Compact single-fiber optical connector for harsh environments and space applications

Abstract

The present invention relates to an optical interconnect assembly comprising two connectors (10, 20) of an optical fiber sealed in a ferrule (11, 21) and a coaxial alignment means for the optical fibers, characterized in that said coaxial alignment means consists of a slotted ceramic tubular sleeve (51) housed in a sleeve cage (50) formed by a tubular body (52) positioned in a central body (30) having on either side a means for connecting a connector (10, 20). Abstract figure: Fig. 1

Description

Title of the invention: Compact single-fiber optical connector for harsh environments and space applications. Field of the invention

[0001] The present invention relates to the field of miniature optical connectors, and more particularly to optical connectors intended for extreme environments, such as space and aeronautical applications and connectors for multimode (MM) optical fiber, for single-mode (SM) optical fiber or polarization-maintaining (PM) fiber.

[0002] These connectors are designed to ensure reliable and high-performance optical transmission under severe conditions, including extreme temperature variations, intense vibrations, radiation, and very low pressures.

[0003] The use of optical connectors in the space sector is of paramount importance to ensure the reliable transmission of optical data and signals between different components and systems on board satellites, space probes, and other spacecraft. Miniature optical space connectors are specifically designed to meet the stringent performance and reliability requirements imposed by space applications.

[0004] These connectors can be deployed in a variety of space applications, including satellite communication, Earth observation, remote sensing, space navigation, space launch vehicles, space weapons, and other space missions. Their use is essential to ensure a robust and reliable optical connection in the extreme environments of space, which greatly contributes to the smooth operation and success of space missions. Furthermore, the aerospace industry can also benefit from the use of these optical connectors in specific applications.

[0005] The invention proposes a robust, lightweight and easy-to-assemble single-fiber optical connector, intended for systems where the reliability and accuracy of optical communications are critical, particularly in satellites, space probes and aeronautical vehicles. State of the art

[0006] In the current state of the art, optical connectors for space applications are mainly represented by solutions such as the Mini AVIM™ connector from Diamond™, a single-fiber connector qualified for space applications. This type of connector uses a 2.5 mm diameter ferrule and relies on an active core alignment (ACA) process to ensure A reliable and high-performance connection. This process requires mechanical correction of the optical fiber's concentricity relative to the ferrule, performed on a factory bench using specific crimping tools. This minimizes insertion loss (IL) and improves optical transmission quality.

[0007] Furthermore, these connectors use materials such as metallic or composite ferrules to ensure the strength and stability of optical connections in complex environments. The active core alignment process is a benchmark in the field of space optical connectors. Disadvantages of the state of the art

[0008] Although current connectors offer good performance in extreme environments, they have several major drawbacks: • Complex and costly manufacturing process: The Active Core Alignment (ACA) process is a delicate and time-consuming operation, requiring manual adjustment of each connector at the factory. Adjusting the concentricity of the fiber relative to the ferrule axis must be performed on a test bench in the factory. This process must be carried out individually on each connector to ensure precise alignment, thus increasing production costs and lead times. This delicate step, performed using crimping tools, is essential in the manufacturing of this connector to guarantee its optical performance, particularly with regard to insertion loss (IL). • Mechanical stress on optical fibers: The crimping process used to correct concentric alignment can generate mechanical stresses on polarization-maintaining (PM) fibers, thus altering their performance, particularly with regard to optical polarization state. This can lead to performance degradation under extreme conditions, especially when PM fibers are used. • Limitation to connectors with epoxy sealing: The ACA process can only be applied to connectors using epoxy sealing. This constraint limits sealing options for fibers, particularly in environments where alternatives such as glass soldering would be preferable due to their superior resistance to extreme conditions. • Weight and size: Current connectors, although robust, remain relatively bulky due to the use of significant size metal or composite ferrules (2.5 mm in diameter), thus increasing the total weight of optical systems on board space or aeronautical vehicles, where every gram counts. Solution provided by the invention

[0009] The proposed invention aims to solve these problems by offering a lighter solution, easier to produce and install, while maintaining optimal reliability and performance in harsh environments.

[0010] To this end, the invention relates to an optical connector assembly comprising two connectors of an optical fiber sealed in a ferrule and a means for coaxial alignment of the optical fibers, characterized in that said means for coaxial alignment is constituted by a slotted ceramic tubular sleeve housed in a sleeve cage consisting of a tubular body positioned in a central body having on either side a means for connecting a connector.

[0011] Advantageously, the sealing of the fiber in the ferrule is ensured by an epoxy glue.

[0012] According to one variant, the sealing of the fiber in the ferrule is ensured by glass soldering.

