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.
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.
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.
In this paper, we report the theoretical study of polymer-based photonic crystals for laser beam steering
which is based on the superprism effect as well as the experiment fabrication of the two dimensional
photonic crystals for the laser beam steering. Superprism effect, the principle for beam steering, was
separately studied in details through EFC (Equifrequency Contour) analysis. Polymer based photonic
crystals were fabricated through double exposure holographic interference method using SU8-2007. The
experiment results were also reported.
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