TM Modes Research Articles

Analysis of Photonic Band Structure Tunability for TE and TM Modes in a Silicon and Polymer Based Ternary Photonic Crystal for Visible Range Devices

Analysis of Photonic Band Structure Tunability for TE and TM Modes in a Silicon and Polymer Based Ternary Photonic Crystal for Visible Range Devices

A Wideband mmWave Microstrip Patch Antenna Based on Zero-Mode and TM-Mode Resonances

Millimeter wave (mmWave) antennas for 5G communication require wide bandwidth, directional radiation patterns, low-profile design and multi-layer compatibility for module-level integration. In this paper, we introduce a method of loading shorting pins to a patch antenna to generate extra zero-modes. By merging the 2nd zero-mode, TM01 mode, 3rd zero-mode and TM20 mode in the frequency spectrum, a wide bandwidth varying from 23 to 34 GHz (relative bandwidth of 38.6%) and with a low-profile of 0.762 mm (0.07λ0, where λ0 is the wavelength at a middle frequency of 28.5 GHz) can be obtained. Based on this wideband patch antenna, a 4 × 2 antenna array is obtained with the ±40° scanning performance. Theoretical analysis, full-wave simulations and experimental performances are presented, validating the effectiveness of this method to achieve a wideband performance in a mmWave band. It can be applied to 5G communication systems using mmWave bands.

Design and analysis of a miniaturized UWB plasmonic absorber in visible light spectrum

This paper proposes a miniaturized UWB resonating THz unit-cell absorber in the visible light spectrum 400–700 THz with an average absorption of more than 95%. This novel structure is tuned to desired photonic spectrum by plasmonic electric and magnetic resonance with the suitable choice of the metal-insulator-metal stacked layers. The arrangement has a metal of thickness 15 nm on top and bottom layers constituted on a SiO2 substrate of 50 nm thickness. The stronger energy concentration due to plasmonic resonance provides higher absorbing efficiency. In this work, an investigation on absorption, S11, and surface impedance for various metals like Chromium (Cr), Gold (Au), Magnesium (Mg), Platinum (Pt), and Titanium (Ti) is presented. It is identified that Chromium (Cr) presents stable and maximum absorption in the entire visible spectrum. A study on different incident and polarization angles is also reported for TE and TM modes. Lumped equivalent models (T and π) for the proposed absorber are also presented. This structure can be utilized to harvest photonic energy for evoking low-power enabled IoT devices and sensors in biomedical applications.

Ultrahigh extinction ratio and ultra-low insertion loss silicon TE polarizer covering 1260-1675 nm bandwidth.

An ultra-broadband TE polarizer with outstanding performance is proposed and demonstrated on a 220 nm-thick silicon-on-insulator platform. The proposed TE polarizer consists of six cascaded directional couplers assisted by subwavelength grating (SWG) structures and two Euler bends. The SWG is introduced to control the coupling strength of the fundamental TE and TM modes. Simulations show that our proposed TE polarizer possesses ultra-low insertion loss (IL < 0.3 dB) for the fundamental TE mode and an ultrahigh polarization extinction ratio (PER > 35 dB) for the fundamental TM mode covering all communication bands from 1260 nm to 1675 nm. The experimental results show that the fabricated TE polarizer has excellent performance of IL < 0.6 dB and PER > 35 dB over a 210 nm bandwidth, which is limited by the measurement equipment. To the best of our knowledge, our proposed TE polarizer is the first single-etched all-silicon TE polarizer with such high PER covering all communication bands.

Dual polarized designs of square microstrip antenna for GSM and LTE applications

SummaryTo obtain the polarization agility in wireless applications, the dual polarized wideband or multi‐band antennas are required. In this paper, modified designs of square microstrip antenna by employing overlap offset parasitic patches are proposed for the dual polarized wideband and multi‐band response. Due to the optimum spacing in between the fundamental TM1045 and TM01135 modes along with TM11 mode, on a total substrate thickness of 0.075λg, the proposed design yields bandwidth of more than 550 MHz (&gt;50%), exhibiting the dual polarized characteristics. A similar design is presented on a thinner suspended substrate. Here, on the substrate thickness of 0.035λg, it yields impedance matching at higher order TM20 mode, which along with TM1045, TM01135, and TM11 modes exhibits triple band response. An impedance bandwidth of 3.4%, 17%, and 4.7% is realized in the three bands with a broadside gain of more than 6 dBi. The proposed design satisfies the requirements of GSM 810/GSM900/LTE applications. In each design, simulated results have been experimentally verified that show close agreement.

