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Change of frequency separation for two-mode quantum dot lasers by using a birefringent etalon filter

We have developed a stable two-mode laser by using a quantum dot optical gain chip in an external cavity. In this study, we demonstrate continuous change of frequency separation of a two-mode laser by using a birefringent etalon filter. Since the polarization of the quantum dot optical gain chip is TE-dominant, the frequency separation of the two-mode laser is controlled by rotating the birefringent etalon filter. We can change the frequency separation from 84 to 93 GHz by using this method.