Pure Bend Loss Research Articles

Reducing bend-induced loss and crosstalk in a two-mode ridge waveguide by steplike thickness structuring.

This study demonstrated that two-step structuring of the waveguide thickness in a bent section significantly reduces bend-related inter-mode crosstalk, excess loss, and pure bending loss. A simple analytical formula was derived linking the thickness change required to compensate for bend-induced effects with geometrical parameters of the waveguide and bending radius. The effectiveness of the proposed approach was verified through rigorous numerical simulations of the loss and inter-mode crosstalk based on transformation optics formalism. The numerical results obtained for a TiO2:SiO2 medium index contrast waveguide exhibited significant improvement of all relevant parameters for TE00 and TE01 modes.

A Novel Force Sensor Based on Optical Fibers Used for Semicircular Flexure Beam Unit

In this article, a novel force sensor is designed based on the optical fiber bending loss theory utilizing a structure with periodically corrugated semicircular flexure beam units. The fiber bending loss theory composed of the pure bending loss and the transition loss is related to the curvature radius according to the theoretical analysis. Both the optical working modes and the mechanical properties of the designed sensor are discussed. The output voltage attenuation of different curvature radii is tested and the curvature radius of 6 mm is selected for further experiment. The actual sensing results are acquired using a commercial force sensor. The result shows that the nonlinear errors of the forward and the reverse force applying process are 11.82% and 17.86%, respectively. The sensitivity is 13 mV/N and the precision is 160 mN. The experiment under different temperatures ensures the temperature-insensitive characteristics of the sensor.

Core depth determination of a slightly buried Si-wire waveguide with a reduced bend loss

The effects of adjusting the distance between a core and an air-cladding interface on the propagation properties are investigated in a bent Si-wire waveguide. The eigenmode analysis is carried out using the imaginary-distance beam-propagation method based on Yee’s mesh in the cylindrical co-ordinate system. The pure bend loss (PBL) is evaluated as a function of core depth for several core aspect ratios. Since a waveguide bend causes polarization coupling, the polarization crosstalk (PCT) is also evaluated by the propagation analysis with the aid of the FDTD method. It is found that a core depth with a minimized PBL exists for the TM mode when the air-cladding interface is placed at the position where the field amplitude decays to approximately 5% of its peak, with a PCT being less than −30 dB.

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 (

Reduction in Bend Losses of a Buried Waveguide on a Silicon Substrate by Adjusting the Core Location

A new technique for reducing pure bend and transition losses in a buried dielectric waveguide is discussed, using the imaginary-distance beam-propagation method. It is numerically shown that only the adjustment of a core location enables us to reduce the bend losses. The reason why a proper location of the core offers minimum bend losses regardless of a bending radius is explained in terms of the generation and suppression of a leaky wave. Significant loss reduction is achieved over a wide spectral range from 1.3 to 1.65 $\mu {\rm m}$ . It is also revealed that a minimum pure bend loss is obtained regardless of the relative refractive index difference, when the air-cladding interface is placed at the position, where the field amplitude decays to approximately 12% of its peak.

Multimode optical waveguide enabling microbends with low inter-mode crosstalk for mode-multiplexed optical interconnects.

A vertical multimode waveguide enabling micro-bends is proposed for mode-multiplexed optical interconnect links. The multimode waveguide is designed to be singlemode in the lateral direction and support higher-order modes in the vertical direction. The characteristic analysis for an SOI (silicon-on-insulator)-based vertical multimode waveguide with a ~0.3μm × ~1.5μm cross section is given as an example. The theoretical pure bending loss is negligible for all the lowest eight modes when the bending radius is even less than 5μm. When light goes through the structure consisting of a straight section connected with a bent section, it is found that some inter-mode crosstalk is caused by the significant mode hybridization happening in the sharply bent multimode waveguide. For the designed SOI-based vertical multimode waveguide, the inter-mode crosstalk is lower than -20dB even when the bending radius is chosen as small as R = 10μm, which is one order smaller than that for the traditional lateral multimode waveguide (whose minimal bending radius is about 130μm). The inter-mode crosstalk can be even reduced to -30dB when choosing R = 30μm. Such a multimode optical waveguide microbend with low inter-mode crosstalk is promising for realizing compact mode-multiplexing links.

Bent Embedded Optical Waveguide With a Loaded Metal Film for Reducing a Polarization Dependent Loss

The beam-propagation method is applied to the analysis of a bent embedded waveguide with a loaded metal film. As a basic study, coupled bent slab waveguides are treated to discuss their mechanism for reducing the pure bend and transition losses. Based on this study, a metal film is loaded on the bent embedded waveguide. The metal film serves to generate the surface plasmon-polariton mode for the transverse-magnetic (TM) wave, so that the embedded waveguide with the metal film can be regarded as coupled bent waveguides for the TM wave. This leads to reduction in the bend losses for the TM wave. As a result, a low polarization dependent loss (PDL) can be obtained over a wide spectral range, since the pure bend loss of the embedded waveguide for the TM wave is larger than that for the transverse-electric wave. Furthermore, the application to a trench structure with a depressed refractive index contributes not only to a low PDL but also to a low pure bend loss.

