April 2010 - June 2010
Publisher: Chairman Sheng-Lung Huang  Editors: Prof. Jui-che Tsai, Ms. Hsiao-wen Lin  July 30, 2010
March “Photonics Forum” Lecture Highlights


March 9th, 2010 (Tuesday) 4:30 PM
Speaker: Professor Chinlon Lin (Nanyang Professor, Director of Photonics Research Center, School of EEE, Nanyang Tech. University, Singapore)
Topic: From G. Marconi to Charles K. Kao--100 Years of Nobel Prize (Physics, 1909-2009) and A Century of Modern Marvels of EECS

Professor Chinlon Lin visited GIPO on March 9th (Tuesday) and lectured in Auditorium 101, Barry Lam Hall. His lecture, “From G. Marconi to Charles K. Kao--100 Years of Nobel Prize (Physics, 1909-2009) and A Century of Modern Marvels of EECS” was attended by GIPO professors and students with enthusiasm. Everyone learned much.

Speaker, Professor Chinlon Lin



March 12th, 2010 (Friday) 2:30 PM
Speaker: Prof. Stephen E. Saddow (Professor of Electrical Engineering, University of South Florida)
Topic: Silicon Carbide: A Robust Semiconductor Material for Harsh Environment MEMS and Biomedical Applications

Professor Stephen E. Saddow attended the GIPO Photonics Forum on March 12th, 2010 (Friday). GIPO professors and students who attended his lecture “Silicon Carbide: A Robust Semiconductor Material for Harsh Environment MEMS and Biomedical Applications” participated with enthusiasm. Professor Saddow’s lecture was fascinating and thorough, and he interacted with his audience throughout the lecture.

Speaker, Professor Stephen E. Saddow



March 26th, 2010 (Friday) 2:30 PM


Director-general Zhu-Shun Zhuo of Value Creation Center, Wistron Corporation


The Transformation and Development of the Photonics and Information and  Communication Industries


Director-general Zhu-Shun Zhuo visited GIPO on March, 26th, 2010 (Friday) to speak at GIPO’s Photonics Forum. His lecture, “The Transformation and Development of the Photonics and Information and Communication Industries” was attended with enthusiasm by GIPO professors and students. Director-general Zhu-Shun Zhuo’s lecture was both informative and fascinating and he interacted with his audience throughout the lecture. Everyone who attended learned much.

Speaker, Director-general Zhu-Shun Zhuo


April “Photonics Forum” Lecture Highlights


April 16th, 2010 (Friday) 2:30 PM
Speaker: Professor Wood-Hi Cheng (Department of Photonics, National Sun Yat-Sen University)
Topic: A Work of Art: The Research and Development of Optical Fiber Lens
  Professor Wood-Hi Cheng visited GIPO on April 16th (Friday) and lectured in Auditorium 101, Barry Lam Hall. His lecture, “A Work of Art: The Research and Development of Optical Fiber Lens was attended with enthusiasm by GIPO professors and students, and everyone learned much from the lecture.

Speaker, Professor Wood-Hi Cheng


May “Photonics Forum” Lecture Highlights


May 7th, 2010 (Friday) 2:30 PM
Speaker: Professor Chi-Shun Tu (Graduate Institute of Applied Science and Engineering, Fu-Jen Catholic University)
Topic: Multiferroics and Solid Oxide Fuel Cell
  Professor Chi-Shun Tu visited GIPO on May 7th (Friday) and lectured in Auditorium 101, Barry Lam Hall. His lecture “Multiferroics and Solid Oxide Fuel Cell” was attended with enthusiasm by GIPO professors and students.

The host of the lecture, Professor Zhe-Chuan Feng (left) pictured with Professor Chi-Shun Tu (right).


