Efficient Waveguide Research Articles

Optical lattice-like cladding waveguides by direct laser writing: fabrication, luminescence, and lasing.

We report on the fabrication of optical lattice-like waveguide structures in an Nd:YAP laser crystal by using direct femtosecond laser writing. With periodically arrayed laser-induced tracks, the waveguiding cores can be located in either the regions between the neighbored tracks or the central zone surrounded by a number of tracks as outer cladding. The polarization of the femtosecond laser pulses for the inscription has been found to play a critical role in the anisotropic guiding behaviors of the structures. The confocal photoluminescence investigations reveal different stress-induced modifications of the structures inscribed by different polarization of the femtosecond laser beam, which are considered to be responsible for the refractive index changes of the structures. Under optical pump at 808 nm, efficient waveguide lasing at ∼1 μm wavelength has been realized from the optical lattice-like structure, which exhibits potential applications as novel miniature light sources.

Facile synthesis of single-crystalline microwires based on anthracene derivative and their efficient optical waveguides and linearly polarized emission

The well-defined single-crystalline microwires of a solid-emissive organic functional molecule, 2-(anthracen-9-yl)-4, 5-diphenyl-1H-imidozole (ADPI) were successfully prepared by a facile solution process without the use of surfactant or additional templates. In addition, the optical loss coefficient is as low as 0.1dB μm−1 for the as-prepared ADPI microwires, which is lower than most previous reported organic optical waveguides. Meanwhile, these microwires also show optically uniaxial properties as demonstrated by the linearly polarized emission, providing potentially orientation-sensitive applications as optical waveguides with low optical loss.

Layer-to-layer compression and enhanced optical properties of few-layer graphene nanosheet induced by ion irradiation

We report on the first experimental study of the layer-to-layer compression and enhanced optical properties of few-layer graphene nanosheet by applying ion irradiation. The deformation of graphene layers is investigated both theoretically and experimentally. It is observed that after the irradiation of energetic ion beams, the space between separate graphene layers is reduced due to layer-to-layer compression, resulting in tighter contact of the graphene sheet with the surface of the substrate. This processing enables enhanced interaction of the graphene with the evanescent-field wave near the surface, which induces reinforced polarization-dependent light absorption of the graphene. Utilizing the ion-bombarded graphene nanosheets as saturable absorbers, we have realized efficient Q-switched waveguide lasing with enhanced performance through the interaction of the graphene and evanescent field.

Hybrid graphene plasmonic waveguide modulators

The unique optical and electronic properties of graphene make possible the fabrication of novel optoelectronic devices. One of the most exciting graphene characteristics is the tunability by gating which allows one to realize active optical devices. While several types of graphene-based photonic modulators have already been demonstrated, the potential of combining the versatility of graphene with subwavelength field confinement of plasmonic waveguides remains largely unexplored. Here we report fabrication and study of hybrid graphene–plasmonic waveguide modulators. We consider several types of modulators and identify the most promising one for telecom applications. The modulator working at the telecom range is demonstrated, showing a modulation depth of >0.03 dB μm−1 at low gating voltages for an active device area of just 10 μm2, characteristics which are already comparable to those of silicon-based waveguide modulators while retaining the benefit of further device miniaturization. Our proof-of-concept results pave the way towards on-chip realization of efficient graphene-based active plasmonic waveguide devices for optical communications.

Current Status of Oxide Dielectric Materials for Terahertz Applications–An Overview

Terahertz electromagnetic radiation, its generation, detection and material interaction is an emerging field of study. Diverse range of researches is going on to explore and understand this frequency range and its potential applications. Situated between microwave and optical frequency domain, THz radiation is non-responding to the techniques commonly used for these two domains, thus insufficiency of supporting technology, high atmospheric absorption, lack of high power source have kept this spectrum away from technical and commercial interest for a long time. Advancements in Photonics like high power ultrafast lasing devices, high-power THz generation by means of nonlinear effects, band-engineered hetero-structures have greatly extended its potential. In order to explore all its merits and realize it as a full-fledged functional frontier, more high power sources, more sensitive sensors and efficient waveguides need to be developed. In order to achieve that, the main focus of the research world has moved towards the study of various classes of materials so that they can be categorized based on the applications they can be used for. In this overview article, recent studies on THz dielectric material interaction, their observations, outcomes and their prospect have been presented in a condensed manner so that the information can be used for further developments in this frequency regime.

