Nanophotonics

Kang, Ji-Hun; Kim, Dai-Sik; Seo, Minah

2018 Nanophotonics

doi: 10.1515/nanoph-2017-0093

AbstractUnderstanding light interaction with metallic structures provides opportunities of manipulation of light, and is at the core of various research areas including terahertz (THz) optics from which diverse applications are now emerging. For instance, THz waves take full advantage of the interaction to have strong field enhancement that compensates their relatively low photon energy. As the THz field enhancement have boosted THz nonlinear studies and relevant applications, further understanding of light interaction with metallic structures is essential for advanced manipulation of light that will bring about subsequent development of THz optics. In this review, we discuss THz wave interaction with deep sub-wavelength nano structures. With focusing on the THz field enhancement by nano structures, we review fundamentals of giant field enhancement that emerges from non-resonant and resonant interactions of THz waves with nano structures in both sub- and super- skin-depth thicknesses. From that, we introduce surprisingly simple description of the field enhancement valid over many orders of magnitudes of conductivity of metal as well as many orders of magnitudes of the metal thickness. We also discuss THz interaction with structures in angstrom scale, by reviewing plasmonic quantum effect and electron tunneling with consequent nonlinear behaviors. Finally, as applications of THz interaction with nano structures, we introduce new types of THz molecule sensors, exhibiting ultrasensitive and highly selective functionalities.

Smolyaninov, Igor I.; Smolyaninova, Vera N.

2018 Nanophotonics

doi: 10.1515/nanoph-2017-0115

AbstractSearching for natural materials exhibiting larger electron-electron interactions constitutes a traditional approach to high-temperature superconductivity research. Very recently, we pointed out that the newly developed field of electromagnetic metamaterials deals with the somewhat related task of dielectric response engineering on a sub-100-nm scale. Considerable enhancement of the electron-electron interaction may be expected in such metamaterial scenarios as in epsilon near-zero (ENZ) and hyperbolic metamaterials. In both cases, dielectric function may become small and negative in substantial portions of the relevant four-momentum space, leading to enhancement of the electron pairing interaction. This approach has been verified in experiments with aluminum-based metamaterials. Metamaterial superconductor with Tc=3.9 K have been fabricated, which is three times that of pure aluminum (Tc=1.2 K), which opens up new possibilities to improve the Tc of other simple superconductors considerably. Taking advantage of the demonstrated success of this approach, the critical temperature of hypothetical niobium, MgB2- and H2S-based metamaterial superconductors is evaluated. The MgB2-based metamaterial superconductors are projected to reach the liquid nitrogen temperature range. In the case of an H2S-based metamaterial, the projected Tc appears to reach ~250 K.

Aghaeipour, Mahtab; Pettersson, Håkan

2018 Nanophotonics

doi: 10.1515/nanoph-2017-0101

AbstractA near-unity unselective absorption spectrum is desirable for high-performance photovoltaics. Nanowire (NW) arrays are promising candidates for efficient solar cells due to nanophotonic absorption resonances in the solar spectrum. The absorption spectra, however, display undesired dips between the resonance peaks. To achieve improved unselective broadband absorption, we propose to enclose distributed Bragg reflectors (DBRs) in the bottom and top parts of indium phosphide (InP) NWs, respectively. We theoretically show that by enclosing only two periods of In0.56Ga0.44As/InP DBRs, an unselective 78% absorption efficiency (72% for NWs without DBRs) is obtained at normal incidence in the spectral range from 300 nm to 920 nm. Under oblique light incidence, the absorption efficiency is enhanced up to about 85% at an incidence angle of 50°. By increasing the number of DBR periods from two to five, the absorption efficiency is further enhanced up to 95% at normal incidence. In this work, we calculated optical spectra for InP NWs, but the results are expected to be valid for other direct band gap III–V semiconductor materials. We believe that our proposed idea of integrating DBRs in NWs offers great potential for high-performance photovoltaic applications.

