Coupled-cavity lasers have attracted wide attention in the past, in particular for telecommunication applications where their wavelength tunability and ability for side mode suppression are desirable. The inherent sensitivity of these devices to changes in the optical coupling has also led to their proposed use in optical sensing systems. Small changes to the refractive index of the coupler section can lead to shifts in the resonance frequency of the laser.
Here we present an alternative approach to coupled-cavity sensing that exploits changes to the imaginary part of the refractive index of the coupler. An optical loss, introduced to the cavity by the passage of micro-particles, influences the optical loss of the lasing mode and changes the threshold gain requirement of the laser. The sub-linear nature of the gain-current density characteristics of the quantum confined gain medium amplifies this effect, producing an even larger perturbation in output power. We demonstrate this sensing mechanism using a monolithic coupled-cavity particle detector with on-chip capillary fill microfluidics and an in-line photo-detector section for photo-voltage transduction. Both laser and detector are pulsed allowing for a time-resolved measurement to be taken.
Sara-Jayne Gillgrass, Robert Thomas, and Peter M. Smowton, "Novel coupled-cavity sensing mechanism for on-chip detection of microparticles (Conference Presentation)," Proc. SPIE 10123, Novel In-Plane Semiconductor Lasers XVI, 101230S (Presented at SPIE OPTO: February 01, 2017; Published: 20 April 2017); https://doi.org/10.1117/12.2253613.5398643849001.
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