Demonstration of a Microfiber-Based Add–Drop Filter Using One Tapered Fiber

We propose a novel approach to demonstrate an add-drop filter based on microfiber knot resonator (MFKR). The two coupled regions and four ports (including input port, through port, drop port, and add port) of this device are formed using the same one microfiber. By reconnecting the ends of the through and add ports with other two microfibers, this structure could serve as an add-drop filter, which is a key building block in the fields of optical networks and optical information processing system. The MFKR-based add-drop filter with the quality factor (Q-factor) of 21 000 and a diameter of 740 μm is demonstrated successfully. The intrinsic loss and extinction ratio are about -2 and 18.5 dB for the drop port, and -4.6 and 10.7 dB for the through port, respectively. The fabrication process also shows the feasibility and simplicity of this device.