RU2849002C1 - Fibre optic connector with expanded beam - Google Patents

Abstract

FIELD: fibre optic technologies.

SUBSTANCE: invention relates to a fibre optic connector with an expanded beam. The connector includes two collimating structures coaxially arranged in a fixture. Each collimating structure comprises an optical fibre and a microlens connected coaxially and has an outer diameter not exceeding 125 mcm. The collimating structures are placed in a fixture with the possibility of separating them along the optical axis relative to each other by a distance limited by the length of the fixture. The microlenses are a section of multimode gradient optical fibre with an increased core diameter of no more than 105 mcm and a quartz cladding diameter corresponding to the diameter of the quartz cladding of the optical fibre connected to it. The output end of the gradient fibre is polished at an angle of 0 to 2° relative to the axis of the optical fibre. The fibres are connected to each other by electric arc welding, placed along a single tooling and fixed in it.

EFFECT: increased efficiency of optical radiation transmission, increased stability of optical contact between transmitting and receiving fibres, reduced reverse optical losses, and simplified device design.

1 cl, 3 dwg

Description

The present invention relates to fiber-optic technologies, in particular to a fiber-optic connector device used as an expanded-beam optical connector in fiber-optic communication lines.

A utility model for a fiber-optic connector is known [Utility Model RU 222410 U1, G02B6/322, 22.12.2023]. The device includes a housing, which is a metal cylinder with an external thread, in which two zirconium ceramic centering bushings are installed. Two ceramic ferrules are installed therein, each of which contains glued segments of an optical fiber. Spherical microlenses are formed at the free ends of the coreless inserts, welded to the segments of the optical fiber with a core. The device operates as follows. Optical radiation propagates through the optical fiber and enters the zone of a monolithic spherical microlens formed at the free end of the coreless insert, located in the housing of the optical connector. The microlens creates a collimated beam of radiation, which, due to the absence of scattering, minimizes optical power loss, ensuring concentrated transmission of radiation to the receiving microlens. As a result, the optical radiation is efficiently transmitted to the receiving optical fiber.

One of the significant drawbacks of this device is the use of spherical microlenses, the manufacture of which is a technologically complex and highly precise process requiring precision machining methods. This not only increases production costs but also increases the likelihood of deviations in lens parameters, which can negatively impact optical transmission. Furthermore, the use of coreless inserts with spherical microlenses complicates the design and assembly process, requiring highly accurate alignment and coaxial alignment of the optical fiber relative to the lens. Furthermore, the presence of two centering bushings further increases the design complexity and the device's size and weight.

A fiber-optic connector with beam expansion is known [Patent US 10036857 B2, G02B6/3877, July 31, 2018]. The device includes a housing in which a ferrule with an optical fiber glued into it and a ball or spherical lens necessary for beam expansion are coaxially located. Epoxy glue can be used to secure the optical fiber inside the ferrule and the lens inside the connector part. The end of the optical fiber is aligned with the end of the ferrule. The ferrule holder is pressed inside the connector housing by a spring. The lens can be made of BK7, SF-8, sapphire, LaSFN9, PBH71 materials. To reduce return optical loss, an antireflective coating is applied to the surface of the end of the optical fiber and the lens. Optical radiation propagates through the optical fiber and enters a ball or spherical lens coaxially positioned with the output end of the ferrule, housed in the optical connector housing. The lens produces a collimated beam that enters the receiving lens of the second connector, increasing the efficiency of radiation coupling into the receiving optical fiber.

The device's disadvantages include the presence of a volumetric ball lens and the need for an additional element—a spring-type compression mechanism—to secure the ferrule in the connector housing. During operation, a connector with a compression spring wears this element, leading to so-called unwinding. This, in turn, reduces the efficiency of optical radiation coupling and, consequently, increases optical loss at the connection. The presence of a volumetric ball lens increases the complexity and cost of manufacturing, as it requires the use of high-precision equipment. Furthermore, the use of this type of lens increases the device's size and weight and necessitates the manufacture of components with a non-standard form factor.

