Traditionally, polymer photonic devices are fabricated using clean-room processes such as photolithography, e-beam lithography, reactive ion etching (RIE) and lift-off methods etc, which leads to long fabrication time, low throughput and high cost. We have utilized a novel process for fabricating polymer photonic devices using a combination of imprinting and ink jet printing methods, which provides high throughput on a variety of rigid and flexible substrates with low cost. We discuss the manufacturing challenges that need to be overcome in order to realize true implementation of roll-to-roll manufacturing of flexible polymer photonic systems. Several metrology and instrumentation challenges involved such as availability of particulate-free high quality substrate, development and implementation of high-speed in-line and off-line inspection and diagnostic tools with adaptive control for patterned and unpatterned material films, development of reliable hardware, etc need to be addressed and overcome in order to realize a successful manufacturing process. Due to extreme resolution requirements compared to print media, the burden of software and hardware tools on the throughput also needs to be carefully determined. Moreover, the effect of web wander and variations in web speed need to accurately be determined in the design of the system hardware and software. In this paper, we show the realization of solutions for few challenges, and utilizing these solutions for developing a high-rate R2R dual stage ink-jet printer that can provide alignment accuracy of <10m at a web speed of 5m/min. The development of a roll-to-roll manufacturing system for polymer photonic systems opens limitless possibilities for the deployment of high performance components in a variety of applications including communication, sensing, medicine, agriculture, energy, lighting etc.
Traditionally, polymer photonic devices are fabricated using clean-room processes such as photolithography, electron
beam lithography, reactive ion etching (RIE) and lift-off methods etc, which leads to long fabrication time, low
throughput and high cost. We describe in this paper a novel process for fabricating polymer photonic devices using a
combination of imprinting and ink jet printing methods, which provides high throughput on a variety of rigid and
flexible substrates with low cost. Particularly, we demonstrate a thermo-optic switch and an electro-optic modulator. In
the rib waveguide patterning, the imprint lithography transfers the waveguide pattern from a soft mold to UV-15LV
bottom cladding layer. The soft mold is replicated from a silicon master mold and rendered hydrophobic to ensure
successful de-molding. Ink jet printing method is used to deposit the core layer in thermo-optic switch and electrode
layers in electro-optic modulator. Compared to spin-coating method, the use of print-on-demand method greatly reduces
material consumption and process complexity. Every step involved has the potential to be fully compatible with roll-toroll
(R2R) volume production. For example, the soft mold can be wrapped around a cylinder to realized roll-to-roll
imprinting. By combining R2R imprint lithography with ink jet printing, fabrication of large volume and large area
multi-layer polymer photonic devices can be realized.
We demonstrate board-to-board optical communication utilizing 45 degree mirrors and print-on-demand micro-lenses as
surface-normal coupler. The presented system which includes polymer waveguides, embedded 45 degree mirrors and
micro-lenses, realizes back-to-back optical interconnects between two boards. The waveguide and mirrors are fabricated
using molding method using a low-cost electroplated nickel mold. Micro-lenses (80 μm in diameter) are fabricated using
a material inkjet-printer, on top of the 45 degree mirrors. Experimental results show that each 45 degree mirror
contributes about 1.88 dB loss (65% coupling efficiency) to the total optical loss. When propagating in free space
without a lens, a 2 mm separation between boards results in a 9.9 dB loss, which is reduced to 7.5 dB when a micro-lens
is inserted in the path. High speed data transmission test is performed at various separations. At a separation of 1mm, the
system can provide 10Gbps error free transmission. At 2mm separation, the maximum error free data rate was measured
to be 3.5Gbps and 7.5Gbps, with and without the micro-lens, respectively. Printing the micro-lenses on both the input 45
degree mirror and the photodiode or the receiving 45 degree mirror in a confocal setup will significantly reduce the freespace
propagation loss. To the best of our knowledge, this is the first report of free-space coupling between waveguides
on separate boards.
In this paper, we discuss the metrology and instrumentation challenges that need to be overcome in order to realize true implementation of roll-to-roll manufacturing of flexible electronic systems. Several metrology and instrumentation
challenges involved such as availability of particulate-free high quality substrate, development and implementation of
high-speed in-line and off-line inspection and diagnostic tools with adaptive control for patterned and unpatterned
material films, development of reliable hardware, etc need to be addressed and overcome in order to realize a successful manufacturing process. Due to extreme resolution requirements compared to print media, the burden of software and hardware tools on the throughput also needs to be carefully determined. Moreover, the effect of web wander and variations in web speed need to accurately be determined in the design of the system hardware and software. Realization of successful metrology and instrumentation by overcoming the challenges for the development of a roll-to-roll manufacturing system for flexible electronic systems opens limitless possibilities for the deployment of high performance flexible electronic components in a variety of applications including communication, sensing, medicine, agriculture, energy, lighting etc.
