Modulator-free quadrature amplitude modulation signal synthesis.

Zhixin Liu,Joseph Kakande,David J Richardson,Richard Phelan,John O’Carroll,Brian Kelly,Radan Slavík

doi:10.1038/ncomms6911

Zhixin Liu, Joseph Kakande + Show 5 more

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https://doi.org/10.1038/ncomms6911

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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.

Highlights

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
We use a combination of optical injection locking (OIL) and direct modulation of semiconductor lasers to generate IQmodulated optical signals
Schematics of our method[11,12,13] showing how to build quadrature amplitude modulation (QAM) signals from directly amplitudemodulated (DM) lasers are sketched in Fig. 1a for two specific exemplar signals (QPSK and 16QAM), we emphasize that the approach can readily be adapted to work for arbitrary IQ modulation

Summary

Introduction

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. The coherent combination of high-power lasers could greatly benefit from the control of amplitude and phase that we have demonstrated from low-cost semiconductor devices and may open the way to significantly higher powers and useful functionalities (for example, beam steering), which require precise control of the phase properties of the combined beams. Another example lies in the photonic generation of arbitrary THz signals as needed in a wide variety of emerging ultrafast applications. A final example is laser radar where complex beam modulation is used to provide high-resolution ranging information

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Conclusion