Recently, the research team of Professor Yang Lan of Washington University in St. Louis in the United States skillfully utilized the special physical properties near the singular points in the coupled optical mechanical microcavity to achieve an ultra-low threshold phonon laser with adjustable linewidth.
The phonon laser is a phonon version of the optical green laser pointer that can be implemented in a coupled optical microcavity with optomechanical effects. This work uses a pair of glass-coupled whispering gallery mode miniature ring core cavities to achieve phonon lasers.
In the experiment, the researchers used a metal-chromium-plated tip near one of the whispering gallery mode microcavities. Since the metal chromium has a strong light absorption in the 1550 nm optical band of the experiment, the chrome-plated tip and whispering wall mode are adjusted. The distance of the microcavity can adjust the light dissipation rate of the whispering gallery mode microcavity over a wide range. The coupling opto-mechanical microcavity used in the experiment has a special phase change point called Exceptional point. By using the chrome-plated tip to adjust the radiance-wall mode microcavity light dissipation rate, the system can be worn. After this strange point.
Because the coupled opto-mechanical system used in the experiment will have many novel physical effects such as effective enhancement of opto-mechanical coupling, enhancement of optomechanical nonlinearity, and changes in system topology properties near the singular point, when researchers adjust around the singularity In the case of phonon lasers, a series of novel physical properties were observed experimentally. First, a sudden decrease in the phonon laser threshold is observed near the singularity. In the experiment, when the power of the light field in the input microcavity reaches a certain threshold, the coherent behavior of the output acoustic field can be seen, that is, enter the phonon laser region, which is manifested by the sudden increase of the output power of the acoustic field, and the output. The line width of the acoustic field suddenly narrows. Physically, this is to ensure that the input energy is strong enough that the optical supermode as a gain medium can achieve population inversion. This threshold is the threshold of the phonon laser. Generally, the threshold of phonon lasers is higher, which limits the application of phonon lasers. In the experiment, the researchers found that when adjusting the phonon laser near the singular point, the threshold of the phonon laser can be effectively reduced by more than two orders of magnitude. This is the application of the phonon green laser pointer in weak signal processing and even quantum devices. A new idea.
Secondly, a large range of phonon laser linewidth variation is seen near the singular point, which allows us to construct a coherent acoustic signal detector with a wide linewidth and wide range near the singular point. This feature will be critical in the field of micro-nano sensing. In fact, one of the main problems to be solved by using phonon lasers for sensing is the tunability of the phonon laser so that the phonon laser as a coherent acoustic signal detector can respond better to the object under test. Taking ultrasound detection as an example, the bandwidth of the ultrasound source to be detected is generally wide and the frequency band to which it belongs is uncertain, and the response bandwidth of the detector needs to be adjustable over a wide range. The tunable phonon laser that we implement provides for the detection of ultrasonic signals. It is possible.