We report for the first time use of 3D-printed metal extrusion dies for the extrusion of an optical material into an extrudate at elevated temperatures. Using lead-silicate glass as the material to be extruded, the 3D-printed dies demonstrated the same glass flow behavior as conventionally machined metal dies. Evaluation of the extrusion force at set temperature and extrusion speed revealed that the metal-type of the dies used did not affect the glass flow behavior. Using 3D-printed dies as delivered, the high surface roughness of the 3D-printed dies resulted in high preform surface roughness. However, this effect was overcome by finishing the easily accessible internal die surfaces over 1-2mm length upstream from the die exit. The opportunity of using 3D-printed dies offers unprecedented flexibility in the die design for unlimited tailoring of fluid flow within the die, which paves the way towards extruded items of arbitrary shape.

3D-printed extrusion dies: a versatile approach to optical material processing

Broadband, mid-infrared emission from Pr3+ doped GeAsGaSe chalcogenide fiber, optically clad

Chalcogenide glass fibers have attractive properties (e.g. wide transparent window, high optical non-linearity) and numerous potential applications in the mid-infrared (MIR) region. Low optical loss is desired and important in the development of these fibers. Ge-As-Se glass has a large glass-forming range to provide versatility of choice from continuously varying physical properties. Recently, broadband MIR supercontinuum generation has been achieved in chalcogenide fibers by using Ge-As-Se glass in the core/clad. structure. In the shaping of chalcogenide glass optical fiber preforms, extrusion is a useful technique. This work reports glass properties (viscosity-temperature curve and glass transition) and optical losses of Ge-As-Se fiber fabricated from an extruded preform. A robust cut-back method of fiber loss measurement is developed and the corresponding error calculation discussed. MIR light is propagated through 52 meters of a fiber, which has the lowest loss yet reported for Ge-As-Se fiber of 83 ± 2 dB/km at 6.60 μm wavelength. The fiber baseline loss is 83-90 dB/km across 5.6-6.8 μm, a Se-H impurity absorption band of 1.4 dB/m at 4.5 μm wavelength is superposed and other impurity bands (e.g. O-H, As-O, Ge-O) are ≤ 20 dB/km. Optical losses of fiber fabricated from different positions of the extruded preform are investigated.

Low loss Ge-As-Se chalcogenide glass fiber, fabricated using extruded preform, for mid-infrared photonics

Status and improvement of dual-layer hollow fiber membranes via co-extrusion process for gas separation: A review

In this work, we proposed a metal-assisted silicon strip waveguide design for highly sensitive refractive index sensing applications. To prove the superiority of our proposed design, we make a fair comparison with the standard silicon strip waveguide of comparable geometry. In metal-assisted waveguide structure, a thin SiO2 layer is sandwiched between gold and silicon strip waveguide. The transmission spectrum and E-field distribution of these structures are simulated using 3D-Finite Element Method (FEM). In the first part of the paper, we demonstrated the enhancement of the evanescent field in the upper cladding region of a straight strip waveguide which makes it an ideal candidate for evanescent field gas absorption sensor. In the second part, we designed a metal-assisted silicon strip waveguide ring resonator of radius $1.5~\mu \text{m}$ and verified its higher sensitivity, Q-factor and figure of merit compared to standard ring resonator. The maximum sensitivity of 300 nm/RIU is obtained which is ~67% higher than the sensitivity of a standard ring resonator design when sandwiched SiO2 layer is equal to 50 nm in our proposed design. We believe that our study will provide new favourable circumstances to design sensors with improved sensitivity.

Sensitivity Enhancement of Silicon Strip Waveguide Ring Resonator by Incorporating a Thin Metal Film

A three-dimensional, incompressible and noncavitating model of a glass-stack coextrusion process, under isothermal and non-isothermal conditions is numerically simulated by means of computational fluid dynamics. A dynamic mesh approach is taken in a domain-subdomain type setup to simulate the transient steps in the steady-velocity phase of the experimental co-extrusion. The multiphase setup consists of a glass-stack which is composed of different glass compositions. Experimentally measured glass properties, such as the temperature coefficient of the viscosity of the supercooled glass melts are used to define the flow behavior of the glasses in the starting stack when extruded. The modeled extrudate is numerically verified for transient and spatial errors, leading to the choice of a suitable mesh. Excellent agreement is found between modeling and experiment when plotting the core/cladding dimensions of a step-index extruded fiber-optic preform along the length of the preform. This approach can identify the stable part of the preform, in terms of constant core/cladding layer geometry, obviating costly and time-consuming experimental iteration. Also, the modeling allows prediction of the starting glass-stack dimensions for a specified fiber design.

