A novel and simple optical fiber structure with a section of no-core fiber for measuring hydrogen concentration is presented. Palladium is sputtered to form the coating on the no-core fiber by magnetron sputtering coater. Under different hydrogen conditions, the absorption of hydrogen induced refractive index changes on the outside coating of no core fiber will lead to the variations of the optical output spectrum. Different concentrations of hydrogen are tested, from 4%-0.5%, shows the concentration is relevant with the response time and recovery time. The response time of this sensor is from 300s (4% H2) to 1800s (0.5% H2) depending on the hydrogen concentration. The recovery time of this sensor is from 1200s (4% H2) to 4800s (0.5% H2) depending on the hydrogen concentration. Furthermore, the repeatability and response time of the sensor of this study are investigated experimentally.
We proposed a compact and cost-effective red–green dual-color fiber optic surface plasmon resonance (SPR) sensor based on the smartphone. Inherent color selectivity of phone cameras was utilized for real-time monitoring of red and green color channels simultaneously, which can reduce the chance of false detection and improve the sensitivity. Because there are no external prisms, complex optical lenses, or diffraction grating, simple optical configuration is realized. It has a linear response in a refractive index range of 1.326 to 1.351 (R2 = 0.991) with a resolution of 2.3 × 10 − 4 RIU. We apply it for immunoglobulin G (IgG) concentration measurement. Experimental results demonstrate that a linear SPR response was achieved for IgG concentrations varying from 0.02 to 0.30 mg / ml with good repeatability. It may find promising applications in the fields of public health and environment monitoring owing to its simple optics design and applicability in real-time, label-free biodetection.
In this paper, we propose and demonstrate a novel self-referencing surface plasmon resonance (SPR) fiber-optic sensor which provides a Fabry-Perot (FP) interference referencing signal for temperature compensating. The sensor is fabricated by splicing a capillary partly coated with gold film between multimode fibers. The multimode fibers act as the lead-in and lead-out fibers while the capillary is used as sensing element. Because the FP interference and SPR effects can occur in the capillary simultaneously, the spectrum of the sensor exhibits SPR absorption and FP interference fringes. Due to the FP interference fringe sensitive to temperature while insensitive to refractive index (RI), it can be used as referencing signal and the SPR absorption was used as measuring signal. Experimental results show that this approach we presented can compensate temperature effect and develop this sensor as a practicable high-sensitivity sensing device. Moreover, as a self-referencing fiber-optic SPR sensor, this simple and low-cost element can be used for highly sensitive biosensing for further investigations.
A novel evanescent field refractometer based on a two-core photonic crystal fiber (TWPCF) sandwiched between multimode fibers(MMFs) is demonstrated. Through splicing a short piece of TWPCF between two MMFs, a simple structure and high sensitivity RI sensor can be constructed. Instead of using wavelength information as sensor signal, we focus more on the light intensity signal different from most PCF based RI sensor. The TWPCF section functions as a tailorable bridge between the excited high order modes and the surrounding refractive index (SRI). With a light filter inserting in the front of white light, the transmission spectrum of the light through the sensing region occurs in a welldefined wavelength bands. As a result, the peak power of the transmission light is tailored with the SRI perturbation via the MMF-TWPCF–MMF structure. The experiment result shows a quadratic relation between the light intensity and samples within RI range of 1.33-1.41 while a linear response can be achieved from the 1.33-1.35 which is a most used RI range for biologically sensing.
We report two fiber multiple-mode interferometers formed in photonic crystal fiber (PCF). The interference between the core and the cladding modes of a PCF is utilized. We use two methods to form a coupling point, and the cladding modes are excited from the fundamental core mode. One method is blowing compressed gas into the air holes and discharging at the coupling point; the air holes will expand due to gas expansion in the discharge process. Similarly, the other is discharging at the coupling point after the air is exhausted from the air holes, and the holes will contract during the process. By making another coupling point at a different location along the fiber, the proposed PCF interferometers are implemented. Experimental results show that the sensitivities of the two devices can achieve 1.54 and 1.45 nm for a 0.01 refractive index change.
We report a type of multimode fiber interferometers (MMI) formed in photonic crystal fiber (PCF). To excite the cladding modes from the fundamental core mode of a PCF, a coupling point is formed. To form the coupling point, we used the method that is blowing compressed gas into the air-holes and discharging at one point, and the air-holes in this point will expand due to gas expansion in the discharge process. By placing two coupling points in series, a very simple all-fiber MMI can be implemented. The detailed fabrication process is that the one end of the PCF is tightly sealed by a short section of single mode fiber (SMF) spliced to the PCF. The other end of the PCF is sealed into a gas chamber and the opened air holes are pressurized. The PCF is then heated locally by the fusion splicer and the holes with higher gas pressure will expand locally where two bubbles formed. We tested the RI responses of fabricated sensors at room temperature by immersing the sensor into solutions with different NaCl concentration. Experimental results show that as refractive-index (RI) increases, the resonance wavelength of the MMI moves toward longer wavelengths. The sensitivity coefficients are estimated by the linear fitting line, which is 46nm/RIU, 154mn/RIU with the interferometer lengths (IL) of 3mm and 6mm. The interferometer with larger IL has higher RI sensitivity. The temperature cross-sensitivity of the sensor is also tested. The temperature sensitivity can be as low as -16.0pm/°C.
