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Optical design for LED illumination in application of implantable retinal prostheses
(2019-01-01)
Huang, Ting-Ming
;
Chen, Fong-Zhi
;
Chiu, Chin-Fong
;
Wu, Chung-Yu
;
電子工程學系及電子研究所
For those patients with degenerated photoreceptors such that fail to transfer visual information to other retinal cells in the retinal network, a 16x16 pixel self-powered implantable subretinal device has been developed trying to restore their vision. The device contains sensing pixels that collect environmental signal, and electrodes that serve neurostimulation. A photovoltaic cell was designed aside of the sensing pixels and electrodes for power supplying. IR LED was selected to radiate on the photovoltaic cells for energy input such that proper optical layout shall be designed. Several extraocular optical layouts for IR LED illumination are studied to evaluate the perfect efficiency of each layout. Suitable design is to be selected through the evaluation process. Some experiments are performed to study the feasibility of optical layout. Images of IR LED are taken by a CMOS sensor. Irradiance on the calibrated CMOS sensor is calculated for comparison.
Efficiency Improvement of Near-Ultraviolet Nitride-Based Light-Emitting-Diode Prepared on GaN Nano-Rod Arrays by Metalorganic Chemical Vapor Deposition
(2014-03-01)
Kuo, Cheng Huang
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Chen, Yu An
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Wu, Ji Pu
;
Chang, Li Chuan
;
照明與能源光電研究所
Near-ultraviolet nitride-based light-emitting diodes (LEDs) were prepared on GaN nanorod arrays (NRAs). Transmission electron microscopy results show that the NRAs partially block threading dislocation propagation from the GaN template. Compared with conventional LEDS, the output power of the prepared LED using GaN NRAs with an injection current of 20 mA was enhanced by a factor of 1.67.
1.7 to 2.3 Gbps OOK LED VLC Transmission Based on 4 x 4 Color-Polarization-Multiplexing at Extremely Low Illumination
(2019-08-01)
Yeh, Chien-Hung
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Weng, Jui-Hung
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Chow, Chi-Wai
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Luo, Chien-Ming
;
Xie, Yue-Ru
To achieve the high traffic rate of a GaN LED-based visible light communication (VLC), a 4 x 4 color-polarization-multiplexing system is demonstrated by using two blue and two green LEDs. In the measurement, an available bandwidth of blue and green LEDs can be greater than 465 MHz for VLC modulation traffic by using the suitable analogy front end circuit. Hence, the proposed VLC system can deliver 1.7 to 2.3 Gbit/s ON-OFF keying traffic rates in the free space transmission length of 1-4 m under the extremely low illumination of 6.9-136.1 lux for the indoor application. Moreover, the measured BER of each LED is less than the forward error correction target of 3.8 x 10(-3) to maintain the better signal performance.
Portable LED-induced autofluorescence imager with a probe of L shape for oral cancer diagnosis
(2015-01-01)
Huang, Ting-Wei
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Lee, Yu-Cheng
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Cheng, Nai-Lun
;
Yan, Yung-Jhe
;
Chiang, Hou-Chi
The difference of spectral distribution between lesions of epithelial cells and normal cells after excited fluorescence is one of methods for the cancer diagnosis. In our previous work, we developed a portable LED Induced autofluorescence (LIAF) imager contained the multiple wavelength of LED excitation light and multiple filters to capture ex-vivo oral tissue autofluorescence images. Our portable system for detection of oral cancer has a probe in front of the lens for fixing the object distance. The shape of the probe is cone, and it is not convenient for doctor to capture the oral image under an appropriate view angle in front of the probe. Therefore, a probe of L shape containing a mirror is proposed for doctors to capture the images with the right angles, and the subjects do not need to open their mouse constrainedly. Besides, a glass plate is placed in probe to prevent the liquid entering in the body, but the light reflected from the glass plate directly causes the light spots inside the images. We set the glass plate in front of LED to avoiding the light spots. When the distance between the glasses plate and the LED model plane is less than the critical value, then we can prevent the light spots caused from the glasses plate. The experiments show that the image captured with the new probe that the glasses plate placed in the back-end of the probe has no light spots inside the image.
LED Induced Autofluorescence (LIAF) Imager with eight multi-filters for Oral Cancer Diagnosis
(2016-01-01)
Huang, Ting-Wei
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Cheng, Nai-Lun
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Tsai, Ming-Hsui
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Chiou, Jin-Chern
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Mang, Ou-Yang
Oral cancer is one of the serious and growing problem in many developing and developed countries. The simple oral visual screening by clinician can reduce 37,000 oral cancer deaths annually worldwide. However, the conventional oral examination with the visual inspection and the palpation of oral lesions is not an objective and reliable approach for oral cancer diagnosis, and it may cause the delayed hospital treatment for the patients of oral cancer or leads to the oral cancer out of control in the late stage. Therefore, a device for oral cancer detection are developed for early diagnosis and treatment. A portable LED Induced autofluorescence (LIAF) imager is developed by our group. It contained the multiple wavelength of LED excitation light and the rotary filter ring of eight channels to capture ex-vivo oral tissue autofluorescence images. The advantages of LIAF imager compared to other devices for oral cancer diagnosis are that LIAF imager has a probe of L shape for fixing the object distance, protecting the effect of ambient light, and observing the blind spot in the deep port between the gumsgingiva and the lining of the mouth. Besides, the multiple excitation of LED light source can induce multiple autofluorescence, and LIAF imager with the rotary filter ring of eight channels can detect the spectral images of multiple narrow bands. The prototype of a portable LIAF imager is applied in the clinical trials for some cases in Taiwan, and the images of the clinical trial with the specific excitation show the significant differences between normal tissue and oral tissue under these cases.
