KEYWORDS: Polyvinyl alcohol, Temperature sensors, Temperature metrology, Fiber optics sensors, Optical fibers, Humidity, Single mode fibers, Sensors, Capillaries, Refractive index
The polyvinyl alcohol (PVA) with non-toxic and environmentally friendly properties has good temperature and humidity sensitivity. The refractive index (RI) is affected by both temperature and humidity. However, the high-temperature irreversibility and the moisture loss of PVA limit its application in temperature sensing. How to effectively reduce the temperature measurement errors caused by moisture loss and cross-sensitivity is an effective way to obtain a highly sensitive temperature sensor based on PVA. In this work, a PVA partly coated singlemode multi-mode single-mode (SMS) fiber temperature sensor is demonstrated. The multi-mode interference (MMI) effect in the SMS fiber structure provides measurable characteristic spectra for temperature sensing. The cross-sensitivity between humidity and temperature in PVA can be effectively reduced by using capillary sealing to prevent water loss. At the same time, partially stripped the coating layer of the coreless fiber to avoid high transmission loss caused by high RI coating. This partly coated structure can reduce dependence on measured light intensity. Experimental measurements indicated that the sensitivity of the sensor is 12.9264nm/°C, which is suitable for measuring small temperature changes with an accuracy of about 1.547 × 10−3 °C.
Suppressing Yb-ASE to overcome the bottleneck effect is the key to optimizing the efficiency bottleneck of the Erbium-Ytterbium co-doped fiber amplifier (EYDFA). In this work, we use three typical commercial laser diodes (LDs) as pump sources to experimentally compare the efficiency with variations of pump wavelength in different fiber lengths. We found that the optimal pump wavelength of EYDFA has a blue shifting with the increment of gain fiber length. The functional relationship between the optimal pump wavelength and the length of gain fiber is predicted according to the experimental results. If the fiber length increases over 20 m, the amplification efficiency under 940 nm-LD pumping conditions is better than other pumping sources. It is necessary to consider appropriately extending the fiber length to optimal efficiency using a pump source with an offset pump wavelength (such as a commercial 940-nm LD). This work provides a reliable technical reference for the practical fabrication of high-power EYDFA.
A hybrid double cladding EYDFA with SMS structure is proposed and theoretically analyzed. The hybrid gain fiber with SMS structure is composed of two kinds of EYDFs with different core diameter. The output power performance and output spectra of the amplifier with hybrid gain fiber are numerical analyzed, and are compared with that of the amplifier with uniform gain fiber. The simulation results demonstrate that this fiber amplifier with SMS structure gain fiber can suppress the Yb-ASE by over 10 dB without output power reduction. It provides a monolithic structure for EYDFA to overcome pump bottleneck effect and achieve high efficiency and high power output.
We have demonstrated an efficient 1720-nm all-fiber laser with ring-cavity configuration based on commercial Tmdoped silica fiber and 1570-nm in-band pump source. The rate equation model was built up to analyze the laser performance of Tm-doped fiber, which exhibits strong absorption in 1.7-μm region. The results show that efficient laser operation can be achieved through the optimization of output coupling and the length of Tm-doped fiber. By using homemade couplers, we experimentally achieved 2.36-W laser output power under 6-W launched pump power. The slope efficiency with respect to the absorbed pump power and optical efficiency were 50.2% and 39.3%, respectively. Due to the employment of ring resonator, a narrow laser linewidth of ~4 GHz at maximum output power was observed.
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