WO2005001532A2

WO2005001532A2 - Optical fibre connector

Info

Publication number: WO2005001532A2
Application number: PCT/GB2004/002752
Authority: WO
Inventors: Aubrey Edward Fenn; Anders Andersson; Jesper Ljung
Original assignee: Micropol Uk Fibre Optics Ltd
Priority date: 2003-06-26
Filing date: 2004-06-25
Publication date: 2005-01-06
Also published as: GB0314879D0; WO2005001532A3

Abstract

A connector (8, 9) for transmitting radiation, especially optical radiation from one optical fibre (11) into another, includes a pair of plano-convex lenses (10) each terminating in an aspheric surface (17) in previously known manner. The aspheric surface (17) is specifically a parabolic surface, the plano-convex lens (10) is preferably a two-part component, and in each such optically matched pair of connector elements the collimating lens components are preferably non-identical. Advantageously the plano-convex lens construction combines a plain (i.e. non-gradientindex) glass rod (16) with a moulded plastics paraboloidal lens (17) component.

Description

A CONNECTOR

Field of the Invention

The invention relates to connectors and more particularly to connectors which, when attached to a corresponding connector in sufficient alignment, allow radiation to be transmitted across the connection.

The invention is especially applicable to the problems encountered when transmitting light from one optical fibre element to another such connected element whilst attempting to minimise the attenuation inevitably caused by the connection.

Classically, small misalignments of the optical fibres of each connector cause substantial losses. The misalignment problems are most severe in direct fibre-to-fibre connector coupling. This is especially the case in harsh environments such as under water, in locations where temperatures fluctuate over a large range, where the components are submitted to vibration or exposed to sand, dust and any other small sized particles which would in prior art systems find themselves in the optical path and affect the performance of the optical transmission. Review of Prior Art Known to the Applicants Generally, the prior art can be divided into two types. A first is concerned with improvements to the physical coupling aspects of connectors to try to ensure and maintain increasingly precise alignment of the connectors when attached to a corresponding connector. A second type ignores (or addresses only in passing) the structural coupling aspects and concentrates instead on optimising the lens arrangements, and/or the individual lens properties, of the connector. One example of coupling improvements can be found in document EP 1 039 320 where a first connector incorporates as connecting means a number of guiding pins and a second connector presents a corresponding number of recesses. Once the connectors are mated together the distal extremity of the first connector's fibre abuts in alignment with the distal extremity of the second connector's fibre. The connection means further comprises either a threaded sleeve or a bayonet mechanism which contributes to the alignment of both connectors.

A further document whose publication number is AU 727292 is also concerned with connectors and is representative of a prior art variant where the connector's ferrule terminates in a spherical lens.

A number of documents have proposed the use of connectors terminating with a spherical lens. One example of such an arrangement can be found in JP 2 281 216. In these arrangements, the ball lens is often spaced from the fibre which creates a small cavity prone to receiving optical wavelength disturbing elements such as dust. In dense wavelength division multiplexing (DWDM) environments where high power concentrations are the norm, this may have fatal consequences to the connector if for example the dust burns, possibly along with other connector elements which would render it unusable. Such occurrences may have severe cost implications particularly when the connector itself is located in a remote location where the replacement operation would require extensive resources. There would also be potentially network difficulties due to the down time associated with the failure of such a connector. In a further document referenced US 4 733 936 a connector sleeve is designed to operate with two plug-in hemispherical lenses. This three part connection emphasises the importance of precisely aligning both connector plugs. This is particularly apparent when you consider that the connector sleeve has portions which precisely taper for accurately locating a given connector plug. Whilst it is true that the alignment requirements between two connectors terminating with a spherical lens are less stringent than the alignment requirements for direct fibre to fibre connector coupling similar to the arrangement described with reference to document EP 1 039 320 above - precise alignment is still essential for high performance.

The best combination of these known teachings would dictate the use of complex aligning connection means and a spherical lens. Even so, however, the performance is generally poor, especially if the optical fibre is a single mode fibre.

Efforts have therefore continued to improve the lens construction and/or lens arrangement as such. EP 1 168 012 is the most recent proposal known to the applicants and discloses a paired connector in which each lens terminates in a surface which is aspheric. The lenses of each such pair of lenses are identical and are separated by a distance approximately equal to the sum of the focal lengths of the lenses. No attempt is made to address the physical coupling requirements - the disclosure concentrates on the lens constructions and arrangements alone.

