Propagating beam analysis of fiber wavelength filters with a depressed-index section |
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Authors: | Junji Yamauchi Takashi Ando Yasuhiro Akimoto Hisamatsu Nakano |
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Institution: |
a College of Engineering Hosei University, Tokyo, Japan |
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Abstract: | A wavelength filter consisting of single-mode and few-mode fibers is investigated numerically. A simple finite-difference beam-propagation method, in which a transparent boundary condition can be imposed, is developed for circularly symmetric waveguides. After confirming the validity of the numerical method by the mode-mismatch loss, we calculate the propagating field in the fiber wavelength filter, in which interference between LP01, and LP02 modes occurs. To improve the filtering operation, a depressed-index fiber is employed for the few-mode fiber. The effects of the radius and refractive index of the depressed section on the transmission power are revealed and discussed. Power is suppressed to less than 0.1% at 1.3 μm, while maintaining power transmission of more than 85% at 1.55 μm. It is also found that the filtering operation shifts to higher wavelengths as the input power is increased when we choose a self-focusing nonlinear material in the depressed section. |
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Keywords: | circularly symmetric geometry depressed-index section fiber wavelength filter finite-difference beam-propagation method |
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