Researchers have developed a highly accurate way to assemble multiple micron-scale optical devices tightly onto a single chip.

This new approach could one day enable the mass manufacturing of chip-based optical systems, enabling more compact optical communication devices and advanced imaging devices.

"The development of electronics based on silicon transistors has enabled systems on a chip to become increasingly powerful and flexible," says Dimitars Jevtics of the University of Strathclyde in the UK. "However, an optical system on a chip requires the integration of different materials on a chip, and so has not seen the same scale development as silicon electronics."

In Optica Publishing Group's journal Optical Materials Letters, Jevtics and colleagues describe their new transfer printing process and demonstrate their ability to place devices made of multiple materials on a single chip. All of these devices are integrated into a footprint similar in size to the device itself.

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Unlike other approaches, which are usually limited to a single material, this new approach provides a toolbox of materials from which future system designers can pick and reference.

"For example, on-chip optical communications will require assembling light sources, channels and detectors into components that can be integrated with silicon chips. "Our transfer printing process can be scaled up to integrate thousands of devices made of different materials onto a single wafer. This will enable micron-scale optical devices to be integrated into future high-density communications computer chips, or into on-chip biosensing laboratory platforms."

One of the biggest challenges in assembling multiple devices on a single chip is finding ways to put them very close together without interfering with devices already on the chip. To achieve this, the researchers developed a method based on reversible adhesion, in which the device is removed from the growing substrate and released onto a new surface.

The researchers also created a multi-wavelength nanolayer system by placing semiconductor nanowires on silicon dioxide. This new transfer printing method could one day allow mass production of chip-based optical systems made from a variety of materials.

The new method uses a soft polymer stamp mounted on the robot's motion console to remove the optical device from the substrate on which it is made. The substrate to be placed is placed underneath the suspension device and is precisely aligned using a microscope. Once properly aligned, the two surfaces touch, freeing the device from the polymer marker and depositing it onto the target surface. Advances in precise micro-assembly robotics, nanomanufacturing and microscopic image processing have made this approach possible.

"By carefully designing the geometry of the seal to match the device and controlling the viscosity of the polymer material, we can design the device to be picked up or released," Jevtics said. "Optimized, the process does not cause any damage and can be scaled up through automation, compatible with wafer scale manufacturing."

To demonstrate the new technology, the researchers integrated optical resonators of aluminum gallium arsenide, diamond and gallium nitride onto a single chip. These optical resonators show good optical transmission performance, indicating that the integration works well.

They also used a printing method to create a semiconductor nanowire laser, placing the nanowire on the main surface in a space-dense manner. The separation between nanowires, as measured by scanning electron microscopy, shows spatial accuracy in the range of 100 nm. By placing semiconductor nanowires on silicon dioxide, they were able to create a multi-wavelength nanolaser system.

"As a manufacturing technique, this method of printing is not limited to optical devices," Jevtics said. "We hope that electronics experts will also see the possibility of its application in future systems."

As a next step, the researchers are working to replicate these results with more devices to prove it works on a larger scale. They also hope to combine their transfer printing method with the automatic alignment technology they have previously developed in order to be able to quickly measure, select and transfer hundreds of isolation devices for imaging and mixing optical circuits