signal confirms that the signal transmission was successful over the entire length of the fiber.

[0007] For safety reasons, the VFLs used for this purpose use Class 2 lasers according to IEC 60825-1 edition 3.0 of May 15, 2014 (version in force on the date of filing of the present application) whose output power does not exceed 1 mW (0 dBm), which do not impose any personal protective equipment (glasses) or restrictions on use particular, the protection of the eye by the palpebral reflex being considered as sufficient. This technique is effective and very easy to implement. It allows for simple and rapid identification of a fiber termination on a patch grid that may contain dozens of terminations placed side by side in a very small space. FR 3 108 736 A1 (Laborie et al.) describes a fiber end connector allowing the visible optical signal to be viewed at the PM even if this connector is plugged into the patch panel. This technique is however limited to fiber lengths not exceeding 5 to 7 km. Indeed, the optical fibers used for distribution networks are single-mode fibers operating in a useful band located in the far infrared (typically 1260 to 1625 nm), with very low attenuation in this band. On the other hand, in the visible wavelength band - which is not their nominal operating range - their attenuation is much higher, of the order of approximately 7 dB / km. In fact, for long fiber lengths, the illumination of the termination at the remote patch grid will be less and less visible, especially in a difficult observation environment (little darkness) or, at the other end, non-optimal injection conditions (imperfect coupling of the VFL to the end of the fiber, VFL with diode or lower quality optics, etc.). However, the fiber lengths of distribution networks can be very long between their ends, several kilometers in areas of low population density, and can reach 10 km or more. The identification and control technique just described is therefore no longer applicable. One solution is to use a higher-power laser at the injection point, for example a 20 to 30 mW VFL. However, this is no longer a Class 2 device, and the laser illuminator is potentially dangerous if a direct beam or reflection reaches the unprotected eye. The operator must then be equipped with personal safety protection equipment (safety glasses) and the handling must be carried out according to a precise, secure but restrictive protocol, involving training and awareness-raising prior to the use of these dangerous — and moreover expensive — devices. Wearing protective glasses, which is mandatory in all circumstances, also has the disadvantage of making it more difficult to visually locate the illuminated termination at the patch panel. The increase in range is significant, around 10 km for a 30 mW VFL, but it is still subject to the significant linear attenuation of the fiber in the visible range (7 dB / km). Even higher ranges would theoretically be probable, but with very powerful lasers, therefore classified as very dangerous, prohibited for indoor use and therefore not suitable for field applications, which are often carried out in harsh environmental conditions. A second solution consists of injecting into the fiber not visible light, but light in the infrared range corresponding to the wavelengths for which the fiber is characterized (typically 1260 to 1625 nm). The linear attenuation will then be much lower, and the classes of lasers emitting this radiation are less restrictive than those of visible lasers. The disadvantage, on the other hand, is that these rays are not in the sensitive spectrum of the human eye and it is necessary to use, on the patch grid side, an infrared radiation detector, which must be connected successively to each of the fiber terminations of the PM grid until the one where the infrared signal has been injected at the other end is found. The simplicity and immediacy of the location by simple visual observation of the patch grid, without any instrument, is therefore lost. Statement of the invention The aim of the invention is to overcome these various drawbacks and limitations by proposing a system and method for identifying and verifying a fiber optic connection that can be used for fiber lengths of up to 10 km or more, in a manner that is immediately perceptible and identifiable to the naked eye, and which does not require the operator to wear any protective equipment or observe any particular safety constraints during the intervention. More specifically, the invention proposes a system for identifying and verifying an optical fiber link extending between a first device located at a first end of the fiber and a second device located at a second, opposite, end of the fiber. The system comprises, in a manner known per se: at the first end, a light source capable of generating incident radiation of coherent light, injected into the fiber at the first end and, at the second end, a light sensor sensitive to received radiation, diffused by the fiber at the second end. Characteristically of the invention: (a) the light source is capable of generating incident radiation at a wavelength in the near infrared and of not generating radiation at wavelengths in the visible range, b) the light source is a Class | or 1M source according to IEC 60825-1 edition 3.0, (c) the light sensor is free of