A device for optical connection of an optical element, for example an optical fibre, with a lens

Abstract: A device for optically connecting an optical element, for example an end portion of an optical fibre (2), with a spherical lens (4), comprises a retainer (6) and a connector element (14). The retainer (6) fixes the optical element in a predeterment position in relation to an outer reference surface (8) of the retainer. The connector element (14) has at least one surface (18) for determining the position of the spherical lens (4) and at least one surface (16) for determining the position of the retainer (6) in relation to the spherical lens (4) and thereby for defining the relative position between the optical element (2) and the spherical lens (4). The surface (18) for determining the position of the spherical lens (4) is constituted by a conical surface (18) tapering in the direction of the optical element (2).

Description: The present invention relates to a device for optical connection of an optical element, for example an end portion of an optical fibre, with a spherical lens. In fibre optical systems there are at different points required optical connections between the different optical elements included in the system. Thus, there are required optical connections between different lengths of optical fibres, between an optical fibre and a light source, for example a diode, between an optical fibre and a light detector etc. Each connection must be established using very great accuracy if the losses shall be kept at a minimum. Of course, the problem of providing a correct connection is caused by the fact that optical fibres have a very small cross sectional area and that also small deviations from a correct position between two fibre end portions to be connected with each other cause substantial losses. It is important especially to avoid angular deviations between the fibres, i.e. it is important that the fibres connected with each other are positioned on the same optical axis. Different devices for providing a correct connection of optical fibres with each other and with other optical elements have been suggested. Such devices comprise lens systems in which the light beam is magnified so that the light transmission in the connection takes place at a sectional area which is magnified several times providing for a corresponding reduction of the sensitivity to deviations from the correct position. Thereby, it is a drawback that the connection of two fibre end portions to each other requires instead of one single connection, i.e. the connection between the fibre end portions, an optical connection of the fibre end portions to one lens each and an optical connection of the lenses to each other, i.e. three connections. It is important that the optical fibres and the lenses are positioned on the same optical axis as well as that the end surfaces of the fibres are positioned in the focus of the lens in question. Thus, the connections between the optical fibres and the lenses are the most sensitive parts of the connection system while the optical connection of the lenses to each other can easily be provided without errors. Different devices for connecting an optical element with a lens are previously known. A drawback of previously known connection devices is that they are either complicated in respect of their construction or use or offer insufficient accuracy with regard to the fact that the optical element and the lens shall be positioned on the same optical axis and that the optical element shall be positioned in the focus of the lens. GB-A-2 190 764, EP-A-402 612, US-A-4 707 067, US-A-4 799 759, US-A-4 989 944 and US-A-4 759 601 show the use of ball lenses in optical fibre connections and terminations. The object of the present invention is to provide a device for optical connection of an optical element, for example an end portion of an optical fibre, with a spherical lens in which the connection between the optical element and the spherical lens is provided while positively determining the correct relative position without the requirement for adjustment operations at the time of connection in the field. Aspects of the invention are set forth in the accompanying independent claims. In the device according to the invention there is positively and in a simple way provided a correct relative position between the optical element and the spherical lens without requirement for any adjustment operations at the time of connection in the field. In a preferred embodiment of the invention the reference surface of the connector element for determining the position of the