Ultra high-speed IC capable of wireless transmission of 100 gigabits per second in a 300 GHz band

Technology expected to pioneer utilization of unexplored terahertz wave frequencies

https://www.webwire.com/ViewPressRel.asp?aId=225148

Nippon Telegraph and Telephone Corporation (NTT; head office: Chiyoda-ku, Tokyo; president & CEO: Hiroo Unoura), and Tokyo Institute of Technology (Tokyo Tech; head office: Meguro-ku, Tokyo; president: Kazuya Masu), have jointly developed an ultra high-speed IC for wireless front-end that operates on a terahertz frequency band, and in the 300 GHz band they have succeeded in developing the world’s fastest 100 gigabit per second wireless transmission data rate.
It is expected that unused terahertz waves can be applied to high-speed wireless transmission since a wide frequency band can be secured. In this research, we implemented a mixer circuit that applied a unique proprietary high isolation design technology with an Indium phosphide high electron mobility transistor (InP-HEMT). This enlarged the transmission bandwidth, which is a problem in the conventional 300 GHz band wireless front end. It also improved the signal-to-noise ratio (SNR). In addition, using this we realized a 300 GHz band wireless front-end module, and we achieved wireless transmission of 100 Gbps (gigabits per second).
In this research, we realized 100 Gbps wireless transmission with one wave (one carrier), so in the future, we can extend to multiple carriers by making use of the wide frequency band of 300 GHz band, and use spatial multiplexing technology such as MIMO and OAM. It is expected to be an ultra high-speed IC technology that enables high-capacity wireless transmission of 400 gigabits per second. This is about 400 times the current LTE and Wi-Fi, and 40 times 5G, the next-generation mobile communication technology. It is also expected to be a technology that opens up utilization of the unused terahertz wave frequency band in the communications field and non-communication fields.
The details of this technology will be presented at the 2018 IEEE MTT-S International Microwave Symposium which will be held in Philadelphia in the United States from June 10 to 15.

1.Research background

With the spread of broadband networks, high-capacity wireless transmission technology of 100 gigabits per second (Gbps) has attracted worldwide attention (Fig. 1.) There are three ways of further increasing the capacity of wireless transmission-- expanding the transmission bandwidth, increasing the modulation multi-level number, and increasing the spatial multiplexing number. To realize future large capacity wireless transmission technology from a level of 400 Gbps to that of one terabit per second (Tbps), it is necessary in one wave (one carrier) to expand both the transmission bandwidth and the modulation multi-level number simultaneously and to increase the number of spatial multiplexing transmissions by superimposing them multiple times.
In the carrier frequencies from 28 GHz to 110 GHz that are currently being researched and developed, the transmission bandwidth is limited. So, researchers are studying the use of frequencies which make it easier to expand the transmission band area, from the 300 GHz band to the terahertz wave*2 frequency band. The 300 GHz band has a frequency that is 10 or more times higher than the 28 GHz band which is being studied for 5G, which will be the next generation mobile communication technology. With the 300 GHz band, it will be easier to secure a wide transmission bandwidth. On the other hand, with a high frequency, leakage of unnecessary signals between the ports inside the IC and mounting tends to occur, and so far, it has been impossible to obtain a sufficiently high signal-to-noise ratio (SNR)*3. For this reason, even if a 300 GHz band is used, it is impossible to obtain both a wide transmission bandwidth and a high modulation multi-level value at the same time, and so wireless transmission up to now has remained at the rate of several-tens Gbps.*4

2.Research results

In this research, we devised our own high isolation design technology and applied this technology to a mixer circuit (Fig. 2), which is a key component responsible for frequency conversion in the 300 GHz band wireless front end. We also developed an IC with an indium phosphide high electron mobility transistor (InP-HEMT)*5. By applying high isolation design technology, we succeeded in suppressing leakage of unnecessary signals inside each IC and between ports in the IC. We also succeeded in improving signal noise reduction and expanding band width, which had been issues confronting the use of conventional 300 GHz band wireless front end technology up to now. With these technologies, we also realized a 300 GHz band wireless front-end module (Fig. 3), and we confirmed reception of a good 16QAM signal in back-to-back transmission (Fig. 4). In a 300 GHz band, we also confirmed transmission at a speed of 100 Gbps, the first time in the world this speed has been attained (Fig. 5).