~ Small-scale Drill for Emergency, Ming-Da Hall, EECS ~

(Time: March 30th, 2010; Location: Ming-Da Hall, EECS, NTU)

Composed by: Tzu-Yu Chen

GIPO and GIBEBI (Graduate Institute of Biomedical Electronic and Bioinformatics) held a small-scale drill for emergency at Ming-Da Hall to ensure that staff developed sufficient skills to deal with emergency situations, and are able to provide immediate assistance, minimizing possible losses. This exercise also served to familiarize participants with important concepts in safety and emergency management, increasing everyone’s ability to deal with such situation.

On the morning of March 30, 2010, experts from Der-An Engineering Consultants, Inc., were invited to give a lecture concerning fire-fighting skills and facilities to our teachers, staff and students. This was done to increase everyone’s knowledge on this topic. Next, a drill for emergency took place: a simulated fire occurred in laboratory 703, on the 7th floor as students were performing research. An extension cord caught fire, and the resulting smoke triggered the smoke detector and fire alarms in Ming-Da Hall. The laboratory immediately reported the situation to the control center on the 3rd floor, to the campus police squad, and to the chairman of GIPO. Fire-fighting and defense units were formed immediately, including a command unit, an information unit, a fire-extinguishing unit, an evacuation assistance unit, a safety unit, and a rescue unit. These teams quickly began to carry out their individual missions. The drill was completed when all personnel in the building had been evacuated and assembled in the square on the ground floor.

After the drill, the experts from Der-An Engineering Consultants, Inc. demonstrated the use of fire extinguishers, and participants practiced with fire extinguishers, the fire hydrants and the rescue descending devices. Through these hands-on experiences, we not only learned how to use the facilities, but also improved our ability to escape from dangerous situations.

We would like to take this opportunity to thank all the participating teachers, staff and students for your kind cooperation. It is our hope that after this experience, we will all pay more attention to building safety and, when accidents do occur, immediately report the danger to the appropriate units and take measures to control the damage.

A lecture on lab safety and fire extinguishing facilities.

After the fire broke out, a command zone, a rescue zone, an assembly zone were formed immediately.

The broadcasting unit proceeded to announce the danger in the building.

The evacuation assistance unit evacuating personnel on the spot.

Experts teaching participants how to use fire extinguishers after the drill.

Participants using the descending devices after the drill.


~ The 2nd GIPO Students' Association Badminton Tournament ~

(Time: May 30, 2010; Location: the multi-function court, 1F, NTU Sports Center)

Composed by: Hsiang-Chun Wei, the President of the GIPO Students' Association

The 2nd GIPO badminton tournament has drawn to a successful close, and we’d like to thank everyone for their enthusiastic participation. There were 15 singles and 14 doubles teams participating, and prizes were plentiful. We had a champion, a second place and 2 third places for the singles and doubles categories. The tournament was held at the 1F multi-function court of NTU's Sports Center, at 10:30 AM on May 30th. Every game was intensely played. Finally, Agnes Lee won the singles champion, with Wei-Chung Chen winning second place, and Ying-Yuan Huang and Yang-Kai Wu winning third. Yu-Ta Wang/Agnes Lee won the doubles champion, with Wei-Hsiuan Tseng/Po-Sheng Wang winning second, with Guan-Jung Lai/Yang-Kai Wu and Jeng-Wei Yu/Wei-Ting Hu in third place. This year's championship match was as exciting to watch as last year's, and as the battle progressed, spectators became more and more excited as well.

From this tournament, one can see that GIPO is full of talent; our students are gifted in many respects, and stay in shape while studying hard. Regrettably, there were no professors participating in this year’s event. Perhaps, in future tournaments, we could arrange matches for professors so that they can enjoy the event with us. There were perhaps some things concerning this event that could have been improved, and so we’d like to thank you for your kind cooperation.

We would like to give special thanks to those who have helped make this event possible, including: Li-Chi, Wei-Ting, Tzu-Yu and Hsiao-Wen of GIPO staff, and our classmates Hsiao-Yuh Wang and Jay-Zway Hong. We would also like to thank Yu-Ming and Jia-Ning of my lab for their invaluable advice. Also, thank you to the participants who took on the job of managing the score board. Finally, thank you to our GIPO chairman for your kind encouragement and financial support which gave us sufficient funds to hold this event.

