A biosensor chip comprising: a substrate; a plurality of optical sensors formed at different locations on the substrate; a plurality of input optical couplers, each input optical coupler for directing incoming probe light incident on the chip toward a respective optical sensor, and each input optical coupler being configured to receive the incoming probe light from an objective lens of an optical interrogator (100, 200) system at an angle that is not normal to an upper surface of the chip; and a plurality of output optical couplers, each output optical coupler being in optical communication with a respective input optical coupler via a respective optical sensor, each output optical coupler for directing outgoing probe light from the respective optical sensor out of the chip, and each output optical coupler being configured to output the outgoing probe light at an angle that is different from the direction of the specular reflection of the incoming probe light and that is along a reciprocal path of the incoming probe light, so that the majority of the specular reflection of the incoming probe light falls outside of the collection aperture of the objective lens of the optical interrogator (100, 200), wherein each output optical coupler is arranged adjacent to the respective input optical coupler such that when the probe light is incident on the respective input optical coupler, the probe light is transformed into a guided wave mode which propagates via waveguides through the biosensor chip and emerges from the respective output optical coupler at an angle that matches the angle of incidence of the incoming probe light and traces the reciprocal path arriving back at the objective lens of the optical interrogator (100, 200) system. a substrate; a plurality of optical sensors formed at different locations on the substrate; a plurality of input optical couplers, each input optical coupler for directing incoming probe light incident on the chip toward a respective optical sensor, and each input optical coupler being configured to receive the incoming probe light from an objective lens of an optical interrogator (100, 200) system at an angle that is not normal to an upper surface of the chip; and a plurality of output optical couplers, each output optical coupler being in optical communication with a respective input optical coupler via a respective optical sensor, each output optical coupler for directing outgoing probe light from the respective optical sensor out of the chip, and each output optical coupler being configured to output the outgoing probe light at an angle that is different from the direction of the specular reflection of the incoming probe light and that is along a reciprocal path of the incoming probe light, so that the majority of the specular reflection of the incoming probe light falls outside of the collection aperture of the objective lens of the optical interrogator (100, 200), wherein each output optical coupler is arranged adjacent to the respective input optical coupler such that when the probe light is incident on the respective input optical coupler, the probe light is transformed into a guided wave mode which propagates via waveguides through the biosensor chip and emerges from the respective output optical coupler at an angle that matches the angle of incidence of the incoming probe light and traces the reciprocal path arriving back at the objective lens of the optical interrogator (100, 200) system.