Session L59: Optical, Laser, and Photonic Devices and Applications

Live

In this work, a novel infinite 3D printing technique is explored to fabricate continuous several-meter-long low-loss and near-zero dispersion suspended-core polypropylene fibers for application in terahertz communications. Furthermore, particular attention is paid to process parameter optimization for printing with low-loss polypropylene plastic, as well as an in-depth theoretical and experimental comparison between fibers printed using standard and infinite 3D printers. Fiber transmission losses as low as 2.42 dB/m and 8.86 dB/m are experimentally demonstrated for the two fibers respectively at 128 GHz. Signal transmission with BER far below forward error correction limit (10-3) are clearly observed, an error-free transmission is realized at the bit rate up to 5 Gbps. The optimal conditions for exciting fibers and the mode field distributions are present intuitively with the near-field imaging. The capabilities of shielding the fundamental mode from external interference granting unique superiorities of easy-handling and convenient-fixing to these effectively single-mode 3D printed fibers. The novel fused deposition modeling (FDM)- based infinite printing technique in our opinion is poised to become a key technique for advanced terahertz fiber manufacturing.   

Live

The free-standing of 2D materials by buckling^[1] or twisting^[2] them, enhance their carrier mobility and stimulates multiple photonic modes which are significantly absent in planar 2D sheets. The flexural strength of 2D material has been exploited to fabricate an encapsulated spirally rolled quasi unidirectional nanoscroll (NS) structure. This self-encapsulating structure can confine the motion of the electron in the 1D axis without having any external perturbation. Upon hybridizing with high yield QDs the physiochemical properties of the NS can get immensely manipulated. The photo-generated excitons after getting dissociated at the QD/2D interfaces enhance the photosensitivity almost 3000 fold compared to the pristine scroll. The subsequent presence of QDs as a scatterer at the inner wall of the NS stimulates lasing action. The multiple internal reflections inside this nanocavity generate coherent lasing action with an unprecedently low threshold. This helical structure predominately localizes the excitons along the circumference of the scroll instigating 12-fold brighter parallel polarized emission compared to the perpendicular one.

References:
[1] Ghosh, R., et al. DOI:10.1021/acsami.9b08294

[2] Ghosh, R., et al.DOI:10.1002/smll.202003944   

Live

Antimonide-based type-II W interband cascade lasers optimized for electrical injection were optically pumped and exhibited lasing at emission wavelengths ranging from 3.2 µm to 3.8 µm, with a maximum operating temperature of 200 K. As the optical pumping wavelengths increased from 1.8 µm to 1.9 µm, decreasing threshold pump intensity and increasing slope efficiency (external differential quantum efficiency) were observed. The generation of photovoltage under illumination and consequent achievement of lasing conditions will be discussed, including comparisons to physical operating principles in thermophotovoltaic interband cascade devices and conventional interband cascade lasers.   

Live

Fast switching optical filters are of vast interest for multiple applications in various fields, from biomedical imaging and microscopy to light detection and ranging (LIDAR) systems. Modern applications require multispectral narrowband tunable devices with fast switching speeds. We present dual frequency nematic liquid crystal tunable filters based on a series of liquid crystal optical retarders, each placed between crossed polarizers. By choosing the liquid crystal retarders thicknesses and using individual biasing schemes, we continuously tune the wavelength and bandwidth of the filter with fine-tuned switching speeds in the ms regime. The filter was added to conventional polarized total internal reflection fluorescent (p-TIRF) microscopy to control which spectral wavelengths from fluorescent samples reach the detector. Our filter switching speeds allow imaging of different cellular processes on a ms time scale, which is an order of magnitude faster than typical mechanical filter switching speeds, resulting in improved temporal resolution. The results of electro-optical filter characterization and an example of its application in p-TIRF microscopy will be presented.   

Live

Terahertz (THz) band (0.1-10 THz) is the next frontier for the ultra-high-speed communication systems. Currently, most of communications research in this spectral range is focused on wireless systems, while waveguide/fiber-based links have been less explored. Although free space communications have several advantages, the fiber-based communications provide superior performance in certain short-range communication applications such as multi-device connectivity in complex geometrical environments, secure signal delivery to hard-to-reach or highly protected environments etc. In this work, we present both experimental and numerical study of the short-range THz communications links that use subwavelength dielectric fibers for information transmission. Particularly, we use air cladded polypropylene-core subwavelength dielectric THz fibers of various diameters to study link performance as a function of the link length of up to ~10 m, and data bitrates of up to 6 Gbps at the carrier frequency of 128 GHz. The power budget of the THz fiber-based links is compared to that of free space links and we conclude that fiber links offer an excellent solution for various short-range applications.   

