Xiaoge Zeng

Ultra-low-loss CMOS-compatible waveguide crossing arrays based on multimode Bloch waves and imaginary coupling

We experimentally demonstrate broadband waveguide crossing arrays showing ultralow loss of 0.0 4dB/crossing (0.9%) on average and converging to 0.033 dB/crossing (0.075%) matching theory and cross-talk suppression over 35 dB in a CMOS-compatible geometry. The principle of operation is the tailored excitation of a low-loss spatial Bloch wave formed by matching the periodicity of the crossing array to the difference in propagation constants of the first- and third-order TE-like modes of a multimode silicon waveguide. Radiative scattering at the crossing points acts like a periodic imaginary-permittivity perturbation that couples two supermodes, which results in imaginary (radiative) propagation-constant splitting and gives rise to a low-loss, unidirectional breathing Bloch wave. This type of crossing array provides a robust implementation of a key component enabling dense photonic integration.

Quantum-correlated photon pairs generated in a commercial 45 nm complementary metal-oxide semiconductor microelectronic chip

Correlated photon pairs are a fundamental building block of quantum photonic systems. While pair sources have previously been integrated on silicon chips built using customized photonics manufacturing processes, these often take advantage of only a small fraction of the established techniques for microelectronics fabrication and have yet to be integrated in a process which also supports electronics. Here we report the first demonstration of quantum-correlated photon pair generation in a device fabricated in an unmodified advanced (sub-100nm) complementary metal-oxide-semiconductor (CMOS) process, alongside millions of working transistors. The microring resonator photon pair source is formed in the transistor layer structure, with the resonator core formed by the silicon layer typically used for the transistor body. With ultra-low continuous-wave on-chip pump powers ranging from 5

Tunable coupled-mode dispersion compensation and its application to on-chip resonant four-wave mixing

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Photonic Crystal Microcavities in a Microelectronics 45-nm SOI CMOS Technology

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Channel add–drop filter based on dual photonic crystal cavities in push–pull mode

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Ultra-low-loss Waveguide Crossing Arrays Based on Imaginary Coupling of Multimode Bloch Waves

W, we demonstrate pair generation rates between 165 Hz and 332 kHz using >80% efficient WSi superconducting nanowire single photon detectors. Coincidences-to-accidentals ratios consistently exceeding 40 were measured with a maximum of 55. In the process of characterizing this source we also accurately predict pair generation rates from the results of classical four-wave mixing measurements. This proof-of-principle device demonstrates the potential of commercial CMOS microelectronics as an advanced quantum photonics platform with capability of large volume, pristine process control, and where state-of-the-art high-speed digital circuits could interact with quantum photonic circuits.

Wavelength conversion in modulated coupled-resonator systems and their design via an equivalent linear filter representation

We propose and demonstrate mode coupling as a viable dispersion compensation technique for phase-matched resonant four-wave mixing (FWM). We demonstrate a dual-cavity resonant structure that employs coupling-induced frequency splitting at one of three resonances to compensate for cavity dispersion, enabling phase matching. Coupling strength is controlled by thermal tuning of one cavity enabling active tuning of the resonant frequency matching. In a fabricated silicon microresonator, we show an 8 dB enhancement of seeded FWM efficiency over the noncompensated state. The measured FWM has a peak wavelength conversion efficiency of -37.9  dB across a free spectral range (FSR) of 3.334 THz (∼27  nm), which is, to the best of our knowledge, the largest in a silicon microresonator to demonstrate FWM to date. This form of dispersion compensation can be beneficial for many devices, including wavelength converters, parametric amplifiers, and widely detuned photon-pair sources. Apart from compensating dispersion, the proposed mechanism can alternatively be utilized in an otherwise dispersionless resonator to counteract the detuning effect of self- and cross-phase modulation on the pump resonance during FWM, thereby addressing a fundamental issue in the performance of light sources such as broadband optical frequency combs.

Microphotonic Channel Add-Drop Filter Based on Dual Photonic Crystal Cavity System in Push-Pull Mode

We demonstrate the first monolithically integrated linear photonic crystal microcavities in an advanced silicon-on-insulator complementary metal-oxide-semiconductor microelectronics process (IBM 45nm 12SOI) with no in-foundry process modifications and a single postprocessing step. The cavities were integrated into a standard microelectronics design flow meeting process design rules, and fabricated alongside transistors native to the process. We demonstrate both 1520- and 1180-nm wavelength cavity designs using different cavity implementations due to design rule constraints. For the 1520- and 1180-nm designs, loaded quality factors of 2000 and 4000 are measured, and intrinsic quality factors of 100 000 and 60 000 are extracted. We also demonstrate an evanescent coupling geometry that decouples the cavity and waveguide-coupling design.

High-Q Contacted Ring Microcavities with Scatterer-Avoiding “Wiggler” Supermode Fields

We demonstrate an add-drop filter based on a dual photonic crystal nanobeam cavity system that emulates the operation of a traveling wave resonator, and, thus, provides separation of the through and drop port transmission from the input port. The device is on a 3×3  mm chip fabricated in an advanced microelectronics silicon-on-insulator complementary metal-oxide semiconductor (SOI CMOS) process (IBM 45 nm SOI) without any foundry process modifications. The filter shows 1 dB of insertion loss in the drop port with a 3 dB bandwidth of 64 GHz, and 16 dB extinction in the through port. To the best of our knowledge, this is the first implementation of a port-separating, add-drop filter based on standing wave cavities coupled to conventional waveguides, and demonstrates a performance that suggests potential for photonic crystal devices within optical immersion lithography-based advanced CMOS electronics-photonics integration.

Linear Photonic Crystal Microcavities in Zero-Change SOI CMOS

We experimentally demonstrate ultra-low-loss waveguide crossing arrays showing loss down to 0.04dB/crossing. They rely on a low loss, focusing Bloch wave that is stabilized by radiative scattering, via a radiative form of coupling.