The rapid growth of high-power light-emitting diode (LED) technologies has gained momentum in developing accurate
tools and methods to measure performances of such products. For instance, it is widely recognized that confirming the
photobiological safety is extremely important since the light of the high-power products may be shone directly into
people's eyes. For many years, the international standard organizations, such as CIE, and researchers have been
developing guidelines and/or improving methods for measuring the LED radiation patterns, respectively. However, the
difficulties in LED measurements have been still highlighted by discrepancies in the experimental results among
different laboratories. In this paper, we first propose a mathematical formulation for the existing approaches, such as
those using two- and three-dimensional goniometers. Then, generalization of the measurement methods is presented to
improve the system measurement accuracy, through making a connection between a predicted accuracy and the
parameters of the optical setups (such as aperture size and working distance). To verify the effectiveness of our approach,
the experiments are conducted to evaluate and compare the performances of the proposed approach. The measurement
results indicate that our approach is consistent from theory to practice.
Confocal imaging is primarily based on the use of apertures in the detection path to provide the acquired three-dimensional images with satisfactory contrast and resolution. For many years, it has become an important mode of imaging in microscopy. In biotechnology and related industries, this technique has powerful abilities of biomedical inspection and material detection with high spatial resolution, and furthermore it can combine with fluorescence microscopy to get more useful information. The objective of this paper is first to present a generalized theoretical framework for confocal imaging systems, and then efficiently to design and implement such systems with satisfactory imaging resolutions. In our approach, a theoretical review for confocal imaging is given to investigate this technique from theory to practice. Also, computer simulations are performed to analyze the imaging performance with varying optomechanical conditions. For instance, the effects of stray light on the microscopic systems are examined using the simulations. In this paper, a modified optomechanical structure for the imaging process is proposed to reduce the undesired effects. From the simulation results, it appears that the modified structure highly improves the system signal-to-noise ratio. Furthermore, the imaging resolution is improved through the investigation on the tolerance of fabrication and assembly of the optical components. In the experiments, it is found that the imaging resolution of the proposed system is less sensitive than that of common microscopes, to the position deviations arising from installations of the optical components, such as those from the pinhole and the objective lens.
Light-emitting diodes (LEDs) have been recognized as a generation of new light sources because they possess the
properties of energy-saving, environmental protection, long lifetime, and those lacking in conventional lighting. To
satisfy the requirements for different applications (e.g., for large-scale displays), determining the spatial radiances of
LEDs is important to identifying their viewing angle and utilizing their lighting efficiency. The objective of this paper is
to build up a real-time spatial radiance measurement system for LEDs, on the basis of digital signal processing (DSP)
techniques. In this paper, the system analysis is given to show the feasibility of this work. Two primary subsystems are
devised to perform the real-time measurements. First, in the optoelectronic sensing and signal processing subsystem, a
wide-bandwidth photodiode sensing circuit is employed to acquire optical signals at a high speed, and an automatic gain
control (AGC) circuit is designed to increase the measurement range. To support high-speed data processing, a
DSP-based platform is developed in the subsystem. Second, a light-source rotation scheme is used in the optomechanical
subsystem. For performance evaluations, we adopt a standard calibrating light source to test and verify our system.
Experimental results indicate that the proposed system gives satisfactory results.
With the rapid growth of optoelectronics technologies, photodiodes (PDs) has been widely used in optical measurement
systems, color measurement and analysis systems, etc. To meet most of the measurement requirements, the
determination of PD spectral responses is very important. The goal of this paper is to develop a high-accuracy and
cost-effective spectral response measurement system for PDs. In this paper, the proposed system contains a grating-based spectral filtering module, an amplifier module, and a digital-signal-processing (DSP) based platform. In the spectral filtering module, a single-grating monochromator based on a Czerny-Turner configuration is first analyzed and simulated, and then the experiments are conducted to check if the measurement accuracy is satisfactory. In the measurement system, optoelectronic signals from the PD under test are acquired from the amplifier module and the DSP-based platform is developed to communicate and manipulate the measured data. Through comparison with the measurement data from a commercially available system, it is found that our approach gives quite satisfactory results.
For many years, the widening use of digital imaging products, e.g., digital cameras, has given rise to much attention in
the market of consumer electronics. However, it is important to measure and enhance the imaging performance of the
digital ones, compared to that of conventional cameras (with photographic films). For example, the effect of diffraction
arising from the miniaturization of the optical modules tends to decrease the image resolution. As a figure of merit,
modulation transfer function (MTF) has been broadly employed to estimate the image quality. Therefore, the objective of
this paper is to design and implement an accurate and cost-effective MTF measurement system for the digital camera.
Once the MTF of the sensor array is provided, that of the optical module can be then obtained. In this approach, a spatial
light modulator (SLM) is employed to modulate the spatial frequency of light emitted from the light-source. The
modulated light going through the camera under test is consecutively detected by the sensors. The corresponding images
formed from the camera are acquired by a computer and then, they are processed by an algorithm for computing the
MTF. Finally, through the investigation on the measurement accuracy from various methods, such as from bar-target and
spread-function methods, it appears that our approach gives quite satisfactory results.
The confocal imaging has become one of the most widely applied microscopic techniques in various fields, such as biotechnology, automation engineering, optical engineering, solid-state physics, metallurgy, integrated circuit inspection, etc. Confocal laser scanning microscopy (CLSM) is primarily based on the use of apertures in the detection path to provide the acquired three-dimensional images with satisfactory contrast and resolution. The major objective of this paper is to analyze the imaging performance of the confocal microscopes with varying opto-mechanical conditions. In this paper, the working principles of the one- and two-dimensional scanning mechanisms in the microscopic systems are first reviewed and verified by opto-mechanical simulations. Then, for the imaging performance, the tolerance to the fabrication and assembly of the optical components in conventional confocal microscopes is also investigated by simulations. The simulation results indicate the importance of eliminating the effects of stray light in the microscopic systems.