GB2201806A

GB2201806A - Optical waveguide branching device

Info

Publication number: GB2201806A
Application number: GB08804733A
Authority: GB
Inventors: Mario Pascucci; Paolo Boero
Original assignee: Pirelli Cavi SpA; Cavi Pirelli SpA
Current assignee: Pirelli and C SpA
Priority date: 1987-03-02
Filing date: 1988-02-29
Publication date: 1988-09-07
Anticipated expiration: 2008-02-29
Also published as: IT8719544A0; IT1202608B; GB2201806B; CA1302135C; BR8800970A; GB8804733D0

Abstract

An optical waveguide device is formed from at least two lengths 16 and 17 of optical fibres in such a way as to provide continuity between their respective cores and claddings. The optical fibre lengths are joined in such a way as to provide the device with three optical waveguide arms, 18, 19 and 20 which are connected together at respective first, or inner, ends 18', 19' and 20', with the optical cores of the waveguide arms in optical communication at these ends. Reflecting surfaces 22 and 23 at the ends 19' and 20' of the arms 19 and 20 extend partly across the cores thereof and slope relative to the longitudinal axes 19'' and 20'' of the arms 19 and 20 so as to face the core at the first end 18' of the third arm 18 so that the outer ends of the three arms are in mutual optical communication. An optical signal entering the device through any one of the three arms will be transmitted to the other two arms. <IMAGE>

Description

OPTICAL WAVEGUIDE DEVICE The present invention relates to an optical waveguide device.

More particularly it is concerned with a waveguide device which may be used to couple three optical waveguides, such as optical fibres, so that they are in mutual optical communication. In other words such that an optical signal from any one of the three wave guides is transmitted to the other two waveguides.

Optical waveguide devices are known for coupling three optical fibres such that an optical signal from one of the optical fibres is transmitted to the other two but an optical signal from either of the other two optical fibres will only be transmitted to the first optical fibre. Such devices are known as monodirectional couplers, and are typically produced by joining one length of optical fibre to another intermediate the ends thereof such that the cores and claddings of the two optical fibre lengths are continuous. As will be appreciated, such an arrangement is provided with three free ends for connection to respective optical fibres.

As will be understood by the skilled man in the art, the terms "core" and "cladding" indicate respectively the central portion of an optical fibre or waveguide and a layer adhering to and surrounding the core and having a lower refractive index than the core.

The above-mentioned monodirectional couplers have a geometrical configuration which may be described as "Y" shaped. Thus they are provided with first and second portions, hereinafter called "Y arms", whose axes subtend an angle generally between 3 and 5 degrees, whilst the third portion, hereinafter called the "Y stem" has an axis substantially bisecting the above-mentioned angle.

An example of such a coupler is described in an article entitled "New planar optical coupler for a databus system with single multi mode fibres", published in the magazine "Applied Optics", volume 16, No. 8, August 1977.

As stated above such couplers are monodirectional in that whilst an input signal to the "Y stem" is transmitted to both of the "Y arms" an input signal to either one of the "Y arms" is not transmitted to the other "Y arm", but is transmitted only to the "Y stem". At present, if it is desired to connect together three optical waveguides in such a way that a signal from any one of them is transmitted simultaneously to the o Mer two, it is necessary to use three conventional couplers, formed into an arrangement, which will be described hereinafter with reference to Figure 1 of the drawings.

Such an arrangement is rather complicated being formed of three couplers connected together and has a much larger overall size compared with the size of a single coupler.

Further, when such an arrangement is subjected to mechanical vibrations, for example when it is used in an optical circuit associated with mechanical plant, machinery, vehicles and the like, the connections between the couplers may be damaged with a consequent reduction in the performance of the arrangements.

The present invention aims to overcome the abovementioned problems by providing an optical waveguide device which is able to be made with an overall size comparable to that of oniy one of the above-mentioned monodirectional couplers but which is capable of coupling three optical fibres in mutual optical communication such that a signal from any one of the optical fibres is transmitted to both of the other two.

