Abstract
Silicon microring resonator has been recognized as a competitive structure for the
electro-optic modulator due to its potential for high-density integration. There are two
silicon-ring-based modulation methods: push-pull coupling modulation and index modulation.
Previous investigations show that the push-pull coupling modulation seems to outperform the
index modulation because of its ultralarge optical modulation bandwidth and chirp-free
property. However, there is no performance comparison for these two schemes in power
consumption, which has emerged as an important parameter for photonics integrated circuit
design. This paper thus studies the power efficiency of these two methods. The analysis of the
static characteristics of the ring shows that the index modulation requires a much lower
driving voltage than that of the push-pull coupling modulation when the modulator is operated
at low frequencies. The dynamic analysis based on the coupled-mode theory in time indicates
that the required driving voltage of the push-pull coupling modulation is still higher than
that of the index modulation when the modulation frequency is not very high. To solve this
problem, we propose a chirp-free two-ring modulator consisting of a push-pull coupling
modulator embedded into a ring with the same resonance. We demonstrate that the two-ring
modulator can reach its transmission null before the push-pull coupling modulator becomes
critical coupled. As a result, the power requirement of the two-ring modulator is lower than
that of the push-pull coupling modulator.
© 2010 IEEE
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