COMPUTER-aided design, or CAD, has been used by architects and engineers for years to design everything from spas to the Space Shuttle. A CAD program called SPICE, used to design integrated circuits, helped to fuel the ongoing revolution in integrated circuit technology that has formed the backbone of the information age. But the information age is changing. Now, many micro-electronic and micro-optic systems combine to form photonic devices, which manipulate light for control, communication, sensing, and information displays. Photonics systems have been found in Lawrence Livermore projects since the late 1980s. Future applications include a nonlinear optical waveguide that is being designed for use in the National Ignition Facility.
Photonic circuits using integrated and micro-optic devices are expected to form the basis of all future high-speed and wide-bandwidth communication systems, computers, and signal- and image-processing hardware. Design of photonics devices, while challenging, is very important because the devices are expensive and difficult to fabricate. Accurate computational simulation for both design and packaging (alignment of the very tiny parts that constitute photonic devices) will reduce costs considerably and remove a major barrier to widespread use of photonic systems.
A team at Lawrence Livermore has created a computer code to allow designers to quickly and accurately explore new photonics design and packaging approaches. The code eliminates tedious trial-and-error fabrication and reduces development cycle time and engineering costs by as much as 80%.
This new software can handle the design of photonics systems with widely disparate component scales, hence the name Multiscale ElectroDynamics, or MELD. No other photonics design software has this capability. Designed by a team that includes Richard Ratowsky, Jeffrey Kallman, Robert Deri, and Michael Pocha, MELD has the potential to revolutionize the design process for photonic devices
and packages.
MELD allows the user to construct a "virtual optical bench," shown in the monitor below, where photonics modules are placed. Each module treats a single photonics element and uses its own optical simulation algorithm. The code then provides for seamless interfaces, or links, between these algorithms, thus allowing simulation of the entire system. The links exchange information between modules, including accumulated transmitted and reflected optical fields. This system can be used for optically large structures such as waveguides, for optically small structures such as abrupt discontinuities in materials, or for optically mixed structures such as antireflection-coated lenses. MELD is written in object-oriented C++, a programming language that allows easy integration of new modules.





MELD's capabilities are valuable only if the resulting system is also accurate. MELD has already proved its accuracy at Hewlett-Packard Company Laboratories in Palo Alto, California, where it was validated for the design of ball lenses, devices that match the mode of a laser diode to a single-mode optical fiber. The HP Labs' microphotonics effort is aimed at developing packaging techniques for low-cost, fiber-optic components, and their researchers had found that traditional methods of calculating the coupling efficiency for a laser into a fiber through a ball lens were not accurate enough. The spherical aberration of the ball lens strongly influences the apparent focal length of the lens and the achievable coupling efficiency. It is also important for optical subassemblies to minimize the coupling of reflections back to the laser. MELD addresses both issues effectively. In fact, one of the HP Labs engineers has said that now when they find any discrepancy between the experimental results and the results indicated by MELD, they go back to check their experimental setup.
MELD has competitors already on the market, but none offers MELD's range of capabilities. Most can simulate optically large waveguiding structures, accurately treat aperture effects, and handle optically large components by ray tracing. MELD is unique in its ability to handle both large and small structures accurately; in particular, MELD invokes a true Maxwell equation solver when necessary. Maxwell's equations are a set of classical equations that govern the behavior of electromagnetic waves. When calculating radiation from small structures, the usual beam propagation techniques will not work, and an accurate calculation can be made only with a Maxwell solver. Solving Maxwell's equations is also needed for calculating reflections, a critical design factor for photonic systems. For example, reflections from ball lenses are often extremely small, but they can destabilize active devices such as laser diodes. MELD allows for the global calculation of reflections from a variety of elements.
The photonics component market today--in information and communications equipment, consumer electronics, and national security applications--amounts to about $15 billion annually worldwide. By sharply reducing development cycle time and nonrecurring engineering costs, MELD offers the potential to increase the U.S. share of this growing market. For uses related to national security, flexible manufacturing through accurate design is particularly crucial, given the small production runs in today's downsized defense industry. Saving time and money, regardless of the situation, is always advantageous.

--Katie Walter

Key Words: computer-aided design, fiber-optic communications, flexible manufacturing, photonics, R&D 100 Award.

For further information contact Richard Ratowsky (510) 423-3907 (ratowsky1@llnl.gov).


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