Technical Field

This invention relates to a fibre optic device unit and a method for its manufacture.

Background Art

It is particularly concerned with a fibre optic device unit in the form of a transmitter or a detector. A typical transmitter comprises a housing, a fibre optic cable end together with a laser, light emitting diode or super luminescent diode. A typical detector comprises a housing, a fibre optic cable end together with a light sensing device. In use a fibre optic cable has a transmitter located at one end and a receiver at the other. In view of the structural similarity of these devices the generic term of 'light unit' will be used when necessary hereafter as a generic term for a transmitter or a detector.

The fabrication of a fibre optic device unit of the general type described involves highly accurate mechanical alignment of the components during assembly. The device must be of stable construction to avoid functional deterioration in use due, for example, to temperature cycling or repeated coupling and un-coupling of the device.

Disclosure of invention

According to a first aspect of the present invention there is provided a fibre optic device unit comprising a housing, a fibre optic cable, a light unit and a lens for a beam of controlled light extending between the light unit and the cable characterised by:

1) a carrier (19) having a light transmitting path (B) through the carrier (19) incorporating the lens (15), one end of the carrier (19) defining a first end (21) of the light path (B), the other end of the carrier to the one end defining a second end (22) to the light path (B);

2) a light unit (17) having a working surface (25) juxtaposed with the first

end (21) of the light path (B);

3) the carrier (19) or the light unit (17) having an outside surface region

(23) in the form of an outwardly convex band extending at least part way around the carrier (19) or the light unit (17), the surface region (23) further lying generally transverse to the light transmitting path (B) or a coaxial extension thereof; the region (23) having a centre of curvature

(24) lying on or near the light transmission path (B) or an extension thereof; the overall external dimension (D') of the surface region (23) being a close fit within an overall internal dimension (D) of the inside (12') of the housing (12); and

4) a fibre optic cable (13) having an end (16) juxtaposed with the second end (22) of the light path (B).

According to a first preferred version of the first aspect of the present invention the device (11) is a transmitter and the light unit (17) comprises a laser, light emitting diode or luminescent diode.

According to a second preferred version of the first aspect of the present invention the device (11) is a receiver and the light unit (17) comprises a light detector.

According to a third preferred version of the first aspect of the present invention or a preceding preferred version thereof the outside surface region (23) is disposed on the carrier (19) .

According to a fourth preferred version of the first aspect of the present invention or a preceding preferred version thereof the outside surface region (23) is disposed on the light unit (17).

According to a second aspect of the present invention there is provided a method of fabricating a fibre optic device according to the first aspect or a preferred version thereof characterised by the steps of:

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1) locating the lens (15) in a carrier (19) on a light transmitting path (B) through the carrier (19), the carrier (19) being adapted at a first end to juxtapose one end (21) of the light transmitting path (B) with a working surface (25) on the light unit (17); the carrier (19) being further adapted at a second end to juxtapose the other end of the light transmitting path (B) with an end (16) of the fibre optic cable (13);

2) causing an outside surface region in the form of a convex band (23) to be located on either the carrier (19) or the light unit (17), the region (23) being formed in a direction perpendicular to the light transmitting path (B) and extending at least part way around the carrier (19), the surface region (23) having a centre of curvature (24) lying in the light transmission path (B) or an extension thereof; the overall external dimension (D') of the surface region (23) in the direction being comparable with the local overall internal dimension (D) of the inside (12') of the housing (12);

3) securing one end of the fibre optic cable (13) within the housing (12) at a predetermined point on an axis (S) of the housing (12);

4) securing the first end (21) of the carrier (19) to the light unit (17);

5) locating the combination (17, 19) of the carrier (19) and the light unit (17) within the housing (12) by way of the outside surface region (23) so that the second end (22) is juxtaposed with the one end (16) of the fibre optic cable (13);

6) operating the light unit (17) so as to either emit a light output along the light transmitting path (B) to the one end (16) of the fibre optic cable (13) and detecting light emission from the other end of the cable (13) or to receive a light signal along the light transmitting path (B) from the one end of the fibre optic cable (13) which has been transmitted from the other end; and thereafter- i) displacing the combination (17, 19) of the carrier (19) and the light unit (17) so that the surface (23) slides along the interior (12') of the housing (12) in the direction of the axis (S) of the

housing (12) to any necessary extent until the detected light emission provides a first optimised light output; and ii) tilting the combination (17, 19) about the centre of curvature (24) so that the surface (23) rolls on the interior (12') of the housing (12) to any necessary extent until the detected light emission provides a second optimised light output;

7) securing the carrier (19) to the housing (12) once the second optimised light output is detected so as to secure the alignment of the light path (B) relative to the cable end (16).

According to a first preferred version of the second aspect of the present invention the method of fabricating a fibre optic device is characterised in that the light unit (17) comprises a light emitter such as a laser, light emitting diode or luminescent diode and the step of operating the light unit (11) causes the unit to emit a light output along the light transmitting path (B) to the one end (16) of the fibre optic cable (13) to provide for the detection of emitted light from the other end of the cable.

According to a second preferred version of the second aspect of the present invention the method of fabricating a fibre optic device is characterised in that the light unit (17) comprises a light detector and that the step of operating the light unit causes the unit to receive a light signal along the light transmitting path (B) from the one end of the fibre optic cable (13) which has been transmitted from the other end thereof.

