Methods and apparatus for reducing the coherence of an optical signal that is used to interrogate optical interferometric sensors are disclosed. The optical field phasor of the interrogation source is modulated in a controlled manner to produce a broadened optical source power spectrum at the output of the source unit. The output from the source unit 1 is launched into an optical sensor network 2, comprising a multiple of optical pathways from its input to the detection unit 20, where pairs of optical pathways form sensor interferometers 100,110. A compensating inteferometer 70 with delay difference similar to the sensor delay difference may be arranged in a serially coupled manner with the optical sensor network 2, either before or after the network. The optical output power from the source unit 1 may either be continuous or pulsed with a pulse duration similar to the sensor delay. The coherence modulation may be performed through direct modulation of the source or through external modulation of the light with piezoelectric ring modulator, a Lithium niobate phase or intensity modulator, or an acoustooptic modulator 30.
Active coherence reduction for interferometer interrogation