PURPOSE: To make a high-precision measurement possible by measuring the far field intensity distribution of optical waves radiated from a single mode fiber and obtaining a spot size in accordance with the near field intensity distribution which is calculated with Hankel transformation on a basis of this far field intensity distribution.
CONSTITUTION: A formula (3) is established when electric field distributions of the far field and the near field are denoted as F(θ) and R(r) respectively and k=2π/λ (λ: wavelength) is true and the Bessel function of 0 order is denoted as J0 and the angle of radiation is denoted as θ. That is, R(r) is obtained when F(θ) is obtained. Consequently, F(θ)2 of the far field intensity distribution is measured to obtain F(θ), and R(r) is obtained in accordance with the formula (3), and R(r)2 of the near field intensity distribution is obtained by calculation, and the spot size based on various definitions is obtained. The far field intensity distribution is measured in a range from the angle of radiation indicating a maximum value to the angle of radiation indicating a value lower than it by ≥25dB.
SUZUKI SHIYUUZOU
TOKUDA MASAMITSU
NIPPON TELEGRAPH & TELEPHONE
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