Cross-Reference to Related Application

This application is being filed on April 29, 2019 as a PCT International Patent

Application and claims the benefit of U.S. Patent Application Serial No. 62/665,911, filed on May 2, 2018, the disclosure of which is incorporated herein by reference in its entirety.

Background of the Invention

The present invention is generally directed to fiber optical communications, and more specifically to elements used for coupling light between fibers or between fibers and waveguides.

Optical fiber connectors are used to connect optical fibers in a variety of applications, including telecommunications networks, local area networks, data center links and for internal links in high performance computers. Optical fiber connectors are also used to connect between one or more fibers and waveguides on an optical chip.

These connectors can be grouped into single fiber and multiple fiber designs and also grouped by type of contact. Common contact methods include physical contact, wherein the mating fiber tips are polished to a smooth finish and pressed together; index-matched, wherein a compliant material with a refractive index matched to that of the fiber core fills a small gap between the fiber tips; and air gap connectors, wherein the light passes through a small air gap between the two fibers or between the fiber and the waveguide.

In general, single fiber optical connectors include a precision cylindrical ferrule for aligning and contacting optical fiber end faces with each other. The optical fiber is secured in the central bore of the ferrule so that the fiber’s optical core is centered on the ferrule axis. The fiber tip is than polished to allow physical contact of the fiber core. Two such ferrules can then be aligned with each other using an alignment sleeve with the polished fiber tips pressed against each other to achieve a physical contact connection from one fiber to another. Multiple fiber connectors use a multiple fiber ferrule, such as the MT ferrule, to provide optical coupling from the source fibers to the receive fibers. The MT ferrule embeds the fibers in an array of molded bores to which the fibers are typically bonded. Each ferrule has two additional bores in which guide pins are located to align the ferrules to each other and thus align the mated fibers. With these contact methods, however, a contaminant, such as a piece of dust on a fiber tip, can greatly increase the optical connection loss. Furthermore, the alignment tolerances are very tight. For example, to get good overlap between two single mode fiber cores each 9 pm in diameter, the alignment has to be within about one micron or less.

Another type of connector is referred to as an expanded-beam connector. This type of connector allows the light beam in the source connector to exit the fiber core and diverge within the connector for a short distance before being collimated to a beam with a diameter substantially larger than the fiber core. In the receiving connector, the beam is then focused back down to the core of the receiving fiber or waveguide. The expanded- beam connector is available for single fiber connections and also for connections between multiple fibers, e.g. in a fiber ribbon. The expanded-beam connector is less sensitive to dust and other forms of contamination, and is less sensitive to alignment tolerances than the contact connector.

On the other hand, the introduction of optical elements and an air gap between optical fibers or between optical fibers and chip waveguides can introduce new problems. For example, where the light collimating element is a refractive element, the surfaces of the refractive element can reflect a small fraction of the optical signal back to the source fiber, which can cause detection errors if the source fiber is being used to transmit two- way optical data traffic. Previous approaches to overcoming this problem include coating the collimating element with anti -reflection (AR) coatings and/or operating the collimating element off-axis. Reflections from a fiber are often countered by cleaving the fiber end at a slight angle, around 8°, so that any reflection from the fiber end is off-axis. While the use of a cleaved fiber end is straightforward, the use of off-axis components between the fibers can introduce aberrations to the optical beam and can be difficult to align.

Furthermore, the need to provide AR coatings on the optical elements increases the component cost of the connector.

Another problem encountered with expanded-beam connectors arises from the wide range of environmental conditions to which some fiber connectors are exposed. It has been found that, due to fluctuations in temperature and humidity, water vapor can condense on the optical surfaces within an expanded-beam connector, which can greatly increase the optical connector loss. One approach to reducing this problem is to seal the expanded-beam space between the fibers, but this is an expensive solution and can be ineffective when the connection is made in a condition of high relative humidity, trapping a large amount of water vapor inside the connector. Another solution is to use coatings within the expanded-bean connector that encourage the water vapor to condense at a location outside the beam path. However, the addition of these coatings adds expense to the connector.

There is a need, therefore, to develop improved methods for connection between fibers and between fibers and waveguide, that are less sensitive to contamination and alignment tolerances, and that also avoid the expense of coating various connector elements while reducing problems of water vapor condensation. Furthermore, the solution should be easy and straightforward for a technical to assemble in the field.

