All-optical long-distance image transmission system

A new publication from Opto-Electronic Advances; DOI 10.29026/oea.2024.230202 describes an all-optical ultra-long distance image acquisition and transmission system.

With the exponential growth of global data, the demand for high-speed acquisition and long-distance transmission of multi-dimensional data is increasing. Online video surveillance in industries such as industrial manufacturing has significantly increased productivity while mitigating security risks. Global real-time video calls have revolutionized people’s daily lives. Existing systems can leverage high-performance detectors, image sensors, and other technologies to collect information on carriers such as light, sound, and microwaves. This data is then transmitted to the operator via various media such as cables, networks, wireless communications, and optical fibers. However, in scenarios where narrow or hard-to-reach areas require observation, front-end acquisition equipment and electronic circuits (for tasks such as information compression, coding, and modulation) are essential to process the data before transmission. This imposes specific requirements on the speed and interference resistance of the system.

In recent years, optical fiber has been widely adopted in data transmission due to its low transmission loss and large capacity. Although technologies such as wavelength division multiplexing (WDM) and spatial division multiplexing (SDM) using multi-core optical fibers have greatly improved the system capacity and transmission efficiency, the transmission process still requires multiple signal conversions. All-optical acquisition and transmission enable the transfer of image information from one end to the other at the speed of light without the need for additional electronic components. Optical fiber bundles can directly convert and transmit two-dimensional light fields from end to end, making them essential in extreme environments such as inaccessible and dark areas such as aerospace, industrial production, and healthcare. However, optical fiber bundles are generally limited in length, expensive, and face challenges in ensuring quality during long-distance data transmission due to manufacturing constraints. Researchers have developed various all-optical networks for tasks such as information collection, encrypted transmission, and image classification, which are expected to underpin next-generation communications. However, these systems face practical challenges in deployment and are generally only compatible with coherent light sources such as lasers. Therefore, there is an urgent need for an efficient, high-capacity, and interference-resistant image acquisition and transmission system.

The authors of this paper propose a single-unit all-fiber multiplexed parallel acquisition and transmission system called Multicore Fiber Acquisition and Transmission Image System (MFAT) to address the above-mentioned challenges. This study was published in Opto-Electronic Advances 2024, Vol. 6, under the title “Seeing at a Distance with Multicore Fibers.” The front-end design, free of electronic circuits, avoids the need for complex signal conversion processes, making it suitable for various environments and resistant to noise from incoherent light sources. Image data is encoded in the optical domain via optical fiber coupling. The multichannel characteristics of multicore optical fibers facilitate high-capacity and high-quality transmission. In addition, numerical aperture technology enables image recovery and reconstruction from an end-plane image that completely hides the original information, thus enabling real-time scene reconstruction at distances of up to one kilometer.

The image acquisition and transmission process consists of two main steps: encoding and decoding. The encoding phase is based on the principle of fiber propagation mode excitation, where different angles of incident light reaching the end faces of different fiber cores excite different propagation modes. In most natural environments, the pattern in each fiber core channel can be perceived as a composite of all object points exciting various modes. Therefore, the incident light field information is encoded into the spatial and modal components of the multicore fiber for transmission. However, accurately determining the occupancy of each mode is usually difficult and requires significant computational resources. To address this problem, the study presents a cost-effective numerical aperture decoding technique based on image processing methodologies to facilitate rapid reconstruction. By extracting and calculating the feature values ​​for different fiber core regions, it is possible to decode various spatial information in the dimension of fiber transmission modes.

This research highlights the system performance in direct image transmission and coded image transmission modes. The direct image transmission mode enables direct observation of the scene at the far end, while the coded image transmission can be integrated with digital coding techniques to enable encrypted transmission of multidimensional data. The simultaneous multiplexing of temporal and spatial channels greatly improves the transmission capacity. In addition, the fusion of polarization, wavelength, and other channel multiplexing techniques further increases the transmission capacity of the system. The study also investigates the factors influencing the system reconstruction efficiency, such as temperature variation, bending, and algorithm robustness. The proposed solution has significant application value in long-distance image acquisition and transmission, especially in extreme environments. The interference-resistant compact structure provides the basis for high-speed real-time global media stream transmission. Exploration and use of more multidimensional information, combined with advanced algorithms, offers the potential to develop next-generation all-optical parallel transmission systems.

Keywords: long-distance optical fiber imaging / image transmission / parallel transmission / all-optical coding / multi-core fiber

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