To better understand the mechanism of ejecting spray droplet and raindrop, a high-speed image analysis for droplet characterization technique was proposed in this study. In our design, three basic units containing a high-speed CCD camera, a light source, and automatic image acquisition and data processing unit, are integrated to assess the droplet motion. Next, a set of multistage image processing algorithms, the droplet detection and droplet tracking, were developed and conducted to analyze the droplet trajectories of the grabbed frames. By controlling a very short exposure time, the droplet size and velocity can be obtained to generate the droplet size distribution (DSD). To examine our proposed approaches, a commercially available spray nozzle and raindrop are used to evaluate the effectiveness. Meanwhile, the pair-matching rate is also involved to validate the recognition rate of the droplet tracking algorithm. Using this proposed framework, it can be used to provide valuable data to assess the spray droplet or the precipitation status by their droplet size to droplet velocity.
A novel concept of confocal sensor based on focal lens is proposed to measure the displacement. The light source is a stabilized fiber coupled LED. A 1x2 graded-index multimode fiber optic coupler is used in this sensor. One port is a LED input port via SMA connector, another port is a LED output port connected to a reflective collimator and the other port is a reflective sensor port connected to a photo detector. The focusing sensor head is the cascade of a focal lens and a 20X objective lens. In this confocal displacement sensor, LED passes through a focal lens and an objective lens so that the LED beam focuses at a fixed focal point. A test target is placed after the objective lens. The displacement between the sensor head and a target can be measured quickly by detecting the reflective power according to the confocal principle. The long-term stability of LED is under 0.5%. The effective back focal length is varied from 5.67mm to 6.57mm by 0-290mA current driving so that the measuring range is about 0.9mm. The FWHM resolution of displacement is about 50μm. This sensor has the features of low cost, high stability, high precision and compact.
The absorbing filter  is an optical element employed for isolating regions of a spectrum. In general, the thicker the absorbing filter material, the more wavelengths it will absorb. However, most optical filter products ignore light diffusion and are made with a constant thickness. While the non-collimated beams pass through the filter, the optical paths vary with incident angles. Thus, the absorption difference happens and leads to the poor uniformity of transmission spectrum. In our work, a filter lens was developed to achieve the similar function of interference filter and ND filter with better spectrum uniformity. It is mounted onto a designed macro lens and supplies it with a good spectrum aberration correction. The shape of the filter lens is designed to eliminate the optical path differences between the light beams in the medium. The macro lens is made of neutral glass and shaped into symmetrical biconvex for achieving macro imaging. The spectrum characteristic of the filter lens depends on the material of the absorbing filter. In the experiment, the filter lens was prepared. The experimental results show that the spectrum uniformity of the filter lens is better than that of the normal filter.
This study proposes an innovative optical mechanism with a miniature motorized circular wheel for polarization optics
for an ultra-broadband polarization state generator. The proposed apparatus can be suitable for a polarimetric
microspectrophotometer for measurements of micro optics and metamaterials with circular dichroism and linear
dichroism. Different types of micro optics have their own wavelength dependence, meaning different curves in the
broadband range of light. This study presents an ultra-broadband platform for measuring and identifying micro optics
such as chiral metamaterials, plasmonics, micro polarizers, and patterned retarders. The key component of a polarimetric
microspectrophotometer is a polarization state generator (PSG). A simple PSG consists of a polarizer and a waveplate.
An arbitrary polarization state can be created by rotating either the polarizer or the waveplate. Sheet polarizers and
achromatic waveplates have a limited bandwidth range. For the ultra-broadband measurement range of 400 nm to 1700
nm, the PSG needs at least three sheet polarizers and three achromatic waveplates: 400 nm-700 nm, 700 nm-1000 nm,
and 1000 nm-1700 nm. This optical mechanism, which consists of only one control motor and two high precision
unidirectional bearings, includes several polarizers and waveplates arranged in a matrix on a circular wheel. This
apparatus can shift one of the polarizers and waveplates to a predetermined position and rotate all the polarizers to
change the polarization status. An ultra-broadband polarimetric microspectrophotometer with a compact motorized
wheel is an advanced polarization optical instrument for research on chiral metamaterials, plasmonics, micro polarization
optics, green optics, and bio optics.
This paper is to design and fabricate an optical homogenizer with hybrid design of collimator, toroidal lens array, and
projection lens for beam shaping of Gaussian beam into uniform cylindrical beam. TracePro software was used to
design the geometry of homogenizer and simulation of injection molding was preceded by Moldflow MPI to evaluate the
mold design for injection molding process. The optical homogenizer is a cylindrical part with thickness 8.03 mm and
diameter 5 mm. The micro structure of toroidal array has groove height designed from 12 μm to 99 μm. An electrical
injection molding machine and PMMA (n= 1.4747) were selected to perform the experiment. Experimental results
show that the optics homogenizer has achieved the transfer ratio of grooves (TRG) as 88.98% and also the optical
uniformity as 68% with optical efficiency as 91.88%. Future study focuses on development of an optical homogenizer
for LED light source.