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J. Eur. Opt. Society-Rapid Publ. 22, 16( 2026)
Fig. 4. Signal processing functional link of Si 3 N 4-TFLN heterointegrated device: from optical input to phase-modulated and frequency-doubled optical signal output.
process, but also ensures the efficient cascaded coupling between DD-MZM and MRR, which is an important guarantee for suppressing the functional crosstalk between modules to below �38 dB.
3.2 Design parameters of DD-MZM
Fig. 5. The cross-sectional diagram of the multi-layer structure of the multifunctional integrated device designed in this paper.
performance limitations of single-material devices. By epitaxially growing a 0.05 lm Si 3 N 4-LN transition layer to optimize the interface characteristics, the structure synergizes the low transmission loss of Si 3 N 4( 0.15 dB / cm) and the strong electro-optic / second-order nonlinear effects of TFLN( r 33 = 30.8 pm / V, d 33 = 30.8 pm / V), which effectively solves the problem that pure Si devices have low electro-optic coefficients and pure TFLN devices have high waveguide loss. Meanwhile, the layered design of Al electrode / SiO 2 cladding / air layer maximizes the optical field confinement and electric field coupling efficiency, laying the foundation for the subsequent optimization of the electro-optic overlap factor C to 0.85.
Table 1 lists the parameters of various materials for multi-layer structures, as well as the width and thickness of each material.
Figure 6 shows the physical layout of the Si 3 N 4-TFLN heterogeneous integrated device, and the compact layout design of DD-MZM and racetrack MRR is the key to realizing device miniaturization. By optimizing the routing of thecompositewaveguideandthesizeoftheMRR( radius 80 lm, straight segment 280 lm), the total chip area is compressed to 3.648 mm 2, which is more than 60 % smaller than the existing similar multifunctional integrated devices( area > 10 mm 2). This compact layout not only reduces the parasitic loss of the microwave signal in the transmission
In the implementation of the phase modulation function, an external voltage source is used to apply a voltage to the DD-MZM arms, which changes the refractive index of the LN material, thereby achieving continuous and precise adjustment of the optical wave phase. The multifunctional device designed in this article uses T-shaped track electrodes to minimize microwave transmission losses, while meeting the group refractive index matching the optical transmission waveguide and matching with a 50 X characteristic impedance to reduce microwave reflections.
3.2.1
Waveguide parameter design
For the fundamental mode( TE₀₀ mode), the characteristic equation can be derived by solving the wave equation combined with the boundary conditions of the rectangular waveguide [ 33, 34 ].
mp
2 np þ w h
2 þ k
2 0 n2 sio 2
¼ k 2
0 n2 LN
� b: ð20Þ
In equation( 20), m, n = 0,1,2... denotes the mode order, b represents the propagation constant, n SiO2 and n LN are the refractive indices of SiO 2 and LN respectively. n eff = b / k 0 stands for the effective refractive index. After simplification, the effective refractive index of the fundamental mode satisfies the following relation:
n 2 eff ¼ n2 � b �2 mp
2 np 2
LN þ: ð21Þ k 0 w h
For the fundamental mode TE 00, it is necessary to ensure that the cut-off wavelengths of all higher order modes are smaller than the operating wavelength k, whichsatisfies the single mode transmission condition.