Regenerated distributed Bragg reflector fiber lasers for high-temperature operation

Abstract

This Letter presents distributed Bragg reflector (DBR) fiber lasers for high-temperature operation at 750°C. Thermally regenerated fiber gratings were used as the feedback elements to construct an erbium-doped DBR fiber laser. The output power of the fiber laser can reach 1 mW at all operating temperatures. The output power fluctuation tested at 750°C was 1.06% over a period of 7 hours. The thermal regeneration grating fabrication process opens new possibilities to design and to implement fiber laser sensors for extreme environments. In comparison with the gratings used in previously discussed fiber lasers, thermally regenerated gratings [5][6][7] are another class of high-temperature-resistant fiber gratings. The thermal regeneration of high-temperatureresistant gratings involves a mechanical relaxation process [8], which is independent from the chemical composition of fibers and hydrogen loading processes. Thus, thermally regenerated gratings can be fabricated in a wide variety of fibers at low cost for extreme environments. Wang et al. has reported linear temperature and strain responses in thermally regenerated gratings from room temperature to 1100°C [9], which render regenerated gratings as a significant enhancement to conventional fiber grating applications, especially for extreme environments. Recently, we have demonstrated a regenerated-grating-based high-temperature pressure sensor, with which hydrostatic pressure 15-2400 psi and high temperature (24°C-800°C) can be accurately measured simultaneously [10].In addition to passive sensing applications, regenerated gratings can offer considerable potential for applications in high-power laser [4] and active fiber sensing areas, where internal temperatures of fiber lasers can anneal conventional gratings out under high laser output power. With specially optimized optical fibers and strong seeds, regenerated gratings with 98.5% reflectance (∼18 dB) can be readily fabricated [11], which is normally sufficient for laser oscillation with a relatively small cavity size.In this Letter, we present studies and characterization of high-temperature stable distributed Bragg reflector (DBR) fiber lasers using the regenerative grating technique. Two regenerated gratings are used as reflectors in a DBR fiber laser for high-temperature operation. The laser performance was characterized from the room temperature to 750°C. Continuous monitoring for the laser output power was performed to quantify its stability at elevated temperatures. The regenerated gratings and output power of the laser are shown to be stable at 750°C for more than 7 hours. For fiber lasers demanding high-temperature stability or high-power operation, regenerated-grating-based DBR fiber laser (RDBR) stands out as a simple and reliable solution.In this work, seed gratings were fabricated in standard telecommunications fibers (Corning SMF-28). To enhance photosensitivity, the fibers were soaked in a hydrogen chamber at T ∼ 25°C, P ∼ 2400 psi (165 bars) for about 1 week. Two L 2.5 cm long FBGs with λ Bragg ...

Extreme Environment Sensing Using Femtosecond Laser-Inscribed Fiber Bragg Gratings

“…For high temperature or high optical power conditions Type I FBGs will not withstand the harsh conditions. Thermally stable regenerated gratings were used to create a fiber laser cavity that could operate at high temperature [ 135 ]. Regenerated gratings typically have low reflectivity and therefore are not appropriate for some fiber laser cavity configurations.…”

Ultrahigh-Temperature Regeneration of Long Period Gratings (LPGs) in Boron-Codoped Germanosilicate Optical Fibre

“…Although the regenerated LPGs reported here are not strong, the basis for much stronger regenerated LPGs through optimization of both fibre design and materials has been established. It is worth pointing out that the first regenerated FBGs were quite weak [ 6 ], but now regenerated FBGs are strong enough for regenerated fibre lasers [ 34 ], and applied in real field tests, such as diesel locomotive turbine temperature diagnostics [ 23 ]. What’s more, for distributed high temperature applications such as those involving aircraft and vehicular interrogation where low resolution and low cost lightweight systems are needed arrays of weak LPGs are required to tap off a small amount of light and to equalize system performances.…”

Simulation of wide wavelength tuning of As2Se3 π-PSFBG narrow band fiber laser based on temperature and strain

“…Particularly, soft glass FBGs exhibit advantages in the sensing field, for example, their higher thermo-optic and thermal expansion coefficient can increase the sensitivity of temperature sensing. Although fiber lasers made by silica PSFBGs have been put into application [29][30][31], those based on soft glass PSF-BGs which have higher sensing performance have rarely been studied.…”