Sensitive optomechanical transduction of electric and magnetic signals to the optical domain

Abstract

We report a radio-frequency-to-optical converter based on an electro-optomechanical transduction scheme where the electrical, optical, and mechanical interface was integrated on a chip and operated with a fiber-coupled optical setup. The device was designed for field tests in a magnetic resonance scanner where its small form-factor and simple operation is paramount. For the appurtenant magnetic resonance detection circuit at 32 MHz, we demonstrate transduction with an intrinsic magnetic field sensitivity of 8 fT/ √ Hz, noise figure 2.3 dB, noise temperature 210 K, voltage noise 99 pV/ √ Hz, and current noise 113 pA/ √ Hz, all in a 3 dB-bandwidth of 12 kHz. Such sensitivity and bandwidth make the transducer a valuable alternative to conventional electronic preamplifiers that additionally is directly compatible with fiber communication networks.

Magnetic resonance imaging with optical preamplification and detection

“…This was particularly important whenever we connected the transducer to circuitry or transported it. In addition, we took several protective steps beyond 13–15,17,19 to prevent the membrane from collapsing during the transmit pulse: first, two crossed diodes were added in parallel to the transducer to short it if the induced voltage exceed their threshold. Such protection is a common way to protect standard preamplifiers, but did not sufficiently protect the transducer on its own.…”

“…Using instead semi-rigid cables with better shielding reduced the noise significantly. Third, electrical noise at the membrane-frequency could drive the mechanical motion because our sample had trapped charges 15 . We cancelled these out with a DC bias on the transducer which gave significant reduction in the overall transducer noise.…”

“…We fabricated the transducer in a cleanroom using standard techniques and a process described in detail elsewhere 15 . Basically, the starting substrate was a fused silica wafer, 100 mm in diameter, with a partially reflective dielectric mirror on top.…”

“…In contrast, this work uses an optical detection scheme based on a micro-electro-mechanical system that is compatible with the industry-standard induction detection. Unlike the mechanical detection used in MR force microscopy 12 , we replace the conventional electrical preamplifier with a transducer 13–15 that up-converts the MR signal onto an optical carrier. The signal can then be analyzed at the other end of a long and low-loss optical fiber, thus moving the receiver electronics away from the coils and high magnetic field near the scanner.…”

Microwave-to-Optical Transduction Using a Mechanical Supermode for Coupling Piezoelectric and Optomechanical Resonators

“…1(a)) to enable, for example, distributed quantum computing and quantum networks based on superconducting quantum nodes [5,6]. This approach is also a key enabling platform for low-noise optical detection of weak microwave signals [7], e.g., in the context of nuclear magnetic resonance [8][9][10].…”