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A variable mechanical optical attenuator

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A new design of a variable mechanical optical attenuator is proposed in this paper. Mechanical attenuators are extensively important in designing optical communication systems. It is also highly used in testing and training purposes. The design consists a novel fiber optic splitter-combiner setup. Each branch of the splitter meets a specific branch of the combiner. A fixed distanced multi-window rotary wheel slides between them. Upon rotation the light is either blocked or allowed to pass from a splitter branch to a combiner branch. By changing the number of open gates, the amount of yielded light can be controlled. There is only one moving part. So, the design is easy to manufacture, use or repair. The basic design and work flow is explained. The formula for calculating the attenuation and calibration guideline is also discussed. Then the design is compared with the other design standards based on the areas of application. The possible effects of linear and non-linear properties of light is also discussed. The primary concerns that should be taken if this design is to be fabricated in photonic integrated circuits is also mentioned briefly.
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  • 1. A variable mechanical optical attenuator Omar Shehab Department of Computer Science and Electrical Engineering University of Maryland, Baltimore County Baltimore, Maryland 21250 shehab1@umbc.edu April 23, 2012
  • 2. Optical attenuators Important component of an optical communication system. Typically used to preserve optical power for further tuning. Can be mechanical, optical, photonic, hybrid, electrical, MEMS, polymeric etc. Electronic and MEMS attenuators are very popular. Mechanical attenuators are extensively used in low price applications and for training purpose.Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 2 / 22
  • 3. Mechanical optical attenuator Light is typically absorbed by semi-reflecting die-electric substance. May have distributed variable refractive index. The substance may also work as reflector or absorber. Mirrors or shutters serve this purpose.Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 3 / 22
  • 4. Electronic optical attenuator Requires additional input power.Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 4 / 22
  • 5. Related works Mechanical attenuators Marxer, Griss, and de Rooij [1999]. Dai, Zhao, Cai, and Li [2002]. Yamashita, Kawada, , and Takeuchi [1985]. MEMS Sun, Noell, Zickar, Mughal, Perez, Riza, and de Rooij [2006]. Photonic crystal Stevenson, Martelli, Canning, Ashton, and Lyytikainen [2005]. Mathews, Farrell, and Semenova [2011]. Kerbage, Ging, Steinvurzel, Hale, Yablon, Windeler, and Eggleton [2002]. Wang and Heab [2006]. Ian, Steven, Xiaole, and Jun [2009]. FPGA Li, Jin, Zhang, and Zou [2006].Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 5 / 22
  • 6. Proposed schematicOmar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 6 / 22
  • 7. A new designA new design for a mechanically operated variable opticalattenuator: Uses the idea of a splitter-combiner (reverse coupler) set up. The design contains two wheels (one outer and the other is inner), GrIn lenses, a fiber splitter and a combiner. Reduce the incident optical power level at two phases. Can be implemented at low cost and may be fabricated at small scale. Traditionally used refraction principal is not used in the first phase of attenuation. The internal spaces are filled with properly chosen index matching fluid.Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 7 / 22
  • 8. How does it work?Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 8 / 22
  • 9. Step 1Light enters into the input channel of the fiber beam splitter. Thedesign proposes industry standard fiber coupling with the input forleast possible insertion loss.Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 9 / 22
  • 10. Step 2The outer windowed rotary wheel is moved one step anticlockwise.So the potential light path from the top most channel of thesplitter to the top most channel of the combiner is blocked. Lightincident along this path will be reflected and eventually absorbedinside the system.Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 10 / 22
  • 11. Step 3Light splits among and propagate through the splitter channels.The GrIn lenses at the windows of the outer wheel guide the lightto pass into the input channels of the combiner. The inputsurfaces of the combiner channels should be cut with appropriatetilt so that back propagation doesn’t occur.Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 11 / 22
