GB2419681A

GB2419681A - Optical receiver with conical cylinder coupler

Info

Publication number: GB2419681A
Application number: GB0424213A
Authority: GB
Inventors: David John Kenneth Meadowcroft; David Healy; Mark Dunn
Original assignee: Agilent Technologies Inc
Current assignee: Agilent Technologies Inc
Priority date: 2004-11-02
Filing date: 2004-11-02
Publication date: 2006-05-03
Also published as: GB0424213D0

Abstract

An optical receiver arrangements 110 comprises a coupling means 40 that enables the efficient coupling of light from eg an optical fibre to a photodetector 10. The coupling means comprises a conical cylinder 44 arranged to receive light from an optical source at its widest end face 46, the light propagating through the cylinder and being received by the photodetector 10. A frusto-conical transparent cylinder (Fig 4) may be received in the cylinder 44. Plinth 20 and connecting leads 30 for the photodetector are shown.

Description

- - 2419681

OPTICAL RECEIVER

The present invention relates to an optical receiver arrangement, and in particular to an optical receiver arrangement that facilitates the coupling of light from an optical fibre into an optical receiver or detector.

Optical communications networks conventionally comprise optical transmitters, such as a laser or LED, that launch an optical signal into an optical fibre. The signal propagates along the fibre and is eventually coupled into an optical detector. For a single mode optical fibre the core of the fibre in which the signal propagates is typically 8-lO/im in diameter and the active region of a high-speed optical receivers can be significantly smaller than this. One consequence of this is that it is difficult to arrange the fibre and the receiver such that a suitable amount of light is coupled from the fibre to the detector. Simply butting the fibre next to the detector is not an appropriate technique as the coupling of the light is inefficient due to the mismatch in diameter.

Various schemes have been proposed that use one or more lenses to focus the light emitted from the fibre onto the detector, but the lens arrangement must be very precise: this requires precision parts and a significant time to set-up the lens arrangement and both of these factors lead to increased cost. Furthermore, it has been observed that changes in temperature can have significant unwanted effects on the efficiency of the light coupling.

According to a first aspect of the present invention there is provided an optical receiver arrangement comprising an optical detector and a coupling means, the coupling means being arranged to couple light onto the active region of the optical detector, characterised in that the coupling means comprises a conical cylinder having a first and a second end, with the first end having a larger diameter than the second end, the first end being arranged to receive light from alight source and the second end being arranged to couple light onto the active region of the optical detector.

According to one embodiment of the present invention, the conical cylinder comprises a cavity within the coupling means. The internal surface of the cavity may be processed to increase its reflectivity.

According to a further embodiment of the present invention the conical cylinder is received within a cavity within the coupling means. The end faces of the conical cylinder may comprise an anti-reflective coating.

Furthermore, or alternatively, the curved outer surface of the conical cylinder may be processed to increase internal reflection. The internal surface of the cavity may be processed to increase its reflectivity.

The invention will now be described, by way of example only, with reference to the following Figures in which: Figure 1 shows a schematic depiction of a conventional optical receiver; Figure 2 shows a schematic depiction of an optical receiver apparatus according to the present invention; Figures 3a & 3b show a schematic depiction of a crosssectional view of the optical receiver apparatus according to the present invention shown in Figure 2; and Figure 4 shows a schematic depiction of a further embodiment of an optical receiver apparatus according to the present invention.

Figure 1 shows a schematic depiction of a conventional optical receiver 100 comprising a photodetector 10, such as a photodiode, which is received on a plinth or header 20. One or more connecting leads 30 are connected to the photodetector to transmit data signals generated within the receiver, provide biasing currents, etc. Figure 2 shows a schematic depiction of an optical receiver apparatus 110 according to the present invention and Figure 3a shows a cross-sectional view of that optical receiver apparatus. The optical receiver apparatus, similarly to the apparatus shown in Figure 1 comprises a photodetector 10, which is received on a plinth 20, and one or more connecting leads 30 are connected to the photodetector. The apparatus further comprises coupling means 40, which is connected to the plinth 20. In this embodiment of the invention, the coupling means comprises a solid body 42 in which there is formed a passage 44. The passage takes the form of a conical cylinder and has first and second ends 46, 48. The first end 46 of the passage is received on the outermost face of the coupling means and has a greater cross-sectional area than the second end 48. The second end of the passage is received on an internal face of the coupling means and is aligned with the photodetector. The area of the second end of the passage is substantially equal to that of the photodetector such that most or substantially all of the light that exits the second end of the passage is received by the photodetector. Thus, any light that is received within the first end of the passage will be internally reflected within the passage, passes through the second end of the passage and illuminates the photodetector (see Figure 3b) The coupling means makes it much easier to efficiently couple light from an optical fibre into a photodetector. As the second end of the passage is aligned with the photodetector, it is necessary to align the output of the optical fibre with the first end of the passage. The first end of the passage should have an area that is equal to or greater than the area of the beam of light that is emitted by the optical fibre.