3.Future developments

In this research, since we realized 100 Gbps transmission with one wave (one carrier), in the future we will expand our research to use multiple carriers or spatial multiplexing technology such as MIMO and OAM*6 together with this results. With this combination, we expect to attain an ultra high-speed IC technology that enables high-capacity wireless transmission of over 400 Gbps. In addition, we expect that our approach can be applied in various fields such as imaging and sensing in which terahertz waves are expected to be used. Through collaboration with partners, NTT aims to create new services and new industries using ultra high-speed ICs, and it aims to further develop ultra high-speed IC technology.*7

4.Technical features

We devised a unique high isolation design technology and used this technology to realize a mixer circuit. A mixer circuit has three ports: a Local Oscillation Frequency Port (LO), a Radio Frequency Port (RF), and an Intermediate Frequency Port (IF). When operating with the very high frequency signals of terahertz waves, unnecessary signals leak easily between ports as the result of a small parasitic capacitance on the mixer circuit and external mounting.
By adding a quarter-wave line and series capacitance, we were able to create a unique design that dramatically improved isolation between ports. The high isolation characteristics realized in this way can suppress unnecessary signals, contributing not only to improvement of SNR, but also to prevention of deterioration of frequency characteristics when the mixer IC is mounted on a module. As a result, we achieved both broadband characteristics and high SNR characteristics for a wireless front-end module.
This work was supported in part by the research and development program on multi-tens gigabit wireless communication technology at subterahertz frequencies of Ministry of Internal Affairs and Communications, Japan.

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Notes and glossary

• *1Speeding up adoption of 5G! Wireless transmission speeds of 120 Gbps achieved February 13, 2018 Tokyo Tech News
  https://www.titech.ac.jp/english/news/2018/040455.html 
• *2Terahertz wave: Just as we use the phrase ‘kilo’ to mean 10³ , so we use the term ‘giga’ to mean 10⁹ and the term ‘tera’ to mean 10¹² . “Hertz (Hz)” is a unit of a physical quantity called frequency. It indicates how many times alternating electric signals and electromagnetic waves change polarity (plus and minus) per second. That is, one terahertz (1 THz = 1,000 GHz) is the frequency of the electromagnetic wave changing the polarity by 1 × 10¹² times per second. In general, a terahertz wave often indicates an electromagnetic wave of 0.3 THz to 3 THz.
• *3Signal-to-noise ratio (SNR) characteristics: Represents the ratio of the power of the signal to the noise
• *4“The world’s-first compact transceiver for terahertz wireless communication using the 300-GHz band—with transmission rate of several-dozen gigabits per second—was developed and experimentally demonstrated high-speed data transmission.” May 26, 2016 NTT press release
  http://www.ntt.co.jp/news2016/1605e/160526a.html
• *5InP-HEMT: High Electron Mobility Transistor (HEMT) using an Indium Phosphide (InP) compound semiconductor
• *6“World first: NTT successfully demonstrates 100 Gbps wireless transmission using the new principle of OAM multiplexing NTT” May 15, 2018 NTT press release
  http://www.ntt.co.jp/news2018/1805e/180515a.html
• *7Opening of “Ultra-high-speed IC Technology Using an Advanced Compound Semiconductor Process,” February 7, 2017 NTT press release.
  http://www.ntt.co.jp/news2017/1702e/170207a.html

IEEE to explore 100 Gbps transmission over extremely high frequency wireless

Potential new applications for possible IEEE 802.15.3 amendment could include wireless data centers, wireless intra-device communication and wireless backhauling

http://www.ciol.com/ciol/news/198239/ieee-explore-100-gbps-transmission-extremely-frequency-wireless

News | by CIOL Bureau

PISCATAWAY, USA: IEEE, the world's largest professional organization advancing technology for humanity, today announced the formation of a new study group (SG100G) within IEEE 802.15 to develop a project proposal for an amendment to IEEE 802.15.3 "Standard for Information technology-Local and metropolitan area networks-Specific requirements-Part 15.3: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for High Rate Wireless Personal Area Networks (WPAN)."

The proposed amendment is targeting data rates of up to 100 Gigabits per second (Gbps) over beam-switchable wireless point-to-point links. Potential new applications of interest include wireless data centers, wireless intra-device communication and wireless fronthauling/backhauling.

