Invited Article: Electrically tunable silicon-based on-chip microdisk resonator for integrated microwave photonic applications

Abstract

Silicon photonics with advantages of small footprint, compatibility with the mature CMOS fabrication technology, and its potential for seamless integration with electronics is making a significant difference in realizing on-chip integration of photonic systems. A microdisk resonator (MDR) with a strong capacity in trapping and storing photons is a versatile element in photonic integrated circuits. Thanks to the large index contrast, a silicon-based MDR with an ultra-compact footprint has a great potential for large-scale and high-density integrations. However, the existence of multiple whispering gallery modes (WGMs) and resonance splitting in an MDR imposes inherent limitations on its widespread applications. In addition, the waveguide structure of an MDR is incompatible with that of a lateral PN junction, which leads to the deprivation of its electrical tunability. To circumvent these limitations, in this paper we propose a novel design of a silicon-based MDR by introducing a specifically designed slab waveguide to surround the disk and the lateral sides of the bus waveguide to suppress higher-order WGMs and to support the incorporation of a lateral PN junction for electrical tunability. An MDR based on the proposed design is fabricated and its optical performance is evaluated. The fabricated MDR exhibits single-mode operation with a free spectral range of 28.85 nm. Its electrical tunability is also demonstrated and an electro-optic frequency response with a 3-dB modulation bandwidth of ∼30.5 GHz is measured. The use of the fabricated MDR for the implementation of an electrically tunable optical delay-line and a tunable fractional-order temporal photonic differentiator is demonstrated.

Analog Coherent-Optical Mobile Fronthaul With Integrated Photonic Beamforming

“…Continuous delay settings can also be obtained using bulk optical assemblies that build on a tunable path delay through internal reflection mechanisms [11,17] or spatial light modulators that enable arbitrary phase shifts [16]. Alternatively, highly compact elements that offer a tunable group delay at resonance, such as micro resonators [31][32][33][34][35][36][37] or waveguide gratings [38][39][40] can be directly implemented in InP, SiN or silicon-on-insulator based integrated circuits. A combination of switched binary delays and a smaller continuous delay element enables larger delays of up to 1.8 ns [32].…”

Recent Trends and Advances of Silicon-Based Integrated Microwave Photonics

“…TTDLs provide a unique solution for broadband signal processing, such as tunable high-resolution microwave filters [89,90], beam forming in phased array antennas [91,92] etc. We review here three different implementations reported in the literature recently: a PN junction loaded microdisk cavity offering electrical tunability of group delay although suffering from lower bandwidth [93], an interesting demonstration involving subwavelength grating (SWG) waveguide which does not suffer from bandwidth limitations [94], and finally, a continuously tunable delay line using a cascade of switches and dual rings [95]. Moreover, we also review a 1 × 4 beam steering system for phased array antennas (PAA) using 1-D grating waveguides based TTDLs [96].…”

“…A microdisk resonator (MDR) based electrically tunable delay line in SOI was demonstrated in [93], as depicted in Figure 8a. A MDR exhibits better performance in terms of footprint and light confinement factors compared to conventional micro ring resonators.…”

“…Moreover, we also review a 1 × 4 beam steering system for phased array antennas (PAA) using 1-D grating waveguides based TTDLs [96]. A microdisk resonator (MDR) based electrically tunable delay line in SOI was demonstrated in [93], as depicted in Figure 8a. A MDR exhibits better performance in terms of footprint and light confinement factors compared to conventional micro ring resonators.…”

Split-disk micro-lasers: Tunable whispering gallery mode cavities

“…16 For semiconductor devices, additionally an injection of free-carriers can be applied to alter the refractive index. 15,23,24 While tuning based on the electro-optical effect and free-carrier dispersion effect can be realized at high speed, the tuning range is rather small. Conversely, thermal tuning operates with low or moderate speed, but typically possesses larger tuning ranges.…”