A periodic tungsten-covered dielectric ridge on substrate assembly is proposed in this article to investigate the perfect absorption in the near-infrared regime. The localized dipolar resonance and ...the propagating surface plasmon mode significantly restrict the reflectance thus forming two discrete absorption peaks. In the process of discovering perfect absorption, the geometrical parameters such as the tungsten layer thickness, ridge depth and width, substrate spacer thickness and the lateral period are correspondingly numerically explored and a rather high absorption rate of 99.9% can be achieved. Furthermore, the absorption peak is sensitive to the ground substrate index which makes it a potential candidate for compactly integrated on chip sensing applications. The polarization direction of the incident light modulates the absorption to a wider bandwidth and the oblique incidence splits the propagating mode along with a rather weak Fano-type absorption peak. The research may pave way for transition metal integrated on chip absorption system.
A compact graphene strip-ring hybrid resonator working in the mid-infrared regime is proposed as an analogue of Fano resonator or electromagnetically induced transparency. The dipolar surface plasmon ...resonance induced by the ring interferes with the
x
-polarized strip resonance forming a symmetric or asymmetric transparency window within the absorption profile. The spectral response can be modulated not only by the Fermi energy level of graphene, but also the geometry shape of the configuration. The sensitivity reaches 2450 nm/RIU and the light in the transparency window is slowed down to over 1/1090 times the speed in vacuum. The analytic analysis is in accordance with the 3D simulation results. Our compact design may have potential view in optical sensors, optical switches and light storage field.
The plasmonic analogy from Fano resonance to Autler–Townes splitting (ATS) in mid-infrared spectral range is observed assisted by a dual parallel graphene-coated grating structure. The analytical ...derivation exhibits a height-dependent resonance which is crucial for discerning Fano resonance from ATS. The mechanism of generating a transparency window seeks a trade-off between Fano resonance and ATS at threshold height. While within the critical height, Fano resonance dominates. The Akaike Information Criterion test is used to discern these two effects quantitatively. Moreover, the device pronounces a good tunability accompanied with a slowing light application. Our ideas open up a new insight view of designing or constructing highly integrated, multi-functional graphene-based metamaterials in nanoscale.
A nanoscale Fano resonator composed of a hybrid graphene disk-gold ring combination is reported in this letter. The inner narrow dipolar resonance of a discrete state induced by graphene interferes ...with the outside broad dipolar resonance of a continuum state induced by gold, thus forming an asymmetric Fano transparency within the absorption window. The metastructure exhibits a wide tunable band along with an excellent refractive index sensing capability of 2344 nm/RIU. The geometry adjustment modulates the spectral response giving chances to the equivalent of electromagnetically induce transparency. Moreover, the group index exceeds 760 within the transparency window enabling a potential use in slow light or light storage applications. The analytic analysis is in accordance with the numerical simulation results.
A directional energy focusing system based on parallel-monolayer graphene sheets is proposed and is analytically and numerically investigated in this paper. By properly designing the chemical ...potential distributions, we obtain a
∼
0.8-nm-size focusing point at desired positions with energy enhancement factor of over 2410. The flexible tunability of the transmission properties enables us to shut one parallel pair propagation down and guide the waves to the other branch. The light signal at the focal point is efficiently slowed down to over 10,000 times the speed in vacuum as well. The proposed structure may find potential applications in integrated circuits, on-chip systems or energy storage.
