GB1587158A

GB1587158A - Optical-fibre connector

Info

Publication number: GB1587158A
Application number: GB2543477A
Authority: GB
Original assignee: Philips Gloeilampenfabrieken NV
Current assignee: Koninklijke Philips NV
Priority date: 1976-06-21
Filing date: 1977-06-17
Publication date: 1981-04-01
Also published as: FR2356167A1; AU503749B2; JPS5778015U; DE2727177A1; CA1083391A; AU2619577A; JPS53143A; FR2356167B1; SE7707041L

Description

(54) OPTICAL-FIBRE CONNECTOR (71) We, N.V. PHILIPS' GLOEILAM PENFABRIEKEN, a limited liability Company, organised and established under the laws of the Kingdom of the Netherlands, of Emmasingel 29, Eindhoven, the Netherlands do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to an optical connection device for detachably coupling an optical fibre bundle to a light-emitter or light-receiver, and including an optical connection between optical fibres and said emitter or receiver.

Hereinafter, an optical fibre bundle is to be understood to mean an optical light conductor comprising a plurality of optical fibres which are arranged one adjacent the other in the longitudinal direction, but this bundle may alternatively comprise only one fibre.

Nowadays, communication systems are being developed in which optical fibres are used as conductors for light waves modulated by the information to be transmitted.

These fibres are thus utilised for transmitting information over long distances in a similar manner to electrical conductors. In such systems use can be made of visible or non-visible light.

The communication networks used comprise bundle-to-bundle connections or connections between fibre bundles and devices for injecting light energy into the network or for the detection of the information. For the designed and developed systems to be operational, it is necessary that their maintenance can be readily performed and that faulty elements of the network can be readily replaced. This is the case, for example, for the light emitters or the light receivers. The user should, therefore, have available connection devices for connecting the fibre bundle to the light-emitter or light-receiver which consist of two parts, one part accommodating the light-emitter or light-receiver, whilst the other part is attached to the end of the fibre bundle, the two parts being connected one into the other by means of a locking system which locates and maintains one of the parts in position relative to the other.

In the present state of the art, devices of this kind have already been proposed, whose construction is similar to that of connectors of electrical cables with a coaxial conductor. A device of this kind is described in U.S. Patent No. 3.948.582.

This connector is constructed to provide direct connection of an opto-electronic emitter or receiver to a fibre bundle. The construction of this connector includes facilities to ensure precise positioning of said element, in the axial as well as in the transverse direction, relative to the entrance face of the fibre bundle and its axis in order to achieve optimum coupling from an energy point of view.

In spite of the steps take, however, the efficiency of the coupling obtained is comparatively low, notably in the case where the light-emitter or light-receiver has an emission or reception surface which is substantially smaller than the cross-sectional area of the end of the fibre bundle. It is known that the half acceptance angle a is one of the characteristic properties of an optical fibre.

Any central ray in the fibre which is inclined at an angle to the optical axis of the fibre, which exceeds a, will traverse the lateral boundary surface of the fibre core instead of being reflected thereby, so that it will not contribute to the transport of light energy along the fibre. Consequently, if the surface area of the light-emitter is much smaller than the entrance face of the fibre bundle in the case of a transmitter, a major part of the luminous energy emitted will not be utilised, notably the energy which is emitted at angles of incidence in excess of the angle of acceptance a, and this part will increase further as the angle a is reduced, whilst, moreover, the fibres at the periphery of the bundles are liable not to transmit any energy at all. These conditions are also applicable to reception, notably if the light-receiver has a light-sensitive region whose dimensions are smaller than the cross-sectional area of the end of the bundle; a quantity of light energy transported in the bundle is then not received by the receiver, even when said receiver is placed in contact with the end of face of the bundle.

It is an object of the invention to provide an improved optical connection device in which these drawbacks can be mitigated and a sufficient location accuracy can be provided on assembly.

