Tunable Laser Frequency Modulation via Single-Axis Mirror Tilt
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Solution Overview
Problem
Existing frequency tunable lasers based on the Littrow and Littman schemes require precise control of the pivoting motion of optical components to avoid mode hopping, which is costly and limits high-frequency modulation speeds due to the need for complex and accurate motion control arrangements.
Innovation Solution
The laser device is designed to allow motion control in only one degree of freedom, making the system insensitive to movements in other degrees of freedom, thereby enabling the use of simpler and more robust actuators, such as piezo-electric elements or flexure mechanisms, to achieve high-frequency modulation rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If precise control of pivoting motion of optical components is implemented to avoid mode hopping, then frequency tuning accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The optical component is segmented into a stationary mounting structure and a movable functional element. The diffraction grating is mounted on a stationary substrate while only the reflective surface is tilted, achieved through a specialized mounting geometry where the grating normal passes through the pivot point. This segmentation allows frequency tuning without requiring precise control of the entire component's pivoting motion.
Solution Approach 2:
A stationary diffraction grating acts as an intermediary element between the laser cavity and the tuning mechanism. The grating is positioned such that its normal passes through the pivot point of the tilting mirror, creating a geometric relationship where frequency tuning is achieved through the mirror's tilt angle alone, while the grating remains stationary and provides the necessary spectral selection without requiring precise pivoting control.
2Reliability
If high accuracy motion control arrangements are used to control the pivot point, then mode hopping is suppressed, but the lifetime of the apparatus is reduced
Solution Approach 1:
The requirement for precise pivoting control is extracted from the system by making the diffraction grating stationary. The critical pivoting motion is confined to a simple mirror whose orientation controls the frequency, while the grating remains fixed in position and orientation. This extraction eliminates the need for complex motion control arrangements that would otherwise be required to maintain mode-hop-free tuning, thereby improving reliability and extending apparatus lifetime.
3Measurement precision
If complex motion control arrangements are implemented, then frequency tuning precision is improved, but modulation speed is limited
Solution Approach 1:
The system transitions from a static diffraction grating configuration to a dynamic mirror tilt mechanism. The mirror is tilted about an axis that passes through the pivot point, allowing rapid frequency modulation by changing the tilt angle. This dynamic adjustment of the mirror orientation enables high-speed modulation (greater than 1KHz) while maintaining frequency tuning precision, as the stationary grating continues to provide spectral selection without requiring motion control.
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 allows for rapid frequency modulation at rates greater than 1KHz while tolerating uncontrolled motion in other degrees of freedom, reducing the complexity and cost of motion control and extending the lifetime of the apparatus.
Implementation Method 1
The actuator may comprise one or more piezo-electric elements to impart linear motion to a moveable optical component
Data Source
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AI summary
A frequency tuneable or chirped laser device is described that includes a laser cavity formed from a plurality of optical components. The optical components include a laser source for generating a beam of light, a spectral tuning element and one or more further optical components for directing the beam of light on to the spectral tuning element. At least one of the plurality of optical components is moveable in a first degree of freedom; such movement simultaneously altering the effective optical path length of the laser cavity and the tuning frequency of the spectral tuning element. The effective optical path length and the tuning frequency of the device are substantially insensitive to any movement of said at least one moveable optical component in degrees of freedom other than the first degree of freedom. This provides frequency tuning in which mode hopping is suppressed.