Fundamental TE Mode Research Articles

Mechanisms for optical loss in SOI waveguides for mid-infrared wavelengths around 2 μm

We report the measurement of optical loss in submicron silicon-on-insulator waveguides at a wavelength of 2.02 μm for the fundamental TE mode. Devices were fabricated at IMEC and at A⋆STAR's Institute of Microelectronics (IME) and thus these measurements are applicable to studies which require fabrication using standard foundry technology. Propagation loss for strip and rib waveguides of 3.3 ± 0.5 and 1.9 ± 0.2 dB cm−1 were measured. Waveguide bending loss in strip and rib waveguides was measured to be 0.36 and 0.68 dB per 90° bend for a radius of 3 μm. Doped waveguide loss in rib waveguides was measured for both n-type and p-type species at two doping densities for each doping type. Measured results from propagation, bending, and free-carrier loss were found to be in good agreement with analytical or numerical models. Loss due to lattice defects introduced by ion-implantation is found to be underestimated by a previously proposed empirical model. The thermal annealing of the lattice defects is consistent with removal of the silicon divacancy.

Wide-band polarization controller for Si photonic integrated circuits.

A circuit for the management of any arbitrary polarization state of light is demonstrated on an integrated silicon (Si) photonics platform. This circuit allows us to adapt any polarization into the standard fundamental TE mode of a Si waveguide and, conversely, to control the polarization and set it to any arbitrary polarization state. In addition, the integrated thermal tuning allows kilohertz speed which can be used to perform a polarization scrambler. The circuit was used in a WDM link and successfully used to adapt four channels into a standard Si photonic integrated circuit.

A Compact Broadband Direct Coaxial Line to SIW Transition

In this letter, a novel coaxial line to substrate integrated waveguide (SIW) broadband transition is presented. The transition is designed by connecting the inner conductor of a coaxial line to an open-circuited SIW. The configuration directly transforms the TEM mode of a coaxial line to the fundamental TE10 mode of the SIW. A prototype back-to-back transition is fabricated for X-band operation using a 0.508 mm thick RO 4003C substrate with dielectric constant 3.55. Comparison with other reported transitions shows that the present structure provides lower passband insertion loss, wider bandwidth and most compact. The area of each transition is $0.08\lambda _{g}^{2}$ where $\lambda _{g}$ is the guided wavelength at passband center frequency of $f_{0}= 10.5$ GHz. Measured 15 dB and 20 dB matching bandwidths are over 48% and 20%, respectively, at $f_{0}$ .

TE-Pass Polarizer Based on Epsilon-Near-Zero Material Embedded in a Slot Waveguide

A horizontal silicon slot waveguide TE-pass polarizer with thin indium–tin oxide (ITO) layer embedded in the slot region is proposed and investigated. Since the dispersion relation of the material can be tuned by properly adjusting the carrier concentration, ITO is able to act as epsilon-near-zero (ENZ) material with high absorption near 1.55- $\mu \text{m}$ wavelength. With thin ENZ material embedded in the slot waveguide, huge polarization-dependent loss between fundamental TE mode and TM mode can be induced. Therefore, the slot waveguide functions as a TE-pass polarizer with good performance. Our simulation shows that in a 3- $\mu \text{m}$ -long polarizer with 10-nm-thick ITO layer embedded in the slot region, insertion loss of 42 dB for TM mode, and 0.38 dB for TE mode can be achieved simultaneously. The polarizer possesses the advantages of low insertion loss, high extinction ratio, ultra-compact, broadband, and large fabrication tolerance.

Analytical and PIC Simulation Studies of a Megawatt Class Gyrotwystron Amplifier

In this paper, the analytical and particle-in-cell (PIC) simulation studies of an ${X}$ -band megawatt class gyrotwystron have been presented. The device employs a tapered output waveguide to achieve stability against self-start oscillations due to azimuthally asymmetric modes, including the fundamental harmonic TE11 and TE21. A full nonlinear self-consistent, single particle, multimode, and multiharmonic, transient code has been developed to study the beam–wave interaction behavior. Furthermore, the device is simulated for studying its transient behavior using a commercial PIC code “CST Particle Studio.” This predicts the saturated RF power of $\sim 20$ MW in the fundamental TE01 mode and $\sim 1$ MW in the TE02 ( $s = 2$ ) mode, which is a self-generated spurious oscillation in the output section. The saturated gain is calculated as $\sim 24$ dB with a power conversion efficiency of $\sim 20$ % for a relativistic electron beam having 7% axial velocity spread.