Game schedule, singles

Game schedule, doubles

Check-in in the morning A singles match

A doubles match

The intense singles championship match

Awarding - third place, singles: Ying-Yuan Huang (left)

Awarding - third place, singles: Yang-Kai Wu (left)

Awarding - second place, singles: Wei-Chung Chen (left)

Awarding - champion, singles: Agnes Lee (left)

Awarding - third place, doubles: Jeng-Wei Yu (left) / Wei-Ting Hu (right) Awarding - third place, doubles: Guan-Jung Lai (middle) / Yang-Kai Wu (right)

Awarding - second place, doubles: Wei-Hsiuan Tseng (left) / Po-Sheng Wang (middle)

Awarding - champions, doubles: Agnes Lee (left) / Yu-Ta Wang (middle)

All participants, at the 2nd GIPO Students’Association Badminton Tournament closing ceremony



~ 13th International Conference on Phonon Scattering in Condensed Matter ~

 (Time: April 18th ~ 23rd 2010; Location: Barry Lam Hall, NTU)

Composed by: Chia-Hsun Chiao

GIPO Professor Chi-Kuang Sun hosted the 13th International Conference on Phonon Scattering in Condensed Matter on April 18th-23rd, 2010. There were over 300 professionals and scholars from 21 countries attended the conference. Professors and students of GIPO, the EE department, and the physics department were also admitted to attend the lectures. In addition to providing an opportunity for scholars from different countries to share their newest research developments, we believe that sponsoring this conference allows other countries to better understand the level of research in Taiwan. Thus, this conference was an important occasion for international cooperation.

The International Conference on Phonon Scattering in Condensed Matter is not only an international conference with excellent traditions and a long history, but is also a flagship conference in phonon science. It has been almost 40 years since the first conference was held at Saint-Maxime, France, in 1972. Since then, it has been held once every 3 years, in France, Germany, USA, Japan, UK and Russia respectively. Aside from the aforesaid long history, it is also the most important occasion for academic exchange in phonon research. The world’s most prominent scholars regard this event as the most influential of conferences. The topics discussed in previous conferences comprehensively covered phonon sciences, and included experiments, theories and numeral simulations. Thus, it can be seen that this event is an authoritative and representative conference.

This year, Professor Sun hosted the conference, which began on April 18, and ended on April 23, lasting 6 days. There was a tutorial talk, 5 plenary talks and 14 invited talks. From over 250 submissions, we selected 91 pieces for oral presentation and 157 pieces for poster presentation. In addition to publishing the conference proceedings, we also worked with the Physical Society of Republic of China (TAIWAN) and have arranged a special issue for the conference in the Chinese Journal of Physics. So far, we have received and are reviewing near one hundred submissions. Due to the volcanic eruption in Iceland, European flights fell to disarray, and some European scholars were unable to attend the conference personally. However, under Professor Sun’s direction, we were able to install a web-conferencing system a day before the conference took place. These measures made it possible for stranded scholars to participate in the conference through the internet. Our solution effectively resolved the difficult situation, and conference participants appreciated our facility in dealing with the contingency. This unexpected development has also made this 13th conference the 1st in the conference history to proceed via the internet.

Aside from inviting world scholars to deliver speeches, we had also hoped to utilize the six days of the conference to increase recognition of NTU internationally, and hoped to raise its internationalization level. During the conference, Professor Sun introduced NTU's history and heritage, its academic standing in Taiwan, and its   current international cooperative research projects. It was arranged for some conference participants to visit NTU campus, hospital, and optics laboratories. During the conference, we also worked with French scholars to perform research, which certainly promoted academic interaction between the two countries. The conference banquet was held at National Taiwan Museum; this event allowed conference participants an opportunity to relax and interact, and also introduced to international scholars Taiwan’s aboriginal history and culture. Also, to allow conference participants to experience Chinese cultural heritage and Taipei's multi-faceted lifestyle, we also arranged visits to the National Palace Museum and introduced several of Taipei's famous landmarks, such as National Chiang Kai-shek Memorial Hall, the Grand Hotel and the Taipei 101.

