Abstract
In this study, a technique for the optimization of the optical characteristics of multi-channel filters after fabrication is proposed. The multi-channel filter under consideration is based on a Si photonic crystal (PhC), tunable liquid crystal and opto-fluidic technologies. By filling air grooves in the one-dimensional, Si-Air PhC with a nematic liquid crystal, an efficiently coupled multi-channel filter can be realised in which a wide stop band is used for channel separation over a wide frequency range. By selectively tuning the refractive index in various coupled cavities, continuous individual tuning of the central channel (or edge channels) up to 25% of the total channel spacing is demonstrated. To our knowledge, this is the first report on the electro-optical solution for the compensation of fabrication tolerances in an integrated platform.
Highlights
Si fabrication technology has significantly developed over the last 20 years, one of the main problems for optical, nano-scale periodic structures, such as Fabry-Perot interferometers and multi-channel photonic crystal (PhC) filters, remains in defining of the critical dimensions precisely in the system [1-3]
Using an example of a coupled triple-cavity PhC filter operated using the first stop band (SB), we have developed a simple model for easier manipulation of the liquid crystal (LC) within individual cavities, enabling the independent fine tuning of each channel in the overall system
Scanning electron microscopy (SEM) investigation of the devices fabricated revealed the presence of a random deviation of the Si wall thicknesses, δdSi, of up to 10.8% of the target thickness
Summary
Si fabrication technology has significantly developed over the last 20 years, one of the main problems for optical, nano-scale periodic structures, such as Fabry-Perot interferometers and multi-channel photonic crystal (PhC) filters, remains in defining of the critical dimensions precisely in the system [1-3]. Fabrication tolerances for modern e-beam lithography are usually assumed to be a minimum of about 5% to 10% of the nominal target dimensions This crucially affects the optical characteristics of multi-channel filter devices [5-7]. One of the most promising solutions to these problems may be a filter device with low-power and low-loss capability to compensate for the optical filter deviations This would allow fine tuning of individual channels in the filter system by varying the temperature or by applying an electric field. One of the more successful attempts to tackle this problem was presented in [8], where the authors demonstrated a solution for an integrated platform This approach requires the incorporation of metallic micro-heaters into large 245 μm resonators, demanding precise temperature control of the device during operation
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