Device for injecting visible light into an optical fiber for diagnostic purposes

Abstract

The invention relates to an optoelectronic sub-assembly (DEV) for transceiving optical signals for a passive optical communications network, comprising an infrared modulated laser source (LAS) capable of generating an optical beam (IRB), a lens (LEN) for guiding the optical beam generated 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) in the direction of the guiding lens.

Description

Visible light injection device for use in optical fibers for diagnostic purposes 1. Scope of the invention

[0001] The technical field is the fiber optic infrastructure for telecommunications. More specifically, 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 high-speed internet access to 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, such as a residential gateway, using a fiber optic patch cord.

[0003] 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 travel to the network operator's premises housing the telecommunications equipment to be checked, such as an optical line terminal (OLT). The technician must disconnect the suspected faulty optical fiber 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 detection, 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 original location to disconnect the "visible laser" type equipment and reconnect the examined fiber to the telecommunications equipment.

[0007] US patent applications 2009 0257048 A1 and EP 4167005 A1 describe such a method involving the use of an injector that must be moved from one end of the 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 subset 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 subset, characterized in that the optoelectronic subset 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 LED, it still allows a portion of the visible light, on the order of a few milliwatts, 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 LED, 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 a mm². Given the small size of a light-emitting diode (LED), whose footprint is also on the order of a mm², an existing optoelectronic subassembly can easily be modified by adding an LED 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] The optoelectronic subassemblies are equipped with several external pins for electrical connection, 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 optoelectronic subassembly according to the invention can therefore remain completely unchanged compared to an optoelectronic subassembly 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, enriching the diagnosis at a point on the fiber that is distant from the injection point, called the diagnostic point, compared to simply checking for the presence or absence of the signal at that diagnostic point. The modulation speed of the information can range from a few bits per second to a few megabits per second. Examples of the information that can be inserted include: Equipment identification at the injection point, Frame number, Transmitted power, Transmitted color, Temperature, Voltage, 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 includes 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, and so on. 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] presents an optoelectronic subset for transmitting and receiving optical signals for a passive optical communications network, according to the prior art,

[0021] This presents an optoelectronic sub-assembly for transmitting and receiving optical signals for a passive optical communications network, according to one aspect of the invention,

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

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

[0024] This 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 Passive Optical Network or Point to Point type optical access networks;

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

[0030] This 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, within 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, such as 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 LEN lens for coupling the IRB optical beam generated by the laser chip to an optical fiber (not shown) that 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 that makes up 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 CAP protective shell, which gives the DEVaa device a footprint on the order of a cubic millimeter.

[0035] This 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 a DEV optoelectronic subassembly. This DEV differs from the DEVaa device in that it additionally includes a light-emitting diode (LED), mounted on the BASE, next to the laser chip LAS. The same LEN lens 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 using prior art typically 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 though the lens optical system, as envisioned 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”, by Philippe Chanclou et al., 50th European Conference on Optical Communications (ECOC), 2024, demonstrated that the infrared (IRB) light beam collimated by the LEN lens, carrying the telecommunications signal, is not significantly affected by the visible light (VLB) portion of the beam 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 example, for red light with a wavelength of 650 nm, 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 a fiber optic patching system.

[0040] According to one embodiment of the invention, the VLB beam emitted by the LED is amplitude (intensity) modulated. This modulation allows information such as, for example: to be added to a frame.

[0041] - the identification of equipment (PON ID, serial number, etc.), for example, 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 one embodiment of the invention illustrated in Figure 1, the diagnostic signal is composed of cycles repeating the same tr1 frame but with different optical powers, for example Pmax, Pmax / 2, then Pmax / 4. The equipment used to analyze the visible signal at the diagnostic point can thus estimate the received optical power. Indeed, based on the number of tr1 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 Figure 1, the diagnostic signal is composed of cycles with the following characteristics. A cycle begins with the frame tr1 carrying the information, followed by pulses ec1 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 ec1 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, allowing a human operator to determine the absence of a cut between the injection point and the diagnostic point, without any diagnostic equipment.

[0049] Laillustrate an example of information structure for a tr1 frame of visible light diagnostics.

[0050] The diagnostic tr1 frame can be constructed with the following fields:

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

[0052] - a delimiter that marks the start of the 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] - visible optical power emitted, POe, 1 byte,

[0058] - a wavelength, λ, 1 octet,

[0059] - a field available for other uses to be defined, such as typically temperature, voltage, etc. data, 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 range from a few bits / s to a few Mbit / s.

Claims

Optoelectronic subset (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 subset, characterized in that the optoelectronic subset further comprises a light-emitting diode (LED) generating a visible light signal (VLB) towards the guiding lens. 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). 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. Optoelectronic subassembly according to any one of the preceding claims, wherein the visible light signal (VLB) is amplitude modulated. 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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