This is the first time that this influential conference was ever held in Taiwan, and only the second time it was held in Asia. With the successful completion of this conference, we have, in both the pre-conference preparation and in the conference itself, showed the world Taiwan's technological strength and advancement during this generation. Since phonon phenomenon covers a wide range of subjects, from fundamental science to applied technology, the success of this conference could indeed unify Taiwan's phonon research projects and inspire Taiwan's scholars to connect further with the world technology trends. In addition, the working staff of this conference has also gained a lot of valuable experiences, and thus, we will do an even better job for future international conferences.

A group photo of the international scholars



Research Accomplishments in 2009, Wide Gap Semiconductor Laboratory

Professor Zhe-Chuan Feng

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

lRaman scattering study on anisotropic property of wurtzite GaN”, Hung Chiao Lin, Z.C. Feng, et al., JOURNAL OF APPLIED PHYSICS 105, 036102 (2009)

lTemperature dependent and time-resolved photoluminescence studies of InAs self-assembled quantum dots with InGaAs strain reducing layer structure”, Lingmin Kong, Zhe Chuan Feng, et al., JOURNAL OF APPLIED PHYSICS 106, 013512 (2009)

lSuppression of phase separation in InGaN layers grown on lattice-matched ZnO substrates”, N. Li, … Z.C. Feng, et al., Journal of Crystal Growth 311 (2009) 4628–4631.

lRapid thermal annealing effects on the structural and optical properties of ZnO films deposited on Si substrates, Y.C. Lee, … Z.C. Feng, et al., J. Luminescence 129 (2009) 148–152.

lMetalorganic chemical vapour deposition of GaN layers on ZnO substrates using α-Al2O3 as a transition layer, S.J. Wang, … Z.C. Feng, et al., J. Phys. D: Appl. Phys. 42 (2009) 245302 (5pp).

lTemperature-Dependent Excitonic Luminescence in ZnO Thin Film Grown by Metal Organic Chemical Vapor Deposition, Y.C. Lee, … Z.C. Feng, et al., Japanese Journal of Applied Physics 48 (2009) 112302.


Enhancing InGaN-based solar cell efficiency through localized surface plasmon interaction by embedding Ag nanoparticles

Professor Yean-Woei Kiang's Laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

