Applications of UV-nanoimprint soft stamps in fabrication of single-frequency diode lasers

Optical modeling of laterally-corrugated ridge-waveguide gratings

“…The designed LC-RWG structure had W = 1.5 µm and D = 0.5 µm. A third-order grating with period ≈ 440 nm was fabricated using UV-NIL (Viheriälä et al 2009) and the achieved un-etched p-side cladding thickness was close to 200 nm. The DFB EEL was 2% / 95% AR/HR-coated and had a length L = 570 µm The simulated grating coupling coefficient for this device was about 25 cm −1 , leading to a κL-product of about 1.425.…”

“…The limited interaction of the carriers with the LC-RWG gratings also implies that simple optical modeling produces more accurate simulation results than in the cases with stronger carrier interaction with the gratings. In the fabrication process we used low-cost UV-based nano-imprint lithography (UV-NIL), which further decreases the fabrication costs and enables pattern resolutions beyond the limitations set by the diffraction and scattering for the conventional techniques (Viheriälä et al 2009). …”

Nanoimprint Lithography - Next Generation Nanopatterning Methods for Nanophotonics Fabrication

“…The replicated stamp might have also advantageous mechanical properties such as a soft surface and flexibility. The softness of the stamp may be tuned by the material selection (Schmid & Michel 2000) and by the geometry of the stamp, as illustrated by us in reference (Viheriälä et al, 2009 figure 4a). The stamp can be used to replicate nanopatterns, but it does not offer high accuracy since PDMS has a high CTE, and the stamp does not have any supporting structure which would prevent the soft material from deforming laterally.…”

“…This change of the load can be caused by the patterns in the stamp (see figure 6 on the right). The deformation can be compensated for by increasing the thickness of the resist (Viheriälä et al, 2009), as the resist layer (liquid) distributes the local pressure effectively over a large area. We have observed that low viscosity NIL-resist distributes pressure more efficiently.…”

“…When the thick residual layer is removed, with plasma etching, the smallest patterns might be washed away since during the residual layer removing linewidth may be reduced. The stamp concept d in figure 4 can significantly reduce the unwanted vertical deformation of the stamp, compared with other soft stamps, since the thickness of the pattern layer can be tuned (Viheriälä et al, 2009). The stamp with a thin pattern layer exhibits smaller vertical deformation on the microscopic scale.…”