Silicon-based horizontal nanoplasmonic slot waveguides for on-chip integration

Horizontal metal/insulator/Si/insulator/metal nanoplasmonic slot waveguide (PWG), which is inserted in a conventional Si wire waveguide, is fabricated using the standard Si-CMOS technology. A thin insulator between the metal and the Si core plays a key role: it not only increases the propagation distance as the theoretical prediction, but also prevents metal diffusion and/or metal-Si reaction. Cu-PWGs with the Si core width of ~134-21 nm and ~12-nm-thick SiO2 on each side exhibit a relatively low propagation loss of ~0.37-0.63 dB/µm around the telecommunication wavelength of 1550 nm, which is ~2.6 times smaller than the Al-counterparts. A simple tapered coupler can provide an effective coupling between the PWG and the conventional Si wire waveguide. The coupling efficiency as high as ~0.1-0.4 dB per facet is measured. The PWG allows a sharp bending. The pure bending loss of a Cu-PWG direct 90° bend is measured to be ~0.6-1.0 dB. These results indicate the potential for seamless integration of various functional nanoplasmonic devices in existing Si electronic photonic integrated circuits (Si-EPICs).

Light Propagation in Curved Silver Nanowire Plasmonic Waveguides

Plasmonic waveguides made of metal nanowires (NWs) possess significant potential for applications in integrated photonic and electronic devices. Energy loss induced by bending of a NW during light propagation is critical in affecting its performance as a plasmonic waveguide. We report the characterization of the pure bending loss in curved crystalline silver NW plasmonic waveguides by decoupling the energy loss caused by bending and propagation. The energy attenuation coefficiency due purely to bending was also determined, which exhibited an exponential relationship with the bending radius. Finite-difference-time-domain (FDTD) methods were utilized for theoretical simulations, which matched the experimental results well.

Fully complementary metal-oxide-semiconductor compatible nanoplasmonic slot waveguides for silicon electronic photonic integrated circuits

Horizontal Al/SiO2/Si/SiO2/Al nanoplasmonic slot waveguides with the SiO2 width at each side of ∼15 nm and the Si core width of ∼136–43 nm were fabricated using a fully silicon complementary metal-oxide-semiconductor compatible technology. The propagation losses were measured to be ∼1.07–1.63 dB/μm at the telecommunication wavelength of 1550 nm, in agreement with those predicted from numerical simulation. A simple tapered coupler with length of ∼0.3–1 μm provides a high coupling efficiency of ∼−0.6–−1.5 dB between the plasmonic waveguide and the conventional Si dielectric waveguide. The plasmonic slot waveguide can achieve a low-loss ultracompact bend. A direct 90° bend was demonstrated to have the pure bending loss as low as ∼0.2–0.4 dB. The losses of propagation, coupling, and bending depend weakly on wavelength in the c-band. These results demonstrate the potential for seamless integration of functional plasmonic devices in existing silicon electronic photonic integrated circuits.

Numerical simulation of a DFB - fiber laser sensor (part 1)

This paper presents the preliminary results obtained in developing a numerical simulation analysis of fiber optic bending sensitivity aiming to improve the design of fiber lasers. The developed numerical simulation method relies on an analysis of both the fundamental mode propagation along an optical fiber and of how bending of this fiber influence the optical radiation losses. The cases of simple, undoped and of doped with Er ions optical fibers are considered. The presented results are based on numerical simulation of eigen-modes of a laser intensity distribution by the use of finite element method (FEM) developed in the frame of COMSOL software package. The numerical simulations are performed by considering the cases of both normal, non-deformed optic fiber and of symmetrically deformed optic fiber resembling micro-bending of it. Both types of fiber optic bending losses are analyzed, namely: the transition loss, associated with the abrupt or rapid change in curvature at the beginning and the end of a bend, and pure bend loss is associated with the loss from the bend of constant curvature in between.

Bending Loss Calculation of a Dielectric-Loaded Surface Plasmon Polariton Waveguide Structure

Based on full 3D finite element method simulations, the transmission of a dielectric-loaded surface plasmon polariton waveguide (DLSPPW) based 1/4 circle is calculated for a 90° bend model and a 270° bend model, respectively. It is found that the 270° bend model gives almost pure bending loss while the 90° bend model contains additional coupling loss. The models are applied to deduce the loss and unloaded quality factor of DLSPPW based waveguide ring resonators (WRRs) and the results of the 270° bend model agree well with direct simulating results of the WRRs. Thus the 270° bend model gives a fast and simple way to calculate bending loss and it is helpful for WRR design because no wavelength scan is needed.

