| 摘要 |
An optical intensity modulator (10) for high-speed RZ and NRZ data modulatio n based on a balanced three-arm Mach-Zehnder interferometer. The three arms (60, 62, 64) are joined at the input and output sides of the device by three-way couplers (12 , 14). The input coupler is structured to couple approximately equal powers into the first and third arms (60, 64) and no more than 50% power into the second arm (62). In the straight sections of the arms, there is arranged an AC electrode structure (40) for applying an RF modulation signal and a DC electrode structure (30) for biasi ng the device at a working point. The AC electrode structure is arranged so that an applied modulation signal induces a negative phase shift (-.DELTA..PHI.) in the firs t arm in relation to the second arm and a positive phase shift (+.DELTA..PHI.) in the third arm i n relation to the second arm. Large notch widths of up to 12 times the notch width of a conventional two-arm Mach-Zehnder modulator are achievable. The device is characterised b y high tolerance to variations in the RF modulating signal and the power splitting ratio into the interferometer arms. The intensity transfer function for a 25:50:25 power split between the arms is comparable to that of two cascaded balanced two-ar m Mach Zehnder interferometers, but has theadvantage of being a one stage device, which is shorter and requires only one RF drive circuit.
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