Tunable narrow-band plasmonically induced transparency (PIT) effect at mid-infrared region is realized in a graphene-spacer-grating-based (GSG-based) hybrid system. A silicon/SiO
2
grating is used to ...compensate wave-vector mismatches between graphene surface plasmons (GSPs) and free space optical waves. The PIT effect can be quickly tuned by small changes in the Fermi energy levels of the graphene sheets. A quality-factor (Q-factor) over 108 of the PIT peak with a group time delay over 0.44 ps within the PIT window can be achieved by setting suitable parameters of the graphene sheets and manipulating desirable geometric parameters of the Silicon/SiO
2
grating and the SiO
2
spacer. A GSG-based device with graded periods of the silicon/SiO
2
grating is further proposed to achieve a slowdown factor over 350 at certain cut-off wavelength and a trapping bandwidth of
∼
0.7
μm (from
λ
∼
7.55
to
λ
∼
8.25
μm) corresponding to
∼
3.3
THz
via dynamically tuning the Fermi level of the graphene sheet. The proposed GSG-based structure has potential applications in graphene-based optical devices such as tunable optical filters, plasmonic switches, and buffers.
We propose a novel polarization-maintaining supermode fiber containing quasi-elliptically arranged high-index cores. Numerical simulation indicates that such a fiber could support up to 20 distinct ...modes with different polarization states and spatial orientations. At 1550 nm, all the 20 modes are separated from their adjacent modes with effective refractive differences beyond 10- 4 . We also investigate the influence of parameters on mode number and effective area of the proposed fiber. Wavelength-dependent performance is analyzed subsequently ranging from 1500 to 1630 nm. The proposed fiber could guide 20 modes with low dispersion over the entire C-band. This letter illustrates that the proposed fiber might be a promising candidate for mode division multiplexing to enhance optical transmission capacity.
An ultrafast high-sensitivity refractive index (RI) and temperature-sensing system based on an optoelectronic oscillator (OEO) is proposed and demonstrated in this paper. A Fabry-Perot fiber Bragg ...grating (FP-FBG), which combines a gap with two FBGs in a silica V-shaped slot and characterizes a narrow notch in the reflection spectrum, is incorporated in the OEO to implement a microwave photonic filter and perform oscillating frequency selection. A microwave signal is generated by the OEO, whose oscillating frequency is determined by the center frequency of the FP-FBG notch, which varies with the surrounding environments. The RI or the temperature change can be accordingly measured by monitoring the frequency shift of the microwave signal using an electrical spectrum analyzer or a digital signal processor. An experiment is performed to verify the proposal. An RI sensitivity of 413.8 MHz/0.001RIU and a temperature sensitivity of 2516 MHz/°C are successively demonstrated.
Plasmonically induced transparency (PIT) in hexagon boron nitride (h-BN)-graphene-silica grating-based structure is proposed and demonstrated. By tuning the chemical potential of graphene and ...changing the geometry parameters of the proposed structure, PIT can be realized both within the upper reststrahlen (RS) band and outside the RS band. The group delay of the PIT window is analyzed and can be up to ~0.15 ps within the upper RS band via changing the chemical potential of graphene and the parameters of the silica grating. Apart from that, a refractive index (RI) sensor with a sensitivity of up to 0.336 μm per RI unit outside the RS band is proposed by changing the RI of the sensor media. The proposed structure may have the application in the graphene-h-BN-based slow light devices and optical sensors.
A U-shaped tunnel connected side coupled nanoring resonator waveguide system is proposed to generate Fano interference in a novel mechanism. By mutually coupling the infrared light through the ...artificially introduced U-tunnel to the two nanorings with the same resonant wavelength, single symmetric Lorentzian resonance transforms to asymmetric Fano resonance within the original resonant spectral range. The transparency window bridges the distinct constructive interferences in either rings instead of the canceling the bright mode resonance compared to former conceptions. The sensitivity of the system reaches 167 μm∕RIU far higher than the level of hundreds nanometers and is highly tunable. The light at resonance is successfully trapped and slowed down to 1/144 times the speed in vacuum, which is also flexible to release by tuning the Fermi energy of graphene rings. Overall, our ideas may pave new avenues to the design of classical analogy of Fano resonance metastructures, sensors or light storage devices.
•This mechanism is novel for generating Fano resonance.•The sensitivity is 167 um/RIU far higher than the previous ones.•The light is slowed down considerably and the tunability is good.
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