Bending Losses In Waveguides Research Articles

PTFE-Based Circular Terahertz Dielectric Waveguides

This paper presents the transmission characteristics of flexible solid circular dielectric waveguides in the terahertz frequency band. In this paper, we measured the electrical properties of certain polymers within 325–500 GHz. Through simulation and measurement, the transmission loss, bending loss, and electric field distribution of solid-core polymer dielectric waveguides were analyzed and discussed. Additionally, we considered the surrounding cladding of the dielectric waveguide, the signal-feeding mode transmitter, and the interconnection of the dielectric waveguide. Ultimately, in the operating frequency range of 325–500 GHz, we selected PTFE rods with diameters of 0.5 mm and 1 mm as the dielectric waveguides, with measured transmission loss of less than 30 dB/m and 33 dB/m, respectively, and bending loss of less than 1 dB/m. The described dielectric waveguide has engineering significance for short-distance connections in complex geometric environments and provides a reference for subsequent research.

Wideband dispersion-free THz waveguide platform

We present a versatile THz waveguide platform for frequencies between 0.1 THz and 1.5 THz, designed to exhibit vacuum-like dispersion and electric as well as magnetic field enhancement. While linear THz spectroscopy benefits from the extended interaction length in combination with moderate losses, nonlinear THz spectroscopy profits from the field enhancement and zero dispersion, with the associated reshaping-free propagation of broadband single- to few-cycle THz pulses. Moreover, the vacuum-like dispersion allows for velocity matching in mixed THz and visible to infrared pump-probe experiments. The platform is based on the motif of a metallic double ridged waveguide. We experimentally characterize essential waveguide properties, for instance, propagation and bending losses, but also demonstrate a junction and an interferometer, essentially because those elements are prerequisites for THz waveform synthesis, and hence, for coherently controlled linear and nonlinear THz interactions.

Mid-infrared integrated silicon–germanium ring resonator with high Q-factor

We report the realization of a silicon–germanium on silicon ring resonator with high Q-factor at mid-infrared wavelengths. The fabricated ring exhibits a loaded Q-factor of 236 000 at the operating wavelength of 4.18 µm. Considering the combined waveguide propagation losses and bending losses, which are measured to be below 0.2 dB/cm, even higher Q-factors could be achieved on this platform. Furthermore, our dispersion engineering of the waveguides should make these microrings suitable for nonlinear optical applications. These results pave the way for sensing applications and nonlinear optics in the mid-infrared range.

Bending Loss Analysis of Chalcogenide Glass Channel Waveguides for Mid-Infrared Astrophotonic Devices

In this study, the bending losses of chalcogenide glass channel optical waveguides consisting of an As2Se3 core and an As2S3 lower cladding layer were numerically evaluated across the astronomical N-band, which is the mid-infrared spectral range between the 8 µm and 12 µm wavelengths. The results reveal the design rules for bent waveguides in mid-infrared astrophotonic devices.

Method for the simultaneous measurement of waveguide propagation loss and bending loss

Abstract: The propagation loss of waveguide is a key indicator to evaluate the performance of an integrated optical platform. The commonly used cut-back method to measure the propagation requires the introduction of the Spiral test structure. In order to remove the effect of bending loss, the bending radius is usually designed to be large enough, taking up a lot of foot print. In this paper, we suggested a method to measure the propagation loss and bending loss of waveguide simultaneously with cut-back structure. The bending loss can be exponentially fitted with the bending radius according to simulation, which can be further simplified as linear fitting between the natural logarithm of the bending loss and the bending radius. A genetic algorithm was used to fit the insertion loss curve of the cutback structure and calculate the propagation loss and bending loss. With this method, we measured a cut-back structure of lithium niobate waveguide and got the propagation loss of 0.558dB/cm and bending

Research of the bending loss of S-shaped waveguides with offsets and trenches

S-shaped polymer waveguides are heavily exploited to connect optical components. Reducing the bending loss of S-shaped polymer waveguides is critical for low-loss and small-size optical circuits. In this paper, the S-shaped waveguide with offsets and trenches (SW-OT) is designed. The dependence of the bending loss on crucial parameters like offsets, trench locations and trench widths is analyzed by the beam propagation method. A comparison of the bending loss among standard S-bend, shifted S-bend, S-bend employing trenches and SW-OT structure is conducted. Results show that the bending loss of the SW-OT with a bending radius of 1000μm is only 0.11dB, reducing by 89.70% compared with the S-shaped waveguide with only shifts. Moreover, a dramatic reduction in the bending loss is obtained by placing trenches properly in the curved region. Therefore, the combination of offsets and trenches can effectively decrease the bending loss of low index contrast polymer S-shaped waveguides.

