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Making color with
semiconductor microdisks
Can scientists generate any color of light? The answer is not really, but the
invention of the laser in 1960 opened new doors for this endeavor. An early
experiment injected high-power laser light through quartz and out popped a
different color. This sparked the field of nonlinear optics and with it, a new
method of color generation became possible: frequency conversion.
Not all crystals can perform this trick and only through careful fabrication of
certain materials is frequency conversion possible. PFC- supported researchers
have developed a new microstructure that does what’s called second harmonic
generation (SHG), where the output light has twice the frequency as the input.
This new device is a factor of 1000 smaller than previous frequency converters.
In the new design, gallium arsenide (GaAs) is fabricated into a micrometer-sized
disk ‘cavity. Notably, GaAs has one of the largest second-harmonic frequency
conversion constants measured. Previously, scientists have harnessed its
extremely nonlinear properties for frequency conversion, leading to device
sizes in the centimeter range. This new device is 1000 times smaller.
In the experiment, light is injected into the cavity. When light travels in a loop
with the proper orientation, as opposed to a linear geometry, color conversion
is achieved. The device can be so small because the light can interact many
times with the medium by circulating around the disk.
In terms of future quantum information applications, this device could be used
in reverse to generate entangled photon pairs. Gallium arsenide (GaAs) is a
common semiconductor and has added benefits such as transmitting and
emitting in the infrared (IR) and near IR light, respectively. IR-colored light has
applications that include telecommunications and chemical sensing.
Figure and caption information from paper reprinted
with permission of Authors: Input light at the
fundamental wavelength (represented by red light) is
converted inside the micro-disk to second harmonic light
(represented by blue light). The inset shows a scanning
electron micrograph of a fabricated device. The scale bar
is 1 mm. Image credit: T. Thomay/JQI
"Second-harmonic generation using -quasi-phasematching
in a GaAs whispering-gallery-mode microcavity," P. Kuo, J.
Bravo-Abad, G.S. Solomon, Nature Communications, 5,
3109 (2014)