ABSTRACT
Optical preamplification in coherent detection can be integrated at the front end of the optical receiver. Coherent optical receivers are important components in long-haul optical fiber communication systems and networks to improve the receiver sensitivity and thus extra transmission distance. This chapter provides the components of coherent receivers and outlines the principles of optical coherent detection under heterodyne, homodyne, or intradyne techniques. It provides the details of optical phase lock loop, which are very important to the development of modern optical coherent detection. The design of an optical receiver depends on the modulation format of the signals and transmitted through the transmitter. Coherent receivers are distinguished between synchronous and asynchronous. Optical homodyne detection requires the phase matching of the frequency of the signal carrier and that of the local oscillator. Optical phase diversity receivers combine the advantages of the homodyne with minimum signal processing bandwidth and heterodyne reception with no optical phase locking required.