According to the invention there is provided an optical connection device for connecting an optical fibre bundle to a lightemitter or light-receiver, said device comprising a first and a second cooperating connector assembly which can be coupled and locked one into the other, and which respectively comprise a first and a second cylindrical housing member on the outer face of each of which is arranged corresponding coupling and locking means which can be of a kind known for connectors for electrical coaxial cables, said housing members being arranged so that when coupled and locked together they are axially located one relative to the other, wherein said first connector assembly further comprises a first suppprt and guidance member housed within said first housing member, and arranged to hold and support a corresponding end portion of an optical fibre bundle so as mechanically to locate the end face of said optical fibre bundle in an image plane and on a common optical axis defined relative to the device when the two connector assemblies are coupled together, said first support and guidance member being located and secured relative to said first housing member, and said second connector assembly further comprises an optical subassembly comprising a light-emitter or light-receiver and an optical image-forming device, the optical axis of which is aligned with the central axis of a corresponding lightemissive or light-sensitive region of said emitter or receiver to form a said common optical axis and a second support and guidance member housed within said second housing member and arranged to hold and support said subassembly, said second support and guidance member being located and secured relative to said second housing member so as to define with reference to the device, the position of said common optical axis and of said image plane, the latter by the location of an image of said emitter or receiver formed by said optical device, said first and second support and guidance members having corresponding guidance portions which cooperate mutually with one another on coupling and locking together said first and second housing members, so that they accurately position in a transverse direction, the end face of the fibre bundle and said optical subassembly in the coupled condition, the arrangement being such that when said first and second connector assemblies are coupled and locked together, the end face of the fibre bundle and the corresponding light-emissive or lightsensitive region of said emitter or receiver are optically coupled by said optical imageforming device.

Thus, an optical image-forming element is introduced between the end of the fibre bundle and the emitter or receiver. The optical image-forming element thus introduced has dimensions and properties such that it optically connects the respective light-emitting or light-sensitive region of the emitter or receiver, to the entrance section of the fibre bundle, the diameter of the image of said region, produced by the optical system, being substantially equal to the diameter of the fibre bundle, the image aperture angle being at least equal to half the acceptance angle of the fibre bundle.

Such an optical image-forming device is described in UK Patent Application no.

50733/76, Serial No. 1571909).

As a result, the invention enables the injection into an optical fibre bundle, having a small acceptance angle, of light energy emitted via a large angular field by a light-emitter having a light-emitting region which is much smaller than the section of said fibre bundle.

The introduction of an optical imageforming element of this kind implies a high precision of location in the axial and transverse directions for the positions occupied by the one relative to the other or by the end face of the fibre bundle and the light-emitter or light-receiver. Any lack of precision as regards these positions will have an adverse effect on the optical connection between them, the more so because of the necessary degree of magnification provided by the optical image-forming device, and hence on the quality of the light energy coupling between the fibre bundle and the emitter or receiver. A satisfactory degree of precision in these respects can be provided by a device manufactured in accordance with the invention.

The optical image-forming system included in an embodiment of the connection device described hereinafter is as described and claimed in UK Patent Application No.

50733/76 (Serial No. 1571909).

An embodiment of a connector arrangement in accordance with the invention will now be described by way of example, with reference to the accompanying drawing, the sole figure of which is a longitudinal axial sectional view of a connection device embodying the invention.

The Figure shows an optical connection device which is rotationally symmetrical about the axis AA'. A housing forming part of a first connector assembly of the device, is denoted by the reference numeral 11, while the housing forming part of a second connector assembly is denoted by the reference numeral 12. These two housings are locked relative to each other. The locking means are of a known type used for connectors for cables comprising metallic coaxial cores. The locking means are formed, for example, by a ring 13 which is movable about the housing member 11 and which is retained by the housing member, and cams 14 and 15 which are provided on the housing member of the second connector assembly 12. The ring 13 is provided with apertures 16 and 17 which are engaged by the cams during the assembly and locking process, these operations being realised by rotation of the ring 13.

It will be apparent that use can alternatively be made of other means, known for connectors for electrical coaxial cables, for the housing members 11 and 12, such as that comprising a threaded ring which is retained by 11 and which is screwed onto a thread formed on the outer surface of the housing member 12.

As is in part shown in the Figure, the housing member 12 can itself be secured to a wall of further related apparatus, by means of a threaded ring (not shown) which is screwed onto the thread 45, thus enabling said wall to be pulled against the part 46 of the housing member 12 which is provided with a recess 47 in which an elastic seal (not shown) can be accommodated, for connection in a suitably sealed manner.

The fibre bundle 18 is arranged along the axis AA' inside the first connector assembly of the connection device. The fibre bundle 18 is located in a support and guidance member 19 for rotation about the axis AA'.

