Characterization Of Optical Waveguides Research Articles

Characterisation of optical waveguides for photonic integrated circuits

Fast signal processing at the speed of light is the main advantage of photonic integrated circuits. Therefore, these circuits have good prospects for the implementation of mathematical calculations, including matrix to vector multiplication. The purpose of the research was to create and investigate a technique for automatic measurement of brightness distribution along optical waveguides of analogue photonic integrated circuits. Empirical methods (observation, measurement, comparison, experiment) and a complex method (analysis and synthesis) have been used during the research. The proposed technique uses a digital camera that captures images of optical waveguide illuminated by light emitting diodes and image processing software to calculate brightness distribution. This technique determines the best approximation of this distribution, calculates parameters of brightness non-uniformity and losses of optical radiation. Measurements of a set of optical waveguides help to identify the best candidates for photonic integrated circuits. It has been found that optical waveguides with grinded surfaces acting as diffusive scattering have good combination of smooth brightness distribution and small losses of optical radiation. Due to multiple diffuse reflection and scattering within waveguide material, these waveguides are promising candidates for analogue photonic integrated circuits. All other waveguides with non-processed surface, with grooves or grinded with a large grain have sufficient losses of optical radiation. These losses are usually caused by the exit of optical radiation from waveguide surface. The obtained results are necessary for accurate design of circuits that takes into account scattering and losses in optical waveguides. The proposed technique can be applied in automatic technological process of manufacturing a fast and economical photonic matrix to vector multiplication, which does not require expensive electron-beam, optical or laser lithographic equipment

Study on fs-laser machining of optical waveguides and cavities in ULE® glass

The potential of ultrafast laser machining for the design of integrated optical devices in ULE® glass, a material known for its low coefficient of thermal expansion (CTE), is addressed. This was done through laser direct writing and characterization of optical waveguides and through the fabrication of 3D cavities inside the glass by following laser irradiation with chemical etching. Type I optical waveguides were produced and their internal loss mechanisms at 1550 nm were studied. Coupling losses lower than 0.2 dB cm−1 were obtained within a wide processing window. However, propagation loss lower than 4.2–4.3 dB cm−1 could not be realized, unlike in other glasses, due to laser-induced photodarkening. Selective-induced etching was observed over a large processing window and found to be maximum when irradiating the glass with a fs-laser beam linearly polarised orthogonally to the scanning direction, akin to what is observed in fused silica laser-machined microfluidic channels. In fact, the etching selectivity and surface roughness of laser-machined ULE® glass was found to be similar to that of fused silica, allowing some of the already reported microfluidic and optofluidic devices to be replicated in this low CTE glass. An example of a 3D cavity with planar-spherically convex interfaces is given. Due to the thermal properties of ULE® glass, these cavities can be employed as interferometers for wavelength and/or temperature referencing.

The impact of various factors on the surface of X-cut lithium niobate and properties of proton-exchanged waveguides

This work describes the effects of various impacts (thermal, plasma, chemical) on X-cut lithium niobate surface and on the structure and optical characteristics of proton-exchanged waveguides. Pre-annealing at 500 °C improved the structural homogeneity of congruent lithium niobate and thus enabled fabricating waveguides of a higher quality. Ar-plasma pretreatment damaged crystal surface and increased lattice deformations. Chemical treatment influenced the surface composition of lithium niobate and the refractive index in annealed proton exchange waveguides. The results provide better understanding of the role of crystal surface in the fabrication of diffusion waveguides and photonic integrated circuits.

Characterization of optical waveguides in Ce3+-doped phosphate glasses formed by He+ion implantation

In this work, the Ce3+-doped phosphate glass is carried out to fabricate the planar waveguides by the 400 keV He+ ion implantation with a dose of 6.0 × 1016 ions cm−2. The dark-mode spectrum of the waveguide at a wavelength of 632.8 nm is obtained by the prism coupling technique. The SRIM 2013 software is used to analyze the energy deposition induced by the ion implantation and the RCM is employed to reconstruct the refractive index profile of the planar waveguide. The end-face coupling technique is applied to the measurement of the propagation mode image of the waveguide at 632.8 nm. The Ce3+-doped phosphate glass waveguide has the potential for an integrated optical device.