Summary of the Invention

An embodiment of the invention is directed to an optical device that includes an optical fiber having a fiber end. A focusing element is disposed in optical communicative relationship with the fiber end. The focusing element has a first side facing the fiber end and a second side facing away from the fiber end. At least one of the first side and the second side of the focusing element is provided with an anti-reflection (AR) structured surface.

Another embodiment of the invention is directed to an expanded-beam optical connector that includes a housing and an alignment block within the housing, the alignment block comprising a plurality of alignment features. A plurality of optical fibers have ends located on respective alignment features of the alignment block. A focusing element array in the housing comprises a plurality of focusing elements. The focusing elements of the focusing element array are disposed in optical communicative relationship with respective ends of the plurality of optical fibers. At least one side of the focusing elements is provided with respective anti -reflection (AR) structured surfaces.

Another embodiment of the invention is directed to a method of forming an expanded beam optical connector. The method includes molding an optically transparent material to form a focusing element having a focal length. Molding the optically transparent material comprises molding an anti -reflection (AR) structured surface on at least one side of the focusing element. The focusing element and an optical fiber are mounted in a connector housing. The optical fiber has a fiber end. The focusing element is spaced from the fiber end in an optically communicative relationship to collimate or focus light emitted from the fiber end. The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.

Brief Description of the Drawings

The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:

FIG. 1 schematically illustrates a first expanded-beam fiber connector coupled to a second expanded beam fiber connector, according to an embodiment of the present invention;

FIG. 2 schematically illustrates a first expanded-beam fiber connector, that carries multiple optical fibers and that uses an array of focusing elements to produce multiple expanded-beams, fibers, connected to a similar second expanded-beam fiber connector, according to an embodiment of the present invention;

FIG. 3 schematically illustrates an expanded-beam fiber connector, that carries multiple optical fibers and that uses an array of focusing elements to produce multiple expanded-beams, fibers, connected to an optical chip having multiple waveguides, according to an embodiment of the present invention;

FIG. 4 schematically illustrates an expanded-beam fiber connector, that carries multiple optical fibers and that uses an array of focusing elements to produce multiple expanded-beams, fibers, connected to an array detector, according to an embodiment of the present invention;

FIG. 5 schematically illustrates an exemplary anti -reflection (AR) structured surface, according to an embodiment of the present invention;

FIG. 6 schematically illustrates an embodiment of an expanded-beam fiber geometry that includes a focusing element with an AR structured surface, according to the present invention;

FIG. 7 schematically illustrates another embodiment of an expanded-beam fiber geometry that includes a focusing element with AR structured surfaces, according to the present invention;

FIG. 8 schematically illustrates an embodiment of a multi-fiber, expanded-beam fiber geometry that includes a focusing element array with focusing elements having an AR structured surface, according to the present invention; FIG. 9 schematically illustrates another embodiment of a multi-fiber, expanded- beam fiber geometry that includes a focusing element array with focusing elements having AR structured surfaces on both sides, according to the present invention;

FIG. 10 schematically illustrates another embodiment of a multi -fiber, expanded- beam fiber geometry that includes a focusing element array with focusing elements having an AR structured surface, the focusing element array having additional anti-reflection features, according to the present invention;

FIG. 11 schematically illustrates another embodiment of a multi-fiber, expanded- beam fiber geometry that includes a focusing element array with focusing elements having an AR structured surface, the focusing element array having additional anti-reflection features, according to the present invention;

FIGs. 12A and 12B schematically illustrate the contact angle formed by a liquid droplet on a surface where the contact is relatively low (FIG. 12 A) and relatively high (FIG. 12B);

FIGs. 13A-13C schematically illustrate embodiments of reflective lenses that may be used in the present invention;

FIG. 14 schematically illustrates an embodiment of a multi-fiber connector having a focusing element array integrally formed with an alignment block, the focusing elements being provided with AR structured surfaces, according to the present invention.

While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

Detailed Description

An embodiment of a single-fiber, expanded-beam connector 100 is schematically illustrated in FIG. 1. The connector 100 is attached at an end of a first optical fiber 102. The end of the fiber 102 is located within a ferrule 104. A housing 106 surrounds the ferrule 104. A transmissive focusing element 108 is located at a distance from the end of the fiber 102. The focusing element 108 is preferably a lens, and may be made of any suitable shape, for example it may be a spherical lens or an aspherical lens. In other embodiments, the focusing element may be in the form of a Fresnel lens or a diffractive element, if the bandwidth of such a focusing element can meet the bandwidth

requirements of the optical signal.

