Lithium Niobate Crystals, Single-Crystal Thin Films, and Their Future Development in the Photonic Chip Industry.
April 21, 2025
Lithium Niobate Crystals, Single-Crystal Thin Films, and Their Future Development in the Photonic Chip Industry.
With the rapid development of applications such as 5G/6G communication technology, big data, and artificial intelligence, the demand for next-generation photonic chips is growing. Lithium niobate crystals, with their excellent electro-optic, nonlinear optical, and piezoelectric properties, have become the core material for photonic chips and are known as the "optical silicon" of the photonic era. In recent years, breakthroughs have been made in the preparation of lithium niobate single-crystal thin films and device processing technologies, which demonstrate advantages such as smaller size, higher integration, ultrafast electro-optic effects, wide bandwidth, and low power consumption. These characteristics offer broad application prospects in fields such as high-speed electro-optic modulators, integrated optics, and quantum optics.
This article introduces the domestic and international research and development progress of optical-grade lithium niobate crystals, single-crystal thin film preparation technologies, and relevant policies, as well as their latest applications in photonic chips, integrated optical platforms, and quantum optical devices. It analyzes the development trends and challenges of the lithium niobate crystal-thin film-device industry chain and provides suggestions for future development. Currently, China is on par with the international advanced level in the fields of lithium niobate single-crystal thin films and lithium niobate-based optoelectronic devices, but there is still a significant gap in the industrialization of high-quality lithium niobate crystal materials. By optimizing the industrial layout and strengthening basic research, China is expected to form a complete lithium niobate industrial cluster, from material preparation to device design, manufacturing, and application.
Lithium niobate thin films have become an important candidate material for the next generation of multifunctional integrated photonic information processing chip substrates. The market capacity forecast for optical modulators based on lithium niobate crystal materials is projected to reach $36.7 billion by 2026. Compared to silicon photonic modulators and indium phosphide modulators, thin-film lithium niobate modulators offer advantages such as high bandwidth, low insertion loss, low power consumption, high reliability, and high extinction ratio. They also enable miniaturization, meeting the growing demand for smaller coherent optical modules and optical modules for data communication. China has achieved independent control over crystal materials, crystal thin films, processing methods, devices, and systems. Currently, several domestic manufacturers have released 800 Gbps thin-film lithium niobate optical module solutions, with downstream customers already testing the corresponding products. The advantages of 1.6 T optical module applications will become more prominent in the future.
1. Research Progress on Lithium Niobate Crystals and Single-Crystal Thin Films
The physical and chemical properties of lithium niobate single crystals largely depend on the [Li]/[Nb] ratio and impurities. Congruent Lithium Niobate (CLN) crystals, which have the same composition, are lithium-deficient, containing a large number of lithium vacancies (VLi) and anti-site niobium (Nb) point defects. Stoichiometric Lithium Niobate (SLN) crystals, with a [Li]/[Nb] ratio close to 1:1, offer excellent performance but are difficult to prepare and have high production costs. Lithium niobate single crystals are classified into acoustic-grade and optical-grade materials. Relevant institutions engaged in lithium niobate crystal growth are shown in Table 1, with Japanese companies being the primary contributors to the growth of optical-grade lithium niobate. Currently, the domestic production rate of optical-grade lithium niobate wafers is less than 5%, making it heavily reliant on imports.
Japanese company Yamamoto Ceramics has successfully industrialized 8-inch lithium niobate crystals and wafers (Figure 1(a)). Domestically, Tiantong Holdings Co., Ltd. (Tiantong) and China Electronics Technology Deqing Huaying Electronics Co., Ltd. (Deqing Huaying) both prepared 8-inch lithium niobate crystals and wafers in 2000 and 2019, respectively, but they have not yet achieved industrial mass production. In terms of stoichiometric and optical-grade lithium niobate, there remains a technological gap of about 20 years between domestic lithium niobate crystal growth companies and Japanese companies. Therefore, there is an urgent need in China to make breakthroughs in the growth theory and process technology of high-quality optical-grade lithium niobate crystals.
