Dynamically reconfigurable nanoscale modulators utilizing coupled hybrid plasmonics

Controllable hybrid plasmonic integrated circuit

In this paper, a controllable hybrid plasmonic integrated circuit (CHPIC) composed of hybrid plasmonic waveguide (HPW)-based rhombic nano-antenna, polarization beam splitter, coupler, filter, and sensor has been designed and investigated for the first time. In order to control the power into a corresponding input port, a graphene-based 1 × 3 power splitter with switchable output has been exploited. The functionality of each device has been studied comprehensively based on the finite element method and the advantages over state-of-the-art have been compared. Moreover, the effect of connection of CHPIC to the photonic and plasmonic waveguides has been studied to exhibit the capability of variety excitation methods of the CHPIC. Furthermore, the performance of the proposed CHPIC connected to inter/intra wireless transmission links has been investigated. The wireless transmission link consists of two HPW-based nano-antennas as transmitter and receiver with the maximum gain and directivity of 10 dB and 10.2 dBi, respectively, at 193.5 THz. The suggested CHPIC can be used for applications such as optical wireless communication and inter/intra-chip optical interconnects.

Efficient binary and QAM optical modulation in ultra-compact MZI structures utilizing indium-tin-oxide

A design for a CMOS-compatible active waveguide is proposed in which the epsilon-near-zero (ENZ) property of the indium-tin-oxide (ITO) is used to induce large variations in the real and imaginary parts of the waveguide effective index. The proposed waveguide comprises a TiN/HfO₂/ITO metal–oxide–semiconductor (MOS) structure where the speed and power consumption are significantly improved by the application of the TiN and realization of double accumulation layers in the ITO. Simulations show the insertion loss (IL) of 0.38 dB/μm, extinction ratio (ER) of 11 dB/μm, the energy consumption of 11.87fJ/bit and electrical bandwidth of 280 GHz when the designed waveguide is used as an electro-absorption modulator. The waveguide is then used in an MZI structure to design binary and quadrature-amplitude-modulator (QAM) modulators. For binary modulator, the IL, ER, and V_πL_π figures of merit are found to be 1.24 dB, 54 dB, and 6.4 V μm, respectively, which show substantial improvement over previous ITO-based designs. In the QAM design, the symmetry in the real and imaginary parts of the waveguide effective index is employed to obviate the need for additional phase shift elements. This considerably reduces the overall length of the proposed QAM modulator and improves efficiency. Simulations show the energy consumption and bit rate, of 2fJ/bit and 560 Gbps, respectively in a 4-QAM modulator with the overall length of 6.2 μm. The symmetry properties of the proposed waveguide can be further exploited to realize quadrature-phase-shift-keying (QPSK) modulators which here is used in combination with the 4-QAM to propose a design for the more advanced modulation scheme of 16-QAM. The design of ITO-based QAM modulators is here reported for the first time and the abovementioned performance parameters show the unique properties of these modulators in terms of footprint, energy consumption and modulation-speed.

Supermode Hybridization: A Material-Independent Route toward Record Schottky Detection Sensitivity Using <0.05 μm3 Amorphous Absorber Volume

Schottky photodetectors are attractive for CMOS-compatible photonic integrated circuits, but the inability to simultaneously optimize the metal emitter thickness for photon absorption and hot carrier emission limits the detection efficiency and sensitivity. Here, we propose and experimentally demonstrate a supermode hybridization waveguiding effect that can overcome the trade-off. By introducing structural asymmetry into coupled plasmonic nanostructures, hybridization-induced field enhancement can help ultrathin metal emitters to achieve greater optical absorption than bulk counterparts. Despite the use of amorphous materials with higher transport losses, our hybridized Schottky detectors demonstrate higher responsivity per device volume compared to crystalline-based and unhybridized Schottky designs with broadband (1.5-1.6 μm) and athermal (15-100 °C) behavior as well as record sensitivity of -55 dBm that approaches Ge counterparts that are 36 times larger. The hybridization effect can be utilized across diverse nanomaterial platforms to facilitate light-matter interaction, paving the way toward backend-compatible, chip-integrated photonics with greater manufacturing flexibility.