In the illustrated embodiment, the focusing element 108 is located at a distance such that light 110 emerging from the fiber 102 is collimated after passing through the focusing element 108. In other words, the end of the fiber 102 is positioned at the focal point of the focusing element 108. In other embodiments, the end of the fiber 102 may be located at a different distance from the focusing element 108. For example, the end of the fiber 102 may be positioned at a distance longer than the focal length from the focusing element 108, in which case the light 110 emerging from the fiber 102 is imaged to e.g. a detector or another waveguide, or creates a virtual image that is then imaged back to a second fiber using another focusing element. The focusing element 108 may be said to be in an optically communicative relationship with the end of the fiber 102, meaning that the focusing element 108 is disposed relative to the end of the fiber 102 so that light from the end of the fiber 102 is received by the focusing element. Because of the focusing properties of the focusing element 108, such light can be collimated or focused, depending on the separation between the end of the fiber 102 and the focusing element 108 and the focal length of the focusing element 108.

In the illustrated embodiment, the focusing element 108 is held in position relative to the fiber 102 by the housing 106. In other embodiments, the focusing element 108 may be held in place by another element within the housing 106 or, for example, by an extension from the ferrule 104.

The figure also shows how a second connector 120 can be used to couple light from the first fiber 102 to a second fiber 122. In this embodiment, the second connector 120 is the same as the first connector 100, and includes a ferrule 124 around the end of the second fiber 122, and a second housing 126 that supports a second focusing element 128. The collimated light 130 from the first focusing element 108 is focused by the second focusing element 128 to the core of the second fiber 122, thus allowing light to couple between the first and second fibers 102, 122. Furthermore, light emitted out of the end of the second fiber 122 is collimated by the second focusing element 128 and focused by the first focusing element 108 to the core of the first fiber 102, thus permitting transmission of two-way optical data traffic between the fibers 102, 122. Various methods, such as the use of clips, screws and the like, may be used to attach the two housings 106, 126 together in a fixed relationship. Also, various methods may be used to maintain the correct alignment of the housings 106, 126, for example the use of alignment pins or the like. A typical requirement for a fiber connector in an optical data communications system is that the return loss is larger than 55 dB, in other words, any light reflected at the connection back along the source fiber should be reduced by more than 55dB of the signal in the source fiber. Thus, it is important to reduce the possibility that light reflected within the connection is redirected back along the source fiber. An examination of the fiber connection shown in FIG. 1 shows that, for light propagating from left to right along the first fiber 102, reflections may take place at any of the following surfaces: the output surface of the first fiber 102, each of the surfaces of the first focusing element 108, each of the surfaces of the second focusing element 128 and the input surface at the end of the second fiber 122.

Possible approaches for reducing reflections at the end surfaces of the fibers 102, 122 include i) cleaving the fiber end at an angle so that light reflected at the surface is directed out of the fiber, ii) including an index matching material between the fiber and the material of the focusing element, iii) patterning the fiber’s end; and iv) butting the fiber against a patterned lens. Use of an index-matching material becomes more difficult when the focusing element is spaced further apart from the end of the fiber, as in the illustrated embodiment, and has most utility when the fiber is butted up against the focusing element.

Possible approaches to reducing reflections from the focusing elements include providing dielectric anti -reflection (AR) coatings on the surfaces of the focusing elements. This can become expensive, however, particularly if the AR coating has to cover a range of wavelengths, for example from about 1250 nm to about 1650 nm, as can be the case with long-haul (> 1 km) single mode fiber communications used for television and/or internet signals.

Another approach to reducing reflections from the surface of the focusing elements is to provide a structure on the surface whose dimensions are small relative to the dimensions of the focusing element that provide the focusing properties. For example, in the case where the focusing element is an equibiconvex lens, a focal length of a 2 mm will typically require that each lens face have a radius of curvature of around 2 mm, where the refractive index is 1.5. In contrast, a structured surface, where the structures have dimensions around the wavelength of the incident light, or less, can be used to reduce the specular reflection at the surface of the focusing element that can return to the source fiber. Exemplary AR surfaces and methods of forming AR surfaces are discussed below.

