Customized Product（LiNbO₃ special integrated optical device）
1、Introduction
Relying on our mature preparation technology of LiNbO₃ optical waveguide (titanium diffusion, proton exchange) and comprehensive manufacturing capability (from chip design to device packaging), we provide customized development services for customers, and the products have been applied to many research and development projects such as high-voltage electric field measurement, optical wavelength demodulation, high-frequency electromagnetic spectrum analysis, and high-speed control of optical polarization.
2、Schematic diagram of main customized products and structures
（1）High voltage electric field sensor（E-Field Sensor）
In this product, an optical waveguide with asymmetric MZ interferometer structure with two arms is prepared in LiNbO₃ crystal with X-cut and Y-propagation by annealing proton exchange technology. A metal electrode with triangular structure or bow-tie structure is placed on one side of the straight waveguide as a sensor of high-voltage electric field, which is loaded into the straight waveguide and modulates the phase of light waves transmitted therein. Schematic diagram of the device structure is as follows:
Note: This product has been applied to a domestic high-voltage electric field sensing project in batches.
（2）Asymmetric intensity modulator（Imbalanced MZI）
In this product, an optical waveguide with asymmetric MZ interferometer structure with two arms is prepared in LiNbO₃ crystal with X-cut and Y-propagation by annealing proton exchange technology. By applying voltage to the device, the optical path difference between the two arms of MZ waveguide can be controlled. Schematic diagram of the device structure is as follows:
Note: Scientific research projects using this product have been published in:
l Double Characteristic Value Method: A Fast Way to Expand the Dynamic Range of Some Spectrum-Based Optical Sensors（2022）
l Nonlinear regression: A possible solution to larger dynamic range for some
spectrum-based optical sensors（2022）
（3）Electro-optical polarizer（Polarization Scrambler）
In this product, a straight optical waveguide which can transmit both TE and TM polarization modes simultaneously is prepared by titanium diffusion technology in lithium niobate crystal with X-cut and Y-propagation, and the input port of the optical waveguide is coupled with the slow axis of polarization-maintaining fiber at a 45°angle, while the output port of the optical waveguide is a single-mode fiber. The linearly polarized light transmitted along the slow axis in the input polarization-maintaining fiber can be divided into TE and TM polarization modes in the optical waveguide. By applying an appropriate voltage to the optical waveguide to control the phase difference between TE and TM modes, a new polarization state (such as linear polarization, circular polarization, elliptical polarization, etc.) can be obtained at the output port of the optical waveguide.
The schematic diagram of the device structure is as follows：
（4）Electro-optical polarization controller（Polarization Controller）
This product adopts titanium diffusion technology to prepare a straight optical waveguide which can transmit both TE and TM polarization modes in the X-cut and Z-transmitted LiNbO₃ crystal. By using the special electro-optical coefficient vector of LiNbO₃ crystal r22, a new polarization state can be obtained at the output port of the optical waveguide by applying an appropriate voltage to the modulation electrodes on both sides of the optical waveguide (the electrode above the optical waveguide is zero potential). This product can also cascade multiple groups of modulation electrodes to control the input and output of any polarization state (similar to the combination of "1/4λ wave plate -1/2λ wave plate -1/4λ wave plate" of the three-ring fiber polarization controller).
Schematic diagram of the device structure is as follows:
Note: Refer to for the principle reference of this product：Modeling and Characterization of an Electrooptic polarization controller on LiNbO₃（1992）
（5）Fabry-Perot Phase Modulator
In this product, a straight optical waveguide with highly stable polarization state is prepared in X-cut and Y-transmitted LiNbO₃ crystal by annealing proton exchange technology, and a high anti-reflective dielectric film (HR film) is deposited on both end faces of the optical waveguide wafer to form an F-P(Fabry-Perot) cavity structure, and the wavelength of resonant output light is modulated by applying a suitable voltage.
Schematic diagram of the device structure is as follows:
The following figure shows the resonance spectrum distribution of the output light obtained by applying the sawtooth wave modulation signal.
（6）Ultrahigh ER Intensity Modulator
The product further improves the extinction ratio of the device switch (20dB → ≥40dB) through the cascaded MZ interferometer intensity modulator. Schematic diagram of the device structure is as follows:
（7）Dual Output Intensity Modulator
This product integrates a 3dB directional coupler behind the MZ interferometer intensity modulator, which can realize dual-fiber light output. Schematic diagram of the device structure is as follows:
（8）Periodically polarized LiNbO₃ waveguide
