多模模態轉換器之耦合模擬研究

Simulation Study of Multimode Mode Converter Coupling

林柏鑑(Bo-Chien Lin)

《大漢學報》 24期 (2009/12) Pp. 15-31

https://doi.org/10.29704/JDIT.200912.0002

摘要

百億級多模光纖以太高速區域網路之訊號係在850 nm波長頻道作傳輸。而所使用之850nm光發射器係為面射型的雷射二極體。由於面射型雷射之光功率輸出模態分佈與多模光纖之波導模態分佈可能不同，且多模光纖因製程中折射率分佈之缺陷因素不一及光纖與雷射耦合時之偏差，而造成彼此間光耦合效率產生不小的變動。而此將致使訊號輸出之光功率變動大及模態間相互干擾所產生之模態間雜訊的現象，此將對高速區域網路之訊號輸出品質造成重大的影響。本文由模擬的角度來探討模態耦合效率之計算及模態調整轉換跳接線對耦合效率的影響。
利用模態耦合理論(Couple-Mode Theory)搭配多模光纖之折射率分佈指數(Alpha)、多模模態調整轉換跳接線之折射率分佈指數(Alpha)及面射型雷射之模態分佈，作為模擬計算依據，並利用OptSim模擬軟體來模擬850nm面射型雷射與50μm多模光纖之光輸出耦合情形。
實際模擬結果顯示，多模光纖與模態轉換跳接線之折射率分佈指數(Alpha)值兩者之差異及光纖連接適配器(adaptor)之橫截面X或Y方向偏移對有使用模態轉換跳接線(mode conditioning patchcord, MCP)的耦合光功率輸出分佈之影響最大，而光纖連接適配器之連接角度的偏差則會影響到耦合後的模態分佈。

關鍵字

百億級多模光纖以太高速網路 ； 面射型雷射二極體 ； 光耦合效率 ； 模態間雜訊 ； 模態耦合理論

並列摘要

The signal transmission in the 10 Gigabit Multimode Ethernet Local Area Optical Network is working at 850 nm wavelength channel. The 850 nm transceiver is now using the Vertical Cavity Surface Emitted Laser (VCSEL). The modal output optical power distribution of VCSEL is different from that of a multimode fiber. Variation of refractive index profile of a multimode fiber during fabrication and deviation of optical power coupling will cause large variation of coupling efficiency between VCSEL and multimode fiber. Thus it will make the signal output optical power fluctuation which will induce modal interference and modal noise. This behavior will degrade the transmission quality of high speed multimode optical local area networks.
In this study, we used the couple-mode theory for the simulation. We select the profile index (Alpha value) of multimode fiber, profile index (Alpha value) of mode conditioning patch cord and VCSEL output power as parameters for the simulation. The influence of using mode conditioning patch cord to the modal noise and modal coupling efficiency is showed. Rsoft OptSim is used to simulate the coupling for 850 nm VCSEL and 50 μm multimode fibers in a 10 Gigabit Ethernet Multimode Optical Local Area Network layout.
Results qualitatively showed two key factors for the fluctuation of coupling optical output power which are the profile index difference (Δ α) between multimode fiber and mode conditioning patchcord and the X (or Y) offset of adaptor between the multimode fiber and MCP patchcord. The alignment angle variation of adaptor will cause the modal power variation mostly.

並列關鍵字

Multimode 10 Gigabit Ethernet Optical Local Area Network ； Vertical Cavity Surface Emitted Laser VCSEL ； Coupling Efficiency ； Modal Noise ； Couple-Mode Theory