Non-covalent Supramolecular 1D Alternating Copolymer in Crystal toward 2D Anisotropic Photon Transport.

To realize organic integrated optoelectronic circuits, there is a need for anisotropic optical waveguides at the micro/nanoscale. Anisotropic alignment of one-dimensional (1D)-ordered supramolecular structures composed of light-emissive π-conjugated molecules in a crystal may meet the requirements of such waveguides. Here, we designed a bipyridyl-appended acrylonitrile-based π-conjugated molecule 1, which produced a 1D supramolecular polymer constructed through non-covalent bonding between a lone pair in 1 and a σ-hole in 1,4-diiodo-2,3,5,6-tetrafluorobenzene 2. The 1D copolymer of 1 and 2 is aligned horizontally with the two-dimensional (2D) crystal surface because of the angle-controlled supramolecular synthons. As a result of control over the non-covalent bonding direction, anisotropic photoluminescence and photon transport (optical waveguiding) characteristics are realized by orienting the transition dipole moment horizontally with respect to the 2D surface. Compared with the loss coefficient αL =52dBcm-1 for the long-axis direction of the 2D platelet cocrystal, a very large difference of αS =2111dBcm-1 is present in the crystal short-axis direction. The anisotropic waveguiding ability, αL/αS, is estimated to be 41, which is more than an order of magnitude greater than previously reported 2D platelet crystal waveguides. This supramolecular synthon provides an approach to designing anisotropic photon transporters and highly regulated optical logic circuits.

Oriented Self-Assembly of Hierarchical Branch Organic Crystals for Asymmetric Photonics.

Organic hierarchical branch micro/nanostructures constituted by single crystals with inherent multichannel characteristics exhibit superior potential in regulating photon transmission for photonic circuits. However, organic branch micro/nanostructures with precise branch positions are extremely difficult to achieve due to the randomness of the nucleation process. Herein, by taking advantage of the dislocation stress field-impurity interaction that solute molecules deposit preferentially along the dislocation line, twinning deformation was introduced into microcrystals to induce oriented nucleation sites, and ultimately organic branch microstructures with controllable branch sites were fabricated. The growth mechanism of these controllable single crystals with an angle of 140° between trunk and branch is attributed to the low lattice mismatching ratio (η) of 4.8%. These as-prepared hierarchical branch single crystals with asymmetrical optical waveguide characteristics have been demonstrated as an optical logic gate with multiple input/out channels, which provides a route to command the nucleation sites and offers potential applications in the organic optoelectronics at the micro/nanoscale.

Efficient optical waveguiding and lasing in needle crystals of thiophene/phenylene co-oligomers grown in solution

Needle organic single crystals of light-emitting π-conjugated compounds are superior platforms for photonic circuits. Thiophene/phenylene co-oligomers have been ideal laser media, however, a facile crystal growth method that controls crystal morphologies and optical waveguiding characteristics has not yet been developed. Here, 2,5-bis(4′-cyanobiphenyl-4-yl)thiophene (BP1T-CN) and 5,5′-bis(4′-cyanobiphenyl-4-yl)-2,2′-bithiophene (BP2T-CN) are crystallized with needle morphologies in solution. The attenuation coefficients estimated via spatially resolved PL measurements were 0.012 ± 0.006 μm−1 for a BP1T-CN crystal and 0.027 ± 0.003 μm−1 for a BP2T-CN crystal. Furthermore, both exhibited lasing in a Fabry–Pérot mode via self-cavity effects.

