In this paper, transparent Er3+/Yb3+/Tm3+ tri-doped tellurite glass samples were prepared by high temperature calcination method and drawn into filaments when in molten state. The tip of each filament selected was melted by flame and subsequently fabricated into a microsphere via the surface tension of liquid. The microsphere resonators were effectively pumped by 976 nm/1550 nm continuous wave (CW) lasers respectively, using the same biconical tapered fiber which acted as a coupler, transmitting the pump light into the microspheres under uniform conditions and collecting the up-conversion (UC) fluorescence from the microspheres at the same time. We obtained blue, green and red UC emission upon both two types of excitation, but with different intensity distributions. The UC luminescence mechanism of the Er3+/Yb3+/Tm3+ tri-doped samples has been investigated in the perspective of the energy level structure of these rare earth (RE) ions. We find that different pump light sources may cause different energy transfer paths among ions, which thus results in the difference on spectral distributions. It is predicted that such kind of multi-color luminescence material has potential to be applied in the white lighting. In addition, we also did some theoretical analyses on the propagation constant matching that greatly influences the coupling between the microsphere and the tapered fiber, and discovered the fact that it may require a pretty small size of the microsphere for effective coupling when there exists a large refractive index difference between them. Besides, it seems that the waist of the fiber has to get thinner when the light has a shorter wavelength. The outcomes from our experiments were in correspondence with the results above. These results will pave the way for the research on further improvement of the coupling efficiency between the microsphere and the tapered fiber.
In this paper, a novel optical inspection apparatus was studied which enables one to inspect both top and bottom surfaces of the thermoelectric cooler (TEC) components. In the optical inspection apparatus, a right angle prism reflector located beneath the glass stage was used to image the bottom surface of the TEC component on top of the stage. In order to obtain the clear images of two surfaces of the TEC component simultaneously, a proper telecentric imaging lens with sufficient large depth of field needs to be selected to address their optical path difference. A telecentric optical imaging lens DH110-03F50 with depth of field of around 6mm together with a right angle prism reflector with solpe side length of 3.6mm was chosen for this experimental setup. With this apparatus three groups of components were inspected in the experiments and each group has some typical samples with specially selected Passed and Failed features on the surfaces to be examined. The experimental results indicate that the images of both top and bottom surfaces obtained using the optical inspection system are sufficiently clear and well resolved which meets the requirements for the following image processing. The results show that the proposed technique allow us to inspect both top and bottom surfaces of the component with simplified configuration and effective cost. This novel inspecting technique will find applications in the automatic optical inspection systems for the TEC components.
In this paper, the Olympic rings pattern is generated by using freeform lens array and illumination light source array. Based on nonimaging optics, the freeform lens array is designed for point light source, which can generate the focused pattern of annular light spot. In order to obtain the Olympic logo pattern of five rings, the array with five freeform lenses is used. By adjusting the emission angle of each light source, the annular spot is obtained at different positions of the target plane and the Olympic rings logo is formed. We used the shading plate on the surface of the freeform lens to reduce the local light intensity so that the light spot overall irradiance distribution is more uniform. We designed a freeform lens with aperture of 26.2mm, focal length of 2000mm and the diameter of a single annual spot is 400mm. We modeled freeform lens and simulated by optical software TracePro. The ray tracing results show that the Olympic rings with uniform illumination can be obtained on the target plane with the optical efficiency up to 85.7%. At the same time, this paper also studies the effects of the target plane defocusing on the spot pattern. Simulations show that when the distance of the receiving surface to the focal plane varies within 300mm, a reasonable uniform and small distorted light spot pattern can be obtained. Compared with the traditional projection method, our method of design has the advantages of high optical efficiency, low cost and the pattern is clear and uniform.