Laser and chips: Raman is a diamond

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  • Published: Nov 1, 2015
  • Author: David Bradley
  • Channels: Raman
thumbnail image: Laser and chips: Raman is a diamond

No rough on this diamond

US researchers have used diamond to develop a new class of Raman laser sufficiently compact to fit on a photonic chip. The device uses a nanoscopic diamond resonator shaped like a racetrack to convert one frequency of laser light to an entirely different range of wavelengths, opening up new options for broadband data communications and many other applications.

US researchers have used diamond to develop a new class of Raman laser sufficiently compact to fit on a photonic chip. The device uses a nanoscopic diamond resonator shaped like a racetrack to convert one frequency of laser light to an entirely different range of wavelengths, opening up new options for broadband data communications and many other applications. The team describes this new proof-of-concept in The Optical Society's journal Optica.

"We present the first observation of Raman lasing in a diamond based device integrated onto a silicon chip," explains Vivek Venkataraman working in the Laboratory of Marko Lončar, at Harvard University, in Cambridge, Massachusetts. "This is, by far, the lowest operating power diamond Raman laser to date, and the longest wavelength produced in any kind of on-chip Raman laser." The researchers suggest that this demonstration makes the carbon allotrope, diamond, only the second material besides silicon that can be used in a Raman laser wholly integrated on to a photonic chip. Such a device holds great promise for research into both short- and long-range optical communications.

Present on-chip lasers are used in telecommunications and operate efficiently but only in a rather narrow bandwidth of just 1.55 micrometres. This narrow range, limits the rate at which data can be transmitted through optical fibres whereas a broader band of wavelengths might allow data bottlenecks to be widened in telecommunications. One way to broaden the band would be to exploit stimulated Raman scattering in which sufficient optical energy is pumped into a material and a fraction of the light loses energy to atomic vibrations and is thus shifted to a specific lower frequency. This amplification of the lower frequency wave can be tapped off using an optical resonator to give us a Raman laser.

Diamond light geyser

Unfortunately, current devices rely on mostly opaque silicon for optics applications in medical devices, chemical sensing and telecommunications. In contrast, diamond is transparent across the ultraviolet, visible and infrared parts of the electromagnetic spectrum. Moreover, it can induce giant colour shifts across the entire spectrum through Raman scattering. Earlier attempts to build a diamond Raman laser require bulky plates in macroscopic cavities as well as precise alignment of components and relatively high operational energies. An on-chip system would at first sight appear off-limits.

Now, Venkataraman and colleagues have found a way to harness diamond's optical prowess in order to create a new class of Raman laser by incorporating a nanoscale circular diamond resonator on their photonic chip. The device functions by pumping laser light at a single frequency down an optical waveguide that passes within hundreds of nanometres of the resonator allowing the light to, in essence, jump the tracks and begin racing around the circular resonator. The constant stream of pump photons leads to a build up as they race around the track until lower energy Stokes photons are generated, feeding back into the system and pumping it up still more until coherent laser light is emitted.

Simple

"The manufacturing process [using standard nanofabrication techniques] is quite simple and enables us to produce resonators of multiple shapes and sizes that could be easily integrated into existing optoelectronic technologies," explains team member Pawel Latawiec. "Ours is a proof-of-principle demonstration," adds Venkataraman, "and many aspects can be further optimized and improved for a commercial product. But these are all engineering and technological improvements and the physics itself is well understood and demonstrated to work."

Related Links

Optica 2015, 2, 924: "On-Chip Diamond Raman Laser"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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