Cascaded-ring-resonator-loaded Mach–Zehnder modulator for enhanced modulation efficiency in wide optical bandwidth

Abstract

A cascaded-ring-resonator-loaded Mach-Zehnder modulator (CRR-MZM) is presented in which a number of cascaded ring resonators (RRs) are loaded in the interferometer as phase modulators. The ability of the design to provide enhanced modulation efficiency at a wide optical bandwidth is demonstrated in comparison with a conventional single-RRtype modulator without an interferometer. The optimization of RRs for the CRR-MZM is investigated experimentally by measuring the transmission spectra in both intensity and group delay of RRs having various structural parameters. Using the optimized parameters, we fabricated a CRR-MZM with 10 cascaded RRs loaded on each arm of the interferometer on a silicon-on-insulate substrate. The RRs had pin-diodes along the waveguides, which were operated with forward bias voltage. Its modulation efficiency was enhanced by a factor of 4.4 at the expense of additional loss of less than 3.5 dB compared with a standard non-resonant MZM. 10 Gb/soperations of CRR-MZM were successfully demonstrated using preemphasized RF signals with amplitude of 1.5 V pp in a wavelength range of 2 nm.

Dynamic response of modulators based on cascaded-ring-resonator

“…The use of optical resonators has shown promise in increasing the response of modulators [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Light dwells in resonators, increasing the interaction of light with matter, and causes the enhancement of any kind of electro-optical effect [16,17].…”

“…Light dwells in resonators, increasing the interaction of light with matter, and causes the enhancement of any kind of electro-optical effect [16,17]. This approach has been actively investigated, particularly for modulators that are based on silicon [2][3][4][5][6][7][8][9][10][11][12][13]. One reason is that silicon lacks the strong electro-optical effect unlike III-V systems [18], and the use of resonators is therefore desired to enhance the modulation.…”

“…One reason is that silicon lacks the strong electro-optical effect unlike III-V systems [18], and the use of resonators is therefore desired to enhance the modulation. The other reason is that the silicon waveguide is suitable for configuring the micrometer-scale resonators needed for modulators, due to the tight confinement of light in the waveguide [2][3][4][5][6][7][8][9][10][11][12][13][19][20][21].…”

“…CRR-MZMs can be used to mitigate this problem, in which a number of RRs are cascaded and loaded in the interferometer as phase modulators [8,10]. For a given change in the refractive index in the waveguide, it is possible to obtain a large response by increasing the Q value of the RRs and also by increasing the number of cascaded RRs.…”

“…Therefore, it is expected that CRR-MZMs provide sufficient intensity modulation while maintaining wide modulation bandwidths by using CRRs with relatively low Q, and thus short lifetime. For CRR-MZMs, while performances have been reported emphasizing the modulation enhancement and optical bandwidth [10], the characteristics and limitations for high-speed operations have not yet been theoretically or experimentally investigated.…”