3D-printed lens by two photon polymerization is promising technology in the filed of optics thanks to its free-form writing with sub-micron accuracy. However, reflection loss on the lens surface is problematic due to Fresnel reflection. In order to solve the problem, we have demonstrated a 3D-printed aspherical lens with moth-eye anti-reflection structure. An aspherical lens with submicron stripe was printed on fiber end face. Reflectance on the lens surface was reduced from 4.4% to 0.005% at 1550 nm wavelength, and furthermore, coupling efficiency to another fiber is improved from -0.52 dB to -0.33 dB thanks to the reduction of Fresnel reflection.
The bandgap tuning of sub-micron wide Germanium (Ge) waveguides by selective epitaxial growth (SEG)
method with a SiO2 mask has been demonstrated. SEG-grown Ge waveguides on Si substrate are designed to show
various compressive strain depending on the growth parameters, such as the width and thickness of Ge waveguides and
SiO2 masks. X-Ray Diffraction (XRD) verifies that -0.25% (compressive) strain is induced in a 0.6μm-wide Ge
waveguide with SiO2 mask of 20μm width and 1.0μm thickness. The strained Ge waveguide should show the absorption
edge wavelength of ~1.55μm. Furthermore, compressive strain can be tuned between -0.03% and -0.25% by changing
the lateral structure of the device, which correspond to the absorption edge wavelength of 1.548~1.568μm. It means that
only one epitaxial growth with specific lateral design of the electro-absorption modulator can modulate light in the
wavelength range.
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