Resolving the thermal challenges for silicon microring resonator devices

Abstract

Silicon microring resonators have been hailed for their potential use in next-generation optical interconnects. However, the functionality of silicon microring based devices suffer from susceptibility to thermal fluctuations that is often overlooked in their demonstrated results, but must be resolved for their future implementation in microelectronic applications. We survey the emerging efforts that have been put forth to resolve these thermal susceptibilities and provide a comprehensive discussion of their advantages and disadvantages.Keywords: integrated photonics; microring resonators; optical interconnects; silicon photonics. The growing bandwidth needs within data applications have motivated the replacement of traditionally electronic links with optical links for information networks as diverse as data centers, supercomputers, and fiber-optic access networks [1,2]. Applications such as these stress the traditional portfolio of optical components, rebalancing the emphasis from expensive high-performance components towards low-cost high-volume components that can be closely integrated with electronics. With these considerations in mind, the silicon photonics platform has received wide attention for its ability to deliver the necessary bandwidth required at an economy-of-scale that will be enabled by its compatibility with CMOS fabrication processes [3].Within the silicon photonic platform, traditional optical components such as low-loss waveguides [4], lowloss waveguide crossings [5], high-speed mach-zhender modulators (MZM) [6], arrayed waveguide-gratings [7], and efficient photodetectors [8,9] have been demonstrated. Leveraging the high index contrast between silicon and silicon-on-insulator, the aforementioned components have been shown with much smaller footprints than their counterparts in more conventional optical platforms. For active devices, these smaller footprints directly translate to higher energy-efficiencies.In addition to providing these improvements in footprint and energy-efficiency for traditional devices, the high-index contrast present in the silicon photonic platform enables the effective use of microring-based devices. A microring is a traveling wave resonator consisting of a ring structure side-coupled to a bus waveguide. While they have also been demonstrated in other material platforms, the high-index contrast of silicon and silicon-oninsulator has allowed them to be manifested as small as 1.5 µm in radius [10], and when used in conjunction with the free-carrier dispersion effect [11], well into Ghz-rate bandwidth. Figure 1A illustrates the optical resonance of the microring and its shift with applied electrical bias [12]. In their most basic capacity they can serve as effective filters [13], switches [14,15], and modulators [16,17]. Additionally, microrings can be cascaded along the same waveguide bus, with each microring being offset to provide functionality for a specific wavelength. In this manner, the microring lends itself naturally for wavelength-divisionmultiplexed ...

Fast wavelength locking of a microring resonator

“…The 100 kHz dithering signal is chosen to minimize the latency of the feedback system while maintaining SNR at the output of the mixer. A convenient way to represent thermal bandwidth is using the thermal time constant, which we measure to be 7 µs for the microring, consistent with other devices found in the literature [5].…”

Capacitive actuation and switching of add–drop graphene-silicon micro-ring filters

“…In particular, switching is achieved by exploiting the thermo-optic effect by means of metallic or Si-based Joule heaters integrated in close proximity of the MRR waveguide. Although the thermo-optic effect is very efficient in silicon, the thermo-optic actuation requires continuous power consumption that can easily sum to some milliwatts [4]. In a complex switching matrix with tens or more MRRs, this power consumption can be detrimental.…”

Athermal silicon optical add-drop multiplexers based on thermo-optic coefficient tuning of sol-gel material

“…There have been a number of efforts to achieve temperature independent silicon photonic devices by using both active and passive thermal compensation methods [7]. The active approach comprises the use of external-heaters or thermo-electric coolers-or integrated heaters and various monitoring mechanisms connected to feedback systems [8][9][10][11].…”