Jui-Wen Pan

Homogenized LED-illumination using microlens arrays for a pocket-sized projector.

We present an LED-based ultra-mini DMD projector with a size of 75 mm x 67 mm x 42 mm. A compact homogenizer consisting of a double-side microlens array and two condensers was proposed to reduce the size of the pocket-sized projector. The homogenizer not only allowed for a reduction in the total track length of the system, but also reduced the angle of the rays emitted from the LED with the micro field lens array. The double-side well-aligned 124 x 146 microlens array was fabricated using backside alignment and hot embossing techniques. The microlens array was square-arranged and the fill-factor was extremely high. The uniformity and total throughput of this projector were higher than those of the current pocket-sized projectors. Moreover, the optical performances of the projector such as color difference and the LED alignment tolerance were also measured and discussed.

High efficiency pocket-size projector with a compact projection lens and a light emitting diode-based light source system

We present a light emitting diode (LED)-based ultramini digital micromirror device projector with a size of 75 mm x 67 mm x 42 mm and a weight of 338 g. The LED illuminator inside this projector makes it possible to achieve a volume of 18 cm(3) by using a dichroic filter and a collimating lens. The illumination system consists of high uniformity of 93% through a microlens array as a homogenizer. A total internal reflection prism is also used to reduce the size of both the illumination system and the telecentric projection lens. A projection lens system with an ultrasmall track of 42 mm, including a high modulation transfer function value of 0.4 at 46.2 line pairs/mm, an optical distortion of only 0.25 %, and a television distortion of 0.01%, is designed. Through the above superior specification, we can produce a 20 in. (51 cm) color display comparable in brightness to a laptop with a contrast of 3700:1. The device is compact and suitable for personal use.

Speckle reduction and maintaining contrast in a LASER pico-projector using a vibrating symmetric diffuser

We proposed a design for a LASER pico-projector with a low speckle contrast value and high contrast ratio that maintains system efficiency. The method for speckle contrast reduction utilizes two diffusers and a Voice Coil Motor (VCM) oscillator. The two different diffusers for a high contrast ratio and high system efficiency can be divided into two categories. In Category 1, the speckle contrast value can be decreased to 2.80% by using a circular symmetric diffuser. At the same time, the full-on/full-off (FO:FO) contrast ratio can be maintained within 1200:1-1300:1, but the system efficiency decreases 1.50%. In Category 2, the speckle contrast value can be reduced to 6.50% by using an elliptically scattering diffuser. At the same time, the FO:FO contrast ratio can be maintained within 1300:1-1400:1, and the system efficiency decreases by only 1.00%.

Light extraction efficiency analysis of GaN-based light-emitting diodes with nanopatterned sapphire substrates

In this paper, we propose a method to analyze the light extraction efficiency (LEE) enhancement of a nanopatterned sapphire substrates (NPSS) light-emitting diode (LED) by comparing wave optics software with ray optics software. Finite-difference time-domain (FDTD) simulations represent the wave optics software and Light Tools (LTs) simulations represent the ray optics software. First, we find the trends of and an optimal solution for the LEE enhancement when the 2D-FDTD simulations are used to save on simulation time and computational memory. The rigorous coupled-wave analysis method is utilized to explain the trend we get from the 2D-FDTD algorithm. The optimal solution is then applied in 3D-FDTD and LTs simulations. The results are similar and the difference in LEE enhancement between the two simulations does not exceed 8.5% in the small LED chip area. More than 10(4) times computational memory is saved during the LTs simulation in comparison to the 3D-FDTD simulation. Moreover, LEE enhancement from the side of the LED can be obtained in the LTs simulation. An actual-size NPSS LED is simulated using the LTs. The results show a more than 307% improvement in the total LEE enhancement of the NPSS LED with the optimal solution compared to the conventional LED.

High luminance hybrid light guide plate for backlight module application

We introduce a hybrid backlight module, which consists of a hybrid light guide plate (HLGP) and a brightness enhancement film (BEF). The HLGP comprises functions of a conventional light guide plate, a reflector, and a BEF. The HLGP allows one-dimensional rays to be collimated. We add a BEF above the HLGP, and let the crossed-dimension rays to be collimated. Comparing with the conventional edge-lit backlight module, the optical efficiency improves to 1.3-times and the on-axis luminance improves to 3.7-times by using the hybrid backlight module.

