Science Island Team Makes Breakthrough in High Pulse Energy Mid-infrared Fiber Optic Transmission

Recently, the group of researcher Jiang Haihe at the Institute of Health, Hefei Institute of Physical Sciences, Chinese Academy of Sciences, has made important progress in the study of high-energy pulsed laser transmission system in the mid-infrared wavelength band, and has designed a 6-hole microstructured anti-resonance hollow-core fiber (AR-HCF) with a larger core diameter of 78 μm, which for the first time realizes the efficient transmission of high energy pulsed laser light of 2.79 μm wavelength band in the room temperature condition. The results have been published in the internationally renowned Optical TTG. The results have been published in Optics and Laser Technology, an internationally recognized optical TOP journal.
Laser medical devices usually require a flexible catheter to transmit the laser light to the patient, but most of the conventional mid-infrared laser medical devices use a light guide arm to transmit the laser light. However, the traditional light-guide arm method of laser transmission has many problems, such as complex system structure, low transmission efficiency, and lack of flexibility. The use of optical fiber transmission can solve the above problems, but the material of solid-core optical fiber in the mid-infrared band of the laser damage threshold is low, and can not meet the 3μm band erbium laser medical instruments with high energy density of light guide needs. Therefore, the research team designed and investigated a simple structure, high coupling transmission efficiency, high damage threshold and flexible transmission of AR-HCF alternative light guide arm to transmit laser energy.
The team used the designed 6-hole microstructure AR-HCF with a large core diameter of 78 μm for the first time to efficiently transmit high-energy pulsed lasers in the 2.79 μm band at room temperature. Without damaging the fiber, the average coupling transmission efficiency in the whole region is 77.3%, and the highest coupling transmission efficiency reaches 85% under high beam quality and small coupling energy. If the air-absorbed attenuation in the core is deducted, the structured fiber system's own transmission efficiency actually exceeds 90%. The system achieves a maximum pulsed laser energy output of 11.78 mJ, with a corresponding energy density threshold of 350 J/cm2, which far exceeds the value required for soft tissue ablation in living organisms. At the same time, the minimum bending radius of the AR-HCF is 20 cm and the corresponding loss can meet the surgeon's clinical needs, and the laser beam quality at the output end of the AR-HCF is better than that at the input end, which is a good improvement.
Compared with the current optical fibers made of other structures and materials for 2.79 μm wavelength transmission, the 6-hole structure of the silica AR-HCF has stronger mechanical stability, higher damage threshold, and lower bending sensitivity and outperforms the transmission of the conventional light guide arms. This study opens up a new way for efficient transmission of 2.79 μm Cr,Er:YSGG medical solid-state lasers.

Figure 1. AR-HCF cross-section structure

Figure 2. 2.79 μm AR-HCF spatial transmission experimental device

Figure 3. Losses of AR-HCF with different bending radii and bending directions