Low Loss Waveguide Optical Switching

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					                                                               Low Loss Waveguide Optical Switching
                                              Adam Jones, Emre Araci, Robert A. Norwood, and Nasser Peyghambarian, College of Optical Sciences, University of Arizona
                                                                                                                                           Thrust 3

      The massive migration of computing and data storage to a relatively small number of increasingly large data centers presents a growing need to manipulate massive data flows (WGI); creating an
      opportunity for optical switching. Current technologies typically use MEMS or thermo-optic switches with response times on the order of milliseconds, which could represent a bottleneck for next generation
      data centers. At the same there is an increasing need for fast optical switching in the aggregation and access parts of the network (WGII). Electro-optic (EO) polymers have been widely used for
      modulation and even switching on a small scale (2 x 2), but the incorporation of such devices commercially has been limited by the high insertion loss of the devices using such materials. EO polymers are
      attractive due to significantly improved nonlinear electro-optic coefficients (r33 > 150 pm/V demonstrated), low dielectric constants, which allows for higher bandwidth, and the potential for economies of
      scale. Our group has developed several innovations in hybrid electro-optic modulators, which we will be able to leverage in the development of state of the art optical switches with record bandwidth, optical
      loss and energy efficiency. Via unique passive materials such as sol-gels and ion exchange glass, intelligent design of passive coupling regions and low loss transitions, our team currently has the
      fabrication tools and expertise to overcome the primary barrier to commercial integration of EO polymer technologies, namely, optical loss.

     Project Description and Impact                                        Current State of the Art and Predicted Competitive Advantage                                                                                Accomplishments & Future Directions
     on CIAN’s Strategic Research Plan                                                                                                                                                                                Hybrid Sol-Gel/EO Polymer Modulators
                                                                        Current State of the Art – Glimmerglass Networks, Inc.                                                                                        • Record low insertion loss
• As cloud computing increases in prevalence, higher bandwidth
                                                                                              • Use MEMS micromirrors to provide millisecond optical switching                                                          phase modulator at 5.7 dB
  switching will be required to maintain functional communications
                                                                                              • Provides a full nonblocking, transparent crossconnect                                                                 • Record low V Mach Zehnder
  networks within data centers. This is of vital importance to                                                                                                                                                                              5 mm
                                                                                              • From 16x16 to 192x192 fiber formats available                                                                           modulator at 0.65 V
  Working Group 1 – Scalable Energy Efficient Data Centers.
                                                                                              • Insertion loss of 2 dB                                                                                                • Record high in device poling
•This project supports WG II – Optimized Access Networks by                                                                                                                                                                        6 mm
                                                                                                                                                                                                                        efficiency with r33 = 170 pm/V
providing a flexible high speed gateway between the core network
and edge nodes, which facilitates access/aggregation and cross-layer    Comparison to Commercially Available Technology
communications.                                                                                                                                                                                                       Hybrid Ion Exchange Glass/EO polymer modulators
                                                                         • Significantly improved switching speeds (ns vs. ms).                                                                                      • Less than 1 dB coupling loss
            2x2 Directional Coupler Switch                               • Use of EO polymer provides superior EO activity, which yields more efficient switching (lower voltage)                                    • Ultralow propagation loss in Ag+
                                                                         • Incorporation of PMMA-like materials provides a cost effective solution                                                                     diffused waveguides at 0.1 dB/cm
                                                                         • All wet process simplifies fabrication and improves throughput                                                                            • 4dB insertion loss demonstrated in
                                                                         •Optical loss is the primary drawback of this technology, but this is mitigated through intelligent device                                    a device with 1 cm active length
                                                                         design and high quality fabrication                                                                                                         • Alignment free fabrication process
• Provides a low loss 4x4 rearrangeably nonblocking switch matrix via
                                                                                                                                                                                                                     • Represents 3dB improvement over
six 2x2 full nonblocking directional coupler switches                   Predicted Optical Loss                                                                                                                          the state-of-the-art (Gigoptix)
• Switching speeds >100GHz possible.
• Low loss 2x2 switching units can be used in more complicated                               Loss Mechanism                   Predicted                       Device Parameter

switch matrices of higher order
                                                                                                                                 Loss               Passive Length                              0.5 cm                 Future Work
                                                                                  Coupling Loss                              0.5 to 1 dB            Active Length                           0.25 to 0.4 cm
                                                                                  Absorption limited loss – passive region 0.3 dB/cm                Number of Transitions – 2X2 Switch             2
                                                                                                                                                                                                                    • Optimize passive waveguide parameters to minimize coupling loss
             Candidate 4X4 Switch Matrix                                          Absorption limited loss – active region      2 dB/cm              Number of Transitions – 4X4 Switch             2
                                                                                                                                                                                                                    • Fabricate a low loss 2X2 switch and 4X4 switch matrix
                                                                                  Excess loss – directional coupler             0.1 dB              Total Expected Loss – 2X2 Switch        2.25 to 2.95 dB         • Test the devices under high bandwidth operation
                                                                                  Excess loss – active to passive transition    0.1 dB              Total Expected Loss – 4X4 Switch              4 dB              • Incorporate the device in the testbed at UCSD to provide ultrafast
                                                                                                                                                                                                                       switching in data center applications
                                                                                                                                                                                                                    •Extend the design to higher order switching fabrics (8X8, 16X16, etc.)
                                                                                 Fabricated Passive Waveguide                                       Directional Coupler in PMMA
                                                                                                                              DUV defined                                                                                 References and Acknowledgements
                                                                                                                              waveguide                                                           0.5 micron
                                                                                              Sol-gel                                                                                             waveguide             1.   Nature Photonics 1, 180 (2007)
                                                                                                                                                                                                  separation            2.   Y. Enami et al., APL 91, 093505 (2008)
                                                                                              PMMA                                                                                                                      3.   C. DeRose, Opt. Exp. 17, 3317 (2009)
                                                                                                                                                                                                                        *    The authors would like to acknowledge support from the
                                                                                                                                                                                                                             National Science Foundation through CIAN NSF ERC under
                                                                                                                                                                                                                             grant # EEC-0812072

                                                                                The authors would like to acknowledge support from the National Science Foundation through CIAN NSF ERC under grant #EEC-0812072.

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