retainer in relation to the spherical lens is constituted by a conical surface which is adapted to engage the reference surface of the retainer, said conical surface being positioned at a distance from and on the same axis as the conical surface for determining the position of the spherical lens and tapering in the direction thereof. The retainer is constituted by a sleeve having a flat end surface coinciding with the end surface of the optical fibre. The device can be used in different combinations of optical elements and a spherical lens, for example for transmitting a light beam from a diode to an optical fibre through two spherical lenses, a device for connecting the diode to the spherical lens and one device for connecting the optical fibre with another spherical lens are used. The correct relative position between the two connector elements for transmitting the light beam between the spherical lenses is in a manner known per se provided by means of guiding pins or other guiding surfaces on the connector elements. It is realized that the relative position between the spherical lenses does not require any adjustment of such a great accuracy as the relative position between the lens and the optical element connected therewith. The invention is described in the following with reference to the accompanying drawings (only Figs. 9 & 10 relate to the invention as claimed). Figs. 1, 2, 3, 4 and 5 are longitudinal sectional views of different embodiment of devices for optically connecting an optical element with a spherical lens. Figs. 6, 7 and 8 are longitudinal sectional views of two devices connected with each other for connecting two optical elements with each other by means of two spherical lenses Figs. 9, 10 and 11 are longitudinal sections of two different embodiments of devices for fixing the spherical lens in connector devices according to the invention. Fig. 12 is a longitudinal sectional view of two devices connected with each other corresponding to figs. 6, 7 and 8. In one system for connecting an optical fibre, with another optical element, for example another optical fibre, the optical elements are connected with one lens each so that the transmission of the light between the optical elements takes place through the lenses. The embodiment of a device according to the invention schematically shown in section in fig. 1 is used for connecting an optical fibre 2 with a spherical lens 4. The end portion of the optical fibre 2 is enclosed in a fibre retainer 6 designed as a sleeve. The fibre retainer 6 is cylindrical along the main portion of its outer surface and has at its right end in the figure a conical reference surface 8 connecting with a flat end surface 10 is formed by an insert 12 of ceramic material moulded into the fibre retainer. The optical fibre 2 is fixed in the fibre retainer 6 in a manner known per se, for example according to the principle shown in the Swedish patent specification No 7901398-3 and/or by means of an adhesive, the end surface of the optical fibre 2 being positioned in the same plane as the flat end surface 10 of the insert 12. A correct position of the end surface of the optical fibre 2 can be provided by fixing the fibre with the end portion projecting somewhat outside the plan end surface 10, whereupon the fibre is ground to the plane of the end surface 10. The flat end surface 10 of the fibre retainer 6 has an exactly predetermined position in relation to the conical reference surface 8 of the fibre retainer, and when the end surface of the fibrer 2 is positioned in the plane of the end surface 10 the end surface of the fibre 2 will consequently be related to the conical reference surface 8 in a predetermined way. The device for optical connection of the optical fibre 2 with the spherical lens 4 comprises in addition to the fibre retainer 6 a connector element 14. The connector element 14 is provided with surfaces for determining the relative position between the fibre retainer 6 and thereby the optical fibre 2 and the spherical lens 4. The surfaces of the connector element 14 for determining the relative position between the fibre retainer 6 and therewith the optical fibre 2 and the spherical lens 4 are constituted by two conical surfaces 16 and 18 positioned at an axial distance from each other on the same axis and tapering in the direction towards each other. Thereby the conical surface 16 is adapted to engage the conical reference surface 8 of the fibre retainer 6 while the conical surface 18 is adapted to engage the spherical lens 4. Between the conical surfaces 16 and 18 there is a cylindrical surface portion 20, thus connecting