Live

We fabricated, characterized, and modeled photoconductive antennas by using black phosphorus (BP; ~ 40 nm thin film as the photoconductor) and hexagonal boron nitride (hBN; a capping layer to prevent the oxidation of BP). BP and hBN flakes were transferred inside a nitrogen glovebox onto dipole antennas (fabricated on oxidized high-resistivity Si substrates). The thickness of the BP and hBN were optimized for maximum absorption within the BP layer using the transfer matrix method. The armchair axis of BP flakes (determined by reflection anisotropy) was aligned with the anode-cathode gap of the antenna. Under illumination with 100 fs pulses at 780 (1560) nm, photocurrent imaging shows a bias-dependent maximum photocurrent localized to the antenna gap with a peak photoconductivity 1 (2) S/cm in the linear regime of bias [1]. Device performance was modeled numerically by solving Maxwell’s and the drift-diffusion equations to obtain the photocurrent density in response to pulsed laser excitation, showing qualitative agreement with the experimental observations. These devices present a step toward high-performance THz photoconductive antennas using BP.

[1] Doha, M. H. et al. (2020). J. Appl. Phys, 128(6), 063104.   

Live

This paper evaluates considerations in minimizing disruptions of scientific data in ultra-sensitive Infrared (IR) spaced-based telescopes by ions in space radiation and neutrons produced when ions react with the nuclei in high Z metallization.. Results of proposed designs are based on a model developed at Boeing. The components modeled are the spectra of the ions in cosmic rays and solar flares, the transport of the primary ions and secondary particles produced including neutrons, the generation electron hole pairs (EHPs) in the focal point array (FPA), and a component modeling transfer of EHPs from generation to recombination. Results indicate noise levels above 100 EHPs by secondary particles alone per pixel in solar flares and extra-galactic sources; these observations agree with empirical data sources. IR astronomical observatories now have a noise level of 100 electrons/pixel indicating the need of detailed radiation transport models; in near future designs where the pixel pitch reduces from 25 to 5 microns, the pixel noise levels are estimated to be as low as 10 electrons/pixel.   

Live

A tremendous mechanical sensitivity can be achieved by a mechanically tunable quantum tunneling barrier. The tunneling resistance across the nanometer-sized gap can be changed by several orders of magnitude through a sub-angstrom-scale displacement. Here we demonstrate a suspended metal/self-assembled monolayer (SAM)/metal nanostructure to implement such a mechanically tunable tunneling barrier and use it as an ultra-sensitive bolometric mid-infrared (IR) detector. Fabricated proof-of-concept metal/SAM/metal bolometers yield a temperature coefficient of resistance (TCR) of up to 0.2 K^-1, and theoretical predictions show that with further optimization the TCRs could be improved to as much as 5 K^-1, which is more than one order of magnitude better than the state-of-the-art VO_x bolometers. Strain, transport, noise and mid-IR scanning photocurrent microscopy measurements are performed to show the full functionality of the devices.   

Live

Aluminum nitride (AlN) is an emerging material for integrated quantum photonics with excellent linear and nonlinear optical properties, in particular its χ(2) that allows single-photon generation. Here we demonstrate the integration of AlN on silicon nitride (SiN) photonic chips. Composite microrings are fabricated by sputtering c-axis oriented AlN on top of pre-patterned SiN. This new approach does not require any patterning of AlN and depends only on reliable SiN nanofabrication. Different thicknesses are sputtered on microrings with different radii and different waveguide widths. The fabrication is characterized using XRD, optical reflectometry, SEM, and AFM. The optical properties, such as the quality factor, absorption losses and group index, are obtained. The hybrid resonators can have a one order of magnitude increase in quality factor after the AlN integration, with propagation losses as low as 0.16 dB/cm. This hybrid fabrication introduces an additional degree of freedom for the phase matching, which is important for photon-pair generation.   

Live

The photo-induced changes in nonlinear refractive index (n₂) of transition metal dichalcogenides (TMDCs) open up the horizon for promising applications in all-optical signal switching. Here, we study the ultrafast third-order nonlinear optical response of WS₂ quantum dots by open and closed aperture Z-scan techniques to get a comprehensive understanding of nonlinear absorption and refraction, respectively. Strikingly, our pulse-width dependent (120 fs and 5 ns) nonlinear spectroscopy measurement reveals a sign reversal of n₂. We demonstrate that free carriers generation obtained by longer (ns) pulse-width excitation is responsible for negative refractive index, showing the relatively large value of 9 × 10^-13cm²/W. On the other hand, the higher concentration of bound carriers (excitons) in shorter (fs) pulse-width excitation is the origin for positive refractive index, resulting in an unusual crossover of n₂. Further, with varying intensity, we observe the transition from saturable absorption to two-photon absorption. Our experimental findings might have provided a new degree of freedom for tuning the third-order nonlinear optical response of TMDCs based materials which can find potential applications in optical modulating and limiting.   

