Since 1980’s, optical fibers have revolutionized the way we communicates, allowing us to transmit voice, data, and video signals at the speed of light, along a thin glass wire. We got so well acquainted in communicating, that at the end of this year, the global Internet traffic will reach a staggering multi Zettabytes increase. To support this tremendous growth, optical fiber communication systems are required to dramatically escalate their capacity, reaching Petabit/s transmission speed. Since the fiber capacity is not as limitless as it had been thought in the past, a coming capacity crunch is worldwide foreseen. Therefore, researchers and scientists are now struggling to fully exploit the overall available optical bandwidth in the most effective way, time or frequency multiplexing independent channels. In fiber optics, time division multiplexing (TDM) requires synchronized transmitter and receivers, and the system performances are is mainly limited by the speed of the electronic devices in the terminal equipment, that is less than 100 Gigabit/s. On the other hand, using the frequency-division multiplexing (FDM) approach, the total bandwidth is divided in a set of subbands, that can be separately optically or electronically multiplexed. There are pros and cons in both approaches, mainly related to the fiber impairments and the availability of commercial devices, but in both cases Terabit/s transmission speed has been demonstrated over a single wavelength.

Within the Japanese STARBOARD project, has demonstrated that the use of the time and frequency domains for optical multiplexing is not as rigidly fixed as it may be thought. Recent experimental results on a field-trial fiber installation showed that it is possible to switch from time to frequency multiplexing and viceversa, allowing to the combined used of both approaches and fully exploiting the physical resources. This revolutionary technique introduces ultimate flexibility in light multiplexing, selecting the best approach depending on system requirements or transmission impairments.

