Method of making an optical component

Abstract: A method of making an opto-electronic component (13) comprises inserting a pre-assembled device carrier (1) into a mould, filling the mould (2) with light and/or thermally curable material, optically aligning the device assembly and, on achieving optical alignment, at least partially curing the material.

Description: This invention relates to optical components for use with optical fibres and other optical waveguides, and to methods of manufacturing such components. In particular, though not exclusively, this invention relates to opto-electronic components for transmitting, receiving or otherwise processing optical signals, and their manufacture. The dimensions of the active, or light emitting, area of light sources (such as semi-conductor lasers and light emitting diodes) used in optical fibre communications systems are typically of the order of a few µm. In a single mode optical fibre suitable for use in the 1.3µm and 1.5µm wavelength regions the core is about 5-10µm in diameter. Efficient optical coupling between the fibre and the light source requires that their alignment be accurate to within a few µm (or less), both transversely and axially. The dimensions of the active areas of photo-detectors are usually larger, of the order of 50-100µm and the alignment tolerances between the fibre and the detector are generally more relaxed. However, in the case of an optical travelling wave amplifier, for example, the light sensitive receiving area of the device is of the same dimensions as the active area of a laser. The need for consistently high accuracy of optical alignments forms one of the major problems which needs to be overcome if optical devices are to be manufactured in large volumes. Large volume manufacture is, of course, essential to reducing the cost of optical fibre communications systems. Permanently attaching a fibre "pigtail" to the device is one of the widely adopted solutions. Here, the critical alignment between the fibre and the device is made during manufacture. To connect the device to an optical fibre transmission line, a relatively easily aligned fibre-to-fibre splice is formed between the pigtail and the transmission fibre. Use of a spliced connection is readily acceptable only in applications where the connection between the optical device and the transmission fibre needs rarely if ever to be broken or re-made. GB Patent 1558063 ("Improvements in or relating to dielectric optical waveguide couplings", The Post Office) discloses an opto-electronic component in which the opto-electronic device is housed in an optical fibre connector. The opto-electronic device may be located in either the male or the female part of the connector. This arrangement of an optical device mounted in an optical fibre connector is sometimes referred to as a "connectorised device". Use of a connector-mounted device permits easy and repeated connection and disconnection between the fibre and the device and is potentially fairly cheap to manufacture. Ensuring adequate optical alignment between the fibre and the device does, however, present some difficulties. Patents Abstracts of Japan, vol.10, no.198, (p-476) [2254] discloses a an optical device comprising a device carrier mounted inside a sleeve. An optical fibre enters the interior of the sleeve through an aperture in the endface of the sleeve, and the carrier is forced into alignment within the sleeve by a groove provided in the sleeve. After insertion, the space between the sleeve, which forms the jacket of the device, and the device carrier, which lies within the sleeve, is filled with resin which is subsequently cured. The present invention aims to provide a method of manufacturing optical components, which will more reliably yield adequately accurate optical alignment. The present invention also aims to provide a connector-mounted optical component made by that method. According to the present invention, a method of making an optical component comprises the steps of inserting a preassembled device carrier comprising an opto-electronic component mounted on a support structure, into a mould having an optical fibre fitted thereto, filling the mould with radiation and/or thermally curable material, and curing the material, wherein the mould has an aperture in which is located a resilient plug to which the fibre is fitted externally and which is transparent at the wavelength of operation of the opto-electronic component, wherein the device carier is moved longitudinally into contact with the plug and thereafter transversely until optical alignment is achieved between the opto-electronic component and the optical fibre, and wherein on achieving alignment the material is at least partially cured and the optical component is thereafter removed from the mould. Any partial curing of the material must be sufficient to ensure adequate rigidity to avoid relative movement of the parts until full curing has taken place. Full curing preferably takes place at elevated temperature. According to another aspect of the present invention, an optical component comprises a pre-assembled device carrier comprising a support structure and an optical component mounted thereon, and further comprises an alignment shell about the device carrier formed of light and/or thermally cured material. Preferably, the optical component is an opto-electronic component capable of converting light into an electric signal or vice versa. The present invention will now be described further by way of example only, and with reference to the accompanying drawings, of which:- Figures 1a to 1f are schematic illustrations of various stages in the manufacture according to the present invention of an opto-electronic component; Figure 2 is a schematic sectional view of an opto-electronic component made according to the method illustrated in Figure 1; and Figure 3 is a schematic sectional view of a modified opto-electronic component. Referring now also to the drawings, Figure 1a shows a preassembled carrier 1 for an opto-electronic device 13. The carrier 1 comprises a tubular carrier member 11 of conductive material, having mounted on a flat mounting surface at a stepped end 12 thereof an opto-electronic device 13. Secured by adhesive resin 14 to the opto-electronic device 13 and the stepped end 12 of the carrier member 11, is a spherical collimating or focussing lens 15. Electrical connections to the opto-electronic device 13 are provided by the tubular member 11 itself, and by a terminal 16 of a wire 17 (see Figure 2) insulated from, and extending the length of, the tubular member 11. Figure 1b shows a mould 2 in which to form an alignment shell around the carrier 1 of Figure 1a. The mould comprises two axially aligned cylindrical sleeve portions 21 and 22, separated by an intermediate wall 23. The sleeve portion 21 is of an internal diameter larger than the maximum transverse dimension of the carrier 1; the sleeve portion 22 provides a push fit about an optical fibre connector ferrule 24 enclosing an optical fibre 25 and ending flush with the fibre 25. The intermediate wall 23 has an aperture 26 which locates a plug 27 of silicone rubber or another suitably resilient material which is transparent at the wavelength of operation of the opto-electronic device 13. As illustrated by Figures 1c to 1f, the manufacture of an opto-electronic component proceeds as follows:- The pre-assembled carrier 1 is inserted fully into the sleeve portion 22 of mould 2 until it touches and slightly deforms the plug 27. Thereupon the mould is filled with a liquid, UV and thermo-curable material as schematically indicated by the funnel 28. To be suitable the material must have good environmental stability when cured. Methacrylate resin providing a matrix for finely ground boro-silcate glass has been found to be satisfactory in this respect. Once the mould is filled, the carrier 1 is moved transversely until optimum alignment between the device 13 and the core 29 of the optical fibre 25 has been achieved as measured by the amount of light coupled into or out of the fibre 25. It should be noted that the resilient plug 27 will provide a barrier to the liquid mould feed thereby to avoid contamination of the front portion of the surface of the lens 15. On reaching optimum alignment, the mould feed is at least partly cured by irradiation with light from a UV source 30, as schematically shown in Figure 1e. This UV curing process must result in adequate dimensional stability to allow removal of the completed component 4 from the mould 2 without adversely affecting the positioning of the carrier 1 within the moulded shell 31. Instead of irradiating the resin from the end of the mould, a transparent mould irradiated from all directions could be used, for example. If required by the material properties, the curing process can be completed at elevated temperatures as indicated by Figure 1f. Suitable elevated curing temperatures are typically 80°C to 150°C. Figure 2 shows a schematic length-wise section through a completed opto-electronic component. In addition to the features of the carrier already described with reference to Figure 1a, there is shown the central conductor 17 leading, within an insulating sleeve 18, from the terminal 16 to a bonding pad 33. A bond wire 34 is attached to the bonding pad 33 at on end, and to a top contact of the device 13 at its other end. The shell 31 provides a highly concentric alignment surface around the component which thus can provide a male portion of an optical fibre connector, for example. Figure 3 shows a schematic length-wise section through a modified form of the component of Figure 2. Using a resin matrix for ground boro-silicate glass provides an external surface to the shell which is of excellent thermal and mechanical stability; however, the glass particles in the material or the matrix material itself may prove to be too abrasive in certain applications. To overcome this, the shell may be enclosed in a thin sleeve 35 of material more closely matched in hardness to the material of the socket into which the component is to be inserted.