An embodiment of a multifiber connection is schematically illustrated in FIG. 2. The connection is made with a first connector 200 that contains the terminal ends of four fibers 202a - 202d in a housing 206. It will be appreciated that the housing may contain terminal ends of a different number of fibers, for example 8, 12 or 16 fibers. The housing 206 also contains a focusing element array 204, for example a lens array, that includes a separate focusing element for light from each respective fiber 202a-202d. A second connector 220 contains the terminal ends of another four fibers 222a-222d in a housing 226. The housing 226 also contains a focusing element array 224 that includes a separate focusing element associated with each respective fiber 222a-222d. Thus, optical signals may propagate between fibers 202a and 222a, fibers 202b and 222b, fibers 202c and 222c and fibers 202d and 222d. The light from a fiber is being collimated or focused by the focusing elements of the focusing element arrays 204, 224, depending on whether the light passes from the left fiber 202a-202d to its respective right fiber 222, or vice versa.

The figure also shows alignment pins 210 that couple in recesses in both housings 206, 226 in a manner that ensures that alignment of the fibers 202, 222 is maintained when the two connectors 200, 220 are mated together. One of ordinary skill will appreciate that some elements of a multifiber connector are omitted from the figure for simplicity. For example, the connectors may include alignment features, such as a grooved block for aligning the fibers, and may include additional elements for aligning the focusing element array to the fiber ends. Also, the connectors are typically provided with a mechanism for maintaining a mated connection between connectors, such as clips, screws and the like.

An expanded-beam connector may be used to connect between one or more fibers and one or more respective waveguides on an optical chip. One approach to this is to use a collimated connector like that shown in FIG. 2, but where light is directed from a set of fibers into the terminal ends of waveguides on an optical chip, instead of a second set of optical fibers. Another approach is schematically illustrated in FIG. 3. A first connector 300 contains the terminal ends of four fibers 302a - 302d in a housing 306. The housing

306 also contains a focusing element array 304, for example a lens array, that includes a separate focusing element for light from each respective fiber 302a-302d. An optical chip 320 contains the terminal ends of chip waveguides 322a - 322d. In this embodiment, the focusing element array 304 is positioned so as to focus light from the end of a fiber 302a- 302d to the end of its respective chip waveguide 322a-322d. The optical chip 320 may include any type of optical elements connected to the waveguides 322a-322d, such as splitters, switches, and the like. While focusing elements in FIG. 3 do not collimate the light from the fibers 302a-302d, this connector 300 may still be considered an expanded- beam connector, because the light beams expand from the fibers 302a-302d and/or the waveguides 322a-322d, to the focusing elements of the array 304.

The use of an expanded-beam connector is not restricted to coupling light between fibers and/or waveguides, but may also be used to couple between one or more fibers and optical devices such as light sources and detectors, as well as an interposer to couple light between different optical chips FIG. 4 shows an embodiment in which light is coupled between fibers and an array of detectors. A first connector 400 contains the terminal ends of four fibers 402a - 402d in a housing 406. The housing 406 also contains a focusing element array 404, for example a lens array, that includes a separate focusing element for light from each respective fiber 402a - 402d. A detector unit 410 includes separate detectors 412a - 412d that receive light from respective fibers 402a - 402d. The detectors 412a - 412d may be any suitable type of optical detector, for example a photodiode. Each detector 4l2a - 4l2d is coupled to a respective detector circuit 4l4a - 4l4d that receives and analyzes the signal produced by the detectors 412a - 412d. The detector unit 410 may be used, for example, in the central office of an optical communications network.

Focusing elements and arrays of such focusing elements are often formed from the optical material using a molding process. For example, many lenses are formed by molding a polymeric material that has suitable optical properties for use as a lens, such as polycarbonate, Ultem ^® (polyetherimide), and the like. One aspect of the present invention is that an AR surface structure is applied to the focusing element during the molding process. Thus, the focusing element is formed, complete with AR properties, in a single step. This avoids the need for post-fabrication processing, such as coating the focusing element, which reduces costs and simplifies production.

An example of an AR surface that may be formed in a molding process is schematically illustrated in FIG. 5. This exemplary surface 500 includes a regular pattern of peaks having a height (z-dimension) of around 700 nm, while the spacing in the x- direction and the y-direction is around 100-200 nm. The dimensions of the features of the AR surface pattern are typically no more than about the wavelength of the light passing through the focusing element, preferably less than the wavelength. In the case where the wavelength of light is in the range of around 1250 nm - 1650 nm, a 700 nm high surface feature has a height about one half of the wavelength. The AR surface pattern need not be regular and may comprise a collection of peaks having a randomized spacing. A mold that transfers such a pattern on to a molded piece such as a focusing element or focusing element array may be formed by precision machining for instance via Electrical Discharge Machining (EDM) or diamond machining.

