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Diode Lasers and Photonic Integrated Circuits von Coldren, Larry A. (eBook)

  • Erscheinungsdatum: 02.03.2012
  • Verlag: Wiley
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Diode Lasers and Photonic Integrated Circuits

Diode Lasers and Photonic Integrated Circuits , Second Edition provides a comprehensive treatment of optical communication technology, its principles and theory, treating students as well as experienced engineers to an in-depth exploration of this field. Diode lasers are still of significant importance in the areas of optical communication, storage, and sensing. Using the the same well received theoretical foundations of the first edition, the Second Edition now introduces timely updates in the technology and in focus of the book. After 15 years of development in the field, this book will offer brand new and updated material on GaN-based and quantum-dot lasers, photonic IC technology, detectors, modulators and SOAs, DVDs and storage, eye diagrams and BER concepts, and DFB lasers. Appendices will also be expanded to include quantum-dot issues and more on the relation between spontaneous emission and gain. Larry A. Coldren is the Fred Kavli Professor of Optoelectronics and Sensors at the University of California, Santa Barbara. He has authored or coauthored over a thousand journal and conference papers, seven book chapters, and a textbook, and has been issued sixty-three patents. He is a Fellow of the IEEE, OSA, and IEE, the recipient of the 2004 John Tyndall and 2009 Aron Kressel Awards, and a member of the National Academy of Engineering. Scott W. Corzine obtained his PhD from the University of California, Santa Barbara, Department of Electrical and Computer Engineering, for his work on vertical-cavity surface-emitting lasers (VCSELs). He worked for ten years at HP/Agilent Laboratories in Palo Alto, California, on VCSELs, externally modulated lasers, and quantum cascade lasers. He is currently with Infinera in Sunnyvale, California, working on photonic integrated circuits. Milan L. Mashanovitch obtained his PhD in the field of photonic integrated circuits at the University of California, Santa Barbara (UCSB), in 2004. He has since been with UCSB as a scientist working on tunable photonic integrated circuits and as an adjunct professor, and with Freedom Photonics LLC, Santa Barbara, which he cofounded in 2005, working on photonic integrated circuits.

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Diode Lasers and Photonic Integrated Circuits

Chapter 2

A Phenomenological Approach to Diode Lasers

2.1 Introduction

Now that we have a basic understanding of what diode lasers are, what is involved in their fabrication and operation, and what characteristics can generally be expected, we are perhaps in a position to delve into the mechanics of how an injected current actually results in an optical output. In this chapter we attempt to develop an engineering toolbox of diode laser properties based largely on phenomenological arguments. In the course of this development, we make heavy reference to several appendices for a review of some of the underlying physics.

The chapter begins by developing a rate equation model for the flow of charge into double-heterostructure active regions and its subsequent recombination. Some of this electron-hole recombination generates photons by spontaneous emission. This incoherent light is important in LEDs, and a section is devoted to deriving the relevant equations governing LED operation.

Sections 2.4 through 2.6 provide a systematic derivation of the dc light-current characteristics of diode lasers. First, the rate equation for photon generation and loss in a laser cavity is developed. This shows that only a small portion of the spontaneously generated light contributes to the lasing mode. Most of it comes from the stimulated recombination of carriers. All of the carriers that are stimulated to recombine by light in a certain mode contribute more photons to that same mode. Thus, the stimulated carrier recombination/photon generation process is a gain process. The threshold gain for lasing is studied next, and it is found to be the gain necessary to compensate for cavity losses. The current required to reach this gain is called the threshold current, and it is shown to be the current necessary to supply carriers for the unproductive nonradiative and spontaneous recombination processes, which clamp at their threshold value as more current is applied. Above threshold, all additional injected carriers recombining in the active region are shown to contribute to photons in the lasing mode. A fraction escape through the mirrors; others are absorbed by optical losses in the cavity.

The next section deals with the modulation of lasers. Here for the first time we solve the rate equations for a modulated current. Under small-signal modulation, the rate equations for carriers and photons are found to be analogous to the differential equations that describe the current and voltage in an RLC circuit. Thus, the optical modulation response is found to have a resonance and to fall off rapidly above this frequency.

Finally, this chapter reviews techniques for characterizing real lasers. These techniques can be used to extract the important device parameters used in the theoretical derivations. They also provide practical terminal parameters that are useful in the design of optoelectronic circuits.

2.2 Carrier Generation and Recombination in Active Regions

In Chapter 1, when we considered the current injected into the terminals of a diode laser or LED, we suggested that it was desirable to have all the current contribute to electrons and holes, which recombine in the active region. However, in practice only a fraction, i , of the injected current, I , does contribute to such carriers. In Fig. 2.1 we again illustrate the process of carrier injection into a double-heterostructure active region using a somewhat more accurate sketch of the energy gap versus depth into the substrate.

Figure 2.1 Band diagram of forward biased double-heterostructure diode.

Because the definitions of the active region and the injection efficiency, i , are so critical to further analysis, we highlight them here for easy reference.

Active region: the

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