Live

Transition metal dichalcogenides (TMDCs) have become forefront in research field due to their outstanding properties like strong light-matter interaction, large exciton binding energy in monolayer (ML) limit, etc. The optical properties in these materials are controlled by the robust excitons. Therefore, a microscopic understanding of exciton interactions and recombination in TMDCs plays an integral role in designing optoelectronic devices. Though the exciton dynamics is studied extensively in atomically thin ML, few layers and heterostructure, such studies are scarce in single crystals. Here, by ultrafast transient differential reflectance spectroscopy, we studied exciton many-body interaction in WS₂ single crystal. Time-resolved studies reveal strongly correlated exciton interaction of A, B and C excitons and their associated transient stark blueshift and excitonic broadening. We observe fluence-dependent photoinduced absorption between A and B exciton, attributed to bandgap renormalization and C exciton is detected only at higher fluence. Furthermore, A and B exciton bleaches are decaying biexponentially and show unusually long decay at higher fluence, which prompts potential application of TMDCs in optoelectronics.   

Live

Color-detection&spectroscopy,two distinct yet inter-related applications of semiconductors,suffer from the same limitations:necessarily large number of identical photoreactors,sophisticated engineering,intricate beam path,and lack of flexibility to adjust for the damaged pixels.2D materials are desirable candidates for optoelectronic applications,but face great challenges due to inherent variabilities in their properties.We report on a novel technique in simultaneously estimating the color&wavelength spectrum of any broadband visible light.The small number of optical thin-film filters of transition metal dichalcogenides(TMDs),fabricated via vapor phase chalcogenization(VPC),are designed to have enough variabilities with respect to each other.We apply artificial intelligence(AI)algorithms such as machine learning(ML)and pattern recognition on emergent optoelectronic responses of the filters upon shining various spectra,and obtain the underlying nonlinear ruling function for the collective of filters.Later,we estimate the color&spectrum of any unknown incident light using the learned function on the optoelectronic data of the light that is collected from the filters.   

Live

Bound states in the continuum (BICs) are widely studied due to their applications in light confinement, sensors, and lasing action with topological characteristics. The formation of BICs in periodic photonic band gap structures are primarily driven by symmetry incompatibility; structural manipulation or variation of incidence angle from incoming light. In this work, we report two methods to drive the formation of BICs in terahertz metasurfaces. First, we experimentally confirm polarization driven symmetry-protected BICs by the variation of the linear polarization state of light at normal incidence. Recent experiments have demonstrated the existence of exotic modes which occur in off-Γ points not accessible by symmetry-protected BICs called Freidrich-Wintgen (FW) BICs. Here, we demonstrate through strong coupling of two radiative modes the formation of capacitively-driven Freidrich-Wintgen BICs. The capacitance-mediated strong coupling at 0° polarization is shown to have a normalized coupling strength ratio of 4.17% calculated by the Jaynes-Cummings model. Furthermore, when the polarization angle is varied from 0° to 90° (0° ≤ φ <90°), the Freidrich-Wintgen BIC can be modulated until it is completely switched off at 90°.   

Live

Resistive switching (RS) is one of the key phenomena proposed for nonvolatile memories, neural networks, and optoelectronics. The unique properties of quantum materials by implementating their functionalities in hardware, provide energy-efficient solutions for these applications. Recent studies based on VO₂ and V₂O₃ have shown the possible development of scalable neuristors and memristors by combining two physical phenomena (electric + thermal or electric +pressure/strain). In this work, we have fabricated and characterized a hybrid composed of the photoconductor CdS on top of V₃O₅ thin film. V₃O₅ exhibits an insulator-metal transition (IMT) around Tc=415K. We have investigated the electrical properties of the V₃O₅ when submitting the bilayer to illumination, under different temperature. At RT, V₃O₅ undergoes a non-volatile RS upon illumination. Cycling V₃O₅ through the high temperature metallic state (above Tc) provides the reset mechanism. Our work demonstrates a new optically controlled RS behavior.
Sci. Rep. 10, 4292 (2020).
Proc. Natl. Acad. Sci. 116, 8798–8802 (2019).   

On Demand

Nonlinear frequency conversion is ubiquitous in laser engineering and entangled photon pair generation, and has applications across quantum technology, for example in erasing spectral distinguishability of single photon emitters. Typically, frequency conversion requires multiple costly and bulky lasers to be coupled into a nonlinear crystal using free space optics that is often challenging due to the large spectral separation of the lasers. Here, we demonstrate nonlinear difference frequency generation (DFG) in an AlGaAs waveguide that is itself the gain medium for one of the required lasers. By including a quantum dot layer in the waveguide, doping the semiconductor and injecting current, we produce laser light at ∼790nm wavelength using the facets of the waveguide to form a cavity. Using this on-chip laser and the Χ⁽²⁾ nonlinearity of AlGaAs, we perform DFG of an external telecom laser. We use the broad phase-matching to perform DFG from 1520-1630nm wavelength. We measure conversion efficiency up to (7.5 ± 2.4) x 10^-2 %/W/cm² which could be readily increased with further engineering to reduce losses and improve thermal management. Our proof-of-concept device has applications in intra-band telecom frequency conversion and for converting quantum emitters to a common wavelength.