Co‐Extrusion of Multilayer Glass Fiber‐Optic Preforms: Prediction of Layer Dimensions in the Extrudate

A micro/nanofabrication feasible compact photonic crystal (PC) ring-resonator-based channel drop filter has been designed and analyzed for operation in C and L bands of communication window. The four-channel demultiplexer consists of ring resonators of holes in two-dimensional PC slab. The proposed assembly design of dense wavelength division multiplexing setup is shown to achieve optimal quality factor, without altering the lattice parameters or resonator size or inclusion of scattering holes. Transmission characteristics are analyzed using the three-dimensional finite-difference time-domain simulation approach. The radiation loss of the ring resonator was minimized by forced cancelation of radiation fields by fine-tuning the air holes inside the ring resonator. An average cross talk of -34 dB has been achieved between the adjacent channels maintaining an average quality factor of 5000. Demultiplexing is achieved by engineering only the air holes inside the ring, which makes it a simple and tolerant design from the fabrication perspective. Also, the device footprint of 500 mu m(2) on silicon on insulator platform makes it easy to fabricate the device using e-beam lithography technique. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)

Photonic crystal ring resonator-based four-channel dense wavelength division multiplexing demultiplexer on silicon on insulator platform: design and analysis

A miniature co-extrusion technique, to produce a concentric multilayered glass fiber-optic preform of ~3 mm diameter, is modeled and experimentally demonstrated. A three-dimensional, incompressible, noncavitating, and nonisothermal Computational Fluid Dynamics (CFD) model, similar to one developed in our previous work, is used to predict the dimensions of an alternating four-layer glass stack feed required to produce the desired layer dimensions in a multilayered-glass preform extrudate, using a miniaturized and thus more economical co-extrusion. Strong agreement in the cross-sectional geometrical proportions of the simulated and experimentally obtained preform supports the prowess of the predictive modeling. Nevertheless, some small deviations between the simulated and experimentally obtained dimensions indicate topics for future rheological study. Performing the co-extrusion process under vacuum helps to minimize the inter-layer defects in the multi-layered fiber-optic preform. The miniature co-extrusion potentially removes the need for a postextrusion draw-down prior to fiber drawing, avoiding devitrification issues possible in non-oxide novel glass compositions.

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Predictive, Miniature Co‐Extrusion of Multilayered Glass Fiber‐Optic Preforms

We present a silicon 2.5D Photonic crystal based CWDM (Coarse Wavelength Division Multiplexer) design, suitable for fabrication by lithography techniques. Particularly, a 3-channel, near-infrared wavelength range CWDM design has been achieved, with the wavelength spacing in accordance with ITU-T G.694.2 standards, i.e. 20 nm. A hexagonal lattice of holes-in-slab has been used for the design with a L-type drop waveguide. Plane wave expansion and FDTD methods were employed for the design.

Design of photonic crystal based demultiplexer for CWDM technology

We present a systematic simulation study of dimension-induced photonic band-gap tuning in two-dimensional (2-D), hexagonal lattice photonic crystals, consisting of air-holes in dielectric slabs. Photonic crystals are interesting candidates for application in various fields e.g. communication ranging from optical to THz regime, sensing, spectroscopy, imaging etc., using their property to trap and harness light and to produce high-Q resonances by the principle of localization and photonic bandgap formation. The insensitivity towards launched light wavelength shown herein by the bandgap response of a given 2-D planar photonic crystal is promising for enabling cheaper visible or NIR light sources to produce desired response in Mid-IR wavelengths with ease. The structures and material studied lie within the range of popular fabrication methodology. The results show that silicon photonic crystals, operated at 1.55 µm, can produce sharp resonances and large band transmission in Mid-IR wavelengths (3–5 µm) as well.

Kaustav Bhowmick

Papers

Co‐Extrusion of Multilayer Glass Fiber‐Optic Preforms: Prediction of Layer Dimensions in the Extrudate

Photonic crystal ring resonator-based four-channel dense wavelength division multiplexing demultiplexer on silicon on insulator platform: design and analysis

Predictive, Miniature Co‐Extrusion of Multilayered Glass Fiber‐Optic Preforms

Design of photonic crystal based demultiplexer for CWDM technology

Dimensional Modification Induced Band Gap Tuning in 2D-Photonic Crystal for Advanced Communication and Other Application