Claims: A method of making an optical component comprising the steps of inserting a pre-assembled device carrier (1) comprising an opto-electronic component (13) mounted on a support structure (12), into a mould (2) having an optical fibre (25) fitted thereto, filling the mould (2) with radiation and/or thermally curable material (31), and curing the material (31), characterised in that the mould (2) has an aperture (26) in which is located a resilient plug (27) to which the fibre (25) is fitted externally and which is transparent at the wavelength of operation of the opto-electronic component (13), in that the device carrier (1) is moved longitudinally into contact with the plug (27) and thereafter transversely until optical alignment is achieved between the opto-electronic component (13) and the optical fibre (25), and in that on achieving alignment the material is at least partially cured and that the optical component is thereafter removed from the mould (2). A method of making an optical component as claimed in claim 1 wherein the material (31) is cured to form an alignment shell about the device carrier (1). A method as claimed in claim 1 or claim 2 wherein said material (31) is a radiation curable material. A method as claimed in claim 3, wherein the material (31) is curable by irradiation with UV radiation. A method as claimed in any preceding claim, comprising curing of said material (31) at elevated temperature. A method as claimed in any preceding claim, wherein the opto-electronic component (13) is capable of converting light into an electric signal. A method as claimed in any of claims 1 to 5, wherein the opto-electronic component (13) is capable of converting an electric signal into light. A method of making an optical connector including making an optical component according to the method of any preceding claim.

Inventors: MUSK ROBERT WILLIAM, MUSK, ROBERT WILLIAM
Applicants: BT & D TECHNOLOGIES LTD, BT&D TECHNOLOGIES LIMITED
Application year: 1989
Main classification: G02B6
IPC codes: H01S5, H01L33, G02B6, B29C39