Bias Control Techniques
Long-haul ˜ber-optic telecommunication systems operating in the S-, C-, and/or L-band of silica singlemode ˜ber typically employ external high-speed modulators to produce optical digital modulation formats for transmission data rates at and beyond 10 Gb/s. ™ese optical modulation formats include conventional on-oŸ keying (OOK) and the widely accepted phase-shi¥ keying (PSK) capable of higher spectral ešciency. An example of a high-speed optical modulator device for OOK or PSK generation is an integrated lithium niobate (LN) waveguide electro-optic traveling-wave Mach-Zehnder modulator (MZM). LN MZMs are also used to generate other modulation formats such as optical single sideband , pulse-position modulation , and quadrature amplitude modulation . LN MZMs are also extensively used in analog RF/microwave photonics (see Chapter 3) and have also been considered in unguided free-space atmospheric line-of-sight laser communications [4,5].