Fiber Bragg sensor is applied for detecting and monitoring the cracks that occur in the reinforced concrete. We use the three-dimensional finite element model to provide the three-axial stresses along the fiber Bragg sensor and then converted the stresses as a wavelength deformation of fiber Bragg grating (FBG) reflected spectrum. For the crack detection, an FBG sensor with 10-mm length is embedded in the reinforced concrete, and its reflection spectrum is measured after loading is applied to the concrete slab. As a result, the main peak wavelength and the ratio of the peak reflectivity to the maximal side-mode reflectivity of the optic-fiber grating represent the fracture severity. The fact that the sharp decreasing of the ratio of the peak reflectivity to the maximal side-mode reflectivity represents the early crack is confirmed by the theoretical calculation. The method can be used to detect the cracks in the reinforced concrete and give safety evaluation of large-scale infrastructure.
We propose a method for generating axial multifocal spots (AMS) with a high numerical aperture (NA) objective. The AMS is generated by using phase-only modulation at the back aperture of the objective. Without using any iteration algorithm, the modulated phase distribution is directly calculated by an additional phase analytical formula with different focal distances. By dividing the back aperture of the objective into multi sectorial zones and applying the corresponding additional phase with different focal distances, the AMS can be created. Numerical simulation shows that the numbers of the axial focus depends solely on the different phase distribution calculated by different focal distances. By engineering the phase pattern with different focal distances, axial multifocal spots with different spacing can be realized. Furthermore, combined with vortex phase, the AMS with specific shape spots also can be created. In addition, the AMS focused by incident beams of circular polarization, radial polarization and angular polarization are also studied. This kind of AMS may be found applications in optical imaging, especially in three-dimensional (3D) biological imaging, and also be attractive in mult-plane optical trapping.
All-optical wavelength conversion using cross-phase modulation in a high nonlinear fiber is demonstrated. The output extinction ratio and bit error rate dependence of the probe wavelength, probe power, input signal power, and fiber length are investigated. A 10-Gbit/s measurement has been performed and a 1.2-dB power penalty at 10 −9 bit error rate level is obtained.
An enhanced theoretical model for wavelength conversion of SOA is presented. The chirp for the converted signal is analyzed and confirmed by numerical simulation.
A improved theoretical model for wavelength conversion into which the mutual coupling parameter is introduced is
present. The bit error rate of wavelength conversion are analyzed and confirmed by value simulation.
With the improved theoretical model for wavelength conversion, we demonstrate that the characteristics of wavelength conversion such as extinction ratio, signal-noise ratio and bit error rate is relative to the mutual coupling parameter introduced into the rate equations.
As the key apparatus, the All optical Wavelength Converter (AOWC) will play an important role in future optical communication system. In this paper, a theoretical model based on mutual coupling effect of laser modes for all-optical wavelength converter in single-model homogeneously broaden laser is presented. With the theory the paper analyze the stability of single-model homogeneously broaden lasers and the influence on its characteristics when there is parameters variety. Numerical value of saw tooth wave is given also. Those results are useful to realization and the optimal design of the wavelength converter.
As the key apparatus, the All optical Wavelength Converter (AOWC) will play an important role in future optical communication and optical signal processing system. In this paper, switching characteristics of wavelength converter based on saturable absorber in semiconductor lasers will be researched. This kind of conversion mechanism possesses some advantage, such as simple structure, low cost, high stability and so on. This paper is organized as follows: Firstly, utilizing rate equations, a new theoretical model on wavelength conversion based on saturable absorber is put forward. Nextly, the frequency modulation response of wavelength conversion will be discussed under the small-signal analysis based on the theoretical model. Lastly, Numerical value solution results will be given out when external signal light injects in saturable absorber region of semiconductor lasers. The characteristics of wavelength conversion are simulated in different optical parameters including the injection current, the input signal optical power and bit rate. Those results are useful to realization and the optimal design of the wavelength converter based on saturable absorber.
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