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Electro-optic (EO) transduction of weak radio frequency (RF) and millimeter-wave signals, such as those received by an antenna, onto laser sidebands for processing in the optical domain requires efficient EO modulators. Microrings offer spatial density and efficiency advantages over Mach–Zehnder modulators (MZMs), but conventional single-ring modulators suffer a fundamental trade-off between resonantly enhanced conversion efficiency and the RF carrier frequency that it can accommodate. Dual-cavity “photonic molecule” modulators resolve this trade-off, allowing high efficiency independent of the RF carrier frequency by providing separate resonant supermodes to enhance the laser local oscillator (LO) and the narrowband RF-detuned sideband. However, the RF frequency is fixed at design time by geometry, with efficiency dropping quickly for RF carriers away from the design value. We propose a novel, to the best of our knowledge, triple-cavity configuration with an off-resonant middle ring acting as an effective tunable coupler between two active modulator cavities. This configuration provides wideband tunability of the target RF carrier while maintaining efficient sideband conversion. When the middle ring is passive (highQ), this configuration provides wide RF tunability with no efficiency penalty over the fixed dual-cavity case and could become an important building block for future RF/mm-wave photonic integrated circuits (PICs). 

We demonstrate a path to scalable, wavelength- multiplexed RF/mm-wave-photonic front-end systems-on-chip for radar and extreme massive MIMO arrays, in 300mm-foundry 45nm RF SOI CMOS. We demonstrate mm-wave-to-optical sensing elements comprising low-noise amplifiers (LNAs) mono- lithically integrated with triply-resonant photonic microring- resonator based modulators. The “photonic molecule” modulator concept breaks the conventional ring modulator conversion efficiency-bandwidth tradeoff and provides optimal performance RF-photonic applications, while supporting high bandwidth den- sities. We show a first experiment with projected noise figure of 24dB at 57GHz (30mW/element, -45dBm RF-input, 6dBm laser LO). The elements are tileable at small pitches, enabling photonic disaggregation of large-scale phased arrays. 

Convergence of high-performance silicon photonics and electronics, monolithically integrated in state-of-the-art CMOS platforms, is the holy grail for enabling the ultimate efficiencies, performance, and scaling of electronic-photonic systems-on-chip. It requires the emergence of platforms that combine state-of-the-art RF transistors with optimized silicon photonics, and a generation of photonic device technology with ultralow energies, increased operating spectrum, and the elimination of power-hungry thermal tuning. In this paper, in a co-optimized monolithic electronics-photonics platform (GlobalFoundries 45CLO), we turn the metal-oxide-semiconductor (MOS) field-effect transistor’s basic structure into a novel, highly efficient MOS capacitor ring modulator. It has the smallest ring cavity (1.5 μm radius), largest corresponding spur-free free spectral range ( FSR = 8.5    THz ), and record 30 GHz/V shift efficiency in the O-band among silicon modulators demonstrated to date. With 1 V pp RF drive, we show an open optical eye while electro-optically tuning the modulator to track over 400 pm (69 GHz) change in the laser wavelength (using 2.5 V DC range). A 90 GHz maximum electro-optic resonance shift is demonstrated with under 40 nW of power, providing a strong nonthermal tuning mechanism in a CMOS photonics platform. The modulator has a separately optimized body layer but shares the gate device layer and the gate oxide with 45 nm transistors, while meeting all CMOS manufacturability design rules. This type of convergent evolution of electronics and photonics may be the future of platforms for high-performance systems-on-chip. 

We report the first photonic crystal microcavity modulator realized in a foundry CMOS photonics platform. Bandwidth of 2.8 GHz and 5 Gbps data rate demonstrated utilizing an interdigitated p-n junction in a WDM compatible structure. 

We report on microring modulators in the new 45CLO photonics-optimized 45 nm electronic-photonic CMOS platform. Interdigitated disk and vertical-junction rib microring de- signs are demonstrated, with 20 GHz bandwidth at 25 Gbps data rate. 

We demonstrate a coupled-cavity electro-optic modulator with 5.5 GHz bandwidth centered at 41 GHz. The device, driven with a −5 dBm RF signal, shows −27 dB pump-to-sideband conversion efficiency, a 15 dB improvement over a regular ring modulator. 

We propose an on-chip triply resonant electro-optic modulator architecture for RF-to-optical signal conversion and provide a detailed theoretical analysis of the optimal “circuit-level” device geometries and their performance limits. The designs maximize the RF-optical conversion efficiency through simultaneous resonant enhancement of the RF drive signal, a continuous-wave (CW) optical pump, and the generated optical sideband. The optical pump and sideband are resonantly enhanced in respective supermodes of a two-coupled-cavity optical resonator system, while the RF signal can be enhanced in addition by an LC circuit formed by capacitances of the optical resonator active regions and (integrated) matching inductors. We show that such designs can offer 15-50 dB improvement in conversion efficiency over conventional microring modulators. In the proposed configurations, the photon lifetime (resonance linewidth) limits the instantaneous RF bandwidth of the electro-optic response but does not limit its central RF frequency. The latter is set by the coupling strength between the two coupled cavities and is not subject to the photon lifetime constraint inherent to conventional singly resonant microring modulators. This feature enables efficient operation at high RF carrier frequencies without a reduction in efficiency commonly associated with the photon lifetime limit and accounts for 10-30 dB of the total improvement. 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 supermode Q-factors that supports a wider instantaneous bandwidth. A second significant 5-20 dB gain in modulation efficiency is expected from RF drive signal enhancement by integrated LC resonant matching, leading to the total expected improvement of 15-50 dB. Previously studied triply-resonant modulators, with coupled longitudinal (across the free spectral range (FSR)) modes, have large resonant mode volume for typical RF frequencies, which limits the interaction between the optical and RF fields. In contrast, the proposed modulators support maximally tightly confined resonant modes, with strong coupling between the mode fields, which increases and maintains high device efficiency across a range of RF frequencies. The proposed modulator architecture is compact, efficient, capable of modulation at high RF carrier frequencies and can be applied to any cavity design or modulation mechanism. It is also well suited to moderate Q, including silicon, implementations, and may be enabling for future CMOS RF-electronic-photonic systems on chip. 

We experimentally demonstrate rapid adiabatic coupling (RAC), a novel design concept that harnesses the benefits and addresses the disadvantages of adiabatic photonic structures. The 31μm long 2x2 coupler shows 3±0.3dB splitting over 130nm bandwidth.