High-power Laser Transmission Research Articles

Low-loss nodeless hollow-core anti-resonant soft glass fiber for the 4 µm mid-infrared spectral range

Infrared soft glass hollow-core anti-resonant fibers (HC-ARF) with low loss, excellent mode purity, and robust high-power transmission capabilities have vast potential in mid-infrared high-power laser transmission and biomedical fields. Despite this, the fabrication of these fibers still faces formidable challenges, coupled with an incomplete understanding of the transmission characteristics, thereby amplifying the value of further exploration. In this paper, we fabricate a six-cell nodeless infrared HC-ARF originating from purified sulfide glass, synthesized using a meticulous “stack-and-draw” method and dual-gas-path pressure control method. Notably, we experimentally validate the theoretical performance expectations of this fiber. The fiber exhibits outstanding transmission capabilities and optical transmission quality, characterized by a recorded loss of 0.56 dB/m at 4.79 µm. This is already comparable to traditional step-index sulfide fibers, fully demonstrating its tremendous research value and application potential. Our work has successfully fabricated the lowest loss anti-resonant fiber on record in the mid-infrared field, propelling the development of sulfide HC-ARFs into a new phase and laying a solid foundation for the realization of fiber applications in laser transmission and the biomedical field.

Extinction of high-power laser radiation under adverse weather conditions.

The propagation of laser radiation over long distances can be significantly affected by atmospheric extinction due to precipitation as well as aerosol particles and molecules. The knowledge of the contribution of precipitation is critical to the operation of a variety of laser-based systems. The study of high-power laser transmission around 1µm is of particular interest because several atmospheric transmission windows are located in this region. To investigate the effect of adverse weather conditions on laser transmission, free-space laser transmission experiments are conducted on the DLR test range in Lampoldshausen, Germany. A high-power laser with a wavelength of 1.03µm is used for the transmission measurements in combination with calibrated power monitors. Local weather conditions are continuously monitored by meteorological instruments during the experiments. Extinction coefficients are derived from transmission measurements showing that the extinction for snow is 7 times higher than for rain, and the extinction for drizzle/rain is 4 times higher than for rain at a given precipitation rate of 1mm/h. For a mixture of rain and snow, the extinction is comparable to that of rain, indicating that the water content strongly influences the optical properties and thus the extinction of laser radiation in mixed precipitation. A good relationship is found between the measured extinction coefficient and visibility for drizzle and rain and a slightly larger scatter of the data for snow. Furthermore, measured extinction coefficients are compared to the extinction coefficients based on the experimental size distributions of precipitation particles and geometric optics. A reasonable agreement is obtained for rain, with no improvement taking the forward-scattering into the detector aperture into account, and a much better agreement is obtained for snow when the forward-scattering contribution is included.

Design and analysis of a weakly coupled few-mode hollow-core U-shaped tube nested antiresonant fiber

In this work, we proposed a weakly coupled few-mode hollow-core U-shaped tube nested antiresonant fiber (FM-UARF) for the potential large-capacity mode-division multiplexing transmission without multiple-in-multiple-out (MIMO) digital signal processing. Through theoretical analysis and numerical simulation, the six-tube FM-UARF can be a good candidate for two-mode and three-mode transmission with better performance. After parameter optimization, the weakly coupled condition of effective refractive index difference (Δneff) larger than 5×10−4 can be achieved. Under the two-mode case, the confinement loss (CL) of the LP01 and LP11 modes is less than 0.005 dB/km and 0.1 dB/km in the 700 nm bandwidth range (0.9−1.6µm), respectively. In addition, LP01 achieves the lowest CL of 0.00038 dB/km at a wavelength of 1.06 µm, which gives it potential applications in high-power laser transmission. Under the three-mode case, the CL of the LP01, LP11, and LP21 modes are less than 0.006 dB/km, 0.1 dB/km, and 10 dB/km, respectively, in the wavelength range of 0.95 to 1.65 µm. Both the CL ratios are larger than 150 (23 dB), which ensures the high purity of the supported fiber modes. The results show that the proposed FM-UARF with optimized parameters has the potential in the MIMO-less large-capacity data transmission and so on.

Aerodynamic Window Sealing of a Large-Aperture Channel for High-Power Laser Transmission

In this study, the sealing of a large-aperture channel for high-power laser transmission is achieved using an aerodynamic window. Further, a numerical model of the gas and dust particle motion in the channel is established under three different blowing schemes, and the sealing performance of the large-aperture channel is analyzed and compared under different blowing schemes. The results indicate that the larger the proportion of purge gas volume flows in the axial direction, the better the sealing effect of the channel. More importantly, the axial blowing scheme can ensure that the large-aperture channel maintains the relative positive pressure to the external environment, effectively blocking the ambient gas and dust particles blowing in. The axial blowing scheme can achieve the sealing requirements of the large-aperture channel in an environment where the ambient wind speed is less than 20 m/s, and the dust particle mass concentration is less than 8×10−3 kg/m3. In this case, the minimum non-zero z-directional wind speed is stable and positive at a position 100 mm away from the port in the channel, and the particle mass concentration is zero.