with the small ends of the conical surfaces 16 and 18. The fibre retainer 6 and the spherical lens 4 are maintained in firm engagement with the conical surfaces 16 and 18, respectively, by means of arrangements not shown in fig. 1. In respect of the fibre retainer 6 these arrangements can be constituted by a conventional sleeve nut engaging a shoulder on the fibre retainer 6 not shown in the drawing while said arrangement in respect of the spherical lens 4 can be constituted by devices of the kind shown in figs. 9, 10 and 11. The conical surfaces 16 and 18 are designed and positioned in relation to each other so that the optical fibre 2 and the spherical lens 4 are positioned on the same optical axis and at such an axial distance from each other that the- end surface of the optical fibre 2 is in the focus of the spherical lens 4 when the conical reference surface 8 and the spherical lens 4 engage its conical surfaces. In order to make sure that the fibre retainer 6 is oriented so that the portion of the optical fibre received in the fibre retainer is over its total length positioned on the optical axis common with the optical axis of the spherical lens, the connector element 14 is provided with support surfaces 22 adapted to engage the fibre retainer 6 at the end of the fibre retainer 6 opposite from the conical reference surface 8. In a plane outside the spherical lens 4 the connector element 14 has a contact surface 24. The contact surface 24 is adapted to engage a corresponding surface of another connector element with which the connector element 14 shall be connected for providing an optical connection of the optical fibre 2 with another optical element, for example another optical fibre, a diode or a light sensor device, included in the other connector element. It is thereby important that the contact surface 24 is exactly perpendicular to the axis of the conical surfaces 16 and 18, and this is suitably provided by manufacturing the conical surfaces 16 and 18 and the contact surface 24 in one and the same machine and in a continuous operation. The embodiment of the device shown in fig. 2 is modified in respect of the design of the retainer 26 enclosing the end portion of the optical fibre 2a and the design of the surfaces of the connector element 30 cooperating with the retainer 26. Thus, the fibre retainer sleeve 26 according to fig. 2 has an cylindrical, outer surface 32 and a flat end surface 34 connected therewith. At its outer surface the retainer 26 has an annular flange 36, having an annular side 40 which forms in relation to the cylindrical reference surface 32 a perpendicular reference surface 40 which takes an exactly predetermined position in relation to the flat end portion 34 of the fibre retainer 26 and thereby in relation to the end surface of the fibre 2a. Thus; the end surface of the fibre 2a takes a predetermined position in relation to the cylindrical reference surface 32 as well as to the annular reference surface 40 extending transversely thereto. The connector element 30 is provided with surfaces for defining the relative position between the fibre retainer 26 and thereby the optical fibre 2a and the spherical lens 4a. The surfaces of the connector element 30 for defining the relative position between the fibre retainer 26 and thereby the optical fibre 2a on one hand and the spherical lens 4a on the other hand are constituted by a conical surface 20a, a cylindrical surface 42 forming an opening for receiving the retainer 26 and an end surface 44 extending perpendicular to the cylindrical surface 42 and surrounding the opening for receiving the retainer 26 formed by the cylindrical surface 42. The conical surface 20a and the cylindrical surface 42 are positioned on the same axis. The conical surface 20a is adapted to engage a spherical lens 4a while the cylindrical surface 42 is adapted to engage the cylindrical surface 32 of the retainer 26 and the surface 44 of the connector element 30 is adapted to engage the annular surface 40 of the flange 36 fixed to the retainer 26. The engagement surfaces of the retainer 26 and the connector element 30 are positioned and designed so in relation to each other that the optical fibre 2a and the spherical lens 4a when the spherical lens 4a engages the conical surface 20a and the surfaces 32 and 40 of the retainer 30 engage the surfaces 42 and 44, respectively, of the connector element 30 are positioned on the same optical axis and at such a distance from each other that the end surface of the optical fibre 2a is positioned in the focus of spherical lens 4a. Also the device shown in section in fig. 3 is provided