Wavelength Combining Laser Cross-Coupling Reduction
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Solution Overview
Problem
Existing wavelength combining laser apparatuses suffer from cross-coupling oscillation, which reduces beam quality and electro-optical conversion efficiency, despite attempts to mitigate this issue using partially-reflective mirrors within the Rayleigh range.
Innovation Solution
A wavelength combining laser apparatus is designed with a cross-coupling reduction optical system that images the light emitting end face onto a partially-reflective mirror, ensuring that laser beams are fed back to the correct emitting layer, preventing cross-coupling oscillation by conjugating the light emitting end face with the partially-reflective mirror in a specific optical plane.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a wavelength combining resonator uses a diffraction grating to combine multiple LD beams, then high power and multiple wavelengths are achieved, but cross-coupling oscillation occurs that lowers beam quality and electro-optical conversion efficiency
Solution Approach 1:
A beam combining element (diffraction grating) is introduced as an intermediary to combine multiple LD beams while a beam separating element (lens system) separates the combined beam back to individual light emitting layers. This intermediary mechanism enables wavelength combining while preventing cross-coupling oscillation by ensuring proper beam routing.
Solution Approach 2:
The patent implements a feedback mechanism where the combined laser beam is reflected by a partially-reflective mirror and fed back to the light emitting layers through the beam separating element. This controlled feedback ensures that beams return to their original sources, preventing cross-coupling while maintaining oscillation for high power output.
2Reliability
If the partially-reflective mirror is disposed within the Rayleigh range to reduce cross-coupling oscillation, then beam quality may be improved, but the required distance (Zr ≥ 160 m) is unrealistic and requires an afocal telescope
Solution Approach 1:
Instead of placing the partially-reflective mirror at a very long distance (Rayleigh range ≥ 160 m) and using an afocal telescope to reduce it to a realistic distance, the patent inverts the approach by using a lens system to image the light emitting end face onto the mirror at a practical distance, achieving cross-coupling reduction without unrealistic dimensions or complex telescopic systems.
Solution Approach 2:
The lens system creates an optical copy (image) of the light emitting end face on the partially-reflective mirror. This copying mechanism ensures that the optical path maintains the correct conjugate relationship without requiring the physical distance to be as large as the Rayleigh range, simplifying the overall system design.
3Device complexity
If an afocal telescope is used to reduce the Rayleigh range distance to a realistic distance, then the setup becomes more compact, but cross-coupling oscillation cannot be prevented
Solution Approach 1:
A lens system acts as an intermediary between the light emitting end face and the partially-reflective mirror, creating an optical image relationship that prevents cross-coupling oscillation. This intermediary maintains the correct optical conjugate relationship without requiring an afocal telescope, thus preventing cross-coupling while keeping the system compact.
4Reliability
If the light emitting end face is imaged onto the partially-reflective mirror through a lens system, then cross-coupling oscillation is reduced and beam quality is improved, but additional optical components are required
Solution Approach 1:
The lens system serves multiple functions: it acts as a beam separating element that directs combined beams back to individual light emitting layers, and simultaneously creates the optical image of the light emitting end face on the partially-reflective mirror to prevent cross-coupling oscillation. This multi-functionality reduces the need for separate components.
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 effectively eliminates cross-coupling oscillation, enhancing beam quality and electro-optical conversion efficiency while maintaining a simple and cost-effective setup.
Implementation Method 1
a wavelength combining element to combine the plurality of laser beams in the laser beam combining direction into a single laser beam
Implementation Method 2
a cross-coupling reduction optical system having a positive power in the laser beam combining direction... the cross-coupling reduction optical system is disposed to image the light emitting end face on the partially-reflective mirror by causing the light emitting end face to be conjugate to the partially-reflective mirror
Implementation Method 3
a partially-reflective mirror to reflect the single laser beam that passes through the cross-coupling reduction optical system and to allow the single laser beam to transmit through and exit the partially-reflective mirror
Data Source
AI summary
A wavelength combining laser apparatus includes: a semiconductor laser emitting laser beams in an optical-axial direction perpendicular to a laser beam combining direction; a wavelength combining element combining the laser beams in the laser beam combining direction into a single laser beam; a cross-coupling reduction optical system having positive power in the laser beam combining direction perpendicular to an optical axis of the single laser beam output from the wavelength combining element; and a partially-reflective mirror reflecting the single laser beam having passed through the cross-coupling reduction optical system and also allowing the single laser beam to transmit through and exit the partially-reflective mirror. The cross-coupling reduction optical system is disposed to image the light emitting end face on the partially-reflective mirror by causing the light emitting end face to be conjugate to the partially-reflective mirror in a plane formed by the optical axis and the laser beam combining direction.