High extinction ratio and broadband polarization beam splitter based on bricked subwavelength gratings on SOI platform

A compact asymmetrical directional coupler (ADC) based on coupling between a conventional subwavelength grating (SWG) and a bricked subwavelength grating (BSWG) is proposed to realize broadband polarization beam splitter (PBS) with high extinction ratio (ER) on silicon-on-insulator (SOI) platform. Apart from conventional SWG structural parameters (duty cycle and period), the BSWG is utilized to provide a new design space to control TE and TM modal effective index for accurate phase match. Accordingly, as to the TM mode, it is possible to satisfy phase-matching condition and then can be coupled more efficiently with higher ER by introducing the BSWG. Meanwhile, there is a significant phase mismatch for the TE mode. In this way, the proposed PBS that separates TE and TM mode to the through and cross ports can be realized. Simulation results show that the proposed PBS with a compact coupling length of 8.4 μm can achieve a high ER of 35.06 dB and an insertion loss of 0.25 dB for the TM mode at 1.55 μm, while the ER is 18.92 dB and insertion loss is 0.01 dB for the TE mode. Moreover, the operating bandwidth is up to 300 nm (1400∼1700 nm) for the TE mode and 155 nm (1487∼1642 nm) for the TM mode when the ER is >15 dB.

Design of a ceramic enhanced normal conducting standing wave accelerator structure for higher shunt impedance

In this paper we present the theoretical study of a dielectric-loaded standing wave accelerator structure with enhanced shunt impedance. The accelerator structure operates in a TM020 mode at 5.10 GHz. At the same accelerating gradient, the ohmic and dielectric power dissipation in the proposed cavity is 40% lower than the ohmic power dissipation in a conventional metallic pillbox cavity operating in a TM010 mode. The enhancement of the microwave power utilization efficiency leads to the cost reduction of the microwave source infrastructure and the operation. In compact accelerator applications, this type of accelerator structures are of potential use in extreme environment conditions such as space missions where close scrutiny must be exercised over the power availability and the waste heat dissipation.

Ultra-Broadband and Compact TM-Pass Polarizer Based on Graphene-Buried Polymer Waveguide.

We report an ultra-broadband and compact TM-pass polarizer based on graphene-buried polymer waveguides. The characteristic parameters of the polarizer were carefully designed and optimized. The standard microfabrication processes were employed to fabricate the device. The presented polarizers exhibit high polarization-dependent transmission imposing a TE mode cutoff while leaving the TM mode almost unaffected. We experimentally demonstrated the polarizer that has an ultra-high extinction ratio of more than 22.9 dB and 41.9 dB for the monolayer graphene film placed on the surface of core layer and buried in the center of core layer, respectively, and as low insertion loss as ~4.0 dB for the TM mode with the bandwidth over 110 nm. The presented polarizer has the advantages of high extinction ratio, ultra-broadband, low cost, and easy integration with other polymer-based planar lightwave devices.

Performance enhancement of an ultrafast graphene photodetector via simultaneous two-mode absorption in a hybrid plasmonic waveguide.

An ultrafast, compact, zero-biased, and complementary metal-oxide semiconductor-compatible graphene photodetector (PD) based on a silicon-on-insulator hybrid plasmonic waveguide (HPWG) is proposed. Lumerical MODE solver is employed to investigate the modal characteristics of TM-polarized modes in the HPWG composing the PD. It is shown that the input light can be completely coupled into the photonic-like and plasmonic-like fundamental TM modes at the PD section. These two modes are exploited together in the photodetection process to enhance the PD performance. A rigorous analysis is performed in order to extract the optoelectronic characteristics of the single-layer graphene (SLG) used in the proposed structure. Lumerical 3D-FDTD solver is then employed to quantify the light interaction of the two aforementioned optical modes with the SLG. With a proper design at a wavelength of 1550 nm, the PD voltage responsivity reaches 2.8 V/W, and the photocurrent responsivity is obtained as 18.5 mA/W, while the corresponding absorption length is kept below 8µm and the noise equivalent power is limited to 3.7pW/Hz. Moreover, as the PD operates under zero bias, its photoresponse is predominated by the photothermoelectric mechanism, exhibiting a bandwidth that exceeds 180 GHz while avoiding the dark current.

