Hole array enhanced dual-band infrared photodetection.

Photonic structures have been attracting more attention due to their ability to capture, concentrate and propagate optical energy. In this work, we propose a photon-trapping hole-array structure integrated in a nip InAsSb-GaSb heterostructure for the enhancement of the photoresponse in both near- and mid-infrared regions. The proposed symmetrical hole array can increase the photon lifetime inside the absorption layer and reduce reflection without polarization dependence. Significant enhancements in absorption and photoelectric conversion efficiency are demonstrated in dual bands for unpolarized incidence. The enhancement factors of responsivity at room temperature under zero-bias are 1.12 and 1.33 for the near- and mid-infrared, respectively, and they are increased to 1.71 and 1.79 when temperature drops to the thermoelectric cooling temperature of 220 K. Besides, such an integrated hole array also slightly improves working frequency bandwidth and response speed. This work provides a promising way for high-efficiency polarization-independent photoelectric conversion in different electromagnetic wave ranges.

Surface plasmon enhanced GeSn photodetectors operating at 2 µm.

Au-hole array and Au-GeSn grating structures were designed and incorporated in GeSn metal-semiconductor-metal (MSM) photodetectors for enhanced photo detection at 2 µm. Both plasmonic structures are beneficial for effective optical confinement near the surface due to surface plasmon resonance (SPR), contributing to an enhanced responsivity. The responsivity enhancement for Au hole-array structure is insensitive to the polarization direction, while the enhancement for Au-GeSn grating structure depends on the polarization direction. The responsivity for GeSn photodetector with Au hole-array structure has ∼50% reinforcement compared with reference photodetector. On the other hand, Au-GeSn grating structure benefits a 3× enhanced responsivity of 0.455 A/W at 1.5V under TM-polarized illumination. The achieved responsivity is among the highest values for GeSn photodetectors operating at 2 µm. The plasmonic GeSn photodetectors in this work offer an alternative solution for high-efficiency photo detection, manifesting their great potentials as candidates for 2 µm optical communication and other emerging applications.

Polarization-Controlled Plasmonic Structured Illumination.

Structured light in the subwavelength scale is important for a broad range of applications ranging from lithography to imaging. Of particular importance is the ability to dynamically shift the pattern of the fields, which has led to the development of structured illumination microscopy. Further extension of structured illumination to plasmonic systems has enabled imaging beyond diffraction limit. However, structured illumination usually requires complicated optical setups entailing moving mechanical parts. Here a polarization tunable structured plasmonic field (SPF) is proposed and experimentally demonstrated. The SPF is formed by surface plasmon interference (SPI) generated by a fishbone-shaped metasurface on a thin gold film. Importantly, the SPF can be continuously shifted by merely varying the linear polarization state of an incident beam. The precise control of the fringes of structured illumination and elimination of mechanical control will have great potential in subdiffractional imaging for practical applications.

Rotated fourfold U-shape metasurface for polarization-insensitive strong enhancement of mid-infrared photodetection.

Metasurface with thin planar resonant elements offers great capability in manipulating electromagnetic waves and their interaction with semiconductors. Split-ring resonator (SRR), as the basic building block, has been extensively investigated for myriad applications owing to its multiple electric and magnetic resonant modes. In this work, we report a rotated fourfold U-shape SRR metasurface for polarization-insensitive strong enhancement of mid-infrared photodetection. The integrated photodetector consists of a rotated fourfold SRR array and an InAsSb based heterojunction photodiode. A photosensitivity enhancement factor as high as 11 has been achieved by adoption of superimposed high order magnetic and electric resonant modes in the SRR metasurface. This work provides a promising pathway for exploring high performance polarization-insensitive photodetection in different electromagnetic wave ranges.

Indium antimonide uncooled photodetector with dual band photoresponse in the infrared and millimeter wave range.

All-InSb film-based and spiral antenna-assisted Au-InSb-Au metal-semiconductor-metal detector is reported with dual-band photoresponse in the infrared (IR) and millimeter wave range. At IR, the detector exhibits a long wavelength 100% cut-off at 7.3 µm. Under an applied bias of 5 mA, the uncooled blackbody responsivity and specific detectivity are 3.5 A/W and 1×108 Jones, respectively. The f-3dB value measured at 2.94 µm is 75 KHz, corresponding to a detector rise speed of 4.7 µs. At millimeter wave range, the detector shows a narrowband response determined by the coupling of the antenna. A voltage responsivity of 25 V/W is achieved at 167 GHz (1.796 mm) under an applied bias of 25 mA, and the corresponding noise equivalent power (NEP) is 1.0×10-10 WHz-1/2, which can be improved to 1.8×10-12 WHz-1/2 if normalized to the real active semiconductor area. A f-3dB value of 17.5 KHz, corresponding to a detector rise speed of 20 µs is achieved in this range. A proof of principle for IR-modulated photoresponse for millimeter wave is achieved with a maximum modulation depth of 47.5%. This All-InSb film-based detector and the modulation are promising for future novel optoelectronic devices in IR and millimeter waves.

CMOS-compatible all-Si metasurface polarizing bandpass filters on 12-inch wafers.

The implementation of polarization controlling components enables additional functionalities of short-wave infrared (SWIR) imagers. The high-performance and mass-producible polarization controller based on Si metasurface is in high demand for the next-generation SWIR imaging system. In this work, we report the first demonstration of all-Si metasurface based polarizing bandpass filters (PBFs) on 12-inch wafers. The PBF achieves a polarization extinction ratio of above 10 dB in power within the passbands. Using the complementary metal-oxide-semiconductor (CMOS) compatible 193nm ArF deep ultra-violet (DUV) immersion lithography and inductively coupled plasma (ICP) etch processing line, a device yield of 82% is achieved.

Nanobridges formed through electron beam image reversal lithography for plasmonic mid-infrared resonators with high aspect ratio nanogaps.

We present the emergence of nanobridge networks through a nanofabrication technique based on image-reversal electron beam lithography and demonstrate plasmonic structures with high aspect ratio sub-20 nm gaps capable of strong intensity enhancement in the mid-infrared range. The proposed technique, which employs the engineering of natural formations of nanobridges in predefined templates, could serve as an alternative path for realizing mid-infrared plasmonic resonators with potential applications in surface plasmon polariton-based integrated optics, and enhancement of light-matter interaction for high efficiency photodetection and nanoscale light emitters.

Electrically controlled enhancement in plasmonic mid-infrared photodiode.

Surface plasmon polaritons (SPPs) have been attracting tremendous attention in application of enhanced optoelectronic devices owing to their capability of localizing electromagnetic waves in deep subwavelength scale. We propose a plasmonic mid-infrared InAsSb-based n-i-p photodiode with electrically-controlled photocurrent enhancement achieved by controlling the overlap between SPP depth and the absorption layer, from which maximum electrically controlled enhancement factors of ~5x and ~6x have been achieved for room temperature (293 K) and 77 K operation, respectively, corresponding to electrical tuning factors of 11.9 and 26. The maximum detectivities obtained at the two temperatures are 0.8 × 1010 Jones and 5 × 1011 Jones, respectively. This electrically controlled enhancement expands the application capability of plasmonic photodiodes.

Multifunctional Hyperbolic Nanogroove Metasurface for Submolecular Detection.

Metasurface serves as a promising plasmonic sensing platform for engineering the enhanced light-matter interactions. Here, a hyperbolic metasurface with the nanogroove structure in the subwavelength scale is designed. This metasurface is able to modify the wavefront and wavelength of surface plasmon wave with the variation of the nanogroove width or periodicity. At the specific optical frequency, surface plasmon polaritons are tightly confined and propagated with a diffraction-free feature due to the epsilon-near-zero effect. Most importantly, the groove hyperbolic metasurface can enhance the plasmonic sensing with an ultrahigh phase sensitivity of 30 373 deg RIU-1 and Goos-Hänchen shift sensitivity of 10.134 mm RIU-1 . The detection resolution for refractive index change of glycerol solution is achieved as 10-8 RIU based on the phase measurement. The detection limit of bovine serum albumin (BSA) molecule is measured as low as 0.1 × 10-18 m (1 × 10-19 mol L-1 ), which corresponds to a submolecular detection level (0.13 BSA mm-2 ). As for low-weight biotin molecule, the detection limit is estimated below 1 × 10-15 m (1 × 10-15 mol L-1 , 1300 biotin mm-2 ). This enhanced plasmonic sensing performance is two orders of magnitude higher than those with current state-of-art plasmonic metamaterials and metasurfaces.

Subwavelength dielectric nanorod chains for energy transfer in the visible range.

We report a new type of energy transfer device, formed by a dielectric nanorod array embedded in a silver slab. Such dielectric chain structures allow surface plasmon wave guiding with large propagation length and highly suppressed crosstalk between adjacent transmission channels. The simulation results show that our proposed design can be used to enhance the energy transfer along the waveguide-like dielectric nanorod chains via coupled plasmons, where the energy spreading is effectively suppressed, and superior imaging properties in terms of resolution and energy transfer distance can be achieved.

Ultra-small v-shaped gold split ring resonators for biosensing using fundamental magnetic resonance in the visible spectrum.

Strong light localization within metal nanostructures occurs by collective oscillations of plasmons in the form of electric and magnetic resonances. This so-called localized surface plasmon resonance (LSPR) has gained much interest in the development of low-cost sensing platforms in the visible spectrum. However, demonstrations of LSPR-based sensing are mostly limited to electric resonances due to the technological limitations for achieving magnetic resonances in the visible spectrum. In this work, we report the first demonstration of LSPR sensing based on fundamental magnetic resonance in the visible spectrum using ultrasmall gold v-shaped split ring resonators. Specifically, we show the ability for detecting adsorption of bovine serum albumin and cytochrome c biomolecules at monolayer levels, and the selective binding of protein A/G to immunoglobulin G.

Aluminum based structures for manipulating short visible wavelength in-plane surface plasmon polariton propagation.

We report aluminum based structures for manipulation of surface plasmon polariton (SPP) propagation at short wavelength range. Our simulation shows that aluminum is a good metal to excite and propagate SPPs with blue light and that the SPP wavelength can be reduced from about 465 nm to about 265 nm by monitoring the thickness of a coated Si(3)N(4) layer above the aluminum film. It is also shown that the damping becomes more significant with the increase of the thickness of the Si(3)N(4) layer. We also experimentally demonstrated the SPP wavelength tuning effect for 20nm Si(3)N(4) layer covered Al, which can be explained by the variation of effective permittivity. The proposed Metal-Insulator-Air (MIA) structures with SPP wavelength tuning ability have potential applications in 2D optics.

Actively tunable Fano resonances based on colossal magneto-resistant metamaterials.

In this Letter, a periodic structure in which each unit cell consists of one manganese oxide (La(0.7)Ca(0.3)MnO(3)) strip and two gold strips is designed. By simulating the electromagnetic responses of the structure, we confirm that Fano resonances can be actively controlled in the infrared region by modulating the intensity of the external magnetic field applied to the structure. This is due to the colossal magneto-resistance of the La(0.7)Ca(0.3)MnO(3) material. Furthermore, a transmission phase can also be effectively tuned. The phase has a shift of ΔΦ=1.05 rad at a frequency of 130 THz when the intensity of the external magnetic field varies from 5083 to 5193 kA/m. Such a tunable method has potential applications in controllable photoelectric elements.

Effect of dielectric cladding on active plasmonic device based on InGaAsP multiple quantum wells.

The Surface Plasmon Polariton (SPP) planar waveguide with amorphous silicon (α-Si) cladding is studied, for empowering the device modulation response. The device is fabricated with multiple quantum wells (MQWs) as the gain media electrically pumped for compensating SPP propagation loss on Au film waveguide. The SPP propagation greatly benefits from the modal gain for the long-range hybrid mode, which is optimized by adopting an α-Si cladding layer accompanied with minimal degradation of mode confinement. The proposed structure presented more sensitive response to electrical manipulation than the one without cladding in experiment.

Transverse mode control in high-contrast grating VCSELs.

This paper presents an extensive numerical analysis of a high-contrast grating VCSEL emitting at 0.98 µm. Using a three-dimensional, fully vectorial optical model, we investigate the influence of a non-uniform grating with a broad range of geometrical parameters on the modal behavior of the VCSEL. Properly designed and optimized, the high-contrast grating confines the fundamental mode selectively in all three dimensions and discriminates all higher order modes by expelling them from its central region. This mechanism makes single mode operation possible under a broad range of currents and could potentially enhance the single-mode output power of such devices. The high-contrast grating design proposed here is the only design for a VCSEL with three-dimensional, selective, optical confinement that requires relatively simple fabrication.

Unidirectional surface plasmon-polariton excitation by a compact slot partially filled with dielectric.

We propose a new scheme on unidirectional surface plasmon-polariton (SPP) excitation with the following advantages: ultracompact size, working at arbitrary incidence angle and over a wide spectrum. The proposed structure utilizes a partially filled metallic slot with dielectric to realize unidirectional SPP excitation via direct field manipulation. We theoretically and numerically show that unidirectional SPP excitation with a ratio of 93% can be achieved by a structure with a 50 nm slot. The proposed structure keeps its functional capability over incident angles from -80° to 80°, and has a broadband working spectrum of more than 70 nm.

Ultrathin multi-band planar metamaterial absorber based on standing wave resonances.

We present a planar waveguide model and a mechanism based on standing wave resonances to interpret the unity absorptions of ultrathin planar metamaterial absorbers. The analytical model predicts that the available absorption peaks of the absorber are corresponding to the fundamental mode and only its odd harmonic modes of the standing wave. The model is in good agreement with numerical simulation and can explain the main features observed in typical ultrathin planar metamaterial absorbers. Based on this model, ultrathin planar metamaterial absorbers with multi-band absorptions at desired frequencies can be easily designed.

Temporal coupled-mode theory of ring-bus-ring Mach-Zehnder interferometer.

The temporal coupled-mode theory (TCMT) for a ring-bus-ring Mach-Zehnder interferometer device is developed by taking energy conservation into account. The intercavity interaction in the device is facilitated via a tricoupler, which makes the decay of modes quantitatively different from that in other existing resonator schemes. The TCMT is related to the transfer matrix formalism with energy conservation and the Q factor, and it predicts results in good agreement with the experimental results. The mode analysis from the TCMT is quite illustrative because it can mimic the transparency as an electromagnetically induced transparency expression. The analysis of the tricoupler is applicable for analyzing the transparent resonance in two other similar configurations.

Short-range surface plasmon propagation supported by stimulated amplification using electrical injection.

We have investigated the propagation of the long-range mode (LRSP) and the short-range mode (SRSP) surface plasmon polaritons (SPPs) along the waveguide made from Au film and quantum wells (QWs) gain medium. Influenced by the gain spectral nonuniformity, the SRSP showed narrower spectrum than the LRSP in output, denoting that the SRSP propagation was supported by stimulated amplification (SA) in electrically-pumped QWs. An SRSP output power as large as 1.6 times of that of the LRSP was obtained over a travelling distance of 80 µm. The mechanism of SA-supported SRSP propagation can be adopted for electrical modulation of SPPs.

Waveguide devices with homogeneous complementary media.

We report the design of microwave waveguide devices based on complementary media. Various kinds of waveguide devices that possess nearly 100% transmission efficiency are proposed, such as waveguide bends, splitters, connectors, and shifters. Compared with previous work on waveguide devices of low reflection and minimized distortion based on transformation optics, our transform media are homogeneous metamaterials. Electromagnetic simulations by a finite-element method on detailed examples have been performed to validate the designs and these functionalities can be close to the practical.