Single Crystal Optical Fiber Research Articles

Oxygen sensing with SrTi1−xFexO3-δ thin films on sapphire optical fiber at extreme temperatures

Optical fiber-based sensors are uniquely suited for in-situ sensing applications that involve high operational temperature and harsh chemical conditions, such as solid oxide fuel cell (SOFC) monitoring, chemical manufacturing, and power generation. Single crystal optical fiber, such as α-alumina (sapphire), provides a substrate that exhibits improved stability over off-the-shelf silica fiber at temperatures above 800 °C. In this work, single crystal sapphire fiber is paired with a high-temperature stable perovskite oxide sensing layer, SrTi0.65Fe0.35FeO3-δ (STF35), to demonstrate all-optical oxygen sensing from 0.01 to 0.19 atm at extreme temperatures (800–1000 °C). The defect chemistry associated with the optical oxygen sensing response is also considered within the context of the current literature and modeled under relevant sensor conditions. Stability is evaluated under dry and humid conditions, and low cross-sensitivity with CO2 is demonstrated, indicating viability for operation on the cathode stream within an operational SOFC or within a post-combustion environment.

Thermally robust and highly stable method for splicing silica glass fiber to crystalline sapphire fiber.

This research reports an advancement in splicing silica glass fiber to sapphire single-crystal optical fiber (SCF) using a specialized glass processing device, including data that demonstrate the thermal stability of the splice to 1000°C. A filament heating process was used to produce a robust splice between the dissimilar fibers. A femtosecond laser is used to inscribe a fiber Bragg gratings sensor into the SCF to measure the high-temperature capabilities and signal attenuation characteristics of the splice joint. The experimental results demonstrate that the proposed splicing method produces a splice joint that is robust, stable, repeatable, and withstands temperatures up to 1000°C with a low attenuation of 0.5dB. The proposed method allows placement of SCF-based sensors in the extreme environments encountered in various engineering fields, such as nuclear, chemical, aviation, and metals manufacturing, to enable improvements in process monitoring, product quality, and production efficiency.

Sensitivity-enhanced Tm3+/Yb3+ co-doped YAG single crystal optical fiber thermometry based on upconversion emissions

Optical thermometry based on Y3Al5O12 (YAG) single crystal optical fiber with end Tm3+/Yb3+ co-doped is presented. The YAG crystal fiber with end Tm3+/Yb3+ co-doped was grown by laser heated pedestal growth (LHPG) method. Under a 976 nm laser diode excitation, the upconversion (UC) emissions, originating from 3F2,3→3H6 and 3H4→3H6 transitions of Tm3+ ions, were investigated in the temperature range from 333 K to 733 K. Interestingly, the UC emission intensity of 3F2,3→3H6 transition was significantly enhanced with increase of temperature, as compared with the other Tm3+/Yb3+ co-doped materials. The temperature dependence of fluorescence intensity ratio (FIR) of these two emission bands (3F2,3/3H4→3H6) suggests that this doped YAG crystal fiber can be used as a highly sensitive optical thermal probe, which demonstrates a high absolute sensitivity with the maximum value of 0.021 K−1 at 733 K. In addition, due to the compact structure, strong mechanical strength and high thermal stability, such thermal probe may be a more promising candidate for temperature sensor with a high spatial resolution.

Compact and sensitive Er3+/Yb3+ co-doped YAG single crystal optical fiber thermometry based on up-conversion luminescence

Compact and sensitive Er3+/Yb3+ co-doped YAG single crystal optical fiber thermometry based on up-conversion (UC) luminescence is presented. The thermal probe is a YAG single crystal fiber with end Er3+/Yb3+ co-doped grown by laser heated pedestal growth method. Excited by a 976nm laser diode, the UC fluorescence intensity ratio (FIR) of the Er3+ ions in two emission bands (2H11/2,4S3/2→4I15/2) was investigated in the temperature range from 298K to 723K. The results indicate that the maximum temperature sensitivity is approximately 0.00486K−1 at 577K. Thus, the Er3+/Yb3+ co-doped YAG single crystal fiber has potential application in optical thermometry by the FIR technique. Furthermore, the thermal probe has compact structure and high thermal stability, making it a more convenient and effective optical fiber temperature sensor.

Single-crystal Y2O3-ZrO2 rectangular waveguides for ultrahigh-temperature sensing applications.

High-quality Y2O3-ZrO2 single-crystal rectangular waveguides have been developed for ultrahigh-temperature sensing applications. Five waveguides, 0.55-1.12 mm wide and 52-65 mm long, were fabricated from a bulky cubic 21.2-mol. % Y2O3 stabilized ZrO2 single crystal that had been precisely cut and finely polished. At 900-nm wavelength, the average optical loss of these waveguides is approximately 0.016 dB/cm, which is much lower than that of Y2O3-ZrO2 single-crystal optical fibers grown by the laser-heated pedestal growth method. The tested waveguides survived a temperature higher than 2,300 degrees C, and their mechanical strength and chemical resistance were also acceptable. Experimental results show that these waveguides are promising for ultrahigh-temperature sensing applications.

Growth of high-quality Y 2O 3–ZrO 2 single-crystal optical fibers for ultra-high-temperature fiber-optic sensors

Y 2O 3–ZrO 2 (Y 2O 3 stabilized ZrO 2) single-crystal fibers are promising candidates for developing ultra-high-temperature fiber-optic sensors; however, grown by conventional laser heated pedestal growth (LHPG) system, these fibers showed relatively low optical and mechanical qualities due to thermal stress caused by large temperature gradient during the growth, preventing the sensors from achieving high performance in our previous work. In order to grow high-quality Y 2O 3–ZrO 2 single-crystal fibers with less stress, in this paper, according to the theoretical analysis, we have improved the growth system by adding an additional heating system, and the temperature gradient during growth has been reduced to an acceptable value. Five Y 2O 3–ZrO 2 single-crystal fibers have been grown by the improved system; experimental test results showed that the optical and mechanical qualities of these fibers have been greatly enhanced, with which the ultra-high-temperature fiber-optic sensors with better performance could be developed.

Two-wave mixing in photorefractive Bi_12SiO_20 fibers

We present what is to our knowledge the first experimental observation of the energy-exchange effect between two coherent beams in Bi(12)SiO(20) single-crystal optical fiber grown by the laser-heated pedestal growth technique.

Single-crystal AgBr infrared optical fibers

Single-crystal optical fibers up to 2 m long with well-defined crystal orientation have been grown from AgBr, which is transparent from ~0.5 to 25μm. The measured attenuation at 10.6 μm was ~2 × 10−2 cm−1, equal to the bulk loss in the raw material.