High spectral efficiency transmission using optical frequency combs
Doctoral thesis, 2019

Modern long-haul optical communication systems transmit data on all available single-mode fiber dimensions, time, polarization, wavelength, phase and amplitude. Powerful digital signal processing and forward error correction has pushed the per-channel throughput towards its theoretical limits and the bandwidth is limited by the erbium-doped fiber amplifiers. Maximizing the spectral efficiency (SE), i.e. the throughput normalized to bandwidth, is therefore of indisputable importance. Even more so in optical networks as large routing guard-bands drastically reduce the SE of traditional WDM systems. Flex-grid networks with optical superchannels can overcome this limitation. Superchannels consist of multiple tightly packed WDM channels routed as a unit. A comb-based superchannel is formed by encoding independent information onto lines from an optical frequency comb, a multi-wavelength light source fully determined by its center frequency and line spacing.

This thesis studies the generation, transmission and detection of comb-based superchannels. Focus is on profiting from unique frequency comb properties to realize systems with capabilities beyond that of conventional systems using arrays of independent lasers. Digital, analog and optical processing schemes are proposed, and combined, to increase the system SE. Superchannel modulation is investigated and a scheme capable of encoding independent information onto the lines from a frequency comb in a single waveguide structure is demonstrated. By combining overhead-optimized pilot-based DSP with a 22GHz-spaced soliton microcomb, superchannel transmission with record SE for distances up to 3000km is realized, closing the performance gap between chip-scale and bulk-optic combs in optical communications. The use of two optical pilot tones (PTs) to phase-lock a transmitter and receiver comb pair is studied, realizing self-homodyne detection of a 50x20Gbaud PM-64QAM superchannel with 4% pilot overhead. The PT gains are furthermore analyzed and a complexity-performance trade-off using a single PT and low complexity DSP is proposed. The scheme is used to demonstrate 12bits/s/Hz SE over the full C-band using 3x50xGBaud PM-256QAM superchannels and DSP-complexity reduction at distances exceeding 1000km is shown. Finally, a comb-enabled multi-channel joint equalization scheme capable of mitigating inter-channel crosstalk and thereby minimizing the SE loss from spectral guard bands is demonstrated.

Optical frequency combs


Coherent optical communication

A423 (Kollektorn), Kemivägen 9
Opponent: Dr. Benn Thomsen, Microsoft Corp., United Kingdom


Mikael Mazur

Chalmers, Microtechnology and Nanoscience (MC2), Photonics

M. Mazur, N. K. Fontaine, H. Chen, R. Ryf, D. T. Neilson, G. Raybon, A. Adamiecke, S. Cortselli and J. Schröder, "Multi-wavelength arbitrary waveform generation through spectro-temporal unitary transformations"

M. Mazur, M.-G. Suh, A. Fülöp, J. Schröder, V. Torres-Company, M. Karlsson, K. J. Vahala and P. A. Andrekson, "High spectral efficiency coherent superchannel transmission with soliton microcombs"

10 Tb/s PM-64QAM Self-Homodyne Comb-Based Superchannel Transmission with 4% Shared Pilot Tone Overhead

Journal of Lightwave Technology,; Vol. 36(2018)p. 3176-3184

Journal article

High Spectral efficiency PM-128QAM Comb-Based Superchannel Transmission Enabled by a Single Shared Optical Pilot Tone

Journal of Lightwave Technology,; Vol. 36(2018)p. 1318-1325

Journal article

Experimental Investigation of Link Impairments in Pilot Tone Aided Superchannel Transmission

IEEE Photonics Technology Letters,; Vol. 31(2019)p. 459-462

Journal article

12 bits/s/Hz Spectral Efficiency Over the C-band Based on Comb-Based Superchannels

Journal of Lightwave Technology,; Vol. 37(2019)p. 411-417

Journal article

M. Mazur, J. Schröder, M. Karlsson and P. Andrekson, "Joint Superchannel Digital Signal Processing for Ultimate Bandwidth Utilization"

Optical communication systems are the workhorses behind the Internet, providing multi-Tb/s throughput to connect humans, machines and data-centers over distances reaching from a few meters to transoceanic links exceeding 10000km. The information is encoded onto a light wave originating from a laser in the optical transmitter. As the throughput requirement of these systems has been growing exponentially over the last decades, following the growth in Internet traffic, more and more laser sources are being used and systems today employ more than 100 lasers in a single link. Each channel is separated by tuning the lasers to a unique frequency so that optical band-pass filters can be used to distinguish each channel at the receiver side.

Alternatively, while lasers are typically viewed as a close-to-ideal realization of a single frequency light source, one could envision a light source that instead lased on multiple frequencies. This thesis focus on a coherent multi-frequency light source, an optical frequency comb, and its role in optical communications. More specifically, schemes to exploit unique properties of frequency combs to make multi-channel optical communication systems more effectively are proposed and experimentally demonstrated. Throughout the thesis, the focus is on effectiveness by means of increasing the spectral efficiency, i.e., the amount of information transmitted normalized to the signal bandwidth used to carry it. The overall goal of these systems is to make optical communications more effective, supporting more data throughput at a lower cost and energy consumption to enable future, unhindered, growth of the Internet.

Areas of Advance

Information and Communication Technology

Subject Categories


Communication Systems

Signal Processing



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4630



A423 (Kollektorn), Kemivägen 9

Opponent: Dr. Benn Thomsen, Microsoft Corp., United Kingdom

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