  • 12. Step 4Light is combined at the output channel of the combiner and itthen pass through the transparent part of the inner wheel. Theinner wheel is rotated clockwise or anticlockwise to achieveappropriate second level attenuation according to the scale drawnon it. There is a little amount of insertion loss at this stage. As thetransparent wheel is concave the reflected light doesn’t interferewith the incoming signal which is along a straight optical path.Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 12 / 22
  • 13. Step 5A particular amount of light is reflected from the wheel and areduced amount of light comes out of the attenuator. This is theexpected output light.Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 13 / 22
  • 14. Interesting features The only part of the device which should meet the present industry standard is the connector. Doesn’t require any additional power input or regular supply of optical fluid. Not wavelength dependent.Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 14 / 22
  • 15. Characterization I If c is the number of closed splitter channels and t is the total number of splitter channels, the attenuation due to the movement of the rotary wheel, Astepwise , is: c Astepwise dB = 10Log10 t There will be an insertion loss, Alenses , when the light is coupled onto the combiner channels through the lenses. This loss is a function of the number of open splitter channels, (t - c).Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 15 / 22
  • 16. Characterization II The amount of attenuation at the final stage is determined by the transmission coefficient, T , of the transparent part of the inner wheel with graded refractive index. 4n1 n2 T = 2(n1 + n2 ) Here n1 and n2 are the refractive indices of two different mediums. So, the continuous loss due to the second inner wheel, Acontinuous , is: 2n1 n2 Acontinuous dB = 10Log10 T = 10Log10 n1 + n2Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 16 / 22
  • 17. Characterization III So, the total attenuation, Atotal , will be: Atotal dB = Astepwise + Alenses + Acontinuous This will also be the dynamic attenuation. So, the dynamic range of the proposed design, Adynamic , is: Adynamic dB = Astepwise + Alenses + AcontinuousOmar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 17 / 22
  • 18. Limitations It needs to be operated manually.Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 18 / 22
  • 19. Future plan Implement the whole design using 2D photonic crystals. Using MEMS to automate it.Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 19 / 22
  • 20. AcknowledgmentsO. S. likes to thank Professor Muhammed Zafar Iqbal, Dr.Muztaba Fuad and Professor Samuel J. Lomonaco Jr. for theirinsights and encouragement.Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 20 / 22
  • 21. Bibliography IXuhan Dai, Xiaolin Zhao, Bingchu Cai, and Wenjun Li. Characterization and development of micromachined variable optical attenuator. In Optical Communication, 2002. ECOC 2002. 28th European Conference on, pages 1–2, 2002.Lapsley Michael Ian, Lin Sz-Chin Steven, Mao Xiaole, and Huang Tony Jun. An in-plane, variable optical attenuator using a fluid-based tunable reflective interface. Applied Physics Letters, 95:083507–083507–3, 2009.C. Kerbage, J. Ging, P. Steinvurzel, A. Hale, A. Yablon, R.S. Windeler, and B.J. Eggleton. Air-silica microstructure fiber based variable optical attenuator device. In Optical Fiber Communication Conference and Exhibit, 2002. OFC 2002, pages 468–469, 2002.Sailu Li, Xiaofeng Jin, Xianmin Zhang, and Yingyin Kevin Zou. Digitally controlled programmable high-speed variable optical attenuator. Microwave and Optical Technology Letters, 48:10191021, 2006.Cornel Marxer, Patrick Griss, and Nicolaas F. de Rooij. A variable optical attenuator based on silicon micromechanics. Photonics Technology Letters, IEEE, 11:233–235, 1999.Sunish Mathews, Gerald Farrell, and Yuliya Semenova. Experimental demonstration of an all-fiber variable optical attenuator based on liquid crystal infiltrated photonic crystal fiber. Microwave and Optical Technology Letters, 53:539543, 2011.M. Stevenson, C. Martelli, J. Canning, B. Ashton, and K. Lyytikainen. Photonic crystal fibre optical attenuators. Electronics Letters, 41:1167–1169, 2005.Winston Sun, Wilfried Noell, Michael Zickar, M. Junaid Mughal, Frank Perez, Nabeel A. Riza, and Nicolaas F. de Rooij. Design, simulation, fabrication, and characterization of a digital variable optical attenuator. Microelectromechanical Systems, Journal of, 15:1190–1200, 2006.Qian Wang and Sailing Heab. Analysis and design of variable optical attenuators based on nematic liquid-crystal cells. Journal of Modern Optics, 53:481–493, 2006.Mikio Yamashita, Yasushi Kawada, , and Satoshi Takeuchi. Experimental demonstration of an all-fiber variable optical attenuator based on liquid crystal infiltrated photonic crystal fiber. Review of Scientific Instruments, 56: 478479, 1985.Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 21 / 22
  • 22. Questions?Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 22 / 22
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