Acousto-optic filter with SAW waveguide thin film
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Solution Overview
Problem
Existing acousto-optic filters do not achieve the expected reduction in sidelobes, limiting their ability to effectively multiplex optical wavelengths and increase the capacity of optical communication systems.
Innovation Solution
The design includes an optical waveguide and a surface-acoustic-wave waveguide that cross each other on a substrate, with the optical waveguide maintaining an optically constant state above the surface-acoustic-wave waveguide, preventing changes in optical propagation constant and phase matching conditions, allowing for increased sidelobe reduction through weighted SAW intensity assignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a SAW waveguide is arranged to obliquely cross optical waveguides for TE-TM mode conversion, then sidelobes are reduced, but the optical propagation constant changes due to influence from the SAW waveguide
Solution Approach 1:
A thin film is introduced as an intermediary layer between the SAW waveguide and the optical waveguide. This thin film mediates the interaction by providing acoustic coupling for the SAW while maintaining optical constant above the optical waveguide, thus reducing sidelobes without changing the optical propagation constant
Solution Approach 2:
The thin film is selectively positioned only in regions where acoustic coupling is needed, while maintaining different properties in different areas. The film has specific acoustic impedance characteristics for SAW coupling but is optically transparent and constant above the optical waveguide, creating local quality differences that resolve the contradiction
2Object-affected harmful factors
If Gaussian distribution weights are assigned in the longitudinal direction of optical waveguides, then sidelobes are reduced, but the reduction effect is less than the theoretical value in practical production
Solution Approach 1:
The thin film acts as an intermediary that enables more effective Gaussian weight assignment by providing controlled acoustic coupling. This intermediary layer allows the SAW intensity to be properly distributed according to Gaussian distribution, achieving the theoretical sidelobe reduction effect that was not attainable in previous practical implementations
3Stability of the object's composition
If the optical waveguide and SAW waveguide are spaced apart at starting and ending portions, then the optical propagation constant is maintained, but the area for acoustic-optic interaction is reduced
Solution Approach 1:
The thin film creates local quality differences that enable acoustic coupling only in specific regions where needed, while maintaining optical constant in other regions. This spatially selective coupling allows the waveguides to be spaced apart overall, maintaining propagation constant stability, while still providing sufficient interaction area where the thin film is present
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration results in an acousto-optic filter with significantly reduced sidelobes, enhancing the capability for optical wavelength multiplexing and improving the capacity of optical communication systems.
Implementation Method 1
an acousto-optic filter that utilizes an acousto-optic effect
Data Source
AI summary
Optical waveguides are provided on a substrate, a thin film whose refractive index is optically less than the refractive indices of the optical waveguides is provided on the surface of the substrate, and a surface-acoustic-wave waveguide is arranged on the thin film so as to cross the optical waveguides in a direction oblique thereto. The optical waveguides are not directly influenced by the location of the SAW waveguide and the phase matching condition of the optical waveguides is not changed, whereby the sidelobe characteristic of an optical filter is not degraded by assigning weights to the SAW intensity.