an IR optical filter and is sensitive to said wavelength located in the near infrared, and d) the light sensor further includes a viewing interface capable of transforming an image formed in the near infrared into an image in the visible range directly observable by an operator using the light sensor. According to various advantageous subsidiary characteristics: the light source is a source capable of generating incident radiation at a power not exceeding +10 dBm; the wavelength located in the near infrared is a wavelength between 780 and 1300 nm, in particular a wavelength of 850 nm + 10%; optical fiber is a single-mode optical fiber capable of operating in a wavelength range between 1260 and 1625 nm; the length of the optical fiber between the first end and the second opposite end is greater than 5 km, in particular between 5 km and 10 km; and / or the light sensor is provided with an optical filter capable of selectively allowing said wavelength located in the near infrared to pass and stopping the wavelengths located in the visible range, preferably a bandpass filter centered on the wavelength of the radiation generated by the light source. The invention also relates to a corresponding method, comprising steps: a) obtaining a Class 1 or 1M light source according to IEC 60825-1 edition 3.0, capable of generating coherent light radiation at a wavelength in the near infrared and not generating radiation at wavelengths in the visible range; b) obtaining a light sensor without an anti-IR optical filter and sensitive to said wavelength located in the near infrared, the light sensor further including a display interface capable of transforming an image formed in the near infrared into an image in the visible range; €) by the light source, injecting radiation into the fiber at the first end; d) by the light sensor, collecting radiation scattered by the fiber at the second end; and €) by an operator using the light sensor, direct observation of said image in the visible range, and the demonstration of the presence of radiation collected by the light sensor. Advantageously: the light sensor comprises a CCD / CMOS sensor and step b) of obtaining the light sensor comprises: b1) obtaining a video camera capable of operating in the range of wavelengths located in the visible range; and b2) removing an optical IR cut filter incorporated in the video camera; and / or step b) of obtaining the light sensor further comprises: b3) placing in front of the CCD / MOS sensor an optical filter capable of selectively letting through said wavelength located in the near infrared and stopping the wavelengths located in the visible range, preferably a bandpass filter centered on the wavelength of the radiation generated by the light source. Brief description of the drawings An example of implementation of the invention will now be described, with reference to the appended drawings where the same references designate identical or functionally similar elements from one figure to another. [Fig.1] is a schematic view of a fiber optic link between subscriber equipment and a patch panel at a remote sharing point. [Fig.2] illustrates the conventional technique implemented for the identification and verification of the optical fiber of a link such as that of [Fig.1]. [Fig.3] is homologous to [Fig.2], for the technique according to the invention. Detailed description of an embodiment of the invention In [Fig.1], reference 10 designates an optical fiber of a distribution network. The optical fibers in distribution networks are generally single-mode fibers operating in the infrared range in the useful band 1260-1625 nm (these values ​​are of course in no way limiting), which is the band usually used for data exchanges with subscribers of telecommunications operators. The optical fiber 10 extends uninterruptedly from a first end 12, where it is for example connected to an optical internal termination device (DTIO) installed in a dwelling 14, to an arrival point 16 at its opposite end, for example at a patch panel 18 of a mutualization point (PM). The patch panel 18 makes it possible to bring together in a street cabinet the terminations of a very large number of fibers connected to a set of dwellings of the same distribution network. In sparsely populated areas, the fiber length between DTIO 12 and endpoint 16 is often greater than | km, and can reach several kilometers, sometimes up to 10 km or more. The patch panel allows, by means of a patch cord, the arrival point 16 of each dwelling in the distribution network to be connected to a counterpart termination of the network of the operator to which the user is subscribed. For an operator having to make this connection, it is appropriate to mark on the patch grid the position of the arrival point 16 corresponding to the subscriber in question. The identification of this arrival point is generally carried out according to a technique illustrated [Fig.2], with, on the DTIO side, a device called "VFL" (Visual Fault Locator) 20 in the form of a pen or similar comprising a laser light source 22 emitting light in the visible spectrum range, perceptible by the eye (corresponding, according to the CIE definition, to wavelengths between 380 and 780 nm). The VFLs used for this purpose are Class 2 low power devices according to IEC 60825-1 edition 3.0, i.e. emitting a