TM Modes Research Articles

Multilayer circular SIW cavity differential bandpass filter with wide‐stopband characteristics

AbstractIn this paper, a compact differential bandpass filter with wide‐stopband is presented. The proposed differential filter is designed using two circular substrate‐integrated waveguide (SIW) cavities coupled through a pair of symmetric coupling slots. The filter operates in TM110 mode of the circular SIW cavity. The degenerate TM110 mode is shifted to higher frequency by the introduction of two pairs of perturbation vias. The center frequency of the differential passband can be tuned by changing different design parameters such as location of perturbation vias and length of the slotlines. As a proof of the proposed concept, a second‐order differential bandpass filter is designed, fabricated, and measured. The measured results are in good agreement with the electromagnetic‐simulated ones.

Intrinsic polarization conversion and avoided-mode crossing in X-cut lithium niobate microrings

Compared with well-developed free space polarization converters, polarization conversion between TE and TM modes in the waveguide is generally considered to be caused by shape birefringence, like curvature, morphology of waveguide cross section and scattering. Here, we study the polarization conversion mechanism in 1-THz-FSR X-cut lithium niobate microrings with multiple-resonance condition, that is the conversion can be implemented by birefringence of waveguides, which will also introduce an avoided-mode crossing. In the experiment, we find that this mode crossing results in severe suppression of one sideband in local nondegenerate four-wave mixing and disrupts the cascaded four-wave mixing on this side. Simultaneously, we propose one two-dimensional method to simulate the eigenmodes (TE and TM) in X-cut microrings, and the mode crossing point. This work will provide one approach to the design of polarization converters and simulation for monolithic photonics integrated circuits, and may be helpful to the studies of missed temporal dissipative soliton formation in X-cut lithium niobate rings.

Polarization-insensitive multimode interference coupler based on a subwavelength grating structure.

A multimode interference (MMI) coupler is one of the basic components for photonic integrated circuits. However, MMI couplers realized by conventional waveguides are polarization sensitive, which is undesired for many applications, such as optical switches and communications. In this Letter, we propose a polarization-insensitive MMI coupler on a 220-nm silicon-on-insulator platform by constructing different effective interference lengths for TE and TM modes assisted with subwavelength grating structures. The designed MMI coupler shows an excess loss of <0.24(0.43) dB and a power imbalance of <0.6(0.5) dB for the TE(TM) mode over the wavelength range of 1.5-1.6 µm in theory. Experimentally, the fabricated MMI exhibits low excess loss <0.64(0.53) dB and power imbalance <1(0.85) dB for the TE(TM) mode over a wavelength range of 1.55-1.61 µm.

Introduction of the orthogonal mode via the polarization conversion parasitic structure for the isolation enhancement of MIMO patch antennas

Abstract In this study, a high-isolation multiple-input multiple-output (MIMO) microstrip patch antenna (MPA), which utilizes an orthogonal mode cancellation method is proposed. This method employs TM10 and TM01 modes, which are simultaneously excited in the rectangular passive MPA. Initially, a rectangular decoupling structure featuring polarization rotation characteristics is designed. Further studies show that by loading the polarization conversion parasitic structure (PCPS), the electric field of the spatial coupling wave can be transformed from the x-polarized TM10 mode to the y-polarized TM01 mode. Therefore, TM10 and TM01 modes from the excited antenna and decoupling structure are concurrently coupled to the passive antenna, forming an evident weak-field region on the passive antenna. Placing the feeding probe of the passive MPA within the weak-field region prevents signal reception at the port. Consequently, this results in an extremely low mutual coupling of −49 dB at a resonant frequency of 5.8 GHz. Finally, a prototype of the proposed antenna is fabricated and tested, and the measured results closely match the simulated results. Additionally, it is observed that PCPS slightly influences the performance of the MIMO antenna.

High performance polarizer on thin-film lithium niobate with width-tapered Euler bending.

