Waist-enlarged Bitapers Research Articles

High Sensitivity Optical Fiber Mach-Zehnder Refractive Index Sensor Based on Waist-Enlarged Bitaper.

A Mach–Zehnder fiber optic sensor with high refractive index response sensitivity was developed. By fabricating a waist-enlarged bitaper structure on the interference arm of a single mode–multimode–single mode (SMS) Mach–Zehnder interferometer (MZI), the spectral contrast and response sensitivity were improved. Subsequently, the response sensitivity was further improved by etching the interference arm. When a beam of light was introduced into the sensor, due to the structural mismatch between the multimode fiber and the normal transmission light, the difference between the low-order mode and the high-order mode was generated in the fiber core and the fiber cladding. In the process of transmission in the sensing arm, due to the different refractive indices of the core and cladding, the optical path difference of the high-order mode and the low-order mode was different, which eventually generated interference fringes. The experimentally measured response sensitivity of SMS MZI in the range of 1.351 RIU to 1.402 RIU is 57.623 nm/RIU; the response sensitivity of a single mode–multimode–bitaper–multimode–single mode (SMBMS) MZI is 61.607 nm/RIU; and the response sensitivity of the etched SMBMS (ESMBMS) MZI is 287.65 nm/RIU. The response sensitivity of the new ESMBMS MZI is three times higher than that of the original SMS MZI. The sensor has the characteristics of compact structure, high sensitivity, easy manufacture, and a wide range of refractive index measurements, and can be used in food processing, pharmaceutical manufacturing and other fields.

Simultaneous Measurement of Temperature and Refractive Index Using Michelson Interferometer Based on Waist-Enlarged Fiber Bitaper.

An all-fiber temperature and refractive dual-parameter-sensing Michelson interferometer is designed based on the waist-enlarged bitaper. At 5 mm from the fiber end, the waist-enlarged bitaper is manually spliced and the probe is formed. Since the input light encounters the waist-enlarged bitaper, it will excite high-order modes to transmit in the fiber cladding, and there will be an optical path difference between the basic mode and the higher-order mode. The light transmitted in the core and cladding is reflected upon encountering the fiber end face and the interference occurs due to the optical path difference between basic mode and higher-order mode. Changes in temperature and refractive index at the fiber probe can be detected by monitoring the interference fringes. The refractive response sensitivity is −191.06 dBm/RIU from 1.351 RIU to 1.4027 RIU, and the temperature response sensitivity is 0.12 nm/°C from 11 °C to 98 °C. Through the sensitivity matrix equation, the superimposed refractive index and temperature signals can be effectively demodulated. The sensor has the advantages of multi-parameter measurement, compact structure, low cost, easy fabrication and high reliability.

Hydrogen Sulfide Gas Sensor Based on Copper/Graphene Oxide Composite Film-Coated Tapered Single-Mode Fibre Interferometer

Abstract A hydrogen sulfide (H2S) gas sensor based on copper (Cu) nanoparticle deposited graphene oxide (GO) composite membrane with two waist-enlarged tapers is proposed. Three segments of the single-mode fibres (SMFs) are sequentially fused to obtain two waist-enlarged bitapers of Mach–Zehnder interferometer (MZI). When the light of a broadband light source transmits through the first bitaper, some light enters the fiber cladding; the lights of core mode and cladding mode are coupled at the second taper and an MZI is successfully fabricated. The copper/graphene oxide (Cu/GO) composite sensing film is coated on the surface of the second SMF, and the effective refractive index of the coating is changed when the sensitive film adsorbs the target gas. The correlation between the gas concentration and the wavelength shift is achieved and the H2S can be measured effectively. The results show that a uniform Cu/GO film is successfully coated on the surface of the fiber, and when the thickness of the sensitive film is about 1.2 μm, the sensor has a sensitivity of 4.42 pm/ppm and a good linearity and selectivity for H2S in the range of 0–60 ppm, and the limit of detection is 2.79 ppm. The response time and recovery time are approximately 31 and 48 s, respectively. The sensor has the advantages of small volume, low cost, simple structure, and easy manufacture and so on, which is suitable for on-line monitoring of H2S.

