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我们知道基模模斑尺寸决定了单模光纤连接损耗和微弯损耗。Matsumura从理论上定义了等效阶跃折射率光纤。它和实际光纤在大于截止波长的任意波长上都有同样的模斑尺寸。他从理论上论证了等效阶跃折射率(ESI)光纤具有和实际光纤几乎同样的传播常数和弯曲损耗,而且模斑尺寸的测量可以很好地预知模色散。由模斑尺寸和ESI光纤也可确定后向散射特性。在这里我们以实验方面证实,按照VAL方法进行模斑尺寸的测量可以预知象弯曲损耗、后向散射特性和色散这类性能。对于仅用单模光纤的长距离高速率传输系统来说,最关心的是了介弯曲损耗、后向散射特性和色散。本文我们从实验上说明通过模斑尺寸的测量,可以以很高的精度预知这些特性。模斑尺寸ω_0定义为:在e~(-2)高斯型强度的光斑半径,高斯场可以最大效率地激励光纤中的HE_(11)模场。
We know that the fundamental mode spot size determines the single mode fiber connection loss and microbend loss. Matsumura theoretically defines the equivalent step index fiber. It has the same speckle size as an actual fiber at any wavelength greater than the cut-off wavelength. He demonstrated theoretically that equivalent-step-index (ESI) fibers have almost the same propagation constants and bending losses as real fibers, and that the measurement of spot size is a good predictor of modal dispersion. Backscatter properties can also be determined by spot size and ESI fiber. Here, we have experimentally confirmed that the measurement of the spot size according to the VAL method can predict properties such as bending loss, backscattering properties and dispersion. For long-distance, high-rate transmission systems that use single-mode fiber only, the most concern is bending loss, backscattering properties, and dispersion. In this paper, we experimentally demonstrate that these characteristics can be predicted with high accuracy through the measurement of the spot size. The spot size ω_0 is defined as the maximum of the HE_ (11) mode field in an optical fiber with a Gaussian field that can excite the Gaussian field with an e ~ (-2) intensity.