Monolithic Fast-Axis Collimator Array for Laser Diode Bars
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Solution Overview
Problem
High power diode laser systems face issues with beam quality due to the limitations of individual fast-axis collimators, such as the 'smile' and 'facet bending' effects, and the mechanical challenges of aligning lenses in close proximity, leading to variable beam pointing and aberrations, which compromise subsequent beam conditioning optics.
Innovation Solution
A monolithic fast-axis collimator array is developed, where each lens form matches the geometry of the laser diode bar stack, allowing for precise positioning and focal length optimization, and is fabricated using laser micro-machining techniques to create a two-dimensional array of identical collimators on a fixed pitch, reducing misalignment and fabrication time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If individual fast-axis collimators are attached to each bar, then collimation is provided for high numerical aperture fast-axis beam, but the collimation lens cannot be correctly positioned for all points along the bar due to smile effect and facet bending effect
Solution Approach 1:
Multiple individual collimation lenses are merged into a single monolithic array structure that is attached as one unit to the heat sink, eliminating the need for separate alignment of each lens and resolving the positioning accuracy issues caused by smile and facet bending effects
Solution Approach 2:
The relative positions of all collimation lenses are pre-determined during the monolithic array fabrication process, ensuring correct positioning for all emitters before the array is attached to the heat sink, thereby eliminating alignment difficulties during final assembly
2Power
If bar pitch is smaller than 1.2mm to achieve high power density, then power levels increase, but aligning and fitting individual collimation lenses becomes mechanically difficult
Solution Approach 1:
Multiple collimation lenses are combined into a single monolithic array that can be attached as one unit even when bar pitch is small (less than 1.2mm), eliminating the mechanical difficulty of fitting and aligning individual lenses in close proximity
3Manufacturing precision
If surface form errors in the acylindrical lens are reduced, then wavefront distortion decreases, but manufacturing precision requirements increase
Solution Approach 1:
Traditional mechanical polishing and grinding processes are replaced with laser micro-machining techniques to create the monolithic collimator array, enabling precise surface form control while simplifying the manufacturing process and reducing the complexity of achieving high surface accuracy
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 monolithic array improves beam quality by aligning collimators with emitter positions, reducing manual assembly time and costs, and enhancing environmental stability, while allowing for higher fill factors and finer pitches without the need for individual lens holders.
Implementation Method 1
edge-emitting laser diode bar stack
Implementation Method 2
plano-acylindrical lenses, which are used to provide low aberration collimation for the high numerical aperture fast-axis beam
Implementation Method 3
cylindrical rod lenses, which provide poorer quality collimation at lower cost
Implementation Method 4
the semiconductor bar is bent in the fast-axis direction by differential expansion during solder bonding
Implementation Method 5
operating the laser, acousto-optic modulator and the translation stage to ablate portions of the substrate in a shot-by-shot raster scan regime and form an array of predetermined lens forms on the substrate
Implementation Method 6
operating a laser, acousto-optic modulator and the translation stage to melt the silica in a raster scan regime to laser micro-polish the surface of the micro-optical element
Data Source
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AI summary
A micro-optical element for use with an edge-emitting diode bar stack, the element comprising a plurality of spaced apart fast-axis collimators formed as a monolithic array, wherein the spacing between the collimators in the fast-axis varies across the micro-optic element. A method of manufacturing a micro-optical element for use with a laser diode bar stack, using a wavelength stabilized CO2 laser is also described.