The AR surface pattern results in a specular reflectivity that is less than one half of the reflectivity that would be expected from a consideration of the refractive index of the focusing element. For example, for a focusing element having a refractive index, m, operating in air (whose refractive index can be assumed to be 1.0), specular reflectivity, R, of a flat, smooth surface is expected to be R = [(m- l)/(nri-l)] ² at normal incidence.

When the surface is provided with the AR surface structure, the specular reflection falls to less than 50% of R, preferably less than 25% of R.

An embodiment of a focusing element having an AR surface is illustrated in FIG.

6. A fiber 602, having a core 603 (dashed lines) directs light 606 to the focusing element 604. In this embodiment, the focusing element 604 is a lens separated from the end of the fiber 602 by a distance equal to its focal length. Any medium can be present between the lens and the optical fiber including air, or an index matching material. It is also possible for the fiber to be directly in contact with the lens. After passing through the focusing element 604, the light 606 is collimated. In this embodiment, the first surface 608a of the focusing element 602, facing the fiber 602, is substantially flat and smooth. The second surface 608b of the focusing element, facing away from the fiber 602 is curved and is provided with an AR surface structure. It will be appreciated that the dimensions of the AR structural components are exaggerated in the figure.

In addition, in this embodiment, the end 610 of the fiber 602 is cleaved at an angle a from being normal to the fiber axis 612. The angle a is selected so that light reflected from the fiber end 610 is not directed along the fiber core 603 and may be, for example, around 8°. In other embodiments, the fiber end may be perpendicular to the axis 612.

An embodiment of a focusing element having two AR surfaces is illustrated in

FIG. 7. A fiber 702, having a core 703 (dashed lines) directs light 706 to the focusing element 704. In this embodiment, the focusing element 704 is a lens separated from the fiber end 710 by a distance greater than its focal length. After passing through the focusing element 704, the light 706 is imaged back to a point on the fiber axis 712. In this embodiment, both the first surface 708a of the focusing element 702, facing the fiber 702 and the second surface 708b of the focusing element 702, facing away from the fiber 702, are provided with an AR surface structure. The fiber end 710 may be cleaved at an angle, as shown, or may be perpendicular to the fiber axis 712. An embodiment of a focusing element array having a single AR surface is schematically illustrated in FIG. 8. The illustrated embodiment shows a focusing element array having two focusing elements, fed by two fibers 802a, 802b, but it will be appreciated that a greater number of fibers may be present, each with its respective focusing element. Optical fibers 802a, 802b, each have respective fiber cores 803a, 803b (dashed lines). Light 806a, 806b from each fiber 802a, 802b is directed to the focusing element array 804 that includes focusing elements 804a and 804b. The light 806a from fiber 802a is directed to focusing element 804a and the light 806b from fiber 802b is directed to focusing element 804b. The focusing elements 804a, 804b may be positioned at a distance from their respective fibers 802a, 802b by a distance equal to, or greater than the focal length of the focusing elements. In the illustrated embodiment, the focusing elements 804a, 804b are positioned at a distance equal to their focal lengths from the fibers 802a, 802b, resulting in the light 806a, 806b being collimated.

In this embodiment, the first surfaces 808a, 808b of the focusing elements 804a, 804b, facing towards the fibers 802a, 802b, are relatively smooth, and not provided with an AR surface structure. The second surfaces 8l0a, 810b of the focusing elements 804a, 804b, facing away from the fibers 802a, 802b are provided with an AR surface structure. The fiber ends 8l2a, 8l2b may be cleaved at an angle, as shown, or may be perpendicular to the fiber axes 814a, 814b.

Portions of the second surface of the focusing element array 804 that do not pass light from the fibers 802a, 802b, may be left smooth. For example, the portions 816a,

816b of the second surface close to the ends of the focusing element array 804, and the portion 816c between the focusing elements 804a, 804b, may be left smooth, without AR surface structure.

Another embodiment of focusing element array 904 is schematically illustrated in

FIG. 9. Optical fibers 902a, 902b, each have respective fiber cores 903a, 903b (dashed lines). Light (not shown) from each fiber 902a, 902b is directed to the focusing element array 904 that includes focusing elements 904a and 904b. The light from fiber 902a is directed to focusing element 904a and the light from fiber 902b is directed to focusing element 904b. The focusing elements 904a, 904b may be positioned at a distance from their respective fibers 902a, 902b by a distance equal to, or greater than the focal length of the focusing elements.