light power not exceeding 1 mW (0 dBm) and requiring no special precautions for use. The VFL 20 is fitted onto an optical connector plug at the end 12 so as to couple the laser source 22 to the optical fiber and thus allow the injection into the latter of an optical stimulus in visible light. At the other end, on the arrival point 16 side, the visible light injected by the VFL source produces a visible light point at the location of the fiber termination (if no plug is inserted at this location of the patch grid), or through a translucent cap closing the arrival point, or again, as illustrated, an illumination 28 of the translucent body of a connector plug 24 of a connection strap 26 already inserted at this location (this translucent body can for example be produced according to the teachings of the aforementioned FR 3 108 736 A1). This visual tracking technique is very simple to implement and allows for the rapid identification not only of the arrival points which correspond to the subscriber concerned by the search, but also for ensuring the integrity of the fiber along its entire length, since an absence of detectable light at the patch panel may result from a defect or break in the fiber preventing the signal from propagating properly from one end to the other. As indicated in the introduction, however, this technique can only be used for fibers whose length does not exceed a few kilometers, usually up to about 5 to 6 km in real conditions. The invention proposes an identification system and method making it possible to overcome this limitation, while maintaining the simplicity of implementation by operators in the field. According to the invention, as illustrated [Fig. 3], the optical stimulus on the subscriber terminal 12 side is produced by a portable device 30 whose light source 32 emits not in the visible range, but in the near infrared (NIR) range whose wavelengths are between 780 and 1300 nm, below the mid-infrared or far-infrared range (wavelengths greater than 1300 nm). Preferably, the wavelength of the optical stimulus emitted by the NIR source 32 is located around 850 nm, for example 850 nm + 10%. Indeed, it is easy to find components that can emit at this wavelength with a power limited to approximately +10 dBm. These components are generally VCSELs (vertical cavity surface emitting laser diodes) unlike conventional laser diode illuminators (edge ​​emitting semiconductor) found in visible light VFLs. A +10 dBm NIR source remains compliant with the requirements of Class 1M according to IEC 60825-1 edition 3.0, i.e. it does not require personal protective equipment (glasses) or special precautions for implementation (use possible even indoors). Given the lack of sensitivity of the eye to infrared radiation, it is in fact possible to emit a higher power than for visible light, without risk of damage that would be caused by accidental exposure. - The NIR light source 32 is coupled to the end 12 of the fiber 10 on the subscriber's DTIO side in the same way as with a conventional VFL, i.e. by plugging into the termination plug 12 of the fiber 10. The infrared signal propagates to the other end 16 located at the patch grid 18, in the same way as in the previous case but with (i) a higher intensity due to the use of a higher power light source and (ii) less attenuation: in fact, the single-mode fibers of the distribution networks have an attenuation in the near infrared of the order of only 3 dB / km, notably lower than their attenuation in the visible, of the order of 7 dB / km. To visualize the infrared radiation at the arrival point 16, the operator uses a camera 34 equipped with a lens 36 producing on a sensor 38 an image of the arrival points of the mixing grid. Advantage can be taken of the fact that the CCD / CMOS sensors of consumer cameras of the "webcam" type are all sensitive to a wide spectrum, going beyond the visible spectrum and including the near infrared NIR. Usually, to avoid glare and improve color reproduction in the visible spectrum, these webcams are equipped with an IR filter which blocks the part of the non-visible spectrum located in the infrared. To implement the invention, it will therefore be sufficient to remove this IR filter so as to allow the NIR radiation produced at the arrival point 16 to pass through the lens 36 and strike the sensor 38. The image formed on the sensor 38 can for example be presented on a display 34 via a conversion interface 40. The desired arrival point can be immediately identified on the image by a luminous halo 44 around the fiber termination diffusing the infrared stimulus produced by the NIR source 32, and by this sole term- fiber mining. The display screen 42 can be the display of a mobile phone 48 connected to the camera 34, which makes it possible to implement the invention with very simple and inexpensive means using pre-existing components (a mobile phone and a webcam from which the IR filter has been removed). To improve the contrast it is possible to add to the camera a filter 46 centered on the wavelength emitted by the source 32 (i.e. a filter centered on a wavelength of 850 nm in the example illustrated) so as to further increase the contrast, in particular to operate in conditions that are not conducive to observation, for example in the case of a PM located outdoors in a sunny environment.

