Laser phase noise suppression and quadratures noise intercoupling in a mode cleaner

•Classical phase noise is the main limited factor for phase sensitive precision measurement.•Mode cleaner plays a low-pass filtering role not only for amplitude quadrature but also for phase one.•The noise suppression process for one quadrature noise is accomplished by a noise intercoupling between the two quadratures.•A complete experimental scheme for a full phase to amplitude noise conversion has been designed for phase noise characterization. Suppression phase noise of a laser is a great practical significance in applications of phase-sensitive precision measurement. To suppress the phase noise, an ultra-stable cavity incorporating with an electrical feedback control loop is always the popular choice, in which the linewidth of the cavity should be narrower than that of the laser to provide a stable reference standard. Here, we experimentally verify that mode cleaner plays a noise suppression role for phase quadrature in the whole frequency range of the photoelectric detectors, even though its linewidth is 103 larger than the laser one. Meanwhile, we found that the noise suppression for one quadrature is codetermined by the noise of the two quadratures of the input field. Our demonstration provides a new and in-depth interpretation for phase noise suppression in a mode cleaner with larger linewidth than the laser one that is important in phase-sensitive sensing application.