In summary, the cumulative prior art gives the addressee no consistent pointer as to the way forward. However complex the physical alignment arrangements proposed, misalignment and/or contamination will inevitably develop in use. Lens array improvements are self-defeating if - as is noticeably the case hitherto - they are pursued separately from (or at best with only passing reference to) some way of overcoming the misalignment problems inevitably imposed, in use, by practical conditions.

EP 1 168 012 just cited might seem to represent the current state of the art when one combines its publication date with the identity of its major-corporation applicant, but in some ways creates more problems than it purports to solve. It takes the developed spherical-lens art and positively contradicts it by insisting on the use of aspherical lenses. It ignores what is overwhelmingly the concern of the majority of prior proposals, namely, the supposed importance of the actual physical coupling arrangements needed for any practical success. Its teaching is concerned, essentially with the detailed components and parameters needed to construct and position the glass GRIN (gradient indexed) lenses which are essential for the optimum functioning of the system.

The problem therefore is well documented and clear enough. What is not at all clear is how best to solve it since the known art, whilst numerous, shows no consistent developmental approach.

Summary of the Invention

Against this background the present applicants propose:

a) that the teaching of EP 1 168 012 be taken as the starting point but that a parabolic, i.e. not just generally aspheric, lens surface is most likely to give best results in practise;

b) that the lens itself can, contrary to the teaching of EP 1 168 012, with advantage be constructed as a two-part lens; and

c) that it is in fact not necessary to have identical lenses in each matched lens pair of the connection.

None of this is shown or suggested in any of the prior art. Each individual invention summarised gives advantages in practical use. All of them are therefore clearly so linked as to form part of the same overall inventive concept whilst being independently applicable to the solution of the problem as stated above.

An arrangement incorporating any of these distinctive features opens up the possibility of doing away with the strict requirement for alignment which was the primary object of the majority of the prior art systems. It would therefore be particularly suited for applications in harsh environments where vibration and temperature change (for example) will inevitably cause and worsen alignment during the life cycle of the connector. Similarly, any one or any combination of these proposed inventive differences from prior proposals will result in a system lacking the lens construction problems so clearly outlined in EP l 168 012. Specifically in accordance with the broadest aspect of the invention there is provided a connector comprising an optical fibre, a collimating means operating with said fibre to transmit optical radiation and connection means for detachably attaching the connector to any other appropriate connector in sufficient alignment to allow radiation to be transmitted across the connection, characterised in that the collimating means terminates with an aspheric surface (known per s€) and in that there is also present at least one of the features selected from the group comprising, firstly, collimating means terminating with a parabolic surface; secondly, collimating means whose optical radiation transmitting region is constructed in multiple-part format; and thirdly, that the connector is designed as one operative half of a two-connector and preferably releasably re-usable connection means in which the optical radiation transmitting components of each connector half are non-identical.

An advantage of this linked series of inventive proposals is that the connection means needn't be unduly complex since the tolerances for alignment are so much larger than in the prior art. For example, a simple snap-fit comiection means may be employed. The connector of this type may also be employed in hostile environments such as underwater, in hot weather conditions and under vibration. When the optical fibre is selected to be a single mode connector by the person skilled in the art, the optical performance is dramatically higher than the optical performance of the prior art connectors discussed in detail in the previous section.

Advantageously, the collimating means may be joined to the distal extremity of the fibre. This further improves the optical properties of the connector and does away with the risk of misalignment between collimating means and fibre during operation and the potential of burning dust at that location when employed in high power arrangements. In this configuration, any obstruction along the optical path is minimised. Brief Description of the Figures

Figure 1 schematically shows two connectors in alignment. Figure 2 shows a cross-sectional view of two connectors in connection.

Figure 3 shows schematically an alternative collimating lens arrangement.

Detailed Description of the Figures

Figure 1 shows a first connector 1 spaced along the Z axis from a connector 2 forming a connection between a first set of optical components and a second set of optical components which for clarity have not been specifically illustrated and may be selected by the person skilled in the art to be any appropriate form of component. Connector 1 incorporates an optical fibre 3. The optical fibre may be of either single mode or multimode and selected from a wide range of available fibres.

The fibre 3 joins at its proximal extremity (not illustrated in the figure) an appropriate optical component and a collimator 4 at its distal extremity 5. An adhesive is used to join distal extremity 5 to the coUimator's proximal extremity 6. The adhesive may be selected as an UV curable adhesive or as an index-matching optical adhesive. The alignment of the fibre 3 with respect to the collimator 4 will preferably be accurately determined to maximise performance of the assembly of the fibre and the collimator.