Optical properties of V-groove silicon nitride trench waveguides.

We numerically investigate the mode properties of the V-groove silicon nitride trench waveguides based on the experimental results. The trench waveguides are suitable for nonlinear applications. By manipulating the waveguide thicknesses, the waveguides can achieve zero dispersion or a maximized nonlinear parameter of 0.219 W-1·m-1 at 1550 nm. Broadband four-wave mixing with a gain of 5.545 m-1 is presented as an example. The waveguides can also be applied in sensing applications with an optimized evanescent intensity ratio. By etching away the top flat slabs, wider trapezoidal trench waveguides can be utilized for plasmonic sensing thanks to their TE fundamental modes.

Low-Loss InGaAsP/InP Surface Ridge Waveguides for Photonic Integrated Circuits

We demonstrate low-loss InGaAsP/InP surface ridge waveguides with loss as low as 0.81 dB/cm measured at 1550 nm for the fundamental TE mode. These waveguides are suitable for monolithic integration with active elements in InP-based photonic integrated circuits. We study the effect of proton implantation on waveguide loss for different ridge widths.

Monte Carlo simulation for stochastic calculus of far‐field radiation from open‐ended waveguide arrays

SummaryIn this paper, Monte Carlo (MC) simulation has been applied for the analysis and stochastic calculus of far‐field radiation from the small, large, and infinite open‐ended waveguide arrays. Elements of the arrays are excited by the fundamental TE10 mode and with equal amplitude and linear phase. The simulated results from MC are compared closely with the finite element method (FEM). Numerical analysis based on FEM is performed using Ansoft High Frequency Structural Simulator to calculate the far‐field radiation characteristics of the arrays. The accuracy and the effectiveness of the aforesaid method, which is based on Monte Carlo integration technique, are also demonstrated in uniformly and nonuniformly spaced waveguide arrays for pattern synthesis or achieving side lobe level reduction. The arrays with arbitrary shapes are simply evaluated by MC method in equal spacing array. It is found that by applying MC simulation, the open‐ended waveguide arrays have the ability to produce the desired radiation pattern and could satisfy requirements for many applications. Copyright © 2016 John Wiley & Sons, Ltd.

Optical microfiber-loaded surface plasmonic TE-pass polarizer

We propose a novel optical microfiber-loaded plasmonic TE-pass polarizer consisting of an optical microfiber placed on top of a silver substrate and demonstrate its performance both numerically by using the finite element method (FEM) and experimentally. The simulation results show that the loss in the fundamental TE mode is relatively low while at the same time the fundamental TM mode suffers from a large metal dissipation loss induced by excitation of the microfiber-loaded surface plasmonic mode. The microfiber was fabricated using the standard microheater brushing–tapering technique. The measured extinction ratio over the range of the C-band wavelengths is greater than 20dB for the polarizer with a microfiber diameter of 4µm, which agrees well with the simulation results.

Reusable EGaIn-Injected Substrate-Integrated-Waveguide Resonator for Wireless Sensor Applications

The proposed structure in this research is constructed on substrate integrated waveguide (SIW) technology and has a mechanism that produces 16 different and distinct resonant frequencies between 2.45 and 3.05 GHz by perturbing a fundamental TE10 mode. It is a unique method for producing multiple resonances in a radio frequency planar structure without any extra circuitry or passive elements is developed. The proposed SIW structure has four vertical fluidic holes (channels); injecting eutectic gallium indium (EGaIn), also known commonly as liquid metal (LM), into these vertical channels produces different resonant frequencies. Either a channel is empty, or it is filled with LM. In total, the combination of different frequencies produced from four vertical channels is 16.

Design of broadband subwavelength grating couplers with low back reflection

We present a methodology to design broadband grating couplers using one-dimensional subwavelength gratings. Using the presented method, we design subwavelength grating couplers (SWGCs) with 1-dB bandwidths ranging from 50 to 90 nm. Our designed SWGCs have competitive coupling efficiency, as high as -3.8 dB for the fundamental TE mode, and state-of-the-art back reflections, as low as -23 dB.

Design and Simulation of a <inline-formula> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula>-Band Gyrotron Backward-Wave Oscillator With Distributed Loss

This paper presents the design and simulation of a $Q$ -band gyrotron backward-wave oscillator that is operated at fundamental TE01 mode. A tapered interaction circuit with distributed loss is employed to suppress both the transverse and axial mode competitions. A nonlinear code is used to study the start-oscillation current and interaction behavior. A Computer Simulation Technology (Particle In Cell) (CST-PIC) method is employed to verify the numerical calculation. A simulation result of 127-kW output power and 22.7% efficiency with a 3-dB bandwidth of 1.3 GHz driven by a beam of 70-kV voltage and 8-A current is predicted. The results of nonlinear code and CST-PIC calculations show good agreement.