The invention provides an optical waveguide device comprising three optical waveguide arms connected together at respective first ends thereof such that the optical cores of the wave guide arms are in optical communication at said first ends, the cores at the first ends of first and second ones of the said arms having first and second longitudinal axes which are aligned, or substantially aligned, and the core at the first end of the third one of said arms having a longitudinal axis which is substantially perpendicular to said first and second axes, respective reflecting surfaces at the first ends of the first and second arms extending partly across the cores thereof and sloping relative to said first and second longitudinal axes so as to face towards the core at the first end of the third arm, whereby the second ends of the three arms are in mutual optical communication.

Each of the two reflecting surfaces may be flat or curved and the two reflecting surfaces may have different areas.

The reflecting surfaces may be provided on the surfaces of a wedge-shaped recess defined between the first ends of the first and second arms and opposite to the first end of the third arm. These reflecting surfaces may comprise reflecting layers on the surfaces of the recess, or alternatively they may comprise reflecting surfaces of a complementary wedgeshaped element inserted in said recess.

In one embodiment of the invention1 the first and second arms are famed from a first length 9f optical fibre and said third arm is formed from a further length of optical fibre which is connected at one end to an intermediate portion of said first length opposite to a wedge-shaped notch formed therein which notch extends partly across the core of said first length of optical fibre towards said one end of said further length and is provided with said reflecting surfaces.

In other embodiments, the first, second and third arms are formed respectively from first, second and third lengths of optical fibre butt joined together at respective dihedral first ends thereof, first faces of the two faces of the dihedral ends of the first and second optical fibre lengths abutting the two faces of the dihedral end of the third optical fibre length and the second faces of the two faces of the dihedral ends of the first and second optical fibre lengths abutting reflecting surfaces on a dihedral end of an element inserted between said second faces.

In one of these embodiments, the two faces of each dihedral end of the optical fibre lengths and the element are perpendicular to each other extending to an edge which lies on a common line which is normal to a plane containing the longitudinal axes of the optical fibre lengths and is intersected thereby.

The above-mentioned element may comprise a portion of an optical fibre having a dihedral end, the two surfaces of which are reflecting.

It is also to be understood that when the first, second and third arms are formed respectively from first, second and third lengths of optical fibre butt joined together at respective dihedral end portions thereof, the reflecting surfaces may be provided on one of the two surfaces of the dihedral end portion of each of the first and second optical fibre lengths.

In order that the invention may be well understood, the above-mentioned arrangement of known monodirectional couplers and some exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 schematically illustrates the abovementioned known arrangement comprising three interconnected monodirectional couplers; Figure 2 is a section through an optical waveguide device forming an embodiment of the invention; Figure 3 is a section of an alternative embodiment of the invention; Figure 4 is a perspective view of a component of the embodiment shown in Figure 3 drawn to a larger scale than Figure 3; and Figures 5-7 are sectional views of three further embodiments of the invention.

Referring first to Figure 1, as mentioned above, presently when it is required to connect three optical waveguides, such as optical fibres, together in such a way that an optical signal from any one of them is simultaneously transmitted to the other two, it is necessary to use an arrangement comprising three conventional monodirectional couplers which are indicated by reference numerals 1, 2 and 3.

Each of these couplers is formed by joining at least two lengths of optical fibre such that there is continuity between their cores and claddings respectively and such that the coupler has a generally "Y" shape providing three coupling ends.

As shown in Figure 1, each of the couplers 1, 2 and 3 comprises a first coupling end 4, 5 and 6 respectively, a second coupling end 7, 8 and 9 respectively, and a third coupling end 10, 11 and 12 respectively.

In each coupler the first and second coupling ends correspond to the "Y arms", whilst the third end corresponds to the "Y stem".

The three couplers re connected together by the coupling ends of the "Y arms".

In particular, end 4 of coupler 1 is butt joined to end 5 of coupler 3 tb provide continuity in the cores and claddings of these ends, whilst end 7 of coupler 1 is similarly butt joined to end 6 of coupler 2. Further, the ends 8 and 9 of couplers 3 and 2 are also similarly butt joined together. The third ends 10, 11 and 12 of the couplers 1, 2 and 3 in the resulting arrangement are butt joined to respective optical waveguides 13, 14 and 15 to connect those waveguides such that a signal entering the arrangement from any one of the waveguides is transmitted to both of the other waveguides. For example, a signal from waveguide 14 enters the coupler 2 connected to that waveguide, passes through the end 11 formed by the "Y stem" of that coupler and is transmitted from the latter to both ends 6 and 9 formed by the "Y arms" of coupler 2.The signals transmitted through ends 6 and 9 of coupler 2 are transmitted to ends 7 and 8 formed by a "Y arm" of eachof the other two couplers 1 and 3, are transmitted from the ends 7 and 8 to the ends 10 and 12 of the couplers 1 and 2, and then to the waveguides 13 and 15.