The collimator is specifically selected as a plain glass rod, in notable contrast to the GRIN (graduated index lens) collimator widely available in the market place and exemplified as conventional teaching by the examples of EP 1 168 012. The connector's collimator terminates at its distal extremity in an aspheric surface which - again in contrast to conventional preference - is a paraboloidal surface

The general equation defining an aspheric surface may be as follows: z = ^■ R ^■ + a ^■ v⁴ + b - v⁶ + .. l + . l - (l + κ) — • R

Where K is co-efficient of a second order aspheric. Following this formula when K is comprised between minus 1 and 0 the aspheric is an ellipse, when K = 1 it is a parabola and when K is comprised between 0 and 1 it is a hyperbola.

The coefficients a and b will be determined by the person skilled in the art and, whilst the formula enables the skilled person to select an aspheric surface appropriate for given collimator dimensions, fibre types and connector applications it has been found that a parabola gives advantages in accommodating misalignments in use.

Aspheric portion 7 of collimator 4 would normally be an integral part of collimator 4 in an attempt to optimise the transmission of optical radiation through the connector, but in accordance with the invention it is in fact a composite multi-pack component as will be described with reference to Figure 2.

Connector 2 may be constructed in an identical manner to comiector 1. Each connector will operate with appropriate connection means. These may be selected to permit the alignment of connector 1 and connector 2 to optimise, again, the transmission of optical radiation across the connection from connector 1 to connector 2. These may be selected from a wide range of known alternatives including bayonet, snap fit, threaded and other appropriate detachable attachment means.

Figure 2 shows a preferred form of connection means embodying all aspects of the inventive concept. There is presented a connector 8 and a connector 9 spaced along the Z axis. Connector 8 incorporates a collimator 10 joining an optical fibre 11. The optical fibre and collimator are enshrouded in a first layer 12. Layer 12 may be selected from any appropriate material available to withstand any environmental condition. A sleeve 13 further enshrouds connector 8 and terminates at its distal extremity with a threaded region 14 which is shown engaged with joining sleeve 15. Joining sleeve 15 also engages a corresponding threaded region of connector 9.

Collimator 10 comprises two portions 16 and 17. Portion 16 is a plain glass rod and portion 17 is a moulded element terminating in the aspheric parabolic surface necessary.

Portions 16 and 17 are selected to have similar indexes of refraction in order to minimise any loss at the junction between the portions but Portion 17 is a moulded plastics element.

Connector 9 in this example could be identical to connector 8 so as to allow hermaphroditic connector applications. However the invention is not limited to the above embodiment, its extent being defined in the claims that follow. For example, it is not essential that the lenses be identical. Their proportions may vary as long as the overall optical transmission performance of the connector is still acceptable, as illustrated in figure 3 schematically where the rods 16, 18 differ in their respective lengths and diameters and the parabolic lenses 17, 19 differ in their respective curvatures.

Claims

1. A connector comprising an optical fibre, a collimating means operating with said fibre to transmit optical radiation and connection means for detachably attaching the connector to any other appropriate connector in sufficient alignment to allow radiation to be transmitted across the connection, characterised in that the collimating means terminates with an aspheric surface (known per se) and in that there is also present at least one of the features selected from the group comprising, firstly, collimating means terminating with a parabolic surface; secondly, collimating means whose optical radiation transmitting region is constructed in multiple-part format; and thirdly, that the connector is designed as one operative half of a two-connector and preferably releasably re-usable connection means in which the optical radiation transmitting components of each connector half are non-identical.

2. A connector according to Claim 1, wherein the collimating means comprises two portions of sufficiently similar index of refraction to prevent anything other than acceptably significant loss when optical radiation passes from the first portion to the second portion.

3. A connector according to Claim 2, wherein the first portion is an optical radiation transmitting rod, and the second portion is an aspheric lens.

4. A connector according to Claim 2, wherein the second portion is a moulded element.

5. A connector according to Claim 3, wherein the moulded element is a moulded plastics element.

6. A connector according to Claim 1, wherein the collimating means is joined to the distal extremity of the fibre.

7. A connector according to Claim 3, wherein the rod is a plain - that is a non- gradient-index - glass rod.

8. A connector substantially as described herein with reference to and/or as illustrated in any appropriate combination of the accompanying text and/or drawings.

9. An optical radiation transmitting connection arrangement incorporating two connectors which are sufficiently optically matched to transmit within acceptably significant loss levels a radiation from one connector to the otlier, at least one of the comiectors being in accordance with Claim 1, characterised in that the connectors have non-identical collimating lens arrangements.