J. Eur. Opt. Society-Rapid Publ. 22, 16( 2026) 149
for multi-material fusion integration [ 17 ]. Boes et al. systematically sorted out the development context of LN photonics in Science, and clarified that TFLN technology is the core path to release the application potential of lithium niobate in the full electromagnetic spectrum [ 18 ]. Domestic research has also yielded fruitful results. Peng Yang and others from Microsystem Packaging Research Center, Institute of Microelectronics of the Chinese Academy of Sciences [ 19 ] proposed a lumped Mach-Zehnder modulator( MZM) based on thin-film lithium niobate( TFLN), which uses a capacitor-loaded lumped electrode. Simulation shows that the device achieves a high electro-optical bandwidth of 32.4 GHz and a low half-wave voltage length product of 1.15 V cm, with a power consumption as low as 0.1 pj / bit. Shanghai University of Technology demonstrated an improvement in the optical-electric field overlap efficiency by employing rib waveguides. This approach achieved a half-wave voltage – length product( V p L) of1.8V cm for a TFLN electro-optic phase modulator [ 20 ]. Not only at the device level, but also in more complex multifunctional scenarios, the potential of TFLN electro-optic modulation technology has emerged. The team led by Yao Xiaotian from Hebei University [ 21 ] integrated the TFLN phase modulation unit into an optical frequency detection chip, achieving a resolution of 2 MHz and a measurement speed of 2500 THz / s. The team led by Li Tao from Nanjing University [ 22 ] developed a 48-channel optical phased array based on TFLN modulation array, achieving a wide scanning field of view of 62.2 ° 8.8 °. These domestic and international studies all indicate that TFLN technology can not only overcome the inherent limitations of bulk LN modulators but also provide core support for high-performance electro-optical modulation applications in fields such as optical communication and LiDAR.
However, the currently reported TFLN devices generally have the problem of a single-function, which can only achieve phase modulation or frequency doubling function. While a few solutions dedicated to functional integration still have key performance indicators that do not meet the standards, with crosstalk exceeding 5 dB, Free Spectral Range( FSR) less than 100 GHz, and chip area exceeding 10 mm 2. These defects significantly limit the practical application of such devices.
To further improve the performance of TFLN phase modulators, efforts need to be made in multiple aspects. At the material and manufacturing process level, heterogeneous integration technology can leverage the advantages of various materials and serves as an effective technical approach to realize large-scale multifunctional photonic integrated chips [ 23 – 25 ]. For the modulator structure, it is necessary to explore new structures to enhance the integration of the system and achieve multi-functionality. This study focuses on the design of a TFLN on-chip device with both phase modulation and frequency doubling functions based on the structure of a Dual-Drive Mach-Zehnder Modulator( DD-MZM) and a Micro-Ring Resonator( MRR), aiming to break through the aforementioned limitations and provide a new path for the development of related fields.
2 Theoretical foundations of heterointegrated DD-MZM and racetrack MRR
The core functional link of the Si 3 N 4-TFLN heterogeneous integrated device as shown in Figure 1 is the structural basis for the realization of dual functions of phase modulation and frequency doubling, and also the logical starting point for the theoretical derivation in this section. The link realizes the monolithic integration of high-speed electrooptic phase modulation and efficient microwave frequency doubling on a single chip via the cascaded design of key functional modules, where the optical signal follows the transmission path of 1550 nm optical carrier? equal-power multi-channel light? phase-modulated light with x₀ ± x m? low-crosstalk combined light? carrier-suppressed sideband light? frequency-doubled microwave signal( 2x m). To ensure the efficient coupling of the modulated optical signal into the MRR cavity and the effective excitation of the second-order nonlinear frequency doubling effect, it is necessary to first clarify the phase evolution law of the optical signal in the DD-MZM and the resonant phase characteristics of the MRR, and then derive the strict phase matching conditions between the two; on this basis, the correlation model between the modulation bandwidth and the frequency doubling efficiency is established by combining the electro-optic modulation characteristics of the DD- MZM and the resonant enhancement characteristics of the MRR, so as to provide theoretical constraints for the subsequent device structure design and parameter optimization.
2.1 Derivation of phase-matching conditions between modulated light and MRR
Phase matching is the prerequisite for the modulated light output by the DD-MZM to be efficiently coupled into the MRR cavity and excite the nonlinear frequency doubling effect, which can avoid the increase of resonance loss caused by phase mismatch. The core requirement of phase matching is that the fundamental frequency and sideband components of the modulated light must simultaneously satisfy the resonant phase characteristic of the MRR, which can be achieved by adjusting the amplitude of the DD-MZM modulation signal or the temperature tuning amount of the MRR.
2.1.1 Phase Characteristic of DD-MZM Modulated Light
The DD-MZM operates in a push-pull driving mode. Let the angular frequency of the input optical carrier be x m and the applied Radio Frequency( RF) modulation signal be [ 26 ]: vðtÞ ¼ V m cos ðx m t þ / 0 Þ; ð1Þ
where V( t) denotes time-varying RF modulation signal voltage, with the unit of volt( V); V m represents the amplitude of the RF modulation signal, which determines