Abstract
The chirp parameter of a silicon optical modulator (SOM) is difficult to measure precisely because the plasma dispersion effect is due to electro-refraction and electro-absorption occurring simultaneously. A novel method for measuring the chirp parameter of a SOM is presented, which is adopted from the beat-frequency method. Firstly, based on the model of the differential driver silicon Mach–Zehnder modulator(DDSMZM), the chirp parameter of the DDSMZM is presented by mathematical derivations, and we prove that achieving the multi-order coefficients of the radio frequency phase shift is a key point for characterizing the chirp accurately. In the proposed method, a wavelength tunable laser, as a local source, is applied to mix with the chirped modulated optical signal of the DDSMZM. In this way, the multi-order electric signals of beat frequency are mapped from high-frequency to low-frequency. Meanwhile, a balanced detector with a low-speed trans-impedance amplifier(TIA) is employed for realizing photo-electric conversion, which can improve the signal-to-noise ratio of the measurement. Finally, we have examined the chirp parameter of the DDSMZM in the case of low-frequency and high-frequency modulation signal condition and the results show the beat-frequency method has a higher frequency resolution and measurement accuracy for measuring the chirp parameter of the DDSMZM compared with the optical spectrum analysis(OSA) method and the optical heterodyne method.
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