In this Letter, we propose and demonstrate an integrated polarizer on thin film lithium niobate (TFLN). The polarizer consists of a width-tapered 180° Euler bending waveguide featuring thin thickness and bilevel mode convertors with silica cladding. Notably, the TE0 mode is efficiently confined in the waveguide, while the TM0 mode confronts significant bending losses. The measurements reveal that the excess loss remains below 1.5 dB, and the extinction ratio surpasses 19 dB within a working bandwidth spanning from 1480 to 1578 nm. The proposed polarizer holds considerable promise for enhancing polarization handling within TFLN photonic circuits.

On-Chip Broadband, Compact TM Mode Mach-Zehnder Optical Isolator Based on InP-on-Insulator Platforms.

An integrated optical isolator is a crucial part of photonic integrated circuits (PICs). Existing optical isolators, predominantly based on the silicon-on-insulator (SOI) platform, face challenges in integrating with active devices. We propose a broadband, compact TM mode Mach-Zehnder optical isolator based on InP-on-insulator platforms. We designed two distinct magneto-optical waveguide structures, employing different methods for bonding Ce:YIG and InP, namely O2 plasma surface activation direct wafer bonding and DVS-benzocyclobutene (BCB) adhesive bonding. Detailed calculations and optimizations were conducted to enhance their non-reciprocal phase shift (NRPS). At a wavelength of 1550 nm, the direct-bonded waveguide structure achieved a 30 dB bandwidth of 72 nm with a length difference of 0.256 µm. The effects of waveguide arm length, fabrication accuracy, and dimensional errors on the device performance are discussed. Additionally, manufacturing tolerances for three types of lithographic processes were calculated, serving as references for practical manufacturing purposes.

Radiation of a TM mode from an open end of a three-layer dielectric capillary

Abstract Modern trends in beam-driven radiation sources include the interaction of Cherenkov wakefields in open-ended circular waveguides with complicated dielectric linings, with a three-layer dielectric capillary recently proposed to reduce radiation divergence being a representative example [Opt. Lett. 45 5416 (2020)]. We present a rigorous approach that allows for an analytical description of the electromagnetic processes that occur when the structure is excited by a single waveguide TM mode. In other words, the corresponding canonical waveguide diffraction problem is solved in a rigorous formulation. This is a continuation of our previous papers which considered simpler cases with a homogeneous or two-layer dielectric filling. Here we use the same analytical approach based on the Wiener–Hopf–Fock technique and deal with the more complicated case of a three-layer dielectric lining. Using the obtained rigorous solution, we discuss the possibility of manipulating the far-field radiation pattern using a third layer made of a low permittivity material.

Topological protection of dual-polarization biphoton states in photonic crystals

Polarization control is a major issue in topological quantum optics that limits reliable generation and transmission of quantum states. This study presents what we believe to be a novel topological photonic crystal design that provides topological protection for biphoton pairs for both TE and TM polarization. By well-designed cell configurations within the lattice, two topological boundaries emerge that can accommodate TM and TE modes at the same time. By adjusting the dispersion curves, we can further design nonlinear four-wave mixing processes within the topological photonic crystals and provide theoretical explanations for the entanglement of the dual-polarization biphoton states. Numerical results confirm the robust transport of entangled photon pairs, even when subjected to sharp bending. Moreover, combining the dual-polarization topological photonic crystal with a polarization beam splitter enables the preparation of polarization-encoded maximally entangled states. Our work exhibits significant potential for applications in robust optical quantum information processing and quantum secure communication.

Polymer-based three-waveguide polarization beam splitter with reduced crosstalk for optical circuitry

Polarization beam splitters are pivotal in manipulating polarized light within photonic integrated circuits for various optical applications. This study introduces a single-mode polarization beam splitter comprising three waveguides realized with polymer materials. The device optimization process employed the beam propagation method, explicitly using the RSoft CAD BeamProp solver. Our proposed beam splitter performs exceptionally well with 99% complete and null light transmission efficiency. In particular, it demonstrates minimal insertion loss (0.04 dB for complete transmission and 0.07 dB for null transmission) and low coupling loss (0.03 dB and 0.04 dB for complete transmission, 21.9 dB and 36.3 dB for null transmission from input to bridge and bridge to output waveguides, respectively). Additionally, the beam splitter showcases significantly reduced crosstalk: −27dB and −26.98dB for TE modes during complete light transfer, and −36.28dB and −33.61dB for TM modes during null light transfer. These results underscore its potential for advancing integrated optical systems.

