Integrated lithium niobate photonic and acoustic microsystems for advanced optical communication and RF sensing applications

Ghoname, Amr O.

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https://hdl.handle.net/2142/129396 Copy

Description

Title

Integrated lithium niobate photonic and acoustic microsystems for advanced optical communication and RF sensing applications

Author(s)

Ghoname, Amr O.

Issue Date

2025-04-15

Director of Research (if dissertation) or Advisor (if thesis)

Gong, Songbin

Doctoral Committee Chair(s)

Gong, Songbin

Committee Member(s)

• Goddard, Lynford L
• Hanumolu, Pavan K
• Dragic, Peter D

Department of Study

Electrical & Computer Eng

Discipline

Electrical & Computer Engr

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Thin film lithium niobate
• Microwave photonics
• Electro-optic modulators
• Michelson interferometer modulator
• Waveguide Bragg grating
• Linearized modulators
• RF acoustics
• Passive wireless sensing
• Surface acoustic wave resonators
• Lamb-wave resonators
• Meander dipole antenna.

Abstract

Lithium niobate (LiNbO3, LN) is one of the most attractive ferroelectric, renowned for its exceptional properties such as strong electro-optic (EO, Pockels), piezoelectric, and photoelastic effects. Its combination of these properties, along with its wide transparency window and relatively large refractive index, makes LN centrally important to modern integrated photonics and acoustic applications, ranging from telecommunications to sensing and quantum technologies. Leveraging the recent advances in nanofabrication techniques, the thin film lithium niobate (TFLN) platform has recently emerged and become a superior candidate for combining the excellent LN material features with high integration capabilities. In this dissertation, we demonstrate integrated devices and circuits on TFLN platform for microwave photonic and acoustic applications. In the microwave photonics domain, we demonstrate three ultra-compact and high-performance electro-optic modulators (EOMs) based on spiral-shaped waveguides on Z-cut LN. The modulators utilize the in-plane isotropy of the Z-cut LN refractive index to achieve space-efficient spiral waveguides that are modulated using bottom and top electrodes. First, Michelson interferometer modulators (MIM) are implemented with a reduced half-wave-voltage-length-product (V_π L) of less than 2.02 V.cm, and EO bandwidth up to 17.8 GHz for 1.2 mm long modulator. The modulator design could fit a 9-mm long phase shifter within a total area of 175×175 µm2. While the spiral Mach-Zehnder modulators (MZMs) have a limited EO bandwidth compared to conventional traveling-wave MZMs due to its lumped configuration, the spiral MIM achieves modulation bandwidths on par with the traveling-wave MIM, due to the inherent velocity mismatch limitation in MIM design, while achieving a more compact area. Second, we present a spiral waveguide Bragg grating (WBG) modulator that utilizes the grating’s optical filter characteristics along with electro-optic tuning of the central Bragg wavelength to achieve simple and efficient intensity modulation. The integrated design wrapped a 2.2 mm long grating into a 120×120 µm2 area, allowing for extremely long WBGs that are required for high extinction-ratio (ER) filter response with steep roll-off slope. The modulator bandgap, with an ER of over 35 dB at 1550 nm, could be efficiently tuned with a sensitivity of 8.36 pm/V and a 3-dB operating bandwidth of 25 GHz. Third, we propose a grating-assisted Michelson interferometer modulator (GAMIM) that achieves linearized performance by modulating Bragg grating reflectors placed at the end of Michelson arms. The nonlinearity of the conventional Michelson interferometer is compensated by the phase response of the Bragg reflector that approaches inverse cosine for long gratings. The modulator utilizes the spiral configuration to realize extensive reflectors, essential for linearized performance, in a highly integrated form. The compact design fits a 3 mm long grating reflector in an 80 µm × 80 µm area, achieving a broad operating bandwidth up to 18 GHz. A spurious free dynamic range (SFDR) of 101.2 dB∙Hz2/3 is demonstrated at 1 GHz, compared to 91.5 dB∙Hz2/3 for a reference Mach-Zehnder modulator fabricated on the same chip. In the RF acoustic domain, we demonstrate harsh environment and monolithically integrated passive wireless sensors on TFLN substrate based on high quality factor acoustic resonators and wideband meander dipole antennas. Among different wireless sensing technologies, acoustic-based sensors have been widely adopted as a perfect candidate, as they offer ultra-compact and reliable devices that can operate as completely passive transponders. We propose a fully integrated design, where the acoustic resonator and antenna are co-designed and fabricated on-chip using simple lithography steps. The resonator, antenna, and system reader, which make up the three system components, have been designed and implemented. A simple reader archeticture based on frequency domain sampling (FDS) using a commercial vector network analyzer (VNA) is adopted. Meander dipole antenna design is selected due to the simplicity of its integration monolithically with the acoustic resonator, as well as its wide bandwidth, which compensates for the possible error in the acoustic resonator frequency and allows for frequency division multiplexing between multiple resonators. Two types of acoustic resonators, namely the surface acoustic wave (SAW) resonators and Lamb-wave (LW) resonators, are addressed for the target sensing application. While SAW resonators are solidly mounted devices that feature high mechanical robustness, simple fabrication process, and adjustable frequency of operation, they have limited quality factor, especially at high frequency of operation that is sought after for monolithic integration to reduce the on-chip antenna size. On the other hand, Lamb wave resonators could achieve high quality factors at high frequencies using the high-order acoustic modes. The fully integrated sensor was successfully demonstrated using 2.2 GHz Lamb wave resonators for high-resolution temperature sensing, supporting operation up to 150°C and an interrogation range of up to 17.5 cm.

Graduation Semester

2025-05

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/129396

Copyright and License Information

Copyright 2025 Amr Ghoname

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