Design of a grating-assisted silicon hybrid mode-, polarization-, and wavelength-division (De)multiplexer for on-chip optical interconnects.

This paper presents a 12-channel hybrid mode-, polarization-, and wavelength-division (de)multiplexer. The proposed device is designed on a silicon-on-insulator platform. The device structure constitutes three coupling sections with a bus waveguide at the middle and two single-mode waveguides on each side. The periodic grating structures are present in between the waveguides for contra-directional coupling of the three TE modes and three TM modes of the bus waveguide to respective fundamental modes of the single-mode waveguides at 1550 and 1560 nm. The device is simulated using the 3D finite-difference time-domain technique, and the resulting insertion loss, cross talk, and return loss are <1.56dB, <-21.74dB, and >12.22dB, respectively. Moreover, the period of the grating structures is varied to perform the fabrication tolerance study.

An ultra-compact polarization-insensitive slot-strip mode converter

Integrated waveguides with slot structures have attracted increasing attention due to their advantages of tight mode confinement and strong light-matter interaction. Although extensively studied, the issue of mode mismatch with other strip waveguide-based optical devices is a huge challenge that prevents integrated waveguides from being widely utilized in large-scale photonic-based circuits. In this paper, we demonstrate an ultra-compact low-loss slot-strip converter with polarization insensitivity based on the multimode interference (MMI) effect. Sleek sinusoidal profiles are adopted to allow for smooth connection between the slot and strip waveguide, resulting reflection reduction. By manipulating the MMI effect with structure optimization, the self-imaging positions of the TE0 and TM0 modes are aligned with minimized footprint, leading to low-loss transmission for both polarizations. The measurement results show that high coupling efficiencies of − 0.40 and − 0.64 dB are achieved for TE0 and TM0 polarizations, respectively. The device has dimensions as small as 1.1 μm × 1.2 μm and composed of factory-available structures. The above characteristics of our proposed compact slot-strip converter makes it a promising device for future deployment in multi-functional integrated photonics systems.Graphic

A compact super wideband antenna with stable and improved radiation using super wideband frequency selective surface

A small bulb shaped planar super wideband (SWB) antenna with the dimension of 35 × 30 × 0.8 mm3 operating over 2.8–40 GHz (14.28:1) spectrum is proposed. The antenna offers a fractional bandwidth of 173.8%, bandwidth dimension ratio (BDR) of 1904, measured peak gain of 5.5 dBi and radiation efficiency of 80%. The proposed antenna is unified to an unique SWB frequency selective surface (FSS), having unit cell size equal to 0.114λL × 0.114λL × 0.008λL (λL is the wavelength at 3.1 GHz). The FSS operates in 3.05 to 35.92 GHz spectrum (168.7%) with transmission level S21 ≤ -10 dB and reflection S11 near 0 dB for TE and TM modes of polarization with adequate angular stability. The linearly decreasing S11 phase of FSS makes it appropriate for radiation improvement of the bulb shaped antenna in the broadside direction by placing the antenna at the top of FSS with an optimal air gap of 19 mm. The SWB ‘antenna-FSS’ exhibits wideband response over 3–36.2 GHz (169.4%) spectrum, including commercial ultra-wideband (3.1–10.6 GHz), ISM bands (5.725–5.875 GHz & 24–24.25 GHz), WiMAX (3.3–3.7 GHz), IEEE 802.11 WLAN bands, S-C-X-Ku-Ka bands, and 5G NR (n77, n78, n79, n257, n258, n261) bandwidth with stable and adequate gain of 5.2–7.16 dBi and an acceptable radiation efficiency.

Enhanced sensing of terahertz surface plasmon polaritons in graphene/J-aggregate coupler using FDTD method

J-aggregates nanostructure proposed for realization of plasmonic manufactories like switchable localized surface resonances (LSR) due to their optical nonlinearities' properties. J-aggregates to enhancement of light-matter interaction is applied. In this regard, we propose a novel graphene/J-aggregate plasmonics coupler with subwavelength structure at telecommunication range. Utilizing device geometries and optical properties optimized for enhanced light-matter interactions lets us to harness the propagation of TM (TE) modes without the change of configuration. Here, the coupling parameters have been numerically and investigated using the finite-difference time-domain (FDTD) method. The results show that the coupling condition can be tuned by optical properties of graphene in turn leads to a tunable plasmonics coupler. It is shown that, by considering magnetic field of 0.01 T and graphene chemical potential of mc = 0.45 eV, the TM mode, and magnetic field of 0.02 T and graphene chemical potential of mc = 0.4 eV, the TE mode can be propagated in the selected ports. With the above behavior, the proposed structure may potentially be applied in telecommunication links.