Jia, Hao; Zhou, Ting; Zhao, Yunchou; Xia, Yuhao; Dai, Jincheng; Zhang, Lei; Ding, Jianfeng; Fu, Xin; Yang, Lin

2018 Nanophotonics

doi: 10.1515/nanoph-2017-0116

AbstractPhotonic network-on-chip for high-performance multi-core processors has attracted substantial interest in recent years as it offers a systematic method to meet the demand of large bandwidth, low latency and low power dissipation. In this paper we demonstrate a non-blocking six-port optical switch for cluster-mesh photonic network-on-chip. The architecture is constructed by substituting three optical switching units of typical Spanke-Benes network to optical waveguide crossings. Compared with Spanke-Benes network, the number of optical switching units is reduced by 20%, while the connectivity of routing path is maintained. By this way the footprint and power consumption can be reduced at the expense of sacrificing the network latency performance in some cases. The device is realized by 12 thermally tuned silicon Mach-Zehnder optical switching units. Its theoretical spectral responses are evaluated by establishing a numerical model. The experimental spectral responses are also characterized, which indicates that the optical signal-to-noise ratios of the optical switch are larger than 13.5 dB in the wavelength range from 1525 nm to 1565 nm. Data transmission experiment with the data rate of 32 Gbps is implemented for each optical link.

Xie, Yiwei; Zhuang, Leimeng; Lowery, Arthur J.

2018 Nanophotonics

doi: 10.1515/nanoph-2017-0113

AbstractChip-scale integrated optical signal processors promise to support a multitude of signal processing functions with bandwidths beyond the limit of microelectronics. Previous research has made great contributions in terms of demonstrating processing functions and device building blocks. Currently, there is a significant interest in providing functional reconfigurability, to match a key advantage of programmable microelectronic processors. To advance this concept, in this work, we experimentally demonstrate a photonic integrated circuit as an optical signal processor with an unprecedented combination of two key features: reconfigurability and terahertz bandwidth. These features enable a variety of processing functions on picosecond optical pulses using a single device. In the experiment, we successfully verified clock rate multiplication, arbitrary waveform generation, discretely and continuously tunable delays, multi-path combining and bit-pattern recognition for 1.2-ps-duration optical pulses at 1550 nm. These results and selected head-to-head comparisons with commercially available devices show our device to be a flexible integrated platform for ultrahigh-bandwidth optical signal processing and point toward a wide range of applications for telecommunications and beyond.

Jia, Hao; Zhou, Ting; Fu, Xin; Ding, Jianfeng; Zhang, Lei; Yang, Lin

2018 Nanophotonics

doi: 10.1515/nanoph-2018-0010

AbstractIn this paper, we propose and demonstrate a five-port optical router based on mode-selective property. It utilizes different combinations of four spatial modes at input and output ports as labels to distinguish its 20 routing paths. It can direct signals from the source port to the destination port intelligently without power consumption and additional switching time to realize various path steering. The proposed architecture is constructed by asymmetric directional coupler based mode-multiplexers/de-multiplexers, multimode interference based waveguide crossings and single-mode interconnect waveguides. The broad optical bandwidths of these constituents make the device suitable to combine with wavelength division multiplexing signal transmission, which can effectively increase the data throughput. Measurement results show that the insertion loss of its 20 routing paths are lower than 8.5 dB and the optical signal-to-noise ratios are larger than 16.3 dB at 1525–1565 nm. To characterize its routing functionality, a 40-Gbps data transmission with bit-error-rate (BER) measurement is implemented. The power penalties for the error-free switching (BER<10−9) are 1.0 dB and 0.8 dB at 1545 nm and 1565 nm, respectively.

Dalir, Hamed; Mokhtari-Koushyar, Farzad; Zand, Iman; Heidari, Elham; Xu, Xiaochuan; Pan, Zeyu; Sun, Shuai; Amin, Rubab; Sorger, Volker J.; Chen, Ray T.