for optical connection of an optical fibre 2b with a spherical lens 4b. The device according to fig. 3 comprises like the device according to fig. 1 a connector element 14b having conical surfaces 16b and 18b which are positioned on the same axis at an axial distance from each other and tapering in direction towards each other. Between the conical surfaces 16b and 18b there is a cylindrical surface portion 20b. The device according to fig. 3 differs from the device according to fig. 1 in respect of the construction of the retainer for the optical fibre. In the embodiment according to fig. 3 the retainer for the optical fibre is constituted by a clamping sleeve 46 which like the retainer 6 in the embodiment according to fig. 1 has a conical reference surface 8b. The clamping sleeve 46 has an axially extending opening in which the end portion of the optical fibre 2b is positioned. The clamping sleeve 46 is designed so that the cross sectional area of the opening can be changed by exerting an outer pressure on the clamping sleeve 46. This provides that the optical fibre 2b after having been introduced into the opening in the clamping sleeve 46 can be fixed therein by exerting on the clamping sleeve 46 an outer force. In the embodiment shown in fig. 3 this is provided by forcing the clamping sleeve 46 into the narrower portion of the conical surface 16b by means of a barrel nut 48.The radial compression of the clamping sleeve 46 which in turn provides that the optical fibre 2b is fixed in the opening in the clamping sleeve can be provided by manufacturing the clamping sleeve from two or several more or less firmly jointed sectors. In this embodiment the correct position of the end surface of the optical fibre in relation to the clamping sleeve 46 and thereby in relation to the spherical lens 4b must be determined prior to and/or subsequent to the positioning of the fibre in the clamping sleeve by more or less manual measures. The embodiment according to fig. 3 can be considered to represent a device in which the requirements for accuracy are less than in the embodiment according to fig. 1 but in which the less accuracy is compensated by a simple construction and easier muonting of the fibre in the fibre retainer. The embodiment shown in fig. 4 is adapted for connecting a diode 50 with a spherical lens 4c. Like the devices according to figs. 1 and 3 the device comprises a connector element 14c having two conical surfaces 16c and 18c positioned at an axial distance from each other on the same axis and tapering towards each other. In addition to the connector element 14c the device according to the embodiment of fig. 4 comprises a retainer for the diode 50 in the form of a clamping sleeve 52. The clamping sleeve 52 has a conical reference surface 8c adapted to engage the conical surface 16c in order to define the position of the diode in relation to the spherical lens 4c which engages the conical surface 18c. Also in this embodiment the conical surfaces 16c and 18c provide a correct relative position between the diode 50 and the spherical lens 4c so that the diode 50 and the lens 4c are positioned on the same optical axis and at a correct axial distance from each other. In a modified embodiment of the device according to fig. 4 the diode is provided with a fixed outer sleeve instead of the clamping sleeve 52. This fixed sleeve is not provided with its final shape until the sleeve has been connected with the diode, for example by providing a conical reference surface of the sleeve by means of turning. Thus, the position of the reference surface is determined so that the axial distance of the diode from the spherical lens is correct. Also the embodiment according to fig. 5 is modified in relation to the embodiment according to fig. 4 in respect of the design of the surfaces of the diode retainer and the connector element engaging each other. The connector element 54 has a conical surface 20d, a cylindrical reference surface 56 and an annular reference surface 58 extending perpendicular to the cylindrical reference surface 56. The device also comprises a retainer for a diode 59 in the form of a sleeve 60. The sleeve 60 has a cylindrical, outer reference surface 62 which is adapted to engage the cylindrical surface 56 of the connector element 54 for defining the position of the diode 59 so that the optical axis thereof coincides with the axis of the cylindrical surface 56. As the axis of the cylindrical surface 56 coincides with the axis of the conical surface 20d the focus of the lens 4d will be positioned on the axis of the diode. For defining the axial distance of the diode 