[0013] According to an advantageous embodiment, said ferrule is made of zirconia.

[0014] Preferably, the sleeve cage is made of a titanium or stainless steel structure 316L.

[0015] According to a particular embodiment, the optical connector assembly according to the invention further comprises an indexing tube enabling angular alignment of the ferrules for APC (Angle-Polished Connector) configurations or for polarization-maintaining optical fibers, said indexing tube having geometric shapes at its ends complementary to the configurations of said ferrules to guarantee the correct orientation of the slow and fast axes of the fibers.

[0016] Advantageously the optical fibers are protected by a sheath made of 304 stainless steel or PEEK. Detailed description of the invention

[0017] The present invention will be better understood upon reading the following description, concerning a non-limiting example of an embodiment illustrated by the accompanying figures where:

[0018] Figure 1 shows an exploded view of a connection assembly according to the invention.

[0019] Figure 2 shows a side view of a connection assembly according to the invention.

[0020] Figure 3 shows a front view of a connection assembly according to the invention.

[0021] Figure 4 shows an exploded view of the sleeve cage according to the invention.

[0022] Figure 5 shows a longitudinal cross-sectional view of the sleeve cage according to the invention.

[0023] Figure 6 shows a perspective view of an indexing sleeve according to the invention.

[0024] Figure 7 shows a perspective view of an example of a ferrule with a square base

[0025] Figure 8 shows a perspective view of an example of the central body of the linkage

[0026] Figure 9 shows an exploded view of the connector. General presentation of the invention.

[0027] The invention relates to a miniature optical connector, particularly suited to the extreme environments encountered in space and aeronautical applications. This connector according to the invention is distinguished by its compact design, its light weight, and its ability to maintain a stable and reliable optical connection under harsh conditions such as vacuum, temperature variations, vibrations, radiation, and high pressures. The connector is designed for multimode (MM), single-mode (SM), or polarization-maintaining (PM) optical fibers, used for high-precision data transmissions.

[0028] The miniature connector according to the invention does not require any prior adjustment of the concentricity of the optical fiber with respect to the diameter of the ferrule.

[0029] The invention is based on the use of a one-piece ceramic ferrule, fixed to the fiber using various types of sealant such as Glas s Solder (glass) or epoxy. The principle of the invention lies in the use of a connection (or feedthrough) equipped with a sleeve cage (30) allowing reproducible alignment of the two ferrules of the connectors (10, 20), while offering optimal resistance to temperature extremes.

[0030] General description of the connector according to the invention

[0031] The connector assembly according to the invention consists of the following main parts: two connectors (10, 20) and a link (or feedthrough), allowing precise and stable alignment of the optical fibers via a fitting (30) formed by a ceramic sleeve cage and an indexing tube (40). The mechanical parts of the fitting (30) and the connectors (10, 20) can be made of 316L stainless steel or titanium to further reduce their weight.

[0032] The type of optical fiber suitable for this connector assembly is a multimode optical fiber, a single-mode fiber or a polarization-maintaining fiber.

[0033] By way of example, the total length of the assembled connector is 28 mm. The length of the connector (10, 20) is 13 mm, with an outside diameter of the connector (10, 20) of 7 mm extended by a threaded base (11, 21) having an outside diameter of 8 mm.

[0034] The fitting (30) has three lobes (31, 32, 33) pierced by holes with a diameter of 2.4 mm for assembly.

[0035] The fiber terminates at the connector (10, 20) with a ferrule (11, 21). The ferrule is a small cylindrical component used in optical connectors to align and hold the end of an optical fiber in place. The ferrule (11, 21) ensures precise fiber alignment when two connectors are connected, thus enabling efficient light transmission between the fibers. The ferrule (12, 22) surrounds and secures the optical fiber inside the connector (10, 20), keeping the fiber end precisely aligned with the axis of the connector (10, 20). This minimizes insertion loss and return loss that can occur if the fibers are not properly aligned.

[0036] Ferrules are generally manufactured from materials such as ceramics, metal, or sometimes composite alloys, depending on the application requirements (resistance to mechanical stress, high temperatures, etc.). In demanding environments, such as those described in the invention, zirconia ferrules are used for their wear, heat, and corrosion resistance properties.

[0037] The ferrule used in the connector according to the invention is a one-piece ceramic ferrule with a diameter of 125 µm. This ferrule is made of zirconia. Zirconia offers excellent wear resistance, low thermal conductivity, and a coefficient of expansion close to that of silica optical fiber, thus ensuring dimensional stability even under extreme temperatures.

[0038] The fiber can be sealed in the ferrule in two ways:

[0039] • By epoxy adhesive guaranteeing low outgassing.

