Phys. Scr. 98 (2023) 125119 https://doi.org/10.1088/1402-4896/ad0d66 PAPER Hybrid multilevel-multiwavelength signaling scheme for optical data transmission Mikhail V Maximov 1 , Yuri M Shernyakov 2 , Nikita Yu Gordeev 2 , Vladimir G Dubrovskii 3 , Alexey M Nadtochiy 1,4 and Alexey E Zhukov 4 1 Alferov University, Khlopina 8/3, St. Petersburg, 194021, Russia 2 Ioffe Institute, Politehnicheskaya 26, St. Petersburg, 194021, Russia 3 Faculty of Physics, St. Petersburg State University, St. Petersburg, Russia 4 National Research University Higher School of Economics, Soyuza Pechatnikov, 16, St. Petersburg,190008, Russia E-mail: al.nadtochy@mail.ioffe.ru Keywords: multilevel signaling, data encoding, quantum dot lasers, two-state lasing Abstract We suggest an idea of data encoding scheme based on the switching from the ground state (GS) to excited state (ES) lasing in quantum dot (QD) lasers with increase in injection current. The groups of two bits are assigned to lasing spectra that comprise either one or both GS and/or ES lasing lines depending on injection current. We expect that the proposed encoding scheme can potentially combine some advantages of multilevel signaling and wavelength division multiplexing. Introduction Rapid increase of intra- and inter-data center traffic inspired by the growth of various network applications like cloud computing, social networking services, the Internet of Things and smart-phones requires the development of high bit rate short-to-medium reach optical transceivers. Presently ‘binary intensity modulation with direct detection’ is the most widely used modulation format for great variety of applications in high-speed short-to-medium reach optical fiber links [1, 2]. In a simple binary scheme, two signals, usually two levels of light intensity, voltage or current, are used to represent a ‘1’ and a ‘0’. Thus, the symbol rate is the same as the bit rate. However, further increase of capacity of the binary scheme is hindered by the limited bandwidth of electrical and optical components. Recently multilevel signaling was proposed for compressing the bandwidth required to transmit data at a given bit rate [1] using one transmitter. The principle of multilevel signaling is to use several signal levels to represent data, so that each signal level represents more than one bit of information. Pulse amplitude modulation (PAM) is the most common example of multilevel signaling [3, 4]. In case of a four- level scheme (PAM4), groups of two data bits (‘00’, ‘01’, ‘10’ and ‘11’) can be represented by one of four values of laser light intensity [3]. Therefore, one optical signal level corresponds to a certain pair of data bits, so the bit rate is twice the signal transmission rate. The drawback of the multilevel scheme is that the difference in light intensities of the optical signals is less than in the binary scheme (three times less in case of PAM4 suggesting that the topmost level of laser intensity remains the same). Thus, inevitable noise of an optical light source and data transmission system makes the probability of changing one symbol to another higher than in the binary scheme. In case of optical data transmission, the problem can be solved by scaling up the light intensities by a factor of (m—1) for an m-level scheme. This, however, leads to the emergence of new problems associated with overheating of the optical source, a reduction of its lifetime, and increased power consumption. To overcome these limitations and reduce the bandwidths sophisticated signaling schemes such as Nyquist modulation [5], Duo-Binary [6], and Faster- Than Nyquist Modulation [7] have been proposed and demonstrated. However, these approaches require tricky signal processing that increases the system complexity and cost. An alternative approach for implementation of high-capacity optical communication systems is Wavelength-Division Multiplexing (WDM) [8]. This technology explores multiple optical transmitters, usually single frequency lasers each emitting at a different wavelength, individually passing on signals. These signals are RECEIVED 15 May 2023 REVISED 2 November 2023 ACCEPTED FOR PUBLICATION 15 November 2023 PUBLISHED 29 November 2023 © 2023 IOP Publishing Ltd