Haijuan Ju

Low-Cost Multipoint Liquid-Level Sensor With Plastic Optical Fiber

A simple and low-cost discrete liquid-level measurement system is present in this letter. It consists of a group of plastic optical fiber segments, which are aligned coaxially and spaced equally. When the spacing between every two adjacent fiber segments is filled with liquid, the light power will be easier to couple from one segment to the next as compared with the situation that the fibers are exposed in air. Based on this point, we design this intensity-based sensor and investigate its working properties theoretically by using the ray-tracing method. The performance of this sensor is demonstrated in detail where different liquids are utilized as specimens.

Online fabrication scheme of helical long-period fiber grating for liquid-level sensing

We present a novel online fabrication scheme of helical long-period fiber gratings (H-LPFGs) by directly twisting a standard single-mode fiber (SMF) in a microheater. This is done by taking advantage of the inherent core-cladding eccentricity in SMF. We adopt a fiber optic rotary joint to eliminate the accompanying twisting spiral for real-time spectral monitoring and a stepping mechanical system to accurately control the twisting length in fabrication. As a consequence, low-cost and high-quality H-LPFGs can be readily fabricated. Meanwhile, by using this kind of H-LPFG, we design a simple and low-cost wavelength-interrogated liquid-level sensor with a high sensitivity of 0.1 nm/mm.

Polarimetric dehazing method for dense haze removal based on distribution analysis of angle of polarization.

Many dehazing methods have proven to be effective in removing haze out of the hazy image, but few of them are adaptive in handling the dense haze. In this paper, based on the angle of polarization (AOP) distribution analysis we propose a kind of polarimetric dehazing method, which is verified to be capable of enhancing the contrast and the range of visibility of images taken in dense haze substantially. It is found that the estimating precision of the intensity of airlight is a key factor which determines the dehazing quality, and fortunately our method involves a high precision estimation inherently. In the experiments a good dehazing performance is demonstrated, especially for dense haze removal. We find that the visibility can be enhanced at least 74%. Besides, the method can be used not only in dense haze but also in severe sea fog.

Visibility enhancement of hazy images based on a universal polarimetric imaging method

Enhancing the visibility of images taken in the hazy weather is important in many applications. Among many dehazing methods, those based on polarimetric imaging techniques have several advantages, such as ease of keeping detailed information, low cost, and high efficiency. In this paper, we propose a novel and robust dehazing algorithm based on polarimetric imaging. By introducing the orientation-angle information from the Stokes matrix, all the parameters used in dehazing performance can be effectively, precisely and automatically estimated, and no additional human-computer interaction is needed. Besides, this method can also be used in handling hazy images without sky region. Experimental results show that such a method can greatly enhance the visibility of hazy images.

Highly Strain and Bending Sensitive Microtapered Long-Period Fiber Gratings

A microtapered long-period fiber grating (MTLPFG) is fabricated successfully by periodically tapering a standard single-mode fiber with CO2 laser heating source. This can be done by taking advantage of that the effective index difference between the core mode and the cladding modes is changed periodically during microtapering. High fabrication reproducibility and MTLPFGs quality can be achieved by this CO2 laser-heater-based fabrication scheme. In addition, the strain, bending, and liquid-level sensing characteristics of the MTLPFGs are investigated experimentally. Compared with the conventional long-period fiber gratings, it is found that the strain and bending sensitivities of fabricated MTLPFGs are improved by factors of about 10 and 5, respectively. Considering the simple and flexible fabrication process as well as the high quality and sensitivity of fabricated MTLPFGs, we believe that this may offer a simpler and alternative choice to current filters or sensing applications.

Polarimetric dehazing method for visibility improvement based on visible and infrared image fusion

Polarimetric dehazing methods have proven effective in enhancing the quality of chromatic hazy images. Considering that the infrared radiance has a better capacity for traveling through the haze, in this paper we propose a polarimetric dehazing method based on visible and infrared image fusion to improve the visibility of hazy images, especially for dense haze conditions. Experimental results demonstrate that the visibility of hazy images can be effectively enhanced, and the color information can be finely maintained. The visibility of dehazed images can be promoted at least 100%. This kind of dehazing method can be used widely in many dehazing applications.

Wide-Range Continuously-Tunable Slow-Light Delay Line Based on Stimulated Brillouin Scattering

Through selectively controlling the stimulated Brillouin scattering in optical fibers with different lengths, a continuously tunable time-delay scheme enabling to work in a large range is proposed in this letter. This is realized by connecting a fixed long single-mode fiber (SMF) to one of the several selectable short SMFs that successively have an equal increment in length. These short-length fibers are, respectively, fixed to the different channels between two identical optical switches. Therefore, a wide-range and continuously tunable slow-light delay line can be constructed by changing the power of the pump beam, assisted by switching to different channels. In the experiment, a time delay from 0 to 201.29 ns is demonstrated for a five-channel configuration. A further large-range time delay can be expected if one adds the number of channels accordingly.

Stability-improved slow light in polarization-maintaining fiber based on polarization-managed stimulated Brillouin scattering

With the idea of controlling the polarizations of the pump and Stokes beams in an optical fiber, a simple scheme is presented for enhancing the stability of the stimulated Brillouin scattering (SBS) interaction and thus that of the SBS-based slow light. For this purpose, a special slow-light element is constructed by fusing a polarization-maintaining circulator (its fast axis being blocked) to each terminal of the polarization-maintaining fiber (PMF). This configuration ensures that the pump and Stokes beams always have identical polarization in the whole fiber during the SBS interaction. An experimental setup is established accordingly. The SBS gain feature and the slow-light performance are studied. A tunable time delay with a slope of 0.82?ns?dB?1 is demonstrated for a Gaussian pulse with a width of 88.9?ns. The experimental results with and without polarization management are compared. It is found that such a polarization-managed scheme can improve both the stability of the Brillouin gain and that of the time delay of the Stokes pulse. Moreover, for the same pump power, the Brillouin gain is also enhanced.

Theoretical and Experimental Study on Nonintrusive Light Injection Via Cladding in Plastic Optical Fibers

Based on the fiber macrobending and the refractive index matching technologies, a novel scheme of nonintrusive light injection, namely, the light signal is injected into the fiber core from the fiber cladding without any destruction, is proposed in plastic optical fibers (POFs). Using the ray-tracing method, a 3-D theoretical model is established to characterize the performance of the light injection. The influences of the fiber bending radius, the light source placement, and the surrounding medium refractive index on the light injection efficiency are investigated and assessed. Meanwhile, correlative experiments have also been conducted to contrast theoretical simulations. The experiment results fit theoretical ones well. This nonintrusive light injection technology in POFs might have many potential applications such as the optical signal uploading and downloading, the optical coupling, and the local area networks.

Chiral long-period gratings: fabrication, highly sensitive torsion sensing, and tunable single-band filtering

A promising technology for fabricating chiral long-period gratings (CLPGs) is demonstrated using a commercial fusion splicer. The key aspect of this technology is the incorporation of a fully automatic program we designed for the fusion splicer. High-quality CLPGs are successfully fabricated from single-mode fibers, which have very flat surfaces and low insertion loss. We also investigate the tuning characteristics of the transmission spectrum with the mechanical twist rate in CLPGs for torsion sensing application. The torsion sensitivity is improved and the shift in resonance wavelength versus the mechanical twist rate shows an almost perfect linear relationship. In addition, by choosing appropriate fabrication parameters, the fabricated CLPGs can be used as tunable single-band-rejection filters in a broad wavelength range.