Visual Passive Ranging Method Based on Re-entrant Coaxial Optical Path and Experimental Verification

To overcome the shortcomings of the traditional passive ranging technology based on image, such as poor ranging accuracy, low reliability and complex system, a new visual passive ranging method based on re-entrant coaxial optical path is presented. The target image is obtained using double cameras with coaxial optical path. Since there is imaging optical path difference between the cameras, the images are different. In comparison of the image differences, the target range could be reversed. The principle of the ranging method and the ranging model are described. The relationship among parameters in the ranging process is analyzed quantitatively. Meanwhile,the system composition and technical realization scheme are also presented. Also, the principle of the method is verified by the equivalent experiment. The experimental results show that the design scheme is correct and feasible with good robustness. Generally, the ranging error is less than 10% with good convergence. The optical path is designed in a re-entrant mode to reduce the volume and weight of the system. Through the coaxial design,the visual passive range of the targets with any posture can be obtained in real time. The system can be widely used in electro-optical countermeasure and concealed photoelectric detection.

Production of Artificial Fog in the PAVIN Fog and Rain Platform: In Search of Big Droplets Fog

In fog, visibility is reduced. This reduction in visibility is measured by the meteorological optical range (MOR), which is important for studying human perception and various sensors in foggy conditions. The Cerema PAVIN Fog & Rain platform is capable of producing calibrated fog in order to better analyses it and understand its consequences. The problem is that the droplets produced by the platform are not large enough to resemble real fog. This can have a major impact on measurements since the interaction between electromagnetic waves and fog depends on the wavelength and diameter of the droplets. To remedy this, Cerema is building a new platform with new equipment capable of generating fog. This study analyses different nozzles and associated usage parameters such as the type of water used and the pressure used. The aim is to select the best nozzle with the associated parameters for producing large-diameter droplets and therefore more realistic fog.

Investigation on performance of all optical buffer with large dynamical delay time based on cascaded double loop optical buffers

Optical buffers are critical for optical signal processing in future optical packet-switched networks. In this paper, a theoretical study as well as an experimental demonstration on a new optical buffer with large dynamical delay time is carried out based on cascaded double loop optical buffers （I：）LOBs）. It is found that pulse distortion can be restrained by a negative optical control mode when the optical packet is in the loop. Noise analysis indicates that it is feasible to realise a large variable delay range by cascaded DLOBs. These conclusions are validated by the experiment system with 4-stage cascaded DLOBs. Both the theoretical simulations and the experimental results indicate that a large delay range of 1-9999 times the basic delay unit and a fine granularity of 25 ns can be achieved by the cascaded DLOBs. The performance of the cascaded DLOBs is suitable for the all optical networks.

Metal-free Optical Pressure Sensor with High Sensitivity and Extensive Range

Pressure monitoring of a transformer oil tank can grasp the pressure change process caused by gas production when severe internal defects occur and take timely measures to ensure the safe operation of the transformer.Existing pressure sensors generally use metal encapsulation or have an air cavity structure,threatening the transformer’s insulation if it is directly used inside the transformer.To this end,this paper proposes a method for developing a high-sensitivity,large-range,and metallizationfree optical pressure sensing device with temperature compensation.Fiber grating is encapsulated by fluorosilicone rubber and supplemented by an epoxy resin shielding shell on the outside.At the same time,a double-grating vertical arrangement is adopted to improve pressure measurement sensitivity,further avoiding the influence of temperature rise caused by a defect of the transformer on the measurement result of the sensor.In addition,by optimizing the geometric structure of the internal sensitizing element,pre-stretching length of the fiber grating,gap distance,and other parameters,probe size can be reduced while ensuring the sensor’s performance.Results show the proposed method can meet the requirements of sensor fabrication with different sensitivities and ranges,and to a certain extent,both high sensitivity and extensive ranges can be taken into account.The sensitivity of the fabricated prototype is 15 pm/kPa,and the range is about 0.2 MPa.At the same time,the metal-free feature of the sensor makes it suitable for use in various oil-immersed power equipment.It records oil pressure changes caused by oil discharge breakdown,making it sensitive to small pressure changes in early failures.

Long dynamic range spread spectrum optical domain reflectometer

The performance of an optical time domain reflectometer(OTDR) is significantly improved using spread spectrum technology. The concept of spread spectrum OTDR(SSOTDR) is proposed, the theoretical basis and simulation results of the new method are given, and the problem of direct application of bipolar spread spectrum codes to OTDR and despreading in the optical domain are solved. The simulation results show the feasibility of the SSOTDR, which exhibits better dynamic range reported to date for a practical long-haul OTDR system without using conventional average technique.

Wideband, 50 dB Attenuation Range Liquid Crystal Based Variable Optical Attenuator

A compact variable optical attenuator, covering C and L bands with over 50 dB attenuation range, is realized using a single liquid crystal cell with a tilted fused silica coating compensating the cell's small residual birefringence.

Proposal for a nuclear light source

This study considers a principal possibility of creating a nuclear light source of the vacuum ultra violet(VUV) range based on the ^(229)Th nucleus.This nuclear light source can help solve two main problems—excitation of the low-lying^(229m)Th isomer and precision measurement of the nuclear isomeric transition energy.The thorium nuclear light source is based on the nuclei implanted in a thin dielectric film with a large bandgap.While passing an electric current through the sample,the^(229)Th nuclei are excited to the low energy isomeric state 3/2^(+)(8.19±0.12eV) through the process of inelastic scattering of conduction electrons.The subsequent spontaneous decay of^(229m)Th is followed by the emission of γ quanta in the VUV range.The luminosity of the thorium nuclear light source is approximately 10^(5)photons/s per 1 A of current,per 1 ng of^(229)Th.The suggested scheme to obtain γ radiation from the^(229m)Th isomer can be considered as a type of nuclear analogue of the optical radiation from the usual metal-insulator-semiconductor(MIS) junction.