DIGITAL OPTICAL PHASE-LOCK-LOOP

SYSTEMS & PROCESSES ENGINEERING CORPORATION (SPEC) HAS DEVELOPED AN INNOVATIVE DESIGN FOR A DIGITAL OPTICAL PHASE-LOCK-LOOP (DOPLL) FOR MEASUREMENT OF STRAIN, DISPLACEMENT, OR VIBRATION IN NONDESTRUCTIVE EVALUATION APPLICATIONS. THE TECHNIQUE OFFERS A NUMBER OF ADVANTAGES OVER PREVIOUS ANALOG PHASE-LOCK-LOOP DESIGNS. THE DIGITAL SYSTEM IS CAPABLE OF SEEKING MULTIPLE LOCK POINTS UNDER SOFTWARE CONTROL, SUCCESSIVELY REFINING THE MEASUREMENT PRECISION BY SEEKING LOCK POINTS AT HIGHER MODULATION FREQUENCIES. THE DIGITAL SYSTEM HAS A BROAD OPERATING BANDWIDTH, USING A DIGITAL FREQUENCY SYNTHESIZER IN PLACE OF A BANDWIDTH LIMITED VOLTAGE CONTROLLED OSCILLATOR. THE DIGITAL SYSTEM IS CAPABLE OF SIGNIFICANTLY FASTER OPERATION, SINCE THE PRECISE MODULATION FREQUENCY IS KNOWN AT PHASE LOCK AND NO PRECISION MEASUREMENT IS REQUIRED TO DETERMINE FREQUENCY. THE DESIGN IS RELATIVELY INSENSITIVE TO THE PATH OF THE INTENSITY MODULATED LIGHT, AND A COMMON DOPLL PATH LENGTH MEASUREMENT SYSTEM CAN BE UTILIZED WITH A NUMBER OF SENSOR TYPES, EACH CONNECTED VIA FIBER OPTICS.