Abstract
In this paper we propose an efficient technique for micromachining lithium niobate that is used in Ti-diffused waveguides. The use of Focused Ion Beam (FIB) etching allows obtaining homogeneous periodic microstructures. Bragg gratings with a period of 1.05 μm and an aspect ratio of 6:1 (depth-to-half period ratio) have been achieved. A reflectivity greater than 95 % associated with a bandwidth at half maximum of about 100 nm within a window centered at 1550 nm, is demonstrated for a Bragg grating of period Λ = 1.8 μm and a length of 144 μm, in good agreement with theoretical predictions.
Highlights
M ANY applications of Bragg reflectors have been developed in the field of biomedical and optical communication systems
Bragg gratings (BGs) have been employed in wavelength multiplexers and demultiplexers to realize in-line optical filters, especially notch filters and wavelength-specific reflectors given their dispersion compensation properties [1]–[4]
Focused Ion Beam (FIB) systems operate in a similar fashion to a scanning electron microscope (SEM) except, rather than a beam of electrons and as the name implies, FIB systems use a finely focused beam of ions that can be operated at low beam currents for imaging or high beam currents for site specific sputtering or milling
Summary
M ANY applications of Bragg reflectors have been developed in the field of biomedical and optical communication systems. BGs have been employed in wavelength multiplexers and demultiplexers to realize in-line optical filters, especially notch filters and wavelength-specific reflectors given their dispersion compensation properties [1]–[4]. These periodic structures recently have attracted much interest since the discovery of photonic crystals. FIB is a high capacity nanostructuring tool providing direct, local and controlled waveguide property modifications Such conditions are ideal to obtain precise waveguide refractive index corrugations and homogeneous BGs. The BGs at low index corrugation can be treated by the coupled modes theory, one can calculate the coupling coefficient, reflectivity, and bandwidth by mathematical expressions based on Maxwell’s equations. Losses due to the method used for etching of BGs are discussed in this paper
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