Visible light injection device for use in optical fibers for diagnostic purposes

Abstract

Visible light injection device for diagnostic purposes in an optical fiber. The invention relates to an optoelectronic subassembly (DEV) for transmitting and receiving optical signals for a passive optical communications network, comprising an infrared-modulated laser source (LAS) capable of generating an optical beam (IRB), a guiding lens (LEN) for the generated optical beam towards an optical fiber intended to be coupled to the optoelectronic subassembly, characterized in that the optoelectronic subassembly further comprises a light-emitting diode (LED) generating a visible light signal (VLB) towards the guiding lens. Figure for the abstract: Figure 2

Description

Title of the invention: Device for injecting visible light into an optical fiber for diagnostic purposes 1. Scope of the invention

[0001] The technical field is the fiber optic infrastructure for telecommunications. More particularly, the invention relates to the localization of a defect impacting an optical fiber or a position of an optical fiber in a patching element of several optical fibers, included for example in a passive optical network, or PON (Passive Optical Network). 2. Prior art

[0002] A PON is a telecommunications network that uses fiber optic cables to provide a high-speed Internet connection in buildings where users are located. The PON infrastructure includes buried or aerial fiber optic cables, street cabinets, and various junction boxes, including the optical connection box connected to the user's terminal equipment, for example, a residential gateway, using an optical patch cord.

[0003] In order to detect a fault affecting an optical fiber or the position of an optical fiber within a patch panel containing multiple optical fibers, a technician must go to the network operator's premises housing the telecommunications equipment to be checked, for example, an optical line terminal (OLT). The technician must disconnect the optical fiber suspected of being faulty from the telecommunications equipment and connect a diagnostic device, also called an injector, to this fiber. This injector injects a light signal into the optical fiber.

[0004] To locate a position in a fiber patching device, the technician must then move to the other end of the optical fiber to identify the illuminated position and, if necessary, perform the necessary patching operations.

[0005] For fault location, the technician must move along the optical fiber path to locate the presence, leakage or absence of visible signal and, if necessary, carry out the necessary repair operations.

[0006] Finally, to finish, the technician must return to the initial room to disconnect the "visible laser" type equipment and reconnect the examined fiber to the telecommunications equipment.

[0007] US patent applications 2009 0257048 Al and EP 4167005 Al describe such a method involving the use of an injector to be moved from one end of fiber to another.

[0008] One of the aims of the invention is to remedy these drawbacks of the prior art. 3. Description of the invention

[0009] The invention improves the situation by means of an optoelectronic sub-assembly for transmitting and receiving optical signals for a passive optical communications network, comprising an infrared modulated laser source capable of generating an optical beam, a lens for guiding the generated optical beam towards an optical fiber intended to be coupled to the optoelectronic sub-assembly, characterized in that the optoelectronic sub-assembly further comprises a light-emitting diode generating a visible light signal in the direction of the guide lens.

[0010] Even if the optical lens arrangement in the optoelectronic subassembly is not necessarily optimal for fully accommodating the visible light beam generated by the light-emitting diode, it still allows a portion of the visible light, on the order of a few mW, to be injected into an optical fiber coupled to the optoelectronic subassembly. This is sufficient for this portion of the visible light to be used as a diagnostic signal injected into the fiber via the lens, while avoiding the need to temporarily decouple the fiber from the optoelectronic subassembly to temporarily couple it to an external injector. Furthermore, a single lens is both necessary and sufficient for the infrared signal generated by the modulated laser and the visible light signal generated by the light-emitting diode, thus simplifying the fabrication of the optoelectronic subassembly according to the invention.

[0011] According to one aspect of the optoelectronic subassembly, the light-emitting diode is fixed next to the laser source on the same face of the base of the optoelectronic subassembly.

[0012] The footprint of a laser source on the base of the optoelectronic subassembly is on the order of mm². Given the small size of a light-emitting diode (LED), whose footprint is also on the order of mm², an existing optoelectronic subassembly can easily be modified by adding a light-emitting diode to its base, in the immediate vicinity of the laser source. The base of the optoelectronic subassembly according to the invention can therefore remain completely unchanged compared to an optoelectronic subassembly according to the prior art.

[0013] According to one aspect of the optoelectronic subassembly, the laser source and the light-emitting diode are electrically connected respectively to a first contact pin and a second contact pin of the optoelectronic subassembly.

[0014] Optoelectronic subassemblies are equipped with several external electrical connection pins for power supply and transmission of electrical signals. It is easy to electrically connect the light-emitting diode to a free pin of the optoelectronic subassembly. The external structure of the sub- The optoelectronic assembly according to the invention can therefore remain totally unchanged compared to an optoelectronic sub-assembly according to the prior art.

