Based On OVA-650 Digital Control Variable Optical Attenuator Design And Research

Variable optical attenuator (VOA) is a very important optical device in optical communication system. According to the user’s requirement, VOA can reduce the energy of optical signal which is expected. It is commonly used in EDFA gain equalization, DWMD optical power network control, optical communication lines, systematic assessment, and kinds of the experiment.Santec OVA-650 is a filter-based electronic optical attenuator module with a micro stepper motor inside. The principle is that using a stepper motor to drive the graded neutral density filter. When the beam of light goes through the filter at different location, we will get different attenuation. OVA-650 internal position sensor offers position voltage interface, by which users can collect the position voltage that reflects the attenuation.This paper takes OVA-650 as the design object, and uses single-chip 89S52 for circuit design, then designs the digital optical attenuator system that users can control. This paper designs stepper motor drive-circuit, and uses 2-phase-8-step pulse to control the stepper motor. We use high precision analog-digital chip MAX197 to sample the position voltage. For the sake of raising the precision voltage, we use the method of repeating sampling the same voltage to get the average. Adaptive loop algorithm is also used in system stream. According to attenuation-voltage table, we get the digital voltage. It will circularly sample the position voltage, and compare the absolute difference between position voltage and converted voltage, then control stepper motor moving direction and steps. Via this way, we precisely locate the position of the attenuation.In the part of test, we establish the test system to test the corresponding relationship of OVA-650 between internal attenuation and position voltage, then define the relationship table. The relationship between stepper motor moving and attenuation is also identified. By using matlab for numerical analysis and curve fitting, we get the fitting curve, and analyze the error between fitting curve and real curve. Through the way of comparing N-order polynomial curve fitting method and sub-function curve fitting method, we use the latter way to describe attenuation-voltage curve. Taking system accuracy±0.1dB as the loop condition, it will divide segments automatically.The range that system can control is 0～35dB, and stepping position accuracy is 0.03dB/step, with±0.1dB system accuracy.