One-dimensional and two-dimensional Er3+-doped germanate glass waveguides by combination of He+ ion implantation and precise diamond blade dicing

Compact and miniaturized Er3+-doped waveguide structure is an important research direction in integrated optics. In this work, the Er3+-doped germanate glass was bombarded by a 400-keV He+ ion beam with a fluence of 6.0 × 1016 ions/cm2 for the formation of the one-dimensional waveguide in a vacuum. Subsequently, the precise diamond blade with a rotating velocity of 20,000 rpm and a cutting speed of 0.1 mm/s was applied to dice the surface of the one-dimensional waveguide for the fabrication of the two-dimensional structure. The formation mechanism and the refractive index profile of the one-dimensional waveguide were studied by the SRIM 2013 and the RCM, respectively. The electromagnetic field profiles for the fundamental modes of both one-dimensional and two-dimensional waveguides were measured by the end-face coupling method. It presents some useful information in the field of fabrication and characterization of optical waveguides for active photonic applications.

Characterization of Optical Redistribution Loss Developed for Co-Packaged Optics

We previously proposed a new package substrate called active optical package (AOP) substrate to realize co-packaged optics. An optical redistribution technology on silicon photonics dies was developed to fabricate the AOP substrate. It is composed of a polymer waveguide, with a mirror-based optical coupling between the polymer and silicon waveguides. The fabricated optical redistribution loss was characterized in this study. An average loss of approximately 4 dB and wavelength dependent loss of ±1 dB were observed for the wavelength range of 1460–1600 nm. It was shown that the low wavelength-dependent optical redistribution was available owing to the broadband characteristics of mirror-based optical coupling and polymer waveguide.

Multi-faceted bending and multi-directional flexible optical waveguide of the elastic organic single crystal

Multi-faceted bending elastic organic single crystals are extremely rare and have potential applications in optical communication, mechanically tunable flexible fluorochromic materials, etc., which have attracted great attention of researchers. Herein, we reported two compounds with simple structures, namely 1,3-dimethylbarbituric acid (DMBA) and its derivative (TPABA). Under stress, both (200) and (002) faces of TPABA crystal could undergo reversible elastic deformation, possessing rare multi-faceted bending properties. The abundant weak isotropic intermolecular interactions (such as H-bonding, etc.) in crystal could buffer mechanical stress and prevent crystal fracture. Fortunately, TPABA crystals showed multi-directional flexible optical waveguide characteristics. The corresponding optical loss coefficients were 0.57 dBmm−1 (582 nm, straight line), 0.75 dBmm−1 (583 nm, (002) face bending), and 0.58 dBmm−1 (587 nm, (200) face bending). Unlike TPABA crystals, under stress, the (040) and (200) faces of the DMBA crystal underwent plastic deformation and fracture, respectively, showing the characteristics of single-faceted plastic deformation.

Self-supported light induced polymer waveguide for thin optical fiber interconnection

Self-written polymer waveguides were integrated by single photon photopolymerization between two single mode fibers with a diameter of 80 µm. The fiber size and photopolymerizable liquid sample allowed bridge length only up to 200 µm long. The optical transmission characteristics of polymer waveguides were investigated in the spectral range of (350 to 1750 nm). The polymer channels showed an average insertion loss value of about 3.5 dB, with bright optical modes on the surface of polymer bridges, making these polymeric photonic structures useful in sensing applications.

Single‐Crystal Organic Heterostructure for Single‐Mode Unidirectional Whispering‐Gallery‐Mode Laser

AbstractOrganic single crystals have attracted great attention for solid‐state lasers owing to their smooth morphologies with inherent optical microcavity, ordered molecular packing mode with minimized defects density, and high photoluminescence quantum efficiency. However, the organic single‐crystal lasers, including whispering‐gallery‐mode (WGM) lasers with nondirectional emission and Fabry–Perot (F–P) lasers with inherent high‐lasing threshold, cannot achieve state‐of‐the‐art performance. Herein, the hierarchical self‐assembly of organic single‐crystal heterostructures made from cube‐shaped microdisks with optical gain and microwires with optical waveguide characteristics is demonstrated, which realize the unidirectional WGM laser action with a low‐lasing threshold of ≈600 nJ cm−2. The lattice mismatch rate principle contributes to the growth of these single‐crystal organic heterostructures. More significantly, the waveguide‐coupled WGM microcavity with a coupling coefficient of 28.8% proves that the unidirectional outcoupling of the single‐crystal WGM lasers from the single‐crystal wire waveguides is achieved. The results will pave an alternative avenue for high‐performance organic single‐crystal lasers.

