Main Waveguide Research Articles

High-power semiconductor laser with a narrow linewidth based on transverse photonic crystal

Broad-area lasers (BA) are practical for producing high output power. However, under a high current operation, high-order modes are easily excited, resulting in the broadened linewidth. Here, based on mode engineering of double-side transverse photonic crystals (TPCs) combined with a longitudinal high-order surface grating, a narrow-linewidth electrically-pumped broad-area laser with high power emission only using I-line lithography is demonstrated. By matching the high-order modes of the wide main waveguide with TPC bands, the effective volume of the high-order modes is expanded, while the fundamental mode remains unchanged. Then, single-lateral mode operation is achieved by selective pumping only for the main waveguide due to the significant distinction in modal gain between the fundamental mode and the high-order modes. In addition, a 27-order grating is constructed above the main waveguide to keep the laser operating in single-longitudinal mode. In the experiment, the device shows an output power of 115 mW, a lasing wavelength of 1552.94 nm with a side-mode suppression ratio (SMSR) of 59.26 dB, a narrow linewidth of 443 kHz, and a relative intensity noise (RIN) < -135 dB/Hz at 600 mA, thus has the potential to meet the needs in fields such as coherent optical communication and LiDAR.

Simulation study of a highly sensitive I-shaped Plasmonic nanosensor for sensing of biomolecules

This paper presents the design and simulation of an I-shaped metal insulator metal waveguide-based nanosensor for biosensing applications. The device’s sensing property is investigated using the three-dimensional finite element method. In the proposed design a I-shaped cavity is coupled to the main waveguide that serves as a resonator to generate the resonance peaks. The refractive index of the material to be sensed is filled inside the I-shaped cavity. This sensor operates in the near and mid-infrared wavelength ranges. The device can identify a variety of biomolecules, including cancer cells and bacterial samples. The simulation results reveal that device shows different resonance dips for different refractive indexes of cancer cells. The device can obtain sensitivity of 1550 nm RIU−1 and 1250 nm RIU−1 among refractive index of normal and cancerous cell for basal and hella cancer cells, respectively. Instead of all these biomolecules, the nanosensor shows different resonance dips in the transmittance spectrum for DNA, RNA, and ribonucleoprotein. Furthermore, the sensor has demonstrated potential applicability as an HB concentration detector and for sensing other blood components. Moreover, we improved the structure characteristics by varying the length and centre area of the cavity, demonstrating that modifying the device parameters can boost sensitivity. After making structural adjustments to the device, the maximum sensitivity of 3000 nm RIU−1 is achieved for some bacterial samples.

Wafer-scale silicon microfabrication technology toward realization of low-cost sub-THz waveguide devices

This paper presents a wafer-scale silicon microfabrication technology for the sub-terahertz (sub-THz) waveguide device mass production. Based on the effective scheme, a WR-5 (140–220 GHz) straight rectangular waveguide and a WR-2.8 (260–400 GHz) rectangular waveguide bandpass filter are implemented as demonstrated examples. The silicon deep reactive ion etching (DRIE) process is employed to etch through the total thickness of the silicon wafer and form the main waveguide channels. Then, a low-temperature thermal compression process is used to bond the trough-etched wafer with the top and bottom metallised silicon wafers to form the closed waveguide structures without any precise alignment process. The fabricated waveguide has the benefit of low transmission loss (0.03–0.05 dB mm−1) at the whole G band. Besides, to measure the fabricated WR-2.8 waveguide filter and solve the measuring equipment standard waveguide difference, silicon micromachined waveguide transitions are explored and fabricated to match two different frequency-band modules for measuring the waveguide filters in the desired full frequency band, which also has a potential application for the different size waveguide conversion. The measured results agree well with the simulated ones. The measured 3 dB bandwidth is 9.3%, with a central frequency of 343 GHz; the average insertion loss (IL) is about 1.6 dB in the pass band, including two extra straight waveguides of 8 mm length on input/output ends and two external waveguide-to-waveguide transitions. The proposed method provides a feasible and cost-effective solution for the mass production of high-performance waveguide devices and integrated systems in sub-THz frequency bands and beyond.

