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1. GaN-based Mach-Zehnder Modulators for Highly Efficient Optical Modulation and Switching Applications

   Su, Patrick; Carlson, John; Dallesasse, John (September 2018, SRC TECHCON)

   The recent development of 8-in Gallium Nitride on Silicon (GaN-on-Si) wafers has facilitated cost effective, large-scale manufacturability of GaN-based electronics. Leveraging its wide band gap, capability to support a two dimensional electron gas (2DEG) layer, and strong built-in polarization effects, GaN-based electronic devices have become a viable cost-effective successor to silicon-based devices for high-performance applications where the large bandgap and high breakdown field are required. The advantageous properties of GaN-on-Si material, however, have yet to be utilized for photonic integrated circuit applications. Therefore, the exploration of GaN for efficient on-chip optical modulation and switching applications is examined. In order to effectively characterize GaN’s capabilities for optical modulation and switching, GaN based Mach-Zehnder modulators are designed and fabricated. Through simulating the propagating optical modes supported in a GaN-based Mach-Zehnder structure, the geometry of the device is designed to optimize optical modal overlap with the 2DEG layer while maintaining single-mode performance. Through electrical and optical characterization, the effective electro-optic coefficient and Vπ length are measured. These measurements provide a method of benchmarking GaN-based photonic devices for their optical modulation and switching efficiency. 

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2. High-speed programmable photonic circuits in a cryogenically compatible, visible–near-infrared 200 mm CMOS architecture

   https://doi.org/10.1038/s41566-021-00903-x  

   Dong, Mark; Clark, Genevieve; Leenheer, Andrew J.; Zimmermann, Matthew; Dominguez, Daniel; Menssen, Adrian J.; Heim, David; Gilbert, Gerald; Englund, Dirk; Eichenfield, Matt (December 2021, Nature Photonics)

   Abstract Recent advances in photonic integrated circuits have enabled a new generation of programmable Mach–Zehnder meshes (MZMs) realized by using cascaded Mach–Zehnder interferometers capable of universal linear-optical transformations onNinput/output optical modes. MZMs serve critical functions in photonic quantum information processing, quantum-enhanced sensor networks, machine learning and other applications. However, MZM implementations reported to date rely on thermo-optic phase shifters, which limit applications due to slow response times and high power consumption. Here we introduce a large-scale MZM platform made in a 200 mm complementary metal–oxide–semiconductor foundry, which uses aluminium nitride piezo-optomechanical actuators coupled to silicon nitride waveguides, enabling low-loss propagation with phase modulation at greater than 100 MHz in the visible–near-infrared wavelengths. Moreover, the vanishingly low hold-power consumption of the piezo-actuators enables these photonic integrated circuits to operate at cryogenic temperatures, paving the way for a fully integrated device architecture for a range of quantum applications. 

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3. Deterministic quasi-continuous tuning of phase-change material integrated on a high-volume 300-mm silicon photonics platform

   https://doi.org/10.1038/s44310-024-00009-6  

   Chen, Rui; Tara, Virat; Choi, Minho; Dutta, Jayita; Sim, Justin; Ye, Julian; Fang, Zhuoran; Zheng, Jiajiu; Majumdar, Arka (December 2024, npj Nanophotonics)

   Abstract Programmable photonic integrated circuits (PICs) consisting of reconfigurable on-chip optical components have been creating new paradigms in various applications, such as integrated spectroscopy, multi-purpose microwave photonics, and optical information processing. Among many reconfiguration mechanisms, non-volatile chalcogenide phase-change materials (PCMs) exhibit a promising approach to the future very-large-scale programmable PICs, thanks to their zero static power and large optical index modulation, leading to extremely low energy consumption and ultra-compact footprints. However, the scalability of the current PCM-based programmable PICs is still limited since they are not directly off-the-shelf in commercial photonic foundries now. Here, we demonstrate a scalable platform harnessing the mature and reliable 300 mm silicon photonic fab, assisted by an in-house wide-bandgap PCM (Sb₂S₃) integration process. We show various non-volatile programmable devices, including micro-ring resonators, Mach-Zehnder interferometers and asymmetric directional couplers, with low loss (~0.0044 dB/µm), large phase shift (~0.012 π/µm) and high endurance (>5000 switching events with little performance degradation). Moreover, we showcase this platform’s capability of handling relatively complex structures such as multiple PIN diode heaters in devices, each independently controlling an Sb₂S₃segment. By reliably setting the Sb₂S₃segments to fully amorphous or crystalline state, we achieved deterministic multilevel operation. An asymmetric directional coupler with two unequal-length Sb₂S₃segments showed the capability of four-level switching, beyond cross-and-bar binary states. We further showed unbalanced Mach-Zehnder interferometers with equal-length and unequal-length Sb₂S₃segments, exhibiting reversible switching and a maximum of 5 ($$N+1,N=4$$ $N+1,N=4$) and 8 ($${2}^{N},N=3$$ $2^N,N=3$) equally spaced operation levels, respectively. This work lays the foundation for future programmable very-large-scale PICs with deterministic programmability. 

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4. A 22nm CMOS 15-25GHz Dual-Differential Driver for RF Silicon Photonic Front-End

   Luo, Y; Paladugu, D; Madsen, C; Entesari, K; Palermo, S (June 2025, IEEE MTT-S International Microwave Symposium)

   An RF photonic front-end using dual-differential driving scheme is reported with a 22nm CMOS FD-SOI driver co-integrated with a silicon traveling-wave Mach-Zehnder modulator. A compact design of power splitter and output routing network are implemented on dual-differential driver. An LC input matching network co-designed with bond wire inductance is implemented on a photonic chip to complete the output matching network. The proposed driver is verified with S-parameter and two-tone measurements, achieving 15-25GHz bandwidth with peak 3dBm IIP3 and consumes 448mW. The link performance is demonstrated 12.1% EVM of 16-QAM modulation with 2Gbd at 20GHz carrier frequency. 

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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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