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1. Electro-optic spatial light modulator from an engineered organic layer

   https://doi.org/10.1038/s41467-021-26035-y  

   Benea-Chelmus, Ileana-Cristina ; Meretska, Maryna L. ; Elder, Delwin L. ; Tamagnone, Michele ; Dalton, Larry R. ; Capasso, Federico ( October 2021 , Nature Communications)

   Tailored nanostructures provide at-will control over the properties of light, with applications in imaging and spectroscopy. Active photonics can further open new avenues in remote monitoring, virtual or augmented reality and time-resolved sensing. Nanomaterials withχ⁽²⁾nonlinearities achieve highest switching speeds. Current demonstrations typically require a trade-off: they either rely on traditionalχ⁽²⁾materials, which have low non-linearities, or on application-specific quantum well heterostructures that exhibit a highχ⁽²⁾in a narrow band. Here, we show that a thin film of organic electro-optic molecules JRD1 in polymethylmethacrylate combines desired merits for active free-space optics: broadband record-high nonlinearity (10-100 times higher than traditional materials at wavelengths 1100-1600 nm), a custom-tailored nonlinear tensor at the nanoscale, and engineered optical and electronic responses. We demonstrate a tuning of optical resonances by Δλ = 11 nm at DC voltages and a modulation of the transmitted intensity up to 40%, at speeds up to 50 MHz. We realize 2 × 2 single- and 1 × 5 multi-color spatial light modulators. We demonstrate their potential for imaging and remote sensing. The compatibility with compact laser diodes, the achieved millimeter size and the low power consumption are further key features for laser ranging or reconfigurable optics.

    

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2. Silicon nitride stress-optic microresonator modulator for optical control applications

   https://doi.org/10.1364/OE.467721  

   Wang, Jiawei ; Liu, Kaikai ; Harrington, Mark W. ; Rudy, Ryan Q. ; Blumenthal, Daniel J. ( August 2022 , Optics Express)

   Modulation-based control and locking of lasers, filters and other photonic components is a ubiquitous function across many applications that span the visible to infrared (IR), including atomic, molecular and optical (AMO), quantum sciences, fiber communications, metrology, and microwave photonics. Today, modulators used to realize these control functions consist of high-power bulk-optic components for tuning, sideband modulation, and phase and frequency shifting, while providing low optical insertion loss and operation from DC to 10s of MHz. In order to reduce the size, weight and cost of these applications and improve their scalability and reliability, modulation control functions need to be implemented in a low loss, wafer-scale CMOS-compatible photonic integration platform. The silicon nitride integration platform has been successful at realizing extremely low waveguide losses across the visible to infrared and components including high performance lasers, filters, resonators, stabilization cavities, and optical frequency combs. Yet, progress towards implementing low loss, low power modulators in the silicon nitride platform, while maintaining wafer-scale process compatibility has been limited. Here we report a significant advance in integration of a piezo-electric (PZT, lead zirconate titanate) actuated micro-ring modulation in a fully-planar, wafer-scale silicon nitride platform, that maintains low optical loss (0.03 dB/cm in a 625 µm resonator) at 1550 nm, with an order of magnitude increase in bandwidth (DC - 15 MHz 3-dB and DC - 25 MHz 6-dB) and order of magnitude lower power consumption of 20 nW improvement over prior PZT modulators. The modulator provides a >14 dB extinction ratio (ER) and 7.1 million quality-factor (Q) over the entire 4 GHz tuning range, a tuning efficiency of 162 MHz/V, and delivers the linearity required for control applications with 65.1 dB·Hz^2/3and 73.8 dB·Hz^2/3third-order intermodulation distortion (IMD3) spurious free dynamic range (SFDR) at 1 MHz and 10 MHz respectively. We demonstrate two control applications, laser stabilization in a Pound-Drever Hall (PDH) lock loop, reducing laser frequency noise by 40 dB, and as a laser carrier tracking filter. This PZT modulator design can be extended to the visible in the ultra-low loss silicon nitride platform with minor waveguide design changes. This integration of PZT modulation in the ultra-low loss silicon nitride waveguide platform enables modulator control functions in a wide range of visible to IR applications such as atomic and molecular transition locking for cooling, trapping and probing, controllable optical frequency combs, low-power external cavity tunable lasers, quantum computers, sensors and communications, atomic clocks, and tunable ultra-low linewidth lasers and ultra-low phase noise microwave synthesizers.