A HORN-LENS ANTENNA FOR THE TERAHERTZ RANGE BASED ON THE “HOLLOW DIELECTRIC CHANNEL” CLASS WAVEGUIDE

In the antenna-feeder paths of the terahertz (THz) range, waveguides of increased cross sections, the so-called "oversized waveguides", have found wide application. This term refers to a waveguide whose transverse dimensions are much greater than the length of the propagating wave in it. A feature of such a waveguide is the possibility of propaga-tion in it of waves of higher types, which are excited on homogeneity of this waveguide and can have a significant impact on the operation of the entire antenna-feeder path. This can lead to resonances at the transcendental section of the oversized waveguide. This phe-nomenon has been studied in detail in quasi-optical paths for radio relay systems. Indeed, since the inputs and outputs of most active components of microwave transceiver systems use a standard single-mode waveguide, to excite an oversized waveguide, waveguide tran-sitions are widely used. In antenna-feeder paths of the THz range oversize section waveguides the so called “oversize waveguides” are widely used. By an “oversize waveguide” we mean a waveguide whose transverse dimensions are much longer than those of the wave propadating in it. A wave type converter for excitation of an oversized waveguide is an important ele-ment of a quasi-optical antenna-feeder path, since it allows matching the output (input) channel of the active components of the transceiver device (generators, amplifiers, etc.) with the quasi-optical path, which are usually made on the basis of waveguides of the main section. At the same time, the design of almost any type of transducers is based on the formation of a field distribution, the transverse structure of which coincides with the field of the working wave of the oversized waveguide, for example, when the field structure of the waveguide of the main section is smoothly transformed into the working type of the wave of the oversized waveguide. In this paper, waveguide transitions for the terahertz range are considered, which pro-vide minimal conversion losses when joining waveguides with different cross sections. A metal-dielectric waveguide of square cross section is used as the main waveguide. A copper-lens antenna of the terahertz range with high technical characteristics has been developed, which can be widely used in various fields of radio communication.

Photospheric magnetic flux and coronal emission properties of small-scale bright and faint loops in the quiet Sun

Context. The study explores the photospheric magnetic properties of bright and faint small-scale loop systems in the solar atmosphere of the quiet Sun, also known as X-ray or coronal bright points. Aims. To understand how plasma confined in small-scale loops is heated to million degrees, the loop-associated photospheric and coronal magnetic flux properties should be known because the magnetic field is generally assumed to be the main energy source or waveguide. This and follow-up studies aim to provide a qualitative and quantitative investigation of these magnetic properties and their impact on the heating of plasma to million degrees. Methods. We used quasi-temporal imaging observations taken in the 193 Å channel of the Atmospheric Imaging Assembly (AIA) and line-of-sight magnetograms from the Helioseismic Magnetic Imager (HMI) on board the Solar Dynamics Observatory. The observations cover 48 h of data at a 6 min cadence with a field of view of 400″ × 400″, from which 90 loop systems (of which 83 are CBPs) were extracted and analysed in full detail. Results. We obtain the evolution properties of both faint and bright small-scale loop systems (SSLSs) related to either magnetic flux emergence or magnetic flux coalescence and a chance encounter of magnetic fluxes. We estimate the lifetimes of the two loop systems and the impact of the magnetic flux evolution on their life span. The photospheric magnetic flux associated with SSLSs confining plasma heated to coronal temperatures is found to cover at least two orders of magnitude from 3.0 × 1018 Mx to 1.8 × 1020 Mx. The analysis of the maximum intensity of SSLSs during their lifetime shows numerous spikes of intensity that are identified as small (a few AIA pixels) compact brightenings associated with cancelling magnetic fluxes. Most of them are identified as microflares. The intensity flux range of these spikes is reported. The coronal intensity flux evolution of SSLSs is strongly correlated with the total unsigned photospheric magnetic flux evolution when there is little or no contamination in the selected field of view of the SSLSs by unrelated magnetic fluxes or intensity features. We report on the footpoint separation and change during the lifetime of the faint and bright SSLSs. The magnetic flux emergence and decay rates of some of the SSLSs are also provided in this study. Conclusions. The power-law index α of the logarithm of the total unsigned magnetic flux and the total intensity for the full lifetime of SSLSs is 1.10 ± 0.02, compared with 1.14 ± 0.03 for a previous study of the whole disc in the same intensity range (Fe XII 193–195 Å). This indicates that the emission of the corona of the quiet Sun at ∼1.25 MK is mostly confined to small-scale loops (some brighter, others fainter). Therefore, it is imperative to understand the mechanism that heats the plasma in these loops.

