lab8 - ECE 415 EXPERIMENT NO 8 FEW-MODE FIBERS PURPOSE To...

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2/28/2011 10-1 ECE 415 EXPERIMENT NO. 8 FEW-MODE FIBERS PURPOSE : To excite and identify the low-order LP modes in weakly guided few-mode fibers experimentally. REFERENCES : 1. C. L. Chen, , Irwin, (1996), Chapter 8. 2. Yeh, C., "Guided waves modes in cylindrical optical fibers," IEEE Trans. on Education , Vol. E-30, pp. 43-51, (1987). 3. Gloge, D., "Weakly guided fibers," Appl. Opt ., Vol. 10, pp. 2252-2258, (1971). 4. Okoshi, T., Optical Fibers , Academic Press, Inc., New York, (1982). PROCEDURES : Assume the fiber used in the experiment has V= 4.00. Use Ref. [1] to determine the expected LP modes supported by the fiber, and the radiant intensity distribution of the LP modes. See, for example, p. 452 of Ref. [1]. It is usually very difficult to excite one and only one mode. The pattern you observe may in fact be a combination of several LP modes. The only exception is the LP 01 mode. (Why?) 1. Arrange your setup as shown in Figure 1. Use a linearly polarized HeNe laser and a 20X (or 40X) objective to couple light into the few-mode fiber. Verify that the beam entering the fiber coupler is linearly polarized. (How?) Measure the power of the polarized beam before coupling it into the fiber. HeNe laser NDF (if nec.) Linear polarizer Half-wave plate Fiber Linear polarizer Screen Figure 1 Setup to observe mode patterns 2. Try to align the fiber axis exactly along the light beam to excite only the lowest order mode (or low-order modes). The output radiant intensity pattern should appear
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lab8 - ECE 415 EXPERIMENT NO 8 FEW-MODE FIBERS PURPOSE To...

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