Claims

Claims

1. . A system for identifying and verifying a fiber link optical, the optical fiber (10) extending between a first equipment located at a first end (12) of the fiber and a second equipment located at a second, opposite end (16) of the fiber, comprising: at the first end (12), a light source (32) capable of generating an incident radiation of coherent light, injected into the fiber at the first end (12); and at the second end (16), a light sensor (34, 48) sensitive to a received radiation, diffused by the fiber at the second end (16), characterized in that: a) the light source (32) is capable of generating the incident radiation on a wavelength located in the near infrared and not to generate radiation at wavelengths located in the visible domain, b) the light source (32) is a Class 1 or 1M source according to IEC 60825-1 edition 3.0, c) the light sensor (34, 48) is devoid of an optical anti-IR filter and is sensitive to said wavelength located in the near infrared, and d) the light sensor (34, 48) further includes a visual interface- lization (48) capable of transforming an image formed in the near in- infrared into an image in the visible range (44) directly ob- serviceable by an operator using the light sensor.

2. The system of claim 1, wherein the light source (32) is a source capable of generating incident radiation at a power not exceeding +10 dBm.

3. . The system of claim 1, wherein the wavelength located in the near infrared is a wavelength between 780 and 1300 nm.

4. The system of claim 3, wherein the wavelength located in the near infrared is a wavelength of 850 nm + 10%.

5. The system of claim 1, wherein the optical fiber (10) is a single-mode optical fiber capable of operating in a field of wavelengths between 1260 and 1625 nm.

6. The system of claim 1, wherein the length of the fiber optic (10) between the first end (12) and the second end opposite (16) is greater than 5 km, in particular between 5 km and 10 km.

7. The system of claim 1, wherein the light sensor (34, 48) is provided with an optical filter (46) capable of selectively letting pass the said wavelength located in the near infrared and stop wavelengths located in the visible range, preferentially a bandpass filter centered on the wavelength of the radiation generated by the light source.

8. A method of identifying and verifying a fiber link optical, the optical fiber (10) extending between a first equipment located at a first end (12) of the fiber and a second equipment located at a second, opposite end (16) of the fiber, the method being characterized in that it comprises: a) obtaining a light source (32) of Class 1 or 1M according to IEC 60825-1 edition 3.0, capable of generating light radiation coherent on a wavelength located in the near infrared and at not generate radiation on wavelengths located in the visible domain: b) obtaining a light sensor (34, 48) without an optical filter anti-IR and sensitive to the said wavelength located in the near in- infrared, the light sensor further including a visual interface- lization (48) capable of transforming an image formed in the near in- infrared into an image in the visible range; c) by the light source, the injection into the fiber (10) of a radiation at the first end (12); d) by the light sensor (34, 48), the collection of scattered radiation by the fiber (10) at the second end; and €) by an operator using the light sensor (34, 48), the observation direct of said image in the visible domain (44), and the implementation evidence of the presence of radiation collected by the sensor light.

9. The method of claim 8, wherein the light sensor (34, 48) comprises a CCD / CMOS sensor and step b) of obtaining the light sensor includes: bl) obtaining a video camera (34) capable of operating in the field wavelengths located in the visible range; and b2) removing an optical IR filter incorporated in the video camera.

10. . The method of claim 9, wherein step b) of obtaining the light sensor further includes: b3) placing in front of the CCD / MOS sensor an optical filter (46) capable of selectively allowing said wavelength located in the near infrared to pass and stopping the wavelengths located in the visible range, preferably a bandpass filter centered on the wavelength of the radiation generated by the light source.