The member 19 is screwed onto the housing member 11 by means of a thread 20. The member 19 is provided with a shoulder 21 which abuts against an abutment formed in the member 11 when it is screwed home.

The positions of the shoulder 21 on the member 19 and of the corresponding abutment on the member 11 are such that the member 19 together with the optical fibre bundle 18, are located inside the housing member 11 so that the end face 26 of the fibre bundle 18, is situated in the plane 20' at a distanceffrom the outer edge 21' of the housing member 11. In the case of mass production of the device, this distance f must be accurately maintained in order to enable connector assemblies to be interchanged.

The other connector assembly of the connection device comprises a number of parts i. e. an optical connection device which associates an optical image forming system with a light receiver or a light emitter mechanical guiding means which serve to ensure the mutual, transverse centering of said optical connection device and the member 19 which locates the end of the fibre bundle 18 and ensures the longitudinal positioning of said optical device, and mechanical means for holding the optical assembly inside the housing member 12.

As is shown in the Figure, the first connector assembly of the connection device may include, as in the case of known connectors for electrical coaxial cables, a ring 42 of a flexible material which bears against a shoulder 43 of the metal housing member 11 and against which the end 44 of the housing member 12 abuts, so that after locking the housing members 11 and 12 of the connection device together the interior is sealed off from the surroundings.

The optical assembly comprises, accommodated inside a cylindrical holder 22 an optical image-forming device which in this case consists of lenses 23 and 24 which are held inside said holder 22, for example, by cementing. This optical device optically couples the emitter or receiver 25 to the end face 26 of the fibre. The optical axis of the optical device is caused to coincide with the direction of the receiver axis or with the direction of the emitter axis by arranging the holder 22 in a cylindrical sleeve 27 which has an internal diameter equal to the outer diameter of the holder 22. The holder 22 is rendered integral with this sleeve 27 by cementing for example, in the region 22'.

The sleeve 27 is provided at one end with a collar 28 which is perpendicular to the side wall.

Moreover, the cylindrical support 29 for the receiver or emitter 25 is rendered integral with a cylindrical part 30, for example, by cementing, or by soldering along the outer edge 31 of the support 29.

The upper edge 32 of the part 30 is fixed to the collar 28 of the sleeve 27 by soldering or cementing, so that the assembly formed by the receiver or emitter and the optical image-forming device forms an integral unit. The soldering or cementing of the collar 28 to the edge 32 is effected when the optical axis of the lenses 23, 24 have been made to coincide with the axis of the emitter or the receiver 25. Adjustment to bring this about effected by displacement of 25 in its plane so that the collar 28 and the edge 32 slide relative to one another.

The centering principle is, for example, as follows, assuming that the reference 25 denotes a light-emitter. The emitter is rendered operative, and radiation is detected beyond the optical device by means of a receiver which has a suitable aperture placed on the optical axis of the optical device. When the detected radiation is optimum, the soldering of collar 28 and edge 32 is performed. In the Figure, the reference numeral 33 denotes respective output or input conductors of the receiver or emitter 25, whilst the reference numeral 34 denotes internal connections between 25 and the conductors 33.

Preferably, as is shown in the Figure, the lens 23 is tapered to form a truncated cone in order to facilitate its making contact with the emitter or receiver 25 without being obstructed by the connections 34.

The optical assembly is introduced into a support and guidance member 35 which is screwed into the housing member 12 by means of the thread 36. The cylindrical end 36' of this support and guidance member 35 has an inner diameter which is equal to the outer diameter of the member 19 in the vicinity of the end of the fibre 26, said part 19 projecting into the end 36' of the member 35. The member 35 has a shoulder 37 and an abutment 38. The shoulder 37 abuts against a tapered abutment in the housing member 12. The abutment 38 of the member 35 arrests the end of the sleeve 27. The reference numeral 39 denotes a supporting member for holding the optical assembly inside the support and guidance member 35.

The member 39 is screwed, by means of the thread 40, onto the housing member 12 and exerts pressure on the optical assembly via its end portion 41.

The position occupied by the optical assembly in the housing member 12 is such that once the coupling of the two connector assemblies of the connection device has been effected, the end face 26 of the fibre bundle 18, is optically coupled to the receiver or emitter 25 by the optical device. This is achieved by proportioning the distance b between the shoulder 37 and the abutment 38 of the member 35 while taking onto account the image distance t from the exit face of said optical device, the distance c between the exit face of said optical device and the end 38' of the member 35, and the said distance f between the end 21' of the housing member 11 and the end face 26 of the fibre 18. In this manner, interchangeability of one of the connector assemblies of the connection device with another assembly of the same type, can be ensured despite the use of mass production techniques.

