Advances in fiber distributed-feedback lasers

Zervas, M.N. (2013) Advances in fiber distributed-feedback lasers. In, Kaminow, I.P., Li, T. and Willner, A.E. (eds.) Optical Fiber Telecommunications VIA: Components and Subsystems. Elsevier.

Record type: Book Section

Abstract

The recent re-introduction of optical coherent techniques has revolutionized modern telecom communications and has resulted in the most spectrally efficient optical system demonstrations to date. In addition to record spectral efficiencies, coherent communication systems offer other advantages in terms of system flexibility, reduced signal-to-noise ratio requirements, increased resilience against fiber chromatic dispersion and in many aspects simplify the system design. However, coherent detection systems, such as, for example, coherent-optical orthogonal-frequency-division- multiplexed (CO-OFDM) systems, and advanced modulation formats, such as quadrature amplitude modulation (QAM), impose much more stringent requirements on source linewidth, stability, and phase/frequency noise characteristics. The development of inexpensive laser sources, with high coherence and stability, is expected to replace expensive external-cavity semiconductor lasers and allow their use as local oscillators similar to the way local oscillators are used in today’s radio communication systems. The performance of CO-OFDM is in general 3 dB better than that of incoherent OFDM since no optical power is allocated for the carrier. However, CO-OFDM requires a laser at the receiver to generate the carrier locally. It is, therefore, more sensitive to phase noise and the main challenge of CO-OFDM is that the phase noise of the local oscillator must be compensated for. It has been shown that the influence of phase noise can be reduced by using lasers with narrow linewidth.

So far, practical commercial telecommunication systems are almost entirely based on semiconductor-based lasers as their optical sources, because of their compact size, high speed and reliability, and direct electronic control. Over the past decade, continuous-wave and pulsed fiber lasers, covering a quite large spectral window, have experienced a remarkable progress and have penetrated successfully quite diverse industrial sectors. Also, a number of different fiber lasers, such as ultrashort, ultrafast, or frequency stabilized ring lasers, operating in the telecom window have already been used extensively in a number of coherent system demonstrators. In addition, fiber distributed-feedback (DFB) laser technology has matured considerably and various sectors, such as the optical sensor sector, have benefited enormously from their unique characteristics, such as their robustness, electromagnetic-radiation immunity, power scalability, narrow linewidth, and exceptional phase-noise performance. A review of the high-performance fiber DFB lasers and their potential use in future high spectral efficiency telecom systems, in particular, is timely. This chapter covers advances in fiber DFB lasers and their potential use in modern telecom systems. It considers different designs and configurations and their impact on the laser performance. Special emphasis is given to power scalability and stability, linewidth, and phase/frequency noise characteristics. A brief comparison with other technologies in the telecom and non-telecom applications space is also given. The chapter concludes with a summary and an outlook of the fiber laser technologies and the future prospects.

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