Monolithic Plasmonic Waveguide Architecture for Passive and Active Optical Circuits

Guided-wave plasmonic circuits are promising platforms for sensing, interconnection, and quantum applications in the subdiffraction regime. Nonetheless, the loss-confinement trade-off remains a collective bottleneck for plasmonic-enhanced optical processes. Here, we report a unique plasmonic waveguide architecture that can alleviate such trade-off and improve the efficiencies of plasmonic-based emission, light-matter-interaction, and detection simultaneously. Specifically, record experimental attributes such as normalized Purcell factor approaching 10⁴, 10 dB amplitude modulation with <1 dB insertion loss and fJ-level switching energy, and photodetection sensitivity and internal quantum efficiency of -54 dBm and 6.4% respectively have been realized within our amorphous-based, coupled-mode plasmonic structure. The ability to support multiple optoelectronic phenomena while providing performance gains over existing plasmonic and dielectric counterparts offers a clear path toward reconfigurable, monolithic plasmonic circuits.

Silicon Mode-Selective Switch via Horizontal Metal-Oxide-Semiconductor Capacitor Incorporated With ENZ-ITO

A silicon mode-selective switch (MSS) is proposed by using a horizontal metal-oxide-semiconductor (MOS) capacitor incorporated with the epsilon-near-zero (ENZ) indium-tin-oxide (ITO). The carrier concentration of the double accumulation-layers in ITO can be adjusted via the applied gate-voltage to achieve the desired switching state. The MOS-type mode of the central MOS-capacitor based triple-waveguide coupler is introduced and optimised by using the full-vectorial finite element method to switch the "OFF" and "ON" states. The thickness of the accumulation layer and the optimal design are studied by using the 3D full-vectorial eigenmode expansion method. The optimised quasi-TE₀ and quasi-TE₁ modes based MSSes are with the extinction ratios of 28.52 dB (19.05 dB), 37.29 dB (17.8 dB), and 37.29 dB (23.7 dB), at "OFF" ("ON") states for the accumulation-layer thicknesses of 1.5, 5.0, and 10.0 nm, respectively. The operation speed can achieve to be 6.3 GHz, 6.2 GHz, and 6.2 GHz for these three accumulation-layer thicknesses, respectively. The performance of the proposed MSS with a 2.5 V gate-voltage is also studied for preventing the oxide breakdown. The proposed MSS can be applied in the mode-division-multiplexing networks for signal switching and exchanging.

Record Purcell factors in ultracompact hybrid plasmonic ring resonators

For integrated optical devices and traveling-wave resonators, realistic use of the superior wave-matter interaction offered by plasmonics is impeded by ohmic loss, which increases rapidly with mode volume reduction. In this work, we report composite hybrid plasmonic waveguides (CHPWs) that are not only capable of guiding subwavelength optical mode with long-range propagation but also unrestricted by stringent requirements in structural, material, or modal symmetry. In these asymmetric CHPWs, the versatility afforded by coupling dissimilar plasmonic modes provides improved fabrication tolerance and more degrees of device design optimization. Experimental realization of CHPWs demonstrates propagation loss and mode area of 0.03 dB/μm and 0.002 μm2, corresponding to the smallest combination among long-range plasmonic structures reported to date. CHPW ring resonators with 2.5-μm radius were realized with record Purcell factor compared with existing plasmonic and dielectric resonators of similar radii.

Multi-layer MOS capacitor based polarization insensitive electro-optic intensity modulator

In this study, a multi-layer metal-oxide-semiconductor capacitor (MLMOSC) polarization insensitive modulator is proposed. The design is validated by numerical simulation with commercial software LUMERICAL SOLUTION. Based on the epsilon-near-zero (ENZ) effect of indium tin oxide (ITO), the device manages to uniformly modulate both the transverse electric (TE) and the transverse magnetic (TM) modes. With a 20μm-long double-layer metal-oxide-semiconductor capacitor (DLMOSC) polarization insensitive modulator, in which two metal-oxide-semiconductor (MOS) structures are formed by the n-doped Si/HfO₂/ITO/HfO₂/ n-doped Si stack, the extinction ratios (ERs) of both the TE and the TM modes can be over 20dB. The polarization dependent losses of the device can be as low as 0.05dB for the "OFF" state and 0.004dB for the "ON" state. Within 1dB polarization dependent loss, the device can operate with over 20dB ERs at the S, C, and L bands. The polarization insensitive modulator offers various merits including ultra-compact size, broadband spectrum, and complementary metal oxide semiconductor (CMOS) compatibility.

