| 摘要 |
A planar waveguide module 1 has integrally formed thereon a waveguide 2 an d, in sequence along the optical transmission path, a first LOA 3, a 90.degree. polarisation rotator 4, a VOA 5 and a second LOA 7. The LOAs 3 and 7 are gain-clamped SOAs having linear gain responses over the required wavelength range. In the absence of the polarisation rotator 4 the PDGs of the LOAs would be added together to provi de an overall PDG of approximately twice the PDG of a single LOA. However the inclusion of the polarisation rotator 4 between the LOAs 3 and 7 causes a substantial reduction in the overall PDG. If TE polarised light is supplied to LOA 3, the polarisatio n rotator 4 will cause TM polarised light to be supplied to LOA 7, and accordingly the overall gain of the module will equal Gain(TE, LOA 3) + Gain(TM, LOA 7) - attenuation. On the other hand, if TM polarised light is supplied to LOA 3, the overall gain wil l be Gain(TM, LOA 3) + Gain(TE, LOA 7) - attenuation which is substantially the same as the gain for the inputted TE polarised light. Such a polarisation insensitiv e optical amplifier is advantageous since it is easily fabricated using known fabrication techniques, for example on a planar lightwave circuit on a SOI platform, and without having to modify the amplifying means.
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