IEEE 802.15.3 is a standard for low-complexity, low-cost, low-power-consumption and high-data-rate wireless connectivity among multimedia devices supporting high levels of Quality of Service (QoS). With the completion of a physical layer (PHY) amendment in 2009, IEEE 802.15.3c^TM "Standard for Information technology-Local and metropolitan area networks-Specific requirements-Part 15.3: Amendment 2: Millimeter-wave-based Alternative Physical Layer Extension" was the first wireless IEEE 802 standard supporting data rates in excess of 2 Gbps at 60 GHz. This new proposed PHY layer amendment is intended to extend IEEE 802.15.3 to data rates up to 100 Gbps.

According to Bob Heile, chair of the IEEE 802.15 Wireless Personal Area Network (WPAN) Working Group, "After many years of hard work in the IEEE 802.15 Working Group, discussing the challenges and feasibility of using the Terahertz (THz) domain, we are very excited that the time is now right to create a project capitalizing on this newly available unlicensed spectrum. A standard in this domain could have significant commercial value and help set the stage for additional uses and applications."

Added Thomas Kürner, chair of the new IEEE 802.15 100G Study Group and professor at Technische Universität Braunschweig in Germany: "The target is to standardize a system that offers high data transfer rates of many 10s of Gbps up to 100 Gbps. We see this supporting transmission distances ranging from the very short, a few centimeters or less, to the relatively long and over distances of several hundred meters with the objective of connecting the wireless and wireline industry."

The new study group is the result of ongoing work in an IEEE 802.15 interest group that's focused on THz communications and related network applications operating in the THz frequency bands (between 275 to 3,000 GHz). The THz interest group was established in 2008, with more than 30 companies and institutions participating from all over the world. Applications under investigation have been component-to-component, board-to-board, machine-to-machine, human-to-machine and human-to-human (indoor and outdoor) wireless communications.

"The formation of the IEEE 802.15 100G Study Group is an excellent example of the IEEE 802 community responding to market forces early on in the practical development of emerging technologies," said Paul Nikolich, chair of IEEE 802 LAN/MAN Standards Committee. "From helping to shape regulatory frameworks that will enable innovation to providing a complete solution at 100 Gbps that crosses between wired and wireless boundaries, the IEEE 802 suite of standards provides the networked world with standardized solutions to address almost every need."

For organizations that have an interest in wireless technology approaching 100 Gbps, including THz communication, optical wireless communications (OWC) and others, visit the IEEE 802.15 Working Group web site at http://www.ieee802.org/15/.

The IEEE 802.15 100G Study Group meets during the regularly scheduled IEEE 802.15 working group meetings. The schedule can be found at http://www.ieee802.org/15/pub/Meeting_Plan.html.

German researchers claim 100 Gbps wireless transmission record

By Richard Chirgwin, 15th October 2013 
http://www.theregister.co.uk/2013/10/15/german_researchers_claim_100_gbps_wireless_transmission_record/


German researchers are claiming a world record, using a 237.5 GHz carrier and photonic mixing to achieve a 100 Gbps wireless link.
Don't throw away that WiFi kit just yet, however: while the reach, at 20 metres, is good enough to cover most household applications, the setup is a little bit exotic at this point in the system's development.

If commercialised, however, the researchers hope their 100 Gbps-capable link could act as a fibre extender in FTTN-style deployments, telling Phys.org “this technology represents an inexpensive and flexible alternative to optical fiber networks, whose extension can often not be justified from an economic point of view”.
The signals were generated using a photonic mixer from NTT Electronics, with custom-made receiver silicon built by the Fraunhofer Institute of Applied Solid State Physics.
Using photonics to generate the carrier wave is important, since it's difficult to work with electrical signals at such high frequencies. The photonic mixer took two light signals generated by lasers, with the difference between them resulting in the modulated 237.5 GHz electrical signal.
That was then fed to a conventional antenna for transmission to the receiver.
As the researchers describe the experiment in their Nature Photonics abstract: “a narrow-band terahertz carrier is photonically generated by mixing comb lines of a mode-locked laser in a uni-travelling-carrier photodiode. The uni-travelling-carrier photodiode output is then radiated over a beam-focusing antenna. The signal is received by a millimetre-wave monolithic integrated circuit comprising novel terahertz mixers and amplifiers.”
Professor Jürg Leuthold explained that the linearity and wide bandwidth of the photonic mixer makes it suitable for “advanced modulation formats with multiple amplitude and phase states”, meaning that it also provides good spectral efficiency.

