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A novel fiber sensor which can detect the concentration of copper ions indirectly was proposed and demonstrated by coating the knotted-shaped fiber with chitosan. The diameter of the knotted-shaped fiber was determined to be 10 mm. The Mach-Zehnder Interference generated due to bending deformation that excited some core-modes into higher order cladding-modes and two modes interfered. Chitosan was selected as the identification material for coating the fiber. In order to enhance the chelation between chitosan and copper ions, and improve the sensitivity of copper ions, glutaraldehyde was used to chemically modify chitosan. The original fiber sensor was annealed to obtain a stable structure, and then it was immersed in the modified chitosan solution and deionized water to form an available chitosan coating on the surface of the sensor. In the detection experiment with copper ions concentration of 0-330 ppm, the results show that interference spectra uniformly red-shift with the increase of the copper ions concentration and the sensitivity of the copper ion was 24.6 pm/10ppm. At the same time, ideal spectral fluctuations were demonstrated in the stability inquiry experiments.

A novel high-sensitive fiber-optic Fabry-Perot sensor with parallel polymer-air cavities based on Vernier effect was proposed and demonstrated for simultaneous measurement of pressure and temperature. The sensor is composed of two parallel Fabry-Perot cavities both are fabricated by splicing a section of silica tube to the single-mode fiber. One cavity is filled with polydimethylsiloxane, and the other cavity is filled with a thin layer of ultraviolet glue at the end-face of silica tube, ensuring that the free spectrum ranges of two Fabry-Perot cavities are similar and generate the Vernier effect. The Fabry-Perot interferometer filled with polydimethylsiloxane was found to be sensitive to pressure as well as temperature, whereas the Fabry-Perot interferometer filled with a thin layer of ultraviolet glue was sensitive to pressure only. Owing to the different features of two Fabry-Perot interferometers, the sensor achieved simultaneous measurement of pressure and temperature. Combined with Vernier effect, the sensor provided a pressure sensitivity of −36.93 nm/MPa and a temperature sensitivity of 10.29 nm/°C, respectively. The sensor has exhibited potential applications in fields of medical diagnostics, environmental monitoring, and biological sensing.

A novel high sensitivity temperature sensor based on polydimethylsiloxane (PDMS) coated the Multi-Thin-Multi mode Fiber was presented. The reliable material PDMS with higher negative thermal optical coefficient and thermal expansion coefficient was selected to improve the sensitivity of the optical fiber’s temperature sensing. A section of thin-mode fiber was connected in the middle of two multi-mode fibers, so as to form the Multi-Thin-Multi mode Fiber structure, which can make the light in the cladding better interact with the external PDMS. For the two dips of the interference spectra, the temperature sensitivities of the original fiber sensor were 47.14 pm/°C and 0.093 dB/°C. After the sensing part of the fiber was coated, its temperature sensitivities were become as 75.04 pm/°C and 0.231 dB/°C, which 1.6 and 2.5 times improved, respectively. In the temperature stability experiment, a standard deviation of the wavelength variation was established to demonstrate the good stability of the sensor.

We design a high-sensitivity optical-fiber sensor for measurements of displacement and refractive index based on dual-coating-stripped loop-shaped single-mode fibers. For this, we produced two unrelated interference dips as a consequence of different radii of two loop-shaped fibers. Since loop-shaped optical fibers are assigned different tasks at the same time, the two dips present their own characteristics; thus, the parameters of displacement and refractive index can be measured by these two loop-shaped fibers. In order to ensure the accuracy of experimental data, we carried experiments with increasing and decreasing displacement and refractive index. The experimental results show that the refractive index and displacement sensitivities of the sensor are 290.35 nm/RIU,† 321.35 nm/RIU, and – 554.40 pm/μm, respectively.

A high sensitivity fiber-optic pressure sensor based on Fabry-Perot interferometer filled with ultraviolet (UV) glue film and Vernier effect was proposed and demonstrated. The sensor is composed of a sensing Fabry-Perot (FP) cavity and a reference FP cavity in parallel. The sensing cavity is fabricated by splicing a section of silica tube (ST) to the lead-in single-mode fiber (SMF), and filling a thin layer of UV glue at the end-face of the ST. The reference cavity is made by sandwiching a section of ST between two SMF. The parallel cavities generate the Vernier effect due to a similar free spectrum range, which significantly improves the sensitivity of the sensor. The proposed sensor with good repeatability and reliability was used to monitor the change of air pressure, and provided a high sensitivity of −38.3 nm/MPa. The sensor exhibited the potential applications in the fields of aerospace industry, biological diagnostics and environmental monitoring.

In order to improve the performance of fiber sensors and fully tap the potential of optical fiber sensors, various optical materials have been selectively coated on optical fiber sensors under the background of the rapid development of various optical materials. On the basis of retaining the original characteristics of the optical fiber sensors, the coated sensors are endowed with new characteristics, such as high sensitivity, strong structure, and specific recognition. Many materials with a large thermal optical coefficient and thermal expansion coefficients are applied to optical fibers, and the temperature sensitivities are improved several times after coating. At the same time, fiber sensors have more intelligent sensing capabilities when coated with specific recognition materials. The same/different kinds of materials combined with the same/different fiber structures can produce different measurements, which is interesting. This paper summarizes and compares the fiber sensors treated by different coating materials.