[0040] • By sealing with fusible glass (glass soldering), which offers greater resistance to space temperatures and radiation. Sleeve cage for coaxial alignment

[0041] The connector according to the invention uses a sleeve cage (made of ceramic to ensure precise coaxial alignment of the ferrules of the two connectors.

[0042] The link (or crossing) with a sleeve cage illustrated by figures [Fig.4] and [Fig.5] allows reproducible alignment of the two ferrules (12, 22) of the connectors, while offering optimal resistance to temperature extremes.

[0043] The sleeve cage plays an essential role in the connection, ensuring precise and stable coaxial positioning of the connector ferrules, thus guaranteeing a reliable optical connection. It consists of a longitudinally split ceramic tubular sleeve (50) that allows for precise alignment of the optical fibers during the insertion of the ferrules (11, 21) on both sides. This sleeve (51) is held in place by a crimped mechanical structure, composed of a tube (52) and two retaining washers (53, 54), which frame it for improved stabilization and protection against external damage and contaminants, such as dust, dirt, and scratches, can affect transmission quality.

[0044] Thanks to the sleeve (50), precise coaxial positioning of the ferrules (11, 21) on the order of 1 pm is achieved. The ceramic, a very hard and stable material, offers excellent resistance to high temperatures, mechanical stresses and vibrations, as well as to corrosion and wear, ensuring a prolonged service life for the sleeve cage.

[0045] Furthermore, the ceramic allows for precise alignment of the ferrules (11, 21), with micrometer accuracy, thus improving the optical performance of the connection. Its smooth surface facilitates the insertion of the ferrules (11, 21) without risk of scratching or damaging the fibers.

[0046] The sleeve cage (50) is made of 316L stainless steel or titanium, offering additional resistance to corrosion and wear.

[0047] The cage (50) in which the sleeve (51) is held is a structure that stabilizes the sleeve (51), ensuring that the latter remains in place and protects the system against physical damage, dust, or contaminants. It guarantees high-precision alignment while providing protection against mechanical or thermal stresses.

[0048] In summary, the sleeve cage (50) plays a crucial role in ensuring the quality and reliability of the optical connection by guaranteeing that the fibers are perfectly aligned during the coupling of the connectors (10, 20), thereby reducing signal loss. Indexing tube for angular alignment

[0049] In certain applications, particularly for Angle-Polished Connectors (APCs) or polarization-maintaining (PM) fibers, precise angular alignment is required. For this purpose, an indexing tube (60) illustrated in Figure 6 is used. The geometric configuration of the indexing tube (60) is determined by the configuration of the ferrules (11, 21). The ferrules (11, 21) have, for example, a diameter of 1.25 mm. They can have different base shapes, such as square or hexagonal, and are associated with this indexing tube (60). The latter has specific geometric shapes at its ends (clamps), thus enabling the desired orientation to be obtained when the ferrules are inserted on each side. This method allows for reproducible angular alignment of the ferrules, which is essential for APC configurations or polarization-maintaining fibers, where it is necessary to align the slow and fast axes of the fibers.

[0050] Figure [Fig. 7] illustrates an example of a ferrule (11, 21) configuration with a square base (13). The ferrules (11, 12) are advantageously made of zirconia 0 1.25 mm, a material frequently chosen for this type of component due to its excellent physical and mechanical properties. Zirconia indeed exhibits a It offers high resistance to bending, wear, and corrosion. Furthermore, it is characterized by very low thermal conductivity and high heat resistance. This material is frequently chosen for this type of component primarily because it allows for very high-precision machining, currently unattainable at the cost level for metals (< Ipm).

[0051] The indexing tube (60) has a tubular central body (61) with specific geometric shapes at its ends (62, 63), allowing the slow and fast axes of the optical fibers to be oriented during the insertion of the ferrules. This shape is, for example, determined by a serration formed by two axial teeth (64, 66; 65, 67). This ensures reproducible angular alignment, essential for maintaining optical performance in sensitive configurations. Central body of the link (30)

[0052] The central body (30) provides the mechanical link between the two connectors (10, 20). It is manufactured in one piece, guaranteeing the robustness of the structure.

[0053] The central body (30) of the linkage is made of a single block, serving to ensure the mechanical connection between the two connectors (10, 20). The sleeve cage (50) is mounted in the indexing tube (60), and then the assembly is fixed inside the cylinder of the central body (30).

[0054] The shape of the central body (30) can vary according to its use: - A cone-shaped base for manual spinners allowing the connector to be fixed to a wall, as illustrated in Figure [Fig.8]. - A cylindrical base welded directly onto a wall, acting as a through-wall fitting. - A base in the form of a cross-section, fixed by a central nut around the body. Connector

[0055] The connector (10, 20) according to the invention consists of a hood (16), a ferrule (11) and a spring (15).

