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      Modulator-free quadrature amplitude modulation signal synthesis

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          Abstract

          The ability to generate high-speed on–off-keyed telecommunication signals by directly modulating a semiconductor laser’s drive current was one of the most exciting prospective applications of the nascent field of laser technology throughout the 1960s. Three decades of progress led to the commercialization of 2.5 Gbit s −1-per-channel submarine fibre optic systems that drove the growth of the internet as a global phenomenon. However, the detrimental frequency chirp associated with direct modulation forced industry to use external electro-optic modulators to deliver the next generation of on–off-keyed 10 Gbit s −1 systems and is absolutely prohibitive for today’s (>)100 Gbit s −1 coherent systems, which use complex modulation formats (for example, quadrature amplitude modulation). Here we use optical injection locking of directly modulated semiconductor lasers to generate complex modulation format signals showing distinct advantages over current and other currently researched solutions.

          Abstract

          Quadrature amplitude modulation signalling is currently enabling rapid data transfer capacity growth, but it still has associated drawbacks. Here, Liu et al. use optical injection locking to generate complex modulation format signals with reduced consumption, small footprint and easy integration.

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          Most cited references2

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          Strong optical injection-locked semiconductor lasers demonstrating > 100-GHz resonance frequencies and 80-GHz intrinsic bandwidths.

          By using strong optical injection locking, we report resonance frequency enhancement in excess of 100 GHz in semiconductor lasers. We demonstrate this enhancement in both distributed feedback (DFB) lasers and vertical-cavity surface-emitting lasers (VCSELs), showing the broad applicability of the technique and that the coupling Q is the figure-of-merit for resonance frequency enhancement. We have also identified the key factors that cause low-frequency roll-off in injection-locked lasers. By increasing the slave laser's DC current bias, we have achieved a record intrinsic 3-dB bandwidth of 80 GHz in VCSELs.
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            A hybrid electroabsorption modulator device for generation of high spectral-efficiency optical modulation formats.

            We report a novel hybrid integrated optic device consisting of AlGaInAs/InP electroabsorption modulators and a four-arm silica-on-silicon planar lightwave circuit optical interferometer. The device is designed for generation of high spectral efficiency optical modulation formats. We demonstrate generation of 21.4 Gb/s quadrature phase shift keyed optical signals with electrical data drives of 2V(pp) amplitudes, achieving a bit error rate of 10(-9) with the required optical signal to noise ratio of ~18 dB in a 0.1 nm resolution bandwidth.
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              Author and article information

              Journal
              Nat Commun
              Nat Commun
              Nature Communications
              Nature Pub. Group
              2041-1723
              19 December 2014
              : 5
              : 5911
              Affiliations
              [1 ]Optoelectronics Research Centre, University of Southampton , Southampton SO17 1BJ, UK
              [2 ]Bell Labs, Alcatel-Lucent , Holmdel, New Jersey 07733, USA
              [3 ]Eblana Photonics Inc. , Unit 31, Pearse Street, Dublin 2, Ireland
              Author notes
              Article
              ncomms6911
              10.1038/ncomms6911
              4284664
              25523757
              41480577-098b-42ea-8e89-925da6d8430c
              Copyright © 2014, Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.

              This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

              History
              : 09 July 2014
              : 19 November 2014
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