Sun-jie Qiu

Demonstration of a compact temperature sensor based on first-order Bragg grating in a tapered fiber probe

We experimentally demonstrate an all-silica first-order fiber Bragg grating (FBG) for high temperature sensing by focused ion beam (FIB) machining in a fiber probe tapered to a point. This 61-period FBG is compact (~36.6 μm long and ~6.5 μm in diameter) with 200-nm-deep shallow grooves. We have tested the sensor from room temperature to around 500 °C and it shows a temperature sensitivity of nearly 20 pm/°C near the resonant wavelength of 1550 nm. This kind of sensor takes up little space because of its unique geometry and small size and may be integrated in devices that work in harsh environment or for detecting small objects.

Temperature sensor based on an isopropanol-sealed photonic crystal fiber in-line interferometer with enhanced refractive index sensitivity

We fabricate a simple, compact, and stable temperature sensor based on a liquid-sealed photonic crystal fiber (PCF) in-line nonpolarimetric modal interferometer. Different from other reported PCF devices, it does not need expensive polarimetric devices, and the liquid is sealed in one fiber. The device consists of a stub of isopropanol-filled PCF spliced between standard single-mode fibers. The temperature sensitivity (-166 pm/°C) increases over an order of magnitude compared with those of the previous sensors based on air-sealed PCF interferometers built via fusion splicing with the same mechanism. In addition, the refractive index sensitivity also increases. Higher temperature sensitivity can be realized by infiltrating some liquid having a higher thermo-optic coefficient into the microholes of the PCF.

Miniature tapered photonic crystal fiber interferometer with enhanced sensitivity by acid microdroplets etching

We fabricate a miniature tapered photonic crystal fiber (PCF) interferometer with enhanced sensitivity by acid microdroplets etching. This method is very simple and cost effective, avoiding elongating the PCF, moving and refixing the device during etching, and measuring. The refractive index sensing properties with different PCF diameters are investigated both theoretically and experimentally. The tapering velocity can be controlled by the microdroplet size and position. The sensitivity greatly increases (five times, 750 nm/RIU) and the size decreases after slightly tapering the PCF. The device keeps low temperature dependence before and after tapering. More uniformly and thinly tapered PCFs can be realized with higher sensitivity (∼100 times) by optimizing the etching process.

Ultra-Sensitive Refractive Index Sensor With Slightly Tapered Photonic Crystal Fiber

We fabricate a miniature ultra-sensitive refractive index sensor based on a tapered photonic crystal fiber (PCF) modal interferometer. The PCF is slightly tapered and a little elongated to keep the size compact. The total length is ~ 2 cm, and the potential sensitivity is more than 1600 nm/RIU (refractive index unit), which is nearly eight times as high as that of an untapered PCF interferometer.

Miniaturized Metal-Dielectric-Hybrid Fiber Tip Grating for Refractive Index Sensing

We fabricate a miniaturized metal-dielectric-hybrid fiber tip grating (FTG) using a focused ion beam (FIB) method with high accuracy for refractive index sensing applications. It is the smallest fiber grating by now (nearly 10 μm in length located at the fiber tip of 3 μm in radius) and it has strong surface corrugations with notches periodically. The grating shows refractive index sensitive [125 nm/refractive index unit (RIU)] and insensitive (nearly zero) properties for reflection channels of different resonant modes by metal-dielectric cladding structure. It can be used as a multichannel sensor for simultaneous refractive index and temperature/pressure measurements. Taking advantage of its flexible design, tiny size, unique modal and spectral characteristics, the metal-dielectric-hybrid FTG has great potential in fast-response detection of ultrasmall objects.

An All-Fiber Reflective Hydrogen Sensor Based on a Photonic Crystal Fiber In-Line Interferometer

A new method based on introducing a photonic crystal fiber (PCF) in-line interferometer for hydrogen sensing is demonstrated. One end-face of the PCF and part of the outer-face of the fiber are plated with a thin palladium film by magnetron sputtering, while the other end is connected to the optical path. Therefore, a set of reflection-type all-fiber hydrogen sensor system is accomplished. Hydrogen concentration from 0% to 5% was detected in the experiment and the related interferometric resonant wavelength-shift was recorded. The maximum wavelength shift is over 1.2 nm. The whole system has an all-fiber optical path without any bulk-optic components, and this design obtains a high level of integration, a high stability, and low production costs.

Lead silicate fiber-based, refractive index-independent temperature sensor

Thee fabrication is reported of a simple, compact, and stable refractive index (RI)-independent temperature sensor based on a soft glass fiber (SGF) interferometer. Because the SGF has a high thermal expansion coefficient and a high RI, it is sensitive to temperature change but not sensitive to the RI change of liquids with lower RI. It thus can be used to detect the temperature change of aqueous solutions accurately. As an example, a temperature sensor with a temperature sensitivity of ∼17 pm/°C and a negligible RI sensitivity of only about −1 nm/RIU (RI unit) in the range 1.32–1.43 is demonstrated. In addition, our SGF interferometer has potential applications and advantages in detecting liquids such as liquid crystals with higher RI.

A compact first-order Bragg grating in a tapered fiber probe for high temperature sensing

We experimentally demonstrate an all-silica first-order fiber Bragg grating (FBG) for high temperature sensing by focused ion beam (FIB) machining in a fiber probe tapered to a point. This 61-period FBG is compact (~ 36.6 μm long and ~ 6.5 μm in diameter) with 200-nm-deep shallow grooves. We have tested the sensor from room temperature to around 500 °C and it shows a temperature sensitivity of nearly 20 pm/°C near the resonant wavelength of 1550 nm.

Tapered photonic crystal fiber interferometer with enhanced sensitivity

We fabricate a miniature tapered photonic crystal fiber (PCF) interferometer with enhanced sensitivity by a new acid microdroplets etching method. This method, without elongating the PCF, moving and re-fixing the device during etching and measuring refractive index sensitivity, is very simple, cost-efficient and highly stable over time. We investigate the refractive index sensing properties with different PCF diameters both theoretically and experimentally. The size decreases and the sensitivity increases an order of magnitude after etching the PCF. If we can optimize the etching process, we can fabricate more uniformly and thinly tapered PCF interferometer with higher sensitivity (∼ 100 times) theoretically in the future.