Integrating inverse design and partially etched platform: an ultra-compact polarization splitter and rotator as an example

Silicon photonics devices benefit greatly from a partially etched platform and inverse design. Herein, we propose a bi-layer polarization splitter and rotator with a topology pattern and demonstrate it on a silicon-on-insulator platform. Our device exhibits a significantly reduced physical footprint of only 2µm×6µm, compared to traditional directional couplers and tapered waveguides. The device accomplishes the functions of polarization conversion and separation in such a compact design without redundant tapered or bending waveguides. The tested minimum insertion loss with the fabrication batch reaches 0.57 and 0.67 dB for TE and TM modes, respectively. The TE mode demonstrates a wider bandwidth and lower ILs than the TM modes, averaging around 1 dB from 1530 to 1565 nm. The M modes exhibit approximately 2 dB ILs at the same wavelength range, decreasing to about 1 dB between 1565 and 1580 nm. Improved designs and fabrication conditions strongly suggest the potential for further performance enhancement in the device. This successful initiative validates the exceptional performance resulting from the integration of the partially etched platform and inverse design, providing valuable insights for future photonic integrated device designs.

Multiband circularly-polarized stacked elliptical patch antenna with eye-shaped slot for GNSS applications

Abstract This paper introduces a tri-band stacked elliptical patch antenna featuring a right-handed circular polarized, designed to operate at the L2, L5, and L1 Global Navigation Satellite System bands. Initially, an elliptic patch is constructed and fed by a probe feed to generate TM110 and TM210 modes at resonance frequencies calculated using Mathieu functions. The probe position is precisely adjusted to excite the quasi-orthogonal mode of TM110 to generate circularly polarized (CP) waves at the L2 and L5 bands. Subsequently, an eye-shaped aperture is engraved into the elliptical patch to enhance the axial ratio (AR) beamwidth in the L2 and L5 bands and stimulate the orthogonal mode of TM210 to produce CP waves at the L1 band. Lastly, a stacked partially elliptical parasitic element is placed beneath the upper slotted elliptical patch to enhance the orthogonality of TM210 surface current versions and thus improve the AR beamwidth at the L1 band. The proposed antenna shows low reflection coefficient values at 1.12–1.33 (L2/L5), and 1.5–1.66 GHz (L1). The AR beamwidths are 133/213∘, 167/163∘, and 36/103∘ at two orthogonal cutplanes at L5, L2, and L1 bands, respectively. The antenna also has decent gains of 6–6.9 dBic across the three bands.

Enhancing power capacity and performance of wide-drift-channel transit-time oscillators for long-pulse high-power microwave generation

This paper addresses the challenge of extending the pulse duration of high-power microwave (HPM) sources, a critical focus in HPM technology. Transit-time oscillators (TTOs) typically modulate electron beams by forming standing waves through the cutoff of the TM01 mode in the modulation cavity. This study proposes enhancing the power capacity of TTOs by widening the drift channel. To enhance modulation capability without compromising power capacity, front and rear reflectors are strategically introduced. In particle-in-cell simulations, the device exhibits an output power of 1.65 GW at a frequency of 12.6 GHz, with an efficiency of 33.6%. The saturation time for the output microwave is 30 ns, and the maximum internal electric field strength is 860 kV/cm. The presented TTO, with design improvements, offers a promising solution for applications requiring prolonged pulse durations in high-power microwave sources.

