Optical coherence domain reflectometry by synthesis of coherence function with nonlinearity compensation in frequency modulation of a laser diode

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Abstract
Optical coherence domain reflectometry (OCDR) is proposed by synthesis of the coherence function for high-spatial-resolution diagnoses of optical systems and waveguide devices. By changing the output frequency of a laser diode using its direct frequency modulation characteristic, the coherence function having the shape of a delta function is synthesized. In the basic experiments, the reflectivity distribution is measured successfully by sweeping the position of the peak. Nonlinearity compensation in the direct frequency modulation is experimentally demonstrated in order to improve the resolution. A three-electrode DFB laser diode with wide-frequency tunable range is introduced as the light source. A spatial resolution of 2-4 mm in air is demonstrated. The measurement range flexibility of this method is confirmed in the experiments.