Si3N4 Optical Resonator Light Source for Broad-Wavelength Frequency Combs
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Solution Overview
Problem
Existing light sources using silicon nitride waveguides on silicon oxide cladding struggle to generate optical frequency combs at wavelengths beyond 800 nm due to high absorption and optical losses, and methods to achieve thicker waveguides result in cracking or interfaces that diminish performance.
Innovation Solution
Using a mono-crystalline aluminum oxide substrate, silicon nitride waveguides are deposited in a single-step low-pressure chemical vapor deposition process to achieve thicknesses of 500 nm or more, minimizing residual stress and enabling reliable fabrication without cracking, thus supporting optical frequency comb generation across a broader wavelength range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If silicon nitride waveguides are deposited on silicon oxide cladding to generate optical frequency combs, then optical frequency comb generation is enabled in the near-infrared spectrum, but high absorption and optical losses occur at wavelengths beyond 800 nm
Solution Approach 1:
The patent introduces aluminum oxide as an intermediary substrate material between the silicon nitride waveguide and the underlying silicon substrate. This intermediary layer has lower optical absorption in the visible and near-infrared spectrum compared to silicon oxide, thereby reducing overall optical losses while enabling broader wavelength range operation.
Solution Approach 2:
The patent changes the substrate material parameter from silicon oxide to aluminum oxide, which fundamentally alters the optical absorption characteristics. This parameter change enables the system to operate efficiently at wavelengths beyond 800 nm where silicon oxide exhibits high absorption, thus expanding the adaptable wavelength range.
2Reliability
If multi-step deposition processes are used to achieve thicker silicon nitride waveguides, then optical confinement is improved, but cracking and interfaces are introduced that diminish performance
Solution Approach 1:
The patent changes the deposition process parameter from multi-step to single-step LPCVD, which eliminates the interfaces between layers that cause cracking. This single-step process maintains manufacturing precision while achieving the required waveguide thickness for sufficient optical confinement without compromising reliability.
Solution Approach 2:
The patent extracts the intermediate layers that would be required in a multi-step deposition process. By using a single-step deposition method, the harmful interfaces between deposition steps are completely removed, eliminating the source of cracking while still achieving the necessary waveguide thickness.
3Reliability
If single-step low-pressure chemical vapor deposition is used to deposit thick silicon nitride waveguides, then residual stress is minimized and cracking is prevented, but achieving sufficient optical confinement becomes challenging
Solution Approach 1:
The patent creates a composite structure with aluminum oxide substrate and silicon nitride waveguide layer. The aluminum oxide provides a low-stress foundation that enables thick silicon nitride deposition without cracking, while the thick silicon nitride layer provides the necessary optical confinement. The composite material system simultaneously achieves both structural stability and optical confinement efficiency.
Solution Approach 2:
The thick silicon nitride waveguide deposited in a single step serves multiple functions: it provides mechanical stability by minimizing residual stress and preventing cracking, while simultaneously providing sufficient optical confinement for frequency comb generation. The single-step process ensures both structural and optical performance requirements are met.
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 allows for the generation of optical frequency combs in the visible, near-infrared, and fundamental infrared spectra with improved optical performance by leveraging the lower absorption of aluminum oxide and reduced stress in silicon nitride waveguides, facilitating the realization of MEMS devices and sensors.
Implementation Method 1
If light is received by the resonator that has this resonant frequency/wavelength, it will circulate through this cavity thereby accumulating optical energy inside the cavity
Implementation Method 2
When sufficient optical energy is inside the optical resonator, the optical material will behave in a non-linear manner, for example due to the Kerr effect or other non-linear effects, and a frequency comb will be generated
Implementation Method 3
depositing a silicon nitride film of at least 500 nm thick on the substrate in a single-step low-pressure chemical vapor deposition, LPCVD, process
Data Source
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AI summary
The present invention relates to a light source for generating an optical frequency comb. The present invention further relates to a method for manufacturing the optical resonator used in this light source. The present invention additionally relates to microelectromechanical systems, MEMS, optical switch and system comprising the same. The present invention also relates to a sensor and to a method for manufacturing a suspended silicon nitride structure comprised in the sensor. According to the present invention, a single-step LPCVD deposited monolithic stoichiometric Si3N4 layer is used on a mono-crystalline aluminum oxide substrate such as sapphire. The thickness of the Si3N4 layer exceeds 500 nm. This layer can be realized with relatively low residual stress.