SBS Ring Resonator FSR Detuning for Narrower Laser Linewidth
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Solution Overview
Problem
Conventional stimulated Brillouin scattering (SBS) lasers operating in integrated photonics platforms are limited by a high gain regime due to alignment of the free-spectral range (FSR) with the Brillouin scattering frequency shift, resulting in a minimum linewidth constraint due to thermal phonon-driven spontaneous light emission.
Innovation Solution
A photonics device with a waveguide ring resonator misaligned from the SBS gain peak, reducing the SBS gain coefficient by altering the resonator length, thereby moving the operation into a lower gain regime and decreasing the laser linewidth, while maintaining a sufficiently low loss coefficient.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the free-spectral range (FSR) is aligned with the SBS gain peak, then the SBS laser operates in a high gain regime, but the linewidth is increased due to high spontaneous light emission
Solution Approach 1:
The patent changes the FSR parameter of the waveguide ring resonator by adjusting the waveguide length, deliberately misaligning it from the SBS gain peak. This parameter change transitions the system from a high gain regime (aligned) to a lower gain regime (misaligned), reducing spontaneous emission and achieving narrower linewidth (sub-10-mHz) while maintaining stable operation
2Measurement precision
If the waveguide ring resonator is misaligned from the SBS gain peak, then the linewidth is reduced, but the SBS gain coefficient is decreased
Solution Approach 1:
The patent optimizes the misalignment parameter (detuning amount) to achieve the desired linewidth reduction while maintaining sufficient gain. By carefully controlling the degree of misalignment rather than complete detunin g, the system achieves sub-10-mHz linewidth while keeping the SBS gain coefficient above the lasing threshold
Solution Approach 2:
The patent employs dynamic control of the pump power to compensate for the reduced SBS gain coefficient. By adjusting the pump power level, the system maintains stable lasing operation despite operating in a lower gain regime, enabling flexible optimization between linewidth and gain
3Measurement precision
If the FSR is misaligned from the SBS gain peak, then frequency pulling is reduced, but the lasing threshold is increased
Solution Approach 1:
The patent adjusts the FSR misalignment parameter to optimize the balance between frequency stability and lasing threshold. The misalignment reduces gain pulling effects and improves frequency stability, while the pump power is simultaneously optimized to ensure the system remains above the lasing threshold
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 approach significantly reduces the fundamental linewidth and frequency pulling of the SBS laser, achieving a linewidth reduction from approximately 700 mHz to 10 mHz, a 20 dB improvement, and minimizing gain pulling effects.
Implementation Method 1
the waveguide ring resonator is configured to generate a stimulated Brillouin scattering (SBS) beam when a pump laser beam is optically coupled into the waveguide ring resonator
Data Source
Figure 1A~2B
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Figure 5
AI summary
A photonics device comprises a waveguide platform including a substrate layer, a cladding layer over the substrate layer, and a waveguide layer embedded in the cladding layer. The waveguide layer includes a waveguide ring resonator, and a bus waveguide in optical communication with the waveguide ring resonator. The waveguide ring resonator is configured to generate a stimulated Brillouin scattering (SBS) beam when a pump laser beam is optically coupled into the waveguide ring resonator from the bus waveguide. The waveguide ring resonator has a radius and corresponding round-trip path length such that a free-spectral range (FSR) of the waveguide ring resonator is misaligned with respect to a SBS gain peak of the SBS beam, such that an SBS gain coefficient has a magnitude to produce a substantially reduced linewidth of the SBS beam.