Abstract
We demonstrated a kind of long-period fiber grating (LPFG), which is manufactured with a thermal diffusion treatment. The LPFG was inscribed on an ultrahigh-numerical-aperture (UHNA) fiber, highly doped with Ge and P, which was able to easily diffuse at high temperatures within a few seconds. We analyzed how the elements diffused at a high temperature over 1300 °C in the UHNA fiber. Then we developed a periodically heated technology with a CO2 laser, which was able to cause the diffusion of the elements to constitute the modulations of an LPFG. With this technology, there is little damage to the outer structure of the fiber, which is different from the traditional LPFG, as it is periodically tapered. Since the LPFG itself was manufactured under high temperature, it can withstand higher temperatures than traditional LPFGs. Furthermore, the LPFG presents a higher sensitivity to high temperature due to the large amount of Ge doping, which is approximately 100 pm/°C. In addition, the LPFG shows insensitivity to the changing of the environment’s refractive index and strain.
Highlights
Long-period fiber gratings (LPFGs) have been widely used in the fields of optical communication, optical fiber sensing, and lasers [1]
LPFGs are usually manufactured by tapering with a CO2 laser [2], inscription with a UV laser [3], or etching with a femtosecond laser [4]
By controlling the diffusion of elements at high temperatures, we developed a technology of technology of point-by-point heating and proposed a novel LPFG in a Ge/P-doped fiber
Summary
Long-period fiber gratings (LPFGs) have been widely used in the fields of optical communication, optical fiber sensing, and lasers [1]. LPFGs are usually manufactured by tapering with a CO2 laser [2], inscription with a UV laser [3], or etching with a femtosecond laser [4]. All of these methods introduce a periodic modulation of the refractive index (RI) along the longitudinal axis of the fiber, creating a permanent LPFG. The temperature fiber sensor has been widely used in many fields, such as security, health, and industry. Many researchers’ work has focused on increasing the sensitivity of temperature sensors
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