Prof. Chao-Hsin Wu

Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei 10673, Taiwan

Prof. Chao-Hsin Wu

Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei 10673, Taiwan

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Academic Career Length

28Years (1999-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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13 February 2022 in Photonics

Journal Article

Recent Advances in 850 nm VCSELs for High-Speed Interconnects

Vertical-cavity surface-emitting lasers (VCSELs) have made remarkable progress, are being used across a wide range of consumer electronic applications, and have particularly received much attention from the telecom and datacom industries. However, several constraints are thus currently being tackled to improve the device characteristics and modulation formats to meet the various demanding requirements of the future 800 GbE and 1.6 TbE Ethernet standards. This manuscript discusses the device characteristics and the key considerations in the device designs and optimizations. Finally, we elucidate the latest developments and vital features of modern 850 nm VCSELs for high-speed interconnects.

7 April 2020 in Optics Letters

Journal Article

High-speed integrated micro-LED array for visible light communication

Hao-Yu Lan

I-Chen Tseng

Yung-Hsiang Lin

Gong-Ru Lin

Ding-Wei Huang

Chao-Hsin Wu

In this Letter, we report high-speed integrated 14 µm in diameter micro-light-emitting diode (μLED) arrays with the parallel configuration, including

2 \times 2

2 \times 3

2 \times 4

, and

2 \times 5

arrays. The small junction area of μLED (

\sim 191 µ m^{2}

) in each element facilitates the operation of higher injection current density up to

13 {k A / c m}^{2}

, leading to the highest modulation bandwidth of 615 MHz. The optical power of

2 \times 5

array monotonically increases (

\sim 10

times higher) as the number of arrays increases (1 to 10), while retaining the fast modulation bandwidth. A clear eye diagram up to 1 Gbps without any equalizer further shows the capability of this high-speed transmitter for VLC. These results mean that tailoring the optical power of μLEDs in a parallel-biased integrated array can further enhance the data transmission rate without degradation of the modulation bandwidth.

1 January 2018 in Opto-Electronic Advances

Journal Article

850/940-nm VCSEL for optical communication and 3D sensing

Chih-Hsien Cheng

Chih-Chiang Shen

Hsuan-Yun Kao

Dan-Hua Hsieh

Huai-Yung Wang

Gong-Ru Lin

This paper is going to review the state-of-the-art of the high-speed 850/940-nm vertical cavity surface emitting laser (VCSEL), discussing the structural design, mode control and the related data transmission performance. InGaAs/AlGaAs multiple quantum well (MQW) was used to increase the differential gain and photon density in VCSEL. The multiple oxide layers and oxide-confined aperture were well designed in VCSEL to decrease the parasitic capacitance and generate single mode (SM) VCSEL. The maximal modulation bandwidth of 30 GHz was achieved with well-designed VCSEL structure. At the end of the paper, other applications of the near-infrared VCSELs are discussed.

19 March 2018 in IEEE Journal of Quantum Electronics

Journal Article

Oxide-Confined VCSELs for High-Speed Optical Interconnects

Milton Feng

Chao-Hsin Wu

Nick Holonyak

The electrically pumped VCSEL was first demonstrated with metal cavities by Iga (1979); however, the device threshold current was too high. Distributed Bragg reflector (DBR) cavities proposed by Scifres and Burnham (1975) were adopted to improve the optical cavity loss. Yet, it was not practical use until the discovery of the native oxide of AlGaAs and the insertion of quantum-wells to provide simultaneous current and optical confinement in semiconductor laser by Holonyak and Dallesasse (1990). Late, the first “low threshold” Oxide-Confined VCSEL was realized by Deppe (1994) and opened the door of commercial application for a Gigabit energy-efficient optical links. Today, the Oxide-Confined VCSELs have advanced error-free data transmission (BER ≤ 10-12) to 57 Gb/s at 25 °C and 50 Gb/s at 85 °C, and also demonstrated the pre-leveled 16-QAM OFDM data at 104 Gbit/s under back-to-back transmission with the received EVM, SNR, and BER of 17.3%, 15.2 dB, and 3.8×10-3, respectively.

13 October 2020 in Journal of Lightwave Technology

Journal Article

Single-Mode VCSEL Transmission for Short Reach Communications

Single-mode VCSEL technology has advanced significantly in the past few years. The advantages of single-mode VCSELs lie primarily on the narrower linewidth, lower numerical aperture and smaller spot size compared to multimode VCSELs. They are suitable for transmitting over both multimode fibers and few-mode fibers. For multimode fiber systems, the narrow linewidth can reduce the chromatic dispersion penalty and increase the system reach. A single-mode VCSEL also allows the coupling into graded-index single-mode fiber, which is few-mode around 850 nm with high bandwidth, for few-mode transmission. We review recent progress and present new experimental results and modeling analyses of single-mode VCSEL transmission over both types of fibers. The experiments and analyses shed new light on how single-mode VCSELs can be used with multimode fibers and graded-index single-mode fibers and relative merits between 850 nm single-mode VCSELs versus 980 nm and 1060 nm single-mode VCSELs to address the needs of various applications.

15 June 2009 in Applied Physics Letters

Journal Article

4.3 GHz optical bandwidth light emitting transistor

G. Walter

Chao-Hsin Wu

H. W. Then

M. Feng

N. Holonyak

We demonstrate a quantum-well base heterojunction bipolar light emitting transistor (HBLET) operating in the common collector configuration with a 3 dB optical response bandwidth

f_{3 dB}

of 4.3 GHz. The HBLET has a current gain,

β

(= | Δ I_{C} / Δ I_{B} |)

as high as 30, and can be operated as a three-port device to provide simultaneously an optical and electrical output with gain. The

f_{3 dB}

of 4.3 GHz corresponds to an effective carrier recombination lifetime of 37 ps, and shows that “fast” spontaneous recombination can be harnessed for high-speed modulation.

About Me

Dr. Chao-Hsin (Wayne) Wu received B.S. and M.S. degrees in electrical engineering from National Taiwan University, Taipei, Taiwan, in 2002 and 2004, respectively, and a Ph.D. in electrical and computer engineering from the University of Illinois at Urbana–Champaign, USA, in 2010. He is currently an Associate Professor with the Department of Electrical Engineering, Graduate Institute of Photonics and Optoelectronics, and also with the Graduate Institute of Electronics Engineering, National Taiwan University, Taipei, Taiwan. His research mainly focuses on three-terminal light-emitting transistors and transistor lasers. He has demonstrated the world record for an optical spontaneous modulation bandwidth of 12 GHz (corresponding to a recombination lifetime of 12.3 ps). He has authored or coauthored more than 60 journal articles and 80 conference articles. His current research at National Taiwan University includes high-speed VCSELs for optical interconnects, GaN-on-Si power, and RF electronics, 2-D material field-effect transistors, Si photonics, transistor lasers for optical logic gates, and GaN LED for visible light communications. Dr. Wu is also a member of SPIE and OSA. He was a recipient of the Nick and Katherine Holonyak, Jr. Award from UIUC in 2010. He received the Academic Contribution Award from EECS College, National Taiwan University, in 2017. He was an Irving T. Ho Outstanding Young Scholar.

Prof. Chao-Hsin Wu

Prof. Chao-Hsin Wu

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