59 from the spherical lens 4d the sleeve 60 is provided with an outer, annular flange 64 having an annular surface 66 engaging the reference surface 58 of the connector element 54. Also in this embodiment the reference surfaces 56, 58, 62 and 66 provide for a correct relative position between the diode 59 and the spherical lens 4d so that the diode 59 and the lens 4d are positioned on the same optical axis and at a correct axial distance from each other. The sleeve 60 can be firmly connected with the diode 59 and can be adapted to obtain its final shape after the connection with the diode for example by forming the cylindrical reference surface 62 and the annular reference surface 66 on the flange 64 by means of turning after the connection of the sleeve with the diode. In fig. 6 there is schematically shown the connection of two optical fibres 2 with each other. Thus, the devices are two deivices of the kind shown in fig. 1 which are connected with each other with the contact surfaces 24 in engagement with each other and the devices centered in relation to each other by means of guiding pins 68. The light beam from one of the optical fibres is magnified by the spherical lens optically connected with the fibre and departs from the lens as a parallel beam having a section which is several times larger than the beam received from the optical fibre, the beam from the lens being received by the other spherical lens which reduces the beam to the optical fibre connected with the second lens. Because of the magnification of the beam in the transition between the optical fibres the losses in the transition are reduced. In fig. 7 there is shown the connection of two devices of the kind shown in fig. 1, where in the devices are centered in relation to each other by means of an outer socket 70 instead of by means of guiding pins. The socket 70 makes it possible to provide a correct position of the devices on line with each other without an engagement between the end surfaces 24 of the devices. Therefore, it is not necessary to manufacture the end surfaces 24 with any special precision. The axial distance between the devices can be determined in any conventional way not shown in the figure. In fig. 8 there is schematically shown the connection of a diode with an optical fibre by means of devices of the kind shown in fig. 4 and fig. 1, respectively. Also in this embodiment the devices engages each other at contact surfaces 24 and the devices are centered in relation to each other by means of guiding pins 68a. It is recognized that the connection principles shown in figs. 6 - 8 can be used also in respect of the devices shown in figs. 2 and 5 and different combinations of the devices shown in figs. 1 - 5. In figs. 9 and 10 there are shown suitable devices for retaining the spherical lens 4 in engagement with the conical surface 18. In the embodiment according to fig. 9 the spherical lens 4 is retained in engagement with the conical surface 18 by means of a plug 72 having an outer thread and being threaded into a hole 74 connecting with the conical surface 18. The plug 72 has at its end which is adapted to engage the spherical lens 4 a ring 76 consisting of elastic material and resiliently forcing the spherical lens 4 against the conical surface 18. In the embodiment according to fig. 10 the spherical lens 4 is retained in engagement with the conical surface 18 by means of a spring ring 78 which is mounted in a groove 80 in a hole 82 connecting with the conical surface 18. Between the spring ring 78 and the spherical lens there is provided a ring 84 of elastic material resiliently forcing the spherical lens 4 against conical surface 18. In fig. 11 there is shown an embodiment in which the relative position of the spherical lens 4e and the retainer 6e with the optical fibre 2e fixed therein is provided by a direct engagement between the spherical lens 4e and the end surfaces of the retainer and the fibre. In this case the spherical lens has a refrective index of such a magnitude that the focus is positioned in the surface of the lens. The invention can be modified within the scope of the following claims and can be adapted to different combinations of connection between optical fibres and other optical elements. In fig. 12 there is shown a connection between a device of the kind shown in fig. 4, comprising a diode 30 and a spherical lens optically connected therewith and a device according to fig. 2 comprising an optical fibre and a spherical lens. In a modified embodiment of the invention the front surfaces of the devices are bevelled so as to prevent reflections of the optical signals.