In this embodiment, the first surfaces 908a, 908b of the focusing elements 904a, 904b, facing towards the fibers 902a, 902b, are provided with an AR surface structure. Likewise, the second surfaces 9l0a, 91 Ob of the focusing elements 904a, 904b, facing away from the fibers 902a, 902b are provided with an AR surface structure. The fiber ends 812a, 812b may be cleaved at an angle, as shown, or may be perpendicular to the fiber axes 914a, 914b.

Portions of the surface of the focusing element array 904 that do not pass light from the fibers 902a, 902b, may be left smooth relative to the AR surface structure. For example, the portions 916a and 916b of the second surface close to the ends of the focusing element array 904, and the portion 916c between the focusing elements 904a, 904b, may be left smooth relative to the AR surface structure of surfaces 9l0a, 910b. Likewise, on the first surface of the focusing element array 904, the portions 918a and 918b of the first surface close to the ends of the focusing element array, and the portion 918c between the focusing elements 904a, 904b, may be smooth relative to the AR surface structure. In certain embodiments, the AR surface structure is provided only at those areas of the focusing element array 904 through which light passes to or from the fibers 902a, 902b, while other areas of the surface of the focusing element array are relatively smooth.

Another embodiment of focusing element array 1004 is schematically illustrated in FIG. 10. Optical fibers l002a, l002b, each have respective fiber cores l003a, l003b (dashed lines). Light (not shown) from each fiber l002a, l002b is directed to the focusing element array 1004 that includes focusing elements l004a and l004b. The light from fiber l002a is directed to focusing element l004a and the light from fiber l002b is directed to focusing element l004b. The focusing elements l004a, l004b may be positioned at a distance from their respective fibers l002a, l002b by a distance equal to, or greater than the focal length of the focusing elements.

In this embodiment, the first surface 1008 of the focusing element array 1004, facing towards the fibers l002a, l002b, are provided with slanted portions l008a, l008b so that light reflected by the first surface 1008 is reflected at an angle to the axes l0l4a, l0l4b. The second surfaces lOlOa, lOlOb of the focusing elements l004a, l004b, facing away from the fibers l002a, l002b are provided with an AR surface structure. The fiber ends l0l2a, l0l2b may be cleaved at an angle, as shown, or may be perpendicular to the fiber axes l0l4a, l0l4b.

Portions of the surface of the focusing element array 1004 that do not pass light from the fibers l002a, l002b, may be left smooth relative to the AR surface structure. For example, the portions l0l6a and l0l6b of the second surface close to the ends of the focusing element array 1004, and the portion !0l6c between the focusing elements l004a, l004b, may be left smooth relative to the AR surface structure of surfaces lOlOa, lOlOb.

In certain embodiments, the AR surface structure is provided only at those areas of the focusing element array 904 through which light passes to or from the fibers 902a, 902b, while other areas of the surface of the focusing element array are relatively smooth.

Another embodiment of focusing element array 1004 is schematically illustrated in

FIG. 10. Optical fibers l002a, l002b, each have respective fiber cores l003a, l003b (dashed lines). Light (not shown) from each fiber l002a, l002b is directed to the focusing element array 1004 that includes focusing elements l004a and l004b. The light from fiber l002a is directed to focusing element l004a and the light from fiber l002b is directed to focusing element l004b. The focusing elements l004a, l004b may be positioned at a distance from their respective fibers l002a, l002b by a distance equal to, or greater than the focal length of the focusing elements.

In this embodiment, the first surface 1008 of the focusing element array 1004, facing towards the fibers l002a, l002b, is provided with slanted portions l008a, l008b so that light reflected by the first surface 1008 is reflected at an angle to the axes l0l4a, l0l4b. The second surfaces lOlOa, lOlOb of the focusing elements l004a, l004b, facing away from the fibers l002a, l002b are provided with an AR surface structure. The fiber ends l0l2a, l0l2b may be cleaved at an angle, as shown, or may be perpendicular to the fiber axes l0l4a, l0l4b.

Portions of the surface of the focusing element array 1004 that do not pass light from the fibers l002a, l002b, may be left smooth relative to the AR surface structure. For example, the portions l0l6a and l0l6b of the second surface close to the ends of the focusing element array 1004, and the portion l0l6c between the focusing elements l004a, l004b, may be left smooth relative to the AR surface structure of surfaces lOlOa, lOlOb.