Controlling plasma distributions as driving forces for ion migration during fs laser writing

The properties of structures written inside dielectrics with high repetition rate femtosecond lasers are known to depend strongly on the complex interplay of a large number of writing parameters. Recently, ion migration within the laser-excited volume has been identified as a powerful mechanism for changing the local element distribution and producing efficient optical waveguides. In this work it is shown that the transient plasma distribution induced during laser irradiation is a reliable monitor for predicting the final refractive index distribution of the waveguide caused by ion migration. By performing in situ plasma emission microscopy during the writing process inside a La-phosphate glass it is found that the long axis of the plasma distribution determines the axis of ion migration, being responsible for the local refractive index increase. This observation is also valid when strong positive or negative spherical aberration is induced, greatly deforming the focal volume and inverting the index profile. Even subtle changes in the writing conditions, such as an inversion of the writing direction (quill writing effect), show up in the form of a modified plasma distribution, which manifests as a modified index distribution. Finally, it is shown that the superior control over the waveguide properties employing the slit shaping technique is caused by the more confined plasma distribution produced. The underlying reasons for this unexpected result are discussed in terms of non-linear propagation and heat accumulation.

Crystalline Waveguide Lasers in the Visible and Near-Infrared Spectral Range

This paper summarizes our recent results on crystalline waveguides and waveguide lasers fabricated by the femtosecond-laser writing technique. Highly efficient waveguide lasers emitting in the near infrared spectral range based on ytterbium and neodymium doped Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> with slope efficiencies above 70% and continuous wave output powers of more than 5 W were demonstrated. Furthermore, pulsed laser operation of passively Q-switched Yb:YAG and Nd:YAG wavequide lasers was achieved by incorporating the saturable absorber Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> :YAG in a monolithic setup. Based on fs-laser written curved structures in Yb:YAG, efficient curved waveguide lasers could be demonstrated. Also, waveguide lasers in the visible spectral range were investigated. We achieved laser emission in the green, orange, red and deep-red spectral region and could demonstrate output powers of more than 1 W with waveguides based on praseodymium doped materials. Additionally, switchable and dual wavelength operation between the orange and red laser emission was achieved. By utilizing the nonlinear crystal KTiOPO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> as substrate material for fs-laser inscription, nonlinear waveguides were realized. With these devices, efficient second harmonic generation into the blue and green spectral range was achieved.

Laser-direct writing of single mode and multi-mode polymer step index waveguide structures for optical backplanes and interconnection assemblies

A laser direct writing (LDW) method is implemented as a cost efficient polymer waveguide (WG) fabrication method for prototyping large substrates for optical backplanes and optical interconnection assemblies. The LDW setup utilizes a 3-axis air-bearing motion platform to reduce WG fabrication error to within ±0.15μm. A UV laser diode coupled single mode fiber with a focusing lens module is capable of LDW WGs at both multimode (50μm) and single mode (6μm) dimensions. Correlation between LDW parameters and fabricated WG dimensions using Dow Corning® OE-4140 UV-Cured Optical Elastomer (ncore=1.5142, nclad=1.5064) is discussed theoretically and confirmed experimentally for both applications. A theoretical model is developed and utilized for producing LDW multi-mode (0.04dB/cm, λ=850nm) and single mode (0.55dB/cm, λ=1310nm) WGs. Measured propagation losses of LDW WGs are comparable to losses of photolithographic multi-mode (0.04dB/cm @ 850nm) and single mode (0.59dB/cm @ 1310nm) WG builds. LDW multi-mode and single mode WG radial bend and crossing losses are evaluated for advanced optical communication channel routing capabilities and do not exhibit significant deviations from photolithographic-manufactured WG device loss.

Design of Folded Waveguide Slow-Wave Structure for &lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;\(W\) &lt;/tex-math&gt;&lt;/inline-formula&gt;-Band TWT

Design of RF structure for W-band folded waveguide traveling-wave tube was accomplished using electromagnetic simulation codes CST-MWS and GdfidL. The parameters characterizing the folded waveguide structure were optimized through a detailed analysis. CST-MWS and GdfidL simulated dispersion results have been compared and found in a close agreement. The CST-particle studio and in-house developed a large-signal analysis code SUNRAY 1-D were used for a large-signal analysis. The results of the parametric analysis and large-signal analysis are presented in this paper. Dimensions have been fixed for getting a gain ~18 dB and 7% bandwidth (95-102 GHz) corresponding to a 16-kV beam line for a uniform section. A gain of nearly 24 dB was obtained by employing pitch tapering near the output section of the tube of same length. Design of folded waveguide RF structure with a simple but efficient waveguide coupler yielding a return loss better than -15 dB has been obtained in the desired band (90-105 GHz).

Compact Optical Antenna Coupler for Silicon Photonics Characterized by Third-Harmonic Generation

We exploit the strong interaction between a focused free-space beam and an optical antenna to construct a compact and efficient silicon waveguide coupler operating simultaneously in several telecommunications bands. The antenna is a directional coupler tuned by the spacing and relative size of its two constituent nanoparticles. Moreover, the antenna’s compact size and short scattering lifetime provide a bandwidth sufficient to couple 200 fs pulses at both 1500 and 1350 nm simultaneously. By measuring the third-harmonic generation (THG) from waveguide-coupled light we verify our estimates of the high in-coupling efficiency of these antennas. Coupling efficiencies were estimated to be as high as 19% and 14% at the wavelengths of 1500 and 1350 nm, respectively.

