Temperature-insensitive Refractive Index Sensor Research Articles

Temperature-insensitive refractive index sensor based on high-order-resonance short-line long-period fiber grating

Temperature-insensitive refractive index sensor based on high-order-resonance short-line long-period fiber grating

Temperature-insensitive refractive index sensor based on a spindle-shaped few-mode fiber modal interferometer.

A designed temperature-insensitive modal interferometer for refractive index measurement based on spindle-shaped few-mode fiber (FMF) is proposed and demonstrated. The interferometer consisting of a specific length of FMF fused between two specific lengths of single-mode fibers is bent into a balloon shape and then burned by a flame into a spindle shape to sensitize. Due to the bending of the fiber, part of the light leaks from the core to the cladding and excites the higher-order modes, and the four modes in the core of FMF interfere with the higher-order modes in the cladding. Therefore, the sensor is more sensitive to the surrounding refractive index. The experimental results show that the highest sensitivity is 237.3nm/RIU from 1.333 to 1.365. The sensor is insensitive to temperature, which solves the problem of temperature cross talk. In addition, with its advantages of a small mechanism, simple fabrication, low loss, and good mechanical strength, the proposed sensor has broad application prospects in chemical production, fuel storage, environmental monitoring, and other fields.

Temperature insensitive refractive index sensor based on collar-shaped fiber ring

A collar-shaped fiber ring (CSFR) with a single mode fiber for refractive index (RI) measurement is proposed and fabricated. Three CSFRs, with fiber lengths of 3.0 cm, 3.5 cm, and 4.0 cm, were fabricated and tested. The maximum RI sensitivity is higher than 630 nm RIU−1 when the RI value is 1.398. Moreover, the temperature experimental result shows that the CSFR is insensitive to temperature in the range of 10 °C–100 °C. Particularly, CSFRs are easily produced without any devices such as a fusion splicer or UV laser system.

A novel temperature insensitive refractive index sensor based on dual photonic crystal fiber

A novel dual photonic crystal fiber (DPCF) temperature insensitive refractive index sensor is proposed in this article. By sequentially splicing lead-in SMF (single mode fiber), PCF_1, PCF_2, and lead-out SMF constitute the Mach-Zehnder interferometer (MZI). The refractive index sensitivity (RIS) of the proposed sensor is improved by making an abrupt-taper on the fusion point of two PCFs. The proposed sensor is compared with a sensor without an abrupt-taper, the RIS value of the proposed sensor is increased by ∼1.9 times. The collapsed area of two photonic crystal fiber air holes is used as a beam splitter and combiner of Mach-Zehnder interferometer. Experimental analysis indicates that the RIS is 152.97 nm/RIU (1.330–1.383 RIU). Besides, the proposed sensor is independent of temperature and its sensitivity towards temperature is only -0.0045 nm/°C (30−80 °C). This sensor has the characteristics of relatively high sensitivity, ease of fabrication, and compact size.

Temperature-insensitive refractive index sensor based on tilted moiré FBG with high resolution.

We proposed and fabricated a tilted moiré FBG (TMFBG), whose grating section was made up of two consecutive scribed TFBGs. By adjusting the Bragg wavelengths and the tilt angles of the two TFBGs, the two cladding mode combs of the transmission spectrum are non-overlapped. When the TMFBG was used for refractive index detection, its resolution can reach 2 × 10-7 RIU, which is an order of magnitude higher than that of a single TFBG. And this result also has a good performance of temperature-insensitivity.

Refractive index insensitive temperature sensor based on waist-enlarged few mode fiber bitapers

A refractive index insensitive temperature sensor based on waist-enlarged few mode fiber (FMF) bitapers is presented. The first section of FMF is spliced between two single-mode fibers. In fusion process, the waist-enlarged FMF bitapers can be obtained by large current discharging repeatedly. The refractive index and temperature sensing mechanisms are analyzed. For the sensors with different sizes, the refractive index and temperature experiments have been performed. The results show that in the refractive index ranges of 1.335 0—1.346 6 and 1.348 2—1.419 3, the refractive index insensitivity is verified. In a temperature range of 31.9—90 °C, the sensor sensitivity can be up to 85.57 pm/°C. In addition, it has a compact structure. Therefore, the sensor can avoid the cross sensitivity for measuring the refractive index and temperature simultaneously.

