Khurram Naeem

High-Sensitivity Temperature Sensor Based on a Selectively-Polymer-Filled Two-Core Photonic Crystal Fiber In-Line Interferometer

A highly sensitive temperature sensor based on an all-fiber Mach-Zehnder interferometer using a selectively polymer-filled two-core photonic crystal fiber is experimentally demonstrated. The sensor fiber was made by the manual gluing and subsequent infiltration of polymer; the cladding air holes surrounding one core were selectively filled with a polymer material with a high thermo-optic (TO) coefficient while leaving those of the other core unfilled, and this led to the large TO mismatch between two cores. It was found from measurements that a very high temperature sensitivity of 1.595 nm/°C could be achieved, which was more than two orders of magnitude higher than that of the sensor fiber before the selective filling process.

Simultaneous multi-parameter measurement using Sagnac loop hybrid interferometer based on a highly birefringent photonic crystal fiber with two asymmetric cores

We have experimentally investigated the multi-parameter sensing characteristics in a novel all-fiber Sagnac loop hybrid interferometer based on a highly birefringent photonic crystal fiber with two asymmetric cores. The sensor device was based on a combination of two types of in-fiber interferences, the intra-core-mode Sagnac interference and the inter-core-mode Mach-Zehnder interference due to the distinct birefringent properties associated with the asymmetric cores. Fast Fourier transform analysis on the transmission spectra of the device exhibited six clear peaks in the spatial frequency domain. By examining the phase shift responses of two distinct Sagnac and one Mach-Zehnder interference peaks, the response matrix that enable simultaneous measurement of torsion, strain, and temperature could be obtained. The proposed all-fiber Sagnac loop hybrid interferometer has the advantages such as simplicity of the device structure, compact device size, and capability for simultaneous sensing of multiple parameters.

Multibeam Interferometer Using a Photonic Crystal Fiber with Two Asymmetric Cores for Torsion, Strain and Temperature Sensing

We present a fiber-optic multibeam Mach-Zehnder interferometer (m-MZI) for simultaneous multi-parameter measurement. The m-MZI is comprised of a section of photonic crystal fiber integrated with two independent cores of distinct construction and birefringence properties characterized for torsion, strain and temperature sensing. Due to the presence of small core geometry and use of a short fiber length, the sensing device demonstrates inter-modal interference in the small core alongside the dominant inter-core interference between the cores for each of the orthogonal polarizations. The output spectrum of the device is characterized by the three-beam interference model and is polarization-dependent. The two types of interferometers present in the fiber m-MZI exhibit distinct sensitivities to torsion, strain and temperature for different polarizations, and matrix coefficients allowing simultaneous measurement of the three sensing parameters are proposed in experiment.

Torsion sensing characteristics of a highly birefringent photonic crystal fiber with two asymmetric cores in the Sagnac loop

We experimentally demonstrated torsion sensing characteristics of a highly-birefringent asymmetric two-core photonic crystal fiber (HB-ATCPCF) in the Sagnac loop configuration. Two cores in the HB-ATCPCF exhibit distinct birefringence properties and light launched into them propagate with negligible coupling. The transmission interference spectrum of the device shows six frequency peaks in the spatial domain, which corresponds to the two Sagnac and four Mach-Zehnder interference spectra characterized by the four-beam interference model. Torsion response of the device was investigated by measuring the shift of the peak wavelength and the fringe visibility of the fiber interferences using fast Fourier transform-based spectrum-demodulation method.

Versatile chemical molecule sensing using multi-wavelength fiber laser based on inter-core interference in twin-core photonic crystal fiber

We propose and experimentally demonstrate a new chemical molecule sensing scheme using multi-wavelength fiber laser based on inter-core interference in twin-core photonic crystal fiber. In our proposed multi-wavelength fiber laser, two separated cores are integrated in a single photonic crystal fiber and surrounded by air channels. The anti-symmetrical super-modes participate in inter-core interference, which leads to the formation of twin-core photonic crystal fiber-based wavelength-selective comb filter. Most of the evanescent waves are localized in the 13 air channels around the two integrated cores, where light-matter interaction takes in place. The presence of chemical molecules in the air channels of TC-PCF leads to perturbation of the inter-core effective index difference between the two propagating core modes and the associated lasing wavelength shift.

Detection of chemical vapor with twin-core photonic crystal fiber based in-reflection interferometer

We report and demonstrate a twin-core photonic crystal fiber based in-reflection interferometer for chemical vapor detection. The interferometer is composed of end-cleaved twin-core photonic crystal fiber (TC-PCF) and fiber circulator. Infiltrating chemical molecules in the air holes of TC-PCF lead to change in inter-core effective index difference and associated fringe shift in the interferometer. The potential applications of the proposed device are also discussed.

Strain characteristics of a photonic crystal fiber with two birefringent cores in the Sagnac loop

We experimentally investigated the strain sensing characteristics of two types of the high-birefringent two-core photonic crystal fibers (HB-TCPCF) in the Sagnac loop configuration using phase-monitoring method, where each elliptic core in a typical birefringent fiber independently forms a distinct Sagnac loop interferometer.

Temperature sensitivity of the inline interferometer based on a two-core photonic crystal fiber selectively filled with polymer

We propose and demonstrate a highly sensitive micro-fluidic temperature sensor based on a two-core photonic crystal fiber (TCPCF). TCPCF has two cores of small asymmetry in sizes that serves as two arms in the inline Mach-Zehnder interferometer (MZI). Using manual gluing and subsequent infiltration technique, the cladding air holes near one core are selectively filled with polymer of high thermo-optic coefficient, which makes its core-mode effective index sensitive to temperature variation and induces large thermo-optic mismatch between the two cores. A high sensitivity of 1.595 nm/ oC is achieved in our experiment, which is almost 200 times improved from that of the sensor device before polymer infiltration process.

All-fiber Sagnac loop hybrid interferometer based on a highly birefringent photonic crystal fiber with two asymmetric cores and its sensing applications

We experimentally demonstrate a novel all-fiber Sagnac loop hybrid interferometer (SLHI) based on a highlybirefringent photonic crystal fiber with two asymmetric cores. Two cores exhibit unique birefringence properties and the light launched into them propagates with negligible coupling. Fast Fourier transform analysis of the transmission spectrum shows six frequency peaks in the spatial domain due to multiple interferences comprising the intra-core and inter-core mode interferences characterized by the four-beam interference model. The device response is investigated under the application of torsion, strain and temperature by measuring the phase-shift responses of three fiber interferences in the SLHI. The device application in simultaneous multi-parameter measurement is also discussed.

Strain and temperature sensing characteristics of asymmetric-twin- core PCF-based hybrid Mach-Zehnder interferometer

We investigate the strain and temperature sensing characteristics of an inline hybrid Mach-Zehnder interferometer (HMZI) formed by splicing a short section of asymmetric twin-core photonic crystal fiber (ATC-PCF) between two single mode fibers. For fixed polarization state of input light, two cores due to their asymmetric construction strongly support the propagation of few dominant core-modes, specifically, a lowest-order, and a set of lowest- and higher-order core-modes, respectively; this leads to a unique phase difference between inter-core and intra-core mode fiber interferometers in our ATC-PCF based HMZI. Experimental results reveal that, among different orders of interferometers involved in the HMZI, the interferometer with higher-value of modal refractive index difference exhibit larger phase-shift sensitivity to the surrounding perturbations.