Development of optical characteristic measurement system for optical fiber coupler fabrication using 3-wavelength light simultaneously

In this paper, a technique is proposed for measuring optical characteristics of an optical fiber coupler at multiple wavelengths simultaneously. The new system can be used in the manufacturing process of fused fiber couplers which helps reducing the optical characteristic measuring time and improving the performance monitoring ability over more wavelength regions. We have demonstrated a three-wavelength system, however more wavelengths can be added by applying the same technique. Three wavelength light sources of different optical powers are modulated by square waves at preselected frequencies, then combined using two stages of 2×1 couplers to be used as the input of the fiber coupler being fabricated. The combined output light is detected by a single photodiode and amplified by a logarithmic amplifier circuit. The detected signal is analyzed in real-time to determine the power of each wavelength by peaks and valleys detection at various frequencies. Through several manufacturing trials, we have shown that the optical characteristic measuring time is reduced by a factor of 6, while the number of monitoring wavelengths is increased over the conventional system from 2 to 3 wavelengths.