Suspended nanocrystalline diamond ridge waveguides designed for the mid-infrared

A comprehensive study and design of air-clad suspended ridge diamond waveguides for operation across the 2.5–16 µm spectral range is presented, specifically targeting nanocrystalline diamond (NCD) thin films directly grown on silicon substrates. Three film thicknesses of 520, 1000 and 2000 nm are considered, to cover overlapping sub-bands of 2.5–5, 4–9 and 8–16 µm, respectively. Within each sub-band, the waveguide dimensions for single mode quasi-TE operation are found and the waveguide material losses and bending losses are estimated at each design point. In addition, in each case the minimum required undercut depth and etch hole placement for optical isolation of the waveguide mode from the silicon substrate is also quantified. We also estimate the losses associated with scattering from surface roughness, which is an unavoidable byproduct of the NCD thin film growth process. Our results indicate that despite the relatively low film thickness-to-wavelength ratio, mechanically stable waveguides with good optical confinement and low material and bending losses can be realised to cover the full 2.5–16 µm range. In addition, scattering loss estimations predict a drastic drop in roughness-induced scattering losses above 6 µm, even for relatively rough films. In addition to highlighting the utility of suspended NCD as a versatile platform for mid-infrared integrated photonics, the approaches and results presented here can be used to inform the design of suspended air-clad waveguides in other material platforms.

An analytical method with numerical results to be used in the design of optical slab waveguides for optical communication system applications

<p>This study develops an analytical method with numerical results for the design of optical slab waveguides for optical communication system applications. An optical slab waveguide structure made of silicon on silicon dioxide material is designed and analyzed. The effective index of the mode is studied against variations in the waveguide dimensions. Transmission and reflection coefficients are studied and compared to the wavelength and dimensions of the waveguide. Variations are sketched with the x-axis, in addition to the electric field intensity distribution and effective refractive index. Waveguide bending loss is also studied with waveguide thickness and length variations within three waveguide transmission windows of 850 nm, 1300 nm, and 1550 nm.</p>

The Influence of Geometry on the Loss of Curved Slot Waveguide

In curved slot waveguide devices, there are often waveguide bending situations. Under certain conditions, the smaller the waveguide bending geometry, the more compact device structure; the smaller the bending geometry, the greater the loss caused by waveguide bending. Based on the study of the loss of a curved slot waveguide, this paper combines the geometric dimensions with it to study the influence of the loss. A new method for calculating the loss coefficient caused by the bending of the waveguide: the effective refractive index method with fixed interference correction. Through this method, the relationship between the bending loss coefficient and the width, height and radius of curvature of the dielectric waveguide is analyzed and calculated. Compare the calculation result with the result calculated by the pattern analysis method. Finally, the results were discussed and analyzed. The conformal transformation method and the normalization method of the geometrical size to the bending loss of the waveguide are analyzed, the relationship between the bending geometrical size of the curved narrow slot waveguide and the bending loss is obtained, and the empirical formula for the bending loss is established. From the formula, four Curves of waveguide bending size and bending loss of a common material. Experimental research results show that with the improvement of bending waveguide loss theory and coupling mechanism, low-loss transmission can be achieved under small bending dimensions, so that the integration of overall geometrical dimensions is the development trend of bending.

Nonlinear increase, invisibility, and sign inversion of a localized fs-laser-induced refractive index change in crystals and glasses

Multiphoton absorption via ultrafast laser focusing is the only technology that allows a three-dimensional structural modification of transparent materials. However, the magnitude of the refractive index change is rather limited, preventing the technology from being a tool of choice for the manufacture of compact photonic integrated circuits. We propose to address this issue by employing a femtosecond-laser-induced electronic band-gap shift (FLIBGS), which has an exponential impact on the refractive index change for propagating wavelengths approaching the material electronic resonance, as predicted by the Kramers–Kronig relations. Supported by theoretical calculations, based on a modified Sellmeier equation, the Tauc law, and waveguide bend loss calculations, we experimentally show that several applications could take advantage of this phenomenon. First, we demonstrate waveguide bends down to a submillimeter radius, which is of great interest for higher-density integration of fs-laser-written quantum and photonic circuits. We also demonstrate that the refractive index contrast can be switched from negative to positive, allowing direct waveguide inscription in crystals. Finally, the effect of the FLIBGS can compensate for the fs-laser-induced negative refractive index change, resulting in a zero refractive index change at specific wavelengths, paving the way for new invisibility applications.

Ultra-thin silicon-on-insulator waveguide bend based on truncated Eaton lens implemented by varying the guiding layer thickness

Silicon-on-insulator (SOI) waveguides with different geometries have been employed to design various integrated optical components. Reducing the bending radius of the SOI waveguides with low bending loss is essential in minimizing the footprint of light-wave circuits. The propagating mode is less confined in the core of the ultra-thin SOI waveguide and penetrates to substrate and cladding, leading to higher bending loss compared to conventional SOI waveguides with a thicker guiding layer. Although various bending mechanisms have been utilized to reduce the bending loss of conventional SOI waveguides, the ultra-thin SOI waveguide bends have not been studied in detail. In this paper, we present a 60-nm-thick SOI waveguide bend based on the truncated Eaton lens implemented by varying thickness of the guiding layer. The three-dimensional full-wave simulations reveal that the designed waveguide bend, with a radius of 3.9 μm, reduces the bending loss from 3.3 to 0.42 dB at the wavelength of 1550 nm. Moreover, the bending loss for the wavelength range of 1260–1675 nm is lower than 0.67 dB while the bending loss in the C-band is lower than 0.45 dB.