Another embodiment of focusing element array 1104 is schematically illustrated in

FIG. 11. Optical fibers 1 l02a, 1 l02b, each have respective fiber cores 1103 a, 1 l03b (dashed lines). Light (not shown) from each fiber 1 l02a, 1 l02b is directed to the focusing element array 1104 that includes focusing elements 1 l04a and 1 l04b. The light from fiber 1 l02a is directed to focusing element 1 l04a and the light from fiber 1 l02b is directed to focusing element 1 l04b. The focusing elements 1 l04a, 1 l04b may be positioned at a distance from their respective fibers 1 l02a, 1 l02b by a distance equal to, or greater than the focal length of the focusing elements.

In this embodiment, the first surface 1108 of the focusing element array 1104, facing towards the fibers 1 l02a, 1 l02b, is substantially flat, being free of elements that focus the light from the fibers 1 l02a, 1 l02b. The second surfaces 11 lOa, 11 lOb of the focusing elements 1 l04a, 1 l04b, facing away from the fibers 1 l02a, 1 l02b, refractively bend the light from the fibers 1 l02a, 1 l02b to provide focusing power. The fiber ends 11 l2a, 11 l2b may be cleaved at an angle, as shown, or may be perpendicular to the fiber axes l l l4a, l l l4b.

Those portions of the focusing element array 1104 that pass light from the fibers 1 l02a, 1 l02b may be provided with AR surface structure. For example, the second surfaces 11 lOa, lOlOb of the focusing elements 1 l04a, 1 l04b may be provided with AR surface structure, while the portions 11 l6a and 11 l6b of the second surface close to the ends of the focusing element array 1104, and the portion 11 l6c between the focusing elements 1 l04a, 1 l04b, may be left smooth relative to the AR surface structure. Likewise, those portions 1 l08a, 1 l08b of the flat first surface 1108 through which light passes to and from the fibers 1 l02a, 1 l02b may be provided with AR surface structure, while those portions of the surface 1108 that do not pass the light are relatively smooth.

An advantage to providing the AR structured surface on a focusing element or on a focusing element array only on those portions of the surface that pass the light passing to and from the fibers is that, in addition to providing desirable AR properties, the AR surface structure provides hydrophobic properties. In illustration, FIG. 12A schematically illustrates a liquid droplet 1202 on a solid surface 1204. The contact angle, cp _c , is that angle, within the liquid, formed by the liquid surface at the solid surface. It is known that submicron surface structure can provide anti-wetting properties, because the effective contact angle of a liquid droplet is increased. This is sometimes referred to as the“lotus effect.” Thus, the contact angle, cpc, for the liquid droplet 1212 on the structured surface 1214 is larger. Larger contact angles are related to increased hydrophobicity. Therefore, areas on the focusing element or focusing element array that are not provided with the AR surface structure, characterized by a lower contact angle, are more likely to provide sites where water vapor can condense. Furthermore, if any water vapor that does condense on an area of high contact angle, i.e. on the AR structured surface, then the water is more likely to be shed quickly, to an area of lower contact angle. Thus, those areas of the focusing element or focusing element array that are provided with an AR surface structure are more likely to remain unaffected by condensing water vapor. The contact angle formed by water on a surface may be referred to as the“water contact angle.” It is also possible to pattern areas of the lenses where no optical signal is present, so as to reduce the surface hydriphobicityto form safe traps for condensation to occur that will not affect transmission of the light through the area of the focusing element, which has high hydrophobicity.

The examples of focusing elements discussed so far may be described as transmissive focusing elements, in which the light is transmitted through a first surface and out a second surface, where either or both of the surfaces is shaped to focus the light. In addition, either or both of the surfaces may provide with AR surface structure. Other embodiments of focusing elements that may be used with an AR surface structure are illustrated in FIGs. 13A-13C. These focusing elements may be referred to as“reflective lenses” in that the light enters a first surface of the focusing element, reflects off at least a second surface while within the focusing element, and then exits via a third surface of the focusing element. Any of the surfaces of the reflective lens may provide focusing power, for example by being curved, having a Fresnel lens structure or a diffractive focusing pattern. FIG. 13A schematically illustrates light 1306 from a fiber 1302 passing along fiber axis 1312 to enter a reflective focusing element 1304. In this embodiment, the focusing element 1304 is in the shape of a hemispherical lens. The light 1306 from the fiber 1302 enters the focusing element 1304 via a first part of the spherical surface 1308, reflects off the flat face 1309 of the hemisphere and exits via another part of the spherical surface 1310. Any of the surfaces through which the light passes or reflects off, 1308,

1309 and 1310 may be provided with an AR surface structure.