Graphene-Based Waist-Enlarged Optical Fibre Sensor for Measurement of Sucrose Concentration

Abstract A novel sucrose sensor based on graphene-coated optical fibre with waist-enlarged bitapers as Mach-Zehnder interferometer is proposed and demonstrated. The sensor is formed by arc fusion splicing a photonic crystal fibre (PCF) sandwiched between two single-mode fibres (SMFs). The intermodal interference is achieved by two waist-enlarged fibre tapers at the coupling points between the PCF and two SMFs. The result shows that the dips of transmission spectra exhibit blue shift with the concentration increase of the sucrose, and the sensor has a high linear response (R2 = 0.98233) to sucrose with an excellent sensitivity of 3.36 pm/ppm in the range of 0–230 ppm. Additionally, the surface adsorption mechanism is also discussed. Such easily fabricated, cost-effective and small volume fibre interferometer could be used for sucrose sensing applications.

High temperature high sensitivity Mach-Zehnder interferometer based on waist-enlarged fiber bitapers

An optical Mach-Zehnder interferometer (MZI) composed of a short section of thin-core fiber (TCF) which inserted into a standard single-mode fiber (SMF) with two waist-enlarged bitapers was proposed for high temperature measurement. MZIs with different lengths were fabricated, and the relationship between length and interference period was studied. The fast Fourier transform (FFT) method was used to determine the transmitted spectra of MZIs, and the results indicate that LP01 and LP02 modes are the main modes. The MZI has a high temperature sensitivity of 0.087nm/°C with a good linearity of 99.8% from 30 to 1000°C. Because it has advantages of compact size, easy fabrication, high sensitivity, high mechanical strength and wide sensing range, the MZI can be used for high sensitivity temperature measurement.

A carboxy-methyl cellulose coated humidity sensor based on Mach-Zehnder interferometer with waist-enlarged bi-tapers

A fiber-optic Mach-Zehnder interferometer (MZI) humidity sensor is proposed, comprising a pair of waist-enlarged bi-tapers and carboxy-methyl cellulose (CMC) coating. The MZI utilizes intermodal interference between the core mode and cladding modes for the measurement of the effective refractive index (RI) of the CMC film that varies with surrounding humidity, through change in the sensor’s interference pattern. The proposed sensor is linearly responsive to relative humidity (RH) within the humidity range from 70% RH to 85% RH, with maximum sensitivity of −0.8578 dB/% RH. The advantages of this sensor are its compact size and a facile fabrication process. More importantly, humidity sensitivity can be improved by changing the thickness of the CMC film, which makes this structure a highly promising for real-time, practical RH monitoring application.

Research on high sensitivity temperature sensor based on Mach-Zehnder interferometer with waist-enlarged fiber bitapers

Optical fiber sensing technology is one of the very promising techniques in sensing fields. A high sensitivity high temperature sensor based on inline optical fiber Mach-Zehnder(M-Z) interferometer by using standard single mode fiber with two waist-enlarged bitapers is proposed in the present paper. The waist-enlarged bitapers are considered as couplers, the distance between the two bitapers is the sensing arm. The light in the lead-in fiber core couples into the sensing arms' fiber core and cladding by the first bitaper, and then propagate in them. The phase difference between core mode and cladding mode is produced when the light reaches the second bitaper. Then the second bitaper couples the light into the lead-out single-mode fiber to get the interference spectrum. The sensors with different length were fabricated. The relationship between the sensor length and interference period, and the temperature response of the.sensor were studied by experiments. The results show that the 35 mm long sensor has a high sensitivity of 0.115 nm x degrees C(-1) in the range of 30-400 degrees C. The transmission spectrum of the sensor was also analyzed by the fast Fourier transform. It shows that only LP01 mode and LP08 mode propagate in the sensor. Thesensor has advantages of small size, high precision, and immunity to electromagnetic inteference. In addition, it is of easy fabrication, high signal-to-noise ratio, light weight, and high sensitivity, and could be operated under high temperature. This kind of sensor is a good candidate for high temperature measurement of hot gas, oil and gas well logging and other areas.

Miniature pH optical fiber sensor based on waist-enlarged bitaper and mode excitation

A polyvinyl alcohol/poly-acrylic acid (PVA/PAA) hydrogel coated optical fiber interferometer was been evaluated as a pH sensor. The interferometer, which comprises a waist-enlarged bitaper, a round tip and a tantalum pentoxide layer displays high refractive index (RI) sensitivity. With the hydrogel coated, the sensor's optical interference fringes shifted with exposure to varying pH solutions. High pH sensitivity of 1.58nm/pH was achieved for pH 2.48–6.47. The miniature sensor demonstrates little hysteresis, high repeatability and low cross-sensitivity to temperature. A rising/falling time of 10/11s for the sensor time response was acquired, respectively.