Optical detector module, measurement system and method of detecting presence of a substance in a test material

An optical detector module for detecting the presence of a substance in a test material, the module comprising:

• a housing having a test window formed therein;
• a optical fibre disposed in the housing, the optical fibre having a tilted fibre grating fabricated therein, the tilted fibre grating being arranged to couple substance-specific optical radiation out of the optical fibre through the test window into test material;
• an optical detector disposed in the housing and arranged to measure the intensity of the substance-specific optical radiation that is scattered by the test material back through the test window;
• and
• a signal collector disposed between the test window and optical detector to collect the substance-specific optical radiation scattered by the test material.

The method of detecting the presence of a substance in a test material, the method comprising:

• introducing optical radiation into an optical waveguide;
• coupling substance-specific optical radiation out of the optical waveguide into test material at a plurality of spatially separated locations along the optical waveguide;
• measuring an intensity of the substance-specific optical radiation that is scattered by the test material at each of the plurality of spatially separated locations along the optical waveguide;
• and
• determining a presence of a substance in the test material at each of the plurality of detection nodes based on the measured intensity obtained at each of the plurality of spatially separated locations along the optical waveguide.