Theoretical calculation and particle-in-cell simulation of a multi-mode relativistic backward wave oscillator operating at low magnetic field

Increasing the dimensions of high power microwave devices is an efficient method to improve the power capacity. However, an overmoded structure usually results in mode competition and a low beam-wave conversion efficiency. In this paper, a multi-mode operation mechanism is used to avoid mode competition and increase the efficiency. The calculation results of nonlinear theory of beam-multimode interaction show that the optimized conversion efficiency is up to 48% when TM01 mode, TM02 mode, and TM03 mode are all considered. As only the TM01 mode, TM02 mode, or TM03 mode is taken into account independently, the corresponding efficiency is 38%, 22%, or 20%. Based on this, a multi-mode relativistic backward wave oscillator is proposed with the ratio of the mean diameter of the slow wave structure (SWS) to the wavelength of the output microwave to be 3.5. The non-uniform SWS is used to increase the beam-wave conversion efficiency, and a combined reflector is adopted to reflect partial of the mixed microwave modes and make the device compact. The particle-in-cell simulations show that as the diode voltage is 1.1 MV, the beam current is 22.8 kA, and the external magnetic field is 0.76 T, the conversion efficiency is 45%, and the output microwave of 11.3 GW is the mixed modes of TM01 mode, TM02 mode, and TM03 modes with the corresponding power ratio of 74%, 7%, and 19%, respectively.

Van der Waals forces enhanced light–graphene interaction in optical microfiber polarizer

A facile and efficient approach to manufacturing optical devices with a plane graphene-coupled microfiber structure is proposed—attaching the optical microfiber onto a monolayer graphene-coated polydimethylsiloxane substrate. Such devices exhibit strong light–graphene interaction via the evanescent fields of the guided light in microfibers and show evident optical polarization and polarization-dependent saturable absorption effect. When the monolayer graphene with propagation distance is 2.5 mm, and the microfiber diameter is 3.9 μm, the polarization extinction ratio can reach up to 31.0 dB with the light wavelength at 1550 nm. The transmission in TM modes could be increased continuously by increasing the input power of light at 980 nm. The transmission with 3 and 10 dB modulation depths in TM modes could be achieved via 980 nm pump power of 15.1 and 66.1 mW, respectively, which is advantageous over unpolarized graphene-coupled microfiber devices. The proposed microfiber on graphene structure could efficiently integrate optical waveguides with two-dimensional materials, with great potential applications in optical polarizers, all-optical modulators, mode-locked fiber lasers, and sensors, especially for all-fiber systems.

A High-Efficiency W-Band Power Combiner Based on the TM₀₁ Mode in a Circular Waveguide

A high-efficiency W-band 12-way power combiner system based on the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode in a circular waveguide has been presented in this study. It is a radial structure composed of three elements: a circular waveguide TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> -mode transducer, an isolated 12-way radial power combiner, and amplifier modules. The measured passive combining efficiency is observed to be greater than 89.5% over the range of 85–100 GHz. The isolation between the inputs is better than 10 dB, with a maximum back-to-back return loss of 13 dB. By using 12 GaN monolithic microwave integrated circuit (MMIC) 2-W power amplifiers, the active combiner system produces a maximum power output of up to 22 W with an average combining efficiency of 81.7% within the band of 92–97 GHz. The power-added efficiency within the operating band has been measured to be up to 20.8%.

