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 ± 3dB 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.

中文翻译：

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通过微尖接触锥形光纤实现可调谐光学带通滤波器

我们展示了一种基于锥形光纤 (TOF) 的可调带通滤光器，该光纤与半球形微纤维尖端 (MFT) 接触。除了干涉和选择性材料吸收效应外，滤光片还依赖于 TOF 中可控且与波长相关的模式-模式相互作用。在实验上，通过控制 MFT 与不同 TOF 半径的 TOF 接触的位置来实现大范围的可调性，并演示了两种不同的带通滤波器机制。带通滤波器的中心波长可在 890 nm 至 1000 nm 范围内调谐，而当 MFT 在 160 nm 至 390 nm 半径范围内接触 TOF 时，FWHM 带宽可在 110 nm 至 240 nm 范围内调谐。实验分辨比可达28±3dB。