It is well known that a fiber taper—an optical fiber whose size varies along its length—must exceed a certain minimum length to be adiabatic and low-loss. In contrast, we show that an optical fiber with a logarithmic refractive index profile can be adiabatically tapered over any length, however short. Its mode field distribution is independent of the fiber’s size and so remains the same along a taper. We report an experimental fiber in which tapers shorter than 2 mm can have losses as low as 0.03 dB. The fiber is compatible with standard telecoms fiber but with low bend loss and should have applications where it is desirable to make tapered fiber components (such as fused couplers and photonic lanterns) as short as possible. The index profile is analogous to the logarithmic potential of quantum mechanics.

中文翻译：

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环形绝热纤维，折射率分布为对数

众所周知，纤维锥度（其尺寸沿其长度变化的光纤）必须超过一定的最小长度，以达到绝热和低损耗的目的。相反，我们表明具有对数折射率分布的光纤可以在任何长度上都绝热地变细，尽管长度很短。它的模场分布与光纤的尺寸无关，因此沿锥度保持不变。我们报告了一种实验光纤，其中锥度小于2 mm的光纤损耗可低至0.03 dB。该光纤与标准电信光纤兼容，但弯曲损耗低，应在需要使锥形光纤组件（例如，熔融耦合器和光子灯笼）尽可能短的应用中使用。折射率分布类似于量子力学的对数势。