MHz-level self-sustained pulsation in polymer microspheres on a chip

We observe MHz-level periodic self-sustained pulsation (SSP) in the transmission spectrum of a polydimethylsiloxane (PDMS) spherical microcavity on a silicon chip, under a fixed-frequency continuous laser excitation. The SSP results from the strong competition between the thermo-optic and thermal expansion effects of PDMS within the cavity mode volume. The experimental results show good agreement with the theoretical prediction by considering the modification of the thermal expansion coefficient and the temperature distribution within the mode volume.