| 摘要 |
The invention concerns an elongated optical form field transformer comprising a core part 50, 52, 53 and a shell part 54 which directly and essentially coaxially surrounds the core part, the diffraction coefficient n0 of which shell part is lower than the diffraction coefficient n3 of the material in the core part 50, 52, 53 where it is in contact with the shell part 6. According to the invention the core part 50, 52, 53 comprises, for example, a central part 1 which is an erbium alloy and consists of a material which has the highest average diffraction coefficient in the transformer, an intermediate part 53 directly surrounding the central part 50 consisting of a material with the lowest diffraction coefficient in the transformer and an outer part 52 directly surrounding the intermediate part, consisting of a material with a diffraction coefficient n3 which is lower than the diffraction coefficient n1 of the material of the central part 50 but higher than the diffraction coefficient n2 of the material of the intermediate part 53. By means of a construction according to the invention for example a semiconductor laser or some other light channel which differs from an ordinary single form fibre can easily be connected to an ordinary single form fibre with good optical efficiency. By means of a fibre which is an alloy according to the invention both the pumping effect can be concentrated on a small cross-section area of the active area and a good level of connection efficiency can be achieved in relation to an ordinary single form fibre by thinning of the fibre. <IMAGE>
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