IMA Workshop: Analysis and Modeling of Optical Devices 9/9/99C. Haggans 1 Application of Optical Simulations from the Perspective of a Device and Module

IMA Workshop: Analysis and Modeling of Optical Devices 9/9/99 C. Haggans1

Application of Optical Simulations from the Perspectiveof a Device and Module Designer

Charles HaggansPhotonic Technologies

CIENA CorporationLinthicum, MD

9/9/99


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


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


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


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


Application of Design Simulations

Characterization of input material properties

develop and apply characterization techniques

Configuration/development of fabrication process

develop and apply repeatable fabrication process (fabricate devices)

Device performance simulation

develop and exercise simulation

Characterization of fabricated device structure

develop and apply characterization techniques

Measured device performance

develop and apply measurement techniques

Simulation Validation

Design Generation


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?


Outline



– examples• free-space (optical disk surface structure design)

• waveguide (photosensitive fiber and fiber Bragg grating design)



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)



• 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).



Field Distribution(in far field)

Focused Spot

Information Surface (with thin films)

Simulation Space

Input Aperture

S1 S2

Simulated Split Detectors

SubstrateMedium

Fig. 6

x

z

TruncationBoundary

Sampling Plane

FocalPlane

Source Boundary

Total FieldRegion

ScatteredField Region

Fig. 7

Simulation Approach



Computational Experimentaltreats 3D problem geometry with2D simulation

limited AFM lateral resolution(limited accuracy on surfacetopography profiles)

neglects top surface of substrate spot size measurementassumes unaberrated focused spot thin film thicknesses and

refractive indicesneglects diffractive effects inbeam path after objective

spinstand calibration (detectorbalancing and sum zero levelinaccuracies)finite detector split width

Sources of Error in Simulation Validation


Outline







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)



• 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



• 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)


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Impact of fiber type on cladding-mode coupling

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Photosensitive Clad Narrow Depressed-Clad

Increasing Azimuthal Asymmetry (grating tilt)


Band rejection filter (tilted fiber grating)with low backreflection

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Challenges for realizing computational design in fabricated grating

• Fiber characterization• Photoinduced index change features and

characterization


Outline







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


Future needs for modeling and analysis of optical devices

• low cost, high reliability switches• reconfigurable/tunable filters• compensation for system impairments


Conclusion

• Reviewed challenges for cost-effective utilization of optical simulations in a device and module development environment


– 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

Documents

IMA Workshop: Analysis and Modeling of Optical Devices 9/9/99C. Haggans 1 Application of Optical Simulations from the Perspective of a Device and Module