Ultra-broadband MMI power splitter from 1.26 to 1.67 μm with photonic bound states in the continuum

Photonic bound states in the continuum (BIC) have excellent effects in localizing light fields. Low propagation loss of TM mode has been achieved in different orders of BICs on an etchless lithium niobate (LiNbO3) platform. Herein, we simulatively demonstrate a 1 × 2 MMI (Multimode interference) power splitter based on waveguides constructed by low-refractive-index structure (ZEP-520A) on a high-refractive-index thin membrane (LiNbO3), which can optimize the bandwidth, insertion loss and other performance indicators of optical devices. Simulation results show that the working wavelength cover the entire communication band ranging from 1260 nm to 1675 nm, and the transmission efficiency is more than 48.7%, while the insertion loss is less than 0.01 dB covering a 415 nm bandwidth. The field distribution results verify that the designed MMI demonstrated high mode purity at the output, and the mode field is well localized in the LiNbO3 film, leading to a reduce of the dependence of the transmission efficiency originated from the quality of the sidewall of the device, and the device can evenly distribute the TM0 mode of the ultra-broadband incident light to the two output ports. Furthermore, the fabrication process of the MMI device can be immensely simplified by a one-step exposure method, which reduces the scattering loss and asymmetry caused by the fabrication.

High performance TM-pass polarizer using multimode Bragg grating waveguide

A novel ultra-broadband TM-pass polarizer with high polarization extinction ratio (PER) and low reflection has been proposed and demonstrated by utilizing multimode Bragg grating waveguide (MBGW) and two tapered waveguides. By optimizing the period of the MBGW, the injected TE0 mode is coupled into the backward TE2 mode and effectively leaked into the cladding. Meanwhile, the injected TM0 mode propagates through the polarizer without any negative impact. The operation bandwidth can be significantly expanded by cascading multiple MBGW structures, each of which operates at a different central Bragg wavelength. The simulation results indicate that the designed polarizer can achieve an insertion loss (IL) below 0.24 dB and a PER above 39 dB simultaneously across a bandwidth of 300 nm (1400 nm∼1700nm), while the reflected signal is below −9.1 dB. The experiment results demonstrate that the fabricated polarizer can realize an IL below 0.56 dB and a PER above 33 dB in a 160 nm bandwidth ranging from 1470 nm to 1630 nm. Due to limitations in the equipment used, measurements for other wavelength ranges are not conducted. With these merits, the proposed device would find significant applications in optical communication systems.

All-liquid frequency selective absorber design with flexibility and wide-angle stability

An all-liquid flexible metamaterial crossing the ultrabroadband range of S, C, X, and Ku bands is reported. This work demonstrates for the first time a frequency selective absorber (FSA) using all-flexible materials, which enables a transmission band of 2.4–4 GHz and a 6–20 GHz ultrawideband absorption. Firstly, liquid metal (LM) as a new functional material with self-healing capability and high reflectivity, based on its metasurface can realize the minimum insertion loss of 0.72 dB at 3.2 GHz. Then, utilizing dielectric resonance and diffraction grating effects of the water-based metasurface, the design can achieve greater than 90% absorption in the frequency band of 6–20 GHz, with a relative bandwidth of 107%. Furthermore, by miniaturizing the design, the FSA exhibits high stability in TM mode with oblique incidence up to 60° and TE mode at 45°. Our design can be fabricated using polydimethylsiloxane lithography and encapsulated with water and LM with a thickness of only 8 mm. Finally, the fabricated FSA are tested by bending to different curvatures, and the good performance indicates its promising applications in electromagnetic stealth, compatibility and wearable devices.

Novel Polyimide-Based Conformal Bandpass FSS for X-band RADAR Communications

A linearly polarized wide bandpass frequency selective surface (FSS) for RADAR communication application has been presented. The proposed FSS is constructed in a single layer with a size of 0.25 λ0. This FSS utilizes a rhombus slot comprised of a head slot and a meander line to provide a single-wideband resonance. The proposed FSS operates in the X-band communication frequency range from 7.98 to 12.1 GHz (4.12 GHz) and achieves a minimum insertion loss of 0.1 dB, respectively. The designed FSS is developed on a flexible substrate with a low profile of 0.05 mm. The FSS exhibits stable angular performance in the scope of incidence angle of 60º for both TE and TM modes. An equivalent circuit model is designed to depict the desired frequency response. Furthermore, a bending analysis has been carried out to verify the conformal nature of the proposed unit cell. The prototype is fabricated and the performances are validated with experimental results.