We have demonstrated the simulation results of using the interaction of metal NP induced LSP with an InGaN absorbing layer for enhancing the efficiency of an InGaN/GaN-based solar cell. The absorption increase is implemented by embedding Ag NPs in InGaN for inducing LSP. The effective LSP absorption and NP scattering lead to the enhancement of InGaN absorption. The embedment of metal NPs in semiconductor may affect carrier transport. However, we show that such an effect is small unless the surface recombination velocity at the interface between a metal NP and surrounding InGaN is extremely high. Fig. 1 shows the photon absorption rates (the left ordinate) of the InGaN layer and Ag NP and the short-circuit current densities (the right ordinate) of the solar cell as functions of wavelength for the cases with and without Ag NP when the surface recombination velocity, S, is 10 m/s. For comparison, the incident photon flux under the condition of AM1.5G (the curve labeled by “incidence”) is also plotted in Fig. 1. The significant absorption enhancement on the long-wavelength side by embedding the Ag NP can be clearly seen. In Fig. 1, the curve labeled by “metal dissipation” represents the part of photons absorbed by the Ag NP and turned into dissipation heat. The embedment of the Ag NP results in an increase of integrated photon absorption rate by 28.44 %. The two curves of short-circuit current density (per unit spectral width), i.e., JSC (without NP) and JSC (with NP), which essentially follow the oscillatory behaviors of the two curves for InGaN absorption show the enhancement of photo-generated current. With the embedded Ag NP, the integrated JSC is increased by 27.87 %. Fig. 2(a) shows the distribution of electrical field magnitude at 580 nm in the region around the Ag NP by assuming that the magnitude of the incident field is unity. Here, one can see that strong near field is generated around the Ag NP. Also, certain backscattered field is distributed in the n-GaN layer. Fig. 2(b) shows the stream line distribution of static electric field inside the solar cell. Here, one can see the distortion of static electric field by the embedded Ag NP. Fig. 3 shows the integrated current densities (the left ordinate) and the output power densities (the right ordinate) as functions of applied voltage for the cases with NP and without NP corresponding to the results shown in Fig. 1. The first and second numbers in the parentheses represent the voltage for the maximum output power (in V) and the maximum output power density (in mW/cm2). Here, one can see that the open-circuit voltage of ~1.51 V is not affected by the embedment of the Ag NP. The integrated current density, J, is significantly increased from 8.08 to 10.17 mA/cm2 by embedding the Ag NP. The maximum output powers of both cases are achieved at 1.4 V in applied voltage. The maximum output power is increased from 10.59 to 13.53 mW/cm2 (roughly from 10.59 to 13.53 % in efficiency), corresponding to an increase of 27.76 %.

Fig. 1.  Fig. 2.  Fig. 3. 


Flexible ZnO transparent thin film transistor using solution-based process

Professor Ching-Fuh Lin

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

Currently, transparent electronics based on a flexible substrate are one of the most crucial technologies for the next generation of optoelectronic devices, such as displays, home electronic appliances, and photovoltaics. Hence, transparent thin-film transistors (TFTs) on flexible substrates are key devices for realizing these transparent electronic products. Although organic TFT and its manufacturing process are suitable for flexible substrates, their low mobility and extreme sensitivities to oxygen and moisture overshadow their device performance attributes. TFTs that use ZnO have the advantages of high charge mobility, excellent environmental stability, and high transparency, in comparison to TFTs that are based on organic semiconductors.

In this study, we have fabricated a highly transparent ZnO-TFT by a hydrothermal method using a polymeric PMMA film as the gate insulating film. An O2-plasma treatment was applied to the PMMA dielectric to enhance compatibility between the ZnO active layer and the PMMA dielectric at the interface. In order to investigate the effects of grain boundaries on the flexible ZnO-TFTs, we studied ZnO-TFTs that had three kinds of ZnO channel morphologies, which grew for 50 min at ZnO solution concentrations of 110, 80, and 50 mM, respectively. The field effect mobility (μ) and threshold voltage (VT) values were calculated from the slope of a plot of the square root of the drain-source current (IDS) versus the gate voltage (VG) in the regime of the drain-source voltage (VDS)=20 V, using the equation IDS= (WCi/2L)μ(VG-VT)2. The saturation mobility was highest at 7.53 cm2/Vs for the 110 mM preparation and lowest at 0.097 cm2/Vs for the 50 mM preparation, with 0.69 cm2/Vs for the 80 mM preparation.

Fig. 1. (a) Schematic illustration of the ZnO-TFT device structure. (b) The chemical structure of the PMMA. (c) Photograph of the ZnO-TFT.

Fig. 2. Transistor output curves for ZnO-TFTs, fabricated with the ZnO solution concentration at (a) 110 mM, (c) 80 mM, and (e) 50 mM. Corresponding transistor transfer characteristics are (b) 110 mM, (d) 80 mM, and (f) 50 mM. The inset shows the corresponding FESEM images. The scale bar is 500 nm.