[0015] According to one aspect of the optoelectronic subset, the visible light signal is amplitude modulated.

[0016] Thus, it is possible to add information to the injected visible light signal, thereby enriching the diagnosis at a point on the fiber that is distant from the injection point, called the diagnostic point, compared to a simple check for the presence or absence of the signal at that diagnostic point. The information modulation rate can range from a few bits per second to a few megabits per second. Examples of the information that can be inserted include: • Identification of equipment at the injection point • Frame number • Power emitted • Emitted color • Temperature • Tension • Etc.

[0017] According to one aspect of the optoelectronic subset, the visible light signal comprises a frame of limited duration, repeated with different optical powers.

[0018] Thus, at the diagnostic point, it is possible to estimate the optical loss by determining which frame powers are not received there. For example, a cycle of repeated frames comprises a first frame transmitted at a maximum power Pmax, followed by a second frame transmitted at a power Pmax / 2, followed by a third frame transmitted at a power Pmax / 4, etc. 4. Presentation of the figures

[0019] Other advantages and features of the invention will become more apparent upon reading the following description of a particular embodiment of the invention, given by way of simple illustrative and non-limiting example, and the accompanying drawings, among which:

[0020] [Fig. 1] [Fig. 1] presents an optoelectronic subset for transmitting and receiving optical signals for a passive optical communications network, according to the prior art,

[0021] [Fig.2] [Fig.2] presents an optoelectronic subset for transmitting and receiving optical signals for a passive optical communications network, according to one aspect of the invention,

[0022] [Fig.3] [Fig.3] presents a diagnostic signal according to one aspect of the invention,

[0023] [Fig.4] [Fig.4] presents a diagnostic signal according to another aspect of the invention,

[0024] [Fig.5] [Fig.5] presents an example of the structure of a diagnostic framework, according to one aspect of the invention.

[0025] 5. Detailed description of at least one embodiment of the invention

[0026] The principle is to allow telecommunications equipment designed to emit a telecommunications signal in the form of invisible light, or optical telecommunications signal, to also emit visible light. This emission of visible light can be controlled remotely, or locally, for example, when the telecommunications signal is no longer received (signal loss).

[0027] The telecommunications equipment concerned is:

[0028] - Optical Network Unit and Optical Line Terminal type equipment for networks Passive Optical Network or Point to Point type optical access;

[0029] - the transceivers of all equipment equipped with optical ports (switch, router, server, etc.).

[0030] Fig. 1 presents an optoelectronic transmit-receive subset of such telecommunications equipment, according to the prior art.

[0031] This figure represents the typical structure of an infrared laser source assembly for telecom applications, in a DEVaa optoelectronic subassembly. The term optoelectronic subassembly is the established name for the electronic and optical device that converts electrical signals into optical signals and vice versa. It comprises various components, for example, an optoelectronic device (optical emitter and optical receiver), one or more electronic circuits, and elements for optical beams (lens, isolator, etc.). A driver chip processes the electrical information received by the emitter at a specific bit rate. After processing, modulated optical signals are emitted at the appropriate speed by a laser emitter (also called a laser chip or laser diode). A photodetector diode converts the optical signals into electrical signals.After passing through the electronic preamplifier chip, the electrical signals are then produced at the appropriate bit rate.

[0032] The DEVaa optoelectronic subassembly is a device composed of a LAS laser emitter (laser chip), an electronic contact PIN1 for powering and modulating the laser chip, and a lens LEN for coupling the IRB optical beam generated by the laser chip to an optical fiber (not shown) which can be connected removably or not to the DEVaa device.

[0033] The LAS laser chip is mounted on the top face of a BASE and is surrounded by a protective CAP cover.

[0034] Not counting the outer pin forming the PIN1 contact which protrudes from the underside of the base, the maximum dimensions of the DEVaa device are those of its base BASE and its protective CAP shell, which gives the DEVaa device a footprint on the order of a cubic millimeter.

[0035] Figure 2 presents an optoelectronic subset for transmitting and receiving optical signals for a passive optical communications network, according to one aspect of the invention.

[0036] This figure shows an example of the structure of an optoelectronic subassembly DEV. This DEV device differs from the DEVaa device in that it further includes a light-emitting diode (LED), mounted on the BASE, next to the laser chip LAS. The same lens LEN is used to couple the visible light beam (VLB) generated by the LED to the optical fiber. The LED is powered using an electronic contact PIN2. Devices according to the prior art usually provide several electronic contacts (including several external pins on the underside of the base), and the PIN2 contact of the DEV device can be selected from among those that remain unused.

[0037] Even if the optical lens system, as provided in the DEVaa device, is not optimized for the visible VLB beam of the LED, it still allows coupling of some of the visible light to the optical fiber, which is sufficient for the intended use, and considerably minimizes the complexity of the optical system in the DEV device.