Tunable fiber confocal sensor with LED
(2015-01-01)
Weng, Chun-Jen
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Lan, Tzu-Hsien
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Hwang, Chi-Hung
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Chu, Nien-Nan
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Huang, Chien-Yao
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 50 mu m. This sensor has the features of low cost, high stability, high precision and compact.
Portable LED-induced autofluorescence spectroscopy for oral cancer diagnosis
(2017-04-01)
Yan, Yung-Jhe
;
Huang, Ting-Wei
;
Cheng, Nai-Lun
;
Hsieh, Yao-Fang
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Tsai, Ming-Hsui
Oral cancer is a serious and growing problem in many developing and developed countries. To improve the cancer screening procedure, we developed a portable light-emitting-diode (LED)-induced autofluorescence (LIAF) imager that contains two wavelength LED excitation light sources and multiple filters to capture ex vivo oral tissue autofluorescence images. Compared with conventional means of oral cancer diagnosis, the LIAF imager is a handier, faster, and more highly reliable solution. The compact design with a tiny probe allows clinicians to easily observe autofluorescence images of hidden areas located in concave deep oral cavities. The ex vivo trials conducted in Taiwan present the design and prototype of the portable LIAF imager used for analyzing 31 patients with 221 measurement points. Using the normalized factor of normal tissues under the excitation source with 365 nm of the central wavelength and without the bandpass filter, the results revealed that the sensitivity was larger than 84%, the specificity was not smaller than over 76%, the accuracy was about 80%, and the area under curve of the receiver operating characteristic (ROC) was achieved at about 87%, respectively. The fact shows the LIAF spectroscopy has the possibilities of ex vivo diagnosis and noninvasive examinations for oral cancer. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)
A Novel Tunable Green- to Yellow-Emitting beta-YFS:Ce3+ Phosphor for Solid-State Lighting
(2011-08-01)
Wu, Yun-Chen
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Wang, De-Yin
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Chen, Teng-Ming
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Lee, Chi-Shen
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Chen, Kuo-Ju
A Ce3+-activated fluorosulfide phosphor (beta-YFS: Ce3+) was synthesized by solid-state reaction in a sealed tube. The crystal structure has been refined from the XRD profiles and there are two different crystallographic rare earth sites, namely, Y(1) and Y(2), where the Ce3+ ions occupied. The emission band with a maximum at 495 nm of beta-Y0.99Ce0.01 FS phosphor was characterized by the 4f-5d transitions of Ce3+ ion. With increasing Ce3+ concentration, the emission variations were observed from 495 to 547 nm. When beta-YFS:Ce3+ phosphors were utilized to incorporate with n-UV/blue chip, greenish-white light with color rendering index of 65-77 were obtained. The results indicate that the tunable green- to yellow-emitting beta-YFS:Ce3+ can serve as a potential phosphor for incorporation in fabrication for solid-state lighting. The preparation, spectroscopic characterization, quantum efficiency, thermal-quenching behavior, and related LED device data are also presented.
InGaN-based light-emitting diodes grown on various aspect ratios of concave nanopattern sapphire substrate
(2018-10-31)
Ke, Wen-Cheng
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Chiang, Chih-Yung
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Son, Widi
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Lee, Fang-Wei
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電子物理學系
This study presented the optoelectronic properties of InGaN-based light-emitting diodes (LEDs) grown on nanoscale-patterned sapphire substrates (NPSSs) with various aspect ratio (AR) concave nanopatterns. Concave nanopatterns with low ARs of similar to 0.5 (LAR-NPSS) and high ARs of 2, 3 and 4 (HAR-NPSS) were achieved using an anodic aluminum oxide template as the dry etching mask. The diffuse transmission (DT) rate of the incident light wavelength at 450 nm increased linearly, from 2.2% for LAR-NPSS to 12.7% for HAR-NPSS with an AR of 4. However, the diffuse reflection (DR) rate for HAR-NPSS did not increase linearly with the increasing AR values. The limit of the DR rate for HAR-NPSS could be attributed to the guiding effect when the incident light entered into the high AR concave nanopattern; most of the incident light could not be reflected (returned to the air), therefore there was no significant contribution to the DR rate. The luminous intensities of LEDs grown on bare sapphire (B-LED), HAR-NPSS (HAR-LED) and LAR-NPSS (LAR-LED) were 39, 38 and 74 mcd, respectively. Interestingly, the lowest brightness of any LED was the HAR-LED, which had higher DT and DR rates. This significant discrepancy could be attributed to a large number of voids occurring at the initial growth stage of the LED epitaxial layer on the HAR-NPSS that caused the emitted photons to remain trapped inside the LED. In addition, increasing the LED epilayer coverage area (i.e. 1.6-fold) with the inclined facets of low AR concave nanopatterns effectively scattered the emitted photons, leading to an increased light emitting intensity of the LED. The experimental results indicated that the specific AR concave nanopattern of an NPSS could increase the LED epitaxial layer coverage area and prevent void formation, which plays a crucial role in achieving high-brightness in InGaN-based LEDs.
400Mbit/s OOK green-LED visible light communication with low illumination
(2018-12-01)
Yeh, C. H.
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Chow, C. W.
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Gu, C. S.
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Guo, B. S.
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Chang, Y. J.
In this work, we propose and demonstrate a LED-based visible light communication (VLC) system. Here, an analog front end (AFE) circuit with optimal equalization design is investigated to enhance the modulation bandwidth of LED. The VLC data rates of 340Mbit/s can be achieved under 1.5-3m free space transmissions with error-free (bit error ratio, BER<1x10(-9)). When the traffic rate is increased to 400Mbit/s, the BER satisfying the forward error correction (FEC) limit (BER=3.8x10(-3)) can be achieved at the low illumination of 34.1 Lux.

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