WO2002075866A2

WO2002075866A2 - Active optical device

Info

Publication number: WO2002075866A2
Application number: PCT/GB2002/001244
Authority: WO
Inventors: Michael Moody; Keith Read
Original assignee: Bookham Technology Plc
Priority date: 2001-03-19
Filing date: 2002-03-18
Publication date: 2002-09-26
Also published as: GB2373589A; GB2373588A; GB0106768D0; AU2002246237A1; AU2002246235A1; GB0111447D0; WO2002075866A3

Abstract

An active optical device comprising a first plate 1, which plate co-operates with a second plate 2, which second plate 2 is adapted to receive an optical fibre 30, wherein the second plate is further adapted to receive at least one PTC element 5, which PTC element is adapted to heat the optical component to a predetermined temperature. The use of a PTC element facilitates the design and manufacture of thin devices with a self-regulating heater.

Description

ACTIVE OPTICAL DEVICE

The invention relates to an active optical device and in particular, but not exclusively, an erbium doped fibre amplifier (EDFA), which is adapted to operate at a predetermined elevated temperature.

A well known characteristic of erbium doped optical fibres is that the gain is variable with changes in temperature, hi components such as optocouplers for example, it is therefore desirable to keep the optocoupler at a constant temperature and to tune the component so that it functions optimally at that temperature.

As the ambient conditions will inevitably change with the weather, it is usual either to cool or heat devices such as EDFAs to a pre-determined temperature. Generally, it is preferred to heat the device as the laser diode in the device generates heat and it is easier to control and maintain elevated temperatures in such a situation in most climates.

In known devices, the heating element is provided by a coil element, which is thermostatically controlled to heat the device up to a standard, pre-determined temperature and to maintain the operating temperature. Coil heaters have proven to be reliable and efficient heaters.

There is also a demand in the communications field to make devices smaller and thinner. Whilst it is possible to decrease the size of the known coil heaters, the need to provide efficient heating and also control circuitry places restrictions on design freedom.

According to the invention, there is provided an optical device comprising an optical component in communication with at least one PTC element arranged, in use, to heat the component to a predetermined temperature.

The invention takes advantage of the property of positive temperature coefficient (PTC) materials (normally ceramics), that the resistance of the material increases in a step-like fashion with temperature. Under ambient conditions the PTC element functions as a heater and will heat the device to a pre-determined temperature at which temperature the PTC element becomes an insulator, in effect switching off. Although the laser diode will provide additional heating during operation, any reduction in temperature due to heat loss will reactivate the PTC element to re-heat the device, which becomes self- regulating.

Preferably the device according to the invention further comprises a first plate adapted to receive the optical component and the, or each, PTC element. Additionally or alternatively the device may advantageously further comprise a second plate, of insulating material.

In a preferred embodiment the device further comprises a cover plate, which cover plate preferably has substantially the same dimensions as the second plate. Preferably the second plate is provided with a plurality of recesses, such that a respective PTC element is received in each recess. Preferably, three or six PTC elements are used.

An exemplary embodiment will now be described in greater detail with reference to the drawings in which,

Fig. 1 shows a perspective view of a first plate adapted to receive PTC elements; Fig. 2 shows a cross section of the first plate; Fig. 3 shows a plan view of an insulating second plate; Fig. 4 shows a cross section of the insulating plate;

Fig. 5 shows a cross section of a cover plate;

Fig. 6 shows an assembled device according to the invention, in schematic cross section.

Fig. 1 shows a perspective view of a generally circular first plate 1 comprising (about a common axis), a circular opening 2, a stepped annulus portion 3 and an annular flange 4. The stepped annulus portion 3 has six equidistantly disposed circular recesses 5, each adapted to receive a disc like PTC element. The power to heat the PTC elements can be taken from a conventional battery or other power source and the connection to the PTC element is via soldered spade clips 6.

Fig. 2 shows a cross-sectional view of the plate having the flange portion 4, stepped annulus 3 with recesses 5 for the PTC elements and central opening. Figs. 3 and 4 show an insulating second plate 10, which comprises a generally annular structure having a central opening 11, which opening is defined by a wall 12 upstanding from the base of the insulating plate 10. The exterior edge of the insulating plate 10 is defined by a lip 13 upstanding from the base of the plate 10.

The diameter of the central opening 11 of the insulating plate 10 is slightly smaller than that of the circular opening 2 of the plate 1 and the diameter to the lip 13 of the insulating plate 10 is slightly greater than the diameter to the edge of the flange 4 of the plate 1, so that the plate 1 can be mounted in the insulating plate 10 over the wall 12, which hence acts as a spindle. The wall 12 and the lip 13 have a height which corresponds to the combined thickness of the plate 1 and a cover plate 20. A particularly suitable material for the insulating plate 10 is nitrogen aerated silicone foam, which combines good mechanical and insulating properties.

Fig. 5 shows a cross-sectional view of a cover plate 20 having substantially the same dimensions as the plate 1 comprising a central opening 21, a stepped annulus 22 and an outer annular flange portion 23. Both plates 1 and 20 are formed from a good conductor, for example copper.

Fig. 6 shows, in schematic cross-section, a device according to the invention assembled from the plates shown in the preceding figures. The assembly comprises the insulating plate 10 having a first plate 1 mounted on the wall 12 thereof and a cover plate 20 mounted on the first plate 1 and the wall 12. PTC elements 5 are located in the recesses located on the plate 1. An optical component such as an optical fibre 30 associated with a device such as an EDFA (not shown) is wound around the spindle formed by the co-operating wall 12 and stepped annular portions 3, 21 in the annular space formed by the co-operating flange portions 4, 23. The three plates 1, 10 and 20 are held together by a plurality of conventional spring clips 31.

In use, when the device is activated, power is supplied to the PTC elements which then heat up the device and the optical fibre to the desired predetermined elevated temperature, which is typically 60-70 °C for example. Once the desired temperature is reached, the PTC elements will become insulating and switch off and remain off until the temperature falls below a pre-determined tolerance, when the elements become conductive and hence switch back on.

h practice, it has proven to be particularly convenient to use three or six substantially equidistantly spaced PTC elements as this arrangement ensures that each element 5 is in contact with the plate 1 and yet provides adequate heating performance combined with easy assembly and minimal costs.

Although the device is described as having a plurality of discrete PTC elements, it would be possible to have almost any geometric arrangement of PTC material providing sufficient heating were achieved.

Claims

1. An optical device comprising an optical component in communication with at least one PTC element arranged, in use, to heat the component to a predetermined temperature.

2. A device as claimed in claim 1, further comprising a first plate adapted to receive the optical component and the, or each, PTC element.

3. A device as claimed in claim 1 or 2, further comprising a second plate, of insulating material.

4. A device as claimed in any one of claims 1, 2 or 3, further comprising a cover plate.

5. A device according to any preceding claim, further comprising at least one recess adapted to receive a said PTC element.

6. A device as claimed in any preceding claim, further comprising a plurality of PTC elements.

7. A device as claimed in claim 6, further comprising a plurality of recesses adapted to receive respective PTC elements.

8. A device according to any preceding claim, wherein three PTC elements are used.

9. An optical communications system incorporating an optical device as claimed in any preceding claim.

10. An optical device heater comprising an element arranged, in use, to be in communication with an optical device and to heat it to a predetermined temperature, wherein the element includes a material having a positive temperature coefficient (PTC).