International breakthroughs in lithium niobate photonic structures, photonic chips, and devices are largely attributed to the development and industrialization of lithium niobate thin film materials. However, due to the brittleness of lithium niobate single crystals, it is very challenging to prepare low-defect, high-quality thin films with thicknesses in the nanometer range (100-2,000 nm). Ion implantation and direct bonding technologies allow for the separation of bulk single crystals into nanometer-thick lithium niobate single-crystal thin films, making large-scale lithium niobate photonic integration possible. Currently, only a few companies globally, including Jinan Jingzheng, Soitec SA of France, and Kyocera Corporation of Japan, have mastered the production technology for lithium niobate single-crystal thin films. Jinan Jingzheng, using ion beam slicing and direct bonding core technologies, was the first to industrialize these processes, creating a globally leading brand of lithium niobate thin films (NanoLN), which supports over 90% of the global basic research and R&D in lithium niobate thin film devices. In 2023, Jinan Jingzheng introduced 8-inch optical-grade lithium niobate thin films (Figure 1(b)), becoming the first company in the industry to produce lithium niobate thin films from 8-inch X-axis lithium niobate crystals. The key indicators of Jinan Jingzheng’s product series, including physical performance, thickness uniformity, defect suppression, and elimination, are at the forefront of international standards.
2. Advanced Applications of Lithium Niobate
Compared to traditional lithium niobate single crystal materials, thin-film lithium niobate offers smaller size, lower cost, higher integration, and the ability to operate stably under a wider range of temperature and electric field conditions. These advantages make it highly applicable in fields such as 5G communication, quantum computing, fiber-optic communication, and sensors. It shows great potential, especially in electro-optic modulation, optical signal processing, and high-speed data transmission (Table 1).
| Application Fields | Typical Devices | Direction |
| Optical Communication | High-performance laser devices for high-speed communications, optical signal processing, and optical sensors. | Advanced telecommunications equipment, optical networks, and digital communications. |
| Laser Technology | High-power lasers, laser sources, and laser systems used for industrial applications. | Laser processing, industrial cutting and welding, environmental monitoring. |
| Optical Signal Processing | Devices used for signal generation, modulation, and processing in telecommunications. | Signal processing, modulation, and optical transmission technologies. |
| Quantum Communication | Quantum communication devices for secure data transmission. | Quantum cryptography, secure communications, and data transmission. |
| Sensor Technology | Devices for environmental monitoring, bio-sensing, and chemical detection. | Sensing technologies for environmental safety and security. |
| Acoustic Signal Processing | Acoustic sensors, transducers for underwater applications. | Acoustic sensing devices for underwater, medical, and industrial uses. |
| Sound Wave Technology | Sound-based devices for applications in medical diagnostics and monitoring. | Technologies for medical diagnostics, monitoring, and sound-based imaging. |
| Laser Technology | Laser-based technologies for high-precision cutting and welding, etc. | Precision manufacturing, material processing, and high-performance technologies. |
2.1 High-speed Electro-optic Modulator Lithium Niobate Modulators
with their advantages of high speed, low power consumption, and high signal-to-noise ratio, are widely used in ultra-high-speed backbone optical communication networks, submarine optical communication networks, metropolitan core networks, and other fields. Key technologies such as large-size photolithography, ultra-low loss waveguide fabrication, and heterogeneous integration have driven the development of thin-film lithium niobate modulators, enabling them to support 800 Gbps and 1.6 T high-speed optical module applications. Compared to materials like indium phosphide, silicon photonics, and traditional lithium niobate, thin-film lithium niobate offers outstanding features such as ultra-high bandwidth, low power consumption, low loss, small size, and the ability to achieve wafer-level mass production, making it an ideal material for electro-optic modulators. The global market for thin-film lithium niobate modulators is steadily growing, with the global market size expected to reach $2 billion by 2029, with a compound annual growth rate of 41.0%.
| Performance | LiNbO3 Crystal | InP | SiPh | LiNbO3 Thin Film |
| Optical Loss (dB) | Excellent | Medium | Medium | Medium |
| Max Bandwidth (GHz) | Excellent | Excellent | Medium | Medium |
| Half-Wave Voltage (V) | Excellent | Medium | Medium | Medium |
| Extinction Ratio (dB) | Excellent | Medium | Medium | Medium |
| Core Length (mm) | Excellent | Medium | Medium | Medium |
| Linearity | Excellent | Medium | Medium | Medium |
| Collecting Efficiency | Excellent | Medium | Medium | Medium |
| Price | Medium | Medium | Medium | Medium |
Internationally, a research team from Harvard University successfully developed a 100 GHz bandwidth complementary metal-oxide-semiconductor (CMOS)-compatible integrated Mach-Zehnder interferometer (MZI) electro-optic modulator in 2018, while Fujitsu Optical Devices Ltd. launched the world’s first commercial 200 GBaud thin-film lithium niobate modulator in 2021. Significant progress has also been made in China.
