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1. 100  GHz bandwidth, 1 volt integrated electro-optic Mach–Zehnder modulator at near-IR wavelengths

   https://doi.org/10.1364/OPTICA.484549  

   Valdez, Forrest ; Mere, Viphretuo ; Mookherjea, Shayan ( May 2023 , Optica)

   Integrated photonics at near-IR (NIR) wavelengths currently lacks high bandwidth and low-voltage modulators, which add electro-optic functionality to passive circuits. Here, integrated hybrid thin-film lithium niobate (TFLN) electro-optic Mach–Zehnder modulators (MZM) are shown, using TFLN bonded to planarized silicon nitride waveguides. The design does not require TFLN etching or patterning. The push–pull MZM achieves a half-wave voltage length product (V_πL) of 0.8 V.cm at 784 nm. MZM devices with 0.4 cm and 0.8 cm modulation length show a broadband electro-optic response with a 3 dB bandwidth beyond 100 GHz, with the latter showing a record bandwidth to half-wave voltage ratio of 100 GHz/V and a high extinction ratio exceeding 30 dB. Such fully integrated high-performance NIR electro-optic devices may benefit data communications, analog signal processing, test and measurement instrumentation, quantum information processing and other applications.

    

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2. 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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3. Y-type hexagonal ferrite-based band-pass filter with dual magnetic and electric field tunability

   https://doi.org/10.1038/s41598-023-28279-8  

   Popov, Maksym ; Xiong, Yuzan ; Zavislyak, Igor ; Chumak, Hryhorii ; Fedorchuk, Oleksandr ; Saha, Sujoy ; Bidthanapally, Rao ; Qu, Hongwei ; Page, Michael R. ; Srinivasan, Gopalan ( January 2023 , Scientific Reports)

   This work is on the design, fabrication and characterization of a hexagonal ferrite band-pass filter that can be tuned either with a magnetic field or an electric field. The filter operation is based on a straight-edge Y-type hexagonal ferrite resonator symmetrically coupled to the input and output microstrip transmission lines. The Zn₂Yfilter demonstrated magnetic field tunability in the 8–12 GHz frequency range by applying an in-plane bias magnetic fieldH₀provided by a built-in permanent magnet. The insertion loss and 3 dB bandwidth within this band were 8.6 ± 0.4 dB and 350 ± 40 MHz, respectively. The electric fieldEtunability of the pass-band of the device was facilitated by the nonlinear magnetoelectric effect (NLME) in the ferrite. TheE-tuning of the center frequency of the filter by (1150 ± 90) MHz was obtained for an input DC electric power of 200 mW. With efforts directed at a significant reduction in the insertion loss, the compact and power efficient magnetic and electric field tunable Zn₂Y band-pass filter has the potential for use in novel reconfigurable RF/microwave devices and communication systems.

    

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4. Ultra-low-power nonvolatile integrated photonic switches and modulators based on nanogap-enhanced phase-change waveguides

   https://doi.org/10.1364/OE.411254  

   Zhang, Jieying ; Zheng, Jiajiu ; Xu, Peipeng ; Wang, Yanqun ; Majumdar, Arka ( November 2020 , Optics Express)

   We propose a nanogap-enhanced phase-change waveguide with silicon PIN heaters. Thanks to the enhanced light-matter interaction in the nanogap, the proposed structure exhibits strong attenuation (Δα = ∼35 dB/µm) and optical phase (Δn_eff = ∼1.2) modulation atλ = 1550 nm when achieving complete phase transitions. We further investigate two active optical devices based on the proposed waveguide, including an electro-absorption modulator and a 1 × 2 directional-coupler optical switch. Finite-difference time-domain simulation of the proposed modulator shows a high extinction ratio of ∼17 dB at 1550 nm with an active segment of volume only ∼0.004λ³. By exploiting a directional coupler design, we present a 1 × 2 optical switch with an insertion loss of < 4 dB and a compact coupling length of ∼ 15 µm while maintaining small crosstalk less than −7.2 dB over an optical bandwidth of 50 nm. Thermal analysis shows that a 10 V pulse of 30 ns (1×1 modulator) and 55 ns (1×2 switch) in duration is required to raise the GST temperature of the phase-change waveguide above the melting temperature to induce the amorphization; however, the complete crystallization occurs by applying a 5 V pulse of 180 ns (1×1 modulator) and a 6 V pulse of 200 ns (1×2 switch), respectively.

    

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5. A MIMO Monopole Antenna for Harsh Conditions

   https://doi.org/10.1109/USNC-URSI52151.2023.10238318  

   Mertvyy, Aleks ; Razumovskiy, Elesey ; Stelmakh, Daniel ; Karacolak, Tutku ( July 2023 , IEEE)

   In this paper, a Multi-Input Multi-Output (MIMO) antenna of 4 monopole elements is presented on Zirconia Ribbon Ceramic (ZRC) substrate. Utilization of this substrate material allows an implementation of an antenna system that is able to withstand harsh environments and high temperatures due to inherent substrate characteristics. The proposed MIMO design supports an operational antenna bandwidth from 2.44 GHz to 2.55 GHz with a center frequency around 2.5 GHz covered by all 4 antenna elements. High antenna isolation below -15 dB is obtained among the ports. The antenna also provides a peak gain over 3 dB through the entire band of interest (3.34 dB at 2.5 GHz) and low cross-polarization. 

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