With the technology trend of using optical interconnects as an alternative to traditional copper interconnects, basic
elements such as waveguides and waveguide bus structure are studied worldwide. A novel 3-node bi-directional 50μm
optical waveguide bus architecture with embedded mirrors is proposed and fabricated on flexible substrate. The
fabrication is achieved by lithography-free molding. Different from other replicating methods, the mold demonstrated
here is a nickel metal mold achieved by low cost electroplating and can be used repeatedly. The data transmission test up
to 10Gbps using vertical cavity surface emitting laser (VCSEL) has been performed to evaluate the device. The results
show that the device is capable of emitting and receiving high speed data. Thus it can serve as a high performance
optical backplane. Such mold fabrication technology can also be applied to smaller features size structure. The molds of
5μm wide waveguides and photonic crystal waveguide structures with 250nm hole size are fabricated and the molded
structure profiles are shown.
Polymer based electro-optic modulators have shown great potentials in high frequency analog optical links. Existing
commercial LiNibO3 Mach-Zehnder modulators have intrinsic drawbacks in linearity to provide high fidelity
communication. In this paper, we present the design, fabrication and characterization of a traveling wave directional
coupler modulator based on electro-optic polymer, which is able to provide high linearity, high speed, and low optical
insertion loss. A silver ground electrode is used to reduce waveguide sidewall roughness due to the scattering of UV
light in photolithography process in addition to suppressing the RF loss. A 1x2 multi-mode interference 3dB-splitter, a
photobleached refractive index taper and a quasi-vertical taper are used to reduce the optical insertion loss of the device.
The symmetric waveguide structure of the MMI-fed directional coupler is intrinsically bias-free, and the modulation is
obtained at the 3-dB point regardless of the ambient temperature. By achieving low RF loss, characteristic impedance
matching with 50Ω load, and excellent velocity matching between the RF wave and the optical wave, a travelling wave
electrode is designed to function up to 62.5GHz. Domain-inversion poling with push-pull configuration is applied using
alternating pulses on a 2-section directional-coupler to achieve a spurious free dynamic range of 110dB/Hz2/3. The 3-dB
electrical bandwidth of device is measured to be 10GHz.
In this paper, we report the transfer and characterization of in-plane silicon nanomembrane based photonic devices on a
Kapton polyimide flexible substrate. Compared with electronic devices and surface normal optical devices, in-plane
photonic devices have stringent requirements on transfer precision because any shift in the position or breakage can
affect the performance of devices. Therefore, a supporting layer consisting of a photoresist is exploited to protect the
device during the transfer process. A modified stamp-assisted transfer technique is employed in order to transfer
nanomembrane devices onto the flexible film and the transfer of large aspect ratio (up to 4000) waveguides and 1x6
multimode interference (MMI) couplers on a flexible Kapton substrate is demonstrated. A two-step cleaving method is
developed in order to prepare the facets of the transferred waveguides and in-plane light coupling into a 60μm wide,
8mm long flexible waveguide from a lensed fiber is demonstrated. This demonstration opens limitless possibilities for a
whole new area of high performance flexible photonic components using silicon nanomembrane technology.
This paper demonstrated a practical fabrication process of polymeric waveguide array (12 channels) with
50μm(W)×50μm(H)×23mm(L) dimension and mirror embedded 45° degree slopes for vertical coupling purpose. The
entire process contained three main parts: a SU8 pre-mold with 45° slope, a PDMS mold and the final waveguide array
device. The key step of fabricating the pre-mold included a bottom side tilted exposure of SU8 photo resist. By placing
the sample upside down, tilting by 58.7° and immersing into DI water, the ultraviolet (UV) beam that shined vertically
was directed to go through from the bottom of the glass substrate into top side SU8 resist with 45° angle to form the
surface. This method was able to guarantee no-gap contact between the mask pattern and the photo resist when exposing.
By comparing the process complexity and achieved structure of the top and bottom side exposure, the later was proved to
be a promising method for making high quality tilted structure without any tailing effect. The reversed PDMS mold was
then fabricated on the SU8 pre-mold. The PDMS mold was used to imprint the cladding layer of the waveguide array.
After metal deposition, core filling and top cladding layer coating, the final polymeric waveguide array device was
achieved. For performance evaluation, 850nm laser beam from VCSEL was modulated to 10Gbps signals and vertically
coupled into the waveguide array. The eye diagrams revealed high Q factor when transmitting signals along these
waveguide array.
In this paper, we presented fabrication of nickel based metal mold with 45° tilted surfaces on both ends of the channel
waveguide through electroplating process. To obtain a precise 45° tilted angle, a 50μm thick SU-8 layer was UV
exposed under de-ionized water, with repeatable error control of 0.5°. The polymeric waveguide array with 45° micromirrors,
which is formed by a UV imprinting method with the fabricated metallic mold, shows total insertion losses
around 4dB, propagation loss around 0.18dB/cm and 75% coupling efficiency.
In this paper, 3-to-3 metallic hard mold for optical bus waveguide with opposite 45° micro-mirrors was successfully
fabricated using electroplating method. The optical bus waveguide pre-mold with 45° surfaces before electroplating was
prepared using photopolymer SU-8 through tilted exposure process under de-ionized water. Metal nickel was
electroplated into SU-8 defined bus waveguide trenches. The 45° slant angles can be well controlled through titled
exposure, which have deviations of 0.15° and 0.27° for SU-8 pre-mold and Ni hard mold, respectively. This metallic hard
mold provides a convenient way to fabricate the polymeric optical bus waveguide devices through imprint technique.
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