    

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3. Engineered second-order nonlinearity in silicon nitride

   https://doi.org/10.1364/OME.478811  

   Zhang, Yi ; Nauriyal, Juniyali ; Song, Meiting ; Granados Baez, Marissa ; He, Xiaotong ; Macdonald, Timothy ; Cardenas, Jaime ( December 2022 , Optical Materials Express)

   The lack of a bulk second-order nonlinearity (χ⁽²⁾) in silicon nitride (Si₃N₄) keeps this low-loss, CMOS-compatible platform from key active functions such as Pockels electro-optic (EO) modulation and efficient second harmonic generation (SHG). We demonstrate a successful induction ofχ⁽²⁾in Si₃N₄through electrical poling with an externally-applied field to align the Si-N bonds. This alignment breaks the centrosymmetry of Si₃N₄, and enables the bulkχ⁽²⁾. The sample is heated to over 500°C to facilitate the poling. The comparison between the EO responses of poled and non-poled Si₃N₄, measured using a Si₃N₄micro-ring modulator, shows at least a 25X enhancement in ther₃₃EO component. The maximumχ⁽²⁾we obtain through poling is 0.30pm/V. We observe a remarkable improvement in the speed of the measured EO responses from 3 GHz to 15 GHz (3 dB bandwidth) after the poling, which confirms theχ⁽²⁾nature of the EO response induced by poling. This work paves the way for high-speed active functions on the Si₃N₄platform.

    

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4. Plasmonic and photonic isolators based on the spatiotemporal modulation of graphene

   https://doi.org/10.1117/12.2519237  

   Correas-Serrano, Diego ; Paul, Nayan ; Gomez-Diaz, J. Sebastian ( May 2019 , Micro- and Nanotechnology Sensors, Systems, and Applications XI, edited by Thomas George, M. Saif Islam, Proc. of SPIE)

   We explore the possibilities enabled by the spatiotemporal modulation of graphene’s conductivity to realize magnetic-free isolators at terahertz and infrared frequencies. To this purpose, graphene is loaded with periodically distributed gates that are time-modulated. First, we investigate plasmonic isolators based on various mechanisms such as symmetric bandgaps and interband photonic transitions and we demonstrate isolation levels over 30 dB using realistic biasing schemes. To lessen the dependence on high-quality graphene able to support surface plasmons with low damping, we then introduce a hybrid photonic platform based on spatiotemporally modulated graphene coupled to high-Q modes propagating on dielectric waveguides. We exploit transversal Fabry-Perot resonances appearing due to the finite-width of the waveguide to significantly boost graphene/waveguide interactions and to achieve isolation levels over 50 dB in compact structures modulated with low biasing voltages. The resulting platform is CMOS-compatible, exhibits an overall loss below 4 dB, and is robust against graphene imperfections. We also put forward a theoretical framework based on coupled-mode theory and on solving the eigenstates of the modulated structure that is in excellent agreement with full-wave numerical simulations, sheds light in the underlying physics that govern the proposed isolators, and speeds-up their analysis and design. We envision that the proposed technology will open new and efficient routes to realize integrated and silicon compatible isolators, with wide range of applications in communications and photonic networks. 

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5. Modular chip-integrated photonic control of artificial atoms in diamond waveguides

   https://doi.org/10.1364/OPTICA.486361  

   Palm, Kevin J. ; Dong, Mark ; Golter, D. Andrew ; Clark, Genevieve ; Zimmermann, Matthew ; Chen, Kevin C. ; Li, Linsen ; Menssen, Adrian ; Leenheer, Andrew J. ; Dominguez, Daniel ; et al ( May 2023 , Optica)

   A central goal in creating long-distance quantum networks and distributed quantum computing is the development of interconnected and individually controlled qubit nodes. Atom-like emitters in diamond have emerged as a leading system for optically networked quantum memories, motivating the development of visible-spectrum, multi-channel photonic integrated circuit (PIC) systems for scalable atom control. However, it has remained an open challenge to realize optical programmability with a qubit layer that can achieve high optical detection probability over many optical channels. Here, we address this problem by introducing a modular architecture of piezoelectrically actuated atom-control PICs (APICs) and artificial atoms embedded in diamond nanostructures designed for high-efficiency free-space collection. The high-speed four-channel APIC is based on a splitting tree mesh with triple-phase shifter Mach–Zehnder interferometers. This design simultaneously achieves optically broadband operation at visible wavelengths, high-fidelity switching (>40dB) at low voltages, submicrosecond modulation timescales (>30MHz), and minimal channel-to-channel crosstalk for repeatable optical pulse carving. Via a reconfigurable free-space interconnect, we use the APIC to address single silicon vacancy color centers in individual diamond waveguides with inverse tapered couplers, achieving efficient single photon detection probabilities (∼15%) and second-order autocorrelation measurementsg⁽²⁾(0)<0.14 for all channels. The modularity of this distributed APIC–quantum memory system simplifies the quantum control problem, potentially enabling further scaling to thousands of channels.

    

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