Hybrid Plasmonic Slot Waveguide Research Articles

Grating-assisted hybrid plasmonic slot resonator for on-chip SERS sensor with built-in filter

A grating-assisted hybrid plasmonic slot resonator is proposed and theoretically investigated as an on-chip surface-enhanced Raman scattering (SERS) sensor. A dielectric Bragg grating and a gold baffle are introduced into the hybrid plasmonic slot waveguide as two mirrors to form a plasmonic–dielectric cavity, in which the constructive interference of the input pump light greatly enhances the electric field. The grating reflects the wasted pump light for reverse secondary coupling and acts as a built-in notch filter for filtering out pump light from Raman scattered light simultaneously, improving the coupling efficiency and realizing a compact and miniaturized on-chip SERS sensor. Both the volumetric electric field enhancement and Raman collection efficiency are taken into account. The proposed scheme provides a simple, effective and universal method for improving the performance of the plasmonic-antennas-type waveguide-based SERS sensors.

Broadband graphene modulator with high modulation depth based on tip plasmonic waveguide

Broadband operation is a critical feature for high-speed electro-optic modulators in optical signal processing. To overcome the obstacle of material absorption-induced optical bandwidth shrinkage, graphene optical modulators based on the tip plasmonic concept have been proposed. The modulator is composed of buried double-layer graphene and Ag-SiO2-Si-SiO2-Ag hybrid structure with taper slots. Due to the tightened field confinement induced by the tip plasmonic effect, the light-graphene coupling is significantly enhanced. The direct metal layers contact with graphene is exploited to serve as the electrode. The simulation results based on the finite element method present a graphene modulator with a high modulation depth (MD) of 1.1 dB/μm and a relatively low propagation loss of 0.14 dB/μm. The power consumption is about 43.80 fJ/bit at the modulation length of 20 µm. The 3 dB-bandwidth is estimated to be around 340 GHz. Comparison with reported graphene modulators adopting hybrid plasmonic slot waveguide proves favorable modulation depth of proposed design, which promise its potentials in hybrid integration and on-chip signal processing.

Hybrid plasmonic slot waveguide with a metallic grating for on-chip biosensing applications.

Designing reliable and compact integrated biosensors with high sensitivity is crucial for lab-on-a-chip applications. We present a bandpass optical filter, as a label-free biosensor, based on a hybrid slot waveguide on the silicon-on-insulator platform. The designed hybrid waveguide consists of a narrow silicon strip, a gap, and a metallic Bragg grating with a phase-shifted cavity. The hybrid waveguide is coupled to a conventional silicon strip waveguide with a taper. The effect of geometrical parameters on the performance of the filter is investigated by 3D finite-difference time-domain simulations. The proposed hybrid waveguide has potential for sensing applications since the optical field is pulled into the gap and outside of the silicon core, thus increasing the modal overlap with the sensing region. This biosensor offers a sensitivity of 270 nm/RIU, while it only occupies a compact footprint of 1.03µm×17.6µm.

Compact hybrid plasmonic slot waveguide sensor with a giant enhancement factor for surface-enhanced Raman scattering application.

In this paper, a surface-enhanced Raman scattering (SERS) sensor with a giant field enhancement factor based on the coupling of surface plasmon polaritons (SPPs) is designed and studied theoretically. The proposed sensor adopts a metal-dielectric layered hybrid slot waveguide structure, combining thin metal (gold) layers and silicon nitride strip waveguides. Unlike other similar sensors, the silicon nitride waveguide structure does not serve as an excitation signal channel, conventionally loaded with the guided modes, but as an auxiliary layer, making it easier to concentrate the light field in the slot. Therefore, the sensor has a higher enhancement factor compared to the pure metal or dielectric slot structure. The results exhibit that we can obtain a maximum enhancement factor exceeding 10^6 under the compact configuration of 510 × 300 × 225nm^3 at the wavelength of 785 nm. By analyzing the dependence of the sensor performance on the structural parameters, we show that the structure of such sensor can directly be applied to SERS spectroscopic analysis as well as integrated with micro-and nano-photonic platform to perform on-chip detection system.

