Achromatic Optical Doppler Frequency Modulator

Linac Inc., R&D group, proposes a completely new approach to provide Doppler frequency offset for a microwave bandwidth (higher than 16 GHz) laser radar signal. The proposed achromatic optical Doppler frequency modulator (AODFM) system uses existing technology of holographic achromatic phase modulation. The modulation is carried out by specially configured three cascaded gratings. The input and output laser radar signal at microwave bandwidth will be collinear where an optical fiber and optical couplers can be used to transmit the lidar signal in and out of the optical modulation unit. The center off-axis component is a traveling grating which will provide the desired Doppler offset frequency to the lidar signal. Precise motion control is achieved using PC monitored electronic servo devices and algorithm. The two symmetric base grating will provide the light direction control and enable the light to be modulated achromatically. This AODFM system will utilize new techniques in fiber connector, optical coupler, achromatic phase modulation diffractive optical element fabrication, electronic control, and precise actuators to provide Doppler ambiguity free lidar signal without complex electronic spectrum analysis and signal process devices.