Research progress on on-chip integrated optical isolators

Yang Zongqi; Li Wenxiu; Sun Xin; Huang Xinyao; Yang He; Zhang Hao; Huang Anping; Xiao Zhisong

doi:10.12086/oee.2025.240285

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Yang Z Q, Li W X, Sun X, et al. Research progress on on-chip integrated optical isolators[J]. Opto-Electron Eng, 2025, 52(2): 240285. doi: 10.12086/oee.2025.240285

Citation:

Yang Z Q, Li W X, Sun X, et al. Research progress on on-chip integrated optical isolators[J]. Opto-Electron Eng, 2025, 52(2): 240285. doi: 10.12086/oee.2025.240285

Research progress on on-chip integrated optical isolators

1.
School of Electronics and Information Engineering, Beihang University, Beijing 100191, China
2.
School of Physics, Beihang University, Beijing 100191, China
3.
School of Instrumentation and Optoelectronic Engineering, Beihang University, Beijing 100191, China
4.
School of Space and Earth Sciences, Beihang University, Beijing 100191, China
5.
School of Instrumentation Science and Opto-electronics Engineering, Beijing Information Science and Technology University, Beijing 100192, China

Fund Project: National Key Research and Development Program of China (2021YFB3900701), the Fundamental Research Funds for the Central Universities of Ministry of Education of China (501XYGG2024117011)

More Information

^*Corresponding authors: haozhang@buaa.edu.cn; yanghe@buaa.edu.cn
CSTR: 32245.14.oee.2025.240285

Received Date 05 December 2024

Revised Date 13 February 2025

Accepted Date 13 February 2025

Published Date 28 February 2025

Abstract

Abstract

As the information age progresses rapidly, the demand for silicon photonic integrated circuits in optical communication, quantum precision measurement, artificial intelligence optical computing, and microwave photonics continues to grow. As an essential component of silicon photonic integrated circuits, optical isolators effectively prevent the backpropagation of optical signals, ensuring system stability and reliability. They are widely used in key technologies such as optical fiber communication, quantum communication, and laser systems. This paper reviews the research progress on on-chip integrated optical isolators, focusing on different implementation methods based on magneto-optic, acousto-optic, electro-optic, and nonlinear optical effects, discussing the advantages and challenges associated with each type. Finally, the paper explores future development directions and potential applications.
- silicon photonics /
- optical isolator /
- non-reciprocal effect

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References

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Overview

Overview

The rapid development of information technology has fueled increasing demand for high-performance, low-cost photonic integrated circuits (PICs) in applications like optical communication, microwave photonics, quantum information processing, optical sensing, and artificial intelligence-driven optical computing. In these systems, non-reciprocal photonic devices, particularly optical isolators, are crucial components. Optical isolators allow light to pass in only one direction, blocking back-reflected light that can interfere with optical sources or even damage lasers. In optical communication systems, they help release multi-path interference and enhance system design flexibility by preventing crosstalk between devices. As the need for highly integrated PICs systems grows, the development of efficient, compact, and scalable on-chip optical isolators has become a key research focus. Several implementation methods for on-chip integrated optical isolators have been proposed, based on magneto-optical (MO), acousto-optical (AO), electro-optical (EO), and nonlinear optical effects. Each approach presents unique advantages and faces specific challenges. Magneto-optical isolators achieve non-reciprocal transmission through the Faraday effect. These devices typically consist of a magneto-optical material, such as Ce: YIG and Bi: YIG, combined with Mach-Zehnder interferometer (MZI), micro-ring (MR) or multimode interference (MMI) structures. While MO isolators offer high isolation ratio and robustness, their integration is limited by material mismatches with semiconductors and high insertion loss due to material absorption. AO isolators rely on the interaction between phonon and photon in a waveguide. These isolators are efficient and compatible with low-loss materials like AlN and LiNbO₃ but have limited bandwidth due to their narrow optical resonance. Electro-optical isolators control light propagation through the Pockels effect. In an EO isolator, an external electric field modifies the refractive index of the waveguide material, such as LiNbO₃, to induce phase changes in the transmitted light. EO isolators are promising due to their fast response times and wide isolation bandwidth but face high power consumption and thermal issues, limiting large-scale integration. Nonlinear optical isolators break reciprocity through effects like Kerr nonlinearity or Four-Wave Mixing, offering broadband operation. However, they require high power levels to achieve strong isolation, making them unsuitable for low-power applications. Additionally, they are complex due to the need for extra pump sources and filters. Future advancements in on-chip optical isolators will focus on optimizing performance while maintaining compactness, scalability, and compatibility with semiconductor processes. Hybrid solutions combining different non-reciprocal effects, improved acoustic wave generation, reduced driving voltages, and the development of new materials with higher nonlinear coefficients will drive the next generation of high-performance isolators.