1. Eliminating Intermodal Dispersion in Multimode Fiber Using Adaptive Optics EE230 David Fryauf 11/29/11

2. Source of MMF disadvantages is Intermodal Dispersion…. Can it be eliminated? Single Mode FibersMulti Mode Fibers Higher quality Higher bit rate Longer distances Intramodal dispersion $$$$$ (Expensive) More hardware $ (Cheap) Cheaper hardware Lower quality Lower bit rate Shorter distances Intermodal + Intramodal dispersion

3. Adaptive Optics (AO) Correct aberrations in the light path between our target and our sensor (eye, camera …). Includes target, sensor, and the path medium between

4. Examples of Aberrations Look at an object across a hot desert or at a penny at the bottom of a pool. They appear to dance and are distorted. Short exposures show a stable but distorted image. Longer exposures show a blurred image because not only was the image distorted, but it was moving

5. How Does it Work?

7. MEMS Deformable Mirrors (DM)

8. Application in Fiber Optics Spatial Light Modulator (SLM) is the Deformable Mirror (DM) used to correct aberrations from the transmission side Intersymbol Interference (ISI) is detected by measuring how open they “eye” is from zero-to-one bit amplitudes

9. Signal Detection Methods Different from classical AO detection Classical AO detects 2D spatial offset Fiber Optics AO detects time offset Use time offset data to modify SLM reflectance function, measure eye opening to determine effectiveness I out = I in (t)*h(t)

11. Higher resolution SLM allows for only phase modification with no amplitude change – easier and cheaper for SLMs

12. Initial SLM solution still allows higher order modes to propogate, so intermodal dispersion is not completely mitigated But, this also allows lower order modes to have higher power Further limiting the higher order modes creates a clean eye, but less open overall So, higher order modes are acceptable

13. Frequency Dependence of AO Optimize SLM for a fixed system, then change input frequency Modal dispersion is still corrected over extended bandwidth AO-corrected MMF can transmit multiple signals

14. References Xiling Shen, Joseph M. Kahn, and Mark A. Horowitz, "Compensation for multimode fiber dispersion by adaptive optics," Opt. Lett. 30, 2985-2987 (2005) http://www.opticsinfobase.org/abstract.cfm?URI=ol-30-22-2985 http://www.opticsinfobase.org/abstract.cfm?URI=ol-30-22-2985 Panicker, R.A.; Wilde, J.P.; Kahn, J.M.; Welch, D.F.; Lyubomirsky, I.;, "10 × 10 Gb/s DWDM Transmission Through 2.2-km Multimode Fiber Using Adaptive Optics," Photonics Technology Letters, IEEE, vol.19, no.15, pp.1154-1156, Aug.1, 2007 doi: 10.1109/LPT.2007.901437 URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=426 7735&isnumber=4265641http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=426 7735&isnumber=4265641 Panicker, R.A.; Kahn, J.M.; Boyd, S.P.;, "Compensation of Multimode Fiber Dispersion Using Adaptive Optics via Convex Optimization," Lightwave Technology, Journal of, vol.26, no.10, pp.1295- 1303, May15, 2008 doi: 10.1109/JLT.2008.917324 URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=449 8396&isnumber=4542899http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=449 8396&isnumber=4542899

15. Thanks!