Interrogation of surface plasmon resonance sensors using temporally stretched ultrashort optical pulses

We propose a novel technique that has the potential to realize interrogation of surface plasmon resonance (SPR) sensors at very high speed. In contrast to the incoherent light source used in the traditional wavelength interrogation schemes, a broadband coherent laser generating short optical pulses at a high repetition rate is used along with a highly dispersive optical element. The dispersion causes strong broadening of the optical pulses, and the temporal pulse shape could exactly resemble the spectral distribution of the pulses due to the induced linear chirp. Therefore, by measuring the changes in the pulse shapes with a single high-speed photodetector, the spectral response of the SPR sensor can be obtained for each input pulse and the interrogation speed could reach the repetition rate of the pulse train. This could enable SPR measurements at the speed of tens of MHz or higher, which is well beyond that of other current SPR interrogation techniques. We experimentally demonstrate that, by measuring the variations in the pulse shapes of the chirped pulses, sensitive SPR measurements can be made. Implementing this scheme with a femtosecond fiber laser and other fiber optic components also show the potential to realize more compact and integrated SPR systems.