Temperature-insensitive refractive index sensor based on Mach–Zehnder interferometer with two microcavities

We propose a temperature-insensitive refractive index (RI) fiber sensor based on a Mach–Zehnder interferometer. The sensor with high sensitivity and a robust structure is fabricated by splicing a short photonic crystal fiber (PCF) between two single-mode fibers, where two microcavities are formed at both junctions because of the collapse of the PCF air holes. The microcavity with a larger equatorial dimension can excite higher-order cladding modes, so the sensor presents a high RI sensitivity, which can reach 244.16 nm/RIU in the RI range of 1.333–1.3778. Meanwhile it has a low temperature sensitivity of 0.005 nm/°C in the range of 33°C–360°C.

Temperature-insensitive refractive index sensor based on an optical fiber extrinsic Fabry–Perot interferometer processed by a femtosecond laser

An optical fiber extrinsic Fabry–Perot interferometer (EFPI) is designed and fabricated for refractive index (RI) sensing. To test the RI of liquid, the following two different methods are adopted: the wavelength tracking method and the Fourier-transform white-light interferometry (FTWLI). The sensitivities of sensors with cavity lengths of 288.1 and 358.5 μm are 702.312 nm/RIU and 396.362 μm/RIU, respectively, by the two methods. Our work provides a new kind of RI sensor with the advantages of high sensitivity, mechanical robustness, and low cross sensitivity to temperature. Also, we provide a new method to deal with gold film with a femtosecond laser.

Temperature insensitive refractive index sensor based on a combination interference structure

A sensing head consisting of fiber loop mirror inscribed with a highly birefringence photonic crystal fiber (HiBi-PCF) was proposed and experimentally demonstrated. The HiBi-PCF was completely collapsed near the splicing points, thus the cladding mode in the HiBi-PCF would be excited, which was sensitive to the refractive index (RI) of surrounding medium. Owing to the low thermo-optic and thermo-expansion coefficient of the HiBi-PCF, the sensing head in our design was temperature insensitive. High sensitivity of 306.6±0.2nm/RIU (refractive index unit) and a resolution of 6.5×10−5RIU have been achieved for the proposed liquid refractive index sensor.

Refractive index insensitive temperature sensor based on specialty triple-clad fiber.

A refractive index (RI) insensitive temperature sensor based on specialty triple-clad fiber (STCF) is proposed. Based on coupling mode theory, the STCF can be equivalent to a rod waveguide and two tube waveguides. Then the cladding mode resonance characteristic of STCF is analyzed by calculating different mode dispersion curves, which indicates that it works only on the mode resonance from core to the fluorine-doped silica cladding, and finally a resonance wavelength can be obtained. Two straightforward experiments are performed to prove its sensing properties. Experimental results show that it has sensitivities of 72.17 pm/°C at temperature range from 35°C~95°C with characteristics of insensitive to external RI in the range from 1.3450 to 1.4607. Thus, this proposed sensor can be used for solution temperature monitoring in real time.

Temperature-insensitive refractive index sensor based on in-fiber Michelson interferometer

A novel intensity-modulated refractive index sensor based on an in-fiber Michelson interferometer is demonstrated by splicing a section of thin core fiber between two standard single mode fibers. Such a refractive index sensor exhibits an ultrahigh sensitivity of −208.24 and 125.44dB/RIU at the refractive index of 1.440 and 1.500, respectively. The refractive index sensor is insensitive to temperature and thus solves the cross-sensitivity problem between temperature and surrounding refractive index. Moreover, the promising RI sensor has the advantages of short size (less than 2mm) and easy fabrication.