[0038] The article “Impact of alien wavelength from visual vault locators (red light) on G- & XG(S)-PON Upstream transmissions”, Philippe Chanclou et al., 50th European Conference on Optical Communications (ECOC), 2024, showed that the infrared (IRB) light beam collimated by the LEN lens, carrying the telecommunications signal, is not or only slightly disturbed by the portion of the visible light beam (VLB) captured by the same LEN lens and injected into the same optical fiber, provided that the visible light emission power is chosen according to well-defined parameters. For red light with a wavelength of 650 nm, for example, emission powers between 1 and 50 mW are possible while remaining within the various existing laser safety classifications.

[0039] The intended use for the visible light signal is to serve as a diagnostic signal to identify a fault and its location in an optical fiber patching system.

[0040] According to one embodiment of the invention, the VLB beam emitted by the LED is amplitude (intensity) modulated. This modulation makes it possible to add information such as, for example:

[0041] - the identification of equipment (PON ID, serial number, ...), for example the equipment including the DEV device,

[0042] - a frame number,

[0043] - the power emitted (mW),

[0044] - the color (wavelength, nm),

[0045] - and other information such as temperature, voltage (in Volts), etc.

[0046] According to an embodiment of the invention illustrated in [Fig. 3], the diagnostic signal is composed of cycles repeating the same tri-frame but with different optical powers, for example Pmax, Pmax / 2, then Pmax / 4. The equipment used to analyze the signal visible at the diagnostic point can thus estimate the received optical power. Indeed, depending on the number of tri-frames correctly detected in a cycle, the optical loss of the link between the injection point and the diagnostic point can be estimated.

[0047] According to an embodiment of the invention illustrated in [Fig. 4], the diagnostic signal is composed of cycles with the following characteristics. A cycle begins with the tri frame carrying the information, followed by ecl pulses with continuous emission but at different optical powers, for example Pmax, Pmax / 2, then Pmax / 4. A simple optical sensor without calibration is sufficient to analyze the visible signal at the diagnostic point. More complex equipment such as a calibrated photometer is not necessary. Indeed, depending on the number of ecl pulses correctly detected by the optical sensor within a cycle, the optical loss of the link between the injection point and the diagnostic point can be estimated.

[0048] It is also understood that another advantage is that the visible light signal VLB, whether emitted continuously or not, can be seen with the naked eye at the diagnostic point, enabling a human operator to determine the absence of a break between the injection point and the diagnostic point, without any diagnostic equipment.

[0049] Figure 5 illustrates an example of information structure for a visible light diagnostic sorting frame.

[0050] The diagnostic sorting framework can be constructed with the following fields:

[0051] - a detection preamble, Pre, 7 bytes,

[0052] - a delimiter that allows marking the start of useful information, SFd, 1 byte,

[0053] - a visible source identifier, Sid, 6 bytes,

[0054] - a frame length in bytes, TrL, 1 byte,

[0055] - a cycle type, CyTy, 1 byte,

[0056] - an iteration number of the frame in the cycle, ItNr, 1 byte,

[0057] - a visible optical power output, POe, 1 byte,

[0058] - a wavelength, X, 1 byte,

[0059] - a field available for other uses to be defined as typically the Temperature data, voltage data, etc., Tbd, from 0 to N bytes,

[0060] - an end-of-sequence check field, FCS, 4 bytes.

[0061] The number of bytes is indicative. The information modulation speed can be from a few bits / s to a few Mbit / s.

Claims

Demands

1. Optoelectronic sub-assembly (DEV) for transmitting and receiving optical signals for a passive optical communications network, comprising an infrared modulated laser source (LAS) capable of generating an optical beam (IRB), a guiding lens (LEN) of the generated optical beam towards an optical fiber intended to be coupled to the optoelectronic sub-assembly, characterized in that the optoelectronic sub-assembly further comprises a light-emitting diode (LED) generating a visible light signal (VLB) towards the guiding lens.

2. Optoelectronic subassembly according to claim 1, wherein the light-emitting diode (LED) is fixed next to the laser source (LAS) on the same face of the base (BASE) of the optoelectronic subassembly (DEV).

3. Optoelectronic subassembly according to claim 2, wherein the laser source (LAS) and the light-emitting diode (LED) are electrically connected respectively to a first contact pin (PIN1) and a second contact pin (PIN2) of the optoelectronic subassembly.

4. Optoelectronic subassembly according to any one of the preceding claims, wherein the visible light signal (VLB) is amplitude modulated.

5. Optoelectronic subassembly according to any one of the preceding claims, wherein the visible light signal (VLB) comprises a frame of limited duration, repeated with different optical powers.

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