KIT's demonstration setup, showing the receiver connected

to an oscilloscope. Image: KIT

The receiver used HEMT (high electron mobility transistor) technology able to operate between 200 and 280 GHz. Funded by Germany's Federal Ministry of Education and Research, the Millilink project could reach 1 Tbps using multiple transmission paths, according to experiment designer Professor Thomas Zwick from the Karlsruhe Institute of Technology. ®

Design of Terahertz Wireless Communications Simulator

http://asiafi.net/meeting/2012/summerschool/submissions/AsiaFI2012_Poster/6_Design%20of%20Terahertz%20Wireless%20Communications%20Simulator%20for%20Future%20Wireless%20Internet.pdf
Seongman Min, Wonjung Kim, Taewon Song, and Sangheon Pack

School of Electrical Engineering

Korea University, Korea

{pobi1020, abcxxxx, crazytb, shpack}@korea.ac.kr

ABSTRACT

Terahertz (THz) waves can offer high transmission rates due to

the ultra-broad bandwidth. So THz communications are recently

received attention. However, due to the absence of a proper

simulator, a diversity of attempts are not performed on THz

communications. In order to alleviate this problem and to

contribute the improvement in the performance of THz

communication, we describe the design of THz simulator in this

paper. Specifically, the design of PHY layer and MAC layer are

handled in detail.

Keywords

terahertz, simulator, PHY layer, MAC layer

1. INTRODUCTION

Future wireless communications systems, which supports

ultrahigh data rates, is expected to apply a variety of field

that need more 10GHz. Conventional WLAN, WPAN, and

UWB systems use the bandwidth between multi-MHz and

multi-GHz. Therefore, these have limited in the

requirement of future wireless communication systems. To

address this limitation, terahertz (THz) technologies have

recently gained momentum in the area of research and

development. As THz region covers 100-10000 GHz range,

THz waves support much more bandwidth than millimeter

waves. Due to its characteristic, THz communication

systems with several tens of Gbps data rates can be applied

to many applications such as wireless extension of highspeed

wired local networks, wireless data center networks,

and high-definition and ultra-high-definition television

(HDTV & UHDTV) [1].

In addition to ultra-high bandwidth, THz waves have

several other characteristics. Firstly, THz waves are

inherently more directional than millimeter waves due to

less free space diffraction of the waves. Consequently, THz

communication systems are typically line-of-sight (LOS)

systems. Secondly, THz waves are severely attenuated

along the propagation path. When the propagation distance

or the carrier frequency becomes double, the attenuation

increases 6dB. Finally, in outdoor condition, THz waves

are significantly influenced by weather condition (i.e., rain,

snow, fog, etc.) because they are mainly absorbed in watervapor

[2]. And the degree of attenuation is different

depending on frequency band, so there are available

bandwidths satisfying a standard point [3]. On the contrary,

in indoor condition, the weather condition does not affect

on THz waves but obstacles (i.e., wall, furniture, human,

etc.) absorb or reflect them [4].

Many research projects on THz are being performed

reflecting these characteristics in the industry and academia.

Most of them evaluate a performance of proposing schemes

by relying on experiments. However, it is hard to perform a

diversity of attempts on THz communications because the

method, relying on experiments, has limitations of time,

space, and cost. If we use the THz communications

simulator, we can predict the performance of proposing

schemes by simulations ahead of experiment and perform a

diversity of attempts at the lowest cost. However, there is

no a simulator on THz region yet. Therefore, in this paper,

we address the development of a methodology for THz

communications simulator.

2. THz COMMUNICATIONS SIMULATOR

In the design of the THz communications simulator, we

consider two things; PHY layer and MAC layer. As figure

1 presents a brief architecture of THz communications

simulator, MAC and PHY layer consist of three modules,

respectively. In our PHY layer, THz waves propagation

model is used to predict the received signal power of each

packet. Using this propagation model, the simulator takes

into account the effects of transmission distance, absorption

and reflection due to obstacles, atmospheric conditions, and

directionality of THz waves. In the MAC layer, the

simulations measure the performance at MAC layer such as

throughput, average delay, and packet loss metrics. Since

there is no standard of wireless communications on THz

region yet, we use the MAC layer of IEEE 802.11ad [

which is a standard of WLAN on 60GHz whose

characteristics are similar to THz waves. In our MAC layer,

as network architecture, we consider personal basic service

set (PBSS) which is newly defined in IEEE 802.11ad to

decrease power consumption of mobile terminals and to

support directional transmission. In PBSS, there is PBSS

central point/AP (PCP/AP) which supports QoS and

manages the frequency spectrum.

