Laser bends and strains tiny mirror

06 Nov 2003

Scientists in Japan grow miniature mirrors by a technique known as micro-origami.

Using a technique known as micro-origami, researchers in Japan have grown miniature mirrors hinged on a gallium-arsenide (GaAs) substrate. As laser light is shone on the mirror, its angle to the substrate changes. The team reckons its tiny devices could be used as switching components in optical links. (Applied Physics Letters 83 3647)

Origami mirror

“The advantage of our devices is that they are made of GaAs-based materials so they are promising for integration into optical systems,” researcher Jose Zanardi told Optics.org. “Optical actuation is a promising, non-contact method. You don’t need to add electrodes to a device and you can even use light as an actuation method in harsh environments.”

Zanardi and his colleagues now plan to fabricate complicated devices such as corner-cube reflectors and directional photodetectors. They also hope to fabricate nano-scale devices.

The team grows its mirrors by molecular beam epitaxy. Grown on a GaAs substrate, each device essentially contains two parts -- a 666-nm thick mirror, and a 144-nm thick hinge.

Making the mirror

The mirror itself is made from layers of AlGaAs, InGaAs and GaAs while the hinge contains layers of GaAs and InGaAs. Etching and photolithography are used to define the mirror, create the hinge and release one edge of the device from the substrate. The mirror initially sits at an angle of 45° to the substrate.

Optical actuation involves shining the 488-nm line of an argon-ion laser on to the mirror. A low-power He-Ne beam monitors the mirror’s movement. “The deflection angle increases as the Ar excitation power is increased, reaching a value of 0.5° for an excitation power density of 450 mW/mm²,” say the authors.

Zanardi and colleagues are now studying the effects that cause the mirror to move. “We have discarded the light-pressure effect as the mirror moves towards the laser beam,” he said. “The two main possible mechanisms are deformation due to the uneven thermal expansion of materials and stresses arising from photo-generated carriers.”

Author
Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.