Enhancements of direct band radiative recombination from Ge

Professor Chee-Wee Liu's group

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

Due to the high carrier mobility, strong photon absorption, and possible integration with Si, the indirect band gap Ge is used for both scientific interest and optoelectronic applications. The methods to enhance the direct bandgap transition include the high pumping level, the elevated temperature, the high concentration of n type doping, and the biaxial tensile strain. Significant enhancement of direct transition fraction in both photoluminescence (PL) and electroluminescence (EL) is demonstrated. The physical recombination models are developed for both direct and indirect transitions.

Fig. 1 and Fig. 2 show the PL infrared emission from the n+p Ge structure. The electrons in Γ valley and L valley recombine with holes in the valence band and emit infrared at the 795meV peak (direct bandgap transition) and the 695meV peak (indirect bandgap transition), respectively. By increasing pumping power and temperature, the electron fraction in Γ valley increases and the electron Fermi level moves upwards. The indirect and direct bandgap transitions are also observed in EL, measured (Fig. 3). The spectra of indirect and direct bandgap emission can be fitted by using the electron-hole-plasma (EHP) recombination model and the direct bandgap recombination model, respectively. To have a reasonable fit, the band tail of absorption edge in the direct bandgap recombination model is taken into consideration. The intensity fraction of direct bandgap transition increases with increasing excitation level and reaches 39% and 22% at EL excitation of 600mA and PL excitation of 360mW, respectively. The intensity fractions of direct bandgap transition are enhanced by 4 times and 1.1 times for EL excitation from 100mA to 600mA and PL excitation from 120mW to 360mW, respectively. By applying biaxial tensile strain, the tensile strain shrinks the direct bandgap more than the indirect bandgap. The direct bandgap transition becomes more and more significant (1.8X) by increasing the biaxial tensile strain up to 0.37% (Fig. 4).

The high PL/EL pumping level, n-type doping concentration, and high temperature can enhance the direct bandgap transition. The strain can be an extra factor to enhance the direct transition of Ge up to ~ 1.8 times with 0.37% strain. The progressive improvement of the radiative recombination makes it possible to have Ge-based light emitting devices for practical applications.

Fig. 1 The PL spectra of the Ge (100) n+p diode at room temperature. Fig. 2 Temperature dependent PL at the temperature of 310 ~ 415K.

Fig. 3 The EL spectra of the Ge (100) n+p diode at current (a) lower than 400mA, and (b) higher than 400mA.

Fig. 4 PL spectra of n-type bulk Ge (100) under biaxial tensile strain.


Efficient and compact design of up-converted 435nm blue lasers

Professor Lung-Han Peng's group

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

We reported a design of up-conversion 435nm blue lasers by simultaneously fulfilling the nonlinear processes of 1st-order quasi-phase-matching optical parametric oscillation (QPM-OPO) with 2nd-order second harmonic generation (QPM-SHG) in a periodically poled lithium tantalate (PPLT) at a single-period of 7.9μm and 75% domain duty cycle (Fig.1).  An optimum PPLT device of 15 mm length, albeit facet uncoated, exhibits a low threshold of 150mW and a differential slope efficiency of 22.6%, rendering a 56mW blue generation when pumped by a pulsed 532nm green laser with an average power rating of 400mW (Fig.2). We noted that the transmitted green power approached saturated values of 108 and 200 mW at PPLT crystal lengths of 20 and 10 mm, respectively.  This phenomenon resembles the optical power limiting effect earlier reported on the doubly- and singly-resonant oscillators (DRO/SRO). In a steady state operation, it signifies a pinning process of the oscillator gain at a threshold value and suggests that excess energy from the pump beam would be transferred to the phase-matched nonlinear optical process.

Fig.1: Calculated spectral and temperature tuning curves for the QPM-OPO and -SHG processes in a PPLT device of 7.9 μm period.

