Transparent Ceramic-based High-speed Variable Optical Attenuator And Its Control Circuit Design

In response to higher levels of traffic on optical communications networks, wave-length-division multiplexing or WDM-the mainstream system now in use-is developing in two directions: higher data rates and a larger number of channels. The erbium-doped amplifier (EDFA) is an indispensable component of WDM system, and, in order to provide dynamically flexible gain level adjustment, is often used in combination with variable optical attenuators (VOAs), which have flat wavelength characteristics over a wide band range. In this thesis, we successfully made a type of high-speed variable optical attenuator, which is based on transparent ferroelectric ceramics, and experimental data demonstrated its good performance.Recently various types of attenuators have been realized which include the use of mechanism, magnetic-optical effect, thermo-optical effect, electro-optic effect, acoustic-optical effect, MEMS, optical wave-guide and so on. In the past people can not get proper material which has high enough EO coefficient, so we seldom heard about VOAs based on EO material. Since Boston ATI had invented its transparent electro-optic ceramics, namely OptoCeramic, which features in high EO effect, low optical loss, broad transmission wavelength range, ceramic ruggedness, and low cost, make it ideal material for many types of optical devices. Yet its hysteresis and temperature dependence exists, therefore the stability is very critical for the variable optical attenuator made by transparent ferroelectric ceramics. High speed VOA module had been fabricated by using back closed-loop control analog circuits. The results indicate that the response time is about 10us, dynamic range is 25dB, and insertion loss is less than 0.6dB, PLD is less than 0.1 dB. In order to further improve the device's response time, we also design higher speed digital control circuits which aimed at micro-second level response time.