For optimum optical adaptation of the emitter or receiver to the optical device, an immersion liquid may be introduced, said liquid being transparent with respect to the radiation passed between the optical device and said emitter or receiver. This liquid may be a lubricating adhesive having a suitable refractive index which facilitates the displacement of the emitter or receiver with respect to the optical device when the optical axes of the receiver or the emitter and the optical device are adjusted to be coincident.

Preferably, use can be made of an optical device which is the subject of UK Patent Application No. 50733/76, (Serial No.

1571909) the principal features of which in respect of the coupling between an emitter and an optical fibre bundle, will be reiterated hereinafter, namely:- A device comprising a first plano-convex lens which is arranged in the propagation direction of the light, followed by a second plano-convex lens, both lenses being thick lenses and their axis being coincident with that of the fibre bundle at its end face, said lenses being arranged so that the convex side of one lens faces in the same direction as the plane side of the other lens i.e. so that the convex surfaces of the two lenses are adjacent, the emitter of luminous energy being disposed substantially perpendicularly to said axis in the vincinity of the centre of the planar surface of said first lens, and the end face of the fibre bundle being situated in the vicinity of the centre of the planar surface of said second lens. An immersion liquid which is transparent for the conducted radiation can be introduced between the source and the lens and, if desired, between the lens and the fibre bundle. The radii of curvature of the doptric faces of the various lenses, their diameter, their thickness and the refractive indices of their constituent materials are arranged to be such that the system formed by the two lenses optically couples the emitter to the end face of the fibre bundle, the diameter of the image of the emitter being substantially the same as the diameter of the fibre bundle, the aperture angle of the image being at least equal to half the acceptance angle of the fibre bundle, the ratio between the radii of the convex dioptric faces being such that the spherical aberration is minimum for the selected magnification and the refractive indices of the chosen lens materals.

The optical system described in the UK Patent Application Number 50733/76, (Serial No. 1571909) is modified so that a thin glass layer of said second plano-convex lens is replaced at the plane dioptic surface by a layer of air in order to obtain a convenient image spacing, for example of the order of from 1 to 2 mm, from the exit face of the optical device, thus facilitating the coupling and locking of the two connector assemblies of the connection device without the risk of damage to the planar surface of said second lens (the lens 24 in the Figure) and to the end face 26 of the fibre bundle 18.

It will be apparent that the emitter can be replaced by a receiver in this embodiment in accordance with the invention.

WHAT WE CLAIM IS: 1. An optical connection device for connecting an optical fibre bundle to a lightemitter or light-recevier, said device comprising a first and a second cooperating connector assembly which can be coupled and locked one into the other, and which respectively comprise a first and a second cylindrical housing member on the outer face of each of which is arranged corresponding coupling and locking means which can be of a kind known for connectors for electrical coaxial cables, said housing members being arranged so that when coupled and locked together they are axially located one relative to the other, wherein said first connector assembly further comprises a first support and guidance member housed within said first housing member, and arranged to hold and support a corresponding end portion of an optical fibre bundle so as mechanically to locate the end face of said optical fibre bundle in an image plane and on a common optical axis defined relative to the device when the two connector assemblies are coupled together, said first support and guidance member being located and secured relative to said first housing member, and said second connector assembly further comprises an optical subassembly comprising a light-emitter or light-receiver and an optical image-forming device, the optical axis of which is aligned with the central axis of a corresponding lightemissive or light-sensitive region of said emitter or receiver to form a said common optical axis, and a second support and guidance member housed within said second housing member and arranged to hold and support said subassembly, said second support and guidance member being located and secured relative to said second housing member so as to define with reference to the device, the position of said common optical axis and of said image plane, the latter by the location of an image of said emitter or receiver formed by said optical device, said first and second support and guidance members having corresponding guidance portions which cooperate mutually with one another on coupling and locking together said first and second housing members, so that they accurately position in a transverse direction, the end face of the fibre bundle and said optical subassembly in the coupled condition, the arrangement being such that when said first and second connector assemblies are coupled and locked together, the end face of the fibre bundle and the corresponding light-emissive or light sensitive region of said emitter or receiver are optically coupled by said optical imageforming device.

