J. Eur. Opt. Society-Rapid Publ. 2025, 21, 2 Ó The Author( s), published by EDP Sciences, 2025 https:// doi. org / 10.1051 / jeos / 2024046 Available online at: https:// jeos. edpsciences. org
Journal of the European Optical Society-Rapid Publications
REVIEW ARTICLE
A review of research on optical true time delay technology
Ting An *, Limin Liu, Chunhui Han, Sai Zhu, and Yunfeng Jiang Army Engineering University Shijiazhuang Campus, Shijiazhuang 050003, China
Received 4 August 2024 / Accepted 13 November 2024
Abstract. Light controlled phased array has the advantages of fast response speed, compact system, diverse functions, and flexible control, and has been widely applied in many scientific and technological fields. Optical true delay technology( OTTD) is the most direct technical means to achieve phase delay of optical carrier signals, and it is also the most basic technical means to implement optical controlled beamforming systems. In order to fully understand the optical true delay technology, this article first elaborates on the principle of phased array antennas and the reasons for beam squint, and analyzes the impact of true delay on the performance of phased array radar. Then, the basic principle, technological progress, and related applications of optical true delay are introduced. Taking four common structures of optical true delay lines as examples, which are micro-ring resonant cavity array, grating true time delay line, multi-path switchable optical true time delay line( OTTDL), and wavelength selective optical delay line, their performance in delay accuracy, adjustable delay range, and frequency bandwidth are compared. Finally, the current problems and future development trends of optical controlled beamforming technology were summarized.
Keywords: Microwave photonics, True time delay( TTD), Optical true delay technology( OTTD), Optically controlled beamforming network, Light controlled phased array.
1 Introduction
With the increasing complexity and diversity of detection environments and targets, radar urgently needs to have higher resolution capabilities to achieve precise detection of targets and complete recognition functions [ 1, 2 ]. However, traditional radar is limited by the“ electronic bottleneck”, making it difficult to achieve substantial breakthroughs in expanding operating bandwidth and improving signal processing speed, and increasingly unable to meet the detection needs in complex environments in the future.
Microwave photonics is an emerging interdisciplinary field that combines microwave technology and photonics [ 3 ]. Different from traditional electronic microwave systems, microwave signals in microwave photon systems are first loaded into the optical domain through electro-optic converters, then transmitted and processed through optical devices and related links, and finally converted into electrical signals for external transmission [ 4, 5 ]. Microwave photon radar utilizes photonics methods to generate and process radar signals, and has outstanding broadband capability, which can significantly improve radar range resolution [ 6 ]. In order to improve the radar angle resolution capability and achieve flexible beam control, the combination of microwave photon radar technology and
* Corresponding author: antinghbdl @ 163. com phased array technology is an inevitable development trend [ 7 – 10 ]. Therefore, optical controlled beamforming technology is receiving increasing attention in modern radar applications and future radar development.
Generally speaking, devices and systems that can achieve active array optical field phase control can be referred to as optically controlled phased arrays. With the rapid development of high beam quality light sources [ 11 – 13 ], electronic engineering technology [ 14, 15 ], materials science, and optoelectronic devices [ 16 ] in recent years, the diverse forms of optically controlled phased array technology have gradually improved and been widely applied in fields such as laser coherent synthesis, optically controlled phased array radar, and atmospheric turbulent calculation [ 17 – 20 ].
2 Principle of phased array antenna and beam squint phenomenon
2.1 Phased array antenna
Phased array antennas achieve beam scanning by generating a certain relative phase shift between the signals reaching each transmitting element.
As shown in Figure 1, N antenna elements are arranged in a linear array with equal spacing [ 21 ]. Assuming that the
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