Chun-Jen Weng

Design and fabrication of optical homogenizer with micro structure by injection molding process

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.

Confocal displacement sensor with varifocal lens

A confocal displacement sensor with a varifocal lens and a multi-wavelength rainbow laser was established in this study. The surface curvature of varifocal lens was varied by different current driving so that the focal length can be easily changed. Thus, we can quickly measure the distance between the sensor head and targets by detecting the reflective power according to the principle of confocal laser. This rainbow laser can operate at four different wavelengths. The laser beams with different colors can be used to measure the dispersion of varifocal lens. The range of measuring displacement with 20X objective lens in this displacement sensor is from 4.9mm to 5.9mm. The FWHM resolution of displacement is about 70μm. The step-height aluminate plate was measured by this system and the error of measuring distance is less than 35μm (0.75%).

Exploiting the image of the surface reflectivity to measure refractive index profiling for various optical fibers

A direct image method of surface reflectivities on a cleaved fiber end with a filtered halogen lamp and a TE-cooled CCD with high dynamic range is proposed to measure the multi-wavelength refractive index profiling (RIP). A polished black glass is used to be a reference standard for measuring the absolute reflectivity of the fiber end. With the developed calibration procedures, both the spatially dependent sensitivity and spectral responsivity of the CCD pixels can be eliminated to achieve the high spatial accuracy. Tested fiber is connected with a fiber terminator to prevent errors from the backside return light. With the present method, the RIP can be precisely measured for not only multi-mode fibers but also single-mode fibers.

Measuring the thickness of transparent objects using a confocal displacement sensor

This paper reports on a confocal displacement sensor with varifocal lens used to measure the thickness of transparent materials. The focal length of the varifocal lens is adjusted by varying the current. Laser light passing through a transparent target lying within the range of the focal length crosses two interfaces; i.e., first from air to glass and then from glass to air. The signals associated with the interface were of higher intensity than that measure at other points along the z axis. A power meter is used to measure the power and LabVIEW is used to record a power-current graph. The current gap between the two peaks can be translated into values of displacement, indicating the thickness of the material.

A study of video-based droplet detection

The disdrometer system is a new imaged-based technique developed to measure the shape of droplets. This system contains three components: a CCD camera for capturing video images, a backlight source for illuminating drops and enhancing images, and a control unit for data acquisition and function control. In our preliminary study, we replaced raindrops with a free fall of droplets from a homemade liquid dropper. Subsequently, the high-speed CCD camera captured images of the falling droplets. We controlled the exposure time to 1 ms, which resulted in the falling droplets blurring in the assessment. To detect the droplet contours precisely, we used Pascals theorem to determine the best-fit ellipse shape. We concluded that the proposed image-based disdrometer system provides a promising approach to measure and monitor the falling droplets. Moreover, this instrument can be less expensive as it only requires basic maintenance for long-lasting daily use.

Developing a microspectrophotometer to measure the dependence of broadband refractive indices on Ge-doped concentrations in GRIN rods.

A confocal microspectrophotometer is utilized to scan the surface reflectivities of a polished gradient-index (GRIN) rod in the range of 400 to 900 nm. The pure fused silica is used to be a reference standard for deducing the absolute reflectivities of the Ge-doped core. Then, multi-wavelength refractive index profiles of the Ge-doped core can be further determined based on the Fresnel equation. Moreover, this work shows a connection between the material dispersion of the GRIN rod and the Ge-doped concentrations measured by an energy dispersive spectrometer. Finally, the dependence of the refractive index of the Ge-doped core on the doping concentrations at a certain wavelength can be easily expressed as a linear form.

Broadband microspectrophotometer with tablet PC control

This study investigated the design, fabrication, and performance characterizations of a broadband microspectrophotometer with tablet PC wireless control. The microspectrophotometer system performed rapid measurements, was highly accurate, and was easy to operate. The calibrations for two measurement modes for transmittance and reflectance spectra were performed with bulk and multilayer thin-film samples. Objective lenses with various magnifications were introduced to verify the possibility of microscopic spectra measurements in the system. A polarization identification capability was also included in the system.

Compact motorized circular wheel of polarization optics for ultra-broadband polarization state generation

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.

Automatic inspection apparatus based on high-speed image analysis: a new characterization technique for particle flow analysis

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.

Rapid displacement sensor based on fitting scan

A rapid displacement sensor with a varifocal lens based on a method of fitting scan is proposed for 3D surface profiling. The focal length of the varifocal lens can be adjusted by varying the driving current. By detecting the reflective power of the reflected laser, the displacement can be obtained. By integrating a LabVIEW program based on a Levenberg-Marquardt algorithm in this system, the measuring speed can be substantially improved. Finally, the 3D surface profile of a step-height sample was successfully scanned by this displacement sensor.