Elastic Organic Crystals Based on Barbituric Derivative: Multi-faceted Bending and Flexible Optical Waveguide.

Elastic organic single crystals with light-emitting and multi-faceted bending properties are extremely rare. They have potential application in optical materials and have attracted the extensive attention of researchers. In this paper, we reported a structurally simple barbituric derivative DBDT, which was easily crystallized and gained long needle-like crystals (centimeter-scale) in DCM/CH3 OH (v/v=2/8). Upon applying or removing the mechanical force, both the (100) and (040) faces of the needle-like crystal showed reversible bending behaviour, showing the nature of multi-faceted bending. The average hardness (H) and elastic modulus (E) were 0.28±0.01 GPa and 4.56±0.03 GPa for the (040) plane, respectively. Through the analysis of the single crystal data, it could be seen that the van der waals (C-H⋅⋅⋅π and C-H⋅⋅⋅C), H-bond (C-H⋅⋅⋅O) and π⋅⋅⋅π interactions between molecules were responsible for the generation of the crystal elasticity. Interestingly, elastic crystals exhibited optical waveguide characteristics in straight or bent state. The optical loss coefficients measured at 627 nm were 0.7 dBmm-1 (straight state) and 0.9 dBmm-1 (bent state), while the optical loss coefficient (α) were 1.5 dBmm-1 (straight state) and 1.8 dBmm-1 (bent state) at 567 nm. Notably, the elastic organic molecular crystal based on barbituric derivative could be used as the candidate for flexible optical devices.

Fast fabrication and gas-sensing characteristics of petal-like Co-MOF membrane optical waveguide

In this work, metal organic frameworks (MOFs) were chosen as sensing materials for the development of a planar optical waveguide (POWG) gas sensor with improved selectivity. Petal-like Co-MOFs ([Co(TpA)dpNDI], where TpA = terephthalic acid and dpNDI = dipyridyl-naphthalenediimide) membranes were fabricated via UV light irradiation of the surface of an Sn-diffused glass optical waveguide slide as the substrate. The obtained film exhibited a high refractive index (1.873–1.875) and optimum thickness to support a strong single-mode (TE0) guided light signal, fulfilling the essential requirements of a POWG sensor. The [Co(TpA)dpNDI] membrane POWGs uniquely responded to ethylenediamine (EDA) coexisting with interfering gases such as methylamine, dimethylamine, and BTXs (benzene, toluene, xylene, and styrene). When the membrane was exposed to EDA gas, host–guest charge transfer and refractive index modulation were induced. The [Co(TpA)dpNDI] membrane POWG exhibited a fast and remarkable response to EDA (S/N = 3.15) even at low concentration (1 ppb), which suggests the capability of this membrane POWG for EDA sensing. The sensor also showed response repeatability in the detection range of 1000 ppm to 1 ppb, and a high adsorption capacity at ambient temperature (17.46 μg cm−2).

Leaky-Wave and DFB Characteristics of Optical Waveguide with Asymmetric Rectangular Grating Profile

Leaky-Wave and DFB Characteristics of Optical Waveguide with Asymmetric Rectangular Grating Profile

Synergistic effects assessment between nuclear damage and electronic energy dissipation in LiTaO3 under heavy ion irradiation using optical waveguides properties and the irradiation angle of incidence

High energy heavy ion irradiation has been performed in LiTaO3 in a broad set of experimental conditions to study the synergistic effects in the damage generation between the nuclear and the electronic energy loss mechanisms. Optical waveguides have been fabricated in LiTaO3, using 20–25 MeV F and 40 MeV Si ions, and their refractive index profiles were used as a very accurate method for the in-depth damage profile determination and its correlation with the energy loss curves. In-situ optical reflectance of low energy irradiations (500 keV F and 300 keV Si ions) has been performed to estimate the nuclear damage kinetics of the buried regions of the high energy irradiations that are not optically accessible with the optical waveguide characterization in the fluence regime when the electronic damage is intense. The angle of incidence has been varied to enhance the damage and further ascertain the existence of a synergistic mechanism.