We present a wavelength-tunable tapered optics fiber surface Plasmon resonance (SPR) sensor by polishing the end faces of multimode fibers(MMF).Two hard plastic clad optical fibers joint closely and are used as the light input and output channels. Their end faces are polished to produce two oblique planes, which are coated with gold film to be the sensing surface and the front mirror. The presence of the tapered geometry formed by the two oblique planes in the orthogonal directions makes it possible to adjust incident angle through changing the tilt angles of the two end faces, so as to achieve tuning the SPR coupling wavelength-angle pair. Compared with previous researches based a tapered optic fiber probe, we report the approach theoretically increase the signal noise ratio (SNR) by separating incident and emergent light propagating in the different coordinate fiber. Since fabricating the sensing surface and the front mirror on the two fibers to replace one single fiber tip, there is more incident light can reach the sensing surface and satisfy SPR effective. In addition, this improvement in structure has advantages of large grinding and sensing area, which can lead to high sensitivity and simple manufacture process of the sensor. Experimental measurement demonstrates the sensor has a favorable SPR resonanceabsorption and the ability of measuring refractive index (RI) of aqueous solution. This novel tapered SPR sensor has the potential to be applied to the biological sensing field.
We present a fiber-optic sensor based on a fiber Bragg grating (FBG) whose core has an offset to that of the lead-in fiber from splicing for simultaneous refractive index (RI) and temperature measurement. Due to the core offset, the core mode in the lead-in fiber is coupled to both the core mode and the cladding modes of the sensing fiber with the FBG. Then the two oppositely propagating code modes, the cladding modes, and the core modes are coupled by the FBG at particular wavelengths determined by the effective indices of the modes and the FBG structure, resulting in two peaks in the FBG reflection spectrum. The peak wavelength corresponding to the core-cladding mode coupling is sensitive to both RI and temperature, while the peak wavelength corresponding to the core-core mode coupling is only sensitive to temperature. Utilizing the difference of two reflection peaks of these coupling modes, both RI and temperature can be detected simultaneously. We fabricate and characterize a sensor. The preliminary experimental results show that it can detect the refractive index in a range of 1.33 to 1.4421, with a temperature sensitivity of 10 pm/°C .
A novel fiber-optic anemometer based on a distributed Bragg reflector (DBR) fiber laser is reported in this paper. We
design a fiber laser pressure sensing setup and a Venturi tube is designed for wind speed measurement. This fiber optic
anemometer overcomes the drawbacks of the existing wind sensors with its unique advantages, such as immunity to
electromagnetic interference, compact structure, remote detection, multiplexing capability. The measuring range of the
anemometer is 8m/s~40m/s, the sensitivity is about 0.3m/s, and the short term repeatability can up to 0.35%.
Experimental results reveal that the sensitivity is impacted by power of pump laser which could be further improved.
This anemometer has high sensitivity and possibility for multiplexing application on a single fiber.
Proc. SPIE. 8418, 6th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Design, Manufacturing, and Testing of Smart Structures, Micro- and Nano-Optical Devices, and Systems
We present a novel fiber optic flow sensor system by using two fiber Bragg gratings (FBGs) and a cantilever beam
structure in this paper. This fiber optic flow sensor uses two FBGs that are bonded on both sides of a cantilever beam
to measure the flow rate by monitoring the FBG wavelength changes caused by the bending of the cantilever beam.
Cross sensitivity of the temperature dependence of the sensor can be compensated automatically. We fabricate the
FBG flow sensor and test it in the laboratory-scaled flow set-up. The testing results demonstrate its high resolution and repeatability for the fluid flow rate measurements. Based on the analysis of test results, the fiber optic flow system will be optimized in the materials of the cantilever beam and the process of sensor fabrication, so as to finally be used in the oil field.
Comparing to core-modes of optical fibers, some cladding-modes are more sensitive to the surroundings which are very
valuable to sensing application; recently, a novel type of FBG sensor with core-offset structure attracts more and more
interests. Normally, the forward core-mode is not only reflected and coupled to the backward core mode by the Fiber
Bragg Grating in the step-type photosensitive single mode fiber, but also coupled to the backward cladding-modes and
the radiation modes, eventually they will leak or be absorbed by the high refraction index coating layer. These backward
cladding-modes can also be used for sensing analysis. In this paper, we propose and develop a core-offset structure to
obtain the backward core-mode and backward cladding-modes by using the wavelength shift of the backward core-mode
and the power of the backward cladding-modes in Fiber Bragg Grating sensor, and the power of the backward
cladding-modes are independent from temperature variation. We develop a mode coupling sensor model between the
forward core-mode and the backward cladding-modes, and demonstrate two coupling methods in the core-offset
structure experimentally. The sensor is fabricated and demonstrated for refractive index monitoring. Some specific works
are under investigation now, more analysis and fabrication will be done to improve this cladding-mode based sensor
design for applicable sensing technology.
Non-equilibrium interferometric Fiber Bragg Grating (FBG) sensor is suitable for the accurate measurements of
high-frequency dynamic stress, vibration, etc because of its high sensitivity and high frequency response compared to
other types of FBG sensors. In this paper, a Phase Generation Carrier (PGC) demodulation technique of non-equilibrium
interferometric FBG sensor that based on ARCTAN algorithm by using an arctangent algorithm with a simple method,
has been investigated ,which can avoid the high-frequency noise increases, the error accumulation, the integrator signal
jump of the integrator and other inherent weaknesses in the system. ARCTAN has a better response characteristic of the
mutant signals, especially for low-frequency large-signal that can be demodulated with a greater range. The experimental
result demonstrate that implementing measured resolution can up to 10nε/√Hz@500Hz in vibration strain, a signal sampling rate to 100 KHz and a frequency response range up to 1 KHz. This method can improve the performance of the system greatly which has potential significance for practical sensor application.