Switchable dual-wavelength mode-locked cylindrical vector beam fiber laser based on unpumped EDF saturable absorber and nonlinear polarization rotation

A switchable single- and dual-wavelength mode-locked pulse laser with cylindrical vector beam (CVB) based on an unpumped EDF saturable absorber and a nonlinear polarization rotation (NPR) hybrid mode-locked mechanism has been proposed and experimentally demonstrated. An unpumped EDF saturable absorber is utilized to generate a mode-locked operation that generates high-order laser pulses. Utilizing a hybrid mode-locked mechanism, the signal-to-noise ratio (SNR) and operating stability of the laser are improved compared to the mode-locked operation with a single unpumped EDF saturable absorber. Through adjusting the polarization controller, single- and dual-wavelength stable mode-locked pulses can be easily realized. The single-wavelength mode-locked pulse operates with central wavelengths of 1550.16 nm and 1549.80 nm, repetition frequencies of 6.33 MHz and 6.35 MHz, corresponding to pulse intervals of 158 ns and 157 ns. Further, the long-period grating (LPFG) is used as a mode converter to achieve pulse output with a purity exceeding 95 % in the TM01 and TE01 modes at different operating wavelengths. The proposed fiber laser with a simple structure has provided a flexible pulsed CVB laser source for laser processing, time division, and mode division multiplexing applications.

High-frequency microwave cavity design for high-mass dark matter axion searches

Abstract The haloscope based on the TM010 mode cavity is a well-established technique for detecting QCD axions. However, the method has limitations in detecting high-mass axion due to significant volume loss in the high-frequency cavity. Utilizing a higher-order mode cavity can effectively reduce the volume loss of the high-frequency cavity. The rotatable dielectric pieces as a tuning mechanism can compensate for the degradation of the form factor of the higher-order mode. Nevertheless, the introduction of dielectric causes additional volume loss. To address these issues, this paper proposes a novel design scheme by adding a central metal rod to the higher-order mode cavity tuned by dielectrics, which improves the performance of the haloscope due to the increased effective volume of the cavity detector. The superiority of the novel design is demonstrated by comparing its simulated performance with previous designs. Moreover, the feasibility of the scheme is verified by the full-wave simulation results of the mechanical design model.

Inverse design of a silicon-based ultra-compact four-channel mode splitter with dual polarizations

We adopt the inverse-designed method and demonstrate an ultra-compact four-channel mode splitter with dual polarizations, which enables mode division multiplexing and polarization division multiplexing simultaneously without changing the mode orders and suitable for fabrication and integration based on silicon-on-insulator platform. The four TE0, TM0, TE1 and TM1 modes at the central wavelength of 1550 nm can be efficiently split with low insertion loss (<1.9 dB), low channel crosstalk (<−17 dB), low reflection loss (<−18 dB). Moreover, the proposed mode splitter has the potential of incorporating the wavelength division multiplexing for mass data transmission and high computing parallelism.

Near-infrared Y-branch polymer splitters realized with compact MMI structures for efficient power splitting

Optical splitters are promising photonic devices for next-generation photonic integrated circuits, which enable signal distribution and routing between the different components, facilitating complex optical functionalities on a single chip. This research introduces what we believe is a novel numerical technique for enhancing optical network efficiency by incorporating a taper-based step-index (SI) Y-branch multimode interference (MMI) splitter with organic-inorganic hybrid polymer materials. The proposed device comprises a core width of 5 µm for the input and output waveguides to satisfy the single-mode conditions. We designed and optimized the MMI splitter using the beam propagation method (BPM). The splitter demonstrates the power splitting property with an efficiency of 86%. The excess losses for the MMI splitter are 0.52 dB and 0.50 dB for TE and TM modes, respectively, at 1.55 µm. The polarization dependence loss (PDL) and propagation loss (PL) are 0.015 dB and 0.00019 dB/µm, respectively.