According to one aspect of the present invention the optical interrogation system comprises: (i) an optical sensor capable of immobilizing biological, bio-chemical and/or chemical substance; and (ii) an optical isolator that filters and eliminates parasitic reflections introduced by the optical sensor. In some embodiments the optical sensor includes a GCW with a surface having a sensing region capable of immobilizing biological, bio-chemical or chemical substances includes, and the optical interrogation system includes an optical detection system for monitoring this sensing region, the optical detection system comprising a light source, an optical delivery system, and a detection instrument.