Optimal Design and Thermal Analysis of Undepressed Collectors for 35-GHz Gyro-TWTs

A new curved-profile undepressed collector designed for a planned 35-GHz gyrotron traveling-wave tube (gyro-TWT) is proposed in this paper. This gyro-TWT, which is driven by a 70-kV, 10-A electron beam, is working at the fundamental TE01 mode with an efficiency of 20% and gain of 45 dB. Studies including theoretical analysis, numerical calculation, and computational simulation have been done. Key issues concerning electronic collecting density, dissipated power distribution, transmission performance, secondary electrons, and thermal property are considered. Simulation results show that curved-profile structure collector has a better heat-handling capacity than the conventional line structure collector.

On-chip beamsplitter operation on single photons from quasi-resonantly excited quantum dots embedded in GaAs rib waveguides

We present an on-chip beamsplitter operating on a single-photon level by means of a quasi-resonantly driven InGaAs/GaAs quantum dot. The single photons are guided by rib waveguides and split into two arms by an evanescent field coupler. Although the waveguides themselves support the fundamental TE and TM modes, the measured degree of polarization (∼90%) reveals the main excitation and propagation of the TE mode. We observe the preserved single-photon nature of a quasi-resonantly excited quantum dot by performing a cross-correlation measurement on the two output arms of the beamsplitter. Additionally, the same quantum dot is investigated under resonant excitation, where the same splitting ratio is observed. An autocorrelation measurement with an off-chip beamsplitter on a single output arm reveal the single-photon nature after evanescent coupling inside the on-chip splitter. Due to their robustness, adjustable splitting ratio, and their easy implementation, rib waveguide beamsplitters with embedded quantum dots provide a promising step towards fully integrated quantum circuits.

Magnetron injection gun design for a Q-band 300 kW 30 A gyrotron traveling wave tube

This paper is intended to present the optimal design of a triode type magnetron injection gun (MIG) for a 300 kW, 30 A gyrotron traveling wave tube (gyro-TWT), which is operated at Q band fundamental TE01 mode. Based on the analysis of velocity ratio (VR) distribution along the emission strip (ES), a further optimization of cathode geometry on the basis of a preliminary optimized gun is performed, and a new cathode structure is proposed. Compared with initial optimal parameters, the new structure demonstrates a decline of transverse velocity spread (TVS) from 3.66% to 0.57% and longitudinal velocity spread (LVS) from 4.11% to 0.72%, while VR is maintained at 1.05. The achieved overall LVS reaches as low as 3.44% when considering cathode surface roughness and thermal temperature effect. The sensitivity study has been carried out by changing the gun parameters like anode voltage, beam current, and cathode magnetic field to ensure the practical operation stability.

A Multifrequency Notch Filter for Millimeter Wave Plasma Diagnostics based on Photonic Bandgaps in Corrugated Circular Waveguides

Sensitive millimeter wave diagnostics need often to be protected against unwanted radiation like, for example, stray radiation from high power Electron Cyclotron Heating applied in nuclear fusion plasmas. A notch filter based on a waveguide Bragg reflector (photonic band-gap) may provide several stop bands of defined width within up to two standard waveguide frequency bands. A Bragg reflector that reflects an incident fundamental TE11 into a TM1n mode close to cutoff is combined with two waveguide tapers to fundamental waveguide diameter. Here the fundamental TE11 mode is the only propagating mode at both ends of the reflector. The incident TE11 mode couples through the taper and is converted to the high order TM1n mode by the Bragg structure at the specific Bragg resonances. The TM1n mode is trapped in the oversized waveguide section by the tapers. Once reflected at the input taper it will be converted back into the TE11 mode which then can pass through the taper. Therefore at higher order Bragg resonances, the filter acts as a reflector for the incoming TE11 mode. Outside of the Bragg resonances the TE11 mode can propagate through the oversized waveguide structure with only very small Ohmic attenuation compared to propagating in a fundamental waveguide. Coupling to other modes is negligible in the non-resonant case due to the small corrugation amplitude (typically 0.05·λ0, where λ0 is the free space wavelength). A Bragg reflector for 105 and 140 GHz was optimized by mode matching (scattering matrix) simulations and manufactured by SWISSto12 SA, where the required mechanical accuracy of ± 5 μm could be achieved by stacking stainless steel rings, manufactured by micro-machining, in a high precision guiding pipe. The two smooth-wall tapers were fabricated by electroforming. Several measurements were performed using vector network analyzers from Agilent (E8362B), ABmm (MVNA 8-350) and Rohde&Schwarz (ZVA24) together with frequency multipliers. The stop bands around 105 GHz (- 55dB) and 140 GHz (-60dB) correspond to the TE11-TM12 and TE11-TM13 Bragg resonances. Experiments are in good agreement with theory.

