Mode separation control of few-mode quantum dot lasers by using a multistep etalon filter

Semiconductor quantum dots can be used for an optical gain-chip in an external cavity to construct a stable two- or few-mode laser. In this study, we demonstrate wide-range mode separation control of a few-mode laser by using a multistep etalon filter. Since the precise control of multistep thickness in one etalon plate was achieved, the frequency separation of the few-mode laser can be changed by choosing the etalon position. We can change the frequency separation from 83 to 104 GHz by using this method.