Published online by Cambridge University Press: 08 August 2009
Introduction
In this chapter we develop the small-signal relationships between the RF and optical parameters for the most common electro-optic devices used in intensity modulation, direct detection links. There are numerous device parameters we could use for this task; we concentrate here – as we will throughout this book – on those parameters that can be measured and selected by the link designer – as opposed to those parameters that can only be measured and controlled by the device designer.
To provide the basis for comparing these and future devices, we develop a figure of merit for optical modulators and detectors: the RF-to-optical incremental modulation efficiency for modulation devices and its converse the optical-to-RF incremental detection efficiency for photodetection devices. These efficiencies are useful in link design because they provide a single parameter for evaluating device performance in a link that represents the combined effects of a device's optical and electrical parameters. Further, by using the same parameter for both direct and external modulation devices, we begin the process – which will carry on through much of the book – of using a single set of tools for evaluating both types of links.
The most common electro-optic devices in use for links today are the in-plane diode laser, both Fabry–Perot and DFB, for direct modulation, the Mach–Zehnder modulator for external modulation and a photodiode for photodetection. Thus on a first reading, one may want to focus on these devices.
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