Temperature Insensitive Filter Using Low Index Propagation Medium
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Solution Overview
Problem
Optical wavelength filters in integrated photonic platforms suffer from temperature-induced drift due to the thermo-optic effect and thermal expansion, leading to inaccurate wavelength readings, and existing solutions such as athermal waveguides, thermally self-compensating filters, and active thermal compensation are either chemically unstable, power-intensive, or require complex control systems.
Innovation Solution
A wavelength-selective filter device with a propagation medium having a significantly smaller refractive index than the substrate materials, where the second optical element is configured to direct diffracted radiation to a predetermined position for a reference wavelength, compensating for both thermo-optic and thermal expansion effects passively, and is integrated on a photonic chip to avoid external components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical filters are used in integrated photonic platforms, then wavelength filtering function is achieved, but temperature-induced drift occurs due to thermo-optic effect and thermal expansion
Solution Approach 1:
The patent changes the physical parameters of the optical path by introducing a propagation medium with significantly smaller refractive index than substrate materials. This parameter change compensates for temperature-induced wavelength drift by modifying how light propagates through the device, thereby maintaining wavelength stability across temperature variations.
Solution Approach 2:
The propagation medium acts as an intermediary between the substrate and the optical elements. This intermediary material with unique refractive index properties mediates the optical path, compensating for thermal effects and enabling temperature-insensitive wavelength filtering without requiring active control systems.
2Stability of the object's composition
If athermal optical waveguides with counteracting material are used, then thermo-optic effect is compensated, but chemical instability and higher waveguide losses occur
Solution Approach 1:
The patent extracts the thermal compensation function from the waveguide structure itself and implements it through a separate propagation medium. This separation allows the waveguide to maintain its original stable materials while the propagation medium provides the necessary refractive index contrast for thermal compensation, avoiding the chemical instability and loss issues of athermal waveguide materials.
3Stability of the object's composition
If thermally self-compensating optical filters with different polarization states are used, then robustness against temperature fluctuations is improved, but drift due to thermal expansion remains and fabrication imperfections sensitivity increases
Solution Approach 1:
The patent achieves temperature robustness by changing the refractive index parameter of the propagation medium rather than relying on complex geometric configurations with different polarization states. This approach provides thermal compensation while being less sensitive to fabrication variations, as it depends on material properties rather than precise dimensional relationships.
4Stability of the object's composition
If active thermal compensation with Peltier element is used, then temperature stability is improved, but large power dissipation and complex control systems are required
Solution Approach 1:
The patent implements passive thermal compensation where the propagation medium automatically compensates for temperature effects through its inherent refractive index properties. The system self-adjusts to temperature changes without requiring external control systems, power consumption, or active thermal management components.
5Stability of the object's composition
If propagation medium with significantly smaller refractive index than substrate is used, then temperature insensitivity is achieved, but integration complexity may increase
Solution Approach 1:
The propagation medium serves multiple functions simultaneously: it provides the optical path for wavelength filtering, enables thermal compensation through its refractive index properties, and can be integrated with standard photonic fabrication processes. This multi-functionality reduces overall device complexity despite the specialized material requirement.
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
The solution provides a temperature-insensitive, compact, and cost-effective wavelength filter that maintains stability over a wide temperature range, reducing temperature sensitivity by a factor of hundred compared to conventional silicon filters, and does not require active tracking or external components.
Implementation Method 1
The first optical element is directing received radiation into a direction defined by a first angle (α)... The propagation medium is formed from a material being different from and having a smaller refractive index than any one substrate material
Implementation Method 2
The second optical element is being configured for receiving the directed radiation... and is being adapted for diffracting the directed radiation under a second diffraction angle
Implementation Method 3
Optical wavelength filters in integrated photonic platforms tend to drift with temperature and this results in incorrect wavelength readings. This is caused by two effects: the change of refractive index of the material due to the thermo-optic (TO) effect and thermal expansion of devices
Implementation Method 4
the change of refractive index of the material due to the thermo-optic (TO) effect
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
An integrated wavelength-selective filter device (10; 20; 30; 40) comprises a first optical element (14) for directing received radiation into a direction defined by a first angle (α), and a second optical element (15) being a diffractive element configured diffracting said directed radiation under a second angle. The second angle is such that for a single reference wavelength the diffracted radiation is directed into a propagation medium for advancing therein towards a predetermined position on the first optical element or on a further optical element (14a) for filtering radiation having a wavelength substantially matching the reference wavelength from radiation having a substantially different wavelength. The propagation medium is formed from a material that is different from any material of the substrate of the first and the second optical element.