Optical signal processing in dual-wavelength optoelectronic drop analyzer

Dual-wavelength optical signals are injected into the liquid drop through optical fibers in order to study the light intensity variation during the drop growth. Modulation and demodulation are used to reduce the influence of ambient light on the valuable optical signals. HA17555 chip composes the oscillating circuit for light modulation, with different high oscillating frequency for different light source. The light signal collected by a fiber detector after propagation inside the drop is changed into electric signal through the OPA2111 photoelectric circuit. The second-order band-pass filter composed of MAX275 chip is used for signal-separation. The high-pass filter is used to prevent the low frequency signal of ambient light. The valuable signal related to the drop is demodulated by a linear demodulation circuit including a half-wave rectifier, full-wave composition and low-pass filter.