Milos A. Popovic

We correct a mathematical error in our previous work [ Opt. Lett. 49 , 3930 ( 2024 ) 10.1364/OL.528080 ]. The normalization factors in original Eqs. (2) and (3), as well as Figs. 5 (a) and (b) that are based on these equations, are corrected. The original discussions and conclusions are not affected.

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 (high Q), 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).

Emerging applications of photonic integrated circuits are calling for extremely narrowband and/or low-insertion-loss bandpass filters. Both properties are limited by cavity losses or intrinsic quality factors. However, the choice of inter-cavity and bus couplings establishes trade-offs between these two properties and the passband shape, which have been little explored. Using the widely used second-order resonant system as an example, we present new, to the best of our knowledge, classes of filter passband shapes that provide the lowest insertion loss and the narrowest bandwidth for a given loss Q. A normalized design and novel properties based on a temporal coupled-mode theory model are presented, including a design tool to apply these results. These results may benefit loss-sensitive filtering applications such as quantum-correlated photon pair sources and RF-photonic integrated circuits.

We report on the design, fabrication, and experimental characterization of photonic crystal (PhC) nanobeam cavities with the smallest footprint, largest intrinsic quality factor, and smallest mode volume to be demonstrated to date in a monolithic CMOS platform. Two types of cavities were designed, with opposite spatial mode symmetries. The opposite mode symmetry, combined with evanescent coupling, allows the nanobeam cavities to be used in reflectionless topologies, desirable in complex photonic integrated circuits (PICs). The devices were implemented and fabricated in a 45 nm monolithic electronics–photonics CMOS platform optimized for silicon photonics (GlobalFoundries 45CLO) and do not require any post-processing. Quality factors exceeding 100 000 were measured for both devices, the highest, to the best of our knowledge, among fully cladded PhC nanobeam cavities in any silicon-on-insulator (SOI) platform. Additionally, the ability of the cavities to confine light into small mode volumes, of the order of (λ/n)³, was confirmed experimentally using near-field scanning optical microscopy (NSOM). These types of cavities are an important step toward realizing ultra-low energy active devices required for the next generation of integrated optical links beyond the current microring resonator-based links and other CMOS PICs.

Optical phased arrays (OPAs) which beam-steer in two dimensions (2D) are currently limited to grating row spacings well above a half wavelength. This gives rise to grating lobes along one axis which limit the field of view (FOV), introduce return signal ambiguity, and reduce the optical efficiency in lidar applications. We demonstrate a Vernier transceiver scheme which uses paired transmit and receive phased arrays with different row periodicities, leading to mismatched grating lobe angular spacings and only a single aligned pair of transmit and receive lobes. This permits a return signal from a target in the desired lobe to be efficiently coupled back into the receive OPA while back-scatter from the other grating lobes is rejected, removing the ambiguity. Our proposal goes beyond previously considered Vernier schemes in other domains like RF and sound, to enable a dynamic Vernier where all beam directions are simultaneously Vernier aligned, and allow ultra-fast scanning, or multi-beam, operation with Vernier lobe suppression. We analyze two variants of grating lobe suppressing beam-steering configurations, one of which eliminates the FOV limitation, and find the conditions for optimal lobe suppression. We present the first, to the best of our knowledge, experimental demonstration of an OPA Vernier transceiver, including grating lobe suppression of 6.4 dB and beam steering across 5.5°. The demonstration is based on a pair of 2D-wavelength-steered serpentine OPAs. These results address the pervasive issue of grating lobes in integrated photonic lidar schemes, opening the way to larger FOVs and reduced complexity 2D beam-steering designs.

Grating coupler devices provide efficient, foundry-compatible vertical fiber-to-chip coupling solutions in integrated photonic platforms. However, standard grating coupler designs are highly polarization sensitive, which hinders their adoption. We present a new, to the best of our knowledge, type of 1D polarization-insensitive grating coupler (PIGC) that is based on a zero-birefringence subwavelength “corelet” waveguide. We demonstrate a PIGC for coupling in the telecommunications O-band in a 45-nm-node monolithic silicon-on-insulator (SOI) CMOS electronic-photonic platform, with measured insertion losses of 6.7 and 6.1 dB to transverse electric and transverse magnetic polarizations, respectively, and a ±1-dB polarization dependent loss bandwidth of 73 nm.

We demonstrate device field c haracterization u sing N SOM c ollection a nd in-teraction measurement modes via the backside buried-oxide of large scale photonic circuits fabricated in monolithic electronics-photonics CMOS platforms (here a microdisk resonator) post-processed using flip-chip substrate-removal.

We present a Si microring-based photon pair source design with tailored pump/signal/idler escape rates allowing configurable purity-rate-heralding tradeoffs, while maintaining efficiency through tunable dispersion compensation. We validate the subcompo-nents using stimulated FWM experiments.