DESIGN &amp; SIMULATION OF LOW LOSS CIRCULAR CORRUGATED WAVEGUIDE FOR 42 GHZ, 200KW GYROTRON

Corrugated waveguide is used to transmit high power microwave from the microwave devices like Gyrotron. HE11 mode has the lowest loss and is a fundamental mode of corrugated waveguide. Corrugated waveguides have proved to be the most efficient waveguides for transmitting high power GHz & THz radiation compared to smooth wall circular waveguide at the operational frequency of the transmission line. This work includes the simulation of circular corrugated waveguide for 42 GHz Gyrotron and also includes the simulation comparison of corrugated metallic waveguide with smooth wall cylinder using HFSS (high frequency structural simulator) software.

Numerical study of mode excitation in a partially illuminated silver rod.

Using electrodynamics theory, we numerically demonstrated that when the incident light polarization direction is parallel to a silver rod axis, the modes that are forbidden in a fully illuminated silver rod can be excited when the rod is partially illuminated. The modes are excited due to the symmetry breaking of the rod when it is partially illuminated. They are characterized by the even number of nodes in the excited surface plasmons and quadrupole pattern of the scattered light in the space. These modes are different from the allowed modes in a fully illuminated rod, which shows an odd number of nodes in the excited surface plasmons and a dipole pattern of the scattered light. The conclusion was further supported by the calculation results when the illuminated spot was moved from the rod end to its center and when the illuminated length was varied. We also demonstrated dark modes when the incident light polarization is perpendicular to the rod axis. Contrary to the hypothesis that a dark mode will be an efficient waveguide mode, the dark mode shows very poor waveguide applications when the incident polarization is perpendicular to the rod axis.

Efficient high order waveguide mode solvers based on boundary integral equations

For optical waveguides with high index contrast and sharp corners, high order full-vectorial mode solvers are difficult to develop, due to the field singularities at the corners. A recently developed method (the so-called BIE-NtD method) based on boundary integral equations (BIEs) and Neumann-to-Dirichlet (NtD) maps achieves high order of accuracy for dielectric waveguides. In this paper, we develop two new BIE mode solvers, including an improved version of the BIE-NtD method and a new BIE-DtN method based on Dirichlet-to-Neumann (DtN) maps. For homogeneous domains with sharp corners, we propose better BIEs to compute the DtN and NtD maps, and new kernel-splitting techniques to discretize hypersingular operators. Numerical results indicate that the new methods are more efficient and more accurate, and work very well for metallic waveguides and waveguides with extended mode profiles.

Proof of principle demonstration of a self-tracking concentrator.

We present to the best of our knowledge the first successful demonstration of a planar, self-tracking solar concentrator system capable of a 2-dimensional angular acceptance of over 40°. The light responsive mechanism allows for efficient waveguide coupling and light concentration independently of the angle of incidence within the angular range. A coupling feature is created at the focal spot of the optical system by locally melting a phase change material which acts as an actuator due to the large thermal expansion. A dichroic prism membrane reflects the visible light so that it is efficiently coupled into a waveguide at the point of the created coupling feature. We show simulation results for concentration and efficiency, validated by an experimental proof of concept demonstration of a self-tracking concentrator array element. Simulations show that a system based on this approach can achieve 150X effective concentration by scaling the system collecting area to reasonable dimensions (40 x 10 cm²).

Efficient low-loss nanometallic suspended waveguide for terahertz generation

A tunable nanosource of continuous wave terahertz (THz) radiation based on difference frequency generation is proposed and investigated. In this work, we extend and optimize surface plasmon-polariton waveguides to confine light to nanoscales. This new structure offers many advantages to produce more efficient THz waves with lower loss. The presented calculations for 0.6 THz indicate that THz efficiency is about three times larger (12×10 −4 W −1 from a 1-cm long device) with lower loss. Indeed, air gap distance variations to find the phase matching condition do not affect overlap factor.

