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Research Papers

Simulation and Measurement of Refractive Index Variation in Localized Rapid Heating Molding for Polymer Optics

[+] Author and Article Information
Xiaohua Liu

School of Mechanical Engineering,
Beijing Institute of Technology,
No.5 Zhongguancun South Street,
Haidian District,
Beijing 100081, China;
Department of Integrated Systems Engineering,
The Ohio State University,
Columbus, OH 43210

Tianfeng Zhou

School of Mechanical Engineering,
Beijing Institute of Technology,
No.5 Zhongguancun South Street,
Haidian District,
Beijing 100081, China

Lin Zhang, Wenchen Zhou

Department of Integrated Systems Engineering,
The Ohio State University,
Columbus, OH 43210

Jianfeng Yu

Nanomaterial Innovation Ltd.,
1109 Millcreek Lane,
Columbus, OH 43220

L. James Lee

Department of Chemical and
Biomolecular Engineering,
The Ohio State University,
Columbus, OH 43210

Allen Y. Yi

Department of Integrated Systems Engineering,
The Ohio State University,
Columbus, OH 43210
e-mail: yi.71@osu.edu

1Corresponding author.

Manuscript received April 12, 2017; final manuscript received August 8, 2017; published online November 3, 2017. Assoc. Editor: Donggang Yao.

J. Manuf. Sci. Eng 140(1), 011004 (Nov 03, 2017) (7 pages) Paper No: MANU-17-1248; doi: 10.1115/1.4037707 History: Received April 12, 2017; Revised August 08, 2017

Localized rapid heating process utilizing carbide-bonded graphene-coated silicon molds is a high-efficiency and energy-saving technique for high-volume fabrication of polymer optics. The graphene coating is used as a rapid heating element because of its high thermal conductivity and low electrical resistivity. However, the optical property of molded polymer and its dependence on process conditions such as heat transfer have not been thoroughly investigated. In this research, finite element method (FEM) simulation was utilized to interpret temperature changes of the graphene coating and heat transfer between graphene and polymethylmethacrylate (PMMA) in localized rapid heating. Experiments were then carried out under different voltages to validate the numerical model. In addition, refractive index variation of the PMMA lens resulting from nonuniform thermal history in molding was demonstrated by simulation modeling as well. Finally, wavefront variation of a PMMA lens molded by localized rapid heating was first studied using an FEM model and then verified by optical measurements with a Shack–Hartmann wavefront sensor (SHWFS). The wavefront variation in a PMMA lens molded by conventional method was also measured. Compared with conventional molding process, localized rapid heating is shown to be a possible alternative for better optical performance with a much shorter cycle time.

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Figures

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Fig. 1

Schematic of localized rapid heating molding process: (a) preloading, (b) heating and cooling, and (c) demolding

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Fig. 2

(a) Three-dimensional FEM molding model for localized rapid heating of PMMA preform and (b) 2D FEM model for electrical heating of graphene coating

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Fig. 3

(a) Localized rapid heating assembly and (b) conventional bulking heating using a conventional compression glass molding machine

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Fig. 4

Schematic of the wavefront variation measurement system: (1) He–Ne laser, (2) polarizers, (3) specimen (molded PMMA lens), (4) relay lenses, (5) microlens array, and (6) CCD

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Fig. 5

Comparison of heating/cooling behavior of graphene coating under three voltages in simulations and experiments

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Fig. 6

(a) Temperature distribution in the PMMA substrate when graphene reaches molding temperature under 50 V and (b) temperature variation versus time at different depths under 50 V

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Fig. 7

Comparison of the refractive index variations in the molded PMMA lens under: (a) 50 V, (b) 70 V, and (c) 90 V

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Fig. 8

The refractive index variation of PMMA for localized rapid heating under three different voltages and conventional bulk heating, and an untreated PMMA preform along: (a) molding direction and (b) inplane direction

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Fig. 9

The wavefront variation in molded PMMA lenses by localized rapid heating (a)–(c) simulation and (d)–(f) measurements. (a) and (d) with 50 V, (b) and (e) with 70 V, and (c) and (f) with 90 V.

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Fig. 10

Comparison of the wavefront variation curves in PMMA between the localized rapid heating and the conventional heating

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