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Metasurfaces Shrink Broadband Photonics to Smallest Sizes Ever

What is the scientific achievement?

In analogy with Moore's Law for microelectronics, miniaturization of photonics increases the signal processing power of photonic integrated circuits. In this work, scientists have demonstrated the smallest and most broadband photonic integrated devices to date, by incorporating optical metasurfaces into the structure to control light propagation in waveguides.

Why does this achievement matter?

These small-footprint, broadband, and low-loss devices are highly desirable for photonic integrated circuits. The size reduction realized here is similar to that achieved in the 1950s when semiconductor transistors replaced vacuum tubes.

What are the details?

Schematic of nanostructured metasurface atop an optical waveguide

Click on the image to download a high-resolution version. (Top) Schematic of nanostructured metasurface atop an optical waveguide. (Bottom) Scanning electron microscope image of a fabricated gold matasurface patterned atop a lithium niobate waveguide.

The work experimentally demonstrated the smallest and most broadband photonic integrated devices — fabricating waveguide mode converters, on-chip polarization rotators, and on-chip perfect absorbers.  In making this advance, the team employed metasurfaces, for the first time, to control light propagation in waveguides.  Metasurfaces are made of phased arrays of optical antennas. The metasurfaces control waveguide modes via strong optical scattering at subwavelength intervals; the unidirectional phase gradient, or effective wavevector, provided by the metasurfaces enables one-way transfer of optical power from one waveguide mode to another.  These two effects make it possible to both substantially shrink the device footprint and broaden the operational bandwidth.  For example, some of the waveguide mode converters in this work have sizes just 1.7 times of the free space wavelength, and can tolerate wavelength variations as large as ±20%.  For comparison, previously demonstrated waveguide mode converters have sizes that range from a few tens to a few hundred times the free space wavelength, and can only tolerate a variation of the wavelength by at most a few percent.  Furthermore, devices based on dielectric metasurfaces shown in this work have negligible insertion losses.  The small-footprint, broadband, and low-loss photonic integrated devices demonstrated here are highly desirable for photonic integrated circuits.

CFN Capabilities:

Integrated photonic waveguide/metasurface devices were made using the CFN Nanofabrication Facility.

Publication Reference

Zhaoyi Li1, Myoung-Hwan Kim1,2, Cheng Wang3, Zhaohong Han, Sajan Shrestha, Adam Christopher Overvig, Ming Lu, Aaron Stein, Anuradha Murthy Agarwal, Marko Loncar, and Nanfang Yu, Controlling Propagation and Coupling of Waveguide Modes Using Phase-Gradient Metasurfaces, Nature Nanotechnology (2017) doi:10.1038/nnano.2017.50.

Collaborating Institutions:
1
Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10027, USA
2
Department of Physics, The University of Texas Rio Grande Valley, Brownsville, TX 78520, USA
3
John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
4
Microphotonics Center and Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
5
Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY 11973, USA

IEEE Spectrum: "Integrated Photonic Circuits Shrunk Down to the Smallest Dimensions Yet"

Science Daily: "Method to control light propagation in waveguides invented"

Phys.org: "Engineers invent method to control light propagation in waveguides"

Novus Light: "Optical Nano-Antennas Control Light Propagation in Waveguides"

Laser Focus World: "Waveguide mode converters have wide bandwidth, small footprint"

Acknowledgement of Support

The work was supported by the Air Force Office of Scientific Research (grant No. FA9550-14-1-0389 through a Multidisciplinary University Research Initiative program), Defense Advanced Research Projects Agency Young Faculty Award (grant No. D15AP00111), and National Science Foundation (grant No. ECCS-1307948). Funding from the Ministry of Defense, Singapore, and from the Defense Threat Reduction Agency Grant No. HDTRA1-13-1-0001 is gratefully acknowledged. A.C.O acknowledges support from the NSF IGERT program (grant No. DGE-1069240). Research was carried out in part at the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under contract no. DE-SC0012704.

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