The efficiency of optical sideband generation with a microring resonator modulator as a function of modulator parameters is studied taking into account the photon dynamics inside the resonator. The best achievable modulation efficiency is determined for any choice of the resonator intrinsic quality factor, and analytic solutions for the optimum modulator parameters, namely the coupling coefficient and the detuning between the frequencies of the input laser light and the microring resonance, are provided. This analysis is carried out both for a narrowband RF signal, in which case the modulator is optimized for the center frequency of this signal, and for wideband signals, when high conversion efficiency over a wide range of RF frequencies is desired. The obtained results are expected to be useful coherent optical links, direct detection RF receivers, and optical wavelength converters.
We propose a triply-resonant electro-optic modulator architecture which maximizes modulation efficiency using simultaneous resonant enhancement of the RF drive signal, the optical pump, and the generated optical sideband. Optical enhancement of the optical pump and the sideband is achieved using resonant supermodes of two coupled optical resonators, and the RF enhancement is achieved with LC circuits formed by the capacitances of the optical resonators and inductors which can be implemented using CMOS technology. In the proposed configuration, the photon lifetime determines the bandwidth of the RF response but not its center frequency, which is set by the coupling strength between the two resonators and is not subject to the photon lifetime constraint inherent to conventional single-mode resonant modulators. This enables efficient operation at high RF carrier frequencies without a reduction in efficiency commonly associated with the photon lifetime limit. Two optical configurations of the modulator are proposed: a "basic" configuration with equal Q-factors in both supermodes, most suitable for narrowband RF signals, and a "generalized" configuration with independently tailored Qfactors of the two supermodes, which makes it possible to broaden the RF bandwidth without sacrificing the resonant enhancement of the optical pump and paying a penalty in modulation efficiency associated with doing so. Additionally, a significant gain in modulation efficiency is expected from RF signal enhancement by LC resonant matching. This results in a modulator which is compact, efficient, and capable of modulation at high RF carrier frequencies. The proposed modulator architecture optimally engineers the interaction of the device with each of the three signals and between them, can be applied to any modulator cavity design or modulation mechanism and promises to enable complex RF-photonic systems on chip. arXiv:1901.00071v1 [physics.optics]
We demonstrate ring and racetrack resonators with
Q
s of 3.8 to 7.5 million and 100 MHz bandwidth racetrack resonator filters, implemented in a thick silicon-on-insulator foundry platform that features a 3 µm thick device layer. We show that special racetrack resonators (with weakly guiding straight sections that transition to strongly confining bends) implemented in this platform can be preferable to rings for applications such as integrated microwave–photonic signal processing that require filters with sub-GHz bandwidth, tens of GHz of free spectral range (FSR), and a compact footprint for dense system-on-chip integration. We demonstrate ring resonators with
7.5
×
10
6
intrinsic
Q
, but limited FSR of 5.1 GHz and a taxing footprint of
21
m
m
2
due to a large 2.6 mm bend-loss-limited radius. In comparison, we demonstrate two racetrack resonator designs with intrinsic
Q
s of
3.8
×
10
6
and
4.3
×
10
6
, larger respective FSRs of 11.6 GHz and 7.9 GHz, and less than
1
/
20
t
h
the area of the ring resonator. Using racetrack resonators, we implemented a four-channel, 100 MHz wide passband filter bank with 4.2 to 5.4 dB insertion loss to drop ports.
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