Bending loss and propagation characterization of hollow pipe polymer terahertz waveguides

AbstractWe investigate the bending loss and propagation characterization of hollow pipe polymer terahertz waveguides, based on 3D electromagnetic simulation and systematic experiments. Bending loss and propagation attenuation of pipe waveguides are investigated for various core diameters and radius of curvature over a wide frequency range (100‐500 GHz). Our results indicate that waveguides with larger core diameters or larger radii of curvature suffer lower loss, with the lowest loss at or near anti‐resonant frequencies, with typical values such as attenuation constant of a straight Teflon waveguide as low as 0.29 m−1 with inner diameter 14 mm, outer diameter 16 mm; and minimal bending loss of 0.45 m−1 with a radius of curvature 50 cm and inner diameter 14 mm, outer diameter 16 mm. Based on the systematic experimental and simulation results, we propose and test a simple relationship that the propagation constant of curved waveguides may follow, which could serve as a design guide for fabrication of hollow pipe polymer waveguides for efficient and long‐distance transmission of terahertz electromagnetic radiation.

Design of a Directional Coupler based on UV-Induced LiNbO3 Waveguides

AbstractA semi-analytical technique, effective index-based matrix method (EIMM), has been applied to determine the coupling length of continuous wave UV-written directional coupler for different gaps between the waveguides as well as the pure bending loss and transition loss of S-curved waveguides estimated to optimize the transition length (

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.

Cascade-coupled racetrack resonators based on the Vernier effect in the mid-infrared.

In this paper we report the experimental demonstration of racetrack resonators in silicon-on-insulator technology platform operating in the mid-infrared wavelength range of 3.7-3.8 μm. Insertion loss lower than 1 dB and extinction ratio up to 30 dB were measured for single resonators. The experimental characterization of directional couplers and bending losses in silicon rib waveguides are also reported. Furthermore, we present the design and fabrication of cascade-coupled racetrack resonators based on the Vernier effect. Experimental spectra of Vernier architectures were demonstrated for the first time in the mid-infrared with insertion loss lower than 1 dB and maximum interstitial peak suppression of 10 dB.

Calculation of bending losses for highly confined modes of optical waveguides with transformation optics

We revisited the fundamental problem of bending loss calculation in optical waveguide theory using transformation optics (TOs). Due to the fact that TOs is based on the form invariance property of Maxwell equations, this new approach provides more accurate calculation of waveguide bending loss compared to the conventional refractive index conformal mapping method, especially for small bending radii typical for plasmonic waveguides or photonic waveguides with high-index contrast. We believe our results provide a simple yet reliable way of bending loss calculation for highly confined optical (including plasmonic) waveguides.

Application of the three-dimensional aperiodic Fourier modal method using arc elements in curvilinear coordinates

This paper deals with a full vectorial generalization of the aperiodic Fourier modal method (AFMM) in cylindrical coordinates. The goal is to predict some key characteristics such as the bending losses of waveguides having an arbitrary distribution of the transverse refractive index. After a description of the method, we compare the results of the cylindrical coordinates AFMM with simulations by the finite-difference time-domain (FDTD) method performed on an S-bend structure made by a 500 nm × 200 nm silicon core (n=3.48) in silica (n=1.44) at a wavelength λ=1550 nm, the bending radius varying from 0.5 up to 2 μm. The FDTD and AFMM results show differences comparable to the variations obtained by changing the parameters of the FDTD simulations.

用于光互连的聚硅氧烷波导弯曲损耗

用于光互连的聚硅氧烷波导弯曲损耗

Athermal Wavelength Filters toward Optical Interconnection to LSIs

Photonic integrated circuits (PICs) produced by large-scale integration (LSI) on Si platforms have been intensively researched. Since thermal diffusion from the LSI logic layer is a serious obstacle to realizing a Si-based optical integrated circuit, we have proposed and realized athermal wavelength filters using Si slot waveguides embedded with benzocyclobutene (BCB). First, the athermal conditions were theoretically investigated by controlling the waveguide and gap width of the slot waveguides. In order to introduce the calculated waveguide structures to wavelength filters, the propagation losses and bending losses of the Si slot waveguides were evaluated. The propagation losses were measured to be 5.6 and 5.3dB/cm for slot waveguide widths of 500 and 700nm, respectively. Finally, athermal wavelength filters, a ring resonator, and a Mach-Zhender interferometer (MZI) with a slot waveguide width of 700nm were designed and fabricated. Further, a temperature coefficient of -0.9pm/K for the operating wavelength was achieved with the athermal MZI.

Lasing in a metal-clad microring resonator

Metal cladding was experimentally demonstrated to be a feasible method to further scale down the size of a microring laser. Shrinking the physical dimensions of semiconductor microring resonators has been difficult due to a large waveguide bending loss. We experimentally show that light can be better confined into a much tighter space by using the plasmonic metal structure, thereby enabling miniaturization of a microring laser.