Microwave-to-optical transduction and sensing

Microwave-to-optical transduction is the conversion of a microwave signal to an optical signal. Digital electronics that produce microwaves are widely applied in fields like radar, communications, imaging and sensing. However, the microwave regime is limited by its available spectrum and lossy properties. Transferring microwave to optical light can overcome these limitations by taking advantage of the high frequency, large bandwidth and low loss properties offered by photonics [1] [2]. Optomechanical resonators are a promising approach to achieve efficient microwave-to-optical transduction. Figure 1 shows a typical optomechanical resonator on the Silica platform [2], which supports mechanical and optical resonances simultaneously. Highly-confined optical and mechanical fields with large field overlap within nano/microscale can significantly enhance the mode interaction, thus resulting in a high microwave-to-optical transduction efficiency. Such systems have been widely explored on various integrated platforms, including silicon, silicon dioxide, silicon nitride (SiN), aluminum nitride (AlN), and more recently lithium niobate (LN). Compared with other platforms, LN has low-optical loss, decent photo-elastic coefficient (0.17), strong piezo-electric (7.5 pC/N) and opto-electric coefficient (30.8 pm/V), which provide multiple paths for microwave-to-optical transduction. Besides, it can achieve f·Q product as high as 1×10¹⁴ based on experimental extraction [3], which implies higher sensitivity and longer coherence times for optomechanical systems. Therefore, we explore the optomechanical sensors with high-sensitivity, low-noise multispectral detectors with low cost, size, weight, and power (C-SWaP) on the thin-film LN platform (Fig.2).

Figure 1. Suspended mechanical resonator [2]

Figure 2. Pixel array of Infrared sensors

Our work in this area is supported by DARPA Optomechanical Thermal Imaging (OpTIm).

[1] Verhagen, E., Deléglise, S., Weis, S. et al. Quantum-coherent coupling of a mechanical oscillator to an optical cavity mode. Nature 482, 63–67 (2012).

[2] Yao, J., Capmany, J. Microwave photonics. Sci. China Inf. Sci. 65, 221401 (2022).[3] L. Shao et al., Optica 6, 1498-1505 (2019).