Nanoscale modeling of electro-plasmonic tunable devices for modulators and metasurfaces

The interest in plasmonic electro-optical modulators with nanoscale footprint and ultrafast low-energy performance has generated a demand for precise multiphysics modeling of the electrical and optical properties of plasmonic nanostructures. We perform combined simulations that account for the interaction of highly confined nearfields with charge accumulation and depletion on the nanoscale. Validation of our numerical model is done by comparison to a recently published reflective meta-absorber. The simulations show excellent agreement to the experimental mid-infrared data. We then use our model to propose electro-optical modulation of the extinction cross-section of a gold dimer nanoantenna at the telecom wavelength of 1550 nm. An ITO gap-loaded nanoantenna structure allows us to achieve a normalized modulation of 45% at 1550 nm, where the gap-load design circumvents resonance pinning of the structure. Resonance pinning limits the performance of simplistic designs such as a uniform coating of the nanoantenna with a sheet of indium tin oxide, which we also present for comparison. This large value is reached by a reduction of the capacitive coupling of the antenna arms, which breaks the necessity of a large volume overlap between the charge distribution and the optical nearfield. A parameter exploration shows a weak reliance on the exact device dimensions, as long as strong coupling inside the antenna gap is ensured. These results open the way for a new method in electro-optical tuning of plasmonic structures and can readily be adapted to plasmonic waveguides, metasurfaces and other electro-optical modulators.

Microfiber interferometer with surface plasmon-polariton involvement

We fabricated a microfiber interferometer with surface plasmon-polaritons (SPPs) involvement. Commonly, the SPPs are not involved in interference due to the mismatch momentum and ultrashort propagation distance. In this Letter, an absorber-doped microfiber is utilized for increasing the matched momentum (i.e., their modal projection), and as a result, an SPP is coherent with an end-fire method-stimulated hybrid SPP. A mathematical model is proposed for investigating the modal-projection-caused interference, and its results show that the proposed interferometer is very dependent on the polarization. Confirmation experiments were carried out, and a good agreement between theoretical predictions and experimental results was found. The proposed interferometer will potentially facilitate many SPP studies in directly related fields.

A voltage-controlled silver nanograting device for dynamic modulation of transmitted light based on the surface plasmon polariton effect

An active-controlled plasmonic device is designed and fabricated based on the index-sensitive properties of surface plasmon polaritons (SPPs). We utilize a one-dimensional silver nanograting with a period of 320 nm overlayered with a liquid crystal (LC) layer (50 μm in thickness), to transmit selectively the surface plasmon resonance (SPR) wavelength. This device realizes the active, reversible and continuous control of the transmitted light wavelength by modulating the external voltage signal applied to the LC layer. This voltage-controlled plasmonic filter has a dynamic wavelength modulation range of 17 nm, a fast respond speed of 4.24 ms and a low driving voltage of 1.06 V μm(-1). This study opens up a unique way for the design of tunable nanophotonic devices, such as a micro light sources and switches.

Plasmonic phase modulator based on novel loss-overcompensated coupling between nanoresonator and waveguide

We present that surface plasmon polariton, side-coupled to a gain-assisted nanoresonator where the absorption is overcompensated, exhibits a prominent phase shift up to π maintaining the flat unity transmission across the whole broad spectra. Bandwidth of this plasmonic phase shift can be controlled by adjusting the distance between the plasmonic waveguide and the nanoresonator. For a moderate distance, within bandwidth of 100 GHz, the phase shift and transmission are constantly maintained. The plasmonic phase can be shift-keying-modulated by a pumping signal in the gain-assisted nanoresonator. A needed length in our approach is of nanoscale while already suggested types of plasmonic phase modulator are of micrometer scale in length. The energy consumption per bit, which benefits from the nano size of this device, is ideally low on the order of 10 fJ/bit. The controllable plasmonic phase shift can find applications in nanoscale Mach-Zehnder interferometers and other phase-sensitive devices as well as directly in plasmonic phase shift keying modulators.