A passive alignment method offers an easy solution for fabricating integrated photonic circuits

November 17, 2011
Schematic of the circuits. Spherical microlenses (blue) self-assemble in optical through-holes (white). Electronic circuits (green) can easily be bonded and aligned on top of the lenses. Copyright : A*STAR

The rise of computers in past decades was made possible largely thanks to the invention of the integrated circuit, a device that combines all necessary electronic components onto a single chip. In a similar vein, the success of optical computing is largely dependent on the possibility of integrating all essential optical components onto a single chip (photonic circuit). Lim Teck Guan at the A*STAR Institute of Microelectronics and co-workers have now developed an enhanced alignment solution for photonic circuits. “Our approach offers a highly accurate, passive optical alignment solution for these devices,” says Guan.

The fabrication of is no easy task because there is little room for error. In order to get the best performance from these devices operating at the visible or near-infrared spectrum, various elements must be aligned with utmost precision, typically within an error of around one micrometer. Even with the slightest misalignment, a microlens, for example, might not be able to focus light into a photodetector.

The researchers came up with an alignment method that is remarkably straightforward and easy to implement. It is based on a circular through-hole with two diameters (see image). The design of the larger hole is not critical and it can either partially or entirely accomodate the spherical lens, depending on the application requirement. A second hole in the chip is smaller than the sphere diameter so that if the lens is pressed against the opening the sphere will automatically be aligned in its center. In this way, light from underneath the chip is guided through the lens and the second hole, and on to a photodetector that is placed directly above.

This guided assembly scheme makes it easy to fabricate more complex photonic circuits, once the spherical lenses are integrated with the layer containing the through-holes. Electronic circuits of virtually any complexity can be placed on the chip with high accuracy, so that they align perfectly with the optical beam shone through the lens. The measured efficiencies of the light coupling between the different components on the chip are promising and demonstrate light propagation with few losses.

In the current assembly, a laser is placed on a chip and through a combination of mirrors and microsphere lenses, the light is guided across the to a photodetector. However, the researchers have already set their sights on the advantages of further integration. “In future, we might come up with more complex circuits,” suggests Guan. “These devices could lead to applications including high-speed, high-bandwidth integrated photonic circuits, particularly if we can integrate conventional silicon electronics with photonic functionality.”

Explore further: Microtechnology: An alignment assignment

More information: Guan, L. T. et al. Integrated optical carrier for optical/electrical interconnect. IEEE Transactions on Components, Packaging, and Manufacturing Technology 1, 125–132 (2011). ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5696784

Related Stories

Microtechnology: An alignment assignment

January 21, 2011

Microelectromechanical systems (MEMS), which consist of tiny moving parts driven by electrical signals, have found ready applications in optical communication systems. They are attractive in part because they can be integrated ...

Recommended for you

Fusion reactors 'economically viable' say experts

October 2, 2015

Fusion reactors could become an economically viable means of generating electricity within a few decades, and policy makers should start planning to build them as a replacement for conventional nuclear power stations, according ...

Iron-gallium alloy shows promise as a power-generation device

September 29, 2015

An alloy first made nearly two decades ago by the U. S. Navy could provide an efficient new way to produce electricity. The material, dubbed Galfenol, consists of iron doped with the metal gallium. In new experiments, researchers ...

Extending a battery's lifetime with heat

October 1, 2015

Don't go sticking your electronic devices in a toaster oven just yet, but for a longer-lasting battery, you might someday heat them up when not in use. Over time, the electrodes inside a rechargeable battery cell can grow ...

Invisibility cloak might enhance efficiency of solar cells

September 30, 2015

Success of the energy turnaround will depend decisively on the extended use of renewable energy sources. However, their efficiency partly is much smaller than that of conventional energy sources. The efficiency of commercially ...

Scientists produce status check on quantum teleportation

September 30, 2015

Mention the word 'teleportation' and for many people it conjures up "Beam me up, Scottie" images of Captain James T Kirk. But in the last two decades quantum teleportation – transferring the quantum structure of an object ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.