Caged light

Papers of interest from Nature Publishing Group’s new research journal Nature Photonics, including: Caged light, Optical buffer on a silicon chip, Blue microdisk lasers hit room temperature, Optical devices lose their sensitive side and Follow the light.

PRESS RELEASE FROM NATURE PHOTONICS

(http://www.nature.com/nphoton)

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[1] Caged light
DOI: 10.1038/nphoton.2006.51

Light likes to keep on moving no matter what. But researchers have built an optical cage that can temporarily catch light and release it again, they report in the January issue of Nature Photonics. The development is an important step towards solid-state optical memory devices that may ultimately play a crucial role in ultra-fast optical communication networks or optical computers.

Takasumi Tanabe and colleagues use a photonic crystal – a piece of silicon riddled with tiny holes – to create an optical cavity that can store light particles for more than a billionth of a second. This may not seem very long, but the beauty of these structures is in their size. Photonic crystals are man-made structures that can control the flow of light on the very smallest length scale possible – down to the wavelength of the waves. The team’s cavity is less than ten millionths of a metre long and made from silicon, which means that it could be integrated into miniature optical chips that can process light in the way microelectronics processes electrons.

The temporary storage effect means that light travelling through the cage is effectively slowed down to a speed of just 5.8 km per second, 50,000 times slower than in a vacuum. This is the slowest speed ever measured in an insulator material.

Author contact:
Takasumi Tanabe (NTT Basic Research Laboratories, Kanagawa, Japan)
Tel: +81 46 240 4825; E-mail: [email protected]

[2] Optical buffer on a silicon chip
DOI: 10.1038/nphoton.2006.42

By exploiting state of the art semiconductor manufacturing technology, scientists have created an optical buffer memory on a miniature silicon chip. The device – a kind of temporary storage area for light signals that works by slowing them down – is described in the January issue of Nature Photonics. Once optimized, it could help future optical networks to synchronize different data streams without needing to convert the signals into the electronic domain.

The optical buffer is made by connecting together a string of up to 100 tiny silicon ring waveguides – tiny oval racetracks with a perimeter of just 55 micrometres. By experimenting with various designs, Yurii Vlasov and colleagues have shown that it is possible to create a buffer with a total footprint of less than 0.1mm squared that is able store up to 10 bits of information at data-rates of up to 20Gbit per second.

Although silicon ring waveguides have been reported before, Vlasov’s team is the first to show that it is possible to make a device from such a large number of rings, and to test its compatibility with real data at gigabit speeds. Although further work is needed to reduce the losses and increase the delay/storage time of the buffer, the work is an important demonstration of the future potential of nanophotonics.

Author contact:
Yurii Vlasov (IBM Thomas J Watson Research Center, Yorktown Heights, NY, USA)
Tel: +1 914 945 2028; E-mail: [email protected]

[3] Blue microdisk lasers hit room temperature
DOI: 10.1038/nphoton.2006.52

Very small and efficient sources of blue laser light could now be on the horizon thanks to the demonstration of the first gallium nitride (GaN) microdisk laser to offer continuous operation at room temperature. In the January issue of Nature Photonics Adele Tamboli and colleagues reveal how they attain the lasing with blue (428nm) light at a threshold of 300 Watts per square centimetre – several orders of magnitude lower than previously reported devices. Until now, GaN microdisks have been limited to pulsed operation or have required cooling to low temperatures.

Microdisk lasers are attractive future sources of light because they are potentially very efficient, small and emit from their top surface rather than the side. With their knowledge that small, smooth microdisks should offer ultra low thresholds, the researchers fabricated microdisks with a diameter of 1.2 micrometres using photoelectrochemical etching, and used electron beam lithography to create very smooth sidewalls.

The development is a step towards the realization of tiny, efficient sources of blue light that could perhaps one day act as an alternative to the conventional edge-emitting semiconductor lasers found in CD and DVD players. But before this can happen, a scheme for directly electrically powering the lasers needs to be found as they currently need another laser as a pump source to power themselves.

Author contact:
Adele Tamboli (University of California, Santa Barbara, CA, USA)
Tel: +1 805 448 7560 or +1 805 893 4875; E-mail: [email protected]

Additional contact for comment on paper:
Shuji Nakamura (University of California, Santa Barbara, CA, USA)
Tel: +1 805 893 5552; E-mail: [email protected]

[4] Optical devices lose their sensitive side
DOI: 10.1038/nphoton.2006.41

Truly useful optical devices built onto microchips are a step closer to becoming a reality, thanks to the work of Tymon Barwicz and colleagues. In the inaugural issue of Nature Photonics, the team describes a way of producing tiny optical devices that process incoming light correctly even if it has a randomly-oriented electric field. They achieve this despite the fact that the individual components making up the device are very picky about the field orientation.

Most devices that control light inside microscopic spaces are, unfortunately, extremely sensitive to the orientation of the light. This limits the usefulness of the technology. Barwicz and co-workers overcome this sensitivity with the aid of a clever miniature photonic circuit. Their circuit splits a light beam into its two constituent perpendicular orientations, rotates one orientation, and recombines the beams after forcing them to pass through identical optical devices. Essentially by aligning the orientation of both beams within the circuit, the initial direction of the field becomes irrelevant and the sensitivity no longer matters.

For the trick to work, Barwicz and co-workers had to design intricate splitters and rotator components and make use of advance manufacturing techniques. By overcoming this barrier, they move us along the path to optical devices that can be integrated onto tiny chips in a big way.

Author contact:
Tymon Barwicz (IBM Thomas J Watson Research Center, Yorktown Heights, NY, USA)
Tel: +1 914 945 3454; E-mail: [email protected]

[5] Follow the light
DOI: 10.1038/nphoton.2006.37

Mapping the orientation of light fields on a microscopic scale is shown to be possible for the first time in the first issue of Nature Photonics. Light is made up of fields with a direction as well as an intensity. Most optical probes measure only the strength of the field. But Kwang Geol Lee and colleagues have built a microscope that allows the direction of the electric field to be captured down to a nanometre scale.

Their device contains a nano-sized gold particle attached to the tip of a glass fibre. By scanning the tip along the surface of an object and capturing light that is scattered off the nanoparticle, they can create an image of the sample and uncover features smaller than the wavelength of the light. Lee and co-workers insert a polarizer just in front of the imaging camera that allows them to identify the components of the electric field.

This new way of ‘seeing’ light tells us how light behaves near very tiny objects. It could help in the design of miniature optical components, or lead to new biosensors, where light interacts with biological molecules in different ways depending on the orientation of the electric field.

Author contact:
DaiSik Kim (Seoul National University, Korea)
Tel: +82 2880 8174; E-mail: [email protected]

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Published: 24 Dec 2006

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