Applied Mechanics and Materials Vols. 284-287

Abstract: ωThis study applies a skew ray tracing approach based on a 4×4 homogeneous coordinate transformation matrix and Snell’s law to analyze the errors of a ray’s light path as it passes through a series of optical elements for axis-symmetrical optical system. The proposed error analysis methodology considers two principal sources of light path error, namely: (1) the translational errors Δx_i, Δy_i and Δz_i and the rotational errors Δω_ix, Δω_iy and Δω_iz, which determine the deviation of the light path at each boundary surface, and (2) the differential changes induced in the incident point position and unit directional vector of the refracted / reflected ray as a result of differential changes in the position and unit directional vector of the light source. The validity of the proposed methodology is verified by analyzing the effects of optical errors in Petzval lens.

Abstract: The laser manufacture has been widely used in micro-machining as a burgeoning technology. Galvanometric scanning systems is an important component in laser machines, but the galvanometric scanning system is usually combines the image field distortion that is from the mechanism and optical devices. The paper has presented a novel correction algorithm based on ride regression method for compensates the image field distortion. And the Euclidean distance error and the maximum error are 0.0422 and 0.09, respectively. This novel correction technique can effectively increase the accuracy of laser spot position and can further improve the performance of the galvanometric scanning system.

Abstract: Wireless mesh networks are expected to provide wireless broadband access to Internet. In such networks, gateway placement is an important topic, which usually dominates the overall wireless performance, and hence there have been lots of the related works. However, recent paper even discovers that the starvation of TCP flows usually occurs near wireless gateways. Some TCP flows will starve just due to TCP flows of the node next to the gateway. Hence, possible ways to improve this critical issue should be developed urgently. However, until now, there have not been the feasible ways without modifying MAC and TCP mechanisms. Hence, in this paper, we plan the gateways placement under the consideration of this issue. To the best of our knowledge, this paper is the first work to plan gateway placement under considering the starvation of TCP flows. Our work also provides a new view in the field of planning wireless mesh networks.

Abstract: In this paper we simulate and analyze the system performance of implementing two Hybrid Automatic Retransmission Request (HARQ) architectures for IEEE 802.16m system, one is a modified Type I HARQ architecture with adaptive modulation and coding (AMC) scheme and the other is the Chase Combining. In the simulation, the buffer size of HARQ has been set to certain limit and under the condition of having the packet error ratio (PER) limited by 10% then the selection of proper HARQ structure with suitable AMC scheme for IEEE 802.16m system has been proposed for mobile speeds at 3 km/hr, 80 km/hr or 350 km/hr and with a distance of 300m between the mobile station and its serving base station.

Abstract: To replace the color filter in the conventional display, we describe a color-separation backlight consisting of three modules: the light collimation module, the light guide and the micro-lens array. With angularly positioned color LEDs, the displaying method requires only two two-color filter layers to display color images. In the light collimation module, the angular rays of two colors from each LED are collimated by a reflective cup and a collimation lens. After entering the light guide, which is composed of V-groove structures at the bottom above a reflective layer, the angular collimated color beams are redirected to the normal of the top surface of light guide. Finally, the output rays are converged by a micro-lens array and mapped into corresponding sub-pixel positions for efficiently displaying color image. The three main advantages of such technology are the reduction of the dye color filter layers from conventional 3 to 2, the gain factor of transmission efficiency two times more than that of conventional color filters, and the larger color gamut.

Abstract: In this article, we present propose a simple method to detect the minor fluid-environmental changes using ringing phenomenon generated by frequency sweeping in a single mode optical fiber resonator. The method is based on the fact that the insertion loss of the optical fiber resonator is determined by the environmental changes alone, which leads to the changes of cavity ringdown time of the fiber resonator. The method has several conspicuous advantages over the frequency-domain method, using which the minimal detectable optical loss is in the order of .We also show that the sensing system is insensitive to the temperature drifting, which overcome the main defect of fiber loop resonator, that it is extremely sensitive to temperature changes. The structure of the sensor is compact and stable due to the characteristic of optical fiber resonator, and it is easy to apply because the structure is not delicate and is easy to construct.

Abstract: In this paper, a CAD system is presented for the design, evaluation and simulation of Luneburg lenses. Since this system focuses on high-frequency spherical antenna design and simulation, electromagnetic waves are replaced by rays. A ray-tracing subroutine is employed to trace ray paths and compute phase variations along rays. In traditional CAD systems, the performance of a Luneburg lens is measured by using numerical algorithms, which are difficult to implement and require tremendous computational efforts. In the proposed system, the effectiveness of the target lens is evaluated solely by using the theory of Geometrical Optics (GO). Ray paths and wavefronts are rendered and displayed to show the directivity and focus characters of the lens. The ray phases along with ray paths are also illustrated in graphical media so that the gain and reflectivity of the lens can be predicted.

Abstract: The concentricity of the optical fiber micro lens affects the coupling efficiency of a laser module a lot. In this paper, the effect of the perpendicularity of the broken edge on the concentricity of the micro optical fiber end-face during the micro polishing process is studied. A mathematical model is derived to describe the variation of the material removal rate (MRR) when the tilt angles and amount of feed of the optical fiber are changed. An experiment is built to measure the concentricity of optical fiber with different tilt angles and feeds. The result shows that both of the dimensionless factor QAB and measured concentricity have the same tendency. The concentricity is better when the tilt angle is smaller and the amount of feed is larger. An improved polishing process is suggested. A good concentricity within 1μm can be achieved when fabricate the double-variable curvatures end-face of the optical fiber.

Abstract: A novel reflective metal anode with different groove structures and a set of parallel long narrow stripe Carbon nanotube (CNT) cathodes to fabricate a 7 inches field emission backlight unit (CNT-FEBLU) has been carried out in this paper. In comparison with a simple diode structure, which has the same stripe cathode unit with screen printing phosphor layer on ITO glass surface as the anode, the reflective metal anode has some advantages such as sustaining high field emission current, no unexpected arcing, and high illumination and uniformity without phosphor degradation. The results show that a reflective metal anode not only conducts the residual charges and heat from the phosphor surface effectively, but also reflects the light to one side of the panel through the cathode end and exhibits high illumination without obvious obstacle by the narrow stripe cathodes. The luminance of the reflective metal groove anode we proposed is 11530 cd/m², with the emission current density of 1.52 mA/cm² under the electric field about 1.07 V/μm.

Abstract: Data synchronization distributes data to users of various configurations, and poses many challenges in today’s collaborative networks. In this paper, we propose a data synchronization scheme to reduce the finish time of distributing data with the understanding that users are free to join late or leave, which is common if the desired data is received. Our scheme involves a heuristic algorithm to push-and-pull segments of data. The numerical results yield significant lesser finish time than the conventional P2P approaches. Besides, there are no redundant transmissions and no need of searching data pieces in our approach, which help to reduce the network traffic and receiving time of data.