Control method to maintain the maximum extinction ratio of output optical pulses from an intensity modulator

In a time-division-multiplexing (TDM) fiber optic sensor system, a continuo us-wave laser source can be externally modulated by an intensity modulator to generate an optical pulse. To enhance sensor system performance, an opti cal pulse with a high extinction ratio (ER) is highly desirable. The high E R increases sensor sensitivity and reduces sensor crosstalk. For optimum TD M operation, it is important not only to select an intensity modulator with a high ER, but to operate the modulator at its most optimum operating poin t. We provide a way to achieve these goals. We demonstrate a control to mai ntain the output optical pulse from an optical guided-wave (OGW) intensity modulator at its maximum ER bias point. Our unique control methodology uses a reference value obtained after the process of amplifying, digitizing and averaging the input signal of the optical pulse. Results are analyzed and processed, using a custom software program and algorithm of our own design, and used to control the OGW, electronics maintaining the optimum bias poin t for best ER. Our experimental results show that this control scheme can b e used to satisfactorily operate an OGW at high sensitivity with output opt ical pulse light intensity variation of less than 15 nW, which provides for improved TDM fiber optic sensor system response and operation. (C) 2000 So ciety of Photo-Optical Instrumentation Engineers. [S0091-3286(00)01108-9].