2.1 Design of PHYSICAL layer

Depending on channel characteristics, PHY layer model

is divided into three modes; free space, outdoor, and indoor.

The free space mode simulates the ideal condition, which

assumes a LOS path between transmitter and receiver. In

the free space mode, free space attenuation is only

considered as a parameter. Therefore, THz waves are

attenuated by the distance between transmitter and receiver

and the carrier frequency based on Friis’ law.

The outdoor mode simulates the realistic condition

which considers atmospheric condition in addition to free

space attenuation. Therefore, water-vapor and atmospheric

gases are also considered as parameters in the outdoor

mode. In the near field wireless communication (under

10m), since the free space attenuation is much higher than

the attenuation due to atmospheric condition, we can

predict the attenuation only considering free space

attenuation. The indoor mode simulates the realistic

condition in a building or house. In an indoor condition,

THz waves are reflected by obstacles (i.e., wall, ground,

ceiling, furniture, human, etc.). As reflection coefficients

depend on material of obstacles, significant reflected waves,

which are once or twice reflected to any materials having

low reflection coefficients, affect on the fading. Therefore,

the indoor THz communication channel can be modeled by

free space attenuation and power delay profile (PDP) [1],

[4]. The PDP refers to the path length difference between

the direct LOS and once or twice reflected waves. Its

important parameters are mean delay and root mean square

(RMS) delay spread. Since RMS delay spread significantly

affects on inter-symbol interference (ISI) so it has a strong

influence on bit-error-rate (BER) of communication system.

2.2 Design of MAC layer

In our MAC layer, three modules are defined; beacon

module, beamforming module, and scheduling module. The

beacon module is used to manage every associated

terminals and connections. And it defines a structure of

beacon frame and the information included in a beacon

frame. Based on it, PCP/AP broadcasts a beacon frame to

every associated terminals periodically.

The beamforming module is used to control the direction

and width of antenna beam. Since THz waves are highly

directional, the antenna direction of terminal should be

adjusted to target terminal for communicating each other.

Also, the beam width of antenna has to be tuned to decrease

power consumption and to reduce interferences. The

scheduling module is used to manage the sequence of

connections and to allocate the resource. Data transfer time

period in a beacon period consists of contention-based

access periods (CBPs) and service periods (SPs). PCP/AP

allocates CBPs and SPs, and it schedules the sequence of

connections on SPs.

3. CONCLUSIONS

In this paper, we present the design of THz

communications simulator with PHY layer channel models

and MAC layer modules. We are currently working on

reflecting THz channel characteristics in ns-3 simulator and

implementing MAC layer protocol by using ns-3 simulator.

THz simulator would allow for further investigation of the

performance of THz communications systems at the low

cost.

4. ACKNOWLEDGMENTS

This research was supported in part by the KCC, Korea,

under the R&D program supervised by the KCA (KCA-

2011-08913-04002), in part by the MKE, Korea, under the

ITRC support program (NIPA-2012-H0301-12-4004)

supervised by the NIPA.

REFERENCES

[1] J. Federici, , and L. Moeller, “Review of terahertz and

subterahertz wireless communications,” J. Appl. Phys.,

vol. 107, pp. 111101-1-111101-22, 2010.

[2] Recommendation ITU-R P.676-7, “Attenuation by

Atmospheric Gases,” 2007.

[3] Saunders, S. R., “Antennas and Propagation for

Wireless Communication Systems,” Wiley John &

Sons, Inc., June 1999.

[4] R. Piesiewicz, R., Jemai, J., Koch, M., and Kürner, T.,

''THz channel characterization for future wireless

gigabit indoor communication systems,'' SPIE Intl.

Symp. on Integrated Optoelectronic Devices, Terahertz

and Gigahertz Electronics and Photonics IV, Vol.

5727, pp. 166-176, San Jose USA, January 2005.

[5] IEEE P802.11ad/D0.1, Part 11: Wireless LAN

Medium Access Control (MAC) and Physical Layer

(PHY) Specifications – Amendment 6: Enhancements

for Very High Throughput in the 60GHz band, June.

