2012清大電資院學士班
「頂尖企業暑期實習」
經驗分享心得報告
 實習企業：工業技術研究院
 實習學生：電資院學士班
電光所
呂軒豪
前言

(一)實習時間：民國101年7月1日至101年8
月31日，共61天

(二)實習地點：工業技術研究院

(三)實習導師：趙嘉信

(四)參與動機：本身對光電領域有興趣，藉
資深工程師
由暑期實習學習相關知識並累積職場經驗。
實習單位簡介 ─ 工研院電光所
 一個跨領域的應用研究機構，致力於研究發展、
產業服務等工作，並配合政府推動產業科技政策，
以培養我國產業科技實力促進產業發展。
 成立宗旨：「世界級的研發機構，產業界的開路先
鋒」。
 實習單位：W200光電元件製程及封裝部，負責的業務
是發光二極體的製程和封裝，其中最主要的研發領域
在於微發光二極體陣列晶片。
實習內容
 題目：LED照明光源在無線通訊之高頻響應分析與設計
 工作內容

閱讀並整理可見光通訊相關期刊資料

發光二極體的專業知識學習

發光二極體的高頻量測

探討現階段照明發光二極體通訊限制
 預期效益：熟悉LED原理及在通訊應用之基礎。
About VLC
Visible Light Communication (VLC)
: A Newer communication technology using “Visible Light”.
Visible Light
: Wavelength between 380 nm (800THz) and 780nm (400THz).
Feature points
Convenience : Easy to build in current lighting system.
Safe : No Electromagnetic Interference (EMI).
Security : Does not penetrate wall and prevents snooping .
Unregulated : Crowded RF spectrum.
Available in the restricted area : Aircraft and hospital.
VLC Apps
VLC Structures
Transmitter
Optical receiver
Concentrator
Input
data signal
PD
Preamplifier
LPF
L
DC
R
Modulators
Recovered
data signal
LED array
Resonant
Capacitor (C) Bias Tee
A
High-speed
buffer
Inductance (Lseries)
DC arm
Signal
Luxeon LED, R
Z
DC bias current
from Laser driver
Individual LED driving circuit
◎ DC current ─ Lighting
《Main Purpose》
◎ Input data signal ─ Communications 《Added Value》
TRADEOFF！
VLC Systems
◎ LED is the first choice for light source (long lifespan, quick modulation).
◎ Modulation can transform the data into a series of light pulses.
◎Photodiode , CMOS and CCD sensors are often used as receivers.
LED Frequency Response
-3dB
◎ Overall bandwidth ─ 3MHz. (narrower)
◎ Blue Component bandwidth ─ 12 MHz (wider)
◎An Optical filter can removes the slow yellow phosphor emission component.
Frequency Response Measurement
Spectrum Analyzer
Photodetector
Bias Tee
Light Emitting Diode
RF Generator
Power Supply
Current Meter
Experiment Results
Number
BW(MHZ)
Series*4
3.80
Series*3
3.42
Series*2
2.93
LED*1
2.54
Parallel*2
2.00
Parallel*3
1.73
Parallel*4
1.69
-3
Though the results show that “LED in series” excel “LED in parallel
“ in modulation bandwidth, the differences aren’t distinct.
The impedance inside the circuit, including signal source and biastee, will provide different interference in frequency response.
Limiting Factor of Bandwidth
Dominant Factor – Diffusion Capacitance
JOURNAL OF LIGHTWAVE TECHNOLOG
VOL. 30, NO. 1, JANUARY 1, 2012
（A function of the carrier lifetime）
 Impurity defects in MQW (NCU)
 Triangular Barrier (Yale)
 Higher current density
However, in our experiment, we
found that there was almost no
change in modulation bandwidth
Current Density Calculation
with current density. (10mA→100mA)
J 
10
mA
 1 0 4 (
)
3 5 0 3 5 0
m 2
J 
10 0
mA
 1 03 (
)
3 5 0 3 5 0
m 2
Bandwidth v.s Diffusion Capacitance
1997 IEEE High-efficiency high-speed Gal1-xA1xAs light-emitting diode characteristics
Where d is the active layer thickness, (p0 + no) the hole and electron
concentration at thermal equilibrium, B the recombination constant
and J the current density.
In what condition will the bandwidth independent of current ?
fc 
1

2
2 J / ed
p0  n0
1
4 J / Bed
( p0  n0 ) 2
2 J / ed
p0  n0
B( p0  n0 )
1



1 4 J / Bed
2
2
1
1
1
2
2 ( p0  n0 )
→The Taylor expansion can be used when the injection current density
is much lower than background concentration.
實習收穫
Researches

Patents Reading

MATLAB Writing

Light Emitting Diodes Studying

IEEE Paper Reading and Sorting
Experiments

Integrating Sphere (I-V &P-I Curve)

Spectrum Analyzer (Frequency Response)

LED Dispenser

LED Phosphor and Color Temperature
心得感想
 要有homesick的準備。
 除此之外，看到朋友出國玩的照片要想辦法鎮定。
 一天坐九個小時，伙食佳，千萬要注意體重控制。
 把暑期實習當作一次學習的機會，多觀察工作環
境和認識其他人。
 在學校所學的永遠不夠。
實習後對未來之生涯規劃、期許及目標
 光電領域的專題 (with Prof.Yang)
 調整修課的規劃（元件端、通訊端）
 千萬別自滿，課堂上所學到的東西都只是一切先
進科技的基礎，能學以致用才是重點。
 期許自己成為一個好的科學家，或是工程師，但
千萬不能失去熱情。
 I need a good vacation :-P