### Publications list:

- G. Cincotti, “All-optical and fully-passive Nyquist OTDM transmission and OFDM demultiplexing,”Keynote speech 9th international workshop on Optical Signal Processing and Optical Switching (IWOO), Osaka 2014.
- G. Cincotti, S. Shimizu, T. Murakawa, T. Kodama, K. Hattori, M. Okuno, S. Mino, A. Himeno, T. Nagashima, M. Hasegawa, N. Wada, H. Uenohara, T. Konishi, “OFDM to OTDM conversion by fractional Fourier transform”
invited paper International Topical Meeting on Microwave Photonics/9th Asia Pacific Microwave Photonics (MWP/APMP), Sapporo, Japan 2014.
- T. Murakawa, T. Nagashima, M. Hasegawa, S. Shimizu, G. Cincotti, K. Hattori, M. Okuno, S. Mino, A. Himeno, N. Wada, H. Uenohara, T. Konishi, “Emulation technique for AWG-based optical fractional OFDM device
development by WSS,” 9th International workshop on Optical Signal Processing and Optical Switching (IWOO), Osaka 2014.
- Cincotti, S. Shimizu, T. Murakawa, T. Kodama, K. Hattori, M. Okuno, S. Mino, A. Himeno, T. Nagashima, M. Hasegawa, N. Wada, H. Uenohara, T. Konishi, “OFDM to OTDM conversion by optical fractional Fourier
transform,” invited paper Photonics in Switching San Diego California 2014.
- T. Murakawa, G. Cincotti, S. Shimizu, T. Nagashima, M. Hasegawa, K. Hattori, M. Okuno, S. Mino, A. Himeno, N. Wada, H. Uenohara, T. Konishi, “Fractional OFDM transmitter and receiver for time/frequency multiplexing
in gridless, elastic networks,” Optical Fiber Communication Conference (OFC), Los Angeles, California 2015.
- T. Konishi, T. Murakawa, T. Nagashima, S. Shimizu, M. Hasegawa, K. Hattori, M. Okuno, S. Mino, A. Himeno, N. Wada, H. Uenohara, G. Cincotti, “Fractional-OFDM transmission for time/frequency multiplexing in elastic
networks,” invited paper Asia Communications and Photonics (ACP), Honk Kong 2015.
- G. Cincotti, S. Shimizu, T. Murakawa, T. Kodama, K. Hattori, M. Okuno, S. Mino, A. Himeno, T. Nagashima, M.Hasegawa, N. Wada, H. Uenohara, T. Konishi, “Flexible power-efficient Nyquist-OTDM transmitter, using a
WSS and time-lens effect,” Optical Fiber Communication Conference (OFC), Los Angeles, California 2015.
- G. Cincotti, T. Konishi. “Time frequency optical multiplexing, or in between?” FIAT-LUX conference, Rome 2015.
- T. Nagashima, G. Cincotti, T. Murakawa, S. Shimizu, M. Hasegawa, K. Hattori, M. Okuno, S. Mino, A. Himeno, N. Wada, H. Uenohara, T. Konishi, “Insertion of cyclic prefix for all-optical fractional OFDM,” Photonics in
Switching (PS), Florence, Italy 2015.
- T. Nagashima, G. Cincotti, T. Murakawa, S. Shimizu, M. Hasegawa, K. Hattori, M. Okuno, S. Mino, A. Himeno, N. Wada, H. Uenohara, T. Konishi, “PAPR management of all-optical OFDM signal using fractional Fourier
transform for fibre nonlinearity mitigation,” 41th European Conference on Optical Communication (ECOC), Valencia, Spain 2015.
- . Konishi, T. Murakawa, T. Nagashima, M. Hasegawa, S. Shimizu, K. Hattori, M. Okuno, S. Mino, A. Himeno, H. Uenohara, N. Wada, G. Cincotti, “Flexible OFDM-based access systems with intrinsic function of chromatic
dispersion compensation,” invited paper for the Topical Issue of Optical Fiber Technology on Next Generation Optical Access Networks 26, 94-99 (2015).
- T. Nagashima, G. Cincotti,T. Murakawa, S. Shimizu, M. Hasegawa, K. Hattori, M. Okuno, S. Mino, A. Himeno, N. Wada, H. Uenohara, T. Konishi “Cost effective fractional OFDM receiver using arrayed waveguide grating,”
Optoelectronics and Communications Conference/International Conference on Photonics in Switching (OECC/PS), Toki Messe, Niigata, Japan 2016.
- C[3]. G. Cincotti, ‘Time-frequency photonics signal processing,’ invited paper Optoelectronics and Communications Conference/International Conference on Photonics in Switching (OECC/PS), Toki Messe, Niigata, Japan 2016.
- M. Hiraoka, T. Nagashima, B. Karanov, G. Cincotti, S. Shimizu, T. Murakawa, M. Hasegawa, K. Hattori, M.Okuno, S. Mino, A. Himeno, N. Wada, H. Uenohara, T. Konishi “Optical serial-to-parallel conversion based
on fractional OFDM scheme,” Optoelectronics and Communications Conference/International Conference on Photonics in Switching (OECC/PS), Toki Messe, Niigata, Japan 2016.
- T. Nagashima, G. Cincotti, T. Murakawa, S. Shimizu, M. Hasegawa, K. Hattori, M. Okuno, S. Mino, A. Himen, N. Wada, H. Uenohara, T. Konishi, “Cost effective all-optical fractional OFDM receiver using an arrayed
waveguide”, Optical Fiber Technology 32, 119–122 (2016).
- T. Nagashima, G. Cincotti, T. Murakawa, S. Shimizu, M. Hasegawa, K. Hattori, M. Okuno, S. Mino, A. Himeno, N. Wada, H. Uenohara, T. Konishi, “Experimental demonstration of cyclic prefix insertion for all-optical
fractional OFDM,” Optics Communications 396, pp.185-190 (2017).
- T. Nagashima, G. Cincotti, T. Murakawa, S. Shimizu, M. Hasegawa, K. Hattori, M. Okuno, S. Mino, A. Himeno, N. Wada, H. Uenohara, T. Konishi, “Peak-to-average power ratio reduction of transmission signal of all-optical
orthogonal time/frequency domain multiplexing using fractional Fourier transform,” Optics Communications 402, pp. 123-127 (2017).
- M. Hiraoka, T. Nagashima, G. Cincotti, S. Shimizu, Y. Yamasaki, K. Hattori, M. Okuno, S. Mino, A. Himeno, N. Wada, H. Uenohara, T. Konishi, “Power efficient optical serial-to-parallel conversion using fractional OFDM-
based linear technique,” IEICE Electronics Express 14, 6 pp. 1-8 (2017)
- C[145]. T. Konishi, Y. Yamamashi, G. Cincotti, S. Shimizu, N. Wada, H. Uenohara, “Symbol interference suppression for a hybrid use of OFDM and N-OTDM based on Fr-OFDM,” International Conference on
"Photonics in Switching and Computing" (PSC), Limassol Cyprus 2018.