Portable digital micromirror device projector using a prism

A newly designed ultrasmall total internal reflection prism with a size of 29 mm x 22 mm x 24 mm and weight of 19.5 g is proposed for use in a pocket-sized Digital Micromirror Device projector. The entire projector, including an arc lamp illumination, relay, and projection system, has a height of 48 mm and a footprint of 80 mm x 132 mm. By using an overdriving f/2.0 projection lens, the geometric efficiency of the projection system, eta(geo-pro), can be enhanced from 80% to 92%. Although, at the same time, the contrast decreased from 1200:1 to 500:1, this can be enhanced using an off-axis stop. By tuning the position of the stop, the contrast can be as high as 3700:1 for a eta(geo-pro) equal to 90%. Using what we believe to be a novel prism design, we can get a very compact optical system with a high efficiency and good contrast ratio.

Light extraction efficiency of GaN-based LED with pyramid texture by using ray path analysis

We study three different gallium-nitride (GaN) based light emitting diode (LED) cases based on the different locations of the pyramid textures. In case 1, the pyramid texture is located on the sapphire top surface, in case 2, the pyramid texture is locate on the P-GaN top surface, while in case 3, the pyramid texture is located on both the sapphire and P-GaN top surfaces. We study the relationship between the light extraction efficiency (LEE) and angle of slant of the pyramid texture. The optimization of total LEE was highest for case 3 among the three cases. Moreover, the seven escape paths along which most of the escaped photon flux propagated were selected in a simulation of the LEDs. The seven escape paths were used to estimate the slant angle for the optimization of LEE and to precisely analyze the photon escape path.

Integration of Non-Lambertian LED and Reflective Optical Element as Efficient Street Lamp

A cost effective, high throughput, and high yield method for the increase of street lamp potency was proposed in this paper. We integrated the imprinting technology and the reflective optical element to obtain a street lamp with high illumination efficiency and without glare effect. The imprinting technique can increase the light extraction efficiency and modulate the intensity distribution in the chip level. The non-Lambertian light source was achieved by using imprinting technique. The compact reflective optical element was added to efficiently suppress the emitting light intensity with small emitting angle for the uniform of illumination intensity and excluded the light with high emitting angle for the prevention of glare. Compared to the conventional street lamp, the novel design has 40% enhancement in illumination intensity, the uniform illumination and the glare effect elimination.

High contrast ratio prism design in a mini projector

In this paper, we present a novel prism with the ability to enhance the contrast ratio and maintain the optical efficiency in a digital light processing projection system. The working theorem for the novel prism is derived as well. In this novel prism design, the ghost ray is directed away from the projection lens by a total internal reflection surface. Since the ghost ray does not even enter the projection lens, the contrast ratio enhancement is more effective than that achieved by an asymmetrical stop. Compared with the conventional method, the full-on/full-off contrast ratio is increased from 921∶1 to 46347∶1 and the American National Standards Institute contrast ratio is increased from 177∶1 to 295∶1. The imaging system efficiency can maintain at 79.8% under the contrast ratio enhancement process. Ghost ray analysis for the novel prism explains the contrast enhancement well.

Dual view capsule endoscopic lens design

A dual view capsule endoscopic (DVCE) lens is proposed with front view and back view functions. This is a hybrid lens with a catadioptric mirror and an aspherical surface to support both view functions. The field of view (FOV) for the front view function is 90 degrees. The FOV for the back view function is 260 to 290 degrees. The TV distortion for the front view and back view function is under 30% and 25%. The corner relative illuminations for the two view functions are above 0.53. The Modulation Transfer Function (MTF) performance at the Nyquist Frequency for the two view functions can be kept above 0.35, even under tolerance they can remain above 0.2. Moreover, the telecentric conditions at the image plane of the DVCE system can support constant magnification through focusing. This condition can reduce the measurement error by slightly defocusing of the lens. Thus, the two view functions can offer physicians a wide viewing angle to deal with lesions over the fold.