The closest technical solution (prototype) to the claimed solution is a fiber-optic connector with beam expansion [Patent US 10718909 B2, G02B6/3845, July 21, 2020]. The device comprises a split centering sleeve, in which two collimating structures are coaxially positioned. The collimating structures consist of a section of single-mode optical fiber secured with adhesive in a ferrule-shaped fixture, to which a volumetric gradient lens is tightly attached and aligned coaxially. The gradient lens and ferrule for attaching the optical fiber are additionally housed in the fixture. A pin-type connector is inserted into a socket-type connector, and the connectors are pressed relative to each other using a spring. The operation of the device is explained as follows. A small-diameter optical beam propagating in an optical fiber enters a collimating element, represented by a gradient-index lens. The beam then passes through a second symmetric gradient-index lens, after which it is focused into the receiving single-mode optical fiber. Due to the absence of scattering, optical power loss is minimized and transmission of the beam to the receiving lens is ensured. As a result, the optical beam is efficiently transmitted into the receiving optical fiber.

The disadvantages of this device include the need for an additional ferrule to ensure alignment between the single-mode fiber and the gradient lens, which complicates the manufacturing process and increases the device's weight and size. The presence of a bulk gradient lens complicates the design and introduces additional optical loss at the interface between the gradient lens and the optical fiber. Furthermore, the need to use springs in the device's design negatively impacts the service life of these connectors, as wear and tear on these springs causes the connectors to unwind, increasing optical loss.

The proposed invention solves the problem of increasing the efficiency of transmitting optical radiation between transmitting and receiving optical fibers by increasing the upper limit of the level of transmitted optical power of the optical signal between the optical fibers while simultaneously reducing the radiation power density in the area of the optical contact of the transmitting and receiving fibers, increasing the stability of the optical contact between the transmitting and receiving fibers, as well as reducing return optical losses, simplifying the design and assembly method of a fiber-optic connector by eliminating additional non-standard elements and spring mechanisms from the design, and ensuring the ability to function both with physical contact and with the distance between the transmitting and receiving optical fibers

The stated task is accomplished through a technical result that ensures effective collimation of optical radiation and an increase in the diameter of the radiation beam at the output of the transmitting optical fiber by using a collimating element based on a multimode graded-index optical fiber with an increased core diameter, polished at an angle from 0° to 2°.

The use of an all-fiber collimating element reduces the number of operations and components required for coaxial alignment of the optical fiber with the lens, which significantly reduces the weight, size, and cost of the device.

The problem is solved in the following way.

A fiber optic connector with an expanded beam comprises two collimating structures coaxially arranged in a fixture, each of which includes an optical fiber and a microlens coaxially connected, wherein the collimating structures with an outer diameter not exceeding 125 μm are arranged in the fixture with the possibility of separating them along the optical axis relative to each other by a distance limited by the length of the fixture in which they are arranged, the microlenses are a section of a multimode graded-index optical fiber with an increased core diameter of not more than 105 μm and a quartz cladding diameter corresponding to the quartz cladding diameter of the optical fiber connected to it, and the output end of the multimode graded-index optical fiber is polished at an angle from 0 to 2° relative to the axis of the optical fiber, said fibers are connected to each other by electric arc welding, arranged along a single fixture and secured in it, wherein the length of the section of the multimode graded-index optical fiber is calculated using the formula:

(1)

Where – gradient lens pitch, – the refractive index at the core-cladding interface of a multimode graded-index optical fiber, – the maximum refractive index of the core of a multimode graded-index optical fiber, – core radius of multimode graded-index optical fiber.

The essence of the claimed fiber-optic connector with an expanded beam is explained as follows.

The device contains two collimating structures coaxially placed and spaced apart along the optical axis, each of which includes an optical fiber and a microlens coaxially connected.

The collimating structure comprises a section of optical fiber coaxially joined by arc welding to a microlens made from a section of multimode graded-index optical fiber. The joined fibers are housed in an adhesive-filled fixture. The length of the placed section of multimode graded-index optical fiber ensures its optimal length. for efficient collimation of optical radiation propagating in an optical fiber, and is calculated using the formula:

(1)

Where – gradient lens pitch, – the refractive index at the core-cladding interface of a multimode graded-index optical fiber, – the maximum refractive index of the core of a multimode graded-index optical fiber, – core radius of multimode graded-index optical fiber.

As is known, exceeding the permissible level of transmitted signal power through a fiber-optic connector can lead to degradation and destruction of the optical fibers. Therefore, existing standard solutions have limitations on the maximum possible level of transmitted radiation power, which is directly related to the beam diameter and the power density at the ends of the transmitting and receiving optical fibers. Increasing the beam diameter allows for a reduction in power density and an increase in the permissible power level of the transmitted optical signal. In the proposed invention, a microlens based on a graded-index optical fiber with an increased core diameter makes it possible to increase the diameter of the collimated beam at the output of the transmitting optical fiber. This, in turn, leads to a decrease in the power density at the junction of two sections of the optical line, thereby raising the maximum transmitted power threshold. This solution solves the problem of increasing the maximum transmitted optical signal power while simultaneously reducing the radiation power density at the optical contact area of the transmitting and receiving fibers.