Development of a Customized Endoscopic Dual-Diffusing Optical Fiber Probe for Pancreatic Cancer Therapy: Toward Clinical Use.

Objective: We developed a dual-diffusing optical fiber probe (DDOFP), capable of uniformly illuminating the anatomical structure of pancreatic duct for photodynamic therapy (PDT) of pancreatic cancer in clinical settings. Background: Optical fiber presents a unique route for pancreatic PDT by enabling access to the pancreatic duct. For effective pancreatic PDT, the optical fiber should produce a uniform illumination covering of the pancreatic duct, while maintaining its transmission property under thermomechanical stresses in surgical environments. Methods: The transmission profiles of DDOFP were measured using a charge-coupled device (CCD) camera at two directions: front-spherical and side-cylindrical areas of the optical fiber. We simulated the change in transmission property by curved tube structures using optically transparent phantom. DDOFP was integrated with 19-gauge needle catheter that is commercially used as an optical guide to treat pancreatic cancer. The temperature of DDOFP was measured at the end face using a thermistor probe in the bovine tissue, while delivering laser energy of over 200 and 500 J. Results: DDOFP was customized to secure the inner diameter of the 19-gauge needle catheter of 686 μm to be integrated as a clinical device. The round ball lens fiber tip minimized the back-burn effect caused by blood carbonization during surgery and induced front-spherical diffusion. DDOFP produced uniform light illumination with intensity difference of <10%. When DDOFP was bent with a small curvature <15 mm, the transmission intensity was consistent. Under high-power laser transmission, DDOFP was found to be robust to cracking or deformation. Conclusions: DDOFP was customized for pancreatic PDT with superior thermomechanical property and uniform light illumination at both the front-spherical and side-cylindrical areas. This is the smallest clinically available optical fiber per our knowledge and officially approved by the Korea Food and Drug Administration (item approval number: 17-516). DDOFP can contribute immensely toward the efficient delivery of pancreatic PDT and photothermal therapy.

Band-gap material selection for remote high-power laser transmission

High-power laser transmission (HPLT) is attracting a huge interest from both the scientific and industrial community due to its large number of potential applications and future perspectives. This technology consists of the use of a monochromatic light source to power supply a remote system by using a photovoltaic converter. HPLT offers a technological paradigm shift with the possibility of transmitting kilowatts to several kilometres without the use of wires. However, HPLT is still under development and the current efficiency, ≈20%, needs to be improved to achieve the actual potential of the technology. This work is focused on the investigation of the most suitable materials to improve the performance of HPLT systems under a wide range of scenarios. For the first time, the monochromatic efficiency of PV converters, considering the attenuation of the atmosphere with the distance, and for various input light intensities and series resistance scenarios, is deeply investigated. The results indicate that high energy gap materials such as ZnS (3.54 eV) or 6H–SiC (3 eV) could lead to record efficiencies and improve current values in more than 30%. We have investigated the most suitable band-gap materials to transfer kilowatts of laser power to remote systems considering a wide range of scenarios, i.e. energy gap, series resistance, laser power, atmosphere and distance. Our results indicate the high energy gap materials (>2 eV) such as ZnS, SiC, AlP, CdS or InN offer a novel route to improve the efficiency of high-power laser transmission in more than 30%. • The suitable band-gap materials for remote laser high-power are investigated. • Different scenario of energy gap, series resistance and power are selected. • The spectral attenuation of the atmosphere with distance is considered. • High energy gap materials could improve the efficiency in more than 30%.

Preparation and mode conversion application of narrowband hollow-core anti-resonant fiber

Owing to the unique characteristics of the hollow core fiber(HCF), more and more researchers pay attention to its application. Because the mode field is mainly limited to the core region of the fiber, which results in low non-linearity, ultra-low group velocity dispersion, low temperature sensitivity, and high material damage threshold. Based on the above, the HCF possesses some attractive nonlinear applications such as in transmission of high-power laser beams, sensing, ultra-wide band low-loss transmission, pulse compression and super-continuum generation. Besides, the HCFs can be further divided into the transmitting band-gap photonic crystal fiber(PBG-PCF) and the hollow-core anti-resonant fiber(HC-ARF). Compared with the PBG-PCF, the latter has wide light guiding characteristics caused by leaking modes. According to the research in the recent year, the HC-ARF has gradually approached to the performance of the PBG-PCF in its transmission loss, showing that it has potential applications in communications, sensing, aerospace, high-power laser transmission and other fields in the future. In addition, the HC-ARF with the special light-guiding properties has also become the important photonic device in the fields of fiber filters, mode conversion, etc. In this paper, a hollow-core anti-resonance fiber is studied and its light transmission performance in the spectral range of 500–1500 nm is verified. The optical loss measured at 980 nm wavelength is about 0.32 dB/m. It is found that a 980 nm multi-mode laser beam can be converted into a single-mode one after transmitting through the hollow core fiber we designed.