[0056] The pressure exerted on the ferrules (11, 21) is generated by the compression of a calibrated spring (15). A support washer (14) allows the ferrule cover (11) to rotate without catching on the base of the spring, thus ensuring uniform support over its entire surface. Contact is established with a ferrule (11) having a square base (13) or another shape.

[0057] The connector (10, 20) can be attached to the central body (30) in different ways, depending on the application: - Screw fastening: This method ensures a robust and durable connection. By screwing the connector in, increased contact pressure is exerted between the contact surfaces of the connector and the base, thus reducing the risk of loosening and connection instability. Furthermore, the screw fastening system is particularly well-suited to space environments subject to significant vibrations. The screw-on connector is prevented from rotating by shrink fitting. A 0.8 mm diameter hole is drilled in the cover (16). - Bayonet fitting: this option allows for quick attachment of the connector with the advantage of being anti-rotation. - So-called "Push-Pull" fastening: although allowing for quick fastening, this method is less common in the space field. Protective sheath

[0058] The sheath is fixed directly to the ferrule base tube. The internal diameter of the sheath must not exceed 0.6 mm and its external diameter must not exceed 0.1 mm. For space applications, the sheaths used are made of Inox, PEEK, or Hytrel.

[0059] Example of a 304 stainless steel protective sheath, 0.1 mm thick: Stainless steel is a material highly resistant to corrosion and high temperatures (< 600°C). It offers reliable protection against radiation and impacts. Furthermore, it is non-outgassing. Note that its maximum length is limited to 2.5 m.

[0060] Example of PEEK 0 0.9 mm Protective Sheath: This material is a very strong and lightweight thermoplastic polymer offering good resistance to chemicals and high temperatures (< 250°C). It also offers high radiation resistance and low density. Note that it is very low outgassing. Variants

[0061] A hybrid connection can be achieved using both a feedthrough and a connector (10, 20). The feedthrough is fixed to a wall, and the fiber ferrule (11, 21) is securely attached to the feedthrough body, ensuring a seal. This seal can be achieved either by using a gasket or by directly soldering the body to the wall. The ferrule can be attached to the body either with a space-grade adhesive or by glass soldering. Opposite, a removable connector (10, 20) connects to the feedthrough either by screwing or by a bayonet fitting.

[0062] The through-hole can withstand temperature ranges from -55°C to +125°C, pressures up to (30 bars compact hybrid version as illustrated below) bars, and vacuums up to 10-8 mbar.l / s. Conclusion

[0063] The proposed invention has several advantages over the prior art, including:

[0064] • Absence of prior manual adjustment of the concentricity of the optical fibers by related to the ferrule, thus simplifying the production and maintenance process.

[0065] • Increased resistance to extreme environments through the use of materials such as ceramics and titanium.

[0066] • Reproducible and stable coaxial alignment without the need for mechanical correction, thus reducing the risk of degradation of optical performance, particularly for polarization-maintaining fibers.

[0067] • Ease of assembly thanks to the modularity of the components and the flexibility of the fixing options (screw, weld, bayonet).

Claims

Demands

1. Optical interconnect assembly comprising two connectors (10, 20) of an optical fiber sealed in a ferrule (11, 21) and a coaxial alignment means for the optical fibers, characterized in that said coaxial alignment means consists of a slotted ceramic tubular sleeve (51) housed in a sleeve cage (50) consisting of a tubular body (52) positioned in a central body (30) having on either side a means for connecting a connector (10, 20).

2. Optical connector assembly according to claim 1 characterized in that the sealing of the fiber in the ferrule (11, 21) is ensured by an epoxy glue.

3. Optical connector assembly according to claim 1 characterized in that the sealing of the fiber in the ferrule (11, 21) is ensured by glass soldering.

4. Optical connector assembly according to claim 1 characterized in that said ferrule (11, 21) is made of zirconia.

5. Optical connector assembly according to claim 1 characterized in that the sleeve cage (50) is composed of a structure (52) made of titanium or 316L stainless steel.

6. Optical connector assembly according to claim 1 characterized in that it further comprises an indexing tube (60) enabling angular alignment of the ferrules for APC (Angle-Polished Connector) configurations or for polarization-maintaining optical fibers, said indexing tube (60) having geometric shapes at its ends complementary to the configurations of said ferrules (11, 21) to guarantee the correct orientation of the slow and fast axes of the fibers.

7. Optical connector assembly according to claim 1 characterized in that the optical fibers are protected by a sheath made of 304 stainless steel or PEEK.

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