Metamaterial based on labyrinthine tubes loaded periodically and ultra-low phase velocity to the low-frequency energy control

Sound energy control at low frequencies (≤1000 Hz) is necessary and very important in acoustics, especially when considering scientific and technological aspects. In this work, a modular acoustic metamaterial composed of a main waveguide loaded with small quarter-wavelength tubes is presented. Theoretical, numerical, and experimental methods are used to describe the accumulation of sound absorption peaks below the structure's bandgap with the number of peaks proportional to the structure's periodicity. The origin of the bandgap is due to the loaded tubes in the main waveguide. Ultra-low phase velocity (c̃p=16 m/s) and critical coupling were obtained in the model, which allowed perfect sound absorption at 292 Hz with a structure reaching a ratio of λ/90. The experimental results in the impedance tube support the theoretical and numerical discussions and demonstrate a sound energy control of 89% and 84% at 686 and 422 Hz, respectively. Finally, this work contributes to advances in the field of control and manipulation of low-frequency sound energy through periodic structures.

Arbitrarily rotated optical axis waveguide induced by a trimming line.

Rotated optical axis waveguides can facilitate on-chip arbitrary wave-plate operations, which are crucial tools for developing integrated universal quantum computing algorithms. In this paper, we propose a unique technique based on femtosecond laser direct writing technology to fabricate arbitrarily rotated optical axis waveguides. First, a circular isotropic main waveguide with a non-optical axis was fabricated using a beam shaping method. Thereafter, a trimming line was used to create an artificial stress field near the main waveguide to induce a rotated optical axis. Using this technique, we fabricated high-performance half- and quarter-wave plates. Subsequently, high-fidelity (97.1%) Pauli-X gate operation was demonstrated via quantum process tomography, which constitutes the basis for the full manipulation of on-chip polarization-encoded qubits. In the future, this work is expected to lead to new prospects for polarization-encoded information in photonic integrated circuits.

A comparative analysis between Drude and Johnson & Christy for nanometric optical demultiplexer

The constant need to miniaturize technological devices has increased the development of novel optical devices in the nanoscale. A common kind of photonic devices are built using Metal-Insulator-Metal (MIM) interfaces to generate Surface Plasmons Polaritons (SPPs) and process light waves in the optical window. In this paper a 12 channel demultiplexer is proposed using 8 cavities coupled to both sides of the main waveguide. Then the nano demultiplexer is modelled in COMSOL Multiphysics using Drude model and Johnson and Christy parameters for the optical constants. Then we compare the transmission spectrum from 400 to 2200 nm for both models and discuss the differences advantages of each method.

Nonlinear guided wave propagation along layers with the exponential index profile, constant index and the Kerr nonlinearity

Layered planar waveguide consisting of the layer with an exponential profile of the dielectric permittivity, optical linear layer, and nonlinear medium of Kerr-type is considered. Exact analytical solutions describing the nonlinear guided waves in such waveguide are found. The profiles of the waves in perpendicular to the layers direction are analyzed. The distinctions between layered waveguide structures with a linear optical substrate and a nonlinear one and the impact of dielectric interlayer separating the exponentially graded-index main waveguide layer and nonlinear material of Kerr-type are discussed. The presence of a dielectric interlayer leads to the possibility of the appearance of field oscillations inside it. The possibility of controlling the field localization length across the layers and its amplitude by changing the interlayer width is shown.