Compositional arrangement of rod/shell nanoparticles: an approach to provide efficient plasmon waveguides

AbstractIn this work, we investigated the optical properties of a novel compositional configuration of gold nanorod and silver nanoshell which is embedded in a SiO2 substance. The proper geometrical sizes for compositional rod/shell arrangement have been obtained based on the position and peak of plasmon resonance at λ ∼1550 nm. Adjusting the plasmon resonance position at declared spectrum helps us to provide an arrangement which shows high efficiency and minimum losses. The influence of destructive components such as internal damping and scattering on the rod/shell combination is demonstrated by corresponding diagrams. Moreover, we proposed a nano-array based on examined configuration and the quality of light transmission along the array is studied. We figured out and depicted optical properties of the array such as transmission loss factors, group velocities, transmitted power, transmission quality, and two-dimensional snapshots of surface plasmons (SPs) coupling between nanoparticles arrangements under transverse and longitudinal modes excitations. Ultimately, it is shown that the suggested nanostructure based on studied nanoparticles configuration has a potential to utilize in designing nanophotonic devices such as splitters, couplers, and routers. Finite-difference time-domain method (FDTD) as a major simulation model has been employed to study the features of the waveguide.

Embedded optical waveguides fabricated in SF10 glass by low-repetition-rate ultrafast laser

Symmetric embedded waveguides were fabricated in heavy metal oxide SF10 glass using slit-shaped infrared femtosecond laser writing in the low-repetition frequency regime. The impact of the writing parameters on the waveguide formation in the transverse writing scheme was systemically studied. Results indicate that efficient waveguides can be inscribed in a wide parameter space ranging from 500 fs to 1.5 ps pulse duration, 0.7-4.2 μJ pulse energy, and 5 μm/s to 640 μm/s scan speed and pointing out the robustness of the photoinscription process. The refractive index profile reconstructed from the measured near field pattern goes up to 10(-3). In addition, propagation losses of the waveguides are tolerable, with the lowest propagation loss estimated at 0.7 dB/cm. With a 5 μm/s scan speed and 3.5 μJ pulse energy in a high-dose regime, few-mode guiding was achieved in the waveguide at 800 nm signal injection wavelength. This is due to a combination of increased refractive index in the core of the trace and the appearance of a depressed cladding.

Functionalized polymer nanofibers: a versatile platform for manipulating light at the nanoscale

As an organic optical fiber with a diameter comparable to or less than the wavelength of light, polymer nanofibers have been attracting increasing attention as a platform for manipulating light at the nanoscale. A variety of applications for polymer optical nanofibers, including waveguides, light sources and sensors, have been reported in recent years. In this article, the recent progress in the field of polymer optical nanofibers is reviewed in terms of their fabrication, characterization and applications. In particular, we focus on functionalized polymer nanofibers doped with functional materials, such as dye molecules, noble metal nanoparticles, quantum dots and rare earth ions, which greatly expand their capabilities of generating, propagating, converting and modulating light at the nanoscale. This Review describes the photonic capabilities and applications of polymer nanofibres. Pan Wang, Yipei Wang and Limin Tong from Zhejiang University report that submicrometre-diameter fibres can act as highly efficient waveguides for guiding light with losses of 0.1 dB mm–1 or less. The mechanical flexibility of such fibres allows them to be bent and assembled into microcouplers, resonators and interferometers. They have been made from poly(methyl methacrylate) (PMMA), polyacrylamide (PAM), and poly(vinyl alcohol) (PVA) and poly(ethylene oxide) (PEO). Furthermore, doping with laser dyes, rare-earth ions, quantum dots, metallic nanoparticles and biomaterials can transform such fibres into miniature light sources, lasers, sensors or wavelength converters for nanophotonic applications.

A 225 GHz Circular Polarization Waveguide Duplexer Based on a Septum Orthomode Transducer Polarizer

In this paper, we present the modeling and experimental validation of an efficient, compact, and high-isolation waveguide duplexer operating at 225 GHz. While duplexers based on ferrite circulators are key components of many monostatic radar systems, at W-band frequencies and above the performance of waveguide circulators rapidly deteriorates. The design presented here uses a ferrite-free duplexing concept based on transmitting and receiving in orthogonal circular polarizations. The circular polarization is efficiently generated in waveguide using a septum orthomode transducer polarizer, leading to a compact device with a single horn antenna. The complete duplexer is designed using efficient numerical algorithms, resulting in a fabricated device with a measured 10% fractional bandwidth, a return loss better than 20 dB, isolation of 30 dB, and insertion loss below 1 dB.

Demonstration of a highly efficient multimode interference based silicon waveguide crossing

We present the design, fabrication and characterization of a highly efficient silicon waveguide crossing based on multimode interference (MMI). The crossing is formed by only one step etching with the grating couplers on a silicon-on-insulator (SOI) platform. High transmission efficiency of 98.5% (loss of −0.07dB) and low crosstalk (<−43dB) are predicted by the 3D FDTD simulation. Our experiment results showed good agreement with the simulation and, loss of −0.1dB per crossing, and crosstalk better than −40dB was obtained over a broad optical spectrum from 1520nm to 1580nm. Such a low loss, low crosstalk waveguide crossing is suitable for future on-chip optical interconnect.