2010

Japanese researchers break the terahertz wireless transmission speed record

http://www.theverge.com/2012/5/16/3023676/terahertz-wireless-record-3gbps-tokyo-university
By Jamie Keene on May 16, 2012

Researchers at Tokyo University have achieved 3Gbps transfers over a 542GHz wireless connection, which falls into the 300GHz-3THz band that's classed as terahertz spectrum. This doubles the previous record held by chipmaker Rohm, set back in November, which managed 1.5Gbps transfers on a 300GHz connection. As with that record, these impressive speeds come at a price — the connection will only work over a range of about 10 meters (just over 30 feet) before it becomes affected by interference. However, this massive short-range bandwidth could be perfect for transmitting media from your AV rack to your TV, or for super-fast Wi-Fi Direct transfers.

The enormous speeds were gained through the use of a resonant tunneling diode, or RTD. This component acts as an oscillator, transmitting electro-magnetic signals at very high frequencies as it vibrates. The RTD was developed especially for the project, and replaces other far more complex systems like quantum cascade lasers.

It's clear that terahertz transfers are the next big thing in wireless communication, with AT&T even holding a conference in December that dubbed the band "the next frontier for radio." The interest in terahertz communication is so widespread not only because of its speed, but because it's unregulated around the world, meaning that the white space is widely available. The project's leader, Dr Safumi Suzuki, says he believes that "everybody will use products related to THz technology within the next decade”.

Record-fast terahertz electro-absorption modulation in quantum dots supports switching rates of at least 3 THz

In an effort led by DTU Fotonik, a group of researchers from 5 different European universities and companies demonstrated a record-fast THz-rate electro-absorption modulator. Such an ultrafast electro-absorption modulator will have a primary application in the wireless data communication systems capable of supporting Terabit-per-second (Tbit/s) data rates.

Application of THz electro-absorption modulator in an ultra-high-speed wireless data communication system. Measurements on an emulated communication channel with the data rate of 88 Gbit/s, and capacity of 0.5 Tbit/s
In an effort lead by DTU Fotonik, a group of researchers from 5 different European universities and companies demonstrated a record-fast THz-rate electro-absorption modulator. Such an ultrafast electro-absorption modulator will have a primary application in the wireless data communication systems capable of supporting Terabit-per-second (Tbit/s) data rates.
Semiconductor quantum dots were used as the switching medium, in which the optical absorption strength was changed by the ultrafast THz signals incident form a free space. Quantum dots (QDs) are the smallest-possible semiconductor elements, only consisting of 10s of thousands of individual atoms, and they can only accomodate up to 2 electron-hole pairs in the lowest energy state. It is this tiny size of the QDs, that allowed the researchers to achieve the unprecedented fast speeds at which the optical absorption in the QDs could be manipulated.
In the experiment, recently described in an article in Applied Physics Letters [1], the researchers managed to encode a THz signal with the spectrum covering the range of 0.2 – 3 THz, onto an optical signal with the wavelength of 1040 nm resonant with the quantum dot absorption. The full 3 THz bandiwdth of a THz signal was encoded onto an optical signal, with individual encoded temporal features being as fast as only 460 fs. It was demonstrated, that such an electro-absorption modulator can be used as a receiver for the THz-range wireless data links supporting the data rates of at least 0.5 Tbit/s.
This project was led by assoc. prof. Dmitry Turchinovich (DTU Fotonik). Matthias Hoffmann (Univ. Hamburg), Boris Monozon (Marine Tech. Univ., St. Petersburg), Daniil Livshits (Innolume GmbH), and Edik Rafailov (Univ. Dundee) participated in the project.
This work is based on DTU Fotonik’s invention (D.Turchinovich, patent pending PCT/DK2010/050200, 05 August 2009), and a DKK 750,000 grant from the Danish Proof of Concept Foundation was recently awarded to Dmitry Turchinovich for further development of this device.
For more information please contact assoc. prof. Dmitry Turchinovich (dmtu@fotonik.dtu.dk)
[1] M.C.Hoffmann, B.S.Monozon, D.Livshits, E.U.Rafailov, and D.Turchinovich, “Terahertz electro-absorption effect enabling femtosecond all-optical switching in semiconductor quantum dots”, Appl. Phys. Lett. 97, 231108 (2010).

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