Low frequency attenuation of acoustic waves using sound-soft scatterers

The attenuation of acoustic waves by silencers is typically achieved through the employment of rigidly backed cavities, connected to a main waveguide by a perforated panel. This invokes a resonant response at frequencies determined by the dimensions of the perforation and the rigidly backed cavity. A limiting factor in this approach is that to achieve low frequency attenuation, either large cavity depths are required, which is often impractical, or narrow neck regions need to be used, where performance is limited due to the viscothermal losses. Within this paper, a non-rigidly backed perforated pipe is presented where the pressure release condition at each perforation creates an acoustic sound-soft boundary condition. By the introduction of sound-soft boundary conditions, a low frequency band gap is created as the first order mode is shifted to a non-zero value, the frequency of which is determined by the dimensions and separation of the perforations. Experimental results displaying this band gap are presented along with numerical models verifying the phenomenon and an ideal analytical model based upon the transfer matrix method.

16-Channel Wavelength Division Multiplexers Based on Subwavelength Grating

Wavelength Division Multiplexing (WDM) plays an important role in optical interconnection. In this paper, a 16-channel WDM device is designed on a Silicon-On-Insulator (SOI) substrate by using a sub-wavelength grating (SWG) structure, which can cover O-band and C-band at the same time, and the output channel is reversely coupled from the main waveguide to realize wavelength demultiplexing. The simulation results show that the loss of our 16-channel wavelength demultiplexing device is less than 0.5 dB and the crosstalk is less than 17 dB. When WDM is performed in O-band, the transmission loss of the C-band in the bus waveguide is less than 0.05 dB and is insensitive to the grating duty cycle, with good process tolerance. The footprint of the device is 200 μm × 150 μm, and the size of the single-channel filter is 200 μm × 2 μm, which can realize WDM with large bandwidth in a compact structure.

Ultralow birefringent glass waveguide fabricated by femtosecond laser direct writing.

Optical waveguides prepared by femtosecond laser direct writing have birefringent properties, which can affect polarization encoding and entanglement on chips. Here, we first propose a shape-stress dual compensation fabrication scheme to decrease birefringence. Ultralow birefringent waveguides (1 × 10-9) were obtained by controlling the cross sectional shape of the main waveguide and adjusting the position of the auxiliary lines. In addition, we prepared polarization-independent directional coupler and demonstrated the evolution of polarization-independent waveguide array with different polarized light. In the future, ultralow birefringent waveguides will be widely applied in polarization encoding and entangled quantum photonic integrated circuits.

A compact graphene-based dual-band band-stop filter using new hook-shaped resonator for THz applications

This paper presents a plasmonic Dual-band band-stop filter for terahertz frequencies using new graphene hook-shaped resonators. The structure of this filter is formed by placing two novel symmetrical resonators in the main waveguide path. The finite-difference time-domain (FDTD) and transmission line methods are used to analyze the proposed filter. This adjustable filter has a high-quality factor and two resonance modes in frequencies of 4.1 THz and 13.8 THz. Furthermore, the simulation results show a shift in the resonant frequencies upon changing the base length of the resonators. The designed filter has very small dimensions (350 nm × 500 nm) and can be a proper candidate for integrated optical circuits due to its compact structure and simple design.

Enhanced coupling efficiency in metal – dielectric – metal waveguide-ring structure for plasmonic temperature sensor and sucrose concentration detector

In this paper, we propose a sensing structure based on metal-dielectric-metal waveguide technology, which comprises of two square ring resonators side linked to the bus waveguide and operates in the infrared and near infrared regions. The results revealed that the proposed device enormously enhanced the coupling effect between the main waveguide and the cavity thereby increasing the sensor's performance parameters. The device has an ability to act as refractive index sensor, temperature sensor for ethanol and sucrose concentration detector with sensitivities of 2880 nm/RIU, 1.375 nm/℃, and 1750 nm/RIU, respectively. The device is also optimized by changing the structural parameters and material medium. The sensor design is simple to construct, has better sensing features, and is small in size. Thus, the proposed plasmonic sensor is relevant for lab-on-chip gas and biochemical detection (having an optical refractive index between 1.0 and 1.5).

