Diode Laser Beam Divergence Reduction via Index Modulation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional diode lasers suffer from high beam divergence due to the excitation of out-of-phase supermodes, leading to poor beam quality and increased losses, especially in anti-index guided lasers which require complex manufacturing processes.
Innovation Solution
The diode laser incorporates longitudinal-lateral structuring with index-guiding trenches of lower refractive index in the injection zone, modulating the real refractive index to support the in-phase supermode, preventing the formation of out-of-phase modes and stabilizing the laser field, thereby reducing beam divergence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If anti-index guided lasers are used to achieve high output power, then power output is improved, but beam quality deteriorates due to high beam divergence
Solution Approach 1:
The patent applies local quality by introducing periodic index-guiding trenches only in specific longitudinal sections (Talbot filter sections) of the laser cavity, rather than uniformly across the entire structure. This localized structuring modifies the refractive index in specific regions to suppress out-of-phase modes and reduce beam divergence, while maintaining the anti-index guided configuration for high power output in other regions.
Solution Approach 2:
The laser cavity is segmented into alternating sections: Talbot filter sections with periodic index-guiding trenches and free-running sections without trenches. This segmentation allows different functional zones to coexist - the Talbot sections provide beam quality control through mode suppression, while the free-running sections maintain high power output capability through anti-index guiding.
2Shape
If stripe-geometry lasers with lateral index modulation are used, then beam quality is improved, but manufacturing complexity increases due to two-step epitaxy
Solution Approach 1:
The patent extracts the essential function of lateral index modulation from the complex two-step epitaxy process by using a simplified single-step growth approach combined with selective trench structuring. Instead of growing different layers with different indices of refraction through complex epitaxy, the invention achieves the desired index modulation by introducing trenches and filling them with materials of different refractive indices, thereby simplifying the manufacturing process while maintaining beam quality control.
3Power
If out-of-phase supermodes are excited in anti-index guided lasers, then high power output is achieved, but beam divergence increases
Solution Approach 1:
The patent applies preliminary anti-action by pre-introducing periodic index-guiding trenches in the Talbot filter sections before laser operation begins. These trenches create a refractive index modulation that preemptively suppresses the formation of out-of-phase supermodes, preventing the beam divergence problem before it can occur during high power operation, while still allowing the anti-index guided configuration to support high power output.
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 results in a central beam lobe with suppressed side peaks, maintaining high power content and improved beam quality even at high powers, without the need for elaborate manufacturing processes.
Implementation Method 1
longitudinal-lateral structuring comprises index-guiding trenches having a lower refractive index compared with the refractive index of the second p-conducting functional layers between the individual p-type contacts of the p-type contact area formed by the structuring
Data Source
AI summary
The present disclosure relates to a diode laser having reduced beam divergence. Some implementations reduce a beam divergence in the far field by means of a deliberate modulation of the real refractive index of the diode laser. An area of the diode laser (e.g., the injection zone), may be structured with different materials having different refractive indices. In some implementations, the modulation of the refractive index makes it possible to excite a supermode, the field of which has the same phase (in-phase mode) under the contacts. Light, which propagates under the areas of a lower refractive index, obtains a phase shift of π after passing through the index-guiding trenches. Consequently, the in-phase mode is supported and the formation of the out-of-phase mode is prevented. Consequently, the laser field can, in this way, be stabilized even at high powers such that only a central beam lobe remains in the far field.