DTA

Dottorato

CAMPONESCHI, FEDERICO

etd-09292024-234845

Hybrid and Heterogeneous Photonic Integrated Circuits for Radar and Remote Sensing Applications

ING-INF/01

Istituto di Tecnologie della Comunicazione, dell'Informazione e della Percezione - PHD IN EMERGING DIGITAL TECHNOLOGIES

relatore BOGONI, ANTONELLA
Presidente Prof. ESPOSITO, FLAVIO
Membro Dott. PEDRO, JOAO

• microwave photonics
• photonic integrated circuits
• radar
• beamforming
• hybrid integration
• heterogeneous integration

06/11/2024;

completa

Microwave Photonics (MWP) is an interdisciplinary field that leverages photonic technologies<br>to address complex functions in microwave systems, offering advantages such as low-loss<br>signal distribution, wide bandwidth, and immunity to electromagnetic interference. MWP<br>finds applications in areas like photonic microwave generation, optically controlled phased<br>array antennas, and radio-over-fiber systems. Photonics-based radar systems, in particular,<br>greatly benefit from these advantages, enabling low phase noise, ultra-wide bandwidth, and<br>flexible signal generation. This dissertation explores the integration of photonic technologies<br>to enhance the performance of radar and remote sensing systems. Due to the inherent<br>complexity of MWP systems and the limitations of current monolithic platforms, this work<br>investigates innovative multi-platform integration techniques to develop fully integrated systems<br>with advanced functionalities. The first chapters holds the theory behind MWP systems<br>and the state-of-the-art of photonics for radar and remote sensing systems and of the main<br>Photonic Integrated Circuit (PIC) platforms and multi-platform integration techniques. Then,<br>the research activities are organized into several chapters, each focusing on systems that use<br>different integration methods.<br>Chapter 2 focuses on monolithic platforms and details the development of an RF receiver with<br>down-conversion capability for electronically scanned active array antenna systems using Silicon-<br>on-Insulator (SOI) technology. Two packaged architectures, both relying on an external Mode-<br>Locked Laser (MLL), are developed. The first architecture consists of a cascade of a Mach-<br>Zehnder Modulator (MZM) and a Balanced Photodetector (BPD), achieving 48 dB of RF-to-IF<br>conversion gain, in line with previous implementations in SOI, and an Spurious Free Dynamic<br>Range (SFDR) of 94 dB · Hz2/3. The second architecture employs two very narrow-band optical<br>filters to select the MLL lines, eliminating the need for electrical filtering after photodetection.<br>Its very limited conversion gain emphasizes the need for active materials to provide on-chip<br>amplification.<br>The subsequent chapter delves into the butt-coupling approach for hybrid integration of<br>distinct platforms. Indium Phosphide (InP) and Silicon Nitride (SiN) chips are die-attached<br>to realize a multibeam beamformer for a Synthetic Aperture Radar (SAR) receiver and an<br>RF scanner for Electronic Support Measurement (ESM) systems. The former leverages the<br>Scan-on-Receive (SCORE) method to achieve precise and continuous beamforming-on-receive<br>of wideband signals from a 12-element antenna array, synthesizing up to three simultaneous<br>receiving beams. The Optical Beamforming Network (OBFN) implemented in low-loss SiN is a<br>Blass matrix. Experimental results demonstrate successful frequency down-conversion from X-<br>band at 9.65 GHz to a low intermediate frequency at 1.35 GHz with a measured conversion loss<br>of 50 dB. Furthermore, multi-beam beamforming operations of the PIC receiver module are, for<br>the first time, experimentally demonstrated through radiation diagrams showing beam steering at different pointing angles. Two distinct architectures implement a 6-channel RF scanner that<br>work up to 40 GHz. In one, frequency scanning is achieved using an electrical oscillator up-<br>converted in the optical domain, while the other relies on a tunable laser. For both architectures,<br>system simulations and PIC designs are presented. Additionally, preliminary device-level testing,<br>enabled by the hybrid approach, is reported for both the SiN and InP chips. The core of both<br>architectures are optical filters implemented as SiN microring resonator-assisted Mach-Zehnder<br>Interferometer (MZI), which show transmission bandwidth as low as 2 GHz, and record values<br>of Free Spectral Range (FSR) and out-of-band rejection of 36 GHz and 57 dB, respectively.<br>Next, the design and device-level characterization of an integrated frequency converter, enabled<br>by butt-coupling of InP and Lithium Niobate-on-Insulator (LNOI) chips, is presented. The<br>LNOI platform is attractive for its potential to implement low half-wave voltage (Vπ) and high<br>bandwidth MZMs, which are crucial for MWP systems. Measurements conducted on the LNOI<br>MZM show a modulation efficiency of 10 V/cm and a bandwidth of 23 GHz, though performance<br>is expected to consistently improve with new fabrication processes.<br>Chapter 4 explores the Micro-Transfer Printing (MTP) technique for heterogeneously integrating<br>InP Semiconductor Optical Amplifiers (SOAs) onto an SOI platform, resulting in the design of<br>a frequency converter for radar transceivers and a coherent Multiple-In-Multiple-Out (MIMO)<br>radar constellation. Device-level characterization of the printed SOAs shows a maximum on-chip<br>gain of 9 dB, which is relatively low compared to InP SOAs on native substrates. System-level<br>testing of the fully packaged frequency converter revealed a limited conversion gain due to<br>damage in the pig-tailed fiber array. However, considering the damage, a higher SOA gain,<br>and the addition of a Trans-Impedance Amplifier (TIA) to electrically amplify the output<br>photocurrent, the system could achieve a gain comparable to standard electronics. System<br>simulation and design of PIC for coherent MIMO SAR constellation is then reported. For this<br>application photonics allows for the flexible generation of multi-band signals and centralized<br>generation in a primary satellite with coherent distribution to all the secondary satellites of the<br>SAR signals over Free Space Optical (FSO) links. Moreover, the use of integrated technologies<br>enables Size Weight and Power Consumption (SWaP) reduction. Numerical analysis shows the proposed<br>system has a Noise Equivalent Sigma Zero (NESZ) &lt; -29.6 dB, satisfying the SAR system<br>requirements. MTP-SOAs on the consolidated SOI platform are intended to decrease the overall<br>conversion gain. Polarization multiplexing is used to consistently reduce system complexity.<br>Finally, measurements of heterogeneously integrated external cavity lasers, enabled by wafer<br>bonding of III-V materials onto SiN and LNOI platforms, are presented. The combination of<br>wafer bonding, which offers significantly low alignment tolerances and compatibility with high-<br>volume production, along with the low-loss properties of the SiN platform and the strong electro-<br>optic characteristics of the LNOI platform, makes these heterogeneous platforms extremely<br>promising for future MWP systems.<br>This research advances MWP systems for radar and remote sensing applications by utilizing<br>innovative integration methods. My primary contributions involved system simulations,<br>PIC design, and testing at both the device level (with bare PICs) and the system level<br>(with fully packaged PICs) to demonstrate system functionalities. Although the photonic<br>integrated platforms reported in this work exhibit specific limitations, multi-platform integration techniques, particularly heterogeneous ones, offer a promising direction for future developments<br>capable of meeting the demanding requirements of MWP systems.

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