2.2 Lithium Niobate Integrated Optical Platform
On the lithium niobate integrated optical platform, applications ranging from frequency combs to frequency converters and modulators have been achieved. However, integrating lasers onto lithium niobate chips remains a significant challenge. In 2022, a research team from Harvard University, in collaboration with HyperLight and Freedom Photonics, successfully demonstrated a chip-level femtosecond pulse source and the world’s first fully integrated high-power laser on a lithium niobate chip (Figure 2(a)). These lithium niobate chip lasers are integrated with high-performance, plug-and-play lasers, which can significantly reduce the cost, complexity, and power consumption of future communication systems. They can also be integrated into larger optical systems and have broad applications in fields such as sensing, atomic clocks, lidar, quantum information, and data telecommunications. Further development of integrated lasers with narrow linewidths, high stability, and high-speed tunable frequency capabilities is also a critical demand in the industry. In 2023, researchers from ETH Zurich and IBM achieved low-loss, narrow-linewidth, high-modulation-rate, stable laser output on a lithium niobate-silicon nitride heterogeneous integrated optical platform, with a repetition rate of approximately 10 GHz, a 4.8 ps optical pulse at 1,065 nm, energy exceeding 2.6 pJ, and peak power exceeding 0.5 W.
Researchers from the National Institute of Standards and Technology (NIST) in the United States, based on the introduction of multi-segment nanophotonic integrated thin-film lithium niobate waveguides, successfully generated a continuous frequency comb spectrum spanning from the ultraviolet to the visible spectrum by combining engineered dispersion and chirped quasi-phase matching. The research team from City University of Hong Kong developed an integrated lithium niobate microwave photonic chip that can use optics for ultrafast simulation of electronic signal processing and computation, achieving speeds 1,000 times faster than traditional electronic processors, with a 67 GHz ultra-wide processing bandwidth and excellent computational accuracy. In 2025, a collaboration between Nankai University and City University of Hong Kong led to the successful development of the world’s first integrated thin-film lithium niobate photonic millimeter-wave radar, based on a 4-inch thin-film lithium niobate platform, achieving breakthrough progress in centimeter-level distance and speed detection resolution, as well as inverse synthetic aperture radar (ISAR) two-dimensional imaging (Figure 2(b)). Traditional millimeter-wave radars typically require multiple discrete components to work together, but through on-chip integration technology, all the core functions of the radar are integrated into a single 15 mm × 1.5 mm × 0.5 mm chip, significantly reducing system complexity. This technology will be applied in fields such as 6G-era vehicle radars, airborne radars, and smart home systems.
2.3 Quantum Optical Applications have integrated various functional devices onto thin-film lithium niobate
such as entangled light sources, electro-optic modulators, waveguide beam splitters, etc. This integrated design enables efficient generation and high-speed manipulation of on-chip optical quantum states, enhancing the functionality and power of quantum chips, providing more efficient solutions for quantum information processing and transmission. Researchers at Stanford University combined diamond and lithium niobate onto a single chip, where the diamond's molecular structure is easy to manipulate and can accommodate fixed quantum bits, while lithium niobate can change the frequency of light passing through it, allowing for optical modulation. This material combination offers new ideas for improving the performance and expanding the functionality of quantum chips. The generation and manipulation of compressed optical quantum states is the core foundation of quantum-enhanced technologies, but their preparation systems typically require additional large optical components. A research team at Caltech successfully developed an integrated nanophotonics platform based on lithium niobate, enabling the generation and measurement of compressed states on the same optical chip. This technique for preparing and characterizing sub-optical period compressed states in the nanophotonics system provides an important technological path for the development of scalable quantum information systems.
| Time | Field | Specific Requirements |
| 5 years | Optical Communication | Laser communication with a frequency of 100 GHz, low loss (<0.3 dB/cm) |
| 5 years | Microwave Communication | High frequency V-band, microwave communication system with >90 GHz and high reliability |
| 10 years | Artificial Intelligence | Large-scale AI processors with power consumption less than 10 W/cm簡, and highly integrated circuits |
| 10 years | High-precision Optical Measurement | Large-scale photonic devices with >10photons, high precision sensors |
3、Development Trends and Challenges: With the development of artificial intelligence and large models
The growth points for the future of lithium niobate will mainly focus on the high-end optical chip field (Table 5), specifically including breakthroughs in core optical chip technologies such as high-speed optical modulators, lasers, and detectors; promoting the application of thin-film lithium niobate in optical chips to enhance device performance; strengthening the research and development of lithium niobate thin-film fabrication technologies to achieve large-scale production of high-quality films; and promoting the integration of thin-film lithium niobate with silicon-based optoelectronic devices to reduce costs.
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