Angle Tuned Immersion Grating for Stable Laser Wavelength Selection
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Solution Overview
Problem
Tunable external cavity lasers face challenges in maintaining a stable output beam direction as the wavelength is tuned due to the rotation of the diffraction grating, which can result in mode-hopping and increased costs from larger lenses and diffraction gratings, and the use of high refractive index materials complicates beam alignment.
Innovation Solution
A retro reflecting prism with a diffraction grating on its surface, constructed from a high index of refraction material, is rotated about an axis that minimizes output beam displacement, and additional actuators and controllers are used to correct any remaining variations, allowing for mode-hop-free tuning while reducing mechanical complexity and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a diffraction grating is rotated to tune the wavelength, then the wavelength selection is improved, but the output beam direction becomes unstable
Solution Approach 1:
A retro-reflecting prism is introduced as an intermediary optical element between the diffraction grating and the output. The prism receives the diffracted beam and reflects it back through the same optical path, ensuring that the output beam direction remains stable regardless of grating rotation angle. This mediator decouples the wavelength tuning function from the beam direction control.
2Reliability
If larger lenses and diffraction gratings are used to reduce mode-hopping, then the wavelength stability is improved, but the device complexity and cost increase
Solution Approach 1:
The patent implements dynamic compensation for beam displacement by making the diffraction grating rotatable. By actively adjusting the grating angle in response to detected beam position deviations, the system maintains wavelength stability without requiring oversized static components. This dynamic approach replaces passive size-based stability with active control.
Solution Approach 2:
A feedback mechanism is introduced where the output beam position is monitored and used to control the diffraction grating rotation. This closed-loop system detects beam displacement and automatically adjusts the grating angle to compensate, maintaining stable operation without requiring larger components that would increase device complexity.
3Reliability
If high refractive index materials are used in the retro-reflecting prism, then the beam direction stability is improved, but the alignment complexity increases
Solution Approach 1:
The retro-reflecting prism utilizes asymmetric geometry with specific angle configurations that compensate for the effects of high refractive index materials. The asymmetric design ensures that beam deviations caused by refraction at the first interface are corrected at subsequent interfaces, maintaining beam direction stability while allowing the use of high-index materials for enhanced optical performance.
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 maintains a stable output beam direction during wavelength tuning, reduces mechanical complexity, and minimizes the economic penalty of larger components, enabling efficient and cost-effective tunable laser operation.
Implementation Method 1
a diffraction grating that is rotated about a rotation axis
Implementation Method 2
A retro reflecting prism with a diffraction grating on its surface
Implementation Method 3
constructed from a high index of refraction material
Data Source
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AI summary
A light source having a gain chip (87), a retro reflecting prism (81) and a first actuator (83) is disclosed. The gain chip amplifies light passing therethrough. The retro reflecting prism is characterized by a pivot axis (82) within the retro reflecting prism, an input light direction (84), an output light direction (85), and a diffraction grating that receives light emitted by the gain chip traveling in the input direction, returns a diffracted light beam to the gain chip along the input light direction and generates an output light beam. The first actuator causes the retro reflecting prism to rotate about the pivot axis in response to a control signal being coupled to the first actuator. The Pivot axis is positioned such that movement of the output beam as a function of the rotation angle is reduced.