2. A device as claimed in Claim 1, wherein said optical image-forming device is of the kind comprising a first plano-convex lens which is arranged in the propagation direction of the light, followed by a second plano-convex lens, both lenses being thick lenses and their axes being coincident with that of the fibre bundle at its end face, said lenses being arranged so that the convex surface of one lens faces the convex surface of the other lens, the corresponding lightemitting or light-sensitive region of the light-emitter or light-receiver extending transversely with respect to said axis in the vicinity of the centre of the planar surface of said first lens, the end face of the fibre bundle being located in the vicinity of the centre of the planar surface of said second lens, an immersion liquid which is transparent for the conducted radiation being introduced between said emitter or receiver and the first lens, the radii of curvature of the dioptric surfaces of the lenses, their diameter, their thickness and the refractive indices of their constituent materials being such that the optical image-forming device formed by the two lenses optically couples said emitter or receiver to the end face of the fibre bundle and causes the diameter of an image of the corresponding lightemission or light-sensitive region of said emitter or receiver formed at the end face of the fibre bundle to be substantially equal to the diameter of the fibre bundle, the aperture angle of said image being at least equal to half the acceptance angle of the fibre bundle, the ratio between the radii of the convex dioptric surfaces being such that the spherical aberration is a minimum for the degree of magnification provided and for the refractive indices of the chosen lens materials.

3. A device as claimed in Claim 1 or 2, wherein said first support and guidance member is provided with a shoulder which abuts against a tapered abutment formed in said first housing member, the positions of the shoulder and.the abutment being such that the end face of the fibre bundle is located within said first housing member at a predetermined distance from a reference end face of said first housing member.

4. A device as claimed in any one of Claims 1 to 3, wherein said optical subassembly is provided with a cylindrical sleeve which is introduced into said second support and guidance member, said second support and guidance member being provided with a shoulder, abutting against a tapered abutment formed in said second

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. of the connection device without the risk of damage to the planar surface of said second lens (the lens 24 in the Figure) and to the end face 26 of the fibre bundle 18. It will be apparent that the emitter can be replaced by a receiver in this embodiment in accordance with the invention. WHAT WE CLAIM IS:

1. An optical connection device for connecting an optical fibre bundle to a lightemitter or light-recevier, said device comprising a first and a second cooperating connector assembly which can be coupled and locked one into the other, and which respectively comprise a first and a second cylindrical housing member on the outer face of each of which is arranged corresponding coupling and locking means which can be of a kind known for connectors for electrical coaxial cables, said housing members being arranged so that when coupled and locked together they are axially located one relative to the other, wherein said first connector assembly further comprises a first support and guidance member housed within said first housing member, and arranged to hold and support a corresponding end portion of an optical fibre bundle so as mechanically to locate the end face of said optical fibre bundle in an image plane and on a common optical axis defined relative to the device when the two connector assemblies are coupled together, said first support and guidance member being located and secured relative to said first housing member, and said second connector assembly further comprises an optical subassembly comprising a light-emitter or light-receiver and an optical image-forming device, the optical axis of which is aligned with the central axis of a corresponding lightemissive or light-sensitive region of said emitter or receiver to form a said common optical axis, and a second support and guidance member housed within said second housing member and arranged to hold and support said subassembly, said second support and guidance member being located and secured relative to said second housing member so as to define with reference to the device, the position of said common optical axis and of said image plane, the latter by the location of an image of said emitter or receiver formed by said optical device, said first and second support and guidance members having corresponding guidance portions which cooperate mutually with one another on coupling and locking together said first and second housing members, so that they accurately position in a transverse direction, the end face of the fibre bundle and said optical subassembly in the coupled condition, the arrangement being such that when said first and second connector assemblies are coupled and locked together, the end face of the fibre bundle and the corresponding light-emissive or light sensitive region of said emitter or receiver are optically coupled by said optical imageforming device.

housing member and an abutment which contacts one end of the sleeve, the distance along the axis of the optical connection device separating the shoulder from the abutment of said second support and guidance member being such that said optical image-forming device optically couples said emitter or receiver to the end face of the fibre bundle in the coupled condition of said first and second connector assemblies of the connection device.

5. An optical connection device for connecting an optical fibre bundle to a light emitter or light receiver, substantially as herein described with reference to the accompanying drawing.