Theoretical analysis of VO2 filled double rectangular cavity-based coupled resonators for plasmonic active switch/modulator and band pass filter applications

In this paper, we have designed an electrically tunable nano-plasmonic waveguide-based band pass filter which works on the phenomena of phase transition of Vanadium dioxide. The device operates on telecommunication wavelength and can work as a modulator and a switch with a modulation depth of 26.40 dB. It has shown its promising applications in the area of filtering by providing a high-quality factor of 156. Whereas, the modulation depth and quality factor of the device can be increased and decreased by changing various device parameters. A large tunability of 280 nm in the resonant wavelength is achieved by changing the applied voltage on the device between 0 V and 2.7 V in switch-on and switch-off states. Figure of merit of 12 is also attained by the device. Our device consists of a main waveguide which is coupled to two uneven length rectangular cavities filled with Vanadium dioxide. Active material present as the dielectric of rectangular cavities transforms its state from insulator to metallic and vice versa according to the applied voltage. However, single band transmission is obtained for the device and this can be tuned by changing different geometrical parameters of the device. The device can find its applications in nano plasmonic on-chip applications due to its small size, good modulation depth, and large quality factor with moderate loss.

Two-dimensional photonic crystal waveguide 1×5 beam splitter reversely designed by downhill-simplex algorithm

Beam splitter, whose main function is to achieve the splitting, combining and routing of optical signals, is an important component of photonic integrated circuits, passive optical network and other fields. Compared with the conventional beam splitter, photonic crystal beam splitter, which has the virtues of smaller size and higher transmission efficiency, is very suitable for high-density and large-scale integration. The traditional control variable method often used in the optimal design of photonic crystal beam splitter is time-consuming and inefficient. When parameter variables are large, it is difficult for beam splitter to achieve the optimal splitting performance. In addition, it is hard to realize flexible design of beam splitting ratio when optimizing multi-channel photonic crystal beam splitter by this method. In this paper, a novel photonic crystal 1×5 beam splitter, in which two special Y-junction waveguides are introduced into a completely two-dimensional square lattice silicon, is proposed and optimally designed by using downhill-simplex algorithm. Firstly, to determine the optimization range of each variable, the influences of the radius of the dielectric rod in the coupling region and the radius and the lateral offset of the regulating dielectric rod in the center of the two Y-junction waveguides on the five output ports of the 1×5 beam splitter are explored respectively by the plane wave expansion method and finite difference time domain method. The results show that the optical energy coupled from the main waveguide W<sub>1</sub> to the upper Y-junction waveguide and lower Y-junction waveguide can be controlled by optimizing the radius of the dielectric rod in the coupling region. The transmittance of the five output ports can be controlled in proportion by optimizing the lateral offset of the regulating dielectric rods. The total transmittance of the five output ports can be improved, and the output of each port can be adjusted by optimizing the radius of the regulating dielectric rod. Then, according to the specific target of the splitting ratio, using downhill-simplex algorithm, the 1×5 beam splitter with different splitting ratio can be reversely designed by optimizing the radius of the coupling dielectric rod and the radius and the lateral offset of the regulating dielectric rod within the selected optimization range. The total transmittance of the 1×5 beam splitter is above 99%, the additional loss is less than 0.044 dB, and the response time is less than 1ps. Besides, to determine the allowable error range of each optimization variable in actual processing, the machining error of the 1×5 beam splitter is analyzed, which provides a theoretical reference for fabricating the device. Owing to the advantages of flexible splitting ratio design, high optimization efficiency, small size and excellent performance, the proposed 1×5 beam splitter will have broad application prospects in the field of photonic integrated circuits and so on.

