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Protein makes phototransceiver debut

20 Oct 2004

Light-sensitive bacteriorhodopsin is combined with electronics to make the world's first bio-phototransceiver.

Scientists from the US and Hungary say they have blended the protein bacteriorhodopsin (bR) with electronics to make the world's first bio-phototransceiver. The device, which uses bR to detect incoming light, could find applications as an optical interconnect in artificial vision systems for robotics and high-speed tracking. (Optics Letters 29 2264)

bR is a light-sensitive protein which is typically found in salt marshes. According to researcher Pallab Bhattacharya from the University of Michigan, US, bR's properties are well-known but not much progress has been made toward a real application.

"Compared with other protein receptors, bR has high resistance to thermal and chemical damage," said Bhattacharya. "It also exhibits excellent long-term stability and light sensitivity and has an extremely short response time on the order of picoseconds."

The key components of the monolithically integrated phototransceiver are a film of bR, a field-effect transistor and an LED, all based on a GaAs substrate.

"It occurred to us that the large photovoltage developed across a bR membrane, with a high resistance across it, could be applied to the gate terminal of a field-effect transistor, which would amplify the photovoltage into a useful current," Bhattacharya explained. "This current then drives the integrated LED."

To test their device, Bhattacharya and colleagues fired 3 s and 10 ms pulses from a He-Ne laser operating at 594 nm at the bR film. A spectrometer picked up a pulsed output from the 655 nm LED. The team noted that for longer incident pulses, the output from the LED exactly resembled the transient response of bR.

Bhattacharya is also confident that the bR film will retain its properties. "It has been reported that light-sensitive thin-films made of bR can be saved on the shelf for twenty years without any functional degradation," he told Optics.org. "In our experiments, after thousands of laser pulses over 8 months, bR retains its photovoltaic properties."

The team is now working on a polarization-sensitive version of its phototransceiver by modifying the molecular arrangement of the bR. "This means that the bR-based photoreceiver is not only sensitive to the light intensity but is also capable of detecting incident light of different polarizations," said Bhattacharya. "We are trying to demonstrate a polarized optical interconnect by replacing the integrated LED with a laser or LED with a polarized light output."

This work is a collaboration between researchers from the University of Michigan, Pennsylvania State University and the Biological Research Center of the Hungarian Academy of Science.

Jacqueline Hewett is technology editor on Optics.org and Opto & Laser Europe magazine.

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