Tunable Fano-like resonance enabled by coupling a microsphere with a fiber Mach–Zehnder interferometer

Abstract

We demonstrate a simple scheme to achieve Fano-like resonance by coupling a microsphere resonator with a fiber Mach-Zehnder interferometer (FMZI), which includes a tapered microfiber in one pathway to evanescently couple with the microsphere. In this system, Fano-like asymmetric lineshapes could be converted into different types by introducing an extra phase shift in the FMZI. In addition, the sharpness of the Fano-like lineshapes could be controlled by changing the coupling strength between the microsphere and the microfiber. This Fano-like resonance with advantages of fiber integration, tunable lineshape, and ease of operation may have great potential in optical signal processing and sensing.

Fano-Like Resonance in an All-in-Fiber Structure

“…3. Compared with WGM-based structures [1], [10], there is a more prominent EIT-like spectrum, and the height of the transparency peak is up to ∼10.2 dB (shown in Fig. 3).…”

“…And electromagnetically induced transparency (EIT) is a result of Fano interference that requires coupling of a discrete transition to a continuum, creating a narrow transparency window due to elimination of the resonant absorption [8]. A variety of optical microresonators with narrow resonance linewidths such as chip-integrated microrings and microtoroids [9], individual microspheres [10], and microbottles [1], [11], have been coupled with interferometers of wide spectrum to form Fano-like resonance lineshapes. However, to access resonant modes in these microresonators, tapered microfibers or lensed fibers are essential, which make the coupling configurations rigorous and require the strict coupling gap and phase matching condition [12], [13].…”

“…However, to access resonant modes in these microresonators, tapered microfibers or lensed fibers are essential, which make the coupling configurations rigorous and require the strict coupling gap and phase matching condition [12], [13]. For instance, coupling with a microtoroid requires the microfiber to have waist diameters smaller than 2 μm [10]- [12], [14], and the coupling efficiency strongly depends on their coupling gap. It is a challenge to package these fibers and micro cavities into a compact system.…”