Sun Weimin

High Efficiency Grating Coupler for Coupling between Single-Mode Fiber and SOI Waveguides

A high efficiency grating coupler between single-mode fiber and silicon-on-insulator waveguide is designed by a formula method. Over 78.5% coupling efficiency (>−1.05 dB) with 3 dB bandwidth about 50 nm for one grating coupler is obtained experimentally and this result is the highest one as far as we know. This grating coupler is CMOS compatible which needs only one etch-step and is designed for a standard SOI chip without any Bragg reflector or bottom reflector.

Embedded structure fiber-optic radiation dosimeter for radiotherapy applications

An investigation into a novel in-vivo PMMA (polymethyl methacrylate) plastic fiber-optic dosimeter for monitoring low doses of ionizing radiotherapy radiation in real time and for integrating measurements is presented. The fabricated optical fiber tip possessed an embedded structure. A scintillation material, terbium-doped gadolinium oxysulfide (Gd2O2S:Tb), capable of emitting visible light at around 545 nm which is ideal for transmission through the PMMA when exposed to ionizing radiation was embedded in the PMMA plastic fiber. The dose rate of incident ionizing radiation is measured by analyzing the signal intensity emitted from the scintillation material which propagates through the fiber to a distal MPPC (multi-pixel photon counter). The dosimeter exhibits good repeatability with an excellent linear relationship between the fiber-optic dosimeter output and the absorbed radiation dose with an outstanding isotropic response in its radial angular dependence.

All-Optical Cesium Atomic Magnetometer with High Sensitivity

An all-optical cesium magnetometer with high sensitivity based on absorptive detection is reported. The experiment achieves a polarized rotational spectrum of the probe light which is induced by circular dichroism and a quarter wave plate together. The frequency response of the rotational spectrum is 1.8 mrad/Hz at Larmor precession resonance. Analyzing the signal-to-noise ratio from the experimentally observed spectrum, we predict that the magnetic measurement sensitivity of 0.3 pT/Hz1/2 would be obtained in the responsive range from 20 nT to 2000 nT.

Tunable Optical Filters Based on Different Configurations with Cholesteric Liquid Crystals

Optical filters with different configurations based on cholesteric liquid crystals (CLCs) are designed. The central wavelength from CLCs can be tuned by the electric field or temperature. For the electric field tuning, the ITO is designed with circular patterns, which can make the tunable range 18 nm. For the temperature tuning, two-layer-CLC configurations are used. The experimental results indicate that a deepened or broadened bandgap from the CLC can be achieved by different handedness or concentrations of chiral dopants. The spectrum study is carried out.

Bandgap properties of phononic crystals with L-shape scatters

In this paper, we study the complete and directional bandgap properties of two-dimensional mercury/air phononic crystals (PnCs) with L-shape scatters based on the plane wave expansion method combined with a parallel shift scheme. As the symmetry of the scatters is lower than the symmetry of a square lattice, we scan the whole first Brillouin zone when performing the calculation. The relationships between the parameters (including geometry and filling fraction) of L-shape scatters and bandgaps are simulated in detail. The complete bandgap could be gained at a very low filling fraction (even below 0.076). The bandgap and directional bandgap width could be adjusted widely by changing its geometry and rotating the L-shape scatters, which could be useful for applications such as an acoustic directional filter or acoustic isolator.

The influence on output spot of large core fibers in noncentral incidence

The situation was discussed when the input light is in noncentral incidence theoretically and experimentally. An optical system was built to detect the output light spot and its changes under different radial direction conditions. Fiber disturbing mode and Two Dimensional Fitting method were used here to improve the spot images captured by CCD camera. The results showed non central incidence would cause focal ratio degradation (FDR).

Multi-wavelength pyrometry for temperature measurement in gas flames

Multi-wavelength pyrometry (MWP) has been used to measure the temperature of gas flames in a physical mock-up of an industrial burner. Even if pyrometric measurements of flame temperatures are difficult on account of the very low emissivity of gases, a self emitted radiation at defined wavelengths (590nm, 672nm, 766nm and 771nm) was detected from the different spectrums. The flame temperature can be obtained by processing the values of the ratio of two detected signals with the two-colour pyrometry procedure. A good correspondence was found between the temperature deduced from this ratio and the one measured by a type K thermocouple.

A picotesla atomic magnetometer operating at normal temperature

The basic principle of atomic magnetometer is to measure the precession frequency of polarized atomic spins in a magnetic field. The paper describes the optical pump, probe process and spin relaxation mechanisms. The magnetometer based on Cs atom is demonstrated in the experiment. At normal temperature 30°C the magnetometer achieves 8nT magnetic resonance widths and magnetic field sensitivity of 4.8pT/Hz1/2. It is more convenient for miniature structure design due to operate in lower temperature.

Grid clustering analysis the big data of spectrum by deep learning

With the Internet plus big data science information era increasing rapidly. To seek special and unknown objects is the human exploration of the mystery of the universe to pursue the goal in the universe. The spectrum by the big data mining are the fairly complex data, the dimension is high, and the correlation between the dimensions is not strong, but it is easy to introduce noise or the missing data. So it is much more difficult to deal with metering data. This article investigates the LAMOST data release star spectrum based on the high resolution spectral parameters. The RFITSIO software package of R language is used to graphically analyze the big data of the spectrum. The deep learning analysis extracts the information from the large data with finding the new knowledge and the unknown outlier data. Now the FITS format spectral large data information rise to 107 levels of data. Since the big data is imported with a large amount of redundant information, the full spectrum signal of the star spectrum making the full use of Multivariable Statistical Analysis to cluster clustering data characterized by line index. Using the Lick line index as the spectral feature, the spectral data are clustered by the K-means mean algorithm of deep learning. Experiments show that the data with strong physical correlation are valid and fast, the clustering outlier analysis of the big data feature in the spectral survey are completed with the characteristics of the data.

Phase-Disturbing Speckle-Suppressing by Contact Fiber Scrambler

To measure the focal ratio degradation of astronomical fibers, we use laser as the light source which can do with bringing the light to a focal point and we can control the injection position. The laser has a high coherency and there are a number of modes in the large-core fiber. Consequently, the output spot will be a speckle. The presence of speckle makes the energy distribution of optical field uneven, so that its hard to calculate the spot radius. To reduce the influence of the speckle, the contact-type mode scrambler is developed in our research. Its used to make the fiber vibrate at a suitable frequency of 0-80 Hz, and the vibration amplitude is 0.5 cm. The phase of different propagation modes is changed randomly in order to vibrate the modes and reduce the influence of the speckle. Different vibration result is observed by setting different vibration frequency and different CCD exposure time. The estimate of the vibration result can be given by using the method of contrast and Fourier Transform. Three different core diameters (10μm, 125μm, 320μm) are contrast with each other for convenience. The result shows that the vibration frequency between 65-70 Hz is best, and the optimum exposure time is 30 ms for all three diameters. The vibration of fiber using mode scrambler can reduce the speckle obviously under coherent illumination.