We report on the fabrication and characterization of a residual layer resulting from UV imprinting of
singlemode optical waveguide. We have measured the residual thickness formed from the imprinting process
for several-um-size singlemode waveguide fabrication using the parameters of the imprinting pressure,
dropped volume, and viscosity of the used polymer. We found that the residual layer thickness is dependent
on both the initial polymer volume and process pressure and the initial polymer volume is more critical than
process pressure. Viscosity of polymer also affects the residual layer thickness, the lowest residual layer
thickness of 29nm is achieved with nano-imprinting resin, 0.3uL volume, and imprint pressure more than
20bar. Even with optical resin, the residual layer thickness of 60nm is achieved with 0.3uL volume and
imprinting pressure of 30bar.
We reports on an experimental result on a wet chemical etching of silicon for the fabrication of a mold
template to be used in the embossing of optical waveguide. The silicon wafers we etched with its sidewall
inclined to 45° and vertical to the bottom by using the anisotropic etching characteristics of the
crystalline silicon. The results show that the surface roughness of the etched (100) and (110) planes is
very much dependent on the etching condition such as the etchant concentration and etching temperature.
The etched surface roughness is reduced by about 10 times from 34.5nm to 3.05nm in the (100) plane
etching by changing the etching condition from 10M KOH solution at 80°C to 18M KOH solution at
40°C. For the (110) plane, the etched roughness is reduced dramatically from 115.75nm to 9.05nm by
changing the etching condition from IPA saturated 5M KOH solution at 80°C to 1.25M KOH at 40°C.
We report on the fabrication of a flexible optical interconnection module that has been incorporated as a part
of an optical printed circuit board (O-PCB). Optical waveguide arrays are fabricated on flexible polyethylen
terephthalate (PET) substrate by UV embossing technology. Electrical layers carrying vertical cavity surface
emitted laserdiode (VCSEL) and photodiode (PD) array are attached to the optical layer. We measured optical
losses of the flexible waveguide arrays bent over various curvatures and characterized transmission
performances of the flexible optical PCB (FO-PCB) module. FO-PCB performed high speed optical
interconnection between chips over four waveguide channels up to 7.5Gbps on each.
This paper reports on a fabrication method of 45°-mirror-ended polymer waveguide using single-step UV embossing
technique. This technique allows us to fabricate an array of twelve channel multimode polymer waveguides having 45°-
mirrors during single-step UV embossing process. For the embossing process we have used a 45°-ended silicon
waveguide mold. The silicon waveguide mold has a 45° slope prefabricated at the end of each waveguide structure.
With this mold, UV embossing is performed to form undercladding and 45° mirror structures simultaneously. And a
metal film is coated on the surface of the 45° slope. And then, core polymer is filled and cured by UV irradiation. By
using this method, small size of micro mirror structures can be formed during waveguide fabrication process and
fabrication steps can be reduced.
We report numerically analyzed results on various parameters of planar-type long period waveguide gratings
(LPWGs) for potential temperature-insensitive refractive index sensor applications. The LPWGs based on polymer
materials can be low cost mass-produceable devices because they can be fabricated in a wafer-level process with a
typical imprinting technology and can be integrated with other multi-functional photonic devices of planar type such as
optical printed circuit board (O-PCB). We have designed a temperature insensitive long-period waveguide grating by
using a 4-layer waveguide structure which consists of a silica substrate, polymer core and clad layers, and the upper clad
layer for materials or analytes to be tested. Our numerical calculation show that there are optimized conditions on the
thermo-optic coefficients of the core polymer materials for a temperature-independent LPWGs with given core and clad
polymer materials as well as with the given waveguide dimensions. The maximum temperature range and the refractive
index sensitivity of the temperature-independent LPWGs have been also calculated for several conditions of the
waveguide parameters.
This paper reports, for the first time, a new method of fabricating a 45°-micro-reflector-ended polymer waveguide using one-step UV embossing technique. This technique allowed us to fabricate an array twelve channel multimode polymer waveguides equipped with a 45°-micro-reflector by using a one-step UV embossing technique. For the embossing we used a 45°-ended silicon waveguide mold. The silicon waveguides mold has a 45° slope prefabricated at the end of each waveguide structure. First, a 1um-thick-SiO2 layer is grown on the (100) silicon substrate. Then, the waveguide channel is patterned. The patterned waveguide channel is tilted at 45° from (100) silicon alignment base line to use the wet etching morphology which has 90° and 45° etched slopes when exposed to KOH and isopropanol saturated KOH solutions. After that, silicon substrate is wet etched with KOH solution to form the rectangular waveguide patterns. Another thin SiO2 layer is deposited again to protect the waveguide patterns and substrate. A thin line is then patterned on the top of the waveguide structure and a thin-line shaped silicon surface of the top of the waveguide structure is opened. Then, the opened silicon surface is wet etched in KOH saturated with isopropanol solution. The other area is protected by SiO2 layer. The etched shape has a V-shape and the angle from the bottom side is 45°. After SiO2 removal and cleaning, 45°-ended silicon waveguide mold is completed. With this mold, UV embossing is performed to form undercladding structure and 45° slope simultaneously. And a metal film is coated on the surface of the 45° slope. And then, core polymer is filled and cured by UV irradiation. This method can be applicable to waveguide structures of sizes ranging from multimode to single mode.
We designed and fabricated an optical-electrical printed circuit board, which we call OE-PCB, by laminating a board of embedded polymer waveguide arrays between two electrical printed circuit boards. The polymer waveguide arrays are molded by embossing technique using a specially designed silicon mold, which can form the optical waveguide arrays and the 45 degree mirrors concurrently. The integrated silicon molds are fabricated by dry etching or wet etching. The layers of the waveguide arrays are sandwiched and laminated between the upper and the lower electrical PCBs to form the OE-PCBs.
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