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
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
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
Electronic optical attenuator Requires additional input power. Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 4 / 22
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
Proposed schematic Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 6 / 22
A new design A new design for a mechanically operated variable optical attenuator: 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
How does it work? Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 8 / 22
Step 1 Light enters into the input channel of the fiber beam splitter. The design proposes industry standard fiber coupling with the input for least possible insertion loss. Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 9 / 22
Step 2 The outer windowed rotary wheel is moved one step anticlockwise. So the potential light path from the top most channel of the splitter to the top most channel of the combiner is blocked. Light incident along this path will be reflected and eventually absorbed inside the system. Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 10 / 22
Step 3 Light splits among and propagate through the splitter channels. The GrIn lenses at the windows of the outer wheel guide the light to pass into the input channels of the combiner. The input surfaces of the combiner channels should be cut with appropriate tilt so that back propagation doesn’t occur. Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 11 / 22
Step 4 Light is combined at the output channel of the combiner and it then pass through the transparent part of the inner wheel. The inner wheel is rotated clockwise or anticlockwise to achieve appropriate second level attenuation according to the scale drawn on it. There is a little amount of insertion loss at this stage. As the transparent wheel is concave the reflected light doesn’t interfere with the incoming signal which is along a straight optical path. Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 12 / 22
Step 5 A particular amount of light is reflected from the wheel and a reduced amount of light comes out of the attenuator. This is the expected output light. Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 13 / 22
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
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, A stepwise , is: c A stepwise dB = 10 Log 10 t There will be an insertion loss, A lenses , 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
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. 4 n 1 n 2 T = 2( n 1 + n 2 ) Here n 1 and n 2 are the refractive indices of two different mediums. So, the continuous loss due to the second inner wheel, A continuous , is: 2 n 1 n 2 A continuous dB = 10 Log 10 T = 10 Log 10 n 1 + n 2 Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 16 / 22
Characterization III So, the total attenuation, A total , will be: A total dB = A stepwise + A lenses + A continuous This will also be the dynamic attenuation. So, the dynamic range of the proposed design, A dynamic , is: A dynamic dB = A stepwise + A lenses + A continuous Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 17 / 22
Limitations It needs to be operated manually. Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 18 / 22
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
Acknowledgments O. S. likes to thank Professor Muhammed Zafar Iqbal, Dr. Muztaba Fuad and Professor Samuel J. Lomonaco Jr. for their insights and encouragement. Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 20 / 22
Bibliography I Xuhan 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
Questions? Omar Shehab (UMBC) A variable mechanical optical attenuator April 23, 2012 22 / 22
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