Optical Simulations for Device and Module Design

1. Application of Optical Simulations from the Perspective of a Device and Module Designer Charles Haggans Photonic Technologies CIENA Corporation Linthicum, MD 9/9/99

2. Outline • Review challenges for cost-effective utilization of optical simulations in a device and module development environment • observations on efficient use • examples • optical disk surface structure design • photosensitive fiber and fiber Bragg grating design • Discuss future needs for modeling and analysis of optical devices in optical communication systems

3. What makes a problem attractive for simulation in an industrial setting? (1) • Understanding desired for process where empirical studies are expensive or impossible • Ideally, it should be possible to obtain an optimized design at a fraction of the cost of an empirical optimization (designed experiment) • Performance measurement, material characterization, and fabrication infrastructure in place to validate simulation and prove knowledge gained through exercise of simulation • Development efforts utilizing simulations may involve fabrication processes that are not well characterized

4. What makes a problem attractive for simulation in an industrial setting? (2) • Simulation applied to core area of business • Relatively long time scale to complete, demonstrate utility • timeframe of many months vs. few months • tool for design of family of components vs. single component • Opportunity to provide strategic advantage

5. Some observations for successful simulation application in an industrial environment • Simulation development is closely tied to simulation validation • Simulation developers understand measurements (and preferably make some measurements) • Simulation developers are part of product/technology development team, so that changes in program direction are seamlessly communicated • Simulation developers have some priority in receiving test resources, validation experiments, and feedback with respect to program direction

6. Application of Design Simulations Characterization of input material properties develop and apply characterization techniques Device performance simulation develop and exercise simulation Simulation Validation Design Generation Measured device performance develop and apply measurement techniques Configuration/development of fabrication process develop and apply repeatable fabrication process (fabricate devices) Characterization of fabricated device structure develop and apply characterization techniques

7. Pitfalls in application of simulations • Are you solving the right problem? (has the problem been defined correctly?) • Can the “knobs” that you are including in the simulation be “turned” in the manufacturing process in a controlled manner?

8. Outline • Review challenges for cost-effective utilization of optical simulations in a device and module development environment • observations on efficient use • examples • free-space (optical disk surface structure design) • waveguide (photosensitive fiber and fiber Bragg grating design) • Discuss future needs for modeling and analysis of optical devices in optical communication systems

9. Example 1:Optical disk surface structure design • Problem: Design surface structure for optimized tracking signal • Motivation: Constantly evolving formats, inefficiency and expense of empirical disk design • State-of-the-art at start of project: Scalar diffraction for focused beams, vector plane-wave diffraction for periodic diffractive structures • Objective: Simulate head-medium interface (focused beam interacting with structured surface coated with absorbing materials)

10. Example 1:Optical disk surface structure design • Simulation approach: hybrid FDTD • Collaborators: Rick Ziolkowski, Justin Judkins (University of Arizona), Jim Kwiecien, Paul Mallak, Chad Sandstrom, Todd Ethen, Tim Badar (3M Company/Imation) • Results summarized in Applied Optics, 10, p. 2477-2487 (1996).

11. Example 1:Optical disk surface structure design Simulation Approach

12. Example 1:Optical disk surface structure design Sources of Error in Simulation Validation

13. Outline • Review challenges for cost-effective utilization of optical simulations in a device and module development environment • observations on efficient use • examples • optical disk surface structure design • photosensitive fiber and fiber Bragg grating design • Discuss future needs for modeling and analysis of optical devices in optical communication systems

14. Example 2: Photosensitive fiber and fiber Bragg grating design • Problem: Develop photosensitive fiber and fiber Bragg grating design tool • Application: Generate fiber designs for reduced cladding-mode coupling, increase applicability of Bragg gratings as narrow-band filters • Following results summarized in: • Journal of Lightwave Technology, 16, 902-909 (1998) • IEEE Photonic Technology Letters, 10, 690-692 (1998)

15. Example 2: Photosensitive fiber and fiber Bragg grating design • Initial result: gave filter design capability for fundamental-to-fundamental mode coupling • Secondary result: gave tool for investigating undesirable out-of-band spectral structure (cladding mode coupling) • Strategic result: utilized tool to explore parameter space for novel designs

16. Example 2: Photosensitive fiber and fiber Bragg grating design • Simulation approach: Coupled-mode theory with solution of fiber modes under weakly-guiding approximation • Collaborators: Jim Onstott, Wayne Varner, Harmeet Singh, Trevor MacDougall, Ed Dowd, Alessandra Chiareli (3M Company)

17. Impact of fiber type on cladding-mode coupling Conventional Matched-Clad Photosensitive Clad Narrow Depressed-Clad Increasing Azimuthal Asymmetry (grating tilt)

18. Band rejection filter (tilted fiber grating)with low backreflection

19. Challenges for realizing computational design in fabricated grating • Fiber characterization • Photoinduced index change features and characterization

20. Outline • Review challenges for cost-effective utilization of optical simulations in a device and module development environment • observations on efficient use • examples • optical disk surface structure design • photosensitive fiber and fiber Bragg grating design • Discuss future needs for modeling and analysis of optical devices in optical communication systems

21. Evolution of modeling and analysis of optical devices • Standard capability: Amplitude and phase response vs. device geometry for chosen material set • Advanced capability: response vs. temperature, polarization, material properties, mechanical deformation • Assessment of long-term device reliability • Design optimization for cost reduction, manufacturability, streamlining design process

22. Future needs for modeling and analysis of optical devices • low cost, high reliability switches • reconfigurable/tunable filters • compensation for system impairments

23. Conclusion • Reviewed challenges for cost-effective utilization of optical simulations in a device and module development environment • observations on efficient use • examples • free-space (optical disk surface structure design) • waveguide (photosensitive fiber and fiber Bragg grating design) • Discussed future needs for modeling and analysis of optical devices in optical communication systems