We determine the fundamental limit of microresonator field uniformity. It can be achieved in a specially designed microresonator, called a bat microresonator, fabricated at the optical fiber surface. We show that the relative nonuniformity of an eigenmode amplitude along the axial length L of an ideal bat microresonator cannot be smaller than 31 π 2 n4 λ−4 Q−2 L4, where n, λ, and Q are its refractive index, eigenmode wavelength, and Q-factor, respectively. For a silica microresonator with Q = 108, this eigenmode has axial speed ∼ 10−4 c, where c is the speed of light in vacuum, and its nonuniformity along length L = 100 µm at wavelength λ = 1.5 µm is ∼ 10−7. For a realistic fiber with diameter 100 µm and surface roughness 0.2 nm, the smallest eigenmode nonuniformity is ∼ 0.0003. As an application, we consider a bat microresonator evanescently coupled to high Q-factor silica microspheres, which serves as a reference supporting ultraprecise straight-line translation.
|Number of pages||4|
|Early online date||4 Mar 2021|
|Publication status||Published - 23 Mar 2021|
Bibliographical noteFunding Information:
Wolfson Foundation (22069); Engineering and Physical Sciences Research Council (EP/P006183/1).
This paper was published in Optics Letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: https://doi.org/10.1364/OL.422053. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.