Nature2014-06-24 6:21 PM

将弱无线电波转化成激光信号的新方法 Optical detection of radio waves through a nanomechanical transducer


从医学成像和射电天文学到导航和无线通信的很多应用都依赖于很弱射频微波的忠实传输和检测。在这项研究中,Eugene Polzik及同事演示了这一领域的一个全新功能——利用一个纳米机械振荡器将弱的无线电波转化成激光信号。该振荡器(由氮化硅制成的一种膜片)能同时与从其表面发射的无线电信号和光耦合,这一特点被用来以达到量子极限的灵敏度将无线电信号作为光相移来测量。与现有检测器相比,这种方法的优势是能在室温下工作,所产生的信号也可以被轻易传输到标准光纤中。


Low-loss transmission and sensitive recovery of weak radio-frequency and microwave signals is a ubiquitous challenge, crucial in radio astronomy, medical imaging, navigation, and classical and quantum communication. Efficient up-conversion of radio-frequency signals to an optical carrier would enable their transmission through optical fibres instead of through copper wires, drastically reducing losses, and would give access to the set of established quantum optical techniques that are routinely used in quantum-limited signal detection. Research in cavity optomechanics has shown that nanomechanical oscillators can couple strongly to either microwave or optical fields. Here we demonstrate a room-temperature optoelectromechanical transducer with both these functionalities, following a recent proposal8 using a high-quality nanomembrane. A voltage bias of less than 10 V is sufficient to induce strong coupling between the voltage fluctuations in a radio-frequency resonance circuit and the membrane’s displacement, which is simultaneously coupled to light reflected off its surface. The radio-frequency signals are detected as an optical phase shift with quantum-limited sensitivity. The corresponding half-wave voltage is in the microvolt range, orders of magnitude less than that of standard optical modulators. The noise of the transducer—beyond the measured  800PVHz(-1/2) Johnson noise of the resonant circuit—consists of the quantum noise of light and thermal fluctuations of the membrane, dominating the noise floor in potential applications in radio astronomy and nuclear magnetic imaging. Each of these contributions is inferred to be 60PVHz(-1/2)  when balanced by choosing an electromechanical cooperativity of ~150  with an optical power of 1 mW. The noise temperature of the membrane is  300K divided by the cooperativity. For the highest observed cooperativity of 6800 , this leads to a projected noise temperature of 40 mK and a sensitivity limit of 5PVHz(-1/2)  . Our approach to all-optical, ultralow-noise detection of classical electronic signals sets the stage for coherent up-conversion of low-frequency quantum signals to the optical domain.






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