This effective increase in the area of the active region of the photodetector allows the receiver design to be simplified, with precisionformed components being replaced by cheaper components (for example formed from plastics materials) . The receiver should also be simpler and quicker to assemble, which leads to further decreased costs. It is believed that the arrangement will be less sensitive to

changes in temperature than prior art solutions.

The coupling means may be formed along with the formation of the photodetector and/or the plinth, for example from a polyamide. Alternatively the coupling means may be formed separately and then subsequently coupled to the plinth and aligned with the photodetector. A separate coupling means may be grown as described above or it may be cast in, or machined from, a suitable material, such as a plastic, mecal or resin.

The internal surface 45 of the passage 44 may be coated in a reflective material, so as to reduce the amount of light that is lost to absorption as the light is transmitted through the passage. Alternatively, the coupling means may be formed from a reflective material. The internal surface 45 of the passage may be polished or otherwise treated in order to increase its reflectivity.

Figure 4 shows a schematic depiction of a further embodiment of an optical receiver apparatus according to the present invention. The optical receiver apparatus is similar to those described above with reference to Figures 1 to 3.

Photodetector 10 is received on a plinth (not shown) and coupling means 140 is connected to the plinth and is aligned with the photodetector 10. The coupling means 140 comprises a frusto-conical cylinder 50 received within a cavity 44 of coupling means body 40. The first end 56 of the cylinder has a greater cross-sectional area than the second end 58 of the cylinder and is received on the outside of the coupling means. The second end of cylinder is arranged to be aligned with the active region of the photodetector 10. The cylinder is of a transparent material such that light incident on the first end 56 of the cylinder will propagate through the cylinder and exit the cylinder at the second end 58 (not shown) of the cylinder. The material used to form the cylinder will be chosen so as to keep the attenuation of the propagating light below a threshold value.

The curved outer surface of the cylinder may be coated with a material that enables total internal reflection to occur within the cylinder. Alternatively the cavity walls of the coupling means body may be coated with a material that decreases the loss of light from within the cylinder. The first and second end faces may be coated with a material having a low reflectivity to reduce losses due to end face reflections. The cylinder may extend above the top surface of the coupling means body (as is shown in Figure 4) or alternatively it may be either substantially level with the coupling means body or entirely received within the coupling means body.

Claims

1. An optical receiver arrangement (110) comprising an optical detector (10) and a coupling means (40), the coupling means being arranged to couple light onto the active region of the optical detector, characterised in that the coupling means comprises a conical cylinder (44) having a first (46) and a second end (48), with the first end having a larger diameter than the second end, the first end being arranged to receive light from a light source and the second end being arranged to couple light onto the active region of the optical detector.

2. An optical receiver arrangement according to claim 1, wherein the conical cylinder (44) comprises a cavity within the coupling means.

3. An optical receiver arrangement according to claim 2, wherein the internal surface (45) of the cavity is processed to increase its reflectivity.

4. An optical receiver arrangement according to claim 1, wherein the conical cylinder (50) is received within a cavity (44) within the coupling means.

5. An optical receiver according to claim 4, wherein the end faces (56, 58) of the conical cylinder (50) comprise an anti-reflective coating.

6. An optical receiver according to claim 4 or claim 5, wherein the curved outer surface (59) of the conical cylinder is processed to increase internal reflection.

7. An optical receiver according to any of claims 4 to 6, wherein the internal surface of the cavity (45) is processed to increase its reflectivity.