Low-cost Refractive Index Sensor Research Articles

The Simulation of a Surface Plasmon Resonance Metallic Grating for Maximizing THz Sensitivity in Refractive Index Sensor Application

Nowadays, the simplicity of both designing and fabrication process of a terahertz (THz) resonator-based sensing technique leads to its ongoing development. The consumable THz resonator needs to be easily integrated into an existing terahertz time domain spectroscopy (THz TDS) measurement system. It should also be able to be fabricated in a mass scale with a low production cost. In this work, a metal-coated surface plasmon resonance- (SPR-) based sensor is simulated and designed as a low-cost refractive index sensor utilizing rigorous coupled wave analysis (RCWA). To demonstrate our methodology, we design a gold-coated grating with a polydimethylsiloxane (PDMS) as a substrate, in order to perform quantitative analysis of gasoline-toluene mixture composition, which has a refraction index variation of 0.1 at THz frequency. The grating period is tuned such that its surface plasmon resonance (SPR) frequency matches with the peak frequency of the THz TDS system. Moreover, other grating parameters, i.e., a filling factor and a grating depth, are optimized to increase the sensor sensitivity and sharpen the resonance dip. High sensitivity up to 500 GHz/RIU with a refractive index resolution up to 0.01 is numerically revealed. The H-field of the designed grating is then evaluated to indicate a strong SPR excitation. The well-developed designed grating introduces a promising, low-cost, and easily fabricated THz refractive index sensor.

Low-Cost Refractive Index Sensor With Optical Fibers Attached to a U-Shaped Glass Tube

A low-cost multimode optical fiber based sensor has been reported for measuring the refractive index (RI) of liquid samples. In this sensor, a light is coupled from a multimode optical fiber to a customized U-shaped glass tube, and light emerging out of the U-shaped glass tube is guided onto a photodetector with the help of another multimode fiber. The intensity of light detected by the photodetector is found to vary with the RI of liquid sample that comes into contact with the U-shaped glass tube. A sensor response has also been observed by changing the bending radius of the glass tube and the depth of surrounding liquid medium. The proposed sensor is expected to be more rugged and reliable, as compared to a tapered optical fiber and the U-shaped optical fiber refractometers.

Depressed index clad fiber as a highly sensitive low-cost refractive index sensor

We present a simple, compact, low cost and ultra high sensitive refractive index sensor based on depressed index clad fiber. The leakage loss of the fiber is highly sensitive to the variations in the refractive index of the outermost leaky layer. We utilize different portions of leakage loss curve to design sensors in different ranges, with different resolutions and for specific applications. One of such designed sensor work in the range 1.4573250–1.4573500, which corresponds to the refractive index of jojoba oil. The resolution within this range is of the order of 4 × 10−7 which is the maximum resolution of the sensor. The fabrication of the sensor only requires etching of some portion of the cladding of the fiber and does not require costly methods of wavelength or polarization interrogation.

Low Cost Refractive Index Sensor Based on Optical Lensed Fiber

A refractive index (RI) sensor based on back reflection of an optical lensed fiber is demonstrated. The sensing device is fabricated by splicing a tiny gradient index fiber (GIF) on the tip of a single mode fiber. Symmetry mirror modeling and fiber coupling efficiency are utilized to estimate the dependence of reflection power on lens pitch. As for sensing test experiments, we measured the reflection power of RI sensor with different concentrations of glycerol solution from 0 to 100% in steps of 20% increasing. The results are consistent with theoretical curve. In terms of the experimental data, important characteristics including resolution and sensitivity are obtained. The RI sensor exhibits high sensitivity −884.62 dB for high RI sensed solution. As the high index GIF spliced on tip of the sensor, it helps to extend the sensing range from 1.45 to 1.472. Due to properties of easy fabrication and low material cost, we believe the RI sensor has potential in mass production and wide application. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1744–1746, 2013

An All Fiber Intrinsic Fabry-Perot Interferometer Based on an Air-Microcavity

In this work an Intrinsic Fabry-Perot Interferometer (IFPI) based on an air-microcavity is presented. Here the air microcavity, with silica walls, is formed at a segment of a hollow core photonic crystal fiber (HCPCF), which is fusion spliced with a single mode fiber (SMF). Moreover, the spectral response of the IFPI is experimentally characterized and some results are provided. Finally, the viability to use the IFPI to implement a simple, compact size, and low cost refractive index sensor is briefly analyzed.

Physical observation of single step UV-written integrated planar Bragg structures and their application as a refractive-index sensor

We present what is to our knowledge the first demonstration of a potentially low-cost refractive-index sensor based on UV processing. A channel waveguide and a Bragg grating are defined in a single UV processing step, resulting in a buried structure with a well-defined grating period. A subsequent wet etch process located over the Bragg grating opens a sensing window in the device and reveals the grating structure. Sensitivity of as much as 5 x 10(-6) was inferred from our device.