Zaker Hossein Firouzeh

Low‐voltage, high‐bandwidth electro‐optic modulators are essential for next‐generation optical interconnects and CMOS‐compatible photonic systems. Here, we demonstrate thin‐film lithium niobate (TFLN) Mach–Zehnder modulators that combine slow‐light optical waveguides with inductively loaded slow‐wave RF electrodes to simultaneously reduce the half‐wave voltage ( V _π ) and extend the modulation bandwidth. The optical section employs a dispersion‐engineered 1D photonic crystal waveguide with an enhanced group index, achieving an ultralow voltage–length product of ≈0.3 V cm across all designs. To maintain broadband operation, the RF transmission lines are engineered to increase the RF effective index and achieve close RF‐optical index matching. Using two distinct electrode configurations, the resulting modulators achieve 3‐dB electro‐optic bandwidths of 75–203 GHz, V _π values of 0.25–1.0 V, and interaction lengths of 2.7–12.8 mm. These findings demonstrate that codesigned optical and RF slow‐wave structures offer an effective strategy for realizing compact, low‐drive‐voltage, and ultrabroadband integrated modulators.

This paper addresses the problem of surface wave confinement and the suppression of undesired transverse electric (TE) mode propagation inside the grounded dielectric slab when excited by the transverse magnetic (TM) slot launcher. As a solution, we propose a surface waveguide (SWG) design based on self‐complementary Bowtie metasurfaces. Leveraging the concepts of TE soft and TM hard bandwidth operations, the SWG effectively confines TM surface waves while suppressing unwanted TE modes. We present an analytical model capable of calculating the Bowtie metasurface's reflection coefficient for oblique‐incidence excitation. Additionally, a simple yet efficient electromotive force (EMF) algorithm is introduced for analysing the reflection phase for oblique‐incidence excitation across a range of wavenumbers and frequencies. We use the proposed EMF model to calculate the TE soft and TM hard bandwidth operations of the Bowtie metasurface. We present a uniplanar, compact and wideband slot launcher to excite directed and well‐trapped TM mode inside the SWG. We fabricated a novel Rotman lens based on the Bowtie SWG and slot launcher to further support our methodology. The SWG lens exhibits a 56° scanning range, similar to that of its microstrip lens counterpart while offering the potential for reconfigurability and suitability in millimetre‐wave applications.

A silicon–based integrated orbital angular momentum (OAM) parity sorter using two-dimensional multimode interference (2D MMI) waveguides is designed and numerically analyzed. An OAM parity sorter, which sorts OAM modes according to their parity (even or odd) is an elegant device in a broad range of OAM states processing applications including quantum gates, quantum key distribution, generation of high dimensional quantum gates, quantum information, and teleportation. The presented three–part integrated parity sorter is realized based on the self–imaging and field–splitting properties of MMI structures. Its total length is 11 444 µm. The proposed device works for OAM modes with |l| ⩽ 5. The performance of OAM sorting is investigated with the results confirming the high purity (up to 98.33% and 94.45% at even and odd ports, respectively) for the telecommunication wavelength λ ₀ = 1550 nm.

The design and numerically investigation of a silicon polarization splitter (PS) is proposed using triple-tapered directional couplers (DCs).The proposed device consists of a triple-tapered DC, a triple-bent DC at through port, and a tapered waveguide at cross port. The coupling length of the device is 20.5 µm. At the 1550 nm wavelength, the realized PS exhibits the extinction ratio (ER) values of 35.7 dB and 37.35 dB as well as the insertion loss values of < 0.58 dB and < 0.4 dB for the TE and TM polarization modes, respectively. Furthermore, the device’s bandwidth for ER > 20 dB and ER > 25 dB are 170 nm and 136 nm, respectively.

This paper analyzes electromagnetic scattering from a microstrip array with a homogeneous dielectric substrate in two symmetry cases. In the first case, the entire structure has discrete rotational symmetry, and the discrete bodies of revolution method is employed for a comprehensive analysis. In the second case, the ground and substrate have discrete rotational symmetry, whereas the patches and feeding lines do not. Therefore, the discrete bodies of revolution method is used to analyze the ground and substrate, the traditional moment method is applied to the patches and feeding lines connected to them, and the domain decomposition method combines the results obtained from these two solutions. As a result, the discrete bodies of revolution method is applied only to one sector of the microstrip array, which reduces the memory requirements and computational time in comparison with the traditional moment method. Consequently, for a structure with N_s symmetric sectors and the total number of unknowns N , the memory requirements and simulation time are reduced by factors of N ² _s and N ³ _s , respectively, in comparison to the traditional moment method. Finally, numerical results are presented to validate the accuracy and efficiency of the proposed method. The results are compared with those obtained from commercial FEKO software and the traditional moment method to show how the proposed method reduces computation time and memory requirements.

Recently, the implementation of rectangular waveguides for generation and manipulation of orbital angular momentum (OAM) modes, has been developed to exploit the outstanding features of these modes in more complex integrated devices. Multimode interference (MMI) structures have been widely used in both one and two dimensions as the basic elements in many integrated optical devices like optical beam splitters, mode converters, couplers, wavelength-division (de)multiplexers, and switches. According to the various applications of OAM modes in quantum and classical communications, the study of their propagation properties in MMI waveguides is useful in order to facilitate the way into higher security and capacity systems. This paper presents the results of numerical investigation of a proposed integrated optical OAM mode converter which is performed based on the mode decomposition properties of propagating OAM modes in 2D MMI waveguides, as well as the fact that any order of OAM mode can be represented as superposition of an odd mode and a quarter-wave shifted even mode. The proposed device, which consists of two MMI waveguides connected by phase shifters and linear waveguides, provides mode conversion between beams carrying OAM with odd opposite topological charges. The design procedure is performed for OAM modes with topological charge values of l=±1 and l=±3 using beam propagation method. The proposed device is passive with reciprocal behavior and has the output mode purity of 94% and 82% for beams carrying l=±1 and l=±3, respectively.

This article presents a new noniterative inverse modeling technique based on machine learning regression and its applications to microwave design optimization. The proposed inverse model accepts the high-dimensional S-parameters computed at many frequency points as the input and estimates the optimal geometrical/physical parameters of the microwave component as its output. The least-squares support vector machine regression is combined with the principal component analysis to simultaneously overcome both the high-dimensional input space and ill-posed challenges of the inverse modeling. We also propose a new empirical method to find the optimum number of principal components (i.e., the compression level) for each example in an automated way. This makes our proposed model general and easy to use compared with the existing data-driven inverse modeling techniques. The inverse model is trained by a set of scattering parameters computed via a 2-D/3-D solver for few configurations of the geometrical parameters. The feasibility and the accuracy of the proposed optimization scheme are investigated by comparing its predictions with the corresponding optimal configuration estimated via a commercial solver.