Fig.2: (a) Measurement of the up-conversion blue efficiency of a 15 mm-long PPLT Sample B of 7.9 μm period. (Red dashed line represents linear fitting to the blue laser power.) Inset: crystal length dependence of the differential slope efficiency for the blue lasers measured at 400mW green pump. (b) Calculated output power of the up-conversion blue lasers at an optical loss Γ of 99% and crystal length of 10, 15, and 20mm. Inset: calculated crystal length dependence of the differential slope efficiency for the blue lasers at a green pump power of 400mW.


Glass-Clad Crystal Fibers Based Ultrahigh Resolution Optical Coherence Tomography

Professor Sheng-Lung Huang's group

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

Optical coherence tomography (OCT) has evolved as a powerful diagnostic modality for non-invasive medical applications. With the great success of OCT in recent years, high resolution and high image fidelity are getting more importance. The axial resolution is inversely proportional to the light bandwidth. So far, several approaches have been proposed to achieve high axial resolution, such as multiplexed superluminescent diode, femtosecond laser, continuum generation from photonic crystal fiber, and xenon illuminator. In general, these solutions either have high cost or exhibit bumpy spectrum. In contrast, spontaneous emission light can generate broadband and near-Gaussian spectrum, but the power level is often very weak. Using waveguide to collect the amplified spontaneous emission (ASE) can improve brightness of the source for OCT system. A double-clad crystal fiber (DCF) growth technique has been developed to guide and amplify the spontaneous emission. Using active medium as the single-crystalline core, the DCF can maintain the high cross section of the crystal environment, and effectively collect the ASE.

By means of the laser-heated pedestal growth (LHPG) method, single crystalline fibers of various active media and diameters were first obtained from 500-μm-diameter source rods with a few diameter-reduction steps to become 30 ~ 100 μm in diameters. They were then gone through a codrawing LHPG process to form DCFs. During the codrawing process, the DCF cores were further reduced to 5 to 20 μm depending on applications. At visible wavelength range, a Ce3+:YAG DCF generating 560-nm center wavelength with a 3-dB bandwidth of 98 nm was fabricated. At near IR wavelength ranges, the active media were Ti3+:sapphire and Cr4+:YAG for a center wavelength of 770 nm and 1380 nm, respectively. For Ce3+:YAG DCF, the broadband emission and short central wavelength of this light source enable the realization of 1.5-μm axial resolution in air or 1.1 μm in bio tissues. The relatively smooth spectrum reduced the side lobe of its point spread function, and therefore, facilitated the generation of a high quality image with less crosstalk between adjacent image pixels.

As a demonstration, an Aplocheilus Lineatus Gold fish was adopted to map out the stroma of its cornea in vivo as shown in Fig. 1. The layers inside the cornea were clearly identified. As time went on, the cornea became thinner and more atrophic because of water dissipation in the dry atmosphere. This OCT system may be useful for the detection of early stage cornea disorders, such as Fuch’s and keratoconus dystrophies. Active broadband DCFs are promising for high resolution and high image fidelity OCT systems. Micron resolution can be achieved with low image pixel cross talk. These CW light sources can enable low-cost OCT systems with cellular resolution for various in-vivo bio-medical applications that fulfill the safety requirement of 20 mJ/cm2 set by US Food and Drug Administration.

Fig. 1. Goldfish cornea images of (a) full range and (b) its partial magnification at t=0.5 h. (b) is the magnified figure from the dot rectangular region of (a), where the length of scale bar in (a) is 100 μm. The cross-sectional image at the same tomographic position of fish cornea at t=0, t=0.5 h, t=1 h, and t=1.5 h is (c), (d), (e), and (f), respectively. (g) is the 3D image of oblique viewpoint at t=0. (i) is the en-face image inside layers (2) and (3) of (g), whereas (h) is the cornea surface imaged by traditional microscope. All the scale bars are 20 μm except for (a).


The authors would like to thank the support from the National Taiwan University and Foresight Taiwan Project Office, National Science Council under grant number NSC 98 2627-E-002-001.


Copyright © Graduate Institute of Photonics and Optoelectronics, National Taiwan University