Wavelength-Dependent Polarization Beam Splitter Based on Birefringent Tapered Multicore Fiber

A newPolarization Beam Splitter (PBS) is proposed by introducing an outer substrate, different from the sophisticated design on the structures themselves. The PBS is fabricated by tapering a multicore fiber (MCF) and assembling with a PDMS substrate, with easy handling and high feasibility. The periodic oscillation transmission demonstrates the interference between the center- and side-core modes with a phase difference of π/2. The polarization dependence of the periodic spectra is observed. The intensity distribution can be modulated either in the center-core or side-cores by adjusting the polarized angle or the wavelength. For specified wavelength, the TE and TM mode can be split into different cores by introducing asymmetry from the PDMS substrate to produce a birefringent tapered MCF. The maximum polarization extinction ratio (PER) of the center-core and side-cores is achieved to be 26 dB and 20 dB for specified wavelengths, respectively. The experimental results show that the center- and side-core have different preservation capabilities of different linear polarized light, corresponding to periodic wavelength. The simulated models are computed by using Rsoft BeamPRO and COMSOL Multiphysics to clarify the fundamental principles of the observed phenomena. The simulated spectra are consistent with the measured spectral response. The proposed structure can serve as a potential PBS with high PER and easy feasibility in various MCF-based applications owing to its capability of the wavelength-dependent and polarization-dependent splitting.

Design and analysis of a polarization-independent and incident angle insensitive triple-band metamaterial absorber

A triple-band metamaterial absorber (MMA) which is composed of a traditional metal-dielectric-metal structure is proposed in this paper, three absorption peaks are located at S-band, C-band and X-band, respectively. The design parameters are obtained by the methods of controlling variables and iterative optimization, and three perfect absorption peaks exceeding 99% are acquired at 3.72 GHz, 5.86 GHz, and 10.54 GHz after numerical calculation and analysis. Subsequently, the impedance matching conditions for absorption are proved through the analysis of equivalent electromagnetic parameters. For the proposed MMA, polarization independent characteristic, which is produced from the symmetry properties of the structure is verified, and it also has a stability of incident angle in both TE and TM modes from the result of the analysis of oblique incident response. In addition, its absorption mechanisms and methods are discussed and analyzed through electromagnetic field and surface current distributions. At the same time, the triple-band absorption performances of the proposed MMA derived from the material losses, 2D microstructure of the top layer and dimension parameters have also been calculated and investigated through the discussing of certain parameters individually. Finally, the absorption performance of the MMA is tested through experiments, and experimental results are basically same as the simulation results. Compared with other studies, the MMA proposed in this paper has higher absorption peaks at the resonance points, and the thickness is only 0.013 times of the longest working wavelength, which has a thinner thickness. The proposed MMA can be utilized in the areas of the decrease of Radar-Cross-Section, electromagnetic shielding, sensing and other applications.

Wideband Patch Antenna with Shorting Vias

A novel patch antenna with three resonant modes is proposed for wideband applications. By introducing the ring slot on the circular patch, the TM02 mode of the smaller circular patch and the TM02 mode of the annular ring can be excited. Also, compared with the traditional circular patch with shorting vias, four components of shorting vias are distributed nonuniformly on the edge of the proposed patch antenna, which can generate another new resonance mode. By merging the three resonant modes, the impedance bandwidth of the antenna is expanded. Meanwhile, the gain of the antenna is enhanced in the wide operating band. The results illustrate that the antenna can operate in the 5.8 GHz ISM band. Its −10 dB impedance bandwidth is from 5.06 to 6.99 GHz, and the relative bandwidth reaches 32%. In addition, the maximum gain of 5.3 dBi is obtained at 6.7 GHz.

Silicon nitride waveguide polarization rotator and polarization beam splitter for chip-scale atomic systems

The design, fabrication, and characterization of a silicon nitride waveguide polarization rotator and polarization beam splitter that operate with a polarization extinction ratio (PER) of ∼30 dB at the rubidium atomic transition of 780 nm wavelength are demonstrated. These polarization devices are fabricated on the same chip using a self-aligned process for integration of the rib and ridge waveguide structures. The polarization rotator is based on the mode evolution approach using adiabatic tapers and demonstrates a PER of ≥20 dB over a 100 nm bandwidth (730–830 nm wavelengths) with an insertion loss (IL) ≤1 dB. The polarization beam splitter is based on a cascaded tapered asymmetric directional coupler with phase matching between the fundamental and higher order TM modes, whereas the TE mode is separated by the through port. This provides a PER ≥ 20 dB with IL ≤ 1 dB over a 50 nm bandwidth for the cross port and a PER ≥ 15 dB with an IL ≤ 1 dB over an 18 nm bandwidth for the through port. These polarization control waveguide devices will enable photonic integrated circuits for saturated absorption spectroscopy of atomic vapors for laser stabilization on-chip.