Acc rding to a third preferred version of the second aspect of the present invention or the first or second preferred version thereof the step of forming the outside surface (23) provides for the generation of the outside surface on the carrier (19).

According to a fourth preferred version of the second aspect of the present invention or the first or second preferred version thereof the step of forming the outside surface region (23) provides for the generation of the outside surface on the light unit (17).

According to a third aspect of the present invention there is provided a communication stage comprising a fibre optic cable (13) according to the first aspect having at one end a transmitter (17) and at the other end to the one end a receiver.

Brief Description of Drawings

An exemplary embodiment of the invention will now be described with reference to the accompanying drawings of a transmission device of which:

Figure 1 is an exploded view of the elements involved;

Figure 2 shows an initial assembly position for the elements shown in Figure 1;

Figure 3 shows a test position prior to the final sealing of the completed device. A component which appears in more than one figure is identified by the same reference in each figure in which it appears.

Best Mode for Carrying Out the Invention

The figures variously show a fibre optic transmitter 11 including: a tubular housing 12 having a circular internal bore 12' of diameter D and a longitudinal axis of symmetry S; a fibre optic cable 13 with an end mounting fitment 14; a lens 15 to enable a controlled beam of light to be fed by way of light path

B into end 16 of cable 13; and a light unit 17 which is in this case a low power laser.

The housing 12 is in this case of stainless steel. However depending on the usage of the transmitter and the temperature cycling to which it may be subjected one of a number of materials can be used. Where the temperature of the housing is likely to fluctuate substantially a material having a low or negligible coefficient of thermal expansion can be used such as 'Covar' or 'Invar'.

The lens 15 is shown mounted co-axially with light path B in a bore 18 of a stainless steel tubular carrier 19 which is in the form of a cup. The bore 18, the carrier 19, and

the light path B, have a common longitudinal axis 20. The light path B has an input end 21 and an output end 22. Carrier 19 has an external convex surface region 23 which is disposed symmetrically about axis 20. In this case the region 23 is frusto spherical with a centre of curvature 24 located on the axis 20 at a position intermediate the ends of the carrier 19. Outside diameter D' of the region 23 is of a size to be an close fit in bore 12'.

Figure 2 shows an intermediate assembly stage where the fibre optic cable 13 has been mounted in the housing 12 by way of end mounting fitment 14. The end of the fibre optic cable in the end mounting fitment is in this case cut to give a face perpendicular to the local longitudinal axis of the cable. However the end face can be angled or curved for other applications.

In addition laser 17 is attached by its output face 25 to input end 21 of the bore 18 in the carrier 19 in such a way as to provide for efficient optical coupling between the laser 17 and lens 15. The laser 17 is energised by way of input leads 26 from an external power source. Devices according to the present invention are available for operating wavelengths form 650 to 1559 nm but there is no reason why devices, utilising light outside this range should not be fabricated.

Figure 3 shows the penultimate manufacturing stage in which the coupled carrier 19 and laser 17 have been inserted into the housing 12. The combination engages the bore 12' of housing 12 through a close fit between the region 23 of the carrier 19 and the bore 12'. At this stage the axis S of the housing 12 and axis 20 of the carrier 19 are substantially coaxial.

In order to optimise the device prior to securing the carrier 19 in its final working alignment relative to the fibre optic cable end position the laser 17 is energised to cause the system to transmit an output signal from the laser to fibre optic cable 13 by way of the light transmitting path B.

The carrier 19 can now be adjusted in two ways so as to position the lens 15 in the optically most suitable location.

Firstly the carrier 19 can be displaced so that the surface region 23 of the carrier 19 slides along the surface of the housing in the direction of the axis S of the housing until the light signal transmitted along the cable 13 is detected as reaching a first predetermined value.

Secondly the carrier 19 is rocked about the centre of curvature 24 by grasping the suitably insulated leads 26 so that the combination of the laser 17 and carrier 19 (and so lens 15) can be tilted causing the surface region 23 to roll on the bore 12' of the housing to change the angular alignment of the lens 15 relative to the cable until the detected light emission from the other end of the cable provides a second optimised light output.

Once the detected light output has reached or exceeded a predetermined threshold value the carrier 19, and so light path B, is secured in the housing 12 by using an adhesive to secure that portion of surface region 23 to the part of the bore wall 12' adjacent to that portion of the surface region. If preferred the two can be secured together by welding or through the use of a casting material.

The embodiment described in connection with Figures 1 to 4 made use of an external rolling region located on the carrier. Since the carrier and the light unit are joined to form a rigid unit the rolling region can be formed on the light unit rather than the carrier while still enabling the combined light unit and carrier to be displaced axially and tilted to provide the desired optimised alignment of the lens relative to the inboard end of the fibre optic cable.

Industrial Applicability

Fibre optic devices of the present invention are used in connection with light emissions mainly having a wavelength in the range from 650 nm to 1550 nm (though

transmission can also be undertaken with light radiation with wavelengths outside this range). They are particularly intended for use in a wide range of computer and other communication links. Typically a communication link will be made up of a fibre optical cable terminated at one end by a transmitter device and at the other end by a receiver device each according to the present invention.