Claims: An optical fibre connector connecting a pair of optical fibres (2) for transmission of an optical signal across the connection, the connector comprising: a retainer (6;26) on an end of each fibre (2), the retainers (6;26) each having a retainer end surface (10;34) which is flush with an end surface of the respective fibre (2), and a first reference surface (8;32,40) in a predetermined position relative to the respective retainer end surface (10;34); a pair of ball lenses (4) optically coupled to each other and to the end surface of a respective fibre (2); a pair of connector elements (14;30), each connector element being integrally formed and comprising a second reference surface (16;42,41) on which the first reference surface (8;32,40) of a respective retainer (6;26) bears and a concave conical surface (18;20a) on which a respective ball lens (4) is positioned, and a screw plug (72) or a spring ring (78) fixedly engaged in said connector element (14, 30) and arranged to hold the respetive ball lens (4) against the respetive concave conical surface (18, 20A) by means of an interposed elastic O-ring. the second reference surface (16;42,44) and the conical surface (18;20a) of the retainer being machined to position the end surface of the respective optical fibre (2) at the focus of the respective ball lens (4) and to position the end of the fibre (2) and the ball lens (4) on the same optical axis, so as to provide a correct relative position between the optical fibre (2) and the ball lens (4) without requirement for any adjustment operations at the time of assembly. A connector as claimed in claim 1, characterised in that the conical surfaces (18;20a) of the connector elements (14;30) open out to respective end surfaces (24) which are machined perpendicular to the axis of the conical surface (18;20a), and the conical surfaces (18;20a) are formed so that the respective ball lenses (4) do not break a plane defined by the end surfaces (24). A connector as claimed in claim 2, characterised in that the connector elements (14;30) abut at the end surfaces (24) and further comprising a ceramic insert (12) provided in the retainer (6; 26) around the end of each fibre (2). A connector as claimed in claim 3, characterised in that guide pins (68) are let into the abutting end surfaces (24). A connector as claimed in any one of claims 1 to 4, characterised in that the first reference surface (8) is a convex conical surface and the second reference surface (16) is a concave conical surface. A connector as claimed in claim 5, characterised in that an end of the retainer (6) distal of the convex conical reference surface (8) is supported by the connector element ( 14), the retainer (6) intermediate the reference surface (8) and the end being unsupported. A connector as claimed in any one of claims 1 to 4, characterised in that the first reference surface (32,40) comprises a convex cylindrical surface (32) and an annular surface (40), and the second reference surface (42,44) comprises a concave cylindrical surface (42) and an end surface (44) of the connector element (30). A termination on an optical fibre, the termination comprising a retainer (6;26) on an end of the fibre (2), the retainer (6;26) having a retainer end surface (10;34) which is flush with an end surface of the fibre (2), and a first reference surface (8;32,40) in a predetermined position relative to the retainer end surface (10;34); a ball lens (4) optically coupled to the end surface of the fibre (2); a connector element (14;30), the connector element being integrally formed and comprising a second reference surface (16;42,41) on which the first reference surface (8;32,40) of the retainer (6;26) bears and a concave conical surface (18;20a) on which the ball lens (4) is provided, and a screw plug (72) or a spring ring (78) fixedly engaged in said connector element (14, 30) and arranged to hold the ball lens (4) against the concave conical surface (18, 20a) by means of an interposed O-ring. the second reference surface (16;42,44) and the conical surface (18;20a) of the retainer being machined to position the end surface of the respective optical fibre (2) at the focus of the respective ball lens (4) and to position the end of the fibre (2) and the ball lens (4) on the same optical axis, so as to provide a correct relative position between the optical fibre (2) and the ball lens (4) without requirement for any adjustment after assembly of the termination. A termination as claimed in claim 8, characterised in that the conical surface (18,20a) of the connector element (14;30) opens out to an end surface (24) which is machined perpendicular to the axis of the conical surface (18;20a), and the conical surface (18,20) is formed so that the ball lens (4) does not break a plane defined by the end surface (24). A termination as claimed in claim 8 or 9, characterised in that the first reference surface (8) is a convex conical surface and the second reference surface (16) is a concave conical surface, and further comprising a ceramic insert (12) provided in the retainer (6; 26) around the end of the fibre (2). A connector as claimed in claim 10, characterised in that an end of the retainer (6) distal of the convex conical reference surface (8) is supported by the connector element (14), the retainer (6) intermediate the reference surface (8) and the end being unsupported. A connector as claimed in claim 8, 9 or 10, characterised in that the first reference surface (32,40) comprises a convex cylindrical surface (32) and an annular surface (40), and the second reference surface (42,44) comprises a concave cylindrical surface (42) and an end surface (44) of the connector element (30).

Inventors: FOELDI PETER, FOELDI,PETER, Földi,Peter
Applicants: STRATOS LTD, STRATOS LIMITED
Application year: 1992
Main classification: G02B6
IPC codes: G02B7, G02B6