The optical waveguide devices embodying the present invention eliminate the need to form an arrangement as shown in Figure 1 from three mo.zodirectional couplers.

e embodiments are formed by joining at least two lengths of optical fibre such that there is continuity between the respective cores and claddings of the fibres and to provide three optical waveguide arms which are connected together at respective first ends thereof such that the optical cores of the waveguide arms are in optical communication at said first ends.

Further, the cores at the first ends of first and second ones of these arms have first and second longitudinal axes which are aligned, or substantially aligned, and the core at the first end of the third one of the arms has a third longitudinal axis which is substantially perpendicular to the first and second axes. Additionally, in all of the embodiments the three longitudinal axes are coplanar.

Additionally, respective reflecting surfaces are provided at the first ends of the first and second arms, extending partly across the cores thereof and sloping relative to the first and second longitudinal axes so as to face towards the core at the first end of the third arm. The above-described arrangement is such that the second ends of the three arms are in mutual optical communication.

In the embodiments, above-mentioned two reflecting surfaces are. provided on or adjacent the surfaces of a wedge-shaped notch which is present in the connection zone of the three arms.

In particular, the wedge-shaped recess partially separates the cores and claddings of the first and second arms and faces at least the core and possibly the core and cladding of the third arm so that the two reflecting surfaces, which may have equal or different areas, are inclined with respect to the longitudinal axis of the core at the first end of the third arm.

These reflecting surfaces may be flat or curved, and in the latter case, they may be concave or convex with respect to an axis perpendicular to the longitudinal axes of the first ends of the three arms.

Moreover, a wedge-shaped element, shaped complementary to the recess, may be inserted in the latter and in this case the reflecting surfaces may be the surfaces of the wedge-shaped element.

As will be appreciated from the above summary of the embodiments, they all have a substantially "T" shape configuration.

It will be understood that in the embodiments, the optical fibre lengths used to form the device arms may be of any type, and that generally they will be selected so as to be optically compatible with the optical fibres which are to be coupled to the second, outer ends of the arms.

It is to be understood however that other optical waveguides can be used instead of optical fibres to form optical waveguide devices embodying the invention. For example, such an optical waveguide device can be provided by joining together at least two cylindrical core elements, having characteristics similar to those of the core of an optical fibre, so that they form a substantially "T" shape geometrical configuration, and then covering the outer surface of the joined core elements with a cladding layer having characteristics similar to those of an optical fibre cladding.

Referring now to the particular embodiment of the invention shown in Figure 2, it will be appreciated from that figure that the optical waveguide device illustrated is formed by joining together two lengths 16 and 17 of optical fibre in such a way as to provide continuity between their respective cores 16' and 17' and their respective claddings 16'' and 17''.

These optical fibre lengths are joined in such a way as to provide the device with three optical waveguide arms 18, 19 and 20 which are connected together at respective first, or inner, ends 18', 19' and 20' with the optical cores of the waveguide arms in optical communication at these ends. Furthermore, it will be clear that the cores at the ends 19' and 20' have longitudinal axes 19'' and 20'' which are aligned, and the core at the end 18' of the arm 18 has a longitudinal axis 18'' which is perpendicular to the axes 19'' and 20''. In the illustrated embodiment the three arms are straight and accordingly the axes 18'', 19'' and 20'' constitute the longitudinal axes of the respective arms as well as the ends 18', 19' and 20' thereof.