Research on Preparation and Mode Conversion Application of Narrowband Hollow-core Anti-resonant Fiber

Due to the unique characteristics of the hollow core fiber(HCF), more and more researchers pay attention to its application. Because the mode field is mainly limited to the core region of the fiber, which results in low non-linearity, ultra-low group velocity dispersion, low temperature sensitivity, and high material damage threshold. Based on above, there are some attractive nonlinear applications of the HCF, such as transmission of high-power laser beams, sensing, ultra-wide band low-loss transmission, pulse compression and super-continuum generation. Besides, the HCF can be further divided into the transmitting band-gap photonic crystal fiber(PBG-PCF) and the hollow-core anti-resonant fiber(HC-ARF). Compared with the PBG-PCF, the latter has wider light guiding characteristics caused by leaking modes. According to the research in the recent year, the HC-ARF has gradually approached the performance of the PBG-PCF in its transmission loss which shows that it has potential applications of communications, sensing, aerospace, high-power laser transmission and other fields in the future. In addition, the HC-ARF with the special light-guiding properties has also become the important photonic devices in the fields of fiber filters, mode conversion, etc. In this paper, a hollow-core anti-resonance fiber is studied and its light transmission performance in the spectral range of 500 ~ 1500 nm is verified. The optical loss measured at 980 nm wavelength is about 0.32 db/m. It is founded that a 980nm multi-mode laser beam can be converted into a singe-mode one after transmitting through the hollow core fiber we designed.

All-Fiber Gas Cavity Based on Anti-Resonant Hollow-Core Fibers Fabricated by Splicing with End Caps

In recent years, fiber gas lasers have obtained a rapid development, however, efficient and stable pump coupling is a key limitation for their applications in the future. Here, we report an all-fiber gas cavity based on anti-resonant hollow-core fibers which have the beneficial properties of adjustable broad transmission bands and potential low transmission attenuation, especially in the mid-infrared. This kind of all-fiber gas cavity is fabricated by directly splicing with end caps at both ends for the first time. The high-power laser transmission characteristics were studied, and the experimental results show that the all-fiber gas cavities have a very stable performance. The maximum input laser power at 1080 nm is about 260 W, and the output power is 203 W, giving a total transmission efficiency of 78.1%. This work opens a new opportunity for the development of high-power all-fiber structured fiber gas lasers.

An Endoscope With 2 DOFs Steering of Coaxial Nd:YAG Laser Beam for Fetal Surgery

This paper reports a rigid endoscope that provides an endoscopic view and transmits a high-power infrared laser beam coaxially to arbitrary points in the view to photocoagulate body tissue, mainly for treatment of twin-to-twin transfusion syndrome. The endoscope system consists of a hot mirror for coaxial transmission of visible light and a neodymium-doped yttrium aluminum garnet laser beam, and an optical galvano scanner for steering the laser beam from the endoscope tip. The optical system of the endoscope is designed for high-power laser transmission, and achieves a small laser beam. The camera and galvano mirrors are calibrated to control the laser spot automatically by pointing a target on the endoscopic image. We evaluated the laser transmission efficiency, firing angle, positioning accuracy, and feasibility of photocoagulation by in vitro experiment. The laser transmission efficiency was 34%. However, the endoscope provided changeable firing angles of 24° in a horizontal direction and 22° in a vertical direction. Furthermore, the positioning accuracy was sufficiently high because the errors in both air and water were mostly smaller than the diameter of target vessels of 1 mm. As an in vitro experiment, we successfully coagulated rabbit's mesenteric vessels by changing the firing angle.

大口径光ファイバの破断寿命に及ぼす曲げ半径の影響(GS10 セラミックス・腐食)

大口径光ファイバの破断寿命に及ぼす曲げ半径の影響(GS10 セラミックス・腐食)

A New Optical Fiber System with Hybrid Functions of Power Delivery and Real-Time Remote Observation for YAG Laser Welding

In the International Thermonuclear Experimental Reactor (ITER), pipe welding/cutting has to be carried out under severe gamma-ray conditions in a limited space inside the pipe. A laser and image transmitting system using a composite-type optical fiber was proposed and tested so as to weld, cut and observe inside a pipe. The composite fiber system consists of one fiber for laser transmission, a number of small fibers for image information transmission located around the laser transmission fiber, and a coupling/distributing device for laser energy and images. As a result, high-power laser transmission for welding/cutting and observation tests using the composite fiber system were successfully carried out. Based on the test results, the proposed laser and image transmission system was determined to be applicable not only in a limited space such as inside the pipe, but also in a human body for medical treatment.

Optical properties of small-bore hollow glass waveguides

Hollow glass waveguides with a 250-µm i.d. have been fabricated with a liquid-phase deposition technique that uses silica tubing as a base material. The losses of the 250-µm-bore guide measured at CO(2) laser wavelengths are as low as 2.0 dB/m. The straight losses for the hollow guides are in good agreement with theoretically predicted losses as a result of the nearly ideal structure of the guides. It is also shown that the guides have low bending losses, a nearly pure-mode delivery, and good high-power laser transmission. By proper design of the dielectric thickness, the guide is also able to deliver Er:YAG laser energy with a low loss of 1.2 dB/m for the 320-µm-bore waveguide. Because the hollow glass waveguide is very flexible and robust, it is quite suitable for medical applications.

Atmospheric high-power laser transmission limitation

Atmospheric high-power laser transmission limitation