The collimating structures are coaxially positioned and secured in the fixture. The absence of spring mechanisms for clamping the optical fiber and collimating lenses in the proposed device significantly simplifies the assembly process and increases the service life of these connectors while maintaining high optical coupling efficiency. This solution is particularly relevant in conditions of increased vibration loads, which can cause unwanted weakening of the spring mechanisms and, consequently, deterioration of the optical signal. In the proposed device, high optical communication efficiency under vibration is ensured by the use of beam expansion and collimation technology at the fiber output using a fiber microlens, eliminating the need for spring clamping mechanisms. This ensures stable optical contact and signal transmission even when the distance between the end faces of the transmitting and receiving optical fibers is limited by the length of the fixture in which the collimating structures are housed. The maximum allowable distance between the end faces of the transmitting and receiving fibers is determined by the length of the fixture in which they are housed. The use of beam expansion and collimation technology will allow the use of such a device in field conditions where contamination of the output ends of the transmitting and receiving optical fibers occurs.

Furthermore, increasing the beam diameter will reduce the impact of optical losses caused by contamination or scratches at the end faces of the collimating structures. To reduce return optical loss, the end faces of the collimating structures are polished at an angle of 0° to 2°. This will reduce return optical loss at the glass-to-air interface, as well as Fresnel reflection losses. This solves the problem of efficient transmission of optical radiation between optical fibers via a connector capable of operating with both physical contact and distance between them; it also eliminates the negative impact of contamination, vibration, dust, and scratches at the end faces of the optical fibers, which can increase optical loss.

The use of electric arc welding, a section of multimode graded-index optical fiber, and standard fiber component hardware allows for simplifying the design and assembly method of a fiber-optic connector with an expanded beam. The coaxial connection of an optical fiber section and a section of multimode graded-index optical fiber using electric arc welding and a fiber optic welding apparatus ensures highly accurate automatic coaxial alignment of the optical fiber section and the section of multimode graded-index optical fiber, thanks to the apparatus's built-in precision manipulators and camera. This, in turn, eliminates the errors introduced by other presented mechanical methods for coaxially connecting optical fiber and a graded-index lens, since the precision connection process occurs automatically. To ensure the use of standard components in the device's design, the collimating structure utilizes multimode graded-index optical fiber with a cladding diameter not exceeding 125 μm and a core diameter not exceeding 105 μm. In this regard, the proposed solution remains a fully fiber design with standard dimensional parameters, which allows it to be used as part of existing standard fiber-optic connectors.

The claimed device ensures highly accurate positioning of a section of multimode graded-index optical fiber relative to another section of optical fiber. This eliminates the need for additional components to collimate optical radiation within the optical fiber, simplifies the assembly process, and allows for the fabrication of a section of multimode graded-index optical fiber of the required length. All of this combined enables optical radiation collimation with high reproducibility of beam parameters.

The use of a fiber-optic connector with an expanded beam, as a graded-index lens for a section of multimode graded-index optical fiber in the claimed device, facilitates highly accurate positioning relative to the fiber section due to the matching diameters of their quartz cladding. Furthermore, a significant advantage of using multimode graded-index optical fiber instead of ball lenses and bulk graded-index lenses is its smaller size (125 µm and 1 mm or more, respectively), the ability to perform any type of polishing (UPC, APC) using polishing machines, and the ability to use standard fiber components. In addition, multimode graded-index optical fiber can be drawn with a quartz cladding diameter equal to the quartz cladding diameter of standard 125 µm optical fibers, which significantly simplifies the design and ensures reliable connection of various components by electric arc welding and eliminates the need to ensure precise alignment between elements with different diameters, as is the case with ball or volumetric graded-index lenses. This significantly reduces the overall dimensions of the device, allows the use of standard fiber-optic components in the assembly of the device, and also provides the ability to manufacture the device with various types of tooling, which expands the scope of its application.

To achieve an additional effect of reducing reverse optical loss, the area between the two collimating structures can be filled with immersion gel, and an antireflective coating can be applied to their ends.

The essence of the claimed invention is explained by the drawings (Fig. 1, Fig. 2, Fig. 3).

Fig. 1 – the device of a fiber-optic connector with a distance between the ends of the transmitting and receiving optical fibers.