The length 16 of optical fibre forming the arm 18 is connected at one end to an intermediate portion of the length 17 of optical fibre opposite to a wedgeshaped notch 21 formed therein. In particular, the end 18' of the length 16 of optical fibre is provided with a semi-cylindrical recess having an axis perpendicular to the axis 18'l and a radius equal to the radius of the core 17 which forms a saddle-joint with the intermediate portion of the length 17 of optical fibre, that intermediate portion having a length equal to the diameter of the length 16 of optical fibre and being devoid of cladding over a semi-cylindrical portion diametrically opposite the wedge-shaped notch 21.

The wedge-shaped notch 21 has flat surfaces 22 and 23, both of which are reflecting due to the presence of reflecting layers thereon.

The wedge-shaped notch 21 with its reflecting surfaces partially interrupts the continuity of the core 17' in the length 17 of optical fibre since it has a depth h which is smaller than the sum of the thickness of the cladding 17'' and the diameter d1 of the core 17' of the optical fibre length 17.

Furthermore, the notch 21 has a maximum width V which is at least equal to the diameter d2 of the core 16' of the optical fibre length 16.

Rather than provide reflecting layers on the surfaces 22 and 23 of the notch 21 as illustrated in Figure 2, an element having a wedge-shape complementary to that of the notch and provided with reflecting surfaces may be inserted into the notch 21 and secured thereto.

In either case, it will. be appreciated that the reflecting surfaces are provided at the ends 19' and 20' of the arms 19 and 20 and extend partly across the cores thereof sloping relative to the longitudinal axes 19" and 20'' so as to face towards the core 16' at the end 18' of the arm 18 formed by the optical fibre length 16 and in this manner the second, or outer, ends of the three arms 18, 19 and 20 are in mutual optical communication.

Referring now to Figure 3, there is shown an alternative embodiment in which three optical fibre lengths 24, 25 and 26 provide the respective three arms of the device and the reflecting surfaces 28 and 29 are provided on a wedge-shaped element 27.

The optical fibre lengths 24, 25 and 26 are butt joined together to provide continuity between their respective cores 24', 25' and 26' and their respective claddings 24'', 25'' and 26''. Each of these optical fibre lengths has a configuration as shown in perspective in Figure 4. In particular, it will be noted that the ends of the optical fibre lengths which are butt joined together are dihedral, having two flat faces 30 and 31. In this embodiment these faces are symmetrical with respect to the longitudinal axis, subtend an angle of 900, and extend to an edge 32.

The wedge-shaped element 27 comprises a dihedral end portion identical in configuration to the dihedral end portions of the optical fibre lengths, and this element 27 may itself be formed from a further length of optical fibre although this is not essential. The two faces 28 and 29 of the dihedral end portion of the element 27 are reflecting due to the presence thereon of respective reflecting layers.

The axes 25''' and 26''' of the optical fibre lengths 25 and 26 are aligned and therefore coplanar, and the axis 24''' of the optical fibre length 24 is coplanar with and perpendicular to them. The two faces of each dihedral end of the optical fibre lengths 24, 25 and 26 and the element 27 are perpendicular to each other as noted above and extend to an edge which lies on a common line which is normal to the plane containing the longitudinal axes 24"', 25''t and 26''' and is intersected by these axes at the point referenced 33 in Figures 3 and 4.

It will be appreciated from Figure 3 that one of the two faces of the dihedral ends of the optical fibre lengths 25 and 26 abut the two faces of the dihedral end of the optical fibre length 24 and the other faces of the dihedral ends of the optical fibre lengths 25 and 26 abut the reflecting surfaces on the dihedral end of the element 27 inserted between those faces.

Figure 5 shows an alternative embodiment which is similar to the embodiment shown in Figure 3 in that its three arms comprise respective optical fibre lengths 34, 35 and 36 which are butt joined together at respective dihedral ends thereof to provide continuity between their respective cores and claddings and the reflecting surfaces are provided by reflecting surfaces 38 and 39 on a dihedral end portion of a wedge-shaped element 37.

The device shown in Figure 5 differs from that illustrated in Figure 3 in that the angle ' subtended by the reflecting surfaces 38 and 39 of the dihedral end portion of the element 37 is less than 900 so that the reflecting surfaces extend further across the cores of the optical fibre lengths 34 and 36 to provide greater optical interruption between those cores. Consequently, the angle subtended by the faces of the dihedral end portion of the optical fibre length 35 is greater than 900 and the dihedral end portions of the optical fibre lengths 34 and 36 are assymetric with respect to their longitudinal axes.