A high sensitivity micro/nano-fiber sensor with asymmetric double tapered structure based on Mach-Zehnder interferometer (MZI) was designed for refractive index (RI) and humidity measurements. The sensor is composed of two different lengths tapered region fabricated in a single-mode fiber, which demonstrated higher sensitivity and better integration with material compared to conventional double tapered fiber sensor. The results showed that the RI sensitivity of the fabricated sensor was 68.6 nm/RIU with the RI ranged from 1.348 to 1.403. Furthermore, the sensing region was deposited with graphene for humidity detection, and the graphene has exhibited great enhancement in terms of sensing performance. The obtained humidity sensitivity of the fabricated sensor was 68.7 pm/%RH with the environment humidity ranged from 50 to 90 %. This work provides a new strategy for designing optical fiber sensor by double tapered fiber sensor, which exhibited the immense potential of tapered optical fiber sensor for future advancements.

A novel composite structured all-fiber sensor was designed and experimentally demonstrated for simultaneous measurement of displacement and temperature. The sensor consists of a knotted shape core cladding optical fiber. The interferometer notch of a knotted shape fiber was found to be highly sensitive to the micro-displacement as well as environmental temperature, while the core-offset fiber was sensitive to temperature only. Thus the different features of these interferometer notchs of two parts can be used to measure the displacement and temperature. The experimental results showed that the sensor exhibited a high displacement sensitivity of −528.57 pm/μm ranges from 0 mm to 0.012 mm. And the temperature sensitivities of the knotted shape core cladding optical fiber were −114.86 pm/℃ and 31.66 pm/℃ ranges from 35 ℃ to 60℃, respectively. Due to the compact size and dual-parameters measurability, the sensor had a great potential in diverse sensing application.

We presented a passively Q-switched (PQS) diode-pumped c-cut Tm, Ho:LuVO4 laser with a black phosphorus saturable absorber for the first time. Under PQS mode, an average output power of 0.86 W and a peak power of 2.32 W were acquired from the Tm, Ho:LuVO4 laser with the pump power of 14.55 W, corresponding to a pulse width of 2.89 μ s , a pulse repetition rate of 71.84 kHz, and a pulse energy of about 6.70 μ J .

Triangular patterns phase shifting profilometry is a method of structured light whose three-dimensional reconstructions are susceptible to error from gamma distortion. In practice, the luminance nonlinearity caused by the gamma distortion effect of a digital projector and a digital camera yields undesired fringe intensity changes, which substantially reduce the measurement accuracy, and while the effects of the gamma distortion diminish with an increasing number of employed phase-shifted patterns. A gamma correction method based on the pre-coding of projected grating is proposed to reduce the measurement error caused by the gamma distortion. By applying an appropriate pre-coding value to the projected patterns, the gamma distortion effect is attenuated and the accuracy is enhanced. The linear least square is compensated the absolute coordinate residuals still existing after gamma correction. To verify the presented method in this paper, a 3D shape measurement experimental system is constructed using digital video projector and CCD camera. The experiment results shown that, the gamma pre-coding correction reduce the maximum residuals error of absolute coordinate by 72.2%. After the linear least square compensation, the maximum absolute coordinate residual is only 6.1% of without any correction or compensation. The reconstruction surface of a complex curve surface is hardly any waviness, which is clearly noted in the reconstruction of the same tested object without any correction or compensation.

This paper puts forward a new kind of structured light 3d measurement system self - Calibration method. At first, this paper sets the polar equation between the feature points on the calibration object and their corresponding points on two images. At second, the paper derives the translation and rotation relationship matrixes of the projector and each camera. Afterwards, projecting 3-coding cycle triangular gray distribution structured light patterns on the calibration object. From the images, the coordinates of the projector of the feature points can be acquired. Finally, the estimation matrix of the relationship matrix can be set based on the improved 8-point method. Using the epipolar distance as the objective function, the relationship matrixes will be optimized, and the parameter matrixes of the two cameras and the projector could be obtained. Making use of the calibrated system are carried out for a plane and a plaster statue respectively. The experimental result shows that the maximum absolute measurement error of the plane is less than 2.3mm and the reconstruction plaster statue surface is close to the target plaster statue. It proves that the 3d measurement system and the self-calibration method used by this paper is effective.

The goal of structured light techniques is to measure the shape of three-dimensional object using automatic non-contact techniques and based on trigonometry measurement. This thesis deals with the device of obtaining range image based on multi-line structured light. The projector is taken as the projecting source of this device and can project multi-line structured light. The digital camera is taken to obtain stripe image and can capture the stripe image in a single frame. The technique of space encoding is utilized to process the stripe image and could avoid the aliasing of the multi-line structured light. This technique can ensure the veracity of the range image obtaining. The experiments have shown that the range image obtained by this device have better results and higher speed of acquisition. Measuring range of this device is 200mm(X)×120.0mm(Y)×150.0mm(Z). The measuring error of Y and Z direction is less than 0.3mm. The measuring error of X direction is less than 0.1mm.The absolute error of the measurement result in the direction of Z is less than 0.2%.

This paper describes a laser scanning range finder that may produce a real time space encoding pattern. Laser diode is modulated by a programmable controller. So a space encoding sequential constructive laser beam is employed as an active illuminating source. Using less frames of space encoding patterns to produce a range image with high resolution is the main goal of this study. The calculation of 3D coordinates of each point on the measured object is explained briefly.