Tech Briefs Magazine - May 2021 - PIT-23

micro-optics that qualified micro-optic suppliers are engaged
as early in the design process as possible and are treated as a
product development and manufacturing partner rather than
a job shop. It is only by doing this and being able to superimpose specific micro manufacturing and micro-optic expertise
on a particular project that an efficient and cost-effective solution can be realized.
Of vital concern when choosing a qualified partner is an
understanding of the necessity for qualified and expert testing
and quality assurance processes that are unique to micro-optic
fabrication. There are numerous challenges when attempting
to manufacture micro-optic devices and components, which
demands that OEMs choose to partner with companies that
have a proven track record and years of experience manufacturing to the tightest tolerances and the most exacting standards achievable.
Of the manufacturing processes used for production of plastic micro-optics, injection molding is the most established,
although it is also possible to use UV embossing and hot
embossing. All require either a mold or an embossing die to
shape the optical component. Inserts for molds or embossing
tools need to be extremely precise (sometimes to less than 90
nanometers), and with extremely low surface roughness characteristics. Such tolerances can typically be achieved through the
use of single-point diamond turning technologies that can be
used to cut complex optical surfaces with sub-micron accuracy.
Very often, it is possible to use precision injection molding
machines using traditional multi-cavity tooling for mass production of many micro-optic components, but for ultra-precise
and very small components, it is usually necessary to use specialized micro molding machines which typically exhibit a
higher inject speed, precise shot control, and ultra-fine resolution for molding small sized parts.
In principle, it is fair to say that micro-optic components
(that is to say micro-scale components, not larger parts with
micro features) are just scaled down macro-optic parts. It is this
scaling down, however, that requires the understanding and
skill of a specialized micro manufacturing agency. Mechanical
tolerances that companies may find very easy to achieve on
larger optical components may not suffice on micro-optics,
where any variation corresponds to a much greater percentage
of error and could massively impact the performance of a lens
or other micro-optic components. Overcoming such problems
requires special focus on tool construction, for example, and
the achievement - typically - of sub-5 micron tolerances.
Accumold routinely assists in the design, tooling, and manufacture of micro-optic devices such as 250-micron fiber optic
lenses, parallel array products, demux devices, and diffractive
lenses. The company also has experience molding attenuated
resins and adding IR, anti-reflective (AR), and reflective coatings onto plastics. The demands associated with running
micro-sized optical couplers, integrating lenses into housings,
replicating lens profiles within a quarter wave, and lens surface
finishes within 50 angstroms requires having a dedicated tooling expert on staff to advise on and optimize design for manufacturability and tooling for any OEM light transmission
requirements.
But tooling challenges are only one consideration. Also of key
importance is molding process parameter control, metrology
equipment capabilities, and post molding handling and assembly.
Precise control of the shot size or volume of resin injected
into the mold on each cycle is vital for the maintenance of
Photonics & Imaging Technology, May 2021

accuracy and repeatability of micro-optics shot to shot and
run to run. Once molded, however, it is important to use a
fully automated and hands-free assembly process, overcoming the basic logistical issues surrounding the removal of
such tiny and delicate components while also ensuring that
orientation is maintained and parts are not contaminated by
touching.
Micro-sized features on larger optical parts are usually found
on lenses that incorporate small optical features, such as
refractive elements with individual apertures from a few
microns to a few millimeters, or diffractive features that consist
of patterns produced on a micron scale. Here, the accuracy of
the optical surfaces is the most critical detail, and the fabrication process for the optical mold inserts presents the largest
challenge. These features are typically machined directly onto
the base curve of the tool inset using ultra-precise technologies
that allow for the manufacturing of complex, non-rotationally
symmetric, optical structures. Alternatively, they can be applied
using photo-etching technologies.
The extremely tight tolerances that are characteristic of
micro-optic applications - coupled with the demands for
expertise in tool construction and material selection -
require that OEMs undertaking a micro-optic project engage
with a qualified partner in development to ensure accurate,
timely, and cost-effective manufacturing solutions.
This article was written by Aaron Johnson, VP of Marketing and
Customer Strategy, Accumold (Ankeny, IA). For more information,
contact Mr. Johnson at ajohnson@accu-mold.com, or visit
http://info.hotims.com/79413-222.

Free Info at http://info.hotims.com/79413-710

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Tech Briefs Magazine - May 2021

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