The four angles subtended by the faces of the dihedral ends of the optical fibre lengths 34, 35 and 36 and the element 37 total 3600.

Figure 6 illustrates a further embodiment formed by joining three optical fibre lengths 40, 41 and 42 at dihedral end portions thereof with an element 43 having a dihedral end portion, the surfaces of which are reflecting. The device illustrated in Figure 6 differs from that shown in Figure 3 in that the angle '' subtended by the reflecting surfaces of the dihedral end portion of the element 43 is greater than 900 and accordingly the reflecting surfaces extend to a lesser extent across the ends of the cores of the optical fibre lengths 40 and 41 thereby decreasing the optical interruption therebetween.

A still further alternative embodiment is shown in Figure 7 and is formed in the sa...e manner s the embodiments shown in Figures 3, 5 and 6 by butt joining three optical fibre lengths 44, 45 and 46 at respective dihedral ends thereof together with a dihedral end portion of an element 48 having faces 49 and 50 which are reflecting. The embodiment shown in Figure 7 differs from those shown in Figures 3, 5 and 6 in that the dihedral end portion of the element 48 is asymmetric with respect to the longitudinal axis 48' thereof.

The angle ''' subtended by the surfaces 49 and 50 of the dihedral end portion of the element 48 is not a right angle, (and is illustrated as being less than 900), and further the angle subtended by the surfaces of the dihedral ends of the optical fibre lengths 44, 45 and 46 are also not right angles.

However, the configuration of the dihedral ends of the optical fibre lengths and the element 48 are such that: the sum of their angles totals 3600; the longitudinal extent h1 of the dihedral end portion of the element 48 is such that the reflecting surfaces thereof extend partly across the cores of the optical fibre lengths 44 and 45; the faces 49 and 50 of the element 48 slope with respect to the axis 46' of the optical fibre length 46; and the longitudinal axes of - the optical fibre lengths 44, 45 and 46 are coplanar, the longitudinal axis 46' of the optical fibre length 46 intersecting the aligned longitudinal axes of the optical fibre lengths 44 and 45.

It is to be understood that in the embodiments shown in Figures 3, 5, 6 and 7, the element provided with the reflecting surfaces may be omitted and the reflecting surfaces of the devices may be provided on those faces of the dihedral ends of the optical fibre lengths whose axes are aligned which do not contact the dihedral end of the other optical fibre length and which form a wedge-shaped recess.

It is to be understood that whilst in all of the above described embodiments the wedge-shaped recess or notch and, when present, the wedge-shaped element have flat surfaces or faces, these faces may be curved. Furthermore when curved they may be concave or convex as mentioned earlier. It will also be appreciated that the term "wedge-shaped" as used in connection with the embodiments means that recess or notch so described has a width which decreases continuously, although not necessarily linearly in a radially inwardly direction from an outer surface of the device. Furthermore the two opposite and converging faces of each recess in t embodiments intersect at the bottom of the recess alona a straight line which is perpendicular to the longitudinal axes of the three arms of the device.

As will be apparent from the foregoing, an important feature of the embodiments is the presence of the two reflecting surfaces which extend. partly across the cores of the optical waveguide arms whose longitudinal axes are aligned and which face towards the core of the third optical waveguide arm.

These reflecting surfaces can be formed by a metal film formed on the faces of the wedge-shaped notch or recess or on the faces of the wedge-shaped element inserted into the notch or recess.

Alternatively they may be formed by a reflecting dielectric coating formed on these faces. Such a coating may comprise alternate layers of silicon dioxide and titanium dioxide or alternate layers of magnesium fluoride and zinc sulphide.

The individual optical fibre lengths which are joined in order to form the embodiments shown in Figures 2, 3 and 5-7 are preferably pre-shaped by being cut using templates or the like as guides and are then inserted into a mould or jig to place them in appropriate relative positions and maintain them in those positions whilst they are joined.

Joining of the optical fibres may be by means of thermally softening then, together with the wedge shaped element provided with the reflecting surfaces when this is present, or by using a transparent bonding agent, for example an adhesive comprising an epoxy resin which is introduced between the ends of the optical fibres being joined.