聚合物脊形光波导TM模色散特性的偏振修正

The dispersion characteristics of organic / polymer optical rib waveguide affect the performances of polymer photonic devices greatly. In this paper,the effective refractive index of optical rib waveguide was calculated by scalar variational formula,and the distribution of optical field used was obtained by using effective index method( EI) approximately. Considering the transverse variations of refractive index distribution and based on the vector wave equation governing the guided modes,the effective index obtained by scalar variational formula( VEI) was modified by perturbation method( PM) for precise dispersion characteristics. The dispersion characteristics of the fundamental and higher order modes were analyzed for polymer multimode rib waveguides. An approach was provided to investigate the effect of the structure parameters and dimensions on the polarized dispersion characteristics of the fundamental and higher order modes for TM,TE modes. The polarized dispersion characteristics of single mode waveguide were analyzed for TM,TE fundamental modes. It is demonstrated that the dispersion characteristics of TM mode obtained by eigenvalue equation must be modified duo to the large error,and the error for TE mode is small relatively.

Bragg Grating Sensors in Laser-written Single Mode Polymer Waveguides

We present a technology for integrating Bragg gratings with single mode polymer waveguides fabricated in the EpoCore/EpoClad material system. The gratings were inscribed in a photosensitive polymethyl methacrylate (PMMA) coatingusing a phase mask and then transferred in the lower cladding layer using reactive ion etching maintaining compatibility withstandard waveguide fabrication technologies. Subsequently, the waveguide core was patterned on top using laser direct-write lithography of a spin-coated polymer layer. When exciting the waveguides with a broadband spectrum around 1550nm, 2 reflection peaks around 1580nm were found corresponding to the fundamental TE and TM mode in the polymer waveguide. Eventually, this technology will be used for structural health monitoring in concrete constructions or composite materials.

Scattering by abrupt discontinuities on photonic nanowires: closed-form expressions for domain reduction.

Semiconductor and metallic nanowires are attractive building blocks for a nanoscale integrated photonic platform. The scattering coefficients of the optical or plasmonic waveguide mode by 3-dimensional nanowire abrupt discontinuities including splices and endfaces are important figures of merit for realistic estimation of the coupling, lasing, or sensing performance. To tackle with such computationally challenging problems, we derive simple closed-form expressions based on linear equations and overlap integrals of normal modes to realize domain reduction and efficient analytical modeling. For the reflection coefficients at nanowire/waveguide endfaces, the analytical expressions incorporating all the bound modes and a few dozen leaky modes are highly accurate; whereas for the transmission coefficients at nanowire/waveguide splices, the model can be further simplified because only the input and the interested output bound modes need to be considered. Exhaustive validations using fully-vectorial simulation results as reference data show that the model is accurate and versatile for fundamental and high-order TE or TM modes, and for various architectures including high-index-contrast dielectric and plasmonic configurations, 3-D geometries or 2-D equivalents, and various operating wavelengths from ultraviolet to visible and the optical telecommunication bands in the infrared. Our model will facilitate the structure design and theoretical investigation of nanowire/waveguide photonic devices, especially lasers, resonators, sensors and couplers.

Widely tunable surface-emitted monochromatic terahertz-wave generation beyond the Reststrahlen band

We proposed a surface-emitted THz-wave generation on the basis of difference frequency mixing in a GaP planar waveguide. By utilizing modal birefringence of fundamental TE and TM modes at telecom wavelengths in the GaP membrane waveguide, phase matching condition for the surface-emitted difference frequency mixing (SE-DFM) can be achieved. THz output power is enhanced near the phonon polariton resonance frequency owing to the strong coupling between the transverse optical (TO) phonon of GaP and THz radiation. The SE-DFM scheme can generate THz waves beyond the Reststrahlen band located between 11 and 12THz, resulting in widely tunable THz wave generation. Our proposed broadband THz sources can be applicable for optically isotropic nonlinear optical materials such as GaAs and InP as well as GaP.