Page 84 - Kaleidoscope Academic Conference Proceedings 2024

2024 ITU Kaleidoscope Academic Conference

The proposed systems were demonstrated under specific REFERENCES
conditions as the examples to prove the proposed concepts.
However, they are flexible and can be applied to different [1] GSMA Vision 2030: mmWave Spectrum Needs, Full
use cases. Photonic technology has been used for radio signal Report https://www.gsma.com/spectrum/wp-
generation and transmission. However, the use of photonic content/uploads/2022/06/5G-mmWave-Spectrum.pdf
technology for radio signal reception and downconversion
[2] Recommendation ITU-R M.2160-0, “Framework and
has not been widely considered. The simplicity of signal
overall objectives of the future development of IMT
generation, transmission, and reception using photonic
for 2030 and beyond,” (11/2023).
technology can enable high-speed, cost-effective, and
energy-efficient radio communications in the mmW and THz [3] NTT Docomo white paper, “5G Evolution and 6G,”
bands. High-speed optical modulators are key components to Jan. 2023.
facilitate the direct conversion of radio signals to optical
signals. The conversion gain is an important parameter; thus, [4] J. Sang et al., “Coverage Enhancement by Deploying
designing a high-conversion-efficiency modulator is crucial RIS in 5G Commercial Mobile Networks: Field
for achieving high performance. These features can be Trials,” IEEE Wirel. Commun., 31(1), 172 - 180, Feb.
realized using thin-layer structure modulators [14]. 2024.
Furthermore, high-speed optical modulators with operating
frequencies of up to 500 GHz have been demonstrated using [5] D. N.P. Thalakotuna et al., “Overcoming 5G
Millimeter Wave Black Holes,” IEEE Future
an electro-optic-polymer-based plasmonic modulator [15]
Networks Tech Focus, Volume 3, Issue 3, Nov. 2019.
and a thin-film LN modulator [16]. These developments
reveal the possibility of converting high-frequency THz [6] S. Koenig et al., “High-Speed Wireless Bridge at 220
signals to optical signals. Consequently, the proposed
GHz Connecting Two Fiber-Optic Links Each
systems are rendered feasible even in higher-frequency Spanning up to 20 km,” Proc. OFC 2012, OM2B.1.
bands. Regarding the transmission capacity, based on the
achieved results, 100- and 50-Gb/s systems can be expected [7] Y. Horst et al., “Transparent optical-Thz-optical link
for fixed access and mobile coverage extension applications, transmission over 5/115 m at 240/190 Gbit/s enabled
respectively. These systems can be further optimized to by plasmonics,” in Proc. Opt. Fiber Commun. OFC,
increase their performance and capacity. Moreover, the San Francisco, CA, USA, 2021, pp. 1–3.
distance of the wireless links was limited in the experiments
because of space limitations. Due to the short wireless links, [8] T. McKenna et al., “Photonic Downconverting
the transmission power was limited to less than -25 dBm. By Receiver Using Optical Phase Modulation,” Proc.
increasing the optical power to the PDs, radio signals with a IMS2014.
power of -5 dBm can be generated. The distance of the [9] P. T. Dat et al., “Transparent Fiber-Millimeter-Wave-
wireless links can be extended to hundreds of meters using a
Fiber System in 100-GHz Band Using Optical
power amplifier and high-gain antennas.
Modulator and Photonic Down-Conversion,” J. Light.
Technol., 40(5), pp. 1483–1493, Mar. 2022.
The technologies presented in this paper can be important
topics for standardization in the ITU and other organizations. [10] A. Kanno et al., “Multigigabit Relay Link Using
Currently, ITU-R is developing a framework for IMT Millimeter-Wave Radio-Over-Fiber Technologies,”
towards 2030 and beyond, in which IMT-2030 is expected to IEEE Photonics J., 5(6), 7902909, Dec. 2013.
support an enriched immersive experience, enhanced
ubiquitous coverage, and new usage scenarios. Radio [11] P. T. Dat et al., “Terahertz Signal Transparent Relay
communications in the mmW and THz bands are considered and Switching Using Photonic Technology,” J. Light.
key technologies for attaining the targets of IMT-2030. A Technol. 42(3), pp. 1173-1182, Feb. 2024.
report on the technical feasibility of IMT in bands above 100
[12] H. Mahmoud et al., “Error Vector Magnitude to SNR
GHz is being studied by the ITU-R. The presented
technologies in this paper can be technical inputs for Conversion for Nondata-Aided Receivers,” IEEE
Trans. Wirel. Commun., 8(5), May 2009.
consideration, and the achieved results can provide valuable
evidence for the feasibility study of radio communications
[13] 3GPP TR 38.834.
above 100 GHz. In addition, Study Group 15 of ITU-T is
studying key optical transport systems for home and access [14] Y. Yamaguchi et al., “Advanced Optical Modulators
networks, including RoF systems. Consequently, the for Sub-THz-to-Optical Signal Conversion,” IEEE J.
presented technologies can be topics for further study as Sel. Top. Quantum Electron., 29(5), Sept.-Oct. 2023.
potential transport solutions and use cases for future fixed
and mobile access networks. [15] M. Burla et al., “500 GHz plasmonic Mach-Zehnder
modulator enabling sub-THz microwave photonics,”
APL Photon., vol. 4, no. 5, 056106, May 2019.
ACKNOWLEGEMENT
[16] A. J. Mercante et al., “Thin film lithium niobate
This work was supported in part by JSPS KAKENHI under
electro-optic modulator with terahertz operating
Grant 22K04116 and by JST SICORP Grant Number
JPMJSC22E1. bandwidth,” Opt. Express, 26(11), 14819, May 2018.

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