2018 Nanophotonics

doi: 10.1515/nanoph-2017-0092

AbstractIn atomic multi-level systems, adiabatic elimination (AE) is a method used to minimize complicity of the system by eliminating irrelevant and strongly coupled levels by detuning them from one another. Such a three-level system, for instance, can be mapped onto physically in the form of a three-waveguide system. Actively detuning the coupling strength between the respective waveguide modes allows modulating light to propagate through the device, as proposed here. The outer waveguides act as an effective two-photonic-mode system similar to ground and excited states of a three-level atomic system, while the center waveguide is partially plasmonic. In AE regime, the amplitude of the middle waveguide oscillates much faster when compared to the outer waveguides leading to a vanishing field build up. As a result, the plasmonic intermediate waveguide becomes a “dark state,” hence nearly zero decibel insertion loss is expected with modulation depth (extinction ratio) exceeding 25 dB. Here, the modulation mechanism relies on switching this waveguide system from a critical coupling regime to AE condition via electrostatically tuning the free-carrier concentration and hence the optical index of a thin indium thin oxide (ITO) layer resides in the plasmonic center waveguide. This alters the effective coupling length and the phase mismatching condition thus modulating in each of its outer waveguides. Our results also promise a power consumption as low as 49.74aJ/bit. Besides, we expected a modulation speed of 160 GHz reaching to millimeter wave range applications. Such anticipated performance is a direct result of both the unity-strong tunability of the plasmonic optical mode in conjunction with utilizing ultra-sensitive modal coupling between the critically coupled and the AE regimes. When taken together, this new class of modulators paves the way for next generation both for energy and speed conscience optical short-reach communication such as those found in interconnects.

Ruan, Zhengsen; Shen, Li; Zheng, Shuang; Wang, Andong; Long, Yun; Zhou, Nan; Wang, Jian

2018 Nanophotonics

doi: 10.1515/nanoph-2017-0090

AbstractWe propose, design, fabricate and characterize a subwavelength grating slot (SWGS) waveguide on silicon platform at short-wave infrared (SWIR) wavelength of 2 μm. The mode guiding mechanism, i.e. SWGS mode, is a combination of surface-enhanced supermode and Bloch mode. We also design and fabricate a low-loss strip-to-SWGS mode converter. We further demonstrate chip-scale direct modulation data transmission at 2 μm through the fabricated SWGS waveguides. Favorable operation performance is achieved in the experiment.

Li, Rui; Zhang, Yajun; Xu, Xuefeng; Zhou, Yi; Chen, Maodu; Sun, Mengtao

2018 Nanophotonics

doi: 10.1515/nanoph-2018-0002

AbstractIn this paper, we employ the nonlinear optical microscopies of coherent anti-Stokes Raman scattering spectroscopy, two-photon excitation fluorescence, and second harmonic generation to characterize the properties of two-dimensional (2D) materials. With these nonlinear optical microscopy methods, we can not only clearly observe the surface topography of 2D materials but also reveal the quality of 2D materials. These nonlinear optical microscopies offer great potential for characterization of the properties of 2D materials.

Zhang, Hui; Zhao, Kangyi; Cui, Songya; Yang, Jun; Zhou, Dahua; Tang, Linlong; Shen, Jun; Feng, Shuanglong; Zhang, Weiguo; Fu, Yongqi

2018 Nanophotonics

doi: 10.1515/nanoph-2017-0135

AbstractGraphene nanowalls (GNWs) exhibit outstanding optoelectronic properties due to their peculiar structure, which makes them a great potential in infrared (IR) detection. Herein, a novel IR detector that is composed of polydimethylsiloxane (PDMS) and designed based on GNWs is demonstrated. Such detector possesses an anomalous temperature coefficient of resistance of 180% K−1 and a relatively high change rate of current (up to 16%) under IR radiation from the human body. It primarily attributes to the ultra-high IR absorption of the GNWs and large coefficient of thermal expansion of PDMS. In addition, the GNW/PDMS device possesses excellent detection performance in the IR region with a responsivity of ~1.15 mA W−1. The calculated detectivity can reach 1.07×108 cm Hz1/2 W−1, which is one or two orders of magnitude larger than that of the traditional carbon-based IR detectors. The significant performance indicates that the GNW/PDMS-based devices reveal a novel design concept and promising applications for the future new-generation IR photodetectors.