Fabrication-Tolerant and Low-Loss Hybrid Plasmonic Slot Waveguide Mode Converter

Integrated plasmonic structures can concentrate light to deep-subwavelength volumes below the diffraction limit and have been explored in many applications including label-free nanophotonic sensing with single molecule sensitivity, nonlinear conversion, and lasing. However, conversion between the dielectric waveguide mode and the plasmonic mode typically suffers from large mode conversion loss and requires high nanofabrication precision because of the mode mismatch and the precise alignment requirements with the plasmonic slot structure, respectively. Here, we report low-loss conversion between a dielectric waveguide mode and a hybrid plasmonic slot waveguide mode in a structure with a large fabrication tolerance. The measured conversion loss between the dielectric waveguide mode to the hybrid plasmonic slot waveguide mode can be <; 2 dB in the wavelength range of 1.54-1.60 μm under the optimal phase match condition. The loss remains low with a lateral misalignment tolerance of >500 nm. We confirmed enhanced light-matter interaction in the plasmonic slot waveguide region by measuring the enhancement in optical absorption of graphene with and without the plasmonic slot structure. Our results demonstrate a new approach to achieve deep-subwavelength light concentration by using an easy-to-fabricate interface with dielectric waveguides.

Low-loss hybrid plasmonic TM-pass polarizer using polarization-dependent mode conversion

A low-loss hybrid plasmonic transverse magnetic (TM)-pass polarizer has been demonstrated utilizing polarization-dependent mode conversion. Taking advantage of the silicon hybrid plasmonic slot waveguide (HPSW), the unwanted transverse electric (TE) fundamental mode can be efficiently converted first to a TM higher-order mode and then suppressed by a power combiner, while the retained TM fundamental mode can pass through with negligible influence. Since the HPSW feature both strong structural asymmetry and a small interaction area in the cross-section between the metal and optical field, the optimized insertion loss of the device is as low as 0.4 dB. At the wavelength of 1550 nm, the extinction ratio is 28.3 dB with a moderate footprint of 2.38 μm × 10 μm . For the entire C band, the average reflection of the TE mode is suppressed below − 14 dB , and the extinction ratio is over 18.6 dB. This work provides another more efficient and effective approach for better on-chip polarizers.

Ultra-compact hybrid plasmonic mode convertor based on unidirectional eigenmode expansion.

An ultra-compact hybrid plasmonic mode convertor is demonstrated based on a hybrid plasmonic slot waveguide structure. Benefiting from the unidirectional eigenmode expansion approach, a mode-interference-based ${{\rm TE}_{00}}$TE00-to-${{\rm TM}_{01}}$TM01 mode convertor is realized for the first time, to the best of our knowledge, with an ultra-compact footprint of only ${2}.{33} \times {7}\,\,\unicode{x00B5} {{\rm m}^2}$2.33×7µm2. At the wavelength of 1550 nm, the insertion loss is below 2.34 dB, and the extinction ratio is 25.6 dB with mode conversion purity as high as 94.6%. The extinction ratio is over 15.5 dB for the entire C-band with a bandwidth of extinction ratio above 10 dB larger than 110 nm. The transmissivity of the crosstalk ${{\rm TE}_{10}}$TE10 and ${{\rm TE}_{02}}$TE02 at 1550 nm is $ - {16.1}$-16.1 and $ - {22.7}\,\,{\rm dB}$-22.7dB, respectively.