A Small Polymeric Ridge Waveguide With a High Index Contrast

In this paper, an optimal design of a small polymeric ridge waveguide with a high index contrast is presented. In order to reduce the leakage to the substrate and pure bending losses, the buffer layer of the present waveguide is etched partially. The single-mode condition, the bending characteristics, and the birefringence of the present small polymeric ridge waveguide are also studied. By adjusting the core width and the core height, it is possible to obtain a polarization-insensitive small polymer ridge waveguide. For the bending loss, the numerical results show that the dominant part is the transition loss between the straight and bending sections (other than the pure bending loss) and the transition loss could be reduced greatly by introducing a lateral offset. However, the transition loss is still too large to obtain a very small bending radius (e.g., 10 mum). When only the pure bending loss is necessary to consider in some special case (e.g., microrings without any transitions), one can have a bending radius less than 10 mum due to the possibility of low pure bending loss.

Passive photonic elements based on dielectric-loaded surface plasmon polariton waveguides

The authors present full three-dimensional numerical modeling of passive photonic elements based on dielectric-loaded surface plasmon polariton waveguides (DLSPPWs). They demonstrate that at telecom wavelengths a highly confined SPP mode can be guided in a single mode DLSPPW of subwavelength cross section and estimate the achievable density of photonic integration. The size of bending and splitting photonic elements based on DLSPPW can be as small as a few micrometers with pure bend loss less than 10% (0.4dB) and the transmission efficiency exceeding 70% (total loss of about 1.3dB). Such DLSPPW elements are important for implementation of photonic integrated circuits, guiding optical and electric signals in the same circuitry, and lab-on-a-chip applications.

Characteristic analysis of nanosilicon rectangular waveguides for planar light-wave circuits of high integration

When a full-vectorial finite-difference method is used, rectangular Si waveguides can be characterized for planar light-wave circuits of high integration. The single-mode condition for a rectangular Si waveguide is obtained first. The birefringence, which can be adjusted by modifying the thickness of the cladding layer, is also studied. For a nano-Si rectangular waveguide the pure bending loss is very small even for an ultrasmall bending radius (e.g., a few micrometers), and the transition loss becomes dominant. The width and height are optimized to minimize the bending radius for the requirement that the bending loss is smaller than 0.1 dB. Finally the coupling between two parallel straight waveguides is analyzed, and it is shown that there is an optimal width for the maximal coupling length.

A novel attenuator based on bending loss in SMF

A novel bending single-mode fiber attenuator is presented. Organic glass plinths are sticked with several iron rods in order to impose bending on a typical single-mode fiber. Changing the space between the plinths, we can simultaneously determine bending magnitude and deduce the relationship between pure bend loss and bending-arc length. The theoretical model is in good agreement with the experimental results is stress-induced changes are considered. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 114–118, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21280

Analysis of characteristics of bent rib waveguides.

With a perfectly matched layer boundary treatment, a semivectorial finite-difference method is used to calculate the eigenmodes of a single-mode (SM) or multimode (MM) bent rib waveguide. A detailed analysis is given for the dependence of the bending losses (including the pure bending loss and the transition loss) on geometrical parameters of the bent rib waveguide such as the rib width, the rib height, and the bending radius. The characteristics of the higher-order modes are analyzed. It is shown that the bending loss of the fundamental mode can be reduced effectively by increasing the width and height of the rib. For an integrated device, undesired effects due to the higher-order modes of a MM bent waveguide can be removed by appropriate choice of the geometrical parameters. An appropriately designed MM bent waveguide is used to reduce effectively the bending loss of the fundamental mode, and a low-loss SM propagation in a MM bent waveguide is realized when the bending losses of the higher-order modes are large enough.

Understanding bending losses in holey optical fibers

Extremely large mode area fibers that are single-moded over a broad wavelength range can be created using holey fiber technology. However, as with any fiber, the largest mode areas that are practically feasible are ultimately determined by bending losses. It is therefore essential to gain an understanding of the factors that influence bend loss in these fibers in order to form accurate predictions that can facilitate improved bend loss design. Here, we present the first detailed study of transition loss and pure bend loss in a holey fiber, and consider the impact of the fiber structure. A theoretical model is derived that retains the full refractive index profile of a holey fiber. This approach is used to predict the bend loss in large mode area holey fibers and is validated through comparison with experimental data. For the fibers under study here, we demonstrate that pure bend loss is the dominant component of macro-bend loss and that the hole configuration within the cladding can strongly influence this loss.

Fiber bend losses produced by soft and swellable materials for hydrocarbon detection

We present results of measurements of fiber bend loss caused by soft and swellable materials with perturbation periods of 1–20 mm. We used swellable materials that have different moduli of Young. We show that the swell of soft materials causes the pure bend loss that increases when the period rises to 10 mm. We show that the higher the modulus of Young the higher the loss caused by swellable materials. These results may be used to choose suitable materials and construction for assembling a fiber optics sensor based in the bend loss.

Coupled-Mode Analysis of Loss in Bent Single-Mode Optical Fibers

In this study, we analyzed the loss formation in bent single-mode optical fibers using a semi-analytical method, which is a combination of conformal mapping and coupled-mode theory based on the two-layer step-index optical fiber model. The pure bend loss results were compared to those reported in the existing literature. The advantage of using this method is that it provides insight into the mode field behavior and loss formation in bent fibers and accurately presents the power distribution in the cross section of the fibers.