Fig. 2 – device of a fiber-optic connector with physical contact between the ends of the transmitting and receiving optical fibers.

Fig. 3 – operating principle of the fiber-optic connector device.

The accepted designations in Fig.1, Fig.2 and Fig.3:

1 – section of multimode graded-index optical fiber

2 – a section of optical fiber in which optical radiation propagates

3 – plane of welded joint

4 – equipment for fastening the collimating structure

5 – adhesive

6 – equipment for fastening collimating structures of a fiber-optic connector

Fig. 1 shows a schematic representation of the design of a fiber-optic connector with an expanded beam. The device contains two collimating structures, each of which includes a section of multimode graded-index optical fiber.1, coaxially connected to a section of optical fiber2, in which optical radiation propagates, the fibers are connected to each other by electric arc welding in the plane of the welded joint3and rigidly fixed in the mounting fixture4using adhesive5; collimating the structures are coaxially located in the equipment6.

The operating principle of the fiber optic connector device with expanded beam is explained as follows (Fig. 3).Optical radiation passing through the first collimating structure consisting of a section of multimode graded-index optical fiber1, coaxially connected to a section of optical fiber2electric arc welding in the plane of the welded joint3,in which optical radiation propagates, and fixed in the 4-piece fixture using adhesive5, after which a collimated beam of radiation is formed at the output end of the first collimating structure, which hits the input end, coaxially aligned using equipment6,the second collimating structure, where it is focused into the core region of the receiving optical fiber.

As a specific example of assembling a fiber-optic connector with an expanded bundle, the following is proposed. A standard splicing operation is used to connect standard single-mode optical fiber (G.657.A2 standard) and multimode graded-index optical fiber (core diameter: 100 µm, cladding diameter: 125 µm) using a standard ILSINTECH SWIFT KF4 splicer.

The internal cavity of the equipment for fastening the collimating structure, which is made of ceramic ferula (V-groove, quartz tube, etc. can also be used as equipment), the inner diameter of which is 125±0.5 µm, the outer diameter is 2.499±0.001 mm, the length is 12.7±0.05 mm, filled with adhesive, which is EPO-TEC 353 ND optical glue. The length of the multimode gradient optical fiber section is 885 µm.

The end of a multimode graded-index optical fiber was polished using polishing films with a grain size of 5 μm, 1 μm, and 0.3 μm.

The collimating structures are placed in a fixture in the form of a ceramic split sleeve with an internal diameter sufficient for their reliable placement (external diameter 3.2±0.02 mm, internal diameter 2.496±0.001 mm, length 11.4±0.1 mm).

Thus, the proposed invention improves the efficiency of optical transmission between transmitting and receiving optical fibers, increases the upper limit of the transmitted optical power of the optical signal between the optical fibers while simultaneously reducing the radiation power density in the optical contact region of the transmitting and receiving fibers, increases the stability of the optical contact between the transmitting and receiving fibers, and reduces optical return loss. Furthermore, the proposed invention simplifies the design and assembly method of a fiber-optic connector, while enabling operation with both physical contact and distance between the transmitting and receiving optical fibers.

Additionally, the proposed invention simplifies the design and assembly method of the fiber optic connector, eliminating the need for additional, non-standard components and spring mechanisms. The proposed invention will reduce the number of operations and components required for coaxial alignment of the optical fiber with the lens, significantly reducing the device's weight, size, and cost.

Claims (3)

A fiber optic connector with an expanded beam, including two collimating structures coaxially placed in a fixture, each of which includes an optical fiber and a microlens coaxially connected, characterized in that the collimating structures with an external diameter not exceeding 125 μm are placed in the fixture with the possibility of separating them along the optical axis relative to each other at a distance limited by the length of the fixture in which they are placed, the microlenses are a section of a multimode graded-index optical fiber with an increased core diameter of not more than 105 μm and a quartz cladding diameter corresponding to the quartz cladding diameter of the optical fiber connected to it, and the output end of the multimode graded-index optical fiber is polished at an angle from 0 to 2° relative to the axis of the optical fiber, said fibers are connected to each other by electric arc welding, placed along a single fixture and secured in it, wherein the length of the section of the multimode graded-index optical fiber is calculated according to the formula: Where – gradient lens pitch, – the refractive index at the core-cladding interface of a multimode graded-index optical fiber, – the maximum refractive index of the core of a multimode graded-index optical fiber, – core radius of multimode graded-index optical fiber.