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Nano-optical solver offers rapid solution

16 Jun 2006

German firm JCMwave, a Zuse Institute Berlin spin-off, has come up with optical software that can model electromagnetic wave propagation on a laptop, solving Maxwell's equations and offering solutions in just 10 s. James Tyrrell learns more about the company that has grabbed the attention of Infineon Technologies and Siemens.

Rigorous simulation of electromagnetic wave propagation can conjure up images of a suite of PCs humming away in an air-conditioned lab, but not if you are running JCMwave's nano-optical software. The German spin-off's powerful light scattering and light propagation algorithms can run on a laptop and deliver accurate solutions within a few seconds. Component optimization rounds that previously took days, weeks or even months, can now be performed in just a matter of hours.

Developed to solve electromagnetic problems, JCMwave's software has a wide range of applications from the design of photonic crystal fibre through to microwave and radar technology. However, it especially suits nano-optics, where structures are smaller than the wavelength of light.

"For macroscopic systems such as binocular lenses, you might use Gaussian optics or ray tracing, but all of these approximations fail when the feature sizes are very small," Sven Burger, JCMwave's research director told OLE. "Our finite element technique is well suited for all electromagnetic problems where small features play a role."

The finite element method can handle complex geometries, as found in integrated optics, isolated features including a single nano-aperture in a metal film or periodic problems such as photonic crystals and diffraction gratings. The technique is the result of years of research and development at Zuse Institute Berlin (ZIB).

Keen to realize the software's commercial potential, ZIB scientists and industry partners from Infineon Technologies and Siemens founded JCMwave in 2001. The spin-off takes its name from the initials of Scottish physicist, James Clerk Maxwell, and with good reason. Maxwell's famous electromagnetic wave equations form the heart of JCMwave's simulation tools and are solved without approximation.

"You don't need to have a farm of supercomputers," said Burger. "We have very fast solvers that allow calculations to be performed on normal computers." The standalone package is based on mathematical concepts developed at ZIB and works with Windows, Linux or Unix operating systems. "It's a tool that can be used by everybody, even on a laptop," he added.

How it works

Once the user has chosen the domain and boundary conditions, the package sub-divides the geometry into triangles and determines the associated electric and magnetic fields using a fast matrix equation solver.

It turns out that the group's finite element method of modelling the light field is incredibly efficient in terms of computing power. This is thanks to a so-called adaptive grid refinement routine, which is steered by an error estimator to apply the computing power where it is needed most. As Burger explains, this non-uniform grid approach allows users to handle multiscale structures or arbitrary geometries and is particularly useful when modelling discontinuities in the refractive index distribution.

The team compared its fast solver software with other competing packages including MIT's MPB solver, which is based on a plane-wave method. "For a target accuracy of 10-2 we have a speed advantage of about 1000 versus other methods that are used within the industry," said Burger. "This means that we can obtain a solution within a few seconds as opposed to a few hours, which is really significant for many users." Alternatively, Burger says that the high-speed JCMwave software can be used to obtain accuracies that are simply impossible for other packages to achieve, making it an attractive design tool.

JCMwave's rigorous simulation software owes a great deal to its strong link with ZIB and the depth of knowledge that this co-operation provides. Researchers at the 150 person-strong, Berlin-based centre for applied mathematics have been working on electromagnetic simulation for more than 20 years. What's more, JCMwave is in a position to build on this, offering not just software, but also a consultancy service to its customers.

Industrial applications

One example is JCMwave's collaboration with German chip maker Infineon Technologies, to improve light propagation through phase masks. "For Infineon, the goal is to develop phase masks that can produce clearer images in the photoresist and sharper contrast in order to shrink the chip's critical dimensions," explained Burger. "This leads to smaller computer chips in the end."

Burger acknowledges that modelling is only one of the many steps in the chip development chain. However, with semiconductor firms placing more and more emphasis on computer simulation to save both time and money, JCMwave could well find itself in the right place at the right time.

"The masks have dimensions that are smaller than the wavelength of light, contain sharp edges and display a strong contrast between the metal and surrounding air," said Burger. "If you want to solve Maxwell's equations for such a situation then it is a big advantage to use our adaptive methods, which lead to a very fast convergence of the algorithm and need little memory requirements."

It's not just Infineon that has turned to JCMwave for advice. "The European Southern Observatory (ESO) in Chile was looking for a glass fibre that transports light at very high power and with very low losses to operate its adaptive optics system," revealed Burger. "They were interested in designing a hollow core photonic crystal fibre with very small air tubes along the fibre direction and nanometre scale struts in between."

As Burger explains, previously it could take up to a whole day to calculate a given mode for a single design. "If you want to optimize the thickness of the fibre core for example, it might take months," he added. "Now, with the finite elements that we use, you can optimize the design within an hour."

With some successful projects already under its belt, JCMwave has ambitions to expand into antennas, mobile phone technology and waveguides. "At the moment our largest field is nano-optics and lithography, but the software is a simulation tool for electromagnetics, so we can also handle micro-wave or radar problems," he concluded.

JCMwave presented this work at Laser Optik Berlin, which took place in Germany on 23-24 March.

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