Curvature investigation in tapered fibers and its application to sensing and mode conversion

Non-adiabatic tapered fibers are basic photonic components used in a wide range of applications. Here we investigate a way to increase their utility through the controllable bending of one of their tapered sections. The experiments carried out explain, for the first time, the mechanics of this approach showing how these tapers can be used to build more sensitive sensors. Their use as highly efficient mode converters is also discussed.     

Autonomous system for data collection: Location and mapping issues in post-disaster environment

Disaster relief requires many resources. Depending on the circumstances of each event, it is important to rapidly choose the suitable means to respond to the emergency intervention. A brief review of the conditions and means demonstrated the usefulness of an autonomous stand-alone machine for these missions. If many techniques and technologies exist, their relevant combination to achieve such a system presents several challenges. This communication tries to outline the possible achievement of an autonomous vehicle under these particular circumstances. This paper focuses on the specific working conditions and welcomes future contributions from robotics and artificial intelligence.In the necessarily limited scope of this article, the authors focus on a particularly critical aspect: location. Indeed, this machine is intended to evolve in heterogeneous and dangerous environment and without any outside contacts that could last up to several days. This blackout, due to the propagation difficulties of electromagnetic waves in the ground, induces an independence of the localisation process and makes the use of any radio navigation support system (GNSS), most of the time, impossible. The knowledge of the position of the system, both for navigation of the autonomous system (Rover) and location of targets (victims buried under debris) must be able to be estimated without contributions from external systems. Inertial classical techniques, odometer, etc., have to be adapted to these conditions during a long period without external support. These techniques also have to take into account that energy optimisation requests the use of low-power processors. Consequently, only poor computing capacity is available on-board.The article starts with a presentation of the context of a post-disaster situation as well as the main missions of Search and Rescue (SaR). It is followed by the analysis of autonomous navigation located in a post-earthquake situation. We will then discuss means to determine the attitude of the autonomous system and its position. The interest of hybridisation with external systems – whenever possible –, will be evaluated with a view to correcting deviations suffered by the system during its mission. Finally, prospects and future work are presented.     

Photonic crystal beam splitters

In this work, the beam splitter with two input ports and two output ports in two-dimensional photonic crystals is studied through the finite-difference time-domain method. The beam splitter consists of two orthogonally cross line defects. The diameter of the two diagonal air holes at the intersection of the two line defects was modified. The input light can be identically divided into the two output ports. The beam splitters can be applied in the photonic crystal Mach-Zehnder interferometers or photonic crystal optical switches.     

双涂层光纤应变传感器的理论与实验研究

对带有聚合物涂敷层和缓冲层的光纤应变传感器的力学特性进行了研究，建立了双涂层光纤与基体材料相互作用的线弹性理论模型.理论研究表明：在小半径近似条件下，双涂层光纤的力学传递特性决定于涂覆层和缓冲层的弹性模量的相对值；当缓冲层的弹性模量远大于涂覆层时，其作用可忽略.实验中，将光纤传感器埋入基体材料内部，利用白光干涉应变测量方法，对平均应变传递系数进行了实验研究.实验结果与理论仿真具有较好的一致性.     

Fiber torsion sensor demodulated by a high-birefringence fiber Bragg grating

A new high-birefringence (Hi-Bi) fiber torsion sensor demodulated by a Hi-Bi fiber Bragg grating (FBG) is proposed in this study. The twisted Hi-Bi fiber sensor characteristics are analyzed using the Jones matrix. The intensity ratio from two reflected Bragg wavelengths is associated with the twist angle of the measured Hi-Bi fiber. It is found that the twist angle resolution is estimated at around 0.3° under ±0.1 dB readout from an optical spectrum analyzer if the polarization state of the light source is stable. The advantages of this new torsion sensor are: (1) insensitivity to intensity variations from the light source, (2) insensitivity to the torsion gauge length, and (3) absolute measurement in the twist angle. However, the polarization state of light in the proposed method needs to be controlled, and any birefringence change in the twisted Hi-Bi fiber needs to be prevented.     

Imprint lithography of pyramidal photonic pillars using hydrazine etching

An inexpensive method to produce a pyramidal-type 2D photonic structures in the silicon substrate was proposed. The method is based on the combination of imprint lithography and wet Si1 0 0 etching in water solution of hydrazine, which etches 1 1 1 faces much more slowly than others. Thermally grown SiO₂ mask for the hydrazine etching was used, because single Al mask cannot be well bonded to the substrate and tends to peel during the etching. It was revealed that transmittance in the infrared spectrum region of the patterned silicon decreases by about five times compared with that of flat silicon substrate and this decrease is almost independent of the angle of the incident beam. In the infrared region, decrease of transmittance of the patterned samples is directly proportional to the wave number. The shape of formed pyramids has strong influence on the transmittance. Decrease of the transmittance is much more rapid and larger in the case of sharpless pillars.     

Fiber-Optic Chemical Sensor for Detection of NO2 Using Poly (3-Octylthiophene)

A fiber-optic chemical sensor (FOCS) for detection of nitrogen dioxide (NO₂) molecules is reported. The FOCS presents an optropode structure because of the transmission properties of the sensitive material. The NO₂ FOCS is activated by using the semiconductor polymer: regioregular head-to-tail poly(3-octylthiophene-2,5-diyl). The operation wavelength of the sensor is 543.5 nm such that a simple LED and detector can be used for the design of this device. The sensor response decreases after each exposure, demonstrating the reduction in sensitivity as well as irreversibility lower than 5%. However, its properties such as rapid response, high selectivity, high sensitivity (0.43 ± 0.01 muW/ppm), hygroscopic properties, and its operation at room temperature make this kind of FOCS a good alternative for NO₂ toxic gas detection.     

Highly enantioselective fluorescent recognition of α-amino acid derivatives

Bisbinaphthyl-based macrocycles are found to carry out enantioselective fluorescent recognition of α-amino acid derivatives. It is observed that one enantiomer of a N-protected phenyl glycine can increase the fluorescence intensity of the binaphthyl fluorophores by over 4-fold but the other enantiomer does not cause much fluorescence enhancement. This highly enantioselective fluorescent response makes the binaphthyl macrocycles practically useful for the enantioselective fluorescent recognition of the amino acid substrate.     

Simulation and fabrication of carbon nanotubes field emission pressure sensors

A novel field emission pressure sensor has been achieved utilizing carbon nanotubes (CNTs) as the electron source. The sensor consists of the anode sensing film fabricated by wet etching process and multi-wall carbon nanotubes (MWNTs) cathode in the micro-vacuum chamber. MWNTs on the silicon substrate were grown by thermal CVD. The prototype pressure sensor has a measured sensitivity of about 0.17-0.77 nA/Pa (101-550 KPa). The work shows the potential use of CNTs-based field-emitter in microsensors, such as accelerometers and tactile sensors.     

Decay distribution of spontaneous emission from atoms in one-dimensional photonic crystal

Spontaneous emission behavior from atoms (or molecules) in one-dimensional photonic crystal with a defect is investigated. Taken all the TE and TM modes into account, the normalized spontaneous emission rate of the atom is calculated as a function of the position of the atom in the crystal. Results for both nonabsorbing dielectric structure and absorbing dielectric structure are presented. With the increase of the thickness of the defect in which the atoms are embedded, the oscillations of the spontaneous emission rate versus the position of the atom become dense and the lifetime distribution becomes narrow and sharp. The PC effect may lead to the coexistence of both accelerated and inhibited decay processes.