Tunable Optical Bandpass Filter via a Microtip-Touched Tapered Optical Fiber
Peng-Fei Zhang1,2*, Li-Jun Song1, Chang-Lin Zou3,1*, Xin Wang1, Chen-Xi Wang1, Gang Li1,2, and Tian-Cai Zhang1,2
1State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China 2Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China 3CAS Key Laboratory of Quantum Information, University of Science and Technology of China, Hefei 230026, China
Abstract：We demonstrate a tunable bandpass optical filter based on a tapered optical fiber (TOF) touched by a hemispherical microfiber tip (MFT). Other than the interference and selective material absorption effects, the filter relies on the controllable and wavelength-dependent mode–mode interactions in TOF. Experimentally, a large range of tunability is realized by controlling the position of the MFT in contact with the TOF for various TOF radii, and two distinct bandpass filter mechanisms are demonstrated. The center wavelength of the bandpass filter can be tuned from 890 nm to 1000 nm, while the FWHM bandwidth can be tuned from 110 nm to 240 nm when the MFT touches the TOF in the radius range from 160 nm to 390 nm. The distinction ratio can reach $28 \pm 3$ dB experimentally. The combined TOF-MFT is an in-line tunable bandpass optical filter that has great application potential in optical networks and spectroscopy, and the principle could also be generalized to other integrated photonic devices.
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2020, Vol. 37 
