Optical frequency combs are a revolutionary light source for high-precision spectroscopy because of their narrow linewidths and precise frequency spacing. Generation of such combs in the mid-infrared spectral region (2-20 mm) is important for molecular gas detection owing to the presence of a large number of absorption lines in this wavelength regime. Microresonator-based frequency comb sources can provide a compact and robust platform for comb generation that can operate with relatively low optical powers. However, material and dispersion engineering limitations have prevented the realization of an on-chip integrated mid-infrared microresonator comb source. Here we demonstrate a complementary metal-oxide-semiconductor compatible platform for on-chip comb generation using silicon microresonators, and realize a broadband frequency comb spanning from 2.1 to 3.5 mm. This platform is compact and robust and offers the potential to be versatile for use outside the laboratory environment for applications such as real-time monitoring of atmospheric gas conditions.
Singlet exciton fission is an efficient multiexciton generation process in organic molecules. But two concerns must be satisfied before it can be exploited in low-cost solution-processed organic solar cells. Fission must be combined with longer wavelength absorption in a structure that can potentially surpass the single junction limit, and its efficiency must be demonstrated in nanoscale domains within blended devices. Here, we report organic solar cells comprised of tetracene, copper phthalocyanine, and the buckyball C(60). Short wavelength light generates singlet excitons in tetracene. These are subsequently split into two triplet excitons and transported through the phthalocyanine. In addition, the phthalocyanine absorbs photons below the singlet exciton energy of tetracene. To test tetracene in nanostructured blends, we fabricate coevaporated bulk heterojunctions and multilayer heterojunctions of tetracene and C(60). We measure a singlet fission efficiency of (71 ± 18)%, demonstrating that exciton fission can efficiently compete with exciton dissociation on the nanoscale.
Triplet exciton dissociation in singlet exciton fission devices with three classes of acceptors are characterized: fullerenes, perylene diimides, and PbS and PbSe colloidal nanocrystals. Using photocurrent spectroscopy and a magnetic field probe it is found that colloidal PbSe nanocrystals are the most promising acceptors, capable of efficient triplet exciton dissociation and long wavelength absorption.
Optical phased arrays are a promising beam-steering technology for
ultra-small solid-state lidar and free-space communication systems.
Long-range, high-performance arrays require a large beam emission area
densely packed with thousands of actively phase-controlled,
power-hungry light emitting elements. To date, such large-scale phased
arrays have been impossible to realize since current demonstrated
technologies would operate at untenable electrical power levels. Here
we show a multi-pass photonic platform integrated into a large-scale
phased array that lowers phase shifter power consumption by nearly 9
times. The multi-pass structure decreases the power consumption of a
thermo-optic phase shifter to a
P
π
of
1.7
m
W
/
π
without sacrificing speed or optical
bandwidth. Using this platform, we demonstrate a silicon photonic
phased array containing 512 actively controlled elements, consuming
only 1.9 W of power while performing 2D beam steering over a
70
∘
×
6
∘
field of view. Our results
demonstrate a path forward to building scalable phased arrays
containing thousands of active elements.
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