Fabrication of free-standing lithium niobate nanowaveguides down to 50 nm in width

Abstract

Nonlinear optical nanoscale waveguides are a compact and powerful platform for efficient wavelength conversion. The free-standing waveguide geometry opens a range of applications in microscopy for local delivery of light, where in situ wavelength conversion helps to overcome various wavelength-dependent issues, such as biological tissue damage. In this paper, we present an original patterning method for high-precision fabrication of free-standing nanoscale waveguides based on lithium niobate, a material with a strong second-order nonlinearity and a broad transparency window covering the visible and mid-infrared wavelength ranges. The fabrication process combines electron-beam lithography with ion-beam enhanced etching and produces nanowaveguides with lengths from 5 to 50 μm, widths from 50 to 1000 nm and heights from 50 to 500 nm, each with a precision of few nanometers. The fabricated nanowaveguides are tested in an optical characterization experiment showing efficient second-harmonic generation.

Helium focused ion beam irradiation with subsequent chemical etching for the fabrication of nanostructures

“…Ion beam irradiation with subsequent chemical etching can be classified as a lithography technique but the development process results in the fabrication of a designed structure directly in the irradiated material without using a resist mask. It has been shown that this method can be applied to the fabrication of nanostructures from various materials, such as silicon [1][2][3], silicon dioxide [4][5][6][7][8][9][10][11][12][13][14], sapphire [15][16][17], lithium niobate [18][19][20][21] and silicon nitride [22][23][24][25]. In our work silicon dioxide was chosen due to its widespread in semiconductor industry.…”

Towards on-chip photon-pair bell tests: Spatial pump filtering in a LiNbO3 adiabatic coupler

“…25 Whereas a single adiabatic coupler only provides limited filtering, a stack of such couplers, similar to other cascaded approaches, 21,22 might be able to provide pump extinction in excess of 100 dB, which can be an interesting topic of study in the future. Furthermore, as the particular implementation using titanium indiffused waveguides in lithium niobate is not very compact, it will be important to investigate whether waveguiding structures based on high-index-contrast waveguides 21,27 allow substantial reductions of the system dimensions while retaining the adiabatic filtering properties.…”