If the optical waveguide device is intended to be coupled to optical waveguides formed of plastics material, the optical fibre lengths, and also the wedge-shaped element, which are used to form the device are preferably made of a plastics material. In this case, the optical fibre lengths may be joined together by the above-mentioned means or alternatively by solvent welding.

General operation of the above-described embodiments of the invention will now be described with particular reference to the embodiment shown in Figure 3. Three optical waveguides, such as optical fibres, which are required to be coupled in mutual optical communication are coupled to respective outer ends of the three optical waveguide arms of the device formed by the optical fibre lengths 24, 25 and 26 by butt joints.

An optical signal from the optical waveguide joined to the arm formed by the optical fibre length 26 is conveyed into the latter r directed towards the zone where the three optical fibre lengths are joined together with the element 27 having reflecting surfaces 28 and 29.

Due to the presence of the reflecting surface 29, this signal is divided into two parts. One part is conveyed into the arm formed by the optical fibre length 25 and is transmitted into the waveguide connected thereto. The other part of the signal is reflected by the reflecting surface 29 and directed into the arm of the device formed by the optical fibre length 24 and is transmitted to the waveguide connected thereto. It will be appreciated that an optical signal from the waveguide joined to the arm of the device formed by the optical fibre lengths 25 will similarly be transmitted into two parts, one of which will pass into the arm formed by the optical fibre length 26 and thence to the optical waveguide connected thereto and the other which will be reflected by the reflecting surface 28 into the arm formed by the optical fibre length 24 and thence to the optical waveguide connected thereto.

An optical signal from a waveguide connected to the arm of the device formed by the optical fibre lengths 24 will be divided into two by the reflecting surfaces 28 and 29 and these parts will be reflected by those surfaces respectively into the arms of the device formed by the optical fibre lengths 25 and 26 and thence be transmitted to the waveguides connected thereto.

Thus, it will be appreciated that an optical signal from any one of the three waveguides coupled to the device will be transmitted to the other two waveguides coupled thereto.

In the device shown in Figure 3, and additionally in the device shown in Figure 2, the signal entering any one of the three arms is divided into two substantially equal parts which are transmitted into the other two arms.

In the embodiments shown in Figures 5, 6 and 7 the signal entering the device is divided in a different manner depending on the particular arm through which it enters the device.

Thus, an optical signal entering the device shown in Figure 5 through the arm formed by optical fibre length 34 is divided into two parts of different intensity, the part having the smaller intensity is transmitted to the arm formed by the optical fibre length 36 whose axis is aligned with the optical fibre length 34 and the part of the signal having the greater intensity is transmitted to the arm formed by the optical fibre length 35 whose axis is perpendicular to the axes of foe optical fibre lengths 34 and 36.

Similarly an optical signal entering the device shown in Figure 5 through the arm formed by the optical fibre 36 is divided into two parts of different intensity, the part of smaller intensity being transmitted into the arm formed by the optical fibre length 34 and the part with the greater intensity being transmitted into the arm formed by the optical fibre length 35.

If the optical fibre signal enters the device shown in Figure 5 through the arm formed by the optical fibre length 35 it is divided into two equal parts by the reflecting surfaces 38 and 39,(whose areas are equal) are directed thereby into the arms formed by the optical fibre lengths 34 and 36.

In the device shown in Figure 6, a signal entering the device through the arm formed by the optical fibre length 40 is also divided into two parts of different intensity, but in contrast with the device shown in Figure 5, the part with greater intensity is transmitted to the arm formed by the optical fibre length 41 whose axis is aligned with the optical fibre length 40 and the signal of smaller intensity is transmitted to the arm formed by the optical fibre length 42. In this embodiment, it will be appreciated that if the optical signal enters the device through the arm formed by optical fibre length 42, it will be divided into two equal parts, which are reflected into the arms formed by the optical fibre lengths 40 and 41.

The division of an optical signal by the device shown in Figure 7 differs in dependence upon the particular arm through which the signal enters. This division is a function of the longitudinal extent hl of the dihedral end portion of the element 48 provided with the reflecting surfaces 49 and 50 and the assymetry of the latter with respect to the longitudinal axis 48' of the element 48.