Another embodiment of reflective focusing element lens 1324 is schematically illustrated in FIG. 13B. Light 1326 from the fiber 1322 passes along fiber axis 1332 to enter the reflective focusing element 1324 via a first surface 1328, reflects off a second surface 1329 within the reflecting lens 1324, and exits via a third surface 1330. Any of the surfaces 1328, 1329, 1330 may be provided with an AR surface structure. Furthermore, any of the focusing element surfaces that transmit or reflect light may be shaped to provide optical focusing power to the focusing element. In the illustrated embodiment, the third surface 1330 is curved so as to provide focusing power to the light 1326.

Another embodiment of reflective focusing element lens 1344 is schematically illustrated in FIG. 13C. Light 1346 from the fiber 1342 passes along fiber axis 1352 to enter the reflective focusing element 1344 via a first surface 1348, reflects off a second surface 1349 within the reflecting lens 1344, and exits via a third surface 1350. Any of the surfaces 1348, 1349, 1350 may be provided with an AR surface structure. In this particular embodiment, the second surface 1349 is curved and provides focusing power to the light 1346. In other embodiments, different combinations of the first, second and/or third surfaces may be curved to focus the light passing through the reflective focusing element.

Any focusing element or array may be integrated into an alignment structure so that the fibers can be aligned relative to the focusing elements. One example of this approach is described in U.S. Patent Publication No. 2009/0154884 Al, incorporated herein by reference, and schematically illustrated in FIG. 14. A connector 1400 includes a V-lens array 1401 which is formed from a v-groove block 1406 integrated with an array of lenses 1404. A fiber 1402, which may be a fiber of a ribbon cable, is located in a v-groove of the v-groove block 1406. The V-lens array 1401 is fabricated from an optical grade plastic with a refractive index similar to that of the optical fiber, such as polycarbonate or Ultem. The lenses 1404 are fabricated within the front frame 1308 and, preferably, to prevent scratches to the lenses 1404 during mating of the ferrule with a corresponding connector or ferrule, slightly recessed within the front frame 1408. In some embodiments, the lenses 1404 may comprise collimating lenses, for those instances where the ferrule is to be mated with a complementary ferrule or, in other embodiments, the lenses 1404 may be focusing lenses, for those instances where the ferrule is to be mated with an active device, i.e., a light source or receiver. The outer surface of the lenses 1404, facing away from the fibers 1402, may be provided with an AR structured surface. Likewise, the inner surfaces of the lenses 1404, facing the fibers 1402, may be provided with an AR structured surface.

Each v-groove comprises a terminus 1410 near the focal point of a corresponding lens 1404. The grooves in the v-groove block 1406 may be provided with any suitable cross-sectional profile, e.g. v-groove, semi-circular groove or rectangular groove, for holding the fiber 1402 in alignment.

A housing 1412 preferably comprises walls 1414, a collar 1416 disposed adjacent a rear portion of the housing 1412 and a cantilever 1418 preferably having an inward-facing protrusion 1420. Pin apertures may also be provided for receiving alignment pins (not shown). The cantilever 1418 may be configured, given the dimensions of that portion of the V-lens 1401 comprising the v-grooves 1406, to substantially retain the optical fibers 1402 aligned with and within corresponding v-grooves. In the illustrated embodiment, the protrusion 1420 engages the fibers 1402 through the biasing force provided by the cantilever 1418. A boot 1422 has a front insertion portion 1424 that fits within the housing 1414 and a stepped portion 1426 that engages with the housing 1414. A suitable adhesive 1428, for example a thermally cured adhesive such as Trabond F253, can be placed within the housing to substantially surround the fibers 1402 to fix them, and the other components of the connector, in place.

Various modifications, equivalent processes, as well as numerous structures to which the present invention may be applicable will be apparent to those of skill in the art to which the present invention is directed upon review of the present specification. The claims are intended to cover such modifications and devices. For example, the invention is intended to cover the provision of an AR structured surface on one side or both sides of a focusing element, and may be used with or without one or more other features, such as cleaved fiber ends, provided with the intention of reducing reflection back into a source fiber. For example, a fiber may be butted against a first side of a focusing element, while the focusing element is provided with an AR structured surface on the first side, a second side, or both sides.

As noted above, the present invention is applicable to optical systems for communication and data transmission. Accordingly, the present invention should not be considered limited to the particular examples described above, but rather should be understood to cover all aspects of the invention as fairly set out in the attached claims.