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High quality-factor (Q) optical resonators are a key component for ultra-narrow linewidth lasers, frequency stabilization, precision spectroscopy and quantum applications. Integration in a photonic waveguide platform is key to reducing cost, size, power and sensitivity to environmental disturbances. However, to date, the Q of all-waveguide resonators has been relegated to below 260 Million. Here, we report a Si3N4 resonator with 422 Million intrinsic and 3.4 Billion absorption-limited Qs. The resonator has 453 kHz intrinsic, 906 kHz loaded, and 57 kHz absorption-limited linewidths and the corresponding 0.060 dB m−1 loss is the lowest reported to date for waveguides with deposited oxide upper cladding. These results are achieved through a careful reduction of scattering and absorption losses that we simulate, quantify and correlate to measurements. This advancement in waveguide resonator technology paves the way to all-waveguide Billion Q cavities for applications including nonlinear optics, atomic clocks, quantum photonics and high-capacity fiber communications., Integrated photonic all-waveguide resonators are a critical component in many future applications. Here the authors develop an optimized photonic all-waveguide resonator with an ultra-high quality factor, Q, of almost half a billion, and a narrow sub-MHz linewidth.

Cherenkov detectors enable a valuable tool to identify high-energy particles. However, their sensitivity and momentum coverage are limited by the refractive index of host materials. Especially, identifying particles with energy above multiple gigaelectronvolts requires host materials with a near-unity refractive index, which are limited to bulky gas chambers. Overcoming this fundamental material limit is important for future particle detectors yet remains a long-standing challenge. Here, we propose a different paradigm for Cherenkov detectors that utilizes the broadband angular filter made from stacks of variable one-dimensional photonic crystals. Owing to the Brewster effect, the angular filter is transparent only to Cherenkov photons from a precise incident angle. Particle identification is achieved by mapping each Cherenkov angle to the peak-intensity position of transmitted photons in the detection plane. Such angular filtering effect, although decreases the photon number collected in the detection plane, enables the realization of a non-dispersive pseudo refractive index over the entire visible spectrum. Moreover, the pseudo refractive index can be flexibly designed to different values close to unity. Our angular-selective Brewster paradigm offers a feasible solution to implement compact and highly sensitive Cherenkov detectors especially in beam lines with a small angular divergence using regular dielectrics., Cherenkov detectors are used to detect high energy particles and their performance capabilities depend heavily on the material used. Here, the authors propose use of a Brewster-optics-based angular filter for a detector with increased sensitivity and particle identification capability.

Graphene integrated photonics provides several advantages over conventional Si photonics. Single layer graphene (SLG) enables fast, broadband, and energy-efficient electro-optic modulators, optical switches and photodetectors (GPDs), and is compatible with any optical waveguide. The last major barrier to SLG-based optical receivers lies in the low responsivity - electrical output per optical input - of GPDs compared to conventional PDs. Here we overcome this shortfall by integrating a photo-thermoelectric GPD with a Si microring resonator. Under critical coupling, we achieve $>$90% light absorption in a $\sim$6 $��$m SLG channel along the Si waveguide. Exploiting the cavity-enhanced light-matter interaction, causing carriers in SLG to reach $\sim$400 K for an input power of $\sim$0.6 mW, we get a voltage responsivity $\sim$90 V/W, demonstrating the feasibility of our approach. Our device is capable of detecting data rates up to 20 Gbit/s, with a receiver sensitivity enabling it to operate at a 10$^{-9}$ bit-error rate, on par with mature semiconductor technology. The natural generation of a voltage rather than a current, removes the need for transimpedance amplification, with a reduction of the energy-per-bit cost and foot-print, when compared to a traditional semiconductor-based receiver., 11 pages, 5 figures

The recent discovery of spin current transmission through antiferromagnetic insulating materials opens up vast opportunities for fundamental physics and spintronics applications. The question currently surrounding this topic is: whether and how could THz antiferromagnetic magnons mediate a GHz spin current? This mismatch of frequencies becomes particularly critical for the case of coherent ac spin current, raising the fundamental question of whether a GHz ac spin current can ever keep its coherence inside an antiferromagnetic insulator and so drive the spin precession of another ferromagnet layer coherently? Utilizing element- and time-resolved x-ray pump-probe measurements on Py/Ag/CoO/Ag/Fe75Co25/MgO(001) heterostructures, here we demonstrate that a coherent GHz ac spin current pumped by the Py ferromagnetic resonance can transmit coherently across an antiferromagnetic CoO insulating layer to drive a coherent spin precession of the Fe75Co25 layer. Further measurement results favor thermal magnons rather than evanescent spin waves as the mediator of the coherent ac spin current in CoO., The mechanism underpinning the frequency mismatch between THz magnons and the GHz spin currents observed in antiferromagnetic insulators remains unknown. Here, the authors demonstrate that, in a Py/Ag/CoO/Ag/Fe75Co25/MgO(001) heterostructure, a GHz spin current transmits coherently across the antiferromagnetic CoO insulating layer to drive a coherent spin precession of the ferromagnetic Fe75Co25 layer.