Gratings Fabricated on Flat Surfaces and Reproduced on Non-Flat Substrates
- Tuesday, 01 December 2009
A method has been developed for fabricating gratings on flat substrates, and then reproducing the groove pattern on a curved (concave or convex) substrate and a corresponding grating device. First, surface relief diffraction grating grooves are formed on flat substrates. For example, they may be fabricated using photolithography and reactive ion etching, maskless lithography, holography, or mechanical ruling. Then, an imprint of the grating is made on a deformable substrate, such as plastic, polymer, or other materials using thermoforming, hot or cold embossing, or other methods. Interim stamps using electroforming, or other methods, may be produced for the imprinting process or if the same polarity of the grating image is required. The imprinted, deformable substrate is then attached to a curved, rigid substrate using epoxy or other suitable adhesives. The imprinted surface is facing away from the curved rigid substrate.
As an alternative fabrication method,
after grating is imprinted on the
deformable substrate as described above,
the grating may be coated with thin conformal
conductive layer (for example,
using vacuum deposition of gold). Then
the membrane may be mounted over an
opening in a pressured vessel in a manner
of a membrane on a drum, grating
side out. The pressure inside of the vessel
may be changed with respect to the ambient
pressure to produce concave or convex
membrane surface. The shape of the
opening may control the type of the surface
curvature (for example, a circular
opening would create spherical surface,
oval opening would create toroidal surface,
etc.). After that, well-known electroforming
methods may be used to create a
replica of the grating on the concave or
convex membrane. For example, the pressure vessel assembly may be submerged
into an electro-forming solution
and negative electric potential applied to
the metal coated membrane using an
insulated wire. Positive electric potential
may be then applied to a nickel or other
metal plate submerged into the same
solution. Metal ions would transfer from
the plate through the solution into the
membrane, producing high fidelity metal
replica of the grating on the membrane.
In one variation, an adhesive may be
deposited on the deformable substrate,
and then cured without touching the
rigid, curved substrate. Edges of the
deformable substrate may be attached to
the rigid substrate to ensure uniform
deformation of the deformable substrate.
The assembly may be performed
in vacuum, and then taken out to atmospheric
pressure conditions to ensure
that no air is trapped between the
deformable and rigid substrates.
Alternatively, a rigid surface with complementary
curvature to the rigid substrate
may be used to ensure uniform
adhesion of the deformable substrate to
the rigid substrate. Liquid may be
applied to the surface of the deformable
substrate to uniformly distribute pressure
across its surface during the curing
or hardening of the adhesive, or the film
may be pressed into the surface using a
deformable object or surface. After the
attachment is complete, the grooves may
be coated with reflective or dielectric layers
to improve diffraction efficiency.
This work was done by David Content of Goddard Space Flight Center and Dmitri Iazikov, Thomas W. Mossberg, and Christopher M. Greiner of LightSmyth Technologies. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Manufacturing & Prototyping category. GSC-15769-1
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Gratings Fabricated on Flat Surfaces and Reproduced on Non-Flat Substrates (reference GSC-15769-1) is currently available for download from the TSP library.
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