| 摘要 |
An optical performance monitor (OPM) 31 comprises an optical chip formed with an input waveguide 32 for a DWDM signal to be analysed. The input signal supplied to the waveguide 32 is split by a polarisation splitter 33 into TE and TM mode signals in two waveguide branches each of which incorporates a respective variable optical attenuator (VOA) 34 or 35. The VOAs 34 and 35 are controlled by appropriate electrical control signals of different frequencies, so as to modulate the TE and TM mode signals in the two branches with identifying signals at different tone frequencies. The modulated mode signals are than applied to spaced inputs of a demultiplexer 38 which serves to demultiplex the signals to supply channel signals to a series of channel waveguides 39 incorporating VOAs 40 which serve to modulate the channel signals with toning signals of different frequencies, or alternatively to sequentially switch the channel signals. The channel signals are then multiplexed by a multiplexer 41 to produce an output signal which is conducted by an output waveguide 42 to a photodiode 43 at the edge 44 of the chip. The electrical output signals from the photodiode of the array 10 are supplied to a digital signal processor (DSP), a digital-to-analogue converter being used to convert the analogue output signals from the photodiode to digital signals which can be processed by the DSP In this manner the channels of the multichannel optical signal may be monitored substantially independently of polarisation using apparatus which can be produced at low cost relative to its accuracy.
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