Demonstration of a high extinction ratio TiN-based TM-pass waveguide polarizer

A high extinction ratio transverse magnetic (TM)-pass plasmonic waveguide polarizer has been designed and optimized. This device exploits two parallel TiN strips embedded in a silicon dioxide cladding to cut off the transverse electric (TE) polarization state, which is either reflected or absorbed, while the TM mode can pass through the main silicon waveguide with significant low losses. Given a device of 5 µm length, an extinction ratio as high as 60.7 dB and an insertion loss of 2.23 dB were achieved at the target wavelength of 1.55 µm. To our knowledge, this extinction ratio is one of the highest values ever reported. In the wavelength of 1.45–1.59 µm, the proposed device provides an optical bandwidth of 140 nm for an extinction ratio more than 30 dB and an insertion loss less than 3 dB. This device is relatively simple and is easier to be fabricated than other architectures that are found in the literature.

Особливості проєктування поздовжньо-співвісних хвилеводно-мікросмужкових з’єднувачів

The authors justify the use of combined longitudinal-coaxial connectors — waveguide-coaxial or waveguide-microstrip type — in new modern antenna-feeder microwave paths. Using the example of a basic coaxial waveguide-coaxial connector based on a section of a regular rectangular waveguide, the study considers the process of converting an electromagnetic wave of a regular waveguide of the main waveguide type H10 into a transverse electromagnetic wave of a coaxial line with a wave resistance (impedance) Z0 = 50 Ohm. Such a connector allows implementing good electrical parameters — matching (standing wave ratio, SWR) and linear losses — but its design is difficult to configure and cannot be reliably reproduced. However, the basic operation principles of this connector make it possible to use it as a prototype when creating modern coaxial waveguide-coaxial or waveguide-microstrip connectors. One example of such a modern connector is the sealed longitudinal-coaxial waveguide-microstrip connector based on a segment of H-shaped waveguide, shorted by an end wall on one end. Correcting the reactive component of both inductive and capacitive nature will allow achieving the required parameters of the wave impedance of the connector. With this in mind, the author has built an inductive-capacitive system consisting of a matching element in the form of a staggered fin and a corrective element in the form of a rectangular parallelepiped. To ensure the air tightness of the connector design, the segment of the coaxial line was replaced by a sealed coaxial insert, which is a serial electronic component. Particular attention was paid to the layout and design of this sealed waveguide-microstrip connector, as well as to the calculation of the overall dimensions of its elements. The article proposes an original technique for measuring the main parameters of both waveguide-coaxial and waveguide-microstrip connectors. The author forms a mathematical model of combined type connectors based on the scattering wave matrix and presents the parameters of real hermetically sealed longitudinally coaxial waveguide-microstrip connectors based on waveguide segments of various standard sizes and measured at various frequencies.

Broadband Low-Frequency Acoustic Metamuffler

In this research, we propose and design an acoustic metamuffler (AMM) by coupling a microperforated plate and a composite waveguide formed by a main waveguide and a Helmholtz resonator. The proposed mechanism and deliberately designed structure are conducive to generating multimode resonances that help to improve the coupling absorption effect and lead to broadband (4 octaves) sound insulation. We develop an effective circuit model to analytically predict the insulation bandwidth and put forward numerical and experimental measurements that demonstrate the effectiveness of the proposed concept. The designed AMM produces sound insulation with an average of 20 dB of sound-transmission loss at a low-frequency range, extending from 100 to 1600 Hz, while having an ultrathin thickness of 6.2 cm (1/55\ensuremath{\lambda} for the lowest working frequency). Our findings could have pragmatic applications for acoustic insulators or absorbers.

High-power single-mode triple-ridge waveguide semiconductor laser based on supersymmetry

To achieve a high-power single-transverse mode laser, we here propose a supersymmetry-based triple-ridge waveguide semiconductor laser structure, which is composed of an electrically pumped main broad-ridge waveguide located in the middle and a pair of lossy auxiliary partner waveguides. The auxiliary partner waveguides are designed to provide dissipative modes that can phase match and couple with the higher-order modes in the main waveguide. By appropriately manipulating the gain–loss discrimination of the modes in the laser cavity, one can effectively suppress all the undesired higher-order transverse modes while keeping the fundamental one almost unaffected, thereby ensuring stable single-mode operation with a larger emitting aperture and accordingly a higher output power than a conventional single-transverse-mode ridge waveguide diode laser.