Figure 1.

SPR Interferometer; (a) Interference of adjacent SP modes; the incident coherent wave couples SP modes on both finite gratings. The probing SP (A) propagates across the cavity and recombines with the reference SP (B), thus forming the combined SP mode (A + B). As the optical path length of the cavity is increased by the presence of biomolecular agents on the surface, the probing SP is phase delayed and the resulting interference pattern will be modified, cycling from constructive to destructive interferences. (b) Conceptualization of the system, where an incident light (I_o) hits a grating pair. The light intensity is then distributed between the transmission (T_o), the reflection (R_o), the coupled SPR (M_SP) and some constant absorption. As M_SP is modulated by the phase shift induced by the cavity, monitoring R_o or T_o can reveal information on the interference conditions of A + B.