Effect of the Structure of the Lithium Niobate Surface Layer on the Characteristics of Optical Waveguides

The surface and surface layer of X-cut plates of congruent lithium niobate (produced by OAO Fomos Materials) have been investigated by structural and optical methods. It is shown that the plate surface is of high optical quality, comparable with that of foreign analogs. The existence of an oxygen-saturated (and, correspondingly, niobium-deficient) damaged surface layer with a depth of up to 20 μm is demonstrated. Ooptical waveguides have been designed based on the investigated crystal using the proton exchange method. The optical characteristics of these waveguides are comparable with those for Crystal Technology lithium niobate crystals; however, the proton exchange and annealing processes should be corrected. A comprehensive analysis of the Fomos Materials samples showed that they can be used to design integrated optical circuit elements for various instrumentation tasks.

Characterization of optical waveguide in chalcogenide glass formed by helium ion implantation

In this work, an optical waveguide in the chalcogenide glass (80GeS2–15Ga2S3–5Sb2S3) is fabricated for the first time and its optical properties are investigated. A one-dimensional chalcogenide waveguide structure has been formed by 550 keV He+ ion implantation with a dose of 4 × 1016 ions/cm2 at room temperature. The effective refractive indices of the guided modes at the wavelength of 632.8 nm were measured with the aid of the Model 2010 Prism Coupler system. The refractive index profile, a critical factor in the analysis of waveguide structure, was reconstructed by the reflectivity calculation method. It was found that a positive change of refractive index occurred in the waveguide region, and an optical barrier with decreased refractive index was built at the end of the ion trajectory, i.e., producing a type of “well + barrier” structure. The SRIM 2013 program was utilized to display the profile of the energy loss versus the penetrated depth when the incident ion beam implanted. The near-field intensity distribution for the fundamental mode along the TE polarization was simulated through the finite-difference beam propagation method. From our experiments, these data provide a great deal of useful information about the manufacture of the chalcogenide waveguide structure.

Fine Fabrication and Optical Waveguide Characteristics of Hexagonal tris(8-hydroxyquinoline)aluminum(Ⅲ) (Alq3) Crystal

Herein, we reported on the precise growth and optical waveguide characteristics of hexagonal tris(8-hydroxyquinoline)aluminum(Ⅲ) (Alq3) micro-crystals (MCs). The hexagonal Alq3 MCs were prepared using surfactant-assisted assembly growth with the help of cetyltrimethylammoniumbromide (CTAB), in which the crystallization occurred as a result of molecular assembly and packing. Also, we adjusted the molar ratio of Alq3 and CTAB for the control degree of crystallization. The formation and structure of Alq3 MCs were investigated using field-emission scanning electron microscopy and X-ray diffraction pattern experiments, respectively. The solid-state laser confocal microscope-photoluminescence spectra and charge-coupled device images for the Alq3 MCs were measured to study the luminescence efficiency and colors, respectively. The optical waveguide performance of the hexagonal Alq3 MCs was measured for each side direction. According to our results, crystalline Alq3 micro-crystals are promising materials for application to the development of optical communication devices.

Electrochemiluminescence Waveguide in Single Crystalline Molecular Wires

AbstractHere we report the first observation of active waveguide of electrochemiluminescence (ECL) in single crystalline molecular wires self‐assembled from cyclometalated iridium(III) complexes, namely tris(1‐phenylisoquinoline‐C2, N) (Ir(piq)3). Under dark conditions, the molecular wires deposited on the electrode surface can act as both ECL emitters and active waveguides. As revealed by ECL microscopy, they exhibit the typical characteristics of optical waveguides, transmitting ECL and generating much brighter ECL emission at their terminals. Moreover, self‐generated ECL can be confined inside the molecular wire and propagates along the longitudinal direction as far as ≈100 μm to the terminal out of touch with the electrode. Therefore, this one‐dimensional crystalline molecular wire‐based waveguide offers the opportunity to switch the electrochemically generated ECL to remote light emission in non‐conductive regions and is promising for contactless electrochemical analysis and study of (bio)chemical systems.