OPTICAL COMMUNICATIONS OVER A WIDE TEMPERATURE-RANGE USING A TUNABLE LIQUID-CRYSTAL FILTER

We have recently shown that electronic feedback can be used to stabilize a liquid-crystal Fabry-Perot tunable filter (LCFP) to variations in temperature. The proportional feedback system we used improved the tracking range substantially, but the error rate still increases noticably with temperature deviation. In this letter, we show that the source of this increase is the increased feedback signal associated with larger temperature deviations and that the temperature range of constant error rate can be dramatically improved through the use of proportional-integral feedback. Error-rate measurements are used to show that while proportional-only feedback extends the communication range to a few degrees, proportional-integral feedback provides a low-error-rate channel over a much larger temperature range.