Hybrid Plasmonic–Photonic–Organic Modulators With Low Insertion Loss and High Modulation Depth

In this article, a novel hybrid plasmonic–photonic–organic electro-optical modulator based on Pockels effect is designed and numerically investigated by employing finite difference time domain and finite element methods at a wavelength of $\lambda \,= \,{\text{1.55}}\,\mu {\text{m}}$ . The presented modulator exhibits unique features such as the half-wave voltage–length product of 0.08 V⋅mm being in the range of modern plasmonic modulators. However, the design presented in this article represents a very low insertion loss of less than 2 dB in the wavelength range of 1.45–1.65 μ m. Moreover, the modulator has an energy consumption of approximately 25 fJ/Bit, modulation depth of approximately 35% and 80% at applied voltages of 5 and 10 V, and electro-optical bandwidth of more than 70 GHz. As the key component of the modulator, a novel hybrid plasmonic slot waveguide is introduced, which combines tight light confinement of plasmonic waveguides with the low loss feature of photonic waveguides. In particular, the presented waveguide enables tight light confinement and guiding in slots as narrow as 40 nm with remarkably low loss of less than 0.2 dB/ μ m, which makes them attractive for other applications in addition to the designed modulator. In this paper, the presented waveguides are thoroughly investigated and compared with plasmonic slot waveguides in terms of loss and modal characteristics.

Label-Free Highly Sensitive Hybrid Plasmonic Biosensor for the Detection of DNA Hybridization

A highly sensitive hybrid plasmonic slot-waveguide (HPSW) biosensor based on silicon-on-insulator is proposed and analyzed for DNA hybridization detection. The reported design is based on increasing the light interaction with the sensing region by using slot waveguide with plasmonic material. Due to the high index contrast and plasmonic effect, an ultrahigh optical confinement is achieved in the low-index regions, which enables the detection of the smallest change in the analyte refractive index with high sensitivity. The normalized power confinement, power density, and effective index of the supported modes by the HPSW are analyzed to achieve high-power confinement through the suggested biosensor and hence high sensitivity can be obtained. The HPSW is also incorporated with straight slotted resonator to calculate the sensitivity of the proposed design. The simulation results are calculated using full vectorial finite element method. The reported biosensor has high sensitivity of 1890.4 nm/RIU (refractive index unit), which is the highest in the literature to the best of our knowledge with a detection limit of 2.65 × 10 –6 RIU.

High Figure of Merit Graphene Modulator Based on Long-Range Hybrid Plasmonic Slot Waveguide

By exploiting the electro-absorption effect of graphene, we present a graphene-based long-range hybrid plasmonic slot (LRHPS) waveguide modulator. The waveguide structure consists of a silica substrate, two high-index silicon strips, two low-index slots, two graphene layers, and a metal. The modes are confined within the two horizontal slot regions, which make graphene layer close to the maximum of tightly confined electric field. The designed LRHPS waveguide takes advantages of both the traditional long-range surface plasmon polariton waveguide and the hybrid plasmonic waveguide. The combined effects of long-range surface plasmon polaritons and discontinuity of electric field at the interface between two dielectrics with high-contrast refractive index enable low insertion loss together with high modulation depth for potential high-density nanophotonic integration. The modulator performance is comprehensively studied in terms of attenuation, insertion loss, modulation depth, and figure of merit (FoM). The designed graphene-based LRHPS waveguide modulator shows a 3-dB modulation depth with only ~363-nm-long waveguide, a 3-dB optical bandwidth of 15 THz with a center wavelength of 1550 nm, a low energy per bit consumption of 0.008 fJ/b, and a high FoM of 218 improved by more than one order of magnitude. Moreover, gate-variable broadband operation is also available covering the entire $O$ , $E$ , $S$ , $C$ , $L$ , and $U$ telecommunication bands.

A CMOS-Compatible Hybrid Plasmonic Slot Waveguide With Enhanced Field Confinement

The emerging field of nanophotonics requires plasmonic devices to be fully compatible with semiconductor fabrication techniques. However, very few feasible practical structures exist at present. Here, we propose a CMOS-compatible hybrid plasmonic slot waveguide (HPSW) with enhanced field confinement. Our simulation results show that the HPSW exhibits significantly enhanced field confinement as compared with the traditional low-index slot waveguides and the hybrid metal dielectric slot waveguides. By controlling the thicknesses of different layers, an optimized HPSW structure with a better tradeoff between field confinement and propagation length has been simultaneously achieved.

