Sub-Millimeter Resolution Laser Ranging At 9.3 Kilometers Using Temporally Stretched, Frequency Chirped Pulses From A Modelocked Laser

A chirped fiber Bragg grating with a dispersion of 1651ps/nm is used to generate temporally stretched, frequency chirped pulses from a passively mode locked fiber laser that generates pulses of ∼1ps(FWHM) duration at a repetition rate of 20MHz with 3.5mW average power (peak power of 175W). The use of a chirped fiber Bragg grating enables the generation of temporally stretched pulses with low peak power so that non-linear effects in the fiber can be avoided. A fiber based interferometeric arrangement is used for interfering a reference signal with the reflected signal from the target to realize a coherent heterodyne detection scheme. In the RF domain, the detected heterodyne beat frequency shifts as the target distance is changed. A round trip target distance of 14km in air is simulated using 9.3km of optical fiber and a resolution of less than a millimeter is observed. ©2009 SPIE