From the foregoing description of the illustrated embodiments of the invention it will be appreciated that each embodiment may have an overall size substantially corresponding to the size of a single conventional monodirectional coupler of the type illustrated in Figure 1.

Further, it will be appreciated that the embodiments enable three optical waveguides to be coupled in such a way that a signal from any one of them is transmitted simultaneously to the other two, thus avoiding the need heretofore of providing an arrangement as shown in Figure 1 formed by three conventional monodirectional couplers. Accordingly, by using an embodiment of the invention, which is formed as a single component, it is no longer necessary to use an arrangement such as that shown in Figure 1 and the disadvantages associated with such an arrangement when subjected to mechanical vibrations are eliminated, or at least substantially reduced.

Consequently, each embodiment of the invention comprises an optical waveguide device which is able to couple three optical waveguides so that they are in mutual optical - communication which is both more compact and more reliable than an arrangement comprising three conventional monodirectional couplers such as that shown in Figure 1.

Claims

CLAIMS:

1. An optical waveguide device comprising three optical waveguide arms connected together at respective first ends thereof such that the optical cores of the waveguide arms are in optical communication at said first ends, the cores at the first ends of first and second ones of the said arms having first and second longitudinal axes which are aligned, or substantially aligned, and the core at the first end of the third one of said arms having a longitudinal axis which is substantially perpendicular to said first and second axes, respective reflecting surfaces at the first ends of the first and second arms extending partly across the cores thereof and sloping relative to said first and second longitudinal axes so as to face towards the core at the first end of the third arm, whereby the second ends of the three arms are in mutual optical communication.

2. A device as claimed in claim 1, wherein each of the two reflecting surfaces is flat.

3. A device as claimed in claim 1, wherein each of the two reflecting surfaces is curved.

4. A device as claimed in claim 1, 2 or 3, wherein the two reflecting surfaces have different areas.

5. A device as c'aimed in any one of the preceding claims, wherein seid reflecting surfaces arè~provided on the surfaces of a wedge-shaped recess defined between the first ends of the first and second arms and opposite to the first end of the third arm.

6. A device as claimed in claim 5, wherein said reflecting surfaces comprise reflecting layers on the surfaces of the recess.

7. A device as claimed in claim 5, wherein said reflecting surfaces comprise reflecting surfaces of a complementary wedge-shaped element inserted in said recess.

8. A device as claimed in claim 1, wherein said first and second arms are formed from a first length of optical fibre and said third arm is formed from a further length of optical fibre which is connected at one end to an intermediate portion of said first length opposite to a wedge-shaped notch formed therein which notch extends partly across the core of said first length of optical fibre towards said one end of said further length and is provided with said reflecting surfaces.

9. A device as claimed in claim 1, wherein said first, second and third arms are formed respectively from first, second and third lengths of optical fibre butt joined together at respective dihedral first ends thereof, first faces of the two faces of the dihedral ends of the first and second optical fibre lengths abutting the two faces of the dihedral end of the third the optical fibre length and the second faces of the two faces of the dihedral ends of the first and second optical fibre lengths abutting reflecting surfaces on a dihedral end of an element inserted between said second faces.

10. A device as claimed in claim 9, wherein the two faces of each dihedral end of the optical fibre lengths and the element are perpendicular to each other extending to an edge which lies on a common line which is normal to a plane containing the longitudinal axes of the optical fibre lengths and is intersected thereby.

11. A device as claimed in claim 7, 9 or 10, wherein said element comprises a portion of an optical fibre having a dihedral end, the two surfaces of which are reflecting.

12. A device as claimed in claim 1, wherein said first, second and third arms are formed respectively from first, second and third lengths of optical fibre butt joined together at respective dihedral end portions thereof, said reflecting surfaces being provided on one of the two faces of the dihedral end portion of each of the first and second optical fibre lengths.

1). A device as claimed in any one of the prcding claims, having respective optical fibres coupled to the second ends of the waveguide arms thereof, whereby said optical fibres are in mutual optical communication.

14. An optical waveguide device substantially as herein described with reference to Figures 2 to 7 of the accompanying drawings.