A special issue on Information Optoelectronics: Devices, Technologies and Applications

Information technology has entered a big-data era. The every-increasing data traffic has driven the rapid development of information optoelectronics, which is related to key devices, crucial technologies, and important applications for the generation, transmission, processing, and detection of optical data information. Recent progresses on devices, technologies and applications of information optoelectronics have led to reduced footprint, improved efficiency, enhanced flexibility and extended functionality generating, delivering/manipulating, and detecting optical data information. Lots of integrated photonic devices, such as silicon-, grapheneand plasmonassisted waveguides, lasers, modulators and detectors, speciality optical fiber, and coherent optical communications, have been widely reported, showing significant advances in devices, technologies and applications of information optoelectronics. It is believed that information optoelectronics will continue its rapid development towards integrated nanophotonic devices, more advanced technologies, flexible and multi-functional applications. It is our intention to draw great attention of the research community to those hot topics in devices, technologies and applications of information optoelectronics. In this “Special Issue on Information Optoelectronics: Devices, Technologies and Applications”, we present 8 review articles and 4 research articles focusing on relevant subjects by internationally active groups in the related fields. In the review articles, Dr. Sudharsanan Srinivasan at University of California, Santa Barbara reviewed recent results on hybrid silicon mode-locked lasers focusing on low phase noise optical pulse generation. Key results included demonstration of the longest (cavity length 9 cm) integrated on-chip mode locked laser, 14 dB reduction of Lorentzian noise on a 20 GHz radio-frequency (RF) signal, and greater than 55 dB optical supermode noise suppression using harmonically mode locked long cavity laser, 10 GHz passively mode locked laser with 15 kHz linewidth using on-chip all optical feedback stabilization. Dr. Ran Hao at Zhejiang University reviewed recent developments of graphene-based optical modulators, including material property, different integration schemes, single-layer graphene-based modulator, multi-layer and few-layer graphene-based modulators, corresponding figure-of-merits, wavelength/temperature tolerance, and graphene-based fiber-optic modulator. Dr. Lai Wang at Tsinghua University reviewed recent progresses on InGaN quantum dot (QD) light emitting diodes (LEDs), including the basic physics model of the strain relaxation in self-assembled InGaN QDs, the growth of InGaN QDs with a growth interruption method by metal organic vapor phase epitaxy, the optimization of GaN barrier growth in multilayer InGaN QDs, and the green, yellow-green and red InGaN QD LEDs. Dr. Xiaowei Guan and Dr. Daoxin Dai at Zhejiang University reviewed progresses on various hybrid plasmonic waveguides as well as ultrasmall functionality devices. Ultra-sharp bending of silicon hybrid nanoplasmonic waveguides, optical couplers/splitters, ultrasmall resonators, and polarization handing devices were discussed. Dr. Jian Wang at Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology reviewed recent progress on plasmon-assisted nanophotonic devices and their wide applications, including long-range hybrid plasmonic slot (LRHPS) waveguide, ultra-compact plasmonic microresonator with efficient thermo-optic tuning, high quality (Q) factor and small mode volume, compact active hybrid plasmonic ring resonator for deep-subwavelength lasing

Long-Range Hybrid Plasmonic Slot Waveguide

We propose and design a silicon-based long-range hybrid plasmonic slot (LRHPS) waveguide. The waveguide structure consists of a thin metal film (silver) inserted into a vertical low-index slot [filled with silicon nanocrystal (Si-nc)] between two high-index dielectrics (silicon), forming two nanoscale low-index Si-nc slot regions. The modes are confined within the two vertical regions. The designed LRHPS waveguide takes advantages of both traditional long-range surface plasmon polariton waveguide and hybrid plasmonic waveguide. The combined effects of long-range surface plasmon polaritons and discontinuity of electric field at the interface between two dielectrics with high-contrast refractive index enable a millimeter-scale propagation range together with a subwavelength mode confinement for potential high-density nanophotonic integration. The resultant quasi-TE mode properties of LRHPS waveguide, including long-range hybrid (LRH) mode and short-range hybrid (SRH) mode, are analyzed, showing a long propagation length up to 14.55 mm (corresponding to a low loss of $3\times 10^{-4} \hbox{dB}/\mu\hbox{m}$ ) with a slot size of 150 nm $\times$ 200 nm. Normalized power and intensity are also calculated, indicating tight mode confinement within subwavelength low-index slot regions. Moreover, nonlinearity and chromatic dispersion are also studied. Due to the design freedom of double-slot structure, a high nonlinearity of $7.82 \times 10^{6} \hbox{W}^{-1}\hbox{km}^{-1}$ and a low chromatic dispersion of $-$ 28.29 ps/nm/km at 1550 nm are achieved, implying possible applications in efficient nonlinear optical signal processing.

Nonlinear hybrid plasmonic slot waveguide for second-harmonic generation

A nonlinear hybrid plasmonic slot waveguide composed of periodically poled lithium niobate (PPLN) and two separated silver films is investigated. The effective refractive index, propagation length, and energy confinement of the hybrid anti-symmetric mode in this waveguide are calculated using the structure parameters at the fundamental wavelength of \lambda=1550 nm and its second harmonic (SH) \lambda= 775 nm. Through the above indices, coupling efficiency (maximum SH conversion efficiency during propagation) and peak position (propagation location of the conversion efficiency) of SH generation are analyzed. Finally, higher conversion efficiency can be achieved at a shorter propagation distance by changing the waveguide into a tapered structure.

Vertical coupling characteristics between hybrid plasmonic slot waveguide and Si waveguide

For development of complementary metal–oxide–semiconductor (CMOS)-compatible integrated optical circuits, vertical directional coupling between a hybrid plasmonic slot waveguide and a Si waveguide is theoretically investigated in detail. To determine the vertical separation gap and efficient coupling length, we investigate the characteristics of the even and odd supermodes at a wavelength of 1.55μm. The vertical coupler transfers 90% of the power carried by the Si waveguide to the hybrid plasmonic slot waveguide after normalizing to reference waveguides when the gap is 60nm and the coupling length is 2.6μm. Because of the lossy hybrid guided mode in the plasmonic waveguide, the transmitted power exhibits damped sinusoidal behavior depending on the overlapping length. The proposed vertical coupler shows more efficient light coupling between a dielectric and plasmonic waveguide in comparison to the other types of hybrid coupler, and can be exploited further for on-chip integrated opto-electronic circuits.

Design and analysis of a nanostructure grating based on a hybrid plasmonic slotwaveguide

A novel nanostructure grating with broadband reflection is proposed and analyzed in thispaper. The grating is based on a hybrid plasmonic slot waveguide that consists of a verticaldielectric-slot incorporated at the gap between the upper silicon rib and the metalsubstrate. The structure could provide an ultra-tight mode confinement in the cross-sectionwhile maintaining a relatively low propagation loss. By exploiting the superior modalproperties, an ultra-compact and broadband Bragg grating is presented, which shows thecapability of efficient wavelength selection near the telecom bandwidths. Thewaveguide-based Bragg grating could be used as a filter in telecommunicationsystems and could be a promising candidate for future integrated photonic circuits.

CMOS-Compatible Hybrid Plasmonic Slot Waveguide for On-Chip Photonic Circuits

For development of on-chip photonic circuits, a complementary metal-oxide-semiconductor (CMOS)-compatible hybrid plasmonic slot waveguide is proposed. The characteristics of its guided hybrid modes at a wavelength of 1.55 μm are investigated by the finite-element method. The combination of a Si gate and metallic features of a CMOS electronic device provides both subwavelength light confinement and long propagation length with high power intensity. The characteristics of the guided hybrid mode are improved by optimizing the configurations of the Si core. The proposed hybrid plasmonic slot waveguide is compatible not only with the silicon electronics fabrication processes but also with the metallic features of CMOS electronic devices.