A method for measuring the incident angle of the light beam based on an axicon lens which defined by cone length and cone angle is presented in this letter. The system is mainly composed of a stop, an axicon lens, a telescopic system, an image receiving device, a display device and a digital image processing device. The light beam is refracted to a larger incident angle when passing through the telescopic system. It then goes through the aperture and the axicon lens, whose refraction times in axicon lens correlate with the incident angle, resulting in different spots captured by image sensor. The angle can be figured out with rich image characteristic information, which includes symmetry axis direction, area, the mass position center, the inertia moment, etc. In a practical design example, the image processing of the spot image shows that the rotational inertia of the spot has a one-to-one correspondence with the incident angle of the light beam, which features an obvious monotonicity. The angle measurement range can reach up to 3°, with an accuracy up to 1×10-3 ". Compared with the traditional angle measurement method, the measurement accuracy of this method based on axicon lens is improved by an order of magnitude. The system has the advantages of high accuracy, compact but simple structure, and no cumbersome installation and debugging. It can be used not only as a high-precision collimator, but also as a high-precision goniometer.
In this paper, we present an interferometric method to measure the shape of X-ray wavefront and the slope error of optical elements using microfocus x-ray source. According to the fractional Talbot effect, we built an x-ray grating interferometer for x-ray wavefront characterization at the working wavelength. The interferometer consists of a phase grating as a beam splitter and an absorption grating as a transmission mask for the detector. however, the determination of the relation between x-ray grating interferometer system parameters and the sensitivity, which is influenced by many optical elements in the system, is crucial for the optimization of the setup. It is very complicated to determine the best optical parameters in the course of experiment. The interferometry system is abstracted into a linear system, and then a mathematical model is constructed. The influence of different physical parameters, such as the source size and the energy spectrum, on the functional capability of an x-ray grating interferometer applied for X-ray wavefront characterization is discussed using numerical simulations based on Fresnel diffraction theory. The slope variations can be detected with an accuracy better than 100nrad.
The whispering-gallery-mode(WGM) resonators have a number of advantages, including ultra-high quality factor(Q factor), extremely small mode volume and so on. It has been widely used in many fields related to high sensitivity sensing measurement, photonics material, linear and non-linear optics, and optical communication. Here we built an experimental platform for microrod resonator fabrication with a high power CO2 laser. Based on this experimental fabrication platform, a microrod resonator with an approximate 2.5mm diameter has been made, which has an ultra-smooth surface. We also designed a test platform used a tapered fiber to measure optical performances of the fabricated microrod resonator. With this test platform, we measured the maximum Q factor of the fabricated resonator, which can reach 1.52×108 under the condition of 1550nm wavelength. The fabrication platform for microrod resonator designed by our laboratory with features of fast (less than 10min), cheap, repeatable and low experimental condition. These features have huge advantages on further scaled sensing application, optoelectronic device. Furthermore, in order to design and fabricate the ultra-high sensitivity temperature sensing device, we demonstrated the frequency shift feature of the fabricated microrod resonator. We heated the microrod resonator from 22 oC to 25 oC , then calculated the experimental data. we demonstrated our microrod resonator has 0.04nm frequency shift, 14.41pm/oC temperature sensitivity, and 6.3♦10−3oC temperature resolution.
We investigate a millimeter-size Calcium fluoride (CaF2) microdisk resonator fabricated by a customized machining procedure. Stable coupling can be realized in our microdisk resonator coupled by a special tapered fiber. The mcirodisktaper coupling system exhibits an ultra-high Q factor up to ~108. In particularly, our coupling system exhibits a freespectral- range low to ~0.03 nm (~3.91 GHz). The frequency is suitable in microwave photonic